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

4 Results and discussion
Table 14 DOH synthesis conditions presenting the molar ratio of the gel composition and the crystallisation
time in days.
SiO2:ADA:EN:H2O Crystallisation conditions Obtained phase
Days Temp. ºC
100:47:420:5500 11 200 SGT
100:47:420:5500 11 ~190 DOH/DDR
100:23:267:7405 24 200 DOH+Gel
100:11:267:7405 27 200 DOH
Table 15 Gel composition with molar ratio 100SiO2:xADA:267EN:yH2O syntheses crystallised at 200ºC
static or dynamic agitation with resulting products.
Gel Crystallisation Product
composition conditions
x y days Agitation
5.5 7405 10 Rotation DOH
5.5 7405 20 Rotation DOH
11 7405 24 Static DOH
23 7405 24 Static DOH+gel
11 3000 24 Static DOH
11 1000 21 Static DOH+gel
The time for complete DOH crystallisation can be reduced from 21 to 7 days by rotating
the autoclave. The crystallisation time was further reduced to only 4 days by stirring the
gel in situ (Table 16). Increasing the gel homogeneity clearly decreases the crystallisation
time. The DOH crystallisation under stirring was further studied for the gels, containing
ammonia instead of ethylenediamine. The DOH crystallinity, using the NH3 route, does
not increase after 5 days of stirring (Figure 27) at 200ºC. The smallest DOH crystals, in
the range of 5-13 µm in diameter, were obtained using the NH3 route in combination with
autoclave rotation for 18 days (Figure 28).
Table 16 Autoclave agitation crystallisation conditions using 100SiO2:11ADA:267EN:7405H2O gel
composition at 200ºC as function of crystallisation time
Autoclave agitation days Product
Static 21 DOH
14 DOH
7 DOH + Gel
Rotation 7 DOH
Stir 4 DOH
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