A forced-flow catalytic membrane reactor was applied for dimerisation of isobutene to isooctene. Several catalysts, such as silica supported Nafion(R) (Nalion(R) SAC-13), Nafion(R) NR50, Amberlyst(TM) 15, and silica supported phosphotungstic acid were mixed in solution with a polymeric binder. Teflon(R) AF, Hyflon(R) 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(R) AD) and space velocity of 530 g(i-C4)/g(cat) h, or high selectivities of >80% at 45% conversion of isobutene and space velocity of 275 g(i-C4)/g(cat) h (binder = Teflon(R) AF) were achieved. Catalyst poisoning was not observed during operation for at least 1 week. (C) 2004 Elsevier B.V. All rights reserved.