Nonpolar Binary Mixtures Research Articles

A density gradient theory based method for surface tension calculations

The density gradient theory has been becoming a widely used framework for calculating surface tension, within which the same equation of state is used for the interface and bulk phases, because it is a theoretically sound, consistent and computationally affordable approach. Based on the observation that the optimal density path from the geometric mean density gradient theory passes the saddle point of the tangent plane distance to the bulk phases, we propose to estimate surface tension with an approximate density path profile that goes through this saddle point. The linear density gradient theory, which assumes linearly distributed densities between the two bulk phases, has also been investigated. Numerical problems do not occur with these density path profiles. These two approximation methods together with the full density gradient theory have been used to calculate the surface tension of various systems, from non-polar binary mixtures to complex multicomponent associating fluids, combined with the Peng-Robinson and the Cubic Plus Association equations of state. From an overall point of view, the approximation method with the density path profile passing the saddle point and the full density gradient theory offer comparable performance in predicting surface tension, while the linear density gradient theory frequently overpredicts. Limitations have been seen for all the three methods in correlating the surface tension of particular systems, with a single adjustable parameter for the cross influence parameter.

Temperature dependent excess free energy of mixing and excess molar polarization of the binary mixture of butanols in nonpolar solvents

The excess free energy of mixing and excess molar polarization in the binary mixture of butanols and nonpolar solvents are evaluated at different temperatures starting from 303K to 318K. Decreases in correlation factor, excess free energy of mixing and excess molar polarization have been observed with an increase in temperature. However, excess molar polarization does not vary much with respect to temperature at about 0.1 molar concentrations of polar liquids. In some mixtures, at this concentration excess molar polarization increases slightly with an increase in temperature. The excess free energy of mixing and excess molar polarization are higher in the binary mixtures of polar solutes with n-heptane due to the presence of an odd number of carbon atoms. It is important to observe that there is slight variation in excess free energy and excess molar polarization in these polar–nonpolar binary mixtures with respect to temperature. The excess free energy of mixing remains positive at all temperatures for most of the concentrations of polar solvents in polar–nonpolar binary liquid mixtures. This is an advantage to use such polar–nonpolar binary molecules for industrial applications.

Hetero-molecular associations in different polar and non-polar binary mixtures

Excess molar volumes and viscosity deviations have been studied comparatively for some binary systems involving nitrobenzene, aniline, methanol, benzene, toluene and CCl_4 by experimentally measured values of viscosity and density. These values are interpreted in the light of hetero-molecular associations among the polar and non-polar constituents.

Monte Carlo Simulations of Mixtures Involving Ketones and Aldehydes by a Direct Bubble Pressure Calculation

Ketone and aldehyde molecules are involved in a large variety of industrial applications. Because they are mainly present mixed with other compounds, the prediction of phase equilibrium of mixtures involving these classes of molecules is of first interest particularly to design and optimize separation processes. The main goal of this work is to propose a transferable force field for ketones and aldehydes that allows accurate molecular simulations of not only pure compounds but also complex mixtures. The proposed force field is based on the anisotropic united-atoms AUA4 potential developed for hydrocarbons, and it introduces only one new atom, the carbonyl oxygen. The Lennard-Jones parameters of this oxygen atom have been adjusted on saturated thermodynamic properties of both acetone and acetaldehyde. To simulate mixtures, Monte Carlo simulations are carried out in a specific pseudoensemble which allows a direct calculation of the bubble pressure. For polar mixtures involved in this study, we show that this approach is an interesting alternative to classical calculations in the isothermal-isobaric Gibbs ensemble. The pressure-composition diagrams of polar + polar and polar + nonpolar binary mixtures are well reproduced. Mutual solubilities as well as azeotrope location, if present, are accurately predicted without any empirical binary interaction parameters or readjustment. Such result highlights the transferability of the proposed force field, which is an essential feature toward the simulation of complex oxygenated mixtures of industrial interest.

Stability of binary mixtures in electric field gradients

We consider the influence of electric field gradients on the phase behavior of nonpolar binary mixtures. Small fields give rise to smooth composition profiles, whereas large enough fields lead to a phase-separation transition. The critical field for demixing as well as the equilibrium phase-separation interface are given as a function of the various system parameters. We show how the phase diagram in the temperature-composition plane is affected by electric fields, assuming a linear or nonlinear constitutive relations for the dielectric constant. Finally, we discuss the unusual case where the interface appears far from any bounding surface.

Prediction of the second cross virial coefficients of nonpolar binary mixtures

The binary interaction parameter, k ij , of 268 nonpolar mixtures were determined from the database of second cross virial coefficients containing 1728 experimental data points by fitting the second cross virial coefficients with a new correlation for pure compounds [L. Meng, Y.Y. Duan, L. Li, Fluid Phase Equilib. 226 (2004) 109–120] and classical mixing rules. Regularity distributions were found for both n-alkane/ n-alkane binaries and fluorocarbon/fluorocarbon binaries. Correlations were developed following Tsonopoulos’ ideas [C. Tsonopoulos, Adv. Chem. Ser. 182 (1979) 143–162] with the quantity of binary compounds enlarged using Dymond's latest complication [J.H. Dymond, K.N. Marsh, R.C. Wilhoit, Virial Coefficients of Pure Gases and Mixtures, Subvolume B, Virial Coefficients of Mixtures, Series IV/21B, Landolt-Börnstein, 2002]. Correlations were also developed for inorganic/ n-alkane binaries using new k ij values. The predictions do not need any thermodynamic property parameters besides the carbon number. Comparisons with the existing correlations show that the present work is more accurate for nonpolar binary mixtures.

Molecular model for the VLE p- T-x relationships of binary mixtures

An analytical expression for the pressure-temperature-composition relations in the vapour - liquid equilibrium of non-polar binary mixtures is proposed. The model is based on a simple analytical expression for the vapour pressure of pure non-polar fluids, which, for a given temperature, requires as input only the Lennard- Jones molecular parameters and the acentric factor of the substance. The equilibrium mixture pressure is then expressed as a function of the vapour pressure of each component and of a mixture contribution. The molecular parameters required for this mixture contribution are related to the molecular parameters of the pure component through a modified Lorentz-Berthelot mixing rule, where the interaction parameters are given as simple functions of the temperature and composition, with eight appropriate constants for each binary mixture. We show that the model permits one to reproduce or predict in a simple way the pressure (for a given liquid mole fraction) or the liquid composition (for a given pressure).

On the gas–gas equilibria of second kind of nonpolar fluid binary mixtures from a hard-sphere EXP-6 molecular model

The phase behavior of a molecular-based model of nonpolar binary mixtures is investigated by the application of thermodynamic perturbation theory. The pair potential interaction model is represented as a reference system of equal size hard-spheres perturbed by the exponential-6 potential. It is found that the qualitative behavior of gas–gas immiscibility of second kind is very much sensitive to the hardness of the potential (ratio of the hard sphere diameter to the size parameter of the perturbation). Calculated theoretical phase diagrams are compared with results from Monte Carlo simulations in the Gibbs ensemble performed for this model mixture.

Application of a generalized van der Waals equation of state to several nonpolar mixtures

A generalized van der Waals equation of state, applied recently (Nguyen Van Nhu and Kohler, 1995) to the calculation of excess properties and phase equilibria for the mixture methane + ethane, is now extended to several nonpolar binary mixtures. Improved mixing rules for the van der Waals attractive term and for the correction term are proposed. With these mixing rules, the equation gives good agreement for vapour-liquid and liquid-liquid equilibria over a large temperature range for 29 binary mixtures. The agreement of mixture volumes and cross second virial coefficients is also satisfactory.

Calculating critical transitions of fluid mixtures: Theory vs. experiment

AbstractThe progress in predicting critical transitions in fluid mixtures is reviewed. The critical state provides a valuable insight into the general phase behavior of a fluid and is closely linked with the nature and strength of intermolecular interaction. Calculations of critical equilibria have been confined mainly to binary mixtures. The prediction of binary gas‐liquid critical properties was initially limited to empirical correlations. These techniques have been superseded by rigorous calculations of the critical conditions using realistic models of the fluid or equations of state. All of the known types of critical phenomena exhibited by binary mixtures can be, at least, qualitatively calculated. If an optimal combining rule parameter is allowed, continuous gas‐liquid properties can be calculated accurately for a wide variety of mixtures. Similarly, the pressure and composition dependence of upper critical solution phenomena can be accurately predicted. Progress has been achieved in predicting discontinuous critical transitions in polar and nonpolar binary mixtures. There is increasing interest in calculating the critical properties of ternary and multicomponent mixtures. Although the techniques applied to binary mixtures often can be directly extended to ternary mixture calculations, calculated critical properties of ternary mixtures indicate that their behavior cannot be considered as a simple extension of binary mixture phenomena. Consequently, ternary critical calculations are likely to provide a superior insight into the phase behavior of multicomponent fluids.

Decay kinetics of the isothermal luminescence in nonpolar binary mixtures at 77 K

The isothermal luminescence of γ-irradiated frozen 3-methylpentane (3MP)-methylcyclohexane (MCH) mixtures (3MP mole fraction from 0 to 0.96) containing naphthalene (Nph) was investigated at 77K. At high Nph concentration (2.5 x 10 −2mol dm −>3) the luminescence is due to molecular ion recombination by tunnelling. In the soft glass (0.96 mole fraction 3MP) at low Nph concentration (10 -3 mol dm -3) electron thermal detrapping seems to contribute to the emission. The experimental decay curves were interpreted based on the Bagdasar'yan relation as well as the continuous-time- random-walk formalism (assuming a first-order rate equation with a time dependent rate constant of the form k( t) = B t ( α−1) .

On the gas—gas equilibria of polar—non-polar binary mixtures from a polarizable hard-sphere dipole model

Perturbation theory is applied to a polarizable hard-sphere dipole model mixture. It is shown that for increasing values of the reduced polarizability of the non-polar component. gas—gas equilibria of the first and second kind can be described for a polar—non-polar binary mixture. However for the latter case, critical lines do not show the minimum in temperature observed in real systems. Comparison between theoretical and experimental results are given for HeNH 3 and ArH 2O mixtures.

Limiting activity coefficients in dilute solutions of nonelectrolytes. I.Determination for polar–nonpolar binary mixtures by a novel apparatus, and a solubility-parameter treatment of results

The activity coefficients of several solutes in dilute binary solutions of nonelectrolytes were determined at 20 °C from vapour–liquid equilibria in a novel static equilibration apparatus, by gas-chromatographic analysis of the equilibrium vapor phase. The solutes were nitromethane, nitroethane, 1-nitropropane, 2-nitropropane, acetonitrile, propionitrile, ethyl acetate, and n-butyl acetate in n-heptane and in benzene as solvents, and also carbon tetrachloride as solute in each of the above-listed polar compounds as the solvent.The modifications by Weimer and Prausnitz and by Blanks and Prausnitz to the Scatchard–Hildebrand equation in order to accommodate binary mixtures containing a polar component were tested by using the values found in the present work for the limiting activity coefficients of these solutes. In addition, it was found that the ratio of the dipole – induced dipole interaction parameter for polar solutes in the two nonpolar solvents was nearly constant.Three methods for evaluating the dispersion contribution to the solubility parameter of a polar compound were considered.

Corresponding states. III. Henry's constants for nonpolar binary mixtures

AbstractA Henry's constant correlation is developed from a macroscopic Corresponding states theory for fluid mixtures. The method requires three interaction parameters which are correlated for mixtures of paraffin with nitrogen, carbon dioxide, hydrogen sulfide, or another paraffin. Henry's constants can be calculated by this method to within experimental accuracy (about ± 5%) for the mixtures tested.