Mechanistic insights into water vapor adsorption behavior and its impact on dynamic adsorption of acetone: experimental and molecular simulation study.

Water vapor significantly impacts volatile organic compound (VOC) adsorption in fixed-bed systems. This study elucidates water vapor's interference mechanisms during acetone adsorption. Dynamic tests (298.15-328.15 K) revealed that water breakthrough times were generally insensitive to relative humidity (RH), except at 298.15 K where duration increased with RH. A distinct plateau in the water breakthrough curve emerged at 298.15 K. This anomalous extension of water breakthrough duration at 298.15 K stemmed from enhanced water cluster formation and micropore filling under low-temperature conditions, where reduced thermal motion favored water aggregation in narrow pores. In binary systems, a bidirectional competitive displacement phenomenon occurred, referring to two concurrent processes: water displaced adsorbed acetone from high-affinity micropore sites via stronger hydrogen bonding, and acetone occupied pore channels, reducing pore blockage and accelerating water breakthrough. During the co-adsorption process, elevated RH amplified acetone roll-up via enhanced micropore-filling water clusters, while water roll-up diminished due to size-exclusion effects. Molecular simulations revealed that although water exhibited a lower average adsorption heat than acetone, it formed stable hydrogen-bonded clusters at oxygen-containing functional groups, resulting in significant localized adsorption enhancement. Although water preferentially occupied high-affinity micropore sites (∼2.7 Å) in competition with acetone, the presence of water didn't alter the primary adsorption configuration or orientation of acetone molecules. In addition, the diffusion coefficients of both components increased in the binary system, confirming that trace water promoted acetone transport via bidirectional competitive displacement, despite generally hindering overall adsorption.