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Journal of Hazardous Materials 153 (2008) 670676

Study on pyrolysis of typicalmaterials by using TG-FTI

Y.Eion, Zg Prost 200r 200

Abstract

Pyrolysis ana(TG-FTIR). . Theconcentrativ G cutwo and thre ateriaacid, hydroc r dioare several d ntialis potential yrolyand pyrolysi atile p 2007 Elsevier B.V. All rights reserved.

Keywords: Medical waste; Pyrolysis; TG-FTIR analysis

1. Introdu

Medicalboth peoplwaste is unproducts duposition ofare alwaystor and bamhas been foincineratiorial, destroywaste unreally, incinein China. Mmass burn,discarded m

CorresponE-mail a

(H.M. Zhu).

0304-3894/$doi:10.1016/jction

waste, if not treated properly, may be hazardous toe and environment. As the incineration of medicalderdeveloped in China, it is important to know thering pyrolysis and incineration. Although the com-medical waste is quite complex, several materials

included, such as absorbent cotton, medical respira-boo stick. Among current technologies, incinerationund to be widely, the most important advantage of

n is that it significantly reduces the volume of mate-s pathogens and hazardous organics, and renders the

cognizable materials in the form of ash. Addition-ration is predicted to be more popular in the futureedical waste incineration plant refers not just to the

but also to any type of thermal treatment systems foraterials that waste resources and generate pollutants.

ding author. Tel.: +87 571 87952629; fax: +86 571 87952438.ddresses: zhuhongmei126@126.com, sophiczhu@hotmail.com

These include systems based upon combustion, pyrolysis, andthermal gasification. So it is necessary to analyze the pyrolysischaracteristics of medical wastes.

Pyrolysis plays an important role in combustion processesdue to the tremendous diversity of medical waste sources. It isimportant to build comprehensive medical waste pyrolysis mod-els that can predict product specification and yields. However,few detailed products information on medical waste pyrolysiswas found in the available literature. The lack of data, combin-ing with the large variety and complexity of medical wastes,leads to difficulties in understanding emission behavior of med-ical wastes during the thermal treatment process. Medical wastepyrolysis characteristics can be clarified after pyrolysis of eachmedical waste is studied.

TG is used widely in thermal analysis and kinetics parame-ters study under both nitrogen and air atmospheres [14]. Forpyrolysis, different heating rates are carried out to obtain thekinetic model. For combustion, different oxygen concentrationsand heating rates are taken into account by using TG. But thecomposition of evolved gas in each weight loss steps cannot beobserved only by using TG. On other hand, Fourier transforminfrared spectroscopy (FTIR) results can be used to evaluate the

see front matter 2007 Elsevier B.V. All rights reserved..jhazmat.2007.09.011H.M. Zhu , J.H. Yan, X.G. Jiang,State Key Laboratory of Clean Energy Utilizat

38# Zheda Road, Hangzhou 310027, ZhejianReceived 4 March 2007; received in revised form 27 Augu

Available online 6 Septembe

of certain medical waste materials was studied using thermogravimetricPyrolysis characteristics of three common materials were discussede, followed by medical respirator and bamboo stick. From TG and DTe stages respectively. Evolved volatile products from all these three marbon, carbon dioxide, carbon monoxide, and water; whereas no sulphuifferences in yield among them. However, the study in this paper is esseto provide valuable inputs for predictive modeling of medical waste ps models that can predict yields and evolution patterns of selected volmedical wasteR analysis. Lai, K.F. Cen

hejiang University,vince, PR China7; accepted 1 September 2007

7

lyzer coupled with Fourier transform infrared spectroscopypyrolysis of absorbent cotton turned out to be the most

rves, pyrolysis of these three materials occurred in single,ls included 2-butanone, benzaldehyde, formic acid, aceticxide, ammonia and hydrogen cyanide was detected. Therefor medical waste pyrolysis model, the TG-FTIR approachsis. More studied are needed to get the kinetic parametersroducts for CFD applications.

H.M. Zhu et al. / Journal of Hazardous Materials 153 (2008) 670676 671

functional groups and prove the existence of some emissions[5,6]. FTIR, which provides plenty of information of mixedgases, can be used to identify the composition of mixture, aswell as be used to quantify CO2, CO, CH4, C2H2, C2H4, HCNand NH3, etc. [7,8].

TG combining with FTIR is a useful tool in dynamic analysisas it monitors continuously both the time dependent evolution ofthe gases and the weight of the non-volatile materials (residue).It has already been used widely to investigate biomass pyrolysis[911] and polymers thermal degradation [12,13], as well asto forecast the hazardous emissions that may be produced inthe case of major accidents [14]. But very limited studies wereconducted using TG combining with FTIR on medical wastes.

In this study, volatile products from TG during TG-FTIRexperimentso that seco3D spectruwas generaloss and cstudy, provcharacteris

2. Experim

2.1. Exper

Absorbechosen as ewastes. In omedical resbamboo sticonductingensured thaimized. Althe moistution in the pelemental a

2.2. Exper

The NicTGA/SDTANicolet TGand gas celthe change

for both TGA and spectrometer. Resolution in FTIR was set as4 cm1, number of scans per spectrum was set as 20 times/min,and the spectral region was set as 4000400 cm1.

The TG curve is similar with the heating rate from 10 C/minto 50 C/min, and the temperature for the maximum rate ofweight loss shifts to higher temperature levels as the heatingrate increases, but the temperature increases less than 20 C,thus the optimization experiment conditions were as follows:nitrogen atmosphere with a flow rate of 30 ml/min, heating rateof 30 C/min, temperature from 30 C to 960 C. Because theevolved gas could be swept into the gas cell immediately afterthey are formed, the slower the purge flow selected, the higherthe sensitivity expected. Flow rate of the purge gas was set also30 ml/min. To FTIR, a weight loss about 10 mg usually gives

te sistudopte

ults

G an

andrves

or hsis psorb. FoCtage

94 Cis:we

oo stiaturboo se pyred b, allmbo

tivelfinaand

tivele th

Table 1Proximate and

Material ate a

CottonRespiratorBamboo stick

Unless stated ygen ca As-receivb Dry basis.were swept into gas cell immediately by carrier-gasndary reactions were minimized. At the same time,m that reflects the effect of time and wavenumberted by Nicolet spectrometer. The results of weight

omposition of evolved gases obtained through theide plentiful information to understand the pyrolysistics of medical wastes.

ental materials and method

iment materials

nt cotton, medical respirator and bamboo stick werexperiment materials for they are popular in medicalrder to make the sample heated sufficiently, we splitpirator to small pieces (square of 1 mm) and grindedck to powder (diameter is less than 100m) beforeexperiment. The small sample size used in this workt temperature gradients within the sample were min-l samples were dried in oven at 105 C for 3 h, sore of sample was removed to minimize the interac-yrolysis phase of particle conversion. The results ofnalysis of samples were shown in Table 1.

iment method

olet Nexus 670 spectrometer and Mettler Toledo851e thermo analyzer were coupled by a Thermo-

A interface model, of which the stainless transfer linel (20 cm path length) were set to 180 C to minimizeof evolved gas. Nitrogen was used as the purge gas

adequain thiswas ad

3. Res

3.1. T

TGthat cu200 CpyrolyFor ab384 Cat 381three sand 4(Ts)TheTf,bambtemperTbamthat thfollowcottonand barespec

Thepiratorrespecof thes

ultimate analysis of materials

Proximate analysis (%) UltimMoisturea Ashb Volatiles Fixed carbon C

6.46 0.20 96.40 3.60 44.927.01 4.14 92.47 7.53 51.289.77 1.96 82.17 17.83 50.76

otherwise, all data are expressed in weight percent on a dry, ash-free basis. Oxed basis.gnal, so approximately 12 mg of samples was usedy. Medium-sized crucible of 70L made of Al2O3d as the sample container.

and discussion

d DTG analysis

DTG curves were shown in Fig. 1(ac), it showsare similar when the temperature is lower than

igher than 520 C. However, from 200 C to 520 C,rocesses are different due to different materials.

ent cotton, the DTG curve exhibits a single peak atr medical respirator, there are two pyrolysis peaksand 494 C. For bamboo stick, pyrolysis occurs ins, the DTG peak temperatures are 313 C, 363 C

respectively. The weight loss start temperatureTs,bamboo stick < Ts,medical repirator < Ts,absorbent cotton.

ight loss finish temperature (Tf) is:ck > Tf,medical repirator > Tf,absorbent cotton. So thee range (T = Tf Ts) for thermal decomposition is:tick >Tmedical repirator >Tabsorbent cotton. It indicatesolysis of absorbent cotton is the most concentrative,

y medical respirator and bamboo stick. To absorbentproducts evolve at one stage; to medical respiratoro stick, products evolve at two and three stages

y.l weight loss of the absorbent cotton, medical res-bamboo stick are 10.81%, 11.43% and 17.91%

y. The residual char and ash in proximate analysisree materials is absorbent cotton < medical respira-

nalysis (%) QHHV (MJ/kg)H O N S

9.00 45.86 0.19 0.03 15.7896.69 41.71 0.18 0.14 18.1035.91 42.98 0.28 0.07 17.446

ontent was determined by difference.

672 H.M. Zhu et al. / Journal of Hazardous Materials 153 (2008) 670676

Fig. 1. Cu

tor < bamboresidual chby differen

3.2. FTIR

Infraredganic and ospectrum oabsorbancespectrum, tis similar tintensity ppeaks; for

the temperature at the spectral intensity peak is decided by TGbecause there are several seconds delay from TG to FTIR.

Analysis of gas compositioner evolved gases from TG were swept into the gas cell,ance information at different wavenumber and different

ation of molecule configuration3.2.1.Aft

absorb

Table 2Identificrve of TG and DTG for materials (heating rate of 30 C/min).

o stick. So the final weight loss has relation with thear and ash. The differences in TG curve may be causedt volatile and moisture contents in each material.

analysis

spectrum is often used to distinguish the various inor-rganic compounds from pyrolysis. The 3D infraredf evolution gases includes information of infrared, wavenumber and temperature. From the infraredhe change of spectral intensity along time directiono TG results, for absorbent cotton, there is a singleeak; for medical respirator, there are two intensitybamboo stick, there are three intensity peaks. But

H.M. Zhu et al. / Journal of Hazardous Materials 153 (2008) 670676 673

time can be obtained by Fourier transform. When the time isfixed, absorbance information at different wavenumber can beobtained to analyze the composition of gases at this moment;at the same time, when the wavenumber is fixed, absorbanceinformation at different time can also be obtained under thiswavenumber to analyze the certain component as a function oftime.

Here we take the first spectral intensity peak of bamboostick for example. First, fixing the time according to maximumspectral intensity, most gases evolve at that time. The spectrumincludes two parts: the spectrum in functional groups region(40001333 cm1), in which the absorption is conspicuous, theother part is fingerprint region (1333667 cm1), in which theabsorption is less conspicuous. Second, we establish preliminaryidentification of functional groups that exist in the spectrum.Main wavenumber corresponding to the functional groups isshown in Table 2. Third, we check the library in OMNIC andfind possible species in the library, pay attention to large andconspicuous peaks of each species spectrum, then compare theexperiment spectrum with the standard species spectrum, alsocheck the absorption band at fingerprint region of the spectrum.Fourth, some compounds such as CO2 and CO can be identifieddirectly, we separate the known compounds by subtracting themfrom the mixture spectrum. That is to say, the mixture spectralis the sum of the spectra of all components. A certain time isselected in Gram-Schmidt to get the spectral at this time; thena referencewhich consyears by apis opened. Atime and retract) is chowindow ap

spectra of reference spectra below it, the AKB operation isselected, the value of K (scaling factor) later can be adjusted bysubtracting the reference spectra. By subtracting a spectrum ofa pure component from the sample spectrum, it provides a sim-pler mixture spectrum. For different possible components, it canbe subtracted other reference spectra from the simpler mixturespectral. Once this is done, features from the spectrum will beread very easily.

Combined with the 3D spectrum, main products are iden-tified as follows: CO2, CO, H2O, acid such as formic acidand acetic acid, aldehyde such as benzaldehyde, ketone suchas 2-butanone, also hydrocarbon. The hydrocarbons have manybranches because the spectral intensity is equal at 1460 cm1 and1380 cm1, at the same time there is absorbance at 880 cm1,which means the phenyl also exists. To ether, its IR characteristicis not unique, whether it exists or not is not sure. The absorbanceof ketone, acid and hydrocarbon is strong and the N takespart of little proportion in element analysis, so the absorbanceof N-product is not enough to be distinguished. There is noconspicuous absorbance in 34003200 cm1, 17001500 cm1,1000900 cm1, which means very little or no HCN evolved.There is no conspicuous absorbance in 34003200 cm1 and800600 cm1, which means very little or no NH3 evolved. Atthe same time, there is no absorbance in 34003200 cm1, so noNH compounds evolved. The possible N-product is amine with-out NH configuration. But on the one hand, HCN and HNCO

oundtectediffeservditioCN iH3 p

t firstspectra of know species is chosen from the librarytitutes a database of reference spectra collected overplying the TG-FTIR technique, the reference spectrafter that, these two spectra (sample spectra at certain

ference spectra) are selected, spectral math (or sub-sen from the process menu. When the spectral mathpears, with the sample spectrum at the top and the

were fwas deciable10 s obsis conalso Hand N

Fig. 2. Identification of bamboo stick pyrolysis ato be the major N-Products, while the NH3 fractiond to a minor extent in wood pyrolysis [9], and appre-rence in product yields for hold times longer thaned only for the species that require harsher pyroly-ns for their release, e.g. HNCO, and to lesser extentn tobacco pyrolysis [11]. On the other hand, no HCNresented in biomass pyrolysis [7]. In this study, the

DTG peak (319 C).

674 H.M. Zhu et al. / Journal of Hazardous Materials 153 (2008) 670676

evolved of NH3 and HCN is either in small amount that cannotbe detected or none of them evolved. To S-product, the func-tional group is 15001000 cm1, which overlap with CH, COstretching, there is no other conspicuous band position, and theS takes part of little proportion in element analysis, so whetherSO2 exists or not is also not sure. In fact, the number of evolvedproducts can be numerous, not all of the products can be iden-tified or separated from each other. In addition, gases like H2,N2, O2, cannot be detected by means of FTIR due to the absenceof a dipole, H2S has its main peaks below the CO2 peaks andCO2 is present in a much larger quantity than H2S, so H2S isimpossible to be detected [10]. Some evolved volatile productsof bamboo stick pyrolysis at first DTG peak is shown in Fig. 2.

3.2.2. Differences of evolution gasAfter the composition of pyrolysis product was identified,

the distribution of each product against time and temperaturecan be obtained. The TG-FTIR pyrolysis product evolution pat-terns for bamboo stick, absorbent cotton and medical respiratorare overlaid in Fig. 3. The curves in Fig. 3 for the three sam-ples are plotted as a function of temperature, the analysis ofthe evolution patterns shown in Fig. 3 leads to the followingobservations:

The evolution patterns of each of the following species werefound to be similar for absorbent cotton and medical respira-tor: aldehyde, ketone, acid, CO2, CO.

Fig stick (. 3. Comparison of TG-FTIR pyrolysis product evolution pattern for bamboo ), absorbent cotton (), and medical respirator ().

H.M. Zhu et al. / Journal of Hazardous Materials 153 (2008) 670676 675

To absorbent cotton, all products evolve at the sametime.

To medical respirator, ketone, aldehyde, acid, CO2, CO andlittle hydrocarbon evolve at first stage, and most of hydrocar-bon evolves at second stage.

To bamboo stick, most of aldehyde, ketone, acid, CO andCO2, also little hydrocarbon evolve at first stage, but mostof hydrocarbon and a few of aldehyde, ketone, acid, CO andCO2 evolve at the next stage.

Absorbent cotton has no high-temperature hydrocarbon peak. Absorbent cotton and medical respirator have a larger alde-

hyde and ketone peak than does bamboo stick. But the bamboostick has a larger acid peak than absorbent cotton and medicalrespirator.

Bamboo stick and medical respirator have a larger hydrocar-bon peak than absorbent cotton.

Absorbent cotton has a larger CO2 and CO peak than medicalrespirator.

In all three samples, the absorbance of ketone is more thanthe absorbance of aldehyde, bamboo stick displays earlierevolution of all species than absorbent cotton and medicalrespirator.

The comparison of Figs. 4 and 5 leads to the following obser-vations:

The pyrolysis of bamboo stick takes place at low temperaturethan absorbent cotton and medical respirator.

Fig. 4. Comp boo sarison of yield ratio for each pyrolysis product from TG-FTIR analysis for bam tick (), absorbent cotton (), and medical respirator ().

676 H.M. Zhu et al. / Journal of Hazardous Materials 153 (2008) 670676

Fig. 5. Compysis.

Most oflow temhydroca

Medicalhydroca

In the caboo stictemperathan the

In addit

The yielof bamb

The yieldrespirato

Bambooof hydro

Bamboo Absorbe

aldehyde

4. Conclu

Three cmedical recessfully ausing TG-Ftive analyswaste pyrovide valuabpyrolysis.experimentwill be usemodel base

Gaussian distribution of activated energies [11]. Then the Dis-tributed Activation Energy Model (DAEM) model [15] wouldbe used to solve the yield and rate of evolution for individualpyrolysis product with given kinetic parameters from TG-FTIRanalysis. The rates of yield of species are used as source terms

pecig of

sis aprov

wled

PRese

A0f Zhcial

nce

OsvalmassH. Lioosph. Bin

ing w22 (20Font,tion438

Kanokluatiods du196Qian,ali-acBecidpyrolyrol. 78Li, J. LFTIR01) 1Jongwooarison of yield ratio of all pyrolysis products from TG-FTIR anal-

the evolution of gases of medical respirator occurs atperature than that of absorbent cotton, exception ofrbon and CO.respirator and bamboo stick exhibit more complex

rbon evolution pattern than absorbent cotton.se of ketone, aldehyde, hydrocarbon, CO, CO2, bam-k seems to evolve from low temperature to highture, but the low temperature evolution is strongerhigh temperature evolution.

ion, the following observations are made:

d ratio of CO2 for absorbent cotton is more than thatoo stick and medical respirator.

ratio of CO is low for all three materials, and medicalr has the least yield ratio of CO among them.stick and medical respirator have higher yield ratio

carbon than absorbent cotton.stick has the highest yield ratio of acid among them.nt cotton has the highest yield ratio of ketone andamong them.

in the sstandinpyrolyand im

Ackno

Thelogy(2007Alogy oProvin

Refere

[1] S.bio

[2] T.-atm

[3] P.AishB1

[4] R.bus429

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[6] G.alk

[7] M.inPy

[8] S.by(20

[9] W.andsions

ommon medical waste materials (absorbent cotton,spirator and bamboo stick) were studied. We suc-nalyzed the pyrolysis process and evolved gases byTIR. But the study here is only based on qualita-

is. Our work in this paper is essential for medicallysis models. TG-FTIR approach is potential to pro-le inputs for predictive modeling of medical waste

Further study is planned. First, TG-FTIR pyrolysiss will carry out at several heating rates and the resultsd to determine kinetic parameters for a pyrolysisd on parallel, independent, first-order reactions with

113911[10] R. Bassi

biomass[11] M.A. Wo

of volatil235261

[12] M. Herreysis stud(2001) 1

[13] M.J. Ferand TGArubber a

[14] A. Lungassessme

compoun[15] A.A. Ros

for CFDes transport equations in CFD simulation, the under-the evolution of volatile species during medical wastend CFD simulation are valuable for understandinging the medical waste incineration.

gments

roject Supported by National High Techno-arch and Development Key Program of China61302), Important Project on Science and Techno-ejiang Province of China (2007C13084), ZhejiangNatural Science Foundation of China (R107532).

s

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Study on pyrolysis of typical medical waste materials by using TG-FTIR analysisIntroductionExperimental materials and methodExperiment materialsExperiment method

Results and discussionTG and DTG analysisFTIR analysisAnalysis of gas compositionDifferences of evolution gas

ConclusionsAcknowledgments

References