Retooling Ethanol Industries: Integrating Ultrasonics into Dry Corn Milling to Enhance Ethanol Yield

Principal Investigator:

David Grewell, 515-294-2036, dgrewell@iastate.edu (other projects)

Co-Principal Investigator:

• Samir Khanal, samirk@iastate.edu (other projects)
• Hans van Leeuwen, leeuwen@iastate.edu (other projects)

Project Status: In Progress

Start Date: 03/01/2006
End Date: 08/01/2007


Research Objective: Ethanol is a renewable and clean fuel produced by the fermentation of the starch in corn. Iowa is the number one corn producing state in the nation, processing annually nearly 350 million bushels of corn into ethanol. Ethanol production keeps Iowa’s economy growing--generating $2.49 billion in total sales (www.iowacorn.org).

Currently, one bushel of corn produces 2.7 gallon of ethanol. Even with a marginal improvement in ethanol yield of just 10%, the revenue generation in Iowa could be increased by nearly $190 million annually. Such an improvement would have a significant impact on the long-term sustainability of the rather marginal ethanol industries in Iowa and beyond. During yeast fermentation, about 1/3rd of the corn is converted into ethanol.

There are considerable amounts of residual starch in the whole stillage, which are not easily accessible by enzymes during liquefaction. However, generation of additional ethanol necessitates some form of pretreatment or use of an improved enzyme. One strategy to improve ethanol production is to integrate a high-power ultrasound into existing dry milling ethanol plants. We hypothesize that retrofitting a high-powered ultrasonic unit in existing ethanol plants will yield more ethanol.

Background: We have investigated such a possible improvement, the use of ultrasound in dry corn milling, that would have a significant impact on the long-term sustainability of bioenergy industries. Ultrasound pretreatment generates cavitation in the aqueous phase resulting in strong hydrodynamic shear forces. The shear forces facilitate the disintegration of corn slurry into fine particles, thereby exposing a much larger surface area to enzymes during liquefaction / saccharification. As a result, the enzymatic activity will be greatly enhanced.

This innovative pretreatment will facilitate complete starch conversion into simple sugars and consequently improving the overall ethanol yield. This will also reduce the total amount of enzymes and nutrient needed, and the processing time.

Preliminary outcome: Ultrasonic pretreatment of corn slurry resulted in nearly a 50-fold reduction in corn particle size during 40 seconds of sonication. The sugar yield improved by 30% in comparison to a control under the same conditions. With the advancement in ultrasonic technology in recent years, the energy conversion efficiency of ultrasonic units has improved to > 90%.

This breakthrough research showed tremendous potential to increase profitability in the rapidly growing dry corn milling ethanol industry, and cut down our dependency on imported fuels. The research team has already filed a patent application and several dry corn milling ethanol industries have shown interest in this technology.

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