Catalysis of Organic..

Knifton and Sanderson 46952. Selective Tertiary-ButanolDehydration to Isobutylene via ReactiveDistillation and Solid Acid CatalysisAbstractJohn F. Knifton and John R. SandersonP.O. Box 200333, Austin, TX 78720Selective tertiary-butanol (tBA) dehydration to isobutylene has been demonstratedusing a pressurized reactive distillation unit under mild conditions, wherein thereactive distillation section includes a bed of formed solid acid catalyst.Quantitative tBA conversion levels (>99%) have been achieved at significantlylower temperatures (50-120 o C) than are normally necessary using vapor-phase,fixed-bed, reactors (ca. 300 o C) or CSTR configurations. Substantially anhydrousisobutylene is thereby separated from the aqueous co-product, as a light distillationfraction. Even when employing crude tBA feedstocks, the isobutylene product isrecovered in ca. 94% purity and 95 mole% selectivity.IntroductionThere has been an enormous technological interest in tertiary-butanol (tBA)dehydration during the past thirty years, first as a primary route to methyl tert-butylether (MTBE) (1) and more recently for the production of isooctane andpolyisobutylene (2). A number of commercializable processes have been developedfor isobutylene manufacture (eq 1) in both the USA and Japan (3,4). Theseprocesses typically involve either vapor-phase tBA dehydration over a silicaaluminacatalyst at 260–370 o C, or liquid-phase processing utilizing eitherhomogenous (sulfonic acid), or solid acid catalysis (e.g. acidic cationic resins).More recently, tBA dehydration has been examined using silica-supportedheteropoly acids (5), montmorillonite clays (6), titanosilicates (7), as well as the useof compressed liquid water (8).(CH 3 ) 3 C−OH → (CH 3 ) 2 C=CH 2 + H 2 O (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 mildoperating conditions required (