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Asymmetric PEI hollow fiber mixed matrix membranes (MMMs) with improved structure and wetting resistance were fabricated via wet phase inversion method. The effects of incorporating hydrophobic MMT into polymer matrix in different loadings on the membrane properties were investigated. The membranes were characterized in terms of scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX), gas permeation test, hydrophobicity, wetting resistance and mechanical stability. All membranes possessed finger-like structures differing in skin layer thickness which increased with clay loading. The results revealed that the MMMs have significantly smaller pore size, higher porosity, hydrophobicity, LEPw and mechanical stability than plain PEI membrane. The membranes were further characterized by CO 2 absorption test via contactor system using distilled water as absorbent and pure CO 2 as solute gas. The results showed that the CO 2 absorption performance increased with addition of MMT nano-clay. The membrane containing 1 wt% MMT recorded the highest absorption flux of 2.35 × 10 −3 mol m −2 s −1 at the liquid velocity of 3 m s −1 , almost 135% higher than the flux of plain membrane at the same velocity. Comparatively, the flux of MMM was superior to several in-house made and commercial membranes. [ABSTRACT FROM AUTHOR]

Porous polyetherimide (PEI) and polyethersulfone (PES) hollow fiber membranes were spun under the same spinning conditions and the fabricated membranes were characterized using various analytical methods. The membranes were then subjected to gas–liquid contactor experiments. While the PEI casing solution was thermodynamically less stable, the PES casting solution was less viscous which resulted in a more porous membrane structure. The mean pore size and effective surface porosity obtained by the gas permeation test showed superior properties of the PES membrane. Both PEI and PES membranes had sufficiently high LEPw values even though both polymers were known to be relatively hydrophilic, most likely due to their small pore sizes. The absorption flux of the PES membrane was 4.4×10 −3 mol m −2 s −1 at the liquid flow velocity V liquid of 1.8 m s −1 , which was 267% higher than that of the PEI membrane (1.2×10 −3 mol m −2 s −1 ) due to the larger pore size and smaller tortuosity of the PES membrane. [ABSTRACT FROM AUTHOR]

Abstract: Carbon dioxide (CO2) stripping from water was conducted through the porous asymmetric polysulfone (PSf) hollow fiber membrane contactor. The effect of the liquid and gas flow rates on the stripping performance, the liquid phase CO2 concentration and the CO2 stripping efficiency of the membrane module and the effect of liquid phase temperature on CO2 stripping flux were studied. The experimental results showed that the stripping gas velocity had a minor effect on the CO2 desorption flux while the increase in the liquid velocity could enhance CO2 desorption flux in the gas stripping membrane contactor. By increasing liquid flow rate to 200ml/min, the maximum CO2 stripping efficiency of almost 66% was achieved. Enhancement of liquid flow rate from 50 to 200ml/min increased the CO2 flux around 482%. It was found that the CO2 stripping flux was significantly affected by the liquid phase temperature. By increasing liquid temperature from 80 to 90°C, the CO2 stripping flux increased from 1.3×10−4 to 4.9×10−4 molm−2 s−1 at liquid velocity of 200mlmin−1. Hence, the higher stripping efficiency can be achieved by applying the higher liquid flow rate in the membrane contactor module. As well, the liquid phase temperature is a key parameter that needs to be controlled. [Copyright &y& Elsevier]

Abstract: Porous asymmetric polyvinylidene fluoride (PVDF) hollow fiber membrane were fabricated via a phase-inversion method using surface modifying macromolecules (SMM) (1wt%) as the additive in the spinning dope. Distilled water and tap water were used as internal and external coagulation bath, respectively. The membranes were characterized in terms of gas permeation, wetting resistance, overall porosity, contact angle and collapsing pressure. CO2 stripping from diethanolamine (DEA) solutions was conducted through the gas–liquid membrane contactor. The effect of some operating conditions such as gas and liquid velocities, DEA concentration and rich solution temperature on the CO2 stripping flux and efficiency were investigated. By increasing liquid flow rate to 200ml.min−1, the maximum CO2 stripping efficiency of almost 82% was achieved. In addition, an increase in the liquid flow rate resulted in a significant increase of CO2 stripping flux. By increasing the liquid flow rate from 50 to 200mlmin−1, the CO2 flux increased by 900%. By increasing the gas velocity the CO2 desorption flux increased but this changing was negligible. The effect of rich solution temperature was investigated and the results showed that the CO2 desorption flux increased with increasing the solution temperature from 80 to 90°C. The results of DEA concentration enhancement on the CO2 desorption flux showed that the CO2 stripping flux increased drastically with enrichment of the DEA concentration from 1.0 to 3.0 (moll−1). Therefore, the higher stripping efficiency can be achieved by applying the higher liquid flow rate, temperature and DEA concentration in the absorbent liquid in the membrane contactor module. [Copyright &y& Elsevier]

Abstract: Porous asymmetric polyetherimide (PEI) hollow fiber membranes were fabricated via a phase-inversion method using ethanol, glycerol and acetone as the additives in the spinning dope. Also, hollow fiber PEI membrane without additives was fabricated. An aqueous solution of 1-methyl-2-pyrrolidone (80wt.%) was used as bore fluid to prevent forming of an inner dense skin layer. The precipitation rate of the polymer dopes with the different additives was studied using cloud point measurement. The effect of the additives on the resulting membrane structure, surface porosity, pore size, critical water entry pressure, collapsing pressure and physical and chemical CO2 absorption performance by distilled water and NaOH (1M) solution in a gas–liquid membrane contactor system were investigated and compared. Cloud point diagrams indicated that the precipitation rate of the polymer dopes increased following the trend of ethanol>acetone>glycerol. Results of gas permeation tests showed that ethanol and glycerol as additives provided the membranes with the largest and smallest pore size, respectively. Moreover, all the additives resulted in an increase in the effective surface porosity. The cross-section of the membranes was examined via a scanning electron microscopy. Ethanol in the spinning dope provided the membrane structure with a sublayer with finger-like macrovoids, originating from the inner and outer surfaces of the hollow fiber and extending to the middle section of the hollow fiber wall, which resulted in a larger pore size and higher CO2 absorption rate than the other PEI hollow fiber membranes. [Copyright &y& Elsevier]

Abstract: Microscopic observation was made to investigate the surface structure of porous polyvinylidene fluoride hollow fiber membranes. Field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and the Guerout–Elford–Ferry equation applied for pure water permeation rate were used to determine the average pore sizes. As well, surface roughness parameters and nodule sizes were determined by AFM. The observed unmodified and modified PVDF hollow fiber membranes were prepared by dry-jet wet spinning method from spinning dope mixtures containing 19wt.% PVDF, 0.98wt.% lithium chloride (LiCl.H2O) and 0, 1.95, and 3.85wt.% titanium dioxide (TiO2). Significant difference of spun fibers surface morphology was observed between inner and outer surface by AFM and FESEM. Higher TiO2 concentration formed rougher surfaces, increased average nodule sizes, and decreased the pore size, resulting in lower permeation flux. Pore size obtained from AFM was intermediate between FESEM and the method based on the Guerout–Elford–Ferry equation. [Copyright &y& Elsevier]

Abstract: Different types of non-solvent additives were introduced into the polyvinylidene fluoride (PVDF) dope to investigate improvement of the hollow fiber membrane structure for CO2 absorption. Phase-inversion behavior of the PVDF dopes was studied using cloud points measurements. Glycerol, phosphoric acid, ethanol and polyethylene glycol (PEG-400) were used as non-solvent additives in the polymer dope. With addition of the additives, precipitation of the polymer dopes increased following the trend of phosphoric acid>glycerol>ethanol>PEG-400. From morphology examination, PEG-400, glycerol and phosphoric acid resulted in the membranes with almost sponge-like structure due to high viscosity of the spinning dopes. The low wetting resistance and high permeability of the plain PVDF and PVDF/ethanol membranes were attributed to the large finger-likes structure. Among the additives, glycerol provided the membranes with larger mean pore size (9.62nm). CO2 absorption by distilled water was conducted through the gas–liquid membrane contactors. The PVDF/glycerol membrane demonstrated higher CO2 absorption flux than the other membranes. At the absorbent flow rate of 280ml/min, CO2 flux of 7.8×10−4 mol/m2 s was achieved, which was approximately 30% higher than CO2 flux of the plain PVDF membrane. In conclusion, a developed membrane structure prepared by controlled phase-inversion process can be a promising alternative for CO2 capture in gas–liquid membrane contactors. [Copyright &y& Elsevier]

Abstract: Porous polyvinylidene fluoride (PVDF) and polysulfone (PSF) hollow fiber membranes were prepared via a wet spinning method. Glycerol was used as phase-inversion promoter additive in the spinning dopes. Cloud point diagrams of polymer/solvent–glycerol/water were obtained to study precipitation rate of the polymers solution. The membrane structure was compared in terms of morphology, gas permeation, critical water entry pressure, collapsing pressure, overall porosity, contact angle and mass transfer resistance. The cloud point diagrams confirmed a significant increase in the precipitation rate of the spinning dopes with addition of glycerol. The PSF membranes indicated more open cross-section structure with smaller pore sizes. However, the PVDF membranes illustrated an ultra thin outer skin layer with high permeability which resulted in significantly lower mass transfer resistance. Physical CO2 absorption with distilled water was conducted through the gas–liquid membrane contactors. With addition of glycerol, the PVDF membrane demonstrated a structure with significantly higher CO2 flux compared to the commercial asymmetric PVDF membrane. The CO2 flux of 8.20×10−4 mol/m2 s was achieved by using the absorbent flow rate of 310mL/min in the shell side of the membrane module. Therefore, using an improved hollow fiber membrane structure can be a promising alternative for CO2 absorption and separation through membrane contactors. [ABSTRACT FROM AUTHOR]

[Display omitted] • ZIF-8, SiO 2 /ZIF-8 and amine modified (A@SiO 2 /ZIF-8) nanofillers were synthesised. • Synthesised nanofillers incorporated polysulfone hollow fiber MMMs were fabricated. • Investigated the gas permeation and selectivity of MMMs for CO 2 , CH 4 and N 2 gases. • A@SiO 2 /ZIF-8 contributed 89 and 61% increase in CO 2 /N 2 and CO 2 /CH 4 selectivities. High tunable properties of metal–organic frameworks (MOFs) allows different modifications to be used for distinct applications. Zeolitic imidazolate frameworks-8 or ZIF-8 are hybrid organic–inorganic porous materials that have shown great potential in membrane-based gas separations. In our study, SiO 2 /ZIF-8 (S/ZIF-8) nanofiller was synthesized via a facile one-step strategy. Furthermore, the S/ZIF-8 nanofiller was subjected to amine modification using an ammonium hydroxide solution. X-ray photoelectron spectroscopy (XPS) analysis confirms the strong binding of amine and SiO 2 on ZIF-8 nanofillers. The synthesized ZIF-8, S/ZIF-8 , and amine-modified S/ZIF-8 (A@S/ZIF-8) of 0.5 wt% were incorporated into the polysulfone (PSf) matrix, and the hollow fiber mixed matrix membranes (MMMs) were fabricated using dry–wet phase inversion technique. The inclusion of an amine group in the S/ZIF-8 nanofillers enhances the interaction between the nanofillers and PSf matrices, thus improving the CO 2 /CH 4 and CO 2 /N 2 separation performances. The fabricated membranes were morphologically characterized by Scanning electron microscope (SEM), Brunauer–Emmett–Teller (BET) surface area, and the pore size distribution. It is noteworthy that the BET surface area was enhanced with nanofillers addition and significantly increased gas separation performance. The fabricated asymmetric hollow fiber MMMs were further studied for gas permeation experiments for CO 2 , N 2 , and CH 4. PSf with A@S/ZIF-8 MMMs showed the best performance as observed from the Robeson upper bound limit, CO 2 permeability of 4.25 barrer with the improvements in CO 2 /N 2 and CO 2 /CH 4 selectivities of 89.75 and 61.46% respectively, compared with neat PSf membrane. The enhanced permselectivity of PSf–A@S/ZIF-8 membranes is explained by CO 2 -facilitated transport, where the high CO 2 affinity of the amine group allows the selective transport of CO 2 rather than CH 4 and N 2. [ABSTRACT FROM AUTHOR]