Common types and types of defoamers
In the process of industrial production, many harmful foams will be generated, and defoamers need to be added. There are many types of antifoaming agents, organosiloxane, polyether, silicon and ether grafting, containing amines, imines and amides, with faster defoaming speed, longer foam suppression time, and a wider range of applicable media, Even harsh media environment such as high temperature, strong acid and strong alkali characteristics. It is widely used to remove harmful foams produced in the production process of industries such as latex, textile sizing, food fermentation, biomedicine, coatings, petrochemicals, papermaking, industrial cleaning and other industries.
1. Natural oil (ie soybean oil, corn oil, etc.)
Advantages: easy source, low price, simple use;
Disadvantages: If the storage is not good, it is easy to deteriorate and increase the acid value.
2. High alcohol
High-carbon alcohol is a linear molecule with strong hydrophobicity and weak hydrophilicity. It is an effective defoamer in water systems. In the early 1970s, former Soviet scholars tested in anionic, cationic, and nonionic surfactant aqueous solutions, and proposed that the defoaming effect of alcohol is related to the solubility and diffusion degree in the foaming liquid. C7 ~ C9 alcohols are the most effective defoamers.
The high-carbon alcohol of C12 ~ C22 is formulated into an aqueous emulsion with a particle size of 4 ~ 9μm and a content of 20 ~ 50% by means of an appropriate emulsifier, which is a defoamer for water systems.
Some esters, such as phenylethanol oleate and lauryl phenylacetate, have defoaming effects in penicillin fermentation, which can also be used as a precursor.
3. Polyether defoamer
There are many types, mainly the following:
a. GP defoamer
Using glycerin as the starting agent, it is made by addition polymerization of propylene oxide, or a mixture of ethylene oxide and propylene oxide
GP-type defoamers have poor hydrophilicity and low solubility in foaming media, so they should be used in thin fermentation broths. Its antifoaming ability is superior to defoaming ability, so it is suitable to be added to the basic medium to suppress foaming during the entire fermentation process.
b. GPE defoamer is the enemy
Add ethylene oxide to the end of the polypropylene glycol link of the GP defoamer to become a polyoxyethylene oxypropylene glycerin with a hydrophilic group at the chain end, also called. According to the addition amount of ethylene oxide is 10%, 20%, ... 50% are called GPE10, GPE20, ... GPE50 respectively.
GPE defoamer has good hydrophilicity, easy to spread in foaming medium, strong defoaming ability, but also has high solubility and short defoaming activity maintenance time, so it is better used in viscous fermentation broth.
c. GPES defoamer: There is a new polyether defoamer. At the end of the GPE defoamer chain is capped with a hydrophobic stearate to form a hydrophobic chain at both ends, with a hydrophilic space in between. Chain block copolymer. Molecules of this structure tend to accumulate horizontally at the gas-liquid interface, so they have strong surface activity and high defoaming efficiency.
The most commonly used is polydimethylsiloxane, also known as dimethicone. 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 is incompatible with polar solvent water and has little affinity with general oils. It has low volatility and chemical inertness, is relatively stable and has low toxicity. Pure polydimethylsiloxane is difficult to use as a defoamer without dispersion treatment. It may be due to its high interfacial tension with water and low spreading coefficient, making it difficult to disperse on the foaming medium. Therefore, the silicone oil is mixed into the SiO2 aerosol, and the composite compound, that is, the hydrophobically treated SiO2 aerosol is mixed into the dimethyl silicone oil, which can be prepared after a certain temperature and a certain time treatment.
The silicone defoamer is made of silicone grease, emulsifier, water repellent, thickener, etc. 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 substances, 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 , Without compromising product quality; it also has physiologically inert LD250g / Kg rat, usually used in food and pharmaceutical 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 making, electroplating, fertilizers, additives, wastewater treatment and so on. 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 controlling or suppressing air bubbles in devices such as drying of ethylene glycol, extraction of aromatic hydrocarbons, processing of asphalt, and dewaxing of lubricating oil. . In the textile industry, it is used for defoaming in dyeing, refining, sizing, etc .; in the chemical industry, it is used for defoaming in synthetic resins, latex, paints, inks, etc .; in the food industry, it is used Defoaming in various concentration, fermentation and distillation processes. Silicone grease can be applied on the wall of the pot, the outlet or on the metal net for defoaming. The silicone grease is formulated into a solution, which can be used to defoam the oil phase system. Silicone grease plus low-viscosity silicone oil can be formulated into an aqueous emulsion, which can be used for defoaming in a variety of water phase systems. In medicine, it is usually used to remove the flatulence of organs or stomach organs before surgery, X-rays and gastroscopy.
Anti-foaming agents can be roughly divided into two categories: one type can eliminate the generated bubbles, such as ethanol, etc .; the other type can inhibit the formation of bubbles such as emulsified silicone oil. The defoamers approved for use in China are emulsified silicone oil, high-carbon alcohol fatty acid ester compound, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropylene amine ether, polyoxypropylene glyceryl ether and polyoxypropylene
5. Polyether modified silicon
Combining the advantages of polyether and silicone defoamer, it is non-toxic and harmless, harmless to bacteria, and has a very small amount of addition. It is a cost-effective product.