Location: Bio-oils Research Unit
Title: Effects of monoacylglycerols on the cold flow properties of biodiesel Author
Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 24, 2012
Publication Date: August 16, 2012
Citation: Dunn, R.O. 2012. Effects of monoacylglycerols on the cold flow properties of biodiesel. Journal of the American Oil Chemists' Society. 89(8):1509-1520. Interpretive Summary: This research determined that the fuel properties of biodiesel are affected by the presence of monoglycerides. Monoglycerides are a side product from the conversion of vegetable oil or animal fat into biodiesel. They may be present in very small concentrations and are known to cause the formation of solid residues when the fuel is stored in cold temperatures. The solid residues can clog dispensers and fuel filters and lead to operational problems if they are allowed into the fuel tanks of vehicles. This study determined that several cold flow properties are impacted by monoglycerides at concentrations less than 0.1 percent. Monoglycerides were similarly shown to affect the viscosity (resistance to flow), density, and refractive index of biodiesel. This research is important to industry, producers, and other scientists because it demonstrates that monoglycerides can affect fuel properties when present in very small concentrations.
Technical Abstract: Biodiesel is a renewable alternative fuel made from plant oils and animal fats that may be burned in a compression-ignition (diesel) engine. It is composed of mono-alkyl esters of fatty acid esters made from plant oils or animal fats mainly by transesterification with methanol or ethanol. This process leaves behind small concentrations of minor constituents including monoacylglycerols (MAG). Saturated MAG have low solubility in biodiesel and may form solid residues during storage in cold weather. Soybean oil-fatty acid methyl ester (SME) samples were mixed with up to 1.0 mass% MAG to evaluate the effects on cloud point (CP), freezing point (FP), cold filter plugging point (CFPP), and wax appearance point (WAP). Differential scanning calorimetry (DSC) results showed that MAG with only 27.6 mass% total long chain (C16-C18) saturated fatty acid content had melting transitions between 54 and 59.0ºC. Furthermore, DSC analysis indicated that pure monoolein may be problematic with respect to melting transitions between 25.42 and 33.4ºC. Solubility data for SME-MAG mixtures indicated a broad transition temperature range from solid at low temperature to liquid at temperatures exceeding 60ºC. Increasing the added MAG content from 0.10 to 1.0 mass% increased both CP and FP. CFPP demonstrated higher sensitivity than CP or FP at added MAG content below 0.10 mass%, though it was not affected by increasing MAG concentration above 0.50 mass%. WAP showed no effects until added MAG content exceeded 0.25 mass%. Kinematic viscosity measured at 5ºC similarly showed no effects until added MAG concentration exceeded 0.20 mass%. Specific gravity at 15.6ºC and refractive index at 25ºC were not greatly affected by added MAG except at concentrations greater than 0.10 mass%.