Water treatment agent is a general term for a class of chemical agents used in water treatment. It is widely used in petroleum, chemical, metallurgy, transportation, light industry, textile and other industrial sectors. The water treatment agent includes a corrosion inhibitor, a scale inhibitor, a bactericide, a flocculant, a purifying agent, a cleaning agent, a pre-filming agent, and the like. In practical applications, it is often used as a water treatment agent for a composite formulation, or a combination of various water treatment agents. Therefore, it is necessary to pay attention to the antagonistic effects between the components due to improper compounding, so that the effect is reduced or lost, and the synergistic effect (the synergistic effect produced by the coexistence of several agents) is also fully utilized to increase the efficiency. In addition, most water treatment systems are open systems with a certain amount of emissions, taking into account the environmental impact of various water treatment agents.
Common water treatment agents are: flocculant, ferrous sulfate heptahydrate, polymeric iron salt, calcium hydroxide, ferric chloride hexahydrate, bactericidal algaecide, chlorine dioxide, scale inhibitor, polyacrylamide ( Cationic, anionic, nonionic), polyaluminum chloride, polyaluminum ferric chloride, ferrous sulfate, and the like.
A type of chemical that can prevent or slow the corrosion of water to metal materials or equipment after being added to water in an appropriate concentration and form, has the advantages of good effect, low dosage, and convenient use. There are many types and varieties of corrosion inhibitors. According to the types of compounds, they can be classified into inorganic corrosion inhibitors and organic corrosion inhibitors. The reaction inhibited by the reaction is an anode reaction, a cathodic reaction or both, and can be classified into an anode type corrosion inhibitor, a cathode type corrosion inhibitor or a mixed type corrosion inhibitor. The corrosion inhibitor can also be classified into a passivation film type, a precipitation film type, an adsorption film type, and the like according to a mechanism of forming a protective film on the metal surface. Passivation film type corrosion inhibitors commonly used in water treatment such as chromate, nitrite, molybdate, etc.; commonly used precipitation film type corrosion inhibitors include polymeric phosphates, zinc salts, etc.; Etchants such as organic amines.
The earliest scale inhibitor dispersant is polyacrylic acid (sodium), which has good scale inhibition properties for calcium carbonate scale, but has a very low inhibitory effect on calcium phosphate deposition. Such a polycarboxylic acid type scale inhibitor not only has agglomeration and dispersion, but also causes lattice distortion of the crystal during growth, thereby hindering the firm deposition of the scale layer on the metal heat transfer surface. It was later found that the acrylic copolymer was excellent in suppressing both, and thus gradually replaced polyacrylic acid (sodium). The organic polyphosphonate is an anionic corrosion inhibitor and a non-stoichiometric chelating scale inhibitor. It not only has a significantly low limiting effect on calcium, magnesium, zinc, iron and other ions, but also has synergistic effects on other agents. Used in cooling water treatment. Organic phosphonates are cationic corrosion inhibitors, and the scale inhibition mechanism is mainly lattice distortion. It is a corrosion inhibitor for metallic iron, but also has the effect of controlling calcium scale; the amount is smaller than that of phosphonate and can be hydrolyzed, so there is no accumulation of drug amount and sewage problem, and the hydrolyzed product can be biodegraded.
Also known as anti-scaling agent, it refers to a class of chemicals that can inhibit the formation of scale by the formation of scale salts such as calcium and magnesium in water. There are natural scale inhibitors such as tannins, lignin derivatives, etc.; inorganic scale inhibitors such as sodium hexametaphosphate, sodium tripolyphosphate, etc.; organic, high molecular scale inhibitors, among which polymer antifouling agents are most effective Good, has a promising future. There are two types of organic and high-molecular scale inhibitors used in water treatment: 1 organic phosphonic acids such as EDTMPS (ethylenediaminetetramethylenephosphonic acid), HEDP (hydroxyethylidene diphosphonic acid), etc. 2 polycarboxylic acid, such as polyacrylate, hydrolyzed polymaleic anhydride, and the like. The scale inhibition of these two types of scale inhibitors is usually achieved by lattice distortion and dispersion-coacervation. It is widely used in oilfield water, boiler water and industrial cooling water.
Also known as bactericidal algaecide or sludge stripper, anti-sludge agent, etc., refers to a class of chemicals used to inhibit the growth of microorganisms such as algae in water to prevent the formation of microbial slime. Usually divided into two types of oxidative fungicides and non-oxidizing fungicides. Oxidizing bactericides, such as commonly used chlorine gas, sodium hypochlorite, bleaching powder (main component calcium hypochlorite), chlorine dioxide, etc.; non-oxidizing bactericides have good effects and are widely used to destroy the cell wall and cytoplasm of bacteria. Products, such as quaternary ammonium salts. Among the quaternary ammonium salts, such as dodecyldimethylbenzylammonium chloride or dodecyldimethylbenzylammonium bromide, etc., often have various effects such as sterilization, peeling, corrosion inhibition, etc., and have a promising future. It has been applied to oilfield water, industrial cooling water and so on.
A class of chemicals used to remove or reduce turbidity or suspended solids in water to accelerate the rate of sediment and sludge settling in water. The earliest application of Ke Chuang flocculant is inorganic flocculants such as alum and ferric chloride. Organic and high-molecular flocculants are widely used as flocculants in feedwater and wastewater treatment. Can be divided into anionic flocculants, such as carboxymethyl cellulose, sodium polyacrylate, etc.; cationic flocculants, such as polyvinylamine; and non-ionic flocculants, such as polyacrylamide. Their flocculation is mainly achieved by charge neutralization and adsorption bridging.
A special chemical used in oilfield water treatment can remove mechanical impurities and oil in oily sewage. Its function, in addition to the separation of suspended solids or mechanical impurities from the above flocculant, also has the purification effect of oil-water separation. Therefore, such a scavenger often contains some surfactants in addition to general flocculant components such as aluminum salts, polyacrylamides and the like. For the purification effect of the purifying agent, it is generally measured by a membrane filter, and the size of the membrane factor (see filtration) indicates the purification effect.
A class of chemicals with a cleaning effect. In the pretreatment step of water treatment, it is often necessary to use some chemicals to clean deposits on the surface of metal equipment, such as corrosion products and scales, as well as microbial slime. According to the different requirements of cleaning, the cleaning agent can be divided into pickling agents such as hydrochloric acid, sulfuric acid, hydrofluoric acid, citric acid, etc.; passivating agents such as sodium benzoate. The sodium bis(α-ethylhexyl) sulfosuccinate used is a surfactant which is used as a special cleaning agent for cleaning impurities such as oil stains and floating rust on metal surfaces.
In the pretreatment step of water treatment, a class of chemicals capable of forming a protective film on a metal surface in advance. There are two purposes for pre-filming: one is to increase the concentration of the chemical in the initial stage of corrosion inhibition; the other is to use a special pre-filming agent to add a small amount of corrosion inhibitor in normal operation. Maintain and repair protective film, saving pharmacy and cost. Commonly used pre-filming agents are sodium hexametaphosphate and zinc salt, sodium tripolyphosphate and the like.
In order to better utilize the efficacy of the water treatment agent, a series of agents for use with the water treatment agent, such as a cleaning agent, an antifoaming agent, an oxygen scavenger, an oily flotation agent, a pre-filming agent, and the like, are also required. Most of these adjuvants are compounded products and have a significant synergistic effect with water treatment agents. For example, cleaning agents are generally compounded products of surfactants, and sometimes used as a combination of corrosion inhibitors and chelating agents. The pre-filming agent is formulated with sodium hexametaphosphate and zinc sulfate, and the running water treatment agent is also increased in concentration to 10 to 30 times as a pre-filming agent.