Enhancing Separation Performances Of Facilitated Transport Membranes For CO₂ Separation

An environment-benign and energy-efficient CO₂ separation technology is a key for CO₂ mitigation and clean & efficient utilization of fossil fuel,as well as CO₂ utilization.Unfortunately,the lack of high-performance membrane materials and membranes hampers the large-scale industrial application of membrane-based technology for CO₂ separation in environment-and energy-related fields.Among various kinds of membranes for CO₂ separation,perhaps facilitated transport membranes will be the first one for industrial application until now.Nowadays,there are some limitations for enhancing separation performances of facilitated transport membranes for CO₂ separation.First,it is tough to simultaneously achieve the high content and high efficiency of functio nal groups which could reversibly react with CO₂,leading to the great difficulty in fully exerting advantages of facilitated transport membranes.Moreover,separation performances of most facilitated transport membranes for CO₂ separation are not competitive under a relatively high feed pressure,which hinders their application in some cases where the relatively high operational pressure is necessary.In addition,it is challenging to develop facilitated transport composite membranes with an ultrathin defect-free selective layer via conventional solution coating method,restricting the application of many facilitated transport membrane materials.In this work,we propose and further demonstrate several approaches to addressing the above limitations.First,the combination of multiple functional groups could simultaneously achieve the high content and high efficiency of functional groups in membranes.Furthermore,separation performances of facilitated transport membranes under a relatively high feed pressure could be notably improved via incorporating amino group-functionalized CO₂-philic nanoporous materials with an excellent compatibility towards amino group-rich polymers for facilitated transport membranes.Last,the introductio n of the highly permeable intermediate layer with favorable water wettability and high adhesive property could benefit the formation of an ultrathin defect-free facilitated transport selective layer.First,we designed and synthesized a novel poly?diallyldimethylammonium carbonate-co-vinylamine?copolymer with primary amino groups,carbonate groups and quaternary ammonium cations,and then multiple functional groups containing facilitated transport composite membranes were developed.First,the combination of different functional group s ensures the high content of functional groups in the membranes.Moreover,more functional groups are in the amorphous region because of the decreased crystallinity.Therefore,they are available to contact with CO₂ and further reversibly react with CO₂.In addition,the enhanced CO₂ loading capacity of primary amino group and the increased reaction rate between carbonate group and CO₂ could be obtained owing to synergistic effects of different functional groups.Therefore,the high content and high efficiency of functional groups are achieved simultaneously.Consequently,the multiple functional groups containing membrane exhibits the state-of-the-art separation performances for CO₂/N2,CO₂/CH4 and CO₂/H2 mixed gases.Furthermore,mixed matrix composite membranes with an excellent interfacial compatibility were developed via incorporating amino group-functionalized CO₂-philic nanoprous material NH2-MIL-53?Al?into amino group-rich polyvinylamine?PVAm?matrix.Owing to the hydrogen bonding interaction between NH2-MIL-53?Al?and PVAm,the resultant favorable interfacial compatibility between NH2-MIL-53?Al?and PVAm restricts the formation of non-selective interfacial zone even under a high feed pressure.Moreover,flexbile NH2-MIL-53?Al?could provide larger CO₂ preferential transport channels which benefits from its unique breathing effects under a relatively high CO₂ partial pressure.Consequently,a significantly improved separation performance is achieved under the relatively high feed pressure.Last,the multilayer composite membranes with an ultrathin defect-free PVAm facilitated transport selective layer were developed with the mediation of polydopamine?PDA?decorated crosslinked polydimethylsiloxane?P DMS?intermediate layer.The pore penetration phenomenon is inhibited via introducing the PDA decorated crosslinked PDMS intermediate layer.Moreover,the enhanced water wettability of the intermediate layer could benefit the uniform spreading of PVAm aqueous solution.In addition,there exist multiple-site interactions?hydrogen bond,ionic bond and covalent bond?between PDA and PVAm,which could guarantee the strong adhesion of PVAm selective layer on the PDA decorated crosslinked PDMS intermediate layer.Consequently,the resultant multilayer composite membrane with an ultrathin defect-free PVAm selective layer displays a notably enhanced CO₂ permeance combined with a slightly improved CO₂/N2 selectivity,as well as superior structural stability.