SBIR-STTR Award

One prominent challenge for the biochemical production of cellulosic ethanol is the utilization of xylose, which can increase ethanol yield 20-40% for typical feedstocks. Efforts toward genetic engineering of conventional yeast to utilize xylose have suffered from metabolic redox imbalance. This project will develop a technology for utilizing an industrial enzyme, glucose isomerase (GI), for the conversion of xylose to xylulose, which then can be metabolized to ethanol by conventional yeasts. The approach involves immobilizing GI in a microchannel reactor that recirculates the fermentation broth: the xylose is converted to xylulose and consumed during the fermentation step while enabling extended use of the expensive enzyme. In Phase I, a series of experiments will be conducted to extract the necessary kinetic parameters from a simple single-tube microreactor. These parameters will be used to model and fabricate a multichannel microreactor scaled for a 5 liter system. In Phase II, the design will be scaled up to a 100 liter system, and full automation of recirculation, pH control, and thermal management will be implemented.

Commercial Applications and Other Benefits as described by the awardee:
Commercialization of this system should enable the widespread utilization of biomass resources for ethanol production in a sustainable manner, by obtaining greater yields from feedstock materials

Concerns over the escalating use of petroleum-based liquid fuels include climate change, trade imbalances, global security issues, and environmental harm resulting from petroleum extraction and processing. Although ethanol is the leading replacement for petroleum-based gasoline, the current corn-based source of ethanol is hindered by serious social and environmental issues. The production of cellulosic ethanol from lignocellulosic feedstocks ¿ including straws, corn stalks, and woody biomass ¿ represents a key, underutilized resource in our energy portfolio. In particular, the effective utilization of xylose would make a much higher fraction of the biomass viable as source materials for cellulosic ethanol. Therefore, this project will develop a next-generation system for increased xylose utilization in the ethanol-production process. In this approach, an industrial enzyme, xylose isomerase, is used to convert xylose to xylulose. Then, familiar brewing yeasts could metabolize the xylulose to ethanol. In Phase I, the feasibility of utilizing xylose by having a separate reactor convert it to xylulose was demonstrated. Phase II will design, build, and characterize a 200-liter-scale xylose isomerization and fermentation system, and the operating conditions needed to achieve high productivity of the isomerase enzyme will be determined. A pilot system (4000 liters) will be built in year 2 of the project.

Commercial Applications and Other Benefits as described by the awardee:
Commercial application of the isomerization technology would expand the economic viability of cellulosic ethanol and increase the sustainability of the US liquid fuel supply. Success with this technology would contribute to meeting the ambitious national targets for the use of alternative fuels in the next decade