Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/20/2002
Publication Date: 3/20/2003
Citation: HAAS, M.J., MICHALSKI, P.J., RUNYON, S., SCOTT, K.M., NUNEZ, A. PRODUCTION OF FAME FROM ACID OIL, A BY-PRODUCT OF VEGETABLE OIL REFINING. JOURNAL OF THE AMERICAN OIL CHEMISTS SOCIETY. 2003. V. 80. p. 97-102. Interpretive Summary: In the U.S. and throughout the world there is interest in the development of renewable engine fuels, that is, fuels made from agricultural products, whose feedstocks are thus renewed each crop season. "Biodiesel' is the name for a renewable fuel for diesel engines. It is made from fats and oils, and has been shown in hundreds of experiments not only to be an acceptable substitute for petroleum-derived diesel fuel, but also to reduc engine emissions of hydrocarbons, particulates, carbon monoxide and sulfur. As a result, biodiesel technology is presently in transition from an experimental to a commercial status. Early biodiesel research focused on the production of fuel from refined fats and oils. There is a need, however, to increase the supply of biofuel by using additional feedstocks, and interest in development of technology to produce biodiesel from feedstocks less expensive than refined edible oils. Thus, researchers have eexpanded the scope of their investigations, developing methods to synthesize biodiesel from other, often less expensive, lipids such as waste greases. Here, we have extended these studies further, identifying conditions to produce biodiesel from 'acid oil', a low cost byproduct of the production of edible vegetable oil. Optimized reaction conditions are presented to achieve a rapid, high efficiency synthesis of biodiesel from acid oil. Adoption of this technology would provide additional uses for acid oil, additional income for oilseed producers and vegetable oil processors, and an increased supply of economically affordable biodiesel to consumers.
Technical Abstract: Simple alkyl fatty acid esters have numerous uses, including serving as 'biodiesel,' a fuel for compression ignition (diesel) engines. The use of acid-catalyzed esterification for the synthesis of fatty acid methyl esters from acid oil, a byproduct of edible vegetable oil refining produced from soapstock, was investigated. Soybean acid oil consisted of 47.9 wt% FFA, 21.8 wt% TAG, 7.2 wt% DAG and less than 1% MAG. Experiments were conducted to identify reaction conditions giving maximum esterification of these species within 26 h incubation at 65 C. Reaction conditions predicted to yield a minimum amount of remaining unesterified fatty acid species were 26 h incubation and a molar ratio of (total fatty acids) / (methanol) / (sulfuric acid) of 1 / 15 / 1.5. The predicted content of residual unreacted species, as a fraction of their content in unesterified acid oil, was FFA: 6.6%; TAG: 5.8%; and DAG: 2.6%. In an alternative approach, all acylglycerol species of soapstock were hydrolyzed by saponification prior to acidulation. The resulting High Acid acid oil had a FFA content of 96.2 wt%, and lacked TAG, DAG or MAG. Conditions for its optimal esterification at 65 C were a mole ratio of FFA / methanol / acid of 1 / 1.8 / 0.17 and a 14 h incubation. The yield of FAME under these conditions was 89% of theoretical, the residual unesterified FFA content was 51 mg/g, and TAG, DAG and MAG were absent. The FFA content of this material exceeded that permissible for biodiesel, but was readily reduced to an acceptable level by a simple washing with aqueous NaCl and CaO solutions.