Studies Of Acetylene Selectivity Hydrogenation Catalyst

Ethylene, as one of the important basic chemical raw materials, is usually used to produce polyethylene, polyvinyl chloride and other chemicals in industry. Ethylene for industrial use mainly comes from petroleum hydrocarbon cracking gas which always contains traces of acetylene need to be removed because it has toxic effects on the catalyst of the follow ethylene polymerization process. Acetylene can be removed by catalytic hydrogenation in industry. In this paper, the Pd/Al2O3, Pd-Ag/Al2O3 and Pd-Ag/Al2O3-KOH catalysts using Al2O3 as supporter are prepared by the incipient wetness impregnation method. The effect of adding Ag and modified catalsyts by K+ promoter on the catalytic performance are studied. Furthermore, the study of the influence of pressure, space velocity and other reaction conditions on catalytic performance is conducted. Finally, the influences of different pretreatment methods of the catalysts on catalytic performance are investigated. Meanwhile a comparation between self-developed catalyst and commercial catalyst is carried out in terms of catalytic performance.The experimental results show that the addition of Ag reduce the conversion of acetylene and MAPD, but increase the ethylene selectivity of the catalyst and increase the reaction temperature window from 17? to 21?. On the basis of Pd-Ag/Al2O3, the activity of the catalyst is reduced when KOH is added as the modification material, but the ethylene selectivity of the catalyst is improved. The selectivity of ethylene increase from 77.9% to 86.5% and the reaction temperature window increase from 21? to 25? when the amount of acetylene decrease to 30 ppm. Acetylene and MAPD conversion can be improved while the selectivity of ethylene can be reduced in a higher pressure. It should be noted that the suitable pressure range is varied with the catalyst component. The optimal pressure for Pd/Al2O3 catalyst is lMPa-1.5MPa and 1.5MPa-2.5MPa for Pd-Ag/Al2O3 or Pd-Ag/Al2O3-KOH catalyst. With the increasing of reaction space velocity, the decrease both in acetylene conversion and MAPD conversion are found, but the selectivity of ethylene will be increased. The optimal reaction space velocity for Pd/Al2O3 is 9000-15000h-1, while that for Pd-Ag/Al2O3 or Pd-Ag/Al2O3-KOH is 6000-12000h-1. The catalyst prepared by pre-reduction-deactivation method can stably exist in the air environment and can be easily stored and transported. In the previous hydrogenation process, this catylyst can be quickly reduced by the H2 in the feed gas, and express high activity and selectivity. Compared with the commercial catalyst 7741B, self-developed Pd-Ag/Al2O3-KOH catalyst presentes the higher acetylene and MAPD conversion, as well as a better selectivity of ethylene.