Revisiting Supercritical CO2 Adsorption Models for Geological Carbon Storage in Coals: A Review

Increasing concerns about climate change have intensified research on enhanced coalbed methane (ECBM) recovery and CO2 sequestration in geological reservoirs. Because of their organic-rich nature and abundant micropores with high specific surface area (SSA), coals are regarded as promising targets for subsurface CO2 storage. Supercritical CO2 adsorption is a major storage mechanism in coal, and the selected adsorption model directly affects the predicted CO2 storage capacity under geological conditions. This study examines the assumptions, parameters, applications, and limitations of Langmuir-based, Dubinin–Radushkevich-based, Ono–Kondo-based, and simplified local density models. The reviewed studies indicate that satisfactory fitting of excess adsorption alone does not establish parameter uniqueness or physically reliable absolute adsorption estimates. Model applicability depends on the underlying assumptions, coal properties, and fluid conditions, and the available evidence does not establish a universally preferred model. Future research should prioritize consistent reporting of adsorption quantities, coal-specific parameter constraints, and independent validation under well-defined temperature, pressure, and moisture conditions.