Fluorocarbon functionalized SAPO-34 zeolite incorporated in asymmetric mixed matrix membranes for carbon dioxide separation in wet gases

• Fluorocarbon modification on SAPO-34 resulted great hydrophobicity.
• MMM with modified SAPO-34 exhibited good adhesion between filler and polymer phase.
• Fluorocarbon modification reduces competitive water adsorption in CO2 separation.

In order to sustain the performance of mixed matrix membrane (MMM) in the separation of wet gases such as biogas, water-resistant MMMs were fabricated by incorporating fluorocarbon functionalized SAPO-34 zeolite into polysulfone (PSf). 1H,1H,2H,2H-perflourodecyltriethoxysilane (HFDS) was used to convert the hydrophilic SAPO-34 zeolite into hydrophobic SAPO-34 zeolite to avoid competitive adsorption of moisture. After dispersing the modified filler in polymer solution, asymmetric MMMs were fabricated via dry–wet phase inversion. N2 adsorption–desorption test and thermal gravimetric analysis indicated that fluorocarbon modification generated minimum impact on the surface area and CO2 adsorption capability of SAPO-34 zeolite. The water contact angle on SAPO zeolite increased from 33° to 130° after modification, while the membrane hydrophobicity was enhanced about 17.64%. The MMM with 10 wt.% of modified SAPO-34 zeolite (PSf-10/HFDS 1.0) exhibited good adhesion between filler and polymer phases, minimizing defect such as interface voids. PSf-10/HFDS 1.0 MMM also showed great enhancement in ideal gas separation (ideal selectivity CO2/CH4 of 38.9 with CO2 permeance of 278 GPU) compared to the neat PSf membrane and MMMs with unmodified SAPO-34 zeolite. In addition, PSf-10/HFDS 1.0 MMM showed actual gas selectivity at wet condition which is similar to its dry mixed-gas selectivity (2% reduction only). The mixed-gas separation performance for PSf-10/HFDS 1.0 MMM was even sustained in both dry and wet conditions during long-hour test. Compared to the dry mixed-gas results, MMM incorporated with 10 wt.% of unmodified SAPO-34 (PSf-10) suffered more than 90% reduction in separation performance during wet mixed-gas test.

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