MECHANISTIC STUDY OF THE SELECTIVE HYDROGENOLYSIS OF CCL2F2 (CFC-12) INTO CH2F2 (HFC-32) OVER PALLADIUM ON ACTIVATED CARBON

The influence of process parameters such as temperature (400-560K), H- 2/CCl2F2 ratio (2.2-20), and Weight Hourly Space Velocity (WHSV) (0.3- 1.0 g/(g . h)) on the hydrogenolysis of CCl2F2 into CH2F2 over palladi um on activated carbon has been investigated. The reactivity of CHCIF2 and CH2F2 and the influence of HCl were also examined. In the reactio n of CCl2F2, the main product is CH2F2. Significant amounts of CHClF2 and CH4 are also found. The catalyst shows a remarkably high selectivi ty to CH2F2, in the range of 70-90 mol%, at all conversion levels in a broad range of process conditions. A mechanism is proposed in which t he reaction proceeds mainly via parallel reaction pathways. One route results in CH2F2 and CHCIF2, while the other route yields CH2. The sel ectivity to CH2F2 and CPIClF2 is determined by the amount of adsorbed chlorine on the catalytic surface and a constant selectivity for CH4 w as found. High selectivity for CH2F2 can be achieved at high H-2/CCl2F 2 ratios and low HCl concentration. The postulated mechanism is suppor ted by thermodynamic data.