Thermodynamic Property Estimation Workbook (NRTL, UNIFAC, Peng-Robinson)

This workbook provides a modular, transparent, and auditable platform for estimating key thermodynamic properties essential in chemical process design and operation. The NRTL model handles highly non-ideal liquid-phase behavior using binary interaction parameters and local composition theory, making it especially effective for polar and hydrogen-bonding mixtures. UNIFAC extends predictability to unseen mixtures by decomposing molecules into functional groups and applying group contribution rules—enabling estimation of activity coefficients without experimental binary data. The Peng-Robinson (PR) equation of state, implemented in its cubic form, computes vapor-phase fugacities, compressibility factors, and PVT relationships for hydrocarbon and supercritical systems, with built-in alpha-function temperature dependence and mixing rules (e.g., van der Waals one-fluid mixing) for multi-component mixtures. The workbook typically includes input sheets for component selection, mixture composition, temperature/pressure conditions, and parameter databases (e.g., UNIFAC group interaction parameters, PR critical properties, and acentric factors); calculation sheets perform iterative phase-equilibrium solving (e.g., bubble-point T/P calculations via successive substitution or Newton-Raphson); and output sheets deliver tabulated results, convergence diagnostics, and visualization-ready data. Its Excel foundation supports integration with VBA macros, sensitivity analysis tools, and live links to digital twin platforms (e.g., via Power Query or API-connected add-ins), enabling real-time property updates based on sensor-derived compositions and operating conditions.