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A recent DOE newsletter reported that the U.S. Department of Agriculture (USDA) is offering loan guarantees for commercial-scale plants producing advanced biofuels (i.e., biofuels produced from materials other than corn kernel starch). Â
The article mentions that U.S. Sugar Corporation (USSC) will apply for the loan guarantees to help fund a 100-million gallon per year ethanol facility in Clewiston, Florida. Â
USGC has teamed up with Coskata, an Illinois cellulosic ethanol company that owns proprietary technology for converting leftover sugar cane material into ethanol. Instead of fermenting the plant material, the Coskata process first converts it to synthesis gas, or syngas, and then ferments the gas using anaerobic microorganisms to produce ethanol.
Coskata owns two related patent applications that cover its ethanol production technology. Patent Application Pub. Nos. 2008/0305539 and 2008/0305540 are directed to a membrane supported bioreactor system for converting syngas to biofuels (collectively “Bioreactor Applications”). Both applications published on December 11, 2008.
According to the Bioreactor Applications, some major challenges of the gasification and fermentation approach to ethanol production are that it requires large quantities of syngas, highly efficient dissolution and transfer of the gas to microorganisms, and growth and maintenance of a large density of microorganisms.Â
Some bioreactors increase the density of the microorganisms using membranes to develop biofilms, but these reactors must be very large or they won’t provide sufficient gas dissolution rates.
The Bioreactor Applications overcome these drawbacks by using one side of a membrane as the syngas contact surface and the opposite side as the surface for growing the microorganisms. The gas is fed onto the contact side and transported through the membrane to a biofilm of anaerobic microorganisms, where it is fermented into biofuels.
According to the Bioreactor Applications:
 The result is a highly efficient and economical transfer of the syngas at essentially 100% dissolution and utilization, overcoming limitations for the other fermentation methods and fermenter configurations. The syngas diffuses through the membrane from the gas side and into the biofilm where it is transformed by the microbes to the soluble product of interest. Liquid is passed in the liquid side of the membranes via pumping, stirring or similar means to remove the ethanol and other soluble products formed; the products are recovered via a variety of suitable methods.
If the USSC-Coskata project comes to fruition, it would be the world’s largest second generation (made of non-food biomass) ethanol facility (see the Green Car Congress article here) and would be a testament to the power of using biofilm to convert biomass to biofuel.
