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Glycerol | Glycerine | Glycerin

Glycerol (or glycerine, glycerin) is a simple polyol compound. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. The glycerol backbone is central to all lipids known as triglycerides. Glycerol is sweet-tasting and of low toxicity.
Glycerol forms the backbone of triglycerides, and is chiefly produced by saponification of fats as a byproduct of soap-making.

It is also a byproduct of the production of biodiesel via transesterification. This form of crude glycerin is often dark in appearance with a thick, syrup-like consistency. Triglycerides (1) are treated with an alcohol such as ethanol (2) with catalytic base to give ethyl esters of fatty acids (3) and glycerol (4):

Glycerol is also produced by various routes from propylene. The epichlorohydrin process is the most important; it involves the chlorination of propylene to give allyl chloride, which is oxidized with hypochlorite to dichlorohydrins, which reacts with a strong base to give epichlorohydrin. Epichlorohydrin is then hydrolyzed to give glycerol.

Because of the emphasis on biodiesel, where glycerol is a waste product, the market for glycerol is depressed, and the old epichlorohydrin process for glycerol synthesis is no longer economical on a large scale. Glycerol can be removed from the process by using a special enzyme that breaks down phytol and starches. This enzyme is biologically produced using a genetically engineered bacterium. Because there is no glycerin produced as a by-product, the biodiesel purity is greatly improved and costs can be reduced.

Only one producer for synthetic glycerol is left, because high-quality glycerol is needed in highly sensitive pharmaceutical, technical and personal care applications. Raw materials used to make glycerol include animal fats, such as beef tallow, and vegetable oils, such as coconut and soybean. Approximately 950,000 tons per annum are produced in the USA and Europe; 350,000 tons of glycerol were produced per year in the United States alone from 2000-2004. Production will increase as the EU directive 2003/30/EC is implemented, which requires the replacement of 5.75% of petroleum fuels with biofuel across all Member States by 2010. It is projected that by the year 2020, production will be six times more than demand.