Weee Recycling
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Waste Management 25 (2005) 203–208 www.elsevier.com/locate/wasman
WEEE recycling: Pyrolysis of fire retardant model polymers M.P. Luda *, N. Euringer, U. Moratti, M. Zanetti Dipartimento di Chimica, IFM dellÕUniversita` Via P. Giuria 7, 10125 Torino, Italy Accepted 17 December 2004
Abstract Pyrolysis treatments of model polymers were made with the aim of studying the recycling of wastes from electronic, electric equipment containing brominated flame retardants. Pyrolysis of flame retarded high impact polystyrene and epoxy resins were made both in flow and closed systems. Products of pyrolysis were analysed with FT–IR spectroscopy and GC–MS and the evolution of bromine was followed with a bromine ion specific electrode. The effect of alkali on pyrolysis was also studied demonstrating, as far epoxy resin is concerned, to be effective on decreasing bromine content in oil and volatile products leading to the recovery of bromine from the residue by washing. The alkali treatment was shown to be less effective in styrenic polymers containing brominated flame retardants. 2005 Elsevier Ltd. All rights reserved.
1. Introduction Polymer wastes from electronic, electric equipment (WEEE) include mainly epoxy resins and styrene polymers. They often contain brominated aromatics; in the early 1980s indeed halogenated fire retardants were largely applied to decrease the flammability of polymeric materials. Reactive fire retardants (FRs) such as diglycidylether of (3,3 0 ,5,5 0 -tetrabromobisphenol) A (DGEBTBA) is often used as comonomer with diglycilylether of bisphenol A (DGEBA) to obtain FR epoxy resins; additive FRs such as polybromo diphenyl oxides are used for styrene polymers instead. Thermal treatment of WEEE is one of the most attractive approaches to recycling which enables the recovery of bromine, monomers and other chemicals and of precious metals which account for the economic convenience of the whole recycling process. However, one of the most relevant drawbacks in dealing with thermal treatment of WEEE is the likely production of *
Corresponding author. E-mail address: [email protected] (M.P. Luda).
0956-053X/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.wasman.2004.12.010
super-toxic halogenated dibenzodioxins and dibenzofurans from the bromine containing structures. Environmentally friendly fire retardant systems currently developed to substitute halogen based systems will decrease the content of halogen in forthcoming WEEE, however actual WEEE and those collected in the near future still contain relatively large amounts of brominated FR (Buekens, 1991; Buser, 1986). In effect, amongst the various technologies of polymer recycling, WEEE are not suitable for foundry operation in the blast furnace due to the amount of halogens, metals and inert materials. On the contrary, WEEE can be thermally treated in the cement industries as a substitute for conventional fuel. Here, because of the alkaline conditions in the cement making process, the exhaust gases will contain only a minimum of pollutants. It has been recently shown that CaCO3 has a suppressive effect in the dioxins emission from PVC incineration (Sun et al., 2003). In this context preliminary experimental results show that electronic scrap can be processed into halogens containing fractions fuels with an amount of about 500 ppm halogens and residues with or nearly without halogens, depending
204
M.P. Luda et al. / Waste Management 25 (2005) 203–208
on process parameters (Bockhorn et al., 1998a,b, 1999a,b). Thus, environmental consideration makes the alkali approach promising in pyrolytic recycling of halogen containing polymers. However, basic conditions affect the whole degradation pathway which must be known to optimise the recycling process. Many studies on the mechanism of thermal degradation of such systems have been carried out (Luda et al., 2002a,b; Blazso´ et al., 2002). Because of the complexity of real WEEE mixtures, studies on model compounds are presently of paramount importance to individuate and control the thermal behaviour of the single WEEE components.
O
Fig. 2. Octabromodiphenylether (OBDPE) formula, where x + y = 8.
2215) was added to all blends. The composition of each sample is reported in Table 1. 2.2. Pyrolysis experiments Flow system pyrolysis was carried out on a tubular horizontal oven at a selected temperature on 50 mg of powdered sample. Light fraction was trapped in a cool trap in series to the pyrolytic chamber. Closed system pyrolysis was performed on a 50-mg sample in a reactor sealed under nitrogen flow and placed in the oven at the selected temperature. Premixing of the basic compounds (17% NaOH or 38% Na2CO3/Ca(OH)2 (Ca/Na) in equimolar amount) was performed in a mortar before the sample underwent the pyrolysis. IR spectra were run on a Perkin–Elmer 2000 FTIR. Samples were analysed as a KBr pellet. The GC–MS measurements were performed with a 6890N gas chromatograph (Agilent) equipped with a capillary HP5MS column and an Agilent 5973 mass spectrometer detector. Quantitative evaluation took the area percentage of the Total Ion Chromatogram into account. A Phoenix Bromide Ion Combination Epoxy Electrode placed in a 1% Na2CO3 solution and connected to an AMEL model 337 potentiometer was employed to determine Bromide. In flow system pyrolysis continuous measurements were performed by connecting the electrode system in series to the pyrolytic chamber. Standard solutions of NaBr were used for calibration of the electrode response.
2. Experimental 2.1. Materials The model brominated epoxy resin (BER) was synthesised from Commercial DGEBA (Epicote 828EL, Shell Chemie) and DGEBTBA (Shell Chemie). The mixture DGEBA/DGEBTBA was cured with 85% of stoichiometric amount of diphenyl diaminosulphone (DDS, HT 976, Ciba Geigy) under air in an oven heated for 1 h at 160 C and for 1 h at 180 C. BER contained 20% bromine. Because of the deficient stoichiometry, mainly tertiary amine groups are present in the final network (Fig. 1). The model high impact polystyrene (HIPS) was HIP STYRON 485-71 (ALBEMARLE s.a.). Three samples with different amounts of octabromodiphenylether (OBDPE, Fig. 2), antimony trioxide (Sb2O3) and calcium carbonate (CaCO3) were prepared by melt blending in an internal mixer working at 190 C for 15 min. In order to prevent oxidation phenomena a 0.1% of a commercial grade antioxidant (CIBA Irganox HP
Br H2C
HC
Br CH3
OH
OH
C
H2C O Br
Br y
Br x
CH3
O CH2
CH CH2 N
Br
O S
H2C
HC
N CH2
CH3
OH H2C O
C CH3
O
O CH2
CH CH2 OH
Fig. 1. Schematic representation of the BER network.
CH CH2 OH
O
M.P. Luda et al. / Waste Management 25 (2005) 203–208 Table 1 Composition of HIPS samples
HIPS OBDPE Sb2O3 CaCo3
205
Table 3 Pyrolysis oil composition from flow system
HIPS0 (%)
HIPS1 (%)
HIPS2 (%)
90 10 // //
85 10 5 //
72.25 8.5 4.25 15.0
Phenol Alkyl phenols Bisphenol A Bromo phenols Polybromo bisphenol A Phenylphenol
300 C · 50 0
325 C · 40 0
375 C · 40 0
3.9 2.2 17.0 3.1 67.0 1.9
4.8 5.9 19.5 2.2 59.2 3.0
21.1 6.9 13.8 4.5 42.8 6.7
3. Results and discussion 3.1. Flow system pyrolysis of BER
3.2. Closed system pyrolysis
In all cases three fractions came out of the pyrolysis treatments: (1) gaseous products, mainly HBr; (2) pyrolysis oil; (3) residue. Flow pyrolysis was carried out at 300, 325 and 375 C and the residence time was determined by reaching a constant HBr concentration, determined by the in series Bromide EIS. Results reported in Table 1 make it evident that a small fraction of HBr is evolved which corresponds to 20% of the maximum allowable for these systems. At 300 C decomposition is quite slow and it is possible that HBr evolution is not finalised yet. The majority of the sample is converted to pyrolysis oil and residue in similar amounts. Temperature increase tends to raise the oil fraction amount (see Table 2). The pyrolysis oil, as reported in Table 3, contains mainly phenols and polyphenols, some of which are brominated. The presence of phenols indicates that the first breakable bond in the network is the epoxy link. Polyphenols are the most relevant species because as soon as they are formed they evaporate. However, decomposition of polyphenols to single ring phenols occurs by increasing the temperature. Phenyl phenol is a typical secondary decomposition product whose amount follows that of phenols. The bromo-containing products account for 48–70% of the oil, the larger amount being at lower temperatures. IR of the residues (Fig. 3) shows that they substantially maintain their original structure up to 325 C, in particular the sulphone group (1144 cm1) and the geminal CH3 (1384 cm1) are preserved; in addition ammonium salts are put in evidence by the broad bands at 2600 cm1; they may be formed by reaction of HBr and amino groups formed in the degradation. At 375 C the residue resembles a carbonised system with most of the absorption badly defined and the appearance of a 750 cm1 peak.
Closed system pyrolysis was carried out at 275, 300 and 350 C, at 15 min of residence time. Longer residence time was also experienced at 275 C when pyrolysis proceeds very slowly. Results reported in Table 4 indicate nearly 50% of the bromine contained in the resin is evolved as HBr at 300 C. As previously noted in flow pyrolysis, here again part of HBr is fixed in the degraded residue as ammonium salt (Fig. 4, 2600 cm1 broad peak). At 275 C for short residence times the structure of the residue resembled that of the original BER, longer residence times enhance degradation. Temperature raises the oil fraction amount. The pyrolysis oil composition reported in Table 5 shows that the majority are phenols coming out of secondary degradation of bisphenols which cannot evaporate out of the closed heated system. In contrast to flow system, here the bromo-containing products account for only 4–7% of the oil, the larger amount being again at lower temperatures. In closed systems the secondary degradation process ‘‘purifies’’ the oil from brominated compound and tends to direct degradation toward single ring phenol and HBr. The concomitant presence of basic amino groups and HBr limits to some extent the evolution of gaseous HBr, which is partially fixed as salt.
Table 2 Pyrolysis fractions composition from flow system HBr# Pyrolysis oila Residue a
300 C · 50 0
325 C · 40 0
375 C · 20 0
1.5 50 48.3
4.5 49 46.6
4.1 55 40.6
Calculated by difference.
3.3. Flow pyrolysis system in the presence of NaOH and basic compounds From Tables 6 and 7 it can be concluded that in a flow system and in the presence of a base the following occurs: The evolution of HBr is strongly limited (0.5–5% of available bromine). The residue contains a large amount of NaBr (50– 100% of the available bromine). The pyrolysis oil contains anilines and other nitrogen containing products (which in the other pyrolysis conditions were blocked as ammonium salts). The pyrolysis oil contains a larger amount of phenols and a low amount of bromine containing substances (7.5–17.5% with NaOH; 33.5–37.5 with Na/Ca system). The residue is not sticky.
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M.P. Luda et al. / Waste Management 25 (2005) 203–208
Fig. 3. From the top to the bottom: IR of original BER and of the residues of pyrolysis in a flow-pyrolysis system at 300 C/50 0 ; 325 C/40 0 ; 375 C/ 40 0 .
3.4. Flow system pyrolysis of HIPS
Table 4 Pyrolysis fractions composition in a closed system
HBr Pyrolysis oil Residuea a
275 C · 15 0
275 C · 45 0
300 C · 15 0
350 C · 15 0
6.7 6.9 86
11.9 33.1 55
11 38.9 50
5.7 53.1 41
Flow pyrolysis has been carried out at 300, 350 and 400 C. The composition of the studied samples is reported in Table 1. Results reported in Table 8 make it evident that a significant amount of Br is evolved only in presence of Sb2O3 (samples HIPS1 and HIPS2). This is reasonable, the Sb2O3 is usually added as a synergistic component to improve the volatilisation of halogenated FR in order to maximize the flame suppression effect in the flame. However, in the case of HIPS2 the amount of volatilised Br is reduced by the presence of CaCO3 that reacts with HBr fixing part of it in the solid residue. In absence of Sb2O3 (sample HIPS0) there is no significant amount of Br in the volatile products. The presence of Br in the volatile product is almost completely suppressed adding NaOH to the samples
Calculated by difference.
All of these effects are really enhanced when NaOH is the selected base. NaOH should be formed by reaction of Na2CO3 and Ca(OH)2; however, this reaction occurs slowly at the selected temperature. Thus, in these types of pyrolysis the effective agents are the weak bases Na2CO3 and Ca(OH)2 which are not really effective either in scavenging HBr or in debromination reactions.
1144
3439 1384
1144 3439
1384
3394 3210
A
1144
2597
2600
1384
2597
753
3394 3210 1144
2600
2597
753 1144 753
3394 3210
4000.0
3000
2000
1500
1000
400.0
cm-1
Fig. 4. From the top to the bottom IR of BER original and of the residues of pyrolysis in a closed reactor at 275 C/15 0 ; 275 C/45 0 ; 300 C/15 0 ; 350 C/15 0 .
M.P. Luda et al. / Waste Management 25 (2005) 203–208
207
Table 5 Pyrolysis oil composition in a closed system
Phenol Alkyl phenols Bisphenol A Brominated phenols Phenylphenol Others
275 C · 15 0
275 C · 45 0
300 C · 15 0
350 C · 15 0
0.0 0.0 100.0 0.0 0.0 0.0
41.4 19.6 23.4 7.3 2.8 5.5
33.1 17.4 33.7 6.7 3.8 5.3
38.5 23.2 25.2 3.6 6.0 3.5
Table 6 Fractions composition from flow pyrolysis in the presence of base a
HBr Pyrolysis oila,b Residue Br in asha a b
300 C + NaOH 50 0
350 C + NaOH 40 0
400 C + NaOH 40 0
350 C + Ca/Na 40 0
400 C + Ca/Na 40 0
0.15 30 69.7 14.0
0.7 35 64.1 19.8
0.9 47 55.8 20.2
0.9 31 68.8 10.7
1 37.5 62.4 14.6
Percentage calculated on pure resin (without base). Calculated by difference.
Table 7 Pyrolysis oil composition from flow system in the presence of base
Aniline N containing substances Phenol Alkyl phenols Bisphenol A Bromo phenols Others, brominated Fenilfenolo
300 C + NaOH 50 0
350 C + NaOH 40 0
400 C +NaOH 0 40 0
350 C + Ca/Na 40 0
400 C + Ca/Na 40 0
3.9 3.0 50.8 15.4 6.9 10.4 6.9 0.8
6.4 8.4 34.7 16.7 13.1 3.7 7.3 0.8
12.0 8.3 35.2 24.5 5.4 3.3 4.2 0.6
0.3 2.4 25.5 10.9 19.8 13.8 19.7 4.8
0.3 3.7 15.5 5.1 30.9 4.6 33.0 2.9
Table 8 Fractions composition from pyrolysis of HIPS in flow system HIPS0
HBr Pyrolysis oila Residue a
HIPS1
HIPS2
300 C
350 C
400 C
300 C
350 C
400 C
300 C
350 C
400 C
<0.005 3.3 84.8
<0.005 5.5 72.8
<0.005 29.9 9.8
0.01 5.3 81.1
0.35 20.2 44.5
0.65 40.9 9.1
<0.005 4.2 85.5
0.14 16.3 60.9
0.20 27.3 27.9
Calculated by difference.
HIPS0 and HIPS1 (Table 9) demonstrating to be most effective respect CaCO3. The amount of organic brominated compounds contained in the volatile product, the residue and the pyrolysis oil were detected in a GC/MS, while inorganic Br (HBr) was detected as described above for BER samples. The results are reported in Figs. 5 (HIPS0) and 6 (HIPS1 and HIPS2) as weight percent of Br respect to the total amount of detected bromine. Fig. 5 shows that the effect of NaOH is the reduction of organic Br in the residue fixing it as inorganic Br. Presence of CaCO3 is not effective in diminishing organic Br of the solid residue (HIPS2, Fig. 6). This effect is reached only by add-
ing a strong base, such as NaOH. Observing Figs. 5 and 6 it is possible to note the absence of a strong relationship between temperature and Br distribution in the pyrolysis product. In such a case, however, the evolution in pyrolysis of bromine containing product is relevant and it is scarcely reduced by using basic scavengers. This is possibly due to the different structure of the brominated compounds. Additives brominated fire retardant are able to evaporate before debromination occurs. Reactive brominated fire retardants are retained in the hot zone for a long enough time to cause debromination. Even a strong base shows a mild effect with brominated substitutes of high volatility.
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M.P. Luda et al. / Waste Management 25 (2005) 203–208
Table 9 Fractions composition from pyrolysis of HIPS in flow system HIPS0 + 8.2% of NaOH
HBr Pyrolysis oila Residue a
HIPS1 + 7.6% of NaOH
300 C
350 C
400 C
300 C
350 C
400 C
<0.005 3.4 85.6
<0.005 6.7 76.4
0.01 18.7 18.8
<0.005 3.7 83.8
<0.005 2.6 74.1
33.5 16.4
Calculated by difference.
100
80 60
% 40 20 0
HIPS0 300˚C HIPS0 350˚C HIPS0 400˚C HIPS0 300˚C + 8,2% NaOH HIPS0 350˚C + 8,2% NaOH HIPS0 400˚C + 8,2% NaOH
Residue (organic Br) Residue (inorganic Br) Pyrolysis oil Volatiles
Fig. 5. Relative amount of Br in the pyrolysis products of HIPS0 at different temperatures, in absence and in presence of NaOH.
Acknowledgement
100 90 80 70 60 % 50 40 30 20 10 0
300˚C HIPS1 350˚C HIPS1 400˚C HIPS1 300˚C HIPS2 350˚C HIPS2 400˚C HIPS2 300˚C HIPS1 + 7,6% NaOH 350˚C HIPS1 + 7,6% NaOH 400˚C HIPS1 + 7,6% NaOH
ing of the residue; the not sticky residue is more suitable for metal recuperation; the oil contains a lower amount of brominated substances which represent a risk when it is intended for fuel usage. In the meantime the oil composition is directed toward phenols production. The low temperature range experienced allows a reduction of pyrolysis costs. However, flow pyrolysis needs relatively long times of residence in the reactor. On the contrary, closed system pyrolysis reaches similar results in shorter residence time. The control of secondary degradation reaction should very much depend on reactant contact and therefore on the scale-up of the reactor, which is difficult to handle. Additional problems could come from the development of elevated pressure inside the reactor. While epoxy resins are the main polymeric component of the circuit boards, the housings of WEEE are often made of styrenic polymer often fire retardant with additive FR on which base treatment is less effective.
This work has been founded by the European Community through the Growth Project G1RD-CT200203014.
References Residue (organic Br) Residue (inorganic Br) Pyrolysis oil Volatiles
Fig. 6. Relative amount of Br in the pyrolysis products of HIPS1 and HIPS2 at different temperatures, in absence and in presence of NaOH (only HIPS1).
4. Conclusions In the pyrolysis recycling strategy of WEEE, the gas fraction should be suitable for HBr recovery, the oil for chemicals recuperation or fuel production, the residue for precious metal recovery. As far as epoxy resin is concerned, nearly all of these goals are matched by alkali treatment: bromine can be recuperated by wash-
Blazso´, M., Cze´ge´ny, Zs., Csoma, Cs., 2002. J. Anal. Appl. Pyrolysis 64, 249–261. Bockhorn, H., Hornung, A., Hornung, U., 1998a. J. Anal. Appl. Pyrolysis 46, 1. Bockhorn, H., Hornung, A., Hornung, U., Jakobstro¨er, P., 1998b. Combust. Sci. Technol. 134, 7. Bockhorn, H., Hornung, A., Hornung, U., 1999a. J. Anal. Appl. Pyrolysis 50, 77. Bockhorn, H., Hornung, A., Hornung, U., Jakobstro¨er, P., Kraus, M., 1999b. J. Anal. Appl. Pyrolysis 49, 97. Buekens, A.G., 1991. In: Proc. UNIDO Conference, Copenhagen, US/ CPR/86/130. Buser, H., 1986. Environ. Sci. Technol. 20 (4), 404. Luda, M.P., Balabanovich, A.I., Camino, G., 2002a. J. Anal. Appl. Pyrolysis 65 (1), 25–40. Luda, M.P., Balabanovich, A.I., Camino, G., Hornung, A., 2002b. Macromol. Symp. 180, 141–151. Sun, R.D., Irie, H., Nishikwa, T., Nakajima, A., Watanabe, T., Hishamoto, K., 2003. Polym. Degrad. Stabil. 79, 253–256.
WEEE recycling: Pyrolysis of fire retardant model polymers M.P. Luda *, N. Euringer, U. Moratti, M. Zanetti Dipartimento di Chimica, IFM dellÕUniversita` Via P. Giuria 7, 10125 Torino, Italy Accepted 17 December 2004
Abstract Pyrolysis treatments of model polymers were made with the aim of studying the recycling of wastes from electronic, electric equipment containing brominated flame retardants. Pyrolysis of flame retarded high impact polystyrene and epoxy resins were made both in flow and closed systems. Products of pyrolysis were analysed with FT–IR spectroscopy and GC–MS and the evolution of bromine was followed with a bromine ion specific electrode. The effect of alkali on pyrolysis was also studied demonstrating, as far epoxy resin is concerned, to be effective on decreasing bromine content in oil and volatile products leading to the recovery of bromine from the residue by washing. The alkali treatment was shown to be less effective in styrenic polymers containing brominated flame retardants. 2005 Elsevier Ltd. All rights reserved.
1. Introduction Polymer wastes from electronic, electric equipment (WEEE) include mainly epoxy resins and styrene polymers. They often contain brominated aromatics; in the early 1980s indeed halogenated fire retardants were largely applied to decrease the flammability of polymeric materials. Reactive fire retardants (FRs) such as diglycidylether of (3,3 0 ,5,5 0 -tetrabromobisphenol) A (DGEBTBA) is often used as comonomer with diglycilylether of bisphenol A (DGEBA) to obtain FR epoxy resins; additive FRs such as polybromo diphenyl oxides are used for styrene polymers instead. Thermal treatment of WEEE is one of the most attractive approaches to recycling which enables the recovery of bromine, monomers and other chemicals and of precious metals which account for the economic convenience of the whole recycling process. However, one of the most relevant drawbacks in dealing with thermal treatment of WEEE is the likely production of *
Corresponding author. E-mail address: [email protected] (M.P. Luda).
0956-053X/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.wasman.2004.12.010
super-toxic halogenated dibenzodioxins and dibenzofurans from the bromine containing structures. Environmentally friendly fire retardant systems currently developed to substitute halogen based systems will decrease the content of halogen in forthcoming WEEE, however actual WEEE and those collected in the near future still contain relatively large amounts of brominated FR (Buekens, 1991; Buser, 1986). In effect, amongst the various technologies of polymer recycling, WEEE are not suitable for foundry operation in the blast furnace due to the amount of halogens, metals and inert materials. On the contrary, WEEE can be thermally treated in the cement industries as a substitute for conventional fuel. Here, because of the alkaline conditions in the cement making process, the exhaust gases will contain only a minimum of pollutants. It has been recently shown that CaCO3 has a suppressive effect in the dioxins emission from PVC incineration (Sun et al., 2003). In this context preliminary experimental results show that electronic scrap can be processed into halogens containing fractions fuels with an amount of about 500 ppm halogens and residues with or nearly without halogens, depending
204
M.P. Luda et al. / Waste Management 25 (2005) 203–208
on process parameters (Bockhorn et al., 1998a,b, 1999a,b). Thus, environmental consideration makes the alkali approach promising in pyrolytic recycling of halogen containing polymers. However, basic conditions affect the whole degradation pathway which must be known to optimise the recycling process. Many studies on the mechanism of thermal degradation of such systems have been carried out (Luda et al., 2002a,b; Blazso´ et al., 2002). Because of the complexity of real WEEE mixtures, studies on model compounds are presently of paramount importance to individuate and control the thermal behaviour of the single WEEE components.
O
Fig. 2. Octabromodiphenylether (OBDPE) formula, where x + y = 8.
2215) was added to all blends. The composition of each sample is reported in Table 1. 2.2. Pyrolysis experiments Flow system pyrolysis was carried out on a tubular horizontal oven at a selected temperature on 50 mg of powdered sample. Light fraction was trapped in a cool trap in series to the pyrolytic chamber. Closed system pyrolysis was performed on a 50-mg sample in a reactor sealed under nitrogen flow and placed in the oven at the selected temperature. Premixing of the basic compounds (17% NaOH or 38% Na2CO3/Ca(OH)2 (Ca/Na) in equimolar amount) was performed in a mortar before the sample underwent the pyrolysis. IR spectra were run on a Perkin–Elmer 2000 FTIR. Samples were analysed as a KBr pellet. The GC–MS measurements were performed with a 6890N gas chromatograph (Agilent) equipped with a capillary HP5MS column and an Agilent 5973 mass spectrometer detector. Quantitative evaluation took the area percentage of the Total Ion Chromatogram into account. A Phoenix Bromide Ion Combination Epoxy Electrode placed in a 1% Na2CO3 solution and connected to an AMEL model 337 potentiometer was employed to determine Bromide. In flow system pyrolysis continuous measurements were performed by connecting the electrode system in series to the pyrolytic chamber. Standard solutions of NaBr were used for calibration of the electrode response.
2. Experimental 2.1. Materials The model brominated epoxy resin (BER) was synthesised from Commercial DGEBA (Epicote 828EL, Shell Chemie) and DGEBTBA (Shell Chemie). The mixture DGEBA/DGEBTBA was cured with 85% of stoichiometric amount of diphenyl diaminosulphone (DDS, HT 976, Ciba Geigy) under air in an oven heated for 1 h at 160 C and for 1 h at 180 C. BER contained 20% bromine. Because of the deficient stoichiometry, mainly tertiary amine groups are present in the final network (Fig. 1). The model high impact polystyrene (HIPS) was HIP STYRON 485-71 (ALBEMARLE s.a.). Three samples with different amounts of octabromodiphenylether (OBDPE, Fig. 2), antimony trioxide (Sb2O3) and calcium carbonate (CaCO3) were prepared by melt blending in an internal mixer working at 190 C for 15 min. In order to prevent oxidation phenomena a 0.1% of a commercial grade antioxidant (CIBA Irganox HP
Br H2C
HC
Br CH3
OH
OH
C
H2C O Br
Br y
Br x
CH3
O CH2
CH CH2 N
Br
O S
H2C
HC
N CH2
CH3
OH H2C O
C CH3
O
O CH2
CH CH2 OH
Fig. 1. Schematic representation of the BER network.
CH CH2 OH
O
M.P. Luda et al. / Waste Management 25 (2005) 203–208 Table 1 Composition of HIPS samples
HIPS OBDPE Sb2O3 CaCo3
205
Table 3 Pyrolysis oil composition from flow system
HIPS0 (%)
HIPS1 (%)
HIPS2 (%)
90 10 // //
85 10 5 //
72.25 8.5 4.25 15.0
Phenol Alkyl phenols Bisphenol A Bromo phenols Polybromo bisphenol A Phenylphenol
300 C · 50 0
325 C · 40 0
375 C · 40 0
3.9 2.2 17.0 3.1 67.0 1.9
4.8 5.9 19.5 2.2 59.2 3.0
21.1 6.9 13.8 4.5 42.8 6.7
3. Results and discussion 3.1. Flow system pyrolysis of BER
3.2. Closed system pyrolysis
In all cases three fractions came out of the pyrolysis treatments: (1) gaseous products, mainly HBr; (2) pyrolysis oil; (3) residue. Flow pyrolysis was carried out at 300, 325 and 375 C and the residence time was determined by reaching a constant HBr concentration, determined by the in series Bromide EIS. Results reported in Table 1 make it evident that a small fraction of HBr is evolved which corresponds to 20% of the maximum allowable for these systems. At 300 C decomposition is quite slow and it is possible that HBr evolution is not finalised yet. The majority of the sample is converted to pyrolysis oil and residue in similar amounts. Temperature increase tends to raise the oil fraction amount (see Table 2). The pyrolysis oil, as reported in Table 3, contains mainly phenols and polyphenols, some of which are brominated. The presence of phenols indicates that the first breakable bond in the network is the epoxy link. Polyphenols are the most relevant species because as soon as they are formed they evaporate. However, decomposition of polyphenols to single ring phenols occurs by increasing the temperature. Phenyl phenol is a typical secondary decomposition product whose amount follows that of phenols. The bromo-containing products account for 48–70% of the oil, the larger amount being at lower temperatures. IR of the residues (Fig. 3) shows that they substantially maintain their original structure up to 325 C, in particular the sulphone group (1144 cm1) and the geminal CH3 (1384 cm1) are preserved; in addition ammonium salts are put in evidence by the broad bands at 2600 cm1; they may be formed by reaction of HBr and amino groups formed in the degradation. At 375 C the residue resembles a carbonised system with most of the absorption badly defined and the appearance of a 750 cm1 peak.
Closed system pyrolysis was carried out at 275, 300 and 350 C, at 15 min of residence time. Longer residence time was also experienced at 275 C when pyrolysis proceeds very slowly. Results reported in Table 4 indicate nearly 50% of the bromine contained in the resin is evolved as HBr at 300 C. As previously noted in flow pyrolysis, here again part of HBr is fixed in the degraded residue as ammonium salt (Fig. 4, 2600 cm1 broad peak). At 275 C for short residence times the structure of the residue resembled that of the original BER, longer residence times enhance degradation. Temperature raises the oil fraction amount. The pyrolysis oil composition reported in Table 5 shows that the majority are phenols coming out of secondary degradation of bisphenols which cannot evaporate out of the closed heated system. In contrast to flow system, here the bromo-containing products account for only 4–7% of the oil, the larger amount being again at lower temperatures. In closed systems the secondary degradation process ‘‘purifies’’ the oil from brominated compound and tends to direct degradation toward single ring phenol and HBr. The concomitant presence of basic amino groups and HBr limits to some extent the evolution of gaseous HBr, which is partially fixed as salt.
Table 2 Pyrolysis fractions composition from flow system HBr# Pyrolysis oila Residue a
300 C · 50 0
325 C · 40 0
375 C · 20 0
1.5 50 48.3
4.5 49 46.6
4.1 55 40.6
Calculated by difference.
3.3. Flow pyrolysis system in the presence of NaOH and basic compounds From Tables 6 and 7 it can be concluded that in a flow system and in the presence of a base the following occurs: The evolution of HBr is strongly limited (0.5–5% of available bromine). The residue contains a large amount of NaBr (50– 100% of the available bromine). The pyrolysis oil contains anilines and other nitrogen containing products (which in the other pyrolysis conditions were blocked as ammonium salts). The pyrolysis oil contains a larger amount of phenols and a low amount of bromine containing substances (7.5–17.5% with NaOH; 33.5–37.5 with Na/Ca system). The residue is not sticky.
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M.P. Luda et al. / Waste Management 25 (2005) 203–208
Fig. 3. From the top to the bottom: IR of original BER and of the residues of pyrolysis in a flow-pyrolysis system at 300 C/50 0 ; 325 C/40 0 ; 375 C/ 40 0 .
3.4. Flow system pyrolysis of HIPS
Table 4 Pyrolysis fractions composition in a closed system
HBr Pyrolysis oil Residuea a
275 C · 15 0
275 C · 45 0
300 C · 15 0
350 C · 15 0
6.7 6.9 86
11.9 33.1 55
11 38.9 50
5.7 53.1 41
Flow pyrolysis has been carried out at 300, 350 and 400 C. The composition of the studied samples is reported in Table 1. Results reported in Table 8 make it evident that a significant amount of Br is evolved only in presence of Sb2O3 (samples HIPS1 and HIPS2). This is reasonable, the Sb2O3 is usually added as a synergistic component to improve the volatilisation of halogenated FR in order to maximize the flame suppression effect in the flame. However, in the case of HIPS2 the amount of volatilised Br is reduced by the presence of CaCO3 that reacts with HBr fixing part of it in the solid residue. In absence of Sb2O3 (sample HIPS0) there is no significant amount of Br in the volatile products. The presence of Br in the volatile product is almost completely suppressed adding NaOH to the samples
Calculated by difference.
All of these effects are really enhanced when NaOH is the selected base. NaOH should be formed by reaction of Na2CO3 and Ca(OH)2; however, this reaction occurs slowly at the selected temperature. Thus, in these types of pyrolysis the effective agents are the weak bases Na2CO3 and Ca(OH)2 which are not really effective either in scavenging HBr or in debromination reactions.
1144
3439 1384
1144 3439
1384
3394 3210
A
1144
2597
2600
1384
2597
753
3394 3210 1144
2600
2597
753 1144 753
3394 3210
4000.0
3000
2000
1500
1000
400.0
cm-1
Fig. 4. From the top to the bottom IR of BER original and of the residues of pyrolysis in a closed reactor at 275 C/15 0 ; 275 C/45 0 ; 300 C/15 0 ; 350 C/15 0 .
M.P. Luda et al. / Waste Management 25 (2005) 203–208
207
Table 5 Pyrolysis oil composition in a closed system
Phenol Alkyl phenols Bisphenol A Brominated phenols Phenylphenol Others
275 C · 15 0
275 C · 45 0
300 C · 15 0
350 C · 15 0
0.0 0.0 100.0 0.0 0.0 0.0
41.4 19.6 23.4 7.3 2.8 5.5
33.1 17.4 33.7 6.7 3.8 5.3
38.5 23.2 25.2 3.6 6.0 3.5
Table 6 Fractions composition from flow pyrolysis in the presence of base a
HBr Pyrolysis oila,b Residue Br in asha a b
300 C + NaOH 50 0
350 C + NaOH 40 0
400 C + NaOH 40 0
350 C + Ca/Na 40 0
400 C + Ca/Na 40 0
0.15 30 69.7 14.0
0.7 35 64.1 19.8
0.9 47 55.8 20.2
0.9 31 68.8 10.7
1 37.5 62.4 14.6
Percentage calculated on pure resin (without base). Calculated by difference.
Table 7 Pyrolysis oil composition from flow system in the presence of base
Aniline N containing substances Phenol Alkyl phenols Bisphenol A Bromo phenols Others, brominated Fenilfenolo
300 C + NaOH 50 0
350 C + NaOH 40 0
400 C +NaOH 0 40 0
350 C + Ca/Na 40 0
400 C + Ca/Na 40 0
3.9 3.0 50.8 15.4 6.9 10.4 6.9 0.8
6.4 8.4 34.7 16.7 13.1 3.7 7.3 0.8
12.0 8.3 35.2 24.5 5.4 3.3 4.2 0.6
0.3 2.4 25.5 10.9 19.8 13.8 19.7 4.8
0.3 3.7 15.5 5.1 30.9 4.6 33.0 2.9
Table 8 Fractions composition from pyrolysis of HIPS in flow system HIPS0
HBr Pyrolysis oila Residue a
HIPS1
HIPS2
300 C
350 C
400 C
300 C
350 C
400 C
300 C
350 C
400 C
<0.005 3.3 84.8
<0.005 5.5 72.8
<0.005 29.9 9.8
0.01 5.3 81.1
0.35 20.2 44.5
0.65 40.9 9.1
<0.005 4.2 85.5
0.14 16.3 60.9
0.20 27.3 27.9
Calculated by difference.
HIPS0 and HIPS1 (Table 9) demonstrating to be most effective respect CaCO3. The amount of organic brominated compounds contained in the volatile product, the residue and the pyrolysis oil were detected in a GC/MS, while inorganic Br (HBr) was detected as described above for BER samples. The results are reported in Figs. 5 (HIPS0) and 6 (HIPS1 and HIPS2) as weight percent of Br respect to the total amount of detected bromine. Fig. 5 shows that the effect of NaOH is the reduction of organic Br in the residue fixing it as inorganic Br. Presence of CaCO3 is not effective in diminishing organic Br of the solid residue (HIPS2, Fig. 6). This effect is reached only by add-
ing a strong base, such as NaOH. Observing Figs. 5 and 6 it is possible to note the absence of a strong relationship between temperature and Br distribution in the pyrolysis product. In such a case, however, the evolution in pyrolysis of bromine containing product is relevant and it is scarcely reduced by using basic scavengers. This is possibly due to the different structure of the brominated compounds. Additives brominated fire retardant are able to evaporate before debromination occurs. Reactive brominated fire retardants are retained in the hot zone for a long enough time to cause debromination. Even a strong base shows a mild effect with brominated substitutes of high volatility.
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M.P. Luda et al. / Waste Management 25 (2005) 203–208
Table 9 Fractions composition from pyrolysis of HIPS in flow system HIPS0 + 8.2% of NaOH
HBr Pyrolysis oila Residue a
HIPS1 + 7.6% of NaOH
300 C
350 C
400 C
300 C
350 C
400 C
<0.005 3.4 85.6
<0.005 6.7 76.4
0.01 18.7 18.8
<0.005 3.7 83.8
<0.005 2.6 74.1
33.5 16.4
Calculated by difference.
100
80 60
% 40 20 0
HIPS0 300˚C HIPS0 350˚C HIPS0 400˚C HIPS0 300˚C + 8,2% NaOH HIPS0 350˚C + 8,2% NaOH HIPS0 400˚C + 8,2% NaOH
Residue (organic Br) Residue (inorganic Br) Pyrolysis oil Volatiles
Fig. 5. Relative amount of Br in the pyrolysis products of HIPS0 at different temperatures, in absence and in presence of NaOH.
Acknowledgement
100 90 80 70 60 % 50 40 30 20 10 0
300˚C HIPS1 350˚C HIPS1 400˚C HIPS1 300˚C HIPS2 350˚C HIPS2 400˚C HIPS2 300˚C HIPS1 + 7,6% NaOH 350˚C HIPS1 + 7,6% NaOH 400˚C HIPS1 + 7,6% NaOH
ing of the residue; the not sticky residue is more suitable for metal recuperation; the oil contains a lower amount of brominated substances which represent a risk when it is intended for fuel usage. In the meantime the oil composition is directed toward phenols production. The low temperature range experienced allows a reduction of pyrolysis costs. However, flow pyrolysis needs relatively long times of residence in the reactor. On the contrary, closed system pyrolysis reaches similar results in shorter residence time. The control of secondary degradation reaction should very much depend on reactant contact and therefore on the scale-up of the reactor, which is difficult to handle. Additional problems could come from the development of elevated pressure inside the reactor. While epoxy resins are the main polymeric component of the circuit boards, the housings of WEEE are often made of styrenic polymer often fire retardant with additive FR on which base treatment is less effective.
This work has been founded by the European Community through the Growth Project G1RD-CT200203014.
References Residue (organic Br) Residue (inorganic Br) Pyrolysis oil Volatiles
Fig. 6. Relative amount of Br in the pyrolysis products of HIPS1 and HIPS2 at different temperatures, in absence and in presence of NaOH (only HIPS1).
4. Conclusions In the pyrolysis recycling strategy of WEEE, the gas fraction should be suitable for HBr recovery, the oil for chemicals recuperation or fuel production, the residue for precious metal recovery. As far as epoxy resin is concerned, nearly all of these goals are matched by alkali treatment: bromine can be recuperated by wash-
Blazso´, M., Cze´ge´ny, Zs., Csoma, Cs., 2002. J. Anal. Appl. Pyrolysis 64, 249–261. Bockhorn, H., Hornung, A., Hornung, U., 1998a. J. Anal. Appl. Pyrolysis 46, 1. Bockhorn, H., Hornung, A., Hornung, U., Jakobstro¨er, P., 1998b. Combust. Sci. Technol. 134, 7. Bockhorn, H., Hornung, A., Hornung, U., 1999a. J. Anal. Appl. Pyrolysis 50, 77. Bockhorn, H., Hornung, A., Hornung, U., Jakobstro¨er, P., Kraus, M., 1999b. J. Anal. Appl. Pyrolysis 49, 97. Buekens, A.G., 1991. In: Proc. UNIDO Conference, Copenhagen, US/ CPR/86/130. Buser, H., 1986. Environ. Sci. Technol. 20 (4), 404. Luda, M.P., Balabanovich, A.I., Camino, G., 2002a. J. Anal. Appl. Pyrolysis 65 (1), 25–40. Luda, M.P., Balabanovich, A.I., Camino, G., Hornung, A., 2002b. Macromol. Symp. 180, 141–151. Sun, R.D., Irie, H., Nishikwa, T., Nakajima, A., Watanabe, T., Hishamoto, K., 2003. Polym. Degrad. Stabil. 79, 253–256.
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