High-speed recovery of antimony using chelating porous hollow-fiber membrane

A porous hollow-fiber membrane containing an iminodiethanol (IDE) group as the chelate-forming group was applied to the recovery of antimony in the permeation mode. An antimony solution was forced to permeate through the pores of the chelating porous hollow-fiber membrane, driven by a transmembrane pressure. The membrane with a thickness of 0.7 mm and a porosity of 70% had an iminodiethanol group of 1.6 mol/kg of the membrane and a water flux of 0.95 m/h at 0.1 MPa and 298 K. The breakthrough curves of antimony overlapped irrespective of the permeation rate of the antimony solution ranging from 2 to 20 ml/min, i.e. the residence time across the membrane thickness ranging from 3.4 to 0.34 s, because of negligible diffusional mass-transfer resistance of the ionic species of antimony to the iminodiethanol group. At antimony concentrations below 10 mg/l (pH 4.0), a linear adsorption isotherm was obtained. The adsorbed antimony was quantitatively eluted by permeation of 2 M hydrochloric acid through the pores of the membrane.     

Ultrafiltration of soybean oil/hexane extract by porous ceramic membranes

This study investigated the ultrafiltration of soybean oil/hexane extract (miscella) using porous ceramic membrane. The evaporation energy can be saved in the soybean oil production by pre-separating a portion of hexane through the ceramic membrane. Raw soybean oil/hexane extract with 33 wt% of oil was used without pretreatment. A cross-flow ultrafiltration was performed using an anodisc membrane with a pore diameter of 0.02 μm and thickness of ∼1 μm. The concentrations of oil/hexane mixture were measured by UV adsorption at a wavelength of 458 nm. The separation mechanism was suggested to be the hindrance diffusion of soybean oil. Agitation in the feed side significantly increased the rejection of soybean oil. A small stage cut could also yield a higher rejection. Above observations were attributed to the reduction of concentration polarization by increasing the shear rate and small permeate flux, respectively. The optimum separation was achieved under the conditions of 4 kg/cm² transmembrane pressure, 0.04 stage cut and 120 rpm agitation speed. The concentration of soybean oil decreased from 33 wt% of feed to 27 wt% in permeate, that is, near 20% rejection. A gel-layer polarization model was proposed to estimate the gel concentration and thickness. The gel concentration was found 43–53 wt%. Agitating feed side reduced gel thickness, thus enhanced the rejection and permeate flux.     

New ceramic microfiltration membranes from mineral coal fly ash

This work aims to develop a new mineral porous tubular membrane based on mineral coal fly ash. Finely ground mineral coal powder was calcinated at 700 °C for about 3 h. The elaboration of the mesoporous layer was performed by the slip casting method using a suspension made of the mixture of fly ash powder, water and PVA. The obtained membrane was submitted to a thermal treatment which consists in drying at room temperature for 24 h then a sintering at 800 °C. SEM photographs indicated that the membrane surface was homogeneous and did not present any macro defects (cracks, etc.). The average pore diameter of the active layer was 0.25 μm and the thickness was around 20 μm. The membrane permeability was 475 l/h m² bar.This membrane was applied to the treatment of the dying effluents generated by the washing baths in the textile industry. The performances in term of permeate flux and efficiency were determined and compared to those obtained using a commercial alumina microfiltration membrane. Almost the same stabilised permeate flux was obtained (about 100 l/h m²). The quality of permeate was almost the same with the two membranes: the COD and color removal was 75% and 90%, respectively.     

Hollow-fiber-type pore-filling membranes made by plasma-graft polymerization for the removal of chlorinated organics from water

Hollow-fiber-type pore-filling membranes were prepared to reduce the emission of toxic chlorinated organics into the environment. These membranes can remove 1,1,2-trichloroethane (TCE) or dichloromethane (DM) from water, and concentrate them in the permeate. The pore-filling membrane can efficiently remove organics from water because of the suppression of the membrane swelling by the porous substrate matrix, and the fact that it can maintain a high solute diffusivity, because of the linear graft chains that fill the substrate pores. Laurylacrylate (LA) or n-butylacrylate (BA) grafted layers were formed inside the porous hollow-fiber substrate, and the pores were filled with the grafted chains formed from plasma-initiated graft polymerization. The hollow-fiber-type LA-grafted membranes showed extremely high separation properties: a 0.09 wt.% TCE aqueous solution was condensed to 99 wt.% TCE in the permeate. The membrane can remove TCE from a water stream, and at the same time, the membrane can purify the TCE for re-use. The membrane also showed high separation performance for an aqueous DM solution. The mass transfer resistance outside the membrane was estimated by using a concentration polarization model. When the mass transfer coefficient at the membrane and feed stream boundary layer was below 10⁻⁴ m/s, the boundary layer resistance affected the membrane performance. This needs to be taken into account when designing the membrane module and operating conditions.     

Pervaporation separation of methanol/methyl t-butyl ether through chitosan composite membrane modified with surfactants

We investigated the efficiency of pervaporation separation of methanol/methyl-t-butyl ether (MTBE) mixture through chitosan composite membrane modified with sulfuric acid and four surfactants. Effects of feed concentration, temperature, crosslinking degree and type of surfactants were studied. The chitosan composite membrane modified with sulfuric acid showed the pervaporation performance of over 70 wt% methanol in the permeate and flux of 100 g/m² h measured at 25°C. At 50°C, the separation factor decreased while the flux increased exceeding 300 g/m² h. For the membrane complexed with surfactants, the permeate showed 98.3 wt% methanol concentration and 470 g/m² h of permeate flux at 25°C. With increasing operating temperature, the permeate flux remarkably increased to 1170 g/m² h and the permeate showed 97.8 wt% methanol concentrations.     

Microfiltration of protein mixtures and the effects of yeast on membrane fouling

The effects of yeast cells on membrane fouling by a protein mixture were studied in dead-end filtration. A 0.2 μm cellulose acetate membrane was used with a 1 g/l protein mixture consisting of equal amounts of bovine serum albumin, lysozyme, and ovalbumin. Yeast cells were used either in suspension or as preformed yeast cakes on top of the membrane. A small concentration of 0.022 g/l yeast cells in suspension enhanced the permeate flux and maintained protein transmission at nearly 100%, compared with a 60% reduction in the protein concentration in the permeate obtained after 3 h for the protein mixture filtered alone. Higher suspended yeast concentrations of 0.043 and 0.18 g/l resulted in lower fluxes and intermediate values for the protein transmission. For the three different thicknesses of preformed yeast cakes studied (0.025, 0.05, and 0.10 cm), the cake with intermediate thickness resulted in protein transmission of nearly 100% and the highest permeate flux. The thinner yeast cake resulted in a lower permeate flux, but it maintained protein transmission at nearly 100%, whereas the thicker cake resulted in a reduction in both permeate flux and protein transmission. The mechanism proposed to explain the results is based on the formation of a secondary membrane by the yeast cells on top of the original membrane. This secondary membrane entraps protein aggregates, which would otherwise cause membrane fouling and reductions in permeate flux and protein transmission.     

The effect of seasoning a membrane-forming solution on the separation properties of chitosan membranes

The ability to retain high-molecular substances is a basic criterion of membrane applicability in the process of ultrafiltration. Separation of high-molecular compounds on flat chitosan membranes was investigated. Membranes were produced by the wet phase inversion method, immediately after preparing the solution and then seasoning for a month. Prior to membrane formation, the change of rheological properties of membrane-forming solutions was determined. Prior to membrane formation, rheological properties of membrane-forming solutions were determined immediately after preparing the solution and after a month seasoning. Testing substances were model proteins: albumin 69 kD, gammaglobulin 159 kD and dextrans 70 and 200 kD, as well as a real system — 1% skim milk solution. The ability to retain proteins was determined by a standard method which consisted in the determination of retention coefficient. Protein concentration was determined by a spectrophotometric method. Dextran separation was determined by the standard method which covered determination of dextran concentration by coulometric titration, and — because of the linear structure of particles and their polydispersity — by gel chromatography through the analysis of molecular weight distribution in the feed and permeate. Practically, chitosan membranes retain proteins above 69 kD, while dextrans of mass 70 kD are retained in 30%, and these of mass 200 kD in more than 75%. This depends on the linear structure of dextran particles and their significant polydispersity which was confirmed by the chromatographic analysis.     

Study on the interaction of 3,3-bis(4-hydroxy-1-naphthyl)-phthalide with bovine serum albumin by fluorescence spectroscopy

The interaction between 3,3-bis(4-hydroxy-1-naphthyl)-phthalide (NPP) and bovine serum albumin (BSA) have been studied by fluorescence spectroscopy. The binding of NPP quenches the BSA fluorescence. By the fluorescence quenching results, it was found that the binding constant K = 5.30 × 10⁴ L mol⁻¹, and number of binding sites n = 0.9267. In addition, according to the synchronous fluorescence spectra of BSA, the results showed that the fluorescence spectra of BSA mainly originate from the tryptophan residues. Finally, the distance between the acceptor NPP and BSA was estimated to be 1.94 nm using Föster's equation on the basis of fluorescence energy transfer. The interaction between NPP and BSA has been verified as consistent with the static quenching procedure and the quenching mechanism is related to the energy transfer.     

Removal of suspended clay from water using transmembrane pressure pulsed microfiltration

Transmembrane pressure pulsing (TPP) uses the frequent and periodic reversal of the transmembrane pressure to reduce flux resistances due to membrane fouling. This study examined the effect of TPP on the microfiltration of simulated drinking water (hydrated aluminum silicate solution). Solutions of kaolin clay (0.1–4.0 μm particles, at an approximate concentration of 500 mg l⁻¹ and a turbidity of 402±17 NTU, 0.5 mM CaCl, 2.0 mM NaHCO₃, pH 7.5–7.8) were microfiltered with polyethersulfone (PES) 0.16 μm microfiltration membranes at an operating pressure of 30 kPa. Crossflow shear rates were varied between 165 and 1490 s⁻¹. Pulse frequency was varied between 0.3×10⁻² and 2 Hz, and pulse amplitude was varied between −3 and −16.5 kPa. It was found that the crossflow shear rates did not significantly effect the non-pulsed permeate flux. An optimum pulse amplitude of about 10 kPa was necessary to maximize the permeate flux for pulse frequencies between 0.3×10⁻² and 2.0 Hz. To insure a reduced solute flux, pulse frequencies less than 0.1 Hz were required. These results indicate that TPP can significantly reduce membrane fouling by inorganic particulate materials that are potentially important constituents of natural waters without negatively impacting the rejection of sub-micron particles due to interactions with material accumulated on the membrane.     

Characterization of BSA-fouling of ion-exchange membrane systems using a subtraction technique for lumped data

Electrical impedance spectroscopy (EIS) techniques were used to gain insight into BSA fouling of the Neosepta CMX and AMX ion-exchange membranes (IEMs). EIS characterizations were made at concentrations above 0.1 M KCl because the conductance of the IEMs was higher than that of bulk solutions of concentration below 0.1 M KCl. Spectra, expressed in terms of dispersions of the conductance and capacitance with frequency, provided an enhanced indication of IEM fouling during separation processes. Bulk conductance measurements of the solution alone, membrane immersed in solution and fouled membrane immersed in solution showed good agreement with general theoretical predictions. Strong dispersions in capacitance were observed below 1 kHz for each of these configurations. Differences in the dispersions arising from fouling were identified by subtracting the impedance of the solution from those of unfouled and fouled IEMs in solution. The conductance and capacitance dispersions of fouled IEMs decreased with the accumulation of the BSA fouling layer on the surface.     

Comparison between filtrations at fixed transmembrane pressure and fixed permeate flux: application to a membrane bioreactor used for wastewater treatment

Membrane bioreactors for wastewater treatment must operate for long periods without chemical cleaning. This paper investigates the critical flux concept introduced by Field et al. as a means for achieving this goal. Experiments were conducted on a membrane bioreactor containing 600 l of activated sludge, equipped with a 0.25 m² ceramic membrane and located in Compiegne wastewater treatment plant. Hydraulic retention time was set at 24 h and sludge retention time at 60 days, so that suspended solids concentration stabilises at 10 g/l. We conducted two series of tests: at fixed transmembrane pressure (TMP) and at fixed permeate flux, set by a volumetric pump on the permeate. In both cases, velocity was varied from 1 to 5 m/s. In fixed flux tests, the flux was increased by 10 l/h m² increments and the TMP was observed to rise moderately first and then stabilise in about 15 min until a critical value of the flux is reached. Above this critical flux, the TMP rises rapidly and does not stabilise, as in dead-end filtration. The critical flux was found to increase approximately linearly with velocity, reaching about 115 l/h m² at 4 m/s. These data were reproducible at various dates between 30 and 120 days of continuous operation of the bioreactor and permit to know at which flux a membrane bioreactor must be operated. Comparison of constant pressure and constant flux tests under same conditions showed that the critical flux is almost identical to the limiting or pressure independent flux obtained in constant pressure. More generally, constant flux procedure below the critical flux avoids overfouling of the membrane in the initial stage and is more advantageous for membrane bioreactor operation.     

Ultrafiltration of mixed protein solutions of lysozyme and lactoferrin: role of modified inorganic membranes and ionic strength on the selectivity

Ultrafiltration of either single protein solutions (lysozyme 14,300 g mol⁻¹, pI=11; lactoferrin 80,000 g mol⁻¹, pI=8–9) or mixed protein solution was performed with inorganic membranes (MMCO 300,000 g mol⁻¹, pore radius 14 nm) chemically modified in order to bear either pyrophosphate (PP, anionic) or ethylenediamine (EDA, cationic) groups.The electrophoretic mobility of modified and unmodified zirconia particles fouled with proteins was similar whatever the grafted groups, meaning that the membrane surface was always made of adsorbed proteins during UF. In spite of that, for the UF of lysozyme/lactoferrin mixed solution, the maximum selectivity (S=lysozyme transmission/lactoferrin transmission=165) was observed with the EDA membrane and allowed an instantaneous purity of lysozyme in the permeate close to 100% to be achieved. Such high selectivitiy was mainly due to the negligible transmission of lactoferrin with the membrane modified with the EDA groups in the ionic strength range 0–100 mmol l⁻¹ of NaCl at pH 7 (achieved either for mixed and single solutions).     

Separation of hydrogen from steam using a SiC-based membrane formed by chemical vapor deposition of triisopropylsilane

A silicon carbide-based membrane was formed in the macropores of an α-alumina support tube by chemical vapor deposition of triisopropylsilane at 700–800°C with a forced cross-flow through the porous wall. The membrane permeated gases except H₂O mainly by the Knudsen diffusion mechanism at permeation temperatures of 50–400°C. The H₂/H₂O selectivity was near or below unity because of the hydrophilic nature of the membrane. After a heat-treatment in Ar at 1000°C for 1 h, however, the membrane formed at a final evacuation pressure of 1 kPa exhibited a H₂/H₂O selectivity of 3–5, for a mixed feed of H₂–H₂O–HBr system, associated in a thermochemical water-splitting process. The H₂ permeance was (5–6)×10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ at 50–400°C. The membrane maintained the H₂/H₂O selectivity for more than 100 h in the H₂–H₂O–HBr mixture at 400°C.     

Factors affecting membrane fouling reduction by surface modification and backpulsing

Several factors affecting microfiltration membrane fouling and cleaning, including backpulsing, crossflushing, backwashing, particle size, membrane surface chemistry, and ionic strength, were investigated with suspensions of latex beads. Approximately two-fold permeate volume enhancements over 1 h of filtration were obtained by using water or gas backpulsing, and 50% enhancement was obtained with crossflushing, for filtration of 1.0 μm diameter carboxylate modified latex (CML) particles using unmodified polypropylene (PP) membranes of 0.3 μm nominal pore diameter. When 0.2 μm diameter CML particles or mixtures of 1.0 and 0.2 μm CML particles were used, however, the average flux decreased 60% compared with using 1.0 μm CML particles for experiments with or without backpulsing.PP membranes were rendered hydrophilic with neutral or positively on negatively charged surfaces by grafting monomers of poly(ethylene glycol 200) monomethacrylate (PEG200MA), dimethyl aminoethyl methacrylate (DMAEMA), or acrylic acid (AA), respectively, to the base PP membranes. Filtration experiments show that fouling is not strongly dependent on membrane surface chemistry for filtration of 1.0 μm CML particles without backpulsing. With backpulsing, however, a 10% increase and a 20% decrease of permeate volumes collected in 1 h were observed when the CML particles and the membranes had like charges and opposite charges, respectively, compared to the permeate collected with the unmodified membrane. Using the PP membranes modified with AA, permeate volumes with backpulsing decreased 30 and 40% when NaCl concentrations of 0.01 and 0.1 M, respectively, were added to the feed. However, the permeate volumes did not vary significantly with changing ionic strength for filtration without backpulsing.     

Preparation and characterization of porous conducting poly(dl-lactide) composite membranes

Solid conducting biodegradable composite membranes have shown to enhance nerve regeneration. However, few efforts have been directed toward porous conducting biodegradable composite membranes for the same purpose. In this study, we have fabricated some porous conducting poly(dl-lactide) composite membranes which can be used for the biodegradable nerve conduits. The porous poly(dl-lactide) membranes were first prepared through a phase separation method, and then they were incorporated with polypyrrole to produce porous conducting composite membranes by polymerizing pyrrole monomer in gas phase using FeCl₃ as oxidant. The preparation conditions were optimized to obtain membranes with controlled pore size and porosity. The direct current conductivity of composite membrane was investigated using standard four-point technique. The effects of polymerization time and the concentration of oxidant on the conductivity of the composite membrane were examined. Under optimized polymerization conditions, some composite membranes showed a conductivity close to 10⁻³ S cm⁻¹ with a lower polypyrrole loading between 2 and 3 wt.%. A consecutive degradation in Ringer's solution at 37 °C indicated that the conductivity of composite membrane did not exhibit significant changes until 9 weeks although a noticeable weight loss of the composite membrane could be seen since the end of the second week.     

Development of MEMS-based direct methanol fuel cell with high power density using nanoimprint technology

Performance of MEMS-based DMFC is low, because graphite-based porous electrodes show poor compatibility with MEMS technology. Nanoimprint technology was adopted in this paper to prepare fine pattern on proton exchange membrane (PEM) in MEMS-based DMFC as a promising alternative to the graphite-based porous electrodes. Micro-convex with the diameter of about 600 nm and the height of 50–70 nm was prepared on Nafion^® 117 membrane by the nanoimprint at 130 °C using silicon mold. Thick Pt film (20 nm) was deposited as catalyst directly on the nanoimprinted Nafion^® 117 membrane. Then the Pt-coated PEM was sandwiched with micro-channeled silicon plates to form a micro-DMFC. With passively feeding of 1 M methanol solution and air at room temperature, the as-prepared cell had the open circuit voltage (OCV) of 0.74 V and the maximum power density of 0.20 mW/cm². The measured OCV was higher than those (0.1–0.3 V) of the state-of-the-art MEMS-based DMFC with planar electrode and pure Pt catalyst.     

Fingerprint imaging by scanning electrochemical microscopy

An efficient strategy for visualizing human fingerprints on a poly(vinylidene difluoride) membrane (PVDF) by scanning electrochemical microscopy (SECM) has been developed. Compared to a classical ink fingerprint image, here the ink is replaced by an aqueous solution of bovine serum albumin (BSA). After placing the “inked” finger on a PVDF membrane, the latent image is stained by silver nitrate and the fingerprint is imaged electrochemically using potassium hexachloroiridate (III) (K₃IrCl₆) as a redox mediator. SECM images with an area of 5 mm × 3 mm have been recorded with a high-resolution using a 25-μm-diameter Pt disk-shaped microelectrode. Pores in the skin (40–120 μm in diameter) and relative locations of ridges were clearly observed. The factors relevant to the quality of fingerprint images are discussed.     

Efficiency of blocking of non-specific interaction of different proteins by BSA adsorbed on hydrophobic and hydrophilic surfaces

The efficiency of a pre-absorbed bovine serum albumin (BSA) layer in blocking the non-specific adsorption of different proteins on hydrophobic and hydrophilic surfaces was evaluated qualitatively and quantitatively using infrared reflection spectroscopy supported by spectral simulations. A BSA layer with a surface coverage of 35% of a close-packed monolayer exhibited a blocking efficiency of 90–100% on a hydrophobic and 68–100% on a hydrophilic surface, with respect to the non-specific adsorption of concanavalin A (Con A), immunoglobulin G (IgG), and staphylococcal protein A (SpA). This BSA layer was produced using a solution concentration of 1 mg/mL and 30 min incubation time. BSA layers that were adsorbed at conditions commonly employed for blocking (a 12 h incubation time and a solution concentration of 10 mg/mL) exhibited a blocking activity that involved competitive adsorption–desorption. This activity resulted from the formation of BSA–phosphate surface complexes, which correlated with the conformation of adsorbed BSA molecules that was favourable for blocking. The importance of optimisation of the adsorbed BSA layer for different surfaces and proteins to achieve efficient blocking was addressed in this study.     

Hydrogen production from hydrogen sulfide using membrane reactor integrated with porous membrane having thermal and corrosion resistance

Using mathematical model and experimental method, the thermal decomposition of hydrogen sulfide in membrane reactor with porous membrane which has Knudsen diffusion characteristics was investigated. With mathematical model, the effect of characteristics of membrane reactor and operating conditions on H₂ concentration in the permeate chamber, y_H2, which increases at higher reaction temperature, lower pressure and higher ratio of cross-sectional area of the permeate chamber to that of the reactor, was evaluated. The reaction experiments with ZrO₂–SiO₂ porous membrane were carried out under the following conditions: temperature T, 923–1023 K; pressure in the reactor p^R_T, 0.11–0.25 MPa absolute; pressure in the permeate chamber p^P_T, 5 kPa absolute and inlet flow rate of H₂S f⁰_H2S, 3.2×10⁻⁵–1.5×10⁻⁴ mol/s. At p^R_T=0.11 MPa and f⁰_H2S=6.4×10⁻⁵, y_H2 increased from 0.02 at T=923 K to 0.15 at 1023 K. With the experimental condition, p^R_T=0.11, T=1023 K and f⁰_H2S=3.2×10⁻⁵, y_H2 was 0.22. The experimental results were compared with the results of the mathematical analysis. The agreement between both the results is found rather good at a lower reacting temperature, but not so good at a higher reacting temperature.     

Application of nanofiltration to re-use the sharpless asymmetric dihydroxylation catalytic system

In this paper, successive batch steps of an osmium-catalyzed asymmetric dihydroxylation reaction using Sharpless conditions and nanofiltration of post-reaction mixture were coupled, allowing us to enhance the cumulative catalyst turn over number to about 3.7 times over six cycles. The nanofiltration step provides for isolation of the chiral product, whereas the catalytic system (osmium and chiral ligand) is re-used in the following batch cycle. In this work the osmium average rejection through the selected nanofiltration membrane, Starmem™120, was 83%; this result may indicate the existence of free osmium in solution and implies residual product osmium contamination at an average value of 1.5 mg Os/g-product. Effective application of this methodology to the model reaction requires improvement of catalyst rejection, which calls for an effective complexation of osmium by the ligand. Nevertheless, the enantioselectivity of the reaction was maintained constant over the six cycles at a value of 69%.