Purification of crude glycerol derived from waste used-oil methyl ester plant

Abstract

The purification of crude glycerol from a biodiesel plant using waste used-oil as a raw material was carried out on a laboratory scale by using the combined chemical and physical treatments based upon repeated cycles of acidification to the desired pH within the range of 1–6 using 1.19 M H₂SO₄, allowing phase separation and harvesting of the glycerol-rich middle phase followed by neutralization of the harvested glycerol phase with 12.5M NaOH. Subsequently, the glycerol-enriched fraction was extracted by ethanol. The results indicated that increasing the pH of the acidification step led to an increased yield of the glycerol-rich layer and decreased amount of inorganic salt and free fatty acids phase. Under strong acid conditions, large quantities of fatty acid and salt in the glycerol-enriched fraction were eliminated and, at pH 1, high purity glycerol (∼93.34%) with relatively low contaminant levels (0.00045% (w/w) ash and 5.16% (w/w) MONG) was obtained.