Hydrogenolysis of CFCs

Catalytic hydrogenolysis of CFCs has become very important in view of its relevance to the production of hydrofluoroalkanes, particularly CH2F2 and CFFFCF3 (Table 1). It is also a method whereby unwanted stocks of CFCs can be converted to useful compounds. Early work in this area was described in 12.1.2 but the past five years have seen an explosion of activity, particularly relating to hydrogenolysis of CCI2F2 and CCI2FCCIF2. Most of the work is outside the scope of this chapter, since it does not involve fluoride catalysts, but we conclude the chapter with two aspects that are relevant. 

In contrast to palladium and other Group VUI metals. Koto et al. have reported an active carbon-catalyzed hydrogenolysis of CFC-114a (43). The process generally operates at a higher temperature, over 400 C, and appears to produce HCFC-124 and HFC-134a as products of sequential reactions, because the former product is produced in higher proportion. 

The similarity between the dispersion and the intensity of a-Pd (maximum intense) signal is not surprising because dispersion is inversely proportion to crystallite size. The hydrogenolysis of CFC-113 activity also follows the same trend PC-2 PCCAFB-2 > PCCA-2 > PCFLA-2 >PA-2... 

Thus it is concluded that a-Pd is responsible for the hydrogenolysis of CFC-113 and this reaction is structure sensitive. 

Process development for the selective hydrogenolysis of CCI2F2 (CFC-12) into CH2F2 (HFC-32)... 

The main synthetic route to CFC, HCFC and Halons is the Swarts fluorination. Technically this is often achieved by reaction of a chlorinated or brominated precursor with anhydrous hydrofluoric acid in the presence of a solid Lewis acid catalyst, for example chromia. Other important reactions are Lewis acid-catalyzed halogen isomerization and hydrogenolysis of chlorine or bromine. 

Palladium on a purified activated carbon support has been selected as a very suitable catalyst for the reaction. We have reported that the performance of this catalyst looks very promising and that a CFC hydrogenolysis plant based on this catalyst is both technically and economically feasible [3-5]. This paper deals with the stability of the selected catalyst, the long term influence of the hydrogen to CCI2F2 feed ratio on the catalyst performance and the influence of the possible recycle components methane and CHCIF2 on the performance of the catalyst. 

In this chapter, recent advances in our understanding of catalytic fluorination under heterogeneous conditions are surveyed from the standpoint of catalyst properties, including developments based on the use of mixed metal fluorides having different structural types, and reaction mechanisms. Much of the newer work has been the result of the need to replace chlorofluorocarbons (CFCs) by alternatives, hydrofluorocarbons (HFCs) or, more controversially, hydrochlorofluorocarbons (HCFCs), following adoption of the Montreal and successor Protocols [2,3]. Where relevant, aspects of catalytic hydrogenolysis, where fluorides have been used as replacement supports in the conventional palladium/carbon catalysts, and isomerization reactions are included. 

Replacement of the chlorines in CFC-114a through catalytic hydrogenolysis produces HFC-134a, as shown in Eq. (14). Bitner et al. have studied... 

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