UA Researchers Create Biodiesel Fuel from Chicken Fat

FAYETTEVILLE, Ark. — In the future, fat shaved off chicken breasts and other parts may power automobiles that emit less pollution.

Chemical engineering researchers associated with the Mack Blackwell Transportation Center at the University of Arkansas have developed an optimized method of converting chicken fat into biodiesel fuel. The novel project could lead to using chicken fat -- a plentiful, accessible and low-cost feed stock -- as an inexpensive supplement to petroleum-based diesel fuel.

“We’re trying to expand the petroleum base,” said Brian Mattingly, a graduate student in the UA Department of Chemical Engineering. “Five to 20 percent blending of biodiesel into petroleum-based diesel significantly reduces our dependence on foreign oil, and we’re using a renewable resource. These are just a few of biodiesel’s benefits.”

Supported by the national transportation center, the research will lead to Mattingly’s master’s thesis in chemical engineering. He is pursuing the project under the direction of R.E. Babcock and Ed Clausen, UA professors of chemical engineering, and Michael Popp, associate professor of agricultural economics.

The study provides data that allows researchers and biodiesel producers to evaluate material and processing costs and product yields for two conversion methods and two types of fat. Mattingly said the research will help producers choose the most economical conversion method based on specific composition of different grades of chicken fat.

Biodiesel fuel is made by converting vegetable oils and animal fats into what is known as fatty acid alkyl esters. To become an ester, the oils or fats must be heated and mixed with a combination of methanol and sodium hydroxide. The conversion process is called esterification or transesterification.

Biodiesel additives have many benefits in addition to reducing U.S. dependence on foreign oil, Mattingly said. They’re better for the environment than purely petroleum-based products; biodegradable and nontoxic, biodiesel additives do not contribute to greenhouse gases, and they decrease sulfur and particulate matter emissions. They also provide lubrication for better functioning mechanical parts, and they even have detergent properties.

“Biodiesel additives are cleaner and better oxygenated,” Babcock said. “They burn better, create less particulate matter and actually lubricate and clean things like cylinders, pistons and fuel lines.”

For these reasons, interest in the use of biological resources for alternative diesel additives has risen, but large-scale U.S. production of biodiesel fuels has not occurred for two significant reasons, both tied to economics. Traditionally, producers have used highly refined, food-based feed stocks, such as soybean oil, because their properties facilitate simple and quick transesterification. But highly refined oils that people consume as food products are expensive; biodiesel producers must compete with grocers for supply. In addition, biodiesel producers must compete with petroleum-based diesel, which historically has been significantly cheaper. However, Popp said, this disadvantage is becoming less of a deterrent because of recent increases in crude oil prices.

Researchers have turned to chicken fat as a less-expensive substitute for soybean oil. They have shown that it is a favorable raw material for biodiesel production because it is available at low costs and has high-yield potential. However, the presence of free fatty acids in raw chicken fat has been a significant obstacle to generating high yields of biodiesel from less-refined raw materials. Fatty acids create problems in the transesterification process because they tend to form soaps as a byproduct. These soaps increase the formation of gels, which make it more difficult to produce a high yield of biodiesel fuel.

Mattingly worked high-quality fat -- chicken fat with a free fatty acid content of less than 2 percent -- obtained from a Tyson Foods plant in Clarksville, Ark., and low-quality, feed-grade fat -- fat with as much as 6 percent free fatty acid content -- obtained from a Tyson plant in Scranton, Ark. High-quality chicken fat is more expensive than feed-grade fat, but both are much less expensive than soybean oil, Mattingly said.

He created biodiesel fuel by subjecting each grade of chicken fat to a one-step and multiple-step conversion process. Mattingly discovered that free fatty acid content is the most important factor to consider for producing biodiesel with a single- or multiple-stage refinement process. Both processes produced biodiesel fuel, but the single-step process could not convert free fatty acids into fuel. Mattingly said this method would be feasible for chicken fat with low concentrations of free fatty acid because there is no more than a 2 percent loss of yield. But producers may want to use the multiple-step process for chicken fat with high concentrations of free fatty acids.

“The project demonstrated that there is a very fine line between facilitating an adequate reaction and generating so much soap that the biodiesel yield is diminished,” Mattingly said. “The differences in yields between the Clarksville fat and the feed-grade fat indicate that an optimized transesterification process may be sufficient for the higher-quality fat, while further processing may be necessary for the lower-quality fat. Basically, deciding which method to use comes down to economics.”

Popp said it is too early to say that producing biodiesel fuel from chicken fat is economically feasible, but he said chicken fat shows a great deal of promise given today’s fossil fuel prices and available subsidies. Popp will evaluate the yield information from Mattingly’s study.

Mattingly said he will submit his thesis to appropriate academic journals.