Converting sweet sorghum into ethanol

Monday, March 20, 2006

Between its dependence on foreign oil and the need to become more environmentally conscious, the United States is looking at domestic agricultural products as energy alternatives.

Ethanol production as an additive to petroleum-based fuel is a popular solution, and sweet sorghum is a crop currently under research as a source of ethanol at the Food and Agricultural Products Center on the Oklahoma State University campus in Stillwater.

“Sweet sorghum has the potential to be used as a renewable energy crop and has become a viable candidate for ethanol production,” said Dr. Danielle Bellmer, FAPC food processing engineer.

According to the U.S. Department of Energy, ethanol is an alcohol-based alternative fuel produced by fermenting and distilling simple sugars, mostly derived from starch crops such as corn.

Unfortunately, an issue with using starch crops is the requirement to use heat processing to convert the starch into simple sugars. Sweet sorghum, however, is exempt from complex processing because the simple sugars are directly “juiced” from the stalks, thus eliminating the starch conversion step.  

Bellmer said the idea of using sweet sorghum for commercial ethanol production is not new; in fact, Brazil is cultivating a similar crop, sugar cane, for the same purpose.  

The benefits of using sweet sorghum are numerous. This crop is a low-input, high-carbohydrate producer and can be cultivated in nearly all temperate climates.

Past concerns

Sweet sorghum is not as popular as corn as a source of ethanol because of the high costs associated with constructing and operating a central processing plant.

While starch can be stored for long periods, the simple sugars derived from sweet sorghum must be fermented immediately.

Bellmer said the harvest season for sweet sorghum is only a few months.

“Since the sorghum juice cannot be easily stored, the processing plant would only be in production for a few months out of the year, making it economically unfeasible,” Bellmer said.

Lee McClune, president of Sorganol Production Co. Inc. in Knoxville, Iowa, initially approached the FAPC for assistance with studying a solution to this problem.

Bellmer, the project's principal investigator, is investigating the process of in-field ethanol production, in which sweet sorghum juice will be collected, fermented, and distilled.  Her goal is to determine the validity and efficacy of this hypothetical solution.  

Harvesting sweet sorghum

McClune built and tested a piece of equipment to harvest and press sweet sorghum. It uses a standard forage chopper/header and feed rollers to harvest and “juice” in a single pass through the field.

McClune said that with this harvester, 4,000 to 6,000 gallons of juice can be harvested per acre.

Fermentation

Immediately after harvesting, the fermentation process must begin.

The FAPC is researching the hypothesis that fermentation can take place in large storage containers in the environment without temperature control.

Bellmer said most yeast used for fermentation operates within a finite optimum temperature range, which poses a problem for the large temperature range of the open environment.  

“Fortunately, many new yeast strains have recently been developed with high-temperature tolerance,” Bellmer said.  

Bellmer said initial experiments investigated the use of temperature-tolerant yeast strains, with results indicating that fermentation is possible and that little or no pretreatment of the “juice” is necessary. More research is being performed to validate fermentation efficiency.

Distillation

After fermenting, the next step is to concentrate the ethanol through distillation. Fasttech, a company located in Ferris, Oklahoma, has developed a small-scale distillation unit. David McDowell, the company's owner, started designing the unit nearly seven years ago.

The distillation unit uses diluted blackstrap molasses, combined with yeast and enzymes, to produce 21% ethanol, which is then distilled to about 99% ethanol. This same distillation unit can be used for the ethanol produced from sorghum.

Fasttech is presently taking the necessary steps to make the distillation unit mobile.  

Bellmer and McDowell agree that a cooperative group of farmers could own one distillation unit.

The future of sorganol

By obtaining university data through research by the FAPC, McClune hopes the entire process of converting sweet sorghum into ethanol will become more marketable.

“[Bellmer] has been very helpful, very encouraging, and I certainly appreciate all the efforts and everything she’s done,” McClune said.

The FAPC is dedicated to helping Oklahoma agriculturalists develop value-added enterprises in order to keep the products, jobs and dollars in Oklahoma.

Bellmer said a system that allows farmers to produce their own alternative fuel is hoped to be developed through research and combining the efforts of agricultural entrepreneurs like McClune and McDowell.  

“Rural agricultural producers will then have the ability to fuel their own machinery, as well as a means of generating additional income,” Bellmer said.