Prediction of Vapor Pressures and Enthalpies of Vaporization Using a COSMO Solvation Model

Abstract

We have developed a general predictive method for vapor pressures and enthalpies of vaporization based on the calculation of the solvation free energy that consists of three components; the electrostatic, dispersion, and cavity formation contributions. The electrostatic contribution is determined using the quantum mechanical COSMO solvation model. Thermodynamic perturbation theory for hard-core molecules is used for the cavity term, and the dispersion term is modeled using a mean field term proportional to the density and molecular surface area. The proposed model uses one set of van der Waals atomic radii to describe molecular shape, two universal interaction parameters for the electrostatic interaction, one set of atom-specific dispersion coefficients, one universal parameter to scale the atomic exposed surface area, and a single universal parameter for the ratio of the hard-core to atomic radii. The model parameters have been determined using 371 pure substances of varying molecular structure, functionality, and size. The average accuracy of the model for vapor pressures and enthalpies of vaporization at the normal boiling temperature is found to be 76% and 4.81 kJ/mol, respectively, with temperature-independent parameters. The average error in the normal boiling temperature is found to be 16 K for species whose boiling points range from 191 to 610 K.

Estimation of pure component properties

“…Several approaches were published to calculate the vapor pressure directly from molecular properties without employing group contribution [14,15].…”

A predictive model for the excess gibbs free energy of fully dissociated electrolyte solutions

“…The detailed procedure of obtaining such a profile can be found elsewhere. 33,37,43,44 Here, we briefly outline the important steps. The equilibrium molecular geometry is determined by minimization of the total energy of the molecule using the quantum mechanical calculation package DMol3.…”

Obtaining Thermodynamic Properties and Fluid Phase Equilibria without Experimental Measurements

“…The segment interaction energy ∆W is determined by considering the electrostatic and hydrogen bonding interactions between two contacting surfaces www.intechopen.com The dispersion solvation free energy is considered to be proportional to the exposed surface area of the atom comprising the molecule (Cramer & Truhlar, 1991, Cramer & Truhlar, 2008, Klamt, 1995, Klamt et al, 1998, Lin et al, 2004, Lin & Sandler, 2002, Still et al, 1990, Tomasi & Persico, 1994. Here we propose a slightly modified form to better describe ring containing and hydrogen bonding chemicals.…”