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Definition and Classification of Water Treatment Agents
Time:2019-3-6 15:53:40  Read:715
Water treatment agents refer to chemical agents used in water treatment. Usually refers to chemical agents used in sewage treatment. It is widely used in chemical industry, petroleum, light industry, daily chemical industry, textile, printing and dyeing, construction, metallurgy, machinery, medicine and health, transportation, urban and rural environmental protection and other industries, in order to save water and prevent water pollution. It includes the chemicals needed for the treatment of cooling water and boiler water, seawater desalination, membrane separation, biological treatment, flocculation and ion exchange technology. Such as corrosion inhibitor, scale inhibitor and dispersant, bactericide and algaecide, flocculant, ion exchange resin, purifier, cleaning agent, pre-film agent, etc.


Therefore, we should not only pay attention to the antagonism between the components due to inappropriate compounding, so as to reduce or lose the effect, but also make full use of the synergistic effect (synergistic effect produced by the coexistence of several medicines) to increase the efficiency. In addition, most water treatment systems are open systems, there will be a certain amount of emissions, use to take into account the impact of various water treatment agents on the environment.

Corrosion inhibitors, a kind of chemicals which can prevent or slow down the corrosion of metal materials or equipment by water after being added in water with appropriate concentration and form, have the characteristics of good effect, less dosage and convenient use.

There are many types and varieties of corrosion inhibitors, which can be divided into inorganic corrosion inhibitors and organic corrosion inhibitors according to the types of their compounds. According to the inhibition reaction, it can be divided into anodic, cathodic or mixed inhibitors. Corrosion inhibitors can also be divided into passivation film, precipitation film and adsorption film according to the mechanism of forming protective film on metal surface. At present, passive film corrosion inhibitors such as chromate, nitrite and molybdate are commonly used in water treatment; common precipitation film corrosion inhibitors are polyphosphate, zinc salt, etc; and common adsorption film corrosion inhibitors such as organic amine.

Scale inhibitors, also known as scale inhibitors, refer to a class of chemicals that can inhibit the formation of scaling salts such as calcium and magnesium in water. There are natural scale inhibitors such as tannins, lignin derivatives, inorganic scale inhibitors such as sodium hexametaphosphate, sodium tripolyphosphate, etc. Organic and macromolecule scale inhibitors, of which macromolecule scale inhibitors have the best effect and have a development prospect. There are two kinds of organic and macromolecule scale inhibitors widely used in water treatment: 1) organic phosphonic acids such as EDTMP (ethylenediamine tetramethylene phosphonic acid), HEDP (hydroxyethylene diphosphonic acid), and 2) polycarboxylic acids such as polyacrylate, hydrolyzed polymaleic anhydride, etc. The scale inhibition effects of these two kinds of scale inhibitors are usually realized by lattice distortion and dispersion-coagulation. They are widely used in oilfield water, boiler water and industrial cooling water systems.

Fungicides, also known as bactericides and algaecides or sludge stripping agents, anti-sludge agents, etc., refer to a class of chemicals used to inhibit microbial growth in water, such as bacteria and algae, in order to prevent the formation of microbial slime. Usually it can be divided into two categories: oxidizing fungicides and non-oxidizing fungicides. Oxidative fungicides, such as chlorine, sodium hypochlorite, bleaching powder, etc. are commonly used. Chemicals such as quaternary ammonium salts, which can destroy the cell wall and cytoplasm of bacteria, are effective and widely used in non-oxidative fungicides. Quaternary ammonium salts, such as dodecyl dimethyl benzyl ammonium chloride or dodecyl dimethyl benzyl ammonium bromide, have many functions, such as bactericidal, stripping and corrosion inhibition. They have a bright future and have been used in oilfield water and industrial cooling water.

Flocculants are chemicals used to remove or reduce turbidity or suspended matter in water and to accelerate the settling rate of impurities and sludge in water. Inorganic flocculants, such as alum and ferric chloride, were first used in flocculants. Organic and polymer flocculants are widely used in water supply and wastewater treatment in the future. It can be divided into anionic flocculants, such as carboxymethyl cellulose, sodium polyacrylate, cationic flocculants, such as polyvinylamine, and non-ionic flocculants, such as polyacrylamide. Their flocculation is mainly realized by charge neutralization and adsorption bridging.

A special chemical used in oilfield water treatment can remove mechanical impurities and oils from oily wastewater. Besides the separation of suspended solids or mechanical impurities by the flocculants mentioned above, it also has the purification effect of oil-water separation. Therefore, in addition to the general flocculant components such as aluminium salts, polyacrylamide and so on, this purifier often contains some surfactants. For the purifying effect of the purifying agent, the membrane filter is usually used to measure the purifying effect, and the size of the filter membrane factor (seen filter) is used to indicate the purifying effect.

A class of chemicals with cleaning effect. In the pretreatment process of water treatment, some chemicals are often used to clean the deposits on the surface of metal equipment, such as corrosion products, scale and microbial sludge. According to the different requirements of cleaning, cleaning agents can be divided into acid detergents such as hydrochloric acid, sulfuric acid, hydrofluoric acid, citric acid, passivator such as sodium benzoate. At present, sodium sulfosuccinate bis (alpha-ethylhexyl ester) is a kind of surfactant, which is used as a special cleaning agent to clean oil and rust on metal surface.

In the pretreatment step of water treatment, the prefilm agent can form a protective film on the metal surface in advance. There are two purposes of pre-film: one is to increase the concentration of pre-film in the initial stage of corrosion inhibition by chemicals; the other is to use a special pre-film agent so that a small amount of corrosion inhibitor can be added in normal operation to maintain and repair the protective film, and to save medicines and costs. At present, the commonly used pre-film agents are sodium hexametaphosphate plus zinc salt, sodium tripolyphosphate and so on.