Enhanced Adsorption of Polar VOCs on MSU-H Mesoporous Silica under Supercritical CO ₂ Conditions

Supercritical CO2 is a sustainable solvent used for separation and purification. Recovering VOCs via adsorption from supercritical CO2 is of great interest, highlighting the need for effective adsorbents. This research examined the adsorption equilibria of ethyl acetate, a representative volatile organic compound (VOC), on MSU-H mesoporous silica under supercritical CO2 conditions. Experimental equilibrium adsorption data were collected using a fixed-bed apparatus over temperatures T = (313 to 353) K and pressures P = (10.0 to 15.0) MPa. The resulting data could be modeled using the Dubinin–Astakhov (DA) equation, enabling a quantitative assessment of key parameters, such as the saturated adsorption capacity and characteristic adsorption energy. The results indicated that MSU-H exhibits a much higher adsorption capacity for ethyl acetate than activated carbon, approximately four times greater under identical pressure and temperature conditions. This is mainly due to strong interactions between the silanol groups on MSU-H’s surface and the polar VOC molecules. Additionally, this study offers a thorough and systematic analysis of how pressure, temperature, and CO2 density influence adsorption equilibria on MSU-H. The findings demonstrate distinct density-dependent behavior, where increasing CO2 density reduces ethyl acetate uptake due to competitive adsorption and solvation effects─an aspect not previously explored. The detailed assessment of these thermodynamic factors provides new quantitative insights into the impact of operating conditions and emphasizes the excellent adsorption performance of mesoporous silica, laying a solid theoretical foundation for designing and optimizing supercritical CO2-based VOC recovery processes.