(400ac) Activity Coefficient Model for Predicting Multicomponent Adsorption of Natural Gas on Chabazite for CO? Capture

Natural gas (NG) is a key transitional energy source with growing global demand, yet its primary processing requires effective CO₂ removal to prevent pipeline corrosion and maintain calorific value. Adsorption on zeolites like chabazite (CHA) offers a promising, energy-efficient method for CO₂ separation. However, modeling multicomponent adsorption accurately remains challenging due to the inadequacy of ideal theories in accounting for strong adsorbate-adsorbent interactions, especially in heterogeneous materials.

This study proposes a new activity coefficient model for multicomponent adsorption on CHA, grounded in Real Adsorbed Solution Theory (RAST). Experimental isotherms were obtained using an Intelligent Gravimetric Analyzer to validate CHA forcefield parameters, while molecular simulations via Grand Canonical Monte Carlo (GCMC) in RASPA code 2.0 provided adsorbed loadings. Modification on classical model expressions (Margules, Wilson, NRTL) by incorporating a surface potential correction (SPC) term was made. The proposed and classical models were used to obtain binary mixtures activity coefficients. The parameters obtained by regressing the activity coefficient from binary mixtures using molecular simulations were obtained and applied to remove adsorbed phase ideality imposed by IAST on NG mixture.

Mean adjusted R-squared of 0.9696 was obtained by comparing simulated and regressed data, while classical methods achieved values below 0.8. The model was validated against simulated adsorption equilibria of NG mixtures (CH₄, C₂H₆, C₃H₈, CO₂), showing improved agreement compared to Ideal Adsorbed Solution Theory (IAST), particularly under non-ideal conditions.