New Lewis Acid Catalyzed Pathway to Carbon-Carbon Bonds from Methanol.

The methanol to hydrocarbon process, discovered about 40 years ago, uses zeolites to catalyze the shape selective conversion of methanol to a mixture of hydrocarbons. It has recently gained very much interest, as it allows the conversion of fossil and renewable carbon sources, via synthesis gas and methanol, to a mixture of hydrocarbons. The composition of this hydrocarbon mixture may range from being rich in aromatic molecules, which can be blended in high-octane gasoline, to being very rich in propene and ethene. One of the attractive features of this process route lies in the fact that, by adjusting the operation conditions without changing the zeolite, very different product distributions can be obtained. The product selectivity is determined by two interlinked catalytic cycles, which are based on aromatic as well as on olefinic intermediates. The zeolite acts as shape selective catalyst, which retains aromatic molecules larger than trior tetramethylbenzenes. Once a steady state of hydrocarbons in the zeolite pores is established, the overall catalysis has been well explored over the past decade. A large number of theories, however, have been proposed as to how these hydrocarbon species in the zeolite pores are initially formed, i.e., how the first carbon– carbon bonds are formed, but have been discarded again when tested thoroughly. At present, the most likely start of this methanol to hydrocarbon chemistry has been attributed to impurities of larger olefins or alcohols in the methanol stream, which are alkylated and cracked in the course of establishing a steady state “carbon pool”.