Gas phase hydration of isobutene to tert-butyl alcohol on H 4SiW 12O 40 as the catalyst

Abstract

Catalytic hydration of isobutene in gas phase on solid dodecatungstophosphoric acid has been studied at 313–353 K in a constant flow microreactor. Besides the main product tert-butyl alcohol (TBA) the isobutene dimer was detected in the gas phase the concentration of which increased with the space time and decreased with temperature. Selectivity to TBA was 40–80% depending on the conditions. The rate of isobutene conversion reached maximum at 328 K. Separate sorption experiments have shown that water vapour is rapidly sorbed by the whole volume of the catalyst while there is no such sorption of isobutene, which is adsorbed only on the surface. Based on these results qualitative model of the reaction pattern was proposed including the formation of carbenium ions on the surface. Subsequently they would react with water molecules supplied from the bulk of the catalyst. The latter is also the source of protons bonded by isobutene molecules.