Effects of transport limitations on rates of acid-catalyzed alkene oligomerization

Abstract

Acid-catalyzed alkene oligomerization is often masked by artifacts of transport limitations. Implications of these limitations on turnover rates and selectivity have been assessed on zeolites with diverse frameworks (MFI, MTW, TON) and crystal sizes over a wide range of temperatures (423-573 K). Measured kinetic data, together with Weisz-Prater estimates, show that reactant diffusion limitations can prevail at high oligomerization temperatures (523-573 K). These data also suggest, through transition state theory treatments, that the zeolite structure has no significant effect on the intrinsic activation energy of oligomerization but does affect profoundly the activation entropy. Isomer speciation of oligomers reveals that the degree of branching increases with the pore diameter and decreases with diffusion limitations. The observed selectivity trends were found to be consistent with sorption transients of structurally relevant hydrocarbons.