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Abstract Carbon dioxide (CO2) is responsible for increment of the Earth surface temperature and the subsequent environmental issues. In this regard, membrane contactor is one of the emerging technologies that can be applied for controlling CO2 emission. More specifically, the intrinsic structure of membrane plays an important role to govern the performance of CO2 absorption. In this study, considering stretching ratio (SR) as a key factor to affect membrane structural properties, highly porous poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) hollow fiber membranes were fabricated by a non-solvent induced phase separation method. The results showed that the membrane dimension and thickness were significantly reduced by optimizing the SR. The optimum membrane structure was found at SR of 1.5 where the mean pore size, CO2 permeance, collapsing pressure and liquid entry pressure of 0.032 μm, 3440 GPU, 550 kPa and 500 kPa were achieved, respectively. The prepared membranes showed open structure with overall porosity of more than 80%. The upgraded membrane at SR of 1.5 presented the maximum CO2 absorption flux of 9.8 × 10− 4 mol/m2 s and the minimum mass transfer resistance of 49,544 (m/s)−1. Furthermore, a stable CO2 absorption performance was achieved during 80 h continuous operation with a flux decline of only about 9%. The findings of this work demonstrated that by applying a cost-effective fabrication method, we can potentially enhance the PVDF-HFP membrane properties for CO2 adsorption without requiring an additional post-modification step.

• SMM coating of porous poly(vinylidene fluoride-co-hexafluoropropylene) membranes was performed. • Contact angle of 109°, porosity of 82% and mean pore size of 18 nm were obtained. • Extraction of phenol through a membrane contactor system was investigated. • The maximum phenol flux of 2.02 × 10−3 kg/m2s was predicted by the response surface methodology. • The modified hollow fiber membrane is a proper option for industrial wastewater treatment. Strict environmental regulations have been recognized for phenolic wastewater treatment due to toxicity of the phenolic compounds. In this study, solvent extraction of a phenolic wastewater was investigated via a liquid-liquid membrane contactor system. Porous poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) hollow fiber membranes were modified by coating an ultra-thin layer of hydrophobic surface modifying macromolecule (SMM). The membranes were characterized by various tests such as SEM-EDS, nitrogen permeation, overall porosity, contact angle and critical water entry pressure (CEP w). From SEM, an open structure with combination of finger-like and sponge-like structure was produced. The membrane exhibited high surface hydrophobicity (water contact angle of 109°) with good wetting resistance, overall porosity of 82% and mean pore size of 18 nm. From response surface methodology (RSM), the maximum phenol extraction flux of 2.02 × 10−3 kg/m2s was estimated by the model at the optimum process variables as phenol concentration of 448 mg/L, feed temperature of 42 °C, aqueous phase flowrate of 196 mL/min and organic phase flowrate of 117 mL/min. The coefficient of determination (R2) of 0.972 showed a close proximity between the model and the experimental data. The membrane showed a reasonable flux that can be a favorable alternative for industrial phenolic wastewater treatment. [Display omitted] [ABSTRACT FROM AUTHOR]

Porous hydrophobic poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) hollow fiber membranes were prepared via a wet spinning process using polyethylene glycol (PEG-400) and ortho-phosphoric acid (PA) in the spinning dope. CO 2 stripping from diethanolamine (DEA) solution was conducted through the gas–liquid membrane contactor modules. By obtaining cloud point diagrams, higher phase inversion rate was confirmed for the solution with PA. The smaller finger-like macrovoids were resulted when using the non-solvent additives. The membranes with higher surface porosity and smaller mean pore size were produced when using the additives in the spinning dope. The improved PVDF-HFP/PA membrane had the mean pore size of 0.015 µm and permeability of 13,100 GPU. This membrane showed a minimum mass transfer resistance of 15,982 (m/s) −1 which is about 68% less than the resistance of plain PVDF-HFP membrane. The improved PVDF-HFP/PA membrane showed CO 2 stripping flux of about 9 × 10 −3 mol/m 2 s at the liquid velocity of 0.045 m/s. [ABSTRACT FROM AUTHOR]

Abstract: The outer surface of polyvinylidene-co-hexafluoropropylene (PVDF–HFP) asymmetric microporous hollow fiber membrane prepared by phase inversion process was activated by 10wt.% of NaOH solution, and subsequently modified with the mixture solution of α,ω-triethoxysilane terminated perfluoropolyether or Fluorolink®S 10 (FS10) and tetraethoxysilane (TEOS) in order to enhance the hydrophobicity of the membrane. The chemical and physical changes of the membranes were investigated by attenuated total reflection infrared spectroscopy FTIR-ATR and scanning electron microscope (SEM). The characteristics of the modified membrane were examined in terms of liquid entry pressure of water (LEPw), pore size and pore size distribution, contact angle and mechanical properties. The modified fibers were also used in the membrane contactor system to evaluate their performance for CO2 absorption. FTIR-ATR result showed the enrichment of fluorine and ethoxysilane on the modified PVDF–HFP membranes leading to higher LEPw and contact angle than those of the unmodified membrane by 36% and 33%, respectively. The contact angle increased from 95.5° to 127.8°. Compared to the unmodified PVDF–HFP hollow fiber, the cross-sectional morphology and mechanical properties of the modified membrane changed insignificantly, while the membrane mean pore size was reduced from 32.7nm to 25.2nm. The CO2 physical absorption performance of the modified fibers was better than the unmodified fibers. The membrane mass transfer coefficients of the unmodified and modified PVDF–HFP hollow fiber were 5.69×10−5 and 7.56×10−5 m/s, respectively, indicating that the modified membranes have good potential for application in the gas absorption process. [Copyright &y& Elsevier]