Effect of shear rate on the performance of nanofiltration membrane for water desalination

Asymmetric nanofiltration membranes were fabricated from a ternary dope composition consisting of cellulose acetate (CA), formamide and acetone using a simple drylwet phase inversion process. In order to fabricate a high performance nanofiltration membrane, the effects of rheological factor of dope solutions, that is shear rate on the performance of nanof~tration membranes for water desalination has been studied. The membranes performances that are based on percentage of rejection of sodium chloride (NaCl) and fluxes with different concentrations of sodium chloride are reported. Generally, the percentage of rejection and fluxes were found to increase with increasing of shear rate until a critical level of shear rate is achieved. The experimental results showed that the fluxes were increased and percentage of rejection is decreased With sodium chloride concentrations. An optimum percentage of rejection and fluxes obtained were about 56.76 % and 7.44 x lo4 ds, respectively. The optimum shear rate was found to be at 304 s'l. It was also found that membranes with shear rate below 152s" are not suitable to be used as a nanofiltration membrane due to their low mechanical strength

Recent progresses of forward osmosis membranes formulation and design for wastewater treatment

Production of potable water or reclaimed water with higher quality are in demand to address water scarcity issues as well as to meet the expectation of stringent water quality standards. Forward osmosis (FO) provides a highly promising platform for energy-efficient membrane-based separation technology. This emerging technology has been recognized as a potential and costcompetitive alternative for many conventional wastewater treatment technologies. Motivated by its advantages over existing wastewater treatment technologies, the interest of applying FO technology for wastewater treatment has increased significantly in recent years. This article focuses on the recent developments and innovations in FO for wastewater treatment. An overview of the potential of FO in various wastewater treatment application will be first presented. The contemporary strategies used in membrane designs and fabrications as well as the efforts made to address membrane fouling are comprehensively reviewed. Finally, the challenges and future outlook of FO for wastewater treatment are highlighted

Limitation in fabricating PSf/ZIF-8 hollow fiber membrane for CO2/CH4 separation

Hollow fiber membrane configuration is way forward in membrane development since it possesses higher packing density and effective surface area per unit module compared to other configuration. Since majority of mixed matrix membrane (MMM) for gas separation reported focuses on flat sheet membrane development, this report aims to address the challenges faced in fabricating hollow fiber MMM. In this study, hollow fiber formulation is fabricated and their MMM using different types of fillers (virgin and modified ZIF-8) are prepared and used as a dispersed phase. The neat hollow fiber membrane shows good results with CO2 permeance of 104.39 GPU and CO2/CH4 selectivity of 29.28, in comparison with reported literature. Upon filler incorporation, the resulted MMMs appear to be diminished in both CO2 permeance and CO2/CH4 selectivity. While using modified ZIF-8, lesser deterioration was shown compared to pure ZIF-8, this phenomenon is likely to occur due to the changes in solution stability which causes notable changes in membrane morphology and performances

Polysulfone hemodialysis membrane incorporated with Fe2O3 for enhanced removal of middle molecular weight uremic toxin

Removing middle molecular weight uremic toxin remains as one of the most challenging tasks in hemodialysis. Hence, in this study a high performance polysulfone (PSf) hemodialysis membrane was developed by incorporating iron oxide (Fe2O3) nanoparticles. The PSf/Fe2O3 hemodialysis membrane and pristine PSf membrane were prepared via dry-wet spinning process. The membranes were characterized by scanning electron microscopy, water contact angle, average pore size, and porosity measurements. The biocompatibility profiles of the membranes were also evaluated in terms of protein adsorption and blood coagulation time. Next, the performance of the membranes was determined by measuring pure water permeability (PWP), bovine serum albumin rejection, and removal of various solutes such as urea and lysozyme. The incorporation of Fe2O3 resulted in significant increment of the PWP from 40.74 L/m2/h/bar to 58.6 L/m2/h/bar, mainly due to the improved water transport properties of the membrane. Moreover, the percent removal of urea and lysozyme was reported to be 75.1% and 35.6%, respectively. PSf/Fe2O3 hemodialysis membrane is proven to have a bright prospect for enhanced blood purification process

A preliminary study of flat sheet asymmetric membrane formation for gas separation applications

The common technique for the preparation of polymeric membranes with asymmetric structure is the phase inversion process. In this process, a polymer is dissolved in an appropriate solvent before casted on a suitable support. The casted film is then immersed in a non-solvent bath and the coagulation process taking place to form a membrane. The asymmetric membrane structure and its properties are influence by many experimental parameters such as the thickness of membrane, the polymer solution composition, coagulation bath composition, choice of solvent and non-solvent, the membrane casting speed and the knife shape which inducing casting shear rate can be determined in the membrane casting procedure. In order to produce a good quality flat sheet asymmetric membrane, a unique pneumatically-controlled flat sheet membrane casting system were designed and fabricated in this study. The present study seeks to optimize those parameters suitable for membrane making, which will exhibits good separation performance in gas separation application. To achieve the above objective, a few framework have been drawn such as optimizing the initial membrane solution formulation, characterizing the thermodynamic and rheological properties of the polymer solution. The orientation of the polymer molecules is also important in membrane making and will also investigated in order to enhance membrane selectivity

Polyetherimide/multiwall carbon nanotube mixed matrix hollow fiber membrane for gas separation

Mixed matrix membrane (MMM) which incorporated with polymeric and inorganic materials has become an interest to engineers in the early twenty due to its potential in advancing the gas separation properties of the polymeric-based membrane. The main objective of this study is to establish an effective approach for mixing and dispersing carbon nanotube (CNT) into the matrix of polyetherimide (PEI) to obtain MMM with optimized gas separation performance efficiency. The changes in gas permeability and selectivity of the fabricated flatsheet MMM was correlated with three different functionalizations on CNT. It was found that aminopropyl-triethoxysilane treated CNT homogeneously dispersed CNT in the polymer solution and gave the best separation on CO2 molecules. The result found that MMM exhibited CO2/CH4 selectivity of 30.59, which is significantly higher than the intrinsic value of PEI ever reported (common PEI CO2/CH4 selectivity = 29.66). Next, using the polymeric solution formulation with the optimum filler loading, hollow fiber (HF) MMM was tailored. The spinning parameters such as extrusion rate and air gap distance during dry phase inversion were optimized. It was found that the produced asymmetric membrane exhibited high permeance and selectivity. The average CO2 permeance obtained was 67.72 GPU with CO2/CH4 selectivity of 58.89. Additionally, increasing the shear rate by a higher extrusion rate resulted in a membrane with higher selectivity. Moreover, the selectivity of all the MMM fabricated surpassed 80% of the recognized intrinsic value, implying that the membrane produced in the study can be considered as defect-free membrane. The best HF MMM was obtained by incorporating 0.5wt% CNT into dope containing 25wt% PEI and extruding the dope at 4 cm3/min using air gap of 300 mm. The optimal HF MMM showed 28 times increment in permeance of pure gas CO2 and 2 times higher selectivity of CO2/CH4, compared to that of neat PEI. A comparative study with other PEI MMM revealed that CNT with proper functionalization and fabrication technique indeed could impart a strong influence in improving the matrix properties for further in-depth development

Surfactant dispersed multi-walled carbon nanotube/ polyetherimide nanocomposite membrane

Carbon nanotube based nanocomposite membranes have been fabricated through solution casting by embedding multi-walled carbon nanotubes (MWCNTs) within polyetherimide (PEI) polymer host matrix. In order to achieve fine dispersion of nanotubes and facilitate strong interfacial adhesion with the polymer matrix, the nanotubes were first treated with surfactants of different charges, namely anionic sodium dodecyl chloride, cationic cetyl trimethyl ammonium chloride and non-ionic Triton X100, prior to the dispersion in the PEI dope solution. Dispersion of MWCNTs in N-methyl-2-pyrrolidone solvent showed that the agglomeration and entanglement of the nanotubes were greatly reduced upon the addition of Triton X100. Scanning electron microscopy and atomic force microscopy examination has evidenced the compatibility of Triton X100 dispersed MWCNTs with the polymer matrix in which a promising dispersion and adhesion has been observed at the MWCNT-PEI interface. The increase in both thermal stability and mechanical strength of the resulting Triton X100 dispersed MWCNT/PEI nanocomposite indicated the improved interaction between MWCNTs and PEI. This study demonstrated the role of Triton X100 in facilitating the synergetic effects of MWCNTs and PEI where the resulting composite membrane is anticipated to have potential application in membrane based gas separation

Effects of process conditions in submerged ultrafiltration for refinery wastewater treatment: optimization of operating process by response surface methodology

The influence of air bubble flow rate (ABFR), hydraulic retention time (HRT), mixed liquor suspended solid (MLSS) concentration, and pH on the performances of modified polyvinylidene fluoride (PVDF) was investigated in submerged membrane ultrafiltration (SMUF).The refinery wastewater process was conducted using an experimental set-up consisted of an SMUF reservoir, a circulation pump, and an aerator. For SMUF, operated at vacuum pressure, deposition and accumulation of suspended solids on membrane surface were prohibited with continuous aeration. The process performance was measured in terms of the membrane water flux and chemical oxygen demand (COD) removal efficiency. The air bubbles flow rate was controlled at 1.2-3.0mL/min while HRT was manipulated in the range of 120-300min. MLSS and pH solution were controlled at 4.5g/L and 6.5, respectively. Results from response surface methodology (RSM) have demonstrated the improvement in water flux and COD removal, achieving 145.7L/m2h and 90.8%, respectively. By using pH at 6.50, the optimized conditions achieved for refinery wastewater treatment were 2.25mL/min, 276.93min, 4.50g/L for ABFR, HRT and MLSS concentration, respectively

Development of asymmetric carbon hollow fiber membrane for gas separation

The objective of this research is to develop a novel asymmetric carbon hollow fiber membrane and to characterize it’s gas separation performance and morphology. Polyacrylonitrile (PAN) was chosen as the precursor for carbon membranes. The hollow fiber membranes were produced using the dry/wet spinning process. PAN hollow fiber membranes were converted to carbon hollow fiber membranes with inert gas pyrolysis process. Carbon hollow fiber membranes were characterized by pure gas permeation measurement, Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and Thermogravimetry Analysis (TGA). The influence of the pyrolysis conditions on carbon membrane performance was investigated. Pyrolysis parameters including pyrolysis temperature, heating duration (soak time) and purge gas flow rate were studied. The results showed that pyrolysis temperatures of 700 oC to 800 oC O2/N2 selectivity from 1.1 to 1.85 and the maximum permeability O2 was increased achieved at 600 oC with 480 GPU. Although the selectivity of 3.1 was achieved at 250 oC, the membrane was not a pure carbon membrane. Longer duration of heating improved the selectivity from 1.1 to 1.8 with an increased in permeability at the initial stage. A decreased in permeability occurred at 180 min heating duration. Carbonized membrane with 10 min heating duration exhibited high selectivity of 3.7 with poorer permeability compared to PAN membranes. However, high purge gas flowrate gave an increase for O2 and N2 permeability from the original 50 – 130 GPU to 150 – 730 GPU without influencing its selectivity. Therefore, pyrolysis condition has pronounced influence on asymmetric carbon hollow fiber membranes for gas separation