Cumene cracking over aluminum-deficient large-port mordenites

Abstract

Cumene cracking activities have been measured over a series of acid-leached, large-port hydrogen-exchanged mordenites ranging in alumina content (on anhydrous basis) from 11.2% (commercial H ex-mordenite) to 0.1% Al 2O 3 at both differential and integral conversions. Although elemental and morphological analyses of the latter material have previously shown it to be of silicic acid composition with a mordenite crystal structure, sufficient Brönsted acid exchange sites remain to produce an active catalyst. Differential conversion results, which are considered more representative of intrinsic cracking activity than those at integral conversion, showed the 0.1% Al 2O 3 content mordenite to be less active, however, than 1.4, 1.9, and 11.2% alumina catalysts, a fact which is interpreted to mean that Brönsted acid sites are counted either by cracking activities or alumina content in the 0.1 to 1% Al 2O 3 region. At integral conversions, the initial cracking activity of the 0.1% Al 2O 3 catalyst approached that of H ex-mordenite, a phenomenon attributed to a limitation on conversion imposed by the rate of mass transfer to the surface of the catalysts. However, in all cases, the 0.1% alumina mordenite had a much lower rate of activity decline than H ex-mordenite and, after a short time on-stream at integral conversion levels, the low alumina material was the more active catalyst. Although the essential nature of the center of catalytic activity, i.e., the Brönsted acid site, did not change as a result of the drastic quantity of alumina removed, the lower density of acid sites in the lowest alumina catalyst reduced the rate of Brönsted catalyzed condensation to higher molecular weight species (capable of blocking micropores) relative to the rate of desorption of these compounds. Helping in this direction of lower fouling rate would be the enhancement of desorption of heavy products as a result of the acid treatment having opened the pore structure.