Introduction - Neutral Fat Saponification
Raw materials
- Continuous saponification plant
Soap is produced commonly with 70 to 85% beef tallow and 15 to 30% coconut oil. Instead of tallow bleached palm oil can also be used, but for high grade toilet soap the palm oil content of soap should be limited to a maximum of 75%. In place of coconut oil palm kernel oil can be used. Depending on fat quality and the grade of final product sometimes a pretreatment for fat cleaning and bleaching is required.
- Liquid neat soap
Caustic soda lye used for saponification of fats can be produced by dissolving crystalline caustic soda in water.
After saponification of fats and reaction of fatty acids with caustic soda glycerin (about 10% of fats) is split and can be extracted with brine (10 - 20% NaCl). The brine is produced by dissolving crystalline sodium chloride in water.
Saponification
The saponification process for production of soap takes place in three steps
saponification - glycerin extraction - soap fitting.
During this treatment fats and electrolyte (NaOH and/or NaCl solutions) are mixed together for reaction and for building new phases to be separated subsequently.
Saponification takes place by reaction of about 130 kg NaOH (100%) with 1000 kg fat producing reaction heat and separating about 90 kg glycerin. The extraction of glycerin increases with intensity of washing, and at the same time the glycerin content of washed soap decreases. By recycling the glycerin spent lye several times, the glycerin concentration of washing lye can reach 15 to 20%, this allowing an economic glycerin recovery.
After glycerin washing the soap is treated for fitting by adjusting the electrolyte content (adding NaOH solution) to build the two phases: neat soap (about 75%) and niger (about 25%). Neat soap has then a water content of 30 - 32%, a content of fatty acid of 60 - 63 % and represents the fitted soap. Niger embodies most of the impurities and has a water content of about 60%. Separation of these two phases becomes expensive by reason of the very low difference of gravities. Niger is recycled to the saponification step.