Glycerol: Origins and Production

Glycerol, also known as glycerin or propanetriol, is a simple polyol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. Its structure consists of a three-carbon chain with a hydroxyl (-OH) group attached to each carbon.

Sources of Glycerol

Natural Production

Glycerol is naturally produced during the metabolism of fats and oils, particularly triglycerides. Triglycerides, composed of glycerol and three fatty acids, undergo hydrolysis or transesterification to release glycerol.

• Saponification: This process, used in soapmaking, involves the alkaline hydrolysis of fats and oils, yielding glycerol and soap (fatty acid salts).
• Transesterification: In the production of biodiesel, triglycerides react with an alcohol (typically methanol or ethanol) in the presence of a catalyst to produce fatty acid esters (biodiesel) and glycerol.

Synthetic Production

Glycerol can also be synthesized from petrochemical feedstocks.

• Epichlorohydrin Process: Propylene is chlorinated to produce allyl chloride, which is then converted to epichlorohydrin. Epichlorohydrin is subsequently hydrolyzed to yield glycerol.
• Propylene Oxide Process: Propylene is oxidized to propylene oxide, which is then isomerized to allyl alcohol. Allyl alcohol is then treated with hydrogen peroxide or performic acid to form glycidol, which is then hydrolyzed to glycerol.

Glycerol as a Byproduct

A significant portion of glycerol is obtained as a byproduct of other industrial processes, most notably biodiesel and soap manufacturing. The increasing production of biodiesel has led to a surplus of glycerol, creating opportunities for developing new applications and refining processes.

Refining and Purification

Crude glycerol obtained from saponification or transesterification often contains impurities, including soaps, methanol, salts, and other organic materials. Purification processes, such as distillation, ion exchange, and activated carbon treatment, are employed to produce refined glycerol suitable for various applications, including pharmaceuticals, cosmetics, and food.