Preparation And Performance Enhancement Of CO₂ Separation Membranes Based On Polymers Of Intrinsic Microporosity

With the advantages of excellent solution-processability and superior CO₂permeability,polymers of intrinsic microporosity（PIMs）are one of the most promising membrane materials for large-scale CO₂ capture.However,relatively low separation selectivity of PIMs membranes restricts them to large-scale industrial applications.This study takes PIM-1 as the research object,aiming at enhancing the selectivity of PIMs membranes.By analyzing the solution-diffusion mechanism,we propose the strategy of enhancing solubility selectivity by membrane surface manipulation,and enhancing diffusivity selectivity by membrane matrix manipulation.A serious of PIM-1 based membranes with largely improved selectivity and excellent CO₂/CH₄ separation performance were designed and fabricated by general physical blending or facial dip coating methods.This study is expected to offer theoretical guidance and technological support to large-scale preparation of CO₂ capture membrane with high performance.The details were summarized as follows:Manipulation of membrane surface and solubility selectivity intensification:Inspired by polyphenol chemistry,we constructed tannic acid molecular layer on the surface of PIM-1 membrane by dip coating to manipulate the surface structure of the membrane.Tannic acid has excellent adhesion on various substrate surfaces,so it is easy to form a stable coating on the surface of PIM-1 membrane;the rich oxygen-containing functional groups of tannic acid give the membrane surface excellent CO₂affinity,which can promote the dissolution of target gas molecule CO₂ on the membrane surface and thus enhance the solubility selectivity.The results showed that the CO₂ permeability of the composite membrane prepared by soaking in 2 mg/ml tannic acid solution for 45 min was 4532 Barrer,and the selectivity of CO₂/CH₄separation was improved to 14.4,which was 41.4%higher than the pure PIM-1membrane.The separation performance of the optimized membrane exceeded the 2008Robeson upper bound.Manipulation of membrane matrix and diffusivity selectivity intensification:ZIF-7 and NH₂-ZIF-7 nanoporous crystals was synthesized and incorporated into PIMs to prepare mixed matrix membranes.ZIF-7 exhibits excellent intrinsic CO₂/CH₄separation ability and favorable interaction with the PIM-1 matrix after amination.The incorporation of NH₂-ZIF-7 enhances the rigidity of the polymer chains at the interface,which contributes to the enhancement of diffusion selectivity.Notably,the CO₂/CH₄selectivity of the membrane containing 20 wt%NH₂-ZIF-7 was increased to 19.8 with CO₂ permeability of 2832 Barrer,exceeding the reported 2008 upper bound.Furthermore,a modified Maxwell model was established to associate the rigidified polymer region and partially blocked skin layer of NH₂-ZIF-7 with the gas transport behavior within MMMs,and it was validated by the good consistency between the experimental and predicted data.