Fayetteville, Arkansas [RenewableEnergyAccess.com] Chemical engineering researchers at the University of Arkansas have investigated supercritical methanol as a method of converting chicken fat into biodiesel fuel. The new study also successfully converted tall oil fatty acid, a major by-product of the wood-pulping process, into biodiesel at a yield of greater than 90 percent, significantly advancing efforts to develop commercially viable fuel out of plentiful, accessible and low-cost feedstocks and other agricultural by-products.
“Major oil companies are already examining biodiesel as an alternative to petroleum,” said R.E. “Buddy” Babcock, professor of chemical engineering. “With the current price of petroleum diesel and the results of this project and others, I think energy producers will think even more seriously about combining petroleum-based diesel with a biodiesel product made out of crude and inexpensive feedstocks.”
Under Babcock’s guidance, Brent Schulte, a chemical-engineering graduate student in the university’s College of Engineering, subjected low-grade chicken fat, donated by Tyson Foods, and tall oil fatty acids, provided by Georgia Pacific, to a chemical process known as supercritical methanol treatment. Supercritical methanol treatment dissolves and causes a reaction between components of a product — in this case, chicken fat and tall oil — by subjecting the product to high temperature and pressure. Substances become “supercritical” when they are heated and pressurized to a critical point, the highest temperature and pressure at which the substance can exist in equilibrium as a vapor and liquid. The simple, one-step process does not require a catalyst.
Schulte treated chicken fat and tall oil with supercritical methanol and produced biodiesel yields in excess of 89 and 94 percent, respectively. With chicken fat, Schulte reached maximum yield at 325 degrees Celsius and a 40-to-1 molar ratio, which refers to the amount of methanol applied. The process also produced a respectable yield of 80 percent at 300 degrees Celsius and the same amount of methanol. At 275 degrees Celsius and the same amount of methanol, the process was ineffective. Ideal results using tall oil fatty acid were achieved at 325 degrees Celsius and a 10-to-1 molar ratio. At 300 degrees Celsius and the same amount of methanol, the conversion produced a yield of almost 80 percent. Again, at 275 degrees Celsius, the process was ineffective.
Previous efforts, including a study two years ago by another one of Babcock’s graduate students (see below), to make biodiesel out of low-cost feedstocks — as opposed to refined oils — have used one of two conventional methods, base-catalyzed or acid-catalyzed esterification. Although successful at producing biodiesel, these conventional methods struggle to be economically feasible due to long reaction times, excessive amounts of methanol required and/or undesired production of soaps during processing.
“The supercritical method hit the free fatty-acid problem head on,” Babcock said. “Because it dissolves the feed material and eliminates the need for the base catalyst, we now do not have the problems with soap formation and loss of yield. The supercritical method actually prefers free fatty acid feedstocks.”
Biodiesel is a nonpetroleum-based alternative diesel fuel that consists of alkyl esters derived from renewable feedstocks such as plant oils or animal fats. The fuel is made by converting these oils and fats into what are known as fatty acid alkyl esters. The conventional processes require the oils or fats be heated and mixed with a combination of methanol and sodium hydroxide as a catalyst. The conversion process is called transesterification.
Most biodiesel is produced from refined vegetable oils, such as soybean and rapeseed oil, which are expensive; they generally account for 60 to 80 percent of the total cost of biodiesel. Due to these high feedstock prices, biodiesel production struggles to be economically feasible. Currently, as Babcock alluded, biodiesel cannot compete with petroleum diesel unless the per-gallon price of diesel remains higher than $3. For these reasons, researchers recently have focused efforts on less refined and less-expensive feedstocks as a more viable competitor to conventional diesel.
Biodiesel has many benefits. In addition to reducing U.S. dependence on foreign oil, it is better for the environment than purely petroleum-based products. As a renewable, biodegradable and thus carbon-neutral material, biodiesel does not contribute to greenhouse gases. In fact, it decreases sulfur and particulate-matter emissions. It also provides lubrication for better-functioning mechanical parts and has excellent detergent properties.
“Biodiesel provides an effective, sustainable-use fuel with many desirable properties,” Schulte said. “In addition to being a renewable, biodegradable and carbon-neutral fuel source, it can be formed in a matter of months from feedstocks produced locally, which promotes a more sustainable energy infrastructure. It also decreases dependence on foreign oil and creates new labor and market opportunities for domestic crops.”
Schulte worked with Ed Clausen, professor of chemical engineering and holder of the Ray C. Adam Chair of Chemical Engineering, and Michael Popp, professor of agricultural economics, in addition to Babcock. Schulte’s study, which led to his master’s thesis and is available upon request, was supported by the University of Arkansas Mack-Blackwell Rural Transportation Center. His work was awarded first place at the inaugural Admiral Jack Buffington Poster Paper Contest sponsored by the transportation center at its annual advisory board meeting.
Editor’s note: The story below, which was released by University of Arkansas on November 29, 2005 was inadvertently posted by RenewableEnergyAccess.com this week. The story above, released by the University on December 19, 2007 is the story that should have been published.
In the future, fat shaved off chicken breasts and other parts of the chicken may power automobiles that emit less pollution.
Chemical engineering researchers associated with the Mack Blackwell Transportation Center at the University of Arkansas (UA) 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.