Emulsification is a phenomenon in which a liquid is closely dispersed in another liquid to form an emulsion. It is a mixture of two liquids rather than mutual dissolution.
Demulsification is the process of separating two liquids from the milky substance. The demulsibility of lubricating oil refers to the performance that the oil does not emulsify when it meets with water, or although it is emulsified, the oil-water can be separated quickly after standing still. Whether two liquids can form a stable emulsion depends on the interfacial tension between the two liquids. Due to the existence of interfacial tension, the dispersed phase always tends to reduce the contact area between the two liquids to reduce the surface energy of the system, that is, the dispersed phase always tends to merge small droplets with large droplets to reduce the total area of the droplets. , The emulsified state is subsequently destroyed. The greater the interfacial tension, the stronger this tendency, and the less likely it is to form a stable emulsion.
The interfacial tension between lubricating oil and water varies with the composition of the lubricating oil. The interfacial tension between deeply refined base oils and some refined oils and water is quite large, so stable emulsions will not be formed. But if the refining depth of the lubricating base oil is not enough, its demulsibility will be poor, especially when the lubricating oil contains some surface active substances, such as detergents, dispersants, oily agents, extreme pressure agents, gums, and asphaltenes. And dust particles, etc., they are some lipophilic and hydrophilic-based substances, they are adsorbed on the surface of oil and water, so that the interfacial tension between oil and water is reduced, and a stable emulsion is formed. Therefore, when selecting these additives, their performance must be considered in order to achieve the best overall balance.
For industrial lubricants used in circulating systems, such as hydraulic oil, gear oil, steam turbine oil, oil film bearing oil, etc., in use, it will inevitably come into contact with cooling water, steam, or even emulsions. This requires these oils to be in contact with The oil-water separation in the oil tank can be rapid (according to the tank capacity, generally requires 6-30min separation), the mixed water is drained from the bottom of the oil tank, which is convenient for the recycling of oil and maintains good lubrication. Generally, when the lubricating oil has air at about 60℃ and is mixed with water, it will not only be easily oxidized and emulsified to reduce the lubricating performance, but also will generate soluble sludge, and heat will generate insoluble sludge, which will greatly increase the fluid viscosity. Cause blockage of the lubrication system and mechanical failure. Therefore, the refining depth of the base oil and the relationship between the additives used and its demulsifier must be handled well. The mixing and contamination of impurities must also be avoided during the process of blending, use, storage, and storage. Otherwise, if an emulsion is formed, the Not only will it reduce the lubrication performance, damage the machine parts, but also easily form sludge. In addition, with the increase of time, the oxidation of oil, the increase of acidity, and the mixing of impurities will make the demulsibility worse, and the user must deal with it or replace it in time.