(750f) Fermentation Techniques and Medium Development for Butanol and Hexanol Production from Syngas By Clostridium Carboxidivorans

Butanol and hexanol have higher energy densities than ethanol and can be produced via syngas fermentation. Syngas components, CO, CO₂ and H₂, can be obtained by gasification of biomass, coal, petcoke and municipal solid waste, reforming of natural gas and from industrial waste gases. Fermentation techniques and medium formulation are important to balance the cost for nutrient supply with the requirement of active syngas fermenting bacterial culture for a selected desired product. A minimal defined medium was formulated to promote selectivity of Clostridium carboxidivorans to produce butanol and hexanol from syngas. Fermentations were performed in serum bottles with model syngas (CO:H₂:CO₂ [70:20:10]). Results showed that trace metals, such as Mo, were required for growth and product formation. The removal of Cu and a tenfold increase in Mo enhanced alcohol production. C. carboxidivorans produced over 3.0 g/L ethanol, over 1.0 g/L butanol and up to 1.0 g/L hexanol. No complex chemical components were required in the medium to support growth or production. However, cell growth and alcohol production were affected by CO inhibition and CO mass transfer limitation. Inhibition particularly caused slow growth and fermentation. A programmed fermentation technique accompanied with managing CO and H₂supply through control of syngas pressure and mass transfer allowed maintenance of strong culture and consistent production of alcohols, particularly butanol and hexanol. Medium design and controlled supply of syngas components should be implemented in isolation of candidate strains and strain development to select for desired products of commercial potential.