Enhancing Separation Performances Of Multi-layer Composite Membranes For CO₂ Separation

The CO₂ separation technology plays a decisive role in achieving the global major goals of clean&efficient utilization of energy,CO₂ mitigation and CO₂ resource utilization.However,the lack of high-performance CO₂ separation membranes restricts the large-scale industrial application of CO₂ separation membrane technology.Among various kinds of membranes for CO₂ separation,multi-layer composite membranes have become one of the most practical industrial application prospects for CO₂separation membranes owing to their advantages of low cost and easy processing.In this work,in order to enhance the separation performances of the composite membrane for CO₂ separation,the nanofillers were connected to the polymer matrix in the form of a covalent bonds to construct a two-phase interfaces with good compatibility and stability;the hydrophobic intermediate layer was modified with a high-adhesion complex to improve the interlayer compatibility of the composite membrane;the pre-wetting process was attempted to reduce the pore penetration of the hydrophilic separation layer,and the effect of the hydrophobic pre-wetting agent on the CO₂separation composite membrane was explored.First,ZIF-8-TA nanoparticles modified in situ by tannic acid（TA）were used as the dispersed phase,and amino-rich polyvinylamine（PVAm）was used as the continuous phase.The hydrophobic silicone rubber（PDMS）/polysulfone（PSf）membranes were used as the support layer.The interaction between TA and-NH₂,Fe³⁺was used to realize the hydrophilic modification of the PDMS layer and the preparation of the separation layer in one step,and then the mixed matrix multi-layer composite membranes PVAm-TA-Fe-（ZIF-8-TA）/PDMS/PSf were prepared.The results showed that oxidized hydroxyl groups on the surface of the ZIF-8-TA particles could undergo Michael addition reaction with-NH₂ on PVAm,so that the dispersed particles were connected to the polymer matrix via the form of chemical bonds,which improved the interfaces compatibility of the two phases in mixed matrix membrane.Moreover,the complex TA-Fe³⁺formed during the preparation of the separation layer adhered to the surface of the PDMS intermediate layer,which promoted the good combination of the hydrophilic separation layer and the hydrophobic PDMS layer.The prepared composite membrane had excellent CO₂/H₂ separation performance.Furthermore,using hydrophobic Isopar G as the pre-wetting material and hydrophilic PVAm as the separation layer material,the pre-wetting process was used to reduce the pore penetration of the separation layer to prepare dense and defect-free PVAm/PSf composite membranes.The results showed that pre-wetting the PSf support pores with Isopar G reduced the embedding depth of PVAm in the membrane pores,and the gas permeance increased significantly.At the same time,with the decreasing of PVAm concentration in the coating solution,the pre-wetting operation effectively avoided the generation of defects in the separation layer,and the prepared composite membrane had more stable CO₂/N₂ separation performance.However,the difference in density between Isopar G and the solvent of the coating solution is small,so that part of the coating solution penetrated into the pores of the PSf support,and the effective thickness of the separation layer increased,which limited the further improvement of the performance of the PVAm/PSf_prewet composite membrane.