Production of Neat Soap
Kettle Process
- Kettle Process
The classic process for production of toilet soap requires a period of five days. For this reason the kettle capacity has to correspond to the production rate of one week. This means, e.g.: for 8 tons of dried soap/day a kettle capacity of about 120 m3 is required.
For continuous processing the necessary kettle capacity should be installed in three to six kettles.
Saponification requires about 1 day. For glycerin extraction and separation of lye (washing solution) 1 to 2 days, for fitting half a day and for subsequent separation of niger 1.5 to 2 days are needed. For boiling and mixing of the different phases about 800 kg steam/ton of soap are required. One kg of fat corresponds to about 1.6 kg neat soap with 60 to 63% of fatty acid content.
One ton of neat soap » 0.89 tons of laundry soap (70% TFA) or 0.8 tons of toilet soap (78% TFA)
Continuous Process
Compared to the kettle process continuous saponification has the following advantages:
- Processing during only a few hours
- Small space requirements (about 20% of kettle process)
- Small amount of utilities (100 to 150 kg steam/ton of soap)
- High glycerin concentration of the lye (15-20%)
- Continuous recycling of niger
- Low raw material losses (e.g. as result of smaller amount of lye)
- No skilled soap specialist is needed
Standard Values for the Production of 1 Ton of Neat Soap with 62% TFM*
| Raw material (kg/ton of neat soap) | ||
| Fat | 660 | |
| NaOH (36 %) | 240 - 330 | |
| NaCl (21 %) | 110 - 190 | |
| Water | 500 - 850 | |
| Fatmixture (% weight) | |||||
| Fancy tallow | 70 - 85 | 50 | 70 | ||
| Bleached Palmoil | 35 | 75 | |||
| Coconutoil / Palm kernel oil | 30 - 15 | 15 | 15 | 15 | |
| Peanut Oil | 15 | 10 | |||
| Utilities (per ton of neat soap) | |||
| Steam kg/hr | Cooling water m³/h | Electric Power kWh | |
| Kettle Saponification | 800 - 1000 | 2 - 3 | |
| Continuous Saponification | 100 - 150 | 2 - 4 | 35 - 45 |
| Neutralization of Fatty Acid | 80 - 110 | 12 - 18 | |
| Semiboiled Saponification | 30 - 40 | 30 - 40 | |
* TFM = Total Fatty Matter
The processing components fat, caustic soda, brine, water and glycerin are fed individually by metering pumps.
Saponification is done continuously in a saponification reactor equipped with a constant recycling system for saponified product. After saponification the soap is cooled by addition of spent lye.
For glycerin extraction soap and washing lye are fed countercurrently to a liquid/liquid extractor while the glycerin is recycled partly to the saponification step for concentration. The fitting solution is fed into the fitting reactor with a recycling loop.
The two phases: neat soap and niger leave the reactor as one mixture and are separated later by settling or centrifugation. Similar to kettle process the continuously processed soap has a fatty acid content of 60 to 63%.
Neutralization of Fatty Acid
Splitting of fats into fatty acids and glycerin can be done also before saponification, e.g. by high pressure hydrolysis. This process usually becomes economic with high production rates (50 tons/day or more). It is mainly used when fatty acid is the base not only for soap but also for other products.
For neutralization the same process as for saponification of fats is used, but without the glycerin washing step.
Semiboiled Process
In addition to the fatty acid kettle process for production of laundry soap a simplified semiboiled process is possible. This is a process without glycerin washing and soap fitting. The semiboiled process requires lower investment costs, handling is simple and there is no waste water.
The components: fat and caustic soda are saponified by mixing in a soap crutcher. The soap produced by this method has a fatty acid content of about 58%. This process is not applicable for the production of high grade toilet soap.