Soap can be produced by reacting oil with a caustic solution. It can also be made from fatty acid by neutralization reaction with a caustic solution. It can also be prepared by saponification of methyl ester with a caustic solution.
From the above three reaction equations, the soap manufacturing process is very simple. However, due to the colloidal properties of soap and soapy water solution, it is not easy to make high-quality soap. In order to make pure soap, different standards and monitoring means are required in different links such as raw material selection, oil refining, saponification refining, glycerin recovery, etc.
The main raw materials for making soap include two categories: grease and alkali. Grease can be replaced by fatty acid or rosin. Because rosin is relatively low in price, the cost of soap can be reduced by replacing grease with rosin. In addition, rosin added to soap can prevent the crystallization of stearic acid soap, so that the soap body is hard, not brittle, not rancid. The disadvantage is that the foaming power and decontamination power of rosin soap are not as good as grease soap. Alkali can use sodium hydroxide, sometimes potassium hydroxide, sodium carbonate, and potassium carbonate. Sodium hydroxide and potassium hydroxide are used to saponify oil and sodium carbonate and potassium carbonate are used to neutralize fatty acids. Sodium hydroxide and sodium carbonate are used to make hard sodium soap, and potassium hydroxide and potassium carbonate are used to make soft or liquid potassium soap, In addition, some additives are needed, such as salt, sodium silicate, decolorizer, colorant, perfume, etc. When salt is used as a salting-out agent in soap making, the content of calcium and magnesium in salt is required to be as small as possible, otherwise, a large number of insoluble calcium and magnesium soaps will be formed. Sodium silicate is mainly used as the additive of laundry soap, and a small amount of it is used as the antioxidant of soap. The color of soap oil is not as good as that of edible oil. Many oils must be decolorized before use, so decolorizer is used. And the use of colorant, on the one hand, can increase the beauty of soap, on the other hand, can cover up or adjust the color of soap with less beautiful. The purpose of adding spices to soap is to cover the unpleasant smell brought by some low-quality oils. Adding spices to soap can make people feel happy and happy to use.