Preparation And CO₂ Separation Of High-Performance PEBA/Modified ZIF-8 Mixed Matrix Membranes

With the development of industrial technology and the increase of population,the problem of global warming has aroused people's concern.Therefore,in order to reduce CO₂ emissions in the atmosphere,it is urgent to use effective methods to capture CO₂ before or after combustion of fossil fuels.In general,the methods of separating CO₂ from gas mixtures mainly include chemical adsorption,physical adsorption,cryogenic separation and membrane separation technology and so on.Membrane separation technology offers an effective way for removal CO₂ from flue gas due to its high efficiency,adaptability,operational simplicity,low energy consumption and investment,and environmental friendliness.In order to obtain the membranes with high CO₂permeability and CO₂/N₂ selectivity,various kinds of mixed matrix membrane by adding modified ZIF-8 into PEBA2533 was prepared.In addition,the gas separation performance was tested and the ways of gas transport in membrane was explored.The specific process is as follows:?1?In this chapter,Ni ions were added into the synthesis process of ZIF-8.And the Ni ions were introduced into ZIF-8 skeleton by in-situ to prepare Zn/Ni-ZIF-8,which exhibited higher CO₂ adsorption capacity.Then Zn/Ni-ZIF-8 was added to PEBA2533 by physical blending method to obtain the mixed matrix membranes.The SEM results showed that Zn/Ni-ZIF-8nanoparticles exhibited smaller particle size and distributed in PEBA uniformly,and good interfacial compatibility between Zn/Ni-ZIF-8 and PEBA was characterized by ATR-FTIR.The effect of filler loading on the membrane mechanical properties and the influence of filler content and feed pressure on the membrane separation performance were explored.The results showed that 10wt%Zn/Ni-ZIF-8-PEBA mixed matrix membrane exhibited optimal separation performance under 5bar with the CO₂ permeability of 408Barrer and CO₂/N₂selectivity of 52,which has surpassed the Robeson upper bound due to bimetallic asymmetric adsorption.The separation performance of mixed matrix membrane in simulated flue gas?CO₂/N₂=20/80vol%?was slightly lower than that in single gas,and the membrane showed long-term operational stability.?2?In this chapter,we selected the Zn/Ni-ZIF-8 as the precursor to produce a metal-and N-doped porous composite Zn/Ni-ZIF-8-800 at 800oC under N₂atmosphere.Zn/Ni-ZIF-8-800 was also added to PEBA2533 to prepare the mixed matrix membranes.XRD,FTIR and N₂ adsorption results showed that porous and graphited Zn/Ni-ZIF-8-800 was successfully synthesized.The effects of operating pressure,temperature and filler content on gas separation performance were also researched,it is concluded that the optimum CO₂permeability and selectivity of MMMs with 1.5%Zn/Ni-ZIF-8-800 loading were 630Barrer and 50 at pressure of 7bar under room temperature,surpassing the Robeson upper bound.The reason was that open metal active sites in Zn/Ni-ZIF-8-800 had a good affinity for CO₂,and the N-doped could act as Lewis basic sites for reacting with acidic CO₂ molecules.The mixed matrix membranes were tested by simulated flue gas,and the results showed that the membranes had good operation stability.?3?In this chapter,ZIF-8 was synthesized on g-C₃N₄ by in-situ to obtain CNZ composites,which were added to PEBA2533 to prepare mixed matrix membranes.XRD and FTIR results indicated that ZIF-8 was successfully loaded on g-C₃N₄,and g-C₃N₄ layer spacing increased with the increasing ZIF-8loading.The influence of different mass ratio of g-C₃N₄ and ZIF-8 on the gas separation performance was investigated.The optimum CO₂ permeability and selectivity was obtained by MMMs containing CNZ1?g-C₃N₄:ZIF-8=1:1?.The gas separation performance with different feed pressure and CNZ1 content were also researched and we found that the CO₂ permeability and CO₂/N₂ selectivity of PEBA2533-CNZ1?1.5?MMMs were 338 barrer and 69 at 5 bar,which surpassed the Robeson upper bound.This was possibly due to?-?complexation between?bond formed by lone pair electrons of g-C₃N₄ and CO₂ and molecular sieving effect of ZIF-8,which may have a synergistic effect on the high CO₂selectivity.Moreover,interlayer spacing of CNZ1 was slightly larger than CO₂molecular diameter,which further improved CO₂ selectivity.The results of the mixed gas test indicated that good operation stability of PEBA2533-CNZ1mixed matrix membranes.