Why is it so extremely difficult to prepare shape-selective Al-rich zeolite membranes like LTA and FAU for gas separation?

Research output: Contribution to journal › Article › Research › peer review

Authors

  • J. Caro
  • D. Albrecht
  • M. Noack

Research Organisations

External Research Organisations

  • Leibniz Institute for Catalysis (LIKAT Rostock)
  • University of Rostock
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Details

Original languageEnglish
Pages (from-to)143-147
Number of pages5
JournalSeparation and Purification Technology
Volume66
Issue number1
Early online date24 Nov 2008
Publication statusPublished - 7 Apr 2009

Abstract

Two possible reasons for the difficulty to prepare shape-selective Al-rich zeolite membranes for gas separation are discussed. One reason is the strongly negative electric surface charge of Al-rich zeolites like LTA or FAU in aqueous media as found by zeta potential (ZP) measurements of suspended zeolite powder. This negative surface charge is expected to prevent the negatively charged silica species to enter the slits between the growing crystallites in a zeolite membrane layer. This effect can be avoided by adsorption of positively charged species called intergrowth supporting substance (ISS) neutralizing the electric surface charges of the growing zeolite membrane surface. Another problem for Al-rich membranes are extreme mismatches in the expansion coefficients between the zeolite layer and the ceramic or metal support upon drying the as synthesized membranes. The as synthesized FAU or LTA membrane layers contain water. We have simulated a membrane activation in the permeation cell by drying zeolite powder and recording in situ the XRD spectra. We found huge expansion and shrinking effects during the in situ de-watering of LTA and FAU powder samples. This observation is correlated with the experimental finding continuous damage of model membranes upon repeated re-activation cycles in vacuum at 150 °C. The model membranes consisted of a few large LTA and FAU crystals embedded into epoxy resin. After each de-watering step, (i) the fluxes of CO2, CH4 and N2 increased and (ii) the ideal selectivities decreased which indicates a continuous membrane damage. However, these semi-damaged LTA and FAU membranes can still separate water from alcohols but do not show any gas separation.

Keywords

    FAU zeolite membranes, Ideal permselectivity, Intergrowth supporting substances, LTA, Mismatch expansion behavior, Mixture separation factor, Permporometry, Zeta potential

ASJC Scopus subject areas

Cite this

Why is it so extremely difficult to prepare shape-selective Al-rich zeolite membranes like LTA and FAU for gas separation? / Caro, J.; Albrecht, D.; Noack, M.
In: Separation and Purification Technology, Vol. 66, No. 1, 07.04.2009, p. 143-147.

Research output: Contribution to journal › Article › Research › peer review

Caro J, Albrecht D, Noack M. Why is it so extremely difficult to prepare shape-selective Al-rich zeolite membranes like LTA and FAU for gas separation? Separation and Purification Technology. 2009 Apr 7;66(1):143-147. Epub 2008 Nov 24. doi: 10.1016/j.seppur.2008.11.009
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AU - Albrecht, D.

AU - Noack, M.

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