Submitted to: Energy and Fuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 24, 2009
Publication Date: July 14, 2009
Citation: Dunn, R.O. 2009. Cold Flow Properties of Soybean Oil Fatty Acid Monoalkyl Ester Admixtures. Energy and Fuels. 23:4082-4091. Interpretive Summary: Biodiesel is an alternative fuel made from vegetable oil or animal fat that is prone to start-up and operability problems during cold weather. The most common types of biodiesel are made from reaction of oil or fat with methanol or ethanol. This work investigates the effects on cold flow properties of making biodiesel by reacting soybean oil with propanols and butanols and preparing admixtures of "propyl" or "butyl" soyate with more commonly produced "methyl" soyate. Making biodiesel with propanol or butanol was shown to have significantly better cold flow properties than methyl soyate. In addition, biodiesel made from reaction with a branched chain alcohol (isopropanol, isobutanol or 2-butanol) had better cold flow properties than biodiesel made from straight-chained alcohols. Results from this study will support fuel producers, distributors and terminal operators in efforts to improve the flow behavior of biodiesel during cold weather. Results will also directly benefit scientists and engineers studying effects of low temperatures on biodiesel.
Technical Abstract: Biodiesel is an alternative fuel made from transesterification of vegetable oil or animal fat with an alcohol that has many attractive fuel characteristics. However, biodiesel is more prone than petrodiesel to start-up and operability problems during cold weather. The present study investigates effects on cold flow properties of mixing soybean oil fatty acid methyl esters (SME) with fatty acid esters derived from transesterification of soybean oil with medium- and branched-chain alkyl alcohols. Admixtures of SME with 0-100 vol% tallow fatty acid methyl esters and with n-propyl, isopropyl, n-butyl, isobutyl and 2-butyl soyates were analyzed for cloud and pour point (CP and PP). CP and apparent solidification point (SP = PP - 1) data were employed to construct temperature-composition phase diagrams for each admixture in SME. Soyates with branched-chain alkyl headgroup moieties were more effective in decreasing CP and PP (or SP) than those with straight-chain headgroups, compared to unmixed SME. An admixture of 65 vol% isopropyl soyate in SME decreased CP by more than 5C compared to unmixed SME. In contrast, the same admixture with n-propyl soyate decreased CP by only 1.9C. Furthermore, an admixture of 65% n-butyl soyate in SME decreased CP by only 2.6C despite having an alkyl headgroup with a larger molecular weight than for isopropyl soyate. Analogous results were observed from sub-ambient differential scanning calorimetry analysis performed on mixtures of pure mono-alkyl stearates in methyl oleate solvent.