SELECTIVE HYDRATION OF ISOBUTENE IN MIXED BUTENES BY USING CONCENTRATED AQUEOUS-SOLUTION OF HETEROPOLYACIDS AS CATALYSTS

The authors found that a concentrated aqueous solution of a heteropolyacid (20~80 wt%) exhibits specific functions as a catalyst. The concentrated aqueous solution of a heteropolyacid has been commercially applied for the novel process : the selective hydration of isobutene in mixed butenes to t-butyl alcohol (TBA). In a concentrated aqueous solution of a heteropolyacid, isobutene is selectively (99. 9%) hydrated to TBA at below 80°C (Fig. 7) without hydration of 1- and 2-butenes (Fig. 8) and dimerization of isobutene (Fig. 9), and the hydration rate of isobutene is about 8 times faster than in an aqueous mineral acid solution (Fig. 1). When a dilute aqueous solution of a heteropolyacid or an aqueous mineral acid solution is used for the hydration of isobutene in mixed butenes, neither high selectivity nor high activity of the isobutene hydration has been observed. The specific functions as a catalyst of the aqueous concentrated solution of a heteropolyacid have been investigated. The study on the kinetics of the selective hydration of isobutene in mixed butenes has suggested that the high activity and the high selectivity of the isobutene hydration can be attributed to the predominant coordination of isobutene and H2O to a he-teropolyanion, among isobutene, 1-butene and H2O (Fig. 10). The authors have found that heteropolymolybdic acids in a concentrated aqueous solution (10 wt% or more) tend to decompose in the reaction conditions to precipitate MoO3.H2O, MoO3 or their mixtures (Fig. 11). The study of the hydrolytic decomposition mechanism of 12-molybdophosphoric acid (PMo12) on heating by 31P-NMR spectroscopy and Raman spectroscopy revealed that PMo12 is stabilized by the combination of additon of a small amount of H3PO4, a slight reduction of the heteropolyanion and an addition of an oxygen-containing substrate such as 2-butyl alcohol and tetrahydrofuran, without causing any deterioration of the catalyst activity. © 1990, The Chemical Society of Japan. All rights reserved.