Deactivation of palladium on activated carbon in the selective hydrogenolysis of CCl2F2 (CFC-12) into CH2F2 (HFC-32)

The stability of the selected 1 wt.% palladium on activated carbon catalyst in the selective hydrogenolysis of CCl2F2 into CH2F2 as function of temper ature (510-540 K) and hydrogen to CCl2F2 feed ratio (1.5-20 mol/mol) has be en studied. A satisfactorily stable catalyst performance for at least 1600 h of operation has been obtained at 510 K and Hz to CCl2F2 feed ratios of 6 and 10. Outside this window, significant deactivation of the catalyst was observed. The conversion of CCl2F2 and the selectivity for CH2F2 were highe r at increasing ratio H-2 to CCl2F2 ratio. These differences in catalyst pe rformance became more pronounced as a function of time on stream. At higher temperatures (520, 525, and 540 K) the catalyst deactivated independent of the Hz to CCl2F2 feed ratio. Addition of methane or CHClF2 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 forma tion of carbonaceous deposits on the catalyst surface. Neither sintering no r loss of palladium was found after reaction. On the contrary, the used cat alysts had a higher palladium dispersion than the fresh catalyst. The degre e of dispersing was dependent of the H-2 to CCl2F2 feed ratio and temperatu re. Poisoning is concluded to be not important. Based on these experiments the operating window of an industrial liquid-coo led multi-tubular CCl2F2 hydrogenolysis reactor is defined. (C) 2001 Elsevi er Science B.V. All rights reserved.