Porous Aromatic Frameworks And Related Hollow Fiber For Gas Separation

Gases play an essential role in industry and our daily life.Gases（such as carbon dioxide,methane,ethylene,nitrogen,etc.）,as the important basic feedbacks for many other products in modern industries,are widely used in different fields.In daily life,the emission of carbon dioxide and methane（greenhouse gases）directly affects the ecological environment of the earth.The separation and storage of gases is an important topic in the field of environmental protection and industrial production,and has received extensive attention from scientific researchers.Pure small-molecule gases are usually produced from the mixture by gas separation and purification technologies,which mainly include:cryogenic distillation,pressure swing adsorption and membrane separation.Pressure swing adsorption and membrane separation have attracted increasing attention and demonstrated great potential in industrial processes due to their advantages such as high efficiency,easy operation,low energy consumption and environmental sustainability.Porous Organic Frameworks（POFs）,an original porous material,possess the excellent properties of high specific surface area,structure stabilization and easy modification.As the excellent adsorbing material,POFs can be used to prepare mix matrix membrane.The main contents are in the followings:1.We prepared porous aromatic frameworks（PAFs）with great CO₂/N₂separation performance and mixed them with polymer to fabricate hollow fiber membranes.The polymers PAF-45 and PDPA are prepared through the Shore reaction by using biphenyl and diphenylamine as monomers,at the same time,the polymer PAF-45DPA is prepared with the above-mentioned monomers in an equimolar ratio.Then,PAF-45/PSF,PAF-45DPA/PSF,PDPA/PSF and PSF hollow fibers were fabricated by the dry-wet method with three products as doping materials and polysulfone（PSF）polymers as matrix materials.The CO₂/N₂ separation performance of the synthesized powder and mixed membrane were characterized respectively.The experimental results showed that PAF-45DPA simultaneously exhibited both the high porosity of PAF-45 and the CO₂/N₂selectivity of PDPA materials(S_BET=679 m² g^-1,S_CO2/N2=63),as well as,this comprehensive performance was also manifested in the prepared mixed membrane.It was worth noting that the doping of PAFs material significantly improves the CO₂/N₂ separation performance of hollow fiber membranes.The selectivity and permeance on CO₂ of PAF-45DPA/PSF hollow fiber can reach 24.2 and 72.6 GPU respectively.2.We explored the effect of different coordinated metal ions on the CH₄/N₂separation performance of PAFs with large conjugated groups and improved the CH₄/N₂ separation performance of gas separation membranes.PAF-40,PAF-40-Fe and PAF-40-Mn materials were prepared through tetraphenyl porphyrin and its metal complexes.In order to test the gas adsorption curves of CH₄ and N₂,the ideal separation ratio of CH₄/N₂was calculated according to the IAST theory.It was shown that PAF-40s have a higher CH₄/N₂ selectivity,among them PAF-40-Fe materials have the best adsorptive selectivity on methane(S_CH4/N2=18.4).Then,PAF-40/PSF,PAF-40-Fe/PSF,PAF-40-Mn/PSF and PSF Hollow fiber membrane were prepared by dry-wet method with PAF-40,PAF-40-Fe and PAF-40-Mn as doping materials and polysulfide polymer as matrix material,after that its CH₄/N₂ separation performance was characterized.The experimental results showed that the doping of PAFs material significantly improved the CH₄selectivity and permeability of the hollow fiber membrane.What’s more,the hollow fiber membrane prepared with PAF-40-Fe as the doping material both has the selectivity and permeability to methane gas,which can be raised to 4.3 and 18.7 GPU,respectively.3.PAFs with high specific surface area and structure stabilization were chosen as precursor to prepare PAF-1-Br and PAF-1-CF₃ by post-modification.The adsorption performance of ethylene and ethane were explored.The adsorption isotherms of Ethylene and Ethane in 273 K and 298 K were characterized and ideal selectivities of PAF-1,PAF-1-Br and PAF-1-CF₃ were calculated according to the IAST theory.It was obvious that after modifying the polar functional groups,the ideal selectivity on C₂H₆/C₂H₄ of PAF-1-CF₃ increased significantly（from 1.1 to 1.8）.