Adsorption\nThermodynamics for Process Simulation

Adsorption has rapidly evolved in recent decades and\nis an established\nseparation technology extensively practiced in gas separation industries\nand others. However, rigorous thermodynamic modeling of multicomponent\nadsorption equilibrium remains elusive, and industrial practitioners\nrely heavily on expensive and time-consuming trial-and-error pilot\nstudies to develop adsorption units. This article highlights the need\nfor rigorous adsorption thermodynamic models and the limitations and\ndeficiencies of existing models such as the extended Langmuir isotherm,\ndual-process Langmuir isotherm, and adsorbed solution theory. It further\npresents a series of recent advances in the generalization of the\nclassical Langmuir isotherm of single-component adsorption by deriving\nan activity coefficient model to account for the adsorbed phase adsorbate–adsorbent\ninteractions, substituting adsorbed phase adsorbate and vacant site\nconcentrations with activities, and extending to multicomponent competitive\nadsorption equilibrium, both monolayer and multilayer. Requiring a\nminimum set of physically meaningful model parameters, the generalized\nLangmuir isotherm for monolayer adsorption and the generalized Brunauer–Emmett–Teller\nisotherm for multilayer adsorption address various thermodynamic modeling\nchallenges including adsorbent surface heterogeneity, isosteric enthalpies\nof adsorption, BET surface areas, adsorbed phase nonideality, adsorption\nazeotrope formation, and multilayer adsorption. Also discussed is\nthe importance of quality adsorption data that cover sufficient temperature,\npressure, and composition ranges for reliable determination of the\nmodel parameters to support adsorption process simulation, design,\nand optimization.