Let’s talk about crude oil demulsifiers.

The mechanism of crude oil demulsifiers is a phase transfer-reverse deformation mechanism. Upon addition of the demulsifier, a phase transition occurs, generating a surfactant of the opposite type to the emulsion formed by the emulsifier (reverse demulsifier). This type of demulsifier reacts with the hydrophobic emulsifier to form a complex, thereby causing the emulsifier to lose its emulsifying properties. Another mechanism is the collision-induced breakdown of the interfacial film. Under heating or stirring conditions, the demulsifier has numerous opportunities to collide with the interfacial film of the emulsion, either adsorbing onto the interfacial film or displacing some of the surface-active substances, thus breaking down the interfacial film, significantly reducing its stability, and leading to flocculation, aggregation, and demulsification.

Crude oil emulsions are frequently encountered in the production and refining of oil products. Most of the world’s major crude oils are produced in the form of an emulsion. An emulsion consists of at least two immiscible liquids. One of them is suspended on the other liquid as an extremely fine dispersion, such as droplets approximately 1 mm in diameter.

One of these liquids is usually water, and the other is often oil. The oil can be dispersed very finely in the water. In this case, the emulsion is an oil-in-water emulsion. The water is called the continuous phase, and the oil is called the dispersed phase. Conversely, if the oil is the continuous phase and the water is the dispersed phase, the emulsion is called a water-in-oil emulsion. Most crude oil emulsions are of this type.

Water molecules attract each other, and so do oil molecules. However, there is a repulsive force between individual water and oil molecules. This repulsive force acts at the oil-water interface. Surface tension reduces this interfacial area to a minimum. Therefore, water droplets in a water-in-oil emulsion are spherical. Furthermore, individual water droplets tend to form aggregates, the total area of which is smaller than the sum of the areas of all droplets. Thus, an emulsion composed of pure water and pure oil is unstable. The dispersed phase tends to aggregate, and the repulsive forces at the interface between the two separated layers cancel each other out, as can be reduced by the accumulation of special chemicals at the interface to decrease surface tension. Technically, this effect is often exploited by adding well-known emulsifiers to produce stable emulsions. Any substance that acts as a stabilizer in this way must have a chemical composition that allows it to interact with both water and oil molecules simultaneously; that is, it should contain one hydrophilic group and one hydrophobic group. Crude oil emulsions are stabilized by natural substances contained in the oil. These substances typically contain polar groups such as carboxyl or phenolic groups. They may exist in the form of a solution or a colloidal dispersion. A particularly significant effect is adhesion to the end phase. In this case, the vast majority of particles are dispersed in the oil phase and accumulate at the oil-water interface, where they are arranged side-by-side with their polar groups pointing towards the water. This ultimately forms a physically stable interfacial layer, resembling a layer of particles or paraffin crystals. This layer encapsulates the surface, as commonly perceived by the naked eye. This mechanism explains the aging and difficulty in breaking down crude oil emulsions.
In recent years, research on the demulsification mechanism of crude oil emulsions has focused on the detailed examination of droplet coalescence processes and the influence of demulsifiers on interfacial rheological properties. However, due to the highly complex role of demulsifiers in emulsions, despite extensive research in this field, there is currently no unified conclusion regarding the demulsification mechanism.

The following are some currently accepted demulsification mechanisms: ③ Solubilization mechanism. One or a few molecules of the demulsifier used can form micelles. These polymer coils or micelles can solubilize emulsifier molecules, causing demulsification of the emulsified crude oil. ④ Wrinkling and deformation mechanism. Microscopic observations show that W/O emulsions have two or more water rings, with an oil ring between the two water rings. Under the action of heating, stirring, and the demulsifier, the internal layers of the droplet become interconnected, causing the droplet to coagulate and demulsify.

In addition, there has been some research in China on the demulsification mechanism of O/W type emulsified crude oil systems. It is believed that an ideal demulsifier must have the following characteristics: strong surface activity; good wetting properties; sufficient flocculation ability; and good aggregation effect.

There are many types of demulsifiers. According to the classification method of surfactants, they can be divided into: cationic, anionic, nonionic, and biionic demulsifiers. Anionic demulsifiers include carboxylates, sulfonates, and polyoxyethylene fatty acid sulfates, etc., which have disadvantages such as large dosage, poor effect, and susceptibility to electrolyte influence. Cationic demulsifiers mainly include quaternary ammonium salts, which have a significant effect on light oils but are not suitable for heavy oils and aged oils. Nonionic demulsifiers mainly include block polyethers with amines as initiators, block polyethers with alcohols as initiators, alkylphenol aldehyde resin block polyethers, phenol-amine aldehyde resin block polyethers, silicone demulsifiers, ultra-high molecular weight demulsifiers, polyphosphate esters, modified products of block polyethers, and biionic demulsifiers represented by imidazoline crude oil demulsifiers.