Investigation of CO2, CH4 and N2 adsorption mechanism on zeolite 4A using statistical physics and site energy distribution analysis

Abstract

In this study, statistical physical modeling and site energy distribution analysis were utilized to provide new insights for elucidating the adsorption mechanisms of CO₂, CH₄ and N₂ on zeolite 4A. The equilibrium uptake behavior of CO₂, CH₄ and N₂ by zeolite 4A was characterized through laboratory experiments conducted at 278 K–328 K. Two classical models and three statistical physics models were employed to correlate the experimental data, and the most appropriate model was identified through nonlinear regression calculations. The results suggest that the monolayer model with one energy (M1E) is the most suitable model for describing gases on zeolites 4A. CO₂ and CH₄ molecules were positioned with parallel and perpendicular mixed attachment to the adsorbent surface (n = 0.7639 to 0.9582). The N₂ molecules shifted from parallel and perpendicular mixed attachment at low-temperature (n = 0.9104 to 0.9895) to perpendicular attachment at high-temperature (n = 1.0109 and 1.0414). The adsorption energy (5.8–11.0 kJ/mol) analysis indicates that the process is dominated by physical adsorption. Lowering the temperature resulted in greater disorder and adsorption spontaneity. SED investigation demonstrated that gas molecules preferentially adsorbed to high-energy sites, followed by subsequent migrating to lower-energy sites. CO₂ adsorption requires the least energy but has the greatest energy heterogeneity. These insights advance the mechanistic comprehension of CO₂, CH₄ and N₂ adsorption on zeolite 4A surfaces. This novel approach to statistical physics and site energy distribution studies has the potential to inform the design of gas adsorption systems for a range of applications.