D.O.E. on Synthesis Gas Fermentation

The U.S. Department of Energy (D.O.E.) has defined "Synthesis Gas Fermentation" (or syngas fermentation) as a scientifically recognized method of producing cellulosic ethanol separate from the more widely know method called "enzymatic hydrolysis."

The promise of syngas fermentation is that it is applicable to the conversion of a much broader range of feedstock (including urban, agricultural, and forestry waste) than either sugar fermentation or enzymatic hydrolysis. As a production technology, it is also much more energy efficient, faster, and more economical(1) than the other two.

According to D.O.E. studies conducted by the Argonne Laboratories of the University of Chicago, one of the benefits of cellulosic ethanol over sugar-fermented ethanol is that it reduces [greenhouse gas emissions] (GHG) by 85% over reformulated gasoline. By contrast, sugar-fermented ethanol reduces GHG emissions by 18% to 29% over gasoline

From the U.S. D.O.E. website.....

Synthesis Gas Fermentation

Biomass can be converted to synthesis gas (consisting primarily of carbon monoxide, carbon dioxide, and hydrogen) via a high temperature gasification process. Anaerobic bacteria are then used to convert the synthesis gas into ethanol. Bioresource Engineering Inc. has developed synthesis gas fermentation technology that can be used to produce ethanol from cellulosic wastes with high yields and rates.

Background
Biomass can be converted to synthesis gas, which consists primarily of carbon monoxide (CO), carbon dioxide (CO2), and hydrogen (H2), via the gasification process. Gasification technology has been under intensive development for the last 2 decades. Large-scale demonstration facilities have been tested and commercial units are in operation worldwide. The problems with the application of gasification have been economic, not technical. In the past, the product from gasification has been electricity or heat source, and the low value of these products in today's market is insufficient to justify the capital and operating costs. However, if gasification is coupled with the production of a higher value liquid fuel, the combination could be a viable alternative energy technology.

After gasification, anaerobic bacteria such as Clostridium ljungdahlii are used to convert the CO, CO2, and H2 into ethanol(1). Higher rates are obtained because the process is limited by the transfer of gas into the liquid phase instead of the rate of substrate uptake by the bacteria.

Commercial Status
BioEngineering Resources, Inc.
Bioengineering Resources, Inc. (BRI) has developed syngas fermentation technology that can be used to produce ethanol from cellulosic wastes with high yields and rates. The process of combined gasification/fermentation has been under development by BRI for several years. The feasibility of the technology has been demonstrated, and plans are under way to pilot the technology as a first step toward commercialization. The conversion of a waste stream, the disposal of which is costly, into a valuable fuel adds both environmental and economic incentives. The yields can be high because all of the raw material, except the ash and metal, is converted to ethanol. BRI has developed bioreactor systems for fermentation that results in retention times of only a few minutes at atmospheric pressure and less than a minute at elevated pressure. These retention times result in very economical equipment costs(1,2). The biocatalyst is automatically regenerated by slow growth of the bacteria in the reactor.

References
1Klasson, K.T.; Elmore, B.B.; Vega, J.L.; Ackerson, M.D.; Clausen, E.C.; Gaddy, J.L., "Biological Production of Liquid and Gaseous Fuels from Synthesis Gas." Applied Biochemistry and Bioengineering, Vol. 24/25, 1990, pp. 857-873.

2Vega, et al. 1989, Proprietary Reports.

More on BRI Energy available at Green Car Congress, 07/09/05