The effect of ethane on the performance of commercial polyphenylene oxide and Cardo-type polyimide hollow fiber membranes in CO<Subscript>2</Subscript>/CH<Subscript>4</Subscript> separation applications

Impurities such as hydrogen sulfide, water vapor and heavy hydrocarbons in natural gas have considerable effects on the membrane performance. Small amounts of condensable and polymer soluble components in the feed gas cause swelling or plasticization of glassy membranes, leading to a reduction in membrane selectivity. In the present research the influence of ethane was investigated on the permeance and selectivity of two commercially available hollow fiber membranes, namely Cardo-type polyimide and PPO hollow fibers for CO₂/CH₄ separations. It was concluded that the gas mixture permeation rate was increased in the presence of C₂H₆. However, the CO₂/CH₄ separation factors remained almost the same in the presence and absence of the C₂H₆.     

Effects of pressure and temperature on fixed-site carrier membrane for CO<Subscript>2</Subscript> separation from natural gas

In this paper, the effect of testing temperature on the performance of fixed carrier membrane for CO₂ separation were studied. The blend composite membranes were developed respectively with a blend of PEI-PVA (polyetheleneimine-polyvinyl alcohol) as separation layer and PS (polysulfone) ultrafiltration membranes as the substrates. The permselectivity of the membranes was measured with CO₂/CH₄ mixed gas. The effect of testing temperature on membrane separation performance was investigated. The results showed that both the permeances of CO₂ and CH₄ decreased with the increase of temperature, and the permeances decreased more quickly under low pressure than those under high pressure. At the feed pressure of 0.11 MPa, the CO₂/ CH₄ selectivity of PEI-PVA/PS blend composite membrane reduced along with temperature increment. Under the feed pressure of 0.21 MPa, as well as 1.11 MPa, the selectivity decreased with the increase of temperature.     

Synthesis and characterization of rubbery/glassy blend membranes for CO<Subscript>2</Subscript>/CH<Subscript>4</Subscript> gas separation

A series of blend membranes made from the rubbery polyether block amide (Pebax®1657) and a glassy polymer, polyethersulfone (PES) or Matrimid 5218, were fabricated by solution casting with different ratios (10–40 %), in order to combine high permeability of the former with high selectivity of the latter polymer for CO₂/CH₄ gas separation. The membranes were characterized by scanning electron microscopy (SEM), differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), and stress–strain tests. These blend membranes showed two distinct T _g s, indicating their immiscible nature as confirmed by SEM images. However, weak intermolecular interaction between polymers, as illustrated by the FTIR results, corresponds to some degree to their compatibility and improved mechanical strength, compared to the pure Pebax®. TGA analysis revealed that addition of glassy polymer improved membranes’ thermal stability. Effect of feed pressure on membrane separation, investigated by three different pressures (4, 8, and 12 bar), indicated increased permeability for higher pressures for both CO₂ and CH₄. Gas separation tests also pointed to improved separation properties of the blend membranes compared to those of the neat polymers, prepared the same way.     

Chitosan- and dehydroascorbic acid-coated Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles: preparation,characterization and their potential as draw solute in forward osmosis process

Forward osmosis (FO) is a natural osmosis process that has attracted a significant attention due to its many advantages. However, the development of FO process depends on the development of proper draw solutions. In this work, chitosan (CS)-coated Fe₃O₄ nanoparticles and dehydroascorbic acid (DHAA)-coated Fe₃O₄ nanoparticles were successfully synthesized by co-precipitation method and their performance as draw solutes was investigated for application in FO systems. CS and DHAA could improve the surface hydrophilicity of the Fe₃O₄ nanoparticles. The synthesized nanoparticles were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometry (VSM) which the results presented a small size, crystalline morphology and high magnetization value for their structure as well as a good dispersion in water. Cellulose triacetate/cellulose acetate (CTA/CA)-based membranes were also prepared by immersion precipitation and used as FO membranes. The synthesized FO membranes were characterized by FESEM. The performance evaluation of synthesized nanoparticles revealed that the water flux of Fe₃O₄ nanoparticles capped with DHAA was higher than that of the chitosan-coated Fe₃O₄ nanoparticles. At the end of the process, the Fe₃O₄ nanoparticles were easily separated from the diluted draw solution by applying the magnetic field.     

Preparation of photo-catalytic copolymer grafted asymmetric membranes (N-TiO<Subscript>2</Subscript>-PMAA-g-PVDF/PAN) and their application on the degradation of bentazon in water

Nitrogen-doped titanium dioxide (N–TiO₂) was prepared and supported on a novel copolymer grafted membrane matrix to avoid the problems associated with the removal of spent photocatalyst from treated water. Membranes of poly (methacrylic acid) grafted onto poly (vinylidene difluoride) and blended with poly (acrylonitrile) (PMAA-g-PVDF/PAN) were prepared through a dry–wet phase inversion technique. Methacrylic acid side chains were grafted onto an activated PVDF backbone by the method of reversible addition fragmentation chain transfer polymerization and then the novel photocatalytic asymmetric membranes of N–TiO₂–PMAA-g-PVDF/PAN were prepared. The casting solutions were blended with 1–5 % N–TiO₂ before immersion into the coagulation bath. PVDF and PAN offer several advantages which include: mechanical strength and toughness, chemical resistance, unaffected by long-term exposure to UV radiation, low weight, and thermal stability. N–TiO₂ was prepared through sol-gel synthesis. The photocatalytic membranes were evaluated by degradation process of herbicide bentazon in water. Photodegradation studies revealed that the optimum photocatalyst loading was 3 % N–TiO₂ and the optimum pH was 7 for the degradation of bentazon in water. UV–Vis, TOC and LC–MS analyses confirmed the successful photodegradation of bentazon. A bentazon removal efficiency of 90.1 % was achieved at pH 7. N–TiO₂–PMAA-g-PVDF/PAN membranes were successfully prepared and characterized. These photocatalytic membranes showed great potential as a technology for the effective removal of pesticides from water. According to literature, N–TiO₂–PMAA-g-PVDF/PAN asymmetric photocatalytic membranes have not been prepared before for the purpose of treating agricultural wastewater.     

Analysis of a gas-phase Br<Subscript>2</Subscript>–H<Subscript>2</Subscript> redox flow battery

The operation of a gas-phase Br₂–H₂ flow battery is analyzed via a mathematical model and compared to experimental data. The model predicts the operating conditions of the cell in both fuel-cell (i.e., discharge) and electrolysis (i.e., charge) mode as a function of current, inlet gas composition, flow rate, and pressure differential across the membrane. The analysis reveals that gas-phase Br₂/HBr reactants significantly enhance mass transfer, which enables higher currents densities to be achieved compared to a liquid-fed system. A key feature of the model is water transport across the membrane, which determines membrane conductivity, reactant concentration and undesired condensation. The model is used to provide insight into cell operation, including operating conditions needed to avoid water condensation.     

Polysulfone membranes containing ethylene glycol monomers: synthesis,characterization, and CO<Subscript>2</Subscript>/CH<Subscript>4</Subscript> separation

Copolymers based on glassy and rubbery units have been developed to take advantage of both domains to enhance solubility and diffusivity. In this study, a series of gas separation membranes from polysulfone (PSF) containing ethylene glycol were synthesized via nucleophilic substitution polycondensation. The structures of copolymers were characterized by nuclear magnetic resonance spectra, Fourier transform infrared spectra, and thermal gravity analysis. The permeability and selectivity of the membranes were studied at different temperatures of 25–55 °C and pressures of 0.5–1.5 atm using single gases CO₂ and CH₄. Gas permeation measurements showed that copolymers with different contents of poly(ethylene glycol) exhibited different separation performances. For example, the membrane from PSF-PEG2000-20 containing 20 wt% poly(ethylene glycol) showed better performance in terms of ideal selectivity over the other seven copolymer membranes. The highest ideal CO₂/CH₄ selectivity was 43.0 with CO₂ permeability of 6.4 Barrer at 1.5 atm and 25 °C.     

Studies on cellulose acetate–carboxylated polysulfone blend ultrafiltration membranes—Part II

Hydrophilic polysulfone ultrafiltration membranes were prepared from blends of cellulose acetate and carboxylated polysulfones of 0.43 and 0.75 degrees of carboxylation. The effects of degree of carboxylation on membrane characteristics such as compaction, pure water flux, water content and membrane hydraulic resistance, have been investigated to evaluate the performance of the membranes. The influence of the degree of carboxylation on the performance of the blend membranes of various blend polymer compositions has been investigated and also compared with earlier reports on blend membranes prepared from cellulose acetate and polysulfone or carboxylated polysulfone of 0.14 degree of carboxylation. © 2003 Society of Chemical Industry     

Performance assessment of electrospun nanofibers for filter applications

The aim of this study was to evaluate the use of nanofiber microfiltration membranes, spun by an innovative electrospinning technique, in water filtration applications. As such, this study bridges between developments in electrospinning techniques for the production of flat sheet membranes and the application of these membranes in water filtration. Three different applications were examined. First, the use of the membrane (functionalized or non-functionalized) for the removal of pathogens was investigated. Second the electrospun flat sheet membranes were applied in a lab scale submerged membrane bioreactor (MBR). Third, the electrospun membranes were applied as stand-alone filter for water treatment. Next to these applications, physical properties such as clean water permeability (CWP) and strength were also examined. The test showed that the electrospun membranes can be used for water filtration applications, but that further research is necessary towards irreversible fouling properties and level of functionalisation.     

Preparation of asymmetric polysulfone/polyimide blended membranes for CO<Subscript>2</Subscript> separation

Asymmetric Flat sheet polysulfone-polyimide (PSF-PI) blended polymeric membranes (with PI content from 5–20%) have been fabricated following phase inversion technique. The membranes have been thoroughly characterized by the measurement of porosity, mechanical properties and also by SEM, FTIR and DSC analyses. With the increase in the PI content, the mechanical properties of the membranes, like Young’s modulus, tensile strength and elongation at break, increased. SEM investigations revealed that the surfaces of fabricated blended membranes possessed adequate homogeneity and their cross-sections showed non-porous top and diminutive porous substructure. From DSC analyses it has been observed that different compositions of the blended membranes exhibited single glass transition temperatures, implying proper compatibility of the polymers. The permeance of CO₂ and CH₄ through the membrane increased with the increase in PI content and it gradually decreased with the increase in the feed pressure in the range of 2–10 bar. Under the present investigation, the membrane with 20% PI content exhibited the maximum selectivity for the separation of CO₂/CH₄ gas mixes.     

Permselectivities of 2,2′‐dimethyl‐4,4′‐bis(aminophenoxyl)biphenyl diphenyl methane–based aromatic polyamide membranes for aqueous alcohol mixtures in pervaporation and evapomeation

The separation of aqueous alcohol mixtures was carried out by use of a series of novel aromatic polyamide membranes. The aromatic polyamides were prepared by the direct polycondensation of 2,2′‐dimethyl‐4,4′‐bis(aminophenoxyl)biphenyl (DBAPB) with various aromatic diacids, such as terephthalic acid (TPAc), 5‐tert‐butylisophthalic acid (TBPAc), and 4,4′‐hexafluoroisopropylidenedibenzoic acid (FDAc). The pervaporation and evapomeation performance of these novel aromatic polyamide membranes for dehydrating aqueous alcohol solution were investigated. The solubility of ethanol in the aromatic polyamide membranes is higher than that of water, but the diffusivity of water through the membrane is higher than that of ethanol. The effect of diffusion selectivity on the membrane separation performances plays an important role in the evapomeation process. Compared with pervaporation, evapomeation effectively increases the permselectivity of water. Moreover, the effect of aromatic diacids on the polymer chain packing density, pervaporation, and evapomeation performance were investigated. It was found that the permeation rate could be increased by introduction of a bulky group into the polymer backbone. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2688–2697, 2003     

Hemodialysis membrane prepared from cellulose/N‐methylmorpholine‐N‐oxide solution. III. The relationship between the drying condition of the membrane and its permeation behavior

The effects of drying condition on the performance (ultrafiltration rate, diffusive solute permeability, and sieving) of hemodialysis membranes prepared from cellulose/N‐methylmorpholine‐N‐oxide (NMMO) solution (NMMO membrane) and cellulose/cuprammonium solution (cuprammonium membrane; the referential membrane) were studied. The drying condition investigated was the glycerin concentration of the solution, which was used to substitute glycerin for the water in the membrane before the membrane was dried. A lower glycerin concentration in the solution brought about a lower reswelling degree (water content) in the dried membrane in pure water, which resulted in a drop in the performance of the as‐cast membrane. The NMMO membrane had a high water content and a high membrane performance compared with the cuprammonium membrane when both the membranes were treated under the same drying condition. The differences in the performance between both membrane series is discussed on the basis of the results of the observation of the membrane morphology by scanning electron microscopy, the observation of the crystallinity of the membranes by wide‐angle X‐ray diffraction, and the estimation of the pore structure of the membranes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1671–1681, 2003     

Synthesis and characterization of poly(ether-<Emphasis Type="Italic">block</Emphasis>-amide) copolymers/multi-walled carbon nanotube nanocomposite membranes for CO<Subscript>2</Subscript>/CH<Subscript>4</Subscript> separation

One of the effective techniques for improving separation properties of polymeric membranes is incorporation of suitable nanoparticles into their matrices. This study presents the preparation of three types of nanocomposite membranes comprising three grades of poly (ether-block-amide) (Pebax 1074, Pebax 1657 and Pebax 2533) and modified multi-walled carbon nanotubes (MWCNTs) with different loadings (1, 1.5, 2 and 2.5 wt%). The prepared membranes were characterized by field emission scanning electron microscopy (FESEM), attenuated total reflection-Fourier transfer infrared spectroscopy (ATR-FTIR) and X-ray diffraction (XRD). Permeation of CO₂ and CH₄ gases through the prepared membranes was measured at the pressure range of 2-8 bars and 25 °C. The results showed that the incorporation of MWCNTs into the polymers matrices improves CO₂/CH₄ selectivity. Further, Pebax 1074/MWCNT nanocomposite membrane exhibits better performance for CO₂/CH₄ separation compared to the neat Pebax and the two other nanocomposite membranes.     

Fundamental studies of homogeneous cation exchange membranes from poly(2,6‐dimethyl‐1,4‐phenylene oxide): Membranes prepared by simultaneous aryl‐sulfonation and aryl‐bromination

Strong acid homogenous cation exchange membranes were obtained by simultaneously introducing sulfonic and bromine groups into poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO). The ion‐exchange capacity (IEC), water content, transport number, diffusion coefficient, contact angle, and tensile strength of the obtained membranes were studied. The results show that the membrane intrinsic properties are largely dependent on the substitution of bromine: the IEC and water content decrease with bromine content, while the area resistance and permselectivity of the membranes increase with this trend. Therefore, by properly balancing them, a series of homogenous cation exchange membranes having good electrical properties and physical stability can be obtained to comply with different industrial electromembrane processes, such as diffusion dialysis, electrodialysis, electrodeionization, etc. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2238–2243, 2006     

Pervaporation separation of IPA‐water mixtures through 4A zeolite‐filled sodium alginate membranes

Incorporation of zeolites into natural polymers has been shown experimentally to enhance both the flux and selectivity in pervaporative dehydration separation of organic compounds. Pervaporation is a promising membrane technique for separation of volatile organic compounds (VOCs)/water mixtures. In this study, hydrophilic sodium alginate (SA) mixed membranes were prepared using solution casting technique by incorporating zeolites into the polymer matrix. The prepared membranes were characterized by ATR‐Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), scanning electron microscopy (SEM), Thermal Gravimetric Analysis (TGA), and differential scanning calorimetry (DSC) were tested in a laboratory scale pervaporation experimental set‐up. The effect of experimental parameters such as the type and composition of zeolites on permeation flux and selectivity was investigated. When tested on IPA‐water mixtures, the zeolite‐filled membrane was found to give much higher selectivity. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Natural rubber/poly(acrylic acid) semi‐interpenetrating polymer network membranes for the pervaporation of water–ethanol mixtures

Pervaporation membranes for the dehydration of water–ethanol mixtures were prepared from a semi‐interpenetrating polymer network (semi‐IPN) of natural rubber (NR) and crosslinked poly(acrylic acid) (PAA). The swelling studies revealed that hydrophilic PAA present in the semi‐IPN membranes caused the membranes to swell greatly in water. The swelling degree of the membranes in water was significantly affected by the amount ratio between the hydrophobic NR and the hydrophilic PAA. The sorption experiments of the NR/PAA membranes in various concentrations of water–ethanol mixtures suggested the preferential sorption to water. However, for the membrane with high PAA content, the water sorption selectivity decreased considerably at high water concentration of water–ethanol mixtures because the membrane was in the highly swollen state. Pervaporation separations of water–ethanol mixtures using NR/PAA membranes were performed and it was found that at low water concentrations of feed mixtures, increasing the PAA content of the membrane can enhance both water permeation flux and selectivity. Additionally, under low feed water concentration, increasing the feed temperature would increase the water flux with the decreasing of the ethanol flux. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Partial crosslinking method for poly(2,6‐dimethyl‐1,4‐phenylene oxide)–poly(vinyl alcohol) membranes to obtain optimized stability and permeability

A partial crosslinking method was developed to modify hydrophilic membranes. The membrane was sandwiched between two porous plates to protect part of the areas, then immersed into a crosslinking solution such as glutaraldehyde, and finally, set free from the plates. The protected and unprotected areas were alternatively distributed to form a heterogeneous membrane. The unprotected areas were crosslinked to enhance the membrane stability, whereas the protected areas retained their original permeability. Three types of hydrophilic base membranes were selected and prepared from poly(2,6‐dimethyl‐1,4‐phenylene oxide) and poly(vinyl alcohol). The base membranes were partially crosslinked (5.56% of the direct area with enlarged areas) to investigate their stability and diffusion dialysis (DD) performances. The partially crosslinked membranes had remarkably reduced water uptake and swelling degrees compared with the base membranes (72.4–250.4 vs 178.2%–544.4% and 94.0%–408.0% vs. 163.8%–814.8%). Meanwhile, the membranes still retained high DD performances for separating HCl–FeCl₂ or NaOH–NaAlO₂ solutions. The dialysis coefficients of HCl and NaOH were much higher than those of the fully crosslinked membranes (0.0209 vs. 0.0109 m/h and 0.0059–0.0085 vs. 0.0017–0.0022 m/h). Hence, partial crosslinking was effective in optimizing the membrane hydrophilicity and permeability. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45305.     

Preparation of mesh-reinforced cellulose acetate forward osmosis membrane with very low surface roughness

Mesh-reinforced cellulose acetate (CA)-based membranes were prepared for forward osmosis (FO) by immersion precipitation. Casting compositions such as CA percent and 1, 4-dioxane/acetone ratio and also preparation conditions such as evaporation time, coagulation bath and annealing temperatures were tested for membranes’ performance. The results were compared with commercially CTA membranes. The best membrane (17.9% polymer and 1, 4-dioxane/acetone ratio of 1.89) showed water flux of 9.3 L/m²h (LMH) and RSF of 0.536 mol NaCl/m²h. Moreover, the membrane structure was reinforced by a polyester mesh, which created micro pores in the back of the membrane. This caused higher water flux and RSF compared to membranes without mesh. FO membrane prepared under best conditions, had a smoother surface than commercial ones. This feature enhances the fouling properties of the membrane, which can be appropriate for wastewater treatment applications.     

Preparation of novel heterogeneous cation‐permeable membranes from blends of sulfonated poly(phenylene sulfide) and poly(ether sulfone)

Novel heterogeneous cation‐exchange membranes using poly (ether sulfone)(PES) as binder and sulfonated poly(phenylene sulfide) (SPPS) powder as polyelectrolyte were prepared by the solution casting‐immersion method. Compared with a conventional route for heterogeneous membrane, the steps of milling resin into fine powders and the pressing at high temperature are avoided, and thus permits a simple technique for the preparation of such membrane. The effect of the particle size and loading of SPPS resin on the properties of the membranes such as ion‐exchange capacity, water content, electrical resistance, transport number, diffusion coefficient of electrolytes, etc., have been studied. It is shown that the membrane fundamental properties are largely dependent on both the resin loading and the particle size of SPPS resin. By adjusting these two important parameters, one can obtain heterogeneous membrane with both good conductivity, selectivity, and proper water content for different industrial purposes such as electrodialysis, diffusional dialysis, etc. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 167–174, 2004     

Structure-property Relationships in Radiation Grafted Poly(tetrafluoroethylene)-<Emphasis Type="Italic">graft</Emphasis>-polystyrene Sulfonic Acid Membranes

Structure-property relationships in poly(tetrafluoroethylene)-graft-polystyrene sulfonic acid (PTFE-g-PSSA) membranes prepared by radiation-induced grafting of styrene onto poly(tetrafluoroethylene) (PTFE) films using simultaneous radiation-induced grafting followed by sulfonation reaction were established. The physico-chemical properties of the membranes such as ion exchange capacity, swelling and ionic conductivity were correlated with the degree of grafting and the structural changes taking place in the membrane matrix during the preparation procedure. The variation in the crystallinity of membranes was studied by differential scanning calorimetry (DSC). The membranes thermal stability was evaluated using thermogravimetric analysis (TGA) and the effect of the heat treatment on the ion exchange capacity and the water uptake was investigated. The membranes were found to undergo substantial structural changes in the form of ionic sites increase, hydrophilicity enhancement, hydrophobicity reduction and crystallinity decrease with the increase in the degree of grafting. These structural changes were found to have a collective effect on the physico-chemical properties of the membranes but their relative contribution depends on the degree of grafting.