Porous Polyvinylidene Fluoride Hollow Fiber Research Articles

Surface modification of porous polyvinylidene fluoride hollow fiber membrane by sulfonated poly(ether ether ketone) coating for membrane distillation of oily wastewater

AbstractHighly porous polyvinylidene fluoride hollow fiber membranes were fabricated by a non‐solvent induced phase separation process. The membranes were modified by coating an ultra‐thin hydrophilic layer of sulfonated poly(ether ether ketone) (sPEEK) onto the inner surface. An industrial oily wastewater treatment was performed through an air gap membrane distillation (AGMD) process. From field emission scanning electron microscopy, the modified membrane showed an open structure with a large finger‐like outer layer and sponge‐like inner layer. The thickness of the coated sPEEK layer on the inner surface was about 0.5 μm. The coated membrane presented mean pore size of 36 nm and overall porosity of 73%. The inner surface water contact angle decreased from about 82° to 57°. Using Langmuir adsorption experiment, minor oil adsorption on the modified membrane surface was confirmed. A stable water flux of about 12 kg m−2 h−1 and oil rejection of 99% were found during 72 h of the AGMD process for treating the oily wastewater of NGL‐900 (Gachsaran, Iran) plant. The high flux recovery ratio of about 98% was related to the improved anti‐oil‐fouling property. The modified membrane can be a potential candidate for oily wastewater treatment through the MD processes.

Fabrication of a super-hydrophobic polyvinylidene fluoride hollow fiber membrane using a particle coating process

Membranes with outstanding anti-wetting property are essential for membrane distillation (MD) applications. In this work, a hydrophobization treatment for porous polyvinylidene fluoride (PVDF) hollow fiber membranes using an etching method combined with an ultrafiltration coating process was developed to achieve this desired property. PVDF particle was subjected to an etching process to coarsen its surface. Etched PVDF particles were subsequently dispersed in a dispersant with a specific PVDF-dissolving capacity and then coated onto the PVDF hollow fiber membrane surface via ultrafiltration to construct a super-hydrophobic surface with a micro/nanostructure. After this process, the super-hydrophobic PVDF hollow fiber membrane with the surface contact angle of 163.8°was obtained, and the coating layer on the membrane surface was exceedingly stable. Moreover, the membrane pores were not blocked by the coating layer. The optimal etching conditions for the PVDF particles were as follows: solubility parameter of the etchant, 25.6 (J/cm3)1/2; etching time, 60min at 25°C. A super-hydrophobic surface with a stable particles coated layer is achieved in an optimal coating condition (solubility parameter of the dispersant, 25.87 (J/cm3)1/2; PVDF particles coated, 18.0g/m2). The direct contact membrane distillation (DCMD) experiments showed that after the surface modification process, the hydrophobicity of the membrane was significantly enhanced. In addition, the anti-wetting property of the membrane improved, the time for membrane to be wetted through the channel increased from 40 to 180min, the pure water DCMD flux increased from 26.0 to 29.9kgm−2h−1, and the critical wetting depth increased from 19.5 to 35.7µm.

Highly porous PVDF hollow fiber membranes for VMD application by applying a simultaneous co-extrusion spinning process

Highly porous polyvinylidene fluoride (PVDF) hollow fiber membranes are of great interest for membrane contactor applications such as sea water desalination by membrane distillation in order to enhance the flux of the process. For the first time in this paper, porous hydrophobic PVDF asymmetric hollow fiber membranes with a high outer surface porosity for use in vacuum membrane distillation (VMD) were successfully fabricated by applying a simultaneous co-extrusion spinning process through the non-solvent induced phase separation (NIPS) method. In this approach, five kinds of dual-layer composite membranes were prepared by employing different inner and outer polymer dopes. Single-layer membrane was also fabricated through the conventional dry-jet wet phase inversion method. Results revealed that the introduction of the simultaneous co-extrusion spinning process greatly increased the outer surface porosity of the dual-layer composite membranes. It was also observed that the VMD flux of the dual-layer membranes spun through the simultaneous co-extrusion spinning process was 54% higher than the single-layer membrane fabricated by the conventional dry-jet wet phase inversion method. A VMD flux as high as 61.8kg/(m2h) at 70°C was obtained for the novel dual-layer composite membranes.

Effect of hydrophobic montmorillonite (MMT) on PVDF and PEI hollow fiber membranes in gas–liquid contacting process: a comparative study

Porous polyvinylidene fluoride (PVDF) and polyetherimide (PEI) hollow fiber mixed matrix membranes are successfully fabricated for CO2 absorption via membrane contactor.

Effect of take‐up speed on polyvinylidene fluoride hollow fiber membrane in a thermally induced phase separation process

AbstractThe porous polyvinylidene fluoride hollow fiber membranes were prepared via the thermally induced phase separation process using mixed diluent. The effects of take‐up speed on the structure of membranes were investigated by scanning electron microscopy, differential scanning calorimetry, and wide‐angle X‐ray diffraction. The membrane properties were measured in terms of the pure water flux, porosity, and mechanical properties. The results showed that the cross‐sectional structure of membrane had an obvious change and presented a uniform structure when TS increased to 72 m min−1, whereas the membrane made from TS <41 m min− presented an interconnected aggregation structure. However, the change of surface structure of all membranes was hardly observed. In addition, the strength and elongation of breakage of membrane increased obviously with the increase of TS, whereas the pure water flux and porosity changed slightly. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Characterization of surface-modified porous PVDF hollow fibers for refinery wastewater treatment using microscopic observation

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 19 wt.% PVDF, 0.98 wt.% lithium chloride (LiCl.H 2O) and 0, 1.95, and 3.85 wt.% titanium dioxide (TiO 2). Significant difference of spun fibers surface morphology was observed between inner and outer surface by AFM and FESEM. Higher TiO 2 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.

CO 2 stripping from water through porous PVDF hollow fiber membrane contactor

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. CO 2 stripping from water was conducted through the gas–liquid membrane contactor. The effect of different operating conditions on the CO 2 stripping efficiency of the membrane was investigated. The results indicated a significant improvement in the CO 2 stripping efficiency by increasing the liquid phase temperature. On the other hand, increasing the liquid flow rate resulted in a considerable decrease in the CO 2 stripping flux. The maximum stripping efficiency of 32% was achieved at 60 ml/min of the liquid flow rate, 60 °C and 0.5 × 10 5 Pa. It was found that the liquid phase temperature, the gas–liquid contact area and contact time are the key parameters for enhancement of CO 2 stripping efficiency.

Effect of operating conditions on the physical and chemical CO2 absorption through the PVDF hollow fiber membrane contactor

Porous polyvinylidene fluoride (PVDF) hollow fiber membranes were fabricated via a wet phase-inversion process and used in the gas–liquid membrane contactor for physical and chemical CO2 absorption. Effect of different operating parameters such as absorbent temperature, CO2 pressure, absorbent flow rate and long-term operation on the CO2 flux of the membrane were investigated. The characterization results showed that the prepared membrane possess small pore size with high surface porosity and wetting resistance, which are favorable for gas absorption application. Results of CO2 absorption experiments revealed that in case of physical absorption with distilled water, CO2 solubility was the key parameter which significantly affected the membrane CO2 flux. A significant increase in the CO2 flux was observed by increasing CO2 pressure and decreasing the absorbent temperature. However, in case of chemical absorption with NaOH (1 M), the reaction rate was dominant, where the CO2 flux was significantly increased by increasing the absorbent temperature. It was also found that when the liquid contacted the outer skin layer of the hollow fiber membrane, the operation was stable at the same gas and liquid pressure without bubble formation in the liquid phase. In addition, the results of long-term study demonstrated that the membrane performance was maintained constant for long-term operation. The initial flux reduction was found to be about 30% within the 23 h of physical absorption, and 20% of gradual reduction within 80 h of chemical absorption.