Demulsification refers to the complete breakdown of an emulsion, resulting in two immiscible phases. In the process of oil extraction, changes in formation pressure, temperature, flow rate, and other factors can cause emulsions in crude oil to rupture, leading to the separation of components such as oil, water, and gas. This phenomenon is known as ‘demulsification’.

1. Demulsification Mechanism

A demulsifier is a substance capable of disrupting the emulsified state of a liquid and separating the phases. Its principle of action is mainly achieved through various mechanisms such as reducing surface tension, disrupting the emulsification film, and changing surface charge. Surface tension is the interaction force between liquid surface molecules and is the force that maintains the surface morphology of the liquid. By changing the surface tension, the demulsifier lowers the surface tension of the dispersed phase, causes the dispersed phase to aggregate, reduces the droplet diameter, and promotes phase separation. In addition, it disrupts the emulsification film between the dispersed phase and the continuous phase, which is formed by surfactants or colloidal particles and stabilizes the emulsion. Demulsifiers can destroy the structure of the emulsification film, causing it to lose stability, thereby achieving phase separation. Furthermore, during the emulsification process, the surfactants or colloidal particles on the surface of the emulsification film carry charges and can form an electric double layer, resulting in electrostatic attraction between the dispersed phase and the continuous phase, which stabilizes the emulsion. Demulsifiers can change the charge on the surface of the emulsification film, destroy the electric double layer structure, and cause the dispersed phase to aggregate and separate.

In short, demulsifiers can destroy the emulsified state and achieve phase separation through multiple mechanisms. In magnetic-based nano-oil displacement agents, the role of the demulsifier is to aggregate the magnetic-based nanoparticles dispersed in the liquid into larger clusters, thereby facilitating subsequent recovery and treatment.

2. Progress in Demulsification Technology

Currently, demulsifiers can be classified into the following categories based on their chemical structure, principle of action, and performance:

Inorganic demulsifiers: Mainly including acids, bases, and electrolytes. They destroy the stability of the emulsification system by changing the pH value or electrolyte concentration. Inorganic demulsifiers have lower costs but are somewhat corrosive to the environment and equipment;

Organic demulsifiers: Mainly including surfactants, solvents, and polymers. Surfactants break the emulsification system by reducing the surface tension of the oil-water interface; solvents destroy the stability of the emulsification system by dissolving the emulsifier or reacting chemically with it; polymers achieve demulsification by changing the structure of the emulsification system;

Biological demulsifiers: Mainly referring to demulsifiers derived from microorganisms or plant extracts, such as enzymes produced by microorganisms or natural surfactants extracted from plants. Biological demulsifiers have advantages such as good biodegradability, environmental friendliness, and low toxicity, but their demulsification effect and stability are relatively low;

Compound demulsifiers: Combine two or more demulsifiers to improve demulsification effects and adaptability. Compound demulsifiers can increase the demulsification effect while reducing the dosage, thereby reducing environmental pollution.

Although demulsification technology has made significant progress, it still faces many challenges, such as performance limitations, insufficient adaptability, and environmental impact. The phenomenon of demulsification can lead to the release of large amounts of harmful substances into the environment, such as oily wastewater, organic matter, and heavy metals, which seriously affect the quality of soil, groundwater, and surface water, causing lasting damage to the ecological environment. Harmful substances after oil-water separation may invade ecosystems, causing toxic effects on plants and animals, destroying biodiversity and stability, and affecting the recovery and reconstruction of ecosystems. Demulsification also leads to the waste of petroleum resources because after oil-water separation, some crude oil is difficult to recover, increasing production costs and resource waste.