Pyrolysis Study of Halogen-Containing Aromatics Reflecting

A treatment of halogen-containing aromatics with PP offers a new perspective on the development of low-environmental-impact disposal processes for ele...
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Environ. Sci. Technol. 2005, 39, 5469-5474

Pyrolysis Study of Halogen-Containing Aromatics Reflecting Reactions with Polypropylene in a Posttreatment Decontamination Process A L I A K S A N D R I . B A L A B A N O V I C H , * ,†,‡,§ ANDREAS HORNUNG,‡ MARIA P. LUDA,§ WOLFGANG KOCH,‡ AND VANDER TUMIATTI| Research Institute for Physical Chemical Problems of the Belarusian State University, ul. Leningradskaya 14, 220050 Minsk, Belarus, ITC-TAB, Forschungszentrum Karlsruhe GmbH, Hermann-von-Helmholz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany, Dipartimento di Chimica IFM, Universita` di Torino, Via P. Giuria 7, 10125 Torino, Italy, and Sea Marconi Technologies Sas, Via Crimea 4, 10097 Collegno, Italy

Halogen-containing aromatics, mainly bromine-containing phenols, are harmful compounds contaminating pyrolysis oil from electronic boards containing halogenated flame retardants. In addition, their formation increases the potential for evolution of polybrominated dibenzo-p-dioxins (PBDDs) and dibenzofurans (PBDFs) at relatively low temperature (up to 500 °C). As a model compound, 2,4-dibromophenol (DBP) was pyrolyzed at 290-450 °C. While its pyrolysis in a nitrogen flow reactor or in encapsulated ampules yields bromine-containing phenols, phenoxyphenols, PBDDs, and PBDFs, pyrolysis of DBP in a hydrogen-donating medium of polypropylene (PP) at 290-350 °C mainly results in the formation of phenol and HBr, indicating the occurrence of a facile hydrodebromination of DBP. The hydrodebromination efficiency depends on temperature, pressure, and the ratio of the initial components. This thermal behavior of DBP is compared to that of 2,4-dichlorophenol and decabromodiphenyl ether. A treatment of halogen-containing aromatics with PP offers a new perspective on the development of low-environmental-impact disposal processes for electronic scrap.

Introduction In the past few decades, growing attention has been gained by polymer waste recycling. In the Forschungszentrum Karlsruhe a new process called Haloclean has been established (1), aimed at a pyrolytic recycling at relatively low temperature (up to 500 °C) of waste from electrical and electronic equipment to obtain purified noble metal residues and pyrolysis oil. However, the pyrolysis oil is contaminated by brominated phenols (up to 12 wt % bromine); one of the * Corresponding author phone: +375-172-224509; fax: +375-172-264696; e-mail: [email protected]. † Research Institute for Physical Chemical Problems of the Belarusian State University. ‡ Forschungszentrum Karlsruhe GmbH. § Universita ` di Torino. | Sea Marconi Technologies Sas. 10.1021/es0500106 CCC: $30.25 Published on Web 06/11/2005

 2005 American Chemical Society

major products is 2,4-dibromophenol (DBP), which comes from the use of brominated fire retardants based on tetrabromobisphenol A (TBBPA) and 2,4,6-tribromophenol. This was supported by relevant experiments carried out with brominated epoxy resins (2, 3), and pure TBBPA as well (4). In addition, brominated phenols contained in the pyrolysis oil can be a source for polybrominated dibenzo-p-dioxins (PBDDs) and dibenzofurans (PBDFs). Therefore, a need came up to investigate the thermal behavior of brominated phenols at 250-450 °C, and DBP was selected as a model compound. If decontamination is necessary for further use of the pyrolysis oil as a “clean” fuel, promising hydrodehalogenation involves use of hydrogen-atom-donating compounds such as tetralin (5), conventional petroleum solvent (6), eicosane (7), and 9,10-dihydroanthracene (8). Polyolefins as well have been tested as hydrogen donors (9), offering the attractive possibility of simultaneously recycling electronic and packaging wastes with reciprocal advantages. However, the level of knowledge of the chemical reactions taking place has to be improved, with the aim of further increasing the hydrodehalogenation effectiveness. To our knowledge, there are few data in the literature concerning thermal degradation of DBP. From the Sakurai investigation (10) on a 300 °C pyrolysis of a mixture of 2,4-dichlorophenol (DCP) and of DBP, an enhanced reactivity of the bromo compounds results, leading to the formation of PXDDs and mixed halogenated phenoxyphenols and phenols; no PXDFs were detected at this temperature. There are also publications on pyrolysis of other brominated phenols, mainly on high-temperature pyrolysis (11-14).

Experimental Section Model compounds DBP, DCP, and decabromodiphenyl ether (DBDPE) were purchased from Fluka and used as received. Polypropylene (PP; BASELL) was used as a reductive medium. To assess the “true” thermal stability of DBP or DCP, an experimental setup (Figure 1) was designed to increase the residence time without affecting the reactor pressure. Flow pyrolyses were carried out in a helical glass reactor, 33 cm3 in volume and 1.0 cm in diameter, equipped with a glass tube in the inlet side and a water condenser in the outlet side. The glass tube was charged with the sample (40 mg), and the whole system was purged with nitrogen for 1520 min. Then the reactor was placed in an oven preheated at the desired temperature (350-450 °C), and simultaneously, the glass tube was heated to 70 °C to melt the sample. Reactant vapor was transported to the isothermal reactor by a nitrogen stream of 1.83 or 2.75 cm3/min, in which the total residence time was 12 or 18 min. Experiments were run for approximately 2.5 or 2 h, with pyrolysis products trapped in the condenser. They were dissolved in acetone for further GC/MS analysis. Insoluble products were analyzed by FTIR (Perkin-Elmer 2000). Closed ampule pyrolyses with the model compounds or their mixtures with PP were carried out in encapsulated glass tubes of 1.70 ( 0.01 cm3 volume under an inert atmosphere at isothermal temperatures of 290-400 °C as has been described elsewhere (9). Both the gaseous pyrolysis products and pyrolysis oil were analyzed using a GC/MS HP 6890/ 5972A equipped with an HP-5 30 m column (outside diameter 0.25 mm, phase thickness 0.25 µm). For analysis of the oil the column was temperature programmed from 40 °C (2 min) to 300 °C at a heating rate of 10 °C/min, whereas for analysis of the gases the heating program -10 °C (2 min), 10 °C/min to 250 °C was used. The mass spectra were obtained by electron ionization at 70 eV, keeping the source at 180 °C. VOL. 39, NO. 14, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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SCHEME 1

FIGURE 1. Experimental apparatus: 1, reactor; 2, glass tube containing the sample; 3, water condenser; 4, oven; 5, microoven operating at 70 °C.

FIGURE 2. Total ion gas chromatograms of (a) untreated DBP, (b-d) DBP heated in a nitrogen flow for 18 min at 350 °C (b), 400 °C (c), and 450 °C (d), (e) untreated DCP, and (f-h) DCP heated in a nitrogen flow for 12 min at 450 °C (f), 500 °C (g), and 550 °C (h): 1, 4-bromophenol; 2, 2,4-dibromophenol; 3, 2,6-dibromophenol; 4, tribromobenzene; 5, 2,4,6-tribromophenol; 6, dibromodibenzofuran; 7, dibromodibenzo-p-dioxin; 8, tribromodibenzofuran; 9, tribromodibenzo-p-dioxin; 10, 2-bromo-4-(2,4-dibromophenoxy)phenol; 11, o-chlorophenol + traces of dichlorobenzene; 12, 2-chloro-2, 5-cyclohexadiene-1,4-dione; 13, 2,4-dichlorophenol; 14, 2,6-dichlorophenol; 15, p-chlorophenol; 16, 17, dichlorodibenzofurans; 18, dichlorodibenzo-p-dioxin; 19, trichlorodibenzofuran; 20, trichlorodibenzo-p-dioxin; 21, tetrachlorodibenzofuran. Technological application of hydrodebromination reaction was assessed within a stirred tank reactor containing 2 L of molten PP and variable amounts of pyrolysis oil purged through continuously. The laboratory scale testing unit of the reactor is depicted in the Supporting Information. The pyrolysis products were identified by their retention time and mass spectra on the basis of both the highest m/z value and the ion decomposition pattern. The typical mass spectra of most important pyrolysis products, namely, dibromodibenzo-p-dioxin, 2-bromo-4-(2,4-dibromophenoxy)phenol, and tribromodibenzofuran, are presented in the Supporting Information. Concerning the structure of 2-bromo-4-(2,4-dibromophenoxy)phenol, its mass spectrum clearly excludes an assignment to 4-bromo-2-(2,4-dibromophenoxy)phenol in which the position of the OH group gives rise to the special fragmentation due to the loss of HBr (15).

Results and Discussion Flow Reactor. When DBP was pyrolyzed at 350 °C (reaction time 18 min), 4-bromophenol, 2,6-dibromophenol, and dibromodibenzo-p-dioxin were formed along with a small amount of 2-bromo-4-(2,4-dibromophenoxy)phenol (Figure 2a). At 400 °C, their yield was higher and 2,4,6-tribromophenol appeared. At 450 °C, 2-bromo-4-(2,4-dibromophenoxy)phenol was not found. Instead of it, tribromobenzene, dibromodibenzofurans, tribromodibenzofuran, and tri5470

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bromodibenzo-p-dioxin were identified (Figure 2c). Pyrolysis of DBP at 450 °C also yielded a thin layer of carbonaceous deposit through the reactor and white crystals (for the IR spectrum see the Supporting Information) of dibromodibenzo-p-dioxin as further supported by the GC/MS data. At 350 °C, the dioxin was detectable after 90 s of pyrolysis, and its amount increased with increasing residence time. With respect to the formation of 2-bromo-4-(2,4-dibromophenoxy)phenol and of dibromodibenzo-p-dioxin, DBP is likely to behave as 2,4,6-tribromophenol (16) and o-chlorophenols (17). o- or p-bromophenols are thermally less stable than corresponding bromobenzenes, in relation to the formation of an unstable cyclohexadienone structure due to tautomerization of the parent phenols (8, 18, 19) (Scheme 1). Upon heating, the structure generates bromine and phenoxyl radicals due to scission of the allylic C-Br bond, which is to a marked degree lower in energy than the aromatic C-Br bond. This reaction acts as an initiation reaction. Propagation occurs through abstraction of protons by radical I or bromine atom from both the phenol and its tautomeric forms, yielding the corresponding phenoxyl radical II and carbon-centered radicals IIa, IIb, and IIc. In the case of chlorinated phenols it has been calculated that the allylic C-H bond in the tautomers is 3.3 kcal mol-1 weaker where H is carried by the carbon atom also carrying the halogen substituent (10). Thus, it seems reasonable to expect IIb to be formed at higher temperature than IIa or IIc. Halogen-containing phenoxyl radicals are precursors for the polyhalogenated dibenzo-p-dioxins, the formation of which can be understood (20) by dibromophenoxyl radicalradical combination (II-IIa). This reaction results in oxygencarbon coupling that yields the keto tautomer of an o-phenoxyphenol (Scheme 2, path A). The radical-radical recombination reaction dominates over radical-molecule reactions (21) (i.e., over reaction of II + DBP). Actually, coupling of II and IIc yields 2-bromo-4-(2, 4-dibromophenoxy)phenol. Progressive condensation with bromine-containing phenoxyl radicals contributes to the formation of a carbonaceous deposit in the reactor. This would explain the disappearance of p-phenoxyphenol intermediate in the 450 °C pyrolysis. Recombination of carbon-centered phenoxyl radicals (i.e., IIa-IIb or IIa-Ia) is essentially accepted as the pathway for

SCHEME 2

FIGURE 3. Total ion gas chromatograms of the pyrolysis oil of DBP + PP ) 76 + 14 (mg) from 330 °C for 20 min (a), DBP + PP ) 77 + 15 (mg) from 310 °C for 20 min (b), DBP + PP ) 75 + 13 (mg) from 290 °C for 20 min (c), DBP + PP ) 136 + 25 (mg) from 290 °C for 20 min (d), and DBP (78 mg) from 330 °C for 20 min (e): 1, phenol; 2, 2-methylphenol; 3, 2-bromophenol; 4, 4-methylphenol; 5, 4-bromophenol; 6, 2,4-dibromophenol; 7, 2,4,6-tribromophenol; 8, dibromophenoxyphenol; 9, dibromodibenzo-p-dioxin; 10, tribromophenoxylphenols; 11, dibromodibenzo-p-dioxin; 12, 13, tetrabromophenoxyphenols.

the formation of halogen-containing dibenzofurans (11, 17, 20). However, coupling of two IIb radicals would lead to tetrabromodibenzofuran (Scheme 2, reaction B), which has not been observed among the pyrolysis products. Similarly Evans (11) did not find dibromodibenzofuran from a 2-bromophenol pyrolysis. On the other hand, more favorable coupling of IIa-IIb and IIa-Ia leads to tribromo- and dibromobenzofurans, respectively, identified in the pyrolysis products (reactions C and D). Involvement of IIb radicals in these reactions explains why dibenzofurans require a temperature of formation higher than that of dibromodibenzop-dioxin. Other possible reactions of the dibromophenoxyl radical IIb might include an attack of the Br atom to form 2,4, 6-tribromophenol (22) or of phenoxyl radical II to form tribromodibenzo-p-dioxin as shown in Scheme 2, paths E and F. Both these products have been observed in the 450 °C pyrolysis products. Formation of a substituted benzene indicates that the reaction reducing the hydroxyl group is of importance (23), as the removal of the hydroxyl group from the phenols is a rather difficult reaction because of the high energy of the phenolic C-O bond (24). The yield of PBDDs and PBDFs is governed by the temperature of pyrolysis, the reactor residence time, and the structure of the parent phenol too, as the formation of PBDDs is restricted by parent ortho-brominated phenols.

With the purpose of comparison, another model compound, DCP, was studied in the flow reactor. The corresponding gas chromatograms of products from the 450, 500, and 550 °C pyrolyses are shown in Figure 2e-h. Apart from dichlorodibenzo-p-dioxin, the pyrolysis of DCP yielded two other main products, trichlorodibenzofuran and tetrachlorodibenzofuran. The formation of the products is in agreement with the related schemes discussed previously for DBP. With respect to the evolution of tetrachlorodibenzofuran, path B of Scheme 2 appears to be operative. While the strength of C-Br or C-Cl bonds accounts for the various temperature regimes of the pyrolysis of the halogenated phenols, steric effects or the higher reactivity of chlorine radical to abstract protons from tautomeric forms is likely to be responsible for the differences in the product formation. It can be concluded that radical reactions play an important role in the pyrolysis of the halogenated phenols. Actually, the most significant process is the initiation reaction (Scheme 1) representing dehalogenation of the parent phenols. Therefore, supplying hydrogen to the phenoxyl and halogen radicals is expected to help in dehalogenating the model phenols. This idea was approached by pyrolyzing the model compounds in a hydrogen-donating medium of PP. To increase the contact between the molecules, the following experiments were carried out in sealed ampules. Pyrolysis in Sealed Ampules. In general, the thermal reactions of neat DBP in sealed ampules are quite similar to that in the flow reactor; however, the extension of the DBP conversion was increased from 3% to about 20% (data related to 350 °C). At 300 °C 4-bromophenol, 2,4,6-tribromophenol, and tribromophenoxyphenol were the main decomposition products; their yield increases with increasing reaction time. Unsubstituted phenol was detectable after 30 min of pyrolysis at 300 °C, as well as at 350 and 400 °C for a shorter residence time. Traces of PBDDs appeared at 300 °C. At higher temperature (350-400 °C) the yield of PBDDs increased. PBDFs were identified from 400 °C. A typical total ion gas chromatogram (TIC) of condensable products from the 330 °C pyrolysis of DBP is shown in Figure 3e. Formation of phenol, bromophenols, brominated phenoxyphenols, and PBDDs is in accordance with the mechanisms previously proposed. The composition of the pyrolysis products dramatically changed when DBP was pyrolyzed in the presence of PP. At 330 °C (Figure 3a) the main product was phenol along with 2- and 4-methylphenols in a much VOL. 39, NO. 14, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 4. FT-IR spectra of PP (a) heated at 350 °C for 20 min and solid products of the thermal degradation of DBP + PP ) 78 + 12 (b) and DBP + PP ) 79 + 15 (c) collected in sealed ampules at 350 °C for 20 min. lower yield (corresponding concentrations in oil were 2% and 1%), with the extension of the DBP conversion increased above 99%. The yield of the gaseous product, HBr and traces of alkyl bromides, essentially rose as well (see Table 1 from the Supporting Information, which also reports the quantification of pyrolysis products). The hydrodebromination efficiency is affected by temperature. At 310 °C 1% undecomposed 2-bromophenol remained (Figure 3b), whereas at 290 °C (Figure 3c) the hydrodebromination proceeded at a very low rate (the concentration of unchanged DBP was 94%). The optimum temperature observed in these experiments was 330 °C (20 min residence time). It is lower than that of the previous experiments (350 °C (9)); we assumed that this occurred because of higher pressure developed in the current ampules (ampule volume 1.7 cm3 compared to 2.0 cm3 in ref 9 loaded with approximately an equal amount of the substrate). In effect, by increasing the DBP loading from 75 to 136 mg, which corresponded to a rise of initial pressure from about 10 to 17 atm, the pyrolysis at 290 °C yielded unbrominated phenol, the concentration of which in the oil was 99% (Figure 3d compared to Figure 3c), indicating that the reaction depends on the pressure inside the ampules. The ratio between PP and DBP influences the yield of the dehalogenation products as well. For instance at 350 °C (20 min reaction time), 2- and 4-bromophenols along with phenol were formed in concentrations of 2%, 3%, and 95%, respectively, from the ratio DBP:PP ) 78.8:8.0. 4-Bromophenol disappeared and the concentration of 2-bromophenol decreased to about 0.5% with increasing ratio DBP:PP ) 78.4: 12.0. No bromine-containing phenols were noticed from DBP + PP ) 73.7 + 15.8. A pyrolysis time of 15 min left some undecomposed DBP. Apart from gases and oil, the pyrolysis of DBP + PP left a black cross-linked deposit on the wall of the ampules, the FTIR study of which from the initial composition DBP:PP ) 78:12 revealed a strong decrease of aliphatic bands at 2961-2838 cm-1 of PP and a formation of polyaromatic structures at 1592, 813, and 751 cm-1 (25) (compare Figure 4b to Figure 4a). The absorption at 1221 cm-1 is likely attributable to C-O ether stretching of phenols. The same spectral changes were observed from the composition DBP: PP ) 74:16 (Figure 4c); however, the absorption bands at 2925, 2855, and 1384 cm-1 point to unconsumed aliphatic structures, indicating a surplus of PP in the initial composi5472

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tion. A further increase of the ratio DBP:PP to 3:1 left liquidized residue. The tautomeric forms of the chlorinated phenols are reported to abstract a H atom from donor media such as 9,10-dihydroanthracene (8). However, the H-donating ability of PP should be much lower than that of the anthracene derivative, and in the present case, the radicals first formed in the system are those from DBP (Scheme 1). Therefore, it seems more reasonable to assume that these radicals formed by the initiation reaction abstract hydrogen from PP to form monobromophenol and HBr. Next, the former gives rise to phenoxyl radical in analogy to Scheme 1. In its turn, the phenoxyl radical undergoes the hydrogen abstraction reaction to form phenol. Therefore, the role of PP is to supply H to the phenoxyl radical to form phenols, avoiding at the same time their coupling to phenoxyphenols and toxic PBDDs and PBDFs. As a result, double bonds are formed in the polymer followed by their polyaromatization (Figure 4). Hydrogen evolved during this process might facilitate the debromination of DBP. The studied hydrodebromination process is reaction between gas (DBP) and liquid (PP). The increase of pressure is likely to result in higher penetration of DBP into PP and consequently its dissolving, thereby increasing the reaction in bulk of the polymer. Formation of methylphenols is likely to come from reaction involving addition of carbon-centered phenoxyl radicals to double bonds of the polymer chain. Successive scission of “polymeric” alkylphenol is favored by the formation of benzyl radical:

HO-C6H4• + CH2dC(CH3)∼ f HO-C6H4-CH2-C(•)(CH3)∼ f HO-C6H4-CH2-CH(CH3)∼ f

HO-C6H4-CH2• + •CH(CH3)∼ f HO-C6H4-CH3 + CH2dCH∼ By pyrolyzing DCP in the presence of PP in the range 350-450 °C, the yield of gaseous products was much lower compared to that from the DBP + PP mixtures (Table 1, Supporting Information). No hydrodechlorination products were recovered from this reaction at 350 °C in the oil fraction, whereas, at 450 °C, small amounts of 2- and 4-chlorophenols (corresponding concentrations in oil were 2% and 4%) were formed and 93% DCP was left. This signifies that HBr can selectively be produced from a mixture of bromine- and chlorine-containing phenols at 350 °C or lower temperature. From the mechanism of dehalogenation presented here only halogen in the ortho/para-positions are easily removed. It appeared important to extend our study to another model compound, DBDPE. As expected the thermal stability of the DBDPE is much higher than that of DBP because the tautomeric equilibrium is no longer possible in this case (Scheme 1). The hydrodebromination reaction starts above 400 °C, i.e., at the temperature of PP decomposition. At 440 °C pyrolysis of pure PP resulted in the formation of gases and oil, whereas pure DBDPE did not decompose. Pyrolysis of the mixture of PP + DBDPE produced gases, oil, and black cross-linked deposit. A TIC of oil from the 440 °C pyrolysis of PP + DBDPE is shown in Figure 5b. For comparison, in Figure 5c a TIC of the pyrolysis oil of PP is shown. It can be concluded that the hydrodehalogenation of DBDPE with PP results in the formation of bromine-containing benzenes, phenols, diphenyl ethers, and dibenzofurans and nonbrominated dibenzofuran. At lower temperature (420 °C) there is an increase in the level of bromine-containing diphenyl ethers, which results from partial debromination of DBDPE (Figure 5a).

FIGURE 5. Total ion gas chromatograms of the pyrolysis oil of DBDPE + PP ) 76 + 14 (mg) from 420 °C for 20 min (a), DBDPE + PP ) 15 + 77 (mg) from 440 °C for 20 min (b), PP from 440 °C for 20 min (c), the gaseous products of DBDPE + PP ) 76 + 14 (mg) from 420 °C for 20 min (d): 1, 2-bromo-2-methylbutane; 2, 4-methylheptane; 3, 3-bromopentane; 4, 1,2-dimethylbenzene; 5, 6, trimethylbenzenes; 7, 1,2-diethylbenzene; 8, ethyldimethylbenzene; 9, 1,2,3,5-tetramethylbenzene; 10, 11, dibromobenzenes; 12, 4-bromophenol; 13, dimethylnaphthalene + tribromobenzene; 14, tribromobenzene; 15, dibenzofuran; 16, dibromophenol; 17, methyldibenzofurans; 18, dibromomethylphenol; 19, tetrabromobenzenes; 20, monobromodibenzofuran; 21, tetrabromomethylbenzene; 22, dibromodibenzofurans; 23, tribromodibenzofurans; 24, tetrabromodiphenyl ethers; 25, pentabromodiphenyl ethers; 26, hexabromodiphenyl ethers; I, methane; II, ethene; III, propane; IV, isobutane; V, HBr; VI, pentane; VII, 2-methylpentane; VIII, bromopropane; IX, 1-bromo-2-methylpropane; X, H2O + HBr.

SCHEME 3

The gas phase from the pyrolyzing mixture becomes enriched by HBr, low-chain aliphatics, and alkyl bromides (Figure 5d). FTIR study of the solid pyrolysis products of the DBDPE + PP mixture revealed (see the Supporting Information) disappearance of the C-O ether stretching at 1324 cm-1 and of the brominated aromatic ring stretching at 1351 cm-1, indicating full decomposition of DBDPE. The formation of polyaromatic char is inferred from the absorption bands at 745, 811, and 1550 cm-1. We believe that the decomposition of DBDPE is assisted by radicals resulting from decomposition of PP. Scission of the PP chain produces two kind of radicals: a primary one and a secondary one. The most active (the primary) radical is likely to attack the bromine atom of DBDPE, producing an alkyl bromide, brominated phenyl radical, and, subsequently, less brominated diphenyl ether due to hydrogen abstraction. If the radical is located in the ortho-position to the ether bond, a ring closure can occur to give PBDFs. The formation of brominated benzenes, methylbenzenes, and phenols is indicative of the C-O ether bond scission which might come from the radical attack. A possible mechanism of the DBDPE dehalogenation is depicted in Scheme 3. Experiments with Technologically Applicable Devises. The technological implementation of the hydrodebromination reaction by PP is a topic of ongoing research and development. Primary tests within a stirred tank reactor charged with PP and variable amounts of pyrolysis oil from electronic boards containing TBBPA have been performed at 350 °C at the company Sea Marconi Technologies, Turin, Italy, in cooperation with the Forschungszentrum Karlsruhe GmbH, Germany. The tests have shown the disappearance of mono- and dibromophenols in the pyrolysis oil, indicating

that the hydrodebromination reaction takes place; however, the total treatment time is too long for technical operation due to a noneffective contacting of the phases. Therefore, an ongoing development is to try to realize a technically feasible solution, increasing the contact time and surface of the molten polypropylene and the vapors coming from the pyrolysis oil. An example of the pyrolysis oil before and after the decontamination treatment is shown in the Supporting Information. In conclusion, the hydrogen-donating media can be helpful in a posttreatment decontamination process, if pyrolysis oil is enriched by brominated phenols, but with respect to dehalogenation of polybrominated diphenyl ethers, more effort should be made. The pyrolysis in the presence of hydrogen-donating media such as PP can help in minimizing the formation of PBDDs and PBDFs by deactivating the active bromophenols toward PBDD and PBDF formation.

Acknowledgments We thank the European Community for funding this work in the frame of Competitive and Sustainable Growth (Growth) Programme G1RD-CT-2002-03014.

Supporting Information Available Table of the quantification of pyrolysis products from the model compounds and their mixtures with PP, figures of mass and IR spectra of pyrolysis products, and pictures of laboratory experiments with technologically applicable devices. This material is available free of charge via the Internet at http://pubs.acs.org.

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Received for review January 3, 2005. Revised manuscript received April 12, 2005. Accepted May 3, 2005. ES0500106