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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]

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: [•] 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: 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 polyvinylidene fluoride (PVDF) hollow fiber membrane was fabricated via a dry–wet phased inversion process. A surface modifying macromolecule (SMM) was used as an additive in the spinning dope. During phase inversion SMM migrates to the membrane surface and functions as both a pore former and surface modifier. The surface modified PVDF membrane showed large pore size, higher effective surface porosity, contact angle and porosity but lower critical water entry pressure compared to the PVDF hollow fiber membrane without SMM. The performance of the surface modified membrane in contactor application for CO2 absorption via distilled water as absorbent was studied. The results show that the surface modified PVDF membrane has higher performance compared to control PVDF membranes. With the membrane prepared from SMM in the spinning dope a maximum CO2 flux of 7.7×10−4 mol/m2 s was achieved at 300ml/min of absorbent flow rate, which was almost 93% more than the other membrane.In a long-term stability study, CO2 flux was decreased only about 7.7% by using surface modified PVDF membrane during 150h operation. [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: 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: 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: 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]

• 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]

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]

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]

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: 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]

Surface modified polysulfone (PSf) hollow fiber membranes (HFMs) using surface modifying macromolecules (SMM) were spun with air-gaps of 0–50 cm. Morphological analysis of the prepared fibers were carried out using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The wetting resistances of the membranes were determined by critical water entry pressure (CEPw) and contact angle (CA) measurements. The HMFs were further subjected to CO 2 capture by membrane contactor (MC) where water was used as absorbent. The test results indicated that both CEPw and CA showed a maximum value at 15 cm air-gap distance. The maximum He permeation was also achieved at 15 cm air-gap. The CO 2 flux of prepared membranes showed a maximum of 4.79 × 10 −3 mol/m 2 s at the absorbent flow rate of 300 ml/min. It was deduced that both He permeation and CO 2 absorption flux were governed by the HFM surface porosity. The long-term stability test revealed the reduction of 25% in CO 2 flux during the first 55 h of operation for the PSf membrane prepared at 15 cm air-gap. This study indicated that the surface modified HFMs prepared using an appropriate air-gap could be a promising option to increase membrane performance in MC systems. [ABSTRACT FROM AUTHOR]

Highlights: [•] Different amounts of SMM were used to improve the surface hydrophobicity of PVDF HFM. [•] The PVDF HFMs were used in contactor application for CO2 stripping from water. [•] The CO2 stripping flux and efficiency increased by increasing SMM concentration. [•] The gas flow rate has no significant effect on the CO2 desorption flux. [ABSTRACT FROM AUTHOR]