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A framework to self-consistently combine a classical equation of state (EoS) and a molecular force field to model polymers and polymer mixtures is presented. The statistical associating fluid theory (SAFT-γ Mie) model is used to correlate the thermophysical properties of oligomers and generate robust and transferrable coarse-grained (CG) molecular parameters which can be used both in particle based molecular simulations and in EoS calculations. Examples are provided for polyethylene, polypropylene, polyisobutylene atactic polystyrene, 1,4-cis-butadiene, polyisoprene, their blends and mixtures with low molecular weight solvents. Different types of liquid-liquid phase behaviour are quantitatively captured both by the EoS and by direct molecular dynamics simulations. The use of CG models following this top-down approach extends the time and length scales accessible to molecular simulation while retaining quantitative accuracy as compared to experimental results.

Agradecimentos: The authors gratefully acknowledge the financial support from the Brazilian Coordination for the Improvement of Higher Education Personnel (CAPES) Abstract: We propose a new thermodynamic approach for nonspherical molecules by applying a perturbation theory in which an anisotropic intermolecular potential, the hard Gaussian overlap, is the reference system. The new equation of state (EoS) modifies the usual statistical associating fluid theory (SAFT) approach by combining both segment and chain contributions as a single anisotropic term. Fluid particles are represented as ellipsoids rather than a set of a few tangential spherical segments. The perturbed potential is taken as a square well, following the original formulation of SAFT with attractive potential of variable range (SAFT-VR SW). The parameters of the proposed model were optimized to fit vapor pressures and saturated liquid densities for ethane and carbon dioxide. Derivative properties, such as isobaric and isochoric heat capacities, speed of sound, Joule-Thomson coefficient, thermal expansion coefficient, and isothermal compressibility, were evaluated at supercritical conditions up to 70 MPa for ethane and 200 MPa for carbon dioxide. The proposed EoS outperforms the original SAFT-VR SW EoS for many of these properties. This implies that an ellipsoidal geometry is an adequate representation of such nonspherical molecules, avoiding the approximations usually applied in Wertheim’s first-order thermodynamic perturbation theory for the calculation of the Helmholtz free energy of chain formation COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Fechado

Experimental determination and theoretical predictions of the isothermal (344.15 K) mass densities and interfacial tensions for the sys tem carbon dioxide (CO2) with heptol (n - heptane + toluene) mixtures varying liquid volume fraction compositions of toluene (0, 25, 50, 75, 100 % v/v) and over the pressure range 0.1 to 8 MPa are reported. Measurements are carried out on a high - pressure dev ice that includes a vibrating tube densimeter and a pendant drop tensiometer. Theoretical modeling of mass densities phase equilibria and interfacial properties (i.e., interfacial tension and interfacial concentration profiles) are performed by employing t he Square Gradient Theory using an extension of the Statistical Associating Fluid Theory equation of state that accounts for ring fluids. The experimental bulk phase equilibrium densities and interfacial tensions obtained are in very good agreement with th e theoretical predictions. Although there are no previous experimental data of these mixtures at the conditions explored herein, the results follow the same trends observed from experimental data at other conditions. The combination of experimental and mod eling approaches provides a route to simultaneously predict phase equilibrium and interfacial properties within acceptable statistical deviations. For the systems and conditions studied here, we observe that the phase equilibrium of the mixtures display z eotropic vapor - liquid equilibria with positive deviations from ideal behavior. The mass bulk densities behave ordinarily whereas the interfacial tensions decrease as the pressure or liquid mole fraction of CO2 increases and/or the ratio toluene/heptane dec reases. The interfacial concentration along the interfacial region exhibits a remarkable high excess adsorption of CO2, which increases with pressure and it is larger in n - heptane than in toluene. Toluene does not exhibit any special adsorption activity wh ereas n - heptane displays surface activity only at low pressure in a very narrow range for the case of CO2 + (25% n - heptane + 75% toluene) mixture.

The development of accurate models to predict the solvation, solubility, and partitioning of nonpolar and amphiphilic compounds in aqueous environments remains an important challenge. We develop state-of-the-art group-interaction models that deliver an accurate description of the thermodynamic properties of alkanes and alcohols in aqueous solution. The group-contribution formulation of the statistical associating fluid theory based on potentials with a variable Mie form (SAFT-γ Mie) is shown to provide accurate predictions of the phase equilibria, including liquid–liquid equilibria, solubility, free energies of solvation, and other infinite-dilution properties. The transferability of the model is further exemplified with predictions of octanol–water partitioning and solubility for a range of organic and pharmaceutically relevant compounds. Our SAFT-γ Mie platform is reliable for the prediction of challenging properties such as mutual solubilities of water and organic compounds which can span over 10 orders of magnitude, while remaining generic in its applicability to a wide range of compounds and thermodynamic conditions. Our work sheds light on contradictory findings related to alkane–water solubility data and the suitability of models that do not account explicitly for polarity.

The aim of this study is to describe the phase equilibrium behavior of aqueous solutions of selected ionic liquids (ILs) as new potential pairs of absorption cooling systems. The ILs under study have a shared cation, 1-butyl-3-methylimidiazolium, [C(4)mim](+), and the following anions: methanesulfonate, [CH3SO3](-), trifluoromethanesulfonate, [CF3SO3](-), acetate, [CH3CO2](-), trifluoroacetate, [CF3CO2](-), tosylate, [TOS](-), bromide, [Br](-), and thiocyanate, [SCN](-). Each binary system was individually studied within the soft-SAFT framework. A mesoscopic simple molecular model was proposed for each IL, being characterized by a specific set of molecular parameters. In combination with one or, in some cases, two additional binary parameters, it was possible to simultaneously describe the vapor-liquid equilibrium (VLE) of the aqueous binary systems at three different pressures (0.10 MPa, 0.07 MPa and 0.05 MPa) and the correspondent isothermal water activity coefficients at 298.15 K, correctly incorporating the different deviations from ideality and water interactions characteristics for each IL. Infinite dilution coefficients were also predicted in reasonable agreement with the experimental data. The simple model used with soft-SAFT to represent ILs provides an overall good description of most of the systems. Results for particular systems showed some space for improvement, nevertheless at expense of increasing the model complexity by changing the originally proposed molecular model. (C) 2016 Elsevier B.V. All rights reserved.

The development of successful and economical CO2 geological storage projects requires a precise estimation of the saturated phase densities and interfacial tension of the CO2/H2O system. The axisymmetric drop shape analysis (ADSA) method was used for measuring the interfacial tension of this system at temperatures over the range (298 to 469) K and pressures up to 69 MPa. The phase densities, required to determine accurate IFT values, were determined by measuring the oscillation period of the equilibrated phases with an Anton Paar densitometer. A correlation to readily determine the density of the CO2-saturated water phase in the range of interest is proposed and the use of pure compound densities for the calculation of the interfacial tension values discussed. The Cubic-Plus-Association equation of state (CPA EoS) was used to estimate the phase behaviour pressure and temperature dependence of the system studied with very good results. Bulk phase properties and influence parameters adjusted to pure compounds surface tensions within the density gradient theory (DGT) were used to predict the CO2/H2O interfacial tensions with remarkably low deviations from the measured values. Crown Copyright (C) 2015 Published by Elsevier Ltd. All rights reserved.

We report experimental measurements of three-phase equilibria in the system (heptane + carbon dioxide + water) obtained with a quasi-static analytical apparatus with compositional analysis by means of gas chromatography. The apparatus was calibrated by an absolute area method and the whole measurement system was validated by means of comparison with the published literature data of the system (heptane + carbon dioxide). The compositions of the three phases coexisting in equilibrium were measured along five isotherms at temperatures from (323.15 to 413.15) K with pressures ranging from approximately 2 MPa to the upper critical end point pressure at which the two nonaqueous phases became critical. The experimental results have been compared with the predictions of the statistical associating fluid theory for potentials of variable range. The unlike binary interaction parameters used here are consistent with a previous study for a ternary mixture of a different n-alkane, while the alkane–water binary interac...

The Mie (λr, λa) intermolecular pair potential has been suggested as an alternative to the traditional Lennard–Jones (12–6) potential for modelling real systems both via simulation and theory as its implementation leads to an accuracy and flexibility in the determination of thermophysical properties that cannot be obtained when potentials of fixed range are considered. An additional advantage of using variable-range potentials is noted in the development of coarse-grained models where, as the superatoms become larger, the effective potentials are seen to become softer. However, the larger number of parameters that characterise the Mie potential (λr, λa, σ, ϵ) can hinder a rational study of the particular effects that each individual parameter have on the observed thermodynamic properties and phase equilibria, and higher degeneracy of models is observed. Here a three-parameter corresponding states model is presented in which a cohesive third parameter α is proposed following a perturbation expansion and assuming a mean-field limit. It is shown that in this approximation the free energy of any two Mie systems sharing the same value of α will be the same. The parameter α is an explicit function of the repulsive and attractive exponents and consequently dictates the form of the intermolecular pair potential. Molecular dynamics simulations of a variety of Mie systems over a range of values of α are carried out and the solid–liquid, liquid–vapour and vapour–solid phase boundaries for the systems considered are presented. Using the simulation data, we confirm that systems of the same α exhibit conformal phase behaviour for the fluid-phase properties as well as for the solid–fluid boundary, although larger differences are noted in the solid region; these can be related to the approximations in the definition of the parameter. Furthermore, it is found that the temperature range over which the vapour–liquid envelope of a given Mie system is stable follows a linear dependency with α when expressed as the ratio of the critical–point temperature to the triple–point temperature. The limit where potentials of the Mie family will not present a stable fluid envelope is predicted in terms of the parameter α and the result is found to be in excellent agreement with previous studies. This unique relation between the fluid range and the cohesive parameter α is shown to be useful to limit the pairs of Mie exponents that can be used in coarse-grained potentials to treat real systems in order to obtain temperature ranges of stability for the fluid envelope consistent with experiment.

We investigate the liquid-vapor interface of a model of patchy colloids. This model consists of hard spheres decorated with short-ranged attractive sites ("patches") of different types on their surfaces. We focus on a one-component fluid with two patches of type A and nine patches of type B (2A9B colloids), which has been found to exhibit reentrant liquid-vapor coexistence curves and very low-density liquid phases. We have used the density-functional theory form of Wertheim's first-order perturbation theory of association, as implemented by Yu and Wu [J. Chem. Phys. 116, 7094 (2002)], to calculate the surface tension, and the density and degree of association profiles, at the liquid-vapor interface of our model. In reentrant systems, where AB bonds dominate, an unusual thickening of the interface is observed at low temperatures. Furthermore, the surface tension versus temperature curve reaches a maximum, in agreement with Bernardino and Telo da Gama's mesoscopic Landau-Safran theory [Phys. Rev. Lett. 109, 116103 (2012)]. If BB attractions are also present, competition between AB and BB bonds gradually restores the monotonic temperature dependence of the surface tension. Lastly, the interface is "hairy," i.e., it contains a region where the average chain length is close to that in the bulk liquid, but where the density is that of the vapor. Sufficiently strong BB attractions remove these features, and the system reverts to the behavior seen in atomic fluids.

We present a corresponding states correlation based on the description of fluid phase properties by means of an Mie intermolecular potential applied to tangentially bonded spheres. The macroscopic properties of this model fluid are very accurately represented by a recently proposed version of the Statistical Associating Fluid Theory (the SAFT-γ version). The Mie potential can be expressed in a conformal manner in terms of three parameters that relate to a length scale, σ, an energy scale, e, and the range or functional form of the potential, λ, while the nonsphericity or elongation of a molecule can be appropriately described by the chain length, m. For a given chain length, correlations are given to scale the SAFT equation of state in terms of three experimental parameters: the acentric factor, the critical temperature, and the saturated liquid density at a reduced temperature of 0.7. The molecular nature of the equation of state is exploited to make a direct link between the macroscopic thermodynamic pa...

The knowledge of fatty acid esters/biodiesels thermodynamic properties is crucial not only for developing optimal biodiesel production and purification processes, but also for enhancing biodiesels performance in engines. This work is intended to apply a simple but reliable theoretically based sound model, the soft-SAFT EoS, as a tool for the development, design, scale-up, and optimization of biodiesels production and purification processes. A molecular model within the soft-SAFT EoS framework is proposed for the fatty acid esters, and the Density Gradient Theory approach is coupled into soft-SAFT for the description of interfacial properties, while the Free-Volume Theory is used for the calculation of viscosities, in an integrated model. For pressures up to 150 MPa, and in the temperature range 288.15-423.15K, density, surface tension, viscosity and speed of sound data for fatty acid methyl and ethyl esters, ranging from C-8:0 to C-24:0, with up to three unsaturated bonds, are described with deviations inferior to 5%. Finally, in order to validate the predictive ability of the model to be applied in the biodiesel groundwork, the high pressure densities and viscosities for 8 biodiesels were predicted with the soft-SAFT EoS, reinforcing the validity of the approach to obtain reliable predictions for engineering purposes. (C) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

The water solubility in fatty acid esters and biodiesels and the vapor-liquid equilibria (VLE) of fatty acid ester + methanol/ethanol systems, formed at biodiesel production and purification industrial units, were modeled in this work to complete the development and application of the soft-SAFT equation of state (EoS) to the design and optimization of biodiesel production plants. The soft-SAFT EoS is able to accurately describe the water solubility and the VLE of methanol and ethanol with a large number of binary systems, composed of a variety of esters, in wide ranges of temperature, including near/supercritical conditions, with the use of just one binary interaction parameter. This parameter is chain length dependent for the water systems, while it is constant for the methanol and the ethanol binary mixtures. An entirely predictive scheme is proposed for the soft-SAFT EoS water solubility in biodiesels description, being only necessary to know the biodiesel fatty acid esters composition to determine the required molecular and binary interaction parameters. A new association scheme to explicitly consider the solvation phenomenon between esters and water/alcohols is also proposed. The results obtained in this work with soft-SAFT are clearly superior, regarding qualitative and quantitative agreement with the experimental data and predictive ability of the model, to those obtained with other similar modeling approaches, namely with the Cubic-plus-Association equation of state (CPA EoS) and other SAFT-type EoSs, as discussed throughout the work. The soft-SAFT EoS is shown here as a valuable tool to assist the design of biodiesel purification units, specifically for applications in the biodiesel washing, drying and alcohol removal, in order to obtain the biodiesel with the quality specifications required by the international standards. (C) 2014 Elsevier Ltd. All rights reserved.

Increasing pollutants emissions, along with the limitations present on the existing control methods and stricter legislation to come, demand the development of new methods to reduce them. Ionic liquids (ILs) have been attracting an outstanding attention during the last decade and rose as a promising class of viable solvents to capture pollutants and for gas separation processes. As part of a continuing effort to develop an ionic liquid based process for high pressure capture of greenhouse gases, the phase equilibria of carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4) and nitrogen (N-2) in 1-ethyl-3-methylimidazolium methyl-phosphonate ([C(2)mim][CH3OHPO2]) were studied in this work. Experimental measurements for the CO2, N2O, CH4 and N-2 solubilities in [C(2)mim][CH3OHPO2] were carried out for gases mole fractions ranging from (0.018 to 0.504), in the temperature range (293.23 to 363.34) K and for pressures from (1.16 to 87.61) MPa. The particular behavior of the selected highly polar ionic liquid is here shown for the first time through the reported experimental data. The low N-2, CH4 and CO2 solubilities, with the later system presenting positive deviations to ideality, show the ionic liquid unfavorable interactions with the studied gases and the necessity to find a proper compromise between the solvent polarity and its molar volume in order to achieve high CO2/N-2 or CO2/CH4 separation selectivities. The good soft-SAFT EoS performance in describing the thermophysical properties of ionic liquids and the phase equilibria of their mixtures with gases was extended in this work for the description of the experimental data reported. New and reliable molecular schemes for N2O and [C(2)mim][CH3OHPO2], not yet studied within the soft-SAFT framework, were proposed. Using no more than one binary interaction parameter, the soft-SAFT EoS is able to take into account the particular pressure and temperature behavior of the different gases solubilities in the selected ionic liquid. This empowers the equation to be reliably used for other similar systems, as tool to optimize the given process, searching for the best conditions for capture. (C) 2013 Elsevier Ltd. All rights reserved.

International audience; The goal of this work was to check the ability of the PC-SAFT equation to represent the solubility of carbon dioxide (CO2) in ionic liquids. Parameters of pure imidazolium-based ionic liquids were estimated using experimental densities over a large range of temperatures and then correlated with respect to the molecular weight and structure of the solvents. It was found that such a correlation is able to predict the density with high accuracy. The solubility of carbon dioxide in such ionic liquids was then studied. The binary interaction parameter k(ij) needed for the representation of such binary systems was first fitted to experimental liquid-vapor equilibria data. In a second step, a correlation based on the group contribution concept was developed to determine this temperature-dependent parameter. The ability of the model to describe accurately carbon dioxide solubility in imidazolium-based ionic liquids is demonstrated.

We present a numerical evaluation of the critical point location for a primitive model for silica recently introduced by Ford et al. [J. Chem. Phys. 121, 8415 (2004)]. We complement the numerical estimate with a theoretical description of the system free energy (and related thermodynamic quantities) by solving (i) the standard parameter-free first order thermodynamic perturbation Wertheim theory and (ii) an ad hoc modeling of the temperature and density dependences of the bonding free energy, inspired by the Wertheim theory but requiring one fitting parameter alpha(rho). This parameter takes into account the correlation between adjacent bonding induced by excluded volume effects. We compare the predicted critical point location in the temperature-density plane with the "exact" numerical Monte Carlo value. The critical temperature is correctly predicted by both theoretical approaches, while only approach (ii) is able to accurately predict the critical density.

We report theoretical and numerical evaluations of the phase diagram for a model of patchy particles. Specifically we study hard-spheres whose surface is decorated by a small number f of identical sites ("sticky spots'') interacting via a short-range square-well attraction. We theoretically evaluate, solving the Wertheim theory, the location of the critical point and the gas-liquid coexistence line for several values of f and compare them to results of Gibbs and Grand Canonical Monte Carlo simulations. We study both ordered and disordered arrangements of the sites on the hard-sphere surface and confirm that patchiness has a strong effect on the phase diagram: the gas-liquid coexistence region in the temperature-density plane is significantly reduced as f decreases. We also theoretically evaluate the locus of specific heat maxima and the percolation line., Comment: preprint, 32 pages, 6 figures, 3 tables, J. Chem. Phys. in press