The influence of acidity on zeolite H-BEA catalyzed isobutane/n-butene alkylation

Abstract

The influence of the concentration of acid sites for isobutane/n-butene alkylation on zeolite BEA with varying degrees of Na+ ion exchange is reported. All catalysts studied showed complete n-butene conversion over a significant time-on-stream. Isooctanes were the dominating products over H-BEA, while the importance of di- and multiple alkylation increased with increasing Na+ concentration in the zeolite. In parallel, the integral number of turnovers per catalytic site markedly decreased. The acid site deactivation is affiliated with blocking by hexadecane species. The higher rate of catalyst deactivation with increasing degree of Na+ exchange is thus attributed to the increase in the probability of having a further butene molecule added to a C8 alkoxy group in place of undergoing hydride transfer from isobutane to desorb as isooctane. This is a direct result of the decreasing concentration of alkoxy groups that can react with n-butene while maintaining the same rate of olefin transport through the pores. Addition of a strong hydride donor/acceptor molecule (adamantane) indicates that the product composition of the isooctane isomers is determined by their lifetime as alkoxy groups. The longer the lifetime before experiencing hydride transfer, the closer the product composition approaches the chemical equilibrium.