Adsorption Isotherm Modeling for Post-Combustion CO2 Capture: A Critical Review and Engineering Perspective

Adsorption isotherm models play a central role in low-to-moderate-temperature adsorption-based postcombustion CO2 capture (PCC), as they provide the thermodynamic basis for predicting working capacity, selectivity, and regeneration energy in cyclic processes. However, existing literature remains fragmented: model-oriented studies are typically not specific to CO2 capture, material-focused reviews treat isotherms descriptively, and process-oriented works adopt equilibrium models without critically assessing their structural assumptions. As a result, model selection is often driven by fitting accuracy rather than by physical consistency and process relevance under PCC conditions. This review addresses this gap through a model-centered analysis of adsorption isotherms applied to CO2 capture, systematically evaluating classical, multisite, heterogeneity-corrected, and pore-filling formulations across major sorbent classes, including zeolites, carbon-based materials, metal–organic frameworks, and amine-functionalized adsorbents. By explicitly linking adsorption mechanisms and material properties to model structure, the work clarifies how apparent model performance depends on pressure range, data set characteristics, and fitting methodology. The analysis shows that variability in experimental data sets and the lack of standardized fitting protocols often obscure the physical meaning and transferability of model parameters. Under PCC-relevant conditions, an accurate representation of the dilute region and thermodynamic consistency are identified as key requirements for reliable process predictions. Bounded Langmuir-type models, including dual-site Langmuir, Sips, and Tóth formulations, emerge as the most robust frameworks, while empirical and unbounded models exhibit limited predictive reliability. Overall, this review provides a unified framework for interpreting isotherm models and establishes practical criteria for their selection in adsorption-based CO2 postcombustion capture.