Study On CO₂/N₂ Separation Performance Of Functionalized Montmorillonite Reinforced Polyvinylamine Facilitated Transport Membranes

Mixed matrix membrane takes polymer matrix as continuous phase and inorganic particles as dispersed phase,which combines the advantages of polymer membrane and inorganic membrane and has excellent gas separation performance.Compared with the traditional mixed matrix membrane,the composite membrane with carrier is composed of mixed matrix films and porous support.This type of membrane is favored by researchers in the field of gas separation because of its ultra-thin selective layer and low requirement for casting solution content,but it is often limited by poor compatibility between filler and polymer matrix.To solve this problem,in this paper,polyvinylamine was used as polymer matrix,and aminated Cu₃（BTC）₂ intercalated montmorillonite,polyaniline modified acid activated montmorillonite and polyethyleneimine modified porous montmorillonite were used as inorganic fillers,respectively,to construct a mixed matrix composite membrane with high-efficiency transmission channels for CO₂/N₂ separation system.The main research contents are as follows:（1）Cu²⁺is exchanged with Na⁺between MMT layers,and then Cu₃（BTC）₂ was generated in situ between MMT layers by coordination and action of trimellitic acid and Cu²⁺,thus preparing hybrid materials with intercalation structure.Then,3-aminopropyltriethoxy-silane（KH550）was used to modify the surface of MMT,and a carrier with the function of facilitating transport was introduced between MMT layers.The amino-modified Cu₃（BTC）₂-MMT composite was added to PVAm matrix as a selective coating and coated on PSf support to prepare PVAm/Cu₃（BTC）₂-MMT-NH₂ MMCMs.XRD and FTIR confirmed that Cu₃（BTC）₂ entered MMT interlayer,which also confirmed that KH550 was successfully modified.A fast lamellar transmission channel of Cu₃（BTC）₂-MMT-NH₂ was contructed for CO₂ transport.When the loading of Cu₃(BTC2)-MMT-NH₂ is 3 wt%,the CO₂ permeance is203 GPU,and the CO₂/N₂ selectivity is 100.7.And the MMCMs exhibited excellent long-term stability performance during 360 h test,far surpassing the Robeson’s upper bound proposed in 2008.（2）The MMT was activated by hydrochloric acid,so that H⁺exchanged with Na⁺between MMT layers to form channels,and the Al–OH group in octahedron was protonated,which led to the dissolution of Al³⁺,and the channels increased after dissolution.Polyaniline nanoparticles were successfully synthesized on the surface and interlayer of acid-activated montmorillonite nanosheets based on cation exchange and in-situ polymerization,and PANI-a/MMT composites were prepared.PANI-a/MMT was added to PVAm matrix to successfully prepare PVAm/PANI-a/MMT MMCMs.XRD and FTIR confirmed the structural change of acid activated MMT and the successful synthesis of PANI between layers.PANI-a/MMT combines a large number of secondary amine groups of PANI and large specific surface area and pore structure of acid-activated montmorillonite nanosheets to construct a straight CO₂ transmission channel,which improves CO₂ permeance and CO₂/N₂selectivity.When the loading of PANI-a/MMT is 1 wt%,PVAm/PANI-a/MMT MMCMs has a CO₂ permeance of 254 GPU and a CO₂/N₂ selectivity of 87.3.And the MMCMs exhibited excellent long-term stability performance during 360 h test,far surpassing the Robeson’s upper bound proposed in 2008.（3）Porous MMT（p-MMT）was prepared by solid-state reaction of NaOH and MMT to produce micropores via desilication.PEI-modified p-MMT（P@p-MMT）composites with interconnected two-dimensional porous structure were constructed by using the electrostatic chemical interaction of polyethyleneimine（PEI）and Si–O^–around p-MMT etching holes.PVAm/P@p-MMT with continuous facilitated transport channels was prepared by adding P@p-MMT into PVAm matrix.SEM of inorganic materials confirmed the generation of porous structure,FTIR and XRD confirmed the change of MMT structure before and after NaOH etching,TG confirmed the existence and approximate concentration of PEI in p-MMT porous structure,and nitrogen adsorption and desorption experiments and pore size distribution verified the pore structure characteristics of p-MMT and P@p-MMT.The ATR-FTIR and SEM of the cross-section of mixed matrix composite membranes were characterized.It can be seen that P@p-MMT is well dispersed in PVAm matrix and has strong interaction with PVAm matrix.P@p-MMT continuously facilitates transport channels to increase the gas transport passway and strengthen the membrane separation process.When the loading of P_3.2@p-MMT2 is 2 wt%,the PVAm/P_3.2@p-MMT2 MMCMs exhibits an excellent gas separation performance with CO₂ permeance of 217 GPU and CO₂/N₂selectivity of 112.3,which surpassed the 2008 Robeson upper-bound.