Soaps manufacture from fatty acid and oil for variety of soap products

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 a section like, how soap is made? Types of soaps, how it works or what does it do?

Soap manufacturing:

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 examples are rosin and neatsfoot oil, tallow, coconut oil, palm oil, castor oil and cottonseed oil. Alkali like sodium hydroxide and caustic potash are commonly used. Additives are added to change the application of soap for different purposes, additives act as building material for a soap they are sodium tripolyphosphate, sodium silicates, sodium hexametaphosphate, trisodium phosphate etc.

The process can be explained by series of unit operation involved:

  • Reacting oil with an alkali
  • Addition of salt which is called as salting
  • Recovery of formed glycerol
  • Graining operation
  • Separation from Niger
  • Drying
  • Milling
  • Combining with additives
  • Finished soap processing


Soap manufacturing process flow sheet using oil and alkali

Commercial Full-Boiled Soap Manufacture Process Flow Diagram

Chemical reaction:

  • 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

The full boiled process is a kettle-soap process which is popular for its speciality in separation of glycerol during the process itself when compared to other two methods. A slurry form of soap float on glycerine which makes 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 the unsaponified matter.

A large CSTR’s (continuous stirred tank reactor) are chosen 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 a weight basis. Feed is mixed with this ratio for optimum soap formation conditions. After the reaction settled glycerine is removed from the bottom and killing change operation is done followed by graining process which means 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 a different form of look and odour, even colour 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 a continuous plant, spray drying is done to carry out cooling and drying operation simultaneously in a single step.

Specification of different types of soaps:

Toilet soap:

  • Alkali content is less than 0.1%
  • Moisture content  12-15%
  • Perfume additives are added,
  • Mostly made from coconut oil

Castile soap

  • Made from olive oil
  • Cold process is used
  • Moisture content 60-50%
  • Used for infants and medical purpose

Carbolic soap

  • Disinfectant soaps
  • Tar acids or cresylic acids are added

Transparent soap

  • The semi-boiled process is used
  • Made from tallow and coconut oil
  • Glycerol and alcohol ratio is about 1:2

Shaving soaps

  • Coconut oil is raw material
  • Free alkali (not present)
  • Stearic acid content fatty acids are preferred

Shampoo soaps

  • Potassium alkali is used with coconut oil
  • EDTA is added
  • Soap content is 25%