Vapor-phase Mole Fraction Research Articles

Vapor–liquid equilibrium and excess Gibbs energies of some binary mixtures of acrylonitrile at 95.5 kPa

Bubble-point temperature data at 95.5 kPa, over the entire composition range are obtained for the binary mixtures formed by acrylonitrile with 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, chlorobenzene and nitrobenzene. A Swietoslawski type ebulliometer is used to measure the bubble point temperatures. The Wilson equation is used to represent the measured liquid phase composition versus temperature data. Computed values of the vapor phase mole fraction, liquid phase activity coefficients and excess Gibbs energy are presented and briefly discussed.

(Vapor + liquid) equilibrium of the binary mixtures formed by acetonitrile with selected compounds at 95.5 kPa

Bubble point temperatures at 95.5 kPa, over the entire composition range, are measured for the binary mixtures of acetonitrile with acetyl acetone, anisole, bromobenzene, isopropyl alcohol, methyl tertiary butyl ether, and tetra ethoxy silane – making use of a Swietoslawski type ebulliometer. The measured liquid phase composition versus bubble point temperature are found to be well represented by the Wilson model. Measured values of the liquid phase mole fraction versus bubble point temperature data are presented, along with the computed values of the vapor phase mole fractions and activity coefficients, and discussed.

(Vapor + liquid) equilibrium of binary mixtures formed by N, N-dimethyl formamide with some compounds at 95.1 kPa

Bubble point temperatures (at 95.1 kPa) over the entire composition range are measured for the binary mixtures formed by N, N-dimethyl formamide with: anisole, 2-cyanopyrazine, n-decane, diisopropyl ether, methyl ethyl ketone and n-octane, making use of a Swietoslawski type ebulliometer. Wilson equation is used to represent the measured liquid phase composition versus bubble point temperature data. Computed values of the activity coefficients, vapor phase mole fractions and excess Gibbs energy are tabulated and discussed.

Excess Gibbs free energies of the binary mixtures of acetonitrile with butanols at 94.83 kPa

Bubble point temperatures at 94.83 kPa, over the entire composition range, are measured for the binary mixtures of acetonitrile with: n-, iso-, sec- and tert-butanols – using a Swietoslawski type ebulliometer. The liquid phase composition versus bubble point temperature measurements are found to be well represented by the Wilson model. Measured values of the liquid phase mole fraction versus bubble point temperature data are presented along with the computed values of the vapor phase mole fractions, activity coefficients and excess Gibbs free energies and discussed.

Activity coefficients of the binary mixtures of o-cresol or p-cresol with C 1–C 4 aliphatic alcohols near ambient pressure

Bubble point temperatures near ambient pressure, for the binary mixtures, formed by o-cresol or p-cresol with – methanol, ethanol, n- and iso-propanols and n-, iso-, sec- and tert-butanols – covering the whole composition range, are measured using a Swietoslawski-type ebulliometer. The liquid phase composition–bubble point temperature measurements are found to be well represented by the Wilson model. Values of the optimum Wilson parameters as well as the computed values of vapor phase mole fractions and activity coefficients are tabulated. The results are discussed in terms of isomerization with reference to the selected set of compounds, constituting the mixtures and the stearic effects in the cresols.

An advanced Gibbs-Duhem integration method: Theory and applications

The conventional Gibbs-Duhem integration method is very convenient for the prediction of phase equilibria of both pure components and mixtures. However, it turns out to be inefficient. The method requires a number of lengthy simulations to predict the state conditions at which phase coexistence occurs. This number is not known from the outset of the numerical integration process. Furthermore, the molecular configurations generated during the simulations are merely used to predict the coexistence condition and not the liquid- and vapor-phase densities and mole fractions at coexistence. In this publication, an advanced Gibbs-Duhem integration method is presented that overcomes above-mentioned disadvantage and inefficiency. The advanced method is a combination of Gibbs-Duhem integration and multiple-histogram reweighting. Application of multiple-histogram reweighting enables the substitution of the unknown number of simulations by a fixed and predetermined number. The advanced method has a retroactive nature; a current simulation improves the predictions of previously computed coexistence points as well. The advanced Gibbs-Duhem integration method has been applied for the prediction of vapor-liquid equilibria of a number of binary mixtures. The method turned out to be very convenient, much faster than the conventional method, and provided smooth simulation results. As the employed force fields perfectly predict pure-component vapor-liquid equilibria, the binary simulations were very well suitable for testing the performance of different sets of combining rules. Employing Lorentz-Hudson-McCoubrey combining rules for interactions between unlike molecules, as opposed to Lorentz-Berthelot combining rules for all interactions, considerably improved the agreement between experimental and simulated data.

Estimation of vapour liquid equilibria for the system carbon dioxide–difluoromethane using artificial neural networks

In this paper, an alternate tool, i.e. the artificial neural network technique has been applied for estimation of vapour liquid equilibria (VLE) for the binary system, carbon dioxide–difluoromethane, which is an attractive alternative to chlorofluorocarbons and hydrochlorofluorocarbons, normally used as refrigerants. The model can satisfactorily estimate the vapour liquid equilibrium pressure and mole fraction carbon dioxide in vapour phase in the temperature range 222.04–343.23 K and in the pressure range 0.105–7.46 MPa. The average absolute error for the system in the estimation of vapour phase mole fraction is 0.0086 and 0.056 MPa for the pressure.

Estimation of vapour liquid equilibria of binary systems, carbon dioxide–ethyl caproate, ethyl caprylate and ethyl caprate using artificial neural networks

Vapour liquid equilibrium (VLE) data are important for designing and modeling of process equipments. Since it is not always possible to carry out experiments at all possible temperatures and pressures, generally thermodynamic models based on equations of state are used for estimation of VLE. In this paper, an alternate tool, i.e. the artificial neural network technique has been applied for estimation of VLE for three binary systems viz. carbon dioxide–ethyl caproate, ethyl caprylate and ethyl caprate which are of importance in supercritical extraction. The temperature range in which these models are valid is 308.2–328.2 K and the pressure range is 1.6–9.2 MPa. The average absolute deviation for all the three systems in the estimation of liquid phase mole fraction was 3% or less and less than 0.02% for the vapour phase mole fraction. The error was less compared to that estimated by SRK or Peng Robinsons equation of state.

Surface Enrichment in Alcohol−Water Mixtures

Molecular beams generated from the vapors above the surfaces of alcohol−water mixtures have been examined by mass spectrometry. The alcohols examined are methanol, ethanol, n-propanol, and n-butanol. The variation of the vapor-phase mole fraction of the alcohol, estimated from the cluster populations in the molecular beam, with the liquid mole fraction is found to be identical to that of the surface concentration of the alcohol in the liquid obtained from surface-tension measurements. The populations of the neat alcohol clusters, as distinct from those of alcohol−water clusters, also exhibit a comparable trend. Surface enrichment is considerably more pronounced in the case of n-butanol and n-propanol compared to that of ethanol.

Vapour–liquid equilibrium data analysis for mixed solvent–electrolyte systems using neural network models

Two-perceptron artificial neural network correlations were proposed for the prediction of vapor–liquid equilibrium for mixed dual-solvents single electrolyte systems, and validated over an extensive VLE database (2,900 data, 16 binary solvents, 24 salts, 11 cations, 6 anions). Performances of these correlations to predict vapor-phase mole fraction, equilibrium temperature and total pressure, were discussed via comparisons with the experimental data, and the UNIFAC electrolyte model (Kikic, Fermeglia & Rasmussen, 1991). Chemical Engineering Science, 46, 2775–2780.) and the Extended UNIQUAC model (Iliuta, Thomsen & Rasmussen, 2000). Chemical Engineering Science, submitted for publication.). The mean absolute deviations in predicted vapor-phase mole fraction, temperature and pressure for the entire database were 0.025, 1.46 K and 1.68 kPa, respectively.

Total Pressure Measurements for Lithium Chloride + Methanol + Ethanol at 303.15 K

Total pressure for the ternary system lithium chloride + methanol + ethanol and constituent binaries was measured at 303.15 K. Measurements were performed as a function of salt concentration along different paths of virtually constant salt-free solvent composition. The results were reduced by Barker's method using an empirical expression for the Gibbs free energy of the liquid phase. The vapor-phase compositions for the two alcohols are calculated in a data reduction procedure. The vapor-phase mole fraction of ethanol increases on the addition of lithium chloride to the methanol + ethanol system, indicating a salting-out effect of lithium chloride on ethanol.

Molecular simulation of the vapor-liquid equilibrium of methanethiol + propane mixtures

We have used the Gibbs ensemble Monte Carlo (GEMC) method to calculate the vapor-liquid equilibrium properties for pure propane and methanethiol as well as their mixtures. We used two different potential-energy surfaces to describe the propane and methanethiol molecules. The results show that the simple site-site potential-energy surfaces work well for the pure components by optimizing the parameters to reproduce the liquid-phase density at the normal boiling point. For mixtures, the site-site potential-energy surface predicts the liquid-phase densities fairly well, but is not accurate enough to give quantitative results for the vapor-phase mole fraction for this system.

Isobaric vapor-liquid equilibria of chloroform + ethanol and chloroform + ethanol + calcium chloride at 94.0 kPa

Vapor-liquid equilibrium data of chloroform + ethanol and chloroform + ethanol + CaCl 2 (at saturation) were measured at a pressure of 94.0 kPa, using a modified Malanowski equilibrium still. The salt investigated in this work, i.e. CaCl 2, exhibits a slight salting-out effect on chloroform. The experimental results of the salt-free binary were compared with those predicted by ASOG, original UNIFAC, and modified UNIFAC models which predicted the bubble-point temperatures with a root-mean-square-deviation (RMSD) of: 0.40, 0.55, and 1.48 K, respectively. RMSD values of the vapor-phase composition given by these models were: 0.020, 0.019 and 0.039 mole fraction, respectively. On the other hand, the experimental data of the salt-containing system were compared with those predicted by Wilson-Tan and NRTL-Tan models for the effect of the electrolyte on the phase behavior of the system under study which has an azeotrope around x 1 = 0.93. Both models showed similar capability in predicting the bubble-point temperatures and vapor-phase compositions: temperatures were predicted by both models with an RMSD of about 0.4 K whereas the RMSD values of the vapor-phase mole fractions, predicted by these models, were 0.026 and 0.022, respectively.

Isobaric vapor-liquid equilibria of the system [formula omitted] at 70.5 and 94.0 kPa

Isobaric vapor-liquid equilibrium (VLE) data of ethyl acetate n- butanol were measured at 70.5 and 94.0 kPa using a modified Othmer equilibrium still. The experimental VLE data of this work, which show a positive deviation from ideal solution behavior, were analyzed using the following four group-contribution methods: the ASOG, UNIFAC, modified UNIFAC and UNIQUAC models. For the first three models, interaction parameters from the literature were utilized in the data analysis, whereas in the case of the UNIQUAC model, the optimum interaction binary parameters were obtained by regressing the experimental data using maximum likelihood principles. ASOG predicted the experimental data with the highest deviation in terms of RMSD (root-mean-square deviation) in temperature and vapor-phase mole fraction (1.12 K and 0.042 mole fraction). The modified UNIFAC correlated the experimental data with a maximum RMSD of 0.38 K and 0.015 mole fraction versus an RMSD of 0.92 K and 0.019 mole fraction given by the original UNIFAC. The best correlation was given by the UNIQUAC model (0.11 K and 0.004 mole fraction) which is expected because of the direct regression of the experimental VLE data. Activity coefficients at infinite dilution were calculated from the experimental data and compared with the prediction of the ASOG, UNIFAC, and modified UNIFAC models. The best agreement with experimental limiting activity coefficients was obtained from the modified UNIFAC model (with an absolute average deviation of 11.5%).

A Modified UNIQUAC Model That Includes Hydrogen Bonding

Based on the association theory of Wertheim, a UNIQUAC association (UNIQUAC-A) model has been developed in which the hydrogen bond is treated as a strong interaction rather than as a chemical reaction. Compared with the original UNIQUAC model, the UNIQUAC-A model results in better correlations of binary vapor-liquid equilibrium data for self-associating mixtures containing either an alcohol or an acid. However, both the UNIQUAC and UNIQUAC-A models produce small errors in pressure and vapor-phase mole fractions for cross-associating mixtures. We report interaction parameters and association parameters for the UNIQUAC-A model that can be used for the extrapolation and prediction of the binary vapor-liquid equilibrium in associating mixtures.

Vapour-liquid equilibrium data for the water-2-propanol system in the presence of dissolved salts

Experimental data are presented on VLE for the water-2-propanol system, and for the water-2-propanolMgCl 2 and water-2-propanolMgBr 2 systems. The salting-out effect of the salts on the binary mixture is shown together with the consequent shifting of the azeotropic composition. To correlate the experimental data, use was made of the Macedo model, which combines the modified UNIQUAC equation, containing concentration-dependent parameters, with a Debye-Hückel type term, thus ensuring a more correct representation of the long-range forces. The UNIQUAC interaction parameters between solvents and ions and between the two solvents are evaluated by the fitting of the experimental data. It is shown that the model represents the VLE for water-2-propanolsalt mixtures with an average acuracy of 2.5% in the total pressure and 2% in the vapour-phase mole fraction.

Vapor-Liquid Equilibria for Methanol + Ethanol + Calcium Chloride, + Ammonium Iodide, and + Sodium Iodide at 298.15 K

Recently, an alternative extractive distillation using a salt as extractive solvent has attracted attention. Vapor-liquid equilibria for methanol + ethanol + CaCl{sub 2}, + NH{sub 4}I, and + NaI were measured at 298.15 {+-} 0.05 K using a static method. The data obtained in this apparatus were confirmed by comparison with the literature data of ethanol + water and ethanol + water + CaCl{sub 2} and tested for thermodynamic consistency. Any salt used in this work exerted salting-in effect on the methanol + ethanol system, the magnitude of which was CaCl{sub 2} > NaI > NH{sub 4}I. The observed data were correlated by use of Hala`s equation, and {beta} was determined for each system. The calculated result of each system reproduced experimental data within an accuracy of {+-}2.12% in vapor-phase mole fraction. From the results of comparison of {beta} obtained in this work with the kind of salt additive for methanol + ethanol and ethanol + water systems, it was found that {beta} depended mainly on the kind of salt but not on the kind of solvent mixture. The application of Hala`s model for an alcohol + alcohol + salt system was confirmed at a temperature of 298.15 K.

Total Pressure Measurements for Copper(II) Chloride + Methanol + Ethanol at 303.15 K

Total pressure is reported as a function of liquid-phase composition for copper(II) chloride + methanol + ethanol at 303.15 K. Pressure was measured as a function of salt concentration along various lines of essentially constant methanol mole fraction (on a salt-free basis). The data were reduced by Barker`s method using an empirical expression for the excess Gibbs free energy of the liquid phase. Calculated vapor-phase compositions for the two alcohols indicate that the vapor-phase mole fraction of ethanol is increased (ethanol is salted out) by addition of copper(II) chloride to liquid mixtures of methanol and ethanol.

Vapour-liquid equilibrium for the acetone-methanol-inorganic salt system

Isobaric VLE data were measured for the acetone-methanol binary system at 101.32 kPa and for the acetone-methanol-salt system at the same pressure at different salt concentrations using a modified Othmer equilibrium still. Both salts investigated in this work, KI and NaI, exhibited a salting-out effect on acetone. The experimental data for the salt-free system were correlated by Wilson, NRTL and UNIQUAC models. For the salt systems, the experimental data were correlated by the electrolytic NRTL model of Mock et al. [Mock, B., Evans, L.B. and Chen, C.C., 1986. AIChE J., 32: 1655–1664], the extended UNIQUAC equation of Sander et al. [Sander, B., Fredenslund, A. and Rasmussen, P., 1986. Chem. Eng. Sci., 41: 1171–1183], and the modified Wilson and NRTL models proposed by Tan [Tan, T.C., 1985. AIChe J., 31: 2083–2085; Tan, T.C., 1987. Chem. Eng. Res. Des., 65: 355–366; Tan, T.C., 1990. Trans. Ind. Eng. Chem., 68: 93–102]. The results were compared with the data predicted by the modified Wilson and NRTL models of Tan. The mean absolute deviations in vapour-phase mole fraction and bubble points for the salt-free system were about 0.002 and 0.02, respectively. The mean absolute deviations in vapour-phase mole fraction and bubble points for both salt systems, over 252 data points, were about 0.004 and 0.21, respectively, using the electrolytic NRTL model of Mock et al., 0.009 and 0.44 using the extended UNIQUAC model of Sander et al., 0.024 and 0.38 using Tan's modified Wilson model, and 0.019 and 0.15 using Tan's modified NRTL model. Both the modified Wilson and the NRTL models proposed by Tan predict the vapour composition of both salt systems with a mean absolute error of about 0.024-0.019, and the bubble points with a mean absolute error of about 0.56.

Vapor-liquid equilibria in nonpolar/weakly polar systems with different types of mixing rules

A comprehensive comparison of six mixing rules: the one- and two-parameter conventional ones (1PCMR and 2PCMR); the pressure- and density-dependent ones (PDMR and DDMR); and two based on G E models (MHV2MR and the Sandler-Wong, SWMR), used with cubic equations of state, is presented using an extensive database of nonpolar/weakly polar binary systems. Parameter values are determined by fitting the P-T-x data and are then used in the prediction of vapor phase mole fractions (y), and saturated liquid (ϱ L) and vapor (ϱ V) densities. Best result are obtained with the 2PCMR, PDMR, MHV2MR and SWMR with typical errors of 2% in P, 3% in ϱ L and 7% in ϱ V ; and deviations in y of 0.012, except for the SWMR which gives poorer predictions for systems where one component is highly supercritical. Surprisingly, the DDMR does not perform as well as it might be expected. All models, however, finally give poorer results in the near-critical region.