Technical assistance: issues with scale inhibitors, oxidants, and cleaners
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This post was last edited by hesonchang214 on 2010-4-6 at 10:46. May I ask what scale inhibitors, oxidants, and cleaning agents are used in water treatment? ? What is its function? ? How is the dosage calculated? ? Is there any formula or software or something like that?
This post was last edited by cdpulin on 2010-4-13 at 10:36. OP, first of all, the water sources used for water treatment are different, such as desalinated water, recycled water, and wastewater. Generally, scale inhibitors/dispersants are divided into phosphorus-containing and phosphorus-free types. Most mid-to-high-end scale inhibitors these days do not contain phosphorus (such as Rohm and Haas, Great Lakes, Corning, Nalco, Qingli, Bedi, HighPass, PWT, etc.) ； Are you referring to the oxidant used for sterilization? Usually sodium hypochlorite, chlorine dioxide, etc ； The most commonly used cleaning agents are acids (HCl) and bases (NaOH), as well as sodium tripolyphosphate, citric acid, ammonia, and so on.
This post was last edited by cdpulin on 2010-4-13 at 10:37. Common scale inhibitors include 1. polycarboxylic acids, 2. phosphonic acids, 3. organic phosphates, etc. Purpose: To prevent or reduce scaling and corrosion in the system. Oxidizing disinfectants include chlorine, chlorine dioxide, hypochlorite, sodium hypochlorite, and liquid bromine; they function by killing or inhibiting the growth and reproduction of microorganisms. The cleaning agent is a mixture of polyphosphates and surfactants, which effectively removes organic substances such as oil from heat exchange equipment, as well as initial rust and calcium deposits. The software you mentioned is usually kept confidential by the company; I’ve forgotten the formula for calculating its usage. I’ve changed careers now, so you can ask other friends.
This post was last edited by cdpulin on 2010-4-13 at 10:40. Scale inhibitors are substances that have the ability to disperse insoluble inorganic salts in water, prevent or interfere with the precipitation and scaling of such salts on metal surfaces, thereby ensuring good heat transfer performance in metal equipment. The mechanism of action of corrosion and scale inhibitors includes: chelation and solubilization effects, lattice distortion effects, and electrostatic repulsion effects. 1. Chelation and solubilization occur when the copolymer dissolves in water and ionizes to form negatively charged molecular chains, which then form water-soluble complexes or chelates with Ca2+, thereby increasing the solubility of inorganic salts and serving to prevent scale formation. 2. The effect of lattice distortion arises from certain functional groups in the molecules occupying specific positions on the nuclei or microcrystals of inorganic salts; this hinders and disrupts the normal growth of these inorganic salt crystals, slowing down their growth rate and thereby reducing the formation of scale. 3. The effect of electrostatic repulsion occurs when copolymers dissolve in water and adhere to the microcrystals of inorganic salts, increasing the repulsive forces between these particles and preventing them from aggregating, thus keeping them in a well-dispersed state and preventing or reducing the formation of scale. Classification of scale inhibitors: organic phosphonate series scale inhibitors, organic phosphonate scale inhibitors, polycarboxylate scale and dispersion inhibitors, composite scale inhibitors, RO scale inhibitors. 1. Organic phosphine-based scale inhibitors ATMP possesses excellent chelating properties, low-threshold inhibition effects, and the ability to distort crystal lattices. It can prevent scaling salts in water from forming scale, especially calcium carbonate scale. ATMP is chemically stable in water and does not hydrolyze easily. It exhibits good corrosion inhibition effects at high concentrations in water. HEDP is an organic phosphonic acid-based scale and corrosion inhibitor that can form stable complexes with various metal ions such as iron, copper, and zinc, and it is capable of dissolving oxides on metal surfaces. It maintains good corrosion and scale inhibition properties at 250°C, remains stable at high pH levels, is not prone to hydrolysis, and does not decompose under normal photothermal conditions. It has better acid and alkali resistance, as well as resistance to chlorine oxidation, compared to other organic phosphonic acids (salts). EDTMPS is a nitrogen-containing organic polyphosphonic acid and belongs to the category of cathodic corrosion inhibitors; compared with inorganic polyphosphates, it offers a corrosion inhibition efficiency 3 to 5 times higher. It is miscible with water, non-toxic and non-polluting, possesses good chemical stability and heat resistance, and still maintains an excellent scale-inhibiting effect at 200°C. EDTMPS can dissociate into 8 cationic and anionic ions in aqueous solution; as a result, it can chelate with multiple metal ions to form large molecular network complexes with a monomeric structure, which are loosely dispersed in water and thereby disrupt the normal crystallization of calcium scale. EDTMPS has an excellent scale-inhibiting effect on calcium sulfate and barium sulfate scales. EDTMPA has a strong ability to chelate metal ions, and its complexation constant with copper ions is the highest among all chelating agents, including EDTA. EDTMPA is a high-purity, non-toxic reagent that can be used in the electronics industry as a cleaning agent for semiconductor chips in the manufacture of integrated circuits ； Used as a carrier for radioactive elements in the pharmaceutical industry, for the diagnosis and treatment of diseases ； The chelating ability of EDMTPA far exceeds that of EDTA and DTPA, and it can replace EDTA in almost all applications where EDTA is used as a chelating agent. 2. Organic phosphonate scale inhibitors ATMP•Na4 is the neutral sodium salt of ATMP; it prevents the scaling salts in water from forming scale, especially calcium carbonate scale. ATMP•Na4 is suitable for the circulating cooling water in thermal power plants and refineries, as well as for oil field reinjection water systems. ATMP•Na4 also exhibits good compatibility with some other additives. ATMP•Na4 is particularly suitable for neutral to acidic formulations, as it does not produce an ammonia odor. ATMP•Kx is a partial potassium salt solution of ATMP; compared to an equal amount of sodium salt, ATMP•Kx has higher solubility, which prevents the scaling salts in water from forming scale, especially calcium carbonate scale. ATMP•Kx is particularly suitable for oilfield reinjection water systems. HEDP•Na4 is widely used in industries such as power, chemicals, metallurgy, and fertilizer production for scale prevention and corrosion inhibition in circulating cooling water, low-pressure boilers, oil field injection systems, and oil pipelines. 3. Polycarboxylate scale-inhibiting and dispersing agents: PAAS are non-toxic, soluble in water, and can operate under alkaline conditions as well as at high concentration levels without forming scale. PAAS can disperse the microcrystals or sediment of salts such as calcium carbonate and calcium sulfate in water to prevent precipitation, thereby achieving scale inhibition. AA/AMPS is a copolymer of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid (AMPS). Due to the presence of carboxyl groups in its molecular structure, which provide good scale-inhibiting and dispersing properties, as well as highly polar sulfonic acid groups, it enhances calcium tolerance and exhibits significant scale-inhibiting effects against calcium phosphate, calcium carbonate, zinc scale, etc. in water, along with excellent dispersing capabilities. When combined with organic phosphines, it exhibits a significant synergistic effect. It is particularly suitable for water with high pH, high alkalinity, and high hardness, and is one of the most ideal scale-inhibiting and dispersing agents for achieving high concentration operation. PESA is a phosphorus-free, nitrogen-free “green” environmentally friendly multi-functional scale and corrosion inhibitor. PESA exhibits excellent scale-inhibiting and dispersing properties against calcium carbonate, calcium sulfate, barium sulfate, calcium fluoride, and silica scale in water, with a better scale-inhibiting effect than common organic phosphonate scale inhibitors. A combination of PESA and phosphonates exhibits good synergistic effects. At the same time, PESA has a certain corrosion-inhibiting effect and is a multi-component scale inhibitor. PASP is a water-soluble polymer and a new type of green water treatment agent, characterized by being phosphorus-free, non-toxic, harmless, and fully biodegradable. It has a very strong chelating ability for ions, offering both corrosion inhibition and scale prevention effects. It is effective in preventing scaling by salts such as calcium carbonate, calcium sulfate, barium sulfate, and calcium phosphate, with a scale prevention rate of up to 100% against calcium carbonate. 4. Composite scale inhibitor The boiler-specific corrosion and scale inhibition agent TH-503 is a composite material composed of organic phosphonic acids and polymers such as polycarboxylic acids. It possesses excellent corrosion and scale inhibition properties, as well as good temperature resistance, making it suitable for use in water treatment within low-pressure boilers. Special scale inhibitors for heat networks are primarily composed of high-efficiency dispersants, phenolic hydroxyl groups, sulfonic acid groups, etc. They cause lattice distortion in scale-forming substances such as calcium carbonate and calcium sulfate in water, preventing the scale from adhering firmly to the vessel walls and keeping it dispersed in the water, thereby exhibiting excellent scale-inhibiting effects. The corrosion and scale inhibition agent TH-601 is composed of organic phosphonic acids, polycarboxylic acids, and carbon steel corrosion inhibitors. It has an excellent chelating and dispersing effect on substances such as calcium carbonate and calcium phosphate in water, and it also provides good corrosion protection for carbon steel. It is primarily used for corrosion and scale inhibition in the circulating cooling water systems of steel plants, offering effective corrosion prevention and strong scale inhibition capabilities. The corrosion and scale inhibition agent TH-604 is composed of organic phosphonic acids, polycarboxylic acids, a carbon steel corrosion inhibitor, and a copper corrosion inhibitor. It exhibits excellent chelating and dispersing effects on calcium carbonate, calcium sulfate, calcium phosphate, etc. in water, and provides good corrosion inhibition for carbon steel and copper. The corrosion and scale inhibition agent TH-604 is primarily used for preventing corrosion and scale formation in circulating cooling water systems, such as those found in power plants, chemical plants, petrochemical facilities, and steel industries. It offers excellent corrosion inhibition effects and strong scale inhibition capabilities. This product is primarily composed of various organic phosphonic acids, polycarboxylic acids, sulfonate-containing copolymers, corrosion inhibitors, and special surfactants. It is suitable for circulating cooling water systems with high concentration ratios, where the requirement for Ca2+ plus alkalinity is 1500 ppm. 5. RO Scale Inhibitor The reverse osmosis scale inhibitor and dispersant TH-0100 is a highly effective scale inhibitor suitable for use in reverse osmosis (RO) systems, as well as nanofiltration (NF) and ultrafiltration (UF) systems. It prevents scaling on the membrane surface, improves water production volume and quality, and reduces operating costs. The reverse osmosis scale inhibitor and dispersant TH-2000 is a highly effective scale-inhibiting dispersant, particularly suitable for reverse osmosis systems where the levels of barium and strontium in the feed water are high, and where there is a strong tendency to form scales of barium sulfate and strontium sulfate. It can effectively prevent scaling from occurring over a wide range of concentration levels of scaling substances. Reverse osmosis scale inhibitors are used in reverse osmosis (RO), nanofiltration (NF) or ultrafiltration (UF) systems. 6. Specialized scale inhibitors Sodium benzotriazole (BTA): BTA (Na) can adsorb onto metal surfaces to form a thin film that protects copper and other metals from corrosion caused by the atmosphere and harmful substances ； In circulating cooling water systems, BTA (Na) can be used in combination with various scale inhibitors and biocides, and it provides excellent corrosion inhibition effects; its dosage in the circulating water is 2–4 mg/L. BTA (Na) can also be used as an anti-discoloration agent for copper and silver, in automotive coolants, and as an additive in lubricants. Sodium thiophenothiazole (MBT): MBT (Na) can be used as a copper corrosion inhibitor in circulating cooling water systems. The corrosion-inhibiting effect of MBT (Na) relies primarily on a chemical adsorption mechanism with the active copper atoms or copper ions on the surface of copper metal ； It may further undergo chelation to form a dense and strong protective film, thereby providing good protection for copper-based equipment. The typical usage amount is 4 mg/L. MBT (Na) can also be used as a plasticizer or as an agent for acidic copper plating. **Triazolium tetraacetate (TTA): TTA can be used as a corrosion inhibitor for non-ferrous metals such as copper and its alloys, and it also has a corrosion-inhibiting effect on ferrous metals. TTA adsorbs on metal surfaces to form a very thin film that protects copper and other metals from corrosion by harmful substances in the atmosphere and water. This product forms a more uniform film, and its effectiveness is even better when used in combination with sodium thiosemicarbazate. After being dissolved in alcohol or alkali by TTA, it is added to the circulating water, with a concentration of 2–10 mg/L in the water. If the non-ferrous metals in the water system are severely corroded, this substance can be added at a concentration 5–10 times higher than normal in order to rapidly passivate the system. Hydrochloric acid pickling corrosion inhibitor: The pickling corrosion inhibitors are a series of products belonging to the imidazoline class. When cleaning metal with hydrochloric acid, adding an acid cleaning corrosion inhibitor can prevent the acid from corroding the steel. The application of acid cleaning corrosion inhibitors is conditional on the cleaning medium being hydrochloric acid, sulfuric acid, or sulfamic acid, and the substrate to be cleaned being a ferrous metal. Pickling corrosion inhibitors are suitable for the pickling of high, medium, and low-pressure boilers of various types, as well as for the pickling of large-scale equipment and pipelines. Corrosion performance in acidic solution (addition rate of 1–3‰): corrosion rate ≤ 1 g/m2•h. Oxidants: Oxidants are substances that gain electrons or have an inclination to accept electrons in redox reactions; in other words, they are substances that change from a higher oxidation state to a lower one. The oxidizing agent gains electrons from the reducing agent and is itself reduced to form a reducing product. Oxidants and reductants are interdependent. Oxidizing agents exhibit oxidizing properties in reactions. The strength of oxidizing ability refers to the ability of an oxidizing agent to gain electrons, not the number of electrons it gains. For example, concentrated nitric acid has a stronger oxidizing ability than dilute nitric acid, yet it gains fewer electrons. Substances containing elements that readily gain electrons are commonly used as oxidizing agents. When analyzing specific reactions, the change in the oxidation state of the elements is often used to determine this: a substance in which the oxidation state of the elements decreases acts as an oxidizing agent. Typical oxidizing agents include Cl2, Br2, O2. Oxides of elements such as Mn in their higher oxidation states, such as MnO2. Oxygen-containing acids of elements such as S and N in their higher oxidation states, such as concentrated sulfuric acid and HNO3. Salts of elements such as Mn, Cl, Fe in their higher oxidation states, such as KMnO4, KClO3, FeCl3. Peroxides, such as Na2O2 and H2O2. In redox reactions, the following rule applies: oxidation occurs when oxygen is lost, while reduction occurs when oxygen is gained. Since beginners generally find it difficult to accurately determine the oxidants and reducers in redox reactions, which can be quite complicated, there is a saying to explain this. In a redox reaction, the substance whose oxidation state increases loses electrons and is oxidized; it acts as a reducer (having reducing properties), and the product formed is an oxidized product that possesses oxidizing properties. On the other hand, the substance whose oxidation state decreases gains electrons and is reduced during the reaction; it acts as an oxidant (having oxidizing properties), and the product formed is a reduced product that has reducing properties. Here, it is important to note a certain rule of reaction: the reducing power of the reductant should be stronger than that of the reduced product, while the oxidizing power of the oxidant should be stronger than that of the oxidized product. Common oxidizing agents: Common oxidizing agents are substances that readily gain electrons and get reduced in chemical reactions. (1) Typical non-metallic elements such as F2, O2, Cl2, Br2, I2, S, etc. (their oxidizing strength is generally consistent with their non-metallic reactivity). (2) High-valent compounds containing variable-valence elements, such as KMnO4, KClO3, H2SO4, HNO3, MnO2, etc. (3) Metal cations such as Fe3+, Cu2+, and (H+). In displacement reactions between metals and acid or salt solutions, such as in the reaction Fe + CuSO4 = FeSO4 + Cu, it is actually the Cu2+ ions that oxidize the Fe atoms; Cu2+ acts as an oxidizing agent, while Fe acts as a reducing agent. Common reducing agents are substances that readily lose electrons and get oxidized in chemical reactions. (1) Typical metal elements such as K, Ca, Na, Mg, etc. (the strength of their reducing power is generally consistent with their metallic activity). (2) Certain non-metal elements and their compounds such as H2, C, CO. (3) Compounds with the lowest oxidation state of elements that can undergo valence change, such as H2S, HI, HBr, HCl. (4) Non-metallic anions such as S2-, I-, Br-, Cl-. Cleaning agent solvents form a very broad category with many different types, including both inorganic and organic cleaning agents. In simple terms, organic cleaning agents are those made from carbon-containing compounds, while inorganic cleaning agents are those made from carbon-free compounds; therefore they belong to inorganic substances: CO, CO2, H2CO3, carbonates (RCO3), (CN)2, HCN, HCNO, hydrocyanates (RCN), cyanates (RCNO), carbon disulfide, calcium carbide, and so on. There are also many ways to classify cleaning agents, and these classifications vary from country to country. Generally, they are divided into three categories: aqueous, semi-aqueous, and non-aqueous cleaning agents. (1) Aqueous cleaning agents Water is the most important cleaning agent, holding a role and significance that no other cleaning agent can replace. Ordinary water is easily available in nature, and it possesses strong dissolving and dispersing capabilities. However, water has high surface tension; therefore, surfactants need to be added during use to reduce this tension and improve surface wetting. In general industrial cleaning processes, a combination of acids, bases, and water is commonly used, and rust inhibitors must be added when using water to clean certain metals ； In precision and ultra-precision industrial cleaning, it is often required that water be made into pure water. Water purity is usually measured by resistivity. The semiconductor industry requires a value of over 18 MΩ·cm, while for the production of TN-type liquid crystals, 10 MΩ·cm is sufficient. There are also industries with strict requirements regarding bacterial content. In recent years, some areas in China have faced severe water shortages, which poses challenges for the water used in cleaning processes. Some cities have strictly prohibited using regular water for car washing, allowing only recycled wastewater or water-saving devices that use misted water. In precision industrial cleaning, the production of pure water is costly. Water washing requires heating and drying, as well as many additional rinsing steps; it consumes a lot of energy, and its operating costs are usually higher than those of solvent cleaning ； Furthermore, in the past, a large amount of wastewater containing chemical agents and dirt was discharged directly without treatment. Some of this wastewater also contained highly toxic heavy metals, causing severe environmental pollution; therefore, it is necessary to increase wastewater treatment facilities.
(2) Semi-aqueous systems
Semi-aqueous cleaning agents, also known as quasi-aqueous cleaning agents, are composed of high-boiling-point solvents and active agents such as alcohols, ethylene glycol esters, organic hydrocarbons, and N-methylpyrrolidone. They typically contain 5% to 20% water and are generally not flammable. However, when cleaning at elevated temperatures, improper control of the water content can lead to combustion. Semi-aqueous cleaning differs from solvent-based cleaning in that its mechanism involves stripping away contaminants rather than dissolving them. To prevent the removed oil stains from reattaching to the surface being cleaned, the cleaning solution must be continuously circulated, and oil-water separators should be used. Semi-aqueous cleaning usually yields good results, but it has higher operating costs. The waste liquid cannot be recycled, and it contains a high level of COD (Chemical Oxygen Demand), requiring wastewater treatment.
(3) Non-aqueous systems
Non-aqueous cleaning agents refer to organic solvents that are insoluble in water. The non-aqueous cleaning agents used in precision industry cleaning are mainly hydrocarbons (petroleum-based substances), chlorinated hydrocarbons, fluorinated hydrocarbons, and brominated hydrocarbons. Alcohols. There are organic solvents such as silicone oils and terpenes. The main parameters used to evaluate solvents include the KB value (cedar rosin butanol value), AP (aniline point), and SP solubility parameter. Surface tension. Parameters such as density, viscosity, boiling point, flash point, and exposure concentration. A solvent with a high KB value, meaning it has strong dissolving power, is not necessarily a good cleaning agent. A good cleaning agent for precision industries must meet the following conditions: ① Stable chemical properties, with little tendency to react with the materials to be cleaned ； ②Low surface tension and viscosity, with strong penetration ability ； ③Low boiling point, allowing it to dry on its own ； ④No flash point, not flammable ； ⑤The KB value should not be too high to avoid dissolution with the substance being cleaned ； ⑥Low toxicity and safe to use: ⑦ It is not an ODS and has a low GWP (Global Warming Potential), making it environmentally friendly. If point 7 above is not taken into consideration, the best cleaning agents are CFC-113 and TCA; they possess good chemical stability and can remain unchanged over time ； For the vast majority of metals and plastics. Lacquer has no effect; it does not dissolve, has no flash point, is low in toxicity, and is safe to use ； Low surface tension, strong penetration, and excellent cleaning power ； It has a low boiling point and rapid evaporation rate; the cleaned parts can dry on their own, so drying is generally not necessary. For this reason, it is widely used in various industrial cleaning applications. However, its only drawback is that it damages the ozone layer, which is why its use is being phased out gradually. In China, the only company that produces CFC-113 as a cleaning agent is Changshu 3F. Production volumes have been decreasing year by year, from 4,800 tons in 2000 to zero by December 2005, with production and use completely halted thereafter. 4. Alternative cleaning agents Although various alternative substances have been developed around the world, no substitute cleaning agent has yet been found that can compare to CFC-113; each of them has its own set of problems. The main alternative products currently in use are: (1) Hydrocarbons Hydrocarbon solvents, which consist only of carbon and hydrogen elements, are also referred to as hydrocarbons or hydrocarbon-based solvents in Japan. Based on their different molecular structures, a variety of products with various properties have been developed, and they are widely used in Japan. The advantages of these cleaning agents are: they are not ODS compounds, they have strong cleaning power against oil stains, they exhibit good penetration, they are odorless or have only a slight smell, they are low in toxicity, their waste liquid can be easily treated, they can be reused, and they are inexpensive ； The disadvantages are its flammability and explosiveness, slow drying speed, high requirements for cleaning equipment, and high initial investment. Currently, the most ideal approach is to use vacuum cleaning to reduce surface tension and improve cleaning efficiency, followed by vacuum drying. However, such equipment is expensive, its operation is complex, and its efficiency is relatively low.
(2) Chlorinated hydrocarbon solvents
The chlorinated hydrocarbon cleaners currently in use are mainly trichloroethylene, dichloromethane, and tetrachloroethylene. These solvents are widely used in cleaning applications, and they have the following advantages and characteristics:
A very low ODP value (Ozone Depletion Potential), ranging from 0.005 to 0.007; they hardly cause any damage to the ozone layer ； It is non-flammable under normal conditions. There is no risk of fire or explosion (dichloromethane may explode under intense light over a long period of time) ； It has a strong dissolving power for oil stains such as metal processing oils and greases. It can also cause swelling or dissolution in plastics and rubber. With low viscosity and surface tension, it possesses strong penetration capabilities, allowing it to penetrate narrow gaps and completely dissolve and remove adhering contaminants ； It has a low boiling point and low vaporization heat, making it suitable for steam cleaning; it can dry on its own after cleaning ； Waste liquid can be separated by distillation and reused ； The same or similar cleaning processes and equipment as those used for CFC-113 and TCA can be employed; it is simple to operate, efficient, and has low operating costs ； The downside is its high toxicity; generally, its concentration in the air is restricted to below 50PPM ； Some labor protection regulations impose explicit restrictions on its use ； Now, some European countries **restrict the import and use of products containing such chlorinated cleaners. (3) Brominated hydrocarbon solvents In recent years, bromine-based cleaners have appeared in the United States and Japan, and they are used in the electronics industry and the aviation industry. It is widely used in the automotive industry and the home appliance sector. It is reported that Boeing uses this type of cleaning agent for cleaning aircraft components. The main component of bromine-based cleaning agents is high-purity n-bromopropane (NPB). Its performance is comparable to that of CFC-113 and TCA. Its key technical parameters are almost identical to those of TCA; it has a better wetting coefficient and a stronger ability to clean metal parts. It has no flash point, can be reused repeatedly, and results in low operating costs. As a substitute for CFC-11 and TCA, its manufacturing process is exactly the same, so there is little need to replace equipment; only the evaporation temperature needs to be adjusted. It is also known as a \"substitute cleaning agent for the third world.\" The ODP of bromine-based cleaning agents is 0.006, and their lifetime in the atmosphere is 11 days, with almost no GWP value. There are still debates regarding their toxicity, and the United Nations Environment Programme (UNEP) has conducted experiments for over 5 years. The results of these experiments differ significantly from theoretical analyses. The U.S. Environmental Protection Agency, in a policy issued on March 27, 2002, approved NPB as a solvent for use in cleaning, aerosols, and adhesives. However, since there is no definitive data on its toxicity, it is necessary to control the concentration of exposure to air when using it. This project was carried out by the China Liquid Crystal Association and the Liquid Crystal Engineering Technology Center at Tsinghua University
(2) Semi-aqueous systems
Semi-aqueous cleaning agents, also known as quasi-aqueous cleaning agents, are composed of high-boiling-point solvents and active agents such as alcohols, ethylene glycol esters, organic hydrocarbons, and N-methylpyrrolidone. They typically contain 5% to 20% water and are generally not flammable. However, when cleaning at elevated temperatures, improper control of the water content can lead to combustion. Semi-aqueous cleaning differs from solvent-based cleaning in that its mechanism involves stripping away contaminants rather than dissolving them. To prevent the removed oil stains from reattaching to the surface being cleaned, the cleaning solution must be continuously circulated, and oil-water separators should be used. Semi-aqueous cleaning usually yields good results, but it has higher operating costs. The waste liquid cannot be recycled, and it contains a high level of COD (Chemical Oxygen Demand), requiring wastewater treatment.
(3) Non-aqueous systems
Non-aqueous cleaning agents refer to organic solvents that are insoluble in water. The non-aqueous cleaning agents used in precision industry cleaning are mainly hydrocarbons (petroleum-based substances), chlorinated hydrocarbons, fluorinated hydrocarbons, and brominated hydrocarbons. Alcohols. There are organic solvents such as silicone oils and terpenes. The main parameters used to evaluate solvents include the KB value (cedar rosin butanol value), AP (aniline point), and SP solubility parameter. Surface tension. Parameters such as density, viscosity, boiling point, flash point, and exposure concentration. A solvent with a high KB value, meaning it has strong dissolving power, is not necessarily a good cleaning agent. A good cleaning agent for precision industries must meet the following conditions: ① Stable chemical properties, with little tendency to react with the materials to be cleaned ； ②Low surface tension and viscosity, with strong penetration ability ； ③Low boiling point, allowing it to dry on its own ； ④No flash point, not flammable ； ⑤The KB value should not be too high to avoid dissolution with the substance being cleaned ； ⑥Low toxicity and safe to use: ⑦ It is not an ODS and has a low GWP (Global Warming Potential), making it environmentally friendly. If point 7 above is not taken into consideration, the best cleaning agents are CFC-113 and TCA; they possess good chemical stability and can remain unchanged over time ； For the vast majority of metals and plastics. Lacquer has no effect; it does not dissolve, has no flash point, is low in toxicity, and is safe to use ； Low surface tension, strong penetration, and excellent cleaning power ； It has a low boiling point and rapid evaporation rate; the cleaned parts can dry on their own, so drying is generally not necessary. For this reason, it is widely used in various industrial cleaning applications. However, its only drawback is that it damages the ozone layer, which is why its use is being phased out gradually. In China, the only company that produces CFC-113 as a cleaning agent is Changshu 3F. Production volumes have been decreasing year by year, from 4,800 tons in 2000 to zero by December 2005, with production and use completely halted thereafter. 4. Alternative cleaning agents Although various alternative substances have been developed around the world, no substitute cleaning agent has yet been found that can compare to CFC-113; each of them has its own set of problems. The main alternative products currently in use are: (1) Hydrocarbons Hydrocarbon solvents, which consist only of carbon and hydrogen elements, are also referred to as hydrocarbons or hydrocarbon-based solvents in Japan. Based on their different molecular structures, a variety of products with various properties have been developed, and they are widely used in Japan. The advantages of these cleaning agents are: they are not ODS compounds, they have strong cleaning power against oil stains, they exhibit good penetration, they are odorless or have only a slight smell, they are low in toxicity, their waste liquid can be easily treated, they can be reused, and they are inexpensive ； The disadvantages are its flammability and explosiveness, slow drying speed, high requirements for cleaning equipment, and high initial investment. Currently, the most ideal approach is to use vacuum cleaning to reduce surface tension and improve cleaning efficiency, followed by vacuum drying. However, such equipment is expensive, its operation is complex, and its efficiency is relatively low.
(2) Chlorinated hydrocarbon solvents
The chlorinated hydrocarbon cleaners currently in use are mainly trichloroethylene, dichloromethane, and tetrachloroethylene. These solvents are widely used in cleaning applications, and they have the following advantages and characteristics:
A very low ODP value (Ozone Depletion Potential), ranging from 0.005 to 0.007; they hardly cause any damage to the ozone layer ； It is non-flammable under normal conditions. There is no risk of fire or explosion (dichloromethane may explode under intense light over a long period of time) ； It has a strong dissolving power for oil stains such as metal processing oils and greases. It can also cause swelling or dissolution in plastics and rubber. With low viscosity and surface tension, it possesses strong penetration capabilities, allowing it to penetrate narrow gaps and completely dissolve and remove adhering contaminants ； It has a low boiling point and low vaporization heat, making it suitable for steam cleaning; it can dry on its own after cleaning ； Waste liquid can be separated by distillation and reused ； The same or similar cleaning processes and equipment as those used for CFC-113 and TCA can be employed; it is simple to operate, efficient, and has low operating costs ； The downside is its high toxicity; generally, its concentration in the air is restricted to below 50PPM ； Some labor protection regulations impose explicit restrictions on its use ； Now, some European countries **restrict the import and use of products containing such chlorinated cleaners. (3) Brominated hydrocarbon solvents In recent years, bromine-based cleaners have appeared in the United States and Japan, and they are used in the electronics industry and the aviation industry. It is widely used in the automotive industry and the home appliance sector. It is reported that Boeing uses this type of cleaning agent for cleaning aircraft components. The main component of bromine-based cleaning agents is high-purity n-bromopropane (NPB). Its performance is comparable to that of CFC-113 and TCA. Its key technical parameters are almost identical to those of TCA; it has a better wetting coefficient and a stronger ability to clean metal parts. It has no flash point, can be reused repeatedly, and results in low operating costs. As a substitute for CFC-11 and TCA, its manufacturing process is exactly the same, so there is little need to replace equipment; only the evaporation temperature needs to be adjusted. It is also known as a \"substitute cleaning agent for the third world.\" The ODP of bromine-based cleaning agents is 0.006, and their lifetime in the atmosphere is 11 days, with almost no GWP value. There are still debates regarding their toxicity, and the United Nations Environment Programme (UNEP) has conducted experiments for over 5 years. The results of these experiments differ significantly from theoretical analyses. The U.S. Environmental Protection Agency, in a policy issued on March 27, 2002, approved NPB as a solvent for use in cleaning, aerosols, and adhesives. However, since there is no definitive data on its toxicity, it is necessary to control the concentration of exposure to air when using it. This project was carried out by the China Liquid Crystal Association and the Liquid Crystal Engineering Technology Center at Tsinghua University
There are many types of scale inhibitors used in water treatment, such as organic phosphates, water-soluble polymers (polycarboxylic acids and polymers with various functional groups), chelating agents, etc. Their function is to exert their effects through mechanisms such as lattice distortion, complexation and solubilization, and dispersion. The dosage is generally 2-10 mg/L. Oxidants mainly include chlorines, bromines, peroxides, ozone, and chlorine dioxide ； The dosage is determined based on the number of bacteria and algae, or by monitoring indicators such as residual chlorine; the general concentration ranges from 4 to 10 mg/L ； Cleaning agents include inorganic acid cleaning agents, organic acid cleaning agents, chelating cleaning agents, polyelectrolyte cleaning agents, etc., which exert a cleaning effect through mechanisms such as neutralization, chelation, dispersion, and stripping. The amount to be used should be determined based on the desired level of cleanliness. Generally between 200-400mg/L ； Since it needs to be combined with the actual conditions of the system, there are currently no formulas or software available.