Oil-water Separation Technology Research Articles

A novel Pumice@PVA membrane with high separation efficiency for oil-water emulsion application

Oil pollution poses a major threat to both human health and economic development, and therefore the development and improvement of oil-water separation technology is urgent. Traditional methods have problems such as complicated preparation, high cost and the vulnerability of lipophilic materials to oil contamination. Therefore, finding an inorganic material that meets the requirements of underwater superoleophobic performance and reduces surface modification has become a new demand. In this study, natural pumice was found for the first time to have excellent underwater superoleophobic performance and chemical stability, and the underwater superoleophobic filter membrane was prepared by vacuum adsorption using hydrogen bond cross-linking between natural pumice and PVA. The experimental data show that the prepared PVA/natural pumice ultrafiltration membrane has superhydrophilic and superoleophobic properties, and exhibits excellent stability (OWA>150°) under the harsh environment of strong acid and strong alkali. In addition, the composite membrane has good emulsion separation efficiency (>97%) and a separation flux of 39.91 Lm-2h-1. It is demonstrated that the composite membrane has oleophobic and wettable properties, and is capable of separating both oil-water mixtures without phase mixing and oil-in-water emulsions without oil contamination. This study provides a new idea for the preparation of superoleophobic materials for oil-water separation, which has the potential for large-scale application.

Design of downhole oil-water separation device and study on separation mechanism based on rod pump heavy oil system

Abstract Downhole oil-water separation technology (DOWS) is a new type of separation technology, which can improve efficiency, reduce energy consumption, and can solve the problem of high water cut oilfield development. At present, there are only two separation methods in the same well injection-production separator, one is the swirl separation technology and the other is the gravity separation technology. Cyclone separation technology mainly relies on cyclone separators to separate oil and water, but it is affected by oil viscosity, water content, and temperature. The gravity separation technology mainly relies on the similar separation principle of a multi-cup equal-flow gas anchor to design a multi-cup equal-flow oil-water separator, but it requires the oil-water mixed production liquid to stay in the settling bowl for a long time. The centrifugal separator has the characteristics of a good separation effect, high efficiency, and low demand for oil. At present, the downhole centrifugal separator is not used in the same well injection-production technology, which mainly needs to solve the driving force problem of the centrifugal separator. The new injection-production device designed in this paper can better solve the driving problem of the centrifugal separator and meet the working requirements of the process.

Magnetic Hyperporous Elastic Material with Excellent Fatigue Resistance and Oil Retention for Oil-Water Separation.

Oily wastewater has caused serious threats to the environment; thus, high-performance absorbing materials for effective oil-water separation technology have attracted increasing attention. Herein, we develop a magnetic, hydrophobic, and lipophilic hyperporous elastic material (HEM) templated by high internal phase emulsions (HIPE), in which free-radical polymerization of butyl acrylate (BA) and divinylbenzene (DVB) is employed in the presence of poly(dimethylsiloxane) (PDMS), lecithin surfactant, and modified Fe3O4 nanoparticles. The adoption of the emulsion template with nanoparticles as both stabilizers and cross-linkers endows the HEM with biomimetic hierarchical open-cell micropores and elastic cross-linked networks, generating an oil absorbent with outstanding mechanical stability. Compressive fatigue resistance of the HEM is demonstrated to endure 2000 mechanical cycles without plastic deformation or strength degradation. By exploiting the synergistic effect of hierarchical structures and low-surface-energy components, the resulting HEM also possesses excellent and robust hydrophobicity (water contact angle of 164°) and good oil absorption capacity, in which Fe3O4 nanoparticles lead to convenient magnetically controlled oil recyclability as well. Notably, the unique biomimetic microporous structure demonstrates superior oil retention capacity (>95% at 1000 rpm and >60% at 10,000 rpm) over the state-of-the-art porous materials for a diverse variety of oils to reduce the risk of secondary oil leakage, along with good recoverability by squeezing owing to the excellent compression resilience. These excellent performances of our HEM provide broad prospects for practical applications in oil-water separation, energy conversion, and smart soft robotics.

A superhydrophilic and robust fabric, featuring self-assembled layers of chitosan and carbon nanotubes, facilitates high-throughput oil–water separation

Petroleum pollution and industrial emissions of organic pollutants have become significant issues affecting both ecological and human living environments. High-performance oil–water separation membranes, due to their advantages such as low cost, environmental friendliness, and ease of operation, hold vast application prospects. Therefore, the development of efficient oil–water separation membranes is crucial. We propose a clever approach involving the synergistic self-assembly of chitosan (CS) and hydroxylated multi-walled carbon nanotubes (MWCNTs) on cotton fabric to construct a rough structure. Combined with hydrophilic modification using polyvinyl alcohol (PVA), not only does this enhance wettability, but it also addresses challenges related to mechanical strength and dispersibility of cotton fabric. The resulting CMF-PVA fabric performs well under challenging conditions, exhibiting excellent separation efficiency and permeance. Particularly noteworthy is that CMF-PVA achieves separation efficiencies exceeding 99.33 % for various organic substances, with a water flux reaching 35,476.52 L m−2 h−1 and a surfactant-stabilized emulsion permeance of 1199.0 L m−2 h−1·bar−1. Furthermore, CMF-PVA demonstrates outstanding mechanical durability under harsh conditions and excellent acid-base resistance. This method harnesses the inherent properties of CS and MWCNT self-assembly while enhancing the material's applicability on cotton fabric through hydrophilic modification. CMF-PVA fabric is poised to enhance selectivity, efficiency, anti-pollution properties, and accessibility in oil–water separation technology.

Reusable, Stable, Efficient and Multifunctional Superhydrophobic and Oleophilic Polyurethane Sponge for Oil-Water Separation Prepared Using Discarded Composite Insulator.

Oil spills and chemical leakages are a serious source of pollution in oceans and rivers, and have attracted worldwide attention. Many scientists are currently engaged in the development of oil-water separation technology. In this study, the umbrella skirt of a discarded silicone rubber insulator was utilized as feedstock, and polydimethylsiloxane (PDMS) was employed to immobilize the prepared powder (FXBW) onto a polyurethane (PU) sponge skeleton. Without any modifications using chemical reagents, a novel oil-water separation material, FXBW-PU, was developed, with a water contact angle of 155.3°. The FXBW-PU sponge exhibited an absorption capacity ranging from 11.79 to 26.59 g/g for various oils and organic solvents, while maintaining an excellent selective adsorption performance, even after undergoing ten compression cycles, due to its exceptional chemical and mechanical stability. With the assistance of a vacuum pump, the FXBW-PU sponge was utilized in a continuous separation apparatus, resulting in a separation efficiency exceeding 98.6% for various oils and organic solvents. The separation efficiency of n-hexane remains as high as 99.2% even after 10 consecutive separation cycles. Notably, the FXBW-PU sponge also separated the dichloromethane-in-water emulsions, which achieved the effect of purifying water. In summary, FXBW-PU sponge has great potential in the field of cleaning up oil/organic solvent contamination due to its low preparation cost, environmental friendliness and excellent performance.

Laser Electrochemical Deposition Hybrid Preparation of an Oil-Water Separation Mesh with Controllable Pore Diameter Based on a BP Neural Network.

With the increasing problem of water pollution, oil-water separation technology has attracted widespread attention worldwide. In this study, we proposed laser electrochemical deposition hybrid preparation of an oil-water separation mesh and introduced a back-propagation (BP) neural network model to realize the regulation of metal filter mesh. Among them, the coating coverage and electrochemical deposition quality were improved by laser electrochemical deposition composite processing. Based on the BP neural network model, the pore size after electrochemical deposition could be obtained only by inputting the processing parameters into the model, enabling the prediction and control of the pore size of the processed stainless-steel mesh (SSM), and the maximum residual difference between the predicted value and the experimental value was 1.5%. According to the oil-water separation theory and practical requirements, the corresponding electrochemical deposition potential and electrochemical deposition time were determined by the BP neural network model, which reduced the cost and time loss. In addition, the prepared SSM was found to achieve efficient separation of oil and water mixtures, reaching 99.9% separation efficiency in a combination with oil-water separation, along with other performance tests without chemical modification. The prepared SSM showed good mechanical durability and the separation efficiency exceeded 95% after sandpaper abrasion, thus, still maintaining the separation ability of oil-water mixture. Compared to other similar preparation methods, the method proposed in this study has the advantages of controllable pore size, simplicity, convenience, environmental friendliness, and durable wear resistance, offering important application potential in the treatment of oily wastewater.

Robust Janus Superwetting Textile with Large Pore Sizes for Oil-in-Water Emulsion Separation.

Developing advanced oil-water separation technology is significant for environmental conservation. According to the synergetic effects of the size-sieving mechanism, superwetting materials with small pore sizes have been designed to realize high-efficiency separation for oil-water emulsions. However, the separation flux limited by the pore size and the weakness of the superwetting material impede its practical application severely. Herein, we construct a robust Janus superwetting textile with large pore sizes for oil-in-water emulsion separation. The pristine textile is coated by the as-prepared CuO nanoparticles as the bottom layer with superhydrophilicity and then grafted by 1-octadecanethiol as the top layer with superhydrophobicity to construct the Janus textile. When used as a filter, the superhydrophobic layer acts as the nucleation site to coalesce the small oil droplets facilely. Then, the coalesced oil fills the pores of the superhydrophobic layer and selectively permeates it but is blocked by the superhydrophilic layer with large pore sizes. Utilizing the unique separation mechanism, the Janus textile realizes efficient and rapid separation. Even after multicycle separation, hot liquid immersion for 24 h, tribological test for 60 min, and sandpaper abrasion for 500 cycles, the Janus textile still retains the superwettability and excellent separation performance, manifesting outstanding stability to resist severe damage. This separation strategy provides a novel guideline for high-efficiency and high-flux emulsion separation and practical application.

Investigation of droplet pairs’ movement under the electric field generated by matrix electrodes

Electric dehydration technology has gained lots of attention as an oil-water separation technology that has only been around for a short time. Many research scholars have studied the laws of droplet motion in electric fields. However, previous research on the droplet motion law in a non-uniform electric field has only focused on the single droplet, ignoring the dipole-dipole interaction between droplets, which plays an important role in the droplet coalescence process. In this paper, the motion of droplet pairs in a non-uniform matrix electric field is studied by means of theoretical analysis and numerical simulation. A mathematical model of the migration velocity and coalescence time of droplet pairs was established. The results show that the migration velocity of droplet pairs under dielectrophoresis and dipole-dipole interactions is significantly greater than that of single droplets and that the droplet velocity is related to the electric field strength, continuous phase viscosity, droplet diameter, and droplet pair center distance. This study increases our understanding of droplet electrocoalescence kinetics, enriches the electrocoalescence mechanism of droplets under non-uniform electric fields, and provides a basis for the design of subsequent electrodehydration equipment.

Contactless Discharge-Driven Method for Separation of Oil-Water Mixtures.

Oil–water separation technology has potential applications in wastewater treatment, petroleum refining and edible oil processing. As the ultimate means in oil-water treatment, electrostatic coalescence technology has been widely used in oil fields and refineries. However, the technology has many problems, such as complex processes, electrode corrosion, and the inability to treat high-water-cut crude oil emulsions. Here, we propose a contactless method of oil-water separation by corona discharge. With corona discharge of a needle–plate electrode configuration, the oil droplet diffuses to the ITO glass surface and the water droplet oscillates at the edge of the PET film. Here, such droplet behaviors are described in detail. Based on the motion behavior of the oil and water droplet, we designed an efficient oil-water separation device. After the oil-water mixture passes through the device, the oil content in the oil region can reach 99.25% with a voltage of 8 kV. In addition, the separation speed of the oil-water mixture can also be adjusted by varying the corona discharge voltage. This paper presents a simple and innovative method for oil-water separation.

Four-Dimensional Visualization of Microscale Dynamics of Membrane Oil Fouling via Synchrotron Radiation Microcomputed Tomography.

Although oil-water separation technology via wettability-controlled membranes has emerged as a promising technology to treat oily wastewater, membrane fouling by faulents such as sludge flocs and colloids, and the consequent clogging of pores, severely degrades the efficiency of filtration systems. One of the main promotors of fouling by faulents is oil fouling, which is also a form of fouling itself. Despite considerable practical and academic interest in the analysis of oil-fouled membranes, direct visualization of the entire process of oil infiltration into hydrophilic membranes is still preliminary owing to (i) the similar optical contrast and physical density between oil and water, (ii) the low penetration depth of imaging methods, and (iii) the lack of 3D segmentation capability. In this study, microcomputed X-ray tomography using tunable synchrotron radiation provided direct high-speed 3D visualization of the microscale dynamics of the oil infiltration of a prewetted hydrophilic filter membrane over time. Direct visualization of the interfacial dynamics of oil infiltration opens a window into the complex liquid (water/oil)-gas-solid interface and thus helps furnish an in-depth understanding of oil fouling in the prewetted membrane.

Superhydrophobic copper foam modified with hierarchical stearic acid/CuSiO3/Cu(OH)2 nanocomposites for efficient water/oil separation

Developing efficient, durable and affordable oil-water separation technologies is critical to address the challenges of oily wastewater treatment. In this work, a microsphere-like CuSiO3 embedded Cu(OH)2 nanowires array was prepared on copper foam (CF) support (defined as CF/Cu(OH)2/CuSiO3) by using a simple chemical etching and hydrothermal method. After modifying with stearic acid (SA), such a novel CF/Cu(OH)2/CuSiO3-SA membrane presented excellent superhydrophobicity with a static water contact angle of 155.6°. The ammonia concentration in the precursor solution and the hydrothermal reaction time were critical for the morphology and the associated hydrophobicity of the CF/Cu(OH)2/CuSiO3-SA membrane. The as-prepared superhydrophobic CF had efficient anti-corrosion and mechanical properties and demonstrated an excellent separation capability of oil-water mixtures with a separation efficiency of 98.4%. It also exhibited a good separation efficiency of 98.3% for various water-in-oil emulsions, and delivered an outstanding separation efficiency of 98.2% towards oil/water mixture after operating successive 30 cycles of oil-water separation. With the inherent advantages of high separation efficiency of oil/water emulsion, good physicochemical stability and durability, and high mechanical and corrosion resistance, the novel CF/Cu(OH)2/CuSiO3-SA membrane is potentially useful in practical applications for oily wastewater treatment.

Three-dimensional biomimetic superhydrophobic nickel sponge without chemical modifications for efficient oil/water separation

The frequent oil spill accidents and a large amount of industrial oil wastewater discharges had caused serious economic losses and damage to the marine ecological environment. Hence, oil–water separation technology had received increasing attention from researchers. Herein, three-dimensional (3D) nickel sponge was prepared via a facile hydrothermal reduction route. The nano-spines structure of nickel sponge could exhibit superhydrophobic/superlipophilic properties without further hydrophobic modification by low-surface-energy chemicals. Due to the opened hierarchical porous structures and higher porosity, nickel sponges have excellent adsorption capacity for various oils and organic solvents. Nickel sponge has good resistance to ultraviolet radiation, corrosive aqueous solution ability, can be used for long-term outdoor applications. Moreover, the nickel sponge can also selectively absorb oil from oil/water mixtures under turbulent flow conditions. In addition, nickel sponges can continuously and rapidly collect oil from immiscible oil/water mixtures with the aid of a vacuum. Nickel sponge can also efficient selective filter oil/water mixture with a high separation efficiency over 97%. Due to the combination of metallic properties and the low density, nickel sponges are expected to have potential applications in oil absorption, flexible electrodes and industrial catalysis.

Superhydrophobic palmitic acid modified Cu(OH)2/CuS nanocomposite-coated copper foam for efficient separation of oily wastewater

Developing an efficient, simple, and low-cost oil-water separation technologies is critical to address the challenges of oily wastewater treatment. In this work, a nanoflower-like CuS embedded into Cu(OH)2 nanowire arrays (Cu(OH)2/CuS) were grown on the surfaces of copper foam (CF) by combination of chemical etching and ion exchange methods, and subsequent modification with palmitic acid (PA) was performed to achieve superhydrophobic CF/Cu(OH)2/CuS-PA oil-adsorption materials. The reaction conditions of ion exchange such as the Na2S concentration and immersion time were demonstrated to be key factors to form hierarchical Cu(OH)2/CuS nanowire arrays, and thus further significantly influenced the hydrophobicity of the copper foam. Such superhydrophobic CF/Cu(OH)2/CuS-PA with a static water contact angle of 153.4° delivered a high separation efficiency of oil-water mixtures at 98.8%, and the separation efficiency was always up to 97.6% for various water-in-oil emulsions. After operating successive 30 cycles of oil-water separation, the high separation efficiency remained unchanged. The CF/Cu(OH)2/CuS-PA also presented high stability, good anti-corrosion and mechanical properties in harsh environments. Thus, this superhydrophobic copper foam offers a potentially promising three-dimensional adsorbent for practical application of spill oil recovery and oil/water separation.

Zwitterionic hydrogel-coated cotton fabrics with underwater superoleophobic, self-healing and anti-fouling performances for oil-water separation

• Zwitterionic hydrogel with self-healing property was coated on the cotton fabric. • The coated fabric exhibited anti-fouling and underwater superoleophobic properties. • The coated fabric had superior oil/water separation property under gravity drive. • The coated fabric displayed the outstanding cyclic stability and reusability. Oil-water separation technology has attracted widespread attention, due to the increasingly serious oil pollution. In this work, novel poly(sulfobetaine methacrylate- co -2-hydroxyethyl acrylate)/poly(vinyl alcohol)/borax (PSBMA/PVA/Borax) hydrogels were prepared. Then, the related gel-coated cotton fabrics for oil-water separation were successfully developed in a facile route. The results presented the as-prepared zwitterionic hydrogels had outstanding self-healing ability, low swelling ratio, and satisfactory mechanical properties because of multiple interactions in the hydrogel’s network. As expected, the zwitterionic hydrogel-coated cotton fabric was imparted with excellent underwater superoleophobicity and outstanding anti-fouling ability due to the existence of zwitterionic groups on the surface. The underwater oil contact angle of the as-prepared fabric was approximately 160° towards a series of oils. Meanwhile, oily contaminations on the zwitterionic hydrogel-coated fabric surface can be rapidly removed just by water immersion. Most importantly, the zwitterionic hydrogel-coated fabric exhibited excellent oil-water separation efficiency (approximately 99%) and water flux (about 15, 181 L -1 ·m −2 ·h −1 ) even after 50 successive cycles. Additionally, the zwitterionic hydrogel-coated fabric also presented remarkable chemical and mechanical stabilities in harsh conditions. The as-prepared cotton fabric presents a great application prospect in oily wastewater treatment.

Fiber coalescence treatment of oily wastewater: A new theory and application

Oil pollution from produced water in the offshore petroleum industry is one of the most serious marine pollutants worldwide, and efficient separation technology is crucial for the control of oil pollutant emission. Medium coalescence is an efficient oil-water separation technology, but its theory is lacking and the development is slow. In this work, the microscopic mechanism of fiber coalescence was revealed, and found that the effective collision positions were the three-phase contact line and the exposed fiber surface. Further, a theoretical model for calculating the separation performance of a fiber bed was established. For a given inlet droplet size distribution and bed geometric parameters, the outlet droplet size distribution and the total separation efficiency of the fiber bed can be predicted. Then, an Ω-shaped woven method composed of oil-wet fibers and oil-phobic fibers was designed and the separation performance of the fiber beds prepared by the method and the influence law of various parameters were clarified through macroscopic experiment. Finally, the novel technology achieved its first engineering application on an offshore platform, with the average oil content of the outlet was less than 25 mg/L, which could reform the current treatment process of produced water.

Multi-scaled, hierarchical nanofibrous membrane for oil/water separation and photocatalysis: Preparation, characterization and properties evaluation

Increasing oily wastewater is produced by various industrial, various oil-water separation technologies and materials have been developed to solve this issue. A facile method is proposed to build multi-scaled and hierarchical membranes with efficiently oil/water separation and photocatalysis. The multi-scaled, hierarchical membrane is fabricated by a hydrophilic polyacrylonitrile (PAN) electrospinning nanofibrous and PAN/TiO2 electrospraying spheres, then the polydopamine (PDA) decorated membrane via in-situ growth. This multi-scaled, hierarchical structure endows the membrane with superhydrophilicity (water contact angle ∼ 0°), and underwater superoleophobicity (oil contact angle ∼152°). And the multi-scaled, hierarchical membrane shows superior water permeation and hydrophilic properties than pure PAN membranes. In addition, the membrane indicates an excellent photocatalytic ability for organic pollutant (∼98 %). And after 5 cycles, the water flux still maintains a high level showing good recyclability. This multi-scaled, hierarchical nanofibrous membrane shows very promising application potentials in oil-water separation and photocatalysis.

Recent advances in novel functional nanomaterials-based oil/water separation techniques

The increasing amount of oily wastewater discharges caused major challenges for current environmental issues, such as oil-water purification and separation [1-6]. Thus, the development of new functional materials for the efficient treatment of oil-water is imperative [7-11]. This paper reviewed the recently developed oil-water separation technologies, which were based on novel functional nanomaterials, and presented representative works in detail. Finally, the challenges and future research directions of this area were briefly discussed.

Synthesis and Evaluation of Novel Naphthenate Inhibitor Demulsifier from Fatty Hydrazide Derivatives

The production of crude oil contained Alkaline-Surfactant-Polymer (ASP)-chemical enhance oil recovery (CEOR) has a significant detrimental effect on flow assurance mainly for formation of microemulsion which is thermally stable and difficult to break and separated into clean crude oil and water phase. Quality of clean crude oil for saleability is important through achievement of crude oil dehydration in terms of basic sediment and water (BS&W) specification less than 0.5%. This paper outlines a case-study where stable microemulsions were formed following mixing of crude oil and ASP brine, requiring operationally intensive remediation. Finally, novel palm oil-derived fatty hydrazide Naphthenate Inhibitor (NI)-Demulsifier were synthesized, formulated and tested using dynamic laboratory tests using a multifunctional mini flow loop (MMFL). Under dynamic laboratory test, crude oil, prepared produced water and ASP were mixed under high shear at separator temperature and pressure. The NI-demulsifiers chemical injection was carried out after microemulsions were formed before the separator, representing a wellhead injection point and for a sufficient time to allow the microemulsion system to reach equilibrium. This work demonstrates the importance of considering the impact of ASP-EOR fluids on existing emulsion and using an appropriate laboratory technique to evaluate potential mitigating treatments for oil-water separation technology. The effects of temperature and water cut on microemulsion stability are shown and the NI-demulsifier demonstrated excellence in demulsifying and dehydration at minimal dosage.

Luminescent and hydrophobic textile coatings with recyclability and self-healing capability against both chemical and physical damage

Luminescent and hydrophobic textile coatings with recyclability and self-healing capability against both chemical and physical damage were prepared, which present multi-functions and long service life cycles. The applications in self-cleaning, oil-water separation, and anti-counterfeit technology were successfully demonstrated. The coatings can be easily created onto different fabrics including cotton cloth, filter paper, and chemical fabric. A rare earth organic complex of SmTTAPhen(NO3)3 (STPN), silane modified epoxy oligomer, and bis(4-maleimidophenyl)methane (BMI) provide luminescence, hydrophobicity, as well as recyclability and self-healing capability, respectively, to the coatings. More specifically, high transparency but high luminescence were achieved due to the good dispersion of STPN in coating matrix, resulting from the hydron bonding between nitrate groups from STPN and hydroxyl groups from epoxy oligomer. Silane modification facilitated the accumulation of Si–O bonds on the free-surface of the coating, which offers hydrophobic features. The introduction of reversible Diels-Alder reactions provided the self-healing capability and recyclability. Upon heating using an electronic iron, the hydrophobicity can be recovered from physical or chemical damage to the coatings. Besides, the coatings on abandoned fabrics can be recycled and reused to a new bare fabric. We believe that the concept and coating materials are useful to further expand the areas of smart and multi-functional coatings with long service life.

Experimental study on the effect of spatial distribution and action order of electric field and magnetic field on oil-water separation

Electromagnetic synergistic promotion of emulsion separation is a new oil-water separation technology under the background of interdisciplinary and multi-field coupling. However, the lack of research on the influence of characteristic parameters on separation efficiency limits the development of this technology. In this paper, the effect of the spatial distribution and the action order of electric field and magnetic field on oil-water separation was investigated by using the electromagnetic synergistic oil-water separation experimental system. The experimental results show that the spatial position and action order of electric field and magnetic field have a significant influence on the separation performance, and the separation efficiency is the highest when they are vertically distributed and synchronously operated. The theory of ion enrichment based on electromagnetic synergism was proposed. It is considered that the polarization-electromagnetic force and ion enrichment effect are the main reasons for the higher separation efficiency of emulsion treated by the electromagnetic synergistic field with vertical distribution and synchronization. Among them, the polarization-electromagnetic force affects the dynamic behavior of droplets in the direction perpendicular to the electric field, while the ion enrichment effect affects the distribution of droplets in the electric field and the forces inside and outside the liquid bridge.