Isobutane Alkylation with Butenes and the Oligomerization of C4 Olefins in Supercritical Reagents

The competing reactions of isobutane alkylation with butenes and butene oligomerization under supercritical and ordinary gas-liquid conditions are studied over a variety of catalysts: sulfated zirconia, titania-supported heteropolyacids and tungstia, and chlorinated aluminum-platinum catalyst. Both reactions proceed rapidly, showing no substantial decrease in catalytic activity, under supercritical conditions at 140–165° C and 40–45 atm. By contrast, alkylation and oligomerization in the liquid phase and particularly in the gas phase are accompanied by a rapid deactivation of the catalyst. Passing from ordinary gas-liquid conditions to supercritical conditions dramatically accelerates the reaction and the regeneration of the deactivated catalyst. Reaction selectivity depends significantly on the isobutane/olefins (butenes) (I/Ol) ratio in the initial mixture. At I/Ol = 14, isobutane alkylation with butenes is the main reaction pathway, which results in the complete conversion of the butenes to C₈ alkylation products. The yield of saturated isoalkanes is as high as 70%. Reducing the I/Ol ratio to 0.5 results in the domination of butenes over alkylation.