STUDY OF DEMULSIFICATION OF WATER-IN-CRUDE OIL EMULSION

Demulsification of water-in-crude oil emulsion was studied at two different salinities, 0.5% and 10% sodium chloride, using five different nonionic surfactants. Equilibrium crude oil-water interfacial tension was measured with drop volume method. Low molecular weight surfactants were found to be completely ineffective as demulsifiers. Three surfactants which were effective demulsifiers, exhibited good interfacial activity, surface adsorption and surface pressure. The performance of the demulsifiers changed with change in salinity of aqueous phase. Surfactants effective as demulsifiers reduced surface tension of water by more than 25 dynes-cm^-1. For a given crude oil-water system, the surfactant which developed surface pressure in excess of 15 dynes-cm^-1 was found to be good demulsifier for that system. Based upon these studies, a physical model of demulsification has been proposed     

The effect of salting out and micellization on interfacial tension

We consider a system consisting of oil and water phases with nonionic surfactant distributed between them and present a model for the effect of salt on the interfacial tension. The model accounts for the salting out of surfactant from water to oil and also for the occurrence of micelles in the aqueous phase. In addition, it is shown that salting out affects micellization in interesting ways, e.g. micelles may form as the salt concentration increases even though none are present initially and then disappear at higher concentrations. The effect of chain length and head group size (and hence of HLB) on the interfacial tension is examined for surfactants of the polyoxyethylene type. The calculated interfacial tension decreases continuously and may become negative under certain condition, indicating that the oil-water interface becomes unstable and a microemulsion forms.     

阴阳离子表面活性剂体系超低油水界面张力的应用

通过阴阳离子表面活性剂复配,在实际油水体系中获得了超低界面张力.通过在阴离子表面活性剂分子结构中加入乙氧基(EO)链段,以及采用阴阳离子加非离子型表面活性剂的三组分策略,有效解决了混合表面活性剂在水溶液中溶解度问题.进而研究了阳离子表面活性剂结构、非离子表面活性剂结构、三者组分配比、表面活性剂总浓度等因素对油水界面张力的影响,从而在胜利油田多个实际油水体系中获得了较大比例范围和较低浓度区域的油水超低界面张力,部分体系甚至达到了10-4 mN·m-1.由于阴阳离子表面活性剂间强烈的静电吸引作用,相关体系具有很好的抗吸附能力.经过石英砂48 h吸附后,体系仍然具有很好的超低界面张力.     

Competitive adsorption of surfactants and hydrophilic silica particles at the oil-water interface: interfacial tension and contact angle studies

The effect of surfactants' type and concentration on the interfacial tension and contact angle in the presence of hydrophilic silica particles was investigated. Silica particles have been shown to have an antagonistic effect on interfacial tension and contact angle in the presence of both W/O and O/W surfactants. Silica particles, combined with W/O surfactant, have no effect on interfacial tension, which is only dictated by the surfactant concentration, while they strongly affect interfacial tension when combined with O/W surfactants. At low O/W surfactant, both particles and surfactant are adsorbed at the interface, modifying the interface structure. At higher concentration, interfacial tension is only dictated by the surfactant. By increasing the surfactant concentration, the contact angle that a drop of aqueous phase assumes on a glass substrate placed in oil media decreases or increases depending on whether the surfactant is of W/O or O/W type, respectively. This is due to the modification of the wettability of the glass by the oil or water induced by the surfactants. Regardless of the surfactant's type, the contact angle profile was dictated by both particles and surfactant at low surfactant concentration, whereas it is dictated by the surfactant only at high concentration.     

New types of self-organizing interfacial alginate membranes

In this publication we describe a new self-association process, which leads to the formation of ultra-thin alginate layers at the interface between oil and water. The water phase contains a highly dilute solution of sodium alginate. These macromolecules are negatively charged and they are not surface active. The oil phase contains a small concentration of positively charged surfactants. At the interface between oil and water, the cationic surfactants tend to form complexes with the negatively charged alginate polyelectrolytes in the aqueous solutions. This leads to striking adsorption processes of the solved polysaccharide molecules at the oil-water interface. Upon the addition of calcium ions, a cross-linking process sets in and one obtains the thin viscoelastic membranes, which are anchored at the interface between oil and water. The thickness of these membranes is of the order of 0.2 mm. Similar structures can also be formed by solving positively charged Gemini surfactants in the oil phase. In this case, the cationic surfactant molecules induce the adsorption processes of alginate macromolecules, and they also act as cross-linking compounds. In a series of experiments, we measured the surface rheological properties of these ultra-thin alginate membranes. The results of these investigations point to the presence of electrostatically stabilized membranes. Special interest was given to the influence of the guluronate content of the alginates, which is important for the cross-linking mechanism according to the egg-box model. Finally, this article finishes with the discussion of the proposed building mechanisms of these membranes.     

The array and interfacial activity of sodium dodecyl benzene sulfonate and sodium oleate at the oil/water interface

There is a close correlation between the interfacial activity and the adsorption of the surfactant at the interface, but the detailed molecular standard information was scarce. The interfacial activity of two traditional anionic surfactants sodium dodecyl benzene sulfonate (SDBS) and sodium oleate (OAS) were studied by experimental and computer simulation methods. With the spinning drop method and the suspension drop method, the interfacial tension of oil/aqueous surfactant systems was measured, and the influence of surfactant concentration and salinity on the interfacial tension was investigated. The dissipative particle dynamics (DPD) method was used to simulate the adsorption of SDBS and OAS at the oil/water interface. It was shown that it is beneficial to decrease interfacial tension if the hydrophobic chains of the surfactant and the oil have similar structure. The accession of inorganic salts causes surfactant molecules to form more compact and ordered arrangements and helps to decrease the interfacial tension. There is an osculation relation between interfacial density and interfacial activity. The interfacial density calculated by molecular simulation is an effective parameter to exhibit the interfacial activity.     

Interfacial tension between water and high pressure CO2 in the presence of hydrocarbon surfactants

Interfacial tension of water–CO₂ interface was measured by pendant drop method in the presence of a surfactant of various concentrations. The surfactants used were three surfynols which are non-ionic blanched hydrocarbon with different length of the alkyl side chain. Prior to the interfacial tension measurements, the solubility of the surfynols in CO₂ were determined from cloud point method. The measured interfacial tensions indicated that an addition of small amount surfactant did reduce the interfacial tension. The interfacial activities of surfactants were evaluated from the slope of the interfacial tension reduction curve against the surfactant concentration and rationalized in terms of the molecular natures such as hydrophobic alkyl chain length.     

Effect of oil soluble surfactant in emulsions stabilised by clay particles

Although surfactants and particles are often mixed together in emulsions, the contribution of each species to the stabilisation of the oil-water interface is poorly understood. We report the results of investigations into the formation of emulsions from solutions of surfactant in oil and aqueous suspensions of laponite. Depending on the salt concentration in the aqueous suspensions, the laponite dispersed as individual disc-shaped particles, 30 nm in diameter, or flocculated into aggregates tens of micrometres in diameter. At the concentrations studied, the flocculated particles alone stabilized oil-in-water emulsions. Synergistic interactions between the particles and octadecylamine at the oil-water interface reduced the average emulsion drop size, while antagonistic interactions with octadecanoic acid enhanced coalescence processes in the emulsions. The state of particle dispersion had dramatic effects on the emulsions formed. Measurements of the oil-water interfacial tension revealed the origins of the interactions between the surfactants and particles.     

Aqueous surfactant solutions which exhibit ultra-low tensions at the oil-water interface

Ultra-low values of the tension at an oil-aqueous electrolyte solution interface can be developed by the addition of water-soluble surfactants of the petroleum sulfonate type. Interfacial tensions in the range of 10⁻³ dyne/cm or lower are readily achieved with surfactant concentrations of the order of 0.1 wt%. For a given oil and aqueous solution, the minimum interfacial tension resulting from the addition of a petroleum sulfonate depends markedly on the average equivalent weight of the sulfonate. Sulfonates having average equivalent weights higher and lower than a previously determined optimum weight, when mixed so as to yield this particular average weight, will also produce ultra-low interfacial tensions. For a given oil, additional control of this unusual type of interfacial activity is accomplished by adjustment of the electrolyte concentration of the aqueous phase.     

Experimental Study of the Effect of Strong Alkali on Lowering the Interfacial Tension of Oil/Heavy Alkylbenzene Sulfonates System

Experimental studies were conducted to explore the fundamental mechanisms of alkali to lower the interfacial tension of oil/heavy alkylbenzene sulfonates (HABS) system. Sodium hydroxide was used as the strong alkali chemical to investigate the interfacial tension (IFT) of oil/HABS system. The influences of salt and alkali on the interfacial activity were studied by the measurement of interfacial tension and partition coefficient. Moreover, the alkali/surfactant solutions were measured by dynamic laser scattering. The results showed that compared with the salt, the function of alkali to lower the interfacial tension and improve partition coefficient is more significant. The micelles formed by surfactants could be disaggregated because of adding alkali, so the size of micelles decreases and the number of mono‐surfactants increases, then more surfactant molecules move to the interface of oil/surfactant system and the adsorption of surfactants at oil‐water interfaces increases, which can lead to the decrease of IFT.     

正负离子混合表面活性剂双水相界面张力的研究

用旋转滴法测定了正负离子混合表面活性剂形成的双水相界面张力, 研究了双水相界面张力与表面活性剂的分子结构、正负离子表面活性剂的摩尔比、总浓度、外加无机盐及温度的关系. 结果表明, 双水相界面张力在一定正、负离子表面活性剂的摩尔比时属于超低界面张力范围. 观察到三种界面张力曲线类型, 第一类为摩尔比1:1 的两边的两条曲线, 界面张力随过剩表面活性剂组分的比例增加而降低; 第二类为一条跨过摩尔比1:1的马鞍型曲线; 第三类为位于摩尔比1:1的一边的一条马鞍型曲线. 界面张力曲线的类型主要取决于表面活性剂的分子结构, 包括亲水基类型、疏水链长度及对称性.     

pH-Sensitive self-propelled motion of oil droplets in the presence of cationic surfactants containing hydrolyzable ester linkages

Self-propelled oil droplets in a nonequilibrium system have drawn much attention as both a primitive type of inanimate chemical machinery and a dynamic model of the origin of life. Here, to create the pH-sensitive self-propelled motion of oil droplets, we synthesized cationic surfactants containing hydrolyzable ester linkages. We found that n-heptyloxybenzaldehyde oil droplets were self-propelled in the presence of ester-containing cationic surfactant. In basic solution prepared with sodium hydroxide, oil droplets moved as molecular aggregates formed on their surface. Moreover, the self-propelled motion in the presence of the hydrolyzable cationic surfactant lasted longer than that in the presence of nonhydrolyzable cationic surfactant. This is probably due to the production of a fatty acid by the hydrolysis of the ester-containing cationic surfactant and the subsequent neutralization of the fatty acid with sodium hydroxide. A complex surfactant was formed in the aqueous solution because of the cation and anion combination. Because such complex formation can induce both a decrease in the interfacial tension of the oil droplet and self-assembly with n-heptyloxybenzaldehyde and lauric acid in the aqueous dispersion, the prolonged movement of the oil droplet may be explained by the increase in heterogeneity of the interfacial tension of the oil droplet triggered by the hydrolysis of the ester-containing surfactant.     

Studies of synergism/antagonism for lowering dynamic interfacial tensions in surfactant/alkali/acidic oil systems. 1. Synergism/Antagonism in surfactant/model oil systems

Experimental studies are conducted in order to elucidate the mechanisms responsible for synergism/antagonism for lowering dynamic interfacial tension in model oil/surfactant/brine systems. A well-defined model oil is selected for controlled design of experiments, thus enhancing verification of known and unknown mechanisms. The systems examined contain model oils and two petroleum sulfonate solutions. The influence of additives in oil phase, such as carboxylic acids with different chain length, n-octadecanol, and oil soluble surfactant SP-60, on the equivalent alkane carbon number (EACN) values has been examined. The interfacial tensions of different model oils with different EACN values against surfactant solutions with different n(min) values have also been obtained. We find that antagonism has been observed when EACN/n(min) value is far from unity by adding organic components, while synergism has been observed when EACN/n(min) value is close to unity. The results present here suggest that organic additives in oil phase controlled interfacial tension by changing the partition of surfactants in oil phase, aqueous phase, and interface.     

餐厨废油制备的生物基两性表面活性剂的油水界面性能

以餐厨废油制备了生物基两性表面活性剂,应用界面张力和动态光散射方法,研究了该生物基两性表面活性剂体系的油水界面性能及在溶液中的聚集行为。 在无外加碱条件下,由餐厨废油制备的表面活性剂表现出良好的界面性能,在50~70 ℃以及pH值为7~12的条件下,均可以将油水界面张力降至超低值(<10^-3 mN/m),在不同的油藏模拟地层水中均保持较好的界面活性;分别在50、-20和4 ℃下保存,其界面活性均未受到明显影响。 在水溶液中形成的聚集体的平均流体力学半径为10~30 nm,无机盐离子的加入可使聚集体的粒径上升。 基于其优良的界面性质和可再生来源,由餐厨废油制备的生物基两性表面活性剂在三次采油方面具有重要的应用价值。     

Effect of Aqueous Phase pH on the Dynamic Interfacial Tension of Acidic Crude Oils and Myristic Acid in Dodecane

The time dependence of the interfacial tension between water–acidic crude oil and water–synthetic oil was investigated for aqueous phase pHs ranging from 2 to 9 using the du Noüy ring method at 20°C. Myristic acid in dodecane was selected as a model (synthetic oil) for acidic crude oil containing indigenous surfactants, and the similarities and differences between the dynamic interfacial tension behaviours of the natural and synthetic crude oil systems were compared. The initial interfacial tension and the relaxation of the interfacial tension are sensitive to the aqueous phase pH for both systems. The adsorption kinetics of the indigenous surfactants and myristic acid could be well fitted with the monoexponential model, and the time constants obtained in this manner indicates that reorganization of the indigenous surfactants and myristic acid at the w/o interface are pH dependent. The experimental results also indicate that indigenous surfactants in acidic crude oil and myristic acid in dodecane have similar film formation behaviours at the w/o interface for the range of pHs investigated.     

Synergistic effect of silica nanoparticles and charged surfactants in the formation and stability of submicron oil-in-water emulsions

The influence of hydrophilic silica nanoparticles on the emulsification of a triglyceride oil (Miglyol812) in the presence of charged surfactants (lecithin or oleylamine) and the long term stability of the resultant oil-in-water emulsions are reported. A synergistic effect of nanoparticles and surfactants in improving emulsification and stability to coalescence is evident only when the silica nanoparticles are initially added to the oil phase. When nanoparticles are included from the water phase, no synergistic stabilisation was observed due to electrostatic bridging or unfavourable attachment due to the repulsive electrostatic and hydration forces. Free energies of adsorption for silica nanoparticles at the oil-water interface calculated from experimentally determined interfacial tensions and three phase contact angles can be correlated to long-term emulsion stability only when silica is added from oil phase.     

Synergistic effect of mixed anionic and cationic surfactant systems on the interfacial tension of crude oil-water and enhanced oil recovery

Surfactant based enhanced oil recovery (EOR) is an interesting area of research for several petroleum researchers. In the present work, individual and mixed systems of anionic and cationic surfactants consisting of sodium dodecyl sulphate (SDS) and cetyltrimethylammonium bromide (CTAB) in different molar ratios were tested for their synergistic effect on the crude oil-water interfacial tension (IFT) and enhanced oil recovery performance. The combination of these two surfactant systems showed a higher surface activity as compared to individual surfactants. The effect of mixed surfactant systems on the IFT and critical micellar concentration (CMC) is strongly depends on molar ratios of the two surfactant. Much lower CMC values were observed in case of mixed surfactant systems prepared at different molar ratios as compared to individual surfactant systems. The lowest CMC value was found when the molar concentration of SDS was higher than the CTAB. When the individual and mixed surfacant systems were tested for EOR performance through flooding experiments, higher ultimate oil recovery was obtained from mixed surfactant flooding compared to individual surfactants. Combination of SDS and CTAB or probably other anionic-cationic surfactants show synergism with substantial ability to reduce crude oil water IFT and can be a promising EOR method.     

Interaction between polymer and anionic/nonionic surfactants and its mechanism of enhanced oil recovery

Various experimental methods were used to investigate interaction between polymer and anionic/nonionic surfactants and mechanisms of enhanced oil recovery by anionic/nonionic surfactants in the present paper. The complex surfactant molecules are adsorbed in the mixed micelles or aggregates formed by the hydrophobic association of hydrophobic groups of polymers, making the surfactant molecules at oil-water interface reduce and the value of interfacial tension between oil and water increase. A dense spatial network structure is formed by the interaction between the mixed aggregates and hydrophobic groups of the polymer molecular chains, making the hydrodynamic volume of the aggregates and the viscosity of the polymer solution increase. Because of the formation of the mixed adsorption layer at oil and water interface by synergistic effect, ultra-low interfacial tension (～2.0?×?10^?3 mN/m) can be achieved between the novel surfactant system and the oil samples in this paper. Because of hydrophobic interaction, wettability alteration of oil-wet surface was induced by the adsorption of the surfactant system on the solid surface. Moreover, the studied surfactant system had a certain degree of spontaneous emulsification ability (D50?=?25.04?µm) and was well emulsified with crude oil after the mechanical oscillation (D50?=?4.27?µm).     

Interfacial characterization of beta-lactoglobulin networks: displacement by bile salts

The competitive displacement of a model protein (beta-lactoglobulin) by bile salts from air-water and oil-water interfaces is investigated in vitro under model duodenal digestion conditions. The aim is to understand this process so that interfaces can be designed to control lipid digestion thus improving the nutritional impact of foods. Duodenal digestion has been simulated using a simplified biological system and the protein displacement process monitored by interfacial measurements and atomic force microscopy (AFM). First, the properties of beta-lactoglobulin adsorbed layers at the air-water and the olive oil-water interfaces were analyzed by interfacial tension techniques under physiological conditions (pH 7, 0.15 M NaCl, 10 mM CaCl2, 37 degrees C). The protein film had a lower dilatational modulus (hence formed a weaker network) at the olive oil-water interface compared to the air-water interface. Addition of bile salt (BS) severely decreased the dilatational modulus of the adsorbed beta-lactoglobulin film at both the air-water and olive oil-water interfaces. The data suggest that the bile salts penetrate into, weaken, and break up the interfacial beta-lactoglobulin networks. AFM images of the displacement of spread beta-lactoglobulin at the air-water and the olive oil-water interfaces suggest that displacement occurs via an orogenic mechanism and that the bile salts can almost completely displace the intact protein network under duodenal conditions. Although the bile salts are ionic, the ionic strength is sufficiently high to screen the charge allowing surfactant domain nucleation and growth to occur resulting in displacement. The morphology of the protein networks during displacement is different from those found when conventional surfactants were used, suggesting that the molecular structure of the surfactant is important for the displacement process. The studies also suggest that the nature of the oil phase is important in controlling protein unfolding and interaction at the interface. This in turn affects the strength of the protein network and the ability to resist displacement by surfactants.     

Studies of Synergism/Antagonism in Sodium Alkyl Benzene Sulfonate/Methyl Oleate Model Oil Systems

Experimental studies are conducted in order to elucidate the mechanisms responsible for synergism/antagonism for lowering interfacial tension in alkyl benzene sulfonate/brine/methyl oleate model oil and alkyl benzene sulfonate/alkali/methyl oleate model oil systems. We found that different mechanisms exist in above two systems. In alkyl benzene sulfonate/brine/methyl oleate model oil systems, methyl oleate influences the partition of added surfactants between oil and aqueous phase by changing equivalent alkane carbon number (EACN) value of model oil. In alkyl benzene sulfonate/alkali/methyl oleate model oil systems, methyl oleate in oil phase has two functions: on the one hand, it influences the partition of surfactant between oil and aqueous phase; on the other hand, it directly affects IFT by displacing surfactant molecule or forming mixed film with surfactant molecule at the interface.