To meet the ASTM D-6751-02 Standard for biodiesel, impurities, particularly glycerol, must be reduced to acceptable levels. Liquid-liquid extraction (i.e., solvent partitioning) is commonly used to achieve this standard. Evaluation of the technical feasibility of a single-stage mixer-settler liquid-liquid equilibrium process to separate glycerol and methyl oleate (as a model for biodiesel) was carried out based on the following criteria: (a) a volume ratio of the liquid phases close to 1:1, (b) a high recovery of biodiesel, (c) a short residence time of the liquid phases in the settler, and (d) achievement of the ASTM Standard for glycerol mass fraction of 0.0002 or less. Eight liquid-liquid extraction processes using different combinations of three potential solvents, hexane, methanol, and water, were studied. All data for the optimal compositions of each solvent system were obtained by calculations using the UNIFAC activity coefficient model, and no experimental measurements were done. Extraction using multisolvent systems containing hexane, methanol, and water were found to be technically feasible and gave the best results.
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