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Carbon dioxide (CO 2 ) is the main culprit of greenhouse gases produced mainly via the combustion of fossil fuel. This paper reviewed the performance of emerging dual-layer hollow fiber membrane, its fabrication via co-extrusion process, improvement, challenges, spinning parameters, advantages and disadvantages in comparison to single-layer hollow fiber membrane for natural gas purification. Development of delamination-free dual-layer hollow fibers via co-extrusion and phase inversion technology is one of the potential solutions for the use of expensive and brittle polymers for the outer selective layer and low cost polymers with high thermal and mechanical properties for the porous inner layer. [ABSTRACT FROM AUTHOR]

Polyphenylsulfone (PPSU) based asymmetric hollow fiber membranes were prepared by the addition of different percentages of ZSM-5 particles by diffusion induced phase separation method. Polyvinylpyrrolidone (PVP) was used as a pore forming agent. The fabricated membranes were characterized by Field Emission scanning electron microscopy (FESEM), Energy Dispersive Spectroscopy (EDS), contact angle, water permeability, water uptake and by porosity measurements. Membranes filtration study was performed using different proteins namely bovine serum albumin (BSA), egg albumin (EA) and hazardous dyes like Reactive black 5 (RB-5), Reactive orange 16 (RO-16) in aqueous solutions. It was found that, addition of ZSM-5 in membrane matrix showed better dye removal capacity because of its hydrophilic and adsorptive nature. The membrane (PZ-3) with higher loading of additive exhibited rejection percentages of 100% for BSA, 95.23% for EA proteins and with reactive dyes 90.81% for RB-5 and 82.84% for RO-16 as compared to the pristine HF membrane. [ABSTRACT FROM AUTHOR]

A simple, efficient and scalable approach was developed for the fabrication of highly fouling resistance nanocomposite hollow fiber membranes with the aim of effective removal of environmentally detrimental reactive dyes. The naturally occurring halloysite nanotubes were functionalized via facile self-polymerization of m -aminophenol in mild acidic condition and employed as a hydrophilic additive. The chemical modification was confirmed by FTIR, TEM and energy dispersed X-ray (EDX) analysis. The hybrid nanocomposite membrane was prepared by dry–wet spin technique with different additive dosage. The resultant membrane was characterized in terms of contact angle, surface energy, porosity, zeta potential, elemental mapping and morphology. The permeation experiments illustrated superior water flux of 104.9 Lm −1 h −1 and 9.6% of irreversible fouling with more than 90.3% of flux recovery by the simple hydraulic cleaning. Most importantly, prepared membrane was subjected for hazardous reactive dye removal application with different experimental parameters. The hybrid membrane with 2 wt. % of additive concentration showed more than 97% and 94% for the Reactive Red 102 and Reactive Black 5 dyes respectively. This approach may also be very useful in developing high flux, fouling resistant ultrafiltration hollow fiber membranes for the other similar type applications such as hemodialysis membranes. [ABSTRACT FROM AUTHOR]

Porous hydrophobic polyvinylidene fluoride (PVDF) composite hollow fiber membranes were fabricated via phase inversion method by embedding different amounts of hydrophobic calcium carbonate (CaCO 3 ) nano-particles in the polymer matrix. The effects of nano-particle loadings on the morphology, structure and performance of the spun membranes in gas–liquid contactors were investigated. The incorporation of hydrophobic nano-particles into the polymer network enabled the formation of more abundant and narrower finger-like pores in the composite membranes compared to plain PVDF membrane. Moreover, the addition of nano-particles enhanced the surface roughness, permeation rate, porosity and wettability resistance of the composite membranes. CO 2 absorption performance of the fabricated membranes was evaluated via a gas–liquid membrane contactor system. The CO 2 flux was improved to some extent by increasing the mixing ratio of CaCO 3 . Peak absorption performance of 1.52 × 10 −3 mol m −2 s −1 at 300 ml/min absorbent flow rate was achieved when 20/100 weight ratio of CaCO 3 /PVDF was employed. However, further increase of the ratio resulted in a composite membrane with lower absorption performance than the other composite membranes. Moreover, a long-term stability study of the composite membrane with the best CO 2 absorption flux showed no decline in performance in the initial 210 h of operation, indicating that the membrane possesses high potential for gas–liquid contactor applications. [ABSTRACT FROM AUTHOR]

The surface hydrophobicity of membrane is a key factor in contactor applications where the penetration of liquid into membrane pores has negative effect on the contactor performance. Therefore, different methods have been proposed for surface modification. Blending hydrophobic polymers such as surface modifying macromolecules (SMM) has been investigated in our earlier researches. In this study, the effect of polyvinylidene fluoride (PVDF) blending on the surface and bulk morphology of polyetherimide (PEI) hollow fiber membrane and its performance in membrane gas absorption process was studied. It was found that the pore size increased from 112 nm to 210 nm from the neat PEI membrane to the PEI membrane spun from the solution blended with 0.25 wt% PVDF. At the same time, the contact angle increased from 78.3 and 84.3. Furthermore, the absorption flux of PVDF blended membrane enhanced by 13% compared to the neat PEI membrane. [ABSTRACT FROM AUTHOR]

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]

Several efforts to produce mechanically robust polymeric hollow fiber membranes have led to the use of polyethylene terephthalate (PET) hollow braided tubes, which offer rigidity to hollow fiber membranes. However, a compensation of flux exists with increased filtration pathway occasioned by braid substrate and thick polymer coating. It is often difficult to control the fabrication parameters to achieve uniformly coated and thin separation layer. In this work, we report a modification of the erstwhile dry-jet wet spinning process for braided hollow fiber by introducing a loop-system to increase resident time in the coagulation bath for effective solvent exchange and leaching of pore former additive. A combination of air gap (5, 15 and 25 cm), polymer concentration (15%, 17% and 19%) and take-up speed (1.2, 2.4 and 3.6 m/min) were varied to produce membranes with optimum filtration performance against crude oil emulsion feed. BRP-HM8 spun with 15 wt% PVDF, 15 cm air gap and take-up speed of 2 rpm exhibited thin and uniform coating outside of braid, well-developed pore structure resulting in high flux up to 620 L/m2h, good hydrophilic/oleophobic characteristics with > 98% rejection of crude oil as well high mechanical properties against harsh feed and elevated pressure. [Display omitted] • Loop-system for improved spinning of braided hollow fiber membranes. • Thin and uniform polymer coating reducing filtration pathway with well-developed finger-like pores. • Excellent rejection properties occasioned by good underwater oleophobicity. • High-strength reusable membranes with simple flushing. [ABSTRACT FROM AUTHOR]

In this study, thin-film composite (TFC) hollow fibers (HFs) were fabricated by an in-situ coating of polyamide layer on the lumen side of PVC/PC blend substrates for desalination by forward osmosis (FO). Particularly, the substrate HFs were spun at two air gap distances of 2 and 6 cm, to investigate the effect of the air-gap distance on the FO performance. The substrate HFs were characterized by pure water flux measurement, FESEM, and gas permeability test. The Interfacial polymerization (IP) method was then utilized for coating polyamide (PA) layer on the lumen surface of the substrate to fabricate TFC HFs. The TFC HFs so fabricated were also characterized by FESEM, before their FO performance was tested. Furthermore, the effect of HF length on the FO flux was investigated. The results showed that the novel TFC HFs exhibited good FO performance. The longer the air gap distance, the better becomes the FO performance in terms of simultaneous water flux and alginate fouling resistance, while the effect of the HF length remains a controversial issue. • Higher surface porosity resulted defect free active layer. • Higher surface porosity enhanced mass transfer coefficient, by reducing CP. • Irreversible fouling is suppressed when HF spun with longer air gap distance. • Water flux decreased with the fiber length, contrary to the model simulation. • In high flux mode increasing number of the fibers can increase productivity. [ABSTRACT FROM AUTHOR]

Highlights: [•] Formation of finger-like macrovoids enhanced by the addition of clay nanoparticles. [•] Wetting resistance, surface hydrophobicity and roughness increased with MMT loading. [•] CO2 flux of fabricated MMMs superior to several commercial and in-house membranes. [•] 350h of constant CO2 absorption flux confirmed high reliability of fabricated membrane. [ABSTRACT FROM AUTHOR]

Highlights: [•] Blending SMM resulted in higher hydrophobicity and gas permeability. [•] The modified membrane showed higher wetting resistance at 24cm air gap. [•] The membrane showed less mass transfer resistance by removing inner skin. [•] Increasing air gap and SMM concentration resulted in higher CO2 flux. [•] A long-term stable operation was achieved by developing PVDF membranes. [ABSTRACT FROM AUTHOR]

Highlights: [•] Effects of tapioca starch and CGTase concentrations on the yield of CDs were studied. [•] Production of CDs in an EMR. [•] The weak adsorption (ra1 ) was the major fouling mechanism. [ABSTRACT FROM AUTHOR]

Highlights: [•] Different amount of SMM were used to improve the surface hydrophobicity of PVDF HFM. [•] Average pore size and contact angle increased by increasing SMM concentration. [•] The fabricated PVDF HFMs were used in contactor application for CO2 absorption. [•] The CO2 flux of the hollow fiber increased by increasing SMM concentration. [•] The membrane mass transfer resistance decreased by enhancement of SMM concentration. [Copyright &y& Elsevier]

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: A series of polyetherimide (PEI) hollow fiber membranes with various polymer concentrations (13–16wt.%) for CO2 stripping process in membrane contactor application was fabricated via wet phase inversion method. The PEI membranes were characterized in terms of liquid entry pressure, contact angle, gas permeation and morphology analysis. CO2 stripping performance was investigated via membrane contactor system in a stainless steel module with aqueous diethanolamine as liquid absorbent. The hollow fiber membranes showed decreasing patterns in gas permeation, contact angle, mean pore size and effective surface porosity with increasing polymer concentration. On the contrary, wetting pressure of PEI membranes has enhanced significantly with polymer concentration. Various polymer concentrations have different effects on the CO2 stripping flux in which membrane with 14wt.% polymer concentration showed the highest stripping flux of 2.7×10−2 mol/m2 s. From the performance comparison with other commercial membrane, it is anticipated that the PEI membrane has a good prospect in CO2 stripping via membrane contactor. [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: Microporous polyvinylidene fluoride (PVDF) hollow fiber membranes with various non-solvent additives, i.e. lithium chloride, glycerol, polyethylene glycol (PEG-400), methanol and phosphoric acid, were fabricated for CO2 stripping via membrane contactors. The membranes were characterized in terms of liquid entry pressure, contact angle, gas permeation and morphology analysis. CO2 stripping performance was investigated by using an in-house made stainless steel module with CO2-preloaded aqueous diethanolamine as the liquid absorbent. Hydrophobicity and gas permeability of the membranes reduced with the addition of a non-solvent additive in the polymer dope but increase in liquid entry pressure was observed as more sponge-like structures developed in the inner layer of the fibers. It was found that PVDF/PEG-400 membrane produced the highest stripping flux of 4.03×10−2 molm−2 s−1 which can be correlated to its high gas permeation and high effective surface porosity. The result of long-term stripping operation indicated an approximatly 80% stripping flux reduction which can be related to the interaction of polymer membrane and amine solution at high temperature. [Copyright &y& Elsevier]

Abstract: A novel surface modified Polysulfone (PSf) hollow fiber membrane was fabricated via dry–wet phased inversion process. surface modifying macromolecule (SMM) was used as additive in the spinning dope. The surface modified membrane showed large pore size, higher effective surface porosity, contact angle and porosity but lower critical water entry pressure (CEPw) compared to Polysulfone hollow fiber membrane without SMM. The performance of surface modified membrane in contactor application for CO2 absorption via distilled water as absorbent was studied. The results show that surface modified membrane has higher performance compared to plain Polysulfone membranes. With the membrane prepared from SMM in the spinning dope a maximum CO2 flux of 5.8×10−4 mol/m2 s was achieved at 300ml/min of absorbent flow rate, which was almost 76% more than the other membrane. In a long-term stability study, the initial flux reduction was found to be about 18% within the 50h of operation for surface modified membrane. [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: The effect of bore fluid type on the structure and performance of polyetherimide hollow fiber membranes in contactor application was investigated. Water was used as phase inversion promoter in spinning dope and water and pure NMP were used as bore fluid. SEM micrographs show that the major parts of both membranes consist of spongelike structure which is related to the high viscosity of spinning dope that reduces the diffusion of coagulant (water) into membrane sublayer and decreases the rate of phase inversion. In the case of water as bore fluid (membrane #M1) there is skin layer on the inner surface of membrane and some drop-shaped voids in the structure of membrane but in the case of pure NMP as bore fluid (membrane #M2), the inner surface of membrane is skinless with big pores and there are fingerlike macrovoids, originating from the inner surface and extending to the vicinity of outer surface which is related to the penetration of bore fluid and dissolving the polymer. Furthermore, membrane #M2 has higher mean pore size and effective surface porosity. The absorption flux of both fabricated membranes was investigated in the case of liquid in lumen side (case #1) and liquid in shell side (case #2) where in case #1, membrane #M1 has higher absorption flux but in case #2, membrane #M2 has higher absorption flux. The different trend in absorption flux confirms that the surface of membrane in contact with the gas phase in a membrane contactor should be skinless with big pores to facilitates the diffusion of solute gas through membrane but the pore size on the surface of membrane in contact with the liquid phase should be adjusted to obtain high absorption flux and low wettability. [Copyright &y& Elsevier]

Abstract: Low wettability is a vital characteristic for the membrane used in membrane contactor. Blending surface modifying macromolecule (SMM) in spinning dope is an interesting method to enhance the hydrophobicity of membrane and in this research, the effect of SMM on the properties and structure of polyetherimide (PEI) hollow fiber membrane in terms of mean pore size, liquid entry pressure of water (LEPw), membrane porosity and contact angle was investigated and compared with the properties of the PEI membrane without SMM. Furthermore the performance of PEI surface modified membrane in contactor applications in terms of CO2 absorption with distilled water was evaluated and compared with the absorption flux of PEI membrane without SMM and also, with the absorption flux of commercial and in-house made hydrophobic membranes which shows superior performance of surface modified PEI membrane e.g. in case of water in lumen side and pure CO2 in shell side of contactor and at V liquid =0.5ms−1, the absorption flux of PEI surface modified membrane is 2.94×10−3 molm−2 s−1 which is 114% higher than PEI without SMM and 73% higher than commercial membrane contactor, Celgard MiniModule® 0.75X5. [Copyright &y& Elsevier]

Abstract: High performance carbon hollow fiber membranes (CHFM) for CO2 separation were prepared by manipulating of carbonization heating rates under a N2 atmosphere. During heat treatment process, carbonization of the polymeric hollow fiber membrane was conducted up to 650°C and in the range of 1–9°C/min for heating rate. The gas permeation properties were determined using a single gas permeation apparatus at room temperature. Fine-tuning of the carbonization conditions appears necessary to obtain desired permeation properties. The gas permeance for all examined gases (N2, CH4, CO2) and selectivity of CO2/CH4 and CO2/N2 was decreased and increased, respectively, for the PEI/PVP-based CHFMs prepared at low heating rate. It was found that the heating rate posses significant effect on structure and gas permeation properties of the resultant CHFMs. Experimental results indicated that, carbonization heating rate of 3°C/min is the best conditions in the preparation of CHFMs derived from polymer blends of PEI/PVP for the CO2/CH4 and CO2/N2 separation. [Copyright &y& Elsevier]

Abstract: Microporous polyvinylidene fluoride (PVDF) hollow fiber membranes were fabricated via a wet-spinning process. The prepared fibers were characterized in terms of contact angle, gas permeability, wetting pressure and morphology. CO2 stripping from preloaded aqueous diethanolamine solution was conducted through the gas–liquid membrane contactors. The effects of lithium chloride (LiCl) concentration on the membrane properties and CO2 stripping performance were investigated. The addition of different LiCl concentration resulted in a less finger-like structure, with highly effective surface porosity and high wetting pressure. Conversely, N2 permeability, contact angle value and membrane pore size were reduced as the concentration of the additives were increased. For stripping flux performance, membrane with 5wt% LiCl demonstrated the highest flux of 1.61×10−2 mol/m2 s at 110ml/min of the liquid flow rate. It was found that the membrane with less finger-like structure and higher effective surface porosity exhibited higher stripping efficiency. These results suggest that developed membrane structure can be an alternative for the CO2 stripping through gas–liquid membrane contactors. [Copyright &y& Elsevier]

Abstract: This study investigated the use of nanosized fumed silica (Aerosil® R106) as fillers in the production of asymmetric hollow fiber mixed matrix membrane (HFMMM) where polysulfone was the host polymer matrix. The presence of fumed silica particles were found to stimulate the flow of CO2 as indicated by an increase (>12%) in CO2 permeability for all HFMMMs. At low loading of 0.1% (w/w), the permeability of CO2 and CH4 were 90.04 and 2.75GPU, respectively, and the calculated selectivity was higher than the neat PSf hollow fiber membrane. At higher loading of 10% (w/w), the FESEM images of the HFMMM showed severe agglomeration of fillers that contributed to nanometric defects between the aggregates, leading to higher permeation of slow gases (CH4 and N2). Hence, the selectivities of CO2/CH4 and O2/N2 were low at 7.43 and 2.02, respectively. The calculation of particle spacing within the polymer macromolecules have shown that for nanoparticles, the agglomeration was unavoidable at high loading due to sheer number of particles within the matrix. At low loading of 0.1%, the polysulfone-fumed silica HFMMM showed no visible sign of particle agglomeration. The selectivities of CO2/CH4 and O2/N2 significantly improved with an average value of 32.74 and 6.35, respectively. The HFMMM also showed an increase in glass transition temperature and has a better thermal stability as measured by DSC and TGA analyzers, respectively. The importance of filler–filler, polymer–filler and filler–gas interactions on the characteristic and permeation performance of HFMMMs are also discussed. [Copyright &y& Elsevier]

Abstract: Wetting resistance and gas permeability are the main factors for membrane contactor applications, which can be optimized according to the membrane morphology. In present study, three different types of the membrane morphology were obtained via a dry–wet spinning technique. By measuring cloud point data and viscosity, the polymer dope composition was adjusted to produce the different morphologies. The membranes with large finger-like, small finger-like and almost sponge-like morphology were obtained. The plain PVDF membrane with large finger-likes morphology presented the higher N2 permeance, lower wetting pressure and larger mean pore size (0.08μm). By addition of phosphoric acid into the spinning dope, the prepared sponge-like morphology resulted in the high surface porosity with small pore sizes, which demonstrated good permeability and wetting pressure. It was found that the mean pore size measured by gas permeation method was approximately three times larger than those from FESEM examination. CO2 stripping from water was conducted through the gas–liquid membrane contactors. The membranes with smaller pore sizes and higher wetting pressure presented higher stripping performance. In conclusion, a structurally developed PVDF hollow fiber membrane for gas–liquid contactor applications can be achieved by controlling the membrane morphology. [Copyright &y& Elsevier]

Abstract: Submerged ultrafiltration process was studied for treatment of refinery wastewater using PVDF hollow fiber membranes. The membranes were prepared via the phase inversion method by dispersing LiCl·H2O and TiO2 in the dope to study the effects of surface properties on membrane performance. The comparison of the performance and morphology was conducted on prepared PVDF composite membranes with various LiCl·H2O and TiO2 contents. The hollow fiber membranes were characterized by field emission scanning electron microscope (FESEM) and energy dispersive x-ray (EDX), average pore size and effective porosity measurements, contact angle measurement, permeability and rejection test. Maximum results were observed for membrane hydrophilicity, membrane porosity and average pore size when the TiO2 concentration was 1.95%. It was also found that interactions between the membrane surface and suspended solid constituents strongly influenced the membrane fouling. The maximum flux and rejection of refinery wastewater were 82.5L/m2 h and 98.8%, respectively, when the PVDF composite membrane with TiO2 content of 1.95% is used at pH=6.9. [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: Carbon hollow fiber membrane derived from polyetherimide (PEI) blend with polyvinylpyrrolidone (PVP) was prepared by pyrolysis under air and N2 environment. The characteristics of the carbon structures and the gas separation properties of carbon hollow fiber membranes pyrolyzed at different temperatures were studied. The prepared membranes were extensively characterized using thermogravimetry analysis, scanning electron microscopy, and X-ray diffraction for its morphology, thermal stability and structure properties, respectively. Pure gases of different molecular size (CO2, N2 and CH4) were used to determine the permeation properties of the carbon membrane. The permeance of the three gases decreased with increasing of pyrolysis temperature, however the selectivity of the gas pairs such as CO2/CH4 and CO2/N2 increased significantly. PEI/PVP is a promising carbon membrane precursor, which resulted in good separation performance for CO2/CH4 and CO2/N2. According to permeation data, it is confirm that the gas separation performance of prepared PEI/PVP-based carbon membranes significantly better than its polymer precursor. [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) hollow fiber membranes were prepared via wet spinning process. The membranes were characterized in terms of gas permeation, wetting resistance and overall porosity, which are important parameters for gas absorption/stripping applications. CO2 stripping from water was conducted through the gas–liquid membrane contactor. The effect of different operating conditions on the CO2 stripping efficiency of the membrane was investigated. The results indicated a significant improvement in the CO2 stripping efficiency by increasing the liquid phase temperature. On the other hand, increasing the liquid flow rate resulted in a considerable decrease in the CO2 stripping flux. The maximum stripping efficiency of 32% was achieved at 60ml/min of the liquid flow rate, 60°C and 0.5×105 Pa. It was found that the liquid phase temperature, the gas–liquid contact area and contact time are the key parameters for enhancement of CO2 stripping efficiency. [Copyright &y& Elsevier]

Abstract: In this study, polysulfone (PSF) hollow fiber membranes with enhanced performance for humic acid removal were prepared from a dope solution containing PSF/DMAc/PVP/TiO2. The main reason for adding titanium oxide during dope solution preparation was to enhance the antifouling properties of membranes prepared. In the spinning process, air gap distance was varied in order to produce different properties of the hollow fiber membranes. Characterizations were conducted to determine membrane properties such as pure water flux, molecular weight cut off (MWCO), humic acid (HA) rejection and resistance to fouling tendency. The results indicated that the pure water flux and MWCO of membranes increased with an increase in air gap distance while HA retention decreased significantly with increasing air gap. Due to this, it is found that the PSF/TiO2 membrane spun at zero air gap was the best amongst the membranes produced and demonstrated >90% HA rejection. Analytical results from FESEM and AFM also provided supporting evidence to the experimental results obtained. Based on the anti-fouling performance investigation, it was found that membranes with the addition of TiO2 were excellent in mitigating fouling particularly in reducing the fouling resistances due to concentration polarization, cake layer formation and absorption. [Copyright &y& Elsevier]

Abstract: Effect of lithium chloride (LiCl) concentration as non-solvent additive in the spinning dopes on the structure and CO2 absorption performance of the polyvinylidene fluoride (PVDF) membranes was investigated. The hollow fiber membranes were prepared via a wet phase-inversion process and characterized in terms of gas permeability, wetting resistance, mass transfer resistance and overall porosity. The morphology study indicated that by increasing LiCl concentration in the spinning dope, the membrane structure changed from the finger-like to the sponge-like. In addition, by increasing LiCl concentration up to 4wt.% a drastic decrease in the N2 permeance and a significant increase in the wetting resistance were observed. CO2 absorption by distilled water was conducted through the gas–liquid membrane contactors. Using LiCl in the spinning dopes, the CO2 flux of the prepared membranes significantly improved. By introducing 2wt.% LiCl, the PVDF membrane showed a CO2 flux of approximately 60% higher than the plain PVDF membrane at the absorbent flow rate of 200ml/min. It can be concluded that a porous hydrophobic hollow fiber membrane with improved structure can be a productive alternative for CO2 absorption and separation through gas–liquid membrane contactors. [ABSTRACT FROM AUTHOR]

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]

Abstract: In this paper, polyetherimide (PEI) hollow fiber membranes were used in gas–liquid contacting process. Porous polyetherimide hollow fiber membranes were fabricated via wet phase inversion method. The polymer concentration in dope solution varied from 10 to 15wt%. Water was used as internal and external coagulant. Gas permeation test using helium as test gas, liquid entry pressure of water (LEPw) test and scanning electron microscopy (SEM) were used for membrane characterization. The mean pore size, effective surface porosity and void fraction of membranes decreased as the polymer concentration increased, while LEPw and membrane density increased. CO2 absorption rate of fabricated membranes were measured in a gas–liquid hollow fiber membrane contactor system using distilled water as absorbent and the results showed that CO2 absorption rate of membranes increases as polymer concentration decreases. In addition, CO2 absorption rate of hollow fiber membranes in which polyetherimide concentration was between 10 and 12wt%, was higher than commercial PVDF hollow fiber membranes. [Copyright &y& Elsevier]

Abstract: Removal of endocrine disrupting compound (viz., bisphenol A, BPA) by laboratory-fabricated hollow fiber polyethersulfone (PES) nanofiltration (NF) membranes have been investigated. The tailor made charged PES hollow fiber NF membranes have been developed by blending negatively charged surface modifying macromolecule (cSMM). It is resulted more than 90% removal of BPA, mainly due to negatively charged properties of the membrane and the negatively charged solute under the influence of higher pH feed water matrix. The PES hollow fiber modified by blending cSMM is associated with sulfonic groups, confirmed by energy dispersive X-ray and Fourier transform infrared analysis. The blending of cSMM has successfully modified PES hollow fiber which is resulted twice better removal of BPA compared to the unmodified PES. [Copyright &y& Elsevier]

In this study, hollow fiber PVC/ZnO-nanocomposite in an MBR was investigated for municipal wastewater treatment. The following parameter were evaluated: BOD, COD, TSS, NTU, TP, TKN. ZnO nanoparticles caused to decrease the contact angle from 78° to 67° for the neat PVC and 0.5 wt% ZNO-nanocomposite membrane, respectively. The majority of the neat membrane resistance was due to irreversible resistance. Because of the antibacterial properties of zinc oxide nanoparticles, with increasing nanoparticles loading, the resistance of irreversible part compared to the reversible resistance experienced a significant decrease. This confirm that the fabricated nanocomposite membranes did not show affinity toward adsorption of the sludge inside the pores hence substantially limited the membrane fouling. The FTIR results showed the reduction of proteins and polysaccharides onto the surface of the nanoparticle-incorporated membranes, approaching the clean PVC membrane. This was most likely due to the antibacterial properties of ZnO NPs. Nitrogen and phosphor removal for PVC0.5 membrane was 99% and 79% and TSS removal up to 100% was achieved. The findings of this study showed that modification of PVC polymer using ZnO nanoparticles with the presence of ferric chloride coagulant is a very effective technique for municipal wastewater treatment to meet the well-known standard levels. [Display omitted] [ABSTRACT FROM AUTHOR]

• Membrane heat treatment is a simple method to improve MC stripping performance. • There was a direct correlation between the temperature and the performance. • The best performance was observed at the shortest heat exposure time. The scope of this study was to investigate the effect of the heat treatment process on the performance of the PEI hollow fiber membrane contactor for CO 2 stripping process. The membranes were fabricated via a wet spinning technique into water as a non-solvent bath. Then, the membranes were heat treated by exposing them to various temperatures of 80,120 and 160 °C for the time intervals of 5, 15 and 30 min under a hot air atmosphere. The observations revealed that the most pronounced enhancement belonged to the membranes with the lowest heat treatment temperature preferentially at the shorter exposure times. It was shown that the absorbent velocity and temperature had substantial influence on the CO 2 stripping flux, however the temperature exhibited a stronger influence. In fact the dual functionality of temperature on the system i.e. (i) thermodynamics (by decrease in CO 2 solubility) and (ii) kinetics (by increase in CO 2 diffusivity) led to the enhancement in CO 2 stripping flux. Also, it was revealed that by increasing the heat treatment temperature, more tendency toward the pore wetting will be observed. There was a meaningful correlation between the wetting ratio and the CO 2 stripping flux. Also experimentally it was revealed that, a marginal progress in the wetting ratio, surprisingly caused to a dramatic decline in the stripping flux. [ABSTRACT FROM AUTHOR]

Comparison studies in suspension and hybrid photocatalytic membrane reactor (HPMR) system was investigated by using Reactive Black 5 (RB5) as target pollutant under UVA light irradiation. To achieve this aim, hybrid TiO 2 /clinoptilolite (TCP) photocatalyst powder was prepared by solid-state dispersion (SSD) methods and embedded at the outer layer of dual layer hollow fiber (DLHF) membranes fabricated via single step co-spinning process. TiO 2 and CP photocatalyst were also used as control samples. The samples were characterized by Scanning Electron Microscopy (SEM), Energy Dispersion of X-ray (EDX), X-ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) analyses. The result shows that TCP was actively functioned as photocatalyst in suspension system and 86% of RB5 photocatalytic degradation achieved within 60 min; however the additional step is required to separate the catalyst with treated water. In the HPMR system, even though the RB5 photocatalytic degradation exhibits lower efficiency however the rejection of RB5 was achieved up to 95% under UV irradiation due to the properties of photocatalytic membranes. The well dispersed of TCP at the outer layer of DLHF membrane have improved the surface affinity of DL-TCP membrane towards water, exhibit the highest pure water flux of 41.72 L/m2.h compared to DL-TiO 2 membrane. In general, CP can help on improving photocatalytic activity of TiO 2 in suspension, increased the RB5 removal and the permeability of DLHF membrane in HPMR system as well. • The work aims to study effect of TiO 2 /clinoptilolite composites in dual layer hollow fiber membranes. • The effect of TiO 2 /clinoptilolite composites prepared by solid state dispersion methods. • TCP actively functioned as photocatalyst and achieved 86% degradation in hybrid system. • The removal of RB5 after filtration process in HPMR system was achieved around 95%. • The well dispersed of TCP at the outer layer of DLHF membrane also have improved the surface affinity. [ABSTRACT FROM AUTHOR]

A novel method, Thermally Modified Non-Solvent Induced Phase Separation (T-NIPS) has been developed to fabricate translucent hollow fiber (THF) photocatalytic membrane for membrane's photodegradation efficiency enhancement. The process involves two-step temperature treatment that attacks crystalline property of polyvinylidene fluoride (PVDF). Graphitic carbon nitride in a modified morphological structure (hollow nanofiber) was used as photocatalyst to investigate the effect of translucency on membrane's photodegradation efficiency. UV-Vis analysis coupled with FTIR highlighted different crystalline phase appearance and membrane's translucency. The membranes showed high translucency, ranging from 60.0% to 93.9%, with THF-PVDF/PVP-GCN (2.0) exhibiting the highest. The filtration experiment showed that membrane with GCN photocatalyst had high PWF (1200 L/m2h) and rejection (90%) OPW compared to neat THF-PVDFs. In suspended mode, GCN demonstrated an impressive photodegradation efficiency of 99.98%. When immobilized in opaque PVDF membrane, the photodegradation has decreased substantially to 49.40%. However, when immobilized in a translucent PVDF membrane, the photodegradation efficiency of HN-GCN significantly improved compared to the opaque PVDF membrane, reaching 95%. Translucent membrane was subjected to five cycle regeneration test and showed 90% recovery even after the fifth cycle. The 10% reduction in the recovery was investigated using FESEM analysis revealed that there is a cake layer formation on the membrane surface. Therefore, this study proved that translucency of membrane has significant effect on immobilized photocatalyst's photocatalytic efficiency. [Display omitted] • Novel T-NIPS method to produce THFM is developed. • HN-GCN successfully immobilized in THFM. • HN-GCN immobilized THFM showed increased degradation efficiency of OPW. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A low cost kaolin was utilized in fabrication of ceramic hollow fibre membrane. • Surface modification with fluoralkylsilane agent was applied. • Modified membrane has a contact angle value of 145 and average pore size of 0.32 µm. • Excellent performance of 100% arsenic removal was achieved. Abstract In this work, a low cost hydrophobic kaolin hollow fiber membranes (h-KHFM) was successfully prepared by phase inversion/sintering technique followed by a modification via grafting with fluoroalkylsilane (FAS) molecules. The influence of sintering temperature varied from 1200 to 1500 °C on the hydrophobization and separation performance of kaolin hollow fiber membrane (KHFM) was investigated through direct contact membrane distillation (DCMD) system towards synthetic arsenic wastewater. The results reveal that h-KHFM prepared at a sintering temperature of 1300° °C induced a high contact angle value of 145°, an excellent LEPw value of 2 bar, and an average pore size of 0.32 µm. As a consequence, a high permeate flux of 28 kg/m2 h for As(III) and 25 kg/m2 h for As(V) with 100% arsenic rejection was obtained at a feed temperature of 60 °C and has met the required standard of maximum contaminant level (MCL) of 10 ppb. In addition, arsenic concentrations of up to 1000 ppm with various pH values of arsenic were also investigated using h-KHFM sintered at 1300 °C and there was no arsenic detected in the permeate. [ABSTRACT FROM AUTHOR]

This study involves the preparation of a double-skinned thin film composite (TFC) and thin film nanocomposite (TFN) hollow fiber (HF) membrane for forward osmosis (FO) applications. The porous substrate consisted of a Polyvinyl chloride (PVC) / Polycarbonate (PC) blend HF membrane. Interfacial polymerization (IP) was then applied to coat a polyamide (PA) layer on the lumen surface and the porous substrate's outer surface. In addition, the impact of the outer PA active layer and the addition of nanoparticles to the outer selective layer on the FO flux and internal concentration polarization (ICP) were studied. By adding the second active layer to the substrate, water flux, reverse salt flux and ICP decreased. Also, the decline of water flux decreased over time due to the fouling agent. To compensate for the decrease in water flux in the double-skinned membrane, graphene oxide (GO) nanoparticles with 0.05% and 0.1%wt were added to the outer active layer. Addition of 0.1%wt graphene oxide nanoparticle to the outer active layer can help to improve water flux about 78% without spoiling the reverse salt flux. Moreover, the performance of double-skinned membranes against osmotic dilution process for oily wastewater treatment was investigated. The findings of this study demonstrated that the novel double-skinned TFN HF membrane exhibited high FO performance with low ICP and fouling. [Display omitted] • Inclusion of a second active layer without reducing the reverse salt flux and fouling. • To improve fouling resistance of membrane, GO was added to second active layer. • By adding GO to outer active layer, reverse salt flux and fouling was reduced. • The Hermia model showed intermediate blocking in neat membrane. • The predominant fouling in double-skin membranes is cake formation. [ABSTRACT FROM AUTHOR]

The aim of this work was to investigate the effects of heat treatment applying hot air at different temperatures and durations on the morphology and the performance of polyetherimide (PEI) hollow fiber membrane contactors for CO 2 separation. The membranes were fabricated via a wet spinning into non solvent bath technique. Then, the membranes were heat treated by exposing them at 80,120 and 160 °C for all time intervals of 5, 15 and 30 min under a hot air atmosphere. To study the influence of the hot air on the membranes structural parameters and the performance of the membranes they were characterized by: gas permeation test, membrane overall porosity measurement, critical entry pressure of water (CEPw) and gas absorption via a membrane contacting process. The experimental results revealed that, the greatest effect on the membranes structure was observed in the shortest time duration and the lowest temperature i.e. 5 min and 80 °C, which exhibited a pore size of 49 (nm), a maximum effective surface porosity of 26.8 (1/m) and a CEPw of 3.4 bar. Also, for all the time periods and the temperatures tested, the density of the fibers reduced and the CEPws along with the overall porosities increased. In conclusion, applying heat treatment technique on PEI hollow fiber membranes is a simple and easy approach to improve the performance of hollow fiber membrane contactors for CO 2 removal. [ABSTRACT FROM AUTHOR]

A photocatalytic reactor based on novel dual-layer hollow fibre membranes with immobilized titanium dioxide (TiO 2 ) nanoparticles was proposed in this study and tested for the degradation of highly recalcitrant endocrine disrupting compound of nonylphenol (NP). The presence of TiO 2 on the outer surface of dual-layer hollow fibres was confirmed by scanning electron microscopy (SEM), energy dispersion of X-ray (EDAX), and atomic force microscopy (AFM). The effect of TiO 2 loading, where the mass fraction TiO 2 /PVDF was varied from 0 to 1, on the degradation of toxic NP was evaluated by high-performance liquid chromatography (HPLC). The addition of TiO 2 nanoparticles showed a significant effect on the membrane pore size and NP degradation rate. The presence of TiO 2 on the outer layer of dual-layer hollow fibre membranes actively functioned as a photocatalyst, with the hollow fibre of TiO 2 /PVDF ratio of 1 possessed the highest NP degradation rate. [ABSTRACT FROM AUTHOR]

In this work a novel method to evaluate the partial pore wetting of gas absorption membranes is proposed. The method consists of two approaches, one by energy-dispersive X-ray spectrometry (EDX), and the other by calculating the mass transfer resistances from the gas and liquid phase in the pore, using the parameter obtained by He gas permeation experiments. For this purpose, hollow fibers were spun from polyetherimide (PEI) and polyethersulfone (PES). As well, the lumen of a PEI hollow fiber was coated with silicone rubber. The hollow fibers were then characterized by He gas permeation experiments, critical entry pressure of water (CEPw), contact angle, scanning electron microscopy (SEM) and EDX. The hollow fibers were then subjected to CO 2 gas absorption using aqueous NaCl solution as absorbent. After drying the hollow fiber was subjected to the EDX analysis. The cross-sectional profile of Na and Cl content in the hollow fiber revealed that the pores of the PES hollow fibers were partially wetted, particularly at the pore inlet. Calculation of mass transfer resistances, on the other hand, revealed that the resistance came from gas phase in most hollow fibers, except for the PES hollow fiber where the liquid phase contribution was significant. Silicone rubber coating of the PEI hollow fiber increased the surface hydrophobicity and reduced the pore wetting considerably. Thus, it was concluded that the proposed method can be used as a powerful tool to investigate the pore wetting for many membrane contactor applications. [ABSTRACT FROM AUTHOR]

Over recent years, there has been an explosive growth of interest in the development of alternative approaches for crude palm oil (CPO) refining. During a typical refinery process, free fatty acid (FFA) is one of the key objectionable impurities that need to be reduced if not completely removed from CPO in order to minimize their detrimental effects on the oil quality. Polyvinylidene fluoride (PVDF) membrane shows great potential in removing FFA from CPO owing to its hydrophobic properties, high mechanical strength and good thermal stability. However, low concentration of FFA in CPO, which is normally ranging from 3% to 5%, has hindered the capability of the membranes to separate the trace amount of FFA from the bulk. Thus, modification of PVDF membrane is essential to enhance the interaction between the membrane surface and FFA molecules, facilitating efficient FFA removal. In order to achieve this purpose in the present study, the outer surface of PVDF hollow fiber membranes was crosslinked with polyvinyl alcohol (PVA). Glutaraldehyde (GA) was used as a crosslinking agent to avoid the PVA dissolution. Despite the negligible morphological change observed in the resultant membranes upon PVA crosslinking, the contact angle has been significantly reduced in proportional to the concentration of PVA used for the crosslinking, suggesting the decrease in membrane hydrophobicity. Additionally, the average roughness of the crosslinked PVDF membranes increased with the increasing PVA concentration. The results obtained suggested that the PVDF hollow fiber crosslinked with 100 ppm PVA exhibited the highest FFA rejection of 5.93% after 3 h of operation. In addition, the membrane also showed good result in reducing the content of phosphorus in the permeate and partial reduction of its color intensity. This study served as the first attempt of CPO deacidification through UF membrane system without the addition of any chemical during the filtration process. [ABSTRACT FROM AUTHOR]

Dual-layer hollow fiber (DLHF) membranes prepared via a phase inversion based co-extrusion technique offer a number of advantages, such as self-supporting structure, high active surface area to volume ratio, easy fabrication and ability to withstand high operating pressure. This paper reports novel DLHF membranes fabricated via a single step co-extrusion technique with immobilized titanium dioxide (TiO 2 ) nanoparticles embedded in their outer layer. In this work, the DLHF membranes were prepared by extruding two different dope solutions simultaneously, in which the inner layer consisted of poly(vinylidene fluoride) (PVDF) and solvent N,N-dimethylacetamide (DMAc) while the outer layer was a mixture of PVDF, TiO 2 and DMAc. The effect of TiO 2 loading, where the mass fraction of TiO 2 /PVDF was varied from 0 to 1, on the morphologies and properties of the DLHF membranes were investigated using scanning electron microscopy (SEM), contact angle goniometer, surface roughness and filtration experiments. The SEM results showed that DLHF membranes have a good interfacial adhesion between layers with no delamination found. The structure of the membranes characterized by the length of their finger-like voids was significantly affected by the TiO 2 addition. The void lengths were elongated by the rise of the TiO 2 loading up to certain fraction of TiO 2 /PVDF. Based on all the findings, it can be concluded that the proposed method of producing the DLHF membranes could provide good layer–layer interfacial adhesion and well-dispersed TiO 2 in their outer layer. [ABSTRACT FROM AUTHOR]

Studies on mixed matrix membrane (MMM) have been sprouting rapidly since the last few decades, but mostly fabricated in the form of dense, flat films. In this work, hollow fiber Polysulfone (PSF)-Cloisite®15A (C15A) MMM were produced using our in-house hollow fiber spinning machine. Various spinning parameters are at play in order to ensure the formation of defect-free high performance hollow fiber. Spinning process parameters such as dry gap height, force convection rate, dope extrusion rate, and take-up speed have been systematically studied in order to identify the optimum fabrication conditions. Extensive characterizations on the membrane morphology, membrane surface properties, polymer d -spacing and gas separation performance were conducted using SEM, AFM, XRD, and pure gas permeation experiment. The appropriate balance between dry-gap residence time and force convective rate is essential to yield membrane with good permeability–selectivity combinations. CO 2 permeance was increased from 17.39 to 56.25 × 10 − 6 cm 3 (STP)/cm 2 s cmHg when the dope extrusion rate was increased from 1.5 cm 3 /min to the optimum extrusion rate of 2.5 cm 3 /min. Membranes spun at high collection speed (up to 35 m/min) exhibited practically attractive fiber geometry comparable to commercial hollow fibers (∼300 μm diameter) but the permeation properties were rather disappointing which might be caused by excessive deformation of polymer chain due to stretching. Hollow fiber MMM containing layered organoclay has exhibited excellent CO 2 /CH 4 pure gas selectivity of 40.26%, 46% higher than that of pristine hollow fiber fabricated under the same optimized conditions without compromising the CO 2 flux. The MMM was also found to be more thermally and mechanically robust in comparison to its neat counterpart. [ABSTRACT FROM AUTHOR]

Highlights: [•] AFM analysis on the PVDF hollow fiber membrane’s surface for CO2 stripping. [•] Increasing LiCl concentration has decreasing effect on membrane surface parameters. [•] Addition of LiCl has improved the overall membrane mass transfer coefficient. [Copyright &y& Elsevier]

Abstract: A more soluble polyaniline derivative, i.e. poly(o-anisidine), (POAn), was synthesized in-house for this study by using an ortho substituted aniline monomer. It was observed that the prepared dope solution was more homogeneous with less visible agglomerates as compared to previously prepared polyaniline (PAni) solution. Integrally skinned hollow fibre membranes were successfully prepared by dry-jet wet spinning from POAn with N-methyl-2-pyrrolidone as a solvent and a more volatile tetrahydrofuran as a co-solvent for gas separation. The spinning air-gap lengths were varied to promote the formation of the membrane skin layer. POAn membranes prepared at higher air gap were more orientated with packed structure and good gas separation characteristics. They showed selectivities of O2/N2, CO2/N2, H2/N2 and H2/CO2 of about 13, 89, 370 and 4.2, respectively with permeation rates of H2, CO2 and O2 about 10.4, 2.5 and 0.37×10−6 cm3 (STP)/cm2 scmHg, respectively. Presence of methoxy group in POAn showed substantial enhancement in gas permeation properties compared to previously developed PAni membranes. The H2/N2 and CO2/N2 selectivities were improved by 3 and 7 times, respectively as compared to PAni membranes. Development of hollow fibre membranes using polyaniline derivative with improved processability and excellent gas separation performance depicts their potential for industrial gas separation applications. [Copyright &y& Elsevier]

Abstract: Low molecular weight organic compounds were added to the spinning dope as phase inversion promoters and their effects on the structure of polyetherimide (PEI) hollow fibers as well as their performance as membrane contactor were investigated. Water, methanol, ethanol, glycerol and acetic acid were added individually to the solvent NMP to prepare a dope containing 15wt% PEI, 4wt% additive, 81wt% NMP and hollow fiber membranes were fabricated via wet spinning method. The solution containing water as the additive had the lowest thermodynamic stability and highest viscosity, which yielded hollow fiber with a thin skin layer of high porosity and a sublayer with sponge-like structure. The four other polymer solutions were more stable thermodynamically and less viscous. Fast solvent/coagulant exchange yielded thick skin layers of lower porosity and sublayers of finger-like macrovoids. Among all fabricated follow fibers, adding methanol resulted in the highest absorption flux, which was ascribed to its high porosity and low tortuosity. [Copyright &y& Elsevier]