Application of a forced-flow catalytic membrane reactor for the dimerisation of isobutene

A forced-flow catalytic membrane reactor was applied for dimerisation of isobutene to isooctene. Several catalysts, such as silica supported Nafion® (Nafion® SAC-13), Nafion® NR50, Amberlyst™ 15, and silica supported phosphotungstic acid were mixed in solution with a polymeric binder. Teflon® AF, Hyflon® AD, polytrimethylsilylpropyne, and polydimethylsiloxane (PDMS) were applied as binder to form a porous, reactive layer on top of a porous, polymeric, supporting membrane. An optional intermediate PDMS film acted as flow regulator and enabled selective product removal. Isobutene was fed to the reactive membrane, the reaction started immediately and a pressure of around 4 bar built-up on the feed side. Liquid product was collected on the permeate side in an iced trap. Depending on the type of binder high conversions up to 98% at 22% selectivity to isooctene (binder = Hyflon® AD) and space velocity of 530 gi−C4/gcat h, or high selectivities of >80% at 45% conversion of isobutene and space velocity of 275 gi−C4/gcat h (binder = Teflon® AF) were achieved. Catalyst poisoning was not observed during operation for at least 1 week.