Sunday, May 4, 2008
4-12

Manipulation of Multienzyme Catalysis with In-Situ Enzymatic Cofactor Regeneration for Production of Methanol from Biomass CO2

Ping Wang1, F. Suhan Baskaya1, and Michael C. Flickinger2. (1) Dept. of Bioproducts and Biosystems Engineering, University of Minnesota, St. Paul, MN 55108, (2) Microbiology; Chemcial and Biomolecular Engineering; BTEC, North Carolina State University, Centennial Campus, Campus Box 7928, Raleigh, NC 27695

Biofuels require a complete rethinking of the science and engineering for liquid fuel alternatives to ethanol.  In developing the next generation biofuels, we should consider not only alternative biomass resources, but also diversified fuel products that can afford more efficient manufacturing. This paper reports our recent study of a multienzyme synthetic pathway for methanol production from CO2, a gasification product of cellulosic biomass.  Specifically we examined the reaction thermodynamic fundamentals of the multistep bioconversion, and evaluated a novel particle-tethered co-factor regeneration method. Our preliminary theoretical analysis showed that low pH’s and elevated temperatures would shift the reaction equilibria to favor production of methanol.  On the other hand, we showed for the first time that cofactor NAD(H) covalently attached to micro particles, which can be easily recovered and reused, effectively mediated multistep reactions catalyzed by enzymes and the enzymatic regeneration of the cofactor.   For a 30-min batch reaction, a productivity of 0.02 m-mol methanol/h/g-enzyme was achieved.  That was lower than but comparable to the 0.04 m-mol methanol/h/g-enzyme observed for free enzymes and cofactor at the same reaction conditions.  The immobilized system showed fairly good stabilities in reusing.  Over 80% of their original productivity was retained after 11 reusing cycles, with a cumulative methanol yield based on the amount of cofactor reached 127%. 

The use of CO2 will make it possible to utilize non-fermentable biomass components such as lignin, and thus approaching 100% carbon efficiency of biomass utilization when the biosynthesis is applied either alone or in combination with bioethanol production. 


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