​Demulsifiers: Unlocking Crude Oil from Emulsions

​Demulsifiers: Unlocking Crude Oil from Emulsions
  • September 23, 2025

​Demulsifiers: Unlocking Crude Oil from Emulsions

What is Demulsifier？

Demulsifier is a specialized chemical agent used to break down stubborn water-in-crude oil emulsions that form during petroleum extraction. It works by destabilizing the interfacial film surrounding water droplets, allowing them to coalesce and separate from the oil phase through mechanisms such as film displacement, flocculation, and wettability alteration.

Critical for crude oil processing, demulsifiers enable efficient dehydration to meet pipeline transport specifications, reduce corrosion risks, and minimize transportation costs. Their performance depends on tailored chemical formulations—often ethylene oxide-propylene oxide copolymers—that address specific emulsion characteristics driven by crude composition, salinity, and production conditions.

The principle and application of demulsifiers

Demulsifiers

Because some solids are difficult to dissolve in water, when one or several of these solids are present in large quantities in an aqueous solution, they can exist in the water in an emulsified state, forming an emulsion, under the agitation of hydraulic or external power. Theoretically, this system is unstable. However, in the presence of some surfactants (soil particles, etc.), the emulsified state can become severe, even making the two phases difficult to separate. The most typical examples are oil-water mixtures in oil-water separation and water-oil mixtures in sewage treatment, where relatively stable water-in-oil or oil-in-water structures form. The theoretical basis for this is the "double electric layer structure."

In this case, certain chemicals are added to destroy the stable double electric layer structure and the stable emulsification system, thereby achieving separation of the two phases. These chemicals used to destroy emulsification are called demulsifiers.

Main Uses

A demulsifier is a surface-active substance that can destroy the structure of an emulsified liquid to separate the phases within the emulsion. Crude oil demulsification refers to using the chemical action of demulsifiers to separate oil and water from an emulsified oil-water mixture, achieving the purpose of crude oil dehydration to meet the specified water content standards for crude oil transportation.

A simple and effective method for the efficient separation of organic and aqueous phases is the use of demulsifiers to eliminate emulsification, break down the emulsified interface which possesses a certain strength, and achieve phase separation. However, the demulsification capabilities of different demulsifiers for the organic phase vary, and their performance directly affects the separation efficiency. In the penicillin production process, a crucial step involves extracting penicillin from the fermentation broth using an organic solvent (such as butyl acetate). Since the fermentation broth contains complex substances like proteins, sugars, and mycelium, the interface between the organic and aqueous phases during extraction is unclear, forming a distinct emulsified zone of certain strength, which greatly affects the final product yield. Therefore, demulsifiers must be used to break the emulsion, eliminate the emulsification phenomenon, and achieve rapid and effective phase separation.

Common Demulsifiers 

Currently, the commonly used nonionic demulsifiers in oilfields mainly include the following types:

1. SP Type Demulsifier
The main component of SP-type demulsifiers is polyoxyethylene polyoxypropylene octadecyl alcohol ether. The theoretical structural formula is R(PO)x(EO)y(PO)zH, where: EO - polyoxyethylene; PO - polyoxypropylene; R - fatty alcohol; x, y, z - degree of polymerization. SP-type demulsifiers appear as light yellow paste-like substances with an HLB value of 10~12 and are soluble in water. SP-type nonionic demulsifiers have good demulsification effects on paraffinic crude oil. Their hydrophobic part consists of C12~18 hydrocarbon chains, and their hydrophilic groups achieve hydrophilicity by forming hydrogen bonds with water through hydroxyl groups (-OH) and ether groups (-O-) in the molecule. Because hydroxyl and ether groups are weakly hydrophilic, one or two such groups cannot pull the C12~18 hydrophobic chain into the water; multiple such hydrophilic groups are necessary to achieve water solubility. The larger the molecular weight of the nonionic demulsifier and the longer the molecular chain, the more hydroxyl and ether groups it contains, and the greater its pulling force, resulting in stronger demulsification ability for crude oil emulsions. Another reason SP-type demulsifiers are suitable for paraffinic crude oil is that this oil contains little or no resins and asphaltenes, has fewer lipophilic surfactant substances, and has a relatively low specific gravity. For crude oil with high resin and asphaltene content (or water content greater than 20%), the demulsification ability of SP-type demulsifiers is weaker due to their singular molecular structure, lacking branched chains and aromatic structures.

2. AP Type Demulsifier
AP-type demulsifiers are polyoxyethylene polyoxypropylene polyethers initiated with polyethylenepolyamine, representing a multi-branched nonionic surfactant. The molecular structural formula is: D(PO)x(EO)y(PO)z H, where: EO - polyoxyethylene; PO - polyoxypropylene; D - polyethylenepolyamine; x, y, z - degree of polymerization.
AP-type demulsifiers perform better than SP-type demulsifiers for breaking paraffinic crude oil emulsions. They are more suitable for crude oil with water content higher than 20% and can achieve rapid demulsification at lower temperatures. For example, if an SP-type demulsifier requires 2 hours at 55~60°C for settling and demulsification, an AP-type demulsifier only needs 1.5 hours at 45~50°C. This is due to the structural characteristics of the AP-type demulsifier molecules. The initiator polyethylenepolyamine determines the molecular structure: long molecular chains with multiple branches, giving it higher hydrophilicity than the singular molecular structure of the SP-type demulsifier. The multi-branched nature gives AP-type demulsifiers higher wetting and penetration capabilities. During demulsification of crude oil emulsions, AP-type demulsifier molecules can quickly penetrate the oil-water interface film, occupying more surface area through their multi-branched arrangement compared to the upright monomolecular film arrangement of SP-type demulsifier molecules. Thus, they require less dosage and show significant demulsification effects. Currently, this type of demulsifier is one of the most effective nonionic demulsifiers used in the Daqing Oilfield.

3. AE Type Demulsifier
AE-type demulsifiers are also polyoxyethylene polyoxypropylene polyethers initiated with polyethylenepolyamine, representing a multi-branched nonionic surfactant. Compared to AP-type demulsifiers, the difference is that AE-type demulsifiers are two-segment polymers with smaller molecules and shorter branches. The molecular structural formula is: D(PO)x(EO)yH, where: EO - polyoxyethylene; PO - polyoxypropylene; D - polyethylenepolyamine; x, y - degree of polymerization. Although the molecular appearance of AE and AP-type demulsifiers differs significantly, their molecular components are the same, differing only in monomer usage and polymerization sequence.
(1) During the design and synthesis of these two nonionic demulsifiers, the amounts of head and tail materials used differ, resulting in polymer molecules of different lengths.
(2) AP-type demulsifier molecules are two-segment block copolymers formed by initiating polyethylenepolyamine with polyoxyethylene and polyoxypropylene; AE-type demulsifier molecules are two-segment copolymers formed by initiating polyethylenepolyamine with polyoxyethylene and polyoxypropylene. Therefore, the designed AP-type demulsifier molecules should be longer than AE-type demulsifier molecules.
AE-type is a two-segment, multi-branched structure crude oil demulsifier, also suitable for demulsifying asphaltenic crude oil emulsions. Asphaltic base crude oil contains more lipophilic surfactants, has stronger viscosity, a smaller oil-water density difference, and is harder to demulsify. Using AE-type demulsifiers results in fast demulsification. Additionally, AE-type demulsifiers are effective paraffin inhibitors and viscosity reducers. Due to their multi-branched molecular structure, they easily form tiny networks, causing the formed paraffin monocrystals in the crude oil to fall into these networks, hindering their free movement and preventing interconnection into a paraffin network structure. This lowers the crude oil's viscosity and pour point, prevents wax crystal aggregation, and thus achieves paraffin inhibition.

4. AR Type Demulsifier
AR-type demulsifiers are novel oil-soluble nonionic demulsifiers synthesized from alkyl phenolic resin (AR resin) combined with polyoxyethylene and polyoxypropylene, with an HLB value around 4~8. The demulsification temperature is as low as 35~45°C. The molecular structural formula is: AR(PO)x(EO)y H, where: EO - polyoxyethylene; PO - polyoxypropylene; AR - resin; x, y - degree of polymerization.
In the synthesis process of the demulsifier, AR resin acts both as an initiator and becomes part of the demulsifier molecule as the lipophilic group. The characteristics of AR-type demulsifiers are: relatively small molecules, good dissolution, diffusion, and penetration effects in crude oil where the pour point is higher than 5°C, promoting flocculation and coalescence of emulsified water droplets. They can remove over 80% of the water from crude oil with 50%~70% water content within 45 minutes at temperatures below 45°C, which is something SP-type and AP-type demulsifiers cannot achieve.

Demulsifier Manufacturer

UNPChemicals' DEMET series comprises a range of high-performance, specialized demulsifiers engineered for the efficient dehydration and desalting of crude oil. This product line is formulated to address the challenges posed by diverse and complex crude oil emulsions, particularly those stabilized by natural surfactants like asphaltenes and resins.

The DEMET series leverages advanced polymer chemistry, primarily based on ethylene oxide (EO) and propylene oxide (PO) block copolymers. These molecules are structured to rapidly adsorb at the oil-water interface, effectively displacing rigid interfacial films and promoting the flocculation and coalescence of fine water droplets. This results in faster water separation, cleaner oil, and reduced residual brine salinity.

Key characteristics of the DEMET series include:

  • Tailored Formulations: Includes multi-branched (e.g., AP-type) and resin-initiated (e.g., AR-type) polymers for specific crude properties, from paraffinic to heavy asphaltenic crudes.

  • High Efficiency: Effective at low dosages and often under lower operating temperatures, reducing energy consumption.

  • Rapid Separation: Designed to achieve quick breakdown of stable emulsions, meeting pipeline specifications for water and salt content.

The DEMET series is a critical solution for upstream production facilities, enabling cost-effective operations, reduced corrosion, and compliance with transportation standards.