We report a molecular simulation study for a model of water adsorption on nonporous and porous activated carbons. The grand canonical Monte Carlo method is used, and the temperature is fixed at 300 K. Water molecules are modeled as a Lennard-Jones sphere with four square-well sites to account for the hydrogen bonding. The carbon surfaces consist of planar graphite sheets, with active chemical sites on the surface modeled as square-well sites. The effect of the density and geometric arrangement of the active sites on the surface is studied. Both macroscopic properties (particularly adsorption isotherms) and molecular configurations are obtained. The adsorption mechanism for water on such surfaces is markedly different from that of simple nonassociating molecules such as hydrocarbons or nitrogen. In contrast to the usual buildup of adsorbed layers on the surface, water adsorption is characterized by the formation of peculiar three-dimensional water clusters and networks, whose formation relies on a cooperative effect involving both fluid−fluid interactions and fluid−solid ones with suitably placed active sites. Both the density and arrangement of the sites on the surface have a pronounced effect on the adsorption. Capillary condensation is observed only for low densities of active sites; for higher densities, continuous filling occurs.

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A modified statistical associating fluid theory (SAFT) equation of state has been applied to predict the phase equilibria behavior of binary and ternary mixtures. In order to study multicomponent systems, the equation is first applied to pure fluids. The SAFT equation is written in the same spirit as that presented by Huang and Radosz [Ind. Eng. Chem. Res. 1990, 29, 2284−2294], but with two important differences:  the reference term is a Lennard−Jones fluid, accounting explicitly for dispersive and repulsive forces, and the equation is extended to heteronuclear chains. The molecular parameters of pure substances are obtained by fitting to the saturated liquid density and by equating the chemical potentials in both phases. Three molecular parameters are needed to obtain the thermodynamic properties of pure substances, namely, the segment size, dispersive energy, and chain length. Two additional parameters are needed to describe the associating molecules, the association energy, and volume. They are obtained by fitting to experimental saturated liquid density and by equating the chemical potentials in both phases over a wide range of temperatures. The molecular parameters are found to scale with the molecular weight for the alkanes. The binary parameters of the mixtures, ξ12 and η12 in the generalized Lorentz−Berthelot combining rules, are fitted to experimental data for the molar fractions on the liquid and vapor sides at a given temperature, in such a way that they do not depend on the composition and/or temperature. These binary parameters are used to predict the behavior of the mixture at different thermodynamic conditions. Ternary mixtures are predicted from the previous parameters without any further adjustment. The agreement between prediction and experimental results is excellent in all cases.

A new set of molecular transferable parameters for the n-alkane series is proposed. n-Alkanes are modeled as homonuclear chainlike molecules formed by tangentially bonded Lennard-Jones segments of equal diameter and the same dispersive energy. Phase equilibria calculations of heavy pure members of the series, up to n-octatetracontane (n-C 48 H 98 ), and of ethane/n-decane and ethane/n-eicosane mixtures are performed with the soft-SAFT (statistical associating fluid theory) equation of state. This SAFT-type equation explicitly accounts for repulsive and dispersive forces in the reference term through a Lennard-Jones interaction potential, and it has been proven to accurately describe the phase behavior of light n-alkanes. Using the new set of parameters, the soft-SAFT equation is able to accurately predict the phase behavior of pure heavy n-alkanes. The dependence of the critical properties of pure n-alkanes with the carbon number is also predicted to be in quantitative agreement with experimental data, validating, at the same time, some recent simulation results of heavy members of the series. For the mixtures, the use of simple Lorentz-Berthelot combining rules provides quantitative agreement with experimental data over a broad range of temperatures and pressures. The physical meaning and transferability of these parameters are also discussed.

A molecular model within a SAFT context for quantitatively predicting the solubility of xenon and oxygen in n-perfluoroalkanes is presented and discussed here. All species are treated as Lennard-Jones chains formed by tangentially bonded spheres with the same diameter and dispersive energy. Optimized meaningful values of both molecular parameters for the pure perfluoroalkanes are also used to accurately predict vapor−liquid and liquid−liquid equilibria of n-alkane + n-perfluoroalkane mixtures. Because of the high nonideality of the mixtures, the Lorentz−Berthelot cross-interaction parameters need to be adjusted using experimental data and ensuring coherent trends. An accurate description of the solubility of oxygen requires additional information to be included in the model. On the basis of ab initio arguments, we considered cross-association between oxygen and perfluoroalkane molecules, which allows solubilities to be described with a deviation below 5%, when compared to experimental data available in the literature and measured in our laboratory.

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Isobaric vapor liquid equilibria (VLE) of binary mixtures of the ionic liquid (IL) 1-butyl-3-methylimidazolium trifluoromethanesulfonate (CmimTfO) with either water or short chained n-alkyl alcohols (methanol, ethanol, propan-1-ol, and butan-1-ol) are described in this study. Two different microebulliometers and a classical VLE apparatus were compared and the VLEs were determined in the composition range 0.4 ≤ x(solvent) ≤ 1 at three different pressure levels ( p = 500 mbar, 700 mbar, and 1000 mbar). The experimental data were modeled using the soft-SAFT equation of state, which was able to accurately describe the nonideal behavior of these mixtures. The combined experimental-modeling results obtained contribute to establish the structure-property relationship between the CmimTfO and n-alkyl alcohol molecules and to infer about its influence on the phase behavior of these solvents.

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