Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Review article
Publication Acceptance Date: 8/3/2006
Publication Date: 9/28/2006
Citation: Knothe, G.H. 2006. Analyzing biodiesel: Standards and other methods. Journal of the American Oil Chemists' Society. 83(10):823-833. Interpretive Summary: Biodiesel is an alternative diesel fuel derived from vegetable oils such as soybean oil or other sources such as animal fats and waste frying oils. It is made by a chemical reaction of the vegetable oil or animal fat with chemical compounds called alcohols. The resulting materials are also known not only as biodiesel but also as fatty acid alkyl esters. During the production of these esters, intermediate materials and glycerol as co-product arise. These materials and others carried over from the parent oil or fat as well as those arising after production during storage can contaminate biodiesel and reduce fuel quality. Therefore, biodiesel standards address these issues by limiting contaminants and prescribing methods for their analysis. The present work details the various specifications in standards regarding categories of specific contaminants as well as their analysis and points out alternatives to the methods prescribed in standards. Other issues such as production monitoring and analyzing blends of biodiesel with petroleum-based diesel fuel are also addressed.
Technical Abstract: Biodiesel occupies a prominent position among the alternatives to conventional petrodiesel fuel due to various technical and economic factors. It is obtained by reacting the parent vegetable oil or fat with an alcohol (transesterification) in the presence of a catalyst to give the corresponding mono-alkyl esters, which are defined as biodiesel. Due to the nature of the starting material, the production process, and subsequent handling, various factors can influence biodiesel fuel quality. These fuel quality issues are usually reflected in the contaminants in biodiesel. This work categorizes the various contaminants in biodiesel and details their analysis by methods prescribed in standards but also by other procedures. Other aspects of biodiesel analysis including production monitoring and assessing biodiesel/petrodiesel blends are also addressed. The types of analyses include chromatographic, spectroscopic, physical properties-based and wet chemical methods. The justifications for specifications in standards are also addressed.