The basic chemical reaction of soap making is the interaction between oil and alkali to form soap and glycerin:
CH2OCOR
| Heating
CHOCOR + 3NaOH --------> 3R-COONa + CH2OH-CHOH- CH2OH
|
CH2OCOR
The soap obtained by the reaction is called soap base after salting out, washing and finishing, and then further processed to become soap in various commercial forms
Refining
Remove impurities from oils and fats. Common refining processes include degumming, alkali refining (deacidification) and decolorization. Degumming is to remove phospholipids and other colloids in oils and fats. There are hydration methods that use water to hydrate phospholipids and other colloids and then precipitate them; and acid refining methods that use concentrated sulfuric acid to carbonize and precipitate phospholipids and similar impurities. The main function of alkali refining is to remove free fatty acids in oils and fats, but due to the formation of flocculent soap, pigments and impurities in oils and fats are removed by adsorption.
Saponification
After oil refining, saponification reaction with alkali occurs. Boiling is the main saponification method, and the soap pot is cylindrical or square.
In addition to the pipelines for conveying grease, alkali, water, and salt water, direct steam or steam coils are also installed to pass steam and stir the soap material. The pot is also equipped with a shaking pipe, the upper end of which can be placed at any liquid level to discharge the soap material in the pot. The bottom of the pot is conical, and there is a discharge pipe at the bottom to discharge the residual liquid left after the shaking pipe is discharged. The grease and caustic soda are boiled in the soap pot until the saponification rate reaches about 95%, and the saponification operation is stopped when the soap material is in a uniform closed state.
Salting out
In the closed soap material, salt or saturated salt water is added to separate the soap from the dilute glycerin water. The lowest concentration that causes the soap to precipitate is called the salting out limit concentration. After the closed soap gel is salted out, the soap on the upper layer is called soap grains; the glycerin water with salt on the lower layer is discharged from the bottom of the soap pot to recover glycerin.
Washing
After separating the waste liquid, add water and steam to boil the soap grains, so that it becomes a uniform soap gel from the separated state, and wash out the residual glycerin, pigments and impurities.
Alkali precipitation
In order to completely saponify the residual oil in the soap particles, glycerin, salt, pigments and impurities in the soap particles are further washed out through alkali precipitation. The lowest alkali concentration that completely precipitates the alkali precipitation water is called the alkali precipitation water limit concentration.
Finishing Adjust the electrolyte and fatty acid content in the soap particles after alkali precipitation, reduce impurities, improve color, and obtain the maximum soap yield and qualified soap base. When finishing, add an appropriate amount of electrolyte (such as caustic soda, salt) to adjust enough to separate the soap material into two soap phases. The upper layer is pure soap base, and the lower layer is soap stock. The soap stock has a dark color and many impurities, and is generally reused in the next pot of alkali precipitation.
Molding
The soap base is condensed into large soap boards, which are then cut into soap bases, printed and dried into laundry soap, toilet soap and other products.
