Study Of CO₂ Adsorption And Separation In Functionalized Metal-organic Framework Under Humid Condition Through Molecular Simulation

Capturing carbon dioxide from flue gas is an important challenge as fossil fuel combustion continues to be a primary source for energy. Recently, Metal Organic Frameworks（MOFs） are considered to be the most promising candidates for CO₂ capture and separation owing to their attractive properties such as high surface area,high porosity, low density, and tunable pore sizes and chemical stability. Lots of MOFs with high CO₂ capture capacity have been reported in the past few years.However, one of the biggest obstacles for applications of MOFs in CO₂ capture is their instability toward water. Therefore, it is necessary to investigate the stability of MOFs under humid conditions, the influence of water molecules on the adsorption amount of CO₂ and separation factor also should be revealed. This is very important for designing MOFs with well CO₂ capture and separation and also well stability toward water.Since molecular simulations have been recently used to investigated the adsorption and separation performance of large amount of MOFs, the relationship between the structure and the adsorption and separation properties could be illustrated. It also presents a supplement to traditional experimental methods and help us to understand the adsorption mechanism from molecular level. In this thesis, Grand canonical Monte Carlo method was employed to investigate the adsorption amount of CO₂ in metal organic frameworks functional with methyl, perfluoromethyl, amino,nitryl groups under dry and humid conditions. The influences of functional group on CO₂ adsorption and separation is also discussed. The major contributions of this work are as follows:（1） The electrostatic interaction between adsorbate and adsorbent would be changed when some functional group was introduced to organic ligands, which influences the adsorption behavior of adsorbate.（2） The adsorption behavior of CO₂ and H₂O in functional MOFs is closely related to the diameter of pore size and their topology. For these MOFs with larger pore size and one dimensional channel, the adsorption amount of CO₂ in all functional MOFs increase, the adsorption amount of H₂O in MOFs-1NH2 and MOFs-1NO2 systems also increase. A hydrophobic pore channel would be formed whenmany methyl or perfluoromethyl group were introduced to the large pore channel. As to these MOFs with small pore channel, the adsorption amount of CO₂ and H₂O would be decreases due to the aperture reduction which causes by the introduction of functional groups. There is no difference between the influence of methyl or perfluoromethyl group on CO₂ adsorption.（3） The adsorption amount of CO₂ in amino and nitryl groups functional MOFs under humid conditions would decrease obviously. It is well known that the adsorption behavior would influenced by H₂O molecule under humid condition, this influences would be reduced through introduction some hydrophobic functional group to the MOFs with larger pore size and one dimensional channel. When a hydrophobic pore channel would be formed or the perferential adsorption sites would be covered effectively by introducting some methyl and perfluoromethyl groups to the MOFs.The hydrophobility of MOFs would be enhanced and the adsorption amount CO₂ under humid conditions would be influenced less. The MOFs-CH₃ shows well CO₂ capture capacity under humid conditions rather than that for MOFs-CF₃ system.（4） The relative sensitivities of MOFs for flues gas（CO₂/N2 mixtures） under humid conditions would be enhanced by the introduction of hydrophobic groups to the MOFs. Ni/DOBDC-CH₃ with hihg CO₂ capture capacity is promising candidates for CO₂ capture from flue gas.