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

4 Results and discussion
The carbon content (≡ cage occupancy) after calcination is lower if titanium had been
present in the gel composition. In addition, more cages are emptied after the calcination
at 900ºC when the crystallisation is performed for smaller DOH crystals. This is indicated
by comparing the samples Ti-2 with sample Ti-4 (Table 17). The reduced path length
(smaller crystals) the combusted species have to travel until they are expelled from the
crystal show a significant contribution to the final cage occupancy.
A broad exothermic peak in the temperature range of 300 to 600ºC is observed for the all
silica DOH sample (Figure 32). The addition of titanium to the gel resulted in an even
broader exothermic peak extending to about 900ºC. The TG results are in agreement with
the DTA results. The addition of titanium results in weight loss of ~5 wt % in the range
of 100-900ºC which is a factor 2 higher compared to the undoped DOH.
DTA in µV/mg
0,0
-0,1
-0,2
-0,3
-0,4
-0,5
exo
D1H
Ti-D1H
100 200 300 400 500 600 700 800 900
92
1000
Temp [ºC]
Figure 32 DTA/TG plots of DOH as function of titanium incorporation.
The decrease in remaining carbon and the larger weight loss as observed by TG suggest
that the small amount of titanium which was added to the synthesis gel has an influence
on the calcination product. Whether this can be explained by catalytic oxidation is still
unclear. This hypothesis should be studied in more detail.
3) Calcination of Ball milled DOH
The smallest synthesised DOH crystal size is in the order of 10 µm. Reducing the crystal
size is attractive for SDA removal and beneficial for the formation of thin DOH layers.
The expulsion of the organic remains from the D1H crystal during the calcination could
61
108
104
100
96
TG weight %