Adjusting Morphology Structure Of PVAm Mixed Matrix Membranes By Layered Materials And Their CO₂/N₂ Separation Performance

The gradual increase in CO₂ emission has led to an increase in the concentration of CO₂ in the atmosphere,causing a greenhouse effect,resulting in various ecological and environmental problems,such as melting ice,rising sea levels and severe weather.Therefore,how to capture and recover CO₂ gas has become one of the most important subject of environment and energy.Absorption,adsorption,cryogenic distillation,and gas membrane separation are the main methods for industrial capture and separation of CO₂.Among them,gas membrane separation technology is currently considered the most promising candidate in the field of CO₂ separation due to its high efficiency,low energy consumption and environmental friendliness.So we prepared a mixed matrix membranes by polysulfone（PSf）ultrafiltration membrane as support,polyvinylamine（PVAm）as matrix and different two-dimensional layered material as filler.The arrangement of the layered material in the matrix is adjusted to construct a layered transport microchannel of CO₂,which can improve the separation performance of CO₂ in the membrane.The main research contents are as follows:（1）In this chapter,a uniform dispersion of monolayer metakaolin（MK）is prepared and added to the PVAm aqueous solution to obtain a PVAm/MK coating solution.Then,the PVAm/MK mixed matrix membranes was prepared on the PSf by coating method.The microstructure of the membrane was characterized using XRD and SEM.The influences of content,pressure and film thickness on the gas separation performance of membrane were studied.The results showed that the gas separation performance of PVAm/MK mixed matrix membrane loaded with 1 wt%MK exhibited optimal separation performance at1 bar with the CO₂ permeance of 152 GPU and CO₂/N₂ selectivity of 78.This is attributed to the generation of hydrogen bonding between the oxygen-containing bond on MK and the amine group on the PVAm,which can construct a layered microchannels facilitates gas transport to increase the CO₂ permeance and CO₂/N₂ selectivity of the membrane.In the mixed-gas conditions,PVAm/MK membrane loaded with 1 wt%MK showed good stability during the 300 h test period,in which the average CO₂ permeance and CO₂/N₂ selectivity were 188GPU,83.8.（2）In this chapter,Zn²⁺was adsorbed on MK,and ZIF-8 was synthesized by in-situ synthesis on MK to prepare composite MK-ZIF-8 by adding dimethylimidazole solution,which was added to PVAm to prepare mixed matrix membranes.FTIR and XRD result indicate that ZIF-8 is successfully loaded on MK.The effects of different molar ratios of MK:Zn²⁺,contents,pressures and temperatures were investigated.The results showed that the best performance is obtained when the molar ratio of MK:Zn²⁺was 1:75.The PVAm/MK-ZIF-8membrane with the loading of 3 wt%MK-ZIF-8 showed CO₂ permeance of 169GPU,and the CO₂/N₂ selectivity of 86.7 at 1 bar.This is attributed to the layered microchannel composed of polyvinylamine and MK-ZIF-8 is beneficial to the rapid transfer of CO₂ and the molecular sieve effect of ZIF-8 of layers on CO₂.The synergistic effect of these improves the separation performance of membrane.Moreover,the mixed matrix membrenes loaded with 3 wt%MK-ZIF-8 exhibited long-term stability of performance in a gas mixture during more than 300 h of testing.（3）In this chapter,polyaniline-coated multi-walled carbon nanotubes（PANI@CNTs）was ultrasonically inserted into the graphene oxide（GO）layer to prepare PANI@CNTs-GO,and then added to PVAm aqueous solution to prepare PVAm/PANI@CNTs-GO mixed matrix membranes.The chemical structure and morphological structure of inorganic materials and membranes were characterized by FTIR,XRD and SEM.The effects of PANI@CNTs-GO content,pressure,temperature and mixed gas on the gas separation performance of membrane were investigated.The results showed that PANI@CNTs is successfully inserted into the GO layer.The interlayer spacing of GO increases gradually with the content of PANI@CNTs increases.The SEM results showed that PANI@CNTs-GO was uniformly dispersed in PVAm.The results also showed that PVAm/PANI@CNTs-GO membrane loaded with 1 wt%PANI@CNTs-GO at 1bar is 170 GPU,and the selectivity is 122.4 is much higher than pure PVAm film.This is due to the synergistic effect of facilitated transport and molecular sieving in the GO layer spacing.In addition,the mixed matrix membrane contained 1 wt%PANI@CNTs-GO exhibited excellent long-term stability performance even under mixed-gas conditions for over 300 h,with a CO₂ permeance of 264 GPU and a CO₂/N₂ selectivity of 149.8.