| Membrane separation,as a new type of separation technology,with the advantages of low energy consumption,simple equipment,and good separation performance,has received extensive attention in recent years.MFI zeolite membrane remains a hot topic in membrane separation due to the unique pore structure,excellent resistance to high temperature,acidic and alkali media,as well as the good hydrothermal stability.The mass transfer path,efficiency and separation performance of MFI zeolite membranes quite depends on the orientations.The preparation of highly oriented and ultra-thin MFI zeolite membranes has always been a challenge in the field of membrane separation.Compared to randomly oriented membranes,the b-oriented MFI zeolite membrane has straight channels perpendicular to the surface of the support,b-Oriented MFI zeolite membranes have reduced mass transfer resistance and exhibit good separation performance due to the short and straight molecular diffusion path across the zeolite membrane.In this thesis,plate-like MFI zeolite crystals,which are used as seeds,are orientedly deposited on the support by the liquid-air interface（LAI）assembly method.After a secondary growth,b-axis oriented MFI zeolite membranes are prepared.The main research contents are as follows.1.Plate-like MFI zeolite was used as seed crystals for the first time.Oriented MFI zeolite seed layers were fabricated on various supports,（such as silicon wafers,andα-alumina supports）by the liquid-air interface assembly method.First,a smooth silicon wafer was used as support to assemble the MFI zeolite seed layer.The effects of linoleic acid addition amount,MFI zeolite concentration and suspension dosage on the seed layer arrangement of MFI zeolite were investigated.SEM showed that when the the addition amount of linoleic acid is 15μL,the concentration of MFI zeolite was0.004 g/m L,and the amount of suspension was 400μL,a well arranged and tightly stacked plate-like MFI zeolite seed layer could be obtained.2.Rough surface of the sintered alumina support was modified by using organic agar or inorganic silica nanospheres followed by depositing MFI zeolite seed layer.It was found that the inorganic silica can stably exist on the alumina support after calcination.The flatness of the surface of the alumina support is improved,which is beneficial to the deposition of the highly oriented MFI zeolite seed layer.The continuous and thin b-oriented MFI zeolite zeolite membranes were obtained by hydrothermal secondary growth of MFI zeolite seed crystal layer deposited the surface of the alumina support modified by silica.The effects of different secondary growth time on the MFI zeolite membrane were studied.SEM and XRD characterizations showed that with the increase of the secondary growth time,the intergrowth of MFI zeolite is more dense,b-Orientation of the membrane lowered.The CPO value changed from 0.94 to 0.66,b-Oriented MFI zeolite membranes were prepared with growth time of 3 h to 24 h.The binary butane isomer separation performance test was conducted on the b-oriented MFI zeolite membrane prepared with the growth time of 12 h.The results showed that the the b-oriented membrane displayed n-butane permeance and separation factor of 1.2×10-7 mol m-2 s-1 Pa-1 and 40.6 for an equimolar n-butane/i-butane mixture at 323 K,respectively.The relationship between membrane performance and temperature,feed flow rate,and feed concentration was further inverstigated.The results showed that the separation performance of the prepared oriented MFI membrane was in close relation to temperature and feed concentration,while was irrelevant to the feed flow rate of the butane mixture. |
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