Types and preparation of silicone oil
◆ Molecular structure and preparation of silicone oil
Silicone oil, a linear polysiloxane product that remains liquid at room temperature, has a variety of molecular structures. It can be either straight chain or branched chain, and is composed of -Si-O-Si-, while the end groups and side groups are all hydrocarbon groups, such as methyl, ethyl, phenyl, etc. It is precisely this molecular structure that allows silicone oil to be prepared through corresponding monomers or intermediates. It is worth noting that the preparation methods of silicone oils with different substituents are different. The preparation method of silicon-functional silicone oils in which some hydrocarbon groups are replaced by hydrogen, hydroxyl, alkoxy, etc. is significantly different from that of ordinary silicone oil.
◆ Chemical types and uses of silicone oil
Silicone oil can be divided into many types in terms of chemical structure, including methyl silicone oil, ethyl silicone oil, etc. At the same time, according to its use, silicone oil can be divided into damping silicone oil, diffusion pump silicone oil, etc. Silicone oil is divided into methyl, ethyl, etc. according to its chemical structure, and can be divided into damping and diffusion pump silicone oils according to its use. In addition, from the processing status, silicone oil can be divided into primary products and secondary products. The former mainly refers to silicone oil products before processing, such as hydroxy silicone oil, silicone functional silicone oil, etc.; the latter is a product made of silicone oil as raw material, thickener, etc., and processed by a specific process, such as silicone grease, defoamer, etc.


Form and characteristics of silicone oil
◆ Basic forms of silicone oil
There are three basic forms of silicone oil commonly found on the market: pure silicone oil, solution and emulsion. Among them, 100% pure silicone oil is favored for its high stability, heat resistance, antifreeze and excellent storage properties.
◆ Market classification and characteristics of silicone oil
Solution. Usually, silicone oil solution needs to be diluted before use, and it may not be convenient for users to configure it by themselves. Adding active auxiliary agents such as catalysts or cross-linking agents to the solution can improve its storage and use performance. When selecting solvents, aliphatic, aromatic or chlorinated hydrocarbons can be used as needed. It should be noted that the concentration of high molecular polysiloxane solution should not be too high, otherwise the viscosity will be too large.
Emulsion. Silicone oil or products containing silicone oil in the form of emulsions account for a large proportion. Compared with solvent silicone oil, they are cheap, non-flammable and harmless to health. All silicone emulsions are "oil in water" type (O/W type) heterogeneous systems, in which silicone oil is dispersed in the water phase in the form of extremely fine droplets and can be easily diluted with water to the required concentration. The stability of this emulsion can be ensured by reducing the droplet size and utilizing the stabilizing effect of emulsifiers.
◆ Physical and chemical properties of silicone oil
Silicone oil has good heat resistance. Polysiloxane molecules have a structure similar to that of inorganic polymers, and their main chain is composed of -Si-O-Si- bonds with high bond energy, which gives silicone oil excellent heat resistance. Silicone oil has the characteristics of heat resistance, electrical insulation, low viscosity-temperature coefficient, compression resistance, and low surface tension, which makes it used in many fields.


Chemical properties and regeneration of silicone oil
◆ Chemical stability of silicone oil
Silicone oil shows a certain inertness, and its Si-C bond is very stable. However, silicone oil is chemically stable, but can react with strong oxidants and acids and bases, especially at high temperatures. In particular, methyl silicone oil may react violently or even explosively when reacting with chlorine. At the same time, the Si-O bond is easily broken by strong bases or acids. For example, at low temperatures, concentrated sulfuric acid can quickly react with siloxane chains, causing the chains to break and attach to sulfuric acid. It is worth noting that silicone oils with high alkane groups and phenyl groups show relatively high stability in this regard.
◆ Silicone oil regeneration method
Since its chemical properties are relatively stable, silicone oil is expensive and needs to be recovered and regenerated separately. Silicone oil regeneration is carried out by adsorption refining and solvent vapor treatment. The regeneration process usually adopts adsorption refining treatment to purify the silicone oil by contact with adsorbents such as silica gel and activated alumina. After filtering to remove the adsorbent, the silicone oil is further purified by vacuum degassing or nitrogen stripping. Another method for treating waste silicone oil is to treat it with solvent vapor. After the liquid waste silicone oil comes into contact with the solvent vapor, the solvent can effectively dissolve and extract the impurities in the waste silicone oil by utilizing the dissolving effect of the solvent during condensation, thereby forming another liquid phase that is immiscible with the silicone oil. This method is particularly suitable for dissolving and removing harmful substances such as polychlorinated polycyclic aromatic hydrocarbons (PCBs) in the waste silicone oil. After the treatment is completed, the trace amount of solvent that may remain in the silicone oil can be further removed by vacuum drying. In this process, commonly used solvents include hydrocarbon solvents and chlorinated hydrocarbon solvents.