Journal of Membrane Science (v.283, #1-2)
Table of units (III).
Editorial Board (CO2).
The passing of Juan I. Mengual by Mohamed Khayet; José M. Ortiz de Zárate (1).
Development of PAMAM dendrimer composite membranes for CO2 separation by Shuhong Duan; Takayuki Kouketsu; Shingo Kazama; Koichi Yamada (2-6).
Poly(amidoamine) (PAMAM) dendrimer composite membranes with high CO2/N2 selectivity and CO2 permeance were developed in situ according to the in situ modification (IM) method. This method utilizes the interfacial precipitation of membrane materials on the surface of porous commercially available, polysulfone ultra-filtration hollow fiber membrane (molecular weight cutoff: 6000) substrates. A thin layer of amphiphilic chitosan, which has a potential affinity for both hydrophobic PSF-substrates and hydrophilic PAMAM dendrimers, was employed as a gutter layer directly beneath the inner surface of the substrate by the IM method. PAMAM dendrimers were then impregnated into the chitosan gutter layer to form a hybrid active layer for CO2 separation. Permeation experiments of the PAMAM dendrimer composite membrane conducted in a pencil module (an effective membrane area: ca. 17 cm2) were carried out using a mixed CO2 (5%)/N2 (95%) feed gas at a pressure difference of 97 kPa at 40 °C. The PAMAM composite membrane exhibited an excellent CO2/N2 selectivity of 230 and a CO2 permeance of 4.6 × 10−7 m3 (STP) m−2 s−1 kPa−1 (=61 GPU).SEM observations of the composite membrane revealed a thin chitosan layer (ca. 200 nm thick) directly beneath the surface of the porous substrate. Hybridization of the PAMAM dendrimer with a chitosan gutter layer afforded a defect free active layer (ca. 300 nm thick) suitable for CO2 separation.
Keywords: Gas separation; Poly(amidoamine) (PAMAM) dendrimer; Composite hollow fiber membrane; CO2/N2 separation; In situ modification;
Incubating lead selenide nanoclusters and nanocubes on the eggshell membrane at room temperature by Huilan Su; Na Wang; Qun Dong; Di Zhang (7-12).
Lead selenide nanoclusters and nanocubes were successfully prepared on the eggshell membrane (ESM) through a room-temperature biosubstrate-directed approach. The nanoclusters were assembled by fine nanocrystallites, while single-crystalline nanocubes came into being through a ripen progress, and obtained lead selenide nanocrystallites were distributed homogeneously over the whole ESM. The morphology and the size were governed mainly by the configuration and chemical functional residues of the ESM and the synthesis conditions as well as their reciprocities. The functional groups such as amido groups and imido residues of the ESM macromolecules could not only direct the formation of 4–7 nm PbSe nanocrystallites and the assembly into nanoclusters and nanocubes, but act as a surfactant to well-distributed fine PbSe nanocrystallites. The as-prepared nanocrystalline PbSe exhibited single-crystalline, small-scaled and well-dispersed performances, which would offer more potential applications in semiconductors, lasers, optoelectronic devices and the like nanoelectronic fields.
Keywords: Biomimetic; Eggshell membrane; Lead selenide; Nanocubes; Na2SeSO3 solution;
Novel thermo-sensitive membranes prepared by rapid bulk photo-grafting polymerization of N,N-diethylacrylamide onto the microfiltration membranes Nylon by Guangguo Wu; Yuanpei Li; Mei Han; Xiaoxuan Liu (13-20).
Novel thermo-sensitive membranes were prepared by photo-grafting N,N-diethylacrylamide (DEAAm) onto the microfiltration membranes of Nylon with benzophenone (BP) as an initiator. Grafted membranes with a wide range of grafting yield were obtained through varying the grafting conditions, including UV intensity, the irradiation time and the mole ratio of initiator. The existence of the grafted layers of poly(N,N-diethylacrylamide) (PDEAAm) was confirmed by ATR-FTIR and XPS measurements. The SEM images indicated that the grafted polymers existed mainly on the top surface and inside the pores rather than on the backside. The water flow rate of the membranes with the appropriate grafting yield increased sharply with increasing temperature to the range of 30–35 °C near the lower critical solution temperature (LCST), which revealed the performance of the thermo-sensitivity after grafting modification. The influence of grafting yield on the filtration property of the membranes was also investigated. The grafted PDEAAm chains existed on the expanded configuration and extended out of the surface of the membranes when dried below the LCST while shrunk to the membrane surface above the LCST, which was measured by AFM.
Keywords: N,N-Diethylacrylamide; Microfiltration membranes of Nylon; Photo-grafting; Water flow rate; Thermo-sensitive performance;
Hypochlorite degradation of crosslinked polyamide membranes by Young-Nam Kwon; James O. Leckie (21-26).
When disinfecting or cleaning agents contact polymer-based membranes, hydrolysis and oxidation with the membrane change surface properties. The research reported here discusses the effect of exposure to solution of hypochloric acid (disinfecting agent) on the chemical and morphological properties of a crosslinked polyamide membrane (LFC1, Hydranautics ©). Effects on the membrane were evaluated using AFM, XPS, FT-IR, contact angle, and streaming potential analysis. Chlorine incorporated in the membrane increased with increasing hypochlorite concentration and decreasing pH of a soaking bath. Exposed membranes were more hydrophilic and had a slightly more negative zeta potential. The chlorination broke and weakened hydrogen bonding by decreasing the number of hydrogen bonding sites. This study shows that the use of chlorine chemically changed the surface properties of the crosslinked polyamide LFC1 membrane, but there was no change in roughness and morphology.
Keywords: Degradation; Chlorine; Crosslinked polyamide; Reverse osmosis; Hydrogen bonding;
Formation and morphology studies of different polysulfones-based membranes made by wet phase inversion process by Jean-François Blanco; Julie Sublet; Quang Trong Nguyen; Pierre Schaetzel (27-37).
Different polysulfones were sulfonated and were used to prepare asymmetric membranes by wet phase inversion. The morphology of the porous structure of the membranes obtained in different coagulation conditions was studied and discussed. Nanofiltration membranes can be formed by coagulating a concentrated solution (e.g. 40 wt.%) of sulfonated cardo polyethersulfone by water. The higher the sulfonation degree, the better the rejection of nanosize solutes, and the bigger the pores and the macrovoids. The data on binodal phase separation suggest that such a behavior is due to a longer time required for the polymer to be vitrified at higher sulfonation degree. When the sulfonated polymer is blended with the original polysulfone, the morphology of the coagulated membranes is different from that of single polymer membranes: irregular macrovoids, and eventually polymer nodules, instead of finger-like macrovoids. Wrinkles were observed in the case of asymmetric membranes made of PSU-based blends. They would be generated by compressive strains that appear in the skin layer bonded to a soft substrate (liquid polymer dope) during the departure of the solvent from the nascent membrane towards the coagulation bath. A decrease in the coagulation temperature or in the total polymer in the casting dope led to larger and more numerous macrovoids, probably due to an increase in the phase separation time before the gelling of the system.
Keywords: Phase inversion; Morphology; Tight ultrafiltration membrane; Sulfonated polysulfone; Wrinkles;
Oxygen permeability and structural stability of BaCe0.15Fe0.85O3−δ membranes by Xuefeng Zhu; You Cong; Weishen Yang (38-44).
Cobalt-free BaCe x Fe1−x O3−δ (x = 0.15–0.85) membranes have both high oxygen permeation flux and high structure stability even in reducing atmosphere at high temperature. The oxygen flux of BaCe0.15Fe0.85O3−δ (BCF1585) membrane reached at 0.5 ml/min cm2 at 900 °C with a thickness of 1.4 mm. Oxygen permeation results showed that oxygen permeation controlling step mainly was oxygen ion diffusion in the membrane bulk if the membrane thicker than 1.0 mm, and mainly was surface oxygen exchange if the membrane thinner than 0.78 mm. Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) porous layer coated on the membrane surfaces could effectively accelerate the surface oxygen exchange rate, thus greatly improve the oxygen permeability of the membrane. In some cases, the oxygen permeation flux of the membrane coated with BSCF was even two times higher than that of the membrane without coating. Perovskite structure of BCF1585 was still maintained at 950 °C even after it was exposed to 5% H2 + Ar mixture gas for 1 h.
Keywords: Oxygen separation; Ceramic membrane; Perovskite; Mixed conductor; Structural stability;
Hydrolysis of whey protein isolate in a tangential flow filter membrane reactor by Seronei Chelulei Cheison; Zhang Wang; Shi-Ying Xu (45-56).
Protease N (IUB 126.96.36.199, Bacillus subtilis) enzyme was used to continuously hydrolyse an initial 5% (w/v) whey protein isolate (86.98%, Kjeldahl nitrogen × 6.38) for 5 h at pH 7.0 and 55 °C in a 10 kDa tangential flow filter (TFF) enzymatic membrane reactor (EMR). The retentate temperature (A: 25–55 °C), initial water permeate flux, J i (B: 1.6–18.4 mL/min) and enzyme concentration (C: 0.5–5.5 g) were varied and optimised using response surface methodology (RSM) central composite rotatable design (CCRD). The residual enzyme activity (A residual), enzyme leakage (A leakage), enzyme loss (A loss), average permeate flux (J average) and nitrogen recovered in permeate (apparent sieving, S apparent) were determined. J average decayed extensively at low retentate temperatures (25 and 30 °C), while at 50 °C the enzyme solubilised the dynamic gel layer, stabilised J average and led to higher S apparent. J average and S apparent increased concomitantly as well as with increasing retentate temperature, J i and enzyme concentration. Principal components analysis isolated the retentate temperature, S apparent, A leakage and J average as factors providing prominent influence in the EMR with significant contributions (ca. 60% of the EMR variance) to principal components 1 and 3 (permeate and substrate hydrodynamics property). Principal component 2 (‘measure’ of Protease N enzyme property) contributed 27.78%. Results provide evidence that when the feed temperature is suitable, high substrate solubility and low viscosity is maintained at the membrane surface and the enzyme used in the EMR solubilises and hydrolyses the concentration polarisation layer (GPL) thus providing a codetergence property necessary to maintain permeate flux stability and hence high product recovery.
Keywords: Permeate flux; Enzymatic membrane reactor; Response surface methodology; Principal component analysis; Multivariate data analysis; Whey protein hydrolysis;
Effect of salt mixture concentration on fractionation with NF membranes by J. Tanninen; M. Mänttäri; M. Nyström (57-64).
Desal-5 DK, NF 270, NF (Dow), NF 20 and ESNA-1-LF nanofiltration membranes were tested for their selectivity, when single and mixed salt solutions (NaCl, NaCl:Na2SO4 1:1 ratio) of different concentrations were filtered at a constant permeate flux. Streaming potential measurements were used to characterise the new NF 20 (Sepro) and NF (Dow) membranes.The membrane surface charge increased the retentions when dilute salt solutions were filtered. The best selectivity was generally achieved using low permeate fluxes and high salt concentrations. At higher salt concentrations the charge effects were diminished. Negative NaCl retention values were obtained for all but the ESNA-1-LF membrane, when concentrated mixed salt solutions were filtered. The use of higher permeate fluxes increased salt retentions in general. The measured isoelectric points (IP) for the NF (Dow) and the NF 20 (Sepro) membranes were 5.1 and 6.6, respectively. Owing to the close proximity of the IP of the NF 20 membrane to the filtration conditions, the effect of the surface charge on the separation was limited and salt fractionation was efficient at all tested salt concentrations. Of the studied membranes, the NF (Dow) and the Desal-5 DK showed the best selectivity. According to the salt retention data, the ESNA-1-LF membrane should not be considered a nanofiltration membrane, but rather a slightly open reverse osmosis membrane.
Keywords: Nanofiltration; Salt separation; Charge effect; Donnan effect; Streaming potential;
Poly(vinyl alcohol)-iron oxide nanocomposite membranes for pervaporation dehydration of isopropanol, 1,4-dioxane and tetrahydrofuran by Malladi Sairam; Boya Vijaya Kumar Naidu; Sanna Kotrappanavar Nataraj; Bojja Sreedhar; Tejraj M. Aminabhavi (65-73).
Poly(vinyl alcohol) (PVA)-based nanocomposite membranes were prepared by coprecipitation of different amounts of Fe(II) and Fe(III) taken in an alkaline medium and their pervaporation (PV) performances were investigated to dehydrate isopropanol, 1,4-dioxane and tetrahydrofuran (THF) from aqueous feeds containing 10–20 wt.% of water in isopropanol and 1,4-dioxane, 5–l5 wt.% of water in THF. The freestanding membranes were characterized by the dynamic mechanical thermal analyzer (DMTA), which showed a shift in glass transition temperature toward higher range along with an increase in storage modulus with increasing amount of iron oxide in the PVA matrix. Furthermore, thin layered membranes were cast on polyester fabric cloths as support layers to improve their PV separation performances for all the three mixtures over that of the pristine crosslinked PVA membrane. In particular, the composite membrane prepared by taking 4.5 wt.% of iron oxide showed an improved selectivity with a slight sacrifice in flux compared to membranes containing lower contents of iron oxide as well as the pristine crosslinked PVA membrane. Flux decreased with increasing content of iron in the PVA matrix, while selectivity increased systematically.
Keywords: Nanocomposite membrane; Iron oxide; Poly(vinyl alcohol); Aqueous-organic mixtures; Pervaporation dehydration;
Partially fluorinated proton exchange membranes based on PVDF–SEBS blends compatibilized with methylmethacrylate block copolymers by A. Mokrini; M.A. Huneault; P. Gerard (74-83).
This paper reports on a new route to prepare functional polymer blends for fuel cell's proton exchange membrane applications. Polyvinylidene fluoride (PVDF) and styrene-ethylene/butylene-styrene (SEBS) thermoplastic elastomer were melt blended and extruded into films. Interface modification using poly(methylmethacrylate-butylacrylate-methylmethacrylate) block copolymer (MAM), and two grades of poly(styrene-butadiene-methylmethacrylate) block copolymer was used to optimize the blends performance. The films made out of these blends were grafted with sulfonic acid moieties to obtain ionic conductivity leading to semi-fluorinated proton exchange membranes. The effect of varying the nature and concentration of the compatibilizer on the morphology and properties of a 50/50 wt.% PVDF/SEBS blends was investigated. SEM analysis showed that the addition of the block copolymers to the blends affected the morphology significantly and in the best case, that as low as 1 wt.% block copolymer was sufficient to dramatically reduces the segregation scale and improves mechanical properties. The samples were characterized in terms of morphology, microstructure and thermo-mechanical properties and in terms of conductivity, ion exchange capacity (IEC) and water uptake to establish the blends morphology–property relationships. Compatibilized blend membranes showed conductivities up to 3 × 10−2 S cm−1 at 100% relative humidity, and an IEC = 1.69 meq g−1. Water swelling decreased for compatibilized blend membranes.
Keywords: Proton exchange membrane; Melt extrusion; PVDF; SEBS; SBM block copolymer; Compatibilization;
Ion exchanger using electrospun polystyrene nanofibers by H. An; C. Shin; G.G. Chase (84-87).
Polymer nanofiber ion exchangers (PNIE) are produced by electrospinning from solutions of dissolved polystyrene followed by sulfonation processes. A polystyrene nanofiber cation exchanger was developed for high ion exchange capacity, and rapid ion exchange velocity. In this paper, new experimental results investigating the performance of PNIE are presented in relation to the relevant parameters (ion exchange capacity (IEC), water uptake, and surface morphology). The ion exchange capacity (IEC) and water uptake of the PNIE depend upon the sulfonation time. The PNIE sample with 30 min sulfonation time showed the maximum IEC of 3.74 mmol/g and maximum water uptake of 0.77 g H2O/g-dry-PNIE at 40 min sulfonation time.
Keywords: Ion exchange; Nanofiber; Electrospin; Polystyrene; Sulfonation;
General solution for the time lag of a single-tank receiver in the Knudsen flow regime and its implications for the receiver's configuration by S. Lashkari; B. Kruczek; H.L. Frisch (88-101).
Constant volume systems are commonly used for the determination of the diffusion, permeability and solubility coefficients of gases in porous and nonporous media. In this paper we present important considerations for the design of an outflow receiver of a constant volume system to minimize the possible resistance to gas transport downstream from the tested medium. The receiver considered in this paper consists of main tube, a tank, and a tube connecting the main tube with the tank. The resistance of the receiver is quantified using the concepts of the asymptotic solution and the time lag by assuming that gas accumulation in the receiver occurs in the Knudsen flow regime. The effects of the volume of the tank, the position at which the tank is connected to the main tube, the length of the connecting tube, as well as, the position of the pressure sensor in the receiver are discussed.
Keywords: Constant volume systems; Time lag; Asymptotic solution; Diffusion coefficient; Fick's second law of diffusion;
Zirconium hydrogen phosphate/disulfonated poly(arylene ether sulfone) copolymer composite membranes for proton exchange membrane fuel cells by Melinda L. Hill; Yu Seung Kim; Brian R. Einsla; James E. McGrath (102-108).
A series of zirconium hydrogen phosphate/disulfonated poly(arylene ether sulfone) random copolymer composite membranes for proton exchange membrane fuel cell applications were prepared and characterized by optical clarity, water absorption, proton conductivity measurements, mechanical testing, direct methanol fuel cell (DMFC) performance, and methanol permeability. Composite membranes incorporating up to 40 wt.% of zirconium phosphate were prepared by an in situ precipitation method. In this method, the water-swollen acid form of directly prepared disulfonated copolymer films were immersed in aqueous solutions of zirconyl chloride (ZrOCl2) at 80 °C, followed by treatment in 1 M phosphoric acid (H3PO4) solution for 24 h. During this time the zirconium hydrogen phosphate (ZrP) nanoparticles precipitated in the swollen pores of the membrane. The content of ZrP in the composite membranes was controlled by the concentration of ZrOCl2 solution, and was determined by weight difference. Zirconium hydrogen phosphate concentration was also dependent upon the ion exchange capacity (IEC) of the polymer as well as the temperature at which the copolymers were acidified. The composite films had good thermal stability and excellent retention of zirconium hydrogen phosphate after water treatment at 120 °C for 100 h. Although the composite membranes exhibited lower proton conductivity than the pure copolymer membranes at room temperature, the presence of the inorganic particles led to an improvement in high-temperature conductivity. For example, fully hydrated membranes (40 mol% disulfonation) with 38 wt.% zirconium hydrogen phosphate had a conductivity of 0.06 S/cm at room temperature and linearly increased up to 0.13 S/cm in water vapor at 130 °C, whereas the pure copolymer which had 0.07 S/cm at room temperature only reached a conductivity of 0.09 S/cm at 130 °C.
Keywords: Proton exchange membrane fuel cells; Zirconium hydrogen phosphate; Poly(arylene ether sulfone); Disulfonated copolymer; Proton conductivity;
Study of membrane morphology by microscopic image analysis and membrane structure parameter model by Lei Wang; Xudong Wang (109-115).
This study adopted scanning electron microscope (SEM), field emission scanning electron microscope (FESEM) and the Hagen–Poiseiulle equation to determine ultrafiltration membrane structure parameters, such as surface pore size, pore size distribution, porosity, pore density and so on. Based on the hydrodynamic theory from the perspective of membrane structure, the mean pore size reducing factor a 1 and pore density reducing factor a 2 were introduced, then the model of membrane structure parameter was established, in which the pore density and mean pore size of the membrane were the major parameters. In addition, five different apparent molecular weight distribution (AMWD) water samples were used to simulate the parameters and check the model. Then, a group of parameters of a 1 and a 2 were calculated, and the influence of water characteristics on a 1 and a 2 was discussed. The results showed that the model could better reflect the UF membrane filtration process of the advanced sewage treatment.
Keywords: Ultrafiltration; Morphology analysis; Scanning electron microscope; Pore size; Pore density; Pore size distribution; Membrane structure parameter model;
Resistance in series model for ultrafiltration of mosambi (Citrus sinensis (L.) Osbeck) juice in a stirred continuous mode by P. Rai; C. Rai; G.C. Majumdar; S. DasGupta; S. De (116-122).
Flux decline during ultrafiltration (UF) of depectinized mosambi juice was quantified by a resistance-in-series model. Resistance against the solvent flux was assumed to be comprised of four components, namely, membrane hydraulic, adsorption, pore plugging and fouling resistance. Apart from the membrane hydraulic resistance, evolution of each of these resistances with time was determined from separate set of experiments independently. The experiments were conducted in a stirred continuous mode both under low as well as high polarization conditions. The range of operating transmembrane pressure drop in the experiments was 276–552 kPa and that of Reynolds number was 1.4–2.1 × 105. Correlations were proposed to quantify the growth kinetics of the resistances, separately. Finally, the profile of total resistance and corresponding flux decline were calculated and compared with the experimental data. The adsorption resistance was found to be about 60% of membrane hydraulic resistance. The pore blocking resistance was about the same as that of membrane resistance at higher Reynolds number and was about four times at lower Reynolds number. The fouling resistance was about six to ten times the membrane resistance in the range of operating conditions, studied herein.
Keywords: Ultrafiltration; Mosambi juice; Resistance-in-series model; Fouling; Pore plugging;
Polymeric hydrophobic membranes as a tool to control polymorphism and protein–ligand interactions by Silvia Simone; Efrem Curcio; Gianluca Di Profio; Marta Ferraroni; Enrico Drioli (123-132).
In recent years, crystallization techniques based on microporous hydrophobic membranes have been successfully applied to biological macromolecules. In this work, the membrane crystallizer has been used to evaluate how the presence of the polymeric surface influences the interactions between a test-protein, hen egg white lysozyme (HEWL), and two metal cations: Cu2+ and Co2+. Different techniques have been used in order to investigate the features of the obtained crystals and elucidate the membrane role during the growth process. Experimental results show large crystal size and improved crystal quality. Unexpectedly, lysozyme–Co2+ crystals having peculiar morphologies as well as a new kind of crystal lattice (orthorhombic P212121 form with unit cell constants a = 36.81 Å, b = 77.56 Å, c = 80.38 Å) have been found. Furthermore, new coordination positions of the copper cation to lysozyme, different with respect to those already described in literature, have been observed. Beside the well demonstrated effectiveness in the field of protein crystallization, these results suggest that polymeric film surfaces could be useful to control the occurring of polymorphs during crystallization and modulate the interactions between proteins and ligands like ions, additives, etc.
Keywords: Microporous hydrophobic membrane; Heterogeneous nucleation; Membrane crystallization; Protein crystallization; Metal–protein interactions;
Study on a novel polyamide-urea reverse osmosis composite membrane (ICIC-MPD) by Li-Fen Liu; San-Chuan Yu; Li-Guang Wu; Cong-Jie Gao (133-146).
In this study, a novel polyamide-urea reverse osmosis composite membrane (ICIC-MPD) was tested for its antifouling performance, and compared with the TMC-MPD and ESPA membranes. The three membranes were characterized for their surface properties such as hydrophilicity and surface roughness. The fouling experiments in laboratory scale were performed with lake water and four simulated aqueous solutions. Membrane fouling data were correlated with the measured surface properties. Further, a combination of scanning electron microscope (SEM) and attenuated total reflectance infrared (ATR-IR) or energy dispersive analysis of X-ray (EDX) was utilized to confirm the existence and to examine the morphology of foulants. Results showed that all three membranes were fouled in the five test solutions during the fouling test; however the ICIC-MPD membrane had a lower fouling rate than TMC-MPD and ESPA membranes. It was also found that the antifouling properties of these membranes were closely correlated with their hydrophilicity and surface roughness: higher hydrophilicity and lower surface roughness lead to higher fouling resistance. In addition, from the contact angle values and the AFM photographs, it was confirmed that the favorable hydrophilicity and smoother surface of ICIC-MPD membrane contributed to its better resistance to fouling. As a result, the ICIC-MPD membrane may have favorable antifouling performance.
Keywords: ICIC-MPD membrane; Antifouling performance; Simulated aqueous solution; Surface roughness; Hydrophilicity;
Predicting flux decline in crossflow membranes using artificial neural networks and genetic algorithms by Goloka Behari Sahoo; Chittaranjan Ray (147-157).
The geometry and internal parameters of artificial neural networks (ANNs) have significant effects on the prediction performance efficiency of the network. The optimal ANN geometry is problem-dependent. Although some guidance is available in the literature for the choice of geometry and internal parameters, most networks are calibrated using the trial-and-error approach. This paper presents the use of genetic algorithms (GAs) to search the optimal geometry and values of internal parameter of a multilayer feedforward back-propagation neural network (BPNN) and a radial basis function network (RBFN). The prediction performance efficiency of the GA–ANN combination is examined using an already published experimental dataset of crossflow membrane filtration. The data includes the permeate flux decline under various operating conditions (e.g. transmembrane pressure and filtration time) with different physicochemical properties of feed water (e.g. different combinations of three particle diameters, three pH values and four ionic strengths). It is illustrated that the GA-optimized ANN predicts the permeate flux decline more accurately than a network in which the ANN calibration is done using a trial-and-error approach. It is shown that scaling the training data to the range of 0–1 helps the modeler find the solution range of an RBFN for GA.
Keywords: Multilayer feedforward back-propagation neural network; Radial basis function network; Genetic algorithms; Crossflow membrane filtration; Input data scaling;
Effects of synthesis methods on oxygen permeability of BaCe0.15Fe0.85O3−δ ceramic membranes by Xuefeng Zhu; You Cong; Weishen Yang (158-163).
Dense BaCe0.15Fe0.85O3−δ (BCF1585) ceramic membranes synthesized by the solid-state reaction (SSR) method and EDTA-citric acid (EC) process were investigated by X-ray powder diffraction, total conductivity, oxygen permeation, etc. XRD results revealed the perovskite structure of the powders prepared by the EC process was easier to be developed than that of prepared by SSR method. Membranes derived from EC had higher density, pure phase structure and fewer defects comparing to those derived from SSR method. However, membranes derived from SSR method had higher oxygen permeability. Thickness experiments revealed that the oxygen permeation fluxes of the membranes synthesized by both methods are all jointly controlled by surface exchange and bulk diffusion in the range of 0.7–2.0 mm. The long-term oxygen permeation operation revealed that the membranes derived from both methods exhibit good oxygen permeation stability.
Keywords: Ceramic membrane; Synthesis methods; Oxygen separation; Mixed conducting; Perovskite oxides;
Effect of high salinity on activated sludge characteristics and membrane permeability in an immersed membrane bioreactor by E. Reid; Xingrong Liu; S.J. Judd (164-171).
The influence of high salinity on the characteristics of the activated sludge and performance of a pilot-scale immersed membrane bioreactor (iMBR) has been studied. The bioreactor was subjected to salinity shocks of up to 5 g/L, and the response with respect to membrane permeability monitored. Key physical and chemical parameters were measured included mixed liquor suspended solids (MLSS), viscosity, capillary suction time (CST), turbidity, and the soluble microbial product (SMP) and extracted extracellular polymeric substances (EPS) of the mixed liquor. The inter-relationships between these parameters and the membrane permeability were then assessed. Results indicate that high salinity greatly affects the physical and biochemical properties of activated sludge, increasing SMP and EPS concentrations, as well as decreasing membrane permeability. Both SMP and EPS were correlated with physical parameters of the activated sludge such as particle size, CST and turbidity. Furthermore, permeability was found to be negatively correlated with SMP carbohydrate at the two different flux rate imposed, corroborating previous reports linking SMP carbohydrate to iMBR membrane fouling.
Keywords: Salinity; Activated sludge; Membrane bioreactor; Permeability; Fouling;
Preparation of organic–inorganic nanocomposite membrane using a reactive polymeric dispersant and compatibilizer: Proton and methanol transport with respect to nano-phase separated structure by Ju Young Kim; Suresh Mulmi; Chang Hyun Lee; Ho Bum Park; Youn Suk Chung; Young Moo Lee (172-181).
A poly(styrene–NaSS–UAN) random copolymer (PSSU) consisting of a sulfonated monomer (NaSS) and a non-sulfonated monomer (styrene) was successfully fabricated through a new copolymerization scheme using a urethane acrylate non-ionomer (UAN) as a compatibilizer to reduce solubility differences and enhance the miscibility of each monomer. The TEM image of the PSSU membranes showed that the nano-phase separated structure was comprised of hydrophilic domains dispersed within the hydrophobic polymer matrix along with a peculiar biphasic swelling behavior. UAN also played a role as a dispersant to uniformly distribute the silica nanoparticles of different hydrophilicity and to obtain subsequent sulfonated polystyrene–silica nanocomposite membranes. In the PSSU nanocomposite membranes, the use of hydrophilic silica nanoparticles improved both the hydrophilicity and methanol barrier property of the membranes via a superior dispersion in the hydrophilic domains. Accordingly, it significantly contributed to an increase of the proton conductivity and a reduction of the methanol permeability. On the other hand, hydrophobic silica nanoparticles, which were mainly dispersed in the hydrophobic domains, compensated for excessive water swelling with an increase in the content of ionic groups. The membrane performances in the fully hydrated state could be conveniently controlled through the direct incorporation of nano-sized silica particles using UAN.
Keywords: Organic–inorganic nanocomposite membrane; Compatibilizer; Dispersant; Silica nanoparticles; Nano-phase separation;
Triethanolamine–cyclohexanone supported liquid membranes study for extraction and removal of nickel ions from nickel plating wastes by Naheed Bukhari; M. Ashraf Chaudry; M. Mazhar (182-189).
The permeation of Ni(II) from its aqueous solution through a supported liquid membrane containing triethanolamine (TEA) dissolved as mobile carrier in cyclohexanone has been studied. The effects of Ni(II) ion, HCl (in feed) and TEA (in membrane) concentrations have been studied. Ni(II) ions concentration increase in the feed leads to an increase in flux from 6.28 × 10−9 to 22.52 × 10−9 mol/m2 s within the Ni(II) ions concentration range (8.43–29.47) × 10−4 mol/dm3 at 2 M HCl in the feed and 3.00 M TEA in the membrane. Increase in H+ concentration by increasing HCl concentration from 0.1 to 2 M results into an increase in nickel ions flux but a decrease in flux has been found beyond 2 M HCl concentration in the feed, providing a maximum flux of 11.67 × 10−9 mol/m2 s at 2 M HCl. Increase in TEA concentration in the liquid inside the membrane enhances flux with its maximum value at 3.00 M TEA. Further increase in the concentration of TEA leads to a decreased rate of transport due to the increase in viscosity of membrane liquid. The optimum conditions for Ni(II) ions transport are, 2 M HCl (feed) and 3.00 M TEA (membrane). It has been observed that Ni(II) flux across the membrane tends to increase with these ions concentration increase. Applying the studied conditions to Ni plating waste solutions indicated more than 99% removal of Ni ions. Similar transport for EDTA-complexed Ni anions was observed across TEA–cyclohexanone based SLM, indicating a Ni anion transport, coupled with protons and chloride or EDTA co-ions.
Keywords: Triethanolamine–cyclohexanone; Ni ions; EDTA;
Fundamental studies of novel inorganic–organic charged zwitterionic hybrids by Junsheng Liu; Tongwen Xu; Ming Gong; Fei Yu; Yanxun Fu (190-200).
A series of novel hybrid zwitterionic membranes were prepared via a coupling reaction of trimethoxysilyl functionalized polyethylene glycol (PEG) and zwitterionic process with 1,4-butyrolactone (BL) thereafter. Both FT-IR and 13C NMR spectra confirmed the step reactions. Thermal analysis shows that the weight loss of the hybrid zwitterionic copolymer decreased slightly compared with the non-ionization hybrid precursor and the thermal stability of such zwitterionic copolymer can reach around 240 °C. Streaming potentials display that whether the membranes were coated once or thrice, they always exhibit negative values and no isoelectric point (IEP) was found in the tested pH range. Ion exchange capacities (IECs) reveal that only the cation-exchange capacities (CIECs) were detected and the CIECs of the membranes coated one to four times were in the region of (1.9–2.5) × 10−2 mequiv. cm−2. Pure water flux shows that it can be affected by the coating times and the substrate. The SEM images suggest that substrates can influence the membrane's microstructures. The increasing electrostatic repulsion between ion pairs and the pendent side structure of polymer chains might be responsible for these unusual behaviors.
Keywords: Zwitterionic hybrids; Hybrid zwitterionic membrane; Charged membrane; Polyethylene glycol (PEG); 1,4-Butyrolactone;
Synthesis and characterization of bipolar membrane using pyridine functionalized anion exchange layer by T. Jeevananda; Kyeong-Ho Yeon; Seung-Hyeon Moon (201-208).
To utilize bipolar membrane in water splitting electrodialysis, bipolar membranes were prepared by a paste method using commercial CM1 as cation exchange layer and optimized poly(GMA-DVB-PVC34) as the anion exchange layer. Chemically and thermally stable aromatic pyridinium was introduced as anion exchange functional group. Iron(III) hydroxide was immobilized at the bipolar membrane junction. The effect of iron(III) hydroxide on water dissociation capacity and current efficiency was investigated using a six-compartment electrodialytic cell. The result showed that with the immobilization of iron(III) hydroxide in the intermediate layer, water dissociation was enhanced and comparable to that of commercial BP1.The observed current efficiency for BPM with 5% (w/v) iron(III) hydroxide was more than 95%.
Keywords: Bipolar membrane; Pyridinium group; GMA; Monomer paste method; Water dissociation capacity;
Preparation and characterization of nanofibrous filtering media by R.S. Barhate; Chong Kian Loong; Seeram Ramakrishna (209-218).
Nanofibrous membranes offer unique properties for filtration- and adsorption-based separations including high specific surface area, good interconnectivity of pores and the potential to incorporate active chemistry on a nanoscale. The most versatile process for producing a nanofibrous membrane is electrospinning. Electrospinning process parameters such as the applied electric field (drawing rate), the rotational speed of collector (collection rate) and the tip-to-target distance strongly influence the extent of fiber crossing that occurs while collecting the nanofibers and affect the fiber arrangements. In turn, they have an effect on structural and transport properties of the electrospun mat. We investigated the structural and transport properties of electrospun membrane in relation to the processing parameters in order to understand the distribution, deposition and orientation of nanofibers in the nanofibrous filtering media. Our results demonstrate that control over the pore size distribution can be achieved by coordinating the drawing and collection rates.
Keywords: Microfilter; Nanofibers; Electrospinning; Microfiltration media; Membrane characterization;
Diphenylsilicate-incorporated Nafion® membranes for reduction of methanol crossover in direct methanol fuel cells by Z.X. Liang; T.S. Zhao; J. Prabhuram (219-224).
We synthesized organically modified silicate microparticles, known as diphenylsilicate (DPS), and showed that the synthesized DPS has a nano-layered microstructure. We utilized this material as a filler for fabricating Nafion®|DPS composite membranes for mitigating the problem of methanol crossover in direct methanol fuel cells (DMFC). The SEM and XRD analyses indicated that the incorporated DPS microparticles were uniformly distributed in the native membrane. The DMFC performance tests demonstrated that the use of the Nafion®|DPS composite membranes resulted in a lower rate of methanol crossover, higher open-circuit voltage (OCV) and better cell performance than did the pure Nafion® membrane, especially with a higher methanol concentration such as 10 M.
Keywords: Direct methanol fuel cells (DMFC); Nafion; Diphenylsilicate; Composite membrane; Methanol crossover;
Cleaning of particle-fouled membranes during cross-flow filtration using an embedded ultrasonic transducer system by Mikko O. Lamminen; Harold W. Walker; Linda K. Weavers (225-232).
Ultrasound was introduced into an “off-the-shelf” cross-flow membrane cell using a Navy Type I lead zirconate titanate transducer embedded opposite a membrane surface. The transducer, only 4.1 mm in thickness, required minimal modification of the existing flat-sheet filtration cell. Hydrogen peroxide and chemiluminescence measurements indicated that the thin transducer system was capable of inducing cavitation, and that the extent of cavitation increased with increasing applied power. For all powers tested, chemiluminescence measurements indicated that the surface of the membrane in the cross-flow system was within the zone of cavitation. Membranes were then fouled by 0.53 μm sulfate polystyrene latex particles. Membrane cleaning results showed that the thin transducer system increased the permeate flux of the membrane, with flux increasing with increasing applied power to the transducer. Both pulsed and continuous operation of the transducer improved flux (with continuous operation resulting in slightly greater improvement), although it may be beneficial to operate the system in pulsed mode to reduce energy consumption. At the highest powers, some damage to the membrane was observed. At lower applied powers, however, no damage to the membrane was found.
Keywords: Membrane fouling; Membrane cleaning; Ultrasound; Transducer; Cavitation;
Bisphenol A retention in the direct ultrafiltration of greywater by Andrea I. Schäfer; Long D. Nghiem; Nadine Oschmann (233-243).
Decentralised treatment is an increasing trend in the attempts to manage water more wisely in light of water restrictions, overconsumption and drought. Greywater is a fraction of household wastewater that offers the potential to be treated locally and then reused for garden irrigation, car washing and toilet flushing. In this paper the performance of submerged and direct ultrafiltration (UF) of synthetic greywater was investigated with regards to organic trace contaminant, namely bisphenol A (BPA), and fouling. The synthetic greywater solution consisted of inorganic particulates (kaolin), organic fibres (cellulose), protein (casein), surfactant (sodium dodecyl sulphate, SDS), humic acid (HA), calcium, sodium chloride electrolyte and sodium bicarbonate buffer.Results indicate that UF can remove 30–45% of BPA. This removal is attributed to partitioning of the compound to the membrane material, suspended and dissolved solids as well as the fouling layer. Humic acid and calcium were the main contributors to fouling, which also affected BPA retention. Fouling increased with an increase in HA concentration, which calcium contributed most to fouling at a concentration of about 0.5 mM. At higher concentration of calcium aggregation appeared to reduce fouling significantly.The implications of this study are that trace contaminant–solute interactions play an important role for retention potential and this relationship offers room for optimization by selecting particulate additives with a high affinity for target compounds. This is of particular importance if such contaminants are a concern (which is dependent on the product water application) and in the absence of biological treatment which is in this case not desired. The separation of greywater into fractions of low and high strength is of advantage if this can eliminate the presence of humic substances.
Keywords: Greywater; Graywater; Direct ultrafiltration; Recycling; Bisphenol A (BPA); Trace contaminant;
Solvent power and depressurization rate effects in the formation of polysulfone membranes with CO2-assisted phase inversion method by Márcio Temtem; Teresa Casimiro; Ana Aguiar-Ricardo (244-252).
Herein we report the preparation of polysulfone (PS) membranes using a CO2-assisted phase inversion method. The effect of the solvent affinity and depressurization rate in the morphology and in the performance in terms of pure water flux of the membranes has been investigated. Different casting solutions were prepared using the following solvents: methylpyrrolidone, dimethylformamide, dimethylacetamide, chloroform, dimethylsulfoxide and dimethylpropionamide. The morphologies of the membranes obtained by fast (less than 1 min) and slow (approximately 1 h) depressurization have been compared. These parameters had a significant effect upon the pore size and on the water fluxes of the membranes. A schematic ternary diagram of the system polymer–solvent–CO2 is discussed.
Keywords: Membrane formation; Polysulfone; Supercritical CO2; Phase inversion;
Relation between network structure and gas transport in crosslinked poly(propylene glycol diacrylate) by Roy D. Raharjo; Haiqing Lin; David F. Sanders; Benny D. Freeman; Sumod Kalakkunnath; Douglass S. Kalika (253-265).
A series of crosslinked poly(propylene oxide) rubbers was prepared by UV photopolymerization of poly(propylene glycol) diacrylate (PPGDA) in the presence of varying amounts of poly(propylene glycol) methyl ether acrylate (PPGMEA). The polar ether oxygen linkages in the resulting copolymers interact favorably with CO2, imparting a high selectivity for CO2 over light, non-polar gases as required for CO2 separation applications. The introduction of mono-functional PPGMEA in the polymerization reaction mixture resulted in the insertion of short side branches along the copolymer network and a corresponding reduction in the effective crosslink density; the concentration of propylene oxide (PO) segments in the networks ranged from 60 to 85 wt.%, depending upon the initial reaction composition. The effect of PPGMEA content on the mass density, free volume, and viscoelastic relaxation properties of the polymer networks was studied, and these results were related to the gas transport performance of the rubbery films. Permeability measurements (35 °C) are reported for H2, N2, CH4, CO2, C2H6, and C2H4; solubility and diffusivity data are presented for CH4, CO2, C2H6, and C2H4. The physical and gas transport characteristics of the crosslinked PPGDA polymers were compared with those obtained for rubbery networks based on poly(ethylene glycol) diacrylate.
Keywords: Poly(propylene glycol) diacrylate; Gas permeation; Solubility selectivity; Dynamic mechanical; Carbon dioxide;
Fouling of microfiltration membranes by natural organic matter after coagulation treatment: A comparison of different initial mixing conditions by Hyun-Chul Kim; Jong-Hyun Hong; Seockheon Lee (266-272).
The flux declines in the low-pressure membrane filtration of waters pre-treated by chemical coagulation using different initial mixing conditions were compared and the influence of natural organic matter (NOM) on the fouling of membranes was investigated. It was suggested that organic matter in the molecular weight ranges 300–2000 and 20,000–40,000 Da were mainly responsible for the fouling. The fouling was greater for hydrophobic than hydrophilic membranes. ATR–FT-IR analysis of the fouled hydrophobic membranes indicated aliphatic amide and alcoholic compounds as well as polysaccharides contributed to significant membrane fouling. These adsorptive foulants are considered as neutral fractions present in hydrophobic and hydrophilic NOM components. In the case of similar hydrophilic fractions, pre-coagulated water with a high hydrophobic content resulted in greater flux decline, which was presumed to be due to the organic matter with neutral properties contained within the hydrophobic fraction. The relative concentrations of each NOM fraction in coagulated water are important. Mechanical mixing for chemical coagulation, with a backmixing-type, rather than pump diffusion mixing, with an in-line type, is likely to be more effective at reducing the fouling caused by NOM.
Keywords: Microfiltration; Natural organic matter; Fouling; Coagulation; ATR–FT-IR;
Anti-fouling application of air sparging and backflushing for MBR by C. Psoch; S. Schiewer (273-280).
In membrane processes, fouling remains the main drawback and the toughest challenge at present and in the foreseeable future. The aim of this work was to combine anti-fouling strategies. In a membrane bioreactor (MBR) fed with synthetic wastewater with mixed liquor suspended solids concentrations between 3 and 10 g/L, the solid/liquid separation was achieved by a tubular membrane in side stream. For longer sustainable flux, air sparging was supplied to fight external fouling with the scouring effect of slug flow. Additional to that, backflushing was provided as a technique against internal fouling. The combination of both techniques showed very promising results and was superior to the operation of only one flux enhancement technique, yielding about three times higher fluxes compared to the NON-enhanced application after continuous filtration for 8 days. Backflushing accomplished significant flux increases with minimal product loss. The flux ratio of enhanced flux versus non-enhanced flux increased linearly with filtration time and air injection ratio. A simple model was developed to describe the development of the flux ratio over time for different air injection ratios. At high mixed liquor suspended solids concentrations (MLSS), where a high fouling potential exists, the combination of air sparging and back flushing was particularly effective in increasing the flux compared to non-enhanced filtration. Dimensionless fouling numbers increased with time, especially for lower air injection ratios.
Keywords: Air sparging; Backflushing; External and internal fouling; MBR; Synthetic wastewater;
Correlation of physicochemical characteristics with pervaporation performance of poly(vinyl alcohol) membranes by M.N. Hyder; R.Y.M. Huang; P. Chen (281-290).
In this research, hydrophilic poly(vinyl alcohol) PVA membranes were prepared and its surface and bulk properties, e.g. surface roughness and crosslinking, were characterized using Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM) and differential scanning calorimetry (DSC) and contact angle measurements. The PVA membranes were crosslinked in two ways: by heating at 125 °C or by chemical reaction with glutaraldehyde at room temperature. They were used for pervaporation applications, and dehydration of ethanol–water mixture was demonstrated in this paper. Compared to non-crosslinked membranes, the crosslinked membranes were shown to change in chemical structure by FTIR and become less hydrophilic by water contact angle measurement. The contact angle of the membranes increases with increasing the glutaraldehyde concentration used in crosslinking solution. AFM surface scans showed that the membrane surfaces are rough in nanometer scale and affected by the crosslinking treatment on the membranes. DSC measurements showed an increase in melting temperature of the polymer membranes after crosslinking. Dehydration of ethanol–water mixture was conducted over a range of ethanol concentrations (10–70 wt.%) in feed solution and at varied temperatures (from 25 to 50 °C). The dehydration results are presented and correlated with the results of the physicochemical measurements of the membranes.
Keywords: Poly(vinyl alcohol); Membranes; Pervaporation; Fourier transform infrared (FTIR); Atomic force microscopy (AFM); Differential scanning calorimetry (DSC); Contact angle;
Optimization of membrane unit for removing carbon dioxide from natural gas by Anjan K. Datta; Pradip K. Sen (291-300).
The aim of this paper is to find out the optimum configuration and design variables for the asymmetric membrane-based separation of carbon dioxide from natural gas for meeting the pipeline specification of 2% carbon dioxide. For this purpose, optimization of gas processing cost of the membrane unit having up to three stages is performed based on a fundamental model of the unit. It shows that there is no unique configuration that is always optimum irrespective of the values of carbon dioxide concentration and natural gas price. However, within certain ranges of the carbon dioxide concentration and the natural gas price, the optimum configuration may be unique and the minimum gas processing cost can be achieved by adjusting only the number of modules in each stage and the compressor power. In most cases, there is no significant cost difference between the two and three staged optimum configurations and the choice of a configuration may depend on engineering assessment.
Keywords: Membrane unit optimization; Multi-stage membrane unit; Carbon dioxide removal; Natural gas treatment; Natural gas purification;
Ion transport behavior in diffusion layer of new designed ion exchange-mosaic composite polymer membrane by Akira Yamauchi; A. Mounir EL Sayed; Kazuo Mizuguchi; Munemori Kodama; Yoshifumi Sugito (301-309).
New designed ion exchange-mosaic composite polymer membrane (MM/AEM) was proposed in this study. The new membrane was made from anionic exchange polymer gel (AEM) that coated onto mosaic polymer membrane (MM) to form MM/AEM polymer composite membrane system. Also, AEM membrane without mosaic membrane layer was used as reference commercial ion exchange membrane. The electrochemical properties of new designed composite polymer membrane system (MM/AEM) and non-composite one (AEM) were investigated by chronopotentiometry measurements (CP) and current–voltage curves (I–V). In the presence of KCl solution, the limiting current density of new designed composite MM/AEM was higher than that of commerical AEM. In other words, at the same current density, the transition time of composite MM/AEM was shorter than that of commercial AEM, and also diffusion layer thickness (δ), of composite MM/AEM was smaller than that of commercial AEM. It can be concluded that the new designed composite anionic exchange polymer membrane provides relatively good ion transport and other good membrane properties. In addition, the production of this new designed composite polymer membrane can be used in industry, like electrodialysis, as an alternative membrane instead of the commercial ion exchange membrane, which suffers from low limiting current density.
Keywords: MM/AEM composite membrane; Limiting current density; Chronopotentiometry; I–V curves;
Effect of MPEG on MPEG-grafted EAA membrane formation via thermally induced phase separation by Jing Zhou; Yijian Lin; Qiangguo Du; Wei Zhong; Haitao Wang (310-319).
By grafting reaction of poly(ethylene glycol monomethyl ether) (MPEG) and poly(ethylene-co-acrylic acid) (EAA), the MPEG-grafted EAA (EAA-g-MPEG) was obtained. The effect of MPEG on the phase diagram of EAA-g-MPEG/MPEG/di-n-octyl phthalate (DOP) system was investigated by varying the composition of MPEG and DOP via thermally induced phase separation (TIPS). The binodal temperature originally shifted to lower temperature as the proportion of MPEG increased, then increased remarkably when the ratio of MPEG to DOP was more than 1/6. The domain growth kinetics of EAA/DOP, EAA-g-MPEG/DOP and EAA-g-MPEG/MPEG/DOP systems was studied by light scattering method. It was found that the domain growth rate of EAA-g-MPEG/MPEG/DOP system was lower than EAA/DOP and EAA-g-MPEG/DOP systems at a certain quench temperature. Moreover, the membrane morphologies were compared, indicating that the pore size became smaller when MPEG was added as a component of diluent. Furthermore, the distribution of the grafted MPEG chains on the imitated interphase was investigated by energy-dispersive X-ray (EDX) analysis. Results showed that more hydrophilic MPEG chains existed on the interphase when MPEG was contained in the solvent.
Keywords: Poly(ethylene-co-acrylic acid); Poly(ethylene glycol monomethyl ether); Thermally induced phase separation; Light scattering; Energy-dispersive X-ray;
The role of the nature of the casting substrate on the properties of membranes prepared via immersion precipitation by P. Aerts; I. Genné; R. Leysen; P.A. Jacobs; I.F.J. Vankelecom (320-327).
The role of the nature of five different casting substrates on the properties of the resulting polysulfone membranes has been investigated. Wetting of the NMP-based polymer dope on the casting substrate has been quantified and linked to shrinkage of the membrane during the spreading and the coagulation phase of the wet phase inversion process. Shrinkage was found to less important when cast on hydrophilic substrates. Addition of a ZrO2 filler to the casting dope decreased the degree of shrinking. These data were then correlated to permeabilities and MWCO-values. The latter decreased upon casting on hydrophobic surfaces and the retention curves became sharper and less pressure dependent. FESEM-pictures of the membrane surfaces in combination with image analysis allowed to conclude that the diameter of the surface pores was surprisingly not influenced by the casting substrate. Casting on a Teflon support decreased the surface porosity.
Keywords: Immersion precipitation; Phase inversion; Membrane casting; Casting substrates; Filled membranes;
Microstructure evolution in dry cast cellulose acetate membranes by cryo-SEM by Sai S. Prakash; Lorraine F. Francis; L.E. Scriven (328-338).
The development of microstructure during drying-induced phase inversion or dry casting of homogeneous water/acetone/cellulose acetate coatings, which evolve into asymmetric separation membranes, was witnessed using ‘time-sectioning’ cryogenic scanning electron microscopy (cryo-SEM). Coating specimens were prepared via the following sequential steps: uniformly coating or casting the polymer solution onto a substrate, drying with environmental control for a specific time, rapidly freezing the specimen in liquid cryogen, fracturing to reveal the coating cross-section, subliming briefly for topographical contrast, sputter-coating to prevent charging and cryo-SEM imaging. Specimens were created with different drying times and hence each specimen is called a ‘time-section’. The earliest time-section, one from a coating soon after deposition, shows a featureless specimen, as expected for a homogeneous polymer solution. As drying proceeds, time-sectioning reveals first the nucleation of polymer-lean droplets dispersed within a polymer-rich matrix across a region bound by the free surface above and a phase separation front below. On further drying, this front travels down to the substrate; the polymer-lean droplets grow and coalesce, forming a smoothly interconnected phase, which eventually becomes the pore space of a honeycomb-like structure as drying progresses. Meanwhile at the free surface, a seemingly dense skin develops on drying, while a nodular intermediate layer appears between the thinner skin and the thicker honeycomb-like substructure. The images are analyzed with composition paths derived from theoretical modeling to elucidate the fundamentals of microstructure development in asymmetric membranes.
Keywords: Phase separation; Dry cast asymmetric membrane; Microstructure evolution; Cellulose acetate; Time-sectioning cryo-SEM; Dry phase inversion;
Characterization of exponential permeate flux by technical parameters during fouling and membrane cleaning by electric field by Carlos C. Tarazaga; Mercedes E. Campderrós; Antonio Pérez Padilla (339-345).
A major limiting step in the use of pressure-driven membrane processes is the membrane fouling, and this is the single most important reason for the relatively slow acceptance of ultrafiltration in many areas of chemical and biological processing. In the present study the variations of the active membrane area with time is evaluated, during the membrane fouling and cleaning with an electric field applications. These operations are characterized by means of some technical parameters described by a mathematical model that interprets the exponential variation of permeate fluxes and permit evaluate the extent of the membrane fouling and cleaning with electric fields. An efficient factor for the cleaning process is defined as a function of active membrane area.The expressions obtained let to evaluate the ultrafiltration of BSA solution and may be applied to other UF systems with different characteristic of the one considered in this study.
Keywords: Ultrafiltration; Fouling; Electric field; Cleaning; Mathematical model;
Influence of heat-treatment on CO2 separation performance of novel fixed carrier composite membranes prepared by interfacial polymerization by Juan Zhao; Zhi Wang; Jixiao Wang; Shichang Wang (346-356).
Novel fixed carrier composite membranes were developed by interfacial polymerization with water-soluble trimethylene tetramine (TETA) and hexane-soluble trimesoyl chloride (TMC) on polyethersulfone (PES) supports. A series of the composite membranes were prepared by adopting various heat-treatment time or temperature. Scanning electron microscope (SEM) pictures show that the surface of these membranes is covered with a honeycomb-like structure and the thickness of the skin layers is about 0.2 μm. The separation performance was tested with CO2/CH4 mixed gas (10/90 by volume) at various feed pressure. The results show that heat-treatment is a successful way in stabilizing membrane performance with pressure. The membrane heat-treated at 65 °C for 15 min had a CO2 permeance of 1.33 × 10−5 cm3 (STP) cm−2 s−1 cmHg−1 and CO2/CH4 selectivity of 94.1 at feed pressure of 1.1 atm. At 5 atm feed pressure, this membrane had a CO2 permeance of 1.28 × 10−5 cm3 (STP) cm−2 s−1 cmHg−1 and CO2/CH4 selectivity of 40.5. The optimum heat-treatment conditions were 65–70 °C and 10–15 min.
Keywords: Fixed carrier; Composite membrane; Heat-treatment; CO2 separation; Interfacial polymerization;
Poly(dimethylsiloxane-urethane) membranes: Effect of hard segment in urethane on gas transport properties by K. Madhavan; B.S.R. Reddy (357-365).
In this study, a series of PDMS-PU membranes based on PDMS soft segment and HMDI, TDI and MDI hard segments were synthesized in order to investigate the structure–gas transport relationships. The PDMS-PU membranes synthesized were characterized by DSC and SEM measurements. The restriction of chain mobility has been shown by the formation of hydrogen bonding in the soft segment and hard segment domains, resulting in the increase in density and glass-transition temperature of the soft segment. SEM analysis showed that the microphase separation involved in the PDMS-PU membranes. Gas permeation measurements were carried for O2, N2 and CO2 gases by employing different pressures. The permeability of O2 and N2 are independent with the pressure and CO2 shows dependency with pressure. Increase in PDMS soft segment led to increase in permeability for all the gases. This might be the phase separation involved in both hard segment and soft segment due to the difference of solubility parameter, and the dispersed PDMS phases in the membranes serve to produce a lower resistance route for diffusing molecules. The permselectivity for O2/N2 gas pairs of the synthesized membranes are in the range of 2.3–2.5 and for CO2/N2 gas pairs from 8.5 to 14.5. The gel content of the membranes was determined by using Soxhlet extraction apparatus.
Keywords: Polydimethylsiloxane; Urethane; Gas separation membranes;
Optimization of flux and selectivity in Cl−/SO4 2− separations with multilayer polyelectrolyte membranes by Seong Uk Hong; Ramamoorthy Malaisamy; Merlin L. Bruening (366-372).
Alternating layer-by-layer deposition of polycations and polyanions on porous substrates is a convenient and versatile method for forming high-flux nanofiltration (NF) membranes. This study compares the NF performance of four different types of multilayer polyelectrolyte membranes in Cl−/SO4 2− separations. Membranes were prepared using two polycations, poly(allylamine hydrochloride) (PAH) and poly(diallyldimethylammonium chloride) (PDADMAC), and two polyanions, poly(acrylic acid) (PAA) and poly(styrene sulfonate) (PSS). NF solution fluxes decreased in the order PSS/PDADMAC, PSS/PAH > PAA/PDADMAC ≫ PAA/PAH, which is consistent with permeability being controlled by the charge density (ionic cross-linking) in the system, as suggested previously. Interestingly, SO4 2− rejections were also highest for the PSS/PDADMAC system, making these membranes the most promising for Cl−/SO4 2− separations. In the best case (PSS/PDADMAC)3PSS deposited on a porous alumina support showed a 96% rejection of SO4 2−, a chloride/sulfate selectivity of 26, and a solution flux of 2.7 m3/m2 day at 4.8 × 105 Pa. In a direct comparison with a commercial NF270 membrane, the (PSS/PDADMAC)3PSS membranes allowed a 2.7-fold higher flux along with greater passage of Cl−, but the NF270 system exhibited higher (99.5%) SO4 2− rejections.
Keywords: Nanofiltration; Polyelectrolytes; Membranes; Anions; Separation;
Preparation of ETFE-based fuel cell membranes using UV-induced photografting and electron beam-induced crosslinking techniques by Jinhua Chen; Masaharu Asano; Yasunari Maekawa; Takahiro Sakamura; Hitoshi Kubota; Masaru Yoshida (373-379).
A novel process comprising UV-induced photografting of styrene into poly(tetrafluoroethylene-co-ethylene) (ETFE) films in vapor and liquid phases, followed by electron beam-induced crosslinking to the ETFE-graft-polystyrene films, and finally sulfonation of the multiple-crosslinked films has been developed for preparing polymer electrolyte fuel cell membranes. The significance of this process is that the photografted polystyrene chains can completely penetrate into the base ETFE film; the resultant sulfonated electrolyte membranes show proton conductibility available for fuel cell applications. On one hand, the proton conductivity of the liquid-phase photografted electrolyte membranes is higher than the vapor-phase one, and is anisotropic in the surface and thickness directions. On the other hand, radiation-induced crosslinking greatly improves the chemical stability of the resultant fuel cell membranes, and maintains the surface concentration of sulfonic acid groups at its higher level, which are very important for the performance of the relevant membrane electrode assembly.
Keywords: Polymer electrolyte membrane; Photografting; Fuel cell; Proton conductivity; Chemical stability;
SrCe0.95Yb0.05O3−α (SCYb) hollow fibre membrane: Preparation, characterization and performance by Yutie Liu; Xiaoyao Tan; K. Li (380-385).
Mixed proton–hole conducting ceramic, SrCe0.95Yb0.05O3−α (SCYb), hollow fibre membranes have been prepared using a combined immersion-induced phase inversion and sintering technique. Two different sintering routes have been adopted in studying the effect of sintering temperatures on gas-tight properties and mechanical strength of the prepared membranes. By employing longer time of heat treatment after thermolysis (i.e. removal of organic binders and additives at 600 °C), the final sintering temperature for preparation of the gas-tight SCYb hollow fibre membranes can be reduced. In addition, mechanical strength of the sintered membrane is found to be remarkably improved. The performance of the prepared SCYb hollow fibre membrane in terms of hydrogen permeation (proton conduction) has also been investigated experimentally.
Keywords: SrCe0.95Yb0.05O3−α (SCYb); Ceramic hollow fibre membrane; Sintering; Proton conduction;
Electrochemical behavior of new designed ion exchange membrane prepared from polymer gel in contact with redox substances: I by Akira Yamauchi; Yu Mishima; A. Mounir EL Sayed; Yoshifumi Sugito (386-392).
A new designed cationic exchange polymer membrane (CEM) and anionic exchange polymer membrane (AEM) were proposed in this study, and the transport properties of these new designed polymer membranes were investigated via diffusion coefficients as well. The diffusion coefficients of these polymer membranes in contact with different redox substances were calculated qualitatively by electrochemical techniques such as cyclic voltammetry (CV). Also, the diffusion coefficients of AEM and CEM were calculated quantitatively by using chronopotentiometry (CP) and chronocoulometry (CC) techniques. One can mention from this study the performance of a membrane depend on content of polymer gel, anionic exchange polymer site (20 wt.%) or cationic polymer exchange site (50 wt.%). Also, the ionic transport of newly designed ion exchange membrane could be explained by using electrochemical measurements such as CV, CP and CC techniques
Keywords: New designed membrane; AEM; CEM; Redox substances; CV; CP;
Gas transport properties of new aromatic cardo poly(aryl ether ketone)s by C. Camacho-Zuñiga; F.A. Ruiz-Treviño; M.G. Zolotukhin; L.F. del Castillo; J. Guzman; J. Chavez; G. Torres; N.G. Gileva; E.A. Sedova (393-398).
New cardo poly(aryl ether ketone)s containing side phthalide groups and aryl ether ketones in different lengths have been synthesized and characterized in terms of their thermal, volumetric and gas transport properties to H2, O2, N2, CH4 and CO2. The polymers show high glass transition temperature (218–420 °C), good solubility in chlorinated solvents and strong acids as well as excellent thermal stability (decomposition temperatures above 510 °C). The most permeable membrane studied shows permeability coefficients of 11 to O2 and 72 to CO2, with ideal selectivity factors of 4.6 for the pair O2/N2 and 25 for CO2/CH4. The results, interpreted in terms of chain rigidity and chain packing ability, show that decreasing the length of the connector moieties between the cardo groups increases the fractional free volume, the glass transition temperature and the gas permeability coefficients.
Keywords: Cardo polymers; Transport properties; Gas separation; Membranes; Poly(aryl ether ketone)s;
Mathematical models of diffusion through membranes from spatially distributed sources by Eugene E. Ley; Christopher E. Goodyer; Annette L. Bunge (399-410).
The objective was to numerically simulate diffusion through a membrane from regularly spaced sources distributed on the membrane surface. Two examples in which this physical situation arise are chemicals applied to the membrane as powdered materials or deposited in a volatile solvent that evaporates leaving behind a residue that partly covers the surface. Transient and steady-state finite element models in 2D and 3D were constructed to simulate diffusion from chemical sources distributed in a regular network on the surface of a membrane subject to either zero concentration or no flux on the membrane surface opposite to the surface in contact with the source. We assumed that local equilibrium was established with the membrane surface in direct contact with the chemical sources of constant concentration and that chemical did not enter or leave the membrane surface in the regions with no chemical contact. We calculated solutions for linear and square chemical sources as a function of the distance between these sources relative to the membrane thickness and as a function of the fraction of the membrane surface covered, including surface fractions that were smaller than have been considered previously. When sources are closely spaced relative to the membrane thickness, they interact such that flux from a spatially distributed source cannot be distinguished from a source that uniformly covers the membrane surface. When the distance between sources is large compared to the membrane thickness, there is no interaction between sources, and the effects of source regions are simply additive. The lag time associated with diffusion across the membrane, when plotted as a function of distance between source regions, has a maximum value that corresponds to the onset of interaction between source regions. The steady-state flux from line and square sources are similar when they cover more than about 25% of the membrane surface, but as the surface area in contact with the source decreases below 25%, the flux from line sources is increasingly greater than from squares. The differences between lines, squares and also circles of the chemical source covering the same fraction of the membrane surface can be explained by differences in the perimeter of the source. An algebraic equation for steady-state flux that was fit by regression to the finite difference solutions of linear and square sources covering 20% or more of the surface reported by Itoh et al. [N. Itoh, T.H. Wu, K. Haraya, Two- and three-dimensional analysis of diffusion through a dense membrane supported on a porous material, J. Membr. Sci. 99 (1995) 175–183] is inaccurate when the area fraction covered is smaller than 20%.
Keywords: Diffusion; Membrane; Finite element models; Three-dimensional analysis; Transient;
Polymeric microsieves produced by phase separation micromolding by M. Gironès; I.J. Akbarsyah; W. Nijdam; C.J.M. van Rijn; H.V. Jansen; R.G.H. Lammertink; M. Wessling (411-424).
The fabrication of polymeric microsieves with tunable properties (pore size, shape or porosity) is described in this work. Perfectly structured freestanding membranes and accurate replicas of polyethersulfone (PES), copolymers of polyethersulfone and polyethylene oxide (PES–PEO), and blends of PES and hydrophilic additives were produced by phase separation micromolding (PSμM) using a microstructured mold. Phase separation occurred in two stages: vapor-induced phase separation (VIPS), where shrinkage and subsequent perforation of the polymer film took place, and liquid-induced phase separation (LIPS), where lateral shrinkage that facilitated the release of the polymer replica from the mold occurred. The dimensions of the perforations were tuned either by using molds with different pillar diameter or by thermal treatment of the polymer above its glass transition temperature. By the latter method, microsieves with initial pore sizes of about 5 or 2.5 μm were reduced to 1.5 and 0.5 μm, respectively, whereas perforations down to 1.2 μm were achieved by tuning the dimensions of the mold features.
Keywords: Polymeric microsieves; Polyethersulfone; Polyvinylpirrolidone; Phase separation micromolding;
Permeation time lag in polymeric hollow fiber membranes by Xinhao Ye; Lu Lv; X.S. Zhao; Kean Wang (425-429).
Permeation time lag in polymer hollow fiber membrane is investigated with the dual mode sorption isotherm and the partially immobilized diffusion model. Analytical solutions are derived for the time lag at the two limit cases while numerical solutions are provided for the general case. It is shown that curvature ratio plays an important role for the permeation time lag in polymer hollow fiber membranes at intermediate pressure range.
Keywords: Time lag; Diffusion; Permeation; Polymer; Hollow fiber membrane;
Modeling the stretching of microporous membranes by Jason A. Morehouse; Douglas R. Lloyd; Benny D. Freeman; Desmond F. Lawler; Kenneth M. Liechti; Eric B. Becker (430-439).
Finite element modeling was used to predict the uni-axial deformation of microporous phase inversion membranes. Pore area, pore aspect ratio, and stress were studied as part of the modeling work. In order to adequately predict the change in pore shape due to the deformation two separate models were constructed. The models were formed in ABAQUS, a finite element solver commonly used for deformation modeling. One model predicts the initial phase of membrane deformation in which pores transition from a random alignment with respect to the direction of stretching to a uniform alignment in the direction of stretching. The second model is used to predict the deformation of the membrane pore structure after all pores have been aligned in the direction of stretching. Both models are successful in capturing the qualitative aspects of membrane deformation when compared to poly(vinylidene fluoride) membrane deformation data.
Keywords: Finite element analysis; Phase inversion; PVDF; Stretching; Elongation;
Pluronic polymers and polyethersulfone blend membranes with improved fouling-resistant ability and ultrafiltration performance by Yan-Qiang Wang; Yan-Lei Su; Xiao-Le Ma; Qiang Sun; Zhong-Yi Jiang (440-447).
Hydrophilic modification of polyethersulfone (PES) membranes was achieved by blending Pluronic polymers with different contents and PEO chain length. The static water contact angle measurements and X-ray photoelectron spectroscopy analysis confirmed the enrichment of PEO chain at blend membranes surface. Effect of Pluronic polymer content and PEO chain length on ultrafiltration performance and fouling-resistant ability of blend membranes was studied. The results indicated that except for PES–P123 blend membranes, the water fluxes of blend membranes were higher than that of PES control membrane. Meanwhile, increasing Pluronic content or PEO chain length both improved the fouling-resistant ability of blend membranes significantly. Finally, the outstanding flux recovery property of blend membranes ensured the long-run utilization time and operation reliability.
Keywords: Polyethersulfone; Pluronic polymer; Blend membranes; PEO chain density; PEO chain length;
Transport kinetics of chromium(VI) ions through a bulk liquid membrane containing p-tert-butyl calixarene 3-morpholino propyl diamide derivative by Ahmet Ö. Saf; Sabri Alpaydin; Abdulkadir Sirit (448-455).
The transport of chromate ions (Cr2O7 2−) from an aqueous solution into an aqueous receiving solution through a bulk liquid membrane containing p-tert-butyl calixarene 3-morpholino propyl diamide as a carrier was examined. The influence of pH on donor and acceptor phase, effect of chromate and carrier concentration, type of solvent, stirring speed and temperature were investigated. The kinetic parameters ( k 1 , k 2 , t max , R m max , J d max , J a max ) were calculated for the interface reactions assuming two consecutive, irreversible first order reactions. The activation energy values are 24.83 kJ mol−1 for extraction and 5.14 kJ mol−1 for reextraction. These values indicate that the process is diffusionally controlled by chromate ions. The experiments demonstrated that calixarene diamide derivative is a good carrier for Cr(VI) transport through liquid membranes in this study.
Keywords: Bulk liquid membrane; Transport of Cr(VI); Transport kinetics; p-tert-Butyl calixarene;