Manipulation Of Interfacial Morphology Within Pims Based Hybrid Membrane And Modified Maxwell Model

As one kind of organic molecular sieve membranes,polymers of intrinsic microporosity?PIMs?membranes have the advantages of both easy processing and high permeability,which are currently one of the most promising membrane materials for large-scale carbon capture.This study aimed at enhancing the selectivity and anti-aging property of PIMs membranes.A series of novel PIMs hybrid membranes with improved interface morphology,controllable interface free volume and interface interactions were designed and fabricated with general physical blending method,and therefore high CO₂/CH₄ separation performance were achieved.By analyzing the multi-structures of the hybrid membrane interface,the influences of the interface parameters on the gas transport behaviors were explained.Furthermore,the modified Maxwell models were established to associate the structure parameters of the fillers,the interface parameters with the membrane separation performance.This study is expected to offer theoretic and technological guidance and support to fabricate high performance hybrid membrane.The details were summarized as follows:Manipulation of interface defects and Maxwell model:A novel approach was introduced to improve the compatibility and remove the interface defects via replacing the dried ZIF-67 powder with drying-free ZIF-67 solution.The intrinsic CO₂permeability and CO₂/CH₄ selectivity of ZIF-67 were 8000 Barrer and 45,respectively.The incorporated ZIF-67 mainly intensified the diffusion-based mechanism,and the optimized membrane showed high selectivity up to 16.8 with fairly good CO₂ permeability of 5206 Barrer,which could not only break through the2008 Robeson upper bound,but also fit well the Maxwell model.Manipulation of interface free volume and modified Maxwell model:A novel ZIF-67 hollow sphere with controllable cavity size was synthesized and introduced into PIMs matrix to adjust the interface free volume.In particular,the microporous shell can function as molecular sieve providing additional selectivity,while the cavity provides high fractional free volume to enable free gas transport.The modified Maxwell model was established to associate the cavity size with the separation performance.It could be predicted from the model that the CO₂ permeability would enhance without compromising the selectivity if the size of cavity increased.ZIF-67hollow sphere with cavity size of 275 nm and wall thickness of 55 nm was synthesized and the optimized membrane showed high CO₂ permeability up to 7128Barrer with fairly good selectivity of 16.4,which could not only break through the2008 Robeson upper bound,but also fit well the modified Maxwell model.Manipulation of interface interaction and modified Maxwell model:ZIF-67crystals with various particle sizes was synthesized and introduced into PIMs matrix to adjust the interface interaction.The ZIF-67 crystals with smaller size afforded more interaction sites and stronger interaction strength with the polymer chains,therefore enhancing the selectivity and anti-aging property.The modified Maxwell model was established to associate the interfacial parameters of the rigidified polymer region and blocked skin layer of filler with the separation performance.It could be predicted from the model that the selectivity would enhance with sacrificing the CO₂permeability if the particle size decreased.ZIF-67 nano-crystal with size of 30 nm was synthesized and the optimized membrane showed high selectivity up to 21.1 with moderate CO₂ permeability of 2805 Barrer.Moreover,the CO₂ permeability only declined by 27%with over 120 days.The separation performance could not only break through the 2008 Robeson upper bound,but also fit well the modified Maxwell model.