Crude glycerine purification by solvent extraction

Abstract

In this work, a process to remove saponifiable matter (fatty acid methyl esters (FAME), free fatty acids, mono-, di-, and tri-acylglycerides) from industrial crude glycerine samples is addressed. The extraction of these impurities with different solvents is analyzed in detail, using diethyl ether, methyl ter-butyl ether, FAME, toluene, hexanes, 1-butanol and 1-hexanol. Hexane and biodiesel were chosen as the main candidates in order to be used in this process. It was found that it is necessary to add water to the crude glycerine to efficiently remove the saponifiable matter. Water increases the polarity of the phase and favors the transference of the impurities to the non-polar phase, e.g. the hexanes. The use of FAME as extraction solvent requires the use of higher temperature than when using hexanes, higher levels of water addition, and pH adjustment before the extraction. The addition of 20 wt% of water, carrying out the extraction at 80 °C with a pH adjustment at 3, and separation by centrifugation represents a good set of process conditions in order to efficiently extract the saponifiable matter from crude glycerine. UV–Vis analysis proved to be very useful in following the purification process, while FTIR carried out directly on the glycerine has not enough sensitivity to follow the extraction.