Research ArticleNOx Removal from Simulated Marine Exhaust Gas by WetScrubbing Using NaClO Solution
Zhitao Han Bojun Liu Shaolong Yang Xinxiang Pan and Zhijun Yan
Marine Engineering College Dalian Maritime University Dalian 116026 China
Correspondence should be addressed to Zhitao Han hanztdlmueducn
Received 31 December 2016 Revised 25 May 2017 Accepted 15 June 2017 Published 13 July 2017
Academic Editor Andrea Gambaro
Copyright copy 2017 Zhitao Han et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
The experiments were performed in a lab-scale countercurrent spraying reactor to study the NOx removal from simulated gasstream by cyclic scrubbing using NaClO solution The effects of NaClO concentration initial solution pH coexisting gases (5CO2 and 13O2) NOx concentration SO2 concentration and absorbent temperature on NOx removal efficiency were investigatedin regard to marine exhaust gas When NaClO concentration was higher than 005M and initial solution pH was below 8 NOxremoval efficiency was relatively stable and it was higher than 60 The coexisting CO2 (5) had little effect on NOx removalefficiency but the outlet CO2 concentration decreased slowly with the initial pH increasing from 6 to 8 A complete removal ofSO2 and NO could be achieved simultaneously at 293K initial pH of 6 and NaClO concentration of 005M while the outlet NO2concentration increased slightly with the increase of inlet SO2 concentration NOx removal efficiency increased slightly with theincrease of absorbent temperature The relevant reaction mechanisms for the oxidation and absorption of NO with NaClO werealso discussedThe results indicated that it was of great potential for NOx removal frommarine exhaust gas by wet scrubbing usingNaClO solution
1 Introduction
The exhaust gas emitted frommarine diesel engines containsa large number of atmospheric pollutants such as sulphuroxides (SOx) nitrogen oxides (NOx) and particulate matters(PMs) which has caused serious damage to the ecologicalenvironment [1] A direct way to reduce SOx emission is toadopt low sulphur fuel oil (LSFO) but this will increase thetransportation cost greatly An alternative way is to installan exhaust gas cleaning system (EGCS) on board to achievethe abatement of SOx emission equivalently But it is verydifficult for SOx scrubbers to remove NOx effectively atthe same time Generally the methods for reducing marineNOx emission can be divided into combustion control andpostcombustion control techniques The combustion controltechniques include exhaust gas recirculation (EGR) [2] fuel-water emulsion (FWE) [3] and direct water injection (DWI)[4] They aim at reducing the formation of NOx during thecombustion process but it will result in the decrease of totalheat efficiency At present the typical postcombustion control
approach for ocean-going ships is selective catalytic reduction(SCR) which can remove NOx with an efficiency of 80ndash95As a relatively mature denitrification technology SCR hasbeen extensively applied in power plants andmobile vehiclesBut there are still some problems that limit the application ofSCR inmarine industry It requires large additional space andhigh investmentoperation cost The ash content or sulfatesalts may result in the inactivation of SCR catalyst A complexcontrol system is also required to reduce the ammonia slip [5ndash7]Therefore ship owners around the world are still seeking abetter way to reduce NOx emission It is of great importanceto develop an efficient denitrification technology that cancater for the needs of ocean-going ships
During the past decades wet scrubbing techniquebecomes more and more attractive for the simultaneousremoval of SOx NOx and other pollutants As to NOx re-moval a preoxidation process is required to oxidize NO intoNO2 or other nitrogen oxides of higher values That is dueto the low solubility (193 times 10minus3molsdotLminus1sdotatmminus1 at 25∘C) ofNO in water The nonthermal plasma (NTP) can be used
HindawiJournal of ChemistryVolume 2017 Article ID 9340856 10 pageshttpsdoiorg10115520179340856
2 Journal of Chemistry
to oxidize NO effectively and then an absorption process isfollowed for NO2 absorption However this method requiresa high energy consumption [8 9] Similarly ozone oxidationmethod encounters the same limitation [10ndash12] Anotherfeasible approach is to add the oxidants into the absorbentFor this purpose various oxidants such as hydrogen peroxide(H2O2) [13ndash15] potassium permanganate (KMnO4) [16]sodium chlorite (NaClO2) [17 18] calcium hypochlorite(Ca(ClO)2) [19] and sodium hypochlorite (NaClO) [20ndash24]have been investigated to enhance the NO removal efficiencyof the scrubbing solution Compared with other oxidantsNaClO has some distinct advantages such as low cost easyavailability strong oxidative ability easy to storage goodstability and low toxicity So it is attractive for researchersto investigate the simultaneous removal of NO and SO2 bywet scrubbing using NaClO solution [25ndash28] A previousstudy implied that NO could be effectively removed by wetscrubbing using NaClO solution in a cyclic mode and theutilization of NaClO oxidant in solution was extremely high[29] But the effect of the operating parameters (such asNaClO concentration solution pH absorbent temperatureNO and SO2 concentrations) on NO removal efficiencyby cyclic scrubbing using NaClO solution had not beeninvestigated In this paper marine exhaust gas was chosen asthe treatment objective Though the components of marineexhaust gas might vary with the engine load and fuel typethe typical compositions of marine exhaust gas containedsim13O2 and sim5CO2The effect of coexisting gases onNOxremoval efficiency had also been studied preliminarily andthe relevant reaction mechanism was discussed
2 Experimental Section
21 Materials As mentioned in [11] exhaust gas scrubbersare designed in accordance with the maximum power andexhaust amount of target engine for the practical applicationin marine industry The exhaust gas compositions are alsomeasured at maximum load of engine In this study theconcern is mainly focused on the NOx removal efficiencyand the concentrations of gas components of a typical marineslow-speed 2-stroke diesel engine are considered as thereference The fuel type is heavy fuel oil with 24 sulphurcontent Thus the concentrations of O2 CO2 SO2 and NOxaresim13 sim5sim600 ppm andsim1000 ppm respectively Herethe simulated exhaust gas was prepared by blending variouskinds of synthetic gases Five kinds of gases N2 (99999)O2(99995) CO2 (99999) NO (1004 NO with N2 as thebalance gas) and SO2 (101 SO2 with N2 as the balance gas)(Dalian Date Gas Co Ltd) were used to make the simulatedflue gas As NO accounted for more than 95 of NOx inmarine exhaust gas only NO span gas was used to preparethe NOx components in simulated gas stream
The NaClO solutions were prepared using the commer-cial NaClO solution (5 available chlorine Shanghai AladdinBio-ChemTechnology Co Ltd) and the deionized waterThevolume of NaClO solution was 1 L for each test The pH valuewas adjusted by adding 05M H2SO4 solution and deter-minated using an acidimeter (Mettler-Toledo InternationalTrading Co Ltd)
Gas mixer
Pump
Drier Gas analyzer
Water bath
ScrubberMFC
Gas distributor
AbsorbentO2 SO2N2 CO2 NO
Figure 1 Schematic diagram of the experimental setup
22 Experimental Apparatus A schematic diagram of theexperimental apparatus is shown in Figure 1 It consistsof a gas distributing system a gas-liquid countercurrentscrubbing reactor and a gas analyzer
N2 O2 CO2 NO and SO2 were provided from separateair bottles and metered through mass flow controllers (MFCBeijing Sevenstar Electronics Co Ltd)The simulated flue gaswas obtained from the feed gases by blending with an on-linemixer and then it was introduced into the spraying columnThe height and inner diameter of the column were 25 cmand 5 cm respectively A spraying nozzle (B14TT-SS+TG-SS04 Spraying System Co Ltd) was located at the top of thecolumn The size of liquid droplet sprayed from the nozzlewas in the range of 80ndash100 120583mThe flow rate of the simulatedflue gas was fixed at 125 LminThe calculated residence timeof flue gas in the column was sim23 s
When the initial gas concentrations were adjusted to therequired level the simulated flue gas was introduced intothe scrubber from the bottom of the column The NaClOabsorbent was sprayed from top to bottom A peristalticpump was used to pump the scrubbing solution cyclicallyThe flow rate of the scrubbing solution was sim027 LminEach run of the test was 20min The outlet concentrationsof flue gas were measured at an interval of 10 s The solutiontemperatures were adjusted by the constant water bath (F34-MA Julabo Labortechnik GmbH) and measured with amercury thermometer AMRUMGA-5 gas analyzer was usedto determinate the gas concentrations of O2 CO2 NO andNO2 in flue gas
23 Data Process The gas concentrations measured by thebypass are taken as the inlet concentrations The averageconcentrations within 20min measured by the gas outletare considered as the outlet concentrations The removalefficiencies of NOx and SO2 are calculated by the followingequation
120578 =119862in minus 119862out119862intimes 100 (1)
in which 120578 is the removal efficiency and 119862in and 119862out are theinlet and outlet concentrations respectively Here NOx refersto the mixture of NO and NO2 in flue gas
Journal of Chemistry 3
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
6 10 124 8
Initial pH of NaClO solution
NaClO concentration00125 M0025 M
005 M01M
Figure 2 Effect of initial solution pH on NOx removal efficiency(gas flow is 125 Lmin inlet NOx concentration is 1000 ppm NaClOconcentration is 00125ndash01M and solution temperature is 293K)
3 Results and Discussion
31 Effect of Initial pH and NaClO Concentration The activecomponents in NaClO solution were available chlorinewhich mainly includes HClO ClOminus and Cl2 The compo-sitions of NaClO solution depended greatly on the solutionpH Firstly it was necessary to investigate the effect of initialsolution pH on the NOx removal efficiency Figure 2 showedthat NOx removal efficiency was very low when the solutionpH was higher than 10 That was because little HClO existedin the solution when solution pH was higher than 10 butHClO was considered to be the main component in NaClOsolution to oxidize NO [22] It demonstrated that NaClOsolution without optimizing the initial pH was not suitablefor removing NOx With the decrease of initial pH from 10to 8 NOx removal efficiency increased quickly which wasdue to the increase of fractional composition of HClO insolution HClO oxidized NO into NO2 N2O3 N2O4 andNO3minus in chain reactions of (2)ndash(9) [30 31] The possible
reaction pathways were summarized as shown in Figure 3
NO +HClO 997888rarr NO2 +HCl (2)
NO +NO2 997888rarr N2O3 (3)
2NO2 larrrarr N2O4 (4)
3NO2 +H2O 997888rarr 2HNO3 +NO (5)
2NO2 +H2O 997888rarr HNO3 +HNO2 (6)
N2O3 +H2O 997888rarr 2HNO2 (7)
N2O4 +H2O 997888rarr HNO3 +HNO2 (8)
HNO2 +HClO 997888rarr HNO3 +HCl (9)
Gas-liquid interface
Gas phase Liquid phase
HNO2
HNO3
(2)(3)
(4)
(5)
(6)
(7)
(8)
(9)
N2O3(g)
NO(g)
NO2(g)
N2O4(g)
N2O3(aq)
NO(aq)
N2O4(aq)
NO2(aq)
Figure 3 Reaction pathways for NOx removal by NaClO solution
As shown in Figure 2 with the initial pH decreasing from 8to 7 a slight drop of NOx removal efficiency appeared Onfurther reducing the initial pH the changes of NOx removalefficiency depended on NaClO concentration When initialNaClO concentration was below 005M NOx removal effi-ciency continued to decrease with initial pH decreasing from7 to 6 This was because the oxidation power of ClOminus wasstronger than that ofHClO in neutral orweak acidicmediumAs shown in Figure 4 HClO concentration increased whileClOminus concentration decreased with solution pH decreasingfrom 7 to 6 However whenNaClO concentration was higherthan 005M the oxidation power of active chlorine washigh enough to oxidize NO effectively at pH 6 and 7 [32]At the moment the effect of the change of active chlorineconcentration was not obvious enough The result indicatedthat a high NaClO concentration might be appropriate forpractical application for it was easy to obtain a high and stableNOx removal efficiency in a relatively wide range of solutionpH
Figure 5 showed the effect of initial solution pH on NOxconcentration in flue gas When NaClO concentration washigher than 005M and solution pH was in the range of 4ndash8outlet NO concentration was lower than 124 ppm It sug-gested that themajority ofNOhad been oxidized intoNO2 byNaClO When NaClO concentration was 005M outlet NOconcentration decreased sharply to 35 ppm with initial pHdecreasing from 10 to 8 At the same time NO2 concentrationin outlet gas increased from 14 ppm to 353 ppm On furtherdecreasing the initial pH down to 6 a complete removal ofNO could be achieved with 005M NaClO while outlet NO2concentration reached about 400 ppm With the initial pHdecreasing from 6 to 4 NO in outlet gas increased to 124 ppmwhile NO2 in outlet gas decreased to 270 ppm NOx removalefficiency changed little in the range of pH 4ndash8 The resultsimplied that to a certain extent NOx removal efficiency forwet scrubbing using NaClO solution was mainly limited tothe absorption of NO2 rather than the oxidation of NO
32 Effect of Coexisting CO2 During wet scrubbing processCO2 in flue gas would react with absorbent thus influencing
4 Journal of Chemistry
0
20
40
60
80
100
Frac
tion
of ac
tive c
hlor
ine (
)
86 10 122 4
pH of NaClO solution
Cl2 HClOClOminusCl3
minus
Figure 4 Equilibrium concentrations of active chlorine species inNaClO solution as a function of solution pH
the oxidation and absorption of targeted pollutants As anacidic oxide CO2 was sensitive to the solution pH Theeffect of coexisting CO2 on NOx removal efficiency wasinvestigated and results were shown in Figure 6 It can beseen that with initial solution pH increasing from 4 to 8 NOxremoval efficiency was relatively stable A complete removalof NO had been achieved and outlet NO2 concentrationwas sim350 ppm The coexistence of CO2 had not affectedthe NOx removal efficiency so much But the average CO2concentration in outlet gas changed obviously with initialsolution pH When initial solution pH was below 6 theaverage CO2 concentration kept stable at 5 However itbegan to decrease quickly with initial pH increasing from 6to 8
The change of outlet CO2 concentration during the cyclicscrubbing process was shown in Figure 7 When initialpH was in the range of 4ndash6 CO2 concentration decreasedto 44ndash45 at the start of the scrubbing process Then itrecovered to the initial level due to the hydrolysis equilibriumbetween CO2 and absorbent solution The hydrolysis reac-tions of CO2 were described in (10) and (11) Furthermorea certain amount of H+ might be produced during thehydrolysis process whichwould affect the chlorine hydrolysisequilibrium reactions as shown in (12) and (13) Since HCO3
minus
andCO32minus had buffering ability to some extent the hydrolysis
of CO2 would not influence the solution pH obviously wheninitial pH was in the range of 4ndash6 But with initial pHincreasing from 6 to 8 the absorption of CO2 might reducethe solution alkalinity resulting in the decrease of the solutionpHThus it was necessary to keep the solution pHat 6 in orderto reduce the consumption of solution alkalinitywhenNaClOsolution was adopted to remove NOx from flue gas
CO2 +H2Olarrrarr CO32minus + 2H+ (10)
CO2 +H2Olarrrarr HCO3minus +H+ (11)
Cl2(aq) +H2Olarrrarr HClO +H+ + Clminus (12)
HClOlarrrarr ClOminus +H+ (13)
When initial pH was in the range of 7-8 CO2 concentrationdecreased largely at the very beginning of the cyclic scrub-bing process It suggested that much more CO2 had beenabsorbed by the scrubbing solution due to the weak alkalinemedium With the proceeding of the scrubbing processCO2 concentration began to increase slowly Although noevidence showed that CO2 would react with NaClO directlythe hydrolyzation and absorption of CO2 would increasethe consumption of solution alkalinity obviously It meantthat extra alkaline solution was required to maintain thesolution pH during cyclic scrubbing process which wouldlargely increase the operation complexity and cost at the sametime Thus initial pH of 6 might be appropriate for practicalapplication
Figure 8 showed the change of NaClO solution pHafter scrubbing for 20min With the proceeding of cyclicscrubbing process the solution pHwould decrease slowly dueto the absorption of NOx and CO2 It was worth noting thatthe solution pH increased from 4 to 463 for NaClO solutionwith initial pH 4 That was because active chlorine speciesin NaClO solution were mainly HClO and Cl2 at pH 4 asshown in Figure 4 During the scrubbing process Cl2 wouldbe purged out easily from the solution and reacted with NOeffectively in gas phase as (14) and (15) [25] The decreaseof Cl2 in NaClO solution would lead to a left shift of thehydrolysis equilibrium of active chlorine as shown in (16)resulting in the increase of solution pH for NaClO solutionwith initial pH 4
Cl2(aq) larrrarr Cl2(g) (14)
Cl2(g) +H2O +NO(g) larrrarr NO2(g) + 2HCl (15)
Cl2(g) +H2Olarrrarr HClO(aq) +H+ + Clminus (16)
It was possible that excessive Cl2 escaped from NaClOsolution might result in secondary pollution In additionacidicmist formed in the flue gasmight result in the corrosionof operation system In view of this NaClO solution with pH6 was appropriate for NOx removal in cyclic scrubbingmode
33 Effect of Coexisting O2 For marine diesel engines therewas typicalsim13O2 in exhaust gas O2 could partially oxidizeNO under certain conditions so it was necessary to investi-gate the effect of coexisting O2 on NOx removal efficiency Inthe experiments only NO standard gas was used to prepareNOx in the initial simulated flue gas The introduction ofO2 has oxidized a little of NO into NO2 in the gas mixerAs shown in Figure 9 the initial NO2 concentration ininlet gas increased almost linearly with the increase of NOconcentrationWhen inlet NOx concentrationwas 1000 ppmthe initial NO2 concentration reached 112 ppm
O2 + 2NO 997888rarr 2NO2 (17)
With the NOx increasing from 250 to 700 ppm the outletNO concentration decreased gradually to 0 When inlet
Journal of Chemistry 5
NaClO concentration00125 M0025 M005 M01M
0
200
400
600
800
1000
NO
conc
entr
atio
n (p
pm)
6 8 10 124
Initial pH of NaClO solution
00125 M0025 M005 M01M
(a)
0
200
400
600
800
1000
NO2
conc
entr
atio
n (p
pm)
86 10 124
Initial pH of NaClO solution
NaClO concentration00125 M0025 M005 M01M
00125 M0025 M005 M01M
(b)
Figure 5 The change of (a) NO concentrations and (b) NO2 concentrations in flue gas with initial pH of NaClO solution (gas flow is125 Lmin inlet NOx concentration is 1000 ppm NaClO concentration is in the range of 00125ndash01M and solution temperature is 293Ksolid points refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
5 6 7 84
Initial pH of NaClO solution
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
0
1
2
3
4
5
Out
let C
O2
conc
entr
atio
n at
aver
age (
)
NOx removal efficiencyOutlet CO2 concentration
Figure 6 The change of NOx removal efficiency and averaged CO2concentration in flue gas with initial pH (gas flow is 125 Lmin inletNOx concentration is 1000 ppm initial CO2 concentration is 5NaClO concentration is 005M and solution temperature is 293K)
NOx concentration was higher than 700 ppm NO could beremoved completely As expected the outlet NO2 concen-tration increased almost linearly with the increase of inletNOx concentration It indicated that NOx removal efficiencydepended to a great extent on the absorption of NO2 duringthe scrubbing process
Figure 10 presented the change of NOx removal effi-ciency and outlet O2 concentration with the initial NOx
0
1
2
3
4
5
Out
let C
O2
conc
entr
atio
n (
)
5 10 15 200
Cyclic scrubbing duration (min)
Initial pH of NaClO solution4
5
6
7
8
Figure 7 The change of CO2 concentration during the cyclicscrubbing duration (gas flow is 125 Lmin inlet NO concentrationis 1000 ppm initial CO2 concentration is 5 NaClO concentrationis 005M and solution temperature is 293K)
concentration Since O2 concentration was relatively highit changed little during the scrubbing process With theincrease of NOx concentration from 250 ppm to 700 ppmNOx removal efficiency increased from 47 to 74 It could
6 Journal of Chemistry
0
2
4
6
8
10
pH o
f use
d N
aClO
solu
tion
5 6 7 84
Initial pH of NaClO solution
Figure 8 NaClO solution pH after scrubbing for 20min (gas flowis 125 Lmin inlet NOx concentration is 1000 ppm initial CO2concentration is 5 NaClO concentration is 005M and solutiontemperature is 293K)
Initial NOx concentration in inlet gas (ppm)1000800600400200
0
200
400
600
800
1000
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
Figure 9 The change of NOx concentration with the initial NOxconcentration (gas flow is 125 Lmin inlet O2 concentration is13 inlet NOx concentration is in the range of 250ndash1000 ppmNaClO concentration is 005M initial solution pH is 6 and solutiontemperature is 293K solid points refer to inlet NOx concentrationsand open points refer to outlet NOx concentrations)
be ascribed to the improvement of the mass transfer at thegas-liquid interface When O2 was present in flue gas NOxremoval efficiency was a little higher than that without O2in flue gas The existence of O2 improved the NOx removalefficiency in way of partly oxidizing NO in initial flue gas
34 Effect of NOx Concentration The effects of NOx con-centration on NOx removal are investigated and the resultsare shown in Figure 11 It can be seen that with initial NO
Initial NOx concentration in inlet gas (ppm)1000800600400200
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
0
3
6
9
12
15
Out
let O
2co
ncen
trat
ion
at av
erag
e (
)
NOx removal efficiencyOutlet O2 concentration
Figure 10The change of NOx removal efficiency and outlet O2 con-centration with the initial NOx concentration (conditions gas flow125 Lmin inlet O2 concentration 13 inlet NOx concentration250ndash1000 ppm NaClO concentration 005M initial solution pH 6solution temperature 293K)
concentration increasing from 250 ppm to 500 ppm NOxremoval efficiency increased from 43 to sim63 NO could beremoved completelywhen inletNOconcentrationwas higherthan 500 ppm Outlet NO2 concentration increased quicklywith the increase of inlet NO concentration resulting in arelatively stable NOx removal efficiency
35 Simultaneous Removal of NOx and SO2 Marine dieselengines usually burn heavy fuel oil (HFO) in order to savethe operating cost At present the mass concentration ofsulphur (S) content in HFO was about 25 at average Thecombustion of HFO fuel would produce a large amountof SO2 in exhaust gas Experiments were conducted toinvestigate the effect of coexisting SO2 on NOx removalefficiency and the results are shown in Figures 12 and 13
Figure 12 depicted the change of NOx removal efficiencyand NOx concentration with inlet NOx concentration Acomplete removal of SO2 and NO had been achieved simul-taneously Due to its high solubility SO2 could be absorbedeffectively by scrubbing solution Then SO2 was removedthrough the hydrolysis reaction as (18) and (19) The hydrol-ysis products of SO3
2minus would be oxidized by active chlorinespecies into SO4
2minus quickly Thus the removal of SO2 wouldconsume the solution alkalinity and oxidants at the sametime The result demonstrated that NaClO solution could beused to remove NO and SO2 simultaneously from marineexhaust gas However outlet NO2 concentration increasedgradually with the increase of inlet NOx concentration
SO2 +H2O 997888rarr HSO3minus +H+ (18)
HSO3minus 997888rarr SO3
2minus +H+ (19)
SO3minus +HClO 997888rarr SO4
2minus +HCl (20)
Journal of Chemistry 7
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
(a)
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
200
400
600
800
1000
1200
1400
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
(b)
Figure 11 The change of (a) NOx removal efficiency and (b) NO119909 concentrations with the initial NOx concentration (gas flow is 125 Lmininlet NOx concentration is 250ndash1250 ppm NaClO concentration is 005M initial solution pH is 6 and solution temperature is 293K solidpoints refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
20
40
60
80
100
Rem
oval
effici
ency
()
SO2
NOx
(a)
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
200
400
600
800
1000
1200
1400
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
(b)
Figure 12 The change of (a) NOx removal efficiency and (b) NOx concentration with the inlet NOx concentration (gas flow is 125 Lmininlet SO2 concentration is 600 ppm inlet NOx concentration is 250ndash1250 ppm NaClO concentration is 005M initial solution pH is 6 andsolution temperature is 293K solid points refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
Figure 13 exhibited the effect of SO2 concentration on NOxremoval efficiency and NOx concentration in flue gas Theresult showed that SO2 together with NO was completelyremoved But with the increase of inlet SO2 concentrationNOx removal efficiency exhibited a slightly downside trendThis phenomenon could be ascribed to the competitionreactions between NOx and SO2 Some oxidants in theabsorbent would be consumed through the hydrolyzation
and absorption of SO2With inlet SO2 concentration increas-ing from 200 ppm to 600 ppm the pHof the scrubbedNaClOsolution decreased from 525 to 452The decrease of solutionpH was negative for the absorption of NO2 through (5) and(6)
36 Effect of Absorbent Temperature The reaction temper-ature could greatly influence the diffusion dissolution and
8 Journal of Chemistry
0
20
40
60
80
100
Rem
oval
effici
ency
()
SO2
NOx
300 500 600400200
Initial SO2 concentration in inlet gas (ppm)
(a)
0
200
400
600
800
1000
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
300 500 600400200
Initial SO2 concentration in inlet gas (ppm)
(b)
Figure 13 The change of (a) NOx removal efficiency and (b) NOx concentration with the initial SO2 concentration (gas flow is 125 Lmininlet SO2 concentration is 200ndash600 ppm inlet NOx concentration is 1000 ppm NaClO concentration is 005M initial solution pH is 6 andsolution temperature is 293K solid points refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
Absorbent temperature (K)340330320310300290
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
(a)
Absorbent temperature (K)340330320310300290
0
200
400
600
800
1000
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
(b)
Figure 14The change of (a) NOx removal efficiency and (b) NOx concentration with the absorbent temperature (gas flow is 125 Lmin inletNOx concentration is 1000 ppm NaClO concentration is 005M initial solution pH is 6 and solution temperature is 293ndash333K solid pointsrefer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
reaction characteristics of molecules or ions in liquid phase[19] The effect of absorbent temperature on NOx removalwas investigated and the results were shown in Figure 14Generally the absorbent temperature was kept below 333Kin industrial application in order to reduce the supply ofmake-up water So the absorbent temperature was chosen tobe in the range of 293ndash333K in the experiments Figure 14showed that NOx removal efficiency increased gradually with
the increase of absorbent temperature The highest NOxremoval efficiency of 69was achieved at 333 K AsNO couldbe removed by 100 easily the increase of NOx removalefficiency resulted from the improvement of NO2 absorptionThis could be explained by the Arrhenius equation of thereaction rate constant The increase of temperature couldenhance the mass transfer of NO2 to the absorbent thusimproving the absorption of NO2 accordingly
Journal of Chemistry 9
4 Conclusion
NOx removal by wet scrubbing using NaClO solution wasstudied based on a spraying reactor in a cyclic mode Theresults showed that when NaClO concentration was higherthan 005M and initial solution pH was below 8 NOxremoval efficiency was relatively stable which was higherthan 60 The coexisting CO2 (5) had little effect on NOxremoval efficiency but the solution pHbegan to decreasewiththe proceeding of cyclic scrubbing process when initial pHwas higher than 6The coexisting O2 (13) could oxidize NOpartially in the gas mixer resulting in a little improvementof NOx removal efficiency When initial NOx concentrationwas higher than 500 ppm NO could be removed completelywhile outlet NO2 concentration increased almost linearlywith the increase of initial NOx concentration resultingin a relative stable NOx removal efficiency A completeremoval of SO2 and NO could be achieved simultaneouslyat 293K initial NaClO solution pH 6 and 005M NaClOconcentration With the increase of inlet SO2 concentrationthe outlet NO2 concentration increased slightly due to thedecrease of solution pH NOx removal efficiency increasedwith the increase of absorbent temperature The relevantreaction mechanism for the removal of NOx and SO2 bywet scrubbing using NaClO solution was also discussed Theresults demonstrated that it was of great potential for NaClOsolution to remove NOx from marine exhaust gas
Conflicts of Interest
The authors declare that there are no conflicts of interestregarding the publication of this paper
Acknowledgments
This study has been financially supported by the NationalNatural Science Foundation of China (Grant nos 51402033and 51479020) the Science and Technology Plan Project ofChinarsquos Ministry of Transport (Grant no 2015328225150) theDoctoral Scientific Research Staring Foundation of Liaon-ing Province (Grant no 201601073) and the FundamentalResearch Funds for the Central Universities (Grant nos3132017003 and 3132016326)
References
[1] M Guo Z Fu DMa N Ji C Song and Q Liu ldquoA short reviewof treatment methods of marine diesel engine exhaust gasesrdquoProcedia Engineering vol 121 pp 938ndash943 2015
[2] M-W Bae ldquoA study on the effects of recirculated exhaust gasupon NO119909 and soot emissions in diesel engines with scrubberEGR systemrdquo SAE Technical Papers 1999
[3] A M A Attia and A R Kulchitskiy ldquoInfluence of the structureof water-in-fuel emulsion on diesel engine performancerdquo Fuelvol 116 pp 703ndash708 2014
[4] X Tauzia A Maiboom and S R Shah ldquoExperimental study ofinlet manifold water injection on combustion and emissions ofan automotive direct injection diesel enginerdquoEnergy vol 35 no9 pp 3628ndash3639 2010
[5] A M Hallquist E Fridell J Westerlund and M Hal-lquist ldquoOnboard measurements of nanoparticles from a SCR-equipped marine diesel enginerdquo Environmental Science andTechnology vol 47 no 2 pp 773ndash780 2013
[6] J Herdzik ldquoEmissions from marine engines versus IMO certi-fication and requirements of tier 3rdquo Journal of KONES vol 18pp 161ndash167 2011
[7] M Magnusson E Fridell and H H Ingelsten ldquoThe influenceof sulfur dioxide andwater on the performance of amarine SCRcatalystrdquoApplied Catalysis B Environmental vol 111-112 pp 20ndash26 2012
[8] T Kuwahara K Yoshida Y Kannaka T Kuroki andMOkuboldquoImprovement of NOx reduction efficiency in diesel emissioncontrol using nonthermal plasma combined exhaust gas recir-culation processrdquo IEEE Transactions on Industry Applicationsvol 47 no 6 pp 2359ndash2366 2011
[9] T Kuwahara K Yoshida T Kuroki K Hanamoto K Sato andMOkubo ldquoPilot-scale aftertreatment using nonthermal plasmareduction of adsorbed NO119909 in marine diesel-engine exhaustgasrdquo Plasma Chemistry and Plasma Processing vol 34 no 1 pp65ndash81 2014
[10] D Xie Y Sun T Zhu and L Ding ldquoRemoval of NO in mist bythe combination of plasma oxidation and chemical absorptionrdquoEnergy and Fuels vol 30 no 6 pp 5071ndash5076 2016
[11] S Zhou J Zhou Y Feng and Y Zhu ldquoMarine Emission Pol-lution Abatement Using Ozone Oxidation by a Wet ScrubbingMethodrdquo Industrial andEngineeringChemistry Research vol 55no 20 pp 5825ndash5831 2016
[12] Y S Mok ldquoAbsorption-reduction technique assisted by ozoneinjection and sodium sulfide for NO119909 removal from exhaustgasrdquo Chemical Engineering Journal vol 118 no 1-2 pp 63ndash672006
[13] E B Myers and T J Overcamp ldquoHydrogen peroxide scrubberfor the control of nitrogen oxidesrdquo Environmental EngineeringScience vol 19 no 5 pp 321ndash327 2002
[14] Z Wang Z Wang Y Ye N Chen and H Li ldquoStudy on theremoval of nitric oxide (NO) by dual oxidant (H2O2S2O82
minus)systemrdquo Chemical Engineering Science vol 145 pp 133ndash1402016
[15] Y Liu Q Wang Y Yin J Pan and J Zhang ldquoAdvancedoxidation removal ofNOand SO2 fromflue gas by using ultravi-oletH2O2NaOH processrdquo Chemical Engineering Research andDesign vol 92 no 10 pp 1907ndash1914 2014
[16] H Chu T W Chien and S Y Li ldquoSimultaneous absorptionof SO2 and NO from flue gas with KMnO4NaOH solutionsrdquoScience of the Total Environment vol 275 no 1-3 pp 127ndash1352001
[17] R Hao Y Zhang Z Wang et al ldquoAn advanced wet method forsimultaneous removal of SO2 andNO fromcoal-fired flue gas byutilizing a complex absorbentrdquo Chemical Engineering Journalvol 307 pp 562ndash571 2017
[18] Z Han S Yang D Zheng X Pan and Z Yan ldquoAn investigationon NO removal by wet scrubbing using NaClO2 seawatersolutionrdquo SpringerPlus vol 5 no 1 article 751 2016
[19] Y Zhou C Li C Fan et al ldquoWet removal of sulfur dioxide andnitrogen oxides from simulated flue gas by Ca(ClO)2 solutionrdquoEnvironmental Progress and Sustainable Energy vol 34 no 6pp 1586ndash1595 2015
[20] S-L Yang Z-T Han J-M Dong Z-S Zheng and X-X PanldquoUV-enhanced naclo oxidation of nitric oxide from simulatedflue gasrdquo Journal of Chemistry vol 2016 Article ID 6065019 8pages 2016
10 Journal of Chemistry
[21] L Chen C-H Hsu and C-L Yang ldquoOxidation and absorptionof nitric oxide in a packed tower with sodium hypochloriteaqueous solutionsrdquo Environmental Progress vol 24 no 3 pp279ndash288 2005
[22] E Ghibaudi J R Barker and S W Benson ldquoReaction ofNO with hypochlorous acidrdquo International Journal of ChemicalKinetics vol 11 no 8 pp 843ndash851 1979
[23] R-T Guo W-G Pan X-B Zhang et al ldquoThe absorptionkinetics of NO into weakly acidic NaClO solutionrdquo SeparationScience and Technology vol 48 no 18 pp 2871ndash2875 2013
[24] S Yang Z Han X Pan Z Yan and J Yu ldquoNitrogen oxideremoval using seawater electrolysis in an undivided cell forocean-going vesselsrdquo RSC Advances vol 6 no 115 pp 114623ndash114631 2016
[25] M K Mondal and V R Chelluboyana ldquoNew experimentalresults of combined SO2 and NO removal from simulated gasstream by NaClO as low-cost absorbentrdquo Chemical EngineeringJournal vol 217 pp 48ndash53 2013
[26] C V Raghunath and M K Mondal ldquoExperimental scalemulti component absorption of SO2 and NO by NH3NaClOscrubbingrdquo Chemical Engineering Journal vol 314 pp 537ndash5472017
[27] J Wang and W Zhong ldquoSimultaneous desulfurization anddenitrification of sintering flue gas via composite absorbentrdquoChinese Journal of Chemical Engineering vol 24 no 8 pp 1104ndash1111 2016
[28] S An and O Nishida ldquoNew application of seawater andelectrolyzed seawater in air pollution control of marine dieselenginerdquo JSME International Journal Series B Fluids and Ther-mal Engineering vol 46 no 1 pp 206ndash213 2003
[29] Z Han S Yang X Pan et al ldquoNew experimental results of NOremoval from simulated flue gas by wet scrubbing using NaClOsolutionrdquo Energy amp Fuels vol 31 no 3 pp 3047ndash3054 2017
[30] N Lahoutifard P Lagrange and J Lagrange ldquoKinetics andmechanism of nitrite oxidation by hypochlorous acid in theaqueous phaserdquo Chemosphere vol 50 no 10 pp 1349ndash13572003
[31] Y G Adewuyi X He H Shaw and W Lolertpihop ldquoSimul-taneous absorption and oxidation of NO and SO2 by aqueoussolutions of sodium chloriterdquo Chemical Engineering Communi-cations vol 174 no 1 pp 21ndash51 1999
[32] A Mukimin K Wijaya and A Kuncaka ldquoElectro-degradationof reactive blue dyes using cylinder modified electrode Ti120573-PbO2 as dimensionally stable anoderdquo Indonesian Journal ofChemistry vol 10 no 3 pp 285ndash289 2010
to oxidize NO effectively and then an absorption process isfollowed for NO2 absorption However this method requiresa high energy consumption [8 9] Similarly ozone oxidationmethod encounters the same limitation [10ndash12] Anotherfeasible approach is to add the oxidants into the absorbentFor this purpose various oxidants such as hydrogen peroxide(H2O2) [13ndash15] potassium permanganate (KMnO4) [16]sodium chlorite (NaClO2) [17 18] calcium hypochlorite(Ca(ClO)2) [19] and sodium hypochlorite (NaClO) [20ndash24]have been investigated to enhance the NO removal efficiencyof the scrubbing solution Compared with other oxidantsNaClO has some distinct advantages such as low cost easyavailability strong oxidative ability easy to storage goodstability and low toxicity So it is attractive for researchersto investigate the simultaneous removal of NO and SO2 bywet scrubbing using NaClO solution [25ndash28] A previousstudy implied that NO could be effectively removed by wetscrubbing using NaClO solution in a cyclic mode and theutilization of NaClO oxidant in solution was extremely high[29] But the effect of the operating parameters (such asNaClO concentration solution pH absorbent temperatureNO and SO2 concentrations) on NO removal efficiencyby cyclic scrubbing using NaClO solution had not beeninvestigated In this paper marine exhaust gas was chosen asthe treatment objective Though the components of marineexhaust gas might vary with the engine load and fuel typethe typical compositions of marine exhaust gas containedsim13O2 and sim5CO2The effect of coexisting gases onNOxremoval efficiency had also been studied preliminarily andthe relevant reaction mechanism was discussed
2 Experimental Section
21 Materials As mentioned in [11] exhaust gas scrubbersare designed in accordance with the maximum power andexhaust amount of target engine for the practical applicationin marine industry The exhaust gas compositions are alsomeasured at maximum load of engine In this study theconcern is mainly focused on the NOx removal efficiencyand the concentrations of gas components of a typical marineslow-speed 2-stroke diesel engine are considered as thereference The fuel type is heavy fuel oil with 24 sulphurcontent Thus the concentrations of O2 CO2 SO2 and NOxaresim13 sim5sim600 ppm andsim1000 ppm respectively Herethe simulated exhaust gas was prepared by blending variouskinds of synthetic gases Five kinds of gases N2 (99999)O2(99995) CO2 (99999) NO (1004 NO with N2 as thebalance gas) and SO2 (101 SO2 with N2 as the balance gas)(Dalian Date Gas Co Ltd) were used to make the simulatedflue gas As NO accounted for more than 95 of NOx inmarine exhaust gas only NO span gas was used to preparethe NOx components in simulated gas stream
The NaClO solutions were prepared using the commer-cial NaClO solution (5 available chlorine Shanghai AladdinBio-ChemTechnology Co Ltd) and the deionized waterThevolume of NaClO solution was 1 L for each test The pH valuewas adjusted by adding 05M H2SO4 solution and deter-minated using an acidimeter (Mettler-Toledo InternationalTrading Co Ltd)
Gas mixer
Pump
Drier Gas analyzer
Water bath
ScrubberMFC
Gas distributor
AbsorbentO2 SO2N2 CO2 NO
Figure 1 Schematic diagram of the experimental setup
22 Experimental Apparatus A schematic diagram of theexperimental apparatus is shown in Figure 1 It consistsof a gas distributing system a gas-liquid countercurrentscrubbing reactor and a gas analyzer
N2 O2 CO2 NO and SO2 were provided from separateair bottles and metered through mass flow controllers (MFCBeijing Sevenstar Electronics Co Ltd)The simulated flue gaswas obtained from the feed gases by blending with an on-linemixer and then it was introduced into the spraying columnThe height and inner diameter of the column were 25 cmand 5 cm respectively A spraying nozzle (B14TT-SS+TG-SS04 Spraying System Co Ltd) was located at the top of thecolumn The size of liquid droplet sprayed from the nozzlewas in the range of 80ndash100 120583mThe flow rate of the simulatedflue gas was fixed at 125 LminThe calculated residence timeof flue gas in the column was sim23 s
When the initial gas concentrations were adjusted to therequired level the simulated flue gas was introduced intothe scrubber from the bottom of the column The NaClOabsorbent was sprayed from top to bottom A peristalticpump was used to pump the scrubbing solution cyclicallyThe flow rate of the scrubbing solution was sim027 LminEach run of the test was 20min The outlet concentrationsof flue gas were measured at an interval of 10 s The solutiontemperatures were adjusted by the constant water bath (F34-MA Julabo Labortechnik GmbH) and measured with amercury thermometer AMRUMGA-5 gas analyzer was usedto determinate the gas concentrations of O2 CO2 NO andNO2 in flue gas
23 Data Process The gas concentrations measured by thebypass are taken as the inlet concentrations The averageconcentrations within 20min measured by the gas outletare considered as the outlet concentrations The removalefficiencies of NOx and SO2 are calculated by the followingequation
120578 =119862in minus 119862out119862intimes 100 (1)
in which 120578 is the removal efficiency and 119862in and 119862out are theinlet and outlet concentrations respectively Here NOx refersto the mixture of NO and NO2 in flue gas
Journal of Chemistry 3
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
6 10 124 8
Initial pH of NaClO solution
NaClO concentration00125 M0025 M
005 M01M
Figure 2 Effect of initial solution pH on NOx removal efficiency(gas flow is 125 Lmin inlet NOx concentration is 1000 ppm NaClOconcentration is 00125ndash01M and solution temperature is 293K)
3 Results and Discussion
31 Effect of Initial pH and NaClO Concentration The activecomponents in NaClO solution were available chlorinewhich mainly includes HClO ClOminus and Cl2 The compo-sitions of NaClO solution depended greatly on the solutionpH Firstly it was necessary to investigate the effect of initialsolution pH on the NOx removal efficiency Figure 2 showedthat NOx removal efficiency was very low when the solutionpH was higher than 10 That was because little HClO existedin the solution when solution pH was higher than 10 butHClO was considered to be the main component in NaClOsolution to oxidize NO [22] It demonstrated that NaClOsolution without optimizing the initial pH was not suitablefor removing NOx With the decrease of initial pH from 10to 8 NOx removal efficiency increased quickly which wasdue to the increase of fractional composition of HClO insolution HClO oxidized NO into NO2 N2O3 N2O4 andNO3minus in chain reactions of (2)ndash(9) [30 31] The possible
reaction pathways were summarized as shown in Figure 3
NO +HClO 997888rarr NO2 +HCl (2)
NO +NO2 997888rarr N2O3 (3)
2NO2 larrrarr N2O4 (4)
3NO2 +H2O 997888rarr 2HNO3 +NO (5)
2NO2 +H2O 997888rarr HNO3 +HNO2 (6)
N2O3 +H2O 997888rarr 2HNO2 (7)
N2O4 +H2O 997888rarr HNO3 +HNO2 (8)
HNO2 +HClO 997888rarr HNO3 +HCl (9)
Gas-liquid interface
Gas phase Liquid phase
HNO2
HNO3
(2)(3)
(4)
(5)
(6)
(7)
(8)
(9)
N2O3(g)
NO(g)
NO2(g)
N2O4(g)
N2O3(aq)
NO(aq)
N2O4(aq)
NO2(aq)
Figure 3 Reaction pathways for NOx removal by NaClO solution
As shown in Figure 2 with the initial pH decreasing from 8to 7 a slight drop of NOx removal efficiency appeared Onfurther reducing the initial pH the changes of NOx removalefficiency depended on NaClO concentration When initialNaClO concentration was below 005M NOx removal effi-ciency continued to decrease with initial pH decreasing from7 to 6 This was because the oxidation power of ClOminus wasstronger than that ofHClO in neutral orweak acidicmediumAs shown in Figure 4 HClO concentration increased whileClOminus concentration decreased with solution pH decreasingfrom 7 to 6 However whenNaClO concentration was higherthan 005M the oxidation power of active chlorine washigh enough to oxidize NO effectively at pH 6 and 7 [32]At the moment the effect of the change of active chlorineconcentration was not obvious enough The result indicatedthat a high NaClO concentration might be appropriate forpractical application for it was easy to obtain a high and stableNOx removal efficiency in a relatively wide range of solutionpH
Figure 5 showed the effect of initial solution pH on NOxconcentration in flue gas When NaClO concentration washigher than 005M and solution pH was in the range of 4ndash8outlet NO concentration was lower than 124 ppm It sug-gested that themajority ofNOhad been oxidized intoNO2 byNaClO When NaClO concentration was 005M outlet NOconcentration decreased sharply to 35 ppm with initial pHdecreasing from 10 to 8 At the same time NO2 concentrationin outlet gas increased from 14 ppm to 353 ppm On furtherdecreasing the initial pH down to 6 a complete removal ofNO could be achieved with 005M NaClO while outlet NO2concentration reached about 400 ppm With the initial pHdecreasing from 6 to 4 NO in outlet gas increased to 124 ppmwhile NO2 in outlet gas decreased to 270 ppm NOx removalefficiency changed little in the range of pH 4ndash8 The resultsimplied that to a certain extent NOx removal efficiency forwet scrubbing using NaClO solution was mainly limited tothe absorption of NO2 rather than the oxidation of NO
32 Effect of Coexisting CO2 During wet scrubbing processCO2 in flue gas would react with absorbent thus influencing
4 Journal of Chemistry
0
20
40
60
80
100
Frac
tion
of ac
tive c
hlor
ine (
)
86 10 122 4
pH of NaClO solution
Cl2 HClOClOminusCl3
minus
Figure 4 Equilibrium concentrations of active chlorine species inNaClO solution as a function of solution pH
the oxidation and absorption of targeted pollutants As anacidic oxide CO2 was sensitive to the solution pH Theeffect of coexisting CO2 on NOx removal efficiency wasinvestigated and results were shown in Figure 6 It can beseen that with initial solution pH increasing from 4 to 8 NOxremoval efficiency was relatively stable A complete removalof NO had been achieved and outlet NO2 concentrationwas sim350 ppm The coexistence of CO2 had not affectedthe NOx removal efficiency so much But the average CO2concentration in outlet gas changed obviously with initialsolution pH When initial solution pH was below 6 theaverage CO2 concentration kept stable at 5 However itbegan to decrease quickly with initial pH increasing from 6to 8
The change of outlet CO2 concentration during the cyclicscrubbing process was shown in Figure 7 When initialpH was in the range of 4ndash6 CO2 concentration decreasedto 44ndash45 at the start of the scrubbing process Then itrecovered to the initial level due to the hydrolysis equilibriumbetween CO2 and absorbent solution The hydrolysis reac-tions of CO2 were described in (10) and (11) Furthermorea certain amount of H+ might be produced during thehydrolysis process whichwould affect the chlorine hydrolysisequilibrium reactions as shown in (12) and (13) Since HCO3
minus
andCO32minus had buffering ability to some extent the hydrolysis
of CO2 would not influence the solution pH obviously wheninitial pH was in the range of 4ndash6 But with initial pHincreasing from 6 to 8 the absorption of CO2 might reducethe solution alkalinity resulting in the decrease of the solutionpHThus it was necessary to keep the solution pHat 6 in orderto reduce the consumption of solution alkalinitywhenNaClOsolution was adopted to remove NOx from flue gas
CO2 +H2Olarrrarr CO32minus + 2H+ (10)
CO2 +H2Olarrrarr HCO3minus +H+ (11)
Cl2(aq) +H2Olarrrarr HClO +H+ + Clminus (12)
HClOlarrrarr ClOminus +H+ (13)
When initial pH was in the range of 7-8 CO2 concentrationdecreased largely at the very beginning of the cyclic scrub-bing process It suggested that much more CO2 had beenabsorbed by the scrubbing solution due to the weak alkalinemedium With the proceeding of the scrubbing processCO2 concentration began to increase slowly Although noevidence showed that CO2 would react with NaClO directlythe hydrolyzation and absorption of CO2 would increasethe consumption of solution alkalinity obviously It meantthat extra alkaline solution was required to maintain thesolution pH during cyclic scrubbing process which wouldlargely increase the operation complexity and cost at the sametime Thus initial pH of 6 might be appropriate for practicalapplication
Figure 8 showed the change of NaClO solution pHafter scrubbing for 20min With the proceeding of cyclicscrubbing process the solution pHwould decrease slowly dueto the absorption of NOx and CO2 It was worth noting thatthe solution pH increased from 4 to 463 for NaClO solutionwith initial pH 4 That was because active chlorine speciesin NaClO solution were mainly HClO and Cl2 at pH 4 asshown in Figure 4 During the scrubbing process Cl2 wouldbe purged out easily from the solution and reacted with NOeffectively in gas phase as (14) and (15) [25] The decreaseof Cl2 in NaClO solution would lead to a left shift of thehydrolysis equilibrium of active chlorine as shown in (16)resulting in the increase of solution pH for NaClO solutionwith initial pH 4
Cl2(aq) larrrarr Cl2(g) (14)
Cl2(g) +H2O +NO(g) larrrarr NO2(g) + 2HCl (15)
Cl2(g) +H2Olarrrarr HClO(aq) +H+ + Clminus (16)
It was possible that excessive Cl2 escaped from NaClOsolution might result in secondary pollution In additionacidicmist formed in the flue gasmight result in the corrosionof operation system In view of this NaClO solution with pH6 was appropriate for NOx removal in cyclic scrubbingmode
33 Effect of Coexisting O2 For marine diesel engines therewas typicalsim13O2 in exhaust gas O2 could partially oxidizeNO under certain conditions so it was necessary to investi-gate the effect of coexisting O2 on NOx removal efficiency Inthe experiments only NO standard gas was used to prepareNOx in the initial simulated flue gas The introduction ofO2 has oxidized a little of NO into NO2 in the gas mixerAs shown in Figure 9 the initial NO2 concentration ininlet gas increased almost linearly with the increase of NOconcentrationWhen inlet NOx concentrationwas 1000 ppmthe initial NO2 concentration reached 112 ppm
O2 + 2NO 997888rarr 2NO2 (17)
With the NOx increasing from 250 to 700 ppm the outletNO concentration decreased gradually to 0 When inlet
Journal of Chemistry 5
NaClO concentration00125 M0025 M005 M01M
0
200
400
600
800
1000
NO
conc
entr
atio
n (p
pm)
6 8 10 124
Initial pH of NaClO solution
00125 M0025 M005 M01M
(a)
0
200
400
600
800
1000
NO2
conc
entr
atio
n (p
pm)
86 10 124
Initial pH of NaClO solution
NaClO concentration00125 M0025 M005 M01M
00125 M0025 M005 M01M
(b)
Figure 5 The change of (a) NO concentrations and (b) NO2 concentrations in flue gas with initial pH of NaClO solution (gas flow is125 Lmin inlet NOx concentration is 1000 ppm NaClO concentration is in the range of 00125ndash01M and solution temperature is 293Ksolid points refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
5 6 7 84
Initial pH of NaClO solution
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
0
1
2
3
4
5
Out
let C
O2
conc
entr
atio
n at
aver
age (
)
NOx removal efficiencyOutlet CO2 concentration
Figure 6 The change of NOx removal efficiency and averaged CO2concentration in flue gas with initial pH (gas flow is 125 Lmin inletNOx concentration is 1000 ppm initial CO2 concentration is 5NaClO concentration is 005M and solution temperature is 293K)
NOx concentration was higher than 700 ppm NO could beremoved completely As expected the outlet NO2 concen-tration increased almost linearly with the increase of inletNOx concentration It indicated that NOx removal efficiencydepended to a great extent on the absorption of NO2 duringthe scrubbing process
Figure 10 presented the change of NOx removal effi-ciency and outlet O2 concentration with the initial NOx
0
1
2
3
4
5
Out
let C
O2
conc
entr
atio
n (
)
5 10 15 200
Cyclic scrubbing duration (min)
Initial pH of NaClO solution4
5
6
7
8
Figure 7 The change of CO2 concentration during the cyclicscrubbing duration (gas flow is 125 Lmin inlet NO concentrationis 1000 ppm initial CO2 concentration is 5 NaClO concentrationis 005M and solution temperature is 293K)
concentration Since O2 concentration was relatively highit changed little during the scrubbing process With theincrease of NOx concentration from 250 ppm to 700 ppmNOx removal efficiency increased from 47 to 74 It could
6 Journal of Chemistry
0
2
4
6
8
10
pH o
f use
d N
aClO
solu
tion
5 6 7 84
Initial pH of NaClO solution
Figure 8 NaClO solution pH after scrubbing for 20min (gas flowis 125 Lmin inlet NOx concentration is 1000 ppm initial CO2concentration is 5 NaClO concentration is 005M and solutiontemperature is 293K)
Initial NOx concentration in inlet gas (ppm)1000800600400200
0
200
400
600
800
1000
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
Figure 9 The change of NOx concentration with the initial NOxconcentration (gas flow is 125 Lmin inlet O2 concentration is13 inlet NOx concentration is in the range of 250ndash1000 ppmNaClO concentration is 005M initial solution pH is 6 and solutiontemperature is 293K solid points refer to inlet NOx concentrationsand open points refer to outlet NOx concentrations)
be ascribed to the improvement of the mass transfer at thegas-liquid interface When O2 was present in flue gas NOxremoval efficiency was a little higher than that without O2in flue gas The existence of O2 improved the NOx removalefficiency in way of partly oxidizing NO in initial flue gas
34 Effect of NOx Concentration The effects of NOx con-centration on NOx removal are investigated and the resultsare shown in Figure 11 It can be seen that with initial NO
Initial NOx concentration in inlet gas (ppm)1000800600400200
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
0
3
6
9
12
15
Out
let O
2co
ncen
trat
ion
at av
erag
e (
)
NOx removal efficiencyOutlet O2 concentration
Figure 10The change of NOx removal efficiency and outlet O2 con-centration with the initial NOx concentration (conditions gas flow125 Lmin inlet O2 concentration 13 inlet NOx concentration250ndash1000 ppm NaClO concentration 005M initial solution pH 6solution temperature 293K)
concentration increasing from 250 ppm to 500 ppm NOxremoval efficiency increased from 43 to sim63 NO could beremoved completelywhen inletNOconcentrationwas higherthan 500 ppm Outlet NO2 concentration increased quicklywith the increase of inlet NO concentration resulting in arelatively stable NOx removal efficiency
35 Simultaneous Removal of NOx and SO2 Marine dieselengines usually burn heavy fuel oil (HFO) in order to savethe operating cost At present the mass concentration ofsulphur (S) content in HFO was about 25 at average Thecombustion of HFO fuel would produce a large amountof SO2 in exhaust gas Experiments were conducted toinvestigate the effect of coexisting SO2 on NOx removalefficiency and the results are shown in Figures 12 and 13
Figure 12 depicted the change of NOx removal efficiencyand NOx concentration with inlet NOx concentration Acomplete removal of SO2 and NO had been achieved simul-taneously Due to its high solubility SO2 could be absorbedeffectively by scrubbing solution Then SO2 was removedthrough the hydrolysis reaction as (18) and (19) The hydrol-ysis products of SO3
2minus would be oxidized by active chlorinespecies into SO4
2minus quickly Thus the removal of SO2 wouldconsume the solution alkalinity and oxidants at the sametime The result demonstrated that NaClO solution could beused to remove NO and SO2 simultaneously from marineexhaust gas However outlet NO2 concentration increasedgradually with the increase of inlet NOx concentration
SO2 +H2O 997888rarr HSO3minus +H+ (18)
HSO3minus 997888rarr SO3
2minus +H+ (19)
SO3minus +HClO 997888rarr SO4
2minus +HCl (20)
Journal of Chemistry 7
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
(a)
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
200
400
600
800
1000
1200
1400
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
(b)
Figure 11 The change of (a) NOx removal efficiency and (b) NO119909 concentrations with the initial NOx concentration (gas flow is 125 Lmininlet NOx concentration is 250ndash1250 ppm NaClO concentration is 005M initial solution pH is 6 and solution temperature is 293K solidpoints refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
20
40
60
80
100
Rem
oval
effici
ency
()
SO2
NOx
(a)
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
200
400
600
800
1000
1200
1400
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
(b)
Figure 12 The change of (a) NOx removal efficiency and (b) NOx concentration with the inlet NOx concentration (gas flow is 125 Lmininlet SO2 concentration is 600 ppm inlet NOx concentration is 250ndash1250 ppm NaClO concentration is 005M initial solution pH is 6 andsolution temperature is 293K solid points refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
Figure 13 exhibited the effect of SO2 concentration on NOxremoval efficiency and NOx concentration in flue gas Theresult showed that SO2 together with NO was completelyremoved But with the increase of inlet SO2 concentrationNOx removal efficiency exhibited a slightly downside trendThis phenomenon could be ascribed to the competitionreactions between NOx and SO2 Some oxidants in theabsorbent would be consumed through the hydrolyzation
and absorption of SO2With inlet SO2 concentration increas-ing from 200 ppm to 600 ppm the pHof the scrubbedNaClOsolution decreased from 525 to 452The decrease of solutionpH was negative for the absorption of NO2 through (5) and(6)
36 Effect of Absorbent Temperature The reaction temper-ature could greatly influence the diffusion dissolution and
8 Journal of Chemistry
0
20
40
60
80
100
Rem
oval
effici
ency
()
SO2
NOx
300 500 600400200
Initial SO2 concentration in inlet gas (ppm)
(a)
0
200
400
600
800
1000
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
300 500 600400200
Initial SO2 concentration in inlet gas (ppm)
(b)
Figure 13 The change of (a) NOx removal efficiency and (b) NOx concentration with the initial SO2 concentration (gas flow is 125 Lmininlet SO2 concentration is 200ndash600 ppm inlet NOx concentration is 1000 ppm NaClO concentration is 005M initial solution pH is 6 andsolution temperature is 293K solid points refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
Absorbent temperature (K)340330320310300290
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
(a)
Absorbent temperature (K)340330320310300290
0
200
400
600
800
1000
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
(b)
Figure 14The change of (a) NOx removal efficiency and (b) NOx concentration with the absorbent temperature (gas flow is 125 Lmin inletNOx concentration is 1000 ppm NaClO concentration is 005M initial solution pH is 6 and solution temperature is 293ndash333K solid pointsrefer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
reaction characteristics of molecules or ions in liquid phase[19] The effect of absorbent temperature on NOx removalwas investigated and the results were shown in Figure 14Generally the absorbent temperature was kept below 333Kin industrial application in order to reduce the supply ofmake-up water So the absorbent temperature was chosen tobe in the range of 293ndash333K in the experiments Figure 14showed that NOx removal efficiency increased gradually with
the increase of absorbent temperature The highest NOxremoval efficiency of 69was achieved at 333 K AsNO couldbe removed by 100 easily the increase of NOx removalefficiency resulted from the improvement of NO2 absorptionThis could be explained by the Arrhenius equation of thereaction rate constant The increase of temperature couldenhance the mass transfer of NO2 to the absorbent thusimproving the absorption of NO2 accordingly
Journal of Chemistry 9
4 Conclusion
NOx removal by wet scrubbing using NaClO solution wasstudied based on a spraying reactor in a cyclic mode Theresults showed that when NaClO concentration was higherthan 005M and initial solution pH was below 8 NOxremoval efficiency was relatively stable which was higherthan 60 The coexisting CO2 (5) had little effect on NOxremoval efficiency but the solution pHbegan to decreasewiththe proceeding of cyclic scrubbing process when initial pHwas higher than 6The coexisting O2 (13) could oxidize NOpartially in the gas mixer resulting in a little improvementof NOx removal efficiency When initial NOx concentrationwas higher than 500 ppm NO could be removed completelywhile outlet NO2 concentration increased almost linearlywith the increase of initial NOx concentration resultingin a relative stable NOx removal efficiency A completeremoval of SO2 and NO could be achieved simultaneouslyat 293K initial NaClO solution pH 6 and 005M NaClOconcentration With the increase of inlet SO2 concentrationthe outlet NO2 concentration increased slightly due to thedecrease of solution pH NOx removal efficiency increasedwith the increase of absorbent temperature The relevantreaction mechanism for the removal of NOx and SO2 bywet scrubbing using NaClO solution was also discussed Theresults demonstrated that it was of great potential for NaClOsolution to remove NOx from marine exhaust gas
Conflicts of Interest
The authors declare that there are no conflicts of interestregarding the publication of this paper
Acknowledgments
This study has been financially supported by the NationalNatural Science Foundation of China (Grant nos 51402033and 51479020) the Science and Technology Plan Project ofChinarsquos Ministry of Transport (Grant no 2015328225150) theDoctoral Scientific Research Staring Foundation of Liaon-ing Province (Grant no 201601073) and the FundamentalResearch Funds for the Central Universities (Grant nos3132017003 and 3132016326)
References
[1] M Guo Z Fu DMa N Ji C Song and Q Liu ldquoA short reviewof treatment methods of marine diesel engine exhaust gasesrdquoProcedia Engineering vol 121 pp 938ndash943 2015
[2] M-W Bae ldquoA study on the effects of recirculated exhaust gasupon NO119909 and soot emissions in diesel engines with scrubberEGR systemrdquo SAE Technical Papers 1999
[3] A M A Attia and A R Kulchitskiy ldquoInfluence of the structureof water-in-fuel emulsion on diesel engine performancerdquo Fuelvol 116 pp 703ndash708 2014
[4] X Tauzia A Maiboom and S R Shah ldquoExperimental study ofinlet manifold water injection on combustion and emissions ofan automotive direct injection diesel enginerdquoEnergy vol 35 no9 pp 3628ndash3639 2010
[5] A M Hallquist E Fridell J Westerlund and M Hal-lquist ldquoOnboard measurements of nanoparticles from a SCR-equipped marine diesel enginerdquo Environmental Science andTechnology vol 47 no 2 pp 773ndash780 2013
[6] J Herdzik ldquoEmissions from marine engines versus IMO certi-fication and requirements of tier 3rdquo Journal of KONES vol 18pp 161ndash167 2011
[7] M Magnusson E Fridell and H H Ingelsten ldquoThe influenceof sulfur dioxide andwater on the performance of amarine SCRcatalystrdquoApplied Catalysis B Environmental vol 111-112 pp 20ndash26 2012
[8] T Kuwahara K Yoshida Y Kannaka T Kuroki andMOkuboldquoImprovement of NOx reduction efficiency in diesel emissioncontrol using nonthermal plasma combined exhaust gas recir-culation processrdquo IEEE Transactions on Industry Applicationsvol 47 no 6 pp 2359ndash2366 2011
[9] T Kuwahara K Yoshida T Kuroki K Hanamoto K Sato andMOkubo ldquoPilot-scale aftertreatment using nonthermal plasmareduction of adsorbed NO119909 in marine diesel-engine exhaustgasrdquo Plasma Chemistry and Plasma Processing vol 34 no 1 pp65ndash81 2014
[10] D Xie Y Sun T Zhu and L Ding ldquoRemoval of NO in mist bythe combination of plasma oxidation and chemical absorptionrdquoEnergy and Fuels vol 30 no 6 pp 5071ndash5076 2016
[11] S Zhou J Zhou Y Feng and Y Zhu ldquoMarine Emission Pol-lution Abatement Using Ozone Oxidation by a Wet ScrubbingMethodrdquo Industrial andEngineeringChemistry Research vol 55no 20 pp 5825ndash5831 2016
[12] Y S Mok ldquoAbsorption-reduction technique assisted by ozoneinjection and sodium sulfide for NO119909 removal from exhaustgasrdquo Chemical Engineering Journal vol 118 no 1-2 pp 63ndash672006
[13] E B Myers and T J Overcamp ldquoHydrogen peroxide scrubberfor the control of nitrogen oxidesrdquo Environmental EngineeringScience vol 19 no 5 pp 321ndash327 2002
[14] Z Wang Z Wang Y Ye N Chen and H Li ldquoStudy on theremoval of nitric oxide (NO) by dual oxidant (H2O2S2O82
minus)systemrdquo Chemical Engineering Science vol 145 pp 133ndash1402016
[15] Y Liu Q Wang Y Yin J Pan and J Zhang ldquoAdvancedoxidation removal ofNOand SO2 fromflue gas by using ultravi-oletH2O2NaOH processrdquo Chemical Engineering Research andDesign vol 92 no 10 pp 1907ndash1914 2014
[16] H Chu T W Chien and S Y Li ldquoSimultaneous absorptionof SO2 and NO from flue gas with KMnO4NaOH solutionsrdquoScience of the Total Environment vol 275 no 1-3 pp 127ndash1352001
[17] R Hao Y Zhang Z Wang et al ldquoAn advanced wet method forsimultaneous removal of SO2 andNO fromcoal-fired flue gas byutilizing a complex absorbentrdquo Chemical Engineering Journalvol 307 pp 562ndash571 2017
[18] Z Han S Yang D Zheng X Pan and Z Yan ldquoAn investigationon NO removal by wet scrubbing using NaClO2 seawatersolutionrdquo SpringerPlus vol 5 no 1 article 751 2016
[19] Y Zhou C Li C Fan et al ldquoWet removal of sulfur dioxide andnitrogen oxides from simulated flue gas by Ca(ClO)2 solutionrdquoEnvironmental Progress and Sustainable Energy vol 34 no 6pp 1586ndash1595 2015
[20] S-L Yang Z-T Han J-M Dong Z-S Zheng and X-X PanldquoUV-enhanced naclo oxidation of nitric oxide from simulatedflue gasrdquo Journal of Chemistry vol 2016 Article ID 6065019 8pages 2016
10 Journal of Chemistry
[21] L Chen C-H Hsu and C-L Yang ldquoOxidation and absorptionof nitric oxide in a packed tower with sodium hypochloriteaqueous solutionsrdquo Environmental Progress vol 24 no 3 pp279ndash288 2005
[22] E Ghibaudi J R Barker and S W Benson ldquoReaction ofNO with hypochlorous acidrdquo International Journal of ChemicalKinetics vol 11 no 8 pp 843ndash851 1979
[23] R-T Guo W-G Pan X-B Zhang et al ldquoThe absorptionkinetics of NO into weakly acidic NaClO solutionrdquo SeparationScience and Technology vol 48 no 18 pp 2871ndash2875 2013
[24] S Yang Z Han X Pan Z Yan and J Yu ldquoNitrogen oxideremoval using seawater electrolysis in an undivided cell forocean-going vesselsrdquo RSC Advances vol 6 no 115 pp 114623ndash114631 2016
[25] M K Mondal and V R Chelluboyana ldquoNew experimentalresults of combined SO2 and NO removal from simulated gasstream by NaClO as low-cost absorbentrdquo Chemical EngineeringJournal vol 217 pp 48ndash53 2013
[26] C V Raghunath and M K Mondal ldquoExperimental scalemulti component absorption of SO2 and NO by NH3NaClOscrubbingrdquo Chemical Engineering Journal vol 314 pp 537ndash5472017
[27] J Wang and W Zhong ldquoSimultaneous desulfurization anddenitrification of sintering flue gas via composite absorbentrdquoChinese Journal of Chemical Engineering vol 24 no 8 pp 1104ndash1111 2016
[28] S An and O Nishida ldquoNew application of seawater andelectrolyzed seawater in air pollution control of marine dieselenginerdquo JSME International Journal Series B Fluids and Ther-mal Engineering vol 46 no 1 pp 206ndash213 2003
[29] Z Han S Yang X Pan et al ldquoNew experimental results of NOremoval from simulated flue gas by wet scrubbing using NaClOsolutionrdquo Energy amp Fuels vol 31 no 3 pp 3047ndash3054 2017
[30] N Lahoutifard P Lagrange and J Lagrange ldquoKinetics andmechanism of nitrite oxidation by hypochlorous acid in theaqueous phaserdquo Chemosphere vol 50 no 10 pp 1349ndash13572003
[31] Y G Adewuyi X He H Shaw and W Lolertpihop ldquoSimul-taneous absorption and oxidation of NO and SO2 by aqueoussolutions of sodium chloriterdquo Chemical Engineering Communi-cations vol 174 no 1 pp 21ndash51 1999
[32] A Mukimin K Wijaya and A Kuncaka ldquoElectro-degradationof reactive blue dyes using cylinder modified electrode Ti120573-PbO2 as dimensionally stable anoderdquo Indonesian Journal ofChemistry vol 10 no 3 pp 285ndash289 2010
Figure 2 Effect of initial solution pH on NOx removal efficiency(gas flow is 125 Lmin inlet NOx concentration is 1000 ppm NaClOconcentration is 00125ndash01M and solution temperature is 293K)
3 Results and Discussion
31 Effect of Initial pH and NaClO Concentration The activecomponents in NaClO solution were available chlorinewhich mainly includes HClO ClOminus and Cl2 The compo-sitions of NaClO solution depended greatly on the solutionpH Firstly it was necessary to investigate the effect of initialsolution pH on the NOx removal efficiency Figure 2 showedthat NOx removal efficiency was very low when the solutionpH was higher than 10 That was because little HClO existedin the solution when solution pH was higher than 10 butHClO was considered to be the main component in NaClOsolution to oxidize NO [22] It demonstrated that NaClOsolution without optimizing the initial pH was not suitablefor removing NOx With the decrease of initial pH from 10to 8 NOx removal efficiency increased quickly which wasdue to the increase of fractional composition of HClO insolution HClO oxidized NO into NO2 N2O3 N2O4 andNO3minus in chain reactions of (2)ndash(9) [30 31] The possible
reaction pathways were summarized as shown in Figure 3
NO +HClO 997888rarr NO2 +HCl (2)
NO +NO2 997888rarr N2O3 (3)
2NO2 larrrarr N2O4 (4)
3NO2 +H2O 997888rarr 2HNO3 +NO (5)
2NO2 +H2O 997888rarr HNO3 +HNO2 (6)
N2O3 +H2O 997888rarr 2HNO2 (7)
N2O4 +H2O 997888rarr HNO3 +HNO2 (8)
HNO2 +HClO 997888rarr HNO3 +HCl (9)
Gas-liquid interface
Gas phase Liquid phase
HNO2
HNO3
(2)(3)
(4)
(5)
(6)
(7)
(8)
(9)
N2O3(g)
NO(g)
NO2(g)
N2O4(g)
N2O3(aq)
NO(aq)
N2O4(aq)
NO2(aq)
Figure 3 Reaction pathways for NOx removal by NaClO solution
As shown in Figure 2 with the initial pH decreasing from 8to 7 a slight drop of NOx removal efficiency appeared Onfurther reducing the initial pH the changes of NOx removalefficiency depended on NaClO concentration When initialNaClO concentration was below 005M NOx removal effi-ciency continued to decrease with initial pH decreasing from7 to 6 This was because the oxidation power of ClOminus wasstronger than that ofHClO in neutral orweak acidicmediumAs shown in Figure 4 HClO concentration increased whileClOminus concentration decreased with solution pH decreasingfrom 7 to 6 However whenNaClO concentration was higherthan 005M the oxidation power of active chlorine washigh enough to oxidize NO effectively at pH 6 and 7 [32]At the moment the effect of the change of active chlorineconcentration was not obvious enough The result indicatedthat a high NaClO concentration might be appropriate forpractical application for it was easy to obtain a high and stableNOx removal efficiency in a relatively wide range of solutionpH
Figure 5 showed the effect of initial solution pH on NOxconcentration in flue gas When NaClO concentration washigher than 005M and solution pH was in the range of 4ndash8outlet NO concentration was lower than 124 ppm It sug-gested that themajority ofNOhad been oxidized intoNO2 byNaClO When NaClO concentration was 005M outlet NOconcentration decreased sharply to 35 ppm with initial pHdecreasing from 10 to 8 At the same time NO2 concentrationin outlet gas increased from 14 ppm to 353 ppm On furtherdecreasing the initial pH down to 6 a complete removal ofNO could be achieved with 005M NaClO while outlet NO2concentration reached about 400 ppm With the initial pHdecreasing from 6 to 4 NO in outlet gas increased to 124 ppmwhile NO2 in outlet gas decreased to 270 ppm NOx removalefficiency changed little in the range of pH 4ndash8 The resultsimplied that to a certain extent NOx removal efficiency forwet scrubbing using NaClO solution was mainly limited tothe absorption of NO2 rather than the oxidation of NO
32 Effect of Coexisting CO2 During wet scrubbing processCO2 in flue gas would react with absorbent thus influencing
4 Journal of Chemistry
0
20
40
60
80
100
Frac
tion
of ac
tive c
hlor
ine (
)
86 10 122 4
pH of NaClO solution
Cl2 HClOClOminusCl3
minus
Figure 4 Equilibrium concentrations of active chlorine species inNaClO solution as a function of solution pH
the oxidation and absorption of targeted pollutants As anacidic oxide CO2 was sensitive to the solution pH Theeffect of coexisting CO2 on NOx removal efficiency wasinvestigated and results were shown in Figure 6 It can beseen that with initial solution pH increasing from 4 to 8 NOxremoval efficiency was relatively stable A complete removalof NO had been achieved and outlet NO2 concentrationwas sim350 ppm The coexistence of CO2 had not affectedthe NOx removal efficiency so much But the average CO2concentration in outlet gas changed obviously with initialsolution pH When initial solution pH was below 6 theaverage CO2 concentration kept stable at 5 However itbegan to decrease quickly with initial pH increasing from 6to 8
The change of outlet CO2 concentration during the cyclicscrubbing process was shown in Figure 7 When initialpH was in the range of 4ndash6 CO2 concentration decreasedto 44ndash45 at the start of the scrubbing process Then itrecovered to the initial level due to the hydrolysis equilibriumbetween CO2 and absorbent solution The hydrolysis reac-tions of CO2 were described in (10) and (11) Furthermorea certain amount of H+ might be produced during thehydrolysis process whichwould affect the chlorine hydrolysisequilibrium reactions as shown in (12) and (13) Since HCO3
minus
andCO32minus had buffering ability to some extent the hydrolysis
of CO2 would not influence the solution pH obviously wheninitial pH was in the range of 4ndash6 But with initial pHincreasing from 6 to 8 the absorption of CO2 might reducethe solution alkalinity resulting in the decrease of the solutionpHThus it was necessary to keep the solution pHat 6 in orderto reduce the consumption of solution alkalinitywhenNaClOsolution was adopted to remove NOx from flue gas
CO2 +H2Olarrrarr CO32minus + 2H+ (10)
CO2 +H2Olarrrarr HCO3minus +H+ (11)
Cl2(aq) +H2Olarrrarr HClO +H+ + Clminus (12)
HClOlarrrarr ClOminus +H+ (13)
When initial pH was in the range of 7-8 CO2 concentrationdecreased largely at the very beginning of the cyclic scrub-bing process It suggested that much more CO2 had beenabsorbed by the scrubbing solution due to the weak alkalinemedium With the proceeding of the scrubbing processCO2 concentration began to increase slowly Although noevidence showed that CO2 would react with NaClO directlythe hydrolyzation and absorption of CO2 would increasethe consumption of solution alkalinity obviously It meantthat extra alkaline solution was required to maintain thesolution pH during cyclic scrubbing process which wouldlargely increase the operation complexity and cost at the sametime Thus initial pH of 6 might be appropriate for practicalapplication
Figure 8 showed the change of NaClO solution pHafter scrubbing for 20min With the proceeding of cyclicscrubbing process the solution pHwould decrease slowly dueto the absorption of NOx and CO2 It was worth noting thatthe solution pH increased from 4 to 463 for NaClO solutionwith initial pH 4 That was because active chlorine speciesin NaClO solution were mainly HClO and Cl2 at pH 4 asshown in Figure 4 During the scrubbing process Cl2 wouldbe purged out easily from the solution and reacted with NOeffectively in gas phase as (14) and (15) [25] The decreaseof Cl2 in NaClO solution would lead to a left shift of thehydrolysis equilibrium of active chlorine as shown in (16)resulting in the increase of solution pH for NaClO solutionwith initial pH 4
Cl2(aq) larrrarr Cl2(g) (14)
Cl2(g) +H2O +NO(g) larrrarr NO2(g) + 2HCl (15)
Cl2(g) +H2Olarrrarr HClO(aq) +H+ + Clminus (16)
It was possible that excessive Cl2 escaped from NaClOsolution might result in secondary pollution In additionacidicmist formed in the flue gasmight result in the corrosionof operation system In view of this NaClO solution with pH6 was appropriate for NOx removal in cyclic scrubbingmode
33 Effect of Coexisting O2 For marine diesel engines therewas typicalsim13O2 in exhaust gas O2 could partially oxidizeNO under certain conditions so it was necessary to investi-gate the effect of coexisting O2 on NOx removal efficiency Inthe experiments only NO standard gas was used to prepareNOx in the initial simulated flue gas The introduction ofO2 has oxidized a little of NO into NO2 in the gas mixerAs shown in Figure 9 the initial NO2 concentration ininlet gas increased almost linearly with the increase of NOconcentrationWhen inlet NOx concentrationwas 1000 ppmthe initial NO2 concentration reached 112 ppm
O2 + 2NO 997888rarr 2NO2 (17)
With the NOx increasing from 250 to 700 ppm the outletNO concentration decreased gradually to 0 When inlet
Journal of Chemistry 5
NaClO concentration00125 M0025 M005 M01M
0
200
400
600
800
1000
NO
conc
entr
atio
n (p
pm)
6 8 10 124
Initial pH of NaClO solution
00125 M0025 M005 M01M
(a)
0
200
400
600
800
1000
NO2
conc
entr
atio
n (p
pm)
86 10 124
Initial pH of NaClO solution
NaClO concentration00125 M0025 M005 M01M
00125 M0025 M005 M01M
(b)
Figure 5 The change of (a) NO concentrations and (b) NO2 concentrations in flue gas with initial pH of NaClO solution (gas flow is125 Lmin inlet NOx concentration is 1000 ppm NaClO concentration is in the range of 00125ndash01M and solution temperature is 293Ksolid points refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
5 6 7 84
Initial pH of NaClO solution
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
0
1
2
3
4
5
Out
let C
O2
conc
entr
atio
n at
aver
age (
)
NOx removal efficiencyOutlet CO2 concentration
Figure 6 The change of NOx removal efficiency and averaged CO2concentration in flue gas with initial pH (gas flow is 125 Lmin inletNOx concentration is 1000 ppm initial CO2 concentration is 5NaClO concentration is 005M and solution temperature is 293K)
NOx concentration was higher than 700 ppm NO could beremoved completely As expected the outlet NO2 concen-tration increased almost linearly with the increase of inletNOx concentration It indicated that NOx removal efficiencydepended to a great extent on the absorption of NO2 duringthe scrubbing process
Figure 10 presented the change of NOx removal effi-ciency and outlet O2 concentration with the initial NOx
0
1
2
3
4
5
Out
let C
O2
conc
entr
atio
n (
)
5 10 15 200
Cyclic scrubbing duration (min)
Initial pH of NaClO solution4
5
6
7
8
Figure 7 The change of CO2 concentration during the cyclicscrubbing duration (gas flow is 125 Lmin inlet NO concentrationis 1000 ppm initial CO2 concentration is 5 NaClO concentrationis 005M and solution temperature is 293K)
concentration Since O2 concentration was relatively highit changed little during the scrubbing process With theincrease of NOx concentration from 250 ppm to 700 ppmNOx removal efficiency increased from 47 to 74 It could
6 Journal of Chemistry
0
2
4
6
8
10
pH o
f use
d N
aClO
solu
tion
5 6 7 84
Initial pH of NaClO solution
Figure 8 NaClO solution pH after scrubbing for 20min (gas flowis 125 Lmin inlet NOx concentration is 1000 ppm initial CO2concentration is 5 NaClO concentration is 005M and solutiontemperature is 293K)
Initial NOx concentration in inlet gas (ppm)1000800600400200
0
200
400
600
800
1000
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
Figure 9 The change of NOx concentration with the initial NOxconcentration (gas flow is 125 Lmin inlet O2 concentration is13 inlet NOx concentration is in the range of 250ndash1000 ppmNaClO concentration is 005M initial solution pH is 6 and solutiontemperature is 293K solid points refer to inlet NOx concentrationsand open points refer to outlet NOx concentrations)
be ascribed to the improvement of the mass transfer at thegas-liquid interface When O2 was present in flue gas NOxremoval efficiency was a little higher than that without O2in flue gas The existence of O2 improved the NOx removalefficiency in way of partly oxidizing NO in initial flue gas
34 Effect of NOx Concentration The effects of NOx con-centration on NOx removal are investigated and the resultsare shown in Figure 11 It can be seen that with initial NO
Initial NOx concentration in inlet gas (ppm)1000800600400200
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
0
3
6
9
12
15
Out
let O
2co
ncen
trat
ion
at av
erag
e (
)
NOx removal efficiencyOutlet O2 concentration
Figure 10The change of NOx removal efficiency and outlet O2 con-centration with the initial NOx concentration (conditions gas flow125 Lmin inlet O2 concentration 13 inlet NOx concentration250ndash1000 ppm NaClO concentration 005M initial solution pH 6solution temperature 293K)
concentration increasing from 250 ppm to 500 ppm NOxremoval efficiency increased from 43 to sim63 NO could beremoved completelywhen inletNOconcentrationwas higherthan 500 ppm Outlet NO2 concentration increased quicklywith the increase of inlet NO concentration resulting in arelatively stable NOx removal efficiency
35 Simultaneous Removal of NOx and SO2 Marine dieselengines usually burn heavy fuel oil (HFO) in order to savethe operating cost At present the mass concentration ofsulphur (S) content in HFO was about 25 at average Thecombustion of HFO fuel would produce a large amountof SO2 in exhaust gas Experiments were conducted toinvestigate the effect of coexisting SO2 on NOx removalefficiency and the results are shown in Figures 12 and 13
Figure 12 depicted the change of NOx removal efficiencyand NOx concentration with inlet NOx concentration Acomplete removal of SO2 and NO had been achieved simul-taneously Due to its high solubility SO2 could be absorbedeffectively by scrubbing solution Then SO2 was removedthrough the hydrolysis reaction as (18) and (19) The hydrol-ysis products of SO3
2minus would be oxidized by active chlorinespecies into SO4
2minus quickly Thus the removal of SO2 wouldconsume the solution alkalinity and oxidants at the sametime The result demonstrated that NaClO solution could beused to remove NO and SO2 simultaneously from marineexhaust gas However outlet NO2 concentration increasedgradually with the increase of inlet NOx concentration
SO2 +H2O 997888rarr HSO3minus +H+ (18)
HSO3minus 997888rarr SO3
2minus +H+ (19)
SO3minus +HClO 997888rarr SO4
2minus +HCl (20)
Journal of Chemistry 7
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
(a)
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
200
400
600
800
1000
1200
1400
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
(b)
Figure 11 The change of (a) NOx removal efficiency and (b) NO119909 concentrations with the initial NOx concentration (gas flow is 125 Lmininlet NOx concentration is 250ndash1250 ppm NaClO concentration is 005M initial solution pH is 6 and solution temperature is 293K solidpoints refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
20
40
60
80
100
Rem
oval
effici
ency
()
SO2
NOx
(a)
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
200
400
600
800
1000
1200
1400
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
(b)
Figure 12 The change of (a) NOx removal efficiency and (b) NOx concentration with the inlet NOx concentration (gas flow is 125 Lmininlet SO2 concentration is 600 ppm inlet NOx concentration is 250ndash1250 ppm NaClO concentration is 005M initial solution pH is 6 andsolution temperature is 293K solid points refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
Figure 13 exhibited the effect of SO2 concentration on NOxremoval efficiency and NOx concentration in flue gas Theresult showed that SO2 together with NO was completelyremoved But with the increase of inlet SO2 concentrationNOx removal efficiency exhibited a slightly downside trendThis phenomenon could be ascribed to the competitionreactions between NOx and SO2 Some oxidants in theabsorbent would be consumed through the hydrolyzation
and absorption of SO2With inlet SO2 concentration increas-ing from 200 ppm to 600 ppm the pHof the scrubbedNaClOsolution decreased from 525 to 452The decrease of solutionpH was negative for the absorption of NO2 through (5) and(6)
36 Effect of Absorbent Temperature The reaction temper-ature could greatly influence the diffusion dissolution and
8 Journal of Chemistry
0
20
40
60
80
100
Rem
oval
effici
ency
()
SO2
NOx
300 500 600400200
Initial SO2 concentration in inlet gas (ppm)
(a)
0
200
400
600
800
1000
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
300 500 600400200
Initial SO2 concentration in inlet gas (ppm)
(b)
Figure 13 The change of (a) NOx removal efficiency and (b) NOx concentration with the initial SO2 concentration (gas flow is 125 Lmininlet SO2 concentration is 200ndash600 ppm inlet NOx concentration is 1000 ppm NaClO concentration is 005M initial solution pH is 6 andsolution temperature is 293K solid points refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
Absorbent temperature (K)340330320310300290
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
(a)
Absorbent temperature (K)340330320310300290
0
200
400
600
800
1000
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
(b)
Figure 14The change of (a) NOx removal efficiency and (b) NOx concentration with the absorbent temperature (gas flow is 125 Lmin inletNOx concentration is 1000 ppm NaClO concentration is 005M initial solution pH is 6 and solution temperature is 293ndash333K solid pointsrefer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
reaction characteristics of molecules or ions in liquid phase[19] The effect of absorbent temperature on NOx removalwas investigated and the results were shown in Figure 14Generally the absorbent temperature was kept below 333Kin industrial application in order to reduce the supply ofmake-up water So the absorbent temperature was chosen tobe in the range of 293ndash333K in the experiments Figure 14showed that NOx removal efficiency increased gradually with
the increase of absorbent temperature The highest NOxremoval efficiency of 69was achieved at 333 K AsNO couldbe removed by 100 easily the increase of NOx removalefficiency resulted from the improvement of NO2 absorptionThis could be explained by the Arrhenius equation of thereaction rate constant The increase of temperature couldenhance the mass transfer of NO2 to the absorbent thusimproving the absorption of NO2 accordingly
Journal of Chemistry 9
4 Conclusion
NOx removal by wet scrubbing using NaClO solution wasstudied based on a spraying reactor in a cyclic mode Theresults showed that when NaClO concentration was higherthan 005M and initial solution pH was below 8 NOxremoval efficiency was relatively stable which was higherthan 60 The coexisting CO2 (5) had little effect on NOxremoval efficiency but the solution pHbegan to decreasewiththe proceeding of cyclic scrubbing process when initial pHwas higher than 6The coexisting O2 (13) could oxidize NOpartially in the gas mixer resulting in a little improvementof NOx removal efficiency When initial NOx concentrationwas higher than 500 ppm NO could be removed completelywhile outlet NO2 concentration increased almost linearlywith the increase of initial NOx concentration resultingin a relative stable NOx removal efficiency A completeremoval of SO2 and NO could be achieved simultaneouslyat 293K initial NaClO solution pH 6 and 005M NaClOconcentration With the increase of inlet SO2 concentrationthe outlet NO2 concentration increased slightly due to thedecrease of solution pH NOx removal efficiency increasedwith the increase of absorbent temperature The relevantreaction mechanism for the removal of NOx and SO2 bywet scrubbing using NaClO solution was also discussed Theresults demonstrated that it was of great potential for NaClOsolution to remove NOx from marine exhaust gas
Conflicts of Interest
The authors declare that there are no conflicts of interestregarding the publication of this paper
Acknowledgments
This study has been financially supported by the NationalNatural Science Foundation of China (Grant nos 51402033and 51479020) the Science and Technology Plan Project ofChinarsquos Ministry of Transport (Grant no 2015328225150) theDoctoral Scientific Research Staring Foundation of Liaon-ing Province (Grant no 201601073) and the FundamentalResearch Funds for the Central Universities (Grant nos3132017003 and 3132016326)
References
[1] M Guo Z Fu DMa N Ji C Song and Q Liu ldquoA short reviewof treatment methods of marine diesel engine exhaust gasesrdquoProcedia Engineering vol 121 pp 938ndash943 2015
[2] M-W Bae ldquoA study on the effects of recirculated exhaust gasupon NO119909 and soot emissions in diesel engines with scrubberEGR systemrdquo SAE Technical Papers 1999
[3] A M A Attia and A R Kulchitskiy ldquoInfluence of the structureof water-in-fuel emulsion on diesel engine performancerdquo Fuelvol 116 pp 703ndash708 2014
[4] X Tauzia A Maiboom and S R Shah ldquoExperimental study ofinlet manifold water injection on combustion and emissions ofan automotive direct injection diesel enginerdquoEnergy vol 35 no9 pp 3628ndash3639 2010
[5] A M Hallquist E Fridell J Westerlund and M Hal-lquist ldquoOnboard measurements of nanoparticles from a SCR-equipped marine diesel enginerdquo Environmental Science andTechnology vol 47 no 2 pp 773ndash780 2013
[6] J Herdzik ldquoEmissions from marine engines versus IMO certi-fication and requirements of tier 3rdquo Journal of KONES vol 18pp 161ndash167 2011
[7] M Magnusson E Fridell and H H Ingelsten ldquoThe influenceof sulfur dioxide andwater on the performance of amarine SCRcatalystrdquoApplied Catalysis B Environmental vol 111-112 pp 20ndash26 2012
[8] T Kuwahara K Yoshida Y Kannaka T Kuroki andMOkuboldquoImprovement of NOx reduction efficiency in diesel emissioncontrol using nonthermal plasma combined exhaust gas recir-culation processrdquo IEEE Transactions on Industry Applicationsvol 47 no 6 pp 2359ndash2366 2011
[9] T Kuwahara K Yoshida T Kuroki K Hanamoto K Sato andMOkubo ldquoPilot-scale aftertreatment using nonthermal plasmareduction of adsorbed NO119909 in marine diesel-engine exhaustgasrdquo Plasma Chemistry and Plasma Processing vol 34 no 1 pp65ndash81 2014
[10] D Xie Y Sun T Zhu and L Ding ldquoRemoval of NO in mist bythe combination of plasma oxidation and chemical absorptionrdquoEnergy and Fuels vol 30 no 6 pp 5071ndash5076 2016
[11] S Zhou J Zhou Y Feng and Y Zhu ldquoMarine Emission Pol-lution Abatement Using Ozone Oxidation by a Wet ScrubbingMethodrdquo Industrial andEngineeringChemistry Research vol 55no 20 pp 5825ndash5831 2016
[12] Y S Mok ldquoAbsorption-reduction technique assisted by ozoneinjection and sodium sulfide for NO119909 removal from exhaustgasrdquo Chemical Engineering Journal vol 118 no 1-2 pp 63ndash672006
[13] E B Myers and T J Overcamp ldquoHydrogen peroxide scrubberfor the control of nitrogen oxidesrdquo Environmental EngineeringScience vol 19 no 5 pp 321ndash327 2002
[14] Z Wang Z Wang Y Ye N Chen and H Li ldquoStudy on theremoval of nitric oxide (NO) by dual oxidant (H2O2S2O82
minus)systemrdquo Chemical Engineering Science vol 145 pp 133ndash1402016
[15] Y Liu Q Wang Y Yin J Pan and J Zhang ldquoAdvancedoxidation removal ofNOand SO2 fromflue gas by using ultravi-oletH2O2NaOH processrdquo Chemical Engineering Research andDesign vol 92 no 10 pp 1907ndash1914 2014
[16] H Chu T W Chien and S Y Li ldquoSimultaneous absorptionof SO2 and NO from flue gas with KMnO4NaOH solutionsrdquoScience of the Total Environment vol 275 no 1-3 pp 127ndash1352001
[17] R Hao Y Zhang Z Wang et al ldquoAn advanced wet method forsimultaneous removal of SO2 andNO fromcoal-fired flue gas byutilizing a complex absorbentrdquo Chemical Engineering Journalvol 307 pp 562ndash571 2017
[18] Z Han S Yang D Zheng X Pan and Z Yan ldquoAn investigationon NO removal by wet scrubbing using NaClO2 seawatersolutionrdquo SpringerPlus vol 5 no 1 article 751 2016
[19] Y Zhou C Li C Fan et al ldquoWet removal of sulfur dioxide andnitrogen oxides from simulated flue gas by Ca(ClO)2 solutionrdquoEnvironmental Progress and Sustainable Energy vol 34 no 6pp 1586ndash1595 2015
[20] S-L Yang Z-T Han J-M Dong Z-S Zheng and X-X PanldquoUV-enhanced naclo oxidation of nitric oxide from simulatedflue gasrdquo Journal of Chemistry vol 2016 Article ID 6065019 8pages 2016
10 Journal of Chemistry
[21] L Chen C-H Hsu and C-L Yang ldquoOxidation and absorptionof nitric oxide in a packed tower with sodium hypochloriteaqueous solutionsrdquo Environmental Progress vol 24 no 3 pp279ndash288 2005
[22] E Ghibaudi J R Barker and S W Benson ldquoReaction ofNO with hypochlorous acidrdquo International Journal of ChemicalKinetics vol 11 no 8 pp 843ndash851 1979
[23] R-T Guo W-G Pan X-B Zhang et al ldquoThe absorptionkinetics of NO into weakly acidic NaClO solutionrdquo SeparationScience and Technology vol 48 no 18 pp 2871ndash2875 2013
[24] S Yang Z Han X Pan Z Yan and J Yu ldquoNitrogen oxideremoval using seawater electrolysis in an undivided cell forocean-going vesselsrdquo RSC Advances vol 6 no 115 pp 114623ndash114631 2016
[25] M K Mondal and V R Chelluboyana ldquoNew experimentalresults of combined SO2 and NO removal from simulated gasstream by NaClO as low-cost absorbentrdquo Chemical EngineeringJournal vol 217 pp 48ndash53 2013
[26] C V Raghunath and M K Mondal ldquoExperimental scalemulti component absorption of SO2 and NO by NH3NaClOscrubbingrdquo Chemical Engineering Journal vol 314 pp 537ndash5472017
[27] J Wang and W Zhong ldquoSimultaneous desulfurization anddenitrification of sintering flue gas via composite absorbentrdquoChinese Journal of Chemical Engineering vol 24 no 8 pp 1104ndash1111 2016
[28] S An and O Nishida ldquoNew application of seawater andelectrolyzed seawater in air pollution control of marine dieselenginerdquo JSME International Journal Series B Fluids and Ther-mal Engineering vol 46 no 1 pp 206ndash213 2003
[29] Z Han S Yang X Pan et al ldquoNew experimental results of NOremoval from simulated flue gas by wet scrubbing using NaClOsolutionrdquo Energy amp Fuels vol 31 no 3 pp 3047ndash3054 2017
[30] N Lahoutifard P Lagrange and J Lagrange ldquoKinetics andmechanism of nitrite oxidation by hypochlorous acid in theaqueous phaserdquo Chemosphere vol 50 no 10 pp 1349ndash13572003
[31] Y G Adewuyi X He H Shaw and W Lolertpihop ldquoSimul-taneous absorption and oxidation of NO and SO2 by aqueoussolutions of sodium chloriterdquo Chemical Engineering Communi-cations vol 174 no 1 pp 21ndash51 1999
[32] A Mukimin K Wijaya and A Kuncaka ldquoElectro-degradationof reactive blue dyes using cylinder modified electrode Ti120573-PbO2 as dimensionally stable anoderdquo Indonesian Journal ofChemistry vol 10 no 3 pp 285ndash289 2010
Figure 4 Equilibrium concentrations of active chlorine species inNaClO solution as a function of solution pH
the oxidation and absorption of targeted pollutants As anacidic oxide CO2 was sensitive to the solution pH Theeffect of coexisting CO2 on NOx removal efficiency wasinvestigated and results were shown in Figure 6 It can beseen that with initial solution pH increasing from 4 to 8 NOxremoval efficiency was relatively stable A complete removalof NO had been achieved and outlet NO2 concentrationwas sim350 ppm The coexistence of CO2 had not affectedthe NOx removal efficiency so much But the average CO2concentration in outlet gas changed obviously with initialsolution pH When initial solution pH was below 6 theaverage CO2 concentration kept stable at 5 However itbegan to decrease quickly with initial pH increasing from 6to 8
The change of outlet CO2 concentration during the cyclicscrubbing process was shown in Figure 7 When initialpH was in the range of 4ndash6 CO2 concentration decreasedto 44ndash45 at the start of the scrubbing process Then itrecovered to the initial level due to the hydrolysis equilibriumbetween CO2 and absorbent solution The hydrolysis reac-tions of CO2 were described in (10) and (11) Furthermorea certain amount of H+ might be produced during thehydrolysis process whichwould affect the chlorine hydrolysisequilibrium reactions as shown in (12) and (13) Since HCO3
minus
andCO32minus had buffering ability to some extent the hydrolysis
of CO2 would not influence the solution pH obviously wheninitial pH was in the range of 4ndash6 But with initial pHincreasing from 6 to 8 the absorption of CO2 might reducethe solution alkalinity resulting in the decrease of the solutionpHThus it was necessary to keep the solution pHat 6 in orderto reduce the consumption of solution alkalinitywhenNaClOsolution was adopted to remove NOx from flue gas
CO2 +H2Olarrrarr CO32minus + 2H+ (10)
CO2 +H2Olarrrarr HCO3minus +H+ (11)
Cl2(aq) +H2Olarrrarr HClO +H+ + Clminus (12)
HClOlarrrarr ClOminus +H+ (13)
When initial pH was in the range of 7-8 CO2 concentrationdecreased largely at the very beginning of the cyclic scrub-bing process It suggested that much more CO2 had beenabsorbed by the scrubbing solution due to the weak alkalinemedium With the proceeding of the scrubbing processCO2 concentration began to increase slowly Although noevidence showed that CO2 would react with NaClO directlythe hydrolyzation and absorption of CO2 would increasethe consumption of solution alkalinity obviously It meantthat extra alkaline solution was required to maintain thesolution pH during cyclic scrubbing process which wouldlargely increase the operation complexity and cost at the sametime Thus initial pH of 6 might be appropriate for practicalapplication
Figure 8 showed the change of NaClO solution pHafter scrubbing for 20min With the proceeding of cyclicscrubbing process the solution pHwould decrease slowly dueto the absorption of NOx and CO2 It was worth noting thatthe solution pH increased from 4 to 463 for NaClO solutionwith initial pH 4 That was because active chlorine speciesin NaClO solution were mainly HClO and Cl2 at pH 4 asshown in Figure 4 During the scrubbing process Cl2 wouldbe purged out easily from the solution and reacted with NOeffectively in gas phase as (14) and (15) [25] The decreaseof Cl2 in NaClO solution would lead to a left shift of thehydrolysis equilibrium of active chlorine as shown in (16)resulting in the increase of solution pH for NaClO solutionwith initial pH 4
Cl2(aq) larrrarr Cl2(g) (14)
Cl2(g) +H2O +NO(g) larrrarr NO2(g) + 2HCl (15)
Cl2(g) +H2Olarrrarr HClO(aq) +H+ + Clminus (16)
It was possible that excessive Cl2 escaped from NaClOsolution might result in secondary pollution In additionacidicmist formed in the flue gasmight result in the corrosionof operation system In view of this NaClO solution with pH6 was appropriate for NOx removal in cyclic scrubbingmode
33 Effect of Coexisting O2 For marine diesel engines therewas typicalsim13O2 in exhaust gas O2 could partially oxidizeNO under certain conditions so it was necessary to investi-gate the effect of coexisting O2 on NOx removal efficiency Inthe experiments only NO standard gas was used to prepareNOx in the initial simulated flue gas The introduction ofO2 has oxidized a little of NO into NO2 in the gas mixerAs shown in Figure 9 the initial NO2 concentration ininlet gas increased almost linearly with the increase of NOconcentrationWhen inlet NOx concentrationwas 1000 ppmthe initial NO2 concentration reached 112 ppm
O2 + 2NO 997888rarr 2NO2 (17)
With the NOx increasing from 250 to 700 ppm the outletNO concentration decreased gradually to 0 When inlet
Journal of Chemistry 5
NaClO concentration00125 M0025 M005 M01M
0
200
400
600
800
1000
NO
conc
entr
atio
n (p
pm)
6 8 10 124
Initial pH of NaClO solution
00125 M0025 M005 M01M
(a)
0
200
400
600
800
1000
NO2
conc
entr
atio
n (p
pm)
86 10 124
Initial pH of NaClO solution
NaClO concentration00125 M0025 M005 M01M
00125 M0025 M005 M01M
(b)
Figure 5 The change of (a) NO concentrations and (b) NO2 concentrations in flue gas with initial pH of NaClO solution (gas flow is125 Lmin inlet NOx concentration is 1000 ppm NaClO concentration is in the range of 00125ndash01M and solution temperature is 293Ksolid points refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
5 6 7 84
Initial pH of NaClO solution
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
0
1
2
3
4
5
Out
let C
O2
conc
entr
atio
n at
aver
age (
)
NOx removal efficiencyOutlet CO2 concentration
Figure 6 The change of NOx removal efficiency and averaged CO2concentration in flue gas with initial pH (gas flow is 125 Lmin inletNOx concentration is 1000 ppm initial CO2 concentration is 5NaClO concentration is 005M and solution temperature is 293K)
NOx concentration was higher than 700 ppm NO could beremoved completely As expected the outlet NO2 concen-tration increased almost linearly with the increase of inletNOx concentration It indicated that NOx removal efficiencydepended to a great extent on the absorption of NO2 duringthe scrubbing process
Figure 10 presented the change of NOx removal effi-ciency and outlet O2 concentration with the initial NOx
0
1
2
3
4
5
Out
let C
O2
conc
entr
atio
n (
)
5 10 15 200
Cyclic scrubbing duration (min)
Initial pH of NaClO solution4
5
6
7
8
Figure 7 The change of CO2 concentration during the cyclicscrubbing duration (gas flow is 125 Lmin inlet NO concentrationis 1000 ppm initial CO2 concentration is 5 NaClO concentrationis 005M and solution temperature is 293K)
concentration Since O2 concentration was relatively highit changed little during the scrubbing process With theincrease of NOx concentration from 250 ppm to 700 ppmNOx removal efficiency increased from 47 to 74 It could
6 Journal of Chemistry
0
2
4
6
8
10
pH o
f use
d N
aClO
solu
tion
5 6 7 84
Initial pH of NaClO solution
Figure 8 NaClO solution pH after scrubbing for 20min (gas flowis 125 Lmin inlet NOx concentration is 1000 ppm initial CO2concentration is 5 NaClO concentration is 005M and solutiontemperature is 293K)
Initial NOx concentration in inlet gas (ppm)1000800600400200
0
200
400
600
800
1000
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
Figure 9 The change of NOx concentration with the initial NOxconcentration (gas flow is 125 Lmin inlet O2 concentration is13 inlet NOx concentration is in the range of 250ndash1000 ppmNaClO concentration is 005M initial solution pH is 6 and solutiontemperature is 293K solid points refer to inlet NOx concentrationsand open points refer to outlet NOx concentrations)
be ascribed to the improvement of the mass transfer at thegas-liquid interface When O2 was present in flue gas NOxremoval efficiency was a little higher than that without O2in flue gas The existence of O2 improved the NOx removalefficiency in way of partly oxidizing NO in initial flue gas
34 Effect of NOx Concentration The effects of NOx con-centration on NOx removal are investigated and the resultsare shown in Figure 11 It can be seen that with initial NO
Initial NOx concentration in inlet gas (ppm)1000800600400200
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
0
3
6
9
12
15
Out
let O
2co
ncen
trat
ion
at av
erag
e (
)
NOx removal efficiencyOutlet O2 concentration
Figure 10The change of NOx removal efficiency and outlet O2 con-centration with the initial NOx concentration (conditions gas flow125 Lmin inlet O2 concentration 13 inlet NOx concentration250ndash1000 ppm NaClO concentration 005M initial solution pH 6solution temperature 293K)
concentration increasing from 250 ppm to 500 ppm NOxremoval efficiency increased from 43 to sim63 NO could beremoved completelywhen inletNOconcentrationwas higherthan 500 ppm Outlet NO2 concentration increased quicklywith the increase of inlet NO concentration resulting in arelatively stable NOx removal efficiency
35 Simultaneous Removal of NOx and SO2 Marine dieselengines usually burn heavy fuel oil (HFO) in order to savethe operating cost At present the mass concentration ofsulphur (S) content in HFO was about 25 at average Thecombustion of HFO fuel would produce a large amountof SO2 in exhaust gas Experiments were conducted toinvestigate the effect of coexisting SO2 on NOx removalefficiency and the results are shown in Figures 12 and 13
Figure 12 depicted the change of NOx removal efficiencyand NOx concentration with inlet NOx concentration Acomplete removal of SO2 and NO had been achieved simul-taneously Due to its high solubility SO2 could be absorbedeffectively by scrubbing solution Then SO2 was removedthrough the hydrolysis reaction as (18) and (19) The hydrol-ysis products of SO3
2minus would be oxidized by active chlorinespecies into SO4
2minus quickly Thus the removal of SO2 wouldconsume the solution alkalinity and oxidants at the sametime The result demonstrated that NaClO solution could beused to remove NO and SO2 simultaneously from marineexhaust gas However outlet NO2 concentration increasedgradually with the increase of inlet NOx concentration
SO2 +H2O 997888rarr HSO3minus +H+ (18)
HSO3minus 997888rarr SO3
2minus +H+ (19)
SO3minus +HClO 997888rarr SO4
2minus +HCl (20)
Journal of Chemistry 7
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
(a)
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
200
400
600
800
1000
1200
1400
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
(b)
Figure 11 The change of (a) NOx removal efficiency and (b) NO119909 concentrations with the initial NOx concentration (gas flow is 125 Lmininlet NOx concentration is 250ndash1250 ppm NaClO concentration is 005M initial solution pH is 6 and solution temperature is 293K solidpoints refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
20
40
60
80
100
Rem
oval
effici
ency
()
SO2
NOx
(a)
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
200
400
600
800
1000
1200
1400
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
(b)
Figure 12 The change of (a) NOx removal efficiency and (b) NOx concentration with the inlet NOx concentration (gas flow is 125 Lmininlet SO2 concentration is 600 ppm inlet NOx concentration is 250ndash1250 ppm NaClO concentration is 005M initial solution pH is 6 andsolution temperature is 293K solid points refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
Figure 13 exhibited the effect of SO2 concentration on NOxremoval efficiency and NOx concentration in flue gas Theresult showed that SO2 together with NO was completelyremoved But with the increase of inlet SO2 concentrationNOx removal efficiency exhibited a slightly downside trendThis phenomenon could be ascribed to the competitionreactions between NOx and SO2 Some oxidants in theabsorbent would be consumed through the hydrolyzation
and absorption of SO2With inlet SO2 concentration increas-ing from 200 ppm to 600 ppm the pHof the scrubbedNaClOsolution decreased from 525 to 452The decrease of solutionpH was negative for the absorption of NO2 through (5) and(6)
36 Effect of Absorbent Temperature The reaction temper-ature could greatly influence the diffusion dissolution and
8 Journal of Chemistry
0
20
40
60
80
100
Rem
oval
effici
ency
()
SO2
NOx
300 500 600400200
Initial SO2 concentration in inlet gas (ppm)
(a)
0
200
400
600
800
1000
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
300 500 600400200
Initial SO2 concentration in inlet gas (ppm)
(b)
Figure 13 The change of (a) NOx removal efficiency and (b) NOx concentration with the initial SO2 concentration (gas flow is 125 Lmininlet SO2 concentration is 200ndash600 ppm inlet NOx concentration is 1000 ppm NaClO concentration is 005M initial solution pH is 6 andsolution temperature is 293K solid points refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
Absorbent temperature (K)340330320310300290
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
(a)
Absorbent temperature (K)340330320310300290
0
200
400
600
800
1000
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
(b)
Figure 14The change of (a) NOx removal efficiency and (b) NOx concentration with the absorbent temperature (gas flow is 125 Lmin inletNOx concentration is 1000 ppm NaClO concentration is 005M initial solution pH is 6 and solution temperature is 293ndash333K solid pointsrefer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
reaction characteristics of molecules or ions in liquid phase[19] The effect of absorbent temperature on NOx removalwas investigated and the results were shown in Figure 14Generally the absorbent temperature was kept below 333Kin industrial application in order to reduce the supply ofmake-up water So the absorbent temperature was chosen tobe in the range of 293ndash333K in the experiments Figure 14showed that NOx removal efficiency increased gradually with
the increase of absorbent temperature The highest NOxremoval efficiency of 69was achieved at 333 K AsNO couldbe removed by 100 easily the increase of NOx removalefficiency resulted from the improvement of NO2 absorptionThis could be explained by the Arrhenius equation of thereaction rate constant The increase of temperature couldenhance the mass transfer of NO2 to the absorbent thusimproving the absorption of NO2 accordingly
Journal of Chemistry 9
4 Conclusion
NOx removal by wet scrubbing using NaClO solution wasstudied based on a spraying reactor in a cyclic mode Theresults showed that when NaClO concentration was higherthan 005M and initial solution pH was below 8 NOxremoval efficiency was relatively stable which was higherthan 60 The coexisting CO2 (5) had little effect on NOxremoval efficiency but the solution pHbegan to decreasewiththe proceeding of cyclic scrubbing process when initial pHwas higher than 6The coexisting O2 (13) could oxidize NOpartially in the gas mixer resulting in a little improvementof NOx removal efficiency When initial NOx concentrationwas higher than 500 ppm NO could be removed completelywhile outlet NO2 concentration increased almost linearlywith the increase of initial NOx concentration resultingin a relative stable NOx removal efficiency A completeremoval of SO2 and NO could be achieved simultaneouslyat 293K initial NaClO solution pH 6 and 005M NaClOconcentration With the increase of inlet SO2 concentrationthe outlet NO2 concentration increased slightly due to thedecrease of solution pH NOx removal efficiency increasedwith the increase of absorbent temperature The relevantreaction mechanism for the removal of NOx and SO2 bywet scrubbing using NaClO solution was also discussed Theresults demonstrated that it was of great potential for NaClOsolution to remove NOx from marine exhaust gas
Conflicts of Interest
The authors declare that there are no conflicts of interestregarding the publication of this paper
Acknowledgments
This study has been financially supported by the NationalNatural Science Foundation of China (Grant nos 51402033and 51479020) the Science and Technology Plan Project ofChinarsquos Ministry of Transport (Grant no 2015328225150) theDoctoral Scientific Research Staring Foundation of Liaon-ing Province (Grant no 201601073) and the FundamentalResearch Funds for the Central Universities (Grant nos3132017003 and 3132016326)
References
[1] M Guo Z Fu DMa N Ji C Song and Q Liu ldquoA short reviewof treatment methods of marine diesel engine exhaust gasesrdquoProcedia Engineering vol 121 pp 938ndash943 2015
[2] M-W Bae ldquoA study on the effects of recirculated exhaust gasupon NO119909 and soot emissions in diesel engines with scrubberEGR systemrdquo SAE Technical Papers 1999
[3] A M A Attia and A R Kulchitskiy ldquoInfluence of the structureof water-in-fuel emulsion on diesel engine performancerdquo Fuelvol 116 pp 703ndash708 2014
[4] X Tauzia A Maiboom and S R Shah ldquoExperimental study ofinlet manifold water injection on combustion and emissions ofan automotive direct injection diesel enginerdquoEnergy vol 35 no9 pp 3628ndash3639 2010
[5] A M Hallquist E Fridell J Westerlund and M Hal-lquist ldquoOnboard measurements of nanoparticles from a SCR-equipped marine diesel enginerdquo Environmental Science andTechnology vol 47 no 2 pp 773ndash780 2013
[6] J Herdzik ldquoEmissions from marine engines versus IMO certi-fication and requirements of tier 3rdquo Journal of KONES vol 18pp 161ndash167 2011
[7] M Magnusson E Fridell and H H Ingelsten ldquoThe influenceof sulfur dioxide andwater on the performance of amarine SCRcatalystrdquoApplied Catalysis B Environmental vol 111-112 pp 20ndash26 2012
[8] T Kuwahara K Yoshida Y Kannaka T Kuroki andMOkuboldquoImprovement of NOx reduction efficiency in diesel emissioncontrol using nonthermal plasma combined exhaust gas recir-culation processrdquo IEEE Transactions on Industry Applicationsvol 47 no 6 pp 2359ndash2366 2011
[9] T Kuwahara K Yoshida T Kuroki K Hanamoto K Sato andMOkubo ldquoPilot-scale aftertreatment using nonthermal plasmareduction of adsorbed NO119909 in marine diesel-engine exhaustgasrdquo Plasma Chemistry and Plasma Processing vol 34 no 1 pp65ndash81 2014
[10] D Xie Y Sun T Zhu and L Ding ldquoRemoval of NO in mist bythe combination of plasma oxidation and chemical absorptionrdquoEnergy and Fuels vol 30 no 6 pp 5071ndash5076 2016
[11] S Zhou J Zhou Y Feng and Y Zhu ldquoMarine Emission Pol-lution Abatement Using Ozone Oxidation by a Wet ScrubbingMethodrdquo Industrial andEngineeringChemistry Research vol 55no 20 pp 5825ndash5831 2016
[12] Y S Mok ldquoAbsorption-reduction technique assisted by ozoneinjection and sodium sulfide for NO119909 removal from exhaustgasrdquo Chemical Engineering Journal vol 118 no 1-2 pp 63ndash672006
[13] E B Myers and T J Overcamp ldquoHydrogen peroxide scrubberfor the control of nitrogen oxidesrdquo Environmental EngineeringScience vol 19 no 5 pp 321ndash327 2002
[14] Z Wang Z Wang Y Ye N Chen and H Li ldquoStudy on theremoval of nitric oxide (NO) by dual oxidant (H2O2S2O82
minus)systemrdquo Chemical Engineering Science vol 145 pp 133ndash1402016
[15] Y Liu Q Wang Y Yin J Pan and J Zhang ldquoAdvancedoxidation removal ofNOand SO2 fromflue gas by using ultravi-oletH2O2NaOH processrdquo Chemical Engineering Research andDesign vol 92 no 10 pp 1907ndash1914 2014
[16] H Chu T W Chien and S Y Li ldquoSimultaneous absorptionof SO2 and NO from flue gas with KMnO4NaOH solutionsrdquoScience of the Total Environment vol 275 no 1-3 pp 127ndash1352001
[17] R Hao Y Zhang Z Wang et al ldquoAn advanced wet method forsimultaneous removal of SO2 andNO fromcoal-fired flue gas byutilizing a complex absorbentrdquo Chemical Engineering Journalvol 307 pp 562ndash571 2017
[18] Z Han S Yang D Zheng X Pan and Z Yan ldquoAn investigationon NO removal by wet scrubbing using NaClO2 seawatersolutionrdquo SpringerPlus vol 5 no 1 article 751 2016
[19] Y Zhou C Li C Fan et al ldquoWet removal of sulfur dioxide andnitrogen oxides from simulated flue gas by Ca(ClO)2 solutionrdquoEnvironmental Progress and Sustainable Energy vol 34 no 6pp 1586ndash1595 2015
[20] S-L Yang Z-T Han J-M Dong Z-S Zheng and X-X PanldquoUV-enhanced naclo oxidation of nitric oxide from simulatedflue gasrdquo Journal of Chemistry vol 2016 Article ID 6065019 8pages 2016
10 Journal of Chemistry
[21] L Chen C-H Hsu and C-L Yang ldquoOxidation and absorptionof nitric oxide in a packed tower with sodium hypochloriteaqueous solutionsrdquo Environmental Progress vol 24 no 3 pp279ndash288 2005
[22] E Ghibaudi J R Barker and S W Benson ldquoReaction ofNO with hypochlorous acidrdquo International Journal of ChemicalKinetics vol 11 no 8 pp 843ndash851 1979
[23] R-T Guo W-G Pan X-B Zhang et al ldquoThe absorptionkinetics of NO into weakly acidic NaClO solutionrdquo SeparationScience and Technology vol 48 no 18 pp 2871ndash2875 2013
[24] S Yang Z Han X Pan Z Yan and J Yu ldquoNitrogen oxideremoval using seawater electrolysis in an undivided cell forocean-going vesselsrdquo RSC Advances vol 6 no 115 pp 114623ndash114631 2016
[25] M K Mondal and V R Chelluboyana ldquoNew experimentalresults of combined SO2 and NO removal from simulated gasstream by NaClO as low-cost absorbentrdquo Chemical EngineeringJournal vol 217 pp 48ndash53 2013
[26] C V Raghunath and M K Mondal ldquoExperimental scalemulti component absorption of SO2 and NO by NH3NaClOscrubbingrdquo Chemical Engineering Journal vol 314 pp 537ndash5472017
[27] J Wang and W Zhong ldquoSimultaneous desulfurization anddenitrification of sintering flue gas via composite absorbentrdquoChinese Journal of Chemical Engineering vol 24 no 8 pp 1104ndash1111 2016
[28] S An and O Nishida ldquoNew application of seawater andelectrolyzed seawater in air pollution control of marine dieselenginerdquo JSME International Journal Series B Fluids and Ther-mal Engineering vol 46 no 1 pp 206ndash213 2003
[29] Z Han S Yang X Pan et al ldquoNew experimental results of NOremoval from simulated flue gas by wet scrubbing using NaClOsolutionrdquo Energy amp Fuels vol 31 no 3 pp 3047ndash3054 2017
[30] N Lahoutifard P Lagrange and J Lagrange ldquoKinetics andmechanism of nitrite oxidation by hypochlorous acid in theaqueous phaserdquo Chemosphere vol 50 no 10 pp 1349ndash13572003
[31] Y G Adewuyi X He H Shaw and W Lolertpihop ldquoSimul-taneous absorption and oxidation of NO and SO2 by aqueoussolutions of sodium chloriterdquo Chemical Engineering Communi-cations vol 174 no 1 pp 21ndash51 1999
[32] A Mukimin K Wijaya and A Kuncaka ldquoElectro-degradationof reactive blue dyes using cylinder modified electrode Ti120573-PbO2 as dimensionally stable anoderdquo Indonesian Journal ofChemistry vol 10 no 3 pp 285ndash289 2010
Figure 5 The change of (a) NO concentrations and (b) NO2 concentrations in flue gas with initial pH of NaClO solution (gas flow is125 Lmin inlet NOx concentration is 1000 ppm NaClO concentration is in the range of 00125ndash01M and solution temperature is 293Ksolid points refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
5 6 7 84
Initial pH of NaClO solution
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
0
1
2
3
4
5
Out
let C
O2
conc
entr
atio
n at
aver
age (
)
NOx removal efficiencyOutlet CO2 concentration
Figure 6 The change of NOx removal efficiency and averaged CO2concentration in flue gas with initial pH (gas flow is 125 Lmin inletNOx concentration is 1000 ppm initial CO2 concentration is 5NaClO concentration is 005M and solution temperature is 293K)
NOx concentration was higher than 700 ppm NO could beremoved completely As expected the outlet NO2 concen-tration increased almost linearly with the increase of inletNOx concentration It indicated that NOx removal efficiencydepended to a great extent on the absorption of NO2 duringthe scrubbing process
Figure 10 presented the change of NOx removal effi-ciency and outlet O2 concentration with the initial NOx
0
1
2
3
4
5
Out
let C
O2
conc
entr
atio
n (
)
5 10 15 200
Cyclic scrubbing duration (min)
Initial pH of NaClO solution4
5
6
7
8
Figure 7 The change of CO2 concentration during the cyclicscrubbing duration (gas flow is 125 Lmin inlet NO concentrationis 1000 ppm initial CO2 concentration is 5 NaClO concentrationis 005M and solution temperature is 293K)
concentration Since O2 concentration was relatively highit changed little during the scrubbing process With theincrease of NOx concentration from 250 ppm to 700 ppmNOx removal efficiency increased from 47 to 74 It could
6 Journal of Chemistry
0
2
4
6
8
10
pH o
f use
d N
aClO
solu
tion
5 6 7 84
Initial pH of NaClO solution
Figure 8 NaClO solution pH after scrubbing for 20min (gas flowis 125 Lmin inlet NOx concentration is 1000 ppm initial CO2concentration is 5 NaClO concentration is 005M and solutiontemperature is 293K)
Initial NOx concentration in inlet gas (ppm)1000800600400200
0
200
400
600
800
1000
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
Figure 9 The change of NOx concentration with the initial NOxconcentration (gas flow is 125 Lmin inlet O2 concentration is13 inlet NOx concentration is in the range of 250ndash1000 ppmNaClO concentration is 005M initial solution pH is 6 and solutiontemperature is 293K solid points refer to inlet NOx concentrationsand open points refer to outlet NOx concentrations)
be ascribed to the improvement of the mass transfer at thegas-liquid interface When O2 was present in flue gas NOxremoval efficiency was a little higher than that without O2in flue gas The existence of O2 improved the NOx removalefficiency in way of partly oxidizing NO in initial flue gas
34 Effect of NOx Concentration The effects of NOx con-centration on NOx removal are investigated and the resultsare shown in Figure 11 It can be seen that with initial NO
Initial NOx concentration in inlet gas (ppm)1000800600400200
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
0
3
6
9
12
15
Out
let O
2co
ncen
trat
ion
at av
erag
e (
)
NOx removal efficiencyOutlet O2 concentration
Figure 10The change of NOx removal efficiency and outlet O2 con-centration with the initial NOx concentration (conditions gas flow125 Lmin inlet O2 concentration 13 inlet NOx concentration250ndash1000 ppm NaClO concentration 005M initial solution pH 6solution temperature 293K)
concentration increasing from 250 ppm to 500 ppm NOxremoval efficiency increased from 43 to sim63 NO could beremoved completelywhen inletNOconcentrationwas higherthan 500 ppm Outlet NO2 concentration increased quicklywith the increase of inlet NO concentration resulting in arelatively stable NOx removal efficiency
35 Simultaneous Removal of NOx and SO2 Marine dieselengines usually burn heavy fuel oil (HFO) in order to savethe operating cost At present the mass concentration ofsulphur (S) content in HFO was about 25 at average Thecombustion of HFO fuel would produce a large amountof SO2 in exhaust gas Experiments were conducted toinvestigate the effect of coexisting SO2 on NOx removalefficiency and the results are shown in Figures 12 and 13
Figure 12 depicted the change of NOx removal efficiencyand NOx concentration with inlet NOx concentration Acomplete removal of SO2 and NO had been achieved simul-taneously Due to its high solubility SO2 could be absorbedeffectively by scrubbing solution Then SO2 was removedthrough the hydrolysis reaction as (18) and (19) The hydrol-ysis products of SO3
2minus would be oxidized by active chlorinespecies into SO4
2minus quickly Thus the removal of SO2 wouldconsume the solution alkalinity and oxidants at the sametime The result demonstrated that NaClO solution could beused to remove NO and SO2 simultaneously from marineexhaust gas However outlet NO2 concentration increasedgradually with the increase of inlet NOx concentration
SO2 +H2O 997888rarr HSO3minus +H+ (18)
HSO3minus 997888rarr SO3
2minus +H+ (19)
SO3minus +HClO 997888rarr SO4
2minus +HCl (20)
Journal of Chemistry 7
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
(a)
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
200
400
600
800
1000
1200
1400
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
(b)
Figure 11 The change of (a) NOx removal efficiency and (b) NO119909 concentrations with the initial NOx concentration (gas flow is 125 Lmininlet NOx concentration is 250ndash1250 ppm NaClO concentration is 005M initial solution pH is 6 and solution temperature is 293K solidpoints refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
20
40
60
80
100
Rem
oval
effici
ency
()
SO2
NOx
(a)
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
200
400
600
800
1000
1200
1400
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
(b)
Figure 12 The change of (a) NOx removal efficiency and (b) NOx concentration with the inlet NOx concentration (gas flow is 125 Lmininlet SO2 concentration is 600 ppm inlet NOx concentration is 250ndash1250 ppm NaClO concentration is 005M initial solution pH is 6 andsolution temperature is 293K solid points refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
Figure 13 exhibited the effect of SO2 concentration on NOxremoval efficiency and NOx concentration in flue gas Theresult showed that SO2 together with NO was completelyremoved But with the increase of inlet SO2 concentrationNOx removal efficiency exhibited a slightly downside trendThis phenomenon could be ascribed to the competitionreactions between NOx and SO2 Some oxidants in theabsorbent would be consumed through the hydrolyzation
and absorption of SO2With inlet SO2 concentration increas-ing from 200 ppm to 600 ppm the pHof the scrubbedNaClOsolution decreased from 525 to 452The decrease of solutionpH was negative for the absorption of NO2 through (5) and(6)
36 Effect of Absorbent Temperature The reaction temper-ature could greatly influence the diffusion dissolution and
8 Journal of Chemistry
0
20
40
60
80
100
Rem
oval
effici
ency
()
SO2
NOx
300 500 600400200
Initial SO2 concentration in inlet gas (ppm)
(a)
0
200
400
600
800
1000
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
300 500 600400200
Initial SO2 concentration in inlet gas (ppm)
(b)
Figure 13 The change of (a) NOx removal efficiency and (b) NOx concentration with the initial SO2 concentration (gas flow is 125 Lmininlet SO2 concentration is 200ndash600 ppm inlet NOx concentration is 1000 ppm NaClO concentration is 005M initial solution pH is 6 andsolution temperature is 293K solid points refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
Absorbent temperature (K)340330320310300290
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
(a)
Absorbent temperature (K)340330320310300290
0
200
400
600
800
1000
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
(b)
Figure 14The change of (a) NOx removal efficiency and (b) NOx concentration with the absorbent temperature (gas flow is 125 Lmin inletNOx concentration is 1000 ppm NaClO concentration is 005M initial solution pH is 6 and solution temperature is 293ndash333K solid pointsrefer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
reaction characteristics of molecules or ions in liquid phase[19] The effect of absorbent temperature on NOx removalwas investigated and the results were shown in Figure 14Generally the absorbent temperature was kept below 333Kin industrial application in order to reduce the supply ofmake-up water So the absorbent temperature was chosen tobe in the range of 293ndash333K in the experiments Figure 14showed that NOx removal efficiency increased gradually with
the increase of absorbent temperature The highest NOxremoval efficiency of 69was achieved at 333 K AsNO couldbe removed by 100 easily the increase of NOx removalefficiency resulted from the improvement of NO2 absorptionThis could be explained by the Arrhenius equation of thereaction rate constant The increase of temperature couldenhance the mass transfer of NO2 to the absorbent thusimproving the absorption of NO2 accordingly
Journal of Chemistry 9
4 Conclusion
NOx removal by wet scrubbing using NaClO solution wasstudied based on a spraying reactor in a cyclic mode Theresults showed that when NaClO concentration was higherthan 005M and initial solution pH was below 8 NOxremoval efficiency was relatively stable which was higherthan 60 The coexisting CO2 (5) had little effect on NOxremoval efficiency but the solution pHbegan to decreasewiththe proceeding of cyclic scrubbing process when initial pHwas higher than 6The coexisting O2 (13) could oxidize NOpartially in the gas mixer resulting in a little improvementof NOx removal efficiency When initial NOx concentrationwas higher than 500 ppm NO could be removed completelywhile outlet NO2 concentration increased almost linearlywith the increase of initial NOx concentration resultingin a relative stable NOx removal efficiency A completeremoval of SO2 and NO could be achieved simultaneouslyat 293K initial NaClO solution pH 6 and 005M NaClOconcentration With the increase of inlet SO2 concentrationthe outlet NO2 concentration increased slightly due to thedecrease of solution pH NOx removal efficiency increasedwith the increase of absorbent temperature The relevantreaction mechanism for the removal of NOx and SO2 bywet scrubbing using NaClO solution was also discussed Theresults demonstrated that it was of great potential for NaClOsolution to remove NOx from marine exhaust gas
Conflicts of Interest
The authors declare that there are no conflicts of interestregarding the publication of this paper
Acknowledgments
This study has been financially supported by the NationalNatural Science Foundation of China (Grant nos 51402033and 51479020) the Science and Technology Plan Project ofChinarsquos Ministry of Transport (Grant no 2015328225150) theDoctoral Scientific Research Staring Foundation of Liaon-ing Province (Grant no 201601073) and the FundamentalResearch Funds for the Central Universities (Grant nos3132017003 and 3132016326)
References
[1] M Guo Z Fu DMa N Ji C Song and Q Liu ldquoA short reviewof treatment methods of marine diesel engine exhaust gasesrdquoProcedia Engineering vol 121 pp 938ndash943 2015
[2] M-W Bae ldquoA study on the effects of recirculated exhaust gasupon NO119909 and soot emissions in diesel engines with scrubberEGR systemrdquo SAE Technical Papers 1999
[3] A M A Attia and A R Kulchitskiy ldquoInfluence of the structureof water-in-fuel emulsion on diesel engine performancerdquo Fuelvol 116 pp 703ndash708 2014
[4] X Tauzia A Maiboom and S R Shah ldquoExperimental study ofinlet manifold water injection on combustion and emissions ofan automotive direct injection diesel enginerdquoEnergy vol 35 no9 pp 3628ndash3639 2010
[5] A M Hallquist E Fridell J Westerlund and M Hal-lquist ldquoOnboard measurements of nanoparticles from a SCR-equipped marine diesel enginerdquo Environmental Science andTechnology vol 47 no 2 pp 773ndash780 2013
[6] J Herdzik ldquoEmissions from marine engines versus IMO certi-fication and requirements of tier 3rdquo Journal of KONES vol 18pp 161ndash167 2011
[7] M Magnusson E Fridell and H H Ingelsten ldquoThe influenceof sulfur dioxide andwater on the performance of amarine SCRcatalystrdquoApplied Catalysis B Environmental vol 111-112 pp 20ndash26 2012
[8] T Kuwahara K Yoshida Y Kannaka T Kuroki andMOkuboldquoImprovement of NOx reduction efficiency in diesel emissioncontrol using nonthermal plasma combined exhaust gas recir-culation processrdquo IEEE Transactions on Industry Applicationsvol 47 no 6 pp 2359ndash2366 2011
[9] T Kuwahara K Yoshida T Kuroki K Hanamoto K Sato andMOkubo ldquoPilot-scale aftertreatment using nonthermal plasmareduction of adsorbed NO119909 in marine diesel-engine exhaustgasrdquo Plasma Chemistry and Plasma Processing vol 34 no 1 pp65ndash81 2014
[10] D Xie Y Sun T Zhu and L Ding ldquoRemoval of NO in mist bythe combination of plasma oxidation and chemical absorptionrdquoEnergy and Fuels vol 30 no 6 pp 5071ndash5076 2016
[11] S Zhou J Zhou Y Feng and Y Zhu ldquoMarine Emission Pol-lution Abatement Using Ozone Oxidation by a Wet ScrubbingMethodrdquo Industrial andEngineeringChemistry Research vol 55no 20 pp 5825ndash5831 2016
[12] Y S Mok ldquoAbsorption-reduction technique assisted by ozoneinjection and sodium sulfide for NO119909 removal from exhaustgasrdquo Chemical Engineering Journal vol 118 no 1-2 pp 63ndash672006
[13] E B Myers and T J Overcamp ldquoHydrogen peroxide scrubberfor the control of nitrogen oxidesrdquo Environmental EngineeringScience vol 19 no 5 pp 321ndash327 2002
[14] Z Wang Z Wang Y Ye N Chen and H Li ldquoStudy on theremoval of nitric oxide (NO) by dual oxidant (H2O2S2O82
minus)systemrdquo Chemical Engineering Science vol 145 pp 133ndash1402016
[15] Y Liu Q Wang Y Yin J Pan and J Zhang ldquoAdvancedoxidation removal ofNOand SO2 fromflue gas by using ultravi-oletH2O2NaOH processrdquo Chemical Engineering Research andDesign vol 92 no 10 pp 1907ndash1914 2014
[16] H Chu T W Chien and S Y Li ldquoSimultaneous absorptionof SO2 and NO from flue gas with KMnO4NaOH solutionsrdquoScience of the Total Environment vol 275 no 1-3 pp 127ndash1352001
[17] R Hao Y Zhang Z Wang et al ldquoAn advanced wet method forsimultaneous removal of SO2 andNO fromcoal-fired flue gas byutilizing a complex absorbentrdquo Chemical Engineering Journalvol 307 pp 562ndash571 2017
[18] Z Han S Yang D Zheng X Pan and Z Yan ldquoAn investigationon NO removal by wet scrubbing using NaClO2 seawatersolutionrdquo SpringerPlus vol 5 no 1 article 751 2016
[19] Y Zhou C Li C Fan et al ldquoWet removal of sulfur dioxide andnitrogen oxides from simulated flue gas by Ca(ClO)2 solutionrdquoEnvironmental Progress and Sustainable Energy vol 34 no 6pp 1586ndash1595 2015
[20] S-L Yang Z-T Han J-M Dong Z-S Zheng and X-X PanldquoUV-enhanced naclo oxidation of nitric oxide from simulatedflue gasrdquo Journal of Chemistry vol 2016 Article ID 6065019 8pages 2016
10 Journal of Chemistry
[21] L Chen C-H Hsu and C-L Yang ldquoOxidation and absorptionof nitric oxide in a packed tower with sodium hypochloriteaqueous solutionsrdquo Environmental Progress vol 24 no 3 pp279ndash288 2005
[22] E Ghibaudi J R Barker and S W Benson ldquoReaction ofNO with hypochlorous acidrdquo International Journal of ChemicalKinetics vol 11 no 8 pp 843ndash851 1979
[23] R-T Guo W-G Pan X-B Zhang et al ldquoThe absorptionkinetics of NO into weakly acidic NaClO solutionrdquo SeparationScience and Technology vol 48 no 18 pp 2871ndash2875 2013
[24] S Yang Z Han X Pan Z Yan and J Yu ldquoNitrogen oxideremoval using seawater electrolysis in an undivided cell forocean-going vesselsrdquo RSC Advances vol 6 no 115 pp 114623ndash114631 2016
[25] M K Mondal and V R Chelluboyana ldquoNew experimentalresults of combined SO2 and NO removal from simulated gasstream by NaClO as low-cost absorbentrdquo Chemical EngineeringJournal vol 217 pp 48ndash53 2013
[26] C V Raghunath and M K Mondal ldquoExperimental scalemulti component absorption of SO2 and NO by NH3NaClOscrubbingrdquo Chemical Engineering Journal vol 314 pp 537ndash5472017
[27] J Wang and W Zhong ldquoSimultaneous desulfurization anddenitrification of sintering flue gas via composite absorbentrdquoChinese Journal of Chemical Engineering vol 24 no 8 pp 1104ndash1111 2016
[28] S An and O Nishida ldquoNew application of seawater andelectrolyzed seawater in air pollution control of marine dieselenginerdquo JSME International Journal Series B Fluids and Ther-mal Engineering vol 46 no 1 pp 206ndash213 2003
[29] Z Han S Yang X Pan et al ldquoNew experimental results of NOremoval from simulated flue gas by wet scrubbing using NaClOsolutionrdquo Energy amp Fuels vol 31 no 3 pp 3047ndash3054 2017
[30] N Lahoutifard P Lagrange and J Lagrange ldquoKinetics andmechanism of nitrite oxidation by hypochlorous acid in theaqueous phaserdquo Chemosphere vol 50 no 10 pp 1349ndash13572003
[31] Y G Adewuyi X He H Shaw and W Lolertpihop ldquoSimul-taneous absorption and oxidation of NO and SO2 by aqueoussolutions of sodium chloriterdquo Chemical Engineering Communi-cations vol 174 no 1 pp 21ndash51 1999
[32] A Mukimin K Wijaya and A Kuncaka ldquoElectro-degradationof reactive blue dyes using cylinder modified electrode Ti120573-PbO2 as dimensionally stable anoderdquo Indonesian Journal ofChemistry vol 10 no 3 pp 285ndash289 2010
Figure 8 NaClO solution pH after scrubbing for 20min (gas flowis 125 Lmin inlet NOx concentration is 1000 ppm initial CO2concentration is 5 NaClO concentration is 005M and solutiontemperature is 293K)
Initial NOx concentration in inlet gas (ppm)1000800600400200
0
200
400
600
800
1000
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
Figure 9 The change of NOx concentration with the initial NOxconcentration (gas flow is 125 Lmin inlet O2 concentration is13 inlet NOx concentration is in the range of 250ndash1000 ppmNaClO concentration is 005M initial solution pH is 6 and solutiontemperature is 293K solid points refer to inlet NOx concentrationsand open points refer to outlet NOx concentrations)
be ascribed to the improvement of the mass transfer at thegas-liquid interface When O2 was present in flue gas NOxremoval efficiency was a little higher than that without O2in flue gas The existence of O2 improved the NOx removalefficiency in way of partly oxidizing NO in initial flue gas
34 Effect of NOx Concentration The effects of NOx con-centration on NOx removal are investigated and the resultsare shown in Figure 11 It can be seen that with initial NO
Initial NOx concentration in inlet gas (ppm)1000800600400200
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
0
3
6
9
12
15
Out
let O
2co
ncen
trat
ion
at av
erag
e (
)
NOx removal efficiencyOutlet O2 concentration
Figure 10The change of NOx removal efficiency and outlet O2 con-centration with the initial NOx concentration (conditions gas flow125 Lmin inlet O2 concentration 13 inlet NOx concentration250ndash1000 ppm NaClO concentration 005M initial solution pH 6solution temperature 293K)
concentration increasing from 250 ppm to 500 ppm NOxremoval efficiency increased from 43 to sim63 NO could beremoved completelywhen inletNOconcentrationwas higherthan 500 ppm Outlet NO2 concentration increased quicklywith the increase of inlet NO concentration resulting in arelatively stable NOx removal efficiency
35 Simultaneous Removal of NOx and SO2 Marine dieselengines usually burn heavy fuel oil (HFO) in order to savethe operating cost At present the mass concentration ofsulphur (S) content in HFO was about 25 at average Thecombustion of HFO fuel would produce a large amountof SO2 in exhaust gas Experiments were conducted toinvestigate the effect of coexisting SO2 on NOx removalefficiency and the results are shown in Figures 12 and 13
Figure 12 depicted the change of NOx removal efficiencyand NOx concentration with inlet NOx concentration Acomplete removal of SO2 and NO had been achieved simul-taneously Due to its high solubility SO2 could be absorbedeffectively by scrubbing solution Then SO2 was removedthrough the hydrolysis reaction as (18) and (19) The hydrol-ysis products of SO3
2minus would be oxidized by active chlorinespecies into SO4
2minus quickly Thus the removal of SO2 wouldconsume the solution alkalinity and oxidants at the sametime The result demonstrated that NaClO solution could beused to remove NO and SO2 simultaneously from marineexhaust gas However outlet NO2 concentration increasedgradually with the increase of inlet NOx concentration
SO2 +H2O 997888rarr HSO3minus +H+ (18)
HSO3minus 997888rarr SO3
2minus +H+ (19)
SO3minus +HClO 997888rarr SO4
2minus +HCl (20)
Journal of Chemistry 7
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
(a)
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
200
400
600
800
1000
1200
1400
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
(b)
Figure 11 The change of (a) NOx removal efficiency and (b) NO119909 concentrations with the initial NOx concentration (gas flow is 125 Lmininlet NOx concentration is 250ndash1250 ppm NaClO concentration is 005M initial solution pH is 6 and solution temperature is 293K solidpoints refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
20
40
60
80
100
Rem
oval
effici
ency
()
SO2
NOx
(a)
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
200
400
600
800
1000
1200
1400
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
(b)
Figure 12 The change of (a) NOx removal efficiency and (b) NOx concentration with the inlet NOx concentration (gas flow is 125 Lmininlet SO2 concentration is 600 ppm inlet NOx concentration is 250ndash1250 ppm NaClO concentration is 005M initial solution pH is 6 andsolution temperature is 293K solid points refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
Figure 13 exhibited the effect of SO2 concentration on NOxremoval efficiency and NOx concentration in flue gas Theresult showed that SO2 together with NO was completelyremoved But with the increase of inlet SO2 concentrationNOx removal efficiency exhibited a slightly downside trendThis phenomenon could be ascribed to the competitionreactions between NOx and SO2 Some oxidants in theabsorbent would be consumed through the hydrolyzation
and absorption of SO2With inlet SO2 concentration increas-ing from 200 ppm to 600 ppm the pHof the scrubbedNaClOsolution decreased from 525 to 452The decrease of solutionpH was negative for the absorption of NO2 through (5) and(6)
36 Effect of Absorbent Temperature The reaction temper-ature could greatly influence the diffusion dissolution and
8 Journal of Chemistry
0
20
40
60
80
100
Rem
oval
effici
ency
()
SO2
NOx
300 500 600400200
Initial SO2 concentration in inlet gas (ppm)
(a)
0
200
400
600
800
1000
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
300 500 600400200
Initial SO2 concentration in inlet gas (ppm)
(b)
Figure 13 The change of (a) NOx removal efficiency and (b) NOx concentration with the initial SO2 concentration (gas flow is 125 Lmininlet SO2 concentration is 200ndash600 ppm inlet NOx concentration is 1000 ppm NaClO concentration is 005M initial solution pH is 6 andsolution temperature is 293K solid points refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
Absorbent temperature (K)340330320310300290
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
(a)
Absorbent temperature (K)340330320310300290
0
200
400
600
800
1000
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
(b)
Figure 14The change of (a) NOx removal efficiency and (b) NOx concentration with the absorbent temperature (gas flow is 125 Lmin inletNOx concentration is 1000 ppm NaClO concentration is 005M initial solution pH is 6 and solution temperature is 293ndash333K solid pointsrefer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
reaction characteristics of molecules or ions in liquid phase[19] The effect of absorbent temperature on NOx removalwas investigated and the results were shown in Figure 14Generally the absorbent temperature was kept below 333Kin industrial application in order to reduce the supply ofmake-up water So the absorbent temperature was chosen tobe in the range of 293ndash333K in the experiments Figure 14showed that NOx removal efficiency increased gradually with
the increase of absorbent temperature The highest NOxremoval efficiency of 69was achieved at 333 K AsNO couldbe removed by 100 easily the increase of NOx removalefficiency resulted from the improvement of NO2 absorptionThis could be explained by the Arrhenius equation of thereaction rate constant The increase of temperature couldenhance the mass transfer of NO2 to the absorbent thusimproving the absorption of NO2 accordingly
Journal of Chemistry 9
4 Conclusion
NOx removal by wet scrubbing using NaClO solution wasstudied based on a spraying reactor in a cyclic mode Theresults showed that when NaClO concentration was higherthan 005M and initial solution pH was below 8 NOxremoval efficiency was relatively stable which was higherthan 60 The coexisting CO2 (5) had little effect on NOxremoval efficiency but the solution pHbegan to decreasewiththe proceeding of cyclic scrubbing process when initial pHwas higher than 6The coexisting O2 (13) could oxidize NOpartially in the gas mixer resulting in a little improvementof NOx removal efficiency When initial NOx concentrationwas higher than 500 ppm NO could be removed completelywhile outlet NO2 concentration increased almost linearlywith the increase of initial NOx concentration resultingin a relative stable NOx removal efficiency A completeremoval of SO2 and NO could be achieved simultaneouslyat 293K initial NaClO solution pH 6 and 005M NaClOconcentration With the increase of inlet SO2 concentrationthe outlet NO2 concentration increased slightly due to thedecrease of solution pH NOx removal efficiency increasedwith the increase of absorbent temperature The relevantreaction mechanism for the removal of NOx and SO2 bywet scrubbing using NaClO solution was also discussed Theresults demonstrated that it was of great potential for NaClOsolution to remove NOx from marine exhaust gas
Conflicts of Interest
The authors declare that there are no conflicts of interestregarding the publication of this paper
Acknowledgments
This study has been financially supported by the NationalNatural Science Foundation of China (Grant nos 51402033and 51479020) the Science and Technology Plan Project ofChinarsquos Ministry of Transport (Grant no 2015328225150) theDoctoral Scientific Research Staring Foundation of Liaon-ing Province (Grant no 201601073) and the FundamentalResearch Funds for the Central Universities (Grant nos3132017003 and 3132016326)
References
[1] M Guo Z Fu DMa N Ji C Song and Q Liu ldquoA short reviewof treatment methods of marine diesel engine exhaust gasesrdquoProcedia Engineering vol 121 pp 938ndash943 2015
[2] M-W Bae ldquoA study on the effects of recirculated exhaust gasupon NO119909 and soot emissions in diesel engines with scrubberEGR systemrdquo SAE Technical Papers 1999
[3] A M A Attia and A R Kulchitskiy ldquoInfluence of the structureof water-in-fuel emulsion on diesel engine performancerdquo Fuelvol 116 pp 703ndash708 2014
[4] X Tauzia A Maiboom and S R Shah ldquoExperimental study ofinlet manifold water injection on combustion and emissions ofan automotive direct injection diesel enginerdquoEnergy vol 35 no9 pp 3628ndash3639 2010
[5] A M Hallquist E Fridell J Westerlund and M Hal-lquist ldquoOnboard measurements of nanoparticles from a SCR-equipped marine diesel enginerdquo Environmental Science andTechnology vol 47 no 2 pp 773ndash780 2013
[6] J Herdzik ldquoEmissions from marine engines versus IMO certi-fication and requirements of tier 3rdquo Journal of KONES vol 18pp 161ndash167 2011
[7] M Magnusson E Fridell and H H Ingelsten ldquoThe influenceof sulfur dioxide andwater on the performance of amarine SCRcatalystrdquoApplied Catalysis B Environmental vol 111-112 pp 20ndash26 2012
[8] T Kuwahara K Yoshida Y Kannaka T Kuroki andMOkuboldquoImprovement of NOx reduction efficiency in diesel emissioncontrol using nonthermal plasma combined exhaust gas recir-culation processrdquo IEEE Transactions on Industry Applicationsvol 47 no 6 pp 2359ndash2366 2011
[9] T Kuwahara K Yoshida T Kuroki K Hanamoto K Sato andMOkubo ldquoPilot-scale aftertreatment using nonthermal plasmareduction of adsorbed NO119909 in marine diesel-engine exhaustgasrdquo Plasma Chemistry and Plasma Processing vol 34 no 1 pp65ndash81 2014
[10] D Xie Y Sun T Zhu and L Ding ldquoRemoval of NO in mist bythe combination of plasma oxidation and chemical absorptionrdquoEnergy and Fuels vol 30 no 6 pp 5071ndash5076 2016
[11] S Zhou J Zhou Y Feng and Y Zhu ldquoMarine Emission Pol-lution Abatement Using Ozone Oxidation by a Wet ScrubbingMethodrdquo Industrial andEngineeringChemistry Research vol 55no 20 pp 5825ndash5831 2016
[12] Y S Mok ldquoAbsorption-reduction technique assisted by ozoneinjection and sodium sulfide for NO119909 removal from exhaustgasrdquo Chemical Engineering Journal vol 118 no 1-2 pp 63ndash672006
[13] E B Myers and T J Overcamp ldquoHydrogen peroxide scrubberfor the control of nitrogen oxidesrdquo Environmental EngineeringScience vol 19 no 5 pp 321ndash327 2002
[14] Z Wang Z Wang Y Ye N Chen and H Li ldquoStudy on theremoval of nitric oxide (NO) by dual oxidant (H2O2S2O82
minus)systemrdquo Chemical Engineering Science vol 145 pp 133ndash1402016
[15] Y Liu Q Wang Y Yin J Pan and J Zhang ldquoAdvancedoxidation removal ofNOand SO2 fromflue gas by using ultravi-oletH2O2NaOH processrdquo Chemical Engineering Research andDesign vol 92 no 10 pp 1907ndash1914 2014
[16] H Chu T W Chien and S Y Li ldquoSimultaneous absorptionof SO2 and NO from flue gas with KMnO4NaOH solutionsrdquoScience of the Total Environment vol 275 no 1-3 pp 127ndash1352001
[17] R Hao Y Zhang Z Wang et al ldquoAn advanced wet method forsimultaneous removal of SO2 andNO fromcoal-fired flue gas byutilizing a complex absorbentrdquo Chemical Engineering Journalvol 307 pp 562ndash571 2017
[18] Z Han S Yang D Zheng X Pan and Z Yan ldquoAn investigationon NO removal by wet scrubbing using NaClO2 seawatersolutionrdquo SpringerPlus vol 5 no 1 article 751 2016
[19] Y Zhou C Li C Fan et al ldquoWet removal of sulfur dioxide andnitrogen oxides from simulated flue gas by Ca(ClO)2 solutionrdquoEnvironmental Progress and Sustainable Energy vol 34 no 6pp 1586ndash1595 2015
[20] S-L Yang Z-T Han J-M Dong Z-S Zheng and X-X PanldquoUV-enhanced naclo oxidation of nitric oxide from simulatedflue gasrdquo Journal of Chemistry vol 2016 Article ID 6065019 8pages 2016
10 Journal of Chemistry
[21] L Chen C-H Hsu and C-L Yang ldquoOxidation and absorptionof nitric oxide in a packed tower with sodium hypochloriteaqueous solutionsrdquo Environmental Progress vol 24 no 3 pp279ndash288 2005
[22] E Ghibaudi J R Barker and S W Benson ldquoReaction ofNO with hypochlorous acidrdquo International Journal of ChemicalKinetics vol 11 no 8 pp 843ndash851 1979
[23] R-T Guo W-G Pan X-B Zhang et al ldquoThe absorptionkinetics of NO into weakly acidic NaClO solutionrdquo SeparationScience and Technology vol 48 no 18 pp 2871ndash2875 2013
[24] S Yang Z Han X Pan Z Yan and J Yu ldquoNitrogen oxideremoval using seawater electrolysis in an undivided cell forocean-going vesselsrdquo RSC Advances vol 6 no 115 pp 114623ndash114631 2016
[25] M K Mondal and V R Chelluboyana ldquoNew experimentalresults of combined SO2 and NO removal from simulated gasstream by NaClO as low-cost absorbentrdquo Chemical EngineeringJournal vol 217 pp 48ndash53 2013
[26] C V Raghunath and M K Mondal ldquoExperimental scalemulti component absorption of SO2 and NO by NH3NaClOscrubbingrdquo Chemical Engineering Journal vol 314 pp 537ndash5472017
[27] J Wang and W Zhong ldquoSimultaneous desulfurization anddenitrification of sintering flue gas via composite absorbentrdquoChinese Journal of Chemical Engineering vol 24 no 8 pp 1104ndash1111 2016
[28] S An and O Nishida ldquoNew application of seawater andelectrolyzed seawater in air pollution control of marine dieselenginerdquo JSME International Journal Series B Fluids and Ther-mal Engineering vol 46 no 1 pp 206ndash213 2003
[29] Z Han S Yang X Pan et al ldquoNew experimental results of NOremoval from simulated flue gas by wet scrubbing using NaClOsolutionrdquo Energy amp Fuels vol 31 no 3 pp 3047ndash3054 2017
[30] N Lahoutifard P Lagrange and J Lagrange ldquoKinetics andmechanism of nitrite oxidation by hypochlorous acid in theaqueous phaserdquo Chemosphere vol 50 no 10 pp 1349ndash13572003
[31] Y G Adewuyi X He H Shaw and W Lolertpihop ldquoSimul-taneous absorption and oxidation of NO and SO2 by aqueoussolutions of sodium chloriterdquo Chemical Engineering Communi-cations vol 174 no 1 pp 21ndash51 1999
[32] A Mukimin K Wijaya and A Kuncaka ldquoElectro-degradationof reactive blue dyes using cylinder modified electrode Ti120573-PbO2 as dimensionally stable anoderdquo Indonesian Journal ofChemistry vol 10 no 3 pp 285ndash289 2010
Figure 11 The change of (a) NOx removal efficiency and (b) NO119909 concentrations with the initial NOx concentration (gas flow is 125 Lmininlet NOx concentration is 250ndash1250 ppm NaClO concentration is 005M initial solution pH is 6 and solution temperature is 293K solidpoints refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
20
40
60
80
100
Rem
oval
effici
ency
()
SO2
NOx
(a)
1000 1200 1400800600400200
Initial NOx concentration in inlet gas (ppm)
0
200
400
600
800
1000
1200
1400
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
(b)
Figure 12 The change of (a) NOx removal efficiency and (b) NOx concentration with the inlet NOx concentration (gas flow is 125 Lmininlet SO2 concentration is 600 ppm inlet NOx concentration is 250ndash1250 ppm NaClO concentration is 005M initial solution pH is 6 andsolution temperature is 293K solid points refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
Figure 13 exhibited the effect of SO2 concentration on NOxremoval efficiency and NOx concentration in flue gas Theresult showed that SO2 together with NO was completelyremoved But with the increase of inlet SO2 concentrationNOx removal efficiency exhibited a slightly downside trendThis phenomenon could be ascribed to the competitionreactions between NOx and SO2 Some oxidants in theabsorbent would be consumed through the hydrolyzation
and absorption of SO2With inlet SO2 concentration increas-ing from 200 ppm to 600 ppm the pHof the scrubbedNaClOsolution decreased from 525 to 452The decrease of solutionpH was negative for the absorption of NO2 through (5) and(6)
36 Effect of Absorbent Temperature The reaction temper-ature could greatly influence the diffusion dissolution and
8 Journal of Chemistry
0
20
40
60
80
100
Rem
oval
effici
ency
()
SO2
NOx
300 500 600400200
Initial SO2 concentration in inlet gas (ppm)
(a)
0
200
400
600
800
1000
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
300 500 600400200
Initial SO2 concentration in inlet gas (ppm)
(b)
Figure 13 The change of (a) NOx removal efficiency and (b) NOx concentration with the initial SO2 concentration (gas flow is 125 Lmininlet SO2 concentration is 200ndash600 ppm inlet NOx concentration is 1000 ppm NaClO concentration is 005M initial solution pH is 6 andsolution temperature is 293K solid points refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
Absorbent temperature (K)340330320310300290
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
(a)
Absorbent temperature (K)340330320310300290
0
200
400
600
800
1000
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
(b)
Figure 14The change of (a) NOx removal efficiency and (b) NOx concentration with the absorbent temperature (gas flow is 125 Lmin inletNOx concentration is 1000 ppm NaClO concentration is 005M initial solution pH is 6 and solution temperature is 293ndash333K solid pointsrefer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
reaction characteristics of molecules or ions in liquid phase[19] The effect of absorbent temperature on NOx removalwas investigated and the results were shown in Figure 14Generally the absorbent temperature was kept below 333Kin industrial application in order to reduce the supply ofmake-up water So the absorbent temperature was chosen tobe in the range of 293ndash333K in the experiments Figure 14showed that NOx removal efficiency increased gradually with
the increase of absorbent temperature The highest NOxremoval efficiency of 69was achieved at 333 K AsNO couldbe removed by 100 easily the increase of NOx removalefficiency resulted from the improvement of NO2 absorptionThis could be explained by the Arrhenius equation of thereaction rate constant The increase of temperature couldenhance the mass transfer of NO2 to the absorbent thusimproving the absorption of NO2 accordingly
Journal of Chemistry 9
4 Conclusion
NOx removal by wet scrubbing using NaClO solution wasstudied based on a spraying reactor in a cyclic mode Theresults showed that when NaClO concentration was higherthan 005M and initial solution pH was below 8 NOxremoval efficiency was relatively stable which was higherthan 60 The coexisting CO2 (5) had little effect on NOxremoval efficiency but the solution pHbegan to decreasewiththe proceeding of cyclic scrubbing process when initial pHwas higher than 6The coexisting O2 (13) could oxidize NOpartially in the gas mixer resulting in a little improvementof NOx removal efficiency When initial NOx concentrationwas higher than 500 ppm NO could be removed completelywhile outlet NO2 concentration increased almost linearlywith the increase of initial NOx concentration resultingin a relative stable NOx removal efficiency A completeremoval of SO2 and NO could be achieved simultaneouslyat 293K initial NaClO solution pH 6 and 005M NaClOconcentration With the increase of inlet SO2 concentrationthe outlet NO2 concentration increased slightly due to thedecrease of solution pH NOx removal efficiency increasedwith the increase of absorbent temperature The relevantreaction mechanism for the removal of NOx and SO2 bywet scrubbing using NaClO solution was also discussed Theresults demonstrated that it was of great potential for NaClOsolution to remove NOx from marine exhaust gas
Conflicts of Interest
The authors declare that there are no conflicts of interestregarding the publication of this paper
Acknowledgments
This study has been financially supported by the NationalNatural Science Foundation of China (Grant nos 51402033and 51479020) the Science and Technology Plan Project ofChinarsquos Ministry of Transport (Grant no 2015328225150) theDoctoral Scientific Research Staring Foundation of Liaon-ing Province (Grant no 201601073) and the FundamentalResearch Funds for the Central Universities (Grant nos3132017003 and 3132016326)
References
[1] M Guo Z Fu DMa N Ji C Song and Q Liu ldquoA short reviewof treatment methods of marine diesel engine exhaust gasesrdquoProcedia Engineering vol 121 pp 938ndash943 2015
[2] M-W Bae ldquoA study on the effects of recirculated exhaust gasupon NO119909 and soot emissions in diesel engines with scrubberEGR systemrdquo SAE Technical Papers 1999
[3] A M A Attia and A R Kulchitskiy ldquoInfluence of the structureof water-in-fuel emulsion on diesel engine performancerdquo Fuelvol 116 pp 703ndash708 2014
[4] X Tauzia A Maiboom and S R Shah ldquoExperimental study ofinlet manifold water injection on combustion and emissions ofan automotive direct injection diesel enginerdquoEnergy vol 35 no9 pp 3628ndash3639 2010
[5] A M Hallquist E Fridell J Westerlund and M Hal-lquist ldquoOnboard measurements of nanoparticles from a SCR-equipped marine diesel enginerdquo Environmental Science andTechnology vol 47 no 2 pp 773ndash780 2013
[6] J Herdzik ldquoEmissions from marine engines versus IMO certi-fication and requirements of tier 3rdquo Journal of KONES vol 18pp 161ndash167 2011
[7] M Magnusson E Fridell and H H Ingelsten ldquoThe influenceof sulfur dioxide andwater on the performance of amarine SCRcatalystrdquoApplied Catalysis B Environmental vol 111-112 pp 20ndash26 2012
[8] T Kuwahara K Yoshida Y Kannaka T Kuroki andMOkuboldquoImprovement of NOx reduction efficiency in diesel emissioncontrol using nonthermal plasma combined exhaust gas recir-culation processrdquo IEEE Transactions on Industry Applicationsvol 47 no 6 pp 2359ndash2366 2011
[9] T Kuwahara K Yoshida T Kuroki K Hanamoto K Sato andMOkubo ldquoPilot-scale aftertreatment using nonthermal plasmareduction of adsorbed NO119909 in marine diesel-engine exhaustgasrdquo Plasma Chemistry and Plasma Processing vol 34 no 1 pp65ndash81 2014
[10] D Xie Y Sun T Zhu and L Ding ldquoRemoval of NO in mist bythe combination of plasma oxidation and chemical absorptionrdquoEnergy and Fuels vol 30 no 6 pp 5071ndash5076 2016
[11] S Zhou J Zhou Y Feng and Y Zhu ldquoMarine Emission Pol-lution Abatement Using Ozone Oxidation by a Wet ScrubbingMethodrdquo Industrial andEngineeringChemistry Research vol 55no 20 pp 5825ndash5831 2016
[12] Y S Mok ldquoAbsorption-reduction technique assisted by ozoneinjection and sodium sulfide for NO119909 removal from exhaustgasrdquo Chemical Engineering Journal vol 118 no 1-2 pp 63ndash672006
[13] E B Myers and T J Overcamp ldquoHydrogen peroxide scrubberfor the control of nitrogen oxidesrdquo Environmental EngineeringScience vol 19 no 5 pp 321ndash327 2002
[14] Z Wang Z Wang Y Ye N Chen and H Li ldquoStudy on theremoval of nitric oxide (NO) by dual oxidant (H2O2S2O82
minus)systemrdquo Chemical Engineering Science vol 145 pp 133ndash1402016
[15] Y Liu Q Wang Y Yin J Pan and J Zhang ldquoAdvancedoxidation removal ofNOand SO2 fromflue gas by using ultravi-oletH2O2NaOH processrdquo Chemical Engineering Research andDesign vol 92 no 10 pp 1907ndash1914 2014
[16] H Chu T W Chien and S Y Li ldquoSimultaneous absorptionof SO2 and NO from flue gas with KMnO4NaOH solutionsrdquoScience of the Total Environment vol 275 no 1-3 pp 127ndash1352001
[17] R Hao Y Zhang Z Wang et al ldquoAn advanced wet method forsimultaneous removal of SO2 andNO fromcoal-fired flue gas byutilizing a complex absorbentrdquo Chemical Engineering Journalvol 307 pp 562ndash571 2017
[18] Z Han S Yang D Zheng X Pan and Z Yan ldquoAn investigationon NO removal by wet scrubbing using NaClO2 seawatersolutionrdquo SpringerPlus vol 5 no 1 article 751 2016
[19] Y Zhou C Li C Fan et al ldquoWet removal of sulfur dioxide andnitrogen oxides from simulated flue gas by Ca(ClO)2 solutionrdquoEnvironmental Progress and Sustainable Energy vol 34 no 6pp 1586ndash1595 2015
[20] S-L Yang Z-T Han J-M Dong Z-S Zheng and X-X PanldquoUV-enhanced naclo oxidation of nitric oxide from simulatedflue gasrdquo Journal of Chemistry vol 2016 Article ID 6065019 8pages 2016
10 Journal of Chemistry
[21] L Chen C-H Hsu and C-L Yang ldquoOxidation and absorptionof nitric oxide in a packed tower with sodium hypochloriteaqueous solutionsrdquo Environmental Progress vol 24 no 3 pp279ndash288 2005
[22] E Ghibaudi J R Barker and S W Benson ldquoReaction ofNO with hypochlorous acidrdquo International Journal of ChemicalKinetics vol 11 no 8 pp 843ndash851 1979
[23] R-T Guo W-G Pan X-B Zhang et al ldquoThe absorptionkinetics of NO into weakly acidic NaClO solutionrdquo SeparationScience and Technology vol 48 no 18 pp 2871ndash2875 2013
[24] S Yang Z Han X Pan Z Yan and J Yu ldquoNitrogen oxideremoval using seawater electrolysis in an undivided cell forocean-going vesselsrdquo RSC Advances vol 6 no 115 pp 114623ndash114631 2016
[25] M K Mondal and V R Chelluboyana ldquoNew experimentalresults of combined SO2 and NO removal from simulated gasstream by NaClO as low-cost absorbentrdquo Chemical EngineeringJournal vol 217 pp 48ndash53 2013
[26] C V Raghunath and M K Mondal ldquoExperimental scalemulti component absorption of SO2 and NO by NH3NaClOscrubbingrdquo Chemical Engineering Journal vol 314 pp 537ndash5472017
[27] J Wang and W Zhong ldquoSimultaneous desulfurization anddenitrification of sintering flue gas via composite absorbentrdquoChinese Journal of Chemical Engineering vol 24 no 8 pp 1104ndash1111 2016
[28] S An and O Nishida ldquoNew application of seawater andelectrolyzed seawater in air pollution control of marine dieselenginerdquo JSME International Journal Series B Fluids and Ther-mal Engineering vol 46 no 1 pp 206ndash213 2003
[29] Z Han S Yang X Pan et al ldquoNew experimental results of NOremoval from simulated flue gas by wet scrubbing using NaClOsolutionrdquo Energy amp Fuels vol 31 no 3 pp 3047ndash3054 2017
[30] N Lahoutifard P Lagrange and J Lagrange ldquoKinetics andmechanism of nitrite oxidation by hypochlorous acid in theaqueous phaserdquo Chemosphere vol 50 no 10 pp 1349ndash13572003
[31] Y G Adewuyi X He H Shaw and W Lolertpihop ldquoSimul-taneous absorption and oxidation of NO and SO2 by aqueoussolutions of sodium chloriterdquo Chemical Engineering Communi-cations vol 174 no 1 pp 21ndash51 1999
[32] A Mukimin K Wijaya and A Kuncaka ldquoElectro-degradationof reactive blue dyes using cylinder modified electrode Ti120573-PbO2 as dimensionally stable anoderdquo Indonesian Journal ofChemistry vol 10 no 3 pp 285ndash289 2010
Figure 13 The change of (a) NOx removal efficiency and (b) NOx concentration with the initial SO2 concentration (gas flow is 125 Lmininlet SO2 concentration is 200ndash600 ppm inlet NOx concentration is 1000 ppm NaClO concentration is 005M initial solution pH is 6 andsolution temperature is 293K solid points refer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
Absorbent temperature (K)340330320310300290
0
20
40
60
80
100
NOx
rem
oval
effici
ency
()
(a)
Absorbent temperature (K)340330320310300290
0
200
400
600
800
1000
NOx
conc
entr
atio
n (p
pm)
NO2
NONO2
NO
(b)
Figure 14The change of (a) NOx removal efficiency and (b) NOx concentration with the absorbent temperature (gas flow is 125 Lmin inletNOx concentration is 1000 ppm NaClO concentration is 005M initial solution pH is 6 and solution temperature is 293ndash333K solid pointsrefer to inlet NOx concentrations and open points refer to outlet NOx concentrations)
reaction characteristics of molecules or ions in liquid phase[19] The effect of absorbent temperature on NOx removalwas investigated and the results were shown in Figure 14Generally the absorbent temperature was kept below 333Kin industrial application in order to reduce the supply ofmake-up water So the absorbent temperature was chosen tobe in the range of 293ndash333K in the experiments Figure 14showed that NOx removal efficiency increased gradually with
the increase of absorbent temperature The highest NOxremoval efficiency of 69was achieved at 333 K AsNO couldbe removed by 100 easily the increase of NOx removalefficiency resulted from the improvement of NO2 absorptionThis could be explained by the Arrhenius equation of thereaction rate constant The increase of temperature couldenhance the mass transfer of NO2 to the absorbent thusimproving the absorption of NO2 accordingly
Journal of Chemistry 9
4 Conclusion
NOx removal by wet scrubbing using NaClO solution wasstudied based on a spraying reactor in a cyclic mode Theresults showed that when NaClO concentration was higherthan 005M and initial solution pH was below 8 NOxremoval efficiency was relatively stable which was higherthan 60 The coexisting CO2 (5) had little effect on NOxremoval efficiency but the solution pHbegan to decreasewiththe proceeding of cyclic scrubbing process when initial pHwas higher than 6The coexisting O2 (13) could oxidize NOpartially in the gas mixer resulting in a little improvementof NOx removal efficiency When initial NOx concentrationwas higher than 500 ppm NO could be removed completelywhile outlet NO2 concentration increased almost linearlywith the increase of initial NOx concentration resultingin a relative stable NOx removal efficiency A completeremoval of SO2 and NO could be achieved simultaneouslyat 293K initial NaClO solution pH 6 and 005M NaClOconcentration With the increase of inlet SO2 concentrationthe outlet NO2 concentration increased slightly due to thedecrease of solution pH NOx removal efficiency increasedwith the increase of absorbent temperature The relevantreaction mechanism for the removal of NOx and SO2 bywet scrubbing using NaClO solution was also discussed Theresults demonstrated that it was of great potential for NaClOsolution to remove NOx from marine exhaust gas
Conflicts of Interest
The authors declare that there are no conflicts of interestregarding the publication of this paper
Acknowledgments
This study has been financially supported by the NationalNatural Science Foundation of China (Grant nos 51402033and 51479020) the Science and Technology Plan Project ofChinarsquos Ministry of Transport (Grant no 2015328225150) theDoctoral Scientific Research Staring Foundation of Liaon-ing Province (Grant no 201601073) and the FundamentalResearch Funds for the Central Universities (Grant nos3132017003 and 3132016326)
References
[1] M Guo Z Fu DMa N Ji C Song and Q Liu ldquoA short reviewof treatment methods of marine diesel engine exhaust gasesrdquoProcedia Engineering vol 121 pp 938ndash943 2015
[2] M-W Bae ldquoA study on the effects of recirculated exhaust gasupon NO119909 and soot emissions in diesel engines with scrubberEGR systemrdquo SAE Technical Papers 1999
[3] A M A Attia and A R Kulchitskiy ldquoInfluence of the structureof water-in-fuel emulsion on diesel engine performancerdquo Fuelvol 116 pp 703ndash708 2014
[4] X Tauzia A Maiboom and S R Shah ldquoExperimental study ofinlet manifold water injection on combustion and emissions ofan automotive direct injection diesel enginerdquoEnergy vol 35 no9 pp 3628ndash3639 2010
[5] A M Hallquist E Fridell J Westerlund and M Hal-lquist ldquoOnboard measurements of nanoparticles from a SCR-equipped marine diesel enginerdquo Environmental Science andTechnology vol 47 no 2 pp 773ndash780 2013
[6] J Herdzik ldquoEmissions from marine engines versus IMO certi-fication and requirements of tier 3rdquo Journal of KONES vol 18pp 161ndash167 2011
[7] M Magnusson E Fridell and H H Ingelsten ldquoThe influenceof sulfur dioxide andwater on the performance of amarine SCRcatalystrdquoApplied Catalysis B Environmental vol 111-112 pp 20ndash26 2012
[8] T Kuwahara K Yoshida Y Kannaka T Kuroki andMOkuboldquoImprovement of NOx reduction efficiency in diesel emissioncontrol using nonthermal plasma combined exhaust gas recir-culation processrdquo IEEE Transactions on Industry Applicationsvol 47 no 6 pp 2359ndash2366 2011
[9] T Kuwahara K Yoshida T Kuroki K Hanamoto K Sato andMOkubo ldquoPilot-scale aftertreatment using nonthermal plasmareduction of adsorbed NO119909 in marine diesel-engine exhaustgasrdquo Plasma Chemistry and Plasma Processing vol 34 no 1 pp65ndash81 2014
[10] D Xie Y Sun T Zhu and L Ding ldquoRemoval of NO in mist bythe combination of plasma oxidation and chemical absorptionrdquoEnergy and Fuels vol 30 no 6 pp 5071ndash5076 2016
[11] S Zhou J Zhou Y Feng and Y Zhu ldquoMarine Emission Pol-lution Abatement Using Ozone Oxidation by a Wet ScrubbingMethodrdquo Industrial andEngineeringChemistry Research vol 55no 20 pp 5825ndash5831 2016
[12] Y S Mok ldquoAbsorption-reduction technique assisted by ozoneinjection and sodium sulfide for NO119909 removal from exhaustgasrdquo Chemical Engineering Journal vol 118 no 1-2 pp 63ndash672006
[13] E B Myers and T J Overcamp ldquoHydrogen peroxide scrubberfor the control of nitrogen oxidesrdquo Environmental EngineeringScience vol 19 no 5 pp 321ndash327 2002
[14] Z Wang Z Wang Y Ye N Chen and H Li ldquoStudy on theremoval of nitric oxide (NO) by dual oxidant (H2O2S2O82
minus)systemrdquo Chemical Engineering Science vol 145 pp 133ndash1402016
[15] Y Liu Q Wang Y Yin J Pan and J Zhang ldquoAdvancedoxidation removal ofNOand SO2 fromflue gas by using ultravi-oletH2O2NaOH processrdquo Chemical Engineering Research andDesign vol 92 no 10 pp 1907ndash1914 2014
[16] H Chu T W Chien and S Y Li ldquoSimultaneous absorptionof SO2 and NO from flue gas with KMnO4NaOH solutionsrdquoScience of the Total Environment vol 275 no 1-3 pp 127ndash1352001
[17] R Hao Y Zhang Z Wang et al ldquoAn advanced wet method forsimultaneous removal of SO2 andNO fromcoal-fired flue gas byutilizing a complex absorbentrdquo Chemical Engineering Journalvol 307 pp 562ndash571 2017
[18] Z Han S Yang D Zheng X Pan and Z Yan ldquoAn investigationon NO removal by wet scrubbing using NaClO2 seawatersolutionrdquo SpringerPlus vol 5 no 1 article 751 2016
[19] Y Zhou C Li C Fan et al ldquoWet removal of sulfur dioxide andnitrogen oxides from simulated flue gas by Ca(ClO)2 solutionrdquoEnvironmental Progress and Sustainable Energy vol 34 no 6pp 1586ndash1595 2015
[20] S-L Yang Z-T Han J-M Dong Z-S Zheng and X-X PanldquoUV-enhanced naclo oxidation of nitric oxide from simulatedflue gasrdquo Journal of Chemistry vol 2016 Article ID 6065019 8pages 2016
10 Journal of Chemistry
[21] L Chen C-H Hsu and C-L Yang ldquoOxidation and absorptionof nitric oxide in a packed tower with sodium hypochloriteaqueous solutionsrdquo Environmental Progress vol 24 no 3 pp279ndash288 2005
[22] E Ghibaudi J R Barker and S W Benson ldquoReaction ofNO with hypochlorous acidrdquo International Journal of ChemicalKinetics vol 11 no 8 pp 843ndash851 1979
[23] R-T Guo W-G Pan X-B Zhang et al ldquoThe absorptionkinetics of NO into weakly acidic NaClO solutionrdquo SeparationScience and Technology vol 48 no 18 pp 2871ndash2875 2013
[24] S Yang Z Han X Pan Z Yan and J Yu ldquoNitrogen oxideremoval using seawater electrolysis in an undivided cell forocean-going vesselsrdquo RSC Advances vol 6 no 115 pp 114623ndash114631 2016
[25] M K Mondal and V R Chelluboyana ldquoNew experimentalresults of combined SO2 and NO removal from simulated gasstream by NaClO as low-cost absorbentrdquo Chemical EngineeringJournal vol 217 pp 48ndash53 2013
[26] C V Raghunath and M K Mondal ldquoExperimental scalemulti component absorption of SO2 and NO by NH3NaClOscrubbingrdquo Chemical Engineering Journal vol 314 pp 537ndash5472017
[27] J Wang and W Zhong ldquoSimultaneous desulfurization anddenitrification of sintering flue gas via composite absorbentrdquoChinese Journal of Chemical Engineering vol 24 no 8 pp 1104ndash1111 2016
[28] S An and O Nishida ldquoNew application of seawater andelectrolyzed seawater in air pollution control of marine dieselenginerdquo JSME International Journal Series B Fluids and Ther-mal Engineering vol 46 no 1 pp 206ndash213 2003
[29] Z Han S Yang X Pan et al ldquoNew experimental results of NOremoval from simulated flue gas by wet scrubbing using NaClOsolutionrdquo Energy amp Fuels vol 31 no 3 pp 3047ndash3054 2017
[30] N Lahoutifard P Lagrange and J Lagrange ldquoKinetics andmechanism of nitrite oxidation by hypochlorous acid in theaqueous phaserdquo Chemosphere vol 50 no 10 pp 1349ndash13572003
[31] Y G Adewuyi X He H Shaw and W Lolertpihop ldquoSimul-taneous absorption and oxidation of NO and SO2 by aqueoussolutions of sodium chloriterdquo Chemical Engineering Communi-cations vol 174 no 1 pp 21ndash51 1999
[32] A Mukimin K Wijaya and A Kuncaka ldquoElectro-degradationof reactive blue dyes using cylinder modified electrode Ti120573-PbO2 as dimensionally stable anoderdquo Indonesian Journal ofChemistry vol 10 no 3 pp 285ndash289 2010
NOx removal by wet scrubbing using NaClO solution wasstudied based on a spraying reactor in a cyclic mode Theresults showed that when NaClO concentration was higherthan 005M and initial solution pH was below 8 NOxremoval efficiency was relatively stable which was higherthan 60 The coexisting CO2 (5) had little effect on NOxremoval efficiency but the solution pHbegan to decreasewiththe proceeding of cyclic scrubbing process when initial pHwas higher than 6The coexisting O2 (13) could oxidize NOpartially in the gas mixer resulting in a little improvementof NOx removal efficiency When initial NOx concentrationwas higher than 500 ppm NO could be removed completelywhile outlet NO2 concentration increased almost linearlywith the increase of initial NOx concentration resultingin a relative stable NOx removal efficiency A completeremoval of SO2 and NO could be achieved simultaneouslyat 293K initial NaClO solution pH 6 and 005M NaClOconcentration With the increase of inlet SO2 concentrationthe outlet NO2 concentration increased slightly due to thedecrease of solution pH NOx removal efficiency increasedwith the increase of absorbent temperature The relevantreaction mechanism for the removal of NOx and SO2 bywet scrubbing using NaClO solution was also discussed Theresults demonstrated that it was of great potential for NaClOsolution to remove NOx from marine exhaust gas
Conflicts of Interest
The authors declare that there are no conflicts of interestregarding the publication of this paper
Acknowledgments
This study has been financially supported by the NationalNatural Science Foundation of China (Grant nos 51402033and 51479020) the Science and Technology Plan Project ofChinarsquos Ministry of Transport (Grant no 2015328225150) theDoctoral Scientific Research Staring Foundation of Liaon-ing Province (Grant no 201601073) and the FundamentalResearch Funds for the Central Universities (Grant nos3132017003 and 3132016326)
References
[1] M Guo Z Fu DMa N Ji C Song and Q Liu ldquoA short reviewof treatment methods of marine diesel engine exhaust gasesrdquoProcedia Engineering vol 121 pp 938ndash943 2015
[2] M-W Bae ldquoA study on the effects of recirculated exhaust gasupon NO119909 and soot emissions in diesel engines with scrubberEGR systemrdquo SAE Technical Papers 1999
[3] A M A Attia and A R Kulchitskiy ldquoInfluence of the structureof water-in-fuel emulsion on diesel engine performancerdquo Fuelvol 116 pp 703ndash708 2014
[4] X Tauzia A Maiboom and S R Shah ldquoExperimental study ofinlet manifold water injection on combustion and emissions ofan automotive direct injection diesel enginerdquoEnergy vol 35 no9 pp 3628ndash3639 2010
[5] A M Hallquist E Fridell J Westerlund and M Hal-lquist ldquoOnboard measurements of nanoparticles from a SCR-equipped marine diesel enginerdquo Environmental Science andTechnology vol 47 no 2 pp 773ndash780 2013
[6] J Herdzik ldquoEmissions from marine engines versus IMO certi-fication and requirements of tier 3rdquo Journal of KONES vol 18pp 161ndash167 2011
[7] M Magnusson E Fridell and H H Ingelsten ldquoThe influenceof sulfur dioxide andwater on the performance of amarine SCRcatalystrdquoApplied Catalysis B Environmental vol 111-112 pp 20ndash26 2012
[8] T Kuwahara K Yoshida Y Kannaka T Kuroki andMOkuboldquoImprovement of NOx reduction efficiency in diesel emissioncontrol using nonthermal plasma combined exhaust gas recir-culation processrdquo IEEE Transactions on Industry Applicationsvol 47 no 6 pp 2359ndash2366 2011
[9] T Kuwahara K Yoshida T Kuroki K Hanamoto K Sato andMOkubo ldquoPilot-scale aftertreatment using nonthermal plasmareduction of adsorbed NO119909 in marine diesel-engine exhaustgasrdquo Plasma Chemistry and Plasma Processing vol 34 no 1 pp65ndash81 2014
[10] D Xie Y Sun T Zhu and L Ding ldquoRemoval of NO in mist bythe combination of plasma oxidation and chemical absorptionrdquoEnergy and Fuels vol 30 no 6 pp 5071ndash5076 2016
[11] S Zhou J Zhou Y Feng and Y Zhu ldquoMarine Emission Pol-lution Abatement Using Ozone Oxidation by a Wet ScrubbingMethodrdquo Industrial andEngineeringChemistry Research vol 55no 20 pp 5825ndash5831 2016
[12] Y S Mok ldquoAbsorption-reduction technique assisted by ozoneinjection and sodium sulfide for NO119909 removal from exhaustgasrdquo Chemical Engineering Journal vol 118 no 1-2 pp 63ndash672006
[13] E B Myers and T J Overcamp ldquoHydrogen peroxide scrubberfor the control of nitrogen oxidesrdquo Environmental EngineeringScience vol 19 no 5 pp 321ndash327 2002
[14] Z Wang Z Wang Y Ye N Chen and H Li ldquoStudy on theremoval of nitric oxide (NO) by dual oxidant (H2O2S2O82
minus)systemrdquo Chemical Engineering Science vol 145 pp 133ndash1402016
[15] Y Liu Q Wang Y Yin J Pan and J Zhang ldquoAdvancedoxidation removal ofNOand SO2 fromflue gas by using ultravi-oletH2O2NaOH processrdquo Chemical Engineering Research andDesign vol 92 no 10 pp 1907ndash1914 2014
[16] H Chu T W Chien and S Y Li ldquoSimultaneous absorptionof SO2 and NO from flue gas with KMnO4NaOH solutionsrdquoScience of the Total Environment vol 275 no 1-3 pp 127ndash1352001
[17] R Hao Y Zhang Z Wang et al ldquoAn advanced wet method forsimultaneous removal of SO2 andNO fromcoal-fired flue gas byutilizing a complex absorbentrdquo Chemical Engineering Journalvol 307 pp 562ndash571 2017
[18] Z Han S Yang D Zheng X Pan and Z Yan ldquoAn investigationon NO removal by wet scrubbing using NaClO2 seawatersolutionrdquo SpringerPlus vol 5 no 1 article 751 2016
[19] Y Zhou C Li C Fan et al ldquoWet removal of sulfur dioxide andnitrogen oxides from simulated flue gas by Ca(ClO)2 solutionrdquoEnvironmental Progress and Sustainable Energy vol 34 no 6pp 1586ndash1595 2015
[20] S-L Yang Z-T Han J-M Dong Z-S Zheng and X-X PanldquoUV-enhanced naclo oxidation of nitric oxide from simulatedflue gasrdquo Journal of Chemistry vol 2016 Article ID 6065019 8pages 2016
10 Journal of Chemistry
[21] L Chen C-H Hsu and C-L Yang ldquoOxidation and absorptionof nitric oxide in a packed tower with sodium hypochloriteaqueous solutionsrdquo Environmental Progress vol 24 no 3 pp279ndash288 2005
[22] E Ghibaudi J R Barker and S W Benson ldquoReaction ofNO with hypochlorous acidrdquo International Journal of ChemicalKinetics vol 11 no 8 pp 843ndash851 1979
[23] R-T Guo W-G Pan X-B Zhang et al ldquoThe absorptionkinetics of NO into weakly acidic NaClO solutionrdquo SeparationScience and Technology vol 48 no 18 pp 2871ndash2875 2013
[24] S Yang Z Han X Pan Z Yan and J Yu ldquoNitrogen oxideremoval using seawater electrolysis in an undivided cell forocean-going vesselsrdquo RSC Advances vol 6 no 115 pp 114623ndash114631 2016
[25] M K Mondal and V R Chelluboyana ldquoNew experimentalresults of combined SO2 and NO removal from simulated gasstream by NaClO as low-cost absorbentrdquo Chemical EngineeringJournal vol 217 pp 48ndash53 2013
[26] C V Raghunath and M K Mondal ldquoExperimental scalemulti component absorption of SO2 and NO by NH3NaClOscrubbingrdquo Chemical Engineering Journal vol 314 pp 537ndash5472017
[27] J Wang and W Zhong ldquoSimultaneous desulfurization anddenitrification of sintering flue gas via composite absorbentrdquoChinese Journal of Chemical Engineering vol 24 no 8 pp 1104ndash1111 2016
[28] S An and O Nishida ldquoNew application of seawater andelectrolyzed seawater in air pollution control of marine dieselenginerdquo JSME International Journal Series B Fluids and Ther-mal Engineering vol 46 no 1 pp 206ndash213 2003
[29] Z Han S Yang X Pan et al ldquoNew experimental results of NOremoval from simulated flue gas by wet scrubbing using NaClOsolutionrdquo Energy amp Fuels vol 31 no 3 pp 3047ndash3054 2017
[30] N Lahoutifard P Lagrange and J Lagrange ldquoKinetics andmechanism of nitrite oxidation by hypochlorous acid in theaqueous phaserdquo Chemosphere vol 50 no 10 pp 1349ndash13572003
[31] Y G Adewuyi X He H Shaw and W Lolertpihop ldquoSimul-taneous absorption and oxidation of NO and SO2 by aqueoussolutions of sodium chloriterdquo Chemical Engineering Communi-cations vol 174 no 1 pp 21ndash51 1999
[32] A Mukimin K Wijaya and A Kuncaka ldquoElectro-degradationof reactive blue dyes using cylinder modified electrode Ti120573-PbO2 as dimensionally stable anoderdquo Indonesian Journal ofChemistry vol 10 no 3 pp 285ndash289 2010
[21] L Chen C-H Hsu and C-L Yang ldquoOxidation and absorptionof nitric oxide in a packed tower with sodium hypochloriteaqueous solutionsrdquo Environmental Progress vol 24 no 3 pp279ndash288 2005
[22] E Ghibaudi J R Barker and S W Benson ldquoReaction ofNO with hypochlorous acidrdquo International Journal of ChemicalKinetics vol 11 no 8 pp 843ndash851 1979
[23] R-T Guo W-G Pan X-B Zhang et al ldquoThe absorptionkinetics of NO into weakly acidic NaClO solutionrdquo SeparationScience and Technology vol 48 no 18 pp 2871ndash2875 2013
[24] S Yang Z Han X Pan Z Yan and J Yu ldquoNitrogen oxideremoval using seawater electrolysis in an undivided cell forocean-going vesselsrdquo RSC Advances vol 6 no 115 pp 114623ndash114631 2016
[25] M K Mondal and V R Chelluboyana ldquoNew experimentalresults of combined SO2 and NO removal from simulated gasstream by NaClO as low-cost absorbentrdquo Chemical EngineeringJournal vol 217 pp 48ndash53 2013
[26] C V Raghunath and M K Mondal ldquoExperimental scalemulti component absorption of SO2 and NO by NH3NaClOscrubbingrdquo Chemical Engineering Journal vol 314 pp 537ndash5472017
[27] J Wang and W Zhong ldquoSimultaneous desulfurization anddenitrification of sintering flue gas via composite absorbentrdquoChinese Journal of Chemical Engineering vol 24 no 8 pp 1104ndash1111 2016
[28] S An and O Nishida ldquoNew application of seawater andelectrolyzed seawater in air pollution control of marine dieselenginerdquo JSME International Journal Series B Fluids and Ther-mal Engineering vol 46 no 1 pp 206ndash213 2003
[29] Z Han S Yang X Pan et al ldquoNew experimental results of NOremoval from simulated flue gas by wet scrubbing using NaClOsolutionrdquo Energy amp Fuels vol 31 no 3 pp 3047ndash3054 2017
[30] N Lahoutifard P Lagrange and J Lagrange ldquoKinetics andmechanism of nitrite oxidation by hypochlorous acid in theaqueous phaserdquo Chemosphere vol 50 no 10 pp 1349ndash13572003
[31] Y G Adewuyi X He H Shaw and W Lolertpihop ldquoSimul-taneous absorption and oxidation of NO and SO2 by aqueoussolutions of sodium chloriterdquo Chemical Engineering Communi-cations vol 174 no 1 pp 21ndash51 1999
[32] A Mukimin K Wijaya and A Kuncaka ldquoElectro-degradationof reactive blue dyes using cylinder modified electrode Ti120573-PbO2 as dimensionally stable anoderdquo Indonesian Journal ofChemistry vol 10 no 3 pp 285ndash289 2010
