Abstract
We report a simple method that efficiently esterifies the fatty acids in soapstock, an inexpensive, lipid-rich by-product of edible oil production. The process involves (i) alkaline hydrolysis of all lipid-linked fatty acid ester bonds and (ii) acid-catalyzed esterification of the resulting fatty acid sodium salts. Step (i) completely saponified all glycerides and phosphoglycerides in the soapstock. Following water removal, the resulting free fatty acid sodium salts were rapidly and quantitatively converted to fatty acid methyl esters (FAME) by incubation with methanol and sulfuric acid at 35°C and ambient pressure. Minimum molar reactant ratios for full esterification were fatty acids/methanol/sulfuric acid of 1∶30∶5. The esterification reaction was substantially complete within 10 min and was not inhibited by residual water contents up to ca. 10% in the saponified soapstock. The product FAME contained >99% fatty acid esters, 0% triglycerides, <0.05% diglycerides, <0.1% monoglycerides, and <0.8% free fatty acids. Free fatty acid levels were further reduced by washing with dilute sodium hydroxide. Free and total glycerol were <0.01 and <0.015%, respectively. The water content was <0.04%. These values meet the current specifications for biodiesel, a renewable substitute for petroleum-derived diesel fuel. The identities and proportions of fatty acid esters in the FAME reflected the fatty acid content of soybean lipids. Solids formed during the reaction contained 69.1% ash and 0.8% protein. Their sodium content indicated that sodium sulfate was the prime inorganic component. Carbohydrate was the predominant organic constituent of the solid.
Similar content being viewed by others
References
Ryan, T.W., T.J. Callahan, and L.G. Dodge, Characterization of Vegetable Oils for Use as Fuels in Diesel Engines, Vegetable Oil Fuels Proceedings of the International Conference on Plant and Vegetable Oils as Fuels, edited by N.D. Fargo, American Society of Agricultural Engineers, pub. 4–82. ASAE, St. Joseph, MI, 1982, pp. 70–81.
Tahir, A.R., H.M. Lapp, and L.C. Buchanan, Sunflower Oil as a Fuel for Compression Ignition Engines, Ibid., American Society of Agricultural Engineering, pub. 4–82, ASAE, St. Joseph, MI, 1982, pp. 82–91.
Fort, E.F., and P.N. Blumber, Performance and Durability of a Turbocharged Diesel Engine Fueleled with Cottonseed Oil Blends, Ibid., pp. 374–382.
Schlick, M.L., M.A. Hanna, and J.L., Schinstock, Soybean and Sunflower Oil Performances in a Diesel Engine, Trans. ASAE 31:1345–1349 (1988).
Peterson, C., D. Reece, J. Thompson, and X. Zhang, Development of Rapeseed Biodiesel for Use in High-Speed Diesel Engines, Report No. 302, Idaho Agricultural Experiment Station, University of Idaho College of Agriculture, Moscow, 1996.
Krawczyk, T., Biodiesel, INFORM 7:800–815 (1996).
Clark, S.J., L. Wagner, M.D. Schrock, and P.G. Piennaar, Methyl and Ethyl Esters as Renewable Fuels for Diesel Engines, J. Am. Oil Chem. Soc. 61:1632–1638 (1984).
Alfuso, S., M. Auriemma, G. Poice, and M.V. Prate, The Effect of Methyl-Ester of Rapeseed Oil on Combustion and Emissions of CI Diesel Engines, Paper No. 932801, Society of Automotive Engineers, Warrendale, PA, 1993, pp. 1–12.
Schumacher, L.G., W.G. Hires, and S.C. Borgelt, Fueling a Diesel Engine with Methyl-Ester Soybean Oil, Liquid Fuels from Renewable Resources, edited by J.S. Cundiff, American Society of Agricultural Engineers, St. Joseph, MI, 1992, pp. 124–131.
Ali, Y., M.A. Hanna, and S.L. Cuppett, Fuel Properties of Tallow and Soybean Oil Esters, J. Am. Oil Chem. Soc. 72:1557–1564 (1995).
Chang, D.Y.Z., J.H. Van Gerpen, I. Lee, L.A. Johnson, E.G. Hammond, and S.J. Marley, Fuel Properties and Emissions of Soybean Oil Esters as Diesel Fuel, Ibid. 73:1549–1555 (1996).
Peterson, C.L., D.L. Reece, J. Taberski, and T. Thompson, Demonstration of the On-the-Road use of Biodiesel: IDWR/University of Idaho Cummins Powered 1992 Dodge 161,000 km (100,000 Mile) On-Road Test, Commercialization of Biodiesel: Producing a Quality Fuel, edited by C.L. Peterson, Department of Biological & Agricultural Engineering, University of Idaho, Moscow, 1998, pp. 240–262.
Ahouissoussi, N.B.C., and M.E. Wetzstein, Life-Cycle Costs of Alternative Fuels: Is Biodiesel Cost Competitive for Urban Buses? Industrial Uses of Agricultural Materials Situation and Outlook, IUS-5S, USDA Economic Research Service, Washington, DC, 1995, pp. 3–9.
Dunn, J.R., and K.C. Schneeberger, Economic Implications for the Potential Development of a Vegetable Oil Fuel Industry, Vegetable Oil Fuels: Proceedings of the International Conference on Plant and Vegetable Oils as Fuels, edited by N.D. Fargo, American Society of Agricultural Engineers pub. 4–82, ASAE, St. Joseph, MI, 1982, pp. 70–81.
Mittelbach, M., and P. Tritthart, Diesel Fuel Derived from Vegetable Oils, III. Emission Tests Using Methyl Esters of Used Frying Oil, J. Am. Oil Chem. Soc. 65:1185–1187 (1988).
Ali, Y., M.A. Hanna, and S.L. Cuppett, Fuel Properties of Tallow and Soybean Oil Esters, Ibid. 72:1557–1564 (1995).
Nelson, L.A., T.A. Foglia, and W.N. Marmer, Lipase-Catalyzed Production of Biodiesel, Ibid. 3:1191–1195 (1996).
Peterson, C.L., Producing a Quality Fuel: The Quality Assurance Plant for the Over-the-Road Truck Demonstration, Commercialization of Biodiesel: Producing a Quality Fuel, edited by C.L. Peterson, Department of Biological & Agricultural Engineering, University of Idaho, Moscow, 1988, pp. 22–31.
Anonymous, Soya Bluebook Plus, Soyatech, Inc., Bar Harbor, 1995, p. 262.
Stern, R., G. Hillion, P. Gateau, and J.C. Guibet, Preparation of Methyl and Ethyl Esters from Crude Vegetable Oils and Soapstock, Proceedings: World Confernece on Emerging Technologies in the Fats and Oils Industry, edited by A.R. Baldwin, American Oil Chemists' Society, Champaign, 1986, pp. 420–422.
Basu, H.N., and M.E. Norris, Process for Production of Esters for Use as a Diesel Fuel Substitute Using a Non-Alkaline Catalyst, U.S. Patent 5,525,126 (1996).
Sonntag, N.O.V., Fat Splitting, Esterification, and Interesterification, in Bailey's Industrial Oil and Fat Products, edited by D. Swern, Vol. 2, 4th edn., J. Wiley & Sons, New York, 1982, pp. 97–173.
Haas, M.J., and K.M. Scott, Combined Nonenzymatic-Enzymatic Method for the Synthesis of Simple Alkyl Fatty Acids Esters from Soapstock, J. Am. Oil Chem. Soc. 73:1393–1401 (1996).
Fritz, E., and R.W. Johnson, Raw Materials for Fatty Acids, in Fatty Acids in Industry. Processes, Properties, Derivatives, Applications, edited by R.W. Johnson and E. Fritz, Marcel Dekker, New York, 1989, pp. 1–20.
Box, G.E.P., W.G. Hunter, and J.S. Hunter, Statistics for Experimenters, Wiley, New York, 1978.
Juneja, V.K., T.A. Foglia, and B.S. Marmer, Heat Resistance and Fatty Acid Composition of Listeria monocytogenes: Effect of pH, Acidulation, and Growth Temperature, J. Food Prot. 61:683–687 (1998).
Windholz, M. (ed.), S. Budavari (co-ed.), R.F. Blumetti (assoc. ed.), and E.S. Otterbein (assist. ed.), The Merck Index, Merck & Co., Inc., Rahway, 1983, p. 779.
Peterson, C., D. Reece, J. Thompson, and X. Zhang, Development of Rapeseed Biodiesel for Use in High-Speed Diesel Engines, Report No. 302, Idaho Agricultural Experiment Station, University of Idaho College of Agriculture, Moscow, 1996, p. 13.
Daniels, R., Agrotech to Convert Soapstock into Fertilizer, INFORM 6:421–423 (1995).
Hodgson, A.S., Alkali Refining of Soybean Oil Using KOH, Ibid. 6:425–426 (1995).
Author information
Authors and Affiliations
Corresponding author
About this article
Cite this article
Haas, M.J., Bloomer, S. & Scott, K. Simple, high-efficiency synthesis of fatty acid methyl esters from soapstock. J Amer Oil Chem Soc 77, 373–379 (2000). https://doi.org/10.1007/s11746-000-0061-1
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/s11746-000-0061-1