UNIVERSITY PARK, Pa. -- Recently people have been using the terms "soy-diesel" and "bio-diesel" interchangeably, according to an expert in Penn State's College of Agricultural Sciences, who warns that there is a major difference between the fuels.

Failing to recognize that difference will spell disaster for diesel engines if run on soy-diesel, says Dennis Buffington, professor of agricultural and biological engineering.

Soy-diesel is a 20/80 blend of filtered and clarified crude soybean oil and diesel fuel.

"According to the U. S. National Renewable Energy Laboratory (NREL) in Colorado," Buffington stresses, "no one should be mixing any crude vegetable oils into fuels for vehicle use."

The glycerin in soybean oil acts like sugar in the fuel tank and will eventually ruin fuel injectors, according to the NREL. Engine durability also is poor. The laboratory points out that no long-term studies exist on engine performance and maintenance requirements because the engines don't last long if run on soy-diesel fuel.

"The NREL states that even if crude soybean oil is first filtered and clarified, it's still a vegetable oil," Buffington explains. "It should not go into a compression ignition engine until it has been refined to the point where it meets American Society for Testing and Materials minimum standards for diesel fuel."

Buffington cautions that diesel engine owners may initially be misled if they try to use the soy-diesel fuel.

"The engines will run on soy-diesel for the short term until the fuel injectors foul," he says. "You may be lulled into a false sense of comfort when burning soy-diesel because everything appears to be fine for a while. You also need to recognize that most, if not all, engine manufacturers will void the engine warranty if soy-diesel (or any blend of crude vegetable or animal oil) is burned in an engine.

"A company representative," he adds, "can easily document if an engine has been fueled by a crude oil/diesel blend by examining internal engine parts."

By contrast, a process called transesterification is used to prepare soybean oil for blending with diesel fuel to make bio-diesel. Alcohol is added to soybean oil with a catalyst and stirred vigorously. The ester (bio-diesel) will rise to the top and glycerol and alcohol will settle on the bottom. After several washings, the bio-diesel then can be marketed as a fuel.

Establishing an economically viable bio-diesel production operation, according to the University of Nebraska, requires a $20 million chemical processing plant that will handle about 100,000 gallons of soybean oil per day (about 2,500 tons of beans per day). Buffington believes a plant may be economical today if scaled back to a $5 million dollar operation processing 20,000 gallons of oil per day.

If the glycerol also can be marketed, he says, then bio-diesel fuel could be produced for about $1.75 per gallon, including the costs of 40 to 50 cents for alcohol and 15 to 20 cents for a catalyst per gallon. However, there are large capital costs involved in starting to process bio-diesel fuel.

Penn State's Energy Institute is conducting both short-term and long-term research to determine if filtered and clarified soybean oil can be used as a diesel fuel supplement. Until the long-term results are analyzed and replicated, Buffington says soy-diesel blends should not be burned in diesel engines.

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EDITORS: Dennis Buffington can be contacted at 814-865-2971 or buffington@psu.edu.

Contact:

Jeff Mulhollem jjm29@psu.edu 814-863-2719 814-865-1068 fax