CONVERSION OF METHANOL AND ISOBUTANOL TO MTBE

Over the resin catalyst Amberlyst 15, and under our reaction condition s, the yield of MTBE (methyl tert-butyl ether), from the reaction of m ethanol and isobutene, is at a maximum in the temperature rang of 40-6 0-degrees-C. Slightly higher temperatures (70-90-degrees-C) are needed when using zeolite H-ZSM-5 as catalyst for the etherification reactio n. When isobutanol and methanol are passed over these catalysts at tem peratures below 100-degrees-C, extremely low conversions (<1% by mass) are obtained. Over the resin catalyst and at 121-degrees-C, 3.3% of M TBE+MIBE (methyl isobutyl ether) is obtained where MTBE:MIBE = 1:7.4. Since the initial rate of the etherification reaction has been shown t o be first order in the alkene, we investigated the dehydration reacti on of isobutanol over H-ZSM-5. It was found that this reaction proceed s at temperatures above 150-degrees-C, indicating that the formation o f the butenes from isobutanol proceeds at a higher temperature than th e etherification reaction. Furthermore, our results with Amberlyst 15 show that the resin catalyst is unable to catalyze the isobutanol dehy dration reaction within its recommended usable temperature range. A tw o-reactor system was therefore employed to implement the overall catal ytic conversion of methanol and isobutanol to MTBE. For the dehydratio n step we employed a silica-alumina catalyst at 225-degrees-C, since t his catalyst exhibits a higher dehydration activity for isobutanol tha n for methanol, as compared with gamma-alumina and H-ZSM-5. The produc t stream from the dehydration step was then fed to reactor 2 which was loaded with the Amberlyst 15 catalyst maintained at 50-degrees-C. The two-reactor system produced a significantly higher yield of MTBE+MIBE (2 7.8%), with the MTBE:MIBE ratio being reversed to 11.7:1.