P. Vimalchand

Vapor-liquid equilibria for binary mixtures of carbon dioxide with benzene, toluene and p-xylene

Abstract Vapor-liquid equilibrium data for carbon dioxide - benzene, carbon dioxide - toluene, and carbon dioxide - p-xylene were measured for pressures up to 6.5 MPa, and at temperatures of 353 K, 373 K, and 393 K. The solubility of benzene in the dense carbon dioxide vapor phase is higher than that of either toluene or p-xylene. In the liquid phase, carbon dioxide is more soluble in p-xylene than in toluene or benzene. The experimental data obtained were compared with calculations from three correlations: the Peng-Robinson equation, the UNIFAC activity coefficient correlation, and the Perturbed-Anisotropic- Chain Theory (PACT). All three correlations predict phase compositions in good agreement with the experimental data.

The Perturbed-Soft-Chain Theory: an equation of state based on the Lennard-Jones potential

Abstract Perturbed-Soft-Chain theory is a perturbation theory for chain-like molecules which uses a soft-core (Lennard-Jones) intermolecular potential energy function. Three pure-component parameters are required for the PSCT equation of state. These parameters are reported for 13 normal alkanes and 25 other compounds. The PSCT equation of state does very well in predicting the thermodynamic properties of molecules over a wide range of fluid densities and molecular complexities. The PSCT equation of state is tested against the PHCT and Peng-Robinson equation of state by determining the errors in calculated liquid-densities and vapor pressures for normal alkanes. The PSCT equation of state predicts these properties slightly better than the PHCT equation of state and much better than the Peng-Robinson equation of state.

The perturbed-hard-chain theory. Extensions and applications

Abstract The Perturbed-Hard-Chain theory (PHCT) was developed by Prausnitz and coworkers in the late 1970s. It can be used to calculate the properties of fluids and fluid mixtures containing both small and large molecules, including polymers, and at all fluid densities. Since that time, the theory has been extended to treat a wider variety of systems. This was done by taking into account several intermolecular interactions which were not considered in the original PHCT. The PHCT and the equations based on it now provide valuable tools for calculating thermodynamic properties of numerous systems since they can treat mixtures of fluids with large differences in molecular size and shape, and differences in both the strength and the nature of intermolecular forces.

Effect of hard-sphere structure on pure-component equation of state calculations

Abstract Hard-sphere fluid structure is shown to be important in describing the thermodynamic properties of the square-well fluid. A simple local composition model using the exponential approximation (EXP) of Anderson and Chandler (1972) for the pair correlation function is developed. The hard-sphere pair correlation function is determined using the analytic solution to the Percus-Yevick theory (Wertheim, 1964). The model is shown to predict the properties of the square-well fluid that are in good agreement with molecular dynamics data. The equation is used to predict the properties of argon and methane. The equation is also incorporated into the Simplified-Perturbed-Hard-Chain Theory (SPHCT), and the new equation improves calculations of vapor pressures and saturated densities for non-polar and polar fluids.

Correlation of equation of state parameters for the associated perturbed anisotropic chain theory

Abstract The Associated Perturbed Anisotropic Chain Theory (APACT) has been applied to four types of pure fluids: non-polar (hydrocarbons), dipolar (chloroalkanes), quadrupolar (aromatics and substituted aromatics), and hydrogen bonding fluids (water and aliphatic alcohols). Molecular parameters for each fluid have been evaluated by fitting the theory to pure-component vapor pressures and liquid densities using a non-linear regression routine. Correlation of the paparameters with Bondis volumes showed nearly linear behavior. Moreover, the slopes and intercepts of the correlations show expected trends. For the appphatic alcohols, the enthalpy of hydrogen bond formation was found to be independent of hydrocarbon chain length for carbon numbers higher than 2, while the entropy of hydrogen bond formation decreased asymptotically to a constant value.

Phase equilibrium predictions for polar and hydrogen bonding mixtures

Abstract The Perturbed-Hard-Chain Theory (PHCT) has been generalized to treat pure compounds and mixtures with polar forces (dipoles and quadrupoles) as well as hydrogen bonding. The generalization to polar compounds is based on the perturbation expansion for anisotropic molecules by Gubbins and coworkers. The effects of hydrogen bonding are taken into account using an approach similar to that of Heidemann and Prausnitz. With these two generalizations, accurate mixture VLE and LLE predictions can be made, even for highly non-ideal systems, using pure component parameters alone.