ABSTRACT
Abstract Selective tertiary-butanol (tBA) dehydration to isobutylene has been demonstrated using a pressurized reactive distillation unit under mild conditions, wherein the reactive distillation section includes a bed of formed solid acid catalyst. Quantitative tBA conversion levels (>99%) have been achieved at significantly lower temperatures (50-120oC) than are normally necessary using vapor-phase, fixed-bed, reactors (ca. 300oC) or CSTR configurations. Substantially anhydrous isobutylene is thereby separated from the aqueous co-product, as a light distillation fraction. Even when employing crude tBA feedstocks, the isobutylene product is recovered in ca. 94% purity and 95 mole% selectivity. Introduction There has been an enormous technological interest in tertiary-butanol (tBA) dehydration during the past thirty years, first as a primary route to methyl tert-butyl ether (MTBE) (1) and more recently for the production of isooctane and polyisobutylene (2). A number of commercializable processes have been developed for isobutylene manufacture (eq 1) in both the USA and Japan (3,4). These processes typically involve either vapor-phase tBA dehydration over a silicaalumina catalyst at 260-370oC, or liquid-phase processing utilizing either homogenous (sulfonic acid), or solid acid catalysis (e.g. acidic cationic resins). More recently, tBA dehydration has been examined using silica-supported heteropoly acids (5), montmorillonite clays (6), titanosilicates (7), as well as the use of compressed liquid water (8). (CH3)3C−OH → (CH3)2C=CH2 + H2O (1) In this research initiative, we have examined the potential of reactive distillation (9) for tertiary-butanol dehydration to isobutylene using solid acid catalysis. Advantages to employing reactive distillation for reaction (1) include: a) the mild operating conditions required (<120oC), b) quantitative tBA conversions per pass, and c) the option to use lower purity/lower cost, tBA feedstocks.
