Effects of Water Vapor and Trace Gas Impurities in Flue Gas on CO2/N2 Separation Using ZIF-68

Understanding the effects of the presence of water vapor and other gas impurities (such as SO2 and O-2) in flue gas on sorbent performance is critical to properly evaluate the use of metal organic frameworks for realistic postcombustion CO2 capture. Grand canonical Monte Carlo calculations were performed to investigate the effects of H2O, O-2, and SO2 on CO2 adsorption and CO2/N-2 separation using ZIF-68. The mechanisms of these effects were also investigated by density functional theory calculations. The presence of H2O affects the CO2 adsorption on ZIF-68 in two opposite ways: the negative effect of competitive adsorption of the impurity gases on the adsorption sites over CO2, and the positive effects of formation of new adsorption sites for CO2. The presence of H2O reduces the CO2 adsorption ability but increases the CO2/N-2 separation factor. SO2 is found to be strongly adsorbed in the pores of ZIF-68 and considered as an adverse factor for CO2 adsorption and CO2/N-2 separation. The presence of O-2 has a negligible effect on CO2 adsorption on ZIF-68.