High-Performance Membranes With Multi-permselectivity For CO₂Separation

Polymeric membranes for CO2separation show promising applications in energygas purification and flue gas CO2capture. However, the membrane technology hasnot been widely applied in practical processes due to the lack of high-performancemembranes. The conventional strategy used to improve separation performance ofmembranes mainly focuses on enhancing single permselectivity of membranesincluding diffusivity-selectivity, solubility-selectivity and reactivity-selectivity.However, because of undesirable membrane structures formed in this process, theimprovement of performance is always limited. In this work, we demonstrate an ideaof developing high-performance membranes for CO2separation through combiningmultiple permselectivities. Unlike the conventional strategy, the combination ofmultiple permselectivities can improve membrane performance more efficiently dueto the optimization of membrane structures. Moreover, through comprehensiveutilization of distinctions between CO2and other gases in size, condensability andreactivity, the multi-permselective membrane can efficiently separate CO2fromvarious light gases, which rarely exhibits in membranes prepared following theconventional strategy.Firstly, membranes with both diffusivity-selectivity and solubility-selectivitywere developed by interfacial polymerization (IP) with hexane-soluble trimesoylchloride (TMC) and water-soluble diamines with ethylene oxide (EO) groups. Thediffusivity-selectivity is enhanced by covalent crosslinking formed in IP process. Thesolubility-selectivity is introduced by EO groups due to the strong affinity for CO2.The influences of EO unit length on structure and separation performance ofmembranes were investigated by using diethylene glycol bis(3-aminopropyl) ether(DGBAmE) and diaminopolyethylene glycol (DAmPEG). The membranes preparedwith DGBAmE and DAmPEG were named EO-3and EO-21according to the lengthof EO units, respectively. The results show that EO-3possesses higher separationperformance due to the higher crosslink density. The higher crosslink density isattributed to the higher diffusion rate of DGBAmE from aqueous phase to organic phase and through the nascent film in the IP process. In this work, the materialdevelopment and thin film frabrication has been combined to speed up applications ofmembrane materials.After that, multi-permselective membranes with diffusivity-selectivity,solubility-selectivity and reactivity-selectivity were developed by IP with TMC inhexane and DGBAmE and3,3’-Diamino-N-methyldipropylamine (DNMDAm) inwater. Results indicate that the membrane possesses ideal structures such ascrosslinked sections containing functional groups, polymer chains of appropriatestiffness, and low crystallinity. Moreover, the membrane could comprehensivelyutilize distinctions between CO2and other gases in size, condensability and reactivity.Thus, the multi-permselective membrane can efficiently separate CO2from H2, CH4and N2, and shows the state-of-the-art CO2separation performance.Moreover, the effects of minor SO2on transport property of themulti-permselective membrane were investigated by combining experimental andmodeling study. Experimental results reveal that the decrease in separationperformance is tolerable at even5000ppm SO2. The modeling results suggest that theSO2partial pressure at the membrane surface is much lower than that in the bulk feedgas due to the serious concentration polarization of SO2under the mixed gascondition, and the decrease in CO2permeance is attributed to the competitive sorptionand competitive reaction. The obtained results indicate that the multi-permselectivemembrane could tolerate a trace amount of SO2present in the flue gas, which showspromising applications in flue gas CO2capture.