Improving CO₂ Plasticization Of Polyimide Membrane Materials By Thermally Induced Crosslinking

In recent years,gas separation technology has also received extensive attention.Compared with other gas separation technologies,gas separation membrane technology has the advantages of easy operation,simple equipment,small footprint,high efficiency,and economical and environment-friendly.One of the most important gas separation membrane applications is the removal of CO2 and H2S from natural gas.However,acidic gases such as C02 and H2S may swell and plasticize the polymer membrane in the separation process and cause decrement in selectivity.Moreover,physical aging of polymers lead to decrease in gas permeability.Therefore,polymer membrane material with resistance to plasticization and aging is the key of gas separation technologies.This study mainly uses cross-linking modification to improve the resistance to plasticization and physical aging of membrane materials.Firstly,a carboxyl-containing polyimide 6FDA-Durene:CADA(3:2)was synthesized,and then the copolymer was modified by thermal decarboxylation cross-linking.The thermal decarboxylation cross-linking increases the C02 permeability of the polymer.Moreover,the 02/N2 selectivity of the PI-375 exceeds the 1991-Robeson upper bond,and the CO2/CH4 selectivity of PI-425 is close to 2008-Robeson upper bond.In addition,the thermal decarboxylation cross-linking improves the anti-CO2 induced plasticization property.However,the lowest temperature for completing the thermal decarboxylation cross-linking reaction is 400 ?,which is higher than the glass transition temperature of this polymer.In order to reduce the impact of high temperature in the polymer structure,it is essential to prepare the polymer that can be cross-linked at low temperature.In order to realize low temperature cross-linking,we synthesized the polyimides containing lactone rings and then the polymers were modified by thermal oxidation cross-linking at temperatures below polymers' Tg.As a result,thermal oxidation cross-linking can effectively improve the C02 plasticizing resistance and aging resistance of the polymer.Due to the complex cross-linked structures formed by thermal oxidation cross-linking,the cross-linked structures of the polymer were studied by molecular dynamics simulations.We studied the effects of cross-linking structures on polymer FFVs.