Defoaming agent polydimethylsiloxane
The most commonly used chemical component in defoamers is polydimethylsiloxane, also known as dimethyl silicone oil. It has low surface energy and 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 not compatible with polar solvent water and has low affinity with general oil. It has low volatility and chemical inertness, is relatively stable and has low toxicity. Pure polydimethylsiloxane is difficult to be used as a defoamer without dispersion treatment. This may be because it has high interfacial tension with water and low spreading coefficient, and is not easy to disperse in the foaming medium. Therefore, the composite formed by mixing silicone oil into SiO2 aerosol, that is, mixing the hydrophobic SiO2 aerosol into dimethyl silicone oil, and treating it at a certain temperature and for a certain time, can be obtained.
Organic silicone defoamer is made of silicone grease, emulsifier, waterproofing agent, thickener, etc. with appropriate amount of water and mechanically emulsified. Its characteristics are low surface tension, high surface activity, strong defoaming power, small 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℃; it has good chemical stability and 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 damaging product quality; it also has physiological inertness LD250g/Kg mouse, and is usually used in food and pharmaceutical industries.
It has both foam suppression and foam breaking functions 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, etc. In the petroleum industry, it is widely used in the desulfurization of natural gas to accelerate oil and gas separation; it is also used in the drying of ethylene glycol, the extraction of aromatic hydrocarbons, the processing of asphalt, the dewaxing of lubricating oils and other devices to control or suppress bubbles. In the textile industry, it is used for defoaming in dyeing, refining, sizing and other processes; in the chemical industry, it is used for defoaming in synthetic resins, latex, coatings, inks and other processes; in the food industry, 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. Silicone grease can be made into a solution and can be used for defoaming in oil phase systems. Silicone grease plus low viscosity silicone oil can be made into a water emulsion and can be used for defoaming in various water phase systems. In medicine, it is usually used to remove flatulence from organs or gastric organs before surgery, X-ray and gastroscopy.
Defoamers can be roughly divided into two categories: one can eliminate bubbles that have been generated, such as ethanol, etc.; the other can inhibit the formation of bubbles, such as emulsified silicone oil. The defoamers permitted for use in my country include emulsified silicone oil, high carbon alcohol fatty acid ester complex, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropanolamine ether, polyoxypropylene glycerol ether and polyoxypropylene.
