What is demulsifier?

Demulsifier is a type of surfactant that plays a significant role in the demulsification process of emulsions, and it is a compound capable of reversing the stabilizing function of emulsifiers. In the context of oilfield produced emulsions, natural emulsifiers such as asphaltenes and resins in crude oil exhibit weak adsorption at the oil-water interface. Demulsifiers can adsorb at the oil-water interface, solubilize and replace these natural emulsifiers, which greatly reduces the stability of the interfacial membrane surrounding the droplets. This reduction in stability leads to membrane drainage, droplet coalescence, and ultimately achieves the demulsification effect, facilitating the separation of oil and water phases in the emulsion.

Crude oil demulsification is a crucial link in the process of crude oil extraction and production. With the continuous development and progress of technology, the effect and efficiency of crude oil demulsification have been constantly improved. This paper reviews the latest progress in the application of demulsification technology in the petroleum industry. The most commonly used demulsification methods for oil-water separation include mechanical methods, thermal methods, electrical methods, biological methods, and chemical methods, and the advantages and disadvantages of these methods are compared.

A large amount of water needs to be injected into the formation during crude oil extraction. Especially with the popularization and application of enhanced oil recovery (EOR) technologies such as polymer flooding, surfactant flooding, and alkaline-surfactant-polymer (ASP) flooding, the oilfield produced fluids are prone to form stable water-in-oil (W/O) emulsions, oil-in-water (O/W) emulsions, and complex oil-in-water emulsions. The presence of emulsions has caused a series of problems in the transportation and processing of crude oil, mainly including increased transportation costs, corrosion of equipment and pipelines, and pollution of downstream refineries. Therefore, the oil-water separation of oilfield produced emulsions is a key step before crude oil transportation and processing, and demulsification technology plays a vital role in the demulsification process of produced emulsions in the petroleum industry.

At present, the most commonly used demulsification methods for oil-water separation include mechanical methods (using large-volume separators to reduce flow velocity to promote gravity separation of oil, gas, and water), thermal methods (increasing the temperature of emulsions), electrical methods (applying electrostatic fields to stimulate coalescence), biological methods (using microorganisms or their metabolites), and chemical methods (using chemical demulsifiers).

1. Mechanical Methods

1.1 Gravity Settling Demulsification

Gravity settling method utilizes the different densities of oil and water, and uses equipment such as three-phase separators, water separators, and settling tanks to separate oil and water under the action of gravity. The main function of the three-phase separator is to initially separate water, oil, and gas in the oilfield produced fluid. Its basic structure mainly includes inlet pre-separation components, gravity settling chambers, baffles, and demisters. To promote the coalescence process and improve separation efficiency, coalescing columns or coalescing plates are often added to the three-phase separator. The schematic diagram of the three-phase separator.

1.2 Centrifugal Demulsification

Centrifugal demulsification technology can effectively separate the aqueous phase and oil phase in crude oil emulsions, and is one of the important methods for crude oil demulsification. Centrifugal force is the driving force for emulsion separation, and centrifugal equipment can accelerate the flocculation and coalescence processes. The schematic diagram of the emulsion centrifugal separation equipment. Utilizing the different densities of oil and water, under high-speed rotation, water droplets (heavier liquid) and oil droplets (lighter liquid) generate different centrifugal forces. Water droplets move downward and outward, while oil droplets flow inward at the top of the disc. The two liquids leave the centrifuge equipment through independent outlets to achieve oil-water separation. The selection of the centrifuge plays an important role in the oil-water separation effect, but the emulsion properties and operating conditions (such as water content, flow rate, pressure, and temperature) also affect the emulsion separation efficiency. In addition, when using centrifugal equipment, chemicals can be added or electric fields can be applied to improve the centrifugal separation effect.

1.3 Membrane Demulsification

Compared with other processes, membrane demulsification is a new demulsification method. Membrane materials can be composed of metals, inorganic nanoparticles, and organic polymers. To remove oil from wastewater, Fernandez et al. evaluated the effect of ceramic microfiltration membranes and compared them with commercial polysulfone ultrafiltration membranes. The results showed that during the membrane demulsification process, solid particles are prone to accumulate on the membrane, leading to a significant decrease in membrane flux and a corresponding increase in the time required for the demulsification process. Yue Xiao et al. summarized different types of membrane treatment technologies used in water treatment, and introduced microfiltration, ultrafiltration, nanofiltration, and reverse osmosis membrane integration technologies and their applications.

2. Thermal Methods

2.1 Conventional Heating

Increasing the temperature will intensify the thermal movement of emulsion molecules, reduce the viscosity of oil, destabilize the rigid membrane, and increase the water settling rate and the thermal energy of water droplets. Due to the reduction of interfacial viscosity, the coalescence frequency increases, thereby improving the demulsification efficiency. Although heating has an effect on accelerating demulsification, heating alone is not sufficient for demulsification in an industrial environment without the help of other mechanisms. There are some problems in the application of heating technology, such as increased crude oil processing costs, possible loss of light components of crude oil, and the consequent increase in crude oil density, scale deposition, and increased container corrosion tendency. Therefore, when using heating as part of the demulsification process, its cost-effectiveness must be analyzed. In addition to the cost of heating itself, the impact of losing light-end products on the price of petroleum products and the cost of using or not using related residual heating methods, such as chemical prices and processing time costs, must also be considered.

2.2 Microwave Heating

Emulsions can be separated when exposed to electromagnetic radiation. The first patent on the method of separating emulsions using microwave radiation was published in 1986. A comparison between the use of microwave radiation and conventional heating methods showed that the former can achieve faster or more effective separation. Santos et al. used microwave radiation to separate water-in-oil mixtures and studied the effect of applying single or multiple modes on separation efficiency. The results showed that although single-mode requires less energy to reach a specific temperature or a specific separation efficiency, multi-mode has better reproducibility. The dielectric constant can be changed by adjusting the appropriate microwave frequency, and demulsification is promoted through thermal effects. At present, microwave demulsification is still in the laboratory research stage, and there is a lack of mature and controllable industrial equipment in China.

3. Biological Methods

Due to the ability of microbial cells and their surfaces to promote demulsification, biological demulsifiers have become one of the main reagents for separating emulsions. Stewart et al. studied the effect of Nocardia and Nocardia petroleophila on water-in-oil emulsions, analyzed the effect of the former on oil-in-water emulsions, and confirmed that Nocardia is an effective demulsifier comparable to chemical demulsifiers. Due to the ability of microbial cells and their surfaces to promote demulsification, Duvnjak et al. studied the effect of Corynebacterium petrophilum and Candida parapsilosis on water-in-oil emulsions. The results showed that cell concentration has a non-linear effect on the demulsification rate. In China, research on biological demulsifiers has been carried out since 2000. Li Xu et al. selected oil-contaminated soil to cultivate bacterial strains, and the demulsification and dehydration rate of the purified demulsifying strains could reach more than 85% within 22 hours.

4. Electrical Methods

Under the action of an electrostatic field, on the one hand, polarized water droplets are more likely to align with the lines of force of the electric field. Within these lines, different polarities bring the droplets closer, making coalescence possible. On the other hand, the charge-inducing electrodes attract water droplets, and the electric field stimulates the faster movement of water droplets, increasing the chance of collision between them to rearrange into larger-sized water droplets. In addition, the electric field weakens the rigid membrane surrounding the droplets, thus promoting its rupture and droplet coalescence. Electrical demulsification methods include electrostatic demulsification, electric pulse demulsification, and eddy current electric field demulsification. The use of electrical methods can also reduce the demand for heating technology, which has a significant impact on scale deposition, corrosion, and light-end loss problems. However, the main disadvantage of electrostatic grids is that short circuits occur when there is too much water in the emulsion. In fact, for low water levels, the two electrodes can be connected by a flow of charged water particles, and the short circuit caused by this phenomenon consumes excessive energy and reduces the efficiency of the demulsification process.

5. Chemical Methods

Demulsifiers are surfactants that play a significant role in demulsification, and are compounds capable of reversing the stabilizing function of emulsifiers. Natural emulsifiers (asphaltenes, resins, etc.) exhibit weak adsorption. Demulsifiers adsorb at the oil-water interface, solubilize and replace natural emulsifiers, greatly reducing the stability of the interfacial membrane, leading to membrane drainage, coalescence, and demulsification.

In the 1920s, soaps, naphthenates, alkylaryl sulfonates, and sulfated castor oil were used as demulsifiers. In the 1930s, petroleum sulfonates, sulfuric acid-oxidized castor oil, and sulfosuccinates were used as demulsifiers. In the 1940s, fatty acids, fatty alcohols, and alkylphenols played the role of demulsifiers. In the 1950s, ethylene oxide-propylene oxide copolymers and alkoxylated cyclic p-alkylphenol formaldehyde resin demulsifiers were developed. In the 1960s, amine alkoxylates were used as demulsifiers. In the 1970s, alkoxylated cyclic p-alkylphenol formaldehyde resins were used as demulsifiers. In the 1980s, polyamine demulsifiers were developed. Since the 1990s, most of the demulsifiers developed in China have been polyether demulsifiers based on polyoxyethylene-polyoxypropylene block polymers.

Polyether demulsifiers with different molecular weights and structures can be obtained by initiating different ratios of ethylene oxide and propylene oxide with different initiators. Polyether demulsifiers can be divided into alcohol-initiated polyether demulsifiers, polyethylene polyamine-initiated polyether demulsifiers, alkylphenol-formaldehyde resin-initiated polyether demulsifiers, and chemically modified polyether demulsifiers based on polyoxyethylene-polyoxypropylene block polyethers.

In recent years, new types of demulsifiers have been continuously developed. Hou Dandan et al. synthesized a series of non-polyether high-efficiency demulsifiers using acrylic acid and acrylate as raw materials through free radical polymerization, which are suitable for different types of crude oils such as heavy oil, high-pour-point heavy oil, and extra-heavy oil.

6. Comparison of Various Methods

The advantages and disadvantages of several demulsification methods are compared in Table 1, and the efficiency, maturity, and cost of various demulsification methods are compared in Table 2.

Table 1 Demulsification Methods Comparison

Method	Advantages	Disadvantages
Mechanical (Gravity)	No chemical pollution; lower energy than thermal methods	Large footprint; sea application hard; long process time
Mechanical (Centrifugation)	Measures oil/water volume	High cost; low separation capacity
Mechanical (Membrane)	Low cost; suitable for micrometer emulsions; high efficiency; low energy; fits nanomaterials	Prone to fouling; regular cleaning needed; high process cost
Chemical	Easy operation; adjustable ratio; short time; low energy	High cost; secondary pollution; environmental risks
Thermal (Conventional)	No secondary pollution	Poor solo effect; needs chemical aids
Thermal (Microwave)	Shorter time & lower energy than traditional thermal methods	Bubble formation; light component loss
Electrical	Lower energy than heating/centrifugation	Tiny secondary droplets hard to separate
Biological	Low investment; biodegradable; eco-friendly	Strict environment requirements

Table 2 Demulsification Tech: Efficiency, Maturity & Cost

Method	Efficiency	Maturity	Cost
Mechanical (Gravity)	Medium	High	Low
Mechanical (Centrifugation)	High	High	High
Mechanical (Membrane)	High	Medium	High
Thermal (Conventional)	High	High	High
Thermal (Microwave)	High	High	High
Electrical	High	High	High
Biological	Medium	Medium	Low
Chemical	High	High	High

It can be seen from Table 1 and Table 2 that each demulsification method has its applicable scope, advantages, and disadvantages. The most widely used methods in the oil and gas industry are mechanical, thermal, electrical, and chemical methods. With the increasingly complex composition and greatly enhanced stability of produced fluids, the difficulty of demulsification and dehydration has further increased. A single demulsification method can no longer meet the on-site needs. The demulsification process on the oilfield site usually combines the above methods to promote the destabilization of the emulsion system, promote coalescence, and finally achieve demulsification and separation. In practical applications, it is necessary to select an appropriate demulsification method according to the properties of the emulsion and production requirements, and perform appropriate pretreatment to improve the efficiency and economic benefits of oil-water separation of the produced fluid.

7. Conclusions

The destabilization or demulsification of emulsions is achieved through flocculation and aggregation, precipitation and demulsification, and coalescence mechanisms. This work focuses on three factors affecting emulsion separation: physical mechanisms (gravity settling, retention time, stirring, heat), chemical interactions, and biological effects.

Gravity settling is a method to promote demulsification, which separates due to the difference in gravity of liquids (such as water and oil) in the well stream. In a non-turbulent state, as long as there is sufficient residence time, the fluid with higher specific gravity will settle naturally. Residence time, which is the amount of time the fluid remains unstirred during the settling process, has a causal relationship with gravity separation. A longer retention time will enable more effective separation. In addition, the geometry of the separator will affect the retention time, meaning that a larger or taller separator will promote the precipitation of water under gravity. Stirring will promote rapid changes in direction and speed, help break the surface tension, and make the separation process possible. In addition, separation can also be promoted by using thermal action. When the temperature of the emulsion increases, the decrease in oil viscosity can be used as the best effective value for separation. A fluid with lower viscosity affects the release of water and gas molecules. Mechanical methods require large equipment and energy, and have certain requirements on the properties and particle size of the emulsion. To improve the quality of the produced fluid, it is necessary to combine other demulsification processes, such as chemical methods and biological methods. Chemical method is an efficient, fast, and economical demulsification method. When chemical substances are used as demulsifiers, they act on the oil-water interface, reduce the strength of the interfacial membrane, increase the coalescence rate, and reduce the heating or residence time during the separation process. For chemical methods, attention should be paid to the selection of chemical demulsifiers, dosage, stirring, and injection rate. These factors must be considered to obtain the best demulsification method and cost-effectiveness. Biological methods have the advantages of environmental protection, safety, and no pollution, and are suitable for emulsions with high oil content. However, there are still some difficulties in the research and application of biological demulsifiers, such as how to select appropriate bacterial strains and how to control the number of bacterial strains.

In conclusion, with the development of modern oilfield production technology, the requirements for the treatment of produced fluids are getting higher and higher. As an important link, the demulsification process needs to be continuously optimized and improved.

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.