Separation of Free Glycerol and Glycerides from Biodiesel by Means of Liquid-Liquid Extraction

Abstract

This paper investigates glycerol and glycerides extraction process from fresh and waste sunflower oil biodiesel. Deep eutectic solvent choline-chloride: ethylene-glycol (molar ratio 1:2.5) was used as extraction media in both batch experiments and continuous Karr column. Biodiesel was synthesized in an alkali catalysed chemical transesterification reaction. Three process variables, namely hydrodynamic conditions, solvent to biodiesel ratio and extraction duration were investigated and their impact on the extraction efficiency was found to be largely negligible. Throughout the whole range of process variables the extraction efficiency was relatively high, getting slightly lower only during the continuous experiments. After the extraction, free glycerol content was below the limit for all samples, but the total glycerol and glycerides content was too high to fully comply with biodiesel quality standards. Selected extraction solvent has proved to be efficient for free glycerol removal in the tested range of conditions, but further process modifications and possible raw material and biodiesel processing will be needed to reduce the content of total glycerol and glycerides.