Metal Organic Frameworks Promoted CO₂ Permeability And Selectivity Of PEO-based Mixed Matrix Membranes

Removing CO₂ from bio-fermentation gas to purify hydrogen and methane is an important way to reduce greenhouse gas emissions and cleanly convert biomass energy.Membrane separation technology is favored for its outstanding advantages of high energy efficiency,easy maintenance and environmental friendliness.Developing highly permeable and selective membrane materials is the key technology for CO₂ separation.In this paper,polyethylene oxide?PEO?-based mixed matrix membranes?MMMs?doped with metal organic frameworks?MOFs?were prepared to enhance CO₂ permeability and selectivity and efficiently separate CO₂ from biohythane.Zn/Co zeolite imidazolite framework?Zn/Co-ZIF?nanoparticles were carbonized and formed abundant carbon and nitrogen active sites for CO₂ adsorption,which were loaded in situ into PEBAX to improve CO₂ permeability and selectivity of MMMs simultaneously.PALS,gas adsorption apparatus and FTIR were used to characterize carbonized Zn/Co-ZIF and MMMs.It was found that carbonizad Zn/Co-ZIF obtained local defective structures with carbon and nitrogen active sites,CO₂ adsorption capacity increased by 1.87 times to 2.64mmol/g.CO₂ permeability of PEBAX-8H membrane loaded with Zn/Co-ZIF carbonized at 600 ? for 8 h increased by 15% to 102.5 barrers,and selectivity of CO₂/N2,CO₂/CH4 and CO₂/H2 increased by 45%,43% and 18% to 52.1,16.4 and 9.4,respectively.SIFSIX-2-Cu-i with high CO₂ adsorption capacity was blended into PEBAX/PEGDME to enhance permeability of PEO-based MMMs for CO₂ separation.Gas adsorption apparatus,XRD and DSC showed that the addition of SIFSIX-2-Cu-i reduced crystallinity of PEBAX/PEGDME and enhanced mobility of polymer chains.Adding 7.5 wt% SIFSIX-2-Cu-i into membranes,CO₂ permeability increased by 38% to 485.0 barrers,and CO₂ selectivity remained excellent?selectivity of CO₂/N2 increased by 4% to 50.2?.Lantern Zn/Co-ZIF nanoparticles were designed to provide efficient channels and reduce diffusion resistance for CO₂,thus enhancing CO₂ permeability of PEGDA/PEGDME MMMs.TEM and SEM results showed that Zn/Co-ZIF nanoparticles?diameter 490⁵50 nm?synthesized at 145 °C possessed a lantern structure with hollow cores?diameter 380⁴50 nm?and thin shells?thickness 20⁸5 nm?.XRD and BET results indicated that the nanocrystal structure and porosity of Zn/Co-ZIF remained intact after etching at 145 °C.Peaks shifts in the infrared spectra confirmed that Zn/Co-ZIF nanoparticles were well integrated with XLPEO membrane through hydrogen bonds.Therefore,doping 15 wt% lantern Zn/Co-ZIF nanoparticles into membrane dramatically increased CO₂ permeability by 72% to 761.9 barrers,while CO₂/N2 selectivity was maintained excellent?above the upper bound established by Robeson in 2008?.