Dimerisation of Isobutene on Acidic Ion-exchange Resins

Dimerisation of isobutene produces diisobutenes that can be hydrogenated to isooctane (2,2,4-trimethyl pentane). Isooctane can be used as a high octane gasoline component. The aim of this work was to study the selective production of diisobutenes through the dimerisation of isobutene on ion-exchange resin catalysts and to construct kinetic models for the reactions in the system for reactor design purposes. High selectivities for diisobutenes were obtained in the presence of polar components such as methanol and tert -butyl alcohol (TBA). The effects of these polar components were found to be basically the same, i.e. the selectivity for diisobutenes increases with the content of the polar component while the activity of the catalyst decreases. Because TBA does not react with isobutene and because small amounts are sufficient to obtain high selectivities, TBA was concluded to be a good selectivity-enhancing component and was used in further studies of the system. Different ion-exchange resin structures in the dimerisation of isobutene were studied and it was observed that good accessibility to the active sites gives high isobutene conversions and medium crosslinking high selectivies for diisobutenes. When linear butenes were added to the feed of the system, they were found to react with isobutene to codimers especially at low TBA contents and at high temperatures. In these experiments some 2-butanol was formed from the linear butenes and the water from TBA dehydration.