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Catalysis Looks to the Future
whereas heavier olefins in the C14-C17 range are used in the preparation of detergent alcohols via hydroformylation. The preparation of yet heavier olefins by catalytic dehydrogenation is also possible for specialized applications, including the manufacture of synthetic lubricating oils and oil additives. Worth noting at this point is the recent introduction of solid (heterogeneous) acid catalysts for the alkylation of benzene with heavy olefins in the production of LAB; this will allow the replacement of traditional catalysts, such as hydrogen fluoride (HF) or aluminum chloride (AlCl3) used for this purpose and will thus avoid the operational hazards associated with the handling and processing of corrosive catalysts and ameliorate the environmental characteristics of this alkylation process.
C1 chemistry (i.e., chemical processes based on carbon monoxide, carbon dioxide, or methanol as the starting material) now provides another interesting arena for feedstock-driven innovations in industrial catalysis. After the oil embargo of 1973, there was an extensive worldwide effort to pursue C1 chemistry for the production of chemicals as well as fuels. This effort eventually subsided when it appeared that the cost of carbon from C1 sources such as coal and natural gas could not really compete effectively with its cost from petroleum-based sources, even at the much inflated prices of the latter. However, it appears that some significant changes have occurred in the past decade (before Iraq invaded Kuwait) and that the opportunities for making chemicals via C1 chemistry should be revisited. In particular, methanol should be considered as a feedstock. Figure 2.2 illustrates the historical and forecasted trends between 1955 and 1998 for the ratio of methanol to ethylene prices. A substantial downward trend in favor of methanol can be observed.
It has recently been reported that rhodium-based homogeneous catalysts promote the reductive carbonylation of methanol to acetaldehyde at selectivities approaching 90% and at much lower pressure than required for prior-art catalysts. With the addition of ruthenium as co-catalyst, it is possible to achieve in situ reduction of acetaldehyde to ethanol, thus providing a new catalyst system for the homologation of methanol to ethanol.
One great challenge for catalysis has been the possibility of producing ethylene glycol via the oxidative coupling of methanol rather than the standard process based on ethylene as feedstock. Significant progress has been made recently in the catalytic oxidative dimerization of dimethyl ether to dimethoxyethane. Dimethoxyethane, in turn, should be hydrolyzable to ethylene glycol. Unlike methane coupling, which requires a temperature in excess of 600° C, the oxidative coupling of dimethyl ether proceeds at about 200° C with a mixed magnesium-tin oxide catalyst. By use of the ether rather than methanol, protection against side reactions has been achieved. These results are an extremely interesting lead which, coupled with the favorable trends in methanol pricing, could pave the way to another major