Adsorption and growth of water clusters on UiO-66 based nanoadsorbents: A systematic and comparative study on dehydration of natural gas

In this study, the potential application of UiO-66(NH2) as an interesting adsorbent for dehumidification of natural gas is investigated by using density functional theory (DFT). On this basis, both UiO-66 and UiO-66(NH2) nano-adsorbents were synthesized by low temperature solvothermal method. The structure and morphology of the prepared adsorbents were then characterized by PXRD, SEM and N-2 adsorption/desorption (BET) techniques. For these novel desiccants, higher regenerability and drying efficiency were acquired compared to those of the commercial silica gel, activated alumina and zeolite. The results showed that the UiO-66 and especially UiO-66(NH2) are effective sorbents for drying the natural gas for which the water capacity at P/P-0 = 0.9 was 40 and 35 wt% (30-50% more than counterparts), respectively. The experiments confirmed that the nanoadsorbents are water stable, and no remarkable loss in adsorption capacity was observed even after twenty adsorption/desorption cycles. Thus, they could be easily regenerated at low temperatures. In addition, the modes of water adsorption on the adsorbents for clusters up to pentamer were systematically studied, where both molecular and cluster adsorption processes have been considered by using the DFT method. The molecular adsorption is shown to be thermodynamically the predominant mechanism on UiO-66(NH2) surface. Remarkably, the cluster adsorption is mainly conducted through trimer and tetramer. However, the tetramer distorts its initial cyclic structure to an adsorbed cyclic trimer plus a monomer after adsorption in order to increase the induced dipole-dipole interactions.