Demulsifier Comprehensive Introduction and Industrial Application|News|UNPChemicals

April 30, 2026

Demulsifier Comprehensive Introduction and Industrial Application

What is a demulsifier?

Demulsifiers are specialty chemical agents designed to break down stable emulsions, enabling efficient separation between oil and water phases. In many industrial processes—such as crude oil production, wastewater treatment, pharmaceutical extraction, and chemical manufacturing—immiscible liquids like oil and water can form highly stable emulsions under mechanical agitation or shear force. These emulsions are stabilized by surfactants, solid particles, proteins, polysaccharides, or colloidal materials, which form a rigid interfacial film at the oil–water boundary and establish a robust electrical double-layer structure that prevents droplet coalescence and phase separation. Such stable emulsions severely hinder production efficiency, reduce product purity, increase transportation costs, and may even cause equipment fouling or environmental non-compliance. By adding demulsifiers, the interfacial tension is sharply reduced, the electrical double layer is destabilized, the protective film is disrupted, and dispersed droplets are encouraged to flocculate, coalesce, and separate into distinct layers, thereby restoring clear phase separation. Rational application of demulsifiers can not only improve production continuity and product qualification rate, but also realize resource recovery of waste oil and reuse of treated wastewater, bringing obvious economic and environmental benefits to enterprises.

Core Mechanism of Demulsification

The fundamental principle of demulsification centers on neutralizing the stabilizing forces that maintain emulsion integrity. Demulsifier molecules are surface-active compounds with balanced hydrophilic and lipophilic groups, allowing them to rapidly adsorb onto the oil–water interface and displace the original emulsifying agents. This displacement weakens the mechanical strength of the interfacial film, reduces electrostatic repulsion between droplets, and promotes the aggregation and merging of dispersed droplets. Over time, gravity or centrifugal force completes the separation into a clear oil phase and a clean water phase.

The whole demulsification process follows four key steps interface adsorption film replacement droplet coalescence and gravity settlement. Different from ordinary surfactants, demulsifiers do not form stable emulsion structures; instead, they infiltrate and destroy the existing emulsion system from the molecular level. In crude oil processing, demulsifiers fulfill the critical task of crude oil dehydration, ensuring that water content in exported crude meets pipeline and refinery specifications. In bioprocessing and pharmaceutical manufacturing, demulsifiers resolve emulsions formed during solvent extraction, such as the separation of organic solvents and aqueous fermentation broths, where proteins, mycelia, and polysaccharides create stubborn interfacial layers that lower product yield; demulsifiers rapidly clarify these layers and boost recovery efficiency. In industrial wastewater treatment, demulsifiers separate oily contaminants from water, allowing water to be reused or safely discharged and oil to be recovered.

Common Types of Nonionic Demulsifiers Used in Oilfields

SP-Type Demulsifiers

SP-type demulsifiers are based on polyoxyethylene polyoxypropylene stearyl ether, typically expressed by the theoretical formula R(PO)x(EO)y(PO)zH, where EO represents polyoxyethylene, PO represents polyoxypropylene, R is a fatty alcohol group, and x, y, z denote degrees of polymerization. These demulsifiers appear as pale yellow paste, with an HLB value ranging from 10 to 12, and exhibit good water solubility. They perform effectively on paraffinic crude oils, which contain little to no resin or asphaltene and have low density and relatively weak naturally occurring surface-active components.

The hydrophobic segment consists of a 12–18 carbon alkyl chain, while hydrophilicity arises from hydrogen bonding between hydroxyl and ether groups and water molecules. Since individual hydroxyl or ether groups have limited hydrophilicity, multiple such groups along the molecular chain are required to solubilize the hydrophobic segment. Generally, higher molecular weight and longer molecular chains correspond to stronger demulsifying performance. However, SP-type demulsifiers have a linear, single-chain structure with no branched or aromatic moieties, making them less effective on crude oils with high resin/asphaltene content or water content exceeding 20%. They are mostly suitable for conventional light crude oilfields with simple oil properties and moderate water content.

AP-Type Demulsifiers

AP-type demulsifiers are branched nonionic surfactants synthesized using polyethylene polyamine as an initiator, with the general structure D(PO)x(EO)y(PO)zH. Compared with SP-type demulsifiers, their multi-branched structure delivers stronger hydrophilicity, faster penetration, and higher wetting ability at the oil–water interface. They can rapidly adsorb onto the interfacial film and occupy a larger area than linear SP molecules, resulting in lower dosage and higher demulsification efficiency.

AP-type demulsifiers excel in treating crude emulsions with water content above 20% and perform reliably at lower temperatures. Whereas SP-type demulsifiers may require 55–60°C and 2 hours for complete sedimentation, AP-type demulsifiers achieve comparable results at 45–50°C within 1.5 hours. This makes them widely used in mature oilfields such as the Daqing Oilfield, where they support energy saving and accelerated dehydration. Their excellent low-temperature adaptability and high water-content emulsion treatment capacity make them a mainstream choice for most onshore conventional oilfields.

AE-Type Demulsifiers

AE-type demulsifiers are also polyethylene polyamine-initiated polyoxyethylene polyoxypropylene ethers, but belong to a two-block polymeric structure with smaller molecular size and shorter branched chains, represented as D(PO)x(EO)yH. Although they share similar raw materials with AP-type demulsifiers, differences in monomer ratios and polymerization sequences result in distinct molecular architectures.

AE-type demulsifiers are particularly suitable for asphaltic crude oils, which feature high viscosity, strong natural emulsifying tendency, and small oil–water density differences that impede separation. The branched structure of AE-type molecules delivers fast film-breaking speeds. In addition, they act as effective paraffin inhibitors and viscosity reducers: their molecular framework forms microscale networks that trap paraffin crystallites, preventing crystal growth, interconnection, and network formation, thereby lowering crude viscosity and pour point and improving flowability. They are widely matched for heavy asphalt crude oil blocks with complex oil properties.

AR-Type Demulsifiers

AR-type demulsifiers are novel oil-soluble nonionic products synthesized from alkylphenol formaldehyde resin, polyoxyethylene, and polyoxypropylene, with the structural formula AR(PO)x(EO)yH and an HLB value of 4–8. The AR resin serves as both initiator and lipophilic segment, supporting strong diffusion and penetration in crude oil. With typical oil-soluble characteristics, they can fully dissolve in crude oil and spread rapidly in the emulsion system.

AR-type demulsifiers operate efficiently at low temperatures, typically 35–45°C, and achieve outstanding dehydration performance for high-water crude. Within 45 minutes, they can remove more than 80% of water from crude with an initial water content of 50–70%, a performance level that SP-type and AP-type demulsifiers cannot match. This makes them highly valuable in heavy oil and ultra-heavy oil production systems where low-temperature operation is required, especially suitable for offshore oilfields and shallow heavy oil reservoirs with low environmental temperature and difficult natural settlement.

Conclusion

Across the petroleum, chemical, pharmaceutical, and environmental industries, demulsifiers represent indispensable chemical additives that ensure stable operation, product quality, and compliance. The selection of an appropriate demulsifier depends on crude oil composition, water content, temperature, system salinity, and processing conditions. Different types of demulsifiers have their own targeted application scenarios and performance advantages, which can be selected individually or compounded according to actual working conditions.

Modern demulsifier development continues to evolve toward higher efficiency, lower dosage, wider adaptability, low-temperature performance, and environmental compatibility. Green and biodegradable demulsifiers have become a major research and development direction, gradually replacing traditional high-pollution products. With the continuous upgrading of oilfield exploitation technology and increasingly strict environmental protection standards, demulsifiers will maintain stable market demand in global petrochemical and environmental protection industries, supporting safer, more economical, and more sustainable industrial production.