Predictive Power of Theoretical Adsorption Models for Hydrogen/Coal System: Implications for Hydrogen Geostorage

Experimental methods are commonly used to determine the ability of a rock to adsorb gas by means of isothermal adsorption experiments. Adsorption isotherms quantitatively describe the relationship between the amount of gas adsorbed onto a rock surface and associated equilibrium conditions. It is imperative to study the adsorption of hydrogen (H₂) on coal for various pressure and temperature conditions to de-risk subsurface hydrogen storage. This study aims to provide a theoretical analysis of the adsorption behavior of hydrogen onto coal, based on representative models in order to assess the suitability of theoretical isotherms. Specifically, we employ a modeling strategy to quantify the applicability of the Langmuir, Tóth, and BET framework for a hydrogen/coal system based on literature data. The novelty of the work derives from that fact that the predictive power of well-known gas adsorption isotherms for experimental H₂coal adsorption data has not been studied yet. To assess storage security and economics via modeling, in situ hydrogen storage requires suitable isotherms. Here we consider data for pressures up to 102 bar and temperature in between 303-333 K. Findings suggest that in a RMSE-sense, adsorption isotherms may be ranked as Langmuir>Tóth>BET for the coals studied. The results of this study contribute to an improved understanding of the predictive powers of adsorption isotherms and provide valuable numerical input variables for modeling coal seam formations at the reservoir scale, facilitating history matching and enabling predictions of formation behavior.