THE INFLUENCE OF ACIDITY ON ZEOLITE H-BEA CATALYZED ISOBUTANE N-BUTENE ALKYLATION/

The influence of the concentration of acid sites for isobutane/n-buten e alkylation on zeolite BEA with varying degrees of Na+ ion exchange i s reported. All catalysts studied showed complete n-butene conversion over a significant time-on-stream. Isooctanes were the dominating prod ucts over H-BEA, while the importance of di- and multiple alkylation i ncreased with increasing Na+ concentration in the zeolite. In parallel , the integral number of turnovers per catalytic site markedly decreas ed. The acid site deactivation is affiliated with blocking by hexadeca ne species. The higher rate of catalyst deactivation with increasing d egree of Na+ exchange is thus attributed to the increase in the probab ility of having a further butene molecule added to a C-8 alkoxy group in place of undergoing hydride transfer from isobutane to desorb as is ooctane. This is a direct result of the decreasing concentration of al koxy groups that can react with n-butene while maintaining the same ra te of olefin transport through the pores. Addition of a strong hydride donor/acceptor molecule (adamantane) indicates that the product compo sition of the isooctane isomers is determined by their lifetime as alk oxy groups. The longer the lifetime before experiencing hydride transf er, the closer the product composition approaches the chemical equilib rium. (C) 1998 Elsevier Science B.V. All rights reserved.