Fabrication of polyimide mixed matrix membranes with asymmetric confined mass transfer channels for improved CO2 separation
2021
Wang, Ting | Jiang, Ling-li | Zhang, Yan-ling | Wu, Li-guang | Chen, Hua-li | Li, Chun-juan
Narrow-mesoporous SiO₂ with ordered helical channels (pore size less than 10 nm) was prepared via a soft template method. Thereafter, the polyimide (PI) mixed matrix membranes (MMMs) incorporated with helical-mesoporous SiO₂ were used for CO₂ separation. Characterization results show that the formation of asymmetric helical channel structures in narrow-mesoporous SiO₂ increased the defect structures and the hydroxyl groups on the pore surface, thus enhancing the affinity between CO₂ molecules and SiO₂. Due to the stronger CO₂ capture ability, the addition of helical-mesoporous SiO₂ introduced confined mass transfer channels into the polymer matrix for facilitated transport of CO₂, thus significantly enhancing the CO₂ separation ability of MMMs. Increasing the loading content of helical-mesoporous SiO₂ not only increased the confined channels to facilitate CO₂ transport, but also improved the CO₂ capture ability of MMMs, thus enhancing their CO₂ selectivity. The gas permeability and CO₂/N₂ ideal selectivity calculated using the Maxwell-Wagner-Sillar model, assuming the helical-mesoporous SiO₂ as a collection of parallel helical channels, agreed well with the experimental data of MMMs at low loading content of SiO₂. When the loading content exceeded 15 wt%, the SiO₂ aggregations caused the formation of non-selective voids in membranes, significantly lowering the CO₂/N₂ ideal selectivity.
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