Hierarchical BEA Zeolite with Trimodal Micro-/Meso-/Macroporosityas a Selective and Long-Lived Catalyst for Isobutane/2-ButeneAlkylation br

Abstract

Isobutane/butene alkylation is an important refineryprocess for producing high-octane gasoline components (e.g.,trimethylpentane), in which highly caustic liquid acids (H2SO4andHF) are still predominantly used as catalysts. Zeolites are promisingsolid acid alternatives to such liquid acids but suffer from fastdeactivation owing to the formation of bulky carbonaceous depositswithin the micropores. In this study, a series of BEA zeolites withdifferent secondary pore structures were synthesized to investigatethe effects of facilitated molecular transport on trimethylpentaneselectivity and catalyst deactivation. The results showed that thehierarchical BEA zeolite containing trimodal micro-/meso-/macro-porosity synthesized by the pseudo-solid-state crystallization ofdiatomaceous earth exhibited significantly enhanced selectivity totrimethylpentane and catalytic lifetime. The highly promising catalytic properties of this zeolite could be attributed to enhanceddiffusion of the hydride donor (isobutane) and bulky alkylate products to or from the zeolite micropores owing to the hierarchicalpore structure. Upon supporting Pt, all zeolite catalysts could be efficiently regenerated by a hydrogenative treatment as long as theywere regenerated before heavy coke formation. The hierarchical BEA zeolite with trimodal porosity required four times less frequentregeneration than an ordinary BEA zeolite containing only micropores. The remarkable catalytic performance of the hierarchicalBEA zeolite will greatly contribute to the reduction of the operating costs of solid-acid-based alkylation processes.