Sequential-refining of crude glycerol derived from waste used-oil methyl ester plant via a combined process of chemical and adsorption

A sequential stage physico-chemical refining of crude glycerol, derived from a waste used-oil utilizing biodiesel (methyl ester) production plant, was performed by acidification, polar solvent extraction and activated carbon adsorption at a laboratory scale and ambient temperature. The effect of varying the acid type (H3PO4, H2SO4 and CH3COOH) and pH (1–6), the type of polar solvent (CH3OH, C2H5OH and C3H7OH) and their ratio to glycerol (3:1–1:3 v/v), and adsorption with activated carbon at different ratios of activated carbon to glycerol (40–200 g/l) on the purity of crude glycerol was explored. The highest glycerol purity (95.74 wt.%) was obtained with the sequential acidification to pH 2.5 with H3PO4 and phase separation, followed by extraction with C3H7OH at a solvent:crude glycerol ratio of 2:1 (v/v). Finally, adsorption with commercial activated carbon at 200 g/l also achieved a 99.7% color reduction.