Study On Preparation Of Polyimide Membranes Modified By [NH₂ebim][PF₆]for CO₂/N₂ Separation Performance

In recent years,the soaring increase of CO₂ emissions from energy-related industrial activities impedes the sustainable development of modern society.Membrane separation technology is becoming a representative technology among many separation methods because of lower energy consumption,lower investment costs and friendly environment.Ionic liquids?ILs?and task specific ionic liquid?TILs?have been used to modify gas separation membranes,however,both of them have the problems of easy loss and poor stability in modified membranes.In addition,graphene oxide?GO?is often used to prepare mixed matrix membranes?MMMs?to improve gas separation performance,but GO is prone to aggregation and has poor dispersion in membranes.In this paper,NH₂-functionalized IL was grafted to polyimide?PI?by chemical reaction to form grafted polyimide?GPI?gas separation membranes.On the one hand,the stability of TILs in PI membranes could be guaranteed.On the other hand,the structure of PI chains could be changed.And then GO was added into GPI by the method of blending and fabricated MMMs.The dispersion of GO in the GPI membranes could be improved by using interaction force between GPI and GO,and the separation performance of gas separation membrane could be further improved.Meanwhile,the effects of different feeding pressures,different operating temperatures,plasticizing pressure and stability of modified membranes on CO₂/N₂ transport properties were also investigated.In this paper,1-aminoethyl-3-buthylimidazolium hexafluorophosphate?[NH₂ebim][PF₆]?,has been grafted to PI chains as side groups to fabricate GPI gas separation membranes.The results show that GPI membranes have more free volume and larger rigidity which is favorable to the improvement of CO₂/N₂ gas separation performance.Compared with PI membrane,CO₂ permeability of the GPI membrane?TIL-0.8 wt%?has been increased from5.28 Barrer to 10.20 Barrer,and CO₂/N₂ selectivity has been increased from 21.9 to 92.8.GPI membranes also have better compression resistance,lower temperature sensitivity and better stability.Meanwhile,the separation performance of GPI membranes has already exceeded Robeson's upper bound.Meanwhile,GO has been added into GPI membranes by the method of blending and fabricated MMMs.The hydrogen bond,?-?conjugation and electrostatic force between GPI and GO are used to improve the dispersion of GO,which play full role of GO in CO₂separation.The results show that the gas separation performance of MMMs has been further enhanced.CO2 permeability has been improved to 17.4 Barrer and CO2/N2 selectivity is increased to 180 when GO concentration is 0.8wt%,and various aspects of performances of MMMs are better than that of GPI membranes.Furthermore,the molecular simulation technique has been used to stimulate the microscopic properties and CO₂/N₂ solution-diffusion process among the PI,GPI,GPI/GO systems.The results show that solubility coefficient of CO₂ has been improved clearly and solubility coefficient of N2 almost keeps constant,which shows that the interaction between functional groups and CO₂ plays a leading role in the process of improving CO₂ permeability.Meanwhile,diffusion coefficient of CO₂ has been improved and diffusion coefficient of N₂ has been decreased obviously,which shows that the increment of diffusion selectivity is the direct cause of the increase of ideal selectivity.