Study On Preparation And O₂/N₂ Permability Of Polymers Of Polymers Of Intrinsic Microporosity Magnetic Mixed Matrix Membranes

Oxygen and nitrogen are widely used in industrial fields such as energy,health care,food preservation,et al.They can be easily obtained by cryogenic distillation or pressure swing adsorption techniques in industry.Compared with those technologies,gas separation membrane technology has many advantages,such as energy saving and economic benefits.Recently,magnetic matrix membranes?MMMs?have attracted much attention due to the distinctive O₂/N₂ separation mechanism.Magnetic MMMs are heterogeneous system formed by embedding magnetic units into polymer matrix.They can strengthen O₂/N₂ separation owing to magnetic sieving of magnetic units/polymers interface-gaps and the difference of magnetic properties of O2 and N2,showing a promised prospect.In this work,Fe₃O₄,Fe₃O₄@PDA and Fe₃O₄@ZIF-8,as three kinds of fillers,were respectively imbedded into polymers of intrinsic microporosity PIM-1 matrix to prepare PIM-1/Fe₃O₄,PIM-1/Fe₃O₄@PDA and PIM-1/Fe₃O₄@ZIF-8 magnetic MMMs by solvent evaporation methods.Furthermore,the effect of factors including loadings,sizes,surface modified structure and external magnetic intensity on micro-structure and O₂/N₂ permeability of magnetic MMMs were analyzed systemically.The following results are listed below:?1?The PIM-1/Fe₃O₄ and PIM-1/Fe₃O₄@PDA magnetic MMMs were prepared by solvent evaporation methods.From the difference of O₂/N₂ permeability between PIM-1/Fe₃O₄ magnetic MMMs and PIM-1/Fe₃O₄@PDA magnetic MMMs,it could be seen that incorporation of dense polydopamine layers could improve interface-gaps of magnetic units/polymers and enhance mechanical properties of magnetic MMMs,but weaken O₂/N₂ permeability of magnetic MMMs.When magnetized in 56 mT,PIM-1/Fe₃O₄@PDA magnetic MMMs containing 2 wt% of Fe₃O₄@PDA exhibited the best O₂/N₂ separation performance with O2 permeability of 616 Barrer and O₂/N₂ selectivity of 3.17.?2?Fe₃O₄@ZIF-8 magnetic core-shell units prepared by in-situ growth were incorporated into PIM-1 polymer matrix to fabricate PIM-1/Fe₃O₄@ZIF-8 magnetic MMMs.Fe₃O₄@ZIF-8 magnetic core-shell units had microporous structure with BET surface area of 552.8 m2/g and SF median pore width of 0.629 nm.From the difference of O₂/N₂ permeability between PIM-1/Fe₃O₄ and PIM-1/Fe₃O₄@ZIF-8 magnetic MMMs,it could be seen that microporous ZIF-8 layer of Fe₃O₄@ZIF-8 magnetic core-shell units could improve the interface-gaps of magnetic units/polymers and offer efficient permeability channel for O2.With fillers loadings increasing,mechanical properties and O₂/N₂ selectivity of magnetic MMMs increased following a decline,however,gas permeability grew steadily.When magnetized in 56 mT,the magnetic MMM containing 8 wt% of Fe₃O₄@ZIF-8 exhibited an excellent O₂/N₂ separation performance with O2 permeability of 967 Barrer and O₂/N₂ selectivity of 3.17,the results of which were very close to 2008 Robeson's upper bound.?3?Fe₃O₄@ZIF-8 magnetic core-shell units with different core sizes and different shell thicknesses were incorporated into PIM-1 polymers to prepare PIM-1/Fe₃O₄@ZIF-8 magnetic MMMs with corresponding core-shell structure.The tests showed that O₂/N₂ permeability and mechanical properties of magnetic MMMs rose up as ZIF-8 layer thicknesses increased.When magnetizated in 56 mT,magnetic MMMs containing 40 nm ZIF-8 layer thicknesses of Fe₃O₄@ZIF-8 possessed O2 permeability of 831 Barrer and O₂/N₂ selectivity of 3.78.As core sizes of Fe₃O₄@ZIF-8 increased,gas permeability of magnetic MMMs were enhanced,whereas its mechanical properties declined.When magnetizated in 56 mT,magnetic MMMs containing 200 nm core size of Fe₃O₄@ZIF-8 possessed O2 permeability of 744 Barrer and O₂/N₂ selectivity of 3.67.