Zeolite membranes are attractive materials to separate gas and liquid mixtures.
MFI is a widely studied zeolite type due to its ease of preparation and
comparable pore size with the molecular size of many substances. In this
study MFI type membranes were synthesized over porous & / #945 / -Al2O3 supports
and characterized with XRD, SEM and gas permeation measurements.
In the first part of this study the effect of soda concentration of the synthesis
solution on the membrane morphology and crystal orientation was investigated.
The synthesis was carried out from solutions with a molar composition of (0-
6.5)Na2O:25SiO2:6.9TPABr:1136H2O at 150oC. At soda concentrations
between 0.45 and 1.8 the membrane layers with (h0h)/c-directed orientation
were obtained. At lower and higher soda concentrations membrane layer
formed from randomly oriented crystals. The (h0h)/c-oriented membranes
showed H2/n-C4H10 ideal selectivities of 478 and 36 at 25° / C and 150° / C,
respectively.In the second part, MFI membranes were synthesized from mixtures with
different concentrations of template molecules. Tetrapropylammonium
hydroxide, tetrapropylammonium bromide or mixture of both types were used
as template. The nucleation period, the size of MFI crystals, membrane
thickness decreased as the tetrapropylammonium hydroxide concentration
increased. Besides conversion of SiO2 in the synthesis solution to MFI passed
through a maximum with increasing concentration of tetrapropylammonium
hydroxide in the synthesis solution. When tetrapropylammonium bromide
was used as template thicker membranes were obtained.
In the third part MFI type membranes with a thickness of 1.5-2 & / #956 / m were
synthesized by mid-synthesis addition of silica to the synthesis medium. The
membranes synthesized with and without mid-synthesis addition of silica have
n-C4H10/i-C4H10 ideal selectivities of 47 and 8 at 100oC, respectively. The
change of composition during the synthesis increases the crystal growth rate
and the size of the crystals forming the membrane, thus better quality
membranes can be obtained by mid-synthesis addition of silica to the synthesis
medium.
In the last part of this study, thin MFI type zeolite membranes were synthesized
in a recirculating flow system at 95° / C on the inner side of the tubular & / #945 / -
alumina supports. A membrane synthesized by two consecutive synthesis steps
had a separation selectivity of 38 and 86 for equimolar mixtures of n-
C4H10/CH4 and n-C4H10/N2 at 25oC, respectively. The membrane selectively
permeated large n-C4H10 over small CH4 and N2, suggesting that the separation
is essentially adsorption-based and the membrane has few nonselective
intercrystalline pores.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/12610603/index.pdf |
| Date | 01 June 2009 |
| Creators | Soydas, Belma |
| Contributors | Kalipcilar, Halil |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | Ph.D. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for public access |
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