Design Of CO₂ Adsorption Material And Regulation Of Adsorption Heat

The greenhouse effect caused by the increase of CO₂ concentration has a serious impact on the global climate and ecological environment,so it is important to develop efficient CO₂ capture and storage technologies.Porous solid materials are considered to be one of the most promising carbon capture materials,and the current adsorption of CO₂ by solid materials is mainly divided into physical adsorption and chemisorption.Physical adsorbents do not form direct chemical bonds with CO₂,but adsorb through relatively weak physical forces（i.e.,van der Waals forces and electrostatic forces）.Chemical adsorbents mainly adsorb CO₂ by chemical reaction such as acid-base reaction,and the adsorption capacity and selectivity of CO₂ are high,but the heat of CO₂ adsorption is generally 60-110 kJ/mol,and the regeneration energy consumption is much higher than that of physical adsorption.Therefore,the accurate regulation of CO₂ adsorption heat of adsorbent and the improvement of adsorption capacity and selectivity of adsorbent for CO₂ are the core problems facing the application of solid adsorbents.This thesis investigates the adsorption of CO₂ by amine groups and the effect of the presence of Cu²⁺and MOF on the adsorption of CO₂ by amine groups;the effect of different metal ions on the adsorption amount and selectivity of the materials is studied by using metal-nitrogen bonds to regulate the CO₂ adsorption heat of the materials.The main content is divided into two parts:（1）PAN-NHx fibers were synthesized using triethylenetetramine aminated polyacrylonitrile（PAN）fibers to study the adsorption effect of different amine group density fibers with CO₂.The amine group adsorbed CO₂ by chemical interaction,and when the amine group density of PAN-NHx fiber was 8 mmol/g,the CO₂ adsorption amount was 3.65 mmol/g（273 K,1 bar）,and the CO₂/N₂ selectivity was 68,meanwhile,the heat of adsorption was as high as 68.66 kJ/mol.After that,the amine group was used to adsorb Cu²⁺to generate Cu-N bond to adsorb CO₂.When the Cu²⁺content was 12 mg/g,the CO₂ adsorption amount of PAN-NHx-Cufiber was 2.16 mmol/g（273 K,1 bar）,the heat of adsorption was reduced to 45.21 kJ/mol,and the CO₂/N₂ selectivity was 37.Further,using the weak alkaline environment on the surface of PAN-NHx fiber,the appropriate amount of Cu-MOF-74 was coated onto the fiber surface to generate MOF@PAN-NHx fiber by controlling the reaction time,and the CO₂ adsorption amount could reach 3.42 mmol/g（273 K,1 bar）when the loading amount was 2 mmol/g,an increase of 58.33%,and the heat of adsorption was53.28 kJ/mol,an increase of 17.85%;meanwhile,the selectivity was increased to 85,an increase of（compared with PAN-NHx-Cu）,which can not only meet the CO₂capture and separation,but also has low regeneration energy consumption.（2）Metal phthalocyanine based covalent organic skeletons（MPc-COF）were prepared using Schiff base reaction with tetraaminophthalocyanine and terephthalaldehyde as monomers.The effect of metal ions(Cu²⁺,Ni²⁺,Mg²⁺)in the center of phthalocyanine on the heat and selectivity of CO₂ adsorption was investigated using metal-free phthalocyanine based covalent organic skeleton（H₂Pc-COF）as a reference.The addition of metal ions can increase the CO₂adsorption by 10-30%（relative to 1.70 mmol/g for H₂Pc-COF）,and Mg²⁺has a larger Lewis acidity,greater ionic strength and electron polarization rate,reaching a maximum CO₂ adsorption of 2.51 mmol/g（273 K,1 bar）.Both Cu²⁺and Ni²⁺have 4s,4p empty orbitals and unsaturated 3d orbitals,and the 3d orbitals of Ni²⁺can accept more charges,so the dipole effect with CO₂ is the strongest,and the heat of adsorption reaches 56.05 kJ/mol.Since the dipole effect of Cu²⁺with CO₂ is weaker than that of Ni²⁺,the heat of adsorption of CuPc-COF is reduced to 51.05 kJ/mol.Mg²⁺has a stable electron When N₂ enters the MPc-COF skeleton,the off-core electron arrangement of Mg²⁺is stable and does not easily accept electrons transferred from the phthalocyanine ring,so Mg²⁺has the strongest repulsion to N₂and the highest CO₂/N₂ selectivity is 54.The selectivity of CuPc-COF is 49,which is greater than that of Ni Pc-COF,which is 34.Therefore,in the COF structure,Mg²⁺has the best adsorption effect on CO₂,not only the adsorption amount and selectivity are greater,but also the heat of adsorption is smaller,which is conducive to reducing the regeneration energy consumption.