Process development for the selective hydrogenolysis of CCl2F2 (CFC-12) into CH2F2 (HFC-32)

A palladium on activated carbon catalyst is a suitable catalyst for the selective hydrogenolysis of CCl2F2 into CH2F2. Its stability is good: no deactivation occurred after 800 hours of operation. Even after addition of possible recycle components methane and CHClF2, only minor deactivation was observed during 1600 hours of total operation. The catalyst performance and stability strongly depend on the hydrogen to CCl2F2 feed ratio. A ratio of 6 leads to higher conversion, higher selectivity to CH2F2 and higher stability. At low H-2 to CCl2F2 ratios the mechanism of deactivation is presumably coke deposition. However, the ratio cannot be raised too high because then sintering of the palladium particles causes deactivation. Addition of methane to the feed leads to additional deactivation, and, therefore, methane is only allowed in a recycle stream when high hydrogen to CCl2F2 feed ratios are applied. Addition of CHClF2 to the feed does not lead to a higher CH2F2 yield. The reaction pathway to CHClF2 and CH2F2 is different from the route to methane. The selectivity to methane depends on the adsorption mode of CCl2F2 and is independent of both the CCl2F2 and the hydrogen concentration. The ratio between CHClF2 and CH2F2 is mainly determined by the CCl2F2 concentration. A CFC-destruction process, which can destruct about 90% of the CFCs in use, based on this catalyst is both technically and economically feasible. The main features of this process are a liquid cooled, multi-tube fixed bed reactor, excess hydrogen, 100% CCl2F2 conversion and a hydrogen recycle, in which methane is allowed.