CONVERSION OF METHANOL AND ISOBUTANOL TO MTBE

Over the resin catalyst Amberlyst 15, and under our reaction conditions, the yield of MTBE (methyl tert-butyl ether), from the reaction of methanol and isobutene, is at a maximum in the temperature rang of 40-60-degrees-C. Slightly higher temperatures (70-90-degrees-C) are needed when using zeolite H-ZSM-5 as catalyst for the etherification reaction. When isobutanol and methanol are passed over these catalysts at temperatures below 100-degrees-C, extremely low conversions (<1% by mass) are obtained. Over the resin catalyst and at 121-degrees-C, 3.3% of MTBE+MIBE (methyl isobutyl ether) is obtained where MTBE:MIBE = 1:7.4. Since the initial rate of the etherification reaction has been shown to be first order in the alkene, we investigated the dehydration reaction of isobutanol over H-ZSM-5. It was found that this reaction proceeds at temperatures above 150-degrees-C, indicating that the formation of the butenes from isobutanol proceeds at a higher temperature than the etherification reaction. Furthermore, our results with Amberlyst 15 show that the resin catalyst is unable to catalyze the isobutanol dehydration reaction within its recommended usable temperature range. A two-reactor system was therefore employed to implement the overall catalytic conversion of methanol and isobutanol to MTBE. For the dehydration step we employed a silica-alumina catalyst at 225-degrees-C, since this catalyst exhibits a higher dehydration activity for isobutanol than for methanol, as compared with gamma-alumina and H-ZSM-5. The product 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.