Vapour–liquid equilibria from molecular simulations: some issues affecting reliability and reproducibility

Journal of Chemical & Engineering Data, 2016

Selected vapor-liquid equilibrium literature data have been analyzed revealing in many cases very large fluctuations or very low precision, and inconsistencies, with some of them being even incorrect. Consequently, use of such data may result in a questionable estimate of other properties as, for example, the critical point location. It is shown that plotting the vapor compressibility factor as a function of temperature along its equilibrium curve may provide a simple but strong test of precision and correctness of such data. Examples are given for several models of water and also for three selected complex organic fluids for which simulation data have been reported in literature.

AIChE Journal, 2011

Vapor-liquid equilibria (VLE) of nine binary mixtures containing Hydrogen chloride or Phosgene in the solvents Benzene, Chlorobenzene, Ortho-Dichlorobenzene and Toluene as well as the mixture Hydrogen chloride + Phosgene are predicted by molecular modeling and simulation. The underlying force fields for the pure substances are developed on the basis of quantum chemical information on molecular geometry and electrostatics. These are individually optimized to experimental pure fluid data on the vapor pressure and saturated liquid density, where the deviations are typically less than 5 and 0.5 %, respectively. The unlike dispersive interaction is optimized for 1 seven of the nine studied binaries. Previously unpublished experimental binary VLE data, measured by BASF in the vicinity of ambient temperature, are predominantly used for these fits. VLE data, including dew point composition, saturated densities and enthalpy of vaporization, are predicted for a wide range of temperatures and compositions.

Fluid Phase Equilibria, 2009

A set of molecular models for 78 pure substances from prior work is taken as a basis for systematically studying vapor-liquid equilibria (VLE) in ternary systems. All 33 ternary mixtures of these 78 components for which experimental VLE data is available are studied by molecular simulation. The mixture models are based on the modified Lorentz-Berthelot combining rule that contains one binary interaction parameter which was adjusted to a single experimental binary vapor pressure of each binary subsystem in prior work. No adjustment to ternary data is carried out. The predictions from the molecular models of the 33 ternary mixtures are compared to the available experimental data. In almost all cases, the molecular models give excellent predictions of the ternary mixture properties.

The Journal of Physical Chemistry B, 1997

The vapor-liquid equilibria of 20 substances, most of them widely used as organic solvents, were obtained by means of a Gibbs ensemble Monte Carlo method. All these substances can be represented by linear or angular models with only two bonds. The intermolecular interaction was described by a Kihara potential and, where appropriate, an additional multipolar potential using meaningful microscopic parameters. The results agree excellently with experiment even for ranges of hundreds of kelvin when potential parameters are obtained only from fitting two critical constants. The largest discrepancies are observed for liquids capable of forming hydrogen bonds, especially alcohols, but even in these cases agreement is very fair for temperaturedensity equilibrium bells. Agreement is also very good for vapor pressure up to close to critical pressure, namely 60-80 bar in all cases. The worst agreement is again observed for hydrogen-bonding liquids. Vaporization enthalpies were also calculated for some substances. In this case agreement was only fair but also over a large range of temperatures. Finally, parameters commonly used in chemical engineering, such as the acentric factor and solubility factor, which enable prediction of the mutual solubilities of some hundreds of mixtures, were calculated. Some of these mixtures are not yet apparently measured in spite of their possible industrial interest.

Periodica Polytechnica Chemical Engineering, 1976

Industrial & Engineering Chemistry Research, 2008

The present work examines the accuracy of the SPEADMD molecular simulation methodology in correlating experimental data relative to a standard low-pressure database for testing VLE models. The database contains 104 binary systems categorized according to polarity and ideality. Although the database is somewhat small, it covers a broad range of chemical functionality, including halocarbons and carboxylic acids as well as hydrocarbons and alcohols. Six models were tested and compared for their characterization of these mixtures. Four standard models were evaluated to establish a basis for comparison: the Margules, NRTL, PR, and PRWS models. The SPEADMD model was evaluated in three forms. In its elementary form, the SPEADMD model includes ∼10% deviations in vapor pressure because of the application of transferable potential functions in the molecular model. An alternative model is developed on the basis of SPEADMD combined with corrected vapor pressures and customized self-interaction parameter for pure compounds. This alternative is referred to as the SPEADCI model, in which CI stands for customized interactions. Results show that SPEADCI model provides accuracy similar to the NRTL and PRWS models, even though it includes only one adjustable parameter per binary system, whereas the NRTL model includes two and the PRWS models include three. Deviations in correlated bubble point pressure are roughly 1-2% for these models. The SPEADMD models have the advantage that transferable potentials can be applied for solvation interactions that are similar to the Kamlet-Taft interaction parameters.

Journal of the Serbian Chemical Society, 2005

The NpT -Gibbs ensemble Monte Carlo computer simulation method was applied to predict the vapour-liquid equlibrium (VLE) behavior of the binary systems ethane + pentane at 277.55 K and 310.95 K, ethane + hexane at 298.15 K, propane + methanol at 313.15 K and propane + ethanol at 325.15 K and 425.15 K. The optimised potentials for the liquid simulating (OPLS) model were used to describe the interactions of alkanes and alcohols. The simulated VLE predictions are compared with experimental data available for the pressure and phase composition of the analyzed binary systems. The agreement between the experimental data and the simulation results is found to be generally good, although slightly better for system in which both components were nonpolar.

The reaction Gibbs ensemble Monte Carlo (RGEMC) computer simulation method [J. Phys. Chem. B 103 (1999) 10496] is used to predict the vapour-liquid equilibrium (VLE) behaviour of binary mixtures involving water, methanol, ethanol, carbon dioxide, and ethane. All these mixtures contain molecularly complex substances, and accurately predicting their VLE behaviour is a considerable challenge for molecular-based approaches, as well as for traditional engineering approaches. The substances are modelled as multi-site Lennard-Jones (LJ) plus Coulombic potentials with standard mixing rules for unlike site interactions. No adjustable binary-interaction parameters and no mixture experimental properties are used in the calculations; only readily-available pure-component vapour-pressure data are required. The simulated VLE predictions are compared with experimental results and with those of two typical semi-empirical macroscopic-level approaches. These latter are the UNIFAC liquid-state activity-coefficient model combined with the simple truncated virial equation of state, and the hole quasi-chemical group contribution equation of state. The agreement of the simulation results with the experimental data is generally good and also comparable with and in some cases better than those of the macroscopic-level empirical approaches.

Fluid Phase Equilibria, 2000

NVT-and NpT-Gibbs Ensemble Monte Carlo 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 K and 520 K by NpT-Monte Carlo 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.

2008

This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are