Selective and efficient dimerization of isobutene over H3PO4/activated carbon catalysts

Abstract

Dimerization of isobutene to branched C8 olefins (precursors of high octane gasoline additives) was performed over eco-friendly activated carbon catalysts impregnated with phosphoric acid, under continuous gas phase operating conditions. A series of catalysts differing in phosphoric acid loading were prepared by incipient wetness impregnation and tested in the reaction carried out at various temperatures (100–260°C), with the use of an isobutene/isobutane mixture at a molar ratio of 4:1 as a feedstock. The conversion and selectivity patterns obtained for a selected sample evolved visibly with the reaction temperature and the best results were obtained at 180°C. The effect of phosphoric acid loading on the catalytic activity of the samples at this temperature was investigated and discussed. For the sake of comparison also other acidic activated carbons and the commercially available catalyst Amberlyst 15 were tested. The high H3PO4-loaded materials exhibited excellent catalytic performance in the process (high isobutene conversion, good selectivity to C8 products and high catalyst stability) which was assigned to a combination of acidic and textural properties of the materials obtained.