Submitted to: Society of Automotive Engineers Transaction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/1997
Publication Date: N/A
Citation: Interpretive Summary: Methyl esters from soybean oil (methyl soyate) have many properties that make them attractive as alternative fuels and extenders for compression-ignition (diesel) engines. However, methyl soyate has been demonstrated to develop low temperature startup and operability problems at much higher temperatures than conventional diesel fuels. Although winterization is a popular technique for improving thermal stability in vegetable oils, earlier studies on winterization of methyl esters indicated unacceptably low yields (<30%). This work examines modifications that enhance yield and shorten process time for winterization of methyl soyate. Additives designed to inhibit crystalline growth and organic solvents (hexane and isopropanol) were tested in several configurations. Results showed that cloud point, a reliable indicator of cold flow properties of methyl esters, may be substantially reduced while maintaining yields in excess of 80%. Also, results from thermal analyses showed that cloud point of methyl esters may be more accurately determined from melting peaks than standardized methods employed by industry.
Technical Abstract: Methyl esters from vegetable oils (biodiesel) are very attractive as alternative fuels for combustion in direct injection compression ignition (diesel) engines. However, one issue that must be resolved before methyl esters are acceptable to markets in moderate temp climates is the improvement of their low temp flow properties during cooler weather. In North America, methyl esters from vegetable oil develop operability problems at temps close to freezing. This value is approx 14C greater than that for No. 2 diesel fuel (DF2). This work examines winterization based methods that may improve low temp flow by altering the composition of fatty acid groups in the methyl ester mixture. Step by step winterization of neat methyl esters reduced cloud point (CP) to as low as -20C. Product yields were relatively low at approx 28 wt%. Step by step winterization of methyl esters treated with cold flow improvers showed similar reductions in CP while boosting yields to 70%. Single step winterization in organic solvents (hexane and isopropanol) reduced CP to as low as -10C and gave yields in the range 78-86%. Finally, results from differential scanning calorimetry (DSC) cooling curves showed that nucleation mechanisms in fatty methyl ester mixtures are significantly affected by modified winterization/fractionation techniques.