Preparation And Performance Study Of Gas Separation Membrane Based On Polyethersulfone Graft Copolymer

In recent years,with the large-scale use of fossil fuels,the concentration of greenhouse gases?such as CO₂?in the atmosphere has risen rapidly,which has seriously affected the ecological environment of the earth.At present,On the other hand,CO₂ is a kind of valuable carbon resource,so,it is important and nesssery to separate and capture CO₂.As a new green separation technology,membrane technology has been widely used because of its green environmental protection,low energy consumption and high efficiency.Because it has been proved to be economically feasible in gas separation,more and more attention and research have been paid to C02 separation.Polyethersulfone?PES?is a common gas separation membrane material with good stability and processability.However,its poor gas permeability limits its application in gas separation.Ether oxygen groups in polyethylene glycol?PEG?are functional groups with high selective dissolution of CO₂/light gases and it is often used as a membrane material for CO₂ separation.However,PEG of high molecular weight has strong crystallinity and low gas flux,while PEG of low molecular weight has poor mechanical properties and cannot be prepared into films.In order to address this issue,we plan to use design and prepare block or graft copolymers with polyethersulfone as the main chain to provide mechanical support,with low molecular weight PEG as the side chain to build gas transport chanell.We believe that the study of graft copolymer gas separation membrane materials with both good mechanical properties and separation properties is meaningful for the application of membrane technology in CO₂ capture.A polyethersulfone graft copolymer with controllable PEG side chain content and adjustable length was designed and prepared in this paper.It can prevent PEG segment crystallization and improve gas separation performance.On this basis,the film is processed in two ways.First,the film is annealed above the glass transition temperature of the graft copolymer.The copolymer segments are fully moved and the phase separation is more thorough,forming microdomains.Secondly,pillared MFI zeolite?PMFI?was added into the membrane to prepare the mixed matrix membrane.PMFI arrangement was induced by graft copolymer self-assembly to construct gas transmission channel accelerating gas transport in the membrane and improving membrane permeability coefficient.The PES of different content of double-bond side groups(PES A?14%?and PES B?28%?was synthesized by condensation reaction using diallyl bisphenol-sulfur,bisphenol-sulfur,4,4-difluorodiphenylsulfone as the reaction monomer.Polyether sulfone graft copolymer?PES-g-PEG?was prepared by grafting mercapto polyethylene glycol of different molecular weights?550,1000,2000?via thio-ene click reaction.The chemical structure of the polymer was characterized by 'HNMR and FTIR,and the thermal analysis of the polymer was performed by DSC and TG.The characterization results showed that polyethersulfone graft copolymer was successfully prepared.The graft copolymer PES-g-PEG was prepared into a casting solution at a mass fraction of 5wt%,and the gas separation membrane was prepared by solvent evaporation.The gas permeance test shows that the PES A-g-PEG550 film has a high CO₂ permeability coefficient of 13 Barrer with CO₂/N₂ selectivity of 24.2;Anneal PES-g-PEG membrane?A PES-g-PEG?was prepared by thermal annealing.The results showed that the CO₂ permeability coefficient of A PES-g-PEG membrane was increased to 26.8 Barrer with CO₂/N₂ selectivity of 27.6.To further improve the permeability coefficient,PES A-g-PEG550 membrane was added with PMFI zeolite to prepare mixed matrix membrane?P-MMM?.The results show that when the zeolite content is 20wt%,the CO₂ permeability coefficient of the P-MMM is 4 times higher than the original membrane,reaching 66.9 Barrer.