Interfacial tension of edible oils in supercritical carbon dioxide

Interfacial properties essentially influence fluid‐liquid separation processes. Thereby, interfacial tension is an important parameter that is associated with mass transfer and mutual solubility of participating compounds. For this reason, interfacial tension of a virgin olive oil with a known amount of free fatty acids was measured in supercritical carbon dioxide atmosphere at 313 K and 353 K and pressures up to 40 MPa. The obtained values were compared to different oils some of which contain appreciable amounts of volatile components. In general, interfacial tension behaviour is dominated by the effect of pressure, whereas differences between oil compositions are secondary. Besides mutual solubility interfacial tension is supposed to be associated with the compressibility of the dense fluid phase. For predicting mass transfer area some general comments on the colloidal behaviour of systems containing supercritical CO₂ are made     

Interfacial Behaviour of Complex Hydrocarbon Fluids at Elevated Pressures and Temperatures

Interfacial tension is unique in the sense that it relates to the interface between two immiscible fluid phases. Hence, interfacial tension between the fluid phases can be used to infer a great deal of information about phase equilibria such as solubility, miscibility and mass transfer interactions between the two bulk fluid phases in contact. In this paper, we examine the utility of interfacial tension to characterize miscibility and mass transfer mechanisms in complex hydrocarbon fluids at elevated pressures and temperatures. This study also provides a new method to estimate the dynamic interfacial tension and miscibility by incorporating counter‐directional diffusivities into the traditional Parachor model.     

Interfacial tension measurements between α-tocopherol and carbon dioxide at high pressures

The interfacial tension of the binary system α-tocopherol/carbon dioxide was measured using the pendant drop method in the pressure range between 10 and 37 MPa at nine different temperatures: 313, 333, 343, 353, 363, 373, 383, 393, and 402 K. At every interfacial tension measurement, densities of both the liquid and the supercritical gas phase were also determined as the knowledge of these values is essential for calculating interfacial tension from the shape and size of drops. The interfacial tension decrease with rising pressure at a constant temperature and increases with increasing temperature at a constant pressure. The interfacial tension was found to be mainly a function of the mutual solubility of the two system components and of the density of pure carbon dioxide.     

气液传质过程中Marangoni对流的观测与定量分析

建立了一套气液传质装置和一套纹影系统对乙醇解吸CO₂过程中产生的Marangoni对流结构进行垂直界面方向上的观察,发现解吸过程中近界面处出现均匀分布的旋涡状的对流结构,并随时间聚合发展变大。此外还利用定量纹影法考察了传质过程中的浓度分布和界面张力梯度等信息。定量的结果表明较大的界面张力梯度位于对流胞型的边缘和中心处,驱动着界面流体的运动,并耦合浮力效应,形成了近界面环流的运动形式。这种环流运动造成了对流胞型边缘浓度较大、内部浓度小的分布,促进了相界面流体微元的更新,加强了传质过程。     

三元体系液液界面张力与溶解度的关联

本文采用界面相模型,推导出一个关联界面张力与溶解度数据的方程.经24个三元体系的检验,方程给出了满意的结果.通过引入部分互溶对的界面张力与互溶度数据所得到的修正方程可作更好的关联     

环丁砜芳烃抽提体系界面性质的研究

采用悬滴张力仪和计算机图象采集系统研究了环丁砜芳烃抽提体系的界面性质及其对传质的影响。结果表明：在存在传质的条件下，相界面存在强烈的Marangoni现象。界面张力随芳烃浓度的增加而减小，但苯、甲苯和对二甲苯等组分的变化幅度不同。非平衡液的界面张力与组分所在的相及传递方向有关，平衡液的界面张力则与芳烃初始所在的相无关。实验还表明，非平衡液产生界面扰动所需的浓度与芳烃的分配系数(即Marangini数Ma)有关。传质推动力越大，Ma越大，界面扰动的程度也越剧烈。     

THE EFFECT OF SURFACTANTS ON THE GROWTH OF UNDERPRESSURIZED, ANNULAR LIQUID JETS

The effects of surfactants on the growth of isothermal, underpressurized, inviscid, annular liquid jets are studied under both steady state and transient conditions by means of an interfacial mass transfer law which depends on the equilibrium interfacial concentration and a mass resistance parameter. Equilibrium interfacial concentrations governed by both Henry's and Sievert's solubility laws are considered. It is shown that, for mass Biot numbers larger than unity, the underpressurized jet grows until the pressure of the gases enclosed by the annular liquid jet is equal to that of those surrounding the jet, while, for mass Biot numbers less than or equal to one, the pressure coefficient increases very little. It is also shown that, in some cases and contrary to the results observed in the absence of mass transfer resistance, the time required by the annular jet to reach a steady equilibrium configuration may be shorter when the equilibrium interfacial concentration is governed by Sievert's law than when it is governed by Hennry's solubility law, particularly at low Peclet numbers and for high mass transfer resistances.     

气液传质界面湍动现象投影观察

In gas-liquid mass transfer processes,interfacial turbulence may occur due to the surface tension gradient and the density gradient produced by mass transfer near the interface.The interfacial turbulence can enhance the mass transfer since it intensifies the movement of interfacial fluid.By means of the shadowgraph optical method,the interfacial turbulence patterns vertical to the interface were observed directly in the volatilization process of binary systems.The images of the amplified interfacial turbulence showed the variation of concentration and the fluid movement under the interface.Two patterns of interfacial turbulence were observed in the experiments：plume and vortex.With the plume,the interfacial fluid moved slowly and penetrated the liquid deeply.With the vortex,the interfacial turbulence occurred in the vicinity of the liquid interface and the fluid moves quite fast.A qualitative analysis was carried out based on the mechanism of Rayleigh-Bénard convection induced by density gradient and Marangoni convection induced by surface tension gradient.     

Grenzflächenspannungsmessungen als Baustein verfahrenstechnischer Stofftransportmodellierungen

The interfacial tension is a material parameter describing the interface between two fluid phases. It is also a changing physical value in mass transfer processes beyond equilibrium. Thus, the measurement of change in interfacial tension characterizes adsorption and mass transfer processes at liquid‐liquid interfaces. The units of a pendant drop tensiometer can represent a mini mass transfer cell.     

硅氟两亲聚合物在柴油/水体系中的分水效能及机理

对4种含氟链段聚合度不同的硅氟聚合物在柴油/水体系中的分水效能进行了评价,并通过界面张力和界面黏弹性研究了其分水机理。结果表明,随着含氟链段聚合度的增加,其油水分离时间先减小后增大。含氟单体平均聚合度为16的聚合物质量浓度为0.2g/L时,在23s内实现柴油/水的完全分离。界面张力不是影响分水效能的主要因素,该类聚合物主要通过降低界面膜黏弹性实现有效分水。     

Interfacial tensions of ethanol-carbon dioxide and ethanol-nitrogen. Dependence of the interfacial tension on the fluid density—prerequisites and physical reasoning

Interfacial tensions in the systems ethanol-carbon dioxide and ethanol-nitrogen are measured. In both systems the interfacial tension decreases with increasing pressure. The interfacial tension in the system ethanol-nitrogen decreases with increasing temperature. In contrast to this, in the system ethanol-carbon dioxide at high pressures an isobaric increase in temperature provokes an increase in interfacial tension. In the system ethanol-carbon dioxide at elevated pressure the density of the carbon dioxide phase is the only influence parameter concerning the interfacial tension. This phenomena can be observed for various other systems with one near critical or supercritical component and a high solubility of this component in the liquid phase and at temperatures above the critical temperature of the gas. For this fact a physical reasoning, which is based on a new concept of partial interfacial tensions, is given. Furthermore, it is stated that the interfacial tension of fatty systems in contact with carbon dioxide has approximately the same dependence on the reduced density (ρ_r=ρ/ρ_c) of the supercritical phase as the interfacial tension of the same systems in contact with ethane. The knowledge of this fact can help to avoid experiments with ethane, which is flammable.     

Effect of interfacial velocity and interfacial tension gradient on momentum,heat and mass transfer

The effect of interfacial velocity and interfacial tension gradient on momentum, heat and mass transfer was studied theoretically. After reviewing current knowledge regarding interfacial velocity effects, the interfacial tension gradient effect is discussed as a numerical solution of the laminar boundary layer equations. The enhancement and suppression of interfacial mobility, and the rates of interphase momentum, heat and mass transfer were related to the Marangoni number. A diagram showing the effect of interfacial tension gradient on momentum, heat and mass transfer is presented.     

微通道中液-液萃取传质特性的研究

研究了在一个内径为400 μm管式直线型玻璃微通道中的液-液两相的传质特性,其中去离子水为水相, 煤油（溶质是苯甲酸）为油相, 氮气为气相。实验研究了表面张力、黏度和气体分散相对体积传质系数的影响,结果表明：在内径为400 μm的微通道内,当停留时间为15 s时微通道内的萃取已达到平衡;水相的表面张力和液体黏度显著影响微通道内的传质效率;在液-液系统中引入气相后,水油两相之间的传质效率显著增加。     

Measurement and correlation of supercritical CO2 and ionic liquid systems for design of advanced unit operations

Ionicliquids combined with supercritical fluid technology hold great promise as working solvents for developing compact processes. Ionic liquids, which are organic molten salts, typically have extremely low volatility and high functionality, but possess high viscosities, surface tensions and low diffusion coefficients, which can limit their applicability. CO₂, on the other hand, especially in its supercritical state, is a green solvent that can be used advantageously when combined with the ionic liquid to provide viscosity and surface tension reduction and to promote mass transfer. The solubility of CO₂ in the ionic liquid is key to estimating the important physical properties that include partition coefficients, viscosities, densities, interfacial tensions, thermal conductivities and heat capacities needed in contactor design. In this work, we examine a subset of available high pressure pure component ionic liquid PVT data and high pressure CO₂ - ionic liquid solubility data and report new correlations for CO₂-ionic liquid systems with equations of state that have some industrial applications including: (1) general, (2) fuel desulfurization, (3) CO₂ capture, and (4) chiral separation. New measurements of solubility data for the CO₂ and 1-butyl-3-methylimidazolium octyl sulfate, [bmim][OcSO₄] system are reported and correlated. In the correlation of the CO₂ ionic liquid phase behavior, the Peng-Robinson and the Sanchez-Lacombe equations of state were considered and are compared. It is shown that excellent correlation of CO₂ solubility can be obtained with either equation and they share some common characteristics regarding interaction parameters. In the Sanchez-Lacombe equation, parameters that are derived from the supercritical region were found to be important for obtaining good correlation of the CO₂-ionic liquid solubility data.     

Effect of Surface Tension on Hydrodynamics and Mass Transfer Coefficient in Airlift Reactors

The hydrodynamics and volumetric mass transfer coefficient play important roles in the design and scale-up of airlift reactors. The effect of surface tension on hydrodynamics and volumetric mass transfer coefficient in internal loop airlift reactors was investigated. With reduction of the surface tension of the fluid, the hydrodynamic parameters raised, namely, gas phase holdup, flow regime transition point, and interfacial area, whereas the bubble diameter as well as the liquid velocity decreased and the volumetric mass transfer coefficient increased. Empirical correlations are proposed for gas-phase holdup and volumetric mass transfer coefficient in terms of dimensionless numbers and can be applied in the design of airlift reactors.     

The marangoni effect and enhanced oil recovery Part 2. Interfacial tension and drop instability

A computer-based method is described for the determination of the interfacial tension between pendant and sessile drops in a surrounding continuous phase. This has been used to determine the effect on interfacial tension of increasing amounts of aliphatic alcohols, from methanol up to n-octanol, equilibrated between a hydrocarbon solvent (Shellsol) and water. The results indicated large decreases in interfacial tension, with n-butanol, followed by n-propanol giving the greatest reduction. Measurements were also made of the rate of change of interfacial tension during the mass transfer of 2.5% of the alcohols between phases. Changes were observed for all alcohols from ethanol to n-pentanol, the effect being greatest for transfer into water drops and out of solvent drops. Application of the linear stability theory of Sørensen to these results failed to predict the observed instability for transfer into solvent drops.     

Determination of dynamic interfacial tension in a pulsed column under mass transfer condition

Interfacial tension is an essential physical property in two-phase flow, and it changes due to the mass transfer. The measurement of dynamic interfacial tension (DIFT) in such a condition is a difficult problem. In the previous study (Zhou et al., Chem Eng Sci. 2019; 197:172–183), we presented the quantitative relation between the droplet breakup frequency function (DBFF) and interfacial tension. It is found that the DBFF is highly depended on interfacial tension. Therefore, the DBFF is a suitable parameter to quantitatively characterize the interfacial tension. Based on this concept, the DIFT in the column is determined by regression method after the DBFF under mass transfer condition is measured. It is found that the DIFT is smaller than the static interfacial tension. This result indicates that interphase mass transfer leads to decreasing of the interfacial tension. The decreasing extent of the DIFT has a positive correlation with the mass transfer flux.     

Stability Modeling of Water-Based Surfactant Covered Micro-bubble Fluids

Currently, due to the decrease in easy access to crude oil reservoirs, oil and gas industries have focused on production from heavy oil and depleted reservoirs. In recent years, micro‐bubble fluids with surfactant and polymer layers around the bubbles are investigated as a part of drilling fluids and their positive effect on the formation damage is proven. Stability of the bubbles in the fluid is very important, and the optimum surfactant and polymer types should be chosen at optimum concentrations. In this work, an attempt is made to analyze the stability of bubbles of the drilling fluid, based on the diffusive mass transfer concept. Mass transfer and interfacial mass transfer coefficients become more important when surfactant concentration gradient exists in micro‐bubble layers. Interfacial mass transfer coefficients have an important effect on mass transfer phenomena in Aphron fluids system; so, the precise selection of these coefficients results in the conformity of modeling and experiments. We can say that reducing the mass transfer rate from bubble layers will result in stable bubbles in the fluid and, thus, the efficiency of the fluid during drilling will not decrease. It is shown that the interfacial mass transfer coefficient decreases with an increase in surfactant concentration.     

表面张力对传质过程的影响

表面张力对传质过程的影响主要是影响传质界面积,当物系为正物系时,对板式塔有较小较稳定的汽泡,对填料塔和湿壁塔,有较稳定的液膜,结果使二者均有较大的传质界面积,传质效果较好;负物系的情况相反。当液体混合物的平均表面张力较小时,也有利于形成较小较稳定的汽泡,从而有利于传质。表面张力对传质过程的影响机理相当复杂,这方面的研究工作有待深入开展。     

淤浆聚合体系乙烯溶解度及传质系数测定

对采用淤浆聚合法聚合生成超高相对分子质量聚乙烯过程中的传质过程进行了研究,考察了压力、温度对平衡溶解度的影响以及搅拌速率和物料对传质系数K_L的影响规律。结果表明：乙烯溶解度随气相中乙烯压力的升高而线性增加,气液平衡关系符合亨利定律;温度升高,气体溶解度减小;搅拌速率增大,相应的传质系数线性增大;加入聚乙烯颗粒会使吸收速率降低,物料量与传质系数基本呈反比例关系。