Synthesis Of Six-Core Rare Earth Cluster MOFs And Their Study On CO₂/CH₄ Separation Performance

Compared to traditional liquid hydrocarbon fuels,natural gas is considered a relatively clean fuel.Natural gas is mainly composed of CH₄and contains other impurities such as carbon dioxide（CO₂）.The presence of CO₂not only lowers the heating value of natural gas but also causes pipeline corrosion.Therefore,removing CO₂from CH₄has become an essential process in the natural gas industry.Traditional low-temperature distillation techniques require high energy consumption due to the similar boiling point and volatility of CO₂and CH₄.Adsorption is currently considered a promising method for separating CO₂/CH₄due to its fast regeneration rate,low energy consumption,simple operation,and high efficiency.Metal-organic framework（MOFs）materials,which are a new type of solid porous adsorbent composed of inorganic and organic building units that self-assemble through coordination bonds,have shown great potential in the field of gas separation in recent years.Due to their advantages such as large surface area,high crystallinity,tunable chemical structure,and pore properties,MOFs have been widely used for CO₂capture.The common strategies for capturing CO₂with MOFs include designing open metal sites,constructing specific-sized pores,introducing strongly polar functional groups through ligand functionalization,and amine grafting.Based on these strategies,this study carried out the following work:（1）Three isomorphic MOFs（Sm-BDC-NH₂,Er-BDC-NH₂,and Y-BDC-NH₂）were synthesized using 2-aminoterephthalic acid as the ligand and rare earth ions（M=Sm,Er,Y）as the metal nodes through a solvothermal method.The separation performance of this type of material was investigated in detail.The three MOFs materials have good solvent stability and thermal stability and can be stable in organic solvents such as dichloromethane,methanol,and ethanol and can maintain good stability at 200 ℃.The adsorption capacity of the three materials for CO₂and CH₄at 273 K and 298 K was tested,and the equal adsorption heat of the three materials for CO₂and CH₄was calculated using the virial equation.The adsorption selectivity of the three materials for different ratios of CO₂/CH₄mixed gas at room temperature was calculated using the IAST theory.The above results all demonstrate that the three materials have the potential to become materials for CO₂/CH₄mixed gas separation.Penetration experiments have shown that all three materials can separate CO₂/CH₄mixed gas at 298 K.（2）Two MOFs materials,Y-MOF-1 and Y-MOF-2,were synthesized using hexanuclear yttrium clusters as secondary building units and biphenyl-4,4’-dicarboxylic acid and 2,2’-bipyridine-5,5’-dicarboxylic acid as ligands through a solvothermal method.The PXRD and infrared spectra demonstrate that the two MOFs materials were successfully synthesized.The single-component gas adsorption data of CO₂and CH₄at 273 K and 298 K showed that the introduction of nitrogen atoms enhanced the ability of the skeleton to adsorb CO₂molecules.The Q_stvalues of the two materials for CO₂and CH₄were calculated by fitting the virial equation,and the selectivity of the two materials for different ratios of CO₂/CH₄was calculated using the IAST theory.The above results preliminarily demonstrate that the two MOFs materials can separate CO₂/CH₄mixed gas.Finally,penetration experiments showed that both materials can effectively separate CO₂/CH₄mixed gas.