Excess Properties Of Mixtures Research Articles

Density and viscosity of three ionic liquids with 2,2,2-trifluoroethanol

Due to the lower boiling point and high solubility, ionic liquids are considered as the green and environmentally friendly chemicals, and widely studied in the absorption refrigeration cycles. However, the ionic liquids always possess high viscosity. In this work, 2,2,2-trifluoroethanol (TFE) was selected as a solvent to reduce the viscosity of ionic liquids. The densities and viscosities of TFE with three ionic liquids were measured at atmospheric pressure and temperature in the range of 293.15–333.15 K. The effect of solvents on reducing the viscosity of ionic liquids was analyzed. The excess properties of mixtures were calculated to analyze the interaction of the binary mixtures. The hard-sphere model was used to study the viscosity of pure substances and binary mixtures to further understand the interactions between ionic liquids and TFE.

Excess properties of mixtures containing 2-(2-ethoxyethoxy)ethanol, methylcyclohexane, cyclohexane and 1‑hexene as fuel representative

The experimental and modelling excess enthalpy, HE, data for the following binary and ternary mixtures: methylcyclohexane (1) + 1‑hexene (2), 2-(2-ethoxyethoxy)ethanol (1) + 1‑hexene (2) + cyclohexane (3), and 2-(2-ethoxyethoxy)ethanol (1) + methylcyclohexane (2) + 1‑hexene (3) are studied in this work at two different temperatures (298.15 and 313.15) K and 0.1 MPa. To measure the HE of the studied binary and ternary mixtures, a quasi-isothermal flow calorimeter was used. All the binary and ternary mixtures present an endothermic behavior at the chosen temperatures. Measured data of HE were correlated using modified Redlich-Kister equation, NRTL and UNIQUAC models.

Properties of Methanol-Water Mixtures in a Coarse-Grained Model

Methanol and water rank among the most important liquids in modern world due to their versatile use. As water, methanol and their mixtures exhibit numerous anomalous properties, their description is challenging. The amphiphilic nature of methanol causes its aqueous solutions to have negative excess volume and enthalpy across the entire composition range. A simple isotropic water model and its coarse-grained extension were used to study the properties of methanol and water-methanol mixtures. Using Monte Carlo simulations, we showed that the model correctly describes the thermodynamic properties of methanol, density dependence of water-methanol mixtures upon temperature and composition, and excess properties of mixtures. Although no conscious effort was made to fine-tune the potential, the results are remarkably close to experimental data.

Influence of Solvent on Ion Aggregation and Transport in PY15TFSI Ionic Liquid–Aprotic Solvent Mixtures

Molecular dynamics (MD) simulations using a many-body polarizable APPLE&P force field have been performed on mixtures of the N-methyl-N-pentylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PY15TFSI) ionic liquid (IL) with three molecular solvents: propylene carbonate (PC), dimethyl carbonate (DMC), and acetonitrile (AN). The MD simulations predict density, viscosity, and ionic conductivity values that agree well with the experimental results. In the solvent-rich regime, the ionic conductivity of the PY15TFSI-AN mixtures was found to be significantly higher than the conductivity of the corresponding -PC and -DMC mixtures, despite the similar viscosity values obtained from both the MD simulations and experiments for the -DMC and -AN mixtures. The significantly lower conductivity of the PY15TFSI-DMC mixtures, as compared to those for PY15TFSI-AN, in the solvent-rich regime was attributed to the more extensive ion aggregation observed for the -DMC mixtures. The PY15TFSI-DMC mixtures present an interesting case where the addition of the organic solvent to the IL results in an increase in the cation-anion correlations, in contrast to what is found for the mixtures with PC and AN, where ion motion became increasingly uncorrelated with addition of solvent. A combination of pfg-NMR and conductivity measurements confirmed the MD simulation predictions. Further insight into the molecular interactions and properties was also obtained using the MD simulations by examining the solvent distribution in the IL-solvent mixtures and the mixture excess properties.

Simultaneous description of excess properties and vapor–liquid equilibria for associating mixtures by hydrogen-bonding lattice fluid equation of state

Since all residual thermodynamic properties can be calculated from an equation of state (EOS), an accurate EOS may also be used for the computation of excess properties and vapor–liquid equilibria (VLE) simultaneously. Cubic equations of state have been used with G E-mixing rules for associating mixtures. In the present study, the applicability of the hydrogen-bonding non-random lattice fluid model (NLF-HB) was investigated for the simultaneous correlation of VLE and excess properties of mixtures containing associating components. The optimized parameters for VLE and H E at room temperature gave reliable results for fitted properties. V E calculation showed large errors but the molar volume was accurate. The allowable range for the temperature extrapolation of the binary parameter was wider for VLE than for for H E.

Determination of Thermodynamic Excess Properties of Mixtures from Computer Simulation

Abstract This paper reports excess Gibbs free energy, excess enthalpy, and excess volume from isothermal-isobaric molecular dynamics simulations of binary Lennard-Jones mixtures at κ T/∊ = 2, pσ3/∊ = 2.5, for three parameter ratios, ∊ BB /∊ AA = 1 and σ BB /σ AA = 1.5, ∊ BB /∊ AA = 1.5 and σ BB /σ AA = 1, ∊ BB /∊ AA = 1.5 and σ BB /σ AA = 1.5, and at different concentrations, xA = 0.02, 0.05, 0.1, 0.25, 0.5, 0.75, 0.9, 0.95, and 0.98. The density range is between 0.25 < ρ∗ < 0.75. The excess Gibbs free energies were determined by fitting the differences in residual chemical potentials, which were evaluated by using the ‘fA – fB sampling’ method. The results showed very good agreement with literature data.

Excess properties of mixtures of some n-alkoxyethanols with organic solvents. Part 7. VE with toluene at 298.15K

The excess molar volume at 298.15K and atmospheric pressure for three (alkoxyethanol + toluene) mixtures have been determined over the whole mole fraction range from densities measured with a vibrating-tube densimeter. The alkoxyethanols were 2-methoxyethanol, 2-ethoxyethanol and 2-butoxyethanol. The three excess volumes curves have a maximum in the toluene rich region and those with 2-ethoxyethanol and 2-butoxyethanol are sigmoidal. The excess molar volumes increase as the alkyl chain length of the alkoxyethanol decreases.

Prediction of thermodynamic properties of fluid mixtures by molecular dynamics simulations: methane-ethane

NPT and NVT molecular dynamics simulation results are reported for the fluid methane-ethane mixture. Methane is modelled as Lennard-Jones fluid and ethane as a two-centre Lennard-Jones fluid with parameters obtained some time ago by fitting WCA-type perturbation theory results to two experimental vapour pressures and one bubble density for each substance. It has also already been shown that these effective pair potentials yield good predictions of the pressures and internal energies of the pure substances in the whole fluid region. In order to obtain an effective potential between the unlike molecules, previously derived fluctuation formulas for the dependence of the mixture excess properties on the unlike molecule interaction parameters are used. A test of these fluctuation formulas shows their statistical uncertainties to be small. Hence, the unlike interaction parameters can be determined from one mixture simulation and a fit to one experimental excess volume and one excess enthalpy. Then second virial coefficients, liquid excess properties, P, V, T data and enthalpy differences are calculated in the temperature range 100–400 K and pressures up to 30 MPa. Comparison is made directly with experimental data and partly also with the DDMIX equation of state showing mostly good to excellent agreement except in the critical region; for some state points in the gas the pressures are slightly too low. Technically, runs for several gas state points are NVT simulations whereas the other runs are NPT simulations part of which were checked again by NVT-simulations. The paper also compares pressures obtained by the Haar-Shenker-Kohler equation for the gas phase with NVT simulation results. All simulations were performed on a CYBER 205.

Effect of molecular shape on liquid mixture excess properties

In mixtures of spherical molecules component B is replaced by dumbbell-like molecules with potential parameters chosen such that the bubble density and the vapor pressure of pure component B remain the same. The excess properties g E, h E, and v E are calculated by a Weeks—Chandler3Āndersen type perturbation theory for several energy-ratios, size-ratios and elongations of the molecules. It is found that starting from spherical molecules of equal size the g E and h E-values become more negative with increasing elongation. The opposite occurs if the B-molecules have a volume larger than the other ones by a factor of about 2. It is argued that these shape effects can roughly be incorporated into the k AB-parameter which then for molecules not too different in size will be negative.

The influence of unlike molecule interaction parameters on liquid mixture excess properties

The dependence of the liquid mixture excess properties g E, h E, and v E on an unlike molecule interaction parameter is considered. Firstly, the derivatives of the excess properties with respect to that parameter are expressed as averages in the isobaric-isothermal (NpT) ensemble which can be evaluated in computer simulations. As a special case the derivatives of the excess properties with respect to the unlike interaction parameters describing the deviations from the Lorentz-Berthelot combining rule for a mixture of n-center Lennard-Jones molecules are given. Then, a hypothetical mixture of equal Lennard-Jones molecules is considered in which case these derivatives can be expressed rigorously by thermodynamic quantities of the pure fluid. Finally, by using a WCA-type perturbation theory it is shown that these thermodynamic relations for the derivatives of the excess properties are also approximately valid for a certain class of mixtures including nonspherical molecules. Relevant conclusions are that the unlike energy parameter influences g E, h E, and v E, whereas the unlike size parameter practically influences only V E. The quantities g E and h E are strongly coupled to each other but not necessarily to v E.

Liquid mixture excess properties by the hard sphere model

The excess properties of mixing were calculated for seven systems Ar-CH4; Ar-N2; Ar-O2; Ar-CO; CO-CH4; O2-N2; N2-CO, using the Caranhan and Starling equation of state of rigid spheres and the Longuet-Higgins and Widom model. Two sets of calculations were done one using the experimentalGE to calculateSE,HE andVE, and the other making use of Miller’s cross parameter values. The calculated values are compared with those of Snider and Herrington and Miller’s values and also with the experimental values. The agreement was found to be good.

Barker–Henderson theory as an accurate theory of simple mixtures

The properties and excess properties of some simple binary mixtures have been calculated from the Lennard-Jones potential and the Barker–Henderson (BH) theory including the second order terms. In these calculations the radial distribution function was approximated by the Percus–Yevick g(R) value combined with the corrections devised by Verlet and Weis and Lee and Levesque. The results show that these corrections eliminate most of the major differences between the Monte Carlo values and the BH theory values obtained previously but in some cases lead to small increases in errors for then excess properties of some mixtures. The comparisons with experimental data while generally qualitatively correct showed greater uncertainties as the interaction potentials and their mixing rules are unspecified for these systems.

Perturbation theory and the excess properties of mixtures of simple liquids

One of the most successful theories of single-component simple liquids is perturbation theory which is based on the assumption that the structure of a liquid is primarily determined by the repulsive forces between its molecules, so that a liquid may be regarded as a system of hard spheres with the attractive forces providing a uniform background energy. Our earlier extension of these ideas to liquid mixtures was only partially successful. In this paper we show that this problem was due to the use of a somewhat unsatisfactory equation of state for the reference hard-sphere mixture. If a more satisfactory equation of state is used, perturbation theory yields results in close agreement with Monte Carlo and experimental results, even when the molecules of the mixture differ appreciably in size.

Effect of different combination rules on excess properties of mixtures of simple liquids as calculated by the one-fluid theory of corresponding states

Effect of different combination rules on excess properties of mixtures of simple liquids as calculated by the one-fluid theory of corresponding states

Liquid Mixture Excess Properties and Gas Solubilities by the Hard-Sphere Model

Thermodynamic properties of binary liquid mixtures containing simple species are calculated with the hard-sphere model originally proposed by Longuet-Higgins and Widom. No liquid mixture data is used. The only mixture parameter employed is k12, the deviation parameter for the geometric-mean mixing rule for intermolecular energy parameters. Very encouraging agreement with experiment is observed for both close-boiling systems and for mixtures containing a supercritical solute. A calculational scheme for mixtures containing the quantum gases hydrogen and helium is also developed with the same model.