Interfacial tension and the behavior of microemulsions and macroemulsions of water and carbon dioxide with a branched hydrocarbon nonionic surfactant

Measurements of interfacial tensions for 2-ethyl-hexanol-(propylene oxide)∼_4.5-(ethylene oxide)∼₈ (2EH-PO_4.5-EO₈) at the planar water-CO₂ interface and the surfactant distribution coefficient are utilized to explain microemulsion and macroemulsion phase behavior from 24 to 60 °C and 6.9 to 27.6 MPa. A CO₂ captive bubble technique has been developed to measure the interfacial tension γ at a known surfactant concentration in the aqueous phase, with rapid equilibration at the water-CO₂ interface. The surface pressure (γ_o − γ) decreases modestly with density at constant temperature as CO₂ solvates the surfactant tails more effectively, but changes little with temperature at constant density. The area per surfactant at the CO₂-water interface determined from the Gibbs adsorption equation decreases from 250 A²/molecule at 24 °C and 6.9 MPa, to 200 A²/molecule at 27.6 MPa. It was approximately twofold larger than that at the water-air interface, given the much smaller γ_o driving force for surfactant adsorption. For systems with added NaCl, γ decreases with salinity at low CO₂ densities as the surfactant partitions from water towards the W-C interface. At high densities, salt drives the surfactant from the W-C interface to CO₂ and raises γ. Compared with most hydrocarbon surfactants, this dual tail surfactant is unusually CO₂-philic in that it partitions primarily into the CO₂ phase versus the water phase at CO₂ densities above 0.8 g/ml, and produces γ values below 1 mN/m. With this small γ, a middle phase microemulsion and a C/W microemulsion were formed at low temperatures and high CO₂ densities, whereas macroemulsions were formed at other conditions.     

Adsorption Behavior of Fatty Alcohol Ether Sulfonate at Different Interfaces

The equilibrium surface tension, dynamic surface tension, and interfacial tension (IFT) of fatty alcohol ether sulfonates (C_mE_nSO) were measured to investigate their adsorption behavior. The effect of NaCl and CaCl₂ concentrations on the IFT was also studied. The results showed that the number of EO units has no significant effect on the critical micelle concentration (CMC) and CMC decreases with increasing the length of the hydrophobic group. The surface tension at the CMC increases with the increase of the number of EO units and the length of the hydrophobic group. At dilute surfactant concentration, the adsorption process for C_mE_nSO is controlled by diffusion; at higher concentration, it becomes a mixed diffusion‐kinetic adsorption mechanism. The IFT between C_mE_nSO solution and dodecane remains around 10^?1 mN/m over a wide range of electrolyte concentrations (NaCl concentration from 25 to 210 g/L, CaCl₂ concentration from 0.1 to 10 g/L).     

New Interfacial Rheology Characteristics Measured using a Spinning‐Drop Rheometer at the Optimum Formulation of a Simple Surfactant–Oil–Water System

A new spinning‐drop tensiometer with an oscillating rotation velocity was used to measure the interfacial rheological properties of systems with very low interfacial tensions in the zone close to the so‐called optimum formulation of surfactant–oil–water systems. 2 simple formulation scans were selected: One with an extended anionic surfactant using a salinity variation in the water phase, and another with a mixture of 2 nonionic surfactants in a scan produced by changing their proportion. With both systems it was corroborated that at optimum formulation (i.e., at hydrophilic–lipophilic deviation (HLD) = 0), both the interfacial tension and the emulsion stability exhibit a deep minimum. A clear relationship was also found between the phase behavior and the interfacial rheological properties (dilational elasticity and viscosity). For the very first time and in both kinds of scans (salinity or average ethylene oxide number), it was found that the interfacial elastic modulus E and the interfacial viscosity, as well as the phase angle also exhibit a minimum at optimum formulation. These groundbreaking findings could be applied to emulsion instability at optimum formulation and to its applications in emulsion breaking.     

Effect of hydrate formation/dissociation on emulsion stability using DSC and visual techniques

A key factor in hydrate risk management for an oil-dominated system is the stability of the emulsified water with gas hydrate formation. We show via differential scanning calorimetry (DSC) that gas hydrate formation and dissociation has a destabilizing effect on water-in-oil (W/O) emulsions, and can lead to a free water phase through agglomeration and coalescence of dissociated hydrate particles. High asphaltene content crude oils are shown to resist hydrate destabilization of the emulsion. Span80 was successfully used as an analog to asphaltene surface activity. Based on our experimental results, a new conceptual hydrate-induced destabilization model is proposed.     

DIFFUSION AND ADSORPTION KINETICS OF A WATER-SOLUBLE NONIONIC SURFACTANT TO THE INTERFACE BETWEEN TWO VISCOUS IMMISCIBLE LIQUIDS

The kinetics of diffusion and adsorption of a water-soluble nonionic surfactant, polyoxyethylene sorbitan monolaurate (Tween-20), to the interface between two viscous immiscible liquids relevant to many applications is experimentally investigated using drop volume tensiometry. The measured variation in dynamic interfacial tension with contact time at different bulk concentrations of the surfactant in the viscous aqueous phase indicates that the equilibrium is slowly attained at low concentrations. As the bulk surfactant concentration is increased by two orders of magnitude, the contact time needed to reach equilibrium decreased by about an order of magnitude. The corresponding values of diffusion coefficient in the viscous liquid, determined using existing theoretical equations, are found to be almost constant. These are about two orders of magnitude smaller than those for the data available in literature for similar surfactants in much less viscous water at the air interface. The molecular area of Tween-20 determined in the present work is found to be very close to the value reported by other authors.     

New Interfacial Rheology Characteristics Measured Using a Spinning Drop Rheometer at the Optimum Formulation. Part 2. Surfactant–Oil–Water Systems with a High Volume of Middle-Phase Microemulsion

This article is a continuation of our first study on dilational interfacial rheology properties at optimum formulation for surfactant-oil–water systems at low surfactant concentration just above the cμc. Here, we have investigated a high content of middle-phase microemulsion with an optimum WIII phase behavior for a system containing sodium dodecyl sulfate, n-pentanol, and kerosene. A new oscillating spinning drop interfacial rheometer was used to measure the interfacial properties. The very low dilational elasticity moduli and phase angle found at or near hydrophilic–lipophilic deviation (HLD) = 0 are related to the presence of the bicontinuous phase microemulsion and to the fast surfactant exchanges between the bulk and the interface, regardless of the phases involved in the measurement using the spinning drop apparatus, i.e., the two-phase excess oil and excess water (O-W) or the bicontinuous microemulsion and excess water (M-W). We show that at or near optimum formulation, the interfacial tension and the dilational modulus for the M-W case almost instantly reach equilibrium, because of the high surfactant content in the microemulsion and the fast exchanges between the bulk and the interface. In contrast, when both excess phases (O-W) are measured, the changes in these properties are slower, due to the scarce presence of surfactants in both phases. The possibility of having almost all the surfactants trapped in the middle-phase bicontinuous microemulsion could explain the emulsion instability in all the WIII range. This is behaving as if there were no surfactant available in the oil and water phases to stabilize the oil or water droplets thus formed.     

RELAXATION OF ASPHALTENES AT THE TOLUENE/WATER INTERFACE: DIFFUSION EXCHANGE AND SURFACE REARRANGEMENT

Upon adsorption at the oil/water interface, asphaltenes slowly form a glassy interphase. This robust, asphaltene-rich interphase is likely the reason for prolonged stability of crude oil/water emulsions and for the propensity of asphaltenic crude oils to alter the wettability of reservoirs. Here we adopt interfacial dilatation rheology using the oscillating pendant drop with axisymmetric drop shape analysis (ADSA) to investigate the relaxation mechanisms of asphaltenes adsorbed at the toluene/water interface. We compare classical viscoelastic models with the measured rheologic data and find that the frequency response of the dilatational moduli fits a combination of diffusion-exchange and surface-rearrangement mechanisms. The combined relaxation model is verified by solvent washing the asphaltenes from the interface and measuring the dilatational response of the resulting irreversibly adsorbed species. After washout, the oil-phase diffusion component of the frequency response disappears, and the relaxation time of the adsorbed film increases by an order of magnitude. Since the studied asphaltenes prove insoluble in the synthetic aqueous brine (pH?=?8.0), this result suggests that reversibly exchanging species in the oil phase weakens an interconnected asphaltene-gel/glass phase at the interface. Our experiments show, for the first time, that most of the surface-active asphaltenic molecules are irreversibly adsorbed from the oil phase.     

RELAXATION OF ASPHALTENES AT THE TOLUENE/WATER INTERFACE: DIFFUSION EXCHANGE AND SURFACE REARRANGEMENT

Upon adsorption at the oil/water interface, asphaltenes slowly form a glassy interphase. This robust, asphaltene-rich interphase is likely the reason for prolonged stability of crude oil/water emulsions and for the propensity of asphaltenic crude oils to alter the wettability of reservoirs. Here we adopt interfacial dilatation rheology using the oscillating pendant drop with axisymmetric drop shape analysis (ADSA) to investigate the relaxation mechanisms of asphaltenes adsorbed at the toluene/water interface. We compare classical viscoelastic models with the measured rheologic data and find that the frequency response of the dilatational moduli fits a combination of diffusion-exchange and surface-rearrangement mechanisms. The combined relaxation model is verified by solvent washing the asphaltenes from the interface and measuring the dilatational response of the resulting irreversibly adsorbed species. After washout, the oil-phase diffusion component of the frequency response disappears, and the relaxation time of the adsorbed film increases by an order of magnitude. Since the studied asphaltenes prove insoluble in the synthetic aqueous brine (pH = 8.0), this result suggests that reversibly exchanging species in the oil phase weakens an interconnected asphaltene-gel/glass phase at the interface. Our experiments show, for the first time, that most of the surface-active asphaltenic molecules are irreversibly adsorbed from the oil phase.     

Interfacial film properties of asphaltenes and resins

Interfacial film properties of asphaltenes and resins have been studied by interfacial shear viscosity measurements. The results show that the structure of the asphaltene film at the interface between oil and water is changed from two-dimensional to three-dimensional network as the concentration of the asphaltene at the interface increased. The film can be divided into three types namely expanded liquid film, condensed liquid film and solid-like three-dimensional network film. Furthermore, the structures of the interfacial films formed by asphaltene molecules and asphaltene particles are different and the strengths of these films are also different. The adsorption and migration processes of asphaltene molecules and migration process of asphaltene particles at the interface are different.     

Determination of the interfacial tension of low density difference liquid-liquid systems containing surfactants by droplet deformation methods

The interfacial tension, σ, between two low density difference liquids containing a surfactant was determined using drop deformation method with a computer-controlled parallel bands apparatus. This device applies a linear homogeneous shear flow field to a fluid matrix in which a droplet of another immiscible and buoyancy-free fluid is immersed. The flow induces topological changes on the initially spherical drop, which deforms into an ellipsoid and orients respect to the flow direction. The time evolution of the sheared droplets was recorded with two CCD cameras (placed along the x and z directions) for extended times, allowing the steady state of the drops to be achieved accurately, and further digitally analyzed. Appropriate theories corresponding to each flow-induced mechanism of the droplet under shear (steady-state deformation and orientation) were employed for determining the interfacial tension, under the basis of reaching equilibrium states of deformation of the sheared drop. The calculated σ values via the drop deformation theories were checked for a wide range of viscosity ratios of binary systems conformed by silicon oils as droplets and a water solution of polyvinylpyrrolidone as continuous phase (both Newtonian), being found that σ is independent on λ. These values were compared with measurements carried out in a conventional tensiometer, using the drop volume method. The comparison showed a very good agreement between both techniques.     

Influence of Nonionic Rosin Surfactants on Surface Activity of Silica Particles and Stability of Oil in Water Emulsions

Rosin as a natural product has become a source for production of less toxic bio-surfactants to produce emulsions which are widely used in various agriculture and food products, cosmetic, and pharmaceutical industries. In this respect, a nonionic surfactant was prepared from reaction of rosin acids and rosin maleic anhydride adduct with poly(ethylene glycol) monomethyl ether 750 (MPEG 750) to produce a rosin ester (RMPEG 750). The surface activity parameters of the prepared surfactants, such as surface excess concentration (Γ _max), the area per molecule at interface (A _min), and the effectiveness of surface tension reduction, were measured to determine the micellization and adsorption characteristics of the prepared surfactants at the water/air interface. The adsorption of the prepared surfactants on the surface of either hydrophilic or hydrophobic silica particles was determined using a spectrophotometric method. Interfacial tension between water and toluene were measured to select the best condition to obtain toluene/water emulsion in the presence of modified solid silica particles. The effects of silica particle hydrophilicity and the surfactant concentrations on the surface, interfacial activity, and on the emulsion drop size were also investigated.     

How the Influence of Different Salts on Interfacial Properties of Surfactant–Oil–Water Systems at Optimum Formulation Matches the Hofmeister Series Ranking

In this work, we present the effects of salts on sodium dodecyl benzene sulfonate micellization and on the interfacial performance of a sodium dodecyl benzene sulfonate–heptane–brine system at optimum formulation, i.e., hydrophilic–lipophilic deviation (HLD) = 0. In order to do that, interfacial tension and dilational interfacial rheology properties of surfactant–heptane–water systems at optimum formulation are measured using an interfacial spinning drop tensiometer with an oscillating velocity, which can accurately measure interfacial rheology properties at both low and ultralow interfacial tensions. The brines used contain one of the following salts: MgCl₂, CaCl₂, NaCl, NH₄Cl, NaNO₃, CH₃COONa, or Na₂SO₄. We performed a one-dimensional salinity scan with each of these salts to achieve an optimum formulation. In relation to the Hofmeister series, we found that, at optimum formulation, systems with chaotropic ions (NH₄⁺, NO₃⁻) present interfaces with ultralow interfacial tensions, very low dilational modulus, and a low phase angle, whereas kosmotropic ions (Mg²⁺, Ca²⁺, SO₄⁻²) generate high interfacial tension and high rigidity monolayers. Intermediate ions in the Hofmeister series (Na⁺, CH₃COO⁻, Cl⁻) present interfaces with intermediate properties. Furthermore, according to the Hofmeister series, interfaces can be respectively ordered from higher to lower rigidity for surfactant counterions Mg²⁺ > Ca²⁺ > Na⁺ > NH₄⁺ and coions SO₄²⁻ > CH₃COO^– > Cl⁻ > NO₃⁻, which correspond to a salting-out (highest rigidity) and salting-in (lowest rigidity) effect. We observed that counterions have a more significant effect on surfactant–oil–water system properties than those that act as coions.     

驱油用聚丙烯酰胺溶液界面特性研究

使用 TRACKR全自动液滴界面张力仪测量了不同试验条件下十二烷 /聚丙烯酰胺溶液界面扩大、缩小时的流变特征及界面张力 ,开发出了用以表征液膜强度的界面黏弹性 E的测量方法。在十二烷 /聚丙烯酰胺界面形成稳定的过程中界面 (扩张 )黏弹模量不断增加 ,并逐渐达到恒定 ,其中弹性成分所占比例远大于黏性成分即 E′>E″。考察的聚合物浓度范围为 5 0～ 2 0 0 0 mg/ L ,界面黏弹模量从 1 7.6提高到 3 0 .6m N·m-1。放置 3 d后的聚合物溶液界面黏弹模量保留率为 82 .8%。实验结果表明聚合物浓度变化对界面张力影响不显著。     

Effect of wax inhibitors on pour point and rheological properties of Iranian waxy crude oil

A variety of techniques have been employed in order to reduce problems caused by the crystallization of paraffin during the production and/or transportation of waxy crude oil. Flow improvers are used extensively to increase the mobility of crude oil. In this study, the influence of the ethylene-vinyl acetate copolymer (EVA), as flow improver, with different ranges of molecular weight on the viscosity and pour point of five Iranian waxy crude oils was evaluated. Five types of Iranian waxy crude oil were selected based on their similar wax (> 10%) but different asphaltene contents. Also, the effect of asphaltene content on the performance of this flow improver was studied. The rheological behavior of these crude oils, with middle range API gravity, in the absence/presence of flow improver was studied. The rheological data cover the temperature range of 5 to 40 °C. The results indicated that the performance of flow improver was dependent on the molecular weight and the asphaltene content. For crude oil with low asphaltene, higher molecular weight flow improvers are the best additive and lower molecular weight flow improvers showed good efficiency for crude oil with high asphaltene content. Addition of small quantities of asphaltene solvents such as xylene (1 wt.%), alone or in combination with flow improver, can improve viscosity of crude oil with high asphaltene content.     

生物柴油低温流动性能的研究

生物柴油是典型的绿色能源,主要成分是脂肪酸甲酯。生物柴油的低温流动性与饱和脂肪酸甲酯的含量及分布有关,还与脂肪酸酯支链程度有关。综述了改善生物柴油低温流动性的方法,分析了降凝剂对生物柴油的降凝机理以及今后的研究方向。     

原油流动改进剂DODE-5的应用

吉林油田部分油井采出液胶质、沥青质含量高,平均洗井周期仅为20 d,严重影响油井的正常生产。2009年4月投加DODE-5型原油流动改进剂起到了良好的降粘防蜡作用。介绍了间歇加药方式加药量与加药周期的确定方法,并从延长洗井周期、降低管路能量损失、降低油井能耗3方面介绍了DODE-5型原油流动改进剂的现场应用效果。     

Modification of sago starch by graft copolymerization. Effect of reaction conditions on grafting parameters

Graft copolymerization of acrylonitrile onto sago starch was carried out by a free radical initiating process in which the ceric ion (Ce 4+ ) was used as an initiator. The reaction conditions significantly influence the graft copolymerization. The percentage of grafting, grafting efficiency and rate of grafting were all dependent on the concentration of ceric ammonium nitrate (CAN), acrylonitrile (AN), sago starch (AGU, anhydro glucose unit), mineral acid (H 2 SO 4 ) and the reaction temperature and period. The optimum yield was obtained when the concentrations of CAN, AN, AGU and H 2 SO 4 were used at 9.61×10 ?3 , 0.653, 0.152 and 0.187 mol L ?1 , respectively. The optimum temperature and reaction period were 50°C and 90 min, respectively. The rate of graft copolymerization was examined using the experimental results and the reaction mechanism. The polya1crylonitrile grafted sago starch was characterized by using FT-IR spectroscopy, DSC and SEM analysis.