Carbon Dioxide Adsorption And Separation In Metal-Organic Frameworks Mg-MOF-74 And Its Derivatives

For the present CO₂ capture,Utilization and storage?CCUS?is well acknowledged as the most efficientive method to mitigate greenhouse effect.Specificly,CO₂adsorption after post-combustion has a promising future because of its advantages,such as low energy consumption for regeneration,easy control and stable adsorption performance.Compared to traditional adsorbents,Metal-Organic Frameworks?MOFs?are a king of porous materials formed by metal ions and organic ligands and popularied these years because of their advantages.The characteristics Such as high specific surface area,high thermal and chemical stability and turnable pore structures make it possible for them to be promising materials in CO₂ storage and separation areas.Due to the existence of the unsaturated metal sites,Metal-Organic Frameworks Mg-MOF-74shows exceptional CO₂ adsorption capacity under low CO₂ pressure,but the strong hydrophilicity of frameworks hinders its further development on CO₂ capture under wet conditions.Considering the features of flue gas with low CO₂ partial pressure and certain amount of water vapor,in this study,Metal-Organic Frameworks Mg-MOF-74 was modified by four types of functional groups?Bromine?Amidogen?Hydroxy?Methyl?or Cu metals substitution to explore their influence on CO₂ adsorption and separation initially.Then based on the previous simulation results,Mg-MOF-74 and its mixed-metal-frameworks were synthesized by one-pot synthesis method,and porous adsorbates with complete crystal structures?high specific surface area and stable CO₂adsorption capacity were obtained.Subsequently,CO₂ adsorption kinetics of frameworks prepared from this study were studied.Consequently,UiO-66 pellets were fabricated by tablet granulation method with UiO-66 as porous powder.the effect of pore forming matrrials and binders as well as regeneration cycles on the CO₂ adsorption performance of fabricated pellets were investigated.In this paper,The main studies and conclusions are as follows:?1?Here Grand Canonical Monte Carlo simulation was launched to explore the effect of four types of functional groups?Bromine?Amidogen?Hydroxy?Methyl?on CO₂ adsorption and separation performance in Mg-MOF-74.The results showed that bromine and methyl modification made it possible to increase single component CO₂uptake.However,the hydrophilicity of framweorks was enhanced simultaneously?except for methyl?,thus CO₂ adsorption capacity decreased under wet conditions as a consequence of the competitive adsorption between CO₂ and H₂O.When it came to amine and hydroxyl modification,it favored CO₂ adsorption performance in both dry and wet conditions.Particularly,CO₂ adsorption uptake in dry and wet conditions increased up to 34%/12.6%?42%/10%respectively at 298 K?1 bar pressure.However,with strong hydrophilic property,competitive adsorption of frameworks between H₂O and CO₂ was still obvious.?2?At first,Grand Canonical Monte Carlo simulation was launched to explore the effect of Cu metals substitution in Mg-MOF-74 on CO₂ adsorption and separation performance.It was suggested that CO₂ adsorption capacity dropped gradually with more Cu metals doped into Mg-MOF-74.However,the hydrophobicity of frameworks were enhanced,which was beneficial for CO₂ adsorption in wet mixtures.Specifically,CO₂ adsorption uptake in CuMg21 was twice over that of Mg-MOF-74 under 298 K?1bar in CO₂/N₂/H₂O mixtures.Secondly,Mg-MOF-74 with high BET surface area was synthesized by solvothermal method and a new mixed-metal MOF-74 with Cu and Mg metals was obtained by one-pot synthesis.Thirdly,CO₂ adsorption kinetics of frameworks synthesized by solvothermal method was studied under different adsorption conditions.Several adsorption models were used to investigate the adsorption mechanism of frameworks.It was found that Lagergren-first order model predicted the CO₂ physisorption behaviors of frameworks well.Besides,the CO₂ adsorption rate of frameworks was mainly controlled by film diffusion resistance and the intraparticle diffusion resistance.?3?With the utilization of pore forming material NH₄HCO₃ and binders?diatomite and kaolin?,UiO-66 pellets with relatively high specific area and desirable mechanical strength were fabricated by tablet gradulation way.Results indicated that the mechanical strength of pellet samples decreased gradually with the increase of NH₄HCO₃.As the concentration of binder increased,the mechanical strength of pellets were enhanced at the beginning but were impacted if more binders were utilized.What is more,compared to pellets with kaolin as binder which showed higher mechanical strength,pellet samples with diatomite as binder revealed better CO₂ adsorption performance.In addition,It appealed that the adsorption capacity of pellets only decreased by 6.5%after6 cycles of regeneration with nearly no impact on its appearance,specific surface area,compared with that of UiO-66 powder which declined by 9.2%on CO₂ uptake.