Many catalytic routes, both heterogeneous and homogeneous, have been demonstrated for conversion of synthesis gas into ethanol. However, to become economically viable for production of commodity chemicals such fuel ethanol, yields will likely need to approach 100%, as is the case in the conversion of synthesis gas into methanol using heterogeneous catalysis and in the industrial homogeneously-catalyzed reaction between methanol and CO to form acetic acid. Despite considerable effort, methods employing heterogeneous catalysts for manufacture of fuel ethanol from syngas have not yet been commercialized, in part due to co-production of numerous side-products and especially low-value methane, which can consume 10 to over 30 mol% of the CO in the syngas. In contrast, homogeneous catalysts formed in solution and consisting of identical single-atom coordination compounds or small cluster compounds of non-volatile carbonyl anions show inherently high selectivity relative to heterogeneous catalysts. Using homogeneous catalysts operating at 220�C, a rate of ethanol production of 0.26 g ethanol/ g metal catalyst/ h has been achieved, which is comparable on a metals basis to some of the best heterogeneous catalysts reported, but with CO losses to methane reduced to about 1 mol%. The homogeneous catalysts also convert methanol into ethanol by the well-established homologation reaction: CH3OH + CO + H2 = CH3CH2OH. From small quantities of additional intermediates detected, one step involves CO insertion, identical to that in the industrial production of acetic acid: CH3OH + CO  = CH3CO OH. In the presence of excess methanol, the acetic acid rapidly reacts to form methyl acetate, which is reduced to ethanol and methanol by hydrogen in the syngas: CH3COOCH3 + 2H2 = CH3CH2OH + CH3OH.  Methanol is re-cycled.  Precedence exists for industrial use of homogeneous catalysts in hydroformylation and synthesis of acetic acid.  Acknowledgement:  U.S. Department of Energy, Office of Science, Contract: DE-SC0004376.

Homologation of methanol for production of ethanol using homogeneous catalysis

246th National Meeting (2013)

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