2. GENERAL INFORMATION ON SOAP
Soaps and detergents belong to the same group of
chemical products called surface-active agents or surfactants.
This group of products are, amongst other properties, well-known for their
detergency which is due to a reduction in water surface tension which
removes the dirt by wetting, emulsification, lathering and removal.
The following distinction is made:
Figure
Detergents are technologically more sophisticated
products designed for more specific use. As they are insensitive to the hardness
of the water - which, conversely, precipitates soap - detergents have their main
outlets in mechanical washing (washing machines and dish-washers) and industrial
washing. These products will not be covered by this technological inventory.
Soaps are obtained either by the saponification
of fats and oils (triglycerides) of vegetable or animal origin, or by the
neutralisation of fatty acids.
SYNTHESIS BY SAPONIFICATION OF OILS
AND FATS
Figure
In the case of the saponification of fatty materials,
oils, greases, or tallows are attacked - "saponified" - by soda (to obtain
hard soap) or potash (to obtain soft or liquid soap). Apart from the soap, a
by-product - glycerine - forms during the chemical reaction. This may be
separated off or may be left, depending on the nature of the manufacturing
process.
SYNTHESIS BY FATTY ACIDS
NEUTRALISATION
Figure
Fatty acid neutralisation is also carried out using soda
or potash and produces the same type of soap as saponification. However, the end
product is glycerine-free. It should be noted that the starting fatty acids are
obtained by hydrolysis of oils and fats, which involves an additional stage. The
glycerine formed is separated off by steam distillation.
Generally speaking, this method of synthesis is suitable only
for large production volumes and is only really justified if the fatty acids
produced are used as raw material in other chemical syntheses. Since it is less
suitable for developing countries, soap produced by means of fatty acid
neutralisation will not be discussed in this guide.
By way of information, the production installations are similar,
if not identical, to saponification installations. Using this method of
synthesis it is often easier to regulate the desired properties of the soap to
be marketed and to guarantee the consistent quality of the end
product.
