Alcohol School: The case for fractionation

By Lisa Gibson | September 12, 2019

Vijay Singh, professor in Agricultural and Biological Engineering at the University of Illinois at Urbana-Champaign, told his Alcohol School audience Sept. 12 that he was going to “make the case for fractionation.” The conventional corn-to-ethanol production process does not maximize coproduct opportunities, he said.  

The Alcohol School, a Lallemend Biofuels & Distilled Spirits event, is being held Sept. 9-13 in Montreal.

Corn contains all kinds of unique proteins and fibers the ethanol industry is not currently separating out, Singh said. Removing these nonfermentables adds high-value coproducts, increases markets for distillers dried grains with solubles (DDGS), and improves final ethanol concentration, he said.

Lipids that are ideal proteins for human food and can reduce cholesterol, for instance, are present in significant quantities. “It’s a natural product that has pharmaceutical properties,” Singh said. He also named antioxidants that can be recovered such as tocols and carotenoids.

Then, there’s fiber, he said. “Right now, all this fiber that’s present in the corn kernel gets concentrated in DDGS. And DDGS, because of its high-fiber content, is only used in ruminant animal diets.” Only about 10 percent goes to poultry and swine because they can’t digest the fiber, he said. Taking that fiber out expands the market for the product, he said. “That’s one reason we need to do fractionation.”

For the front end, Singh detailed wet and dry fractionation. Wet fractionation, which consists of soaking corn in water and separating coproducts in an aqueous medium, uses wet grinding mills, hydrocyclones and screens for separation. Wet fractionation is very similar to the corn wet milling process, he said.

From one bushel of corn, wet fractionation removes 3.3 pounds of germ, 4 pounds of pericarp fiber and 4 pounds of endosperm fiber, Sing said. The result is higher protein in DDGS and higher final ethanol concentration, he said.

The same separation can be done with the dry fractionation process, borrowing the unit operations from the corn dry milling process, including degerminators, gravity tables and sifters. The process removes 4 pounds of germ and 4 pounds of pericarp fiber.

Comparing wet and dry fractionation showed wet fractionation resulted in better quality germ and pericarp fiber, as well as better nutritional DDGS quality, Singh said. “You get much better results with wet fractionation than in dry fractionation,” he said. “It’s very clear.” Yet, Badger State Ethanol in Monroe, Wisconsin, is the only plant that has tried a wet fractionation process, he cited. He added he’s not certain whether the plant still uses the technology.

On the back end, DDGS fractionation utilizes the Elusieve Process to remove 4 pounds of pericarp fiber from a bushel of corn, resulting in 11 pounds of DDGS that are digestible by poultry and swine, Singh said. The DDGS undergoes a physical separation process, sieved into different categories based on size, using different thermal velocities to separate fiber and enhanced DDGS.

The DDGS after fractionation have higher protein and fat content, as well as lower fiber content. The payback period of installing a system for DDGS fractionation is less than two years, he said, and the process has been commercialized in Hungary.

Thin stillage fractionation recovers crude oil through evaporation and centrifugation. The oil serves as an additional coproduct and reduces the oil content in DDGS, Singh said.

Singh’s audience was incredibly interested in his research results. He acknowledged the lack of fractionation being practiced in the fuel ethanol industry, despite its many benefits.