T. Battal et al., EFFECT OF FEED COMPOSITION ON THE PERFORMANCE OF POLYMER-ZEOLITE MIXED MATRIX GAS SEPARATION MEMBRANES, Separation science and technology, 30(11), 1995, pp. 2365-2384
An emerging membrane morphology with future potential is mixed matrix
membranes composed of two interpenetrating matrices of different mater
ials. In this study, mixed matrix membranes of an amorphous glassy pol
ymer(polyethersulfone) and hydrophilic zeolite (4A) were prepared. An
elaborate membrane preparation technique that enables incorporation of
high zeolite loading into the membrane was developed. Performance of
membranes was tested by using a laboratory-scale gas separation appara
tus. The permeation rates of N-2, CH4, Ar, O-2, CO2, and H-2 were eval
uated through a dense homogeneous PES membrane and a PES-4A mixed matr
ix membrane. For the mixed matrix membrane, gas permeabilities were ei
ther not changed or significantly improved. The ideal separation facto
rs of economically important gas pairs were substantially increased du
e to the faster permeation of H-2 and CO2 through the mixed matrix mem
brane. In order to understand their interaction with each ether and wi
th membrane matrices, permeabilities and selectivities of CO2/CH4, CO2
/Ar, and H-2/CH4 binaries as a function of gas composition were measur
ed through a dense homogeneous PES membrane and a PES-4A mixed matrix
membrane. Observed selectivity independence with respect to gas compos
ition for a dense homogeneous PES membrane indicates that ternary inte
ractions and factors like plasticization and gas fugacity do not affec
t the gas permeation mechanism appreciably for this type of membrane.
However, selectivities demonstrated a strong concentration dependency
through a PES-4A mixed matrix membrane. For CO2/CH4 and CO2/Ar systems
, when the CO2 concentration in the feed increased, selectivity decrea
sed linearly. In the case of H-2/CH4 binaries, unlike the cases with C
O2 binaries, a higher H-2 concentration in the feed caused higher sele
ctivity values, The trend was also linear with H-2 concentration in th
e feed. This indicates that. for mixed matrix membranes, the existence
of a third component causes the gas molecules to interact with the he
terogeneous membrane matrix, affecting selectivities. Selectivity depe
ndency indicates the importance of gas-membrane matrix and gas-gas-mem
brane matrix interactions.