Association model of fluids. Simultaneous representation of excess Gibbs energies and excess enthalpies for liquid mixtures with alkanols

The binary excess Gibbs energies and excess enthalpies of liquid mixtures of alkanols and hydrocarbons, acetone, methyl acetate, acetonitrile, organic acid, etc., are simultaneously correlated with a new association model whose equilibrium constants are defined in terms of the modified segment fractions of chemical species. The model predicts ternary vapor-liquid, liquid-liquid equilibria and excess molar enthalpies of those mixtures well using only binary parameters.     

Representation of Multicomponent Liquid-Liquid Equilibria for Aqueous and Organic Solutions Using a Modified UNIQUAC Model

A modified form of the UNIQUAC model is presented to accurately reproducebinary phase equilibria and ternary and quaternary liquid-liquid equilibria ofaqueous and organic solutions. The model gives a good representation in thereproduction of binary coexistence curves over a wide temperature range usingtemperature-dependent parameters and of binary vapor-liquid equilibria usingtwo binary energy parameters, and in the correlation of ternary and quaternaryliquid-liquid equilibria using ternary and quaternary parameters, in addition tobinary parameters. The quaternary calculated results are compared with thoseobtained from the modified Wilson and extended UNIQUAC models.     

A molecular theory for the thermodynamic behavior of polar mixtures. II. Development of an equation of state based on the local composition mixing rules

In this study, the essential features of a molecular theory developed earlier for the local composition model in solution thermodynamics is used as the basis for more applied calculations of vapor-liquid equilibria for mixtures of molecules vastly different in size, polarity, and strength of interaction. An accurate equation of state is introduced into the method by incorporating the Helmholtz free energy through the Gibbs-Helmholtz relation. In the local composition mixing rules, the interaction energy effects are represented by a multifluid model, while molecular size effects are represented by a one-fluid model, which in spirit corresponds to a mean density approximation for the molecular pair distribution functions. Calculations of the vapor-liquid equilibria of a wide variety of binary mixtures including nonpolar hydrocarbons, hydrogen-bonding alcohols, water, ammonia , and carbon dioxide show good agreement with experimental data.     

Liquid-liquid equilibria for the acetonitrile + methanol + saturated hydrocarbon and acetonitrile + 1-butanol + saturated hydrocarbon systems

Tie-line results at 25°C and atmospheric pressure are presented for {(acetonitrile + methanol) + cyclohexane, or + n-hexane, or + n-heptane or + n-octane} and for {(acetonitrile + 1-butanol) + cyclohexane, or + n-hexane or + n-heptane}. Vapor-liquid equilibria for acetonitrile + methanol at 25° C are reported. The UNIQUAC associated-solution model is used to correlate binary vapor-liquid equilibria and mutual solubilities for the 13 systems constituting the ternary systems and to predict the ternary liquid-liquid equilibria by using binary parameters alone.     

二氧化碳-水混合体系的相平衡和汽-液-液三相点研究

在微扰链统计缔合流体理论(PC-SAFT)的基础上建立了适用于二氧化碳-水体系相行为研究的状态方程, 以汽-液平衡和液-液平衡实验数据关联体系的交叉作用参数, 关联结果与实验数据吻合良好. 预测了二氧化碳-水体系存在汽-液-液三相平衡的温度和压力区间, 确定了三相点的汽-液-液三相密度及其与温度和压力的关系.     

室温离子液体混合物的相平衡研究进展

室温离子液体混合物的相平衡数据是设计和优化涉及离子液体的化学反应与分离工程的重要基础。本文综述了近年来室温离子液体混合物,特别是室温离子液体＋有机物体系的气－液平衡、液－液平衡和固－液平衡的研究进展,总结了这些混合物相行为的基本热力学规律以及对萃取分离工程的指导作用。     

Isobaric vapor-liquid equilibria of the methanol,methyl acetate and methyl acrylate system at atmospheric pressure

Isobaric vapor-liquid equilibrium (VLE) data were determined at atmospheric pressure for the binary and the ternary mixtures of methanol, methyl acetate and (stabilized) methyl acrylate. The thermodynamic consistency of the data for the three binary mixtures was tested via Herington analysis. The experimental VLE data were reduced and binary parameters for four activity coefficient models, such as Margules, Wilson, NRTL and UNIQUAC, were fitted. The four models with their best-fitted parameters were used to predict the ternary vapor-liquid equilibria. A comparison of model performances was made by using the criterion of average absolute deviations in boiling point and in vapor-phase composition.     

Phase equilibria in carbon dioxide expanded solvents: Experiments and molecular simulations

We present complementary molecular simulations and experimental results of phase equilibria for carbon dioxide expanded acetonitrile, methanol, ethanol, acetone, acetic acid, toluene, and 1-octene. The volume expansion measurements were done using a high-pressure Jerguson view cell. Molecular simulations were performed using the Gibbs ensemble Monte Carlo method. Calculations in the canonical ensemble (NVT) were performed to determine the coexistence curve of the pure solvent systems. Binary mixtures were simulated in the isobaric-isothermal distribution (NPT). Predictions of vapor-liquid equilibria of the pure components agree well with experimental data. The simulations accurately reproduced experimental data on saturated liquid and vapor densities for carbon dioxide, methanol, ethanol, acetone, acetic acid, toluene, and 1-octene. In all carbon dioxide expanded liquids (CXL's) studied, the molecular simulation results for the volume expansion of these binary mixtures were found to be as good as, and in many cases superior to, predictions based on the Peng-Robinson equation of state, demonstrating the utility of molecular simulation in the prediction of CXL phase equilibria.     

Application of association models to mixtures containing alkanolamines

Two association models, the CPA and sPC-SAFT equations of state, are applied to binary mixtures containing alkanolamines and hydrocarbons or water. CPA is applied to mixtures of MEA and DEA, while sPC-SAFT is applied to MEA-n-heptane liquid-liquid equilibria and MEA-water vapor-liquid equilibria. The role of association schemes is investigated in connection with CPA, while for sPC-SAFT emphasis is given on the role of different types of data in the determination of pure compound parameters suitable for mixture calculations. Moreover, the performance of CPA and sPC-SAFT for MEA-containing systems is compared. The investigation showed that vapor pressures and liquid densities were not sufficient for obtaining reliable parameters with either CPA or sPC-SAFT, but that at least one other type of information is needed. LLE data for a binary mixture of the associating component with an inert compound is very useful in the estimation. The simple 4-site scheme is suitable for both CPA and sPC-SAFT and little is gained by using more complex association schemes. Finally, the results of CPA and sPC-SAFT are overall similar and whatever differences are seen appear to be more related to details in the parametrization rather than the different functional forms of the two equations of state.     

Equations of state for strongly nonideal fluid mixtures: Application of local compositions toward density-dependent mixing rules

A local-composition, two-fluid model has been developed for equation-of-state calculations of fluid-phase equilibria for asymmetric mixtures; it is applicable to any equation of state of the van der Waals form. A modification of the quasichemical theory of Guggenheim is applied to mixtures at all fluid densities. Desirable boundary conditions are met at low densities, at high densities, and at high temperatures.In effect, the local-composition model uses density-dependent mixing rules. It contains no new adjustable binary parameters and can be extended to multicomponent mixtures without ternary (or higher) parameters. It appears that, when compared to conventional one-fluid models, significant improvement may be obtained in predictions for vapor-liquid equilibria of typical asymmetric mixtures.     

Liquid-liquid equilibria of (cyclohexane + acetonitrile + methylcyclohexane + toluene) and of {(acetonitrile + methylcyclohexane) + benzene or + toluene or + cyclohexane or + chlorobenzene} at 298.15 K

Tie-line results at 298.15 K and atmospheric pressure are reported for (cyclohexane + acetonitrile + methylcyclohexane + toluene) and for {(acetonitrile + methylcyclohexane) + benzene or + toluene or + cyclohexane or + chlorobenzene). The extended UNIQUAC and UNIQUAC equations are used to correlate binary vapour-liquid equilibria and mutual solubilities for 10 mixtures constituting the ternary mixtures and to predict the ternary and quaternary liquid-liquid equilibria by use of only binary parameters.     

Molecular thermodynamics on the basis of an equation of state for argon. II. Binary mixtures of weakly nonspherical molecules

Using a molecular perturbation theory based on an equation of state for pure argon, excess properties and vapor-liquid equilibria are predicted for various binary mixtures composed of weakly nonspherical molecules. The results are rather satisfactory and generally much better than obtained using typical empirical methods. It is further demonstrated that a binary parameter in the dispersion energy results in only modest improvement     

A semi-empirical equation of state applied to vapor-liquid equilibria calculations

A five-parameter equation of state is proposed to calculate the vapor-liquid equilibria of compounds in binary and multicomponent mixtures. This equation is closely related to a previous equation of state proposed by the author, the main modification being in the entropic term where the parameter m assumes a constant value for all compounds. It is shown that the van der Waals conditions at the critical point and the Morbidelli-Carra' algorithm enable the calculation of three other constants. Rules are given to calculate the remaining constant K which pertains to the enthalpic term. The proposed method only requires knowledge of the critical constants and of the normal boiling temperature as input parameters. A wide application of the new equation to both polar and non-polar binary systems indicates the following: the proposed method is predictive for ideal or nearly ideal mixtures; the correlation of mixtures of hydrocarbons having very different molar volumes can be obtained by optimizing only the binary interaction parameter linked to the enthalpic term; the new equation also correlates well with strongly non-ideal systems which exhibit a miscibility gap; the prediction of multicomponent vapor-liquid equilibria from the binary data alone is also reliable for both polar and non-polar mixtures.     

Application of a generalized van der Waals equation of state to several nonpolar mixtures

A generalized van der Waals equation of state, applied recently (Nguyen Van Nhu and Kohler, 1995) to the calculation of excess properties and phase equilibria for the mixture methane + ethane, is now extended to several nonpolar binary mixtures.Improved mixing rules for the van der Waals attractive term and for the correction term are proposed. With these mixing rules, the equation gives good agreement for vapour-liquid and liquid-liquid equilibria over a large temperature range for 29 binary mixtures. The agreement of mixture volumes and cross second virial coefficients is also satisfactory.     

Liquid-liquid equilibrium data: Their retrieval,correlation and prediction Part I: Retrieval

Part one of this series of articles contains a status report covering the published liquid-liquid equilibrium data for binary and multicomponent mixtures with organic components. Different methods of measuring liquid-liquid equilibrium data are briefly mentioned, and a new, computerized data bank for storage and retrieval of the data is described.This part will be followed by articles on the correlation and prediction of liquid-liquid equilibria.     

Binary phase behavior and aggregation of dilute methanol in supercritical carbon dioxide: a Monte Carlo simulation study

Configurational-bias Monte Carlo simulations in the Gibbs and isobaric-isothermal ensembles using the transferable potentials for phase equilibria force field were carried out to investigate the thermophysical properties of mixtures containing supercritical carbon dioxide and methanol. The binary vapor-liquid coexistence curves were calculated at 333.15 and 353.15 K and are in excellent agreement with experimental measurements. The self-association of methanol in supercritical carbon dioxide was investigated over a range of temperatures and pressures near the mixture critical point. The temperature dependence of the equilibrium constants for the formation of hydrogen-bonded aggregates (from dimer to heptamer) allowed for the determination of the enthalpy of hydrogen bonding, DeltaHHB, in supercritical carbon dioxide with values for DeltaHHB of about 15 kJ mol(-1) falling within the range of previously proposed values. No strong pressure dependence was observed for the formation of aggregates. Apparently the decrease of the entropic penalty and of the enthalpic benefit upon increasing pressure or solvent density mostly cancel each other's effect on aggregate formation.     

Peng-Robinson equation of state for vapor-liquid equilibrium calculations for carbon dioxide + hydrocarbon mixtures

Lin, H.-M., 1984. Peng-Robinson equation of state for vapor-liquid equilibrium calculations for carbon dioxide + hydrocarbon mixtures. Fluid Phase Equilibria, 16: 151–169.Binary interaction parameters δ_ij in the Peng-Robinson equation of state have been determined from vapor-liquid equilibrium data for binary mixtures of carbon dioxide with a variety of hydrocarbons. A constant value of δ_ij ? 0.125 appears to represent the experimental data well in most cases. Comments are made on the recent work of Kato, Nagahama and Hirata, who correlated δ_ij as a function of temperature for CO₂ + n-paraffin binary mixtures.     

Modeling of Liquid-Vapor Equilibrium in Systems Including a Light Oil-Gas Component and Aromatic and Polyaromatic Hydrocarbons

The Victorov-Smirnova's hole lattice quasichemical group-contribution model (HM) is used to simulate the vapor-liquid equilibrium in binary and ternary mixtures systems composed by aromatic (benzene, toluene) and polyaromatic (naphthalene, phenanthrene) hydrocarbons and light oil-gas components (carbon dioxide, hydrogen sulfide, nitrogen, methane, ethane, propane). Eighteen binary and two ternary systems are examined. New group parameters for these systems are estimated. The results of modeling are compared with the experimental data and those predicted by the Peng-Robinson equation of state.     

Analytical applications of liquid-liquid phase equilibria: analysis of binary mixtures of chemically similar components

A new, simple and rapid method based on the principle of liquid-liquid phase equilibria has been developed for the analysis of binary mixtures of chemically similar organic compounds. The method does not require elaborate instrumentation and can be used to analyse mixtures of members of homologous series. The application of the method has been illustrated by analysing binary mixtures of n-hexane and n-octane; the maximum uncertainty in this analysis is ~2%.     

Modification of the NRTL model for ternary and quaternary liquid-liquid equilibrium calculations

The original NRTL model is modified for the correlation of ternary liquid-liquid equilibria. The ternary expression of the modified NRTL model includes three additional ternary parameters and the ternary terms vanish when a ternary system degenerates to a binary. The ability of the modified NRTL model has been evaluated in the calculations of ternary vapor-liquid-liquid equilibria and quaternary liquid-liquid equilibria.