Preparation Of OPBI Mixed Matrix Membrane And Its H₂/CO₂ Separation Performance

Membrane separation is based on the principles of molecular sieving and dissolution-diffusion to achieve an efficient separation process.Membrane separation processes have received more attention,which due to its simple process,low energy consumption,and environmentally friendly.Currently,membrane separation processes were mainly utilized in gas separations,such as hydrogen purification,carbon dioxide capture,natural gas purification,and air purification.Gas separation membranes can be divided into two types,which based on the different membrane materials:inorganic membranes and organic membranes.Inorganic membranes have good mechanical,chemical and thermal stability,and high gas selectivity.However,the transportation and installation of inorganic membranes are difficult,which due to the high manufacturing cost and fragile materials.Organic membranes are composed of different polymers,which have a low cost,easy preparation,and commercialization,and have been widely used in the gas separation.But the poor thermal stability and trade-off of limited the progress of organic membranes,which limited the improvement of gas separation performance.In recent years,mixed matrix membranes（MMMs）have gradually attention on gas separation,which combined the characteristics of organic and inorganic membranes.The MMMs have some advantages,such as easy processing,excellent molecular sieving performance,and high gas perm-selectivity,which breaking the upper-bound of the gas separation membrane.In this paper,the preparation of zeolite imidazolate（ZIF-7）nanoparticles were introduced,and the transition process between different phase states of ZIF-7 was explored.The transition relationships of ZIF-7 nanoparticles with different phases were investigated under the induced guest molecules,such as ZIF-7-I with the large pore crystal structure,ZIF-7-Ⅱ with the narrow pore crystal structure,and ZIF-7-Ⅲwith the dense pore crystal structure.The characterizations of XRD,FTIR,SEM,gas adsorption and desorption have proceeded.The macrostructure（morphology,size,etc.）and the microstructure（pore size,pore structure,and CO₂ adsorption performance,etc.）of ZIF-7nanoparticles were compared.And the ZIF-7 nanoparticles with different phases were obtained.A certain amount of ZIF-7 nanoparticles blended a[2,2’-（p-oxydiphenyl）-5,5’-bibenzimidazole]（OPBI）polymer to obtained the ZIF-7/OPBI MMMs.The effects of ZIF-7 content and crystal structure on the gas separation performance of MMMs were systematically studied.The"locked phase transition"was proposed,which was regulated the phase transition of ZIF-7 and the tightness of the OPBI polymer with 300℃heat treatment.Under the single-gas and mixed-gas permeation,the results showed that the 30 wt%ZIF-7-Ⅱ/OPBI MMM has the highest H₂/CO₂separation performance with exceeded the 2008 Robeson Upper Bound.The H₂ permeability of MMM was 170.7 Barrer and H₂/CO₂ selectivity was 13.5 under 180℃with 6 bar.The correlation between the movement of the OPBI chains and the phase transition of ZIF-7 was proved,and the controllable phase transition of ZIF-7 was realized.Besides,the 30 wt%ZIF-7-Ⅱ/OPBI MMM has excellent stability and separation performance under elevated pressure and high-temperature operation,which due to the rigid segment structure and good thermal properties of OPBI polymer.In summary,the effect of the phase transition of ZIF-7 on the H₂/CO₂separation performance of MMMs was discussed.The interaction between the phase transition of ZIF-7 and OPBI polymer was clarified,and the space-limiting effect of OPBI chains was proposed to achieve controlling the phase transition of ZIF-7.This strategy provides a promising method of MMMs preparation for gas separation membranes.