ELEMENTARY MECHANISTIC STEPS AND THE INFLUENCE OF PROCESS VARIABLES IN ISOBUTANE ALKYLATION OVER H-BEA

Liquid phase conversion of n-butene in excess iso-butane was investiga ted over zeolite BEA as catalyst in a continuously operated slurry rea ctor. Single and multiple alkylation and cracking were the main reacti on pathways. Only saturated products were observed indicating that hyd ride transfer reactions were fast, compared to desorption of olefins u nder the experimental conditions chosen. An optimal reaction temperatu re of 350 K was identified for single alkylation, higher reaction temp eratures favoring cracking of intermediately formed products and lower temperatures, multiple alkylation. Under optimum reaction conditions over 80 wt% butene was converted via single alkylation. The C-8 produc t selectivity is determined by the balance between isomerization of th e C-8 alkoxy and the hydride transfer to release iso-octanes from the acid sites. Once desorbed from an acid site, the alkanes do not isomer ize. Independent of the space velocities the catalyst and, hence, the individual acid sites deactivate after approximately 30 butene turnove rs at 350 EC by deposition of polyalkylates. A simplified reaction mod el for alkylation over solid acid catalysts and the implications for c atalyst design are discussed. (C) 1998 Academic Press.