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

4 Results and discussion
the α-Al2O3 support and the DOH layer (Figure 40-B). The delamination is likely a result
of the stresses occurring during the heat-treatment of 700ºC.
The thickness of the DOH layer is in the range of 50 to 80 µm. No DOH nuclei can be
distinguished which could have grown into crystals of 10-20 µm in size (Figure 40-C).
The thickness/width ratio is about 10, indicating thin plates. Figure 40-C presents a
highly porous zeolitic area close to the α-Al2O3 surface and on the membrane surface. A
more dense area is observed between these porous layers and is magnified (Figure 40-D).
The intercrystalline channels transport liquids despite the dense areas in the zeolitic layer.
A B
DOH
α-Al2O3
C D
DOH
Figure 40 Cross section SEM images of DOH layer on α-Al2O3 support. A) presents the full thickness of the
membrane. The zeolitic layer is delaminated. B) higher magnification resulting. C) orientation of the zeolite
crystals on the α-Al2O3 surface and D high density area of the zeolitic layer.
The DOH crystals are present on the α-Al2O3 surface. The alumina layer did not contain
any silicon and the zeolitic layer was free of any aluminium. This indicates that all-silica
DOH can be prepared on alumina supports without interfering.
Striking is the crystallisation time if compared to other synthesis attempts. While a
crystallisation time with a minimum of 4 days is required to form highly crystalline DOH
68
DOH
α-Al2O3
DOH