Electrostatic Splitting of the Emulsion Used in Liquid Surfactant Membranes Process for Metals Separation

Abstract

A study has been carried out to investigate the effect of different parameters on the splitting process of the emulsion used in the liquid surfactant membranes process for metals separation. The influence of electric field strength, frequency of the applied ac voltage, and membrane recycling on emulsion stability have been studied. The investigations have revealed that there exists a unique optimal frequency range in which the best separation of the emulsion phases is obtained. The effect of the membrane composition and the variation of tri-n-butyl phosphate (TBP) concentration has been shown to vary linearly with the splitting efficiency. This finding correlates quite well with Sadek and Hendrick's equation on the force causing coalescence in an electric field.     

Movement of dispersed droplets of W/O emulsion in a uniform DC electrostatic field:Simulation on droplet coalescence☆

Considering the droplet coalescence, the motion of a group of dispersed droplets in W/O emulsion in a DC electric field is simulated. The simulation demonstrates the evolutions of droplet number, size as wel as its distribution, local concentration distribution and droplet size-velocity relation with the applied time of electric field. The sim-ulated average droplet size is roughly consistent with the experimental value. The simulated variation of droplet number with time under several applied voltages shows that increasing voltage is more effective for raising the rate of droplet coalescence than extending exerting time. However, with the further raise of applied voltage, the improvement in droplet coalescence rate becomes less significant. The evolution of simulated droplet size–velocity relationship with time shows that the inter-droplet electric repulsion force is very strong due to larger electric charge on the droplet under higher applied voltage, so that the magnitude and the direction of droplet velocity become more random, which looks helpful to droplet coalescence.     

高压脉冲电场破乳的影响因素探讨

在高压脉冲电场中,W/O乳状液的分散相液滴产生聚结和沉降,可与连续相分离开来。采用以新型电极作为内电极的同心圆柱状破乳装置对模拟W/O乳状液进行破乳,对其影响因素电极、试验电压、破乳时间、温度等进行试验研究。试验结果表明：采用3#电极时破乳率最高;随着试验电压的提高,时间增长,温度升高,其破乳率都能提高。对各影响因素的影响机理进行了分析,同时指出了试验的不足之处。     

Electric Field-Enhanced Coalescence of Liquid Drops

Abstract

A fundamental understanding of drop coalescence and growth is of importance to separations and materials processing. Under external driving forces, drops dispersed in an immiscible fluid collide and coalesce with each other due to their relative motion. As a result of drop coalescence, the average drop size in the dispersion increases over time, improving the separation process. Collision and coalescence of spherical, conducting drops bearing no net charge in dilute, homogeneous dispersions are considered theoretically under conditions where drop motion results from gravity settling and electric field-induced attraction. A trajectory analysis is used to follow the relative motion of two drops and predict pairwise collision rates. A population dynamics equation is then solved to predict the time evolution of the size distribution and the average size of drops. The results show that the rate of drop collision and growth can be increased significantly by applying an electric field, in accord with fundamental experiments and patents on electrocoalescence.     

新型静电聚结器中水滴聚结特性研究

传统电脱水器采用裸电极,含水率较高时在高强电场作用下容易发生击穿现象,今设计了包覆绝缘层的高压电极并加工了新型静电聚结器,可有效避免击穿现象的发生。采用水/原油乳状液为实验介质,并利用显微高速摄像系统结合图像处理技术对水滴的聚结规律进行了观察和分析,探索了电场强度、流量、含水率等因素对水滴聚结特性的影响。结果表明:包覆绝缘层的高压电极可有效防止电击穿现象的发生,增加电场强度有助于油水分离,但高于临界场强后容易导致液滴破碎;含水率为10%、20%、30%时,最优电场强度不同,分别是372、320和204 kV m 1;含水率10%和30%乳化物液滴粒径增大倍数明显大于含水率20%的工况;电场作用时间影响液滴聚结效果,高强电场在低流量下具有很显著的作用;随着流量的增加电场作用降低,但高强电场在高流量下依然使液滴粒径明显增大。     

流花油田老化油高频/高压脉冲交流电场破乳脱水研究

在测定老化油乳化液粘度-温度曲线、含水率反相点曲线的基础上,采用静态静电聚结破乳实验装置研究了油水反相特性对电场破乳脱水效果的影响,使用自主搭建的动态破乳脱水特性快速评价装置研究了高频/高压脉冲交流电场下电场强度和频率对老化油乳化液破乳脱水效果的影响. 结果表明,流花油田老化油反相点含水率约为40%,油水反相过程中乳化液粘度增加,电场破乳脱水难度增大;老化油乳化液含水率为30%时,最优电场强度1.25 kV/cm、电场频率2.5 kHz下破乳后的离心脱水率为97.8%,远高于工频电场下的离心脱水率(4.2%),高频/高压电场破乳比工频/高压电场破乳优势明显.     

Electrostatic enhancement of coalescence of water droplets in oil: a review of the technology

The technology for electrostatic enhancement of coalescence of water droplets in oil emulsions is critically reviewed. Historically, the electrostatic coalescer was invented for the petroleum-related industries in California [US Patent 987 115 (1911)]. Nowadays, this technology is generally considered for the separation of an aqueous phase dispersed in a dielectric oil phase with a significantly lower dielectric constant than that of the dispersed phase. Various designs have been introduced, with most using alternating current (AC) electric fields with mains frequency (50 or 60 Hz). The direct current (DC) electric field has been less common in the past as compared to the AC. In 1981, the concept of pulsed DC electric fields was introduced, together with insulated electrodes [Trans. IChemE 59 (1981) 229–237; UK Patent 217 1031A (1986)]. Since then, this has become more common in the electrocoalescence technology. Pulsed DC and AC fields are especially useful, when the aqueous phase content of the emulsion is high, to prevent short-circuiting between the pair of electrodes. Processing of oil from old wells is a good example, where the volumetric water content could vary significantly. Reported work by some workers indicates the existence of an optimum frequency, which depends on the electrode coating material, its thickness and the liquid emulsion composition. This is however, a contentious issue which has not been completely resolved. The characteristics and geometry of the electrode system (generally cylindrical or plate) influence the performance of the electrostatic coalescer, and are closely related to the type of the applied electric field and the emulsion used. There are basically two types of electrode: uninsulated electrode and insulated electrode. Combination of electrocoalescence and mechanical separation (e.g., centrifugal force) has also been introduced. Heating and the addition of chemicals have been shown to further enhance the electrocoalescence of water droplets. Other methods that can be combined with the electrical treatment are filtration, methods employing high pressure and temperature, and mixing. This review paper also looks at some of the current specific industrial applications using the electrocoalescence technology. Besides the oil and petroleum industries, this technology has potential applications in the edible oil industries such as palm oil, sunflower oil and vegetable oil processing. Most of the currently available equipment is very big and bulky, having a large inventory of emulsion. Therefore, we see the future trend for new developments to be in the direction of inventing small portable devices, incorporating features such as optimum electric fields and combined electrical and centrifugal forces to further enhance the separation of water-in-oil emulsions. Furthermore, a better understanding of the fundamentals of electrocoalescence will enable a better design of the geometry of the electrodes, of the flow field with respect to the electric fields, the type of dispersion used and the type of the applied electric field.     

静电强化乳液中油滴(纳米尺度)聚并过程(英文)

Oil droplets in nanometer scale which are dispersed in water cannot be separated easily.An attractive technique is carried out by electrical phenomena to demulsify oil in water emulsion.In this research,non-uniform electric field or dielectrophoresis(DEP) is applied to remove sunflower oil(which is dispersed in the water).Effects of temperature,time and voltage(using AC-electric field) were considered to get the highest DEP-force(Fdi) and the best results.The oil particles sizes with average of approximately 76 nm have been shown using a ZetaSizer Nano ZS,Model ZEN 1600(Malvern Instrument Ltd.).The maximum separation efficiency of 85% is obtained at the optimum temperature of 38 ℃ and voltage of 3000 V.     

Coalescence of Water Droplets in Crude Oil Emulsions: Analytical Solution

In petroleum refineries, water is used in desalting units to remove the salt contained in crude oil. Typically, 7 % of the volume of hot crude oil is water, forming a water‐and‐oil emulsion. The emulsion flows between two electrodes and is subjected to an electric field. The electrical forces promote the coalescence of small droplets of water dispersed in crude oil, and these form bigger droplets. This paper calculates the forces acting on the droplets, highlighting particularly the mechanisms proposed for droplet–droplet coalescence under the influence of an applied electric field. Moreover, a model is developed in order to calculate the displacement speed of the droplets and the time between droplet collisions. Thus, it is possible to simulate and optimize the process by changing the operational variables (temperature, electrical field, and water quantity). The main advantage of this study is to show that it is feasible to increase the volume of water recycled in desalting processes, thus reducing the use of freshwater and the generation of liquid effluents in refineries.     

Physical and electroresponsive characteristics of the intercalated styrene‐acrylonitrile copolymer/clay nanocomposite under applied electric fields

Styrene‐acrylonitrile copolymer (SAN)/clay nanocomposites were synthesized through an emulsion copolymerization of styrene and acrylonitrile in the presence of sodium montmorillonite, and their physical properties and electroresponsiveness under an applied electric field were characterized. Thermogravimetric analysis (TGA) showed that the thermal stability of the synthesized polymer was sustained. X‐ray diffraction (XRD) analysis confirmed the insertion of SAN into the interlayers of clay, whose separation consequently increased, as compared to those of the pristine clay. Transmission electron microscopy (TEM) was used to observe the suspended state of clay. Dry‐base electrorheological (ER) fluids were prepared by mixing intercalated SAN nanocomposite particles into silicone oil. Typical ER behavior, i.e., enhancement of shear and yield stresses in the presence of an applied electric field, was observed using a rotational rheometer equipped with a high‐voltage generator. A universal yield stress scaling equation was also found to fit our experimental data well. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 821–827, 2003     

电场作用下双液滴聚合特性

乳状液破乳分离是目前高含水期油田开采过程中难以解决的技术问题,电场破乳方法具有高效清洁等优点,是解决该问题的有效手段。采用数值模拟与试验验证相结合的方法研究电脱水过程中阶跃、斜坡电场诱导下双液滴的聚合与分离特性。结果表明,在斜坡电场作用下,界面张力引起的泵吸作用大于电场力引起的颈缩作用,有利于液滴聚并,且液滴发生二次乳化现象的概率降低。而施加阶跃电场时,一定范围内能够达到液滴破乳的目的,但液滴在聚并过程中易发生二次乳化现象。从电场对连续相影响的角度分析发现,阶跃电场不仅对液滴具有驱动作用,对连续相的影响也较为明显,阶跃电场会增大连续相内湍流作用,不利于电脱水过程。因此,采用斜坡信号诱导液滴聚合能够降低二次乳化现象发生的概率。     

Response time measurements of liquid crystal dispersed in polyester resin film

New material consisting of nematic liquid crystal droplets from 2-30 μm in radius in a crosslinked UV-cured polyester resin binder was prepared. Micrographs of the samples were taken in the optical microscope with cross-polaroids. Reorientation of the droplets by application and removal of an electric field is discussed. Electrooptic properties of the material were measured using polarized light from a helium-neon laser. Transmittance and response time vs. voltage applied with driving frequency 2 kHz were detected on the oscilloscope and photographed. The response times were: rise time τ^on shorter than 20 ms at applied voltage higher than 50 V, and decay time τ^off = 80 ms. They are a promising feature for this material for a display application.     

Electrocoalescence of binary water droplets falling in oil: Experimental study

The approaching movement and consequent coalescence of binary water droplets falling in stagnant oil and exposed to an external electric field are investigated using a high speed camera. Different situation of the droplets and electric field intensities are applied in the experiments. The qualitative results of the experimental observations are exhibited through the scaled images of the binary droplets snapshots in milliseconds. Furthermore, different approaching trends of the droplets are presented as quantitative plots and discussed based on the theoretical electrostatic and hydrodynamic models. The effect of the applied voltage amplitude, initial distance of the drop pair, and skew angle of the electric field are investigated. The experimental results prove the electrostatic theories; as acceleration in electrocoalescence demonstrated using a stronger electric field as well as closer distance between the droplets. It was also revealed that the skew angle of the electric field decelerates the electrocoalescence until alignment of the droplets.     

Two-Phase Electrophoresis of Proteins

Abstract

Proteins have been directed into either the top or bottom phase of a polyethylene glycol/dextran aqueous two-phase system by applying an electric field perpendicular to the phase interface. Protein migration across the interface was manipulated by varying polarity, pH, electrophoresis time, field strength, and phase volume ratio. Mixtures of hemoglobin and albumin were separated by operating between isoelectric points and directing oppositely charged proteins into separate phases. Applying 50 V/cm for 2 hours to 58 mL of an equal phase volume two-phase system containing 0.2 g/L of each protein at pH 6 resulted in a bottom phase containing 99% of the hemoglobin and a top phase containing 95% of the albumin. This represents a significant improvement over the separation obtained either by partitioning in the same two-phase system with no applied field or by electrophoresis under the same conditions in homogeneous buffer. The two-phase system divides the electrophoresis device into two distinct regions, providing stability against convective mixing and facilitating product isolation.     

非均匀电场下乳化油中液滴变形动力学行为

外加电场下液滴的变形动力学行为是乳化液电脱水机理研究的重要内容。基于Cahn-Hilliard方程的相场方法,建立了液滴在非均匀电场下的仿真模型,研究了电场作用下乳化液中液滴在形变、移动和聚结过程中电荷密度和电场力的分布规律,以及流场和电场的耦合作用。仿真分析了液滴粒径、电场强度以及电场非均匀系数对液滴运动行为的影响。利用实验室小型脱水系统开展了乳化液脱水实验,并通过高速摄像机对乳化液中液滴的运动行为进行了观测与分析。研究结果表明,在非均匀电场中液滴表面的极化电荷分布不均,由液滴中部向两端逐渐增大,在靠近电场集中方向处的电荷密度和Maxwell应力值最大;在一定范围内增大电场强度、电场非均匀系数或液滴粒径,可使液滴形变量增大,液滴向电场集中区域的移动速度以及液滴间的聚结速度增加。     

静电场和离心力场联合分离水/油型乳状液

（1）对搅动下水／油型（W／O)乳状液的静电分离过程作了理论分析,从极化角度对外电场促使水滴聚结的原因给予定量解释;提出极化水滴“二分子”碰撞、聚结的假设,并阐述了极化水滴聚结的动力学过程.(2)采用一种新型（同时具有静电场和离心力场）静电分离器对水／煤油─Span80乳状液进行了分离实验．分别研究了乳状液停留时间、含水量、电压以及油相粘度等对破乳率的影响,结果表明水滴“二分子”碰撞、聚结的假设较好地描述了水滴在电场下聚结的动力学过程;破乳实验设备由于使用高速离心场替代传统重力场,使得破乳效果有明显提高．     

Removal of Submicron Silica Particles from tert-Amyl Alcohol by Dielectric/Electric Packed Bed Filtration

Abstract

A packed bed with an applied electric field is used to remove submicron and nanometer particles from a nonconducting or slightly conducting solution. Several studies have shown that the application of an electric field to a packed bed significantly increases the performance of the filtration. To enhance the electric-field filtration efficiency, it is desired that the packing materials have a higher dielectric constant than the solution so that the electric-field lines will be diverted into the packing materials.

In the present studies, a dc voltage of 0 to 8 kV/cm is applied to a packed bed (2.5-cm diameter and 3.0-cm length) filled with 1-mm-diameter glass beads. The filtration medium contains submicrometer or nanometer SiO₂ particles dispersed in tert-amyl alcohol. Two particle sizes are investigated: the average particle sizes are about 300 nm and 50 nm, respectively.

Visible light spectrophotometry is used to estimate the amount of SiO₂ particles in the effluent. The experimental results are presented as a series of breakthrough curves. The effect of the applied electric field on the breakthrough curve on two different particle sizes is presented. Depending on the applied electric field and the conductivity of the system, heating of the packed bed may occur. The operating current and temperature of the packed bed are also presented.     

Synthesis and characterization of poly(butyl acrylate)/silica and poly(butyl acrylate)/silica/poly(methyl methacrylate) composite particles

Poly(butyl acrylate)/poly(methyl methacrylate) (PBA/PMMA) core–shell particles embedded with nanometer‐sized silica particles were prepared by emulsion polymerization of butyl acrylate (BA) in the presence of silica particles preabsorbed with 2,2′‐azobis(2‐amidinopropane)dihydrochloride (AIBA) initiator and subsequent MMA emulsion polymerization in the presence of PBA/silica composite particles. The morphologies of the resulting PBA/silica and PBA/silica/PMMA composite particles were characterized, which showed that AIBA could be absorbed effectively onto silica particles when the pH of the dispersion medium was greater than the isoelectric potential point of silica. The critical amount of AIBA added to have stable dispersion of silica particles increased as the pH of the dispersion medium increased. PBA/silica composite particles prepared by in situ emulsion polymerization using silica preabsorbed with AIBA showed higher silica absorption efficiency than did the PBA/silica composite particles prepared by direct mixing of PBA latex and silica dispersion or by emulsion polymerization in which AIBA was added after the mixing of BA and silica. The PBA/silica composite particles exhibited a raspberrylike morphology, with silica particles “adhered” to the surfaces of the PBA particles, whereas the PBA/silica/PMMA composite latex particles exhibited a sandwich morphology, with silica particles mainly at the interface between the PBA core and the PMMA shell. Subsequently, the PBA/silica/PMMA composite latex obtained had a narrow particle size distribution and good dispersion stability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3425–3432, 2006     

Investigation of water separation from water-in-oil emulsion using electric field

In this study, water separation from water-in-oil emulsion was investigated in an oil treater using direct current electric field. A commercial motor oil was used as a model oil. Water-in-oil emulsions including 15 wt% water and 85 wt% oil were prepared with an ultrasonic generator at 27,000–28,000 Hz frequency.The performance of oil treater was evaluated in terms of water separation efficiency by changing the current, voltage, temperature, and residence time. The water separation was hardly affected by the electric current. The optimal operating voltage range was from 2 to 5 kV. The highest water separation efficiency of 77.2% was achieved at 75 °C. The efficiency of water separation tends to increase as the temperature increases and the residence time decreases due to decreasing viscosity and increasing exposure frequency.     

EHD-ENHANCED DRYING WITH WIRE ELECTRODE

ABSTRACT

The enhancement of drying rate by electrostatic field (corona wind) has been experimentally evaluated in this study. The samples used are 3 mm and 6 mm glass beads saturated with water. Two sets of experiments were conducted, with and without cross-flow, at 1 kV increment from the corona threshold voltage until the occurrence of sparkover. For each case a companion experiment was carried out simultaneously under the same ambient conditions but without the application of electric field. The result of which is used as a basis in the evaluation of drying enhancement using electric field (with or without cross-flow). Each experiment lasted for at least 5 h. The weight loss of water as well as the ambient temperature and humidity were measured. For EHD drying without cross-flow, the enhancement in drying rate increases with the applied voltage. With the presence of cross-flow, the enhancement in drying rate is nearly independent of the applied voltage and is close to the result obtained by drying with cross-flow alone.