Saponification . It is the synthesis of soap from the chemical reaction of oils or fats in an alkaline medium, which could well be sodium hydroxide .


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  • 1 Chemical reaction
  • 2 Saponification index
  • 3 Laboratory preparation
  • 4 Industrial process
  • 5 Other methods of obtaining soaps
  • 6 Sources
  • 7 External links

Chemical reaction

The reaction consists of the hydrolysis in basic medium of the fats or lipids , which are broken down into potassium or sodium salts (soaps) and glycerin , as shown below:

The same occurs with heat release , a very necessary element to achieve a quality product, therefore the higher the heat produced by the reaction the higher quality the soaps produced will have (transparency and cleanliness), although this reaction rarely produces the necessary heat therefore it is very convenient to supply it so that the neutralization of fatty acids occurs completely, thus achieving a higher quality in the product.

The lipids that can intervene in the reaction are the saponifiable ones that would be those that are composed of an alcohol bound to one or more fatty acids (the same or different). This union is made through an ester bond, very difficult to hydrolyze. But it can be broken easily if the lipid is in a basic medium. In this case, alkaline saponification occurs.

Saponification index

The saponification index is the amount in milligrams of an alkali, specifically potassium hydroxide , that is needed to saponify a gram of a certain oil or fat. This varies for each particular fat or oil. This data is obtained from complex calculations, which are simplified with the use of existing tables.

These tables record the saponification indices of the substances, that is, the amount in milligrams of sodium or potassium hydroxide that they need to saponify each of them, depending on the substance used to obtain the soap.

Below is the saponification indexes of some of the oils and fats, frequently used in the manufacture of soaps:

Substance Saponification index Substance Saponification index
Olive oil 0.134 Coconut oil 0.190
Palm oil 0.141 Sunflower oil 0.134
Castor oil 0.128 Sweet almond oil 0.136
Avocado oil 0.133 Soy oil 0.135
Corn oil 0.136 Sesame oil 0.133
Jojoba oil 0.069 Palm kernel oil 0.156
Wheat germ oil 0.132 Bee wax 0.069
Cocoa butter 0.137 Shea Oil 0.128

Laboratory preparation

Laboratory soap making.

This process can be carried out on a small scale in a laboratory with either oils or fats:

  • With oil:
  1. Dissolve the pearls of sodium hydroxide NaOH (sol), for this we weigh 20 gr of NaOH on the scale, transfer the content to a 100 ml graduated pot and make up to the mark with distilled water to obtain a 20% solution.
  2. Put 100ml of oil in a container, and mix it with the sodium hydroxide solution.
  3. Heat for 30 min. approximately, to the bain-marie carefully.
  4. Let stand for 24 h at room temperature, so that the soap forms.
  • With animal fat:
  1. Dissolve the hydroxide beads to obtain a 20% solution.
  2. Weigh 100 g of animal fat on the scale.
  3. Heating in a water bath because it is in a semi-solid state should be more fluid.
  4. Then mix with the sodium hydroxide solution and again heat the mixture in a water bath carefully.
  5. Let stand to see results.

Industrial process

Industrial soaps produced from saponification.

The use of this chemical reaction in industry is based on two methods: task-based (intermittent) or continuous. The choice of the procedure and the raw materials depend on the quality to be obtained, the facility for handling and treating the raw materials, and the means to produce the soap and recover the glycerin.
Most of the soap factories operate by the Full-fired boilers method with neutral fats. This procedure produces high-quality soaps and inferior industrial products, and glycerin is used.
Some ways to make soaps from this chemical reaction:

  • Total cookingmethod: The boiler or total cooking method consists of several times or operations, by means of which the saponification of fats is carried out, the precipitation of soap in the concentrated soap lye or soap glue, the separation of glycerin and colored materials from the soapy mass by washing, and finishing cooking to give the mass a point so that it forms a clean soap when it rests.
  • Continuous method with neutral fats: In recent years, soap factories based on the continuous process have been installed worldwide. The basic manufacturing phases are analogous to the operations carried out in the boiler method: Saponification, soap washing to recover glycerin, finishing. It is operated in countercurrent, and the number of washes depends on the amount of glycerin that has to be recovered from the soap.
  • Modified procedures:
  1. Semicoction Procedure: The fatty matter is mixed with a quantity of caustic soda sufficient to completely saponify it. The reaction is verified by stirring and heating with closed steam. Glycerin is left in the soap mass.
  2. Procedure without boiler: The heat generated by the exothermic reaction produced between the fats and the alkali is used to complete the saponification. The fat is heated to the appropriate temperature and mixed with the caustic alkali. If the mixture is left in an insulated container in which the saponification reaction occurs slowly. This method does not produce high-quality soaps, because some unsaponified fat remains in the soap masses.
  3. Autoclave Procedure: The alkali reacts with the fat at high temperature and pressure. The mixture is stirred by pumping it with exothermic heated coils. In these conditions saponification is very fast. The hot mass undergoes instantaneous expansion in a vacuum chamber, into which the soap particles fall, and much of the glycerin and moisture are removed in the vapor phase. The glycerin is condensed from the vapor mixture and collected. Due to the high temperature applied, the soaps produced by this method are usually darker. This method is not for general use.
  4. Methyl ester procedure: In recent years, a procedure has been worked to make soap by transforming triglycerides into methyl esters. These are treated with methyl alcohol in the presence of a catalyst. The glycerin is separated, the methyl esters are distilled and saponified with caustic soda .
  5. Jet saponification: The hot fatty matter and the caustic soda are continuously adjusted in annular openings of a nozzle through whose central opening a steam stream emerges that emulsifies the mixture and drops it into a boiler. In this, complete saponification with temperature rise occurs. The washes and the finishing are carried out in the ordinary way or by continuous method. Jet saponification is widely used in England with modified washing and sedimentation methods.

Other methods of obtaining soaps

By neutralizing fatty acids, significant tonnage of soap is produced, either by continuous process or by tasks. Caustic soda is normally used for this process, but sodium carbonate is also used. In this method glycerin is produced and nothing is lost in the product.


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