Anionic surfactants are surface actives that ionize negative charges in water. In the production of surfactants, anionic surfactants occupy the maximum variety and quantity.
Anionic surfactants are one of the most frequently employed surfactants and make up about 41% of all consumed surfactants. Anionic surfactants are not only the main active components of daily chemical detergents and cosmetics, but also have a wide range of uses in many other industrial fields. Anionic surfactants can play an important role in both industrial and civil applications.
Figure. 1. Schematic structure of anionic surfactants molecule
According to compositions and structures, anionic surfactants fall into three categories:
Soap surfactants: Soap surfactant is an advanced fatty acid salt with hydrocarbon chain between C11 to C18. Soap surfactants that are frequently used include stearic acid, oleic acid and lauric acid. According to the different metal ions (Mn+), soap surfactants can be divided into alkali metal soaps, alkaline earth metal soaps and organic amine soaps.
Sulfate surfactants: Sulfate surfactants can be mainly divided into sulfated oils and higher fatty alcohols. The chemical structure of sulfate surfactant can be shown as ROSO4-M+, in which the higher alcohol hydrocarbon chain R is between C12 and C18. Sulphated castor oil, commonly known as turkish red oil, is a representative type of sulphated oil. It is a yellow or orange viscous liquid with a slight odor. It can be mixed with water and is a non-irritating detergent and wetting agent. Soaps wash the skin and can also be used to solubilize volatile oils or water-insoluble bactericides.
Sulfonate Surfactants: Sulfonate surfactants mainly include aliphatic sulfonates, sulfoaryl sulfonates and sulfonaphthalene sulfonates. The general structure of the molecule is ROSO3-M+. Their water solubility, resistances to calcium and magnesium salt are slightly less soluble than sulfuric acid.
Anionic surfactants are a wide group of chemical compounds which have a large number of applications in household cleaning detergents, personal-care products, textiles, paints, polymers, pesticides, pharmaceuticals, mining, oil recovery, and the pulp and paper industries, agriculture, cosmetic industry, sewage treatment industry, textile industry and daily chemical industry.
Agriculture: It is reported that anionic surfactants which are used as pesticide emulsifiers can reduce the amount of emulsifier from 20% to 3%. This will help to improve the chemical stability of pesticides, reduce costs and pollution, and increase the efficiency of utilization. Anionic surfactants are added to insecticides, rust removers and plant growth regulators to improve soils. Anionic surfactants can improve pesticide efficiency by multiple mechanisms. In particular anionic surfactants can increase the foliar uptake of herbicides, growth regulators, and defoliants. Mixed with insecticides, rust removers and plant growth regulators, anionic surfactants can also be used as soil conditioners.
Cosmetic industry: Anionic surfactants have been widely used in cosmetics industry and in our daily life due to their pharmacological and toxicological safety. Anionic surfactants are mainly used as emulsifier, solubilizer, wetting agent and effective component synergist.
Sewage treatment industry: Anionic surfactants can be used for the treatment of domestic sewage and organic wastewater. Anionic surfactants show cationicity in both acidic and alkaline media. This makes it possible to flocculate precipitates with negatively charged aerosol particles. As the king of new flocculants, anionic surfactants have extensive sources, good effect of treating sewage and simple equipment for subsequent sludge disposal, so they are widely used in sewage treatment field, such as the treatment for grain alcohol wastewater, papermaking wastewater, brewery wastewater, monosodium glutamate wastewater, sugar wastewater, high organic content wastewater, feed wastewater, textile printing and dyeing wastewater.
Textile industry: A large amount of anionic surfactants are used in the textile dyeing and printing industry every year. For example, anionic surfactants with cleaning effect are used in the pretreatment process, and anionic surfactants with percolation effect are used in the dyeing and finishing processes. In addition, some functional products such as leveling agents and fixing agents are also anionic type.
Daily chemical industry: Anionic surfactants are widely used in our daily life. The most common soap consisting of sodium stearate is a kind of anionic surfactants. Anionic products have the characteristics of smooth, high foam and low price, which can reduce the cost of the detergents and other products, while improving the product transparency.