(CBrClF2) to Halon 1301 (CBrF3) - American Chemical Society

Halon 1301 (CBrF3) and CFC 13 (CClF3) are the main pyrolysis products, although their yields vary with temperature and catalyst type. If accepted by r...
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Ind. Eng. Chem. Res. 2003, 42, 6000-6006

Catalytic Process for the Conversion of Halon 1211 (CBrClF2) to Halon 1301 (CBrF3) and CFC 13 (CClF3) Md. Azhar Uddin,† Eric M. Kennedy,*,† Hai Yu,† Yusaku Sakata,‡ and Bogdan Z. Dlugogorski† Process Safety and Environment Protection Group, School of Engineering, The University of Newcastle, Callaghan, NSW 2308 Australia, and Department of Applied Chemistry, Okayama University, Tsushima Naka, Okayama 700-8530, Japan

This paper reports the catalytic pyrolysis of CBrClF2 over γ-Al2O3 and β-AlF3 in a plug-flow reactor operated at atmospheric pressure and within the temperature window of 523-673 K. The results indicate a very high conversion of halon 1211, in excess of 90% for γ-Al2O3 and 60-80% for β-AlF3, over the entire temperature range. Halon 1301 (CBrF3) and CFC 13 (CClF3) are the main pyrolysis products, although their yields vary with temperature and catalyst type. If accepted by regulators, this process offers a reaction pathway for converting stockpiled halon 1211 into more widely used halon 1301. A mechanistic interpretation of the results is proposed, including the reaction pathways and the transformations taking place in the catalysts. The mechanism involves the initial activation of the catalysts, which is reflected by the formation of the surface aluminum fluoride species identified by XRD analysis. This species then facilitates the halogen exchange between Br and Cl in CBrClF2 and F in the catalyst framework, leading to the formation of CBrF3 and CClF3. It is also proposed that two minor species (CBr2F2 and CCl2F2) are formed by dismutation of CBrClF2. 1. Introduction Brominated fluorocarbons and chlorofluorocarbons are denoted as halons. Halons are very stable and have atmospheric lifetimes long enough to allow their transport into the stratosphere, where they are dissociated by ultraviolet radiation. This dissociation process causes the release of bromine and chlorine atoms, which catalyze the destruction of the stratospheric ozone.1 The Montreal Protocol mandated a ban on the manufacture of halons and other ozone-depleting substances in industrialized (article V) countries.2 The ban on the manufacture of these substances has not only stimulated interest in the development of alternative agents, but also accentuated the need to develop technologies capable of treating the existing stockpiles of these chemicals. For this reason, the development of treatment technologies for halons and chlorofluorocarbons (CFCs) is currently an active area of research. At present, the only established treatment technology for halons is based on destruction of the material by pyrolysis in a plasma arc at very high temperatures.3 Halon conversion, in contrast to destructive technologies, is attracting considerable research interest. Hydrodehalogenation is one such conversion approach, in which halons react with hydrogen or hydrogen donors. We have examined the hydrodehalogenation of halon 1301, both catalytically and in the gas phase.4-6 In both cases, the major hydrofluorocarbon (HFC) product is CHF3, regardless of whether the reaction is performed with CH4 or H2 as the hydrogen-donor reactant. The importance of this finding is that a process has been developed in which CHF3 is converted to CF3I (also * To whom correspondence should be addressed. Tel.: (+61 2) 4921 6177. Fax: (+61 2) 4921 6920. E-mail: eric.kennedy@ newcastle.edu.au. † The University of Newcastle. ‡ Okayama University.

known as halon 13001).7 CF3I is a chemically active fire suppressant that is being considered as a replacement for halon 1301, although because of occupational exposure problems, there is significant resistance to adopting CF3I as a flooding agent.8-9 For this reason, it is generally considered for use only in unoccupied spaces.10 The process for conversion of CHF3 to CF3I, developed by Nagasaki et al., involves the catalytic reaction of CHF3 with I2.7 Nagasaki and his co-investigators argue that the reaction proceeds via the formation of a surface carbene (CF2:) species, also resulting in the generation of HF. The carbene then disproportionates to carbon and CF3, which rapidly produces CF3I. The formation of carbene leads to catalyst deactivation. Perhaps for this reason, Nagasaki et al. subsequently modified the process to include oxygen in the feed stream to react with the deposited carbon. The catalyst consists of alkali metals on a carbon support. Processes can also be found that convert CBrF3 to CF3I without proceeding via CHF3 intermediate. The conversion developed by Naumann et al. is based on a two-stage process.11 In the initial stage, CBrF3 reacts with zinc metal in dimethyl formamide (DMF) using I2 as a catalyst. The mixture is left overnight, during which the complex CF3ZnBr‚2DMF is precipitated. The further reaction of the CF3ZnBr‚2DMF complex with ICl produces CF3I and ZnClBr. A similar process has also been reported by Paratian et al., who used an electrochemical cell to form the CF3ZnBr‚2DMF complex.12 Whereas a number of processes exist for the conversion of CBrF3 to useful products, the same cannot be said for halon 1211, CBrClF2. The presence of both Br and Cl in the halon structure complicates the hydrodehalogenation process, resulting in the production of a wide variety of halogenated and nonhalogenated species under most conditions. Indeed, we have studied the hydrodehalogenation of CBrClF2 in some detail, and although we have been able to convert CBrClF2 to CH2-

10.1021/ie0300981 CCC: $25.00 © 2003 American Chemical Society Published on Web 10/22/2003

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Figure 1. Experimental setup.

CF2 in relatively high yields (>50%), the reaction conditions are quite extreme, and a significant amount of coke is formed during reaction.13 Here, we present the results of a catalytic process for the conversion of halon 1211 to halon 1301 under relatively mild conditions, at a significantly high single-pass yield (>40%). This process potentially will allow one to apply conversion techniques developed for halon 1301 for the treatment of halon 1211. Aluminum-based catalysts such as γ-Al2O3 and β-AlF3 have long been known as effective catalysts for the transformation of chlorofluorocarbons (CFCs) through dismutation, gas-phase fluorination, isomerization, and halogen-exchange (Cl/F) reactions.14-20 γ-Al2O3 and β-AlF3 have also been widely studied as catalytic supports for the hydrodechlorination of CFCs.21-25 Although γ-Al2O3 and β-AlF3 have been studied extensively for CFCs in fluorination and related reactions, very little is known about the catalytic reaction of halons over these catalytic materials. Halon 1211 (CBrClF2) represents a unique example of a probe fluorocarbon molecule that contains both chlorine and bromine atoms. The catalytic reactions of this molecule over γ-Al2O3 and β-AlF3 are of special interest because of their fundamental significance and practical importance. This paper presents the results of the catalytic reaction of CBrClF2 over γ-Al2O3 and β-AlF3. The conversion and product selectivities as a function of reaction temperature and time on stream over these catalysts are reported. This work is part of a larger study designed to develop new routes for the conversion of halons to useful products. 2. Experimental Section Commercially available γ-Al2O3 and β-AlF3 samples were examined as catalysts for the thermolysis of halon 1211. The γ-Al2O3 catalyst, characterized by a specific surface area of 118 m2/g, was obtained from Mizusawa Chemical Co., Japan, and β-AlF3, with a specific surface area of 18 m2/g, from Sigma-Aldrich in powder form. Both catalysts were used in granular form (mesh size 20-40). Catalytic reaction of CBrClF2 was carried out in a plug-flow alumina reactor (i.d. ) 0.65 cm) under atmospheric pressure. The experimental setup is shown in Figure 1. Details of the experimental setup have been described previously.5 To demonstrate the effect of the

alumina reactor on the conversion of CBrClF2, a gasphase reaction was performed at 673 K in the absence of any catalysts; it was found that the alumina reactor has negligible activity for CBrClF2 pyrolysis, as the conversion rate was less than 1%. In a typical catalytic run, 200 mg of the solid catalyst (pelletized, crushed, and sieved to 20-40 mesh) was placed between two quartz wool beds in the reactor and heated in flowing N2 to the desired reaction temperature. The reaction commenced when a reaction mixture of CBrClF2 diluted with nitrogen in a volumetric flow ratio of 5.4:56.8 (total flow rate ) 62.2 cm3/min, standard temperature and pressure) was fed into the reactor. The exhaust gases were passed through a caustic (0.1 M NaOH) scrubber and a tube packed with silica gel to remove mineral acids (HF, HCl, HBr) and moisture, respectively. Reaction products were analyzed with an on-line micro GC (Varian Chrompac) equipped with Poraplot Q and molecular sieve columns and a TCD detector. Helium was used as the carrier gas at a pressure of 175 kPa, and both columns were operated at 348 K. A QP5000 (Shimadzu) GC-MS equipped with a Poraplot U capillary column and a quadruple mass spectrometer was used for product identification. Quantitative analysis of the product halocarbons was performed using relative molar response (RMR) factors estimated from published correlations for TCD detectors.26 The mineral acids trapped in the NaOH scrubber over a fixed, predetermined time period were analyzed with an ion chromatograph (Dionex DX-100) furnished with an IonPac AS14A analytical column and a conductivity detector. Conversion of CBrClF2 was estimated by two methods: (1) by comparing the amount of CBrClF2 consumed during the reaction with the amount of CBrClF2 fed into the reactor and (2) by summing the amount of carboncontaining products formed, that is, by the ratio of the sum of all carbon-containing products formed to the amount of CBrClF2 fed into the reactor. Selectivity to product species was computed from the following expression

Si )

ni × [product species i]

∑i ni × [product species i]

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tation of CHClF2 over γ-Al2O3 catalyst.15 In the present study, γ-Al2O3 became fully active at 523 K after 20 min on stream for the reaction of CBrClF2, which is in agreement with the findings of Kemnitz et al. They reported that no structural changes of the bulk alumina could be detected by XRD, although chemical analysis showed a significant amount of halogen in the solid. Furthermore, they suggested that an amorphous aluminum fluoride phase contains the active sites for the CFC and HCFC dismutation reactions. In the results presented here, the portion of CBrClF2 that is converted into gaseous products was about 30% less than the portion consumed by the reaction, and coke formation was observed on the catalyst surface. These results indicate that the dissociation of the reactant occurs on the surface of γ-Al2O3, which leads to the formation of coke. The products of the catalytic reaction of CBrClF2 over γ-Al2O3 were CBrF3, CClF3, CCl2F2, CBr2F2, and CCl3F, and their selectivities varied with time on stream as illustrated in Figure 2b. During the initial stages of the reaction (after the activation period), CBrF3 and CClF3 were produced as the major products with selectivities of 45 and 35%, respectively. The selectivity to CCl2F2 was 15%, whereas the selectivities of minor products CBr2F2 and CCl3F were less than 5%. With further time on stream, the selectivity to CBrF3 remained almost constant, whereas the selectivity to CClF3 decreased and that to CBr2F2 increased slowly. We suggest that CCl2F2 and CBr2F2 were produced by the dismutation of CBrClF2, as this reaction has negative standard Gibbs free energy change of -7.6 kJ/mol at 523 K and -8.9 kJ/mol at 673 K.

2CBrClF2 f CBr2F2 + CCl2F2 Figure 2. Catalytic reaction of halon 1211 over γ-Al2O3 at 523 K.

where Si is the selectivity to species i and ni is the number of carbon atoms in species i, with the square brackets denoting the concentration of species i in the outlet gases from the reactor. The fresh and used catalysts were characterized by nitrogen adsorption and X-ray diffraction (XRD) techniques. Specific surface areas of the catalysts were measured by nitrogen adsorption isotherm at 77 K using the BET (Brunauer, Emmett, and Teller) method. X-ray diffraction patterns of the catalysts were obtained on a RINT2500/Rigaku diffractometer using Cu KR radiation. 3. Results and Discussion Figure 2 shows the conversion of CBrClF2 and selectivities of products as functions of time on stream over Al2O3 catalyst at 523 K. During the early stages of the reaction, the conversion of CBrClF2 increases rapidly with time on stream and reaches a steady state of 90% conversion after 20 min time on stream. This implies that the γ-Al2O3 catalyst requires activation by CBrClF2 for it to become catalytically active. A similar phenomenon has been reported by others in the dismutation of CFCs and HCFCs over γ-Al2O3 and Cr2O3 catalysts,20,27-29 where the time and temperature needed to achieve full catalytic activity depended on the type of catalyst (metal oxide) and the reacting fluoroalkanes. Kemnitz et al. reported an activation temperature of 523 K and an activation time of 10-15 min for the dismu-

However, the observed concentrations of CCl2F2 and CBr2F2 differ significantly under these conditions. We suggest that this is because these species are intermediates that react further (at different rates) to a variety of secondary products. Thus, their concentrations in the final product stream are different. CCl2F2 and CBr2F2 can also be formed by halogen-exchange reactions between CCl3F and Al-F sites and between CBr3F and Al-F sites, respectively. The formation of major products CBrF3 and CClF3 can be explained only by halogen-exchange reactions (Cl, Br with F). During the initial catalyst activation step, adsorption and dissociation of one molecule of CBrClF2 over two surface Al-OH* species produces CO2, HCl, HBr, and two Al*-F sites.

CBrClF2 +2Al-OH* f CO2, HCl, HBr, 2Al*-F Production of HCl and HBr at the earlier stage of the reaction was confirmed by ion chromatographic analysis of the NaOH trap (caustic scrubber) solution for Cl- and Br- anions. It is suggested that CBrF3 and CClF3 are produced by the halogen-exchange reaction between the reactant CBrClF2 and surface aluminum fluoride (Al*F) species, with the surface Al*-F species being halogenated with Cl and Br.

CBrClF2 + Al*-F f CBrF3 + Al*-Cl CBrClF2 + Al*-F f CClF3 + Al*-Br It is also possible that the surface aluminum halides (Al*-Cl and Al*-Br) undergo further transformation into Al*-F by the dissociation of a CBrClF2 molecule,

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Figure 3. Catalytic reaction of halon 1211 over γ-Al2O3 at 573 K.

producing coke (C), Cl2, and Br2.

CBrClF2 + 2Al*-X f C, Cl2 Br2, 2Al*-F Although quantification of Cl2 and Br2 was not performed, the observation of a greenish-yellowish color of the condensate in the water trap, at the reactor outlet, indicates the presence of Br2 and Cl2 in the gaseous product. It has been reported that γ-Al2O3 prefluorinated with fluorocarbons or chlorofluorocarbons transforms into β-AlF3, which exhibits Lewis acidity and catalyzes halogen-exchange and dismutation reactions of chlorofluorocarbons.30 We suggest that, in the present investigation, the halogen-exchange reaction occurs on the Lewis acid sites of the catalysts, although we have not yet characterized the CBrClF2-treated γ-Al2O3 catalysts for Lewis acidity. Figures 3 and 4 show the results for the reaction of CBrClF2 over γ-Al2O3 at 573 and 673 K. Because no catalyst activation period was observed, it is assumed that the activation of γ-Al2O3 is very fast at these temperatures. The conversion of CBrClF2 was maintained at a high level (more than 90%); however, significant differences in the conversion levels, based on CBrClF2 consumption and product formation, were observed. At 573 K, CBrF3 and CClF3 were the two major products and constituted more that 80% of all products. The selectivity to CBrF3 increased, whereas

Figure 4. Catalytic reaction of halon 1211 over γ-Al2O3 at 673 K.

the selectivity to CClF3 decreased slightly with time on stream and reached a steady state after 180 min. On the other hand, at 673 K, CClF3 was the predominant product, formed with a selectivity of 65-70%, whereas the selectivity to CBrF3 was 22-25%. This suggests that Cl/F exchange is favored over Br/F exchange at higher temperatures. Figures 5-7 show the results for CBrClF2 conversion and product selectivity as functions of time on stream over the AlF3 catalyst at 573, 623, and 673 K. At 573 K, no significant conversion of CBrClF2 (less than 1%) was observed for the first 50 min, but later, the conversion level of CBrClF2 increased sharply with time and reached a steady state of 70% after 100 min on stream (Figure 5a). It is evident that AlF3 also requires an activation period, which is 50 K higher and 40 min longer than that of Al2O3. The main products of the reaction of CBrClF2 over AlF3 were the same as for the Al2O3-catalyzed reaction. During the catalyst activation period, CClF3, CBr2F2, CCl2F2, and CBrF3 were the major products (Figure 5b). After completion of the activation period, selectivity to CBr2F2 decreased dramatically from 30 to 8%, and selectivity to CBrF3 increased from 17 to 43%. As mentioned earlier, CBrF3 and CClF3 are produced by exchange of the gas-phase Br and Cl (from CBrClF2) with the solid-phase F (from the catalyst). Kemnitz et al. suggested a mechanism for the dismutation of CCl2F2 on metal oxides and metal halides catalysts that involved concerted Cl/F and F/Cl exchange between the solid and gas phase.31 The halogen-exchange reaction might also proceed via an

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Figure 6. Catalytic reaction of halon 1211 over β-AlF3 at 623 K.

Figure 5. Catalytic reaction of halon 1211 over β-AlF3 at 573 K.

adsorbed species at the surface.32 It seems likely that F from the bulk AlF3 phase is not active in the halogenexchange reaction, but rather, the surface F species generated by the decomposition of CBrClF2 on the catalyst is the source of F in the halogen-exchange reaction. The conversion of CBrClF2 based on the consumption of CBrClF2 is higher than that based on product formation because of the significant coke formation and production of Br, Cl, and F species. We attribute this difference to coke formation, which was evident from the catalyst turning black after the reaction. It was not possible to quantify coke formation by simply weighing the catalysts before and after reaction, given that weight changes in the catalysts might be related to changes in the chemical structure of the catalysts, i.e., transformation of Al2O3 to AlF3. This precludes the possibility of undertaking a detailed carbon mass balance. At 623 and 673 K, no activation period was required for AlF3 to achieve a high conversion of CBrClF2 (Figures 6a and 7a, respectively). At 623 K, a CBrClF2 conversion of 75% was attained at the initial stage of the reaction, which then slowly decreased with time on stream to 65% in 120 min. On the other hand, at 673 K, a higher conversion of CBrClF2 (more than 90%) was achieved initially, but it dropped rapidly to 65% after 110 min. The deactivation of the catalyst is most probably due to the formation of coke on the catalytic surface. However, surface modification during the progress of the halogen-exchange reaction cannot be ruled out at this stage.

Product yields over AlF3 changed both with temperature and with time on stream. At 623 K, the selectivity to CBrF3 was approximately 40% decreased slightly with time on stream (Figure 6b). The initial selectivities to CClF3 and CCl2F2 were about 25%; however, the CClF3 selectivity decreased and the CCl2F2 selectivity increased slightly with time on stream. Dramatic changes in product selectivities were observed at 673 K (Figure 7b). The initial selectivities to CBrF3 and CClF3 were approximately 40%, but these values decreased with time (more rapidly for CClF3 than for CBrF3), whereas the selectivities to CCl2F2 and CBr2F2 increased with time on stream. These results suggest that, at higher temperatures and over the AlF3 catalyst, the dismutation of CBrClF2 into CCl2F2 and CBr2F2 is favored over the halogen-exchange reaction. In contrast, γ-Al2O3 remains highly active at 673 K for halogen-exchange reaction, forming more than 90% of halogen-exchange products (CClF3 and CBrF3). Differences in the CBrClF2 conversion level between γ-Al2O3 and β-AlF3 are observed. The BET surface areas of γ-Al2O3 (118 m2/g) and β-AlF3 (18 m2/g) are very different, but a comparison of surface-area-corrected catalytic activity is not reasonable here, given that the exact nature and quantity of the catalytically active sites are not known. The representative X-ray diffraction patterns for the Al2O3 catalyst before and after the reaction with CBrClF2 at 623 K are shown in Figure 8. The X-ray pattern of Al2O3 before reaction discloses the presence of the γ-Al2O3 phase only, whereas after the reaction with CBrClF2, the appearance of new peaks can be observed. These new peaks in the used Al2O3 catalyst are assigned to an aluminum fluoride/aluminum hydroxide hydrate

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Figure 9. XRD patterns of fresh and used AlF3 catalysts.

Figure 7. Catalytic reaction of halon 1211 over β-AlF3 at 673 K.

a phase transformation into aluminum fluoride, and subsequently, heterogeneous halogen-exchange reactions (Br or Cl with F) occur over the aluminum fluoride phase to produce CBrF3 and CClF3 from CBrClF2. Figure 9 shows the X-ray diffraction patterns of fresh and used (573 K) AlF3 catalysts. The XRD pattern of the fresh catalyst shows the presence of the β-AlF3 phase (JCPDS card no. 43-435), but there is no change in the XRD pattern of the catalyst. It has been reported that β-AlF3 is very active in reactions with fluorohaloalkanes (e.g., dismutation of CHClF2) and requires no activation period.14 However, we observed an activation period of 50 min at 573 K for the reaction with CBrClF2, although there was no detectable change in the crystalline phase in the catalyst. There is no parallel example in the literature for the reaction of halon 1211 (CBrClF2) with AlF3. We speculate that, for the heterogeneous halogen-exchange reaction (Br or Cl with F) of CBrClF2 over AlF3, an active aluminum fluoride phase that is XRD-insensitive, i.e., amorphous, is formed during the activation period. 4. Conclusions

Figure 8. XRD patterns of fresh and used Al2O3 catalysts.

phase (JCPDS card no. 74-940). A plausible explanation for the observed XRD results is that, during the reaction of Al2O3 with CBrClF2, surface-active aluminum fluoride (AlFx) phases are formed but are rapidly converted into an aluminum fluoride/aluminum hydroxide hydrate phase when the catalyst is exposed to atmospheric moisture after its removal from the reactor. When the used γ-Al2O3 catalyst was heat-treated at 773 K, the aluminum fluoride/hydroxide hydrate phase disappeared, and the new AlF3 phase was formed.27 Therefore, we suggest that, during the activation of the surface of Al2O3 with CBrClF2, the catalyst undergoes

Catalytic reaction of halon 1211 (CBrClF2) was performed over γ-Al2O3 and β-AlF3 within a temperature range of 523-673 K. The conversion of CBrClF2 over γ-Al2O3 was in excess of 90% for the entire range of temperatures studied. A catalyst activation period was observed at 523 K for γ-Al2O3. CBrF3, CClF3, CCl2F2, and CBr2F2 were the major products of the reaction, and their selectivities varied both with reaction temperature and with time on stream. CCl2F2 and CBr2F2 are the products of the dismutation of CBrClF2, whereas CBrF3 and CClF3 are the products of halogen-exchange reactions (Cl and Br with F). Between 523 and 573 K, CBrF3 was produced at a selectivity of more than 40%; however, CClF3 was the dominant product formed at a selectivity of 65% at 673 K. For AlF3, the onset temperature for catalyst activation shifted to 573 K (50 K higher than that for Al2O3). For a given temperature, the CBrClF2 conversion level was lower over β-AlF3 than over γ-Al2O3. Unlike for γ-Al2O3, in the case of β-AlF3, CBrF3 remained one of the major products at all temperatures, but the selectivity to CClF3 decreased, and the selectivities to CCl2F2 and CBr2F2 increased with time on stream and temperature. For both γ-Al2O3 and β-AlF3, a difference in CBrClF2 conversion levels based on halon consumption and

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product formation exists, and this difference is attributed to the dissociative adsorption of CBrClF2, which results in coke formation on the catalyst surface. The incorporation of fluoride from the reactant (CBrClF2) into the surface of γ-Al2O3 and β-AlF3 activates the catalysts, forming surface Al-F species that are, in turn, involved in halogen-exchange reactions with the reactant. Acknowledgment The Australian Research Council is gratefully acknowledged for financial support of this project. Literature Cited (1) Molina, M. J.; Rowland, F. S. Stratospheric sink for chlorofluoromethanes. Chlorine atom-catalyzed destruction of ozone. Nature 1994, 249, 810. (2) Montreal Protocol on Substances That Deplete the Ozone Layer, with later amendments. Available at http://www.ciesin.org/ TG/PI/POLICY/montpro.html. January, 1999. (3) Dickman, J. C.; Emmel, T. E.; Harris, G. E.; Hummel, K. E. Technologies for CFC/Halon Destruction; Report EPA/600/789/011; Environment Protection Agency: Washington, DC, 1998. (4) Li, K.; Kennedy, E. M.; Dlugogorski, B. Z.; Howe, R. F. Nonoxidative reaction of CBrF3 with methane over NiZSM-5 and H-ZSM-5. Catal. Today 2000, 63, 355. (5) Li, K.; Kennedy, E. M.; Dlugogorski, B. Z. Gas-phase reaction of halon 1301 (CBrF3) with methane. Ind. Eng. Chem. Res. 1999, 38, 3345. (6) Howe, R. F.; Thomas, S.; Yang, Y.; Li, K.; Kennedy, E. M.; Dlugogorski, B. Z. Zeolite catalysts for halon conversion. J. Mol. Catal. A: Chem. 2002, 181, 63. (7) Nagasaki, N.; Suzuki, N.; Tokoyoda, T.; Arai, S. A novel catalytic technology for CF3I manufacture. In Proceedings of the 10th Halon Options Technical Working Conference, Albuquerque, NM, May 2-4, 2000; New Mexico Engineering Research Institute, Albuquerque, NM, 2000; p 180. (8) Dodd, D.; Vinegar, A. Cardiac sensitisation testing of the halon replacement candidates trifluoroiodomethane (CF3I) and 1,1,2,2,3,3,3-heptafluoro-1-iodopropane (C3F7I). Drug Chem. Toxicol. 1998, 21, 137. (9) McCain, W. C.; Macko, J. Toxicity review for iodotrifluoromethane (CF3I). In Proceedings of the 9th Halon Options Technical Working Conference, Albuquerque, NM, April 27-29, 1999; New Mexico Engineering Research Institute, Albuquerque, NM, 1999; p 242. (10) Skaggs, S. R.; Rubenstein, R. Setting the occupational exposure limit for CF3I. In Proceedings of the 9th Halon Options Technical Working Conference, Albuquerque, NM, April 27-29, 1999; New Mexico Engineering Research Institute, Albuquerque, NM, 1999; p 254. (11) Naumann, D.; Tyrra, W.; Kock, B. Electrochemical synthesis of trifluoromethylcadmium and trifluoromethylzinc species using bromotrifluoromethane and sacrificial anodes. J. Fluorine Chem. 1994, 67, 91. (12) Paratian, J. M.; Labbe, E.; Sibille, S.; Nedelec, Y. J.; Perichon, J. Preparation and properties of ZnBr(CF3)‚2LsA convenient route for the preparation of CF3I. J. Organomet. Chem 1995, 487, 61. (13) Tran, R.; Kennedy, E. M.; Dlugogorski, B. Z. Gas-phase reaction of halon 1211 (CBrClF2) with methane. Ind. Eng. Chem. Res. 2001, 40, 3139. (14) Bell, T. N.; Kirszensztejn, P.; Czajka, B. Catalytic conversion of CCl2F2 on γ-Al2O3 catalyst. Catal. Lett. 1994, 30, 305. (15) Kemnitz, E.; Menz, D. H. Fluorinated metal oxides and metal fluorides as heterogeneous catalysts. Prog. Solid State Chem. 1998, 26, 97.

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Received for review February 6, 2003 Revised manuscript received August 6, 2003 Accepted August 9, 2003 IE0300981