Effects of minor constituents on cold flow properties and performance of biodiesel

Biodiesel is an alternative fuel or extender made from renewable agricultural lipids that may be burned in a compression-ignition (diesel) engine. It is defined as the mono-alkyl esters of fatty acids derived from plant oils or animal fats. Biodiesel has many important technical advantages compared to petrodiesel including superior inherent lubricity, low toxicity, high (non-flammable) flash point and biodegradability, very low or negligible sulfur content and lower exhaust emissions of most regulated species. Biodiesel is generally produced by transesterification of the lipid with a short-chain monohydric alcohol. This process may leave behind very small (trace) concentrations of minor constituents such as saturated monoacylglycerols (MAGs) or free steryl glucosides (FStGs). These materials have high melting points and very low solubilities allowing them to form solid residues when stored during cold weather. Blending with petrodiesel exacerbates the problem. Settling solid residues were found to clog fuel filters in fuel dispensers and vehicles. In response to documented problems the biodiesel industry in the United States collaborated with the American Society of Testing and Materials (ASTM) to develop a cold soak filterability performance test that will help identify fuels that may have a propensity to clog filters if exposed to long-term storage in cold weather.