A Novel Catalytic Technology for the Manufacture of CF 3 I

et al. 2005

Environ. Sci. Technol.

The gas-phase reaction of halon 1211 (CBrClF2) with hydrogen has been studied experimentally at atmospheric pressure in a plug flow, isothermal reactor over the temperature range of 673 to 973 K, at residence times ranging from 0.5 to 2.5 s with an input ratio of N2:H2:halon 1211 of 19:10:1. The major carbon containing products include CHClF2, CHBrF2, CH2F2, and CH4. Gas-phase reactions of CHClF2, CCl2F2, and CH2F2 with hydrogen are also investigated under the conditions similar to those for halon 1211 hydrodehalogenation, and the results are used to assist in understanding the mechanism of the reaction of halon 1211 with hydrogen. A kinetic reaction scheme involving 90 species and 430 reaction steps is developed and used to model the halon 1211 hydrodehalogenation reaction. Generally, satisfactory agreement between experimental and computational results is obtained for the production of major species. Using the software package AURORA, the reaction pathways leading to the formation of major products are elucidated. It has been found that the reaction steps involving CF2 are responsible for the formation of CH4.

Section: Introductionmentioning

confidence: 99%

Experimental and Computational Studies of the Gas-Phase Reaction of Halon 1211 with Hydrogen

et al. 2005

Environ. Sci. Technol.

“…A relatively small number of studies on the gas-phase hydrodehalogenation of halons have been reported. [2][3][4][5][6][7] For example, Li et al studied the gas-phase hydrodehalogenation of CBrF 3 (halon 1301) with hydrogen and methane 3,4 and found that these reactions can be used to produce CHF 3 , a precursor for the synthesis of CF 3 I, 8 a promising halon replacement chemical.…”

Section: Introductionmentioning

confidence: 99%

Gas-Phase and Pd-Catalyzed Hydrodehalogenation of CBrClF₂, CCl₂F₂, CHClF₂, and CH₂F₂

et al. 2005

Ind. Eng. Chem. Res.

Hydrodehalogenation of CBrClF 2 , CCl 2 F 2 , CHClF 2 , and CH 2 F 2 with hydrogen has been studied in the gas phase and over supported Pd catalysts in a tubular alumina reactor. During gasphase reactions, selectivity to CH 2 F 2 is low for the hydrodehalogenation of CBrClF 2 , CCl 2 F 2 , and CHClF 2 . CHClF 2 is the primary product for the hydrodehalogenation of CBrClF 2 and CCl 2 F 2 , whereas C 2 F 4 is the major product for the hydrodehalogenation of CHClF 2 . Over Pd/C catalysts, CH 2 F 2 is the primary product, with selectivities generally over 60% for the hydrodehalogenation of CBrClF 2 , CCl 2 F 2 , and CHClF 2 . Halocarbons and hydrogen compete for the available surface sites on Pd, and it is suggested that the rate-limiting step during the catalytic hydrodehalogenation of the four halocarbons involves the cleavage of C-halogen bonds, that is, C-Br in CBrClF 2 , C-Cl in CCl 2 F 2 and CHClF 2 , and C-F in CH 2 F 2 .

“…The importance of this finding is that a process has been developed in which CHF 3 is converted to CF 3 I (also known as halon 13001). 7 CF 3 I 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 CF 3 I as a flooding agent. [8][9] For this reason, it is generally considered for use only in unoccupied spaces.…”

Section: Introductionmentioning

confidence: 99%

“…10 The process for conversion of CHF 3 to CF 3 I, developed by Nagasaki et al, involves the catalytic reaction of CHF 3 with I 2 . 7 Nagasaki and his co-investigators argue that the reaction proceeds via the formation of a surface carbene (CF 2 :) species, also resulting in the generation of HF. The carbene then disproportionates to carbon and CF 3 , which rapidly produces CF 3 I.…”

Section: Introductionmentioning

confidence: 99%

Catalytic Process for the Conversion of Halon 1211 (CBrClF₂) to Halon 1301 (CBrF₃) and CFC 13 (CClF₃)

et al. 2003

Ind. Eng. Chem. Res.

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.