E. McLaughlin

Solubilities of families of heterocyclic polynuclear aromatics in organic solvents and their mixtures

The solubilities of anthracene, acridine, xanthene, thioxanthene, carbazole, dibenzofuran, and dibenzothiophene have been experimentally determined in benzene, cyclohexane, thiophene, and pyridine from ambient temperature to approximately 440 K. The results have been correlated using the classical equation for solid-liquid solubility to obtain the experimental activity coefficient of the solute in the solvent. These experimental activity coefficients have been regressed, using three common solution models, to find the binary interaction parameters needed in those models. The solubilities of biphenyl, dibenzofuran, and dibenzothiophene have been experimentally determined in five binary mixtures of the solvents. The experimental activity coefficients have been found and compared to the values predicted by the four solution models, using the binary interaction parameters obtained from the solubilities in the pure solvents and solventsolvent binary interaction parameters obtained from literature vaporliquid equilibria data. The effect of substituting various heteroatoms into the ring structure has been discussed.

Isothermalisobaric molecular dynamics simulation of diatomic liquids and their mixtures

Abstract Isothermalisobaric ensemble molecular dynamics simulations have been performed for systems of two-center Lennard-Jones molecules for pure fluids as well as binary mixtures. The results obtained from various ensemble averages have been compared for pure fluid simulations of Lennard-Jones model diatomic fluids. The excess enthalpy and excess volume of three equimolar mixtures (argonnitrogen, argonoxygen, and nitrogenoxygen) have been calculated and compared with values obtained from previous NVT molecular dynamics and perturbation theory. Pair distribution functions obtained from various methods are compared for the equimolar mixture of nitrogen and oxygen and used to study the effect of attractive forces on the local structure. For four other systems (argonethane, methaneethane, carbon disulfidecarbon tetrachloride, and carbon disulfidetetrachloroethylene), excess enthalpies and excess volumes from NPT simulations are used to test the ability of perturbation theory to predict these properties and are also compared with experimental data. The comparison of simulation and experiment clearly shows the need to improve the available parameters for cross interactions in binary mixtures.

Computer simulation of benzene using the modified gaussian overlap and six-site potentials

Molecular dynamics simulations have been performed to study the modelling of saturated liquid benzene using the modified gaussian overlap and the six-site pair potentials. Zero-pressure densities and internal energies in the simulated liquids have been obtained for these model potentials and compared with the experimental data for saturated liquid benzene. Inclusion of a quadrupole moment in the potentials is shown to be important in order to utilize these for modelling thermodynamic properties of liquid benzene. It is also shown that a form of the modified gaussian overlap potential predicts the thermodynamic properties of benzene well and future implications of this are discussed.

Simulation and theory of fluids of axisymmetric molecules

Molecular dynamics simulation results, for fluids modelled using a slight modification of the gaussian overlap potential of Gay and Berne, are reported for pressure and internal energy and also for the residual Helmholtz free energy via thermodynamic integration. Simulation results have been used to test predictions from a nonspherical reference potential based perturbation theory and a sphericalized potential method. These theoretical methods are shown to work well, qualitatively and quantitatively, when compared with simulation results for both prolate and oblate molecules. This is in contrast with our earlier calculations using the original gaussian overlap potential model of Berne and Pechukas where only qualitative agreement with simulation results was obtained for the cases of highly anisotropic molecules. The perturbation expansion is further investigated through molecular dynamics simulations of fluids modeled using the nonspherical reference potential and the first order perturbation expansion is...

Measurement of vapor—liquid equilibrium for binary systems containing polynuclear aromatic compounds

Abstract Vapor—liquid equilibrium (VLE) data are measured using a Stage-Mueller vapor—liquid recirculating still for ten binary systems containing polynuclear aromatic hydrocarbons at two temperatures (170 and 190°C). These data are correlated using five different thermodynamic activity coefficient models to determine the necessary binary interaction parameters. The measured vapor—liquid equilibrium data are compared with those predicted using Scatchard—Hildebrand regular solution theory. It is found that the regular solution theory predicts the bubble point pressures within an average absolute deviation of 2% and the vapor phase mole fractions within 10%. Therefore, regular solution theory can be used as a first approximation to determine the vapor—liquid equilibrium for these moderately nonideal systems.

A comparison of solid—liquid equilibrium with vapor—liquid equilibrium for prediction of activity coefficients in systems containing polynuclear aromatics

Abstract This study compares activity coefficients from conventional vapor—liquid equilibria (VLE) experiments with those from solid—liquid solubilities for a number of systems consisting of polynuclear aromatic compounds. The solubility studies involved 12 polynuclear aromatic hydrocarbons which have been studied from ambient temperature to near the melting point of the solutes with tetralin and decalin (an isomeric mixture of cis - and trans -decalin) as solvents. Solubilities of seven of the solutes in a 50%-50% mixture of tetralin and decalin, typical hydrogen donor solvents, have also been measured. The results have been correlated using the classical equation for solid—liquid solubility to obtain the experimental activity coefficients of the solutes in the solvents or solvent mixtures and the binary interaction parameters necessary for three well-known solution models. These parameters have been used to predict the solubilities of the solutes in the three-component systems. The VLE data were measured for four of the binary systems covered in the solubility studies. These data were analyzed to obtain the experimental activity coefficients, which were compared with those obtained from the solubility studies. The results of the two methods are discussed, particularly the uncertainties associated with the binary parameters obtained from each kind of data. Conclusions concerning the two methods are given, together with some ideas for future work.

Computer modeling of naphthalene

Molecular dynamics simulations have been performed to model naphthalene using an anisotropic two‐site pair potential with the interactions between these sites modeled using the modified Gaussian overlap potential. This potential works reasonably well for thermodynamic properties of saturated liquid naphthalene and is shown to be comparable to an isotropic ten‐site potential for thermodynamics and microscopic liquid structure. Adding point quadrupoles to the interaction sites further improves the comparison for density of the saturated liquid. However, the effect of electrostatics on thermodynamics in this case is much less than that found earlier for liquid benzene. Feasibility of perturbation theory, for the nonpolar potential, is demonstrated through the reference fluid simulations. Predictive methods are discussed in site frame as well as center frame and in a preliminary testing the latter is shown to be qualitative for predicting the residual Helmholtz free energy. The idea of anisotropic site–site p...

Diffusion in a Mixed Dense Fluid

By using Thornes extension of the Enskog theory for diffusion in a dense mixed hard‐sphere fluid, equations are developed expressing the mutual diffusion coefficient as a function of composition. Use is made in the derivation of the expression for the contact distribution function obtained by Lebowitz from the theory of Percus and Yevick. For molecules of the same size, the equations reduce to those of Longuet‐Higgins, Pople, and Valleau. Variation of the diffusion coefficient with density is discussed and the theory is applied to the diffusion of gases in liquids and to systems where either solute or solvent are dissimilar in size and mass. The Stokes–Einstein equation is also discussed.

CORRELATION OF SOLID-LIQUID AND VAPOR-LIQUID EQUILIBRIUM DATA FOR POLYNUCLEAR AROMATIC COMPOUNDS

Abstract Solid—liquid equilibrium (SLE) data were measured for five solutes in cis-decalin from ambient temperature to the melting point of the solutes. These SLE data plus our previous data for the same solutes in tetralin were used to determine experimental activity coefficients and interaction parameters using the UNIQUAC model. This set of interaction parameters gave a good representation of the experimental SLE data but were not satisfactory generally for predicting vapor—liquid equilibria for these systems. However, in an alternative approach, the solid solubility data and one vapor—liquid equilibrium point for each isotherm from previous work were used to determine another set of binary interaction parameters in the UNIQUAC model using a gradient-based search technique. The calculated values of parameters were used then to predict the vapor—liquid equilibrium for that system. It was found that the solid solubility and one vapor—liquid equilibrium data point were sufficient to predict the vapor—liquid equilibrium curve for the binary systems studied. Finally, all the solid solubility and vapor—liquid equilibrium data were combined to determine global parameters for the ten binary systems using the UNIQUAC model.

Mutual diffusion in dense supercritical fluids

An expression for the mutual diffusion coefficient of a dense binary system of hard spheres, derived by using the Percus-Yevick approximation for the contact radial distribution function, together with Thornes extension of the Enskog theory, is used to study the variation of the mutual diffusion coefficient with pressure, composition and ratio of the molecular diameters. Applications are made to real systems.