On the mechanism of catalyzed isobutane/butene alkylation by zeolites

Well-characterized examples of the large-pore zeolites X and Y in their acidic form were explored as catalysts for isobutane/butene alkylation in order to understand the principal requirements for successful solid acid catalysts. The materials were tested in a continuously operated stirred tank reactor under industrially relevant conditions. A high ratio of Brønsted to Lewis acid sites and a high concentration of strong Brønsted acid sites are seen to cause high hydride transfer activity and are mandatory for long catalyst life. Isobutane "self-alkylation" activity is higher in catalysts with a high hydride transfer activity. The catalyst lifetime is very sensitive with respect to the reaction temperature reaching the optimum between 70 and 80°C concurrent with a maximum in self-alkylation activity. The lifetimes were found to be correlated linearly with the reciprocal of the olefin space velocity, while it hardly influenced the total productivity of the catalysts. The selectivities on the other hand strongly depended on the butene feed rate per active site.