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Membranes, Volume 8, Issue 4 (December 2018)

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Cover Story (view full-size image) Currently, light is transmitted through polluted feed water to reach a photocatalyst coating on a [...] Read more.
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Open AccessReview A Review on the Progress in Nanoparticle/C Hybrid CMS Membranes for Gas Separation
Membranes 2018, 8(4), 134; https://doi.org/10.3390/membranes8040134
Received: 1 November 2018 / Revised: 3 December 2018 / Accepted: 11 December 2018 / Published: 17 December 2018
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Abstract
Carbon molecular sieve (CMS) membranes are novel materials derived from the pyrolysis of the polymeric precursors and have a well-developed ultra-microporous structure that can separate small gas pairs with minor difference in diameter, and thus exhibit higher gas permeability and selectivity than polymeric
[...] Read more.
Carbon molecular sieve (CMS) membranes are novel materials derived from the pyrolysis of the polymeric precursors and have a well-developed ultra-microporous structure that can separate small gas pairs with minor difference in diameter, and thus exhibit higher gas permeability and selectivity than polymeric membranes. However, the gas permeability for traditional pure CMS membranes now cannot satisfy the requirements of commercial applications due to their disordered pore structure and high gas molecular diffusion resistance. Incorporating functional materials into membrane precursors to fabricate hybrid CMS membranes has been regarded as an effective way to tune the disordered pore structure of traditional pure CMS membranes, and thus to greatly improve their gas permeability. Many nanoparticles have been tested as the functional foreign materials to fabricate the hybrid CMS membranes with more developed microporous structure and enhanced gas separation performance. This review discusses the hybridized nanoparticle selection and effect of the species, quantities and particle sizes of the foreign materials on CMS membrane characteristics and performance. The function of the materials incorporated inside the hybrid CMS membranes is also analyzed. It is identified that preparation of hybrid CMS membranes provides a simple and convenient route to efficiently improve the trade-off relationship between permeability and selectivity, and to enable the construction of carbon-based composite materials with novel functionalities in membrane science. Full article
(This article belongs to the Special Issue Novel Membrane Materials)
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Open AccessArticle Alkali Attack on Anion Exchange Membranes with PVC Backing and Binder: II Prediction of Electrical and Mechanical Performances from Simple Optical Analyses
Membranes 2018, 8(4), 133; https://doi.org/10.3390/membranes8040133
Received: 15 November 2018 / Revised: 3 December 2018 / Accepted: 11 December 2018 / Published: 14 December 2018
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Abstract
Performance of anion exchange membranes (AEMs), including polyvinyl chloride (PVC) as backing and binder, decreases during a repetitive cleaning-in-place (CIP) treatment using alkali. In this study, we have systematically performed two optical analyses, relative total visible (VIS) reflectance and handheld X-ray fluorescence (XRF),
[...] Read more.
Performance of anion exchange membranes (AEMs), including polyvinyl chloride (PVC) as backing and binder, decreases during a repetitive cleaning-in-place (CIP) treatment using alkali. In this study, we have systematically performed two optical analyses, relative total visible (VIS) reflectance and handheld X-ray fluorescence (XRF), for alkali-attacked commercially available AEM (Neosepta® AMX, Tokyo, Japan) with different NaOH immersion conditions (0–1.0 M NaOH at 40–80 °C for 0–168 h). The VIS reflectance and XRF data were then compared with the electrical and mechanical performances (i.e., membrane resistance, proton rejection, amount of fixed-charge sites, and Young’s modulus) of the alkali-attacked AMXs. The result indicated that there are clear linear relationships between their performances and both VIS reflectance and XRF data especially at 40 °C, indicating both optical analyses have a good possibility as a quick diagnosis-in-place (DIP) to predict the resulting performance of the alkali-attacked AMXs. In addition, we also found a clear linear relationship between VIS reflectance and XRF data, so that polyene formations through dehydrochlorination of PVC during alkali attack is one of dominant mechanisms for the performance reduction of the alkali-attacked AMX at 40 °C. These results are promising to be useful for the analysis of ion exchange membranes (IEMs) used in real commercial processes on-site in future. Full article
(This article belongs to the Special Issue Mass Transfer in Membranes)
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Open AccessArticle Temperature and Pressure Dependence of Gas Permeation in a Microporous Tröger’s Base Polymer
Membranes 2018, 8(4), 132; https://doi.org/10.3390/membranes8040132
Received: 31 October 2018 / Revised: 30 November 2018 / Accepted: 5 December 2018 / Published: 14 December 2018
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Abstract
Gas transport properties of PIM-EA(H2)-TB, a microporous Tröger’s base polymer, were systematically studied over a range of pressure and temperature. Permeability coefficients of pure CO2, N2, CH4 and H2 were determined for upstream pressures up
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Gas transport properties of PIM-EA(H2)-TB, a microporous Tröger’s base polymer, were systematically studied over a range of pressure and temperature. Permeability coefficients of pure CO2, N2, CH4 and H2 were determined for upstream pressures up to 20 bar and temperatures up to 200 °C. PIM-EA(H2)-TB exhibited high permeability coefficients in absence of plasticization phenomena. The permeability coefficient of N2, CH4 and H2 increased with increasing temperature while CO2 permeability decreased with increasing temperature as expected for a glassy polymer. The diffusion and solubility coefficients were also analysed individually and compared with other polymers of intrinsic microporosity. From these results, the activation energies of permeation, diffusion and sorption enthalpies were calculated using an Arrhenius equation. Full article
(This article belongs to the Special Issue Gas Transport in Glassy Polymers)
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Open AccessArticle Antifouling Properties of PES Membranes by Blending with ZnO Nanoparticles and NMP–Acetone Mixture as Solvent
Membranes 2018, 8(4), 131; https://doi.org/10.3390/membranes8040131
Received: 31 October 2018 / Revised: 8 December 2018 / Accepted: 10 December 2018 / Published: 14 December 2018
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Abstract
In this study, the antifouling properties of polyethersulfone (PES) membranes blended with different amounts of ZnO nanoparticles and a fixed ratio of N-methyl-2-pyrrolidone (NMP)-acetone mixture as a solvent were investigated. The properties and performance of the fabricated membranes were examined in terms of
[...] Read more.
In this study, the antifouling properties of polyethersulfone (PES) membranes blended with different amounts of ZnO nanoparticles and a fixed ratio of N-methyl-2-pyrrolidone (NMP)-acetone mixture as a solvent were investigated. The properties and performance of the fabricated membranes were examined in terms of hydrophilicity, porosity, pore size, surface and cross-section image using scanning electron microscopy (SEM), surface roughness using atomic force microscopy (AFM), pure water flux, and humic acid filtration. Addition of ZnO as expected was found to improve the hydrophilicity as well as to encourage pore formation. However, the agglomeration of ZnO at a higher concentration cannot be avoided even when dissolved in a mixed solvent. The presence of highly volatile acetone contributed to the tight skin layer of the membrane which shows remarkable antifouling ability with the highest flux recovery ratio and negligible irreversible fouling. ZnO NPs in acetone/NMP mixed solvent shows an improvement in flux and rejection, but, the fouling resistance was moderate compared to the pristine membrane. Full article
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Open AccessArticle Fabrication of Stacked Graphene Oxide Nanosheet Membranes Using Triethanolamine as a Crosslinker and Mild Reducing Agent for Water Treatment
Membranes 2018, 8(4), 130; https://doi.org/10.3390/membranes8040130
Received: 31 October 2018 / Revised: 30 November 2018 / Accepted: 5 December 2018 / Published: 13 December 2018
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Abstract
Two-dimensional (2D) nanosheets show promise for the development of water treatment membranes with extraordinary separation properties and the advantages of atomic thickness with micrometer-sized lateral dimensions. Stacked graphene oxide (GO)-based membranes can demonstrate unique molecular sieving properties with fast water permeation. However, improvements
[...] Read more.
Two-dimensional (2D) nanosheets show promise for the development of water treatment membranes with extraordinary separation properties and the advantages of atomic thickness with micrometer-sized lateral dimensions. Stacked graphene oxide (GO)-based membranes can demonstrate unique molecular sieving properties with fast water permeation. However, improvements to the structural stability of the membranes in water to avoid problems such as swelling, disruption of the ordered GO layer and decreased rejection are crucial issues. This study reports the fabrication of stacked GO nanosheet membranes by simple vacuum filtration using triethanolamine (TEOA) as a crosslinker and mild reducing agent for improved structural stability and membrane performance. Results show that GO membranes modified with TEOA (GO-TEOA membranes) have a higher structural stability in water than unmodified GO membranes, resulting in improved salt rejection performance. Furthermore, GO-TEOA membranes show stable water permeance at applied pressures up to 9 bar with Na2SO4 rejection of 85%, suggesting the potential benefits for water treatment applications. Full article
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Open AccessArticle Design of a Semi-Continuous Selective Layer Based on Deposition of UiO-66 Nanoparticles for Nanofiltration
Membranes 2018, 8(4), 129; https://doi.org/10.3390/membranes8040129
Received: 20 October 2018 / Revised: 3 December 2018 / Accepted: 8 December 2018 / Published: 12 December 2018
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Abstract
Deposition of UiO-66 metal–organic framework nanoparticles onto a porous polymer support is a promising approach to designing highly-permeable, size-selective, flexible, and stable membranes for water filtration. In this article, a series of UiO-66 nanoparticles having different particle sizes were synthesized and employed to
[...] Read more.
Deposition of UiO-66 metal–organic framework nanoparticles onto a porous polymer support is a promising approach to designing highly-permeable, size-selective, flexible, and stable membranes for water filtration. In this article, a series of UiO-66 nanoparticles having different particle sizes were synthesized and employed to prepare UiO-66-deposited composite membranes. It was found that the size of the UiO-66 nanoparticles had great influences on the performance of the composite membranes for the filtration of a methylene blue aqueous solution. The deposition of smaller nanoparticles afforded a selective layer having a greater external surface area and narrower interparticle voids. These features made the deposition of smaller nanoparticles more advantageous in terms of the flux and rejection, while the deposition of greater nanoparticles afforded a selective layer more tolerant for fouling. Bimodal composite membranes were prepared by depositing mixed UiO-66 nanoparticles of smaller and bigger sizes. These membranes successfully combined the advantages of nanoparticles of a distinct size. Full article
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Open AccessArticle Study of the Effect of Inorganic Particles on the Gas Transport Properties of Glassy Polyimides for Selective CO2 and H2O Separation
Membranes 2018, 8(4), 128; https://doi.org/10.3390/membranes8040128
Received: 6 November 2018 / Revised: 30 November 2018 / Accepted: 5 December 2018 / Published: 9 December 2018
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Abstract
Three polyimides and six inorganic fillers in a form of nanometer-sized particles were studied as thick film solution cast mixed matrix membranes (MMMs) for the transport of CO2, CH4, and H2O. Gas transport properties and electron microscopy
[...] Read more.
Three polyimides and six inorganic fillers in a form of nanometer-sized particles were studied as thick film solution cast mixed matrix membranes (MMMs) for the transport of CO2, CH4, and H2O. Gas transport properties and electron microscopy images indicate good polymer-filler compatibility for all membranes. The only filler type thatdemonstrated good distribution throughout the membrane thickness at 10 wt.% loading was BaCe0.2Zr0.7Y0.1O3 (BCZY). The influence of this filler on MMM gas transport properties was studied in detail for 6FDA-6FpDA in a filler content range from one to 20 wt.% and for Matrimid® and P84® at 10 wt.% loading. The most promising result was obtained for Matrimid®—10 wt.% BCZY MMM, which showed improvement in CO2 and H2O permeabilities accompanied by increased CO2/CH4 selectivity and high water selective membrane at elevated temperatures without H2O/permanent gas selectivity loss. Full article
(This article belongs to the Special Issue Gas Transport in Glassy Polymers)
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Open AccessArticle Molecular Dynamics Simulation Study of Polyamide Membrane Structures and RO/FO Water Permeation Properties
Membranes 2018, 8(4), 127; https://doi.org/10.3390/membranes8040127
Received: 31 October 2018 / Revised: 17 November 2018 / Accepted: 26 November 2018 / Published: 6 December 2018
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Abstract
Polyamide (PA) membranes possess properties that allow for selective water permeation and salt rejection, and these are widely used for reverse osmotic (RO) desalination of sea water to produce drinking water. In order to design high-performance RO membranes with high levels of water
[...] Read more.
Polyamide (PA) membranes possess properties that allow for selective water permeation and salt rejection, and these are widely used for reverse osmotic (RO) desalination of sea water to produce drinking water. In order to design high-performance RO membranes with high levels of water permeability and salt rejection, an understanding of microscopic PA membrane structures is indispensable, and this includes water transport and ion rejection mechanisms on a molecular scale. In this study, two types of virtual PA membranes with different structures and densities were constructed on a computer, and water molecular transport properties through PA membranes were examined on a molecular level via direct reverse/forward osmosis (RO/FO) filtration molecular dynamics (MD) simulations. A quasi-non-equilibrium MD simulation technique that uses applied (RO mode) or osmotic (FO mode) pressure differences of several MPa was conducted to estimate water permeability through PA membranes. A simple NVT (Number, Volume, and Temperature constant ensemble)-RO MD simulation method was presented and verified. The simulations of RO and FO water permeability for a dense PA membrane model without a support layer agreed with the experimental value in the RO mode. This PA membrane completely rejected Na+ and Cl ions during a simulation time of several nano-seconds. The naturally dense PA structure showed excellent ion rejection. The effect that the void size of PA structure exerted on water permeability was also examined. Full article
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Open AccessArticle Gel Polymer Electrolytes Based on Silica-Added Poly(ethylene oxide) Electrospun Membranes for Lithium Batteries
Membranes 2018, 8(4), 126; https://doi.org/10.3390/membranes8040126
Received: 17 October 2018 / Revised: 27 November 2018 / Accepted: 30 November 2018 / Published: 5 December 2018
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Abstract
Solid polymer electrolytes, in the form of membranes, offering high chemical and mechanical stability, while maintaining good ionic conductivity, are envisaged as a possible solution to improve performances and safety in different lithium cell configurations. In this work, we designed and prepared systems
[...] Read more.
Solid polymer electrolytes, in the form of membranes, offering high chemical and mechanical stability, while maintaining good ionic conductivity, are envisaged as a possible solution to improve performances and safety in different lithium cell configurations. In this work, we designed and prepared systems formed using innovative nanocomposite polymer membranes, based on high molecular weight poly(ethylene oxide) (PEO) and silica nanopowders, produced by the electrospinning technique. These membranes were subsequently gelled with solutions based on aprotic ionic liquid, carbonate solvents, and lithium salt. The addition of polysulfide species to the electrolyte solution was also considered, in view of potential applications in lithium-sulfur cells. The morphology of the electrospun pristine membranes was evaluated using scanning electron microscopy. Stability and thermal properties of pristine and gelled systems were investigated uisng differential scanning calorimetry and thermal gravimetric analysis. Electrochemical impedance spectroscopy was used to determine the conductivity of both swelling solutions and gelled membranes, allowing insight into the ion transport mechanism within the proposed composite electrolytes. Full article
(This article belongs to the Special Issue Membranes for Lithium Batteries)
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Open AccessArticle Synthesis and Gas Transport Properties of Poly(2,6-dimethyl-1,4-phenylene oxide)–Silica Nanocomposite Membranes
Membranes 2018, 8(4), 125; https://doi.org/10.3390/membranes8040125
Received: 25 October 2018 / Revised: 30 November 2018 / Accepted: 30 November 2018 / Published: 4 December 2018
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Abstract
The emulsion polymerized mixed matrix (EPMM) method is a new approach to prepare nanocomposite membranes, in which inorganic nanoparticles are synthesized in situ at the interface of a dispersed aqueous phase in a continuous phase of polymer solution. In this paper, we report
[...] Read more.
The emulsion polymerized mixed matrix (EPMM) method is a new approach to prepare nanocomposite membranes, in which inorganic nanoparticles are synthesized in situ at the interface of a dispersed aqueous phase in a continuous phase of polymer solution. In this paper, we report the synthesis and characterization of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO)-based EPMM membranes, in which silica nanoparticles are synthesized by the polymerization of tetraethylorthosilicate (TEOS) in the presence of two different co-solvents, ethanol and acetone, which are soluble in both the aqueous phase and the polymer solution. The EPPM membranes prepared in the presence of acetone show greater conversions of TEOS and a different structure of the synthesized silica nanoparticles compared to the EPMM membranes prepared in the presence of ethanol. The former membranes are both more permeable and more selective for O2/N2 and CO2/CH4. Both types of EPMM membranes are more permeable than the reference PPO membranes. However, while their O2/N2 selectivity is practically unchanged, their CO2/CH4 selectivity is decreased compared to the reference PPO membranes. Full article
(This article belongs to the Special Issue Nanocomposite Membranes)
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Open AccessArticle Towards Biohydrogen Separation Using Poly(Ionic Liquid)/Ionic Liquid Composite Membranes
Membranes 2018, 8(4), 124; https://doi.org/10.3390/membranes8040124
Received: 19 October 2018 / Revised: 28 November 2018 / Accepted: 28 November 2018 / Published: 2 December 2018
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Abstract
Considering the high potential of hydrogen (H2) as a clean energy carrier, the implementation of high performance and cost-effective biohydrogen (bioH2) purification techniques is of vital importance, particularly in fuel cell applications. As membrane technology is a potentially energy-saving
[...] Read more.
Considering the high potential of hydrogen (H2) as a clean energy carrier, the implementation of high performance and cost-effective biohydrogen (bioH2) purification techniques is of vital importance, particularly in fuel cell applications. As membrane technology is a potentially energy-saving solution to obtain high-quality biohydrogen, the most promising poly(ionic liquid) (PIL)–ionic liquid (IL) composite membranes that had previously been studied by our group for CO2/N2 separation, containing pyrrolidinium-based PILs with fluorinated or cyano-functionalized anions, were chosen as the starting point to explore the potential of PIL–IL membranes for CO2/H2 separation. The CO2 and H2 permeation properties at the typical conditions of biohydrogen production (T = 308 K and 100 kPa of feed pressure) were measured and discussed. PIL–IL composites prepared with the [C(CN)3] anion showed higher CO2/H2 selectivity than those containing the [NTf2] anion. All the membranes revealed CO2/H2 separation performances above the upper bound for this specific separation, highlighting the composite incorporating 60 wt % of [C2mim][C(CN)3] IL. Full article
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Open AccessArticle In Situ SAXS Measurement and Molecular Dynamics Simulation of Magnetic Alignment of Hexagonal LLC Nanostructures
Membranes 2018, 8(4), 123; https://doi.org/10.3390/membranes8040123
Received: 5 October 2018 / Revised: 8 November 2018 / Accepted: 27 November 2018 / Published: 2 December 2018
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Abstract
The alignment of nanostructures in materials such as lyotropic liquid crystal (LLC) templated materials has the potential to significantly improve their performances. However, accurately characterising and quantifying the alignment of such fine structures remains very challenging. In situ small angle X-ray scattering (SAXS)
[...] Read more.
The alignment of nanostructures in materials such as lyotropic liquid crystal (LLC) templated materials has the potential to significantly improve their performances. However, accurately characterising and quantifying the alignment of such fine structures remains very challenging. In situ small angle X-ray scattering (SAXS) and molecular dynamics were employed for the first time to understand the hexagonal LLC alignment process with magnetic nanoparticles under a magnetic field. The enhanced alignment has been illustrated from the distribution of azimuthal intensity in the samples exposed to magnetic field. Molecular dynamics simulations reveal the relationship between the imposed force of the magnetic nanoparticles under magnetic field and the force transferred to the LLC cylinders which leads to the LLC alignment. The combinational study with experimental measurement and computational simulation will enable the development and control of nanostructures in novel materials for various applications. Full article
(This article belongs to the Special Issue Nanostructured Membranes)
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Open AccessArticle Proof of Concept for Light Conducting Membrane Substrate for UV-Activated Photocatalysis as an Alternative to Chemical Cleaning
Membranes 2018, 8(4), 122; https://doi.org/10.3390/membranes8040122
Received: 31 October 2018 / Revised: 21 November 2018 / Accepted: 26 November 2018 / Published: 2 December 2018
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Abstract
Adopting an effective strategy to control fouling is a necessary requirement for all membrane processes used in the water/wastewater treatment industry to operate sustainably. The use of ultraviolet (UV) activated photocatalysis has been shown to be effective in mitigating ceramic membrane fouling by
[...] Read more.
Adopting an effective strategy to control fouling is a necessary requirement for all membrane processes used in the water/wastewater treatment industry to operate sustainably. The use of ultraviolet (UV) activated photocatalysis has been shown to be effective in mitigating ceramic membrane fouling by natural organic matter. The widely used configuration in which light is directed through the polluted water to the membrane’s active layer suffers from inefficiencies brought about by light absorption by the pollutants and light shielding by the cake layer. To address these limitations, directing light through the substrate, instead of through polluted water, was studied. A UV conducting membrane was prepared by dip coating TiO2 onto a sintered glass substrate. The substrate could successfully conduct UV from a lamp source, unlike a typical alumina substrate. The prepared membrane was applied in the filtration of a humic acid solution as a model compound to study natural organic matter membrane fouling. Directing UV through the substrate showed only a 1 percentage point decline in the effectiveness of the cleaning method over two cleaning events from 72% to 71%, while directing UV over the photocatalytic layer had a 9 percentage point decline from 84% to 75%. Adapting the UV-through-substrate configuration could be more useful in maintaining membrane functionality during humic acid filtration than the current method being used. Full article
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Open AccessArticle Thickness Effect on CO2/N2 Separation in Double Layer Pebax-1657®/PDMS Membranes
Membranes 2018, 8(4), 121; https://doi.org/10.3390/membranes8040121
Received: 9 November 2018 / Revised: 27 November 2018 / Accepted: 29 November 2018 / Published: 2 December 2018
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Abstract
The effect of thickness in multilayer thin-film composite membranes on gas permeation has received little attention to date, and the gas permeances of the organic polymer membranes are believed to increase by membrane thinning. Moreover, the performance of defect-free layers with known gas
[...] Read more.
The effect of thickness in multilayer thin-film composite membranes on gas permeation has received little attention to date, and the gas permeances of the organic polymer membranes are believed to increase by membrane thinning. Moreover, the performance of defect-free layers with known gas permeability can be effectively described using the classical resistance in series models to predict both permeance and selectivity of the composite membrane. In this work, we have investigated the Pebax®-MH1657/PDMS double layer membrane as a selective/gutter layer combination that has the potential to achieve sufficient CO2/N2 selectivity and permeance for efficient CO2 and N2 separation. CO2 and N2 transport through membranes with different thicknesses of two layers has been investigated both experimentally and with the utilization of resistance in series models. Model prediction for permeance/selectivity corresponded perfectly with experimental data for the thicker membranes. Surprisingly, a significant decrease from model predictions was observed when the thickness of the polydimethylsiloxane (PDMS) (gutter layer) became relatively small (below 2 µm thickness). Material properties changed at low thicknesses—surface treatments and influence of porous support are discussed as possible reasons for observed deviations. Full article
(This article belongs to the Special Issue Mass Transfer in Membranes)
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Open AccessReview Review of Recent Nuclear Magnetic Resonance Studies of Ion Transport in Polymer Electrolytes
Membranes 2018, 8(4), 120; https://doi.org/10.3390/membranes8040120
Received: 18 September 2018 / Revised: 16 November 2018 / Accepted: 20 November 2018 / Published: 30 November 2018
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Abstract
Current and future demands for increasing the energy density of batteries without sacrificing safety has led to intensive worldwide research on all solid state Li-based batteries. Given the physical limitations on inorganic ceramic or glassy solid electrolytes, development of polymer electrolytes continues to
[...] Read more.
Current and future demands for increasing the energy density of batteries without sacrificing safety has led to intensive worldwide research on all solid state Li-based batteries. Given the physical limitations on inorganic ceramic or glassy solid electrolytes, development of polymer electrolytes continues to be a high priority. This brief review covers several recent alternative approaches to polymer electrolytes based solely on poly(ethylene oxide) (PEO) and the use of nuclear magnetic resonance (NMR) to elucidate structure and ion transport properties in these materials. Full article
(This article belongs to the Special Issue Membranes for Lithium Batteries)
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Open AccessArticle Synthesis and Optimization of Chitosan Ceramic-Supported Membranes in Pervaporation Ethanol Dehydration
Membranes 2018, 8(4), 119; https://doi.org/10.3390/membranes8040119
Received: 15 October 2018 / Revised: 26 November 2018 / Accepted: 27 November 2018 / Published: 30 November 2018
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Abstract
In the present work, ceramic-supported chitosan hybrid membranes were prepared for the pervaporation dehydration of ethanol. Mullite and combined mullite-alumina (50% alumina content) tubular low-cost ceramic supports were fabricated, and their influence on membrane performance was compared to a commercial α-alumina support. The
[...] Read more.
In the present work, ceramic-supported chitosan hybrid membranes were prepared for the pervaporation dehydration of ethanol. Mullite and combined mullite-alumina (50% alumina content) tubular low-cost ceramic supports were fabricated, and their influence on membrane performance was compared to a commercial α-alumina support. The membrane preparation parameters were different ceramic supports and the concentration of chitosan solution (varying from 2 wt.% to 4 wt.%). The supports and hybrid membranes were characterized by field emission scanning electron microscopy (FE-SEM) and contact angle measurements. The results show, with increasing chitosan concentration, the permeability decreases, and selectivity increases. It was also found that the separation factor decreases with increasing feed temperature and feed water content, while the permeation flux increases. The membrane that was coated on α-alumina support with a 3 wt.% chitosan concentration exhibited the best pervaporation performance, leading to a permeation flux and separation factor of 352 g·m−2·h−1 and 200 for 90 wt.% ethanol in feed at 60 °C, respectively. Full article
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Open AccessArticle Process Simulation and Cost Evaluation of Carbon Membranes for CO2 Removal from High-Pressure Natural Gas
Membranes 2018, 8(4), 118; https://doi.org/10.3390/membranes8040118
Received: 19 October 2018 / Revised: 22 November 2018 / Accepted: 27 November 2018 / Published: 30 November 2018
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Natural gas sweetening is required to remove the acid gas CO2 to meet gas grid specifications. Membrane technology has a great potential in this application compared to the state-of-the-art amine absorption technology. Carbon membranes are of particular interest due to their high
[...] Read more.
Natural gas sweetening is required to remove the acid gas CO2 to meet gas grid specifications. Membrane technology has a great potential in this application compared to the state-of-the-art amine absorption technology. Carbon membranes are of particular interest due to their high CO2/CH4 selectivity of over 100. In order to document the advantages of carbon membranes for natural gas (NG) sweetening, HYSYS simulation and cost evaluation were conducted in this work. A two-stage carbon membrane process with recycling in the second stage was found to be technically feasible to achieve >98% CH4 with <2% CH4 loss. The specific natural gas processing cost of 1.122 × 10−2 $/m3 sweet NG was estimated at a feed pressure of 90 bar, which was significantly dependent on the capital-related cost. Future work on improving carbon membrane performance is required to increase the competitiveness of carbon membranes for natural gas sweetening. Full article
(This article belongs to the Special Issue New Advances in Membrane Technologies for CO2 Separation)
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Open AccessArticle Treatment of Flue Gas Desulfurization Wastewater by an Integrated Membrane-Based Process for Approaching Zero Liquid Discharge
Membranes 2018, 8(4), 117; https://doi.org/10.3390/membranes8040117
Received: 25 October 2018 / Revised: 19 November 2018 / Accepted: 22 November 2018 / Published: 26 November 2018
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An integrated membrane process for the treatment of wastewaters from a flue gas desulfurization (FGD) plant was implemented on a laboratory scale to reduce their salt content and to produce a water stream to be recycled in the power industry. The process is
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An integrated membrane process for the treatment of wastewaters from a flue gas desulfurization (FGD) plant was implemented on a laboratory scale to reduce their salt content and to produce a water stream to be recycled in the power industry. The process is based on a preliminary pretreatment of FGD wastewaters, which includes chemical softening and ultrafiltration (UF) to remove Ca2+ and Mg2+ ions as well as organic compounds. The pretreated wastewaters were submitted to a reverse osmosis (RO) step to separate salts from water. The RO retentate was finally submitted to a membrane distillation (MD) step to extract more water, thus increasing the total water recovery factor while producing a high-purity permeate stream. The performance of RO and MD membranes was evaluated by calculating salts rejection, permeate flux, fouling index, and water recovery. The investigated integrated system allowed a total recovery factor of about 94% to be reached, with a consequent reduction of the volume of FGD wastewater to be disposed, and an MD permeate stream with an electrical conductivity of 80 μS/cm, able to be reused in the power plant, with a saving in fresh water demand. Full article
(This article belongs to the Special Issue Membrane Distillation Process)
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Open AccessArticle Fouling Mitigation and Wastewater Treatment Enhancement through the Application of an Electro Moving Bed Membrane Bioreactor (eMB-MBR)
Membranes 2018, 8(4), 116; https://doi.org/10.3390/membranes8040116
Received: 15 October 2018 / Revised: 8 November 2018 / Accepted: 16 November 2018 / Published: 22 November 2018
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High operational cost due to membrane fouling propensity remains a major drawback for the widespread application of membrane bioreactor (MBR) technology. As a result, studies on membrane fouling mitigation through the application of integrated processes have been widely explored. In this work, the
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High operational cost due to membrane fouling propensity remains a major drawback for the widespread application of membrane bioreactor (MBR) technology. As a result, studies on membrane fouling mitigation through the application of integrated processes have been widely explored. In this work, the combined application of electrochemical processes and moving bed biofilm reactor (MBBR) technology within an MBR at laboratory scale was performed by applying an intermittent voltage of 3 V/cm to a reactor filled with 30% carriers. The treatment efficiency of the electro moving bed membrane bioreactor (eMB-MBR) technology in terms of ammonium nitrogen (NH4-N) and orthophosphate (PO4-P) removal significantly improved from 49.8% and 76.7% in the moving bed membrane bioreactor (MB-MBR) control system to 55% and 98.7% in the eMB-MBR, respectively. Additionally, concentrations of known fouling precursors and membrane fouling rate were noticeably lower in the eMB-MBR system as compared to the control system. Hence, this study successfully demonstrated an innovative and effective technology (i.e., eMB-MBR) to improve MBR performance in terms of both conventional contaminant removal and fouling mitigation. Full article
(This article belongs to the Special Issue Membrane Bioreactor (MBR) Technology for Wastewater Treatment)
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Open AccessArticle Nitrogen Removal by Sulfur-Based Carriers in a Membrane Bioreactor (MBR)
Membranes 2018, 8(4), 115; https://doi.org/10.3390/membranes8040115
Received: 14 October 2018 / Revised: 16 November 2018 / Accepted: 19 November 2018 / Published: 22 November 2018
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Abstract
Sulfur-based carriers were examined to enhance the nitrogen removal efficiency in a mixed anoxic–anaerobic-membrane bioreactor system, in which sulfur from the carrier acts as an electron donor for the conversion of nitrate to nitrogen gas through the autotrophic denitrification process. A total nitrogen
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Sulfur-based carriers were examined to enhance the nitrogen removal efficiency in a mixed anoxic–anaerobic-membrane bioreactor system, in which sulfur from the carrier acts as an electron donor for the conversion of nitrate to nitrogen gas through the autotrophic denitrification process. A total nitrogen removal efficiency of 63% was observed in the system with carriers, which showed an increase in the removal efficiency of around 20%, compared to the system without carriers. The results also indicated that the carriers had no adverse effect on biological treatment for the organic matter and total phosphorus. The removal efficiencies for chemical oxygen demand (COD) and total phosphorus (TP) were 98% and 37% in both systems, respectively. The generation of sulfate ions was a major disadvantage of using sulfur-based carriers, and resulted in pH drop. The ratio of sulfate in the effluent to nitrate removed in the system ranged from 0.86 to 1.97 mgSO42−/mgNO3-N, which was lower than the theoretical value and could be regarded as due to the occurrence of simultaneous heterotrophic and autotrophic denitrification. Full article
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Open AccessArticle A Contribution for the Valorisation of Sheep and Goat Cheese Whey through Nanofiltration
Membranes 2018, 8(4), 114; https://doi.org/10.3390/membranes8040114
Received: 1 August 2018 / Revised: 27 August 2018 / Accepted: 14 October 2018 / Published: 20 November 2018
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Abstract
The amount of cheese whey generated from the production of speciality sheep and goat cheese is significantly growing due to the acclaimed nutritional and medicinal benefits of the milk from these species. However, most of the cheese whey generated has no applications, thus
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The amount of cheese whey generated from the production of speciality sheep and goat cheese is significantly growing due to the acclaimed nutritional and medicinal benefits of the milk from these species. However, most of the cheese whey generated has no applications, thus giving rise to environmental problems. This work focuses on the study of the performance of the nanofiltration process for recovering the permeates of ultrafiltration from sheep and goat cheese whey. Nanofiltration experiments were carried out with membranes of nanofiltration (NF) in total recirculation and concentration modes, at 25 °C. Nanofiltration of the ultrafiltration permeates from sheep cheese whey was done at a pressure of 3.0 × 106 Pa and a circulation velocity of 1.42 m·s−1, until a volume concentration factor (VCF) of 2.5. Nanofiltration of the permeates from ultrafiltration of goat cheese whey was performed at a pressure of 2.0 × 106 Pa and a circulation velocity of 0.94 m·s−1, until a VCF of 2.0. From the results, it was concluded that osmotic pressure was the most important factor affecting the performance of the process. In both cases, the final permeates had a much lower organic load and its future use in the process of cheese making should be evaluated. Full article
(This article belongs to the Special Issue Fouling in Liquid Separation Membrane Technologies)
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Open AccessArticle Preparation of Polybenzimidazole Hollow-Fiber Membranes for Reverse Osmosis and Nanofiltration by Changing the Spinning Air Gap
Membranes 2018, 8(4), 113; https://doi.org/10.3390/membranes8040113
Received: 18 September 2018 / Revised: 2 November 2018 / Accepted: 7 November 2018 / Published: 19 November 2018
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Abstract
High-performance polybenzimidazole (PBI) hollow-fiber membranes (HFMs) were fabricated through a continuous dry-jet wet spinning process at SRI International. By adjusting the spinning air gap from 4″ (10.2 cm) to 0.5″ (1.3 cm), the HFM pore sizes were enlarged dramatically without any significant change
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High-performance polybenzimidazole (PBI) hollow-fiber membranes (HFMs) were fabricated through a continuous dry-jet wet spinning process at SRI International. By adjusting the spinning air gap from 4″ (10.2 cm) to 0.5″ (1.3 cm), the HFM pore sizes were enlarged dramatically without any significant change of the fiber dimensional size and barrier layer thickness. When fabricated with an air gap of 2.5″ (6.4 cm) and a surface modified by NaClO solution, the PBI HFM performance was comparable to that of a commercial reverse osmosis (RO) HFM product from Toyobo in terms of salt (NaCl) rejection and water permeability. The PBI RO HFM was positively surface charged in acidic conditions (pH < 7), which enhanced salt rejection via the Donnan effect. With an air gap of 1.5″ (3.8 cm), the PBI HFM rejected MgSO4 and Na2SO4 above 95%, a result that compares favorably with that achieved by nanofiltration. In addition, the PBI HFM has a defect-free structure with an ultra-thin barrier layer and porous sublayer. We believe PBI HFMs are ideal for water purification and can be readily commercialized. Full article
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Open AccessArticle Intensified LOHC-Dehydrogenation Using Multi-Stage Microstructures and Pd-Based Membranes
Membranes 2018, 8(4), 112; https://doi.org/10.3390/membranes8040112
Received: 28 September 2018 / Revised: 13 November 2018 / Accepted: 14 November 2018 / Published: 19 November 2018
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Abstract
Liquid organic hydrogen carriers (LOHC) are able to store hydrogen stably and safely in liquid form. The carrier can be loaded or unloaded with hydrogen via catalytic reactions. However, the release reaction brings certain challenges. In addition to an enormous heat requirement, the
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Liquid organic hydrogen carriers (LOHC) are able to store hydrogen stably and safely in liquid form. The carrier can be loaded or unloaded with hydrogen via catalytic reactions. However, the release reaction brings certain challenges. In addition to an enormous heat requirement, the released hydrogen is contaminated by traces of evaporated LOHC and by-products. Micro process engineering offers a promising approach to meet these challenges. In this paper, a micro-structured multi-stage reactor concept with an intermediate separation of hydrogen is presented for the application of perhydro-dibenzyltoluene dehydrogenation. Each reactor stage consists of a micro-structured radial flow reactor designed for multi-phase flow of LOHC and released hydrogen. The hydrogen is separated from the reactors’ gas phase effluent via PdAg-membranes, which are integrated into a micro-structured environment. Separate experiments were carried out to describe the kinetics of the reaction and the separation ability of the membrane. A model was developed, which was fed with these data to demonstrate the influence of intermediate separation on the efficiency of LOHC dehydrogenation. Full article
(This article belongs to the Special Issue Pd-based Membranes: Overview and Perspectives)
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Open AccessArticle Role of Nanocomposite Support Stiffness on TFC Membrane Water Permeance
Membranes 2018, 8(4), 111; https://doi.org/10.3390/membranes8040111
Received: 26 October 2018 / Revised: 13 November 2018 / Accepted: 14 November 2018 / Published: 18 November 2018
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This paper discusses the role played by the mechanical stiffness of porous nanocomposite supports on thin-film composite (TFC) membrane water permeance. Helically coiled and multiwall carbon nanotubes (CNTs) were studied as additives in the nanocomposite supports. Mechanical stiffness was evaluated using tensile tests
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This paper discusses the role played by the mechanical stiffness of porous nanocomposite supports on thin-film composite (TFC) membrane water permeance. Helically coiled and multiwall carbon nanotubes (CNTs) were studied as additives in the nanocomposite supports. Mechanical stiffness was evaluated using tensile tests and penetration tests. While a low loading of CNTs caused macrovoids that decreased the structural integrity, adding higher loads of CNTs compensated for this effect, and this resulted in a net increase in structural stiffness. It was found that the Young’s modulus of the nanocomposite supports increased by 30% upon addition of CNTs at 2 wt %. Results were similar for both types of CNTs. An empirical model for porous composite materials described the Young’s modulus results. The nanocomposite supports were subsequently used to create TFC membranes. TFC membranes with stiffer supports were more effective at preventing declines in water permeance during compression. These findings support the idea that increasing the mechanical stiffness of TFC membrane nanocomposite supports is an effective strategy for enhancing water production in desalination operations. Full article
(This article belongs to the Special Issue Nanocomposite Membranes)
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Open AccessArticle Application of Physical and Chemical Enhanced Backwashing to Reduce Membrane Fouling in the Water Treatment Process Using Ceramic Membranes
Membranes 2018, 8(4), 110; https://doi.org/10.3390/membranes8040110
Received: 15 October 2018 / Revised: 7 November 2018 / Accepted: 8 November 2018 / Published: 15 November 2018
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This study investigated the improvement of operating efficiency through physical cleaning and chemical enhanced backwashing (CEB) using ceramic membranes with high permeability and chemical safety compared to organic membranes. The turbidity and DOC (Dissolved Organic Carbon) concentrations were selected to ensure that the
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This study investigated the improvement of operating efficiency through physical cleaning and chemical enhanced backwashing (CEB) using ceramic membranes with high permeability and chemical safety compared to organic membranes. The turbidity and DOC (Dissolved Organic Carbon) concentrations were selected to ensure that the degree of contamination was always constant. The operating pressures were fixed at 100, 200, and 300 kPa, and the filtration was terminated when the effluent flow rate decreased to 30% or less from the initial value. After filtration, backwashing was performed at a pressure of 500 kPa using 500 mL backwash water. The membrane was cleaned by dipping in NaOCl, and a new washing technique was proposed for steam washing. In this study, we investigated the recovery rate of membranes by selectively performing physical cleaning and CEB by changing the influent water quality and operating pressure conditions. Full article
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Open AccessArticle Mass Transfer Coefficient in Multi-Stage Reformer/Membrane Modules for Hydrogen Production
Membranes 2018, 8(4), 109; https://doi.org/10.3390/membranes8040109
Received: 23 October 2018 / Revised: 7 November 2018 / Accepted: 9 November 2018 / Published: 14 November 2018
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Abstract
Hydrogen is a promising energy carrier, and is exploitable to extract energy from fossil fuels, biomasses, and intermittent renewable energy sources and its generation from fossil fuels, with CO2 separation at the source being one of the most promising pathways for fossil
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Hydrogen is a promising energy carrier, and is exploitable to extract energy from fossil fuels, biomasses, and intermittent renewable energy sources and its generation from fossil fuels, with CO2 separation at the source being one of the most promising pathways for fossil fuels’ utilization. This work focuses on a particular configuration called the Reformer and Membrane Module (RMM), which alternates between stages of Steam Reforming (SR) reactions with H2 separation stages to overcome the thermodynamic limit of the conventional SR. The configuration has numerous advantages with respect to the more widely studied and tested membrane reactors, and has been tested during a pilot-scale research project. Although numerous modelling works appeared in the literature, the design features of the material exchanger (in the so-called RMM architecture) of different geometrical configurations have not been developed, and the mass transfer correlations, capable of providing design tools useful for such membrane modules, are not available. The purpose of this work is therefore to apply a physical-mathematical model of the mass transfer, in three different geometries, considering both concentration polarization and membrane permeation, in order to: (i) simulate the cited experimental results; (ii) estimate the scaling-up correlations for the “material exchange modules”; and (iii) identify the mass transfer limiting regime in relation to the gas mass flow rate. Full article
(This article belongs to the Special Issue Modeling and Design of Membrane Reactors)
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Open AccessReview The Application of Lipid Membranes in Biosensing
Membranes 2018, 8(4), 108; https://doi.org/10.3390/membranes8040108
Received: 8 October 2018 / Revised: 1 November 2018 / Accepted: 12 November 2018 / Published: 14 November 2018
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Abstract
The exploitation of lipid membranes in biosensors has provided the ability to reconstitute a considerable part of their functionality to detect trace of food toxicants and environmental pollutants. This paper reviews recent progress in biosensor technologies based on lipid membranes suitable for food
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The exploitation of lipid membranes in biosensors has provided the ability to reconstitute a considerable part of their functionality to detect trace of food toxicants and environmental pollutants. This paper reviews recent progress in biosensor technologies based on lipid membranes suitable for food quality monitoring and environmental applications. Numerous biosensing applications based on lipid membrane biosensors are presented, putting emphasis on novel systems, new sensing techniques, and nanotechnology-based transduction schemes. The range of analytes that can be currently using these lipid film devices that can be detected include, insecticides, pesticides, herbicides, metals, toxins, antibiotics, microorganisms, hormones, dioxins, etc. Technology limitations and future prospects are discussed, focused on the evaluation/validation and eventually commercialization of the proposed lipid membrane-based biosensors. Full article
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Open AccessArticle Recent Developments in Compact Membrane Reactors with Hydrogen Separation
Membranes 2018, 8(4), 107; https://doi.org/10.3390/membranes8040107
Received: 1 October 2018 / Revised: 2 November 2018 / Accepted: 9 November 2018 / Published: 14 November 2018
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Abstract
Hydrogen production and storage in small and medium scale, and chemical heat storage from renewable energy, are of great interest nowadays. Micro-membrane reactors for reforming of methane, as well as for the dehydrogenation of liquid organic hydrogen carriers (LOHCs), have been developed. The
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Hydrogen production and storage in small and medium scale, and chemical heat storage from renewable energy, are of great interest nowadays. Micro-membrane reactors for reforming of methane, as well as for the dehydrogenation of liquid organic hydrogen carriers (LOHCs), have been developed. The systems consist of stacked plates with integrated palladium (Pd) membranes. As an alternative to rolled and electroless plated (Pd) membranes, the development of a cost-effective method for the fabrication of Pd membranes by suspension plasma spraying is presented. Full article
(This article belongs to the Special Issue Pd-based Membranes: Overview and Perspectives)
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Open AccessArticle Engineering the Surface and Mechanical Properties of Water Desalination Membranes Using Ultralong Carbon Nanotubes
Membranes 2018, 8(4), 106; https://doi.org/10.3390/membranes8040106
Received: 2 October 2018 / Revised: 5 November 2018 / Accepted: 7 November 2018 / Published: 13 November 2018
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Abstract
In this work, novel polysulphone (PS) porous membranes for water desalination, incorporated with commercial and produced carbon nanotubes (CNT), were fabricated and analyzed. It was demonstrated that changing the main characteristics of CNT (e.g., loading in the dope solutions, aspect ratio, and functionality)
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In this work, novel polysulphone (PS) porous membranes for water desalination, incorporated with commercial and produced carbon nanotubes (CNT), were fabricated and analyzed. It was demonstrated that changing the main characteristics of CNT (e.g., loading in the dope solutions, aspect ratio, and functionality) significantly affected the membrane properties and performance including porosity, water flux, and mechanical and surface properties. The water flux of the fabricated membranes increased considerably (up to 20 times) along with the increase in CNT loading. Conversely, yield stress and Young’s modulus of the membranes dropped with the increase in the CNT loading mainly due to porosity increase. It was shown that the elongation at fracture for PS/0.25 wt. % CNT membrane was much higher than for pristine PS membrane due to enhanced compatibility of commercial CNTs with PS matrix. More pronounced effect on membrane’s mechanical properties was observed due to compatibility of CNTs with PS matrix when compared to other factors (i.e., changes in the CNT aspect ratio). The water contact angle for PS membranes incorporated with commercial CNT sharply decreased from 73° to 53° (membrane hydrophilization) for membranes with 0.1 and 1.0 wt. % of CNTs, while for the same loading of produced CNTs the water contact angles for the membrane samples increased from 66° to 72°. The obtained results show that complex interplay of various factors such as: loading of CNT in the dope solutions, aspect ratio, and functionality of CNT. These features can be used to engineer membranes with desired properties and performance. Full article
(This article belongs to the Special Issue Nanocomposite Membranes)
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Open AccessArticle Pilot–Scale Production of Carbon Hollow Fiber Membranes from Regenerated Cellulose Precursor-Part I: Optimal Conditions for Precursor Preparation
Membranes 2018, 8(4), 105; https://doi.org/10.3390/membranes8040105
Received: 17 September 2018 / Revised: 25 October 2018 / Accepted: 8 November 2018 / Published: 13 November 2018
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Abstract
Industrial scale production of carbon membrane is very challenging due to expensive precursor materials and a multi-step process with several variables to deal with. The optimization of these variables is essential to gain a competent carbon membrane (CM) with high performance and good
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Industrial scale production of carbon membrane is very challenging due to expensive precursor materials and a multi-step process with several variables to deal with. The optimization of these variables is essential to gain a competent carbon membrane (CM) with high performance and good mechanical properties. In this paper, a pilot scale system is reported that was developed to produce CM from regenerated cellulose precursor with the annual production capacity 700 m2 of CM. The process was optimized to achieve maximum yield (>95%) of high quality precursor fibers and carbonized fibers. A dope solution of cellulose acetate (CA)/Polyvinylpyrrolidone (PVP)/N-methyl-2-pyrrolidone (NMP) and bore fluid of NMP/H2O were used in 460 spinning-sessions of the fibers using a well-known dry/wet spinning process. Optimized deacetylation of spun-CA hollow fibers (CAHF) was achieved by using 90 vol% 0.075 M NaOH aqueous solution diluted with 10 vol% isopropanol for 2.5 h at ambient temperature. Cellulose hollow fibers (CHF) dried at room temperature and under RH (80% → ambient) overnight gave maximum yield for both dried CHF, as well as carbon fibers. The gas permeation properties of carbon fibers were also high (CO2 permeability: 50–450 Barrer (1 Barrer = 2.736 × 10−9 m3 (STP) m/m2 bar h), and CO2/CH4 selectivity acceptable (50–500). Full article
(This article belongs to the Section Membrane Preparation and Characterization)
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