Soap-stock oil is obtained from the chemical refining process of edible oils. During the refining process, the sodium hydroxide reacts with free fatty acid of the oil and give a soap-stock composed by soap, water, fatty acids, glycerine, caustic soda, pigments and oxidation products. The colour is yellow/brown and becomes dark when soap-stock is in contact with air.
The acidulation process is used to recovery the fatty acids from the soap-stock. Sulphuric acid is mixed with heated soap-stock and the fatty acids are extracted, (refined and bleached if required) and used for soap manufacturing. Depending on the process and the type of oil, the soap-stock can normally includes from 20 to 45% of fatty acids.
PFAD - PALM FATTY ACID DISTILLATE
PFAD is obtained from Palm Oil refining process. PFAD contains mainly fatty acids and other impurities. It is a low cost raw material used in soap manufacturing but also used in animal feed and to produce biodiesel. If obtained from crude palm oil, the PFAD is brown solid at room temperature and melts to a brown liquid on heating. This type of PFAD is mainly used for laundry soap; it needs to be bleached for toilet soap manufacturing.
Fatty Acids are organic acids derived from Vegetable Oils / Animal Fats. Fatty acids are produced by the hydrolysis of Neutral Oils; this process is well know with the name of Splitting, where the Glycerine is a by-product in the process of Fatty Acids manufacturing.
A process called Fractionation is used in order to obtain different types of Fatty Acids, each of which with the proper carbon chain length.
If available a Splitting Plant to process the Palm Oil, the soap is produced from Fatty Acids; while if the soap is produced starting from Palm Oil (and its fractions like Palm Stearin) the glycerin is removed after the Saponification Process.