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This report demonstrates the fabrication of a composite hollow fiber membrane that efficiently recovers dissolved methane (dCH 4) from anaerobic wastewater treatment effluents via membrane contactor (MC) process. We first fabricated highly porous hollow fiber membranes (∼85% porosity) using polyvinylidene difluoride (PVDF). Then, we coated the whole structure (bulk), or lumen side of PVDF supports with polydimethylsiloxane (PDMS), a hydrophobic polymer possessing high gas permeability. The adjustment of the concentration of PDMS precursor mix could effectively serve for tuning the performance characteristics of MC membranes and helped suppress membrane wetting, a major performance-reducing factor. Despite their denser skin layers, the lumen-modified membranes demonstrated superior dCH 4 recovery flux. Mass transfer analyses have confirmed the importance of preserving bulk porosity while coating the membrane surfaces. The long-term performance tests performed using actual anaerobic effluents suggested that the PDMS coating did not accelerate fouling, such that the lumen-modified MC membranes showed an almost steady flux for 8 days with an anaerobic membrane bioreactor effluent. A high-strength effluent, obtained from an up-flow anaerobic sludge blanket reactor, induced faster fouling. However, we observed only a ∼20% flux decline in a 10-day operation. Thus, we propose that the designed PDMS-PVDF composite membranes are promising for industrial practices. Image 1 • We prepared PDMS-coated PVDF porous hollow fiber membranes for membrane contacting. • Both lumen- and bulk-modified PVDF membranes were successful in methane recovery. • Lumen-modified PDMS-PVDF membrane outperformed commercial PP and PDMS membranes. • Lumen-modified PVDF achieved long-term performance with actual anaerobic effluents. [ABSTRACT FROM AUTHOR]

Gas-liquid membrane contactor (GLMC) has been regarded as a promising alternative to conventional contacting processes for CO 2 absorption. In this work, a composite hollow fiber (HF) membrane with an aminosilane-modified zeolitic imidazolate framework-8 (mZIF-8) based dense skin layer was designed and synthesized for high-efficiency biogas upgrading in the GLMC process, by dispersing mZIF-8 nanocrystals into poly(dimethylsiloxane) matrix and then depositing on a porous polyvinylidene fluoride (PVDF) substrate. (3-aminopropyl)triethoxysilane was introduced to modify the ZIF-8 nanocrystals, thereby enabling the chemical bonding with PDMS chains for avoiding interfacial voids and further enhancing hydrophobicity. Compared with the control membrane, the newly developed mZIF-8 based composite membrane with a dense skin exhibited competitive hydrophobicity with a contact angle of 130°, ensuring its anti-wetting ability. It exhibited an enhanced biogas upgrading performance with the absorption fluxes of 2.3 and 3.8 × 10−3 mol m−2·s−1 using water and 1 M monoethanolamine (MEA) as absorbents, respectively (liquid velocity = 0.25 m s−1). In particular, a comparable selectivity of CO 2 /CH 4 with the value of ∼20 was achieved by using MEA as absorbent in the GLMC process. A robust long-term stability of the mZIF-8 based composite HF membrane was also achieved in a 15-day operation. This work offers a new perspective for promoting CO 2 mass transfer with mZIF-8 based composite HF membranes, thereby improving the biogas upgrading performance in GLMC applications. • A composite hollow fiber membrane with a ZIF-8 based dense skin layer was designed and synthesized. • The ZIF-8 nanocrystals were modified to cross-link with PDMS chains for further hydrophobicity enhancement. • The newly developed membrane exhibited competitive hydrophobicity, ensuring its anti-wetting ability. • An enhanced biogas upgrading performance was achieved in gas-liquid membrane contact applications. [ABSTRACT FROM AUTHOR]

Abstract A highly-efficient zeolitic imidazolate framework-8 (ZIF-8) embedded polydimethylsiloxane (PDMS) mixed matrix membrane (MMM) supported by a polyvinylidene fluoride (PVDF) nanofibrous substrate was developed for phenol removal in an aqueous-aqueous membrane extractive process. Homogeneous nano-scaled dispersion of ZIF-8 in the PDMS matrix was achieved by direct incorporation without intermediate drying process, where the interaction of the randomly-moved nanofillers could be prevented, leading to evenly dispersed ZIF-8 nanofillers and defect-free ZIF-8@PDMS/PVDF nanofibrous composite membranes. The newly-developed ZIF-8@PDMS/PVDF membrane exhibited an exceptionally high overall mass-transfer coefficient, k 0 of 35.7 ± 1.1 × 10−7 m/s, doubling that of the pristine membrane in the membrane extractive process. The high performance was maintained for over 360 h without loss of salt rejection. These results could be attributed to the organophilic-assisted "bi-mode" transporting mechanism of ZIF-8 nanofillers in PDMS matrix, namely: (1) the solution-diffusion transport mode; (2) the pore-flow transport mode, where the synergistic effects are expected to significantly improve the phenol transfer efficiency through the membranes. Overall, the results achieved in this work demonstrate promising potential of highly-efficient ZIF-8@PDMS/PVDF nanofibrous composite membranes used for aqueous-aqueous membrane extractive processes for organic-containing wastewater treatments. Highlights • A drying-free method for incorporating ZIF-8 nanofillers into membrane was proposed. • The membrane is used for phenol removal in membrane extractive process. • Presence of ZIF-8 nanofillers in PDMS matrix enhances mass transfer efficiency. • Membrane properties can be tuned by controlling ZIF-8 nanofillers doping. [ABSTRACT FROM AUTHOR]