Voice: 215-233-6580/6579
Fax:  215-233-6406
e-mail:  khicks@errc.ars.usda.gov

Improving the Economic
Competitiveness of
Ethanol Production

Neil Goldberg, 215-233-6590
dgoldberg@errc.ars.usda.gov

Andrew McAloon, 215-233-6619
amcaloon@errc.ars.usda.gov

Objectives:

Devise and exploit commercial process efficiencies for the production of ethanol from corn, stover, and related processing residues and biomass in order to reduce the selling price of fuel ethanol.  The goals include lowering process costs and the development of valuable coproducts which reduce the net cost of ethanol.

Sub-Projects:

1.  Bioreactors Research

• Corn Milling Pretreatment  with Anhydrous Ammonia
• High-Solids Batch and Continuous Fermentation

2.  Separations Research in Fuel Ethanol Production

• Continuous Fermentation with Pervaporation Membrane
• Lysine Recovery from Corn Steepwater

Frank Taylor,  215-233-6501
ftaylor@errc.ars.usda.gov

Gerard Senske, 215-233-6728
gsenske@errc.ars.usda.gov

Fuel ethanol production by fermentation of hammer-milled whole corn (dry-grind process) requires the addition of ammonia, urea, or proteolytic enzymes to make nitrogen available for yeast growth. In some dry-grind plants it is cost-effective to use high levels of available nitrogen, which permits fermentation to high alcohol concentrations. It may be possible to lower the costs of dry-grind or wet-milling ethanol production by supplying the nitrogen as anhydrous ammonia in a first processing step. Such pretreatment may facilitate grinding, steeping and separations.

In the laboratory, test batches (800 g) of whole corn were exposed to anhydrous ammonia, then coarsely ground, and steeped for six hours. It was found that pretreatment with ammonia loosened the pericarp (hull), so it could be partially torn off by coarse grinding. The amount of ammonia taken up by the corn was only as much as needed for fermentation (about 0.1% by weight). These results suggest that cost-effective new milling and separation processes can be developed, in which cleaner separations are achieved, and much shorter steeping times are needed.

U.S. Patent No. 6,592,921, “Method of Removing the Hull from Corn Kernels” was recently assigned to the U.S. and the University of Illinois, with Frank Taylor and Vijay Singh of University of Illinois at Urbana-Champaign as inventors. Currently, pilot plant development is proceeding with the design and construction of a continuous corn ammoniator. We welcome the involvement of the dry and wet-milling industries in this project, whether through formal or informal cooperation, and expect that such involvement will improve the quality and value of this research.

Selected Publications:

• Corn Milling Pretreatment with Anhydrous Ammonia, F. Taylor, J.C. Craig, Jr., M.J. Kurantz, and V. Singh.

[Back]

Efforts to improve the process technology available to current and potential fuel ethanol producers, to lower the cost of fuel ethanol production from corn, have led to the development of a new fermentation process, high-solids continuous fermentation with CO₂ stripping. As shown in the figure, the byproduct CO₂ is utilized to transport ethanol from a low-temperature (40 C) stripping column to a condenser. Thereby, ethanol is removed from the fermentor during the fermentation, enabling the complete and rapid conversion of a highly concentrated fermentable sugar stream.

Process simulation and cost analysis indicate that this process will save approximately 3 cents per gallon when integrated into a state-of-the-art dry-grind corn-to-ethanol process design. The savings increase as the solids concentration of the mash increases. In dry-grind whole corn fermentation, the achievable solids concentration may be limited by the non-fermentable suspended solids, which interfere with mixing and heat transfer. Savings of up to 10 cents per gallon are predicted, when the continuously stripped fermentor is combined with a process alternative such as Quick-Germ, in which valuable co-products are recovered before fermentation, leaving a high-starch, low non-fermentable suspended solids feed stream to the fermentor.

Stable performance of the continuously stripped fermentor has been demonstrated at one bushel per day during continuous runs lasting up to 180 days. One-bushel batch fermentation experiments were also completed, and equipment sizing and performance algorithms were generated from the pilot plant data. These mathematical models for both continuous and batch fermentors are included in process simulation and cost models that are available to the public. Further development of new process designs such as this may require interest and investment from the private sector, and we are seeking cooperators.

Selected Publications:

• Fermentation and Costs of Fuel Ethanol from Corn with Quick-Germ Process, F. Taylor, A.J. McAloon, J.C. Craig, Jr., P. Yang, J. Wahjudi, and S.R. Eckhoff
• Dry-Grind Process for Fuel Ethanol by Continuous Fermentation and Stripping, F. Taylor, M.J. Kurantz, N. Goldberg, A.J. McAloon and J.C. Craig, Jr.
• Kinetics of Continuous Fermentation and Stripping of Ethanol, F. Taylor, M.J. Kurantz, N. Goldberg and J.C. Craig, Jr.

[Back]

Dennis J. O'Brien,  215-233-6601
dobrien@errc.ars.usda.gov

Gerard Senske, 215-233-6728
gsenske@errc.ars.usda.gov

Dennis J. O’Brien of the Engineering Science Research Unit, Eastern Regional Research Center (ERRC), has been studying the continuous removal of ethanol from fermentation broths via pervaporation. The major goal of this effort is to develop and demonstrate a continuous, high-rate process for fuel ethanol production at lower cost than the current industrial process.

Description of the Technology

In pervaporation, a separation of two or more components is accomplished across a non-porous membrane by the combination of two phenomena; differing rates of diffusion through the thin polymer membrane and an evaporative phase change analogous to a simple flash distillation step. Applied to an alcohol fermentation, pervaporation can be used to selectively remove ethanol from all other components of the broth, although some water is also passed through the membrane. Pervaporation, when compared to distillation processes with which it often competes industrially, is considered to be a less energy-intensive unit operation. Pervaporation is an emerging technology in the chemical process industries, finding applications in the dehydration of solvents and organic separations.

Pervaporation in Fuel Ethanol Production

In order to establish a truly continuous fermentation for fuel ethanol production, ethanol must be removed from the broth at approximately the rate at which it is produced. In our laboratory we have coupled a pervaporation module to a fermentor which has successfully maintained the broth ethanol concentration at 5%, a level which is not inhibitory to the fermenting yeast. The system has the following advantages: a concentrated ethanol stream is produced by the pervaporation module, the permeate stream is free of cells and other broth components which, along with its high ethanol content, facilitates further downstream processing, a significantly higher fermentor capacity for ethanol production, and reduced fermentor sizes and resulting costs.

Research Progress

We have operated our small pilot plant fermentation-pervaporation system for periods up to 200 hours, producing a 45% ethanol product. Fermentor productivities have been as high as 25 g ethanol/L-hr, a tenfold increase over industrial batch fermentation processes. A robust engineering model has been developed to predict the performance of the pervaporation model. A preliminary cost evaluation has determined that, based on our laboratory performance data, costs for the system are in the range of those for current ethanol plant designs.

Future Directions

The next phase of the research will seek to optimize the parameters of the whole fermentation-pervaporation-distillation section of an ethanol plant and examine these costs. Industrial collaborations are welcomed and encouraged in two areas: ethanol producers for pilot testing and demonstration projects and membrane suppliers for membrane testing and industrial module demonstrations.

Selected Publications:

[Back]

Most current co-products of ethanol production are low-valued and their markets are becoming saturated.  In a search for new coproducts, we have developed a potential process to recover the amino acids lysine and arginine from corn steepwater, and internal processing stream in corn wet milling.  Utilizing ion exchange technology, lysine and arginine were selectively recovered from steepwater to yield a product containing up to 36% (db) total amino acids (20% lysine) with low levels of ash, lactate, and phytate.

[Back]

Rolando Flores,  215-233-6489
rflores@errc.ars.usda.gov

Areas of Research:

• Develop processes to fractionate grain ethanol feedstock prior to fermentation to improve the ethanol competitiveness and process efficiency
• Develop processes and applications for byproducts of the ethanol process

[Back]

Akwasi Boateng, 215-233-6493
aboateng@errc.ars.usda.gov

Areas of Research:

• Thermal conversion of crop-related biomass and energy crops to hydrogen and valuable coproducts
• Integration of renewable hydrogen production processes with dry-grind (grain) fuel ethanol plants
• Development of mobile processes for conversion of biomass to renewable hydrogen and co-products

[Back]

Updated: September 12, 2005