Because some solids are insoluble in water, when one or several of these solids are present in large quantities in an aqueous solution, they can become emulsified in the water under the agitation of hydraulic forces or external energy, resulting in the formation of an emulsion. Theoretically, such a system is unstable; however, the presence of certain surfactants (such as soil particles) can make the emulsified state very stable, to the point where the two phases are difficult to separate. The most typical examples of this are oil-water mixtures in oil-water separation and water-oil mixtures in wastewater treatment, where relatively stable oil-in-water or water-in-oil structures are formed. The theoretical basis for this is the "double-layer structure."

In such cases, chemicals are added to disrupt the stable double-layer structure and stabilize the emulsion, thereby achieving the separation of the two phases. These chemicals, which are used to break the emulsion, are known as demulsifiers.

A demulsifier is a type of surfactant that can disrupt the emulsified liquid structure, allowing the various phases in the emulsion to separate. The demulsification of crude oil involves using demulsifiers to chemically separate the oil and water in the emulsified mixture, in order to dehydrate the crude oil and meet the water content standards for its transportation.

For the effective separation of the organic phase from the aqueous phase, one of the simplest and most effective methods is to use demulsifiers to eliminate the emulsion and the resulting strong emulsification interface, thereby achieving phase separation. However, different demulsifiers have varying abilities to demulsify the organic phase, and the performance of the demulsifier directly affects the effectiveness of the phase separation. In the production of penicillin, an important step is to extract penicillin from the fermentation broth using organic solvents such as butyl acetate. Since the fermentation broth contains complex substances such as proteins, sugars, and mycelium, the interface between the organic and aqueous phases during extraction is unclear, resulting in a strong emulsified zone that significantly affects the yield of the final product. Therefore, it is necessary to use demulsifiers to break the emulsion and achieve rapid and effective separation of the two phases.