CATALYST DEACTIVATION IN LIQUID-PHASE AND GAS-PHASE HYDROGENATION OF ACETYLENE USING A MONOLITHIC CATALYST REACTOR

The deactivation of a monolithic Pd/alpha-alumina catalyst in the sele ctive hydrogenation of acetylene in the presence of excess ethylene ha s been studied. The deactivation behavior of the monolithic catalyst i n the gas-phase hydrogenation was compared to that of the liquid-phase hydrogenation. It was shown that the deactivation behavior was differ ent in the two systems. It was concluded that in the gas-phase hydroge nation the rate of the deactivation is strongly dependent on the opera ting conditions. In the liquid-phase hydrogenation, both the catalytic activity and the ethylene selectivity declined during the first 60 h of operation and then stabilized. This was not observed in the gas pha se. Here, the activity and the selectivity passed through a maximum. T emperature programmed analyses of spent catalysts from liquid and gas phase processes revealed that the amount and nature of the species ads orbed on the catalyst surfaces are different for these two types of pr ocesses. In the case of a gas phase process, the amount of oligomers f ormed on the catalyst surface was much higher. In the liquid-phase hyd rogenation, these compounds showed a lower H/C ratio and were adsorbed more strongly in comparison to those from the gas phase process.