Liquid phase synthesis of MTBE from methanol and isobutene over acid zeolites and amberlyst-15

The liquid phase synthesis of methyl tert-butyl ether (MTBE) from methanol and isobutene over II-Beta and US-Y zeolite catalysts was studied in the te mperature range 30-120 degrees C. Up to 100 degrees C, commercial II-Beta z eolite samples with small crystal size were more active than acid Amberlyst -15 (reference catalyst) and noticeably more active than US-Y, confirming r esults obtained under vapour phase conditions. The influence of methanol/is obutene (MeOH/IB) molar ratio, pressure, and space time on the conversion a nd MTBE selectivity was investigated. At optimized reaction conditions, MTB E yields of 85-90% can be reached with zeolite Ii-Beta as well as Amberlyst -15. On zeolites, side reactions of isobutene are more important than on Am berlyst-15, necessitating operation at MeOH/IB ratios higher than 1:1. For the same reason, at high conversion on Ii-Beta, the MTBE yields are more se nsitive to contact time compared to Amberlyst-15. On II-Beta zeolite, no de activation was observed during a period of more than 50 h on stream at 65 d egrees C, 1.4 MPa pressure, and a WHSV of 14 h(-1). The catalytic activity of the zeolites is related to the external specific surface area, and to th e concentration of bridging hydroxyls and silanol groups in the mesopores. A zeolite H-Beta sample with a Si/Al ratio of 36 has an optimum silanol and bridging hydroxyl content leading to stoichiometric methanol and isobutene adsorption, highest activity and MTBE yields. (C) 1999 Academic Press.