Inorganic Microporous Membranes for Gas Separation in Fossil Fuel ...

4 Results and discussion
4.2 Zeolite materials and layers
All silica clathrasil 8-ring deca-dodecasil 3R (DDR) zeolite type might be a potential
membrane material to separate CO2 from other gasses. 6-ring dodecasil 1H (DOH), also
an all silica clathrasil, could be an interesting membrane material for H2 to CO2
separation.
First, DDR syntheses results will be described briefly. Second, the successful syntheses
of DOH will be described including the results to obtain quasi SDA-free DOH structures,
followed by a discussion on the formation of secondary grown DOH layers on α-Al2O3
supports.
4.2.1 Deca-dodecasil-3R synthesis
Deca-dodecasil-3R (DDR) is not commercially available but can be synthesised from
silicon precursors which are hydrolysed in the presence of the structure directing agents
(SDA) at high pH. These reactions are performed in Teflon lined steel autoclaves at high
temperatures for several days. Aminoadamantane (ADA) is the most frequently used
known SDA for the formation of DDR.
Dodecasil-1H is one of the competing phases of DDR using the same gel composition. 60
DOH is synthesised at temperatures above 190ºC while DDR requires synthesising
temperatures in the range of 160-170ºC.
Table 12 presents the obtained phases as a function of the synthesis temperature. It shows
shown that DOH is synthesised at higher temperatures. Changing the gel composition did
not result in single phase DDR zeolite material. Different polymorphs of DOH, SGT and
DDR (SGT is zeolite type Sigma 2) are formed at temperatures below 200ºC, as seen in
Figure 26 A and B.
A)
Polymorphs
Figure 26 A) Optical microscope image of polymorph products obtained at 170ºC for 25 days. B) DOH-
DDR polymorphs found by den Exter et al. 67 .
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B)