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Integration of chemical catalysis with extractive fermentation to produce fuels


Nearly one hundred years ago, the fermentative production of acetone by Clostridium acetobutylicum provided a crucial alternative source of this solvent for manufacture of the explosive cordite. Today there is a resurgence of interest in solventogenic Clostridium species to produce n-butanol and ethanol for use as renewable alternative transportation fuels1,2,3. Acetone, a product of acetone–n-butanol–ethanol (ABE) fermentation, harbours a nucleophilic α-carbon, which is amenable to C–C bond formation with the electrophilic alcohols produced in ABE fermentation. This functionality can be used to form higher-molecular-mass hydrocarbons similar to those found in current jet and diesel fuels. Here we describe the integration of biological and chemocatalytic routes to convert ABE fermentation products efficiently into ketones by a palladium-catalysed alkylation. Tuning of the reaction conditions permits the production of either petrol or jet and diesel precursors. Glyceryl tributyrate was used for the in situ selective extraction of both acetone and alcohols to enable the simple integration of ABE fermentation and chemical catalysis, while reducing the energy demand of the overall process. This process provides a means to selectively produce petrol, jet and diesel blend stocks from lignocellulosic and cane sugars at yields near their theoretical maxima.

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Figure 1
Figure 2: Product distribution in Pd-catalysed alkylation as a function of reaction parameters and time course.
Figure 3
Figure 4: Block flow diagram for integration of ABE fermentation with chemical catalysis.

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We are grateful to H.-J. Song for performing initial experiments on the catalytic alkylation of acetone, and V. Mitchell for analysing acid pretreatment hydrolysate inhibitors present in Miscanthus giganteus. F.D.T. and E.G. acknowledge funding from the Director, Office of Science of the US Department of Energy, under contract no. DE-AC02-05CH11231. This work was funded by the Energy Biosciences Institute.

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Z.C.B. and P.A. contributed equally to this work. P.A. and S.S. performed experiments on the chemical catalysts, and E.G. performed experiments in the flow reactor. Z.C.B. optimized the fermentation and extractive processes. All authors contributed to the conception of the experiments, discussion of the results and preparation of manuscript.

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Correspondence to F. Dean Toste.

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The authors declare no competing financial interests.

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Anbarasan, P., Baer, Z., Sreekumar, S. et al. Integration of chemical catalysis with extractive fermentation to produce fuels. Nature 491, 235–239 (2012).

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