Page 497 - Book Hosokawa Nanoparticle Technology Handbook

12 ZEOLITE MEMBRANE APPLICATIONS

Vapor
Membrane

Gel

Solution

Figure 12.3
Schematic experimental flow for the synthesis of zeolite membranes by the dry-gel conversion method.

into the gel layer with reaction time. A representative 10 − 4
experimental set-up is schematically illustrated in
Fig. 12.3 for the dry-gel conversion method. 10 − 5

The synthesis of ultra-thin zeolite membranes with (a)
both dense body and orientation is still difficult, 10 − 6
although dense membranes without orientation or ori- Permeance (s −1 m −2 Pa −1 )
ented membranes without pinhole-free microstructure − 7
have been synthesized until now. However, since 10
recent progress in microstructure-controlling tech-
nologies including nanotechnology is dramatic, it is 10 − 8
expected that synthesis of pinhole-free and oriented
ultra-thin zeolite membranes with thickness in a − 9
nanoscale is achieved in no distant future. 10

3. Separation properties of zeolite membranes 30
Zeolite membranes have the potential for continuous (b)
separation of gas, vapor and non-aqueous mixtures. 20
Various attempts have been reported. For example,
hydrophilic A-type zeolite membranes with excellent CO 2 /N 2 selectivity
separation properties for alcohol dehydration and sol-
vent dewatering have been applied to production of 10
bio-ethanol and dehydration of waste isopropyl alco-
hol. The dehydration of isopropyl alcohol in pervapo-
ration process using the A-type zeolite membranes is
the first commercial application of zeolite mem- 0 0 5 10 15 20 25
branes.
On the other hand, gas separation using zeolite Treatment time (h)
membranes has been limited for practical applica-
tions. One of the reasons comes from the difficulty in Figure 12.4
syntheses of zeolite membranes. Recently, selective Permeance changes found for Y-type zeolite membranes in
separation of p-xylene from xylene isomers has been the binary mixture of CO and N as a function of
2
2
reported on MFI zeolite membranes, and evaluation hydrothermal reaction time for the secondary growth of
of MFI membranes for xylene separation has been precursors formed electrophoretically (a) permeances of
made from the industrial side. CO ( ) and N ( ) and (b) the CO /N selectivities.
2
2
2
2
As mentioned above, various types of separation
can be expected using zeolite membranes, because of Fig. 12.4 shows the permeances of N and CO and
2
2
the unique physical and chemical properties of zeo- the CO /N selectivities in the binary mixture for Y-type
2
2
lites. In this part, separation of CO from a binary zeolite membranes. Membranes with thickness of about
2
mixture of CO and N on Y-type zeolite membrane is 35 m synthesized by secondary growth of elec-
2
2
reported. The selective separation of CO results from trophoretically fabricated Y-type zeolite precursor films
2
a difference in affinity of CO and N to pore walls of were used [5]. The values on the abscissa in Fig. 12.4
2
2
the Y-type zeolite crystal. indicate the hydrothermal treatment times for the
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