Effect of feed composition on methanol conversion to light olefins over SAPO-34

Effects of adding ethene, propene, and water to methanol feed on conversion of methanol to olefins are investigated over SAPO-34 catalyst. When ethene is fed to the reactor along with methanol and water, selectivity to ethene decreases, but the selectivity to propene and butenes increases, When prop ene is fed with methanol and water. the selectivity to propene decreases bu t increases to ethene and butenes. An analysis of the results indicates tha t ethene and propene react with methanol over SAPO-34 to form propene and b utenes, respectively. These reactions need stronger acidic sites than the c onversion of methanol to olefins. The presence of propene in the feed inhib its the reaction of ethene with methanol through competition for the strong er acidic sites. The addition of water to the feed with methanol results in the reduction of the rate of coke formation and aids in maximizing the sel ectivity to olefins. The optimum water content in the feed appears to be 73 -80 mol%. At this concentration, the catalyst can process more than eight t imes the amount of methanol than when feeding pure methanol prior to a decr ease in the methanol conversion < 100%. (C) 2001 Elsevier Science B.V. All rights reserved.