First-Principles Predictions of Vapor−Liquid Equilibria for Pure and Mixture Fluids from the Combined Use of Cubic Equations of State and Solvation Calculations

Abstract

A novel approach combining first-principles solvation calculations and cubic equations of state is proposed for the prediction of phase equilibria of both pure and mixture fluids. The temperature and composition dependence of the energy parameter, a (T,x), in the EOS is determined from the attractive contribution to the solvation free energy. The volume parameter, b(x), is estimated to be the mole-fraction-weighted average volume of the molecular solvation cavity. This approach does not require the input of any experimental data (e.g., critical properties or acentric factor) for pure components and does not presume any composition dependence of the energy parameter. The Peng-Robinson EOS combined with a solvation model based on COSMO-SAC calculations, denoted as PR+COSMOSAC, is used to illustrate the applicability of this approach. It is found that the relative error from PR+COSMOSAC is 48% in vapor pressure, 21% in liquid density at the normal boiling point, 10% in critical pressure, 4% in critical temperature, and 5% in critical volume for 1295 pure substances and 27.56% in pressure and 5.18% in vapor-phase composition for 116 binary mixtures in vapor-liquid equilibrium. The errors in binary mixtures can be reduced significantly to 6.24% and 2.25% if experimental vapor pressures are used to correct for any errors in the calculated charging free energies of pure species.

Improved Prediction of Vapor Pressure for Pure Liquids and Solids from the PR+COSMOSAC Equation of State

“…[42][43][44] Further details can be found in the literature. 33,38,45 Since this method combines the PR EOS and the COSMO-SAC model, it is denoted as the PR+COSMOSAC EOS. The last term on the right hand side of Eq.…”

“…42 42 Once the required data are available, the energy parameter a and volume 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 11 parameter b in PR+COSMOSAC EOS can be obtained easily according to the computational procedure in literature. 33 The computational procedure of the modified PR+COSMOSAC EOS is slightly different from that of the original PR+COSMOSAC EOS and is summarized as follows:…”

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

“…Our previous studies (Hsieh & Lin, 2009b) showed that C=-0.623 is a good choice for the Peng-Robinson equation of state. The size parameter b(x) can be approximated in a way similar to the van der Waals mixing rule…”

“…The consequence is a completely predictive approach for almost any thermodynamic properties of all types of fluids (pure and mixture) at all conditions (above and below the critical point) without the need of any experimental data. We show that this is a practical approach for the prediction of pure fluid properties such as the vapor pressure, liquid density, the critical temperature and pressure, as well as the vapor-liquid (Hsieh & Lin, 2009b), liquid-liquid (Hsieh & Lin, 2010), and solid-liquid phase equilibria of mixture fluids. This method also allows for accurate predictions of the distribution of a trace amount of pollutant between two partially miscible liquids, such as the octanol-water partition coefficient (Hsieh & Lin, 2009a).…”