Application of Quantum Chemistry Insights to the Prediction of Phase Equilibria in Associating Systems

Abstract

Thermodynamic models that explicitly account for association have become essential tools for correlating and predicting multiphase equilibria. These models have many adjustable parameters, which create difficulties for uniquely fitting experimental data. Reducing the number of adjustable parameters is an important pathway to increase the reliability and extrapolation power of thermodynamic models for practical applications. In this work, we revisit the relationship between the chemical and perturbation theories of association. This relationship creates a pathway for estimating association parameters using quantum chemistry calculations and statistical mechanics. Estimated parameters are applied to pure-component calculations, which demonstrate that they can be used to reduce the number of adjustable model parameters for the cubic plus association and perturbed-chain statistical associating fluid theory equations of state.

Wertheim’s Association Theory for Phase Equilibrium Modeling in Chemical Engineering Practice

“…The effects of solvation are often predicted by a mean field technique. Recent quantum calculations show that hydrogen bonding is cooperative, changing with cluster size and complicating determination of the “best” TPT1 parameter values. , The enthalpy of hydrogen bonding can be discerned, but accurate determination of the entropy of bonding needed for an association constant is elusive …”

“…Information beyond density and vapor pressure is needed for confident determination of association parameters. Determination of bonding energy is more advanced from first-principles (quantum) than the bonding volume Practitioners prefer models for association strength that do not require correlation of significant quantities of pure component data to obtain size/shape parameter values or methods to estimate the pure component size/shape parameters. Progress continues to be made for association of small non-electrolytes.…”

“…221,222 The enthalpy of hydrogen bonding can be discerned, but accurate determination of the entropy of bonding needed for an association constant is elusive. 223 Spectroscopy has been used to study hydrogen bonding in both chemistry and engineering literature. Solvatochromic studies such as acidity and basicity 224−227 have been utilized for the MOSCED model intended only for infinite dilution activity coefficients.…”

“…Information beyond density and vapor pressure is needed for confident determination of association parameters. Determination of bonding energy is more advanced from first-principles (quantum) than the bonding volume …”