Enhancing Compatibility To Prepare High-performance CO₂ Separation Membranes Containing COF Particles

CO₂ separation membrane technology exhibits the advantages of low energy consumption and fixed investment,which attract huge attention for its application in the fields of energy gas purification and greenhouse gas emission reduction.Currently,the commercial CO₂ separation membranes have a low permselectivity,which restricts the industrial application.Mixed matrix membranes（MMMs）are considered to be novel CO₂ separation membranes with great development potential because of high permeance and good processability.However,there are interfacial compatibility problems between nanomaterials and polymers.The undesirable interfacial morphologies could lead to the formation of defects in the MMMs,resulting a significant decrease of membrane performance.For the above problems,we propose two approaches to slove them.Firstly,the developed covalent organic frameworks（COFs）-polyvinylamine（PVAm）membranes were used to systematically study the effects of COF surface structures on interfacial morphologies and membrane performance.Secondly,interfacial polymerization was used to covalently embed COFs into the polymers,strengthen the interaction between COFs and polymers,and make them tightly combined to prepare high-performance composite membranes for CO₂ separation.Firstly,PVAm was served as the continuous phase,and modified COFs were served as the dispersed phase to prepare MMMs on the surface of modified polysulfone（mPSf）support layer.Then,the the effects of COF structures on the COF-PVAm interfacial morphologies were investigated.Meanwhile,the effects of feed pressure on the membrane performance were also investigated.The results showed that the PVAm penetration degree was closely related with the strength of hydrogen bonds formed beween the COF surfaces and PVAm.The CO₂ adsorption sites of COFs had an important effect on the CO₂ transport in the COF channels.The optimal COF-PVAm membrane with appropriate penetration interfacial structures exhibited excellent CO₂permselectivity,and revealed the economic potential of separating and purifying H₂ from syngas.Secondly,TpPa-1（COFs）and piperazine（PIP）,which possessed rich secondary amine groups（-NH-）,were dispersed in the aqueous phase,and trimesyl chloride（TMC）was dispersed in the oil phase.The composite membranes were prepared on the surface of mPSf support layer via interfacial polymerization between the aqueous phase and oil phase.The results showed that the-NH-groups of TpPa-1 could react with the-COCl groups of TMC to form covalent bonds,optimizing the membrane structure,enhancing the COFs compatibility with polymer and plasticization resistance of the composite membrane.The incorporation of TpPa-1 could increase the carrier contents,provide fast transport channels and facilitate CO₂ transport in the membrane.The composite membrane prepared by interfacial polymerization exhibited excellent permselectivity for CO₂/N₂ mixed gas and showed good stability in the simulated flue gas environment.