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Permeation and separation properties of engineered zeolite membranes

Authors Au, Louisa Tak Yin
Issue Date 2000
Summary This thesis is devoted to illustrate the preparation of MFI-type engineered supported zeolite membranes. An ex-situ technique involving pre-seeding the porous support with nano-sized zeolite particles followed by hydrothermal treatment was described and applied. The membrane microstructures were mainly defined by crystal grain size, morphology and boundary, as well as the membrane thickness and orientation. To vary and control these parameters, different synthesis compositions based on concentration of silica source, organic template, alkaline metal and dilution were used. Besides, different synthesis conditions, i.e. reaction temperature and time, were also employed. All of the prepared zeolite films showed continuity and excellent intergrowths as characterized using electron microscopy which render them the potential for membrane separation processes. This study also demonstrated that the growth environment could also play an important role in dictating crystallographic preferred orientation of the zeolite film. It was illustrated that the zeolite film microstructure and orientation can be directly manipulated by changing the growth environment through controlled seeding of the support. The study demonstrated the effect of two main membrane microstructures on the gas permeation properties: film thickness and film orientation. The zeolite membranes were grown on the same support layer-by-layer successively to eliminate the effect of support variations for permeation study. The apparent thickness of the films ranged from 0.5 μm to ~ 12 μm for each of the film orientation. The prepared films exhibit highly (l0l)- and (002)- orientation accordingly as confirmed by x-ray diffraction. Single gas permeation measurements (H2, He, N2, Ar, CH4, i-C[subsript 4], n-C4 and SF6), and, in particular, Towngas gas separation tests were conducted for evaluating the membrane quality and permeation properties. The ideal selectivities of He/SF6 was used to indicate the membrane quality and it was ranged from 20 to 110 at 323 K, in all cases higher than Knudsen ratio. The H2/n-C4, H2/CH4 and i-C4/n-C4 single gas permeance ratios at the same temperature range from 13 - 27, 2 - 3 and 1.4 - 3, respectively. These data also demonstrate the film thickness and orientation were critical in controlling the molecular transport pathways.
Note Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2000
Language English
Format Thesis
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