Engine performance of biodiesel fuel prepared from soybean soapstock: A high quality renewable fuel produced from a waste feedstock

A previously-developed bench-scale method for the production of fatty acid methyl esters (biodiesel) from soybean soapstock (Haas, M. J.; Bloomer, S.; Scott, K. J. Am. Oil Chem. Soc. 2000, 77, 373-379) was taken to the small pilot scale, producing approximately 2.5 L of material per run. By multiple successive reactions, 25 L of product was accumulated. The fatty acid composition of the ester product (wt %) was palmitic: 16.2, stearic: 4.7, oleic: 16.2, linoleic: 54.4, and linolenic: 6.9. This mirrors the fatty acid composition of soy soapstock and is quite similar to that of commercial biodiesel produced from refined soybean oil. The ester product met the provisional biodiesel specifications of the American Society for Testing and Materials with regard to all variables examined: flash point, water and sediment, carbon residue, sulfated ash, density, kinematic viscosity, sulfur, cetane number, cloud point, copper corrosion, acid number, free glycerin, and total glycerin, and had density and iodine number values comparable to those of commercial soy-based biodiesel. Emissions data for both the neat fuel and a 20 vol % blend in low-sulfur petroleum diesel were collected according to the Environmental Protection Agency heavy-duty transient cycle protocol using a DDC Series 60 engine on an engine test stand. The emissions profile of biodiesel from soapstock was quite similar to that of biodiesel produced from refined soy oil. Compared with petroleum diesel fuel, emissions,of total hydrocarbons, particulates, and carbon monoxide were reduced 55%, 53%, and 48%, respectively, with neat soapstock biodiesel. Total nitrogen oxides increased 9%. Operation on a 20 vol % blend of soapstock biodiesel in petroleum diesel gave reductions of 27.7%, 19.7%, and 2.4%, respectively, in total hydrocarbons, particulate matter, and carbon monoxide, relative to petroleum diesel. Nitrogen oxide emissions increased 1.3%. In the context of engine emissions, these data suggest the suitability of the methyl esters of soy soapstock as a diesel fuel.