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The Synthesis of Silicalite-1 Membranes on Alumina Hollow Fibers

Author: DanLiJun
Tutor: WangZhengBao
School: Zhejiang University
Course: Chemical Engineering
Keywords: Zeolite membranes silicalite-1 Hollow fiber Pervaporation High-throughput
CLC: TQ028.8
Type: Master's thesis
Year: 2011
Downloads: 54
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Abstract


And adsorption properties of the pore structure due to its rules, the zeolite membrane can be applied to the separation of mixtures of gases and liquids, and having a strong mechanical strength, chemical stability and thermal stability. Silicalite-1 zeolite membrane molecular sieve framework does not contain aluminum, with a strong surface hydrophobicity, is particularly applicable to the recovery of organic matter in the organic / aqueous solution or concentrated. As will be applied to the bio-fermentation process of the preparation of fuel ethanol, can be removed by continuous product alcohol, continuing to promote the reaction, thereby improving the efficiency of fuel ethanol production. Synthesis of silicalite-1 zeolite membrane carrier almost all sheet or tubular carrier, such carriers have in common is the thick walls, increasing the mass transfer resistance of the material separation process, reducing the permeate flux of the membrane, limiting industrial applications. This paper presents the use of wall is thinner (150 m) and packing density (gt; 1000m2/m3) alpha-Al2O3 hollow fiber as the carrier, secondary hydrothermal synthesis method silicalite-1 zeolite membrane Synthesis optimization, preparing a good performance of the molecular sieve membrane. The synthesis of silicalite-1 zeolite membrane used in pervaporation separation of ethanol / water mixtures, the the better ethanol / water separation. Research and experimental results are as follows: TPAOH content and seed crystal concentration in the synthesis solution silicalite-1 zeolite membrane, and found that the separation factor of the membrane increased with decreasing TPAOH content, but when TPAOH content is too low (x ≤ 0.12), the surface of the film is not dense, the surface crystal flaky structure; TPAOH content is too high (x ≥ 0.32), the surface of the film is relatively dense, but EDX prove more serious the dissolution of alumina carrier and reduce the hydrophobicity of the surface of the film, resulting in a decrease in performance of the membrane pervaporation. TPAOH in the synthesis solution concentration is within the appropriate range, since the seed crystal can not be completely covered by the carrier, in a hydrothermal synthesis process, the carrier also eluted with a low concentration of the solution of the seed crystal, is possible; the concentration of the seed crystal is too high, the surface of the carrier will be thicker seed layer is formed between the film layer and the carrier after the crystallization, there will still be a seed layer of a layer of loose, resulting in the generation of defects and cracks of the surface of the film in the high-temperature calcination process , thus reducing the separation performance of the membrane. When the synthetic fluid TPAOH content of x = 0.17-0.22, the seed crystal concentration to 5 wt%, 175 ° C, 12 h synthesis of silicalite-1 zeolite membrane on 60 ° C, 3 wt% and 75 ° C, 5 wt% ethanol / aqueous solution flux and separation factors were 2.95 kg · m-2 h-1, 66 and 5.40 kg · m-2 · h-1, 54. The study also found silicalite-1 zeolite membrane permeation flux and the porosity of the hollow fiber carrier linear relationship between porosity of 69% alpha-Al2O3 hollow fiber carrier synthesized silicalite-1 zeolite membrane on 60 ° C, 3 wt% ethanol / water solution permeate flux up to 4.74 kg · m-2 · h-1, much higher than the values ??reported in the literature. To reduce the the TPAOH concentration of carrier dissolution and shorten the time of hydrothermal synthesis, this study also has adopted the use of synthetic liquid TPAOH: TEOS: H2O = 0.17:1:165 and TPAOH: TEOS: H2O = 0.64:1:165 two footwork synthesis of silicalite-1 zeolite membrane. Than a short period of time (hours or 4 hours) one-step synthesis of silicalite-1 zeolite membrane was found a short time two-step method can significantly improve the separation performance of the membrane. With the extension of the second step crystallization time, the zeolite membrane separation performance significantly improved, when the second step crystallization time extended from 2h to 4h, molecular membrane separation factor increased from more than 20 to more than 40. The second step of crystallization time is too long, the accumulation of a large number of crystal film surface, interested in membrane separation performance. The dynamic rotation method and to reduce the content of the templating agent (TPA) can significantly reduce the bulk of the film surface of the crystal.

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CLC: > Industrial Technology > Chemical Industry > General issues > Chemical processes ( physical processes and physical and chemical processes ) > Separation process > New separation method
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