Membrane Science Research Papers - Academia.edu (original) (raw)

Mass transfer coefficients in commercial modules, including blood oxygenators, agree with literature correlations at high flows but are smaller at low flows. The smaller values at low flows probably result from channelling in the hollow... more

Mass transfer coefficients in commercial modules, including blood oxygenators, agree with literature correlations at high flows but are smaller at low flows. The smaller values at low flows probably result from channelling in the hollow fiber bundle. For the special case of flow within the fibers, the slight polydispersity of the hollow fibers causing this channelling can be used to predict deviations from the Ldvbque limit. These deviations can not be predicted from extensions to the L&&que analysis, or the analysis by Graetz. For the special case of flow outside the fibers, the mass transfer coefficients in commercial modules of various geometries are surprisingly similar, and fall below those of carefully handmade modules. These results can be used to develop still better membrane module designs.

There exist structural inhomogeneities of different scales in ion-exchange membranes. We suggest a microheterogeneous model for the description of inhomogeneities on the microphase scale, and show that they are the main factor determining... more

There exist structural inhomogeneities of different scales in ion-exchange membranes. We suggest a microheterogeneous model for the description of inhomogeneities on the microphase scale, and show that they are the main factor determining the concentration dependence of membrane transport properties such as electrical conductivity, diffusion permeability and transport numbers. A set of tests is proposed for determination of model structural-kinetic parameters of membranes.

The instability of supported liquid membranes has been a major impediment to practical applications. To address this shortcoming, we have developed a method to form semi-permeable polyamide skin layers in situ on supported liquid... more

The instability of supported liquid membranes has been a major impediment to practical applications. To address this shortcoming, we have developed a method to form semi-permeable polyamide skin layers in situ on supported liquid membranes containing an anion-exchange extractant (trioctylamine) and a neutral extractant (tributyl phosphate). These skin layers encapsulate large extractant molecules within the membranes but allow the transport of small species across the membranes. A liquid±liquid interfacial polymerization reaction was employed to form the polyamide skin layers utilizing monomers that are compatible with the extractants. SEM examination of the membranes shows the polyamide skin layer to be about 1 micron thick with pore sizes below resolution. Membranes with polyamide skin layers showed a typical¯ux of 1 mmol/s m 2 of Cr(VI), about half that exhibited by similar membranes without skin layers. # 1998 Elsevier Science B.V. All rights reserved.

Although several models have been developed to describe the evaporative casting of dense polymer films, none of them has included the convective transport terms which arise owing to the densification which occurs. In this paper we first... more

Although several models have been developed to describe the evaporative casting of dense polymer films, none of them has included the convective transport terms which arise owing to the densification which occurs. In this paper we first describe a new finite element solution to the binary nonisothermal evaporative casting process which is used to confirm the predictions of the finite

Crosslinked dense poly(vinyl alcohol) (PVA) membranes with different degrees of hydrolysis were prepared and used in sorption and pervaporation of isopropanol (IPA)/water mixtures. Partial flux of water permeation was increased with the... more

Crosslinked dense poly(vinyl alcohol) (PVA) membranes with different degrees of hydrolysis were prepared and used in sorption and pervaporation of isopropanol (IPA)/water mixtures. Partial flux of water permeation was increased with the water content in the liquid mixture, but the partial flux of IPA due to the coupling effect of sorption and permeation, had a maximum value. The degree of PVA hydrolysis and the feed temperature influenced the permeation flux and water selectivity due to crystallinity and the number of polar side groups in PVA. Thus the partial flux of water and IPA was inversely proportional to the degree of PVA hydrolysis and the selectivity of PVA for water was proportional to the hydrolysis level of PVA.

Pervaporative dehydration of acetic acid over the entire concentration range of 0-100% is studied using four copolymer membranes of acrylonitrile and high performance Nation and polyimide membranes. From each copolymer of acrylonitrile,... more

Pervaporative dehydration of acetic acid over the entire concentration range of 0-100% is studied using four copolymer membranes of acrylonitrile and high performance Nation and polyimide membranes. From each copolymer of acrylonitrile, three different membranes were produced with three different copolymer compositions. Polyimide showed high water selectivity but very low flux, while Nation showed highest flux but lowest selectivity. Copolymers of acrylonitriles showed reasonable flux and selectivity behavior. Among the acrylonitrile copolymers, copolymers with hydroxyethyl methylacrylate yielded water selectivity comparable to that of polyimide with much higher flux.

This paper focuses on the differences between the thermal behaviour of cation exchanged membrane based on Short Side Chain (SSC) and Long Side Chain (LSC) polymers. The a relaxation of alkali and Cu 2 þ exchanged membranes showed... more

This paper focuses on the differences between the thermal behaviour of cation exchanged membrane based on Short Side Chain (SSC) and Long Side Chain (LSC) polymers. The a relaxation of alkali and Cu 2 þ exchanged membranes showed dependency on ion exchange capacity and the length of the side chain similar to that of H þ -form membranes. The modulus drop of multivalent contaminated membranes was attributed to a degradation process except for Ba 2 þ and Zn 2 þ LSC exchanged membrane. The thermal behaviour as function of the Lewis Acid Strength, LAS, of the cation could originate from infrared (IR) vibrational changes. For cations with LAS o 0.3, the 1060 cm À 1 and 970 cm À 1 mode induce concurrent shift towards high wavenumbers. This suggests a stiffening of the corresponding bonds resulting in the improvement of the membrane's thermal stability. The cations with LAS 40.3 decrease the 970 cm À 1 wavenumber which could explain the enhancement of the degradation.

Nickel ion-imprinted membrane was synthesized using PVDF microfiltration membrane as support. In the current study, thermodynamic and kinetic of Ni(II) and Co(II) ions adsorption onto the membrane was investigated. Classical adsorption... more

Nickel ion-imprinted membrane was synthesized using PVDF microfiltration membrane as support. In the current study, thermodynamic and kinetic of Ni(II) and Co(II) ions adsorption onto the membrane was investigated. Classical adsorption isotherms including Langmuir, Freundlich, Redlich-Peterson and Langmuir-Freundlich (Sips) were employed to describe the adsorption equilibria. The Sips equilibrium model could superiorly represent the equilibrium adsorption of the ions. Calculation of principle thermodynamic parameters such as free energy, enthalpy and entropy change revealed exothermic and spontaneous adsorption on the basis of the negative H • and G • values, respectively. Meanwhile, adsorption of Co(II) ions on the imprinted membrane was less favorable than that of Ni(II) ions. Moreover, negative values of S • demonstrated randomness reduction at the solid-liquid interface. Pseudo-firstorder, pseudo-second-order and intra-particle diffusion models were utilized to describe the adsorption kinetic. Ion diffusivity through the membrane was also examined versus time and initial concentration. The kinetic results indicated superior adsorption-permeation rate of Ni(II) compared with Co(II) ions. In addition, a novel mathematical model was developed for prediction of the ions adsorption-transport behavior. Well fitted to the experimental data, the model provided a new insight into the phenomena involved in ion adsorption on imprinted membranes.

Modified polysiloxane membranes containing different organofunctional side chains were produced and tested fl)r the recovery of various organic contaminants from aqueous streams, using the process of pervaporation. Four separate organic... more

Modified polysiloxane membranes containing different organofunctional side chains were produced and tested fl)r the recovery of various organic contaminants from aqueous streams, using the process of pervaporation. Four separate organic components, phenol, chloroform, pyridine and methylisobutylketone <MIBK), each representative of an industrially significant family of chemicals, were chosen for evaluation. In each case significant performance enhancements, over that achieved with an unfunctionalised poly(dimethylsiloxane) membrane, were realised. Phenol transport is significantly facilitated by the incorporation of basic groups into the membrane structure. This is thought to be due to a weak acid-base interaction, increasing phenol sorption into the membrane. For pyridine, chloroform and MIBK separations from water, selectivity towards the organic component is greatly enhanced by the incorporation of long chain alkyl groups. A dual effect of the increased organic content of the membrane leading to increased organic component sorption and reduced water sorption is thought to be responsible. The effect of varying the three process parameters, feed concentration, membrane cross-linking density and membrane functional loading, were investigated. Some flux coupling effects were apparent, particularly affecting the transport of water with changing organic component concentration. Changing the cross-linking density of the membrane was found to have negligible effect across the range studied. An optimal functional loading generally close to l()~ exists. < 1997 Elsevier Science B.V.

The interplay between the dynamics of phase inversion, membrane formation, and drug release kinetics has been studied for solvent-cast films of a poly(n-butyl cyanoacrylate) (PBCA)-naproxen system. Films cast from solutions containing... more

The interplay between the dynamics of phase inversion, membrane formation, and drug release kinetics has been studied for solvent-cast films of a poly(n-butyl cyanoacrylate) (PBCA)-naproxen system. Films cast from solutions containing various amounts of polymer, solvent (acetone) and non-solvent (water) were analyzed via electron microscopy to determine optimal compositions and casting conditions leading to the formation of desired porous morphologies. In the presence of drug, the formation and locking-in of porous morphologies are found to be controlled by the interplay between the plasticizing effects of the drug and its crystallization kinetics during the phase inversion. Drug release rates from dried films exhibit a non-monotonic pattern with drug loading (DL), depending on whether a collapsed, dense structure or a porous structure forms. The role of glass transition and crystallization for both as-cast and remelted films is separately analyzed by differential scanning calorimetry (DSC). The discussion includes an analysis of the effect of DL on the quaternary (polymer-solvent-non-solvent-drug) phase diagram, indicating the role of glass composition curves on the locking-in process.

The separation of olefin-paraffin mixtures is one of the most important and expensive processes in petrochemical industries. In this research, the performance of cellulose acetate-silica nanocomposite membranes in the separation of... more

The separation of olefin-paraffin mixtures is one of the most important and expensive processes in petrochemical industries. In this research, the performance of cellulose acetate-silica nanocomposite membranes in the separation of ethylene/ethane and propylene/propane has been studied. Silica nanoparticles were prepared via hydrolysis of tetraethoxysilane (TEOS). Membranes were prepared by the solution-casting method. The prepared membranes were characterized using FT-IR, SEM and TGA analyses. Pure gas permeation experiments were performed by the constant volume/variable pressure method at 2 bar feed absolute pressure and 35 1C. The results showed the permeability of ethylene and propylene increased from 0.052 barrer and 0.046 barrer in pure cellulose acetate to 0.11 and 0.098 barrer in the composite membrane containing 30 wt% silica particles, respectively. The comparison of the selectivities of C 2 H 4 /C 2 H 6 and C 3 H 6 /C 3 H 8 indicates an increase from 2.16 and 2.55 in pure cellulose acetate to 4.07 and 6.12 in composite membrane containing 30 wt% silica particles. The diffusion coefficients of prepared hybrid membranes were determined by the time lag method. The solubility coefficient was calculated indirectly from permeability and diffusivity coefficients. The results showed an increase in the solubility coefficient and a decrease in the diffusion coefficient of gases while increasing the silica mass fraction. To investigate the possible plasticization phenomena, the effect of feed pressure on gas permeability and O 2 /N 2 selectivity, before and after exposure of membranes with propylene, was studied. The results showed no plasticization effects up to 8 bar feed pressure.

Methods of selecting applicable membranes for use in membrane contactors for flue gas desulfurization are proposed in this paper. The mass transfer mechanism for SO2 diffusion through gas filled pores is explored by simple measurements in... more

Methods of selecting applicable membranes for use in membrane contactors for flue gas desulfurization are proposed in this paper. The mass transfer mechanism for SO2 diffusion through gas filled pores is explored by simple measurements in order to identify suitable membrane structures for use in contactors for flue gas cleaning. It is attempted to correlate the experimentally determined membrane mass transfer coefficient to intrinsic physical properties of the membrane by applying theoretical and empirical correlations for the porosity-tortuosity relationship of the porous structure. Thereby limiting fluxes can be predicted with good accuracy from data quoted in the manufactures catalogue.

A chronocoulometric electrochemical measuring technique was used to evaluate the gas flux and permeation properties of sulphuric acid dissolved SO 2 across various polymeric membranes, using an in-house assembled permeation setup. This... more

A chronocoulometric electrochemical measuring technique was used to evaluate the gas flux and permeation properties of sulphuric acid dissolved SO 2 across various polymeric membranes, using an in-house assembled permeation setup. This was done in the temperature and differential pressure range of 298-353 K and 0-2 bar respectively. The sulphuric acid concentration was varied between 30 and 90 wt%. The electrochemically measured current due to SO 2 oxidation at the platinum electrode was converted to molar gas flux using Faraday's law. The flux was found to decrease as the temperature increased for all the evaluated membranes for example from 2.16 Â 10 À 8 7 0.15 mol s À 1 cm À 2 at 298 K to 1.46 Â 10 À 8 7 0.15 mol s À 1 cm À 2 at 353 K for Nafion s 112. The flux was found to increase with increasing Dp across the membrane and decrease with increasing acid concentration. From the flux data we were able to calculate the SO 2 permeation, diffusion and solubility parameters for the various membranes.The measured and calculated values were compared to existing literature values. The lowest SO 2 crossover was observed at high temperatures, low differential pressures and high H 2 SO 4 concentrations.

This study focuses on the surface modification of the commercial aromatic polyamide (PA) thin-film composite (TFC) reverse osmosis (RO) membranes with thermo-responsive copolymers poly(N-isopropylacrylamide-co-acrylamide) (P(NIPAM-co-Am))... more

This study focuses on the surface modification of the commercial aromatic polyamide (PA) thin-film composite (TFC) reverse osmosis (RO) membranes with thermo-responsive copolymers poly(N-isopropylacrylamide-co-acrylamide) (P(NIPAM-co-Am)) for improved membrane properties. Firstly, thermo-responsive copolymers P(NIPAM-co-Am) with certain lower critical solution temperature (LCST) were synthesized by free radical copolymerization in aqueous solution. The resultant copolymers were then used to modify the commercial TFC

Contact angle measurements (captive bubble technique) were used to determine the surface energy of three experimental thin-film composite nanofiltration membranes and a commercial nanofiltration membrane (Hydranautics NTR 7450). The two... more

Contact angle measurements (captive bubble technique) were used to determine the surface energy of three experimental thin-film composite nanofiltration membranes and a commercial nanofiltration membrane (Hydranautics NTR 7450). The two experimental membranes of practical interest were thin film composites (diblock copolymer on a polysulfone support layer). The two blocks were poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) and poly(1,1-dihydroperfluorooctyl methacrylate) (PFOMA). The concept was to devise a membrane material that takes advantage of the low adhesion of PFOMA to prevent fouling and the hydrophilic nature of PDMAEMA to produce high water permeation rates. Hydranautics NTR 7450 is a sulfonated polysulfone membrane that purportedly lessens fouling because the surface is more hydrophilic. The change in surface energy upon wetting, permeation of water containing natural organic matter (NOM) and chemical cleaning was of interest. Wetting caused reorganization of the experimental block copolymer surface to move more of PDMAEMA block to the membrane-water interface. After permeation of ultrapure water, however, the surface became more hydrophilic. After permeation of NOM containing water, the surface of both experimental and commercial membranes reached about the same surface energy, indicative of adsorption of NOM. The contact angle measurements were used to calculate a negative change in surface free energy for all but the PFOMA membrane; hence, with this exception, the deposition of NOM into a layer adjacent to the membrane surface was spontaneous. Scanning electron micrographs and atomic force micrographs showed that rigorous chemical cleaning failed to remove the NOM. Although the new polymeric materials were not more resistant to NOM fouling than commercial membranes, the surface energy calculations may help in the search for more successful polymers. Systematic study of charge, molecular size and specific functional groups of NOM on membrane fouling warrants further research to understand why similar fouling occurred on very different polymeric materials.

In order to validate the dry-cast model developed by us, a multifaceted experimental approach was undertaken whereby three process variables can be followed independently in real time. Since it is extremely difficult to determine... more

In order to validate the dry-cast model developed by us, a multifaceted experimental approach was undertaken whereby three process variables can be followed independently in real time. Since it is extremely difficult to determine experimentally the concentration and temperature profiles within the cast polymer solution, experiments were designed so as to provide information on the coupled mass-and heattransfer processes by measuring other process variables. The experimental data-acquisition technique combined gravimetric, inframetric, and light-reflection analyses which provided information on the overall mass change, surface temperature, and the onset and duration of phase separation, respectively. Structural studies were conducted using scanning electron microscopy. These studies revealed that macrovoids or "fingers" can be formed in dry-cast membranes. A hypothesis for the formation of fingers based on the model predictions and experimental observations is proposed.

Osmotic distillation (OD) is a concentration technique for aqueous mixtures based on porous hydrophobic membranes in contact on both sides with liquid phases at pressure lower than the pressure needed to displace the gas phase in the... more

Osmotic distillation (OD) is a concentration technique for aqueous mixtures based on porous hydrophobic membranes in contact on both sides with liquid phases at pressure lower than the pressure needed to displace the gas phase in the pores. The driving force for the water vapour diffusion through the gas phase immobilised within the membrane pores is sustained by an activity difference by using a hypertonic solution, typically concentrated brines, downstream the membrane. The mass transfer causes a cooling down of the feed and a warm up of the brine, as a consequence a temperature difference is created which reduces the effective driving force for mass transfer. This 'thermal effect' is investigated both theoretically and experimentally, it is shown that the effect on the flux is substantial. 0376-7388/99/$ -see front matter ©1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 6 -7 3 8 8 ( 9 9 ) 0 0 1 5 7 -X

Fouling is a major obstacle for maintaining efficient membrane-based drinking water treatment processes. Natural organic matter (NOM) components such as humic substances (HS)-and protein-like matter as well as colloidal/particulate matter... more

Fouling is a major obstacle for maintaining efficient membrane-based drinking water treatment processes. Natural organic matter (NOM) components such as humic substances (HS)-and protein-like matter as well as colloidal/particulate matter are known to be the major membrane foulants in ultrafiltration-based drinking water processes. In this study, a fluorescence excitation-emission matrix (EEM) approach was used for characterization of these major membrane foulants. Unlike most NOM and colloidal/particulate matter characterization techniques, this method can provide fast and consistent analyses with high instrumental sensitivity. Principal component analysis (PCA) of fluorescence EEM measurements collected during cross-flow ultrafiltration of river water was used to extract principal components (PCs) that contained information relevant to membrane fouling. These PCs were related to the major membrane foulants, HS, protein-like and colloidal/particulate matter present in natural water. PC score analysis revealed that colloidal/particulate matter mostly contributed to reversible fouling. HSand protein-like matter were largely responsible for irreversible fouling behaviour. Fluorescence EEMs of the foulants extracted from the membranes also revealed different rejection characteristics for two different membranes, 60 kDa and 20 kDa. The proposed method proved suitable for identifying the major foulant components and their contribution to reversible and irreversible membrane fouling, illustrating its potential for monitoring and controlling membrane fouling in drinking water treatment applications.

Cationic partitioning (Cu(II), Ni(II), and Fe(III)) into Nafion and ceramic membranes equilibrated with different salt solutions was investigated in this study. Both single-ion and multicomponent partitioning in a Nafion-117 membrane in a... more

Cationic partitioning (Cu(II), Ni(II), and Fe(III)) into Nafion and ceramic membranes equilibrated with different salt solutions was investigated in this study. Both single-ion and multicomponent partitioning in a Nafion-117 membrane in a 2.12 M chromic acid solution was well characterized with the Freundlich isotherm. The affinity for the Nafion membrane was Fe(III) > Ni(II) > Cu(II). The partition coefficients of the divalent cations in multicomponent partitioning experiments were similar to those in single-ion experiments whereas the partition coefficients of the trivalent cation decreased. Among the factors investigated, pH had the most significant influence on the partition coefficients, especially in the pH range of about 0.5-1.5. In contrast, temperature in the range of 25-55 • C had an insignificant effect. The ceramic diaphragm had partition coefficients equal to the porosity (0.4) of the ceramic for all of the species implying that cations were not adsorbed to its surface.

The separation properties of Nafion ® and sulfonated polyimide (SP) membranes have been compared for the recovery of acids from effluents containing metallic salts. To improve the selectivity, we have deposited a polyethylene imine (PEI)... more

The separation properties of Nafion ® and sulfonated polyimide (SP) membranes have been compared for the recovery of acids from effluents containing metallic salts. To improve the selectivity, we have deposited a polyethylene imine (PEI) anion-exchange layer on the membrane surface by using two different techniques, a conventional electrodeposition and the plasma polymerization technique involving an ethylene/ammonia monomers mixture. We have pointed out the efficiency of the latter technique since the transport number of multivalent cations has been decreased by 74 and 54% for the Nafion ® and the SP membranes, respectively. Plasma modified sulfonated polyimides are therefore good candidates for electrodialysis processes and constitute an alternative to the Nafion ® membrane.

In this communication we demonstrate a conception of an artificial microkidney using pertinent microtools that more accurately mimic organ functions in vitro. We present a technique to integrate polyethersulfone (PES) membranes usually... more

In this communication we demonstrate a conception of an artificial microkidney using pertinent microtools that more accurately mimic organ functions in vitro. We present a technique to integrate polyethersulfone (PES) membranes usually used in hemodialysis inside a polydimethylsiloxane (PDMS) microchip. The purpose of the microchip is to model glomerular filtration "on-chip". Mass transfer of urea (60 Da), vitamin B12 (1355 Da) and albumin (70,000 Da) are investigated by using two types of membranes (cut-off at 500,000 Da and 40,000 Da) in co-current and counter-current flow conditions. The time of urea, vitamin B12 and albumin removal, and the mechanisms of mass transfer, are controlled either by controlling the pore size of the membranes or by controlling the pressure profiles along the membrane via the flow conditions. An analytical model, which is supported by our data, is put forth. The model allows the extraction of the diffusion coefficients of each molecule through the various membranes studied. Due to the downscaling, the model and the experiments demonstrate that the dialysance in the microchip is expressed by the sum of the diffusion and convection mass transfer components. The results of this work support an analytical model which describes the mass transfer in a microchip modelling a glomerular unit. Coupled with the advantages of the microfluidic biochip (high surface/volume ratio, reduction of the fluid volumes), our data will complete the integration of further cellular functions for the utilisation of the present microchip as a future in vitro model of a miniaturized bio artificial kidney.

Ethanol/water pervaporation through ultrathin polyelectrolyte multilayer membranes is described. The membranes were prepared by the layer-by-layer technique, i.e. by alternating sequential adsorption of cationic and anionic... more

Ethanol/water pervaporation through ultrathin polyelectrolyte multilayer membranes is described. The membranes were prepared by the layer-by-layer technique, i.e. by alternating sequential adsorption of cationic and anionic polyelectrolytes on a porous support. The separation capability was optimized by variation of the chemical structure of the polyelectrolytes, by variation of pH and ionic strength of the polyelectrolyte solutions used for membrane preparation and by annealing of the polyelectrolyte membranes. It was found that the separation is mainly affected by the charge density of the polyelectrolytes which is controlled by the chemical structure and the degree of ionisation of the polar groups. Selectivity for water was highest, if polyelectrolytes of high charge density such as polyethyleneimine (PEI), polyvinylamine (PVA) and polyvinylsulfate (PVS) were used and if the pH of the polyelectrolyte solutions was equal to the mean of the pK a values of the corresponding cationic and anionic polyelectrolyte. Best results were obtained for PVA/PVS and PEI/PVS membranes which are characterized in detail with regard to their separation behavior.

Graphene oxide-molybdenum disulfide hybrid membranes were prepared using vacuum filtration technique. The thickness and the MoS 2 content in the membranes were varied and their H 2 permeance and H 2 /CO 2 selectivity are reported. A 60 nm... more

Graphene oxide-molybdenum disulfide hybrid membranes were prepared using vacuum filtration technique. The thickness and the MoS 2 content in the membranes were varied and their H 2 permeance and H 2 /CO 2 selectivity are reported. A 60 nm hybrid membrane containing ~75% by weight of MoS 2 exhibited the highest H 2 permeance of 804×10-9 mol/m 2 sPa with corresponding H 2 /CO 2 selectivity of 26.7; while a 150 nm hybrid membrane with ~29% MoS 2 showed the highest H 2 /CO 2 selectivity of 44.2 with corresponding H 2 permeance of 287×10-9 mol/m 2 sPa. The hybrid membranes exhibited much higher H 2 permeance compared to graphene oxide membranes and higher selectivity compared to MoS 2 membranes, which fully demonstrated the synergistic effect of both nanomaterials. The membranes also displayed excellent operational longterm stability.

Poly(N-vinyl-2-pyrrolidone) (PVP) is widely used in medicine due to its high biocompatibility. In this study, itaconic acid (IA) was co-polymerized with N-vinyl-2-pyrrolidone (NVP) monomer to prepare the pH sensitive hydrogels. These... more

Poly(N-vinyl-2-pyrrolidone) (PVP) is widely used in medicine due to its high biocompatibility. In this study, itaconic acid (IA) was co-polymerized with N-vinyl-2-pyrrolidone (NVP) monomer to prepare the pH sensitive hydrogels. These copolymer hydrogels were prepared using ultra-violet (UV) induced methods at ambient temperature. Monomer and cross-linking agent (N,N -methylene-bisacrylamide (MBAAm)) concentration effects on preparation of this copolymer hydrogel were investigated using swelling, FT-IR, and SEM. The prepared copolymer hydrogel is highly pH sensitive. The percentage swell of the copolymer hydrogels was found to increase from 150 to 3011% as the pH value of the swelling solution varied from 4 to 10. These pH sensitive copolymer hydrogels present a promising approach for drug delivery applications.

Homogeneuosly sulfonated poly(styrene) (SPS) was prepared with various concentration of sulfonic acid groups in the base polymer. Membranes cast from these materials were investigated in relation to proton conductivity and methanol... more

Homogeneuosly sulfonated poly(styrene) (SPS) was prepared with various concentration of sulfonic acid groups in the base polymer. Membranes cast from these materials were investigated in relation to proton conductivity and methanol permeability in the temperature range from 20 • C to 60 • C. It was found that both these properties increase as the polymer is increasingly sulfonated, with abrupt jumps occurring at a concentration of sulfonic acid groups of about 15 mol%. The most extensively sulfonated membrane exhibited conductivity equal to that of Nafion. As a consequence, this membrane material is potentially an appealing alternative to the very expensive Nafion, for a number of electrochemical applications. For the membrane with the highest degree of sulfonation we measured a methanol permeability about 70% smaller than for Nafion. This characteristic is especially desirable in applications related to the direct methanol fuel cell (DMFC).

The effects of fluidized media characteristics on membrane fouling and energy consumption in the anaerobic fluidized membrane bioreactor (AFMBR) were evaluated. Both adsorbing granular activated carbon (GAC) and non-adsorbing silica and... more

The effects of fluidized media characteristics on membrane fouling and energy consumption in the anaerobic fluidized membrane bioreactor (AFMBR) were evaluated. Both adsorbing granular activated carbon (GAC) and non-adsorbing silica and polyethylene terephthalate (PET) beads were evaluated. For fresh GAC, the energy requirement for fluidization increased with size, but smaller sizes led to greater reduction in membrane fouling. But when the GAC adsorption capacity was first exhausted, the reverse was noted, the larger particles reduced membrane fouling best. Non-adsorbing silica particles and PET beads demonstrated similar results to pre-adsorbed GAC, lower fouling was accomplished by the larger media that had a higher energy requirement for fluidization. The media packing ratio was also of importance, the higher the packing ratio up to 50%, the greater the reduction in fouling. Fouling reduction was also somewhat better at a given energy expenditure with lower specific gravity PET beads than with denser and smaller pre-adsorbed GAC particles.

Sodium chloride Binary ternary and quaternary systems a b s t r a c t In this paper, pervaporation (PV) of dichloromethane (DCM) from binary and multicomponent systems at different feed concentrations and temperatures using a commercial... more

Sodium chloride Binary ternary and quaternary systems a b s t r a c t In this paper, pervaporation (PV) of dichloromethane (DCM) from binary and multicomponent systems at different feed concentrations and temperatures using a commercial hydrophobic membrane CMX-GF-010-D (CELFA AG, Switzerland) is reported. Coupling effects are studied by permeating DCM/n-butanol/water ternary mixtures. The effect of sodium chloride on the process performance is also evaluated by PV of ternary DCM/sodium chloride/water and quaternary DCM/n-butanol/sodium chloride/water mixtures. PV performance was evaluated by permeate flux and enrichment factor. Further, permeance was calculated for pure water, DCM/water and DCM/n-butanol/water systems at 40 • C.

A theoretical model is proposed to describe hydrogen permeation in palladium and silver-palladium membranes in presence of a non-inert gas as CO; it is known indeed that hydrogen flux through palladiumbased membranes drastically decreases... more

A theoretical model is proposed to describe hydrogen permeation in palladium and silver-palladium membranes in presence of a non-inert gas as CO; it is known indeed that hydrogen flux through palladiumbased membranes drastically decreases when H 2 is fed in mixtures containing carbon monoxide due to the interaction of the latter gas with the membrane surface. To model this process, the adsorption step of the well-known approach suggested by Ward and Dao has been suitably modified, since it must be considered as a competitive adsorption of the different non-inert molecules on the metal interface. In particular, the competitive adsorption of CO and H 2 has been examined accounting for the spectrum of information available for CO adsorption on palladium, as well as for hydrogen in palladium and palladium-silver alloys. A validation of the model proposed has been performed through a comparison between several literature data and model calculations, over a rather broad range of operating conditions. A quite good agreement was obtained in the different cases; the model, thus, can be profitably used for predictive purposes.

Water sorption, desorption, and permeation in and through Nafion 112, 115, 1110 and 1123 membranes were measured as functions of temperature between 30 and 90 • C. Water permeation increased with temperature. Water permeation from liquid... more

Water sorption, desorption, and permeation in and through Nafion 112, 115, 1110 and 1123 membranes were measured as functions of temperature between 30 and 90 • C. Water permeation increased with temperature. Water permeation from liquid water increased with the water activity difference across the membrane. Water permeation from humidified gas into dry nitrogen went through a maximum with the water activity difference across the membrane. These results suggested that the membrane was less swollen in the presence of water vapor and that a thin skin formed on the dry side of the membrane that reduced permeability to water. Permeation was only weakly dependent on membrane thickness; results indicated that interfacial mass transport at the membrane/gas interface was the limiting resistance. The diffusivity of water in Nafion deduced from water sorption into a dry Nafion film was almost two orders of magnitude slower than the diffusivity determined from permeation experiments. The rate of water sorption did not scale with the membrane thickness as predicted by a Fickian diffusion analysis. The results indicated that water sorption was limited by the rate of swelling of the Nafion. Water desorption from a water saturated film was an order of magnitude faster than water sorption. Water desorption appeared to be limited by the rate of interfacial transport across the membrane/gas interface. The analysis of water permeation and sorption data identifies different regimes of water transport and sorption in Nafion membranes corresponding to diffusion through the membrane, interfacial transport across the membrane-gas interface and swelling of the polymer to accommodate water.

In this study, we report the effects of shear rates and polymer concentrations in the formation of asymmetric nanofiltration membrane using a simple dry/wet phase inversion technique. Employing the combination of irreversible... more

In this study, we report the effects of shear rates and polymer concentrations in the formation of asymmetric nanofiltration membrane using a simple dry/wet phase inversion technique. Employing the combination of irreversible thermodynamic model, solution-diffusion model (Spiegler-Kedem equation), steric-hindrance pore (SHP) model and Teorell-Meyers (TMS) model, the transport mechanisms and membrane structural properties were determined and have been characterized for different cases of those formation parameters. The experimental and modeling showed very promising results in terms of membrane performance with interesting structural details. The optimum shear rate (critical shear rate) was found to be at about 203.20 s −1 and the best polymer concentration toward the formation of high performance nanofiltration membrane is in the range of 19.60-23.10%. The modeling results suggested that the pore radius of the membranes produced lies within the range of pore radius of 29 commercial available membranes. This study also proposed that the electrolytes transport through nanofiltration membrane was dominated by a convection factor which accounted approximately 30% more than a diffusion factor. This study also indicated that shear rate and polymer concentration were found to affect the membrane performance and structural properties by providing, to a certain extent, an oriented membrane skin layer which in turn exhibiting an improvement in membrane separation ability.

A novel nanoporous carbon membrane produced by carbonization of poly(vinylidene chloride) is described. The membrane separates gas mixtures by selective adsorption and surface diffusion of the more strongly adsorbed components. In... more

A novel nanoporous carbon membrane produced by carbonization of poly(vinylidene chloride) is described. The membrane separates gas mixtures by selective adsorption and surface diffusion of the more strongly adsorbed components. In particular, the membrane can very efficiently separate hydrocarbons from hydrogen from low-pressure gas streams.

Two a-alumina ceramic membranes (0.2 and 0.8 jam pore sizes) and a surface-modified polyacrylonitrile membrane (0.1 jam pore size) were tested with an oily water, containing various concentrations (250-1000 ppm) of heavy crude oil... more

Two a-alumina ceramic membranes (0.2 and 0.8 jam pore sizes) and a surface-modified polyacrylonitrile membrane (0.1 jam pore size) were tested with an oily water, containing various concentrations (250-1000 ppm) of heavy crude oil droplets of 1-10 ~tm diameter. Significant fouling and flux decline were observed. Typical final flux values (at the end of experiments with 2h of filtration) for membranes at 250ppm oil in the feed are ~30-40kg m-2 h-1. Increased oil concentrations in the feed decreased the final flux, whereas the crossflow rate, transmembrane pressure, and temperature appeared to have relatively little effect on the final flux. In all cases, the permeate was of very high quality, containing <6 ppm total hydrocarbons. The addition of suspended solids increased the final membrane flux by one order of magnitude. It is thought that the suspended solids adsorb the oil, break up the oil layer, and act as a dynamic or secondary membrane which reduces fouling of the underlying primary membrane. Resistance models were used to characterize the type of fouling that occurs. Both the 0.2 jam and the 0.8 jam ceramic membranes appeared to exhibit internal fouling followed by external fouling, whereas external fouling characterized the behavior of the 0.1 jam polymer membrane from the beginning of filtration. Examination of the external fouling layer showed a very thin hydrophobic oil layer adsorbed to the membrane surface. This oil layer made the membrane surface hydrophobic, as demonstrated by increased water-contact angles. The oil layer proved resistant to removal by hydrodynamic (shear) methods. By extracting the oil layer with tetrachloroethylene, followed by IR analysis, its average thickness at the end of a 2 h experiment under typical conditions was determined to be 60 ~tm for the 0.2 jam ceramic membrane and 30 jam for the 0.1 jam polymer membrane. These measured amounts of oil associated with the membrane at the end of the experiments are in good agreement with those determined from a simple mass balance, in which it is assumed that all of the oil associated with the permeate collected is retained on or in the membrane, indicating that the tangential flow did not sweep the rejected oil layer to the filter exit.

Poly(ethylene chlorotrifluoroethylene) (ECTFE) is a 1:1 alternating copolymer of ethylene and chlorotrifluoroethylene that offers excellent resistance in chemically and thermally challenging environments. ECTFE membranes with a variety of... more

Poly(ethylene chlorotrifluoroethylene) (ECTFE) is a 1:1 alternating copolymer of ethylene and chlorotrifluoroethylene that offers excellent resistance in chemically and thermally challenging environments. ECTFE membranes with a variety of microstructures have been fabricated via thermally induced phase separation (TIPS) with dibutyl phthalate (DBP) as the diluent. A continuous flat sheet extrusion apparatus with a double rotating drum was used that permitted controlling both the casting solution thickness and axial tension on the nascent membrane. Initial compositions of ECTFE/DBP solutions in the liquid-liquid region of the binary phase diagram were chosen, resulting in membranes with an interconnected pore structure. The effects of several important process parameters were studied to determine their effect on the structure and properties of the membrane. The parameters evaluated included the initial ECTFE concentration, cooling rate, membrane thickness, co-extrusion of diluent, and stretching of the nascent membrane. The resulting membranes were characterized using SEM, porometry, and permeation measurements. For the range of process parameters studied, ECTFE membranes exhibited a decrease in surface porosity with increasing initial polymer concentration and cooling rate. The effect of membrane thickness on the permeation flux was not significant. Co-extrusion of diluent increased the surface porosity and eliminated the dense skin that was otherwise present under rapid cooling conditions. Subsequent stretching of the nascent membrane resulted in a more open structure and a significant increase in the permeation flux.

In this work, we report the direct methanol fuel cell (DMFC) performance of micro-patterned (p) Nafion ® 117 (N117) membranes prepared by hot embossing and compare them with that of normal N117 and heat and pressure treated (hp) N117... more

In this work, we report the direct methanol fuel cell (DMFC) performance of micro-patterned (p) Nafion ® 117 (N117) membranes prepared by hot embossing and compare them with that of normal N117 and heat and pressure treated (hp) N117 non-patterned (smooth) membranes.

Dimensional analysis of the mass, length and time shows that the steady state flux observed for microfiltration or ultrafiltration through inorganic composite membrane can be expressed using two dimensionless numbers. The shear stress... more

Dimensional analysis of the mass, length and time shows that the steady state flux observed for microfiltration or ultrafiltration through inorganic composite membrane can be expressed using two dimensionless numbers. The shear stress number Ns compares the shear stress against the membrane wall to the driving pressure, while the resistance number Nf compares the convective cross-flow transport to the drived transport through a layer, whose resistance is the sum of all the resistances induced by the different processes which limit the mass transport. Experimental data obtained in ultrafiltration of hydrocarbon emulsions and microfiltration of methanogenic bacteria suspensions and secondary treated wastewater were recalculated in terms of these dimensionless groups. Straight lines were plotted whose slope depends solely on the suspension and the membrane and not on the solute concentration. A negative slope and a positive intersection with the Ns axis means that a cake layer or a polarization layer can be completely eliminated at a critical cross-flow velocity; this was the case for an inorganic particles suspension and for the methanogenic suspension. A straight line of negative slope followed by a plateau means that an irreversible fouling is superimposed to the reversible phenomenon; this was observed for a secondary treated wastewater. A positive slope means that fouling predominates; this was observed with hydrocarbon emulsions. ~ 1998 Elsevier Science B.V.

The stability of polymer inclusion membranes (PIMs) relative to other liquid membranes is amongst the major reasons for the recent rejuvenation of interest in carrier-mediated transport for selective separation and recovery of metal ions... more

The stability of polymer inclusion membranes (PIMs) relative to other liquid membranes is amongst the major reasons for the recent rejuvenation of interest in carrier-mediated transport for selective separation and recovery of metal ions as well as numerous organic solutes. This is reflected by an increasing number of PIM investigations reported in the literature over the last two decades. Given the outstanding performance of PIMs compared to other types of liquid membranes particularly in terms of membrane lifetime, it has been predicted that practical industrial applications of PIMs will be realized in the near future. This review provides a comprehensive summary of the current knowledge relevant to PIMs for the extraction and transport of various metal ions and small organic solutes. PIM studies reported to date are systematically summarized and outlined accordingly to the type of carriers used, i.e. basic, acidic and chelating, neutral or solvating, and macrocyclic and macromolecular. The paper reviews the various factors that control the transport rate, selectivity and stability of PIMs. The transport phenomena observed by various authors are related to the membrane characteristics, physicochemical properties of the target solutes as well as the chemistry of the aqueous solutions making up the source and receiving phases. The results from these studies reveal an intricate relationship between the above factors. Furthermore, while the interfacial transport mechanisms in PIMs are thought to be similar to those in supported liquid membranes (SLMs), the bulk diffusion mechanisms in PIMs governing their permeability and selectivity require better understanding. This review also delineates two mathematical modeling approaches widely used in PIM literature: one uses a set of assumptions that allow the derivation of analytical solutions valid under steady-state conditions only; the other takes into account the accumulation of the target species in the membrane during the initial transport state and therefore can also be applied under non-steady-state conditions. The latter is essential when the interfacial complexation reaction kinetics is slow. It involves more complex mathematics and requires the application of numerical techniques. The studies included in this review highlight the potential of PIMs for various niche applications on a practical scale. The discussions provided, however, also emphasize the need for more fundamental research before any such practical applications of PIMs can be realized. This is specifically important for small organic compounds because to date scientific investigation involving the extraction and transport of these compounds remains limited. Transport mechanisms of small organic compounds are less well understood and are likely to be more complex than those observed with the transport of metal ions.

In the present work, the potential of polyPOSS-imide membranes designed for the purification of H 2 from a coke gas (utilized in the steelmaking industry) is investigated. Aiming at upscaling the membrane fabrication, tubular... more

In the present work, the potential of polyPOSS-imide membranes designed for the purification of H 2 from a coke gas (utilized in the steelmaking industry) is investigated. Aiming at upscaling the membrane fabrication, tubular single-channel and multi-channel membranes were prepared, using polyhedral oligomeric silsesquioxane (POSS) nanostructures and 6FDA as reactive precursors. The gas separation performance has been investigated by means of single gas and quaternary (H 2 , CH 4 , CO 2 , N 2) mixtures, the latter used to simulate the conditions expected at the membrane module inlet in the process of upgrading H 2 from a coke oven gas. Preliminary results obtained on tubular membranes showed that the fabricated membranes can achieve high H 2 permeance (>2000 GPU), displaying also suitable selectivity towards CO 2 , N 2 and CH 4. The selectivity of these upscaled tubular membrane samples meets the performance of those previously obtained for the disc-shaped lab-scale membranes. These results revealed the promising potential in the upscaling of polyPOSS-imide membranes fabricated via interfacial polymerization on ceramic porous supports for H 2 upgrading.

The permeance of Pd-Cu alloys containing 40, 53, 60, and 80 wt.% Pd has been determined over the 623-1173 K temperature range for H 2 partial pressure differences as great as 2.6 MPa. Pure palladium and copper membranes were also... more

The permeance of Pd-Cu alloys containing 40, 53, 60, and 80 wt.% Pd has been determined over the 623-1173 K temperature range for H 2 partial pressure differences as great as 2.6 MPa. Pure palladium and copper membranes were also evaluated. The Pd-Cu alloys exhibited predictable permeances that reflected the crystalline phase structures as shown in the binary phase diagram. Under conditions of face-centered-cubic (fcc) stability, the permeance increased steadily with palladium content, approaching the permeance of pure palladium membranes. The 53 and 60 wt.% Pd alloys were evaluated at temperatures within the body-centered-cubic (bcc) stability region. For both alloys, the bcc permeance was several times greater than the fcc permeance with the 60 wt.% Pd bcc permeance at 623 K reaching about 70% of the permeance of palladium. These bcc alloys were subjected to temperature increases during testing that resulted in transition from bcc to fcc, followed by temperature decreases that should revert the alloys to bcc. The permeances dropped abruptly during the transition from bcc to fcc. However, on cooling back to the bcc stability region, neither the 60 nor 53 wt.% Pd alloy completely regained a bcc permeance during the test period. All of the Pd-Cu alloys subjected to testing at 1173 K showed some permeance decline that was attributed to intermetallic diffusion between the membrane and support. The application of a diffusion barrier between the support and membrane foil in a 53 wt.% Pd permeance test successfully blocked the intermetallic diffusion and prevented degredation of the membrane's performance.

In this paper, representative polymeric (a PSf/PVP membrane), ceramic (a ZrO2 membrane) and organo-mineral (a ZrOJ PSf membrane) ultrafiltration membranes, all in the tubular configuration, are being compared for their basic membrane... more

In this paper, representative polymeric (a PSf/PVP membrane), ceramic (a ZrO2 membrane) and organo-mineral (a ZrOJ PSf membrane) ultrafiltration membranes, all in the tubular configuration, are being compared for their basic membrane properties, and for the typical ultrafiltration application of protein recovery of cheese whey. These three different membranes with a quite similar pore size (the cut-off values for each of the three membranes were comprised between 25 000 and 50 000 Dalton) showed pure water permeability coefficients between 135 and 1250 1/h m 2 bar. The highest pure water flux was found for the organo-mineral membrane, the lowest for the polymeric membrane. By FESEM analysis of the top-surfaces (skin) of both the PSf/PVP and the ZrO2/PSf membrane a strong difference in surface-porosity was found. These results were claimed to partially explain the difference in pure water flux. From SEM pictures of the cross-section of the ZrOz/PSf membrane it could also be seen that the skin layer thickness is smaller, at these places where particles are present near the skin-surface, compared to the rest of the membrane as well as to the skin of the PSf/PVP membrane. These latter observations were also used to further explain the flux difference between the PSf/PVP and the ZrOJPSf membrane.

The separation of Pb(II) and Hg(II) via a hollow fiber supported liquid membrane (HFSLM) is presented. The experiment studied the influence of types of extractants, the concentration of selected extractants, setting modules, operating... more

The separation of Pb(II) and Hg(II) via a hollow fiber supported liquid membrane (HFSLM) is presented. The experiment studied the influence of types of extractants, the concentration of selected extractants, setting modules, operating time together with flow rates of feed and stripping solutions. The mathematical model used to predict the concentration of Pb(II) and Hg(II) in both feed and stripping solutions was developed based on chemical reactions. The results clearly showed that a double-module HFSLM can selectively separate Pb(II) and Hg(II) at a very low concentration. Optimum condition was achieved using 0.03 M D2EHPA and 0.06 M Aliquat 336 as the extractant for first and second modules. The flow rates of the feed and stripping solutions were 100 mL/min. The complicated series of differential equations arising from the model was solved using the concept of Generating Function. The concentration of Pb(II) and Hg(II) in feed and stripping solutions, obtained from the model, fitted well with that from the experimental results as shown in . This indicated that the extraction and stripping reactions were important factors that governed the rate of Pb(II) and Hg(II) transport across the liquid membrane phase.

The role of chemical and physical interactions in natural organic matter (NOM) fouling of nanofiltration membranes is systematically investigated. Results of fouling experiments with three humic acids demonstrate that membrane fouling... more

The role of chemical and physical interactions in natural organic matter (NOM) fouling of nanofiltration membranes is systematically investigated. Results of fouling experiments with three humic acids demonstrate that membrane fouling increases with increasing electrolyte (NaC1) concentration, decreasing solution pH, and addition of divalent cations (Ca2+). At fixed solution ionic strength, the presence of calcium ions, at concentrations typical of those found in natural waters, has a marked effect on membrane fouling. Divalent cations interact specifically with humic carboxyl functional groups and, thus, substantially reduce humic charge and the electrostatic repulsion between humic macromolecules. Reduced NOM interchain repulsion results in increased NOM deposition on the membrane surface and formation of a densely packed fouling layer. In addition to the aforementioned chemical effects, results show that NOM fouling rate increases substantially with increasing initial permeation rate. It is demonstrated that the rate of fouling is controlled by an interplay between permeation drag and electrostatic double layer repulsion; that is, NOM fouling of NF membranes involves interrelationship (coupling) between physical and chemical interactions. The addition of a strong chelating agent (EDTA) to feed water reduces NOM fouling significantly by removing free and NOM-complexed calcium ions. EDTA treatment of NOM-fouled membranes also improves the cleaning efficiency dramatically by disrupting the fouling layer structure through a ligand exchange reaction between EDTA and NOM-calcium complexes.

In this work, the experimental procedure and mathematical model formerly developed was used to describe the electrodialytic (ED) recovery of trisodium citrate. By performing several voltage-current, electro-osmosis and desalination tests,... more

In this work, the experimental procedure and mathematical model formerly developed was used to describe the electrodialytic (ED) recovery of trisodium citrate. By performing several voltage-current, electro-osmosis and desalination tests, the main engineering parameters (i.e., the ion transport numbers in solution and membranes, effective solute and water transport numbers, effective surface area and resistances of membranes, and limiting electric current) of the ED process under study were assessed.

Despite intensive research, fouling remains a severe problem in membrane filtration. It is often controlled by applying turbulent flow which requires a higher energy consumption. So-called turbulence promoters or static mixers can be... more

Despite intensive research, fouling remains a severe problem in membrane filtration. It is often controlled by applying turbulent flow which requires a higher energy consumption. So-called turbulence promoters or static mixers can be inserted into the flow channel of tubular membranes. They deflect the fluid, induce vortices, enhance particle back-transport and increase the shear rate at the membrane surface, thus mitigating fouling. However, little is known how

Polyvinylidene fluoride (PVDF) ultrafiltration membranes were modified using a new type of hydrophilic polyurethane additive, called L2MM. During phase inversion L2MM migrates to the membrane surface and functions as both a pore former... more

Polyvinylidene fluoride (PVDF) ultrafiltration membranes were modified using a new type of hydrophilic polyurethane additive, called L2MM. During phase inversion L2MM migrates to the membrane surface and functions as both a pore former and surface modifier. L2MM improved the surface hydrophilicity and significantly increased the PVDF membrane's pure water permeation (PWP) rate. PVDF membranes were modified with two L2MMs: L2MM(PEG-600) and L2MM(PEG-200). PWP tests, contact angle measurements, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to assess the impact of L2MM type, L2MM concentration and PVDF concentration on the performance and characteristics of modified PVDF membranes. XPS analysis and contact angle measurements indicated that the L2MM migrated to the membrane surface and the contact angle decreased by up to 19%. SEM and AFM images were used to investigate the relation between surface morphology and ultimate performance. The L2MMs had a significant effect on flux; increasing the L2MM concentration improved membrane PWP fluxes up to a maximum with further increases resulting in flux decreases. Both L2MM(PEG-200) and L2MM(PEG-600) increased the final PWP flux of modified PVDF membranes up to 6.5 times that of the control membranes. Furthermore, L2MM(PEG-200) increased the 100 kDa polyethylene oxide (PEO) separation from 88 to 96% compared to the control membrane.

Öz Abstract Bu çalışmada, kağıt atıksuları için literatürde etkinliği bilinen basınç sürücülü sistemlerin kesikli şartlarda işletimleri, NFgevşek/NFsıkı membran sistem kombinasyonu kullanılarak yerine getirilmiştir. Kesikli... more

Öz Abstract Bu çalışmada, kağıt atıksuları için literatürde etkinliği bilinen basınç sürücülü sistemlerin kesikli şartlarda işletimleri, NFgevşek/NFsıkı membran sistem kombinasyonu kullanılarak yerine getirilmiştir. Kesikli NFgevşek/NFsıkı deneyleri sırasıyla 12 ve 20 barda klasik membran filtrasyon yöntemiyle 300 rpm'lik karıştırma hızında, pH 10'da ve 25 °C sıcaklıkta uygulanmıştır. Kesikli işletim şartlarında kullanılacak en uygun membran türlerinin tespiti NFgevşek için NP010, NFG, MPF36 ve CK3001 ve NFsıkı için NP030, NF270, DS-5DK, ESNA olmak üzere toplamda 8 farklı membran kullanılarak, organik madde giderimi ve süzüntü akı değerleri üzerinden belirlenmiştir. NFgevşek membranlarda 4.12 L/m 2 sa'lik süzüntü akısında, %61.0 TOK ve %76.9 KOİ giderimi ile MPF36 membran en iyi NFgevşek membran olarak belirlenmiştir. Sürekli işletimle MPF36 ile elde edilen süzüntü suyu daha sonra NFsıkı membranlardan geçirilmiştir. Tüm NFsıkı membranlarda, genel olarak iyi seviyelerde organik madde giderim etkinliği elde edilmiş olmakla birlikte 10.05 L/m 2 sa süzüntü akısında, %93.9 TOK ve %94.2 KOİ oranlarında organik madde giderimi sağlanarak en iyi çıkış suyu kalitesi eldesi bakımından ESNA uygun membran olarak seçilmiştir. Bu noktadan hareketle, kâğıt atıksularının etkinliği bilinen basınç sürücülü NFgevşek/NFsıkı bütünleşik membran sistemiyle kısa süreli işletimlerinde, 7.35 pH ve 144 S/cm iletkenlik değerlerinde 13 mg/L TOK ve 28 mg/L KOİ konsantrasyonlarında iyi kalitede arıtılmış çıkış suyunun elde edilebildiği, ayrıca hedeflenen çıkış suyu açısından, iyi kalitede yeniden kullanım suyu üretilebildiği görülmüştür. In this study operating pressure driven systems which is known their efficiency in literature, for paper and pulp industry wastewaters in batch conditions were executed by using NFloose/NFtight membrane combination. The batch NFloose/NFtight experiments were respectively applied at 12 and 20 bars by conventional membrane filtration process, at a stirring rate of 300 cycle/min, at pH 10 and at a temperature of 25 °C. Determination of most suitable membrane at batch operating conditions were made by using 8 different membranes (for NFloose NP010, NFG, MPF36 and CK3001 and for NFtight NP030, NF270, DS-5DK, ESNA) through organic matter removal and filtrate flux values. In NFloose membranes at a filtrate flux of 4.12 L/m 2 h removal of 61.0% TOC and 76.9% COD and MPF36 membrane was determined to be best NFloose membrane. The filtrate water obtained by MPF36 were later passed through NFtight membranes. In all NFtight membranes generally the organic matter removal efficiency was good and ESNA was selected to be the best membrane in terms of effluent quality by obtaining organic matter removal at rates of 93.9% TOC and 94.2% COD with 10.05 L/m 2 h filtrate flux. From this point of view, in short term operation of paper wastewaters by pressure driven NFloose/NFtight integrated membrane system, it was seen that good quality of outlet water with 7.15 pH and a conductivity coefficient of 144 µS/cm and at 13 mg/L TOC and 28 mg/L COD concentrations could be obtained also that good quality of reuse water could be produced in terms of aimed effluent water.

Reverse electrodialysis (RED) is a non-polluting, sustainable technology used to generate energy by mixing water streams with different salinity. The key components in a RED system are the ion exchange membranes. This paper evaluates the... more

Reverse electrodialysis (RED) is a non-polluting, sustainable technology used to generate energy by mixing water streams with different salinity. The key components in a RED system are the ion exchange membranes. This paper evaluates the potential of commercially available anion and cation exchange membranes for application in RED. Different membrane properties and characterization methods are discussed and a theoretical membrane model for RED was used to allow fair comparison of the characterization results for application in RED. The results of this study suggest that the membrane resistance should be as low as possible, while the membrane selectivity is of minor importance. Based on the results, the best benchmarked commercially available anion exchange membranes reach a power density of more than 5 W/m 2 whereas the best cation exchange membranes show a theoretical power density of more than 4 W/m 2 . According to the membrane model calculations, power densities higher than 6 W/m 2 could be obtained by using thin spacers and tailor made membranes with low membrane resistance and high permselectivity, especially designed for reverse electrodialysis. This makes RED a potentially attractive alternative for energy production.

Previous experiments have shown that when selenium was attached to a surface, biofilm development on the surface was inhibited. Selenium is a catalytic producer of superoxide radicals via oxygen reduction. The superoxide radicals can... more

Previous experiments have shown that when selenium was attached to a surface, biofilm development on the surface was inhibited. Selenium is a catalytic producer of superoxide radicals via oxygen reduction. The superoxide radicals can cause damage to the outer membrane of bacterial cells that frequently results in cell death. Therefore, we propose selenium attachment to an RO membrane surface as a biofouling inhibition technique. Selenium was attached to the surface of RO membranes via monomer (selenocystamine) and polymer (aceto acetoxy ethyl methacrylate) attachment mechanisms. Using confocal microscopy and Staphylococcus aureus cell counting to evaluate S. aureus biofilm growth, the number of attached S. aureus cells was seen to be significantly reduced on RO membranes coated with selenium. While both selenium coatings had similar S. aureus inhibition, the selenium coatings had much different impacts on permeate flux. The selenocystamine attachment method maintained a higher permeate flux compared to the AAEMA attachment method due to AAEMA requiring a harsh attachment procedure. Ultimately, attached selenocystamine showed great potential to serve as a biofouling inhibitor by reducing attached S. aureus growth on RO membranes without excessive permeate flux loss.

The influence of co-ion leakage through a bipolar membrane on both I-V response and current efficiency of water dissociation was studied. The monofilm bipolar membrane was synthetized from a pretreated ETFE film functionalized by... more

The influence of co-ion leakage through a bipolar membrane on both I-V response and current efficiency of water dissociation was studied. The monofilm bipolar membrane was synthetized from a pretreated ETFE film functionalized by quatemized ammonium groups on one side and sulphonic groups on the other. The co-ion leakage of this bipolar membrane immersed in NaCl solutions was measured by means of radiotracers. The results showed that the greater the co-ion leakage, the lower was the current efficiency of water dissociation. A theoretical analysis of ion transfer through the bipolar membrane pointing out the effect of boundary layer on the limiting leakage current is presented.

In this study, polyacrylonitrile (PAN) nano-fibrous membranes with fiber diameters of ∼450 nm were prepared by the technique of electrospinning; amidoxime nano-fibrous membranes were then prepared through treatment of PAN nano-fibrous... more

In this study, polyacrylonitrile (PAN) nano-fibrous membranes with fiber diameters of ∼450 nm were prepared by the technique of electrospinning; amidoxime nano-fibrous membranes were then prepared through treatment of PAN nano-fibrous membranes in hydroxylamine (NH 2 OH) aqueous solution. The -C N groups on the surface of PAN nanofibers reacted with NH 2 OH molecules and led to the formation of -C(NH 2 ) N-OH groups, which were used for coordination of Ag + ions. Subsequently, the coordinated Ag + ions were converted into silver nanoparticles (AgNP) with sizes being tens of nanometers. Morphologies, structures, and antimicrobial efficacies (against Staphylococcus aureus and Escherichia coli) of the membranes of electrospun PAN (ESPAN) nanofibers, ESPAN surface functionalized with amidoxime groups (ASFPAN), ASFPAN coordinated with silver ions (ASFPAN-Ag + ), and ASFPAN attached with silver nanoparticles (ASFPAN-AgNP) were investigated. The study revealed that, with treatment of ESPAN membranes in 1 M NH 2 OH aqueous solution for 5 min, the resulting ASFPAN membranes became antimicrobial without distinguishable morphological variations; further treatment of ASFPAN membranes in 0.1 M AgNO 3 aqueous solution for 1 h and the subsequent treatment in 0.01 M KBr aqueous solution for 2 h followed by photo-decomposition made the respective membranes of ASFPAN-Ag + and ASFPAN-AgNP highly antimicrobial, which were capable of killing the tested microorganisms in 30 min. The water permeability test indicated that these membranes possessed adequate transport properties for filtration applications. This study demonstrated a convenient and cost-effective approach to develop antimicrobial nano-fibrous membranes that are particularly useful for the filtration of water and/or air.