Preparation And Modification Of New Organic Polymer Gas Separation Membrane

Gas separation membranes have received widespread attention in the field of gas separation due to its advantages of low energy consumption,simple operation,easy preparation,and no pollution.At present,most polymer gas separation membranes are still limited by the trade-off between selectivity and permeability,and permeability increases and selectivity decreases,and vice versa.In order to break this limitation,this paper prepared two new polymer membranes and modified them to improve the gas separation performance.（1）Preparation and modification of polymers of intrinsic microporosity（PIM-1）membrane by ozone oxidation.PIM-1 is a new type of self-contained microporous polymer,due to the twisted structure contained in the chain,PIM-1 membrane has high gas permeability and relatively low selectivity.This paper uses5,5’,6,6’-tetrahydroxy-3,3,3’,3’-tetramethyl-1,1’-spiral bisindan（TTSBI）and 2,3,5,6-Tetrafluoroterephthalonitrile（TFTPN）are used as monomers to synthesize PIM-1 at a high temperature of 150°C through a diaromatic nucleophilic substitution reaction,and then use the casting-solvent volatilization method to obtain a uniform PIM-1membranes.Using ozone to purge the surface of the prepared PIM-1 membranes,focusing on the effect of different purge times（30 s,60 s,300 s,600 s）on the gas separation performance of the membranes.The results show that the oxidation of ozone produces two oxygen-containing groups,carboxyl and carbonyl,which occupy the original free volume of the PIM-1 membranes.As the ozone oxidation time increases,the more oxygen-containing groups are generated.The membranes after60s of ozone oxidation has the best gas separation performance,H₂ permeability is1294 Barrer,H₂/N₂ selectivity is 93.7,which is close to the Robeson upper bound of2015,H₂/CH₄ selectivity is 121,H₂/CO₂ selectivity is 2.92,which surpasses the Robeson upper bound of 2015 and 2008,respectively.The pressure dependence tests of the PIM-1 membranes after 60s of ozone oxidation show that the CO₂/CH₄selectivity is still 18.19 at a high pressure of 15 bar,which is higher than the CO₂/CH₄selectivity of the original membranes（15.40）;The temperature dependence test results show that the oxidation of ozone increases the activation energy of the gas permeation membranes.（2）Preparation and performance study of ZIF-8/polyimide mixed matrix membranes.ZIF-8 nanoparticles were prepared by in-situ synthesis of N,N-dimethylformamide（DMF）using dimethylimidazole（Hmim）and zinc nitrate hexahydrate（Zn（NO3）2·6H2O）.Using3,3,3’,3’-tetramethyl-1,1’-spirobisoctane-5,5’-dia mino-6,6’-diol（SBIDA）and 3,5-diamino Benzoic acid（DABA）two new diamine monomers are copolymerized with 6FDA dianhydride at a molar ratio of 8:2 to form a new type of copolyimide（PI）.Then the ZIF-8 nanoparticles were physically blended with PI at different loadings（10 wt.%,15 wt.%,25 wt.%,40 wt.%）to prepare a mixed matrix membranes,and the effects of different loadings of ZIF-8 nanoparticles on the gas separation performance of PI membranes were investigated.The results show that:ZIF-8 nanoparticles with a specific surface area as high as 1945.02 m²/g were successfully prepared using DMF in-situ synthesis method,and they can maintain a good dispersion state in DMF;Increasing the loading of ZIF-8nanoparticles helps to improve the gas permeability of the membrane,but too high loading will cause non-selective voids in the membrane and reduce the gas selectivity of the membranes.ZIF-8 nanoparticles havs the best gas separation performance when the loading amount is 25 wt.%,the permeability of H₂ is 171 Barrer,the selectivity of H₂/N₂ is 65 which is close to the Robeson upper bound of 2008,and the H₂/CH₄ selectivity is 149,which surpasses the Robeson upper bound of 2008;The permeability of CO₂ was 80.2 Barrer,the selectivity of CO₂/N₂ was 30.5,and the selectivity of CO₂/CH₄ was 69.7,which also surpasses the Robeson upper bound of 2008.