Evaluating the Thermodynamics of Self and Cross-Clustering on Strongly Associating Systems Donald P. Visco, Jr., Department of Chemical Engineering, Tennessee Technological University Thermodynamic Modeling of Aqueous Hydrogen Fluoride (HF) On comparing the correlative and predictive ability of the 14 different pure component models, 1-6 (monomer and hexamer), 1-2-6, 1-2-6-8, 1-2-3-6-9, 1 to 9 and 1 to 12 are found to be reasonable and the poor ones were 1-2, 1-4, 1-2-3-4-5 and 1-2-3-4-6 HF+ water mixture properties correlated and predicted using 14 different pure component association schemes for HF and with inclusion of both self as well as cross association for HF and water (HF)1-(H2O)4 (HF)2-(H2O)4 (HF)1-(H2O)5 (HF)3-(H2O)3 (HF)2-(H2O)5 (HF)4-(H2O)2 (HF)4-(H2O)3 (HF)5-(H2O)1 (HF)4-(H2O)1 Adding the ‘key’ cross-clusters obtained from the molecular level cluster studies in to the bulk phase thermodynamic model reduced the binary interaction parameter value by ~ 3.5 % when compared to the self-association models HF + Water Association Patterns First study to report the molecular level clustering in (HF)n­(H2O)m mixture with m+n up to 8, using hybrid meta density functional theory method (mPW1B95) and 6-31+G(d,p) basis set More than 214 different stable geometries were reported Regression results indicated that the strongest interaction is of the type H2O…H–F ΔE and ΔG results indicate that equimolar (HF)m(H2O)n (m = n) clusters are highly preferred Larger (HF)m(H2O)nclusters (m + n > 3) are preferred in the solution phase Association Based 1-2-3 Model An exact expression is reported for an association based equation of state that allows the formation of monomers, dimers and trimers (1-2-3) The utility of the exact expression for this model over the numerical evaluation was demonstrated by comparing the computational time required to calculate the phase equilibrium curve for acetic acid. The importance of having an exact expression was also shown by comparing the CP results between the exact expression and a fitted functional form. The mismatch between the fitted form and the exact expression was understood in terms of the poor description of the derivative behavior of the chemical contribution to the compressibility factor by the former.