Study On The Gas Separation Of Polyimide/Graphene Oxide Mixed Matrix Membranes For CO₂ Separation

Membrane separation technology is one of the most potential approaches for industrial carbon capture,which has the advantages of high efficiency,energy saving and flexible operation.The development of high-performance gas separation membrane materials is the key to reducing costs and achieving industrialization.In this study,polyimide（PI）is taken as the research object,and the goal is to prepare a gas separation membrane with excellent comprehensive performance.Mixed Matrix Membranes（MMMs）is prepared by doped graphene oxide as fillers into the polyimide matrix to enhance the gas transfer process and improve the gas permeability and separation factor,which simultaneously has theoretical and guiding significance for the development and application of high-performance gas separation membranes.The main research work is as follows:Aimed for preparing high-performance MMMs,monomer materials with different functional group structures were selected and synthesized into a series polymide polymers.The physical properties of different monomer groups and polyimide polymer were constructed through the solubility test,X-ray diffraction test,thermogravimetric-differential scanning calorimetry analysis and calucation of free volume fraction.Among the as-prepared four polyimide,6FDA-2,6-DAT polyimide membrane showed the best comprehensive performance.The PI-GO MMMs was prepared by incorporating GO nanosheets into the preferred PI matrix.GO nanosheets with high aspect ratio can interfere the arrangement of polymer chains.Besides,the abundant oxygen-containing functional groups can promote the transfer of CO₂.The gas permeability of PI-GO membrane was increased from 47 barrer to 58 barrer,and the separation factor of CO₂/CH₄and CO₂/N₂was increased to 48.9 and 24.4 at the the filler contents of 0.3 wt%,respectively,which was increased by 23%and 22%compared to polyimide membrane.With the goal of promoting CO₂transfer and improving the thermal stability at room temperature and moderate temperature,the reduced sulfonated graphene oxide（rs-GO）was doped in the as-prepared 6FDA-2,6-DAT polyimide to fabricate MMMs.The charged sulfonic acid groups on rs-GO enabled the nanosheets well dispersed in organic phase.As-prepared MMMs exhibited good gas permeability and separation performance both at room temperature 35°C and moderate temperature 75°C.For the CO₂/CH₄system,the CO₂permeability increased by 48%compared with the initial membrane,and the separation performance was improved by 104%;for the CO₂/N₂system,the CO₂permeability increased by 105%,the separation performance increased by 107%at an optimal filling contents.Moreover,the corresponding MMMs showed good long-term stability at moderate temperature conditions.The superior performance can be mainly attributed to the hydrogen bonding between CO2and sulfonated group and the extra rapid gas transfer pores created by reduction process proved by Raman spectroscopy.