Detoxification of brominated pyrolysis oils
A.Hornung *,A.I.Balabano v ich 1,S.Donner,H.Seifert Forschungszentrum Karlsruhe GmbH,ITC-TAB,Hermann-v on-Helmholtz-Platz 1,76344Eggenstein-
Leopoldshafen,Germany
Accepted 14March 2003
Abstract
The de v elopment of an inno v ati v e technology for the pyrolytic con v ersion of brominated phenols in a reducti v e medium aimed at product reco v ery for use is discussed in this paper.Brominated phenols are toxic products,which contaminate pyrolysis oil of wastes from electronic and electrical equipment (WEEE).The pyrolysis experiments were carried out with 2,6-dibromophenol,tetrabromobisphenol A,WEEE pyrolysis oil and polypropylene or polyethylene in encapsulated ampoules under inert atmosphere in quasi-isothermal conditions (300Á4008C)with a different residence time (10Á30Optimal conditions were found to be the use of polypropylene at 3508C with a residence time of 20min.The main pyrolysis products were identified as HBr and phenol.A radical debromination mechanism for the pyrolytic destruction of brominated phenols is suggested.
#2003Elsevier Science B.V.All rights reserved.
Keywords:Pyrolysis;Debromination;Brominated phenols;Polypropylene;Polyethylene;WEEE
1.Introduction
Until the late 1980s,halogenated additi v es,especially brominated aromatics,were used in polymeric compositions for electronic and electrical industries to impart flame retardant properties.For this purpose,Tetrabromobisphenol A (TBBA)was applied in epoxy resins,which are used in manufacturing of printed circuit boards.*Corresponding author.Tel.:'49-72-4782-6138;fax:'49-72-4782-2959.
E-mail address:andreas.hornung@itc-tab.fzk.de (A.Hornung).
1Permanent address:Research Institute for Physical Chemical Problems,Belarussian State Uni v ersity,ul.Leningradskaya 14,220050Minsk,Belarus.
J.Anal.Appl.Pyrolysis 70(2003)723Á
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www.else v ier/locate/jaap
0165-2370/03/$-see front matter #2003Elsevier Science B.V.All rights reserved.doi:10.1016/S0165-2370(03)00049-4
Today,TBBA shares about 50%of the market of the used brominated flame retardants [1].As a result,the wastes from electronic and electrical equipment (WEEE)contain high amounts of bromine (up to 12therefore,a pyrolytic treatment (recycling)of WEEE aimed at material/energy reco v ery will r
esult in the formation of highly toxic brominated compounds,mainly brominated phenols,side by side with non-brominated organics,mainly phenols.In connection with this,the pyrolytic oil must be subjected to dehalogenation prior to the further use.
Many methods are known to decompose halogen-containing organic compounds.Among them,hydrodehalogenation offers attracti v e features for material reco v ery.Catalytic hydrodehalogenation is carried out at 250Á4008in the presence of metal-
containing (group VIII is widely used)catalysts and pure hydrogen [2].Howe v er,in the absence of catalysts,higher temperatures (700Á14008C)are required to exchange
halogen atoms for hydrogen.This is likely to be because of the high C(arom)ÃBr bond strength,and high energies are necessary for its homolytic Beside pure hydrogen,hydrocarbons (methane,n -hexane)can be applied for the exchange reaction [3].In the literature [4]pyrolysis of TBBA,bromonaphthalene,bromocy-clohexane and bromohexane in the presence of hydrogen donors (tetralin,eicosane)was performed at 6008C in encapsulated ampoules and high
reco v ery were reported for 30and 60min residence times.perform a reducti v e dehalogenation can be lowered e v en further phenols,a formation of radicals due to the homolytic scission of reported for
temperatures from 2508C [5].The aim of this work polyethylene (PE)and polypropylene (PP)as a reducti v e source of brominated phenols at 300Á4008C [6].2.Experimental
2,6-Dibromophenol (DP,I,Aldrich),TBBA (II,Aldrich)and pyrolysis oil (PO)from WEEE (circuit board fraction)obtained in a rotary kiln o v en at 350and 4508C were used as basic model samples in this study.PE (BASF)and PP (BASEU)were used as reducti v e media.
Because continuous experiments in a bubble column reactor are in preparation,pyrolysis experiments were carried out with the model samples in encapsulated ampoules.Glass ampoules were charged under nitrogen or helium atmospheres with the model samples or with their mixtures with PE or PP (3Á5:1)of about 80Á100mg and then melted.The ampoules were treated at 350Á4008C for 10Á30min in a
A.Hornung et al./J.Anal.Appl.Pyrolysis 70(2003)723Á733
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preheated o v en.After that,they were opened and pyrolysis oils were washed out with acetone and successi v ely analyzed by GC/MS (HP 6890/5972A)using a HP-160m column and the following heat
ing program:2min at 708C,temperature increase to 2908C at a rate of 108C min (1and 40min at 2908C.
To in v estigate gaseous pyrolysis products,the ampoules were broken in a closed tube which was pre v iously filled with helium,and gases were injected into the GC/MS.In this study,the 60m HP-5capillary column was also found to be an excellent choice.The column was temperature programmed to 250at 108C min (1after initial 5min period at (408C.The mass spectra were obtained by electron ionization at 70eV keeping the source at about 1808C.A mass spectrometric identification was carried out using WILEY and NBS Mono-and polybrominated dioxins (PBDDs)were identified on the basis of both the molecular ion m /z v alue and of the ion decomposition pattern constructed for the best fit with the mass spectrum.The PBDDs mass spectra are presented Figs.1Á3.
3.Results
3.1.2,6-Dibromophenol
The pyrolysis of DP at 3508C (Fig.4a)or 4008C (Fig.5a)resulted in the formation of mono-,di-,tribrominated phenols and PBDDs.When DP was heated with PE or PP the composition of the degradation products drastically changed.The effect of PE at 3508C (residence time 20min)is sh
own in Fig.4b.The formation of phenol (1)is indicating progress of debromination and the PBDDs (11Á
16)and 2,4,6-tribromophenol (10)formation is pre v entedparison of Fig.4b and Fig.5b it is seen that the influence of PE is e v en stronger at 4008C as (7)and monobrominated phenols (3and 5)are consumed during 20min residence time.In addition,the formation of other brominated products was also prohibited.
The effect of PP on the pyrolysis of DP at 3508C is shown in Fig.4c and is in terms of debromination as effecti v e as that of PE at 4008C indicating the
higher
Fig.1.Mass spectrum of monobromodibenzo-p -dioxin.
A.Hornung et al./J.Anal.Appl.Pyrolysis 70(2003)723Á733725
seifertFig.2.Mass spectrum of dibromodibenzo-p
-dioxin.
Fig.3.Mass spectrum of tribromodibenzo-p
-dioxin.
Fig.4.Gas chromatogram of the pyrolysis oil of:DP (a)DP 'PE 03:1(b)DP 'PP 04:1(c).Pyrolysis conditions:3508C,20min.(1)Phenol,(2)2-methylphenol,(3)4-methylphenol,(4)2-bromophenol,(5)2-ethylphenol,(6)2-isopropylphenol,(7)4-bromophenol,(8)2,4-dibromophenol,(9)2,6-dibromophenol,
(10)2,4,6-tribromophenol,(11)bromodibenzodioxin,(12Á14)dibromodibenzo-p -dioxins,(15,16)tribromodibenzo-p -dioxins.
A.Hornung et al./J.Anal.Appl.Pyrolysis 70(2003)723Á733
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reduction acti v ity of PP in comparison with PE.It is seen that DP (9)is destroyed during 20min residence time whereas PE induces only partial debromination at the same conditions (Fig.4b).It should be noted that the reco v ery of phenol is accompanied by formation of small quantities of alkylphenols 2,3,5,6(Fig.4c)and 2(Fig.5b).
Fig.4b shows that the pyrolysis oil collected at 3508C does not contain products taking origin from PE.PE gi v es rise to hydrocarbons at the pyrolysis temperature 4008C as shown in Fig.5b (unmarke
d peaks between 14and 32min).In opposite to PE,PP produces
between 15and 32min).
A gas chromatogram min)is presented in Fig.6b.While HBr is the main product,howe v er,small amounts of methyl and isopropyl bromides are also formed.For comparison,a gas Fig.5.Gas chromatogram of the pyrolysis oil of:DP (a),DP 'PE 03:1(b).Pyrolysis conditions:4008C,20min.(1)Phenol,(2)2-methylphenol,(3)2-bromophenol,(4)naphthaline,(5)4-bromophenol,(6)2,4-dibromophenol,(7)2,6-dibromophenol,(8)biphenyl,(9)biphenylether,(10)2,4,6-tribromophenol,(11)bromodibenzo-p -dioxin,(12Á14)dibromodibenzo-p -dioxins,(15,16)tribromodibenzo-p -dioxins.
Fig.6.Gas chromatogram of the gaseous pyrolysis product of:DP (a),DP 'PP 05:1(b).Pyrolysis conditions:3508C,20min.(1)HBr,(2)2-methylpropane,(3)methyl bromide,(4)pentane,(5)H 2O,(6)2-methylpentane,(7)2-bromo-2-methylpropane.A.Hornung et al./J.Anal.Appl.Pyrolysis 70(2003)723Á733727

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