Study On Catalyst And Catalytic Kinetics Of Acetylene Selective Hydrogenation

Ethylene is an important basic synthetic monomer in petrochemical industry.Part of acetylene is produced during the cracking of petroleum hydrocarbons into ethylene.Industrially produced ethylene usually contains acetylene with a molar fraction of 0.5%～1.5%.This acetylene in the subsequent processing causes catalysts poisoning,especially during the polymerization of ethylene.So the content of acetylene in the raw material ethylene is required no more than 1 ppm.This paper investigated effects of carbon nanotubes support on the acetylene selective hydrogenation.The effects of different carbon supports,diameter carbon nanotubes,heat treatment temperatures,modified metals and Pd-Ag ratios on the selective hydrogenation performance of acetylene were investigated.The results show that the catalytic hydrogenation performance of carbon nanotubes after high temperature acidification pretreatment is the best;when the diameter of carbon nanotubes is >50 nm,the hydrogenation performance of the catalyst is the best;when the diameter is about 10-20 nm,the catalyst has the highest reaction temperature window of 34 °C;the optimum heat treatment temperature of the catalyst is 600 °C;the addition of Ag improved the selectivity and stability of the catalyst;the catalyst exhibited the best hydrogenation performance when the Pd-Ag ratio is about 2:1.That provided a basis for the study of subsequent kinetics.Simultaneously,using industrial catalyst PEC-21 as research object,the internal circulation non-gradient reactor was used for the kinetic experiment to simulate the selective hydrogenation of industrial acetylene.Through calculation and analysis with Matlab,simulation verification with Aspen Plus,the kinetic model was established according to the optimization mechanism of acetylene selective hydrogenation,and the kinetic parameters suitable for the model were fitted.The reactor inlet temperature,CO content and space velocity analysis were carried out based on the kinetic model for selective hydrogenation of acetylene.The simulation results show that in order to achieve 60% conversion of acetylene in the first stage reactor,the reactor feed temperature is65.49 °C,and the selectivity of ethylene is 80.57%.When the total conversion of acetylene in the second stage reactor reaches 95%,the reactor feed temperature is 70.38 °C,and the selectivity of ethylene is67.89%.The third stage reactor outlet acetylene content is less than 1ppm,the reactor feed temperature should be controlled to 70.93 °C,and the selectivity of ethylene is 50.57%.The increase of CO content causes the conversion of acetylene decreasing,while the selectivity of ethylene increasing.The increase of space velocity causes the conversion of acetylene decreasing,while the selectivity of ethylene increasing.The kinetics of the Pd-Ag/CNTs catalyst was investigating by the same method.The best kinetic parameters were obtained and the kinetic analysis was performed.Compared to PEC-21,it is found that when the conversion of acetylene on Pd-Ag/CNTs in the frist stage reactor is about60%,the selectivity of ethylene is increased by 7.52% and its conversion of MAPD is increased by 40.39%;when the total conversion of acetylene on Pd-Ag/CNTs in the second stage reactor reaches 95%,the selectivity of ethylene is increased by 3.56% and its conversion of MAPD is increased by 19.11%;when the third stage reactor outlet acetylene content is less than 1 ppm,the selectivity of ethylene is increased by14.53% and its conversion of MAPD is increased by 9.44%.