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iO2-encapsulating PVC capable of catalytic self-suppression of dioxin emissionn waste incineration as an eco-friendly alternative to conventional PVC
yonggoo Yoo, Seung-Yeop Kwak ∗
epartment of Materials Science and Engineering, Seoul National University, 599 Gwanak-ro, Gwanak-gu, Seoul 151–744, Republic of Korea
r t i c l e i n f o
rticle history:eceived 20 May 2010eceived in revised form 12 January 2011ccepted 11 February 2011vailable online 21 February 2011
eywords:itanium dioxideioxin
ncineration
a b s t r a c t
Here, we describe the preparation of TiO2-encapsulating poly(vinyl chloride) (TEPVC), and demonstratethe potential applicability of the material as an eco-friendly alternative to conventional PVC. In partic-ular, TEPVC shows lower emission of toxic chemicals upon waste incineration compared to PVC, owingto the catalytic oxidation and decomposition of such chemicals by the encapsulated TiO2 nanoparticles.Surface-modified TiO2 nanoparticles (M-TiO2) are used for the preparation of TEPVC to facilitate the uni-form dispersion of monomeric TiO2 in the initial reaction mixture, which is the key to the preparation of afinal TEPVC showing a high dispersion of functional TiO2 nanoparticles in the PVC matrix, without signif-icant agglomeration. The content of encapsulated M-TiO2 in TEPVC was determined to be approximately0.93 wt%, and the high dispersity of M-TiO2 minimizes PVC deterioration, as determined by examinations
of morphology, and thermal and mechanical properties. The emission levels of toxic chemicals uponincineration of TEPVC and unmodified PVC samples were analyzed by gas chromatography with high-resolution mass spectrometric detection, using internal standards composed of 13C-labeled congeners ofpolychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and polychlorinated biphenyls. Thelevels of toxic chemicals produced by incineration of TEPVC were 50% of those seen after unmodified PVCincineration; the sum of toxic equivalent values of all toxic chemicals generated from the incineration ofTEPVC was thus only half that seen after incineration of unmodified PVC.
. Introduction
Poly(vinyl chloride) (PVC) is extensively used as a thermoplas-ic material because of its flame retardant properties, high chemicalesistance, and low price [1,2]. More than 30 million tons of PVC areonsumed annually; this will inevitably cause serious PVC wasteroblems within a few years [2,3]. PVC recycling is particularlyroblematic because of high separation and collection costs, lossf material quality after recycling, and a limited market for recy-late. Most PVC waste management has involved landfilling andncineration [4]. However, because of high population densities,imited landfill areas, high disposal costs, and contamination leach-ng into the soil and groundwater, waste handling policies havencreasingly shifted from landfilling to incineration, especially inountries with limited land [5–7]. Although incinerating PVC offers
high degree of destruction, reduced landfill use, and the potential
or energy recovery, this option can cause serious ecological andnvironmental problems arising from the emission of toxic dioxinsnd polychlorinated biphenyls (PCBs) [8–13].
The term “dioxin” is a general designation for polychlorinateddibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans(PCDFs), which each consist of two aromatic rings covalently linkedby two and one oxygen bridges, respectively. Dioxins are consid-ered to be the most toxic chemicals ever made with toxicities over10,000 times that of potassium cyanide, and the adverse effects ofdioxins on human health, the human environment, and ecosystemshave been known for many years [14–16]. Among many sources ofatmospheric dioxin emission, the incineration of municipal wasteis of great importance because such processes contribute signif-icantly to overall dioxin emission [8,9]. Among municipal wasteingredients, PVC is known to be the most problematic because PVCis the single largest chlorine source, playing a significant role in theformation of dioxins and other toxic chemicals, such as PCBs, inmany countries [9,17]. Therefore, finding ways to reduce the gen-eration of such toxic chemicals has been of great interest to manyresearchers.
In the early stages of these efforts, researchers focused on
improving PVC waste processing, mostly by maintaining an optimalcombustion state during waste incineration and/or establishingnew air purification facilities, some of which were reported to besuccessful in reducing dioxin emission [18,19]. However, upgradingall incineration facilities to optimal combustion and/or air purifica-
ion standards may take many years and a very large monetarynvestment. There are lots of incinerators such as home wastencinerators which are generally too small to sustain the optimalombustion condition during waste incineration [20]. The openurning of household and agricultural wastes in rural regions isnother unmanagable source of dioxin, too [21]. More recently,lternative approaches have been reported to be effective in reduc-ng dioxin emission. These include the use of secondary measuresuch as catalytic decomposition, photolysis, and catalytic combus-ion [22–28]. Combining the combustion method with a catalyticrocess in the treatment of toxic pollutants has several advantages,ecause the two-step process requires only low temperatures and
s energy-efficient [26,28,29]. In one such combined approach, tita-ium dioxide (TiO2) or TiO2-supported metal oxide is used touppress dioxin emission. Various studies have examined the cat-lytic decomposition of chlorinated aromatic compounds on theurfaces of these catalysts [28,30–33]. In these systems, dioxinolecules are first adsorbed on the catalyst surface and are then
xidized via a redox reaction with nearby oxide or hydroxide nucle-philic species [31–35]. In post-combustion exhaust gas treatmentystems, it is desirable that catalysts have a high catalytic activ-ty to chlorinated aromatic compounds at a temperature below00 ◦C because large amounts of cooled flue gas pass through thequipment quickly. TiO2-supported oxide of transition metal suchs V and W has the favorable characteristics for this applicationnd has been successfully applied. Nevertheless, there are stillnmanageable sources remained outside the coverage of the postreatment systems [20,21]. Considering the widespread use of PVC,t is necessary to find an alternative solution which could coverhese areas.
If catalyst nanoparticles with decomposition activity of chlo-inated aromatic compounds are incorporated in PVC matrix, theanoparticles can decompose chlorinated aromatic compoundsuring the incineration of PVC and consequently reduce dioxinmission although PVC is incinerated in the place where there iso appropriate dioxin treatment system. Previously unmanageableources such as small waste incinerators and open burning cane managed through this approach. Moreover, catalyst nanopar-icles embedded in PVC can effectively reduce dioxin generation,ecause catalyst nanoparticles applied as part of a post-treatmentystem will not have the opportunity to encounter dioxin moleculesuring incineration, whereas catalyst nanoparticles incorporatedithin PVC will be exposed to dioxins during incineration. Because
atalyst nanoparticles incorporated within a PVC sample have auch higher probability of encountering dioxin molecules, the
ioxin emission caused by PVC can be readily reduced to sig-ificant low-level anywhere PVC is incinerated or combustedven if the catalyst which has a relatively low activity to dioxins applied instead of high performance catalyst commonly usedn post treatment system. Among the various catalysts, TiO2as a comparatively low catalytic activity to dioxin but is col-rless, odorless, biologically innoxious, and chemically resistivenough to be not dissolved in most of solvents [36]. Above all,iO2 is inexpensive and productive enough to be applied toass production polymer PVC. However, such TiO2 incorporation
as unresolved problems arising mostly from the limited dis-ersion of TiO2 nanoparticles in the polymer matrix when theonventional process is used to mix most non-polar polymersith nanoparticles. The formation of micrometer-sized agglom-
rates of TiO2 nanoparticles can significantly decrease the areaf the interface between the polymer matrix and TiO2, leading
o reduced efficiency of adsorption of toxic chemicals and thuso inferior suppression of dioxin emission. In a previous paper,e reported the suppression of the emission of dioxin and itsrecursors upon co-incineration of PVC with TiO2-encapsulatingolystyrene (TEPS), in which a nanoscale uniform dispersion of
nvironmental 104 (2011) 193–200
TiO2 was obtained by encapsulation [37]. In practice, however,this approach is intrinsically limited because TEPS shows suppres-sion effects only when PVC and TEPS are co-incinerated. To furtherincrease the practical applicability of TiO2 use, we investigated thedirect encapsulation of TiO2 in PVC, the physical properties of thematerial synthesized, and dioxin emission by this material whenincinerated.
In this paper, we report an optimal preparation procedure forTiO2-encapsulating poly(vinyl chloride) (TEPVC). The reactor usedin this study mimicked industry-scale reactors producing com-mercial PVC, and the preparation process was not significantlydifferent from that of a commercial PVC production process; ourapproach can thus be readily applied in existing PVC industries. Themorphology and dispersion of TiO2 nanoparticles were observedwith field-emission scanning electron microscopy (FE-SEM) andtransmission electron microscopy (TEM), respectively. Quantita-tive determination of TiO2 in TEPVC was performed using X-rayfluorescence (XRF) spectrometry. We then evaluated the effects ofTiO2 encapsulation on the physical properties of TEPVC by com-paring the thermal and tensile properties with those of unmodifiedPVC using differential scanning calorimetry (DSC) and a tensile test,respectively. Finally, we measured emission of PCDDs, PCDFs, andPCBs from TEPVC and unmodified PVC, with the aid of a commercialresearch laboratory specializing in dioxin analysis.
2. Experimental
2.1. Materials
Titanium tetraisopropoxide, Ti(OCH(CH3)2)4, used in the prepa-ration of TiO2, was obtained from Aldrich. 3-(Methacryloxy)propyltrimethoxysilane (MPS), and anhydrous toluene (99.8%), both usedfor the surface modification of TiO2, were also from Aldrich.All materials were used without further purification. Reagentsused for suspension polymerization were obtained from the fol-lowing sources: vinyl chloride (VC) from Korea Standard GasCo. Ltd.; octyl peroxyneodecanoate (BND) and dioctyl perox-ydicarbonate (OPP) from Chemex Co. Ltd.; poly(vinyl alcohol)(trade name K-420TM) from Kuraray Co. Ltd.; octadecyl dibutyl-4-hydroxyphenylpropionate (IR), dilauryl thiodipropionate (DL),and aluminum sulfate (AS) from Hanwha Chem. Corp.; di-(2-ethylhexyl) phthalate (DEHP) from LG Chem. Ltd.; and methyl tin(trade name MT-800) from Songwon Industrial Co. Ltd. All of thesechemicals were used as received. Amorphous TiO2 nanoparticlesused for encapsulation were prepared through hydrolysis of tita-nium tetraisopropoxide in ethanol solution, as described in theliterature [38]. Next, MPS was grafted onto the hydroxyl groupsof the TiO2 nanoparticles to prepare surface-modified TiO2 (M-TiO2). The primary particle size of the TiO2 nanoparticles was about5 nm in diameter, as characterized by high-resolution transmissionelectron microscopy (HR-TEM) (Fig. S1 in Supplementary data),and the particles were determined to be amorphous based onthe observation of no peaks in the X-ray diffraction (XRD) anal-ysis (Fig. S2). The Brunauer–Emmett–Teller (BET) surface area ofthe prepared TiO2 was 443.4 m2/g. The dispersity of M-TiO2 inhydrophobic liquid medium was estimated by dynamic light scat-tering (DLS) using an DLS-7000 spectrophotometer coupled with aGC-1000 autocorrelator (Otsuka Electronics Co., Ltd., Osaka, Japan)by utilizing an Ar laser (� = 488 nm) at a scattering angle of 90◦.From the DLS measurements, the mean ± SD diameter of the M-
TiO2 particles dispersed in hydrophobic solvent was determinedto be 40.6 ± 11.2 nm. The grafted amount and grafting densitywere determined to be 1.1 mmol/g and 2.7 groups/nm, respectively.Detailed experimental procedures and characterization methodsfor both TiO2 and M-TiO2 can be found in our previous report [37].
H. Yoo, S.-Y. Kwak / Applied Catalysis B: E
Table 1Recipe for the preparation of PVC and TEPVC.
Ingredient Amount (g)
PVC TEPVC
Deionized water 396 396Vinyl chloride (VC) 248 2481,1,3,3-Tetramethylbutyl
TEPVC was prepared by conventional suspension polymeriza-ion in a high-pressure PVC polymerization reactor equipped withtemperature controller, a high-speed mechanical agitator, and aalance-controlled vacuum VC feeder. A typical reaction recipe isummarized in Table 1, and a schematic illustration of the reactionrocedure is shown in Fig. 1. The experimental procedure was asollows. First, the reactor was charged with water and cooled topproximately 4 ◦C. The additives used in the suspension polymer-zation were K-420TM (as a suspending agent), BND and OPP (asnitiators), IR and DL (as antioxidants), and AS (as a scale inhibitor);hese additives and M-TiO2 were combined in the reactor. VC gasas pressurized and added to the dispersion, which was thenixed with vigorous agitation at a speed of 1000 rpm for 5 h at◦C. After the dispersion of the initiator mixture with M-TiO2 into
he monomer phase, polymerization was carried out at a temper-
ture of 57.5 ± 0.5 ◦C and a pressure of approximately 9.0 ± 0.5 barhile agitating the suspension at a speed of ca. 650–700 rpm until
here was a pressure drop of approximately 0.5 bar from the max-mum pressure attained. At the end of the reaction, the remainingas was vented out. The crude product was then washed several
Fig. 1. Schematic illustration of the synthetic
nvironmental 104 (2011) 193–200 195
times with ethanol and water, filtered, and dried overnight undervacuum. Unmodified PVC for the comparison with TEPVC was pre-pared by essentially same procedure as the one for the TEPVC withthe exceptions of nanoparticle addition and the stage of vigorousagitation as a means of dispersing the nanoparticle.
2.3. General characterization
The morphology of the TEPVC was determined with a JEOL JSM-6330F FE-SEM operating at 5 kV. The FE-SEM samples were coatedwith platinum for 5 min using a JEOL JFC-1100 ion sputter coater.The dispersion of TiO2 in TEPVC was investigated with TEM. ForTEM, the PVC grains were embedded in Gartan G-1 epoxy and curedat 60 ◦C for 90 min. Ultra-thin cross-sections of the specimens wereprepared using a Leica Ultracut UCT ultracryomicrotome at roomtemperature. The TEM analyses were performed with a JEOL JEM200CX operating at 200 kV. XRF was used to determine the TiO2content of TEPVC. The XRF measurements were performed on aTi element with a Shimadzu XRF-1700 sequential XRF spectrom-eter using lithium fluoride (LiF) as an analyzing crystal with a 2dvalue of 0.4028 nm. The XRF spectrometer was operated at a cur-rent of 30 mA and a voltage of 40 kV in a technical vacuum. Thethermal properties of TEPVC were characterized by DSC performedwithin the temperature range of 40–140 ◦C at a heating rate of10 ◦C/min under a nitrogen atmosphere, employing a TA Instru-ments DSC 2920. The glass transition temperatures were measuredas the mid-points of the transitions. A Lloyd LR10K universal testingmachine was also used to evaluate the tensile properties of plas-ticized TEPVC with 8 parts per hundred resins of di-(2-ethylhexyl)phthalate (DEHP). The test specimens were in the form of dumb-bells (ASTM D-638). Sheets with a gauge length of 50 mm and awidth of 10 mm were stretched at a crosshead speed of 10 mm/minwith a load cell of 1 kN.
2.4. Incineration
To investigate the suppression of dioxin emission by TiO2 inTEPVC, TEPVC and unmodified PVC were incinerated in a tublarfurnace designed to reflect the incineration conditions of small
monomer phase. The grafting of MPS onto inorganic particles hasbeen reported to render the particles hydrophobic [40]. Thus, itwas expected that M-TiO2 could be readily dispersed in liquefieddroplets of vinyl chloride (VC). Droplets containing the M-TiO2 par-ticles were subsequently polymerized to form TEPVC. As shown in
Fig. 2. FE-SEM images of (a) unmodified PVC prepared in this study
aste incinerators [20,39]. In this test, 0.75 g of the respectiveowder samples were used as purified and dried after polymeriza-ion, without any further sample manipulation. The incinerationas performed in a temperature-controllable electric furnace at
00 ◦C with synthetic air (21%, v/v, oxygen) as the carrier gas withflow rate of approximately 1.8 L/min. The dioxins and PCBs emit-
ed as a result of incineration were collected using a method basedn US EPA method 23 for sampling dioxins and dioxin-like com-ounds. A schematic diagram of the incineration apparatus andhe toxic chemical collectors is shown in Fig. S3. A small sam-le (approximately 25 mg) was placed onto a quartz boat with aicro-spatula and slid to the central position, and then the sam-
le was combusted in the tube furnace. After the sample wasonsumed, the operation was repeated 29 times, correspondingo combustion of 0.75 g of sample over a 75 min experimentaleriod. The sample residues and soot generated by combustionere trapped in a thimble filter. The exhaust gases produced were
rapped using a thimble filter, two water impingers and a diethy-ene glycol impinger in an ice-bath, and an absorption tube filled
ith Amberlite XAD-2 resin, sequentially along the stream. A vac-um pump was located at the exit port. The vacuum pump was
n operation over the entire time course of the experiment. Theumping rate was 2 L/min, to accommodate the thermal expan-ion of gas supplied from the cylinder. The volume of sample forach test was chosen to prevent flow-back of combustion gasesnd to maintain incineration temperature during combustion. Afteresting, the test rig from the quartz tube (including areas wherettached combustion residue was confirmed) to the absorptionnit was rinsed with water, acetone, and dichloromethane, andhese solutions were also recovered. After a series of pretreat-
ents (as illustrated in a flow diagram in Fig. S4), the concentratedolutions of produced toxicants were subjected to quantitativenalysis.
.5. Analyses of dioxins and PCBs
Pretreated concentrated samples of produced toxic chemicalsere analyzed by gas chromatography with high resolution mass
pectrometric detection (GC/HRMS), using a Waters Micromassutospec Ultima magnetic sector high resolution mass spectrom-ter equipped with a Hewlett–Packard 6890 gas chromatograph.wo separate analyses were conducted according to US EPA pro-ocols. PCDDs/PCDFs were measured following the protocol ofPA Method 1613B; PCBs were quantified by the protocol of EPA
ethod 1668A. Quantification of target analytes was achieved
y isotope dilution using 13C-labeled surrogate standards. Moreetailed procedures including operating conditions for both GC andS, as well as lists of native and internal standards, can be found
n Supplementary data.
) commercial-grade PVC (Hanwha Chemical Corporation P-1000TM).
3. Results and discussion
3.1. Preparation and general characterization
Because PVC production processes have evolved in diversedirections to impart better properties to final products in a time-and energy-efficient manner, industrial production processes areoften very different from simple laboratory-scale syntheses. Forexample, commercial processes may use multiple and complexinitiator mixtures, antioxidants, and scale inhibitors. To make ourapproach more practically applicable to the existing PVC industry,we used a home-made l L high-pressure pilot reactor designed tomimic industry-scale reactors, and chose a general TEPVC recipeand preparation procedure typical of a process used to synthe-size commercial-grade PVC, as summarized in Table 1. Prior to thepreparation of TEPVC, unmodified PVC without TiO2 nanoparticleswas prepared, and the general properties of this PVC were com-pared with those of commercial PVC, to verify the validity of ourapproach to the production of PVC with properties equivalent tothose of commercial-grade PVC.
Fig. 2 shows FE-SEM images of the prepared unmodifiedPVC and commercial-grade suspension PVC (Hanwha Chem.Corp., P-1000TM), with degree of polymerization of approximately1000 ± 50; comparison of the images demonstrates that the size,shape, and size distribution did not difer significantly between thesamples. The diameter of the prepared unmodified PVC was deter-mined to be in the range 100–160 �m by particle size analysis,which was identical to that of the commercial PVC. Other physicalproperties of the prepared unmodified PVC such as the bulk densityand cold plasticizer absorption were found to meet the standardrequirements for commercial-grade materials (Table 2).
The encapsulation of TiO2 via PVC suspension polymerizationrequires an additional process step to disperse M-TiO2 in the
Fig. 3. FE-SEM images of TEPVC with magnifications of (a) ×100 and
able 1, a proportion of 1 wt% of M-TiO2 (compared to VC weight)as used for encapsulation. Fig. 3 shows FE-SEM images of TEPVC
t various magnifications. The diameter of the TEPVC grains wasn the range 100–160 �m, and was thus similar to the grain sizeange of commercial-grade suspension PVC. As can be clearly seenn Fig. 3, there were no significant TiO2 agglomerates on the sur-ace of the TEPVC sample. The dispersion of TiO2 nanoparticles inEPVC particles was examined by TEM, as shown in Fig. 4. TheiO2 nanoparticles were well dispersed on a scale of ∼20–60 nmithout significant agglomeration. When it is considered that large
gglomerates of nanoparticles, with sizes ranging from hundredsf nanometers to a few micrometers, are commonly observed inonventional polymer/inorganic nanoparticle composites preparedy mechanical mixing, the degree of dispersion of nanoparticles inhe polymer matrix was found to be significantly enhanced by thencapsulation approach.
Quantitative analysis of the encapsulated TiO2 nanoparticles inEPVC was performed by wavelength-dispersive XRF (WD-XRF).D-XRF is regarded as a valuable technique for characterizing the
ontents of specific components in samples, based on the detectionf characteristic fluorescence X-rays. In addition, we have reportedhat WD-XRF is effective in both qualitative and quantitative char-
cterization of TiO2 encapsulation into a polymeric matrix, andetails of our analysis method have been published [37]. Prior touantitative analysis of the TiO2 content of TEPVC, a calibrationurve was established using a series of standard samples made byechanical mixing of unmodified PVC with various concentrations
Fig. 4. TEM images of TEPVC showing the nanoscale dispersion of TiO2
00 showing no TiO2 agglomerates adsorbed onto the TEPVC surface.
of M-TiO2 from 0 to 2.0 wt%. From the intensity of Ti K� measured inthe TEPVC sample, the M-TiO2 content in TEPVC was determinedto be approximately 0.93 wt%, after reference to calibration data.When it is considered that unencapsulated free TiO2 was com-pletely removed by the successive washing treatments (Fig. 3),it is clear that the measured M-TiO2 content directly reflects theamount of M-TiO2 encapsulated in TEPVC.
The glass transition temperature, Tg, as measured using DSC,is an important indicator of the thermal properties of a polymer.Fig. S5 shows DSC thermograms of TEPVC and unmodified PVC.The unmodified PVC sample had a Tg of approximately 85.2 ◦C,in good agreement with that of the commercial product. A simi-lar Tg value was obtained for TEPVC, although TiO2 encapsulationresulted in a little difference (ca. 0.5 ◦C) in Tg. Fig. S6 shows thestress–strain curves of plasticized samples of various forms of PVC.Here, TEPVC/DEHP is a plasticized material derived from TEPVC,and PVC/DEHP is the plasticized sample of unmodified PVC; bothwere prepared using DEHP as a plasticizer. In particular, PVC/M-TiO2/DEHP was prepared (for comparison purposes) by mechanicaladdition of M-TiO2 to unmodified PVC. As can be seen in Fig. S6, theultimate maximum stress and the elongation of the specimen atmaximum stress were markedly lower for PVC/M-TiO2/DEHP than
for PVC/DEHP, indicating that the addition of a small amount ofM-TiO2 by mechanical mixing seriously degraded the mechanicalproperties of PVC. By contrast, the TEPVC/DEHP sample showedsubstantially increased mechanical properties compared with thePVC/M-TiO2/DEHP sample, and showed almost the same or slightly
in the TEPVC matrix with cluster sizes ranging from 20 to 60 nm.
1 is B: Environmental 104 (2011) 193–200
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etter mechanical properties than did PVC/DEHP. These findingsmply that M-TiO2 is well dispersed in the polymer matrix afterncapsulation, and that encapsulation of M-TiO2 does not resultn any serious deterioration in the ductility or toughness of theVC. The data show that the encapsulation of TiO2 nanoparticlesn PVC was successfully accomplished without causing any signifi-ant changes to the morphology or physical properties of PVC. Thiss essential if the new technology is to be readily applied in exist-ng PVC industries, to offer the advantage of lower dioxin emissionpon incineration, as described below.
.2. Incineration, analyses of dioxins and PCBs
Incineration experiments were performed using the unmodi-ed PVC and TEPVC prepared in this study, and the weights ofroduced toxic chemicals including dioxins (PCDDs and PCDFs)nd PCBs were determined by GC/HRMS with the aid of Shimadzuechno-Research Inc., a commercial research laboratory special-zing in dioxin analysis. The overall weights of dioxins and PCBs
ere estimated by using 13C-labeled internal standards consistingf over 30 congeners of PCDDs, PCDFs, and PCBs. Fig. 5 shows theeights of selected congeners of (a) PCDDs, (b) PCDFs, and (c) PCBs,ith respect to the weight of sample used for the incineration. The
uppression efficiencies of TEPVC for dioxin and PCB emission cane calculated with the following equation:
suppression (%) =(
1 − CTEPVC
CPVC
)× 100
here Esuppression is the suppression efficiency of TEPVC, withespect to PVC, for the selected PCDDs, PCDFs, and PCBs, and CPVCnd CTEPVC are the weights of the toxic substances of interest withespect to the weights of samples used for the incineration of PVCnd TEPVC. In Fig. 5, the weights of dioxins and PCBs from the TEPVCample are shown to be reduced compared with PVC, with suppres-ion efficiencies in the range 40–80%. According to our literatureurvey, the catalytic activity of catalyst nanoparticle incorporatedithin polymeric material to individual dioxin congener is not
eported. The catalytic activities of the pure TiO2 to chlorinatedromatic compounds diluted in gas phase were reported in sev-ral literatures. Khaleel et al. reported that 0.15 g of TiO2 has ∼30%f removal efficiency to 1 �L pulse introduction of chlorobenzenet 325 ◦C [41]. Liu et al. also reported that 1.0 mL of TiO2 show70% of removal efficiency to 1300 ppm of chlorobenzene at 400 ◦C
29]. Choi et al. reported TiO2 has 20% of removal efficiency to000 ppm of 1,2-dichlorobenzene at 300 ◦C and the removal effi-iency increased with increasing temperature [42]. TiO2-supportedransition metal oxide catalysts applied municipal waste incinera-or have higher efficiency than pure TiO2. According to the reviewf catalytic combustion by Everaert et al., commoncatalytic flueas management systems attached to municipal waste incinera-ors have 80–99.5% of removal efficiencies at temperature rangef 180–240 ◦C when they operate separate dioxin abatement [43].omparing efficiency data with each other, however, it should beonsidered that all dioxins contained fly ash as well as flue gasre included in self-suppression efficiency of TEPVC. Recently, Choit al. reported a similar approach with our presented study [42].hey embedded 5–10 wt% of oxide particles including TiO2, Fe3O4nd TiO2-masked Fe3O4 inside polyethylene and polystyrene, andhen showed CO2 conversion rate increased from ∼10% to 20–60%y embedded oxide during the incineration of them. This resulteveals the emission of volatile organic compounds (VOCs) dur-
ng the incineration of polymeric materials could be reduced bymbedded catalyst nanoparticles. This study is, however, limitedy lacks of individual VOC substances observation and data onhlorine-contained polymers such as PVC, considering the impor-ance of halogenated and more especially chlorinated VOCs due to
Fig. 5. Weights of congeners of (a) PCDFs, (b) PCDDs, and (c) PCBs, in exhaust gasesand ashes from incineration of unmodified PVC (stripes) and TEPVC (solid), withrespect to the weight of sample used for the incineration.
their toxicity and high stability. The suppression efficiency data inFig. 5 show a clear trend: higher suppression efficiency is observed
for higher chlorinated dioxins. Recent results of in situ FT-IR stud-ies suggest that the catalytic oxidation of chlorinated aromaticcompounds on TiO2 or TiO2-supported metal oxide occurs via aconcerted mechanism [31,32,35]. In this mechanism, the aromatic
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ig. 6. Toxic equivalent (TEQ) values for various toxic chemicals generated fromncineration of unmodified PVC (unfilled bars, left axis), total TEQ values for unmodi-ed PVC (striped bar), and for TEPVC, with estimated suppression efficiencies showny TEPVC (solid bar, right axis).
ompound is first adsorbed on the catalyst, and then the remainingromatic ring is oxidized via a nucleophilic attack on the chlorineosition in the aromatic ring. Hetrick et al. observed the surface
ntermediates during the oxidation of the different chlorophenolsnd chlorobenzenes over these catalysts, and suggest that a similareaction pathway is operating in the oxidation of chlorinated aro-atic compounds [35]. In the first step of the oxidation, chlorinated
romatic compounds are dissociatively adsorbed on Lewis acidites via Cl abstraction [31,34]. In the adsorbed aromatic molecule,oreover, chlorine plays an important role in activating the aro-atic ring towards nucleophilic attacks [31,34]. Consequently, a
igher number of chlorine atoms in a dioxin molecule offers morehances for oxidation, which would explain our observation ofigher suppression efficiencies in highly chlorinated dioxins.
Because toxicities vary among the congeners of PCDDs, PCDFs,nd PCBs, the representation of combined toxicity as one simpleeasure can provide intuitive and direct information on the toxi-
ities of all emitted chemicals. The toxic equivalent (TEQ) measures one such example; TEQ is calculated by comparing the toxicityf each individual PCDD, PCDF, and PCB congener to that of theost toxic form of dioxin, 2,3,7,8-TeCDD. This means that some
ioxins/furans/biphenyls might count as only half a TEQ if the com-ound is half as toxic as 2,3,7,8-TeCDD. The three unfilled bars onhe left side of Fig. 6 show the total generations of PCDDs, PCDFs, andCBs (reading from the left), in terms of WHO-TEQ values (basedn the toxic equivalent factors established by World Health Organ-sation), from the incineration of unmodified PVC. The data showhat the bulk of the toxicity of unmodified PVC derived from PCDFs,n agreement with the experimental results of Aracil et al. [12].he striped and solid bars in Fig. 6 represent the WHO-TEQ valuesf all toxic chemicals generated from unmodified PVC and TEPVC,espectively. As highlighted with a solid two-way arrow in the finalortion of Fig. 6, the emission of toxic substances from the incin-ration of TEPVC is up to ∼50% less than that from PVC, whichmplies that the substitution of current commercial-grade PVC byhe TEPVC of this study can halve dioxin emission upon PVC wastencineration, although focused studies to evaluate the applicabilityf TEPVC in specific PVC applications remain to be performed.
. Conclusions
We have demonstrated the fabrication of TiO2-encapsulating
VC as an approach to dispersing functional inorganic nanoparti-les in a polymeric matrix without significant agglomeration of theanoparticles. This provides an increased total adsorptive surfacerea and thus a higher catalytic efficiency of TiO2, and minimizeshe deterioration of general material characteristics, such as mor-
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nvironmental 104 (2011) 193–200 199
phology, and thermal and mechanical properties, of PVC. Fromcomparative analyses of toxic chemicals produced by the inciner-ation of unmodified PVC and TEPVC, we found that the emissionof PCDDs, PCDFs, and PCBs from unmodified PVC decreased by40–80% when TEPVC was incinerated, depending on the individ-ual congener examined. The overall reduction in toxin emissionupon incineration of TEPVC was estimated by comparing the sumof TEQ values of all toxic chemicals generated from the incinerationof TEPVC with that from the incineration of unmodified PVC. Thisanalysis showed that the emission of dioxins and other toxic chem-icals during PVC incineration can be halved using TEPVC, indicatingthe potential applicability of TEPVC as an eco-friendly alterna-tive to conventional PVC. It is obvious that subsequent studies onthe detailed mechanisms of dioxin decomposion on the surface ofincorporated TiO2 nanoparticle and the improvements of physicalproperties of TEPVC remain to be performed for the commercialapplication of this polymer–catalyst nanocomposite. It is hopedthat this study will stimulate further investigations in the field ofcatalytic elimination of environmental pollutants.
Acknowledgments
This work was supported by a part of the research Grants (2008-E005-00) funded by the Korea National Cleaner Production Center(KNCPC) and the Ministry of Knowledge Economy (MKE) of theRepublic of Korea
Appendix A. Supplementary data
Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.apcatb.2011.02.010.
References
[1] H.F. Mark, N. Bikales, C.G. Overberger, G. Menges, J.I. Kroschwitz, Encyclopediaof Polymer Science and Engineering, John Wiley & Sons, NY, 1985.
[2] Y. Saeki, T. Emura, Prog. Polym. Sci. 27 (2002) 2055–2131.[3] D. Braun, Prog. Polym. Sci. 27 (2002) 2171–2195.[4] Municipal Solid Waste in the United States: 2005 Facts and Figures United
States, Environmental Protection Agency, 2006, EPA530-R-06-011.[5] Y.H. Ahn, H.C. Choi, Water Sci. Technol. 50 (2004) 245–253.[6] K.J. Shin, Y.S. Chang, Chemosphere 38 (1999) 2655–2666.[7] R.B.H. Tan, H.H. Khoo, J. Air Waste Manage. Assoc. 56 (2006) 244–254.[8] T. Hatanaka, T. Imagawa, M. Takeuchi, Environ. Sci. Technol. 34 (2000)
3920–3924.[9] T. Hatanaka, A. Kitajima, M. Takeuchi, Environ. Sci. Technol. 39 (2005)
213–220.11] J.E. Oh, K.T. Lee, J.W. Lee, Y.S. Chang, Chemosphere 38 (1999) 2097–2108.12] I. Aracil, R. Font, J.A. Conesa, J. Anal. Appl. Pyrolysis 74 (2005) 465–478.13] J. Aguado, D.P. Serrano, Feedstock Recycling of Plastic Wastes, Royal Society of
Chemistry, London, 1999.14] P. Cole, D. Trichopoulos, H. Pastides, T. Starr, J.S. Mandel, Regul. Toxicol. Phar-
macol. 38 (2003) 378–388.15] D. Mukerjee, J. Air Waste Manage. Assoc. 48 (1998) 157–165.16] A. Schecter, L. Birnbaum, J.J. Ryan, J.D. Constable, Environ. Res. 101 (2006)
419–428.17] E. Shibata, S. Yamamoto, E. Kasai, T. Nakamura, Chemosphere 50 (2003)
1235–1242.18] K. Raghunathan, B.K. Gullett, Environ. Sci. Technol. 30 (1996) 1827–1834.19] J.M. Sanchez-Hervas, L. Armesto, E. Ruiz-Martinez, J. Otero-Ruiz, M. Pandelova,
K.W. Schramm, Fuel 84 (2005) 2149–2157.20] T. Nakao, O. Aozasa, S. Ohta, H. Miyata, Chemosphere 62 (2006) 459–468.21] P.M. Lemieux, C.C. Lutes, D.A. Santoianni, Prog. Energy Combust. Sci. 30 (2004)
1–32.22] S. Horikoshi, N. Serpone, Y. Hisamatsu, H. Hidaka, Environ. Sci. Technol. 32
(1998) 4010–4016.23] M.K. Kim, P.W. O’Keefe, Chemosphere 41 (2000) 793–800.
24] N. Lingaiah, M.A. Uddin, K. Morikawa, A. Muto, K. Murata, Y. Sakata, Green
Chem. 3 (2001) 74–75.25] A. Ghattas, R. Abu-Reziq, D. Avnir, J. Blum, Green Chem. 5 (2003) 40–43.26] M. Taralunga, B. Innocent, J. Mijoin, P. Magnoux, Appl. Catal. B: Environ. 75
28] R. Weber, T. Sakurai, H. Hagenmaier, Appl. Catal. B: Environ. 20 (1999) 249–256.29] Y. Liu, M. Luo, Z. Wei, Q. Xin, P. Ying, C. Li, Appl. Catal. B: Environ. 29 (2001)
61–67.30] F. Bertinchamps, C. Gregoire, E.M. Gaigneaux, Appl. Catal. B: Environ. 66 (2006)
1–9.31] J. Lichtenberger, M.D. Amiridis, J. Catal. 223 (2004) 296–308.
32] E. Finocchio, G. Busca, M. Notaro, Appl. Catal. B: Environ. 62 (2006) 12–20.33] S. Albonetti, S. Blasioli, R. Bonelli, J.E. Mengou, S. Scirè, F. Trifirò, Appl. Catal. A:
Gen. 341 (2008) 18–25.34] M.A. Larrubia, G. Busca, Appl. Catal. B: Environ. 39 (2002) 343–352.35] C.E. Hetrick, J. Lichtenberger, M.D. Amiridis, Appl. Catal. B: Environ. 77 (2008)
255–263.
[
[[
[
nvironmental 104 (2011) 193–200
36] D.S. Kim, S.J. Han, S.-Y. Kwak, J. Colloid Interface Sci. 316 (2007) 85–91.37] J. Choi, O. Kim, S.-Y. Kwak, Environ. Sci. Technol. 41 (2007) 5833–5838.38] M. Inagaki, T. Imai, T. Yoshikawa, B. Tryba, Appl. Catal. B: Environ. 51 (2004)
247–254.39] N.P. Cheremisinoff, Handbook of Solid Waste Management and Waste Mini-
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