Preparation And Perforemance Of Polyoxyethylene Based Membrane For CO₂ Separation

The increase of carbon dioxide(CO2)emissions in the atmosphere leads to the intensification of the greenhouse effect,which poses serious threat to the global climate and the development of human society.Because of the small footprint,e environmental benignity,high efficiency and low energy consumption of membrane separation equipment,the usage of membrane separation for CO2 capture and storage is considered to be an economical and environmentally efficient choice.Polymer membrane has excellent commercial value because of its low material cost and easy mass production.Strong four-angle dipole between ether oxygen groups of PEO molecular chain and CO2 results in high solubility of CO2.However,the high crystallization capacity of PEO limits its CO2 separation performance.In order to improve the separation performance of PEO-based gas separation membrane,highpermeability and high-CO2 selective polymer membrane materials were designed,and the preparation method,structure,separation performance and gas transport mechanism of the membranes were discussed in detail,providing ideas for the rational design and controllable preparation of high-efficiency CO2 membrane separation polymer substrate materials.In order to solve the problem of easy crystallization of PEO,amino polyethylene glycol diglycidyl(Jeffamine? ED-600),polyethylene glycol diglycidyl ether(PEO-500)and amino functionalized cage-like polyhedral oligomeric silsesquioxanes(POSS-NH2)were selected to prepare hybrid POSS/PEO crosslinked membrane.The ethylene oxide(EO)group of PEO and abundant amine group of POSS-NH2 in the membrane,the diffusivity and the solubility of the CO2 was improved.As a result,the gas permeability and selectivity of CO2 was elevated.Compared with pure crosslinked PEO membrane,the CO2 permeability of hybrid membranes increased from 159.4 Barrer to 385.2 Barrer,increased by 142.5%.In order to utilize the advantages of POSS-NH2 nanoparticles and molecular chain interface between POSS-NH2 and PEO matrix to accommodate small molecules of polyethylene glycol(PEG)to break through the performance limitations of traditional mixed matrix membrane,PEG impregnated hybrid POSS/PEO crosslinked membrane(FIHMs)with high gas permeability was prepared to further improve the CO2 separation performance of hybrid POSS/PEO cross-linked membrane.The results show that the introduced low molecular weight(500 g/mol)polyethylene glycol dimethyl ether(PEGDME-500)can reduce the glass transition temperature of hybrid POSS/PEO cross-linked membrane,and increase the content of ether oxygen groups.Therefore,the CO2 affinity of the separation membrane is improved,and the CO2 separation performance of the hybrid POSS/PEO cross-linked membrane is improved.Compared with pure PEO cross-linked membrane,the gas separation performance of PEG-impregnated cross-linked membranes(FIHMs)is also improved under the synergistic effect of low molecular weight PEG impregnation and nanoporous POSS-NH2 framework.The impregnation amount of PEGDME-500 of the hybrid POSS/PEO cross-linked membrane increased from 44.4 wt.% to 180 wt.%,the CO2 gas permeability was also significantly increased from 159.4 Barrer to 1566.8 Barrer,an increase of 982.9%,and the selectivity of CO2/N2 and CO2/H2 were 35.1 and 12.0,respectively.Compared with POSS-NH2,dendritic mesoporous silica(DFNS)has a unique mesoporous structure,high monodispersity,large specific surface area and a large amount of hydroxyl groups on the surface,which makes it easy to form hydrogen bonds with PEO to further improve the separation performance of CO2.DFNS/PEO mixed matrix membrane with good interface morphology was prepared by UVinduced PEO crosslinking.When the amount of DFNS was 2 wt.% in the DFNS/PEO membrane,the CO2 permeability of the DFNS/PEO mixed matrix membrane was 770.5 Barrer,which was 95.3% higher than that of the UV-induced pure cross-linked PEO membrane.In order to further improve the gas separation performance of the prepared DFNS/PEO mixed matrix membrane,a low molecular weight PEGDME-500 impregnated DFNS/PEO mixed matrix membrane was prepared to increase the affinity of the mixed matrix membrane for CO2 and improve its solubility in the membrane.Thereby the gas transport and CO2 selection performance was improved.The results show that the prepared PEGDME-500 impregnated DFNS/PEO mixed matrix membrane showed excellent CO2 separation performance.When the impregnation amount of PEGDME-500 is 48.9 wt.%,the CO2 permeation flux of DFNS/PEO mixed matrix membrane MMM-2 is 2281.1 Barrer,which is 478.5% higher than that of UV-induced pure cross-linked PEO membrane;and the CO2/N2 and CO2/H2 selectivity can be as high as 48.1 and 13.7.