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Synthesis and characterization of ZSM-5 zeolite membranes


Lai, Re (2001) Synthesis and characterization of ZSM-5 zeolite membranes. Dissertation (Ph.D.), California Institute of Technology.


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Synthesis of ZSM-5 zeolite membranes supported on porous alumina substrates was conducted in autoclave reactors. The film morphologies and structures were characterized by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Gas adsorption was used to estimate the crystalline fraction of the products. The gas permeation properties of the membranes were evaluated for H2, CH4, O2, N2, and n-butane and other gases singly or in mixtures.

ZSM-5 film formation on alumina and other surfaces in certain clear, tetrapropylammonium(TPA+)-containing synthesis solutions was found to be preceded by a gel layer. The presence of alumina and other substrates of a high Hamaker constant facilitated formation of the surface gel layer and accelerated zeolite crystallization. Aluminum added to the solution or leached from alumina substrates had dual effects, to induce surface gelation and to retard crystallization of that layer as well as crystallization in the bulk solution.

Growth of ZSM-5 membranes was facilitated by using alumina tubes pre-coated with silicalite seeds. Accompanied with gradual growth of an external polycrystalline layer, siliceous deposits accumulated as deep as 100 [...] inside the pores of the support, converting gradually from amorphous to crystalline. Pure gas permeation results are presented for membranes prepared in a solution of composition SiO2: 0.15TPAB4: 0.7NaOH: 98H2O using 0.4 and 2 [...] seeds.

Organic-free hydrogel reaction mixtures were further used to grow ZSM-5 membranes on seeded porous alumina substrates, eliminating the crack-prone calcination step for removing organic TPA+ templates from as-synthesized ZSM-5. The optimum composition SiO2: 0.0125Al2O3: 0.2675Na2O: 46H2O was identified to produce membranes with permeation selectivities for H2 over n-butane above [...] and for O2 over N2 9-10. The permeation was strongly activated with the activation energies increasing sharply with molecular size.

Parallel synthesis of zeolite films was developed to expedite composition screening. The films prepared in an array reactor of multiple wells each containing 35 micro-liter synthesis solution displayed morphology similar to that produced by the conventional synthesis. The method was applied to explore the composition space of clear, organic-free synthesis solutions for ZSM-5 films growth: SiO2: (700-300)Al2O2: (0.5-0.7)NaOH: 80H2O.

Item Type:Thesis (Dissertation (Ph.D.))
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Gavalas, George R.
Thesis Committee:
  • Unknown, Unknown
Defense Date:24 July 2000
Record Number:CaltechETD:etd-11102005-103556
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:4490
Deposited By: Imported from ETD-db
Deposited On:10 Nov 2005
Last Modified:02 Dec 2020 02:49

Thesis Files

PDF (Lai_r_2001.pdf) - Final Version
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