Deactivation of palladium on activated carbon in the selective hydrogenolysis of CCl 2F 2 (CFC-12) into CH 2F 2 (HFC-32)

Abstract

The stability of the selected 1 wt.% palladium on activated carbon catalyst in the selective hydrogenolysis of CCl 2F 2 into CH 2F 2 as function of temperature (510–540 K) and hydrogen to CCl 2F 2 feed ratio (1.5–20 mol/mol) has been studied. A satisfactorily stable catalyst performance for at least 1600 h of operation has been obtained at 510 K and H 2 to CCl 2F 2 feed ratios of 6 and 10. Outside this window, significant deactivation of the catalyst was observed. The conversion of CCl 2F 2 and the selectivity for CH 2F 2 were higher at increasing ratio H 2 to CCl 2F 2 ratio. These differences in catalyst performance became more pronounced as a function of time on stream. At higher temperatures (520, 525, and 540 K) the catalyst deactivated independent of the H 2 to CCl 2F 2 feed ratio. Addition of methane or CHClF 2 to the feed led to additional deactivation of the catalyst, both at lower and higher temperatures. The observed phenomena of deactivation could be well explained by the formation of carbonaceous deposits on the catalyst surface. Neither sintering nor loss of palladium was found after reaction. On the contrary, the used catalysts had a higher palladium dispersion than the fresh catalyst. The degree of dispersing was dependent of the H 2 to CCl 2F 2 feed ratio and temperature. Poisoning is concluded to be not important. Based on these experiments the operating window of an industrial liquid-cooled multi-tubular CCl 2F 2 hydrogenolysis reactor is defined.