Molecular simulation on competitive adsorption of ethanol, acetaldehyde and acetic acid on zeolites in humid conditions

Adsorption is a key technique for purifying volatile organic compounds (VOCs) from indoor air. Due to the complexity of multi-component VOCs and humid environment, the competitive adsorption among VOCs under the influence of water vapor remains unclear, which limits adsorbent selection and performance prediction. In this work, adsorption characteristics of typical indoor VOCs (ethanol, acetaldehyde, and acetic acid) on commercial zeolites (BETA-25 and ZSM5-300) under varying humidity were studied through molecular simulation. The simulation based on charge-corrected molecular structures and force field was validated by experiments. The unary, binary and ternary adsorption isotherms of three VOCs were obtained. At both dry and wet conditions, the VOCs with higher polarity shows greater adsorption capacity: acetic acid > ethanol > acetaldehyde. BETA-25 exhibits stronger adsorption on all three gases under dry conditions, while under wet conditions ZSM5-300 shows greater adsorption capacity of ethanol and acetaldehyde with lower polarity as compared to BETA-25. Simulation of adsorption energy and adsorbate density distribution in ternary equilibrium demonstrates the presence of water vapor alters the sorbate-sorbent interaction, particularly for ethanol and acetaldehyde showing stronger adsorption on BETA-25 than on ZSM5-300 at dry conditions but reversely at wet conditions. The lower-silica zeolite favors the adsorption of highly-polar VOC regardless of water, and the higher-silica counterpart with greater hydrophobicity facilitates adsorption of less-polar compounds in competing with water. The findings in this work can provide methodological reference for adsorbent screening and data basis for real VOCs purification applications.