In the process of industrial production, many harmful foams are generated, and defoamers need to be added. There are many types of defoamers, including organosiloxane, polyether, silicon and ether grafts, containing amines, imines and amides, with faster defoaming speed, longer foam suppression time, and a wider range of applicable media. Even harsh medium environment such as high temperature, strong acid and strong alkali characteristics. It is widely used to remove harmful foam produced in the production process of latex, textile sizing, food fermentation, biomedicine, coating, petrochemical, papermaking, industrial cleaning and other industries.

1. Natural oils (ie soybean oil, corn oil, etc.)

advantages: easy source, low price, simple to use;

Disadvantages: If the storage is not good, it is easy to deteriorate and increase the acid value.

2. Higher alcohols Higher alcohols are linear molecules with strong hydrophobicity and weak hydrophilicity. They are effective defoamers in water systems. In the early 1970s, scholars from the former Soviet Union tested in aqueous solutions of anionic, cationic, and nonionic surfactants and proposed that the defoaming effect of alcohol is related to its solubility and diffusion in the foaming liquid. C7~C9 alcohols are effective defoamers.

C12~C22 higher alcohols are formulated into an aqueous emulsion with a particle size of 4~9μm and a content of 20~50% with the help of an appropriate emulsifier, which is the defoamer of the water system.

Some esters, such as phenylethyl oleate and lauryl phenylacetate, have defoaming effects in penicillin fermentation, and the latter can also be used as a precursor

3. Polyether defoamer

There are many types, mainly the following:

a. GP type defoamer is made by addition polymerization of propylene oxide or a mixture of ethylene oxide and propylene oxide with glycerin as the starting agent.

The GP type defoamer has poor hydrophilicity and low solubility in the foaming medium, so it should be used in thin fermentation broth. Its antifoaming ability is superior to that of defoaming, and it is suitable to be added to the basic medium to inhibit the production of foam during the entire fermentation process.

b. GPE-type defoamer, namely foam enemy, is added with ethylene oxide to the end of the polypropylene glycol chain of GP-type defoamer to become polyoxyethylene oxide propylene glycerin with a hydrophilic group at the chain end, also called. According to the addition amount of ethylene oxide, 10%, 20%,...50% are called GPE10, GPE20,...GPE50, respectively.

GPE-type defoaming agent has good hydrophilicity, easy to spread in the foaming medium, strong defoaming ability, but the solubility is also large, and the defoaming activity is maintained for a short time, so the effect is better when used in viscous fermentation broth.

c. GPES type defoaming agent: There is a new polyether defoaming agent. The GPE type defoaming agent is capped with hydrophobic stearate at the end of the chain to form a hydrophobic chain at both ends, with a hydrophilic interval in the middle. Chain of block copolymers. Molecules with this structure tend to gather in the gas-liquid interface in a flat state, so the surface activity is strong and the defoaming efficiency is high.

4. Silicon

Commonly used is polydimethylsiloxane, also known as dimethyl silicone oil. It has low surface energy, low surface tension, low solubility in water and general oil, and high activity. Its main chain is a silicon-oxygen bond, which is a non-polar molecule. It has no affinity with polar solvent water, and has little affinity with general oils. It has low volatility and chemical inertness, relatively stable and low toxicity. Pure polydimethylsiloxane is difficult to be used as a defoaming agent without dispersion treatment. It may be due to its high interfacial tension with water and low spreading coefficient, which makes it difficult to disperse on the foaming medium. Therefore, silicone oil is mixed into SiO2 aerosol to form a composite, that is, the hydrophobically treated SiO2 aerosol is mixed into dimethyl silicone oil, and then treated at a certain temperature and a certain time, and then it can be prepared.

Silicone defoamer is made of silicone grease, emulsifier, water repellent, thickening agent, etc., mixed with appropriate amount of water and mechanically emulsified. It is characterized by low surface tension, high surface activity, strong defoaming power, low dosage and low cost. It is immiscible with water and most organic matter, and can defoam most bubble media. It has good thermal stability and can be used in a wide temperature range of 5℃-150℃; its chemical stability is good, and it is difficult to react with other substances. As long as it is properly configured, it can be used in acid, alkali, and salt solutions. , No damage to product quality; it also has a physiologically inert LD250g/Kg mouse, usually used in food and medicine industries. It has the functions of suppressing and breaking bubbles for all bubble systems, and belongs to the category of broad-spectrum defoamers. It is widely used for defoaming in the production process of detergents, papermaking, pulp, sugar, electroplating, fertilizers, additives, and wastewater treatment. In the petroleum industry, it is widely used for the desulfurization of natural gas to accelerate the separation of oil and gas; it is also used for the drying of glycol, the extraction of aromatic hydrocarbons, the processing of asphalt, the dewaxing of lubricating oil and other devices to control or suppress bubbles. . In the textile industry, it is used for defoaming in the process of dyeing, scouring, sizing, etc.; in the chemical industry, it is used for defoaming in the process of synthetic resin, latex, paint, ink, etc.; in the food industry, it is used It is used for defoaming in various concentration, fermentation and distillation processes. Silicone grease can be applied to the pot wall, outlet or metal mesh for defoaming. Mixing silicone grease into a solution can be used for defoaming in oil phase systems. Silicone grease and low-viscosity silicone oil are combined to form a water emulsion, which can be used for defoaming in a variety of water phase systems. In medicine, it is usually used to remove flatulence from organs or stomach organs before surgery, X-ray and gastroscopy.

Defoamers can be roughly divided into two categories: one type can eliminate the bubbles that have been generated, such as ethanol; the other type can inhibit the formation of bubbles, such as emulsified silicone oil. The defoamers that are permitted to be used in my country are emulsified silicone oil, higher alcohol fatty acid ester compound, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropanol amine ether, polyoxypropylene glycerol ether and polyoxypropylene

5. Polyether modified silicon

Combining the advantages of polyether and organosilicon defoamer, it is non-toxic and harmless, harmless to bacteria, and has a very small amount of addition. It is a cost-effective product.