Production of methyl tert-butyl ether (MTBE) over MFI-type zeolites synthesized by the rapid crystallization method and modified by varying Si/Al ratio and steaming

The reaction of isobutene and methanol to produce methyl tert-butyl ether (MTBE) has been studied over MFI-type zeolites (ZSM-5) with varying Si/Al ratios. All the zeolites were synthesized by the rapid crystallization method, The number of Bronsted acid sites on the zeolite surface have been shown to increase proportionally with the aluminum contents of the zeolites. Under kinetically limited reaction conditions, the activity of the catalysts increased with number of acid sites. However near reaction equilibrium, the rate of increase of catalyst activity slowed down. The maximum activity was achieved at 80 degrees C which was an optimum temperature considering the catalyst activity and equilibrium conversion. Mild steaming caused a modest increase in isobutene conversion which was close to equilibrium conditions. On the other hand, severe steaming resulted in a decrease in activity. The effect of steaming was best attributed to new adsorption sites and/or enhanced Bronsted acidity. The zeolite gave a stable performance in an extended test up to at least 30 h on Stream. All the catalysts tested displayed 100% selectivity for the production of MTBE at all the reaction conditions studied. (C) 1997 Elsevier Science B.V.