Preparation Of Polymer/Metal-Organic Frameworks Mixed Matrix Membranes And Gas Separation Performance Study

The continuing rapid growth in energy demand has motivated researchers to search for energy-efficient gas separation technology.Membrane separation technology gradually replace the thermally-driven phase-change-based separations to be broadly utilized in the important gas separations because it has the advantages of high energy–efficiency and small foot-print.Mixed matrix membranes?MMMs?based on inorganic materials/polymers which combine the high selectivity of inorganic membranes with the ease of processing of polymer membranes has attracted the attention of researchers.Metal-organic framework materials?MOFs?with the advantages of large specific surface area,uniform particle size and controllable structure are ideal dispersed phases of mixed matrix membranes.In this paper,NH₂-MIL-53?Al?was selected as the dispersed phase of MMMs and Tr?ger's base and Pebax2533 polymer were used as matrix materials to prepare TB/NH₂-MIL-53?Al?and Pebax2533/NH₂-MIL-53?Al?.NH₂-MIL-53?Al?has simple synthetic process,controlled particle size,good stability and excellent carbon dioxide selectivity.Tr?ger's base polymer is an N-heterocyclic microporous polymer with good interaction with NH₂-MIL-53?Al?to enhance the compatibility between nanocrystalline and polymers.Pebax2533 is a commercial block copolymer with excellent membrane-casting properties,thermal and chemical stability.In this paper,the effects of NH₂-MIL-53?Al?content on gas separation performance of membranes were studied.Through detailed analysis of membrane structure,physical properties and gas transfer characteristics,the structure-property relationships of membrane materials were revealed.In this paper,we successfully prepared TB/NH₂-MIL-53?Al?hybrid membranes with good transparency,excellent gas separation performance and plasticization-resistance.SEM and BET results showed that NH₂-MIL-53?Al?had a particle diameter of 40 to 50 nm and a BET specific surface area of 1934 m²/g.IR,SEM and translucent photos of membranes showed that hydrogen bonding existed between TB and NH₂-MIL-53?Al?,and the compatibility was good.The resulting membranes incorporated with MOFs show a remarkable increase in gas permeability up to 3 times as a result of improved gas diffusivity and solubility without the selectivity loss.Much more improvements in CO₂ solubility arise from the presence of CO₂-adsorbing sites in Tr?ger's base polymers and the CO₂-selective adsorption properties of NH₂-MIL-53?Al?,correspondingly leading to increased CO₂ permeability.The gas separation performance shifts toward Robeson upper bounds because of the addition of MOFs.Particularly,the H₂/CH₄ separation performance overcomes the 2008 Robeson upper bound.In mixed gas feeds,the membranes display CO₂ gas permeability up to 308 Barrer and CO₂/N₂and CO₂/CH₄ mixed gas selectivities of 25.4 and 23.6,and the inclusion of MOFs inhibits the plasticizing effect of CO₂ on membrane materials.The pure gas permeability test of Pebax2533/NH₂-MIL-53?Al?mixed matrix membrane showed that gas selectivity was basically unchanged with the increase of MOFs content,the permeability shows the maximum value when the content was 5 wt.%,CO₂permeability was 246 Barrer,and the CO₂/N₂ and CO₂/CH₄ selectivity was 25.0 and 7.3.However,when the content of MOFs continues to increase,the CO₂ separation performance of the mixed matrix membrane was not improved.There are two main reasons:on the one hand,because of the strong interaction between the polymer and MOFs,the mobility of the polymer chains reduces.On the other hand,excessive MOFs particles and agglomeration of MOFs increase the gas diffusion path curvature.Pebax2533 pure membrane has excellent mechanical properties,elongation at break and tensile strength as high as 1404.86%and 21.5 MPa.And when the amount of MOFs was 10 wt.%,the elongation at break and tensile strength of the mixed matrix membrane only decreased by 14%and 5%.So the mixed matrix membrane with low content MOFs still has very good mechanical properties.