Refining Crude Glycerol to 99.5%

Fats and oils are triglycerides: glycerol joined to three fatty acids. Splitting them, by saponification with sodium hydroxide in soap making, by hydrolysis, or by transesterification in biodiesel making, frees the glycerol. That crude glycerol is of variable quality. It is refined in steps: activated carbon takes out organic impurities, alkali deals with glycerol esters that have not reacted, and ion exchange removes salts. Glycerol of more than 99.5% purity is then distilled in several stages under vacuum, because at normal pressure it boils at 290 °C.