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This study aimed to improve surface polarity of polydimethylsiloxane (PDMS) membranes and provide surface active sites which were easy to react with other chemicals. 3-Aminopropyltriethoxysilane (APTES) containing an amino group was introduced into a PDMS membrane by crosslinking to prepare polyacrylonitrile hollow fiber-supported PDMS membranes with an amino-functionalized surface. Fourier transform infrared and X-ray photoelectron spectroscopic analyses proved the existence of APTES and its amino group in the PDMS membrane. The concentration of N atoms on the PDMS membrane surface reached ∼6% when the mass ratio of APTES/PDMS oligomer in the PDMS coating solution was increased to 4/3. The water contact angle decreased from ∼114° to ∼87.5°, indicating the improved surface polarization of the PDMS membrane. The density and swelling degree of the PDMS membrane decreased and increased, respectively, with increasing APTES content in PDMS. This phenomenon increased CO 2 permeability and decreased CO 2 /H 2 selectivity, CO 2 /CH 4 selectivity, and CO 2 /N 2 selectivity. When the mass ratio of APTES/PDMS oligomer was increased from 0 to 4/3, the CO 2 permeation rate of the hollow fiber-supported PDMS membranes initially decreased from ∼2370 GPU to ∼860 GPU and then increased to ∼2000 GPU due to the change in coating solution viscosity.

To research effects of CO 2 absorption capacity and type of CO 2 absorbent on the CO 2 separation and free-volume properties of facilitated transport membranes, two types of CO 2 absorbents, namely monoethanolamine (MEA) and ionic liquids (ILs:[P 66614 ][Triz] and [P 66614 ][2-Op]), were adopted. The CO 2 absorption capacities of MEA, [P 66614 ][Triz] and [P 66614 ][2-Op] were about 0.561 mol CO 2 per mol, 0.95 mol CO 2 per mol and 1.60 mol CO 2 per mol, respectively. All mean free-volume hole radiuses of membranes decreased after blending CO 2 absorbents. After polymer membrane blended with two ILs, number of free-volume hole increased, resulting in modest increase of the fractional free volume. Both CO 2 permeability and selectivity increased after blending MEA and ILs. The increasing range of CO 2 permeability corresponded with CO 2 absorption capacity of CO 2 absorbents, and membrane blending with [P 66614 ][2-Op] showed the highest CO 2 permeability of 672.1 Barrers at 25 °C. Pebax/PEGDME membrane blending with MEA obtained the highest CO 2 /H 2 and CO 2 /CH 4 selectivity at 17.8 and 20.5, respectively.

Mixed matrix membranes with ionic liquids and molecular sieve particles had high CO 2 permeabilities, but CO 2 separation from small gas molecules such as H 2 was dissatisfied because of bad interfacial interaction between ionic liquid and molecular sieve particles. To solve that, amine groups were introduced to modify surface of molecular sieve particles before loading with ionic liquid. SAPO 34 was adopted as the original filler, and four mixed matrix membranes with different fillers were prepared on the outer surface of ceramic hollow fibers. Both surface voids and hard agglomerations disappeared, and the surface became smooth after SAPO 34 was modified by amine groups and ionic liquid [P 66614 ][2-Op]. Mixed matrix membranes with composites of amine-modified SAPO 34 and ionic liquid exhibited excellent CO 2 permeability (408.9 Barrers) and CO 2 /H 2 selectivity (22.1).