DEVELOPMENT OF POL YPHENYLENE OXIDE-SILICOALUMINOPHOSPHATE MIXED MATRIX MEMBRANES FOR GAS SEPARATION

This present research has developed new flat sheet dense mixed matrix membranes
(MMM) that were comprised of poly (2,6-dimethyl-1,4-phenyleneoxide) (PPO) as
polymer matrix and three different silicoaluminophosphates (SAPO) namely pure
SAPO, sodium glycinate drived SAPO (GlyNa-SAPO) and aminopropyl
triethoxysilane modified SAPO (APTES-SAPO) as molecular sieves via the solution
casting method. Morphological analysises have shown that the newly developed
MMMs provide evidence for good interfacial contact between the PPO polymer and
the particles (SAPO, GlyNa-SAPO and APTES-SAPO) loadings at 2 wt.% and 5
wt.%. It was also found out that the introduction of the aforementioned molecular
sieves into the PPO matrix improved the thermal stability of the newly developed
MMMs over the PPO homogenous membrane. The differential scanning calorimetry
(DSC) results showed that when the loadings of the (SAPO, GlyNa-SAPO and
APTES-SAPO) molecular sieves increased from 2 wt.% to 10 wt.%, the glass
transition temperature (T g) of MMMs also increased from 223.29°C to 225.83°C
indicating the presence of rigidification effect. It was also found out that the annealing
treatment has improved the thermal stability (thermal degradation temperature) and
the Tg of the newly developed MMMs over unannealed membranes. The Fourier
transform infrared (FTIR) analysis has also showed that the introduction of the SAPO,
GlyNa-SAPO and APTES-SAPO functional groups and their specific interactions
present in the PPO matrix. The gas permeation studies of the newly developed
MMMs (SAPO-PPO, GlyNa-SAPO-PPO and APTES-SAPO-PPO) showed better gas
separation performance in terms of ideal selectivity (C02/CH4 and C02/N2) over the
homogenous PPO membranes. However, it was found that the addition of2 wt% to 10
wt% loading of the SAPO, GlyNa-SAPO and APTES-SAPO molecular sieves
decreased the permeance of the tested gases over the PPO homogenous membrane.
Within a pressure range of (2-1 0) bar, the permeation of C02 across the MMMs
increased in the order of APTES-SAPO-PPO MMMs followed by GlyNa-SAPO-PPOMMMs and SAPO-PPO MMMs, respectively. However, the permeation slightly
decreased in the order APTES-SAPO-PPO MMMs followed by GlyNa-SAPO-PPO
MMMs and SAPO-PPO MMMs for N2 and CH4 gases, respectively. From the newly
developed twelve MMMs, the best ideal selectivity of target gases was found in
APTES-SAPO-PPO MMMs at 10 wt.% loadings and 10 bar as much as 23.90 and
5.65 for the respective gas pairs of C02/CH4 and COz/Nz system. It was also found
out that the annealing treatment at temperature of 235 °C reduced the permeance of
target gases but improved the ideal selectivity of target gases (COz/CH4 and COz/Nz)
of the developed MMMs compared with PPO homogenous membrane. The highest
ideal selectivity achieved was found in annealed APTES-SAPO-PPO MMMs at 10
wt.% loadings and 10 bar with the values of 26.89 and 7.54 for the respective gas
pairs of COz/CH4 and COz/Nz system, respectively. A modified Pal model which is
developed in this work by taking into account of the presence of the interfacial
rigidified matrix chain effect has been able to predict well the permeability and
selectivity of these new MMMs. The permeation data of the newly fabricated poly
(2,6-dimethyl-1 ,4-phenylene oxide )-SAPO MMMs were used for further validation of
the newly developed model. Based on the computation, AARE % was found less than
I%. Hence, the present developed model proved that the permeability and the
selectivity of gases through non-ideal MMMs, could be predicted accurately.