Preparation And Performance Study Of Epoxy Cross-linked Polyimide Gas Separation Membrane

Polyimide membrane materials are of great potential application in the field of gas separation membranes because of their excellent thermal stability,good chemical resistance and high selectivity.Linear polyimide membranes have high permeability but low selectivity,while network polyimide membranes exhibit high selectivity and low permeability.Combining the two advantages to prepare polyimide membranes with excellent comprehensive performance is of great significance to promote the industrial application of these membranes.Based on this,this paper is designed to synthesize linear polyimide,introduce reactive groups by copolymerization,and prepare membrane materials with network structure by epoxy ring opening reaction to improve the gas separation performance of the membrane.1)Linear polyimides were prepared by copolymerization of2,4,6-trimethyl-1,3-phenylenediamine（DAM）and 2,2-bis（3-amino-4-hydroxyphen-yl）hexafluoropropane（APAF）as diamine monomers with 4,4’-（hexafluoroisopropy-lidene）diphthalic anhydride（6FDA）,and the effect of the ratio of the two diamine monomers on the polyimide The effects of the ratio of two diamine monomers on the structure and properties of polyimide films were investigated.The structure,surface morphology and thermal stability of the films were characterized by applying IR,XRD,SEM,DSC and other analytical equipment.It was found that the membrane material PI-4 prepared when the molar ratio of diamine monomer DAM:APAF=9.5:0.5 had the best thermal stability and gas separation performance with a glass transition temperature of 382°C,gas permeability to CO₂ of 607.92Barrer and gas selectivity of CO₂/N₂ of 21.2)Rigid 1,4-bis（glycidyloxy）benzene（BGOB）and flexible polyethylene glycol diglycidyl ether（PGGE）were selected as cross-linking agents,and the cross-linked membranes CPI-1 and CPI-2 were prepared by epoxy ring-opening reaction with the above linear polyimide membrane PI-4 containing-OH group,respectively.the gas selectivity of the chemically cross-linked membranes both increased,while the gas permeability decreased.Then CPI-1T and CPI-2T were obtained by heat treatment at 300°C,respectively,where CPI-2T had the best gas separation performance with a permeability coefficient of 326.78 Barrer for CO₂ gas and the selectivity of CO₂/N₂ increased to 32.5.The results showed that the flexible PGGE,when used as a cross-linking agent,could significantly improve the selectivity of the membranes after heat treatment and improve the plasticization resistance of the membranes.This is due to the formation of a network structure after heat treatment of cross-linking and the increase of inter-chain distance,which led to the increase of gas permeability and selectivity.3)The di-tert-butyl dicarbonate（Boc₂O）was reacted with tris（4-aminophenyl）amine（TAPA）to produce diamine monomer TAPA-B,which was polymerized with DAM and 6FDA by copolymerization to produce linear polyimide,and the Boc group was removed by acid hydrolysis to produce PI-5containing NH₂ group.Then,the cross-linked membranes CPI-3 and CPI-4 were prepared with the cross-linking agents BGOB and PGGE by epoxy ring opening reaction,respectively.then CPI-3T and CPI-4T were obtained by heat treatment at300°C,respectively,where CPI-4T had the best gas separation performance with a permeability coefficient of 209.36 Barrer for CO₂ gas and improved selectivity to 30.