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Membranes, Volume 1, Issue 1 (March 2011), Pages 1-90

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Editorial

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Open AccessEditorial Welcome to Membranes — A New Open Access Journal on Membrane Separation and Technology
Membranes 2011, 1(1), 1-2; doi:10.3390/membranes1010001
Received: 10 December 2010 / Published: 12 December 2010
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Abstract Membrane separation, from its infancy as a predominantly laboratory technique in the middle of the last century, has advanced with remarkable speed and now underpins a range of mature industrial technologies. [...] Full article

Research

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Open AccessArticle The Fabrication of Biomimetic Chitosan Scaffolds by Using SBF Treatment with Different Crosslinking Agents
Membranes 2011, 1(1), 3-12; doi:10.3390/membranes1010003
Received: 7 October 2010 / Accepted: 8 December 2010 / Published: 15 December 2010
Cited by 5 | PDF Full-text (305 KB) | HTML Full-text | XML Full-text
Abstract
In this study, a chitosan substrate was modified by simulated body fluid (SBF) treatment, in which the effect of the chosen crosslinking agent was investigated. Two crosslinking agents, glutaraldehyde (GA) and sodium tripolyphosphate (TPP), were used before the SBF process. By using TPP
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In this study, a chitosan substrate was modified by simulated body fluid (SBF) treatment, in which the effect of the chosen crosslinking agent was investigated. Two crosslinking agents, glutaraldehyde (GA) and sodium tripolyphosphate (TPP), were used before the SBF process. By using TPP as the crosslinking agent, the Ca/P ratio and the degree of crystallinity were very close to the natural bone matrix. On the contrary, the substrate properties were very different from natural bone when the crosslinking agent GA was used. The results indicate that the produced substrates were  biomimetic when the TPP was applied. On the SBF-modified chitosan substrates with TPP crosslinking, the cultured osteoblastic cells expressed better proliferation, mitochondria activity and differentiation ability. The chitosan crosslinked using TPP was a good template in the SBF process, which resulted in a highly biomimetic layer. This biomimetic substrate possesses excellent biocompatibility and osteoconduction ability, promising high potential in the promotion of bone tissue engineering. Full article
(This article belongs to the Special Issue Selected Papers from the AMS6/IMSTEC10 Conference)
Open AccessArticle A Model for Transport Phenomena in a Cross-Flow Ultrafiltration Module with Microchannels
Membranes 2011, 1(1), 13-24; doi:10.3390/membranes1010013
Received: 1 October 2010 / Accepted: 8 December 2010 / Published: 16 December 2010
Cited by 1 | PDF Full-text (331 KB) | HTML Full-text | XML Full-text
Abstract
Cross-flow ultrafiltration of macromolecular solutions in a module with microchannels is expected to have the advantages of fast diffusion from the membrane surface and a high ratio of membrane surface area to feed liquid volume. Cross-flow ultrafiltration modules with microchannels are expected to
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Cross-flow ultrafiltration of macromolecular solutions in a module with microchannels is expected to have the advantages of fast diffusion from the membrane surface and a high ratio of membrane surface area to feed liquid volume. Cross-flow ultrafiltration modules with microchannels are expected to be used for separation and refining and as membrane reactors in microchemical processes. Though these modules can be applied as a separator connected with a micro-channel reactor or a membrane reactor, there have been few papers on their performance. The purpose of this study was to clarify the relationship between operational conditions and performance of cross-flow ultrafiltration devices with microchannels. In this study, Poly Vinyl Pyrrolidone (PVP) aqueous solution was used as a model solute of macromolecules such as enzymes. Cross-flow ultrafiltration experiments were carried out under constant pressure conditions, varying other operational conditions. The permeate flux decreased in the beginning of each experiment. After enough time passed, the permeate flux reached a constant value. The performance of the module was discussed based on the constant values of the flux. It was observed that the permeate flux increased with increasing transmembrane pressure (TMP) and feed flow rate, and decreased with an increase of feed liquid concentration. A model of the transport phenomena in the feed liquid side channel and the permeation through the membrane was developed based on the concentration and velocity distributions in the feed side channel. The experimental results were compared with those based on the model and the performance of the ultrafiltration module is discussed. Full article
(This article belongs to the Special Issue Selected Papers from the AMS6/IMSTEC10 Conference)
Open AccessArticle Control of Porosity and Pore Size of Metal Reinforced Carbon Nanotube Membranes
Membranes 2011, 1(1), 25-36; doi:10.3390/membranes1010025
Received: 8 December 2010 / Accepted: 16 December 2010 / Published: 21 December 2010
Cited by 15 | PDF Full-text (1092 KB) | HTML Full-text | XML Full-text
Abstract
Membranes are crucial in modern industry and both new technologies and materials need to be designed to achieve higher selectivity and performance. Exotic materials such as nanoparticles offer promising perspectives, and combining both their very high specific surface area and the possibility to
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Membranes are crucial in modern industry and both new technologies and materials need to be designed to achieve higher selectivity and performance. Exotic materials such as nanoparticles offer promising perspectives, and combining both their very high specific surface area and the possibility to incorporate them into macrostructures have already shown to substantially increase the membrane performance. In this paper we report on the fabrication and engineering of metal-reinforced carbon nanotube (CNT) Bucky-Paper (BP) composites with tuneable porosity and surface pore size. A BP is an entangled mesh non-woven like structure of nanotubes. Pure CNT BPs present both very high porosity (>90%) and specific surface area (>400 m2/g). Furthermore, their pore size is generally between 20–50 nm making them promising candidates for various membrane and separation applications. Both electro-plating and electroless plating techniques were used to plate different series of BPs and offered various degrees of success. Here we will report mainly on electroless plated gold/CNT composites. The benefit of this method resides in the versatility of the plating and the opportunity to tune both average pore size and porosity of the structure with a high degree of reproducibility. The CNT BPs were first oxidized by short UV/O3 treatment, followed by successive immersion in different plating solutions. The morphology and properties of these samples has been investigated and their performance in air permeation and gas adsorption will be reported. Full article
(This article belongs to the Special Issue Selected Papers from the AMS6/IMSTEC10 Conference)
Open AccessArticle Synthesis of Carbon Nanotube (CNT) Composite Membranes
Membranes 2011, 1(1), 37-47; doi:10.3390/membranes1010037
Received: 26 November 2010 / Accepted: 23 December 2010 / Published: 27 December 2010
Cited by 13 | PDF Full-text (804 KB) | HTML Full-text | XML Full-text
Abstract
Carbon nanotubes are attractive approach for designing of new membranes for advanced molecular separation because of their unique transport properties and ability to mimic biological protein channels. In this work the synthetic approach for fabrication of carbon nanotubes (CNTs) composite membranes is presented.
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Carbon nanotubes are attractive approach for designing of new membranes for advanced molecular separation because of their unique transport properties and ability to mimic biological protein channels. In this work the synthetic approach for fabrication of carbon nanotubes (CNTs) composite membranes is presented. The method is based on growth of multi walled carbon nanotubes (MWCNT) using chemical vapour deposition (CVD) on the template of nanoporous alumina (PA) membranes. The influence of experimental conditions including carbon precursor, temperature, deposition time, and PA template on CNT growth process and quality of fabricated membranes was investigated. The synthesis of CNT/PA composites with controllable nanotube dimensions such as diameters (30–150 nm), and thickness (5–100 µm), was demonstrated. The chemical composition and morphological characteristics of fabricated CNT/PA composite membranes were investigated by various characterisation techniques including scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDXS), high resolution transmission electron microscopy (HRTEM) and x-ray diffraction (XRD). Transport properties of prepared membranes were explored by diffusion of dye (Rose Bengal) used as model of hydrophilic transport molecule. Full article
(This article belongs to the Special Issue Selected Papers from the AMS6/IMSTEC10 Conference)
Open AccessArticle Direct Contact Membrane Distillation of Dairy Process Streams
Membranes 2011, 1(1), 48-58; doi:10.3390/membranes1010048
Received: 26 November 2010 / Accepted: 22 December 2010 / Published: 4 January 2011
Cited by 10 | PDF Full-text (203 KB) | HTML Full-text | XML Full-text
Abstract
Membrane distillation (MD) was applied for the concentration of a range of dairy streams, such as whole milk, skim milk and whey. MD of a pure lactose solution was also investigated. Direct contact MD (DCMD) mode experiments were carried out in continuous concentration
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Membrane distillation (MD) was applied for the concentration of a range of dairy streams, such as whole milk, skim milk and whey. MD of a pure lactose solution was also investigated. Direct contact MD (DCMD) mode experiments were carried out in continuous concentration mode, keeping the warm feed/retentate and cold permeate stream temperatures at 54 °C and 5 °C respectively. Performance in terms of flux and retention was assessed. The flux was found to decrease with an increase of dry-matter concentration in the feed. Retention of dissolved solids was found to be close to 100% and independent of the dry-matter concentration in the feed. Fourier Transform Infrared Spectroscopy (FTIR) of the fouled membranes confirms organics being present in the fouling layer. Full article
(This article belongs to the Special Issue Selected Papers from the AMS6/IMSTEC10 Conference)
Open AccessArticle Characteristics of Filter Cake Exfoliation in Upward Ultrafiltration of Nanoparticle Suspensions
Membranes 2011, 1(1), 59-69; doi:10.3390/membranes1010059
Received: 26 November 2010 / Revised: 6 January 2011 / Accepted: 17 January 2011 / Published: 20 January 2011
Cited by 1 | PDF Full-text (173 KB) | HTML Full-text | XML Full-text
Abstract
Downward and upward ultrafiltration (UF) was performed using the suspensions of nanosized colloidal silica with different particle diameters and their filtration rates were compared. In downward UF, the filtration rate decreases as the particle diameter decreases because the specific filtration resistance of the
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Downward and upward ultrafiltration (UF) was performed using the suspensions of nanosized colloidal silica with different particle diameters and their filtration rates were compared. In downward UF, the filtration rate decreases as the particle diameter decreases because the specific filtration resistance of the filter cake becomes significantly higher. In contrast, the filtration rate in upward UF increases with the decrease in the particle diameter because the filter cake consisting of small particles is exfoliated much more easily under the influence of gravity than that of large ones. In order to evaluate the characteristics of the filter cake exfoliation, the steady filtration rate in the upward mode was measured. The steady filtration rate has a tendency to decrease with particle concentration as well as mean particle diameter. Therefore, when the small particles are added into a given concentration of large particle suspension, the mean particle diameter decreases and the total particle concentration increases due to the dosage of small particles. This results in a maximum of the steady filtration rate at a certain dosage of small particles. Moreover, an estimation equation was proposed for predicting the steady filtration rate in upward UF of colloidal silica suspensions with various mean particle diameters and total particle concentrations. Full article
(This article belongs to the Special Issue Selected Papers from the AMS6/IMSTEC10 Conference)
Figures

Open AccessArticle Continuous Membrane-Based Screening System for Biocatalysis
Membranes 2011, 1(1), 70-79; doi:10.3390/membranes1010070
Received: 30 December 2010 / Revised: 17 February 2011 / Accepted: 17 February 2011 / Published: 25 February 2011
Cited by 5 | PDF Full-text (317 KB) | HTML Full-text | XML Full-text
Abstract
The use of membrane reactors for enzymatic and co-factor regenerating reactions offers versatile advantages such as higher conversion rates and space-time-yields and is therefore often applied in industry. However, currently available screening and kinetics characterization systems are based on batch and fed-batch operated
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The use of membrane reactors for enzymatic and co-factor regenerating reactions offers versatile advantages such as higher conversion rates and space-time-yields and is therefore often applied in industry. However, currently available screening and kinetics characterization systems are based on batch and fed-batch operated reactors and were developed for whole cell biotransformations rather than for enzymatic catalysis. Therefore, the data obtained from such systems has only limited transferability for continuous membrane reactors. The aim of this study is to evaluate and to improve a novel screening and characterization system based on the membrane reactor concept using the enzymatic hydrolysis of cellulose as a model reaction. Important aspects for the applicability of the developed system such as long-term stability and reproducibility of continuous experiments were very high. The concept used for flow control and fouling suppression allowed control of the residence time with a high degree of precision (±1% accuracy) in a long-term study (>100 h). Full article
(This article belongs to the Special Issue Selected Papers from the AMS6/IMSTEC10 Conference)
Open AccessArticle Volatile Organic Compound (VOC) Removal by Vapor Permeation at Low VOC Concentrations: Laboratory Scale Results and Modeling for Scale Up
Membranes 2011, 1(1), 80-90; doi:10.3390/membranes1010080
Received: 24 January 2011 / Revised: 24 February 2011 / Accepted: 25 February 2011 / Published: 3 March 2011
Cited by 6 | PDF Full-text (280 KB) | HTML Full-text | XML Full-text
Abstract
Petroleum transformation industries have applied membrane processes for solvent and hydrocarbon recovery as an economic alternative to reduce their emissions and reuse evaporated components. Separation of the volatile organic compounds (VOCs) (toluene-propylene-butadiene) from air was performed using a poly dimethyl siloxane (PDMS)/α-alumina membrane.
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Petroleum transformation industries have applied membrane processes for solvent and hydrocarbon recovery as an economic alternative to reduce their emissions and reuse evaporated components. Separation of the volatile organic compounds (VOCs) (toluene-propylene-butadiene) from air was performed using a poly dimethyl siloxane (PDMS)/α-alumina membrane. The experimental set-up followed the constant pressure/variable flow set-up and was operated at ~21 °C. The membrane is held in a stainless steel module and has a separation area of 55 × 10−4 m². Feed stream was set to atmospheric pressure and permeate side to vacuum between 3 and 5 mbar. To determine the performance of the module, the removed fraction of VOC was analyzed by Gas Chromatography/Flame Ionization Detector (GC/FID). The separation of the binary, ternary and quaternary hydrocarbon mixtures from air was performed at different flow rates and more especially at low concentrations. The permeate flux, permeance, enrichment factor, separation efficiency and the recovery extent of the membrane were determined as a function of these operating conditions. The permeability coefficients and the permeate flux through the composite PDMS-alumina membrane follow the order given by the Hildebrand parameter: toluene > 1,3-butadiene > propylene. The simulated data for the binary VOC/air mixtures showed fairly good agreement with the experimental results in the case of 1,3-butadiene and propylene. The discrepancies observed for toluene permeation could be minimized by taking into account the effects of the porous support and an influence of the concentration polarization. Finally, the installation of a 0.02 m2 membrane module would reduce 95% of the VOC content introduced at real concentration conditions used in the oil industry. Full article
(This article belongs to the Special Issue Selected Papers from the AMS6/IMSTEC10 Conference)

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