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

5 Conclusions and recommendations
5 Conclusions and recommendations
First, this chapter includes the conclusions of the studied zeolite materials. The basic aim
was to prepare zeolite material that could separate gasses by molecular sieving.
Recommendations on the zeolite materials are discussed to achieve this goal.
Second, the results on sol-gel derived TiO2-ZrO2 sols, bulk materials, layers and
membranes are summarised and related to the preparation of the TiO2-ZrO2 gas
separation membrane goal. Additionally, suggestions for further research are outlined to
achieve industrial goals.
8-ring Deca-dodecasil 3R and 6-ring Dodecasil 1H zeolite materials
Deca-dodecasil 3R (DDR) hydrothermal synthesis is complex and formed zeolite
mixtures of DDR with DOH or SGT (Dodecasil 1H or Sigma 2). The synthesis of DDR
as a potential CO2/N2 separation membrane material was unsuccessful. Further syntheses
with varying gel compositions of nutrients from several suppliers and reaction conditions
should be performed in order to understand how to prepare single phase DDR.
Dodecasil 1H (DOH) crystal synthesis, structure directing agent (SDA) free synthesis and
SDA-free DOH by means of post synthesis treatments were performed to prepare allsilica
zeolite material with pores inaccessible to gasses with the exception of gasses with
a kinetic diameter of H2 or smaller.
DOH can be synthesised under standard conditions (Teflon lined autoclave heated
under static conditions, 200°C, gel composition: 100SiO2:9-11ADA:70-270EN:3000-
7400H2O forming crystals >100 µm). Changing the synthesis conditions from static to
dynamic by means of autoclave rotation or stirring the gel in situ to obtain a more
homogeneous gel mixture reduces the DOH crystallisation time from 21 days to 4 days
coupled with a decrease in crystal size. The DOH crystal size can also be reduced by
aging the gel at 80ºC for several hours before hydrothermal crystallisation at 200ºC. The
DOH nucleation and growth can be decoupled.
The DOH crystal size can be reduced to thin hexagonal plates with sizes in the order of
10 µm being too large for membrane formation or to act as seeds for the layer formation
by means of the secondary growth of DOH nuclei. The DOH crystal size might be
synthesised smaller by means of further crystallisation optimisation. This might be
accomplished by changing the gel composition, aging of the gel and reaction condition
such as the heating ramp and stirring/rotating conditions.
Secondary growth of DOH crystals in gel composition with the absence of SDA
was unsuccessful. Low DOH yield was obtained using a small amount of SDA in the gel
composition. These synthesised DOH crystals have a ~75% SDA cage occupancy. SDAfree
DOH synthesis by means of seeded synthesis was not obtained. This proposed
110