Evaluation of the Impact of H2O, O2, and SO2 on Postcombustion CO2 Capture in Metal−Organic Frameworks

摘要

Molecular modeling methods are used to estimate the influence of impurity species:nwater, O2, and SO2 in flue gas mixtures present in postcombustion CO2 capture using a metal organicnframework, HKUST-1, as a model sorbent material. Coordinated and uncoordinated water effects onnCO2 capture are analyzed. Increase of CO2 adsorption is observed for both cases, which can benattributed to the enhanced binding energy between CO2 and HKUST-1 due to the introduction of ansmall amount of water. Density functional theory calculations indicate that the binding energy betweennCO2 and HKUST-1 with coordinated water is ∼1 kcal/mol higher than that without coordinatednwater. It is found that the improvement of CO2/N2 selectivity induced by coordinated water maynmainly be attributed to the increased CO2 adsorption on the hydrated HKUST-1. On the other hand,nthe enhanced selectivity induced by uncoordinated water in the flue gas mixture can be explained onnthe basis of the competition of adsorption sites between water and CO2 (N2). At low pressures, ansignificant CO2/N2 selectivity increase is due to the increase of CO2 adsorption and decrease of N2nadsorption as a consequence of competition of adsorption sites between water and N2. However, withnmore water molecules adsorbed at higher pressures, the competition between water and CO2 leads tonthe decrease of CO2 adsorption capacity. Therefore, high pressure operation should be avoided in HKUST-1 sorbents for CO2ncapture. In addition, the effects of O2 and SO2 on CO2 capture in HKUST-1 are investigated: The CO2/N2 selectivity does notnchange much even with relatively high concentrations of O2 in the flue gas (up to 8%). A slightly lower CO2/N2 selectivity of anCO2/N2/H2O/SO2 mixture is observed compared with that in a CO2/N2/H2O mixture, especially at high pressures, due to thenstrong SO2 binding with HKUST-1.