Study On Preparation And CO₂/N₂ Separation Performance Of Pebax-1657 Based Mixed Matrix Membranes

In recent years,the greenhouse effect has been further intensified due to the excessive emission of CO₂ gas,causing many environmental problems.Carbon capture and storage technology（CCS,Carbon Capture and Storage）is regarded as an effective method to solve the greenhouse effect and has received extensive attention.Compared with traditional CO₂ separation technologies such as cryogenic rectification and pressure swing adsorption,membrane separation technology has the advantages of low energy consumption,easy scale,and environmental friendliness.The selection of membrane materials is crucial to membrane separation performance,and the preparation of high-performance gas separation membranes is still a research hotspot.Mixed matrix membranes（MMMs）are an emerging membrane material,composed of dispersed particles and continuous polymer phases.It combines the advantages of inorganic membrane and polymer membrane,and has shown great application potential in the field of gas separation.In this work,using polyether polyamide copolymer（Pebax,Pebax1657）as the polymer matrix,different kinds of fillers were prepared and two kinds of mixed matrix membranes were constructed,which showed significantly enhanced gas separation performance compared with pure Pebax membrane.The main research contents and results are as follows:1.MAF-7/Pebax1657 mixed matrix membrane was prepared by solution casting method with MAF-7（SOD-[Zn（mtz）₂],Hmtz=3-methyl-1,2,4-triazole,window:d=0.34 nm）as the filler.The Hmtz ligand in the MAF-7 backbone was coordinated using only 2-and 4-N atoms,and the uncoordinated 1-N atoms had a dipole-quadrupole interaction with the positively charged carbon in the CO₂ molecules,so the adsorption of guest CO₂ molecules was obviously enhanced.Due to the existence of uncoordinated1-N atoms,the complex chemical modification process of the filler was avoided.The results of gas permeability showed that when the filler loading was 5 wt.%,the separation performance of the mixed matrix membrane reached the optimal value,with the CO₂ permeability of 76.15 Barrer and CO₂/N₂ideal selectivity of 124.84,which exceeded the Robeson upper bound in 2008.2.The Polyethylenimine（PEI）was used to modify multi-walled carbon nanotubes（MWCNTs）,and the novel PEI@MWCNTs composite filler was synthesized,effectively improving the dispersion of the filler and the compatibility with Pebax matrix.The composite filler retained the unique one-dimensional tubular structure of MWCNTs,providing a low-resistance transport path for gas molecules.In addition,the abundant amino groups in the PEI structure could provide more active sites for CO₂molecules,maintaining better CO₂/N₂ ideal selectivity and ensuring excellent CO₂permeability of MMMs.This synergistic effect of the composite filler achieved a good balance between the permeability and selectivity of the carbon-based MMMs.When the filler loading was 5 wt.%,the separation performance of the MMMs reached the optimal value,with the CO₂ permeability of 150.51 Barrer and CO₂/N₂ ideal selectivity of 82.06.The gas separation performance was also exceeded the Robeson upper bound in 2008.