Submitted to: Biomass and Bioenergy
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/21/2009
Publication Date: 10/23/2009
Citation: Joshi, H., Moser, B.R., Toler, J., Walker, T. 2010. Preparation and Fuel Properties of Mixtures of Soybean Oil Methyl and Ethyl Esters. Biomass and Bioenergy. 34:14-20. Interpretive Summary: Biodiesel is normally prepared from a vegetable oil or animal fat through a chemical reaction with methanol and a catalyst. However, methanol is obtained from refining of petroleum, so biodiesel produced in this fashion is not truly 100% bio-derived. Therefore, we report the production of biodiesel using ethanol instead of methanol to provide fatty acid ethyl esters (biodiesel). Ethanol is obtained from various biomass sources such as corn or sugarcane, so the resultant biodiesel is truly bio-based. Benefits elucidated in this study of ethyl esters over methyl esters with regard to fuel performance include enhanced ability to serve as a lubricant, improved cold flow properties, and superior oxidative stability. Cost is a major drawback to the use of ethanol instead of methanol: ethanol is more expensive than methanol. Consequently, a series of mixtures of methanol and ethanol were investigated in an effort to discover an optimum mixture of fatty acid methyl and ethyl esters which provided fuel properties comparable to that of pure ethyl esters. We found that a mixture of 33% methanol in ethanol accomplished this goal. This study is important because it improves the performance properties of biodiesel, an important domestically produced and renewable agricultural product, and further reduces American dependence on imported petroleum products.
Technical Abstract: Soybean oil was transesterified using methanol, ethanol, and various mixtures of methanol and ethanol at a constant mole ratio of alcohol to oil of 12:1 in the presence of 1 wt % potassium hydroxide (KOH) catalyst at 30 deg C for 60 minutes. The effect of mixtures of methanol and ethanol on percentage yield and fuel properties of soybean oil methyl and ethyl esters (SME/SEE) was studied. With mixtures of methanol and ethanol, the formation of methyl esters was faster in comparison to ethyl esters. However, due to the high solubility of ethanol in soybean oil, high yields (94.6–97.9%) were obtained for all mole ratios of reactants studied. The resultant SME/SEE mixtures prepared from a methanol to ethanol mole ratio of 1:2 or greater with respect to the ethanol component exhibited enhanced low temperature properties, oxidative stability, and superior lubricity in comparison to neat SME and also satisfied ASTM D 6751 and EN 14214 standards with respect to kinematic viscosity and acid value. All other ratios which contained a higher percentage of methanol displayed similar behavior to pure SME. These results indicate that the fuel properties of soybean oil-based biodiesel can be improved by substituting a portion of the methanol reagent with ethanol during transesterification, albeit at a higher production cost due to the higher price of ethanol in comparison to methanol.