Preparation Of High-Performance CO₂ Separation Membrane By Modifying Polyvinylamine With Mesoporous Molecular Sieve And Cyclic Small Molecular Amine

Improvement of the performance of CO₂ separation membranes under normal temperature and high temperature, is greatly meaningful for the industrial application of CO₂ separation technology based on membranes. To achieve this target, in this work, firstly, MCM-41 mesoporous molecular sieve was used to blend with polyvinylamine?PVAm? and mixed matrix composite membranes were fabricated with high permance and selectivity under normal temperature. Secondly, the cyclic small molecular amine, 2-aminoterephthalic acid?AA?, was used to chemically cross-link PVAm and the composite membrane was prepared to improve the separation performance of the membrane under high temperature.Firstly,MCM-41 grafted by amines?MCM-NH₂? was used to modify PVAm and PVAm-MCM-NH₂/polysulfone?PSf? mixed matrix composite membranes were prepared. The amine groups grafted to MCM-41 improved the filler-polymer interface compatibility and simultaneously facilitated the transport of CO₂ through reversible reaction. Besides, the pore of the molecular seive is conducive to the faster transport of CO₂ molecules. As a result, the separation performance of the membranes was improved by the introduction of MCM-NH₂. The permselectivity of PVAm-MCM-NH₂/PSf membranes with different MCM-NH₂ contents was tested using CO₂/N2 mixture. When mMCM-NH₂/mPVAm in the coating solution was 0.2, the testing temperature was 22 oC and the feed gas pressure was 0.15 MPa, the membrane exhibited a CO₂ permeance of 1269 GPU and a CO₂/N2 selectivity of 136. Moreover, the effects of the wet coating thickness, introduction of ethanediamine and heat treatment on the separation performance of PVAm-MCM-NH₂/PSf membrane were investigated respectively. The results indicated that the increase of wet coating thickness?from 50 ?m to 100 ?m?, introduction of ethanediamine and heat treatment?80 oC, 1 h? would reduce the separation performance of the membrane, except that the increase of wet coating thickness could improve CO₂/N2 selectivity under high pressure.Secondly, AA was used to chemically cross-link PVAm and the PVAm-AA/PSf composite membrane was prepared. The results of infrared spectroscopy and X-ray photoelectron spectroscopy indicated the covalent bonds formed between AA and PVAm, which could limit the the mobility of the polymer chain and enhance the thermal stability of the membrane. The introduction of AA also increased the effective carrier content for CO₂ separation, resulting in a higher permance and selectivity. The separation performance of PVAm/PSf and PVAm-AA/PSf membranes was investigated using CO₂/N2 mixture and the results indicated that the chemical cross-linking improved the permselectivity under relatively high temperature obviously. Under the testing temperature 120 °C and feed gas pressure 0.3 MPa, the membrane showed a CO₂ permeance of 661 GPU and CO₂/N2 selectivity of 95, which was greatly higher than the performance of PVAm/PSf membrane under the same conditions. PVAm-AA/PSf membrane also showed excellent time stability during the separation performance test under 120 °C. Moreover, PVAm-AA/PSf membrane displayed excellent separation performance under high temperature for the separation of CO₂/CH4 and CO₂/H2 mixture.