A “free volume” model of permeation of gas and liquid mixtures through polymeric membranes

A recent “free volume” model of gas permeation (3) has been extended to the transport of gas mixtures through nonporous polymeric membranes. The present model assumes that the rates of transport of the components of a mixture depend on the free volume of the gas-polymer system, and that the effect of these components on the free volume is additive. The latter assumption limits the model to relatively dilute systems, with total penetrant concentrations of perhaps less than 0·2 volume-fraction. The prediction of permeation fluxes and permeability coefficients requires the knowledge of specified free-volume parameters which can be determined from measurements of diffusion coefficients and viscosities of the pure penetrant-polymer systems. When the systems are sufficiently dilute to obey Henry's law, the permeability coefficients for the components of a gas mixture can be predicted using only permeability measurements with the pure components. The extended free-volume model can be applied also to the permeation of liquid mixtures. The theoretical predictions are compared with the results of several experimental studies, and the potential usefulness and limitations of the model are discussed.     

Unified equation of state based on the lattice fluid theory for phase equilibria of complex mixtures part II. Application to complex mixtures

In part I of the present article [Yoo et al., 1995], new rigorous and simplified lattice-fluid equations of state (EOS) were derived and their characteristic features of the molecular thermodynamic foundation were discussed by applying to pure fluids. In this part II, both EOSs were extended to various phase equilibrium properties of mixtures. Comparison of the models with experimental mixture data ranges from density, to equilibria of vaporliquid, vapor-solid and liquid-liquid phases for nonpolar/nonpolar, nonpolar/polar, polar/polar mixtures. Both models were also applied to supercritical fluid phase equilibria and activities of solvents in polymer solutions. With two temperature dependent parameters for pure compounds and one temperature-independent binary interaction energy parameter for a binary mixtures, results obtained to date illustrated that both EOSs are quantitatively applicable to versatile phase equilibria of mixtures over a wide range of temperatures, pressures and compositions.     

由各向同性双势能测定含有CO2的稀二元混合物的传输性质简

The present work is concerned with extracting information about intermolecular potential energies of binary mixtures of CO2 with C2H6, C3H8, n-C4Hlo and iso-C4Hlo, by the usage of the inversion method, and then predicting the dilute gas transport properties of the mixtures. Using the inverted pair potential energies, the Chap- man-Enskog version of the kinetic theory was applied to calculate transport properties, except thermal conductivity of mixtures. The calculation of thermal conductivity through the methods of Schreiber et al. and Uribe et al. was discussed. Calculations were performed over a wide temperature range and equimolar composition. Rather accurate correlations for the viscosity coefficients of the mixtures in the temperature range were reproduced from the pre- sent unlike intermolecular potential energies. Our estimated accuracies for the viscosity are within ±2%. Acceptable agreement between the predicted values of the viscosity and thermal conductivity with the literature values demon- strates the predictive power of the inversion scheme. In the case of thermal conductivity our results are in favor of the preference of Uribe et al.＇s method over Schreiber et al.＇s scheme.     

MOLECULAR PRINCIPLE OF CORRESPONDING STATES FOR VISCOSITY AND THERMAL CONDUCTIVITY OF FLUID MIXTURES

Conformal solution theory is developed for the viscosity and thermal conductivity of fluid mixtures. The procedure involves expanding the transport coefficient for the mixture about the value for an ideal solution, using groupings of the potential parameters and molecular mass as expansion coefficients. The parameters for the ideal solution are chosen so as to annul the first-order term in this expansion, thus encouraging rapid convergence. This yields mixing rules (similar to those of the van der Waals 1 theory for thermodynamic properties) for the potential parameters and molecular mass of the reference fluid. Reference fluid properties are obtained from pure fluid corresponding states correlations

By making calculations for dilute gas mixtures and comparing with Chapman-Enskog theory, it is found that the first-order theory works well for mixtures of quite widely different energy parameters (ε) and molecular masses; it is more sensitive to the size difference of the molecular components, however. For cryogenic liquid mixtures composed of simple liquids good results are obtained using two-parameter corresponding states for the reference fluid. For polyatomic fluids it is necessary to use a three-parameter corresponding states approach for the pure fluids. A method of introducing a third parameter, while retaining the simplicity of having only two independent variables, is used for such fluids. Good results are obtained for a variety of binary mixtures. The method is of particular value for multicomponent fluids. Thus, without fitting any parameters from ternary data the theory predicts viscosities for the system carbon tetrachloride/n-hexane/benzene over the full composition range with a standard deviation of only 1.69%.     

MOLECULAR PRINCIPLE OF CORRESPONDING STATES FOR VISCOSITY AND THERMAL CONDUCTIVITY OF FLUID MIXTURES

Conformal solution theory is developed for the viscosity and thermal conductivity of fluid mixtures. The procedure involves expanding the transport coefficient for the mixture about the value for an ideal solution, using groupings of the potential parameters and molecular mass as expansion coefficients. The parameters for the ideal solution are chosen so as to annul the first-order term in this expansion, thus encouraging rapid convergence. This yields mixing rules (similar to those of the van der Waals 1 theory for thermodynamic properties) for the potential parameters and molecular mass of the reference fluid. Reference fluid properties are obtained from pure fluid corresponding states correlations

By making calculations for dilute gas mixtures and comparing with Chapman-Enskog theory, it is found that the first-order theory works well for mixtures of quite widely different energy parameters (ε) and molecular masses; it is more sensitive to the size difference of the molecular components, however. For cryogenic liquid mixtures composed of simple liquids good results are obtained using two-parameter corresponding states for the reference fluid. For polyatomic fluids it is necessary to use a three-parameter corresponding states approach for the pure fluids. A method of introducing a third parameter, while retaining the simplicity of having only two independent variables, is used for such fluids. Good results are obtained for a variety of binary mixtures. The method is of particular value for multicomponent fluids. Thus, without fitting any parameters from ternary data the theory predicts viscosities for the system carbon tetrachloride/n-hexane/benzene over the full composition range with a standard deviation of only 1.69%.     

Phase behavior of laundry surfactants in polar solvents

Laundry surfactants are usually mixtures of ionic and nonionic detergents that exhibit a complex phase behavior. Here the ternary phase behavior of an isotropic and a liquid crystalline (LC) surfactant mixture has been examined in water/solvent systems. The size of the LC area in the ternary phase diagram was correlated to solvent parameters including the dielectric constant and the Gordon cohesiveness parameter. The Gordon parameter was found to have a linear relationship with the amount of solvent needed to go from an LC to an isotropic state over a wide range of solvents from polar to apolar. For solvents in which no surfactant aggregation (micellar or inverted micellar) is expected, the size of the LC area is linear with the reciprocal of the dielectric constant of the solvent. On diluting practical detergent liquids with water, a large LC area can be avoided by using solvents with a relatively low dielectric constant and with a relatively low molecular weight. The aggregated state of the surfactant mixtures in the isotropic regions of the phase diagram was studied using the solvatochromic fluorescent probe Nile Red. In the water corner of the phase diagram, the surfactants are aggregated into micelles. In strongly polar solvents, such as glycerol, ethylene glycol, formamide, and ethanolamine, the surfactants are also aggregated into micelles. In somewhat less polar solvents, such as methanol, ethanol, and t-butanol, the surfactant molecules are randomly distributed. In the surfactant-rich corner of the phase diagram of the isotropic mixture, the surfactant forms inverted micelles. An inverted micelle-to-micelle transition could be observed on dilution in ethylene glycol as a discontinuity in the trend of the Nile Red fluorescence maxima.     

Transport properties of simple non polar binary liquid mixtures

Theorems of corresponding states for predicting the temperature and density dependence of liquid mixture transport properties are presented. The technique is tested for thirteen systems of spherical molecules (eight cryogenic mixtures, and five others) in which viscosity is predicted within 3%. For cryogenic mixtures, temperatures range from the triple point to temperatures close to the critical. In the present method, the only quantities required are pair potential parameters between like pair interactions, as determined from gas phase viscosity measurements, and pure component data. The lack of accurate measurements of thermal conductivity and diffusivity (mutual or self diffusion coefficients) for mixtures of spherical molecules⁽¹⁾ does not make it possible to test the present theory of those transport properties.     

USING THE GROUP-INTERACTION CONTRIBUTION APPROACH (GIC) IN MIXTURES 1. Prediction of Azeotropic Parameters

We have demonstrated the capability of the recently reported Group-Interaction Contribution Approach (GIC) (Pardillo-Fontdevila, 1997a) for predicting mixture properties. Up to day GIC approach has been reported exclusively for estimating pure-component properties. As a result: (1) it is reported a new approach for estimating mixture properties without the use of the Analytical-Solution-of-Groups Theory and (2) new models have been met for estimating azeotropic parameters in binary mixtures.

New models reported, based on GIC, distinguish between isomers in mixtures. These models give better estimates of the azeotropic parameters if estimates are compared with those obtained by the same equation but using the well-known Group Contribution method.

Estimation models reported in this work do not require of correlation equations for pure-component vapour pressures, as well as any equation for activity or fugacity coefficients. No algorithm is necessary for fitting equilibrium and azeotropic points     

Modified free-volume model for pervaporation of water/ethanol mixtures through membranes containing hydrophilic groups or ions

The free-volume model for pervaporation has been modified by considering the polar path, in order to apply the model to membranes containing hydrophilic groups. The free-volume parameters were determined by inverse gas chromatography. For the polyacrylonitrile (PAN) membrane, the transport mechanism could be analyzed only by the free-volume model; however, for a membrane containing a hydrophilic moiety, the transport properties could be interpreted by the modified model. In water/ethanol mixtures, ethanol transports through the membrane matrix, while water permeates through the polar pathways consisting of polar groups or ions and water molecules as well as through the membrane matrix. © 1995 John Wiley & Sons, Inc.     

用于描述三元水醇系统汽液平衡的活度系数模型

In this study, three semipredictive activity coefficient models: Wilson, non-random-two liquid model (NRTL), and universal quasi-chemical model (UNIQUAC), have been used for modeling vapor-liquid equilibrium properties of ternary mixtures that include substances found in alcoholic distillation processes of wine and musts. In particular, vapor-liquid equilibrium in ternary mixtures containing water + ethanol + congener has been modeled using parameters obtained from binary and ternary mixture data. The congeners are substances that although present in very low concentrations, of the order of part per million, are important enological parameters. The results given by these different models have been compared with literature data and conclusions about the accuracy of the models studied are drawn, recommending the best models for correlating and predicting phase equilibrium properties of this type of mixtures.     

基于分子表面电荷密度分布与机器学习的混合物设计方法研究

由于混合物性能的可调控性,当前市场对其关注与日俱增。对于这类产品,基于模型的设计方法由于具有高效性以及普适性,相较于其他产品设计方法得到了更快的发展。但是对于很多性质,如气味、颜色等,准确且普适的模型尚不可得。因此,本文提出了一种基于分子表面电荷密度分布描述符（S描述符）和机器学习模型的混合物设计方法,采用描述符表征产品、再通过机器学习模型将其与性质关联,直接用于混合物产品设计。具体地,根据给定的产品性质需求,机器学习模型直接预测/设计混合物产品的S描述符;然后以欧几里德距离为指标,在给定的数据库中筛选出S描述符满足要求的候选混合物组成。最后,对候选混合物及其组分性质进行实验验证,完成设计。本文以香精的混合替代物设计作为算例,设计得到丙酸叶醇酯的两种混合香精替代物,通过实验对混合物进行了验证。结果表明,混合替代物的气味及其组分的各理化性质均与丙酸叶醇酯相近,证实本文所提出方法的有效性。     

Modeling infinite dilution activity coefficients of organic-aqueous systems using a modified regular solution equation and cubic equations-of-state

Expressions derived from the regular solution equation and the generalized cubic equations-of-state (EOS) were employed to model the infinite dilute activity coefficient (γ^∞) of organic-aqueous systems. A database of 119 organic species in aqueous systems, divided into six classes, was gathered for models evaluations. The use of the molar density, the first order molecular connectivity, and the dipole moment appear to be adequate correlating variables for describing the structural dependence of the residual part in the modified regular solution equation (MRS). The Soave-Redlich-Kwong (SRK) and Peng-Robinson (PR) were specified and employed in the generalized cubic EOS form. The excess activity coefficient concept was used in the SRK and PR EOS models to account for the deficiency of EOS in dealing with highly non-ideal or polar systems. The abilities of two existing correlation models along with two modified versions of the UNIFAC model were also assessed. The proposed models provide creditable equations for correlating γ^∞ of organic-aqueous systems.     

ESTIMATION OF CRITICAL PROPERTIES OF BINARY MIXTURES USING GROUP CONTRIBUTION METHODS

A new method for estimating critical temperature (T_c), critical pressure (P_c), and critical volume (V_c), of both nonpolar and polar binary mixtures displaying continuous critical loci is proposed. The methodology is based on the group contribution concept for estimation of critical constants of pure compounds, and the combining rule concept for estimation of mixture properties. Lydersen group contribution method is used to demonstrate the application of this methodology. The combining rules are formulated and their adjustable parameters are determined using 43 nonpolar and polar binary mixtures including 417 data points for (T_c), 390 data points for (P_c), and 219 data points for (V_c), respectively. The method is then evaluated with 15 independently selected binary mixtures containing hydrocarbons, alcohols, ethers, amine, carbon dioxide, nitrous oxide, sulfur dioxide, chloroform, and hydrogen sulfide. The average deviations of the estimated (T_c), (P_c), (V_c) are 1.60%, 7.26%, and 3.64%, respectively. The present procedure does not require experimentally adjusted interaction parameters for estimation of the critical properties of a given binary mixture.     

Mass- and momentum transfer in hydrogen/air and methane/air mixtures

In this article we present results for the viscosity and the mass transfer rates of hydrogen/air, hydrogen/oxygen, methane/air and methane/oxygen mixtures in the temperature range from 1000 to 7000 K and a pressure range from 10³ to 10⁶ Pa. In addition, the combustion ratio is varied from 0 to ∞. The transport properties are calculated from the first order solution of the Chapman Enskog approach to the Boltzmann equation, assuming chemical equilibrium composition. An extensive literature study was performed to derive experimental and/or theoretically based data for the respective binary interaction potentials. The values of the collision integrals, as derived from a complex numerical integration procedure, are correlated to an approximation formula. In addition, the exact solutions of the kinetic theory are compared to frequently used empirical mixture rules. For the mixture viscosity an easy approximation formula is deduced from the gas-kinetic theory.     

Vapour-Liquid Equilibrium with a New Ebulliometer: Ester+Alcohol System at 0.5 MPa

A new dynamic ebulliometer is used to determine vapor-liquid equilibrium (VLE) data experimentally. In the equipment, both phases are recirculated. Its operation is a consequence of the Cotrell pump effect produced when the mixture is heated in a double-walled inverted vessel. The reliability of the apparatus is tested with the mixtures studied previously by various authors. VLE data for the binary systems of methyl acetate + methanol and the methyl acetate + ethanol at 0.5 MPa are determined. The experimental data are confirmed with the point-to-point test of van Ness, applying the Fortran program of Frendslund et al. In addition, the experimental results are compared with the UNIFAC (including different versions) and ASOG prediction models.     

New polymer multilayer pervaporation membrane

The formation, morphology and transport properties of a new multilayer pervaporation membrane have been studied. This membrane consists of a microporous support based on a poly(amideimide), an intermediate poly[2-(N,N-dimethylamino)ethyl methacrylate] layer, and a top diffusion layer of ladder polysiloxane. The membrane has low permeability for weakly polar liquids (e.g. cyclohexane); it exhibits dehydrating properties for waterisopropanol mixtures and has high productivity (up to 14.5 kg h^-1 m^-2) and high separation factor (up to 27430) when methanol is isolated from mixtures with cyclohexane. The transport properties of the membrane are discussed with respect to the Henis-Tripodi resistance model, taking into account the hydrophobic-hydrophilic nature of the polymers used.     

醋酸稀溶液的络合萃取

络合萃取法对于极性有机物稀溶液的分离具有高效性和高选择性。本文以醋酸稀溶液为分离对象,通过系统的相平衡实验筛选出30 wt％三辛胺(或7301)+20 wt％正辛醇+50 wt％煤油混合溶剂。同时,探讨了叔胺类萃取剂对醋酸萃取的过程机理,研究了混合溶剂萃取稀醋酸工艺的可行性。     

The free energy of transfer of Pb(II) ion and electrode kinetics of the Pb(II)/Pb(Hg) system in dimethyl sulfoxide (DMSO) and DMSO-water mixtures

The electrode kinetics of the Pb(II)/Pb(Hg) system has been studied in DMSO and DMSO-water mixtures using the faradaic impedance measurements. With the increase of the mole fraction of the organic component in the mixture rate constant decreases steadily from 2 cm s^?1 in pure water to 5 × 10^?2 cm s^?1 in DMSO in rough proportion to the coverage of the electrode by DMSO. The change of the kinetics with the solvent composition was discussed in the frame of existing models.Basing on the determined potentials of the Pb(II)/Pb(Hg) electrode expressed vs the ferrocinium ion/ferrocene electrode potential, the free energy of transfer of Pb(II) from water to DMSO and its mixtures was calculated and discussed.