Theoretical Investigation Of Carbon Dioxide Separation And Its Extraction Of Kerogen Moieties

CO₂ capture and separation is very important due to its rapid increase in recent decades,which has caused serious environmental pollution.After its capture and separation,CO₂recycling in field of energy and invironment also attracts increasing attentions these days.By using computer simualtions,we investigated carbon dioxide separation by using porous graphene.And gas separation mechanism was excluided.Moreover,CO₂ extraction of kerogen moieties from oil shale under supercritical condition was investigated to explore its potential application in exploitation of oil shale.Firstly,using molecular dynamic?MD?simulations,we studied the effect of fluorine modification for pore rim of porous graphene on CO₂/N₂ separation.It is demonstrated that the fluorine modified porous graphene membrane has excellent selectivity for CO₂/N₂separation.We also detailedly investigated the mechanism of the fluorine modified porous graphene membrane for CO₂/N₂ separation by using first principles simulations.We found that the diffusion barriers for CO₂ and N₂ to pass through the pore-22?with 22 carbon atoms drilled out?graphene membrane were relatively small,which indicated that the pore-22 had a low selectivity for CO₂/N₂ separation.After fluorine modification,the diffusion barrier for CO₂ to pass through decreased to 0.029 eV,while the diffusion barrier for N₂ greatly increased to 0.116 eV.Therefore,N₂ got more difficult,while CO₂ got easier to penetrate through the fluorine modified pore-22.The fluorine modified pore-22 porous graphene shew a great enhancement of selectivity for CO₂/N₂ separation,which was consistent with the MD results.Our studies propose an economical and efficient means of separating CO₂ and reveal the separation mechanism,which may be useful for designing new concept membranes for gas separation.Then,the extraction process and mechanism of kerogen moieties with supercritical CO₂are elucidated using molecular dynamics simulations.It is demonstrated that supercritical CO₂can effectively dissolve the kerogen moieties adsorbed onto the shale surface,and the kerogen moieties dissolved in supercritical CO₂ can be easily extracted from oil shale,because the interaction between the kerogen moieties dissolved in supercritical CO₂ and the shale surface is greatly reduced.The dissolving capacity of supercritical CO₂ is found to effectively increase with increasing pressure before the pressure reaches a critical value?approximately50 MPa?and then increases slowly.Moreover,the dissolving capacity of supercritical CO₂increases with increasing temperature at high pressure,which is consistent with experimental results.In addition,the hydroxyl functional groups modified on the shale surface promote the extraction of kerogen moieties with supercritical CO₂,and the polar kerogen moieties are more easily dissolved in supercritical CO₂.To conclude,all of these good extractions from the shale surface result from the decrease of the electronic interaction of kerogen-shale after the injection of supercritical CO₂,which further changes the wettability of the shale surface and has profound implications for studies of the future exploitation of oil shale using carbon dioxide.