(36c) Kinetic Studies of Liquid Phase Ethylene Production By Hydrogenation of Acetylene Using a Selective Solvent in a Basket Reactor

Ethylene is the simplest of the olefins and a primary building block in petrochemical industries. It is produced mainly by steam cracking of naphtha with acetylene as the byproduct in the cracker effluent. Small traces of acetylene can deactivate the catalyst used in the polymerization of ethylene to manufacture polyethylene and other valuable products. Although acetylene can be absorbed from the gas mixture, it is more beneficial to selectively hydrogenate the acetylene to ethylene. Selective hydrogenation of acetylene to ethylene using supported catalysts in gas phase mostly leads to thermal runaway. Recently, liquid phase hydrogenation of acetylene has been developed as it reduces the risks of runaway conditions as the liquid phase itself acts as a heat transfer medium. The liquid phase reduces the formation of green oil due to oligomerization on the catalyst thereby improving the catalyst stability. This proposed study is novel as only the gas phase hydrogenation kinetics has been investigated as found in the open literature. The kinetics of selective hydrogenation of acetylene in the liquid phase over Pd/Al₂O₃ catalyst was investigated in a 300 mL stirred-tank basket reactor. Since acetylene is highly soluble in polar solvents, N-methyl pyrrolidone was used in our studies to selectively absorb acetylene from the gas mixture hydrogenating it to ethylene over Pd/Al₂O₃ catalyst. The reactor was operated at a temperature range of 80-120 ^oC under a pressure range of 200-250 psig. The liquid phase was operated in batch mode while the gas phase was continuous. A kinetic model was developed and fitted on simple power law equations and Langmuir-Hinshelwood-Hougen-Watson approach. The predictions of these approaches on the acetylene conversion was compared. The surface reaction between the adsorbed species was assumed to be the rate controlling step. The parameters studied to understand the liquid phase kinetics were temperature, H₂:C₂H₂ feed ratio, catalyst loading and operating pressure. The sensitivity of the variation of different parameters on the conversion was also studied. The results and discussions from this investigation are in progress and will be presented in the conference.