Ultramicroporous Structure Regulation And Separation Performance Mechanism Of Polyimide Gas Separation Membran

How to effectively control the ultra-micropore structure of gas separation membranes,increase the permeability and selectivity,elucidate the relationship between polymer structures and gas separation performance are always the key problems in the development of high-performance gas separation membranes.In this dissertation,the ultra-microporous regulation method and mechanism of polyimide and polymers of instrinsic microporousity were systematically studied based on the monomer structure design.The ultra-micropores of the polyimide and its carbon molecular sieve membrane were regulated by monomer isomers;the ultraporous regulation mechanism of the polymer intrinsic pore structure was explored by replacing the hydrogen atom with a fluorine atom;the hollow fiber gas separation membrane was modified,which laid a foundation for improving the separation capacity and application of gas separation membranes.2,6-triptycene diamine（CTA）and 2,7-triptycene diamine（MTA）were used as monomers to synthesized the corresponding polyimides of CTPI and MTPI.After pyrolysis at 550℃,their CMSMs corresponding to CTPI-550 and MTPI-550 were obtained.The effects of different dipole moments of isomers on the pore structure of polyimide were systematically investigated.Furthermore,the effect of the thermal stability of polymer precursors,and the gas separation properties of the CMSMs were studied.The results show that the larger dipole moment of MTA leads to the tighter chain packing of MTPI,which leads to higher thermal stability,smaller ultra-microporous than CTPI.And this endows MTPI higher selectivity but lower permeability.After pyrolysis,the permeability and selectivity of membranes are greatly improved.And the MTPI-550 exhibits higher permeability but lower diffusion selectivity than CTPI-550,because of the delayed thermal cracking of MTPI induced more micropore.Based on the prepared tripterotene-containing polyimide（TPI）and another polyimide（PPI）with a larger specific surface area,the existing pore structure was regulated by fluorination method.The effects of the fluorination process on polyimide and the structure of fluorinated molecular sieve on the gas separation performance were investigated.In addition,the role of the specific surface area of polymers in the regulation process and the influence mechanism on the separation performance were analyzed.The results show that fluorination can effectively screen CH₄（larger kinetic diameter）and He（smaller kinetic diameter）.After fluorination,fluorinated PPI with more ultra microporous channels could obtain higher He diffusion coefficient,its diffusion selectivity for He/CH₄was higher than the diffusion selectivity of fluorinated TPI.To enhance the sieving effect of the membrane material on the gas pairs further,the fluorinated PIM-1（the polymer with larger specific surface area）gas separation membrane was prepared by fluoridation method.Direct fluorination was an effective method to regulate the ultramocropore structure of PIM-1 and greatly improved the diffusion selectivity of He/CH₄.PIM-1 fluorinated for 5 min has the best gas separation performance,and shows good anti-aging and anti-plasticization properties,with high He permeability（754 Barrer）and He/CH₄selectivity（3370）,which can enrich He to 84.9%from 0.6%feed gas.The Ultem 1000 hollow fiber gas separation membrane was prepared by non-solvent induced phase separation method.After that,the hollow fiber was modified by direct fluorination technology,and the small membrane module was encapsulated.The selectivity,flux and mixed gas separation performance of fluorinated Ultem 1000 hollow fiber membrane module was performed,which show high He flux（10.2 GPU）and He/CH₄selectivity（567）.The He can be enriched to58.9%from 0.3%feed gas at 20 bar pressure.