Competitive adsorption of benzene and water vapor on lignite-based activated carbon: Experiment and molecular simulation study

Exploring the effect of water vapor on the benzene adsorptive behavior is of practical importance and scientific interest. The presence of water vapor in the gas stream altered the breakthrough curves of benzene, as well as the selectivity of carbon materials towards adsorbates. The work herein elucidated the competitive adsorption mechanism based on experimental observation and molecular simulation. At relative humidity (RH) 10%, water molecules showed less effect on the benzene adsorption that benzene entered the micropores and mesopores while water molecules were primarily adsorbed in the mesopores. Since the polar water molecules presented higher affinity towards the surface functionalities, these molecules preferentially occupied the adsorption site via hydrogen bonding with increased RH. Water cluster was gradually formed through water-water interactions which were characteristics of pore filling. A two-layer stacking of adsorbates was observed for co-adsorption. The first layer was primarily composed of water molecules with the average distance of 2.99 ~ 3.19 Å to the surface functionalities. The second layer was primarily benzene molecules which were aggregated in T-shaped, displaced T-shaped and parallel configurations. These molecules were separated at 4.67 ~ 6.17 Å from the functional groups, and mainly adsorbed by water-benzene interaction (via hydrogen bonding).