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. Polyether defoamer
There are many types of , mainly as follows:
A. GP type 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 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 is foam enemy
Ethylene oxide is added to the end of the polypropylene glycol chain of the GP type defoamer to form a 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 defoamer has good hydrophilicity, is easy to spread in the foaming medium, has 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 a 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 of this structure are easy to gather in the gas-liquid interface in a horizontal state, so the surface activity is strong and the defoaming efficiency is high.
3. High-carbon alcohol
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 conducted experiments 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 the most 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 appropriate emulsifiers, which are defoamers for water systems.
There are also some esters, such as phenylethyl oleate, lauryl phenylacetate, etc., which have defoaming effects in penicillin fermentation, and the latter can also be used as a precursor.
Tributyl phosphate (CAS: 126-73-8), as an ancient defoamer, is still widely used in the industry because of its extremely low surface tension (27.79 25°C) and extremely low water solubility (0.61 25 ℃, the solvent is soluble in water), the defoaming effect is remarkable, but because of its irritation and certain toxicity, it is mostly used in other industries that are not in contact with food/daily cosmetics.
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 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 defoamer 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 processed at a certain temperature and a certain time, and then it can be prepared.
Organic silicon defoamer is made of silicone grease, emulsifier, waterproofing agent, thickening agent, 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 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 the 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, electroplating, fertilizers, additives, wastewater treatment, etc. 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 ethylene glycol, the extraction of aromatic hydrocarbons, the processing of asphalt, the dewaxing of lubricating oil and other devices to control or suppress air 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. The silicone grease is formulated into a solution, which can be used to defoam the oil phase system. 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, etc.; 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 glyceryl ether and polyoxypropylene
5. Polyether modified silicon
Combining the advantages of both 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.
Polyether-modified silicone is a polyether-siloxane copolymer (silicon ether copolymer for short) made from polyether segments in the siloxane molecule. Polysiloxane defoamers have the characteristics of rapid defoaming, long time of foam suppression, safety and non-toxicity, but it is difficult to dissolve in water, high temperature resistance, poor resistance to strong alkalis, and polyether defoamers have good water solubility and resistance High temperature, strong alkali resistance, but its defoaming speed and foam suppression time are not ideal. The polyether chain is grafted on the polysiloxane chain by condensation technology to make it have the advantages of the second type of defoaming agent. Become a defoamer with excellent performance and broad application prospects. In the molecule of the silicone ether copolymer, the siloxane segment is a lipophilic group, and the polyether segment is a hydrophilic group. In the polyether segment, the polyethylene oxide chain saves energy to provide hydrophilicity and foaming, and the polypropylene oxide chain saves energy to provide hydrophobicity and permeability, which has a strong effect on reducing surface tension. The polyether end groups also have a strong influence on the properties of the siloxane ether copolymer. Common end groups are hydroxyl, alkoxy and so on. Adjusting the relative molecular mass of the siloxane segment in the copolymer can make the copolymer highlight or weaken the characteristics of silicone. Similarly, changing the relative molecular weight of the polyether segment will increase or decrease the proportion of organosilicon in the molecule, which will also affect the performance of the copolymer. Polyether modified silicone defoamer is easy to emulsify in water, also known as "self-emulsifying defoamer". Above its cloud point temperature, it loses water solubility and mechanical stability, and is resistant to acids and alkalis. And inorganic salt, can be used for defoaming under harsh conditions, and widely used for defoaming in polyester fabric high temperature dyeing process and fermentation process. In addition, it can also be used for the defoaming of diethanolamine desulfurization system and the defoaming of various oils, cutting fluids, antifreeze, water-based inks and other systems. It is also suitable for the printing industry to wash off the uncured resin after the photosensitive resin plate is made. Defoaming is a representative, excellent performance and versatile silicone defoaming agent. Polysiloxane defoamers are usually made up of the two main components of polydimethylsiloxane and silicon dioxide. The defoamers based on polydimethylsiloxane are one of the defoamers in the defoaming system. It is an ideal defoamer because it is insoluble in water and more difficult to emulsify. Polydimethylsiloxane has lower surface properties than carbon chain hydrocarbons and therefore has lower surface tension than surfactants usually used in the textile industry. Simple polydimethylsiloxane has poor foam suppression performance and is slow. The defoaming effect needs to be strengthened by silica particles. The silica particles are carried by the silicone oil to the air-water interface of the foam and enter the bubble liquid film due to its hydrophobicity. The contact angle of the foam droplets with the surfactant is greater than 90°, which forces the foaming liquid to be expelled from the surface of the solid hydrophobic particles, causing rapid local drainage of the foam and leading to rupture. In this way, due to the synergistic effect, the two compositions produced a good defoaming effect.
6. New self-emulsifying defoamer
Contains specially modified polysiloxane. With excellent heat resistance, acid and alkali resistance and chemical stability, it can be widely used in the elimination and suppression of various harsh systems in a wide temperature range.
7. Polysiloxane defoamer
Polysiloxane defoamers are usually made up of the two main components of polydimethylsiloxane and silicon dioxide. The defoamers based on polydimethylsiloxane are one of the defoamers in the defoaming system. It is an ideal defoamer because it is insoluble in water and more difficult to emulsify. Polydimethylsiloxane has lower surface properties than carbon chain hydrocarbons and therefore has lower surface tension than surfactants usually used in the textile industry. Simple polydimethylsiloxane has poor foam suppression performance and is slow. The defoaming effect needs to be strengthened by silica particles. The silica particles are carried by the silicone oil to the air-water interface of the foam and enter the bubble liquid film due to its hydrophobicity. The contact angle of the foam droplets with the surfactant is greater than 90°, which forces the foaming liquid to be expelled from the surface of the solid hydrophobic particles, causing local rapid drainage of the foam and rupture. In this way, due to the synergistic effect, the two compositions The substance produced a good defoaming effect. Due to its excellent defoaming performance and other advantages, polysiloxane defoamers have been widely used in many fields, especially in the dyeing and finishing of textiles. The development is particularly rapid. Research has found that polydimethylsiloxane The silicone glycol defoamer with polyethylene copolymer as the base material has an ideal defoaming effect in jet dyeing and other textile processing due to its special solubility.