Highly concentrated multivariate ZIF-8 mixed-matrix hollow fiber membranes for CO₂ separation: Scalable fabrication and process analysis

Here, we report on the fabrication of mixed matrix hollow fiber membranes (MMHFMs) for CO₂ separation using highly-concentrated 6FDA-DAM/triple-ligand, amine-modulated zeolitic imidazolate framework-8 (TAZIF-8) (60/40 w/w) via a dip coating process. The application of a γ-alumina interlayer serves a dual purpose of reducing the infiltration of the 6FDA-/TAZIF-8 coating solution into the porous α-alumina support, while also providing a smooth surface for the support. Importantly, the co-solvent comprising N-methyl-2-pyrrolidone and dichloromethane further inhibits the formation of defects by maintaining an appropriate balance of volatility and polarity. This balanced combination is crucial in promoting phase separation and facilitating the dispersion of nanofillers within the polymer matrix, enabling the formation of a thin defect-free selective layer. The subsequent 40 wt% TAZIF-8 MMHFM attains superior CO₂ separation performance to most existing MMHFMs (CO₂ permeance of 648 GPU and CO₂/N₂ and CO₂/CH₄ selectivity of 39.0 and 34.2, respectively). Furthermore, it maintains excellent CO₂ separation performance over 120 d owing to good interfacial interaction between 6FDA-DAM and TAZIF-8s. Last, but not least, our process analysis reveals that the introduction of the TAZIF-8 MMHFM into the first stage of a dual-stage membrane process can improve the total energy demand for post-combustion CO₂ capture due to its excellent CO₂/N₂ selectivity. Our current study provides significant progress toward the industrial application of post-combustion CO₂ capture.