Hierarchical BEA Zeolite with Trimodal Micro-/Meso-/Macroporosity as a Selective and Long-Lived Catalyst for Isobutane/2-Butene Alkylation

Isobutane/butene alkylation is an important refinery process for producing high-octane gasoline components (e.g., trimethylpentane), in which highly caustic liquid acids (H2SO4 and HF) are still predominantly used as catalysts. Zeolites are promising solid acid alternatives to such liquid acids but suffer from fast deactivation owing to the formation of bulky carbonaceous deposits within the micropores. In this study, a series of BEA zeolites with different secondary pore structures were synthesized to investigate the effects of facilitated molecular transport on trimethylpentane selectivity and catalyst deactivation. The results showed that the hierarchical BEA zeolite containing trimodal micro-/meso-/macroporosity synthesized by the pseudo-solid-state crystallization of diatomaceous earth exhibited significantly enhanced selectivity to trimethylpentane and catalytic lifetime. The highly promising catalytic properties of this zeolite could be attributed to enhanced diffusion of the hydride donor (isobutane) and bulky alkylate products to or from the zeolite micropores owing to the hierarchical pore structure. Upon supporting Pt, all zeolite catalysts could be efficiently regenerated by a hydrogenative treatment as long as they were regenerated before heavy coke formation. The hierarchical BEA zeolite with trimodal porosity required four times less frequent regeneration than an ordinary BEA zeolite containing only micropores. The remarkable catalytic performance of the hierarchical BEA zeolite will greatly contribute to the reduction of the operating costs of solid-acid-based alkylation processes.