Preparation Of Metal-organic Frameworks For CO₂ Capture And Separation Performance

The impact of climate change on human health is one of the most concerned issues in today’s society.It is well known that carbon dioxide,the main greenhouse gas of global warming,is removed from the atmosphere through different natural processes.Unfortunately,the amount of carbon dioxide released into the atmosphere exceeds the natural repair process.Therefore,it is urgent to choose appropriate methods to remove excess carbon dioxide from the atmosphere.Adsorption is a low-cost and high-efficiency method,which is regarded as one of the most promising methods.MOFs consist of strong interaction between metal clusters and organic ligands.With the diverse selection of inorganic-metal nodes and organic ligands,as well as different synthetic methods,MOFs exhibit controllable physical/chemical properties,it is characterized by ultra-high porosity,large surface area and high thermal/chemical stability,which makes it the most promising adsorbent and has been widely used in CO₂capture field.There are several strategies to improve the CO₂ capture by MOFs,such as the introduction of Lewis basic site,the introduction of unsaturated active center,the design of appropriate pore size,the use of flexible structure,etc.these strategies can also improve the separation ability of the gas mixture.According to the above strategies,which have high ability to capture CO₂,the following work is carried out in this paper.In chapter 1,the common adsorbents for CO₂ capture and the most promising adsorbent MOFs are introduced in detail.In chapter 2,microporous MOFs,namely CPM-20,were synthesized by solvothermal method with cobalt chloride as metal salt,1,4-dicarboxybenzene and isonicotinic acid as organic ligand.The specific surface area is 713 m~2/g and the aperture is about 6（?）.Under the condition of 273 K and 1 bar,the CO₂adsorption capacity is 57 cm~3/g.At 298 K and 1 bar,the selectivity of mixed gas CO₂/CH₄ is 47and CO₂/N₂ is 350 by using IAST calculation.This value exceeds the reported SIFSIX-2-Cu-i and MOF-5 materials.The heat of adsorption of CPM-20 on CO₂ was calculated by virial equation.The value of heat of adsorption of CPM-20 was 21 k J/mol.The penetration experiments of dynamic gas mixtures CO₂/CH₄ and CO₂/N₂ show that CPM-20（CO）is a promising material for industrial separation.In chapter 3,microporous MOFs,namely ZBD and ZND,were synthesized by solvothermal method with zinc nitrate as metal salt,1,4-dicarboxybenzene,2-aminoterephthalic acid and triethylenediamine as organic ligands,the aim of this study was to investigate the effect of amino groups on the adsorption capacity and selectivity of CO₂.The structure and properties of ZBD and ZND were characterized.XRD patterns showed that the material was synthesized successfully.The N₂ Sorption isotherm data at 77 K showed that the specific surface area of the material decreased from 1497 m~2/g to 645 m~2/g and the pore size decreased from 6（?）to 5（?）.Under the condition of 273 K and 1 bar,the adsorption capacity of CO₂ increased from 103 cm~3/g to 132 cm~3/g.The selectivity of CO₂/CH₄ increases from 6 to 27,and the selectivity of CO₂/N₂ increases from 71 to 251 by using IAST calculation.The adsorption heat of ZBD and ZND to CO₂ was calculated by virial equation,and the values were 19 k J/mol and 23 k J/mol,respectively.The increase of the values indicated that the introduction of amino group could produce a positive adsorption to CO₂,and the adsorption heat of ZBD and ZND was lower,it shows that the adsorbent is easy to regenerate.Finally,the penetration experiments of dynamic mixed gas CO₂/CH₄ and CO₂/N₂ show that ZBD and ZND can separate mixed gas,and the separation effect of ZND is better than ZBD.The fourth chapter is the conclusion and prospect.The research contents and results of this paper are summarized,and the future research direction of MOFs with higher CO₂ capture ability is prospected.