HKUST-1, an inexpensive metal–organic framework possessing open metal sites, has a great potential for capture and recovery of SF6. In this work, the structural property of HKUST-1 was modified to yield a hierarchically structured HKUST-1 nanocrystal exhibiting a superior performance with higher SF6 uptake (4.98 mmol g–1 at 25 °C and 1 bar), better SF6/N2 selectivity (∼70 at 25 °C), faster SF6 adsorpton kinetics, and lower energy penalty for regeneration compared to those of bulk HKUST-1 crystal as well as those of conventional zeolite and porous carbon adsorbents. Higher surface area and the presence of mesoporosity to facilitate the transport of SF6 to active sites residing in microporous spaces were found to be key factors contributing to such enhancement. The outstanding potential utility of our HKUST-1 crystal in industrial applications was also validated with an idealized vacuum swing adsorption model.

•5A zeolite was inorganically modifed to increase surface roughness.•Selective uptake of CO2 over CH4 was observed in the surface modifed 5A.•Defect-free mixed-matrix membranes were successfully synthesized.•CO2/CH4 separation properties were improved in mixed-matrix membranes.LTA zeolite with highly roughened surfaces were prepared in an aqueous phase by the ion-exchange-induced growth of Mg(OH)2 nanostructures on the zeolite surfaces. The morphology of LTA crystals was tuned by the systematic modification of reaction parameters such as the pH of the reaction medium and the amount of magnesium loaded in the substrates. After converting surface-modified LTA to 5A, which has been known as a good candidate for selective CO2 uptake and transport, by replacing extra-framework cations remaining in LTA with Ca2+, a series of mixed-matrix membrane incorporating Matrimid® and 5A was fabricated. Owing to improved zeolite/polymer adhesion property along with the selective transport of CO2 by the fillers, mixed-matrix membranes containing surface modified 5A showed enhanced CO2/CH4 separation properties, which were measured by a binary mixture permeation testing. In light of that, a dramatic increase in CO2 permeability (ca. 120%) was observed for Matrimid®/20 wt% 5A membrane which also showed an improved CO2/CH4 selectivity. In contrast, untreated 5A decreased CO2/CH4 selectivity of Matrimid® membrane due to defects formed at zeolite/polymer interfaces.

Two-dimensional (2-D) CuBDC nanosheets (ns-CuBDC) with high-aspect-ratios were deliberately paired with polymers possessing high free volumes to fabricate high performance gas separation membranes. Owing to the molecular sieving effect of the filler, a small ns-CuBDC loading (2–4 wt%) could significantly improve the CO2/CH4 selectivities of membranes, resulting in performances that surpass the upper bound limit for polymer membranes.

•Highly porous hollow fiber substrates were fabricated with Matrimid®.•Fluorinated silica nanoparticles were anchored on the substrate surfaces.•The composite membrane showed an excellent CH4 recovery performance.•The composite membrane demonstrated long-term stability in a membrane contactor.In this study, polymer-fluorinated silica composite hollow fiber membranes were fabricated and applied to a membrane contactor system for the recovery of methane dissolved in the anaerobic effluent. Such composite membranes allowed us to tailor the physical property such as porosity and mechanical strength and the surface hydrophobicity in separated processes. To develop the composite membranes, porous hollow fiber substrates were first fabricated with Matrimid®, a commercial polyimide. Subsequently, fluorinated silica particles were synthesized and anchored on the substrates via a strong covalent bonding. Due to the high porosity as well as the high hydrophobicity, our membrane showed an outstanding performance for the recovery of CH4 in the membrane contactor, such that the CH4 flux reached 2900 mg CH4/m2–h at the liquid velocity of 0.42 m/s at which the liquid phase still controlled the overall mass transfer. The composite membrane prepared in this work also showed a much better performance in the CH4 recovery than a commercial polypropylene membrane made for degasification of water. In addition, a long-term test with tap water saturated with the model biogas made up of 60:40 CH4/CO2 mixture demonstrated that our membrane can be stably operated for more than 300 h without experiencing pore wetting problem.

•A mathematical model to describe the mass transport in membrane contactor for biogas recovery was developed.•The model was validated with experimental results.•Effect of CO2 desorption on the CH4 recovery was studied.•Effects of operation parameters on biogas recovery were investigated.A significant amount of methane (CH4) produced from anaerobic digestions of wastewater is dissolved in liquid effluent and discharged. The recovery of dissolved CH4 is therefore essential in ensuring an enhanced energy production of the anaerobic processes, and minimizing environmental impacts of the greenhouse gas. In this work, a membrane contactor is employed as a mass transfer equipment for the CH4 recovery. A mathematical model considering simultaneous desorption of CH4 and carbon dioxide (CO2) is developed using a resistance-in-series model to calculate the overall mass transfer coefficients. The simulations were validated with experimental results obtained using an in-house fabricated hollow fiber membrane as well as a real effluent from Anaerobic Membrane Bioreactor (AnMBR) and synthetic effluent made of water saturated with biogas. Results showed that the CO2 fluxes were higher than those of CH4 fluxes due to its higher concentration in liquid phase. A decrease of liquid phase mass transfer resistance by an increase in liquid velocity significantly enhanced both CH4 and CO2 fluxes. While, an increase in gas velocity slightly affected the CH4 flux but enhanced the CO2 flux considerably. It was also found that the CO2 desorption increased the CH4 recovery rate. The desorbed CO2 helped to increase the mass transfer driving force by reducing the partial pressure of CH4 in the gas side, and enhancing the gas phase mass transfer coefficient to facilitate CH4 desorption. The increase of liquid velocity increased mole fraction of CH4 in the gas outlet but decreased the rate of CH4 recovery. On the other hand, applying vacuum conditions to decrease gas pressure enhanced the rate of CH4 recovery but lower the CH4 mole fraction in the product gas.

•Various PP-N-x having high surface areas as well as strong hydrolytic and acid stability were synthesized.•The working capacity of adsorbents including commercial ones were estimated using an idealized PSA model.•PP-N-25 displayed the highest CO2/H2 selectivity and a decent working capacity which is comparable to that for HKUST-1.•PP-N-25 retained 80% of the CO2 capture capacity while HKUST-1 completely lost its capability in the presence of moisture.Various adsorbents including zeolites, activated carbon and metal-organic frameworks have demonstrated a potential capability for applications in pre-combustion carbon capture and H2 purification owing to their large surface areas and affinity for CO2. However, most adsorbents showing promising performances in dry condition are not stable or lose their capability for capturing CO2 in the presence of H2O and acidic gases such as H2S. To address this issue, a series of triphenylamine-containing microporous organic copolymers (PP-N-x) possessing high surface areas (1010–1251 m2 g−1) as well as excellent hydrolytic and acid stability were synthesized and evaluated for potential application in high pressure CO2 capture above-mentioned. Among the adsorbents tested, PP-N-25 exhibited the highest CO2/H2 selectivity over the entire pressure range along with the good CO2 uptake capability which is comparable to HKUST-1, a commercial metal-organic framework possessing coordinatively open metal sites. Subsequent breakthrough experiment revealed that PP-N-25 maintains decent CO2 adsorption capability even in the presence of H2O while HKUST-1 lost CO2 capturing capability in humid condition.Download high-res image (92KB)Download full-size image

Two-dimensional (2-D) CuBDC nanosheets (ns-CuBDC) with high-aspect-ratios were deliberately paired with polymers possessing high free volumes to fabricate high performance gas separation membranes. Owing to the molecular sieving effect of the filler, a small ns-CuBDC loading (2–4 wt%) could significantly improve the CO2/CH4 selectivities of membranes, resulting in performances that surpass the upper bound limit for polymer membranes.