New local composition model for electrolyte solutions

A new model for representation of the excess Gibbs energy of electrolyte solutions is proposed. The excess Gibbs energy of an electrolyte solution is expressed as a sum of contributions of a long-range and a short-range excess Gibbs energy term. The Pitzer–Debye–Hückel model is used as a long-range contribution to the excess Gibbs energy. A new expression based on the local composition concept, which is the non-random factor (NRF)–Wilson model, is developed to account for the short-range contribution to the excess Gibbs energy. The main difference between this model and the electrolyte-NRF model available in the literature is the assumption that the short-range energy parameter between species in a local cell has an enthalpic rather than Gibbs energy nature. The utility of the model is demonstrated with the successful representation of the mean ionic activity coefficient of several aqueous electrolyte solutions. The results show that with only two adjustable parameters per electrolyte, the model is valid for the whole range of electrolyte concentration, from dilute solution up to saturation. The results are compared with those obtained from the NRTL, NRF and Wilson models. The model presented in this work produces better results.     

A nonelectrolyte local composition model and its application in the correlation of the mean activity coefficient of aqueous electrolyte solutions

The local composition models have been widely used for the correlation of activity coefficient of nonelectrolyte and electrolyte solutions. A new equation for the excess Gibbs energy function is developed based on the local composition expression of Wilson and the random reference state. This new function, the nonelectrolyte Wilson nonrandom factor (N-Wilson-NRF) model, is presented in the form of a molecular framework so that it can be used for both nonelectrolyte and electrolyte solutions. Without any particular assumptions for ionic solutions, the new function is used to described the short-range contribution of the excess Gibbs energy of electrolyte solutions. The long-range contribution is represented by Pitzer–Debye–Hückel model. With two adjustable parameters per electrolyte, the new model is applied to correlate the mean activity coefficients of more than 150 binary aqueous electrolyte solutions at 25 °C. The results are compared with various local composition models such as the electrolyte-NRTL, electrolyte NRF-Wilson and electrolyte-NRTL-NRF models. The comparison of the results with experiment demonstrates that the new model can correlate the experimental data accurately. Moreover, the model shows high precision of predictability for the osmotic coefficient of binary electrolyte solutions.     

Measurement and modeling of osmotic coefficients of aqueous solution of ionic liquids using vapor pressure osmometry method

Osmotic coefficients of binary mixtures containing an ionic liquid, (1-butyl-3-methylimidazolium tetrafluoroborate, [BMIm]BF₄, 1-ethyl-3-methylimidazolium ethyl sulfate, [EMIm]ES, and 1-butyl-3-methylimidazolium methyl sulfate, [BMIm]MS) with water were measured until about 3 molal concentrations using vapor pressure osmometry method (VPO) at temperature ranges 298.15–328.15 K and modeled using different electrolyte excess Gibbs free energy models including electrolyte non-random two liquids (NRTL), modified NRTL (MNRTL), mean spherical approximation NRTL (MSA-NRTL), non random factor (NRF), and extended Wilson models. The results show that osmotic coefficient data increase with increasing temperature. The calculated standard deviations of the studied systems show that the applicability of these models for the correlation of VLE properties of ionic liquid solutions. The average standard deviations for the models have the order σ(?) MNRTL < σ(?) Wilson < σ(?) NRTL < σ(?) MSA-NRTL < σ(?)NRF. The results show MNRTL model is able to reproduce experimental osmotic coefficients of aqueous solution of studied ionic liquids with good precision.     

Thermodynamic representation of phase equilibrium behavior of aqueous solutions of amino acids by the modified Wilson model

The polymer–electrolyte Wilson model [R. Sadeghi, J. Chem. Thermodyn. 37 (2005) 323–329] which has a molecular thermodynamic framework has been extended to model the vapor–liquid and liquid–solid equilibrium behavior of amino acids and small peptides in aqueous solutions as functions of temperature, ionic strength and amino acid compositions. The utility of the model is demonstrated with a successful representation of the activity coefficients and the solubility of several amino acids in different aqueous solutions and the results are compared with those obtained from the NRTL model.     

Comparative Evaluation of Six Electrolyte Local Composition Activity Coefficient Models Applied to Binary Aqueous Solutions of Ionic Liquids

The capability of six popular local composition models including electrolyte NRTL, modified electrolyte NRTL, electrolyte NRTL–NRF, electrolyte Wilson, modified electrolyte Wilson, and electrolyte NRF–Wilson models to predict the activity coefficients of ionic liquids in aqueous solutions was examined by correlating the experimental data of 16 ionic liquids available in the literature. The adjustable parameters and standard deviations of the fit were estimated for all of these models. Results indicate that the modified electrolyte Wilson model represents the activity coefficients with higher precision.     

Electrolyte-UNIQUAC-NRF model for the correlation of the mean activity coefficient of electrolyte solutions

The new electrolyte-UNIQUAC-NRF excess Gibbs function is obtained for calculation of the activity coefficient of the binary electrolyte solutions. The excess Gibbs energy of the model consists of the Pitzer–Debye–Hückel equation, describing the long-range electrostatic contribution and the electrolyte-UNIQUAC-NRF model to account for the short-range contributions. With two adjustable parameters per electrolyte, the new model is applied to correlation of the mean activity coefficients of more than 130 binary aqueous electrolyte solutions at 25 °C. Also the binary parameters, obtaining from regression of mean activity data, are used for prediction of osmotic coefficient data for the same electrolytes. The results are compared with various local composition models such as the electrolyte-NRTL, electrolyte NRF-Wilson, electrolyte-NRTL-NRF, N-Wilson-NRF models. The comparison of the results with experiment demonstrates that the new model can correlate the experimental activity coefficient data and predict the osmotic coefficient data of binary electrolytes accurately.     

Solubility of selected dibasic carboxylic acids in water,in ionic liquid of [Bmim][BF4], and in aqueous [Bmim][BF4] solutions

The solubilities of three dibasic carboxylic acids (adipic acid, glutaric acid, and succinic acid) in water, in the ionic liquid of 1-butyl-3-methyl-imidazolim tetrafluoroborate ([Bmim][BF₄]), and in the aqueous [Bmim][BF₄] solutions have been measured by a solid-disapperance method. The binodal curve of water + [Bmim][BF₄] was also determined experimentally from solid–liquid–liquid coexistence temperature up to near the upper critical solution temperature. Experimental results showed that each acid-containing binary behaved as a simple eutectic system. The solid–liquid equilibrium (SLE) data were correlated with the NRTL model for each binary system. The NRTL model with these determined binary parameters predicted the solid-disappearance temperatures of the aqueous ternary mixtures containing [Bmim][BF₄] and the dibasic acids to within an average absolute deviation of 2.0%.     

Measurement of water activities of alanine + tri-potassium citrate + water system at temperatures between 293.15 and 313 K—Experimental and modeling

Water activity measurements by isopiestic method have been carried out on the aqueous solutions of alanine + tri-potassium citrate (K₃Cit) over a range of temperatures at atmospheric pressure. From these measurements, values of the vapor pressure of solutions were determined. The effect of temperature on the vapor–liquid equilibrium of alanine + K₃Cit + H₂O systems has been studied. The experimental water activities have been correlated successfully with the segment-based local composition Wilson and NRTL models. The agreement between the correlations and the experimental data is good.     

Equilibrium modeling of xylene adsorption on molecular sieves

The separation of xylene isomers is an important application in separation processes that is based on their adsorption properties on different adsorbents. In this work, the Price and Danner method was employed with a neural network to investigate the adsorption behavior of binary systems of p-xylene/m-xylene, p-diethyl benzene/m-xylene, and p-diethyl benzene/p-xylene and the ternary system of p-diethyl benzene/m-xylene/p-xylene at 130 and 175 °C. The Redlich–Kister, Wilson, and NRTL models were used to determine the activity coefficients in the adsorbed phase. Comparison with experimental data from the literature indicated that the proposed thermodynamic model would best determine surface excess when it is used along with the Redlich–Kister activity coefficient model.     

A three-characteristic-parameter correlation model for strong electrolyte solutions

In this study, a characteristic-parameter correlation model was developed for the aqueous strong electrolyte solutions. This correlation model consisted of the long-range ion–ion interaction described by Pitzer–Debye–Huckel model and short-range ion-solvent molecule interaction attributed to solvation effect. The proposed approach is based on our previous paper of Lin et al. [C.-L. Lin, L.-S. Lee, H.-C.Tseng, Fluid Phase Equilibria, 90 (1993) 57–79.]. However, the significant improvement was made that the differential equation was solved analytically instead of numerically. This proposed model contains three parameters of physical significance and has been used to estimate the mean activity coefficients of electrolytes and osmotic coefficients of 144 aqueous strong electrolyte solutions from literature. Comparisons were made to the models of Chen et al. [C.C. Chen, H.I. Britt, J.F. Boston, L.B. Evans, AIChE, 28 (1982) 588–596; C.C. Chen, L.B. Evans, AIChE, 32 (1986) 444–454.], Ananth and Ramachandran [M.S. Ananth, S. Ramachandran, AIChE, 36 (1990) 370–386.], and Lin et al. [C.-L. Lin, L.-S. Lee, H.-C. Tseng, Fluid Phase Equilibria, 90 (1993) 57–79.]. The results also showed that the present model is at least as good as above models for 1-1 and 1-2 electrolyte solutions and improved very much for 2-1, 2-2, 3-1, and 3-2 electrolyte solutions.     

Preparation of Nafion/PTFE/Zr(HPO4)2 composite membranes by direct impregnation method

The viscosities of as received 5.1 wt.% Nafion solutions (EW = 1100, Du Pont Co) blended with various concentrations of ZrOCl₂ were studied. We show the solution viscosity decreases as the wt. ratio of [ZrOCl₂]/[Nafion] is increased from 0.0 to 0.03, then the viscosity does not change significantly as the wt. ratio of [ZrOCl₂]/[Nafion] is increased from 0.03 to 0.16, and then the viscosity increases dramatically as the wt. ratio of [ZrOCl₂]/[Nafion] is increased above 0.16. Four Nafion solutions consisting of 5.1 wt.% Nafion and ZrOCl₂ with [ZrOCl₂]/[Nafion] wt. ratios of 0.019–0.24 were used with porous poly(tetrafluoroethylene) (PTFE) film to prepare zirconium hydrogenphosphate (ZrP) hybridized Nafion/PTFE (NF–ZrP) composite membranes by direct impregnating porous PTFE in Nafion/ZrOCl₂ solutions. The influence of [ZrOCl₂]/[Nafion] wt. ratio of Nafion/ZrOCl₂ solution on the membrane morphology of NF–ZrP and polyelectrolyte membrane fuel cell (PEMFC) performance at temperatures of 110–130 °C with relative humidity of 51.7–28.8% RH was investigated.     

Correlation of the mean ionic activity coefficients of electrolytes in aqueous amino acid and peptide systems

The activity coefficients of electrolytes in amino acid (peptide) aqueous systems were predicted using an expression for the excess Gibbs free energy of the solution. The model combines the contribution of long-range interactions given by the Khoshkbarchi–Vera model and the contribution of short-range interactions by the local composition based models such as the Wilson, the NRTL and the NRTL–NRF. The local composition models accurately correlate the activity coefficients of 30 amino acid (peptide)–water–electrolyte systems. The results show that the Wilson model can accurately correlate the activity coefficient of the electrolyte in amino acid (peptide) aqueous systems.     

Vapor pressures and apparent molal volumes of the solutions of ZnCl2 in ethanol at 298.15 K

Vapor pressures and apparent molal volumes of solutions of ZnCl₂ in ethanol are reported at 298.15 K. The vapor pressure of ethanol has been evaluated from the osmotic coefficients measured by an improved isopiestic method. The experimental osmotic coefficients have been correlated with the Pitzer model and local composition models including electrolyte non-random two liquid (e-NRTL), non-random factor (NRF), modified NRTL (MNRTL) and extended Wilson (EW) models. Apparent molal volumes have been calculated from the densities of the solutions measured by a vibrating-tube densimeter, and fitted with the volumetric equations based on the Pitzer model and the local composition models. All of the models successfully correlate the experimental osmotic coefficients and apparent molal volume data.     

Binary and ternary (liquid + liquid) equilibrium for {methylcyclohexane (1) + toluene (2) + 1-hexyl-3-methylimidazolium tetracyanoborate (3)/1-butyl-3-methylimidazolium tetracyanoborate (3)}

This paper focuses on the study of the solubility behaviour of 1-hexyl-3-methylimidazolium tetracyanoborate [HMIM][TCB] and 1-butyl-3-methylimidazolium tetracyanoborate [BMIM][TCB] in combination with methylcyclohexane and toluene as representatives for non-aromatic and aromatic components. Binary and ternary (liquid + liquid) equilibrium data were collected at three different temperatures and at atmospheric pressure (0.1 MPa). The experimental data were well-correlated with the NRTL and UNIQUAC thermodynamic models; however, the UNIQUAC model gave better predictions than the NRTL, with a root mean square error below 0.97%. The non-aromatic/aromatic selectivities of the ionic liquids make them suitable solvents to be used in extractive distillation processes.     

Experimental studies on a mixture of HFC-32/125/161 as an alternative refrigerant to HCFC-22 in the presence of polyol ester

In this work, experiment was conducted to examine the thermo-physical properties of an alternative refrigerant to HCFC-22 in the presence of polyol ester (POE). The new alternative refrigerant is a mixture of HFC-32/125/161, whose physical properties are similar to HCFC-22 but has a lower global warming potential (GWP) than that of R407C. POE is used as the tested lubricating oil in the experiment. The saturated vapor pressure data and vapor–liquid equilibrium data of nine different mass fractions of the new refrigerant and polyol ester (POE) in the temperature range of 253–323 K were measured by single-phase cycle method. The experiment results showed that there was no stratification, no sediment generation in the liquid phase of the mixture, and the color of liquid phase of the mixture had no change in the equilibrium cell before and after the experiment with the POE concentration greater than 20% and the temperature higher than 258 K; with POE concentration lower than 20% and temperature lower than 258 K, stratification began to appear. Meanwhile, when POE and the refrigerant were miscible, the saturated pressure data of the mixture (HFC-32/125/161 + POE) revealed that POE had a very small impact on saturated vapor pressure of the mixture (almost negligible) when POE was less than 10% of the mixture; POE has an obvious effect on the saturated vapor pressure of the mixture when there is more than 10% POE in the mixture, especially when the temperature is higher than 283.15 K. Experimental data were correlated by Flory–Huggins model, Heil model, NRTL model and Wilson model. The results showed that to the average and maximum pressure deviation, the results were better with considering the effects of temperature on the energy parameters. Among the above models, the NRTL activity coefficient model was the best, the Heil and Wilson models followed and the Flory–Huggins model had the largest deviation from the experimental data.     

Determination and correlation of liquid–liquid equilibria for four binary N,N-dimethylformamide + hydrocarbon systems

Liquid–liquid equilibrium measurements for four binary N,N-dimethylformamide + hydrocarbon (hexane, heptane, octane, and cyclohexane) systems were performed using a laser scattering technique. The experimentally determined cloud points were satisfactorily correlated with two local composition models (NRTL, and Tsuboka–Katayama's modification of the Wilson equation). In addition, the prediction of LLE by means of the modified UNIFAC (Dortmund) model was also tested.     

Application of the GV-MSA model to the electrolyte solutions containing mixed salts and mixed solvents

In this work the Ghotbi–Vera mean spherical approximation (GV-MSA) model, coupled with two different expressions for the cation-hydrated diameters, was used in predicting the mean ionic activity coefficients (MIAC) of electrolytes for a number of the mixed-solvent and mixed-salt electrolyte solutions at 25 °C. In all cases the cation diameters in solutions changed with concentration of electrolyte while the anion diameters were considered to be constant and equal to the corresponding Pauling diameters. In application of the GV-MSA model to the electrolyte systems, two different expressions were used for concentration dependency of cation-hydrated diameters, i.e., the GV-MSA1 and GV-MSA2 models. In case of the electrolyte solutions containing the mixed-solvent of water and alcohol, the dielectric constants of the mixed solvents were obtained by simple regression of polynomial equations in terms of weight fraction of alcohol to the pertinent experimental data available in the literature. For the mixed-salt and mixed-solvent electrolyte solutions, in order to directly calculate the MIAC of electrolytes without introducing any new adjustable parameter, the values obtained in this work for the cation-hydrated diameters in the single aqueous electrolyte solutions were used. The results obtained in this work showed that the GV-MSA2 could more accurately correlate the MIAC of electrolytes in the single aqueous electrolyte solutions in comparison to those of the GV-MSA1 and Pitzer models. Also, the results showed that the GV-MSA-based models could accurately predict the MIAC of electrolytes in the mixed-solvent electrolyte solutions in comparison to those obtained from the model of Pitzer. In case of the mixed-salt electrolyte solutions the results of the two GV-MSA-based models studied in this work reasonably predict the MIAC of electrolytes in the mixed-salt electrolyte solutions without introducing any additional adjustable parameters compared to those obtained from the model of Pitzer with two adjustable parameters.     

Nonelectrolyte NRTL-NRF model to study thermodynamics of strong and weak electrolyte solutions

An electrolyte activity coefficient model is proposed by combining non-electrolyte NRTL-NRF local composition model and Pitzer–Debye–Hückel equation as short-range and long-range contributions, respectively. With two adjustable parameters per each electrolyte, the present model is applied to correlation of the mean activity coefficients of more than 150 strong aqueous electrolyte solutions at 298.15 K. Also the results of the present model are compared with the other local composition models such as electrolyte-NRTL, electrolyte-NRTL-NRF and electrolyte-Wilson-NRF models. Moreover, the present model is used for prediction of the osmotic coefficient of several aqueous binary electrolytes systems at 298.15 K. Also the present activity coefficient model is adopted for representation of nonideality of the acid gases, as weak gas electrolytes, soluble in alkanolamine solutions. The model is applied for calculation of solubility and heat of absorption (enthalpy of solution) of acid gas in the two {(H₂O + MDEA + CO₂) and (H₂O + MDEA + H₂S)} systems at different conditions. The results demonstrate that the present model can be successfully applied to study thermodynamic properties of both strong and weak electrolyte solutions.