SBIR-STTR Award

Butanol is an important industrial solvent used for the manufacture of explosive cordite, industrial solvents, and rubber monomers. It also has been used as a fuel and, if produced from corn or other biomass, would be a better value-added fuel extender than ethanol, now used in the formulation of gasohol. Butanol can be produced by the acetone-butanol-ethanol (ABE) fermentation of biomass by the bacterium Clostridium acetobutylicum. However, the yield of the butanol component is very low compared to the acetone and ethanol components, and almost all butanol is now produced via petrochemical routes. This project will develop a novel approach using two sequential fermentation steps to short-cut the complex ABE fermentation pathway by directing the glucose fermentation to butyric acid and then to butanol. By separating acid (i.e., butyric acid) production (using an asporogenic strain) from solvent (i.e., butanol) formation (using C. acetobutylicum), more glucose carbon can be used for butanol production, and butanol yields greater than 40 percent can be expected -- almost 100 percent higher than that from conventional ABE fermentations. Phase I will evaluate the feasibility of the proposed two-step butanol fermentation process. Phase II will optimize important process parameters, scale-up the design, and build a small pilot to test the process.

Commercial Applications and Other Benefits as described by the awardee:
The technology has the potential to make renewable resources a major source of affordable fuels and chemicals, thereby reducing our Nation’s dependence on foreign oil, improving air and water quality, and reducing the net production of greenhouse gases.

In a process known as ABE furmentation (acetone, butanol, ethanol), butanol is produced from biomass carbohydrates via fermentation using the bacteria strain Clostridium acetobutylicum. The process involves the uptake of butyric acid while maintaining the bacteria in a solventogenic phase. In this project, the process will be scaled up to produce only butanol and to determine the efficiency of the new configuration in creating value-added agricultural products. Phase I proved the stability of the strain in maintaining solventogensis and its efficacy in converting butyric acid from outside sources. For the butyric acid strain, the ancillary products were inhibited so that more of the biomass was converted to butyric acid. A second strain, Clostridium thyrobutyricum, was held in its solvent producing mode and a butyric-acid-only medium was fed which produced butanol only—not acetone or ethanol. A material and energy balance was performed that predicted a yield of 2.5 gallons of butanol per bushel of corn—nearly double the historical yields for ABE. Phase II will optimize and develop a strain that enhances the production rate, thus reducing the capital costs of a manufacturing facility. The first scale up will be to a 150-liter reactor, then to a 2,000-liter reactor by year two. An economic, material, and energy balance study will be performed and design drawings generated for a 10 million gallon per year (MGPY) facility.

Commercial Applications and Other Benefits as described by the awardee:
The ability of a 10 MGPY butanol facility to produce 2.5 gallons per bushel in a worst case scenario should have a larger net income that produced by than a 40 MGPY ethanol plant.