Phase equilibria for liquid mixtures of (butanenitrile + a carboxylic acid + water) at 298.15 K

Liquid–liquid equilibrium data are presented for mixtures of (butanenitrile (1)+acetic acid or propanoic acid or butanoic acid or 2-methylpropanoic acid or pentanoic acid or 3-methylbutanoic acid (2)+water (3)) at 298.15 K. The relative mutual solubility of all the carboxylic acids is higher in the butanenitrile layer than in the aqueous layer. The influence of acetic acid and propanoic acid on the solubility of water in butanenitrile is greater than that of the other acids. Three parameter equations have been fitted to the binodal curve data. These equations are compared and discussed in terms of statistical consistency. Selectivity values for solvent separation efficiency were derived from the tie-line data. The NRTL and UNIQUAC models were used to correlate the experimental results and to calculate the phase compositions of the ternary systems. The NRTL equation fitted the experimental data far better than the UNIQUAC equation.     

Phase equilibria for liquid mixtures of (benzonitrile + a carboxylic acid + water) atT = 298.15 K

(Liquid  +  liquid) equilibrium data are presented for mixtures of {benzonitrile(1)  +  acetic acid or propanoic acid or butanoic acid or 2-methylpropanoic acid or pentanoic acid or 3-methylbutanoic acid(2)  +  water(3)} atT =  298.15 K. The relative mutual solubility of each of the carboxylic acids is higher in the benzonitrile layer than in the aqueous layer. The influence of 3-methylbutanoic acid, pentanoic acid, 2-methylpropanoic acid, and butanoic acid on the solubility of the hydrocarbons in benzonitrile is greater than that of the acetic and propanoic acids. Three three-parameter equations have been fitted to the binodal curve data. These equations are compared and discussed in terms of statistical consistency. The NRTL and UNIQUAC models were used to correlate the experimental tie lines and to calculate the phase compositions of the ternary systems. The NRTL equation fitted the experimental data far better than the UNIQUAC equation. Selectivity values for solvent separation efficiency were derived from the tie line data.     

顺丁烯二酸酐与邻苯二甲酸二甲酯二元体系在4.00, 8.00和12.00 kPa下的等压气液平衡

采用沸点仪测定了顺丁烯二酸酐和邻苯二甲酸二甲酯二元体系在4.00, 8.00和12.00 kPa下的等压气液平衡数据以及纯DMP组分饱和蒸气压数据, 将实验数据回归得到了纯DMP在417~525 K范围内的Antoine方程. 根据实验平衡温度、 压力和组成数据进一步回归得到NRTL方程参数, 推算出平衡气液相组成, 并利用UNIFAC方程对实验数据进行了预测, 其结果与沸点仪测定结果及NRTL拟合的结果基本相符.     

Transferable potentials for phase equilibria. 8. United-atom description for thiols, sulfides, disulfides, and thiophene

An extension of the transferable potentials for phase equilibria united-atom (TraPPE-UA) force field to thiol, sulfide, and disulfide functionalities and thiophene is presented. In the TraPPE-UA force field, nonbonded interactions are governed by a Lennard-Jones plus fixed point charge functional form. Partial charges are determined through a CHELPG analysis of electrostatic potential energy surfaces derived from ab initio calculations at the HF/6-31g+(d,p) level. The Lennard-Jones well depth and size parameters for four new interaction sites, S (thiols), S(sulfides), S(disulfides), and S(thiophene), were determined by fitting simulation data to pure-component vapor-equilibrium data for methanethiol, dimethyl sulfide, dimethyl disulfide, and thiophene, respectively. Configurational-bias Monte Carlo simulations in the grand canonical ensemble combined with histogram-reweighting methods were used to calculate the vapor-liquid coexistence curves for methanethiol, ethanethiol, 2-methyl-1-propanethiol, 2-methyl-2-propanethiol, 2-butanethiol, pentanethiol, octanethiol, dimethyl sulfide, diethyl sulfide, ethylmethyl sulfide, dimethyl disulfide, diethyl disulfide, and thiophene. Excellent agreement with experiment is achieved, with unsigned errors of less than 1% for saturated liquid densities and less than 3% for critical temperatures. The normal boiling points were predicted to within 1% of experiment in most cases, although for certain molecules (pentanethiol) deviations as large as 5% were found. Additional calculations were performed to determine the pressure-composition behavior of ethanethiol+n-butane at 373.15 K and the temperature-composition behavior of 1-propanethiol+n-hexane at 1.01 bar. In each case, a good reproduction of experimental vapor-liquid equilibrium separation factors is achieved; both of the coexistence curves are somewhat shifted because of overprediction of the pure-component vapor pressures.     

GEMC和GDI方法计算流体气液相平衡的比较

考察采用TraPPE联合原子和OPLS全原子力场两种分子力场, Gibbs系综蒙特卡罗(GEMC)方法和Gibbs-Duhem积分(GDI)方法计算流体气液相平衡的适用性、计算速度、计算精度等问题. 结果表明, 在采用全原子力场情况下, GDI方法比GEMC方法极大地节省了计算时间. 从计算结果来看, 两种方法各有适用范围, 在使用时可互为补充. 在给定力场的前提下, 两种方法所得到的液相密度、蒸发焓、临界温度和临界密度相差不大, 而当力场中的缺陷导致蒸发焓的计算不够准确时, 两种计算方法得到的气体的压力和密度明显不同,进而导致预测的临界压力也明显不同.     

Extension of the exp-6 model to the simulation of vapor-liquid equilibria of primary alcohols and their mixtures

Configurational-biased Gibbs ensemble Monte Carlo simulations were performed to obtain the phase behavior of the homologous series of primary alcohols from ethanol to 1-heptanol. Molecular interactions in these systems are modeled by a newly developed exp-6 potential in combination with a Coulombic intermolecular potential. Some of exp-6 potential parameters required to describe these alcohols were taken from the previous literature data reported for methanol and n-alkanes. The oxygen's potential parameters were optimized to fit the coexistence curve of these alcohols to the experimental data. Simulated values of saturated liquid and vapor densities, vapor pressures and critical constants of the alcohols are in good agreement with experimental data. The efficiency of the new model in the prediction of binary phase diagram of water/ethanol and n-hexane/1-propanol mixtures is also evaluated. The calculated mole fractions in the vapor and liquid phases of these binary mixtures also show satisfactory agreement with the experimental data.     

Phase compositions and saturated densities for the binary systems of carbon dioxide with ethanol and dichloromethane

The compositions and densities of the liquid and vapor phases of two binary systems at equilibrium were measured on a new experimental apparatus over a range of temperatures and pressures. The studied systems are: CO₂–ethanol at 313.2 and 328.2 K; CO₂–dichloromethane at 308.2, 318.2 and 328.2 K and for pressures ranging from ambient up to ca. 9 MPa. Some of our measurements are critically compared with corresponding literature values. These measurements are ideally suited for testing equation-of-state models. The recently developed quasi-chemical hydrogen-bonding (QCHB) model was used for correlating the experimental data. A satisfactory agreement was obtained between experimental and calculated phase compositions and saturated densities.     

Comparison of the AMBER,CHARMM, COMPASS,GROMOS, OPLS,TraPPE and UFF force fields for prediction of vapor–liquid coexistence curves and liquid densities

Monte Carlo simulations in the isobaric–isothermal and Gibbs ensembles are used to compute liquid densities and vapor–liquid coexistence curves for a series of small organic molecules for the AMBER-96, CHARMM22, COMPASS, GROMOS 43A1, OPLS-aa, TraPPE-UA, and UFF force fields. The simulation results are compared with experimental measurements to provide an assessment of the accuracy expected when using these force fields to study unknown molecules.     

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.     

Pressure dependence of the vapor-liquid-liquid phase behavior in ternary mixtures consisting of n-alkanes, n-perfluoroalkanes, and carbon dioxide

Expansion of an organic solvent by an inert gas can be used to tune the solvent's liquid density, solubility strength, and transport properties. In particular, gas expansion can be used to induce miscibility at low temperatures for solvent combinations that are biphasic at standard pressure. Configurational-bias Monte Carlo simulations in the Gibbs ensemble were carried out to investigate the vapor-liquid-liquid equilibria and microscopic structures for two ternary systems: n-decane/n-perfluorohexane/CO2 and n-hexane/n-perfluorodecane/CO2. These simulations employed the united-atom version of the transferable potential for phase equilibria (TraPPE-UA) force field. Initial simulations for binary mixtures of n-alkanes and n-perfluoroalkanes showed that special mixing parameters are required for the unlike interactions of CHx and CFy pseudoatoms to yield satisfactory results. The calculated upper critical solution pressures for the ternary mixtures at a temperature of 298 K are in excellent agreement with the available experimental data and predictions using the SAFT-VR (statistical associating fluid theory of variable range) equation of state. The simulations yield asymmetric compositions for the coexisting liquid phases and different degrees of microheterogeneity as measured by local mole fraction enhancements.     

Isobaric vapor–liquid equilibria of the binary system maleic anhydride and di-isobutyl hexahydrophthalate at 2.67, 5.33 and 8.00 kPa

Isobaric vapor–liquid equilibrium (VLE) data for the binary system maleic anhydride (MAN) + di-isobutyl hexahydrophthalate (DIBE) at 2.67, 5.33 and 8.00 kPa were measured with a modified ebulliometer. Also, saturated vapor pressures of pure DIBE were measured and Antoine constants were obtained. These data were used to calculate equilibrium vapor and liquid compositions for this binary system using the NRTL model. Prediction of the VLE was done with the universal quasi-chemical functional-group activity coefficients (UNIFAC) model. The predicted results generally agree with those from experiment.     

Monte Carlo predictions of phase equilibria and structure for dimethyl ether + sulfur dioxide and dimethyl ether + carbon dioxide

A new force field for dimethyl ether (DME) based on the Lennard-Jones (LJ) 12-6 plus point charge functional form is presented in this work. This force field reproduces experimental saturated liquid and vapor densities, vapor pressures, heats of vaporization, and critical properties to within the statistical uncertainty of the combined experimental and simulation measurements for temperatures between the normal boiling and critical point. Critical parameters and normal boiling point are predicted to within 0.1% of experiment. This force field is used in grand canonical histogram reweighting Monte Carlo simulations to predict the pressure composition diagrams for the binary mixtures DME + SO(2) at 363.15 K and DME + CO(2) at 335.15 and 308.15 K. For the DME + SO(2) mixture, simulation is able to qualitatively reproduce the minimum pressure azeotropy observed experimentally for this mixture, but quantitative errors exist, suggesting that multibody effects may be important in this system. For the DME + CO(2) mixture, simulation is able to predict the pressure-composition behavior within 1% of experimental data. Simulations in the isobaric-isothermal ensemble are used to determine the microstructure of DME + SO(2) and DME + CO(2) mixtures. The DME + SO(2) shows weak pairing between DME and SO(2) molecules, while no specific pairing or aggregation is observed for mixtures of DME + CO(2).     

Vapor+liquid equilibrium of water, carbon dioxide, and the binary system, water+carbon dioxide, from molecular simulation

NVT- and NpT-Gibbs ensemble Monte Carlo (GEMC) simulations were applied to describe the vapor–liquid equilibrium of water (between 323 and 573 K), carbon dioxide (between 230 and 290 K) and their binary mixtures (between 348 and 393 K). The properties of supercritical carbon dioxide were determined between 310 and 520 K by NpT-MC simulations. Literature data for the effective pair potentials (for water: the SPC-, SPC/E-, and TIP4P potential models; for carbon dioxide: the EPM2 potential model) were used to describe the properties of the pure substances. The vapor pressures of water and carbon dioxide are calculated. For water, the SPC- and TIP4P models give superior results for the vapor pressure when compared to the SPC/E model. The vapor–liquid equilibrium of the binary mixture, carbon dioxide–water, was predicted using the SPC- as well as the TIP4P model for water and the EPM2 model for carbon dioxide. The interactions between carbon dioxide and water were estimated from the pair potentials of the pure components using common mixing rules without any adjustable binary parameter. Agreement of the predicted data for the compositions of the coexisting phases in vapor–liquid equilibrium and experimental results is observed within the statistical uncertainties of the simulation results in the investigated range of state, i.e. at pressures up to about 20 MPa.     

Isobaric (vapor + liquid) equilibria of the binary system maleic anhydride and diethyl phthalate at p = (2.67, 5.33, and 8.00) kPa

Saturated vapor pressures of pure diethyl phthalate were measured with the ebulliometer. And isobaric (vapor + liquid) equilibrium data for the binary system (maleic anhydride + diethyl phthalate) at p = (2.67, 5.33, and 8.00) kPa were determined using the ebulliometric method. The parameters of the NRTL model for the binary system were obtained by calculating equilibrium compositions of the liquid and vapor phase with the experimental equilibrium temperatures, pressures and feed compositions. Moreover, (vapor + liquid) equilibrium data for the binary system were predicted by use of the UNIFAC model. Predicted results were compared with those from the ebulliometric method, and showed good agreement.     

Prediction of vapor–liquid equilibria properties of several HFC binary refrigerant mixtures

New correlations have been developed to estimate saturated vapor pressures of eight HFC binary refrigerant mixtures, namely HFC125/134a, HFC125/143a, HFC134a/236fa, HFC134a/245fa, HFC143a/134a, HFC143a/152a, HFC32/125, and HFC32/134a. In this prediction method, the saturated vapor pressures of mixtures can be calculated by the thermoproperties of pure components, without any adjustable parameters determined by experimental data. The overall average absolute deviation of pressures is <1% compared with experimental data.     

Critical and phase-equilibrium properties of an ab initio based potential model of methanol and 1-propanol using two-phase molecular dynamics simulations

Two-phase molecular dynamics simulations employing a Monte Carlo volume sampling method were performed using an ab initio based force field model parameterized to reproduce quantum-mechanical dimer energies for methanol and 1-propanol at temperatures approaching the critical temperature. The intermolecular potential models were used to obtain the binodal vapor-liquid phase dome at temperatures to within about 10 K of the critical temperature. The efficacy of two all-atom, site-site pair potential models, developed solely from the energy landscape obtained from high-level ab initio pair interactions, was tested for the first time. The first model was regressed from the ab initio landscape without point charges using a modified Morse potential to model the complete interactions; the second model included point charges to separate Coulombic and dispersion interactions. Both models produced equivalent phase domes and critical loci. The model results for the critical temperature, density, and pressure, in addition to the sub-critical equilibrium vapor and liquid densities and vapor pressures, are compared to experimental data. The model's critical temperature for methanol is 77 K too high while that for 1-propanol is 80 K too low, but the critical densities are in good agreement. These differences are likely attributable to the lack of multi-body interactions in the true pair potential models used here.     

High pressure phase equilibrium for ethylene + 1-propanol system at 283.65 K

Phase equilibria and saturated densities for ethylene+1-propanol system at high pressures were measured using a static-circulation apparatus at 283.65 K. The equilibrium composition and saturated density of each phase were determined by using gas chromatograph and vibrating tube density meters, respectively. The saturated points near the critical region are further measured by the conventional indirect method. The present experimental results include vapor–liquid equilibria (VLE), liquid–liquid equilibria (LLE), and vapor–liquid–liquid equilibria (VLLE). The experimental data were correlated with various equations of state.     

Prediction of viscosities and vapor–liquid equilibria for five polyhydric alcohols by molecular simulation

Reverse nonequilibrium molecular dynamics in the canonical ensemble and coupled–decoupled configurational-bias Monte Carlo simulations in the Gibbs ensemble were used to predict the low-shear rate Newtonian viscosities and vapor–liquid coexistence curves for 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, and 1,2,4-butanetriol modeled with the transferable potentials for phase equilibria-united atom (TraPPE-UA) force field. Comparison with available experimental data demonstrates that the TraPPE-UA force field yields very good predictions of the viscosities and vapor–liquid coexistence curves. A detailed analysis of liquid structure and hydrogen bonding is provided.