Prediction of multicomponent liquid adsorption using excess quantities. III. Calculations for the liquid/air interface

The utilization of excess quantities as the basis of a thermodynamic approach can simplify the prediction of multicomponent data from binary ones. Whereas in Part II the excess formalism was applied to the prediction of liquid phase adsorption on solids, in this paper, the liquid/air interface is investigated. In order to show the generality of the suggested approach, thermodynamic equations are developed in analogy to Part II. Surface tensions are predicted by different excess models and compared with experimental data. From predicted surface tensions, ternary adsorption isotherms on the liquid/air interface are calculated.     

Prediction of multicomponent liquid adsorption using excess quantities. II. Calculations for the liquid/solid interface

The utilization of excess quantities as the basis for a thermodynamic approach can simplify the prediction of multicomponent liquid adsorption from binary data. A new method for predicting liquid adsorption on solids is suggested, which is different from the existing equations with respect to the theoretical background and formulation. The applicability of the new model is tested with three ternary adsorption systems. The predicted surface excesses are discussed and compared with experimental ones and with those of other prediction models in the literature. The accordance between measured and predicted ternary data is convincing.     

Correlation between excess adsorption data measured for solvent mixture/adsorbent systems and RM values obtained for different solutes chromatographed in binary mobile phases

This paper concerns the application of excess adsorption isotherms, measured for solvent mixture/adsorbent systems, to the characterization of TLC data. For this purpose the excess adsorption isotherms for three liquid mixtures: cyclohexane/ benzene, benzene/acetone, and carbon tetrachloride/ethyl acetate on silica gel at 20°C have been measured. These mixtures have been used as binary mobile phases in TLC measurements. It has been shown for a given solute in binary mobile phase that the quantity R_M is a simple function of the excess adsorption. Parameters of this function have been used to characterize chromatographic systems with binary mobile phases.     

Interpretation of adsorption excess quantities: the absolute surface excess concentration

The concept of absolute surface excess of adsorption accounts for the expansion of compression of the volume of a pure liquid under the influence of a solid surface. The absolute surface excess amount of substance can prove to be a powerful measure of the adsorption at a solid/binary liquid interface, too. The contributions of the composition and volumetric effects to the adsorption can be separated from each other in this concept, and both of them are experimentally accessible quantities.     

Sorption of binary liquid mixtures on polymer networks Part I. Determination of surface excess isotherms and free energy functions

Two groups of polymer networks (polymer resins) are investigated by selective liquid sorption fromn-propanol-water mixtures. Group 1 consists of gel polymerized polar (hydrophilic) ion exchangers which swell in the binary liquid mixture. Group 2 consists of non-polar, non-swelling, macroporous resins. The free energy isotherms accompanying the sorption processes are calculated from the excess isotherms and the bulk activities. The adsorption excess free energies reveal the differences in polarity of the polymer network.     

Adsorption volume and absolute adsorption: 2. Adsorption from liquid phase

A critical analysis of the isotherms of excess and absolute adsorption, as well as the adsorption space performed in the first part [1] is continued; however, as applied to the equilibrium physical adsorption from the liquid phase. The correct method is proposed for evaluating the adsorption volume of solid adsorbents with an arbitrary structure by the isotherm of excess adsorption of binary mixture of liquids. This method is successfully tested for nine different adsorption systems.     

Calculation of immersion enthalpy data from adsorption isotherms

The thermodynamic equations for the calculation of binary and ternary immersion data in excess formalism are presented. Immersion enthalpies and entropies of the n-hexane/n-octane, n-octane/n-tetradecane and n-hexane/n-tetradecane binary mixtures as well as the n-hexane/n-octane/n-tetradecane ternary mixture on activated carbon are calculated from the temperature dependence of adsorption isotherms. In order to evaluate the quality of the calculations, the calculated immersion enthalpies of the binary mixtures on activated carbon are compared with those that were measured calorimetrically. It is shown that phenomenological thermodynamics can be used successfully to predict calorimetric data on the basis of adsorption excess isotherms.     

Correlation and prediction of ternary excess enthalpy data

Methods for predicting ternary excess enthalpies from excess enthalpy data for the three binary mixtures involved are examined and tested for forty-two sets of ternary data. In order to study the relation between the performance of the methods and the characteristics of the components in the mixture, the sets of data were classified into four groups according to the chemical nature of their components. The asymmetric equations proposed by Scatchard, Toop, and Hillert are shown to provide accurate predictions. The ratio of the standard deviations between experimental and predicted excess enthalpies and the maximum absolute value of this magnitude is 0.05 or less for most of the systems. These equations are asymmetric with respect to the numbering of components. A rule is given for selecting which component is to be designated as component 1 for systems showing endothermic mixing, exothermic mixing, or a combination of endothermic and exothermic mixing. Correlation methods are also examined and a partial differential approximant is proposed to represent the ternary contribution to the excess enthalpy.     

Algebraic and geometric interpretations of adsorption excess quantities

The algebraic methods of Hansen and Goodrich and the geometric methods of Motomura, Good and Everett were applied to define and investigate adsorption excess quantities at a solid/binary liquid interface. Both single-plane and two-plane geometric constructions were found to be consistent with the algebraic method. Relations between the relative, molar reduced and volumetric reduced areal excess concentrations and the amounts of components actually present in the interfacial layer are discussed.     

内压与液体混合物的超额焓

本文在前文提出的通用液体混合模型的基础上, 对其中某些近似假设和混合规则进行了合理的修正, 从而得到了一个液体混合物的超额焓与组分内压间的关系式。对于正常液体混合物, 式中有两个可调的修正系数, 对于醇-烃混合物, 则有三个可调参数。对十六个二元液体混合物的计算结果表明, 关系式不仅能准确地描述一般液体混合物的超额焓随浓度的变化规律, 而且亦适用于具有S型H^E-x曲线的复杂液体混合物。     

Adsorption of styrene at a binary solution-gas interface

The surface tension isotherms of styrene solutions in 2-propanol-water solvents are obtained experimentally. Isotherms of excess and absolute adsorption at the liquid-gas interfaces are also obtained. A thermodynamic model for the adsorption of styrene from 2-propanol-water binary solvent at the solutiongas interfaces is proposed on the basis of the stoichiometric approach. The isosteric adsorption heats are calculated using the experimental isotherms of surface tension and excess adsorption of styrene from 2-propanol-water binary solvent, and it is shown that the formation of the surface layer occurs according to a mechanism combining the processes of displacement adsorption between molecules of the components of the solvent, styrene, and 2-propanol.     

Structural analysis of organic interfacial layers by ellipsometry

Ellipsometry has ‘come of age’ as a technique for the analysis of problems related to colloid and interface science. It has advanced far beyond applications of measuring film thickness or optical constants — although these remain important uses. Studies of the structure of polymers at the solid/liquid interface have been advanced significantly by the realisation of Fourier transform ellipsometry. Another important achievement has been the calibrated measurement of the dynamic surface excess at the flowing surface of a liquid jet. The uses of ellipsometry to study critical adsorption in binary liquids and to measure the width of liquid/liquid interfaces are also noteworthy. An important development is the use of infrared — rather than visible — light, which opens up numerous possibilities for the simultaneous structural and chemical interrogation of interfaces non-invasively.     

Topological investigations of molar excess volumes of quinoline with alkanols

Excess volumes V ^E of binary liquid mixtures of quinoline with alkanols have been determined from densities at 30°C as a function of composition. The excess volumes are negative over the whole mole fraction range for all the mixtures and decrease with increasing length of alkanol (C₁–C₁₀). The V^E data have been analyzed in terms of an approach which uses graph theoretical connectivity parameters of the third degrees for two components. The analysis gives information regarding associated species in the pure state and in the mixture. It is suggested that, in the mixture state, no change occurs in the association of alkanols.     

Adsorption from binary solvent mixtures onto silica gel by HPLC frontal analysis

Summary The chromatographic technique of frontal analysis is applied to measuring adsorption from binary liquid mixtures by silica gel. The complete adsorption isotherm of a solvent mixture is obtained by measuring the break-through curves for a series of small concentration steps of the mobile phase. This method offers a direct way to determine the composition of the stationary phase in liquid-solid chromatography with mixed mobile phases. The surface excess isotherms of all binary systems formed by benzene, cyclohexane, and 1,2-dichloroethane, at the solution-silica gel interface at 25 °C are presented. The data of the three systems are shown to be thermodynamically mutually consistent.     

An interpretative model for the anomalous behavior of some excess properties in mixed liquid systems: a relationship between excess molar volumes and excess compressibilities in strongly self-aggregated fluids

A simple theoretical model based on the hole theory of the liquid state has been developed in order to find a relationship between the excess molar volume and the excess compressibility of a two-component fluid. The model has been extended to investigate strongly associating fluids dissolved in an apolar solvent. Such a model nicely explains our recent results obtained from a Brillouin scattering study of the nonideal mixture between tert-butyl alcohol and 2-2(') dimethyl butane. Its validity, however, seems to be rather general and it could be usefully applied to rationalize the excess properties of several nonideal binary fluid mixtures.     

Ethanol, acetic acid, and water adsorption from binary and ternary liquid mixtures on high-silica zeolites

Adsorption isotherms were measured for ethanol, acetic acid, and water adsorbed on high-silica ZSM-5 zeolite powder from binary and ternary liquid mixtures at room temperature. Ethanol and water adsorption on two high-silica ZSM-5 zeolites with different aluminum contents and a high-silica beta zeolite were also compared. The amounts adsorbed were measured using a recently developed technique that accurately measures the changes in adsorbent/liquid mixture density and liquid concentration. This technique allows the adsorption of each compound in a liquid mixture to be measured. Adsorption data for binary mixtures were fit with the dual-site extended Langmuir model, and the parameters were used to predict ternary adsorption isotherms for each compound with reasonable accuracy. In ternary mixtures, acetic acid competed with ethanol and water for adsorption sites and reduced ethanol adsorption more than it reduced water adsorption.     

Symmetrization of excess Gibbs free energy: A simple model for binary liquid mixtures

A symmetric expression for the excess Gibbs free energy of liquid binary mixtures is obtained using an appropriate definition for the effective contact fraction. We have identified a mechanism of local segregation as the main cause of the contact fraction variation with the concentration. Starting from this mechanism we develop a simple model for describing binary liquid mixtures. In this model two parameters appear: one adjustable, and the other parameter depending on the first one. Following this procedure we reproduce the experimental data of (liquid + vapor) equilibrium with a degree of accuracy comparable to well-known more elaborated models. The way in which we take into account the effective contacts between molecules allows identifying the compound which may be considered to induce one of the following processes: segregation, anti-segregation and dispersion of the components in the liquid mixture. Finally, the simplicity of the model allows one to obtain only one resulting interaction energy parameter, which makes easier the physical interpretation of the results.