Soap is a basic cleaning agent, called as surfactant means surface active agent. Vegetable oils and fats are commonly used as raw material to make soap. To know in brief we can split the discussion into section like, how soap is made? Types of soaps, how it works or what does it do?
Saponification is the name of the process and raw material required is vegetable oil which contains fatty acids having minimum 12 to 18 carbon atoms, some of the example are rosin and neats foot oil, tallow, coconut oil, palm oil, castor oil and cotton seed oil. Alkali like sodium hydroxide and caustic potash are commonly used. Additives are added to change the application of soap for different purposes, additives acts as building material for a soap they are sodium tripolyphosphate, sodium silicates, sodium hexametaphosphate, trisodium phosphate etc.
Process can be explained with series of unit operation involved:
- Reacting oil with alkali
- Addition of salt which is called as salting
- Recovery of formed glycerol
- Graining operation
- Separation from Niger
- Combining with additives
- Finished soap processing
- R-COOH + NaOH(caustic soda) —> R-COONa +H2O
- C3H5(O2CR3)[triglycerides] + 3NaOH—> 3RCO3Na(soap) + C3H5(OH)3(glycerol)
Soap making process classification:
Three methods are used for making soap in large scale
- Cold process
- Semi boiled process
- Full boiled process
Full boiled process is kettle-soap process which is popular for it specialty in separation of glycerol during the process itself when compared to other two method. Slurry form of soap float on glycerine which make easy to separate the layer after reaction completion, alkali is taken as limiting reactant and so all the quantity is reacted leaving traces about less than 0.1% in unsaponified matter.
A large CSTR’s are choose by a chemical engineer to carry out the reaction have a heat of reaction approximately 272 KJ/Kg of fatty acid. A standard ratio of alkali and fatty acid is 3:5 on weight basis. Feed is mixed with this ratio for optimum soap formation conditions. After the reaction settled glycerine is removed from bottom and killing change operation is done followed by graining process which mean brine is added to the soap slurry and washing operation is carried out with fresh brine and water to remove all the trace of impurities leaving of clean soap paste. By drying out this paste it starts getting harder and stamping is done along with cutting the soap bar operation.
The crude soap is subjected to addition and mixing with builders and perfumes to get different form of look and odour, even color is also added to give it bright look in the process of crutching. The hot crude cooled by two methods, 1) frame cooling and 2) press cooling, but in continuous plant spray drying is done to carryout cooling and drying operation simultaneously in single step.
Specification of different types of soaps:
- Alkali content is less than 0.1%
- Moisture content 12-15%
- Perfume additives are added,
- Mostly made from coconut oil
- Made from olive oil
- Cold process is used
- Moisture content 60-50%
- Used for infants and medical purpose
- Disinfectant soaps
- Tar acids or cresylic acids are added
- Semi-boiled process is used
- Made form tallow and coconut oil
- Glycerol and alcohol ratio is about 1:2
- Coconut oil is raw material
- Free alkali (not present)
- Stearic acid content fatty acids are preferred
- Potassium alkali is used with coconut oil
- EDTA is added
- Soap content is 25%