Prediction of pure and mixture thermodynamic properties and phase equilibria using an optimized equation of state - part 2: Vapor pressure modelling and extension to mixtures

The Almajose–Dalida equation is used to develop thermodynamically consistent energy parameter coefficients using three established alpha functions in the literature. Specifically, the Twu function, the Heyen function, and the Mathias–Copeman alpha functions were applied to model the energy parameters of 100 compounds commonly used in process simulations. Thermodynamic consistency rules were applied to each function; however, since the Mathias–Copeman function is not inherently thermodynamically consistent, numerical boundary conditions were imposed to ensure its consistency up to 3000 K. Additionally, thermodynamically-consistent generalized correlations were developed for the Twu two-parameter and Heyen alpha functions, enabling the generalized Almajose–Dalida equation to extend to species with unavailable parameters.

Furthermore, the equation was applied to fluid mixtures using advanced mixing rules, including the van der Waals one-fluid (vdW1f) rule and the Huron–Vidal–Orbey–Sandler (HVOS) rule. Enhanced by the Panagiotopoulos cross-interaction model, the vdW1f rule provided accurate fits for nonideal systems, achieving precise phase equilibrium and volumetric behavior predictions. By integrating the modified HVOS mixing rule alongside the modified UNIFAC method, the equation attains fully predictive capabilities. This comprehensive approach advances the accuracy and reliability of thermodynamic modeling using the Almajose–Dalida equation, particularly in cases where access to experimental data is limited.