Direct conversion of ethene to isobutene using a combination of Ni-loaded amorphous silica-alumina and ferrierite zeolite catalysts

Abstract

Direct conversion of ethene to isobutene was studied by combining heterogeneous catalysts for ethene dimerization and skeletal isomerization of normal butene. NiO/SiO₂-Al₂O₃ and zeolite were simultaneously loaded to a flow reactor in separate layers, and the conversion of ethene was performed at 300 ℃. Reaction using NiO/SiO₂-Al₂O₃ alone produced normal butene predominantly, and isobutene selectivity was low at 1 %. However, introduction of zeolite into the lower catalyst phase greatly enhanced isobutene selectivity. The crystal structure and SiO₂/Al₂O₃ ratio of zeolite had marked influences on isobutene selectivity, and ferrierite with a moderate amount of acid sites was most effective. The activity of ferrierite was further increased by ion-exchange with metal ions such as Fe, which enhanced not only isobutene selectivity but also catalyst durability. Effects of the reaction conditions were also studied, with the optimal setup affording isobutene at a selectivity of 31 %, which is the highest selectivity reported to date.