How Soaps are Made

This article is the continuation of my previous article (Soap, Detergent and cleaning Chemistry).

Saponification of fats and oils is the most widely used soapmaking process. This method involves heating fats and oils and reacting them with a liquid alkali (Lye

) to produce soap and water (neat lye) plus glycerine as you can see on the above equation.

Other major soapmaking process is the neutralization of fatty acids with an alkali(Lye). Fats and oils are hydrolyzed (split) with a high-pressure steam to yield crude fatty acids and glycerine (crude lye). The fatty acids are then purified by distillation and neutralized with an alkali to produce soap and water (neat lye) as you can see above.

There two major alkali used in soap making, sodium for hard soap and potassium soft soap.

Soap is made up two ends, the carboxylate end of its molecule that is attracted to water. It is called the hydrophilic (water-loving)  The hydrocarbon chain of its molecoule that is attracted to oil and grease and repelled by water. It is called hydrophobic (water-hating) end. 

Hardness Affects on Cleaning Action

Although soap is a good cleaning agent, its effectiveness is reduced when used in hard water. Hardness in water is caused by the presence of mineral salts - mostly those of calcium (Ca) and magnesium (Mg), but sometimes also iron (Fe) and manganese (Mn). The mineral salts react with soap to form an insoluble precipitate known as soap scum this is one of its main properties that distinguishes it from detergent that has surfactant.

Soap scum does not rinse away easily. It tends to remain behind and produces visible deposits on clothing and makes fabrics feel stiff. It also attaches to the insides of bathtubs, sinks and washing machines.

Some soap is used up by reacting with hard water minerals to form the scum. This reduces the amount of soap available for cleaning. Even when clothes are washed in soft water, some hardness minerals are introduced by the soil on clothes. Soap molecules are not very versatile and cannot be adapted to today's variety of fibers, washing temperatures and water conditions.

Surfactants in Detergents

A detergent is an effective cleaning product because it contains one or more surfactants. Because of their chemical makeup, the surfactants used in detergents can be engineered to perform well under a variety of conditions. Such surfactants are less sensitive than soap to the hardness minerals in water and most will not form a film.

Detergent surfactants were developed in response to a shortage of animal and vegetable fats and oils during World War I and World War II. In addition, a substance that was resistant to hard water was needed to make cleaning more effective. At that time, petroleum was found to be a plentiful source for the manufacture of these surfactants. Today, detergent surfactants are made from a variety of petrochemicals (derived from petroleum) and/or oleochemicals (derived from fats and oils). 

Petrochemicals and Oleochemicals

Like the fatty acids used in soapmaking, both petroleum and fats and oils contain hydrocarbon chains that are repelled by water but attracted to oil and grease in soils. 

These hydrocarbon chain sources are used to make the water-hating end of the surfactant molecule.

Other Chemicals

Chemicals, such as sulfur trioxide, sulfuric acid and ethylene oxide, are used to produce the water-loving end of the surfactant molecule.

Alkalis

As in soapmaking, an alkali is used to make detergent surfactants. Sodium and potassium hydroxide are the most common alkalis.

How Detergent Surfactants Are Made

Anionic Surfactants13Chem

The chemical reacts with hydrocarbons derived from petroleum or fats and oils to produce new acids similar to fatty acids.

A second reaction adds an alkali to the new acids to produce one type of anionic 

surfactant molecule.

Nonionic Surfactants

Nonionic surfactant molecules are produced by first converting the hydrocarbon to an alcohol and then reacting the fatty alcohol with ethylene oxide.

Nonionic Surfactants

Nonionic surfactant molecules are produced by first converting the hydrocarbon to an alcohol and then reacting the fatty alcohol with ethylene oxide.

These nonionic surfactants can be reacted further with sulfur-containing acids to form another type of anionic surfactant.

How Soaps and Detergents Work

These types of energy interact and should be in proper balance. Let's look at how they work together.

Let's assume we have oily, greasy soil on clothing. Water alone will not remove this soil. One important reason is that oil and grease present in soil repel the water molecules.

Now let's add soap or detergent. The surfactant's water-hating end is repelled by water but attracted to the oil in the soil. At the same time, the water-loving end is attracted to the water molecules.

These opposing forces loosen the soil and suspend it in the water. Warm or hot water helps dissolve grease and oil in soil. Washing machine agitation or hand rubbing helps pull the soil free.

Safety 

 To be continued in the next article, but feel free to ask any question about soap and detergent quality at the comment section.