In modern industrial production, foam is everywhere: the trough of various processing fluids; Various industrial cleaning pools; In various industrial and agricultural products and preparations; In all production links of petrochemical industry, water treatment and so on. Foam, to bring various problems to industrial production: in order to prevent foam overflow, the feeding coefficient is forced to reduce 30%~ 50%; Foam overflow leads to waste of raw materials; Foam occupies space, affects the reaction speed, and the production cycle is forced to extend; Foam will affect the quality of products, such as paint, plastic products; The production of foam has an impact on the stability of industrial production, resulting in fluctuations in operation and unstable quality. For the foam problem, the most direct solution is to use defoamer. The ability of silicone to defoamer or suppress bubbles is due to its very low surface tension. Silicone compounds (silicone oil) interfere with the surface tension of the gas-liquid boundary, resulting in a defoaming effect.
When silicone is added to the foam medium, small particles of silicone oil fall to the surface of the bubble, while effectively reducing the surface tension of the contact point, causing a weak point in the bubble skin, resulting in bubble bursting. The criteria for optimal defoaming activity can be described as follows: small particles of free silicone oil must be dispersed completely, as quickly and efficiently as possible into the active zone. Silicone oil is rapidly dispersed by means of SiO2 filler with a small proportion and large surface area added during production and processing, and causes emulsification and bubble breaking outside the contact point of SiO2 particles. The foam squeezed together causes an unstable state due to the collapse of the foam near it, speeding up the effect of continuous bubble breaking, and finally reaches a stable state. If it is an emulsion defoamer, the emulsion is too stable, which will reduce the defoamer effect. When the stability is poor, it has greater activity. Therefore, it is necessary to balance between stability and activity, and select organosilicon compounds with low solubility in the water phase and the oil phase, but with extremely high activity. The function of defoamer is also defined by three mechanisms: breaking, defoaming and suppressing bubbles. Bubble breaking: Relative to the foam, from the air side into the bubble, the bubble will be destroyed. Bubble suppression: from the liquid side into the bubble, the bubble will be destroyed. Defoaming: invading the bubble from the interface of the bubble, so that the bubble emerges from the liquid surface. The advantages and disadvantages of silicone defoamer: 1. Wide application. Due to the special chemical structure of silicone oil, it is neither soluble with water or substances containing polar groups, nor is it soluble with hydrocarbons or organic compounds containing hydrocarbon groups. Because of the insolubility of silicone oil to various substances, it is widely used, which can be used for water system defoaming and oil system. 2. Low surface tension. The surface capacity of silicone oil is generally 20-21 dynes/cm, which is smaller than the surface tension of water (72 dynes/cm) and general foaming liquid, and the antifoam effect is good. 3. Good thermal stability. Taking the commonly used dimethyl silicone oil as an example, it can withstand 150 ° C for a long time, and can withstand more than 300 ° C for a short time, and its Si-O bond does not decompose. This ensures that the silicone defoamer can be used over a wide temperature range. 4. Good chemical stability. Because the Si-O bond is relatively stable, the chemical stability of silicone oil is very high, and it is difficult to chemically react with other substances. Therefore, as long as the preparation is reasonable, the silicone defoamer is allowed to be used in the system containing acid, alkali and salt. 5. Physical inertia. Silicone oil has been shown to be non-toxic to humans and animals at semi-lethal doses greater than 34 g/kg. Therefore, silicone defoamer (in the combination of suitable non-toxic emulsifiers, etc.) can be safely used in food, medical, pharmaceutical and cosmetics industries. 6. Strong defoaming. Silicone defoamer can not only effectively break the foam that has been formed, but also significantly inhibit the foam and prevent the formation of the foam. Its use is very small, as long as the weight of the foaming medium is added one millionth (1ppm), that can produce defoaming effect. Its common range is 1 to 100 PPM. Not only the cost is low, but also does not pollute the defoaming material. Disadvantages: 1. Polysiloxane dispersion is more difficult. Polysiloxane is difficult to dissolve in water, hindering its dispersion in the water system, dispersant must be added, dispersant added more, the emulsion is stable, the defoaming effect will become worse, emulsifier must be used less, so that its defoaming effect is good, the emulsion is stable. 2. Silicone is oil-soluble, reducing its defoaming effect in the oil system. 3. Long-term high temperature resistance and strong alkaline resistance. Classification of silicone defoamer
Ointment type defoamer


Oil type defoamer is the direct use of silicone oil as defoamer. It is mainly used in oil phase foaming systems that do not allow the presence of dispersants and emulsifiers. It is generally believed that silicone oils with different viscosity show different defoaming effects on the same foaming system. Low viscosity silicone oil defoamer has fast defoamer effect but poor continuity, while high viscosity silicone oil defoamer has slow defoamer effect but good continuity. Ointment type defoamer is an ointment type defoamer prepared by adding silica, aluminum oxide and other micro-powders into silicone oil, which is mainly used for defoamer of non-aqueous system.


The defoaming effect of dimethylsilicone oil depends on the degree of dispersion of silicone oil in the foaming system. In order to improve the degree of dispersion, mechanical agitation can be used, such as high-speed agitation under heating, or a uniform dispersion of silicone oil and mineral oil can be configured with a colloid mill in advance. Or pre-mix silicone oil with white carbon black and other micro-powder into a cream type defoamer, which is used by means of the dispersion of micro-powder such as white carbon black.


Solution type defoamer


Silicone solution defoamer can be prepared by dissolving dimethylsilicone oil in appropriate solvent. Silicone defoamer prepared with organic solvents such as polychloroethane, toluene and xylene is selected. Can be used for oil soluble media defoaming operation; The silicone defoamer is prepared with organic solvent which is easily soluble in water, such as hexanediol and glycerol. It can be used for defoaming of aqueous solution. The preparation process of solution silicone defoamer is very simple. Easy to use, silicone oil dispersed in the foaming liquid with organic solvents to play a defoaming role, while some solvents in the diffusion process will also play a certain defoaming role. However, this method is not widely used, mainly because a large number of use will increase the cost of defoamer, while it may cause environmental pollution.


Emulsion type defoamer


The dispersion of silicone oil in aqueous phase can be effectively improved by making silicone oil emulsion with strong stirring or emulsifier. Therefore, it is widely used as a defoamer in water system. Emulsion type defoamer is also the most widely used and the largest amount of silicone defoamer.


Emulsion type silicone defoamer is generally prepared by dimethylsilicone oil, emulsifier, emulsion stabilizer and deionized water. The emulsifiers used are mainly non-ionic emulsifiers with low foamability, such as pan, Tween and polyethylene glycol, etc. The effect of mixed emulsifiers is better than that of single emulsifiers. The particle size of silicone oil emulsion is the most important control index of emulsion silicone defoamer. In order to obtain high defoaming efficiency and good storage stability of silicone oil emulsion, the particle size is usually required to be less than 10μm.


Therefore, in addition to the selection of appropriate emulsifiers and mixed grinding conditions, thickening agents such as polyvinyl alcohol and methyl cellulose can also be added to improve the viscosity of continuous phase.


When using emulsion silicone defoamer, the temperature, acidity and alkalinity of the foaming system should be understood first, because they will affect the stability of the emulsion and even lead to demulsification.


Although emulsion silicone defoamer has the disadvantages of difficult long-term storage, easy stratification and easy deterioration, it has the characteristics of convenient use, wide application, obvious defoamer effect and moderate price, all of which are still welcomed by users, and with the progress of process technology, emulsion silicone defoamer will have a larger space for development.


Solid type defoamer


Solid silicone defoamer has the characteristics of good storage stability, easy transportation and easy use, which can be used not only for the production of non-foaming and low-foaming detergent, but also for other occasions that need defoaming operations.


There are three preparation methods for solid silicone defoamer: (1) The silicone oil is directly dispersed on the surface of the solid carrier; (2) Melt the silicone oil with fatty alcohols, fatty acids, fatty amides, fatty acid esters or paraffins with a lower softening point, and then attach the melt to the surface of the solid carrier; (3) The organic silicone oil is mixed with the film-forming substance, so that the film-forming substance is enclosed in the outside of the anti-foaming component of the organic silicone oil to form dispersed solid particles.


Modified silicone oil type defoamer


The modified silicone oil introduces some methyl silicone oil of hydrophilic polyether chain segment, which can become a self-emulsifying defoamer, and maintain the dispersibility in the foaming system for a long time, extending the service life of the defoamer. At present, the modified silicone oils commonly used as defoamer are polyether silicone oil, fluoroalkyl silicone oil and long chain alkyl silicone oil, and their application and effect are remarkable.


End group, side group and branch chain polyether silicone oil can be used as defoamer. They all have a clear cloud point, only above the cloud point has a strong defoaming, and below the cloud point has the effect of promoting foaming. In addition, the use of polyether silicone oil strong emulsifying ability, and silicon paste, in the water system can be self-emulsified into a stable, efficient defoamer, has been widely used as polyester fiber high temperature dyeing, a variety of lubricating oil, cutting oil, antifreeze and strong acid system defoamer.


Long chain alkyl silicone oil defoamer can be used in fermentation, food adding, medical, textile, petroleum, synthetic rubber and resin, paint and ink and other fields. Due to its good affinity for organic materials, long-chain alkyl silicone oil defoamer does not affect the post-processing properties of the product. However, the surface tension increases with the increase of the carbon chain, and the defoaming performance decreases, so it is very important to choose the appropriate length of the carbon chain. Long chain alkyl silicone oil has been used in the defoaming of both non-aqueous systems and aqueous systems.


The surface tension of fluoroalkyl silicone oil is lower than that of other silicone oils, so the defoamer prepared by fluoroalkyl silicone oil is more effective in reducing the surface tension of various foaming systems, and the effect is better than other silicone oil defoamer. It is mainly used for foaming medium of non-aqueous system with strong solubility to methyl silicone oil or methyl phenyl silicone oil, such as aliphatic hydrocarbon, aromatic hydrocarbon and naphtha.


Application field of silicone defoamer
Textile printing and dyeing


1. Sizing process: water-emulsion silicone defoamer, such as: silicone polyether, add 0.2-0.25g/L in sizing tank.


2. Chemical fiber oil agent: chemical fiber oil agent added 0.02-0.04% water emulsion type defoamer. Organic silicone oil should be included in the formula of chemical fiber oil.


3. Desizing and refining: Use polyether silicone.


4. Bleaching: strong acid, silicone defoamer.


5. Dyeing: silicone emulsion defoamer. Jet dyeing is best to choose polyether silicone, high temperature defoaming, low temperature water soluble, non-staining fabric.


petrification


1. Drilling: ethyl silicone oil (or methyl silicone oil layer emulsion) is used as a mud additive.


2. Oil recovery: oil and gas separation, defoaming rod. The melting point is 2.8-13.9℃ higher than the wellhead foam temperature.


3. Natural gasoline absorption: Use gasoline to mix dimethyl silicone oil into 2% solution.


4. Oil and gas separation and demulsification:


A. Oil and gas separation, adding 0.025 ~ 0.0065mg/Kg to crude oil can improve production capacity;


B. Demulsification: oil and gas separation of crude oil is generally micro W/O emulsion, adding about 0.2mg/Kg of appropriate defoamer, can achieve the effect of demulsification and defoamer.


5. Refining: vacuum distillation adds defoamer, the color of the fraction is improved, the range of the fraction is relaxed, and the diesel solution with silicone oil is commonly used.


6. High energy fuel (internal combustion, jet, aviation fuel) is dispersed in high flash point kerosene with cyanalkyl polysiloxane, and then added to high energy fuel as a high efficiency defoaming agent.


7. Asphalt and residual oil: the amount of silicone oil added is 0.2×10-6 ~ 2.0×10-6


8. Delayed coking, coke removal, scale elimination: reference amount of defoamer addition: 0.05 ~ 100×10-6


9. Antifoam drilling fluid: high viscosity sulfonate metal salt (petroleum calcium sulfonate: sodium sulfonated asphalt = 1:1), the amount of siloxane added about 100 ~ 400×10-6 or 5 ~ 15mg/Kg, sulfonate: siloxane close to 1:1 is better.


10. Lubricating oil: such as internal combustion engines, automotive lubricants, metal working fluids, compressor oil, etc., when silicone oil is added for defoaming, it is because of the following advantages:


A. insoluble in lubricating oil, in A dispersed state, is conducive to adsorption on the bubble film bubble breaking;


B. There are alkyl groups similar to mineral oil, which can squeeze into the bubble membrane and weaken the molecular attraction;


C. Low surface tension, good penetration, when adsorbed on the surface of the bubble film, the local surface tension is reduced, and the bubble is broken due to uneven surface tension of the bubble film. Heavy oil is selected with small viscosity silicone oil, and the addition amount is 1 ~ 10×10-6. In addition, alkyl polyacrylates are also better and have better gas release. Branched chain amine added to crude gasoline, naphtha, and then added to the lubricating oil, can also be used as a defoamer, adding a small amount of 0.05 ~ 1%, this defoamer can be added to the metal cutting fluid.


papermaking


1.Pulping: silicone emulsion defoamer (90g/T paper).


2. Coating paper: coating paint, paper for printing pictures after calender, etc., coated bubbles are generally coated with non-silicon defoamer.


3. Sewage treatment: water-emulsion silicone defoamer.


Paint, ink


Requirements for defoamer in coating production


1. It has a certain affinity with the active substance on the surface of the foam, but it should be insoluble and insoluble in the bubble liquid;


2. The surface tension is lower than the surface tension of the bubble liquid, and has a low HLB value;


3. The emulsion (latex) should be stable;


4. The coating can not cause adverse consequences of fisheye and shrinkage after film formation;


5. Water-based coating defoamer: use more insoluble substances in water, such as mineral oil, advanced alcohol, silicone resin, silicone is the best water-based coating defoamer.


Non-water-based coating defoamer: commonly used substances that are insoluble in organic solvents, such as low alcohols and silicone resins (the amount of silicone resin should be appropriate, excessive is easy to shrink and crack, and more modified silicone resins or emulsified silicone resins are used)


Silicone defoamer recommended for use in water-based coatings


1. Silicone oil, hydrophobic SiO2 mixture suitable for: epoxy resin, pouring coating, dosage 0.3%; Thermoplastic acrylic resin, sprayed, dosage 0.3%


2. Polyether polysiloxane and hydrophobic SiO2 mixture is suitable for thermosetting alkyd resin, dipping amount 0.3%, scraping amount 0.1%


3. The mixture of hydrophobic SiO2, hydrocarbons and silicone oil is suitable for: thermoplastic acrylic resin, printing and ink, the amount is 0.1%; Air-dried acrylic resin, poured, dosage 0.5%.


4. Silicone oil and hydrophobic SiO2 mixture emulsion suitable for: alkyd modified styrene acrylic resin, pouring, dosage 0.5%


abluent


Polysiloxane and modified sodium tripolyphosphate are used as powder detergent additives, and dimethylsilicone oil (1500c.s) emulsion containing SiO2 of 2 ~ 6% is mixed with anhydrous sodium tripolyphosphate, and the emulsion dosage is 10 ~ 40% to form hydrate as an additive.


Metal cleaning solution, required to be alkali resistant, preferably transparent and antifoaming when added to the liquid product.


food


Food special polysiloxane resin: dimethylpolysiloxane as the main body, containing less than 15% SiO2 food is an aqueous solution, with its emulsified products, other can be directly oil-type products, the amount of control.


Development trend of silicone defoamer
Silicone defoamer not only has good defoaming and defoaming effect, but also has the characteristics of low dosage, good chemical inertia, and can play a role under harsh conditions. In recent years, it has achieved rapid development, and new varieties and models suitable for different use environments are constantly produced, and the application surface is constantly expanding. In the future, new high-efficiency silicone defoamer with strong applicability and can further improve product quality and equipment utilization will be further developed, especially polyether modified silicone defoamer and emulsion defoamer with excellent performance will occupy a major position in the market.