Purification of biodiesel from used cooking oils

In Europe, methyl esters cannot be classified as biodiesel until the EN 14214 Standard specifications are fulfilled. The aim of this paper is to examine the efficiency of removing several impurities in biodiesel from used cooking oils by means of three basic operations under conditions that have been kept as close to commercial operating practice as possible: (a) adsorption (magnesium silicate and bentonite); (b) liquid–liquid extraction (distilled water, tap water, glycerol); and (c) ion exchange (cation resin). The results show that all the purification methods can remove soap, methanol and glycerol effectively, while none had an effect on density, kinematic viscosity, FAME content or glyceride content. However, some of them have shown an influence on FFA and water content. The liquid–liquid extraction with glycerol at 15 wt.% and a 2-step contact proved to be the most suitable.

► Liquid-liquid extraction with glycerol at 15 wt% and 2-step contact is the most suitable method of biodiesel purification.
► The post-treatment for the purifying agents is essential for comparing purification methods.
► All the tested purification methods can remove soap, methanol and glycerol effectively.
► None of the methods had an effect on density, kinematic viscosity or FAME and glyceride content.