Analysis of dielectric relaxations of w/o emulsions in the light of theories of interfacial polarization

An attempt is made to apply dielectric theories of interfacial polarization to observations of dielectric relaxations for W/O emulsions. Approximate formulas for disperse systems in a W/O type were derived from the two theories: one proposed by Maxwell and Wagner for dilute disperse systems of spherical particles, and the other developed by Hanai for concentrated disperse systems. Dielectric measurements were carried out on concentrated W/O emulsions prepared from kerosene and distilled water or KCl aqueous solutions by minimal use of emulsifiers. Marked dielectric relaxations were observed with the emulsions, the dielectric parameters having been determined to characterize the relaxation data. Phase parameters such as relative permittivity, electric conductivity and volume fraction of the disperse phase were evaluated from the dielectric parameters by use of the approximate formulas of the respective theories. The phase parameters evaluated and the frequency dependence of complex permittivity of the W/O emulsions deduced from the theory for concentrated disperse systems are in excellent agreement with the observed data in comparison to that for dilute disperse systems. It is concluded that the dielectric relaxations due to the interfacial polarization of disperse systems of spheres are explained satisfactorily by the theory for concentrated disperse systems.     

Electrokinetic sonic amplitude method as applied to studying adsorption of high-molecular-mass compounds at interfaces

It is shown that the regularities of the adsorption of high-molecular-mass compounds on particle surfaces in disperse systems can be studied by the electrokinetic sonic amplitude method. Procedures are developed for calculating parameters of polymer adsorption layers and the quantitative analysis of their structure. The parameters of the adsorption layers are calculated by the example of a hydrophilic polymer, ethyl-hydroxyethylcellulose, and hydrophilic particles of titanium dioxide and iron oxide dispersed in aqueous disperse systems subjected and nonsubjected to an intense mechanical treatment. The treatment of the disperse systems in the field of intense wave vibrations is found to enhance the adsorption interaction.     

Concentration factor and rheology of aqueous titanium dioxide dispersions

The rheological properties of aqueous titanium dioxide dispersions have been studied by rotational viscometry. It has been established that the studied disperse systems are highly structured, and their degree of structuring dramatically increases with the volume fraction φ of the solid phase. At solid phase contents φ ≥ 0.164, the breakage of the disperse structure is accompanied by the appearance of local discontinuities and an abnormal dependence of viscosity on shear stress. The results obtained have been analyzed in terms of the Uriev theory of aggregated systems. The radii of aggregates and maximum solid phase content φ_m that corresponds to the formation of a continuous disperse structure under the conditions of dynamic impact have been calculated.     

Influence of physical properties and operating parameters on hydrodynamics in Centrifugal Partition Chromatography

Besides the selection of a suitable biphasic solvent system the separation efficiency in Centrifugal Partition Chromatography (CPC) is mainly influenced by the hydrodynamics in the chambers. The flow pattern, the stationary phase retention and the interfacial area for mass transfer strongly depend on physical properties of the solvent system and operating parameters. In order to measure these parameters we visualized the hydrodynamics in a FCPC-chamber for five different solvent systems with an optical measurement system and calculated the stationary phase retention, interfacial area and the distribution of mobile phase thickness in the chamber. Although inclined chambers were used we found that the Coriolis force always deflected the mobile phase towards the chamber wall reducing the interfacial area. This effect increased for systems with low density difference. We also have shown that the stability of phase systems (stationary phase retention) and its tendency to disperse increased for smaller values of the ratio of interfacial tension and density difference. But also the viscosity ratio and the flow pattern itself had a significant effect on retention and dispersion of the mobile phase. As a result operating parameters should be chosen carefully with respect to physical properties for a CPC system. In order to reduce the effect of the Coriolis force CPC devices with greater rotor radius are desirable.     

煤液化沥青分析表征及结构模型

对从煤液化残渣中萃取出的沥青类物质进行了固体13C-CP/MAS NMR分析、元素分析、红外光谱分析(FT-IR)和光电子能谱(XPS)分析,得到煤液化沥青的芳香结构单元信息及相关结构参数信息。结果表明,煤液化沥青芳香桥碳与周碳之比为0.115,芳香碳原子的存在形式以苯结构为主;脂肪结构多以甲基和环状亚甲基形式存在;氧主要以羰基、酯基的形式存在;氮主要以吡咯的形式存在。利用结构参数和分析表征结果构建了煤液化沥青的大分子结构模型,并运用13C-NMR预测软件ACD/CNMR Predictor计算了煤精制沥青大分子结构模型的13C化学位移。根据计算结果对大分子结构模型进行了修正,获得了与实验谱图吻合较好的大分子结构模型。     

A small angle neutron scattering study of the adsorbed asphaltene layer in water-in-hydrocarbon emulsions: structural description related to stability

We have developed a specific protocol to study with SANS measurements, the structure of the interfacial film layer in water-in-oil emulsions stabilized by asphaltene. Using the contrast matching technique available for neutron scattering, we have access to both the composition and the quantity of interface. The results obtained give us a view of the asphaltene aggregates in the interfacial film, which are structured as a monolayer and show a direct correlation between the size of asphaltene aggregates in solution and the thickness of the film layer. The organization of the interface has been studied as a function of several parameters such as the quantity of resins, i.e., the size of aggregates, the pH of the aqueous phase, and the aging time of the emulsions and the consequences of these variations on the macroscopic stability of these emulsions. We show that the key parameter for the stability is the inter-asphaltene aggregate interaction inside the film layer. Changing the attractive/repulsive balance between the aggregates in the film at the microscopic scale, by changing the aggregate's size or the aggregate's ionization, has a direct incidence on the quantity of water recovered after centrifugation: the stronger the attraction between aggregates in the film, the more stable the emulsion is.     

Computer simulation of the structure formation and disruption processes in the solid-liquid disperse systems

Results of the computer simulation of solid-liquid disperse systems are reported. Main regularities of the formation and disruption of the internal structure of such systems are demonstrated under static and dynamic conditions (including the combination of shear and orthogonal vibrations). The effect of the character of the interaction of dispersed phase particles, as well as of a number of parameters concerning the type and intensity of external actions on the behavior of disperse systems is shown. The possibility of the regulation of the character of microstructure and rheological properties of disperse systems by the combination of shearing and orthogonal vibrations is illustrated.     

Experimental and modeling studies on the asphaltene precipitation in degassed and gas-injected reservoir oils

The asphaltene precipitation in a Chinese crude oil has been studied experimentally under normal-pressure and high-pressure conditions. The onset of asphaltene precipitation was detected by using light transmission method. Normal pentane and hexane were used as precipitating agents for studying the onset of asphaltene deposition in (asphaltene+toluene) and (degassed crude oil+toluene) mixtures under normal pressure. A total of eighteen sets of normal pressure data have been measured. For high-pressure gas-injected reservoir oil systems, the effects of injection-gas concentration, temperature, pressure, and the presence of a coexisting aqueous electrolyte (brine) phase on the amount of asphaltene deposition were studied and a total of seven sets of data have been measured. In the modeling part, a modified Hirschberg solubility model and a new solubility parameter correlation were proposed. The model parameters determined from low-pressure precipitation data have been successfully extended to high-pressure systems. Extensive tests vs. the data measured in this work and literature data show that the proposed model is capable of giving reasonable calculation results for most cases.     

Photoinduced phase separation

A novel approach of photoinduced phase separation has been demonstrated with a photolabile anionic surfactant, mixed with an inert nonionic surfactant in the presence of salting-out electrolyte. Breakdown of the photolyzable surfactant results in hydrophobic photoproducts, which are emulsified by the remaining inert surfactant; added electrolyte resolves the emulsion into macroscopic oily and aqueous phases. The initial micellar systems can disperse an insoluble additive marker dye (shown), which may be spatially segregated from the aqueous environment by the action of UV light.     

石油沥青质的NMR测定及其模型分子推测

从6种不同原油中分离提取了正己烷不溶的沥青质，测定了沥青质的1H NMR(Nuclear Magnetic Resonance)和13C NMR谱，从不同类型氢和碳原子的质量分数计算得到了一系列平均结构参数，结合相对分子质量测定和元素分析，给出了沥青质基本结构单元的平均分子式，推测了模型分子的结构。结果表明，沥青质的基本结构单元可以用稠环芳烃连接环烷烃和烷基侧链并含氧、氮和硫等杂原子的单元表示，结构单元之间形成缔合体，缔合数为4～6。     

聚苯乙烯/顺丁橡胶共混过程中的相结构

利用激光背散射装置结合密炼机对聚合物共混过程进行了在线分析．以典型完全不相容体系聚苯乙烯／顺丁橡胶为共混体系，对不同共混速度下结构参数随共混时间及共混条件如剪切速率等的变化进行了详细讨论．利用扫描电镜与激光背散射在线分析对聚合物共混过程结构参数变化进行了比较，结果显示聚苯乙烯／顺丁橡胶共混物处于熔融态与处于固态时结构基本相同．     

多元气-液-固复杂体系相平衡

石油流体中含有气相、液相及可能遇到的固相包括水合物、石蜡和沥青质等,涉及多元气-液-固复杂体系的相平衡问题.为防止这些沉积物堵塞造成安全隐患,需要确定水合物、石蜡、沥青质沉积起始条件以及沉积量.本文针对化学热力学理论在含水合物、石蜡和沥青质的多元-多相平衡研究中的应用进行了综述.水合物相平衡模型较为成熟,主要有两类,其一为基于等温吸附理论的van der Waals-Platteeuw型热力学模型;其二为基于双过程水合物生成机理的Chen-Guo水合物热力学模型.石蜡沉积一般采用活度系数法、状态方程法及多固相模型描述.沥青质絮凝、沉积则可采用溶解度参数模型、状态方程法、胶体模型和标度理论模型进行计算.同时对多元气-液-固复杂体系的相平衡研究发展方向进行了展望.     

Electrical Properties of Chain Microstructure Magnetic Emulsions in Magnetic Field

The work deals with the experimental study of the emulsion whose dispersion medium is a magnetic fluid while the disperse phase is formed by a glycerin-water mixture. It is demonstrated that under effect of a magnetic field chain aggregates form from the disperse phase drops. Such emulsion microstructure change affects its macroscopic properties. The emulsion dielectric permeability and specific electrical conductivity have been measured. It is demonstrated that under the effect of relatively weak external magnetic fields (～1 kA/m) the emulsion electrical parameters may change several fold. The work theoretically analyzes the discovered regularities of the emulsion electrical properties.     

胜利超稠油的乳化降黏机理研究

研究了胜利油田滨南超稠油单56-4X4高黏的内在原因。油品性质分析结果表明,影响其高黏度的主要因素有两个:胶质、沥青质的总含量超过30%;有机杂原子O、N、S及过渡金属Ni等形成的配位络合物增加了沥青质分子的内聚力。实验筛选出的降黏剂OP-10对该超稠油降黏率高达99.59%。通过FT-IR、SEM、分子量和偶极矩等分析对比了降黏剂作用前后胶质、沥青质的结构性质变化,结果表明,OP-10使胶质、沥青质的氢键缔合作用减弱,部分拆散沥青质的堆积结构,从而使胶质、沥青质的分子量和偶极矩减小,分析得到降黏剂分子能渗透及分散胶质、沥青质的堆砌聚集体。偏光显微镜对乳状液及蜡晶微观形态的分析表明,降黏剂OP-10使超稠油乳状液由W/O型反相为O/W型而起到降黏作用;使蜡晶的聚集形态由细小均匀转变为尺寸较大的絮凝体,破坏蜡晶的三维网络结构,促进稠油黏度的下降。     

Studying the curing of epoxyamine mixtures via dynamic light scattering and differential scanning calorimetry

The curing of epoxy oligomers with different structures and reactivity using an aliphatic amine curing agent was studied and quantitatively characterized by the methods of dynamic light scattering and differential scanning calorimetry. The presence of disperse phase in the initial reagents, as well as in the reacting systems is established. It is shown that the particles of the disperse phase are involved in the process of curing even in the early stages. By changing the width of the devitrification region, the change in the molecular homogeneity of epoxyamine systems during curing is estimated.     

Electrostatic Repulsion in Concentrated Disperse Systems

Electrostatic interactions are considered in the framework of the cell model to predict the osmotic pressure in concentrated disperse systems. A procedure was developed to represent the osmotic pressure as a function of two parameters, namely, the dispersed phase volume fraction and the electric potential attributed to the interface between the continuous and dispersed phases. The procedure is based on a general formula which was derived to express the electrostatic contribution to the osmotic pressure through the electric potential at the cell boundary. The potential of the cell boundary is predicted from the solution of the Poisson-Boltzmann problem which was specified for the cell model approach. The Poisson-Boltzmann problem is solved by a perturbation technique using a normalized interface potential as the perturbation parameter. Three leading terms were obtained in the expansion of the osmotic pressure in terms of the normalized interface potential. Two options for the formation of the interface electric potential are discussed in the analysis of the interface potential dependency on the volume fraction of the dispersed phase. The first one is associated with the difference between the individual ionic distribution coefficients characterizing the equilibrium ratio between the concentrations in the bulk of the constituent phases. The second one deals with preferential adsorption of the carriers having a given electric charge sign. The dependency of the osmotic pressure on the system parameters is discussed and interrelated with other relevant theories. Special discussion is presented concerning the theory's application for the study of hydrocarbon disperse systems, e.g., water-in-oil emulsions. Copyright 2001 Academic Press.     

Status of cross-flow membrane emulsification and outlook for industrial application

Cross-flow membrane emulsification has great potential to produce monodisperse emulsions and emulsions with shear sensitive components. However, until now, only low disperse phase fluxes were obtained. A low flux may be a limiting factor for emulsion production on a commercial scale. Therefore, the effects of membrane parameters on the disperse phase flux are estimated. Besides, the effects of these parameters on the droplet size and droplet size distribution are qualitatively described. Wetting properties, pore size and porosity mainly determine the droplet size (distribution). Membrane morphology largely determines the disperse phase flux. As an example, industrial-scale production of culinary cream was chosen to evaluate the required membrane area of different types of membranes: an SPG membrane, an -Al₂O₃ membrane and a microsieve. Due to the totally different morphologies of these membranes, the fraction of active pores is 1 for a microsieve and is very low for the other membranes. The choice of the optimal membrane did not depend on the production strategy: either to produce large quantities or to produce monodisperse emulsions, the best suitable was a microsieve with an area requirement of around 1 m². In general, the total membrane resistance should be low to obtain a large disperse phase flux. In contrast, the membrane resistance should be high to obtain monodisperse emulsions when using membranes with a high porosity.     

Understanding the fluid phase behaviour of crude oil: Asphaltene precipitation

We present a simplified but consistent picture of asphaltene precipitation from crude oil from a thermodynamic perspective, illustrating its relationship to the familiar bubble curve via the calculation of constant-composition p-T phase diagrams that incorporate both the bubble curve and the asphaltene precipitation boundary. Using the statistical associating fluid theory (SAFT) we show that the position of the precipitation boundary can be explained using a very simple fluid model including relatively few components. Our results support the view that the precursor to asphaltene precipitation is a liquid-liquid phase separation due to a demixing instability in the fluid. Moreover, the bubble curve for these systems is seen to represent a boundary between regions of two-phase (liquid-liquid) and three-phase (vapour-liquid-liquid) equilibria.     

ELECTROCHEMICAL PROPERTIES OF ASPHALTENE PARTICLES IN AQUEOUS SOLUTIONS

The electrical properties of colloidal asphaltene/water solution interface were determined by carrying out the potentiometric titration and electrokinetic measurements. Asphaltenes in aqueous solutions exhibit typical organic colloid properties i.e. surface charge and electrophoretic mobility. It was considered that the surface charge at the asphaltene particles is a result of protonation and dissociation reactions of surface functional groups. On the base of the surface charge density data vs. pH the surface reaction constants were calculated by numerical method. The agreement of these values with calculated ones, on the base of ζ potential data, is noticeable.

The characteristic feature of the investigated systems is the maximum, appearing on the curve ζ potential vs. electrolyte concentration. This behaviour is explained by _”hair layer ” structure of the asphaltene surface     

Properties of Langmuir Surface and Interfacial Films Built up by Asphaltenes and Resins: Influence of Chemical Demulsifiers

The influence of chemical additives on asphaltene films on water surface and at oil/water interface is studied by means of the Langmuir technique. It was found that some demulsifiers of high molecular weight alter the asphaltene film on water surface in the same way as the resin fraction, i.e., increasing the compressibility of the film which results in a reduced film rigidity. The films that build up at the oil/water interface in model oil systems, containing naturally occurring surfactants, are studied during compression. In this system chemical additives of high molecular weight totally prevent formation of a rigid film at the interface. Adding resins to the bulk phase together with asphaltenes hamper the adsorption of the heavy fraction.