Location: Bio-oils Research Unit
Title: Effects of high-melting methyl esters on crystallization properties of fatty acid methyl ester mixtures Author
Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 22, 2012
Publication Date: May 21, 2012
Citation: Dunn, R.O. 2012. Effects of high-melting methyl esters on crystallization properties of fatty acid methyl ester mixtures. Transactions of the American Society of Agricultural and Biological Engineers. 55(2):637-646. Interpretive Summary: This research determined that cold flow properties of biodiesel are significantly affected by the physical nature and relative concentration of its chemical components. Cold flow properties can compromise the stability and performance of biodiesel and its blends with conventional diesel fuel during cold weather. This study was conducted to answer fundamental questions related to predicting how biodiesel blends will perform during cold weather. Results showed that a particular chemical component, known as saturated fatty acid methyl esters, can, in small concentrations, disproportionately affect the cold flow properties of biodiesel. Outcomes from this study will be of most use to engineers and scientists working on mathematical models based on the thermodynamics of mixtures to improve accuracy in calculating temperatures where fuels will begin to form solid crystals. Results showing the effects of chemical composition will be utilized by entities seeking to develop alternative feedstocks for increased production of biodiesel.
Technical Abstract: Biodiesel is a renewable alternative diesel fuel made from vegetable oils and animal fats. The most common form of biodiesel in the United States are fatty acid methyl esters (FAME) from soybean, canola, and used cooking oils, waste greases, and tallow. Cold flow properties of biodiesel depend on the crystallization properties of high-melting FAME in the mixture. For soybean oil-FAME, the saturated FAME (SFAME) have melting points (MP) that are more than 45 ºC higher than the unsaturated FAME (UFAME). The present study evaluates the use of equations from freezing point depression theory to model crystallization onset temperatures (Tf) for binary mixtures of SFAME (MeC10-MeC20) and UFAME (MeC18:1 and MeC18:2). Melting and crystallization properties were determined by differential scanning calorimetry (DSC) melting and cooling curve analyses. Results showed that the DSC scan rate did not significantly affect onset temperatures or peak enthalpies for analyses of pure FAME. Hysteresis effects were observed for pure FAME where freezing points (FP) from DSC cooling curves were at slightly lower temperature than melting points (MP) from melting curves. For independent crystallization of SFAME from binary mixtures with UFAME, the effects of changes in heat capacity ('Cp) as the mixture temperature decreased below the standard MP of the SFAME were negligible. Calculated Tf values were lower than FP from DSC analysis of mixtures, leading to the conclusion that binary SFAME/UFAME mixtures deviated from ideal solution behavior at low temperatures.