.
Chapters
0:00 Introduction
0:33 what is glycerin
1:18 What does Glycerin do for the skin?
1:58 Can Glycerin irritate the skin?
Glycerol (/ˈɡlɪsərɒl/),[6] also called glycerine in British English and glycerin in American English, is a simple polyol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known as glycerides. Due to having antimicrobial and antiviral properties it is widely used in FDA approved wound and burn treatments. Conversely, it is also used as a bacterial culture medium.[7] It can be used as an effective marker to measure liver disease. It is also widely used as a sweetener in the food industry and as a humectant in pharmaceutical formulations. Owing to the presence of three hydroxyl groups, glycerol is miscible with water and is hygroscopic in nature.[8]Although achiral, glycerol is prochiral with respect to reactions of one of the two primary alcohols. Thus, in substituted derivatives, the stereospecific numbering labels the molecule with a "sn-" prefix before the stem name of the molecule.[9][10][11]
Triglycerides can be saponified with sodium hydroxide to give glycerol and fatty sodium salt or soap.
Typical plant sources include soybeans or palm. Animal-derived tallow is another source. Approximately 950,000 tons per year are produced in the United States and Europe; 350,000 tons of glycerol were produced per year in the United States alone from 2000 to 2004.[12] The EU directive 2003/30/EC set a requirement that 5.75% of petroleum fuels are to be replaced with biofuel sources across all member states by 2010. It was projected in 2006 that by 2020, production would be six times more than demand, creating an excess of glycerol.[8]
Glycerol from triglycerides is produced on a large scale, but the crude product is of variable quality, with a low selling price of as low as 2-5 U.S. cents per kilogram in 2011.[13] It can be purified, but the process is expensive. Some glycerol is burned for energy, but its heat value is low.[14]
Crude glycerol from the hydrolysis of triglycerides can be purified by treatment with activated carbon to remove organic impurities, alkali to remove unreacted glycerol esters, and ion exchange to remove salts. High purity glycerol (99.5%) is obtained by multi-step distillation; a vacuum chamber is necessary due to its high boiling point (290 °C).[8]
Synthetic glycerol
Although usually not cost-effective, glycerol can be produced by various routes from propene. 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. This epichlorohydrin is then hydrolyzed to give glycerol. Chlorine-free processes from propylene include the synthesis of glycerol from acrolein and propylene oxide.[8]