Crude glycerine characterization: analysis of free fatty acids, fatty acid methyl esters, and acylglycerides

Abstract

Crude glycerine is a product obtained in a biodiesel production plant by processing the glycerine phase formed in the transesterification reactor. Crude glycerine contains approximately 80 wt% of glycerine, water, salts, and matter organic non-glycerol. This product is used mainly as a feedstock to obtain high-purity glycerine in a refining unit. Due to a large variability in biodiesel production processes and technologies, the crude glycerine has significant variations in its composition, making it difficult to run the latter process. Particularly, the content of saponifiable matter (free fatty acids, fatty acid methyl esters, and mono-, di-, and tri-acylglycerides) is relevant not only in the refining process, but also in other applications such as bioconversion processes to obtain value-added products. In this work, a method to quantify free fatty acids, fatty acid methyl esters, and mono-, di-, and tri-acylglycerides is presented. The method is based on a quantitative extraction with hexanes, and an analysis by GC with derivatization. It is possible to detect very low concentrations of these impurities. The confidence intervals for each of these impurities have been determined, being the highest for the quantification of the fatty acid methyl esters and mono-acylglycerides. In all cases, the 95% confidence intervals represent an error smaller than 20%.