Clemson University bioenergy researcher and Animal Co-Products Research and Education Center (ACREC) member Dr. David A. Bruce has conducted an energy life cycle analysis comparing animal fats to vegetable oil for the production of biodiesel. Assisted by Dr. Dora E. Lopez, Bruce used the life cycle analysis methodology along with data collected from the rendering industry to quantify the amount of fossil energy input required to produce biodiesel from animal fats and yellow grease. The study demonstrated very favorable results for animal fats. Specifically, the conversion of tallow, poultry fat, or yellow grease to biodiesel was shown to be more renewable than using purified vegetable oils for the same energy end-product. The researchers also concluded that the production of biofuels from animal fats is a significantly more energy efficient process than making renewable ethanol from corn.
As trends continue toward renewable fuels, questions arise concerning the costs of production both in financial terms and energy input/outputs. The economic, energetic, and environmental costs/benefits of converting animal fats into biodiesel were examined via a detailed life cycle analysis. In their ACREC report, Bruce and Lopez evaluated “the energy efficiency of operating a commercial diesel engine on animal-derived biofuels as compared to traditional diesel fuels.”1 They also compared animal- versus plant-derived biofuels. For the study, they considered tallow, pork fat, poultry fat, and yellow grease for biodiesel manufacture.
During a literature search, Bruce and Lopez discovered several published studies on economics, environmental information, and life cycle analysis for vegetable crop-derived feedstocks such as corn and soybeans. However, very little information had been published concerning the economics of fuels and chemicals derived from animal fat. One study reviewed by Bruce and Lopez reported that engine performance is nearly identical for fossil fuel diesel, vegetable-based biodiesel, and animal-based biodiesel, but there are differences in cold flow and lubricity properties. However, engine emission profiles indicate that biofuels have zero sulfur emissions whereas fossil fuel powered diesel engines have significantly higher sulfur emissions.
So-called nitrogen oxide (NOx) emissions are approximately the same for all of these fuels, but some studies have shown that animal fat-derived biodiesel can lead to small increases in NOx emissions as compared to fossil fuels. These NOx emissions largely arise from the oxygenation of gaseous nitrogen that comprise 78 percent of the air that is used for fuel combustion and do not come from nitrogen contaminants in the biodiesel. These studies have also shown that engine modifications as well as state-of-the-art catalyst converter technologies can significantly reduce NOx emissions.
As other life cycle energy assessments focused on biodiesel production from vegetable crops in terms of net energy ratio, Bruce and Lopez chose to examine biodiesel made from rendered fats in the United States using the same methodology. The net energy ratio, which is commonly used to evaluate the renewability of bio-derived fuels, is the ratio of energy outputs to fossil energy inputs (renewable fuels have a net energy ratio of less than one).
The researchers examined three different scenarios in their study. Scenario I involved the energy for converting post-rendered fats into biodiesel. Scenario II included the energy required to render the fats and then convert them into biodiesel, and scenario III included the energy required for raising the animals, rendering the residual fats, and then converting them to biodiesel. The amount of energy necessary for farming and conversion to biodiesel was obtained from the literature. The amount of thermal energy and electricity required in rendering was derived from data obtained in a survey of 26 U.S. rendering facilities.
As expected, their results indicated that the choice of boundary conditions (or scenario) greatly affected the net energy ratio. For scenario III, using animal fats to generate biodiesel resulted in a net energy ratio less than one, which indicated that it cost more energy to make the biodiesel than could be derived from the fuel. However, this scenario assumes that animal livestock are raised solely for the production of biodiesel, ignoring the fact that these animals are primarily raised for meat production. Using the more realistic conditions for scenarios I and II, the net energy ratios were found to be greater than one. The net energy ratio for scenario I was greater than 3.6, which is larger than is normally reported for producing biodiesel from soybean oil. For waste cooking oil, the net energy ratios were greater than 2.8 for both scenarios I and II. This life cycle analysis information and proof that the environmental impact of animal fat-derived fuels is less than fossil fuels could have an impact on federal and state government decisions about subsidies for rendered animal fats. The team recently submitted a journal article to Industrial and Engineering Chemical Research describing the results of this study.
Rising soybean oil prices and fluctuating fuel prices has had a profound impact on the biodiesel industry. Vegetable crops such as soybeans can have multiple end uses from foods to commercial products to biofuels. As soybean prices increase and biofuel prices decrease, the energy dynamics reported by Bruce and Lopez indicate that rendered animal fats are a competitive feedstock for the biofuel industry that does not directly compete for use in the human food chain.
Bruce will continue his work on life cycle analysis for animal fat-derived fuels. He stated in a poster presented at the recent National Renderers Association/Fats and Proteins Research Foundation meeting held at Clemson University, “Current animal fat processing techniques and end uses were developed over many years; however, recent changes in the cost of fossil fuels and potential changes to gas emission standards necessitates that the rendering industry reevaluate the economic, environmental, and health basis for their practices. To ensure that the most effective use of animal fats is realized, a complete life cycle analysis is being completed for this important industry.”1
Bruce is now working on a life cycle analysis for the poultry, swine, and beef industries, examining alternative uses of post-rendered animal fats “including incineration in boilers and conversion to biofuels and chemicals.” This study will include evaluations of energy cycles as well as environmental impact. Results of this study will provide a comparison of the overall impact of different animal fat applications in comparison with existing data on such petroleum products as on-road diesel, No. 2 heating oil, and marine fuel oil.
An associate professor in the Clemson University Department of Chemical and Biomolecular Engineering, Bruce and his team conduct research in a variety of areas including biofuels, bio-derived polymers, catalysis, kinetics, pollution abatement, and molecular modeling of reactions. Lopez recently completed a post-doctoral study at Clemson University. The team was assisted by Emeritus Professor Dr. Joseph Mullins, also with the Clemson University Department of Chemical and Biomolecular Engineering, who helped with the development of advanced biodiesel production models.
The Clemson University Animal Co-Products Research and Education Center is very proud to have Dr. David Bruce and his team working on the assessment of animal fats and grease in the manufacture of biodiesel.
1. Lopez, Dora E., Joseph Mullins, David A. Bruce. 2009. Life Cycle Energy Analysis for the Production of Biodiesel from Rendered Lipids in the United States. Poster presented at the National Renderers Association/Fats and Proteins Research Foundation Spring Conference, April 21, 2009, held at Clemson University, Clemson, SC.
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ACREC Solutions – August 2009 RENDER | back