EXTENDED ALKYLATE PRODUCTION ACTIVITY DURING FIXED-BED SUPERCRITICAL 1-BUTENE ISOBUTANE ALKYLATION ON SOLID ACID CATALYSTS USING CARBON-DIOXIDE AS A DILUENT/

Employing a molar excess of carbon dioxide (P-c = 71.8 bar; T-c = 31.1 degrees C), supercritical 1-butene/ isobutane alkylation is performed at temperatures lower than the critical temperature of isobutane (<13 5 degrees C), resulting in virtually steady alkylate (trimethylpentane s and dimethylhexanes) production on both microporous zeolitic (H-USY) and mesoporous solid acid (sulfated zirconia) catalysts for experimen tal 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 degrees 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 mitigat e coking and thereby to maintain better pore accessibilities is also e vident from the narrow product spectrum (confined to C-8's), the light er color of the spent catalyst samples, and relatively low surface-are a and pore-volume losses (<25%) in the spent catalysts. For identical weight hourly l-butene space-velocity and feed isobutane/olefin. ratio s, the alkylate formation declines continuously with time when the rea ction is carried out without employing carbon dioxide. At the high tem peratures (>135 degrees C) required for supercritical operation withou t carbon dioxide, cracking and coking reactions are dominant as inferr ed from the rather wide product spectrum and extensive surface area/po re volume losses (up to 90%) in the spent catalysts. The carbon dioxid e based, fixed-bed, solid acid alkylation process shows promise as an environmentally safer alternative to conventional alkylation that empl oys liquid acids.