Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 24, 2007
Publication Date: October 1, 2007
Citation: Haas, M.J., Scott, K.M., Foglia, T.A., Marmer, W.N. 2007. The general applicability of in situ transesterification for the production of fatty acid esters from a variety of feedstocks. Journal of the American Oil Chemists' Society. 84(10):963-970. Interpretive Summary: Biodiesel, a renewable diesel engine fuel that consists of the simple alkyl esters of fatty acids and can be synthesized from domestically-produced fats and oils, is making the transition from a research item to a commercial fuel. Economics is a major barrier to this transformation, in that biodiesel produced from refined oils is generally not cost competitive with petroleum fuels. In addition, there is growing concern for ensuring adequate supplies of the lipid feedstocks from which biodiesel is produced, and doing so without placing economic pressure on edible oil supplies. We have previously developed and described a novel method for biodiesel production, termed ‘in situ transesterification’. This method eliminates the need for the prior isolation and purification of the fat or oil to be used for biodiesel production. Instead, the synthesis uses raw agricultural oil-bearing material as feedstock. This eliminates the cost and technology of oil isolation, and could reduce overall production costs. We originally studied only soybeans in this application. Here we expand the exploration of the applicability of the in situ transesterification reaction, testing it on distillers dried grains with solubles (DDGS, a coproduct of ethanol production from corn) and meat & bone meal (MBM, the product of the rendering industry). The lipids in both of these materials are shown to readily and in high yields produce the fatty acid esters that constitute biodiesel. Optimal conditions for the reactions are defined. It can be concluded that the in situ transesterification method is generally applicable to all lipid-bearing materials, potentially providing large new feedstock supplies for biodiesel production.
Technical Abstract: We have previously described a new approach to fatty acid methyl ester (FAME) production wherein acylglycerol transesterification was achieved by reacting flaked full fat soybeans with methanol containing NaOH. Efficient conditions for nearly quantitative transesterification of the lipid in the substrate have been identified, and the ester product has been shown to meet the ASTM specifications for biodiesel. Here we explore the general applicability of this approach, termed in situ transesterification, to glyceride transesterification from feedstocks other than soybean. Materials investigated were distillers dried grains with solubles (DDGS), which is a coproduct of the fermentative production of ethanol from corn, and meat & bone meal (MBM), which is the proteinaceous product of the animal rendering industry. Conditions giving maximum lipid transesterification were identified by statistical experimental design and response surface regression analysis. FAME yields near maximum theoretical could be achieved with DDGS containing their full moisture content. However, partial drying of the feedstock markedly reduced the methanol requirement. For DDGS retaining 30% of their original moisture, maximum theoretical FAME production was predicted to occur in 1.2 h in reactions at 35°C containing 5 g (dry wt equivalent) of substrate and 14.0 ml of methanol containing 0.40 N NaOH. Confirmatory reactions run under these conditions achieved 91.1% of maximum theoretical transesterification. The fatty acid composition of the resulting FAME was comparable to that of corn oil. Protein was not removed from the DDGS during this treatment. For MBM, drying was not required to achieve maximum transesterification, which was predicted to occur in 2.5 h in reactions conducted at 35°C containing 5 g of feedstock and 12 ml of 0.20 N NaOH in methanol. Actual FAME yields under these conditions were 93.3% of theoretical. Free fatty acids and acylglycerols were undetectable in the product. The fatty acid composition of the FAME product was comparable to that of beef tallow. Approximately 10% of the protein in MBM was removed by in situ transesterification. Coupled with the previous demonstration of the successful in situ transesterification of soybean lipid, the data presented here indicate that this method is generally applicable for FAME synthesis from lipid-bearing materials. Some of these have not yet been demonstrated to be amenable to extraction of their lipids for FAME production. In situ transesterification may thus offer a route for the use of these lipids as new sources of biodiesel.