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Friday, 06 December 2019
Glycerol
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Glycerol is the common name for 1,2,3-propantriol (C3H8O3), an alcohol with a molecular weight of 92.1. There are two recognised glycerol strengths: 99% (content - min. 98.0 to max. 101.0%; typically: 99.5% ) and 85% (content - min. 83.5 to max. 88.5%; typically: 85.5%). In each case, the content relates to anhydrous substance.

Glycerol was discovered in 1779, by the German chemist Scheele, during saponification of olive oil with lead oxide. In 1811, the French chemist Chevreul introduced the name 'glycerol', which is derived from the Greek (8L6`l (glycos) = sweet. In 1836, Pelouze came up with the empirical composition and, in 1872, Friedel managed to synthesise glycerol from acetone, via isopropanol, propene, 1,2-dichlorpropane and 1,2,3-trichlorpropane. Glycerol, in the form of a fatty acid ester, is to be found in all fats and oils, which means that it is distributed widely in Nature.

Coconut and palm oils, tallow and soya oil contain 17%, 11%, 10% and 10% glycerol, respectively, making this substance part and parcel of our daily dietary intake. It also occurs as a lecithin in egg yolk, brain tissue, blood cells, bile and neural tissue. Glycerol is also formed, to a lesser extent, during alcoholic fermentation and small quantities are, therefore, to be found in wine.

Nowadays, four different methods are used to obtain glycerol:

1. hydrolysis from fats (splitting fatty acid esters),
2. synthesis, starting with propene,
3. saccharide hydrolysis, followed by catalytic hydrogenation (glycerogen) and
4. alcoholic fermentation.

Originally, glycerol was a by-product of fat saponification. Back in the 1940s, when synthetic detergents dominated the market, particularly in the USA, there was no longer enough fatty acid-based glycerol to meet demand, so synthesising processes were developed (see above). Today, in many countries, petrochemical-based glycerol production has peaked.

Glycerol is a clear, colourless to approximately colourless, syrupy liquid with a greasy texture. It is highly hygroscopic, water- and ethanol-miscible, poorly soluble in acetone and ether and practically insoluble in fats and volatile oils. Glycerol is used primarily in the plastics (alkyd resins, polyurethane foams) and chemical industries (quinoline, benzanthrone, Alizarin blue). Large amounts of glycerol are used in humectants (tobacco), as ointment base (toothpaste), in skin-care products (hand creams) and to sweeten drinks and extract natural substances.

In the textiles industry, glycerol is used in the production of size and finishes. Further uses include: fluid for heat exchangers in heating systems, sealing liquid, brake fluid and coolant (Arctic beetles can survive temperatures as low as -85°C, since they are able to synthesise glycerol in their blood), softeners for rubber products (tyres), high-pressure fluids for hydraulic systems and for industrial printing dye manufacture (stamp and printing dyes, copier inks). Today, approx. 4% of glycerol production is used in the manufacture of explosives (nitroglycerine).

In the pharmaceuticals trade glycerol is used (rectally) as a purgative. Glycerol may not be administered parenterally or intravenously (e.g. solubilisers for drugs), since this would result in hæmolysis.

INCI Name: Glycerin
 

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