Preparation And CO₂ Separation Performance Of Fluorine-Containing Acrylate-MFI Nanosheet Membranes

Membrane separation technology has the advantages of high efficiency,energy saving and low carbon emission,showing promising potential in industrial separation.Zeolite acts as an ideal membrane material due to its excellent physical and chemical properties.Among them,the unique pore structure of MFI zeolite makes it of important value in the field of membrane separation.Two-dimensional MFI zeolite nanosheets show unique advantages in constructing zeolite membrane due to their high surface-thickness ratios.The MFI nanosheets exfoliated from multilayer MFI zeolite（ML-MFI）,have quite high surface-thickness ratios,with the thickness of 1.5 unit cell in b-axis.The MFI nanosheets have been used as building blocks to prepare isomer-selective MFI nanosheet membranes.However,the selectivity of the nanosheet membrane is much lower than the conventional membrane,possibly due to the interlayered crystal gaps between MFI nanosheets.In this thesis,the fluorinated acrylate（PFHI）membranes were firstly investigated in the binary gas CO₂/N₂ separation.Then,the MFI nanosheet membranes were modified with PFHI in order to eliminate the interlayered gaps and improve the separation performance of the nanosheet membranes.The content mainly consists of as follows:1)PFHI/Nylon6 composite membranes were prepared by a simple drop coating method using the microporous Nylon6 filter as the base membrane and PFHI solution as the coating solution.FT-IR,XPS and WCA results showed that PFHI contained C-F,N=C=O,carbamate bond and so on,which exhibited good hydrophobicity.FT-IR revealed that the infrared absorption peak of the base membrane was covered,which indicated that PFHI formed a membrane on the surface of the base menbrane.SEM showed that the membrane was continuous and compact,with the thickness of about 18μm in case of the dosage of 300μL.The effect of different PFHI solution dosage on the gas permeability of CO₂/N₂was investigated.Single gas permeation tests demonstrated that the membrane prepared with 300μL dosage showed the highest ideal selectivity.Binary CO₂/N₂ gas separation tests indicated that the separation factor for CO₂/N₂ could reach 30 at room temperature and a pressure of700 k Pa,with a permeance of CO₂ was 1.9×10^-8mol·m^-2·s^-1·Pa^-1.PFHI/Nylon6membranes have the ability to separate CO₂.2)Dispersed MFI nanosheets were prepared by exfoliation of ML-MFI.SEM images indicated that the MFI nanosheets were uniform in size without large particles.Usingα-alumina（α-Al₂O₃）as the support,MFI nanosheets were deposited on theα-Al₂O₃ support by vacuum filtration method.SEM images showed that the MFI nanosheets were well stacked.Pure gas of CO₂,N₂ permeation test indicated that the MFI nanosheet membrane had low ideal selectivities.After modification with PFHI solution,the CO₂/N₂ gas permeability test results revealed that the membrane had selectivity to CO₂.The binary gas CO₂/N₂ separation tests were carried out on the membrane.The results showed that the separation factor of CO₂/N₂ reached 10.4,at a pressure of 400 k Pa and the CO₂/N₂=8:2,with a CO₂ permeation rate of 3.4×10^-8mol·m^-2·s^-1·Pa^-1.These results indicated that PFHI patched the interlayered gap between MFI nanosheets.