Crude glycerine is merely glycerine in a less pure form. Hence, in its chemical composition, it does not differ from glycerol, as glycerine is correctly called.
It consists of carbon, hydrogen and oxygen atoms that, in their type of chemical bond – C3H5(OH)3 – represent a trihydric alcohol. In common language, glycerol is also known as propanetriol, irrespective of its degree of purity.
Therefore, we cannot conclude from the formula alone whether a chemical compound with the chemical formula C3H5(OH)3 is highly pure pharmaceutical grade glycerine or a less pure “crude” glycerine.
A Less Pure by-Product
Less pure glycerine like crude glycerine is not a contaminated and thus unusable substance. On the contrary: the secret lies in its production. A large quantity of glycerine is generated in the production of biodiesel. The proportion of glycerine in vegetable oils such as rapeseed or palm is approx. 10%. Following initial processing, it has a typical purity grade of about 80 per cent and is still nothing more than a by-product.
The degree to which glycerine is condensed in a further distillation process and thus becomes purer is decisive for its later name. Crude glycerine contains a high proportion of hydrogen; i.e. it has a water content of 10 to 15 per cent. It also contains other substances, e.g. between two and eight per cent of crude ash.
After further chemical processing, glycerine can be used as a valuable raw material for the manufacture of numerous products in the chemical, pharmaceutical, and food industries. The glycerine content of then pure glycerine can be up to 99.9 per cent.
Properties of Crude Glycerine
While pure glycerine is colorless and has a sweet taste, less pure glycerol stands out due to its usually brown color. It can also vary in color. In crude glycerine, the sweet taste that pure glycerine has is masked by the higher salt content. Otherwise, this substance has the same properties as pure glycerol. It dissolves in water and attracts moisture. Because it is less pure, crude glycerine is mainly used for industrial purposes. It is not pure enough for use in the pharmaceutical industry or for the production of food. Here its degree of purity would have to be 99.5 per cent.
The substance is also used in the agricultural sector, particularly for feeding cattle and fattening pigs as crude glycerine is very high in energy and much less expensive than pure glycerine. Therefore, it is used both as a technological additive in the production of animal feed, for example for stabilizing pellets, and as a single feedstuff. However, only glycerine with a degree of purity of 80 per cent is suitable as animal feed. According to the “white list” applicable since 2006, the substance may only be used for feeding animals if it was gained from vegetable fats and oils.
Roberto Echeverría Botero
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