Preparation And Butane Isomer Separation Properties Of Two-dimensional MFI Zeolite Nanosheet-PDMS Mixed Matrix Membranes

Membrane separation has received more attention in the field of industrial separation due to the merits of ease of operation,high efficiency,low energy consumption and environmentally friendly properties.The key point of membrane technology is membrane,whose structure and property closely relate to the efficiency of the membrane separation technology.Two-dimensional?2D?MFI zeolite nanosheets with high aspect ratio exhibit a promising potential in the construction of membrane materials.Mixed matrix membranes?MMMs?combine the easy film forming of polymeric matrix with the high selectivity of MFI zeolite when using the 2D MFI nanosheets as fillers.However,the preparation of large size,particulate-free and open-pore two-dimensional?2D?MFI zeolite nanosheets as well as MMMs with high MFI nanosheet loadings still remains challenges.In this thesis,a novel wet oxidation method was applied to remove organic structural directing agent?OSDA?from the multilamellar MFI zeolite?ML-MFI?,which was then treated by ultrasonication to obtain the 2D MFI zeolite nanosheets.Then the open-pore MFI zeolite nanosheets were used as fillers for the fabrication of 2D MFI zeolite nanosheets-polydimethylsiloxane?PDMS?MMMs.The permeability of the MFI-PDMS MMMs for butane isomers was studied as well.The main content includes two parts as follow:1)Preparation and characterization of 2D MFI zeolite nanosheets:ML-MFI zeolite was synthesized by using an organic structure-directing agent?OSDA?which composed long-chain alkyl group and dual-quaternary ammonium.Then the ML-MFI was repeatedly treated with piranha solution?3H₂SO₄:1H₂O₂?.Characterizations of XRD,TG,IR,N₂ adsorption and desorption revealed that the OSDA was efficiently removed and the micropore were completely opened with micropore surface area up to 427 m²/g,after the ML-MFI was repeatedly treated by piranha solution for 4 times.Afterwards,ultrasonication and sodium poly acrylate stripping method was adopted to exfoliate the OSDA free ML-MFI,respectively.According to the exfoliation efficiency and SEM characterization,after ultrasonication with an ultrasonic frequency of 45 kHz and 10 h ultrasonic time followed by sedimentation for 7 d,exfoliated MFI zeolite nanosheets could be obtained.The sizes of the MFI nanosheets could reach up to 1?m with regular straight-pore channel at the axial of b,confirmed by SEM and TEM.2)Preparation of MFI-PDMS mixed matrix membrane and its separation performance of butane isomer:2D MFI nanosheets-polydimethylsiloxane?MFI-PDMS?mixed matrix membranes?MMMs?were prepared by incorporating the open-pore 2D MFI zeolite nanosheets into PDMS.Characterizations of SEM,IR and XRD indicated that the 2D MFI zeolite nanosheets could be uniformly dispersed in the PDMS matrix to form defect free MMMs.The effects of different MFI zeolite nanosheet loadings and different operating temperatures on the butane isomers separation performance of the MMMs were investigated.Single gas permeance test on MFI-PDMS mixed matrix membrane indicated that with the increase of MFI zeolite nanosheets,the permeability as well as the ideal selectivity for n-butane isomer increased correspondingly.Ideal selectivities for n-butane over i-butane of 15.6 with a n-butane permeability of 15615barrer achieved,when the loading of MFI nanosheets is 1.0 wt.%,which is much larger than the pure PDMS film.The ideal selectivity decreased when increase the operating temperature.