A Semi-Predictive Modified Sips Model for CO2 Adsorption under Humid Conditions: Quantifying Water Effects in 13X Zeolite

Abstract

The presence of water vapor severely limits the performance of zeolite-based CO2 capture processes by preferentially occupying adsorption sites and altering equilibrium behavior. Despite extensive studies on CO2/H2O systems, conventional multicomponent isotherm models often fail to accurately describe competitive adsorption under humid conditions, limiting their applicability in process design. In this work, a correlative equilibrium model based on a modified Sips equation is proposed to describe CO2 adsorption on 13X zeolite in the presence of preadsorbed water. The model explicitly incorporates the effect of water loading on adsorption capacity, affinity, and surface heterogeneity. Experimental adsorption isotherms for CO2 and H2O were obtained at 50–90 °C using gravimetric and fixed-bed techniques, including measurements under controlled prehydration conditions. The proposed model accurately reproduces CO2 equilibrium data over a wide range of temperatures and water loadings, with residual analysis confirming its statistical robustness and absence of systematic bias. Results show that even low levels of preadsorbed water significantly reduce CO2 uptake and modify adsorption energetics. The developed approach provides a practical and reliable framework for predicting CO2 adsorption under humid conditions without requiring extensive multicomponent experiments, offering direct applicability for the design and optimization of adsorption-based carbon capture processes.