Surface modified polyvinylydene flouride hollow fiber membrane contactor with different air-gaps for carbon dioxide absorption

The main objective in this research was to study the effect of air-gap length, one of the main spinning parameters, on the structure and carbon dioxide (CO2) absorption performance of hollow fiber membrane (HFM), while other spinning conditions were kept constant. Firstly, surface modified Polyvinylidene fluoride (PVDF) hollow fiber membranes were spun via dry-wet spinning method under different air-gap lengths (0-20 cm). Then the morphology of prepared membranes was evaluated by scanning electron microscopy (SEM). Also membranes structure was examined in terms of gas permeation, overall porosity, critical water entry pressure (CEPw) and contact angle. To determine the CO2 flux of HFMs, a system of gas-liquid membrane contactor was used. Experimental results of this study reveal that by increasing the air-gap distance from 0 to 20 cm, wetting resistance and contact angle of fabricated membranes increased due to enhancement of membrane surface hydrophobicity in higher air-gaps. Moreover, a decrease in average pore size of fabricated membranes was observed in higher air-gaps. The highest helium (He) permeation was achieved for the spun fiber at the air-gap of 10 cm. From CO2 absorption experiment it was found that the prepared membrane at the air-gap of 10 cm had the maximum CO2 flux of 1.57×10-3 mol/m2.s at the absorbent flow rate of 300 ml/min, which was significantly higher than CO2 flux of other PVDF membranes produced by other researchers. This significant increase in the CO2 flux could be related to its high effective surface porosity. Considering the high CO2 flux of this membrane, it can be concluded that in this study, the optimum air-gap distance was 10 cm to fabricate surface modified PVDF hollow fiber membranes using dry-wet spinning method. Lastly, it was found that applying an appropriate air-gap length for fabrication of surface modified hollow fiber membranes could be a promising method to improve CO2 removal in membrane contactor systems

Surface modification of polysulfone hollow fiber membrane spun under different air-gap lengths for carbon dioxide absorption in membrane contactor system

Surface modified polysulfone (PSf) hollow fiber membranes (HFMs) using surface modifying macromolecules (SMM) were spun with air-gaps of 0-50cm. 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 CO2 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 15cm air-gap distance. The maximum He permeation was also achieved at 15cm air-gap. The CO2 flux of prepared membranes showed a maximum of 4.79×10-3mol/m2s at the absorbent flow rate of 300ml/min. It was deduced that both He permeation and CO2 absorption flux were governed by the HFM surface porosity. The long-term stability test revealed the reduction of 25% in CO2 flux during the first 55h of operation for the PSf membrane prepared at 15cm 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

Mass transfer analysis of CO2 capture by PVDF membrane contactor and ionic liquid

Post-combustion processes based on ionic liquids (ILs) and membrane contactors are attractive alternatives to traditional systems. Here, a gas stream composed of 15% CO2 and 85% N2 flowed through the lumen side of a hollow-fiber membrane contactor containing poly(vinylidene fluoride)-IL (PVDF-IL) fibers. The IL 1-ethyl-3-methylimidazolium acetate [emim][Ac] served as an absorbent due to its high chemical absorption and CO2 solubility. The overall mass transfer coefficient (Koverall), activation energy (Ea), and resistances of the hollow-fiber membrane were quantified. The Koverall value was one order of magnitude higher than those reported in previous works with conventional solvents, and the Ea was lower than formerly stated values for other solvents. A theoretical simulation was conducted to estimate the operational parameters required for 90% CO2 capture and to quantify intensification effects related to CO2 absorption in a packed column.This research was funded by the Spanish Ministry of Economy and Competitiveness (Projects CTQ2013-48280-C3-1-R and CTQ2016-76231-C2-1-R). The authors thank Dr. J. C. Remigy (Laboratoire de Genie Chimique, UPS, Toulouse, France) for the preparation of 1AQ2-PVDF fibers

Effect of air-gap length on carbon dioxide stripping performance of a surface modified polysulfone hollow fiber membrane contactor

Surface Modifying Macromolecule (SMM) blended PSf hollow fibers were spun at different air-gaps to evaluate CO2 stripping from aqueous DEA solution and water. The fabricated membranes were firstly subjected to different characterization methods such as contact angle and liquid entry pressure measurement to evaluate the membrane's hydrophobicity and wetting resistance, respectively. To determine pore size and effective porosity of the membranes, a pure helium permeation test was performed. Morphological study of the membranes was conducted by scanning electron microscopy (SEM) and atomic force microscopy (AFM). A CO2 stripping test was carried out to investigate the effects of operating variables such as liquid and gas velocity, temperature and DEA concentration on the CO2 stripping flux. It was found that the increase of liquid velocity resulted in enhanced CO2 stripping flux. On the other hand, the increase in gas velocity did not exert significant influence on the stripping flux. The increase in temperature and DEA concentration both enhanced the stripping flux. Lastly, it was concluded that the hollow fibers spun in this work at a 15 cm air-gap could achieve the best stripping flux among all the membranes fabricated so far for CO2 strippin

Study on the effect of air-gap length on properties and performance of surface modified PVDF hollow fiber membrane contactor for carbon dioxide absorption

Surface modified polyvinylidene fluoride (PVDF) hollow fiber membranes (HFMs) were spun via dry-wet spinning technique at different air-gap lengths (0-20 cm). The morphology of prepared membranes was evaluated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Membranes were also characterized in terms of gas permeation, overall porosity, collapsing pressure, critical water entry pressure (CEPw) and contact angle. To determine the CO2 absorption flux of HFMs, a gas-liquid membrane contactor system was used. Experimental results of this study revealed that by increasing the air-gap distance from 0 to 20 cm, wetting resistance and contact angle of fabricated membranes increased due to enhancement of membrane surface hydrophobicity. The highest helium (He) permeation was achieved for the spun fiber at the air-gap of 10 cm. From CO2 absorption experiment it was found that the hollow fiber spun at the air-gap of 10 cm had the maximum CO2 absorption flux of 1.41 x 10(-3) mol/m(2) s at the absorbent flow rate of 300 ml/min, which was significantly higher than CO2 absorption flux obtained by other researchers. It was also found that both highest He gas permeance and CO2 absorption flux were controlled by the surface porosity of the hollow fiber due to the maximum values obtained. Thus, the choice of an appropriate air-gap distance for fabrication of surface modified membranes was found to be a promising method to improve CO2 removal in membrane contactor systems

Influence of air-gap length on CO2 stripping from diethanolamine solution and water performance of surface modified PVDF hollow fiber membrane contactor

Surface Modifying Macromolecule (SMM) blended PVDF hollow fibers (HFs) were spun at different air-gaps (o to 20 cm) and used for CO2 stripping from aqueous DEA solution and water. The manufactured fibers were firstly subjected to various characterization tests such as contact angle and critical water entry pressure measurement to evaluate the HF hydrophobicity and wetting resistance, respectively. The pure helium permeation experiments were also conducted to obtain membrane pore size and effective porosity. Morphology of the HFs was investigated by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The SEM images showed that both outer and inner diameters of HFs decreased significantly by increasing air-gap length which mainly because of elongation of HF caused by gravity while travelling through the air-gap. Also, the gradual decrease in roughness on the external surface of the produced HFs was observed from the AFM images. It was found that the increase of liquid velocity enhances the CO2 stripping flux. It was found that 10 cm air-gap gave maximum stripping flux of 3.34 x 10(-2) and 1.34 x 10(-3) (mol/m(2)s) for DEA solution and water, respectively. The increase in gas velocity, on the other hand, did not affect the stripping flux significantly. It was observed that the increase of temperature from 25 to 80 degrees C led to the marked enhancement of stripping flux from 6.30 x 10(-3) to 3.34 x 10(-2) (mol/m(2)s) and 6.5 x 10(-5) to 1.34 x 10(-3) (mol/m(2)s), for DEA solution and water, respectively. Furthermore, the increase in DEA concentration from 0.25 to 1 mol/L, led to the enhancement of the stripping flux from 6.84 x 10(-3) to 3.34 x 10(-2) (mol/m(2)s) at a liquid velocity of 0.7 m/s. It was concluded that the HF spun at 10 cm air-gap exhibited the best stripping performance among all fabricated HFs

Arsenate removal from contaminated water by a highly adsorptive nanocomposite ultrafiltration membrane

In order to overcome the limitations of the adsorption process, a new type of nanocomposite ultrafiltration (UF) membrane consisting of polyethersulfone (PES) and titanate nanotubes (TNTs) was fabricated in this work via the phase inversion technique and used for adsorptive arsenate (As(v)) removal. The effects of impregnating TNTs on the structural morphology, hydrophilicity, porosity, pure water permeability and As(v) uptake capacity of the nanocomposite membranes were studied for different weight ratios of TNT:PES in the membrane matrix, ranging from 0 to 1.5. Of the membranes studied, an As(v) uptake capacity as high as 125 mg g-1 was achieved using the membrane containing the highest amount of TNTs (designated as PES/TNT 1.5) and the performance of this membrane is comparable to most of the available adsorbents and other As removal systems. Increasing the TNT:PES weight ratio from 0 to 1.5 led to an increase of membrane pure water permeability from 39.4 to 1250 L m-2 h-1 bar-1 with the water contact angle decreased from 69.5° to 5.2°. The experimental findings from the continuous UF process revealed that the nanocomposite membrane of the highest TNT content could generate a permeate of high quality to meet the maximum As level set by the World Health Organization (WHO), i.e. <10 µg L-1. Furthermore, the adsorptive performance of the nanocomposite membrane could be easily regenerated using alkaline solution

A novel super-hydrophilic PSf/HAO nanocomposite ultrafiltration membrane for efficient separation of oil/water emulsion

In this work, flat sheet polysulfone (PSf)-based membranes modified with inorganic hydrous aluminum oxide (HAO) nanoparticles were used as antifouling ultrafiltration membranes for removing oil molecules from oily solution. SEM, AFM and FTIR analyses were performed on the fabricated membranes to study the effect of HAO nanoparticles loading on the membrane properties. The membrane hydrophilicity and separation performance were determined through contact angle measurement and cross-flow ultrafiltration of oily solution, respectively. Results showed that the hydrophilicity of HAO-modified membrane was increased remarkably upon addition of the highest weight ratio of HAO nanoparticles to PSf (i.e. 2:1), which led to a significant rise in permeate flux, achieving 1194 L/m2 h bar in comparison to 151 L/m2 h bar shown by the plain PSf membrane. With respect to oil removal efficiency, the modified membrane was found to exhibit almost complete elimination of oil molecules with flux recovery ratio of around 67% after a simple water washing process. The promising results achieved by the modified PSf membrane could be mainly due to the presence of hydroxyl functional groups on the membrane surface upon addition of highly hydrophilic HAO nanoparticles, which improved not only membrane water permeability but also its antifouling ability