Isobutene oligomerization on MCM-41-supported tungstophosphoric acid

Abstract

Oligomerization offers a broad potential for converting light olefins into liquid fuels. Here, tungstophosphoric acid, TPA, was impregnated on a mesoporous silica support, MCM-41, at varying loadings from 1 to 90 wt%. The IR and XRD results indicated the presence of interactions between the TPA clusters and MCM-41, especially at loadings below 50 wt%. These interactions led to variations in acid site density and their corresponding strength as evidenced by the results of temperature programmed desorption of ammonia measurements. Consequences of these changes were investigated on isobutene oligomerization. Results obtained at 393 K and 15 bar indicated that the TPA/MCM-41 catalysts provide more than 75 wt% isobutene conversions at a weight hourly space velocity (WHSV) of 46 h−1. Results further showed that the catalysts were more selective towards distillate range products especially at very low TPA loadings. The relative selectivity of trimers over dimers in the oligomerization product pool was approximately four at a TPA loading of 1 wt% and it decreased to 1.5 with increasing TPA loading. Ruling out the presence of any strong correlations between acid strength and catalytic performance, the data presented a strong dependence of the product selectivity on the availability and vicinity of the acid sites.