Prediction of Vapor/Liquid Equilibrium Behavior from Quantum Mechanical Data

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Gnap, Marshall J
Thermodynamics; VLE; Phase Equilibrium; UNIFAC; MOSCED
project description
MOSCED (Modified Separation of Cohesive Energy Density) is a particularly attractive model for activity coefficients because it offers intuitive insights into how to tune solvent-solute interactions to achieve optimized formulations. Unfortunately, only 133 compounds have been characterized with the MOSCED method. Furthermore, there is no convenient method for extending MOSCED predictions to new compounds. The hypothesis of the present research is that the surface charge density of a molecule, once normalized over the molecule surface area, provided graphically by a σ-profile from density functional theory (DFT) computations, can be used to estimate the parameters used in the MOSCED model. DFT results are readily available for 1432 compounds through a public database at Virginia Tech, and further DFT computations for new compounds are relatively quick and simple due to minimal additional molecular properties.The predictive functions were regressed based on 4375 binary solution infinite dilution coefficients. The average logarithmic deviation for the predictive MOSCED model was 0.280 while using the original correlative model had a deviation of 0.106 compared to 0.183 for the UNIFAC model. Phase equilibrium predictions were also compared where various models were used for interpolating finite compositions. The average percent deviations of the pressure for the 39 binary systems tested were 17.39% for Wilson, 18.90% for NRTL, and 13.83% for SSCED.