Extended Alkylate Production Activity during Fixed-Bed Supercritical 1-Butene/Isobutane Alkylation on Solid Acid Catalysts Using Carbon Dioxide as a Diluent

Abstract

Employing a molar excess of carbon dioxide (Pc = 71.8 bar; Tc = 31.1 °C), supercritical 1-butene/isobutane alkylation is performed at temperatures lower than the critical temperature of isobutane (<135 °C), resulting in virtually steady alkylate (trimethylpentanes and dimethylhexanes) production on both microporous zeolitic (H−USY) and mesoporous solid acid (sulfated zirconia) catalysts for experimental durations of up to nearly 2 days. At a space velocity of 0.25 g of 1-butene/g of catalyst/h, a feed CO2/isobutane/olefin ratio of 86:8:1, 50 °C, and 155 bar, roughly 5% alkylate yield (alkylates/C5+) and 20% butenes conversion are observed at steady state. The ability of the carbon dioxide based supercritical reaction mixtures to mitigate coking and thereby to maintain better pore accessibilities is also evident from the narrow product spectrum (confined to C8's), the lighter color of the spent catalyst samples, and relatively low surface-area and pore-volume losses (<25%) in the spent catalysts. For ident...