Vapor-liquid equilibria for the system water + tert.-pentanol at 4 temperatures

Precise isothermal vapor-liquid equilibrium data at 10, 30, 55 and 70°C for the system water + tert.-pentanol were measured using a computer-operated differential static apparatus. Activity coefficients at infinite dilution were derived from the experimental P − x data in the dilute region using a flexible Legendre polynomial, and the vapor-liquid-liquid locus was derived directly from the P − x data near the liquid-liquid phase boundary. Heteroazeotropic points were measured directly by distillation using a rotating band column. Furthermore the UNIQUAC and the NRTL models were used to correlate the experimental P − x data and to derive the azeotropic data.

Experimental H^E data were taken from literature and used together with the experimental P − x data to simultaneously fit temperature dependent interaction parameters for UNIQUAC and NRTL. The parameters were used to predict the azeotropic composition over a large temperature range. The results were compared with those of a simple analytical thermodynamic equation using only the pure component vapor pressure data, heats of mixing in the heterogeneous region and the azeotropic composition at one temperature.

Heats of mixing were measured at 140°C with the help of a flow calorimeter in order to determine the slope of H^E vs. x₁ in the heterogeneous region. The H^E data were used to check the reliability of the G^E model parameters and the equation to calculate the temperature dependence of the heteroazeotropic composition.     

Phase equilibria and excess properties for binary systems in reactive distillation processes Part I. Methyl acetate synthesis

Isothermal vapor–liquid equilibrium (VLE) and excess enthalpy (H^E) data were measured for binary systems required for the design of reactive distillation processes for the methyl acetate production. The isothermal P–x data were measured with the help of a computer-operated static apparatus. A commercial isothermal flow calorimeter was used for the determination of the heats of mixing. Temperature-dependent interaction parameters for the UNIQUAC model were fitted simultaneously to the experimental data from this work and other authors.     

The excess enthalpies of liquid freon-22 + N,N-dimethylacetamide mixtures from 263 to 363 K at 5500 kPa

The excess enthalpies, H^E, for liquid Freon-22 + N,N-dimethylacetamide mixtures were measured from 263 to 363 K at 5500 kPa using isothermal flow calorimeters with a reproducibility of better than 1%. At all temperatures the mixtures showed negative (exothermic) nonideal behavior of H^E. The H^E values are essentially invariant with temperature from 263 to 363 K, but H^E values become successively more negative for 343, 353, and 363 K. The Redlich-Kister equation was found to give a good fit of the H^E data over the entire composition and temperature ranges investigated.     

Excess properties of binary alkanol-ether mixtures and the application of the ERAS model

Experimental results are reported of excess molar volumes V^E and excess molar enthalpies H^E for binary mixtures of 1-propanol, 2-propanol, 1-butanol and 2-butanol with diisopropyl ether (DIPE) and dibutyl ether (DBE) at 298.15 K. A vibrating-tube densitometer was used to determine V^E, and H^E was measured using a quasi-isothermal flow calorimeter. The applicability of the ERAS model has been investigated for describing the experimental data as well as literature data of alkanol-ether mixtures containing DBE or dipropyl ether (DPE).     

Thermodynamics of (1,4-difluorobenzene + an n-alkane) and of (hexafluorobenzene + an n-alkane)

Excess molar enthalpies H^E and excess molar volumes V^E have been measured, as a function of mole fraction x₁, at 298.15 K and atmospheric pressure for the five liquid mixtures (x₁1,4-C₆H₄F₂ + x₂n-C_lH_2l+2), l = 7, 8, 10, 12 and 16. In addition, H^E and excess molar heat capacities C_P^E at constant pressure have been determined for the two liquid mixtures (x₁C₆F₆ + x₂n-C_lH_2l+2), l = 7 and 14, at the same temperature and pressure. The instruments used were flow microcalorimeters of the Picker design (the H^E version was equipped with separators) and a vibrating-tube densimeter, respectively.

The excess enthalpies of the five difluorobenzene mixtures are all positive and quite large; they increase with increasing chain length l of the n-alkane from H^E(x₁ = 0.5)/(J mol⁻¹) = 1050 for l = 7 to 1359 for l = 16. The corresponding excess volumes V^E are all positive and also increase with increasing l: V^E(x₁ = 0.5)/(cm³ mol⁻¹) = 0.650 for l = 7 and 1.080 for l = 16. Interestingly, the excess enthalphies of the corresponding mixtures with hexafluorobenzene are only about 5% larger, whereas the excess volumes of (x₁C₆F₆ + x₂n-C_lH_2l+2) are roughly twice as large as those of their counterparts in the series containing 1,4-C₆H₄F₂. Specifically, at 298.15 K H^E(x₁ = 0.5)/(J mol⁻¹) = 1119 for (x₁C₆F₆ + x₂n-C₇H₁₆) and 1324 for (x₁C₆F₆ + x₂n-C₁₄H₃₀), and for the same mixtures V^E(x₁ = 0.5)/(cm³ mol⁻¹) = 1.882 and 2.093, respectively. The excess heat capacities for both systems are negative and of about the same magnitude as the excess heat capacities of mixtures of fluorobenzene with the same n-alkanes (Roux et al., 1984): C_P^E(x₁ = 0.5)/(J K⁻¹ mol⁻¹) = −1.18 for (x₁C₆F₆ + x₂n-C₇H₁₆), and −2.25 for (x₁C₆F₆ + x₂n-C₁₄H₃₀). The curve C_P^E vs. (x₁ for x₁C₆F₆ + x₂n-C₁₄H₃₀) shows a sort of “hump” for x₁ 0.5, which is presumed to indicate emerging W-shape composition dependence at lower temperatures.     

Correlation,verification and prediction of vapour–liquid equilibria using equation of state with association term: II. Alcohols + non-aliphatic hydrocarbons

An equation of state with association term was used to correlate all available binary VLE data sets for mixtures of alkanols with non-aliphatic hydrocarbons. The self association of alkanols was described using a uniform set of parameters. The cross association between alkanols and aromatic compounds was taken into account. The verification of the VLE data for mixtures of alkanols and non-aliphatic hydrocarbons is described and recommended data are given.The method of prediction of the VLE in the investigated mixtures is described. The recommended data were compared with the results of the prediction.     

Excess molar enthalpies of binary mixtures containing dimethylcarbonate, diethylcarbonate or propylene carbonate + three chloroalkenes at 298.15 K

Excess molar enthalpies H^E_m of dimethylcarbonate, diethylcarbonate or propylene carbonate + trans-1,2-dichloroethylene, + trichloroethylene, and + tetrachloroethylene, respectively have been determined at 298.15 K using an LKB flow-microcalorimeter. Experimental data have been correlated by means of the Redlich-Kister equation and adjustable parameters have been evaluated by least-squares analysis. The H^E_m values range from a minimum value of − 1000 J mol⁻¹ for diethylcarbonate + trans-1,2-dichloroethylene up to a maximum of 920 J mol⁻¹ for dimethylcarbonate + tetrachloroethylene. For each series of mixtures, a systematic increase in H^E_m with an increase in the number of Cl atoms in the chloroalkene molecule has been noted. The results are discussed in terms of the molecular interactions.     

Thermoynamic properties (Hm, CP,m, Vm, κT) of binary mixtures {x1,3-Dioxane + (1−x)Cyclohexane} at 298.15 K

Molar excess enthalpies H_m^E, isobaric heat capacities C_P,m^E, volumes V_m^E and isothermal compressibilities κT^E for the 1,3-dioxane(3DX) + cyclohexane mixture were measured at 298.15 K, in order to compare to those of the 1,4-dioxane(4DX) + cyclohexane mixture. H_m^E is endothermic and the maximum value about 1.5 kJ mol⁻¹ at x ≈ 0.45, and lower than that of the 4DX mixture by about 80 J mol⁻¹. V_m^E is positive over the whole concentration and the maximum value is about 0.85 cm³ mol⁻¹ at x ≈ 0.45, and lower than that of the 4DX mixture. The above results suggest the energetic unstabilization, resulting in the volume expansion in the mixture. C_P,m^E shows the characteristic W-shaped concentration dependence, which has maximum at x ≈ 0.45 and two minima at x ≈ 0.1 and 0.9. The maximum C_P,m^E value for 3DX mixture shifts toward the positive side, compared to that of 4DX mixture. κT^E were estimated from speeds of sound, densities, thermal expansion coefficients and isobaric heat capacities of the pure component liquids and the mixtures. The κT^E result shows the positive concentration dependence over the whole composition range. The 3DX mixture has the similar thermodynamic properties to the 4DX mixture, despite that 4DX is the nonpolar solvent and 3DX is the dipolar liquid. this means that there exists the local dipolar interaction between 4DX molecules, and the prevalence of “microheterogeneity” in the both mixtures.     

Prediction of vapor-liquid equilibrium from excess enthalpy data for binary ether +n-alkane or cyclohexane mixtures

Vapor liquid equilibrium (VLE) is successfully predicted from excess enthalpy H^E data for binary ether + n-alkane or cyclohexane mixtures. Parameters for the continuous linear association model (CLAM) and for the UNIQUAC Model for the excess Gibbs energy G^E were determined from H^E data measured at a low temperature (ambient temperature). These parameters are used to predict VLE data at low and high temperatures. The dependence of the accuracy of predictions on the set of H^E data chosen to evaluate the parameters and on the model for G^E are discussed.     

Excess enthalpies of alcohol + amine mixtures. Experimental results and theoretical description using the ERAS-model

New experimental data of the molar excess enthalpy H^E of mixtures containing eight liquids - propylamine + methanol, ethanol, propan-1-ol, butan-1-ol, butylamine + methanol, ethanol, propan-1-ol, butan-1-ol - are presented using a quasi-isothermal flow calorimeter. The results are used for testing the ERAS-model which provides a theoretical concept accounting for the self-association and cross-association of alcohol and amine molecules, as well as for non-associative intermolecular interactions. Excess molar volumes V^E are also successfully described by the model. It turns out that the strong cross-association occurring between alcohol and amine molecules is the predominant reason for the remarkably low exothermic values of H^E observed for the mixtures studied.     

Vapor–liquid equilibria and excess properties for methyl tert-butyl ether (MTBE) containing binary systems

Methyl tert-butyl ether (MTBE) is recently widely used in the chemical and petrochemical industry as a non-polluting octane booster for gasoline and as an organic solvent. The isobaric or isothermal vapor–liquid equilibria (VLE) were determined directly for MTBE+C₁–C₄ alcohols. The excess enthalpy (H^E) for butane+MTBE or isobutene+MTBE and excess volume (V^E) for MTBE+C₃–C₄ alcohols were also determined. Besides, the infinite dilute activity coefficient, partial molar excess enthalpies and volumes at infinite dilution (γ^∞, H^E,∞, V^E,∞) were calculated from measured data. Each experimental data were correlated with various g^E models or empirical polynomial.     

Isothermal vapor–liquid equilibria and excess molar volumes for 2-methyl pyrazine (2MP) containing binary mixtures

2-Methyl pyrazine (2MP) has led to significant interest for its industrial and pharmaceutical uses. The new vapor–liquid equilibria (VLE) at 353.15 K and excess molar volumes (V^E) at 298.15 K over the whole mole fraction range for seven binaries (water, n-hexane, cyclohexane, n-heptane, methylcyclopentane (MCP), methylcyclohexane (MCH) and ethyl acetate (EA) with 2MP) have been measured. VLE were measured by using headspace gas chromatography and V^E were determined using precision density meter. The water+2MP system has only the minimum boiling azeotrope. The experimental VLE and V^E data were well correlated in terms of common g^E models and Redlich–Kister equation, respectively.     

Local-composition models and prediction of binary liquid-liquid binodal curves from heats of mixing

The temperature dependence of several local-composition models has been studied in conjunction with the Gibbs-Helmholtz identity. Binary heat-of-mixing data at temperatures near but above the critical solution temperature have been used to fit parameters obtained from excess-free-energy models in conjunction with the Gibbs-Helmholtz equation. These models, if the temperature dependence is adequate, should allow prediction of liquid-liquid equilibria (LLE) from the fitted parameters. The NRTL, UNIQUAC, and modified NRTL and UNIQUAC models (modified by inclusion of temperature-dependent parameters) seldom provide even qualitatively correct LLE predictions. A new local-composition model due to Wang and Chao (1983) yields reasonably good predictions for some systems but incorrect results for others. Reasons for these model inadequacies are discussed in terms of a local-composition model for the excess enthalpy which can be used to predict binodal curves accurately, including reasonably accurate values for the critical solution temperature, if reference excess-free-energy data at higher temperatures are available from VLE maesurements.     

Hm and Vm thermodynamic surfaces for binary mixtures in the near critical region

Even for such simple mixtures as (argon+methane), the excess enthalpy H^E_m and the excess volume V^E_m in the near critical region are about two orders of magnitude higher than for the liquid mixture at low temperatures and pressures near ambient conditions. Mixtures for which the critical temperatures are close together, and for which the critical pressures are far apart, have similar H^E_m (x,p,T) and V^E_m (x,p,T) surfaces, and near critical isotherms show double maxima in the supercritical fluid region. Mixtures for which the critical pressures are close together, and the critical temperatures are far apart, also have similar H^E_m (x,p,T) and V^E_m (x,p,T) surfaces, but isobars on the surfaces are ‘S’ shaped. The shapes of these near-critical excess-function surfaces can be understood from an inspection of the enthalpy, or residual enthalpy curves of the mixture and of the pure components. Examples of both are given. Attention is drawn to the large value that these excess functions can have close to a pure component critical point.     

Excess enthalpies of binary mixtures containing poly(propylene glycols) + benzyl alcohol, or + m-cresol, or + anisole at 308.15 K and at atmospheric pressure

Excess enthalpies, H^E, of binary mixtures containing poly(propylene glycols) of different molecular masses + benzyl alcohol, or + m-cresol, or + anisole were determined using a flow microcalorimeter at 308.15 K and at atmospheric pressure. Data was correlated using the Redlich–Kister polynomial. Results were qualitatively discussed in terms of molecular interactions and of the regular solution model.     

Viscometric and volumetric studies on binary mixtures of 1,2-dichloroethane and chlorinated methanes or their binary equimolar mixtures at 303.15 K

Excess viscosities, η^E and molar excess volumes V^E were obtained for binary mixtures of 1,2-dichloroethane and chlorinated methanes and for pseudobinary mixtures of 1,2-dichloroethane and equimolar binary mixtures from chlorinated methanes at 303.15 K. The chlorinated methanes include carbon tetrachloride, chloroform and dichloromethane. Grunberg—Nissan interaction parameter d and interaction energy for flow of activation W_vis were also presented. The relationship between the η^E's and the V^E's has been quantitively considered using Singh's equations. The excess viscosities for all the systems are negative over the entire compositions. There are specific interactions between 1,2-dichloroethane and chlorinated methanes, but the specific interactions are not strong. The interactions of 1,2-dichloroethane with chlorinated methanes decrease in the order: chloroform > dichloromethane > carbon tetrachloride. ‘Pseudochloroform’ has been defined by us for the first time as the equimolar mixture of dichloromethane and carbon tetrachloride.     

Excess volumes of binary mixtures of anisole with bromobenzene, o-dichlorobenzene, o-chloroaniline and p-dioxane at 298.15, 303.15, 308.15 and 313.15 K

Excess molar volumes, V^E, and partial molar volumes, _i, have been calculated for binary liquid mixtures of anisole with bromobenzene, o-dichlorobenzene, o-chloroaniline and p-dioxane from the results of densities measured at 298.15, 303.15, 308.15 and 313.15 K over the entire range of composition. In the temperature interval studied the values of V^E are positive for anisole + p-dioxane, anisole + bromobenzene and anisole + o-dichlorobenzene, whereas negative values are observed for anisole + o-chloroaniline. The negative V^E for the latter system was due to specific interactions between mixing components. The positive V^E for the remaining systems was ascribed to the dispersion-type interactions.     

Isobaric vapor–liquid equilibria for the quaternary reactive system: Ethanol + water + ethyl lactate + lactic acid at 101.33 kPa

Isobaric vapor–liquid equilibrium (VLE) data of the reactive quaternary system ethanol (1) + water (2) + ethyl lactate (3) + lactic acid (4) have been determined experimentally. Additionally, the reaction equilibrium constant was calculated for each VLE experimental data. The experimental VLE data were correlated using the UNIQUAC equation to describe the chemical and phase equilibria simultaneously. For some of the non-reactive binary systems, UNIQUAC binary interaction parameters were obtained from the literature. The rest of the binary UNIQUAC parameters were obtained by correlating the experimental quaternary VLE data obtained in this work. A maximum pressure azeotrope at high water concentration for the binary reactive system ethyl lactate + water has been calculated.