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Title: Butter as a Feedstock for Biodiesel Production

item Haas, Michael
item Wagner, Karen

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/7/2010
Publication Date: 6/16/2010
Citation: Haas, M.J., Berry, W., Feldman, E., Kasprzyk, S., Bockian Landsburg, E., Ratigan, B., Wagner, K., Adawi, N. 2010. Butter as a Feedstock for Biodiesel Production. Journal of Agricultural and Food Chemistry. 58:7680-7684.

Interpretive Summary: The biodiesel industry in the United States is expanding rapidly. This expansion has put predictable demand pressure on the vegetable oils and animal fats from which biodiesel is produced, and triggered interest in the potential of all lipids to serve as feedstocks for this renewable fuel. In this manuscript we explored the suitability of butter, a lipid-rich material, as a starting material for biodiesel production. Although butter is a premier edible material and sells for much more than standard biodiesel feedstocks such as soybean oil, it is in some cases rendered unfit for human consumption and does appear on the fuel feedstock markets. In this work, butter lipids were converted to fatty acid methyl esters and their suitability as biodiesel was judged by subjecting the preparation to the accepted standards for biodiesel quality. The material failed 4 of the 15 tests that constitute the official test panel for biodiesel quality. However, further investigation demonstrated that 3 of these 'failures' were only apparent, not actual, and were the result of the very unique composition of butter, which has fatty acids shorter than those normally seen in biodiesel feedstocks. In that these fatty acids are also found in other lipids that might be used in the future for biodiesel production, the work here highlights for the first time the possible discrepancies that might result when the quality of such fuels is tested, and alerts the industry to be aware of possible anomalous performance on the part of such biofuels when subjected to accepted standard tests. Modification of these tests to broaden their feedstock scope may be in order.

Technical Abstract: The acylglycerides in 348 L of cow’s milk (Bos taurus) butter were converted to fatty acid methyl esters (FAME) via acid-catalyzed esterification/transesterification in the presence of methanol at elevated temperature and pressure. The FAME recovery was 67% of maximum theoretical yield. This product was assayed according to the Standard Specification for Biodiesel Fuel Blend Stock (B100) for Middle Distillate Fuels (D 6751) specified by ASTM International. The ester product failed to meet the Standard Specifications for flash point (91 deg C observed, vs. 130 deg C minimum allowed), free glycerin content (3.493 mass % determined by ASTM D 6584 vs. 0.02 maximum allowed), total glycerin (3.506 mass % determined vs. 0.240 mass % allowed, maximum) and total sulfur (19 ppm observed, vs. 15 ppm allowed for S15 grade biodiesel). However, subsequent analysis indicated that the sample actually deviated from acceptability in only sulfur content. A specific assay for methanol, the contaminant typically responsible for reduced flash point values in biodiesel, demonstrated very low actual levels (214 ppm). The low flash point of the butter FAME preparation was most likely the result of the volatility and flammability of the methyl esters of shorter chain fatty acids, such as methyl butyrate (C4:0) and caproate (C6:0), which are typically present at the levels of 4 and 2%, respectively, in butter lipids. A glycerin-specific enzymatic assay indicated very low levels of free glycerin (0.03 mass %) in the butter FAME preparation. The substantially higher value determined via the official method of biodiesel analysis can be attributed to the fact that the short chain FAME produced from butter exhibit mobilities comparable to that of free glycerin when subjected to ASTM D6584, the standard gas chromatographic method for glycerin determination in biodiesel. This contributed to erroneously high calculated values for both free and total glycerin. Pending reduction of the slightly excessive sulfur levels, butter could be an acceptable feedstock for biodiesel production. This work illustrates some potential weaknesses in the accepted methods for biodiesel characterization when employed in the analysis of FAME preparations containing mid- and short-chain fatty acid esters.