The mechanism of crude oil demulsifiers is rooted in the phase-transfer–reverse-deformation principle. Upon addition of a demulsifier, a phase transition occurs: surfactants capable of generating an emulsion type opposite to that formed by the emulsifier (known as reverse-phase demulsifiers) come into being. Such demulsifiers react with hydrophobic emulsifiers to form complexes, thereby stripping the emulsifier of its emulsifying capacity.
Another mechanism is the collision-induced rupture of the interfacial film. Under conditions of heating or agitation, the demulsifier has ample opportunity to collide with the interfacial film of the emulsion, either adsorbing onto it or displacing and replacing portions of the surface-active substances, thus rupturing the film. This drastically reduces stability, prompting flocculation and coalescence that lead to demulsification.
Crude oil emulsions frequently arise in the production and refining of petroleum products. Most of the world’s primary crude oils are obtained in an emulsified state. An emulsion consists of at least two immiscible liquids, one of which is finely dispersed—droplets roughly 1 μm in diameter—within the other.
One of these liquids is typically water, the other usually oil. Oil may be so finely dispersed in water that the emulsion becomes oil-in-water (O/W) type, where water is the continuous phase and oil the dispersed phase. Conversely, if oil forms the continuous phase and water the dispersed phase, the emulsion is water-in-oil (W/O) type—most crude oil emulsions belong to this latter category.
Water molecules attract each other, as do oil molecules; yet between individual water and oil molecules there exists a repulsive force active at their interface. Surface tension minimizes the interfacial area, so droplets in a W/O emulsion tend toward sphericity. Moreover, individual droplets favor aggregation, whose total surface area is smaller than the sum of separate droplet areas. Thus, an emulsion of pure water and pure oil is inherently unstable: the dispersed phase gravitates toward coalescence, forming two separated layers once interfacial repulsion is counteracted—for instance, by accumulation of specialty chemicals at the interface, which lowers surface tension. Technologically, many applications harness this effect by adding well-known emulsifiers to produce stable emulsions. Any substance stabilizing an emulsion in this manner must possess a chemical structure enabling simultaneous interaction with both water and oil molecules—that is, it should contain a hydrophilic group and a hydrophobic group.
Crude oil emulsions owe their stability to natural substances within the oil, often bearing polar groups such as carboxyl or phenolic groups. These may exist as solutions or colloidal dispersions, exerting particular influence when attached to interfaces. In such cases, most particles disperse in the oil phase and accumulate at the oil–water interface, aligning side by side with their polar groups oriented toward the water. A physically stable interfacial layer thus forms, akin to a solid sheath resembling a particulate layer or paraffin crystal lattice. To the naked eye, this manifests as a coating enwrapping the interface layer. This mechanism explains the aging of crude oil emulsions and the difficulty of breaking them.
In recent years, research on crude oil emulsion demulsification mechanisms has focused largely on fine-scale investigation of droplet coalescence processes and the impact of demulsifiers on interfacial rheological properties. Yet because the action of demulsifiers on emulsions is highly complex, and despite extensive studies in this field, no unified theory of demulsification mechanism has emerged.
Several mechanisms are currently recognized:
③ Solubilization mechanism– A single molecule or a few molecules of the demulsifier can form micelles; these macromolecular coils or micelles solubilize emulsifier molecules, precipitating the breakdown of emulsified crude oil.
④ Folded-deformation mechanism– Microscopic observations reveal that W/O emulsions possess double or multiple water shells, with oil shells sandwiched between them. Under the combined effects of heating, stirring, and demulsifier action, the internal layers of droplets become interconnected, leading to droplet coalescence and demulsification.
Additionally, domestic research on demulsification mechanisms for O/W emulsified crude oil systems suggests that an ideal demulsifier must meet the following criteria: strong surface activity; good wetting performance; sufficient flocculating power; and effective coalescing capability.
Demulsifiers come in a great variety; classified by surfactant types, they include cationic, anionic, nonionic, and zwitterionic varieties.
Anionic demulsifiers: carboxylates, sulfonates, polyoxyethylene fatty acid sulfate esters, etc.—disadvantages include high dosage, poor efficacy, and susceptibility to reduced performance in the presence of electrolytes.
Cationic demulsifiers: mainly quaternary ammonium salts—effective for light oils but unsuitable for heavy or aged oils.
Nonionic demulsifiers: block copolymers initiated by amines; block copolymers initiated by alcohols; alkylphenol-formaldehyde resin block copolymers; phenol-amine-formaldehyde resin block copolymers; silicone-based demulsifiers; ultra-high molecular weight demulsifiers; polyphosphates; modified block copolymers; and zwitterionic demulsifiers represented by imidazoline-based crude oil demulsifiers.
Post time: Dec-04-2025