Metal-organic Skeleton Composites For Carbon Dioxide Capture And Separation

Carbon dioxide（CO₂）is currently the main greenhouse gas.Capture and separation of CO₂ is of great significance to improve human living environment.Flue gases emitted in industry are the main source of CO₂.In addition,CO₂ is also a pollutant in the process of acetylene purification and natural gas upgrading.Adsorption separation is a more energy-saving separation method than traditional separation methods.The choice of adsorbent is crucial in the process.The physical and chemical properties of porous materials modified by ionic liquids（ILs）have been widely studied.The combination advantages of ionic liquids and porous materials make them have great potential in gas adsorption and separation.In this paper,different IL@MOF composites were designed and synthesized to realize the selective adsorption separation of CO₂/C₂H₂,CO₂/N₂ and CO₂/CH₄.The work done in this paper is as follows:1.The"solution-diffusion"mechanism in core-shell IL@MOF composites is proposed to realize the highly selective separation of CO₂/C₂H₂.The core-shell composite BUCT-C19 was constructed.The[TRIEN]L of the shell has high solubility to CO₂ but almost insoluble C₂H₂,which promotes the transport of CO₂,thus realizing the highly selective separation of CO₂/C₂H₂.Density functional theory（DFT）calculations and molecular dynamics（MD）revealed the mechanism of solution-diffusion in CO₂ composites.MD simulations and DFT calculations reveal the“solution-diffusion”mechanism of CO₂ in BUCT-C19.The CO₂ uptake of BUCT-C19 is 40.30 cm³·g^-1.The IAST selectivity for CO₂/C₂H₂（1/1 and 1/3）is 10700 and 4142,which is better than other materials reported.Breakthrough experiments show that BUCT-C19 can directly obtain high purity C₂H₂（≥99.9%）in one step.More importantly,the proposed solution-diffusion strategy can avoid the precise design of MOF channels and is of great significance for the construction of adsorbents.2.Flue gas is the main source of CO₂ emission in industry,three kinds of metal cation chelating ionic liquids[M（HDA）₂][Im]were designed and loaded on MIL-101（Cr）to form composites for the selective separation of CO₂/N₂ in flue gas.The experimental results show that[K（HDA）₂][Im]@MIL-101（Cr）shows the highest CO₂ adsorption capacity(44.60 cm³·g^-1)and almost no adsorption of N₂(1.34 cm³·g^-1).The order of CO₂ uptake is consistent with the coordination ability of metal cations and the viscosity of ionic liquids observed in the experiment.Its IAST selectivity for CO₂/N₂（0.01/99.99）is more than 10⁴,achieving selective separation of CO₂/N₂.3.Three kinds of ionic liquids[Na（M）₂][Im]with different ligands were designed and used to form composites for natural gas upgrading.Experimental results show that the CO₂ uptake of[Na（DGA）₂][Im]@MIL-101（Cr）had the highest CO₂ uptake of 45.25 cm³·g^-1 and almost no adsorption of CH₄.Its IAST selectivity for CO₂/CH₄（0.01/99.99）reached the molecular sieving level（>10⁵）,which is superior to most porous materials reported in the literature.Breakthrough experiment further proves that[Na（DGA）₂][Im]@MIL-101（Cr）can realize the full separation of CO₂/CH₄ for natural gas upgrading.