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

The aggravation of global warming makes CO₂ capture an urgent problem to be solved.Membrane separation technology is one promising gas separation technology,with the advantages of low energy consumption,low cost,high efficiency,and small footprint.It has become the focus of current research.Mixed matrix membranes（MMMs）are a type of membrane materials based on inorganic materials/polymers.They combine the advantages of ease of processibilty of polymer membranes and good stability of inorganic membranes.At the same time,they overcome the drawbacks that the permeability and selectivity cannot be improved simutaneouely and have attracted widespread attention from scientific researchers.However,due to the poor compatibility of two phases,there have been existing problems such as particle agglomeration,segment rigidity,and non-selective voids in membranes.In order to reduce the interface defects and improve the separation performance of MMMs,various modification methods have been investigated.In order to solve the problem of CO₂capture,several mixed matrix membranes were prepared in this paper,and the gas separation performance was studied to obtain membrane materials with better separation ability.In this paper,6FDA-based polyimide（6FDA-BI）containing imidazole structure was used as the continuous phase,and ZIF-8 was used as the dispersed phase to prepare a mixed matrix membrane for CO₂/CH₄,H₂/CH₄,and CO₂/N₂ separation.Although these MMMs have good gas separation performance,there are still problems such as interface defects in the membrane.Then MMMs were treated with Zn²⁺to further improve their gas separation capabilities.At the same time,the effect of polymer types on the gas separation performance of membranes were explored.The separation performance of two MMMs were compared by mixing Ni₂（dobdc）with two different types of polymers,6FDA-6Fp DA and Pebax,respectively.A highly selective mixed matrix membrane based on 6FDA-BI and ZIF-8 was successfully prepared.The ZIF-8 with imidazole linker offers a more compatible interface with imidazole containing polyimides.When ZIF-8 content increased,the H₂and CO₂ gas permeabilities increased while the gas selectivities for H₂/CH₄,CO₂/CH₄and CO₂/N₂ gradually reduced.The Zn²⁺post-modification enables the formation of the metal coordination crosslinking with enhanced polymer/ZIF-8 interaction.For the Zn²⁺modified membranes,the gas permeabilities of H₂ and CO₂ can be increasedwith the constant H₂/CH₄ and CO₂/CH₄ gas selectivity.At the same time,the nanocrystals of Ni₂（dobdc）with particle size of 50 nm were synthesized to prepare MMMs with glassy polymer 6FDA-6Fp DA and rubbery polymer Pebax.Obvious particle agglomerations were observed in the SEM of MMMs.The gas permeability test showed that the separation performance between 6FDA-6Fp DA and Pebax were quite different.However,Pebax/10%Ni₂（dobdc）was relatively less affected by agglomeration because of its polymer chain segments mobility.This result shows that the separation performance is affected by polymer types and defects such as particle agglomeration,so they should be avoided during the preparation of membranes.