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Membranes, Volume 9, Issue 10 (October 2019)

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Open AccessArticle
Chemical Enhancement for Retrofitting Moving Bed Biofilm and Integrated Fixed Film Activated Sludge Systems into Membrane Bioreactors
Membranes 2019, 9(10), 135; https://doi.org/10.3390/membranes9100135 (registering DOI) - 22 Oct 2019
Abstract
Positive effects of retrofitting MBBR and IFAS systems into MBRs can be exploited by introducing chemical enhancement applying coagulants in the membrane separation step. The current study reports basic principles of chemical enhancement with aluminium sulphate coagulant in biofilm-MBR (Bf-MBR) based on results [...] Read more.
Positive effects of retrofitting MBBR and IFAS systems into MBRs can be exploited by introducing chemical enhancement applying coagulants in the membrane separation step. The current study reports basic principles of chemical enhancement with aluminium sulphate coagulant in biofilm-MBR (Bf-MBR) based on results of total recycle tests performed at different dosages of the chemical enhancer and properties characterization of filtrates, supernatants and sediments. It demonstrates a possibility to achieve lower membrane fouling rates with dosing of aluminium sulphate coagulant into MBBR and IFAS mixed liquors by extending operational cycles by 20 and 80 time respectively as well as increasing operating permeability of membrane separation by 1.3 times for IFAS. It has been found that charge neutralization is the dominating mechanism of aluminium sulphate action as a chemical enhancer in Bf-MBR, however, properties of the membrane surface influencing charge repulsion of foulants should be considered together with the secondary ability of the coagulant to improve consolidation of sediments. Full article
(This article belongs to the Special Issue Point-of-use Membrane Technologies: Challenges and Opportunities)
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Open AccessArticle
Study of Annealed Aquivion® Ionomers with the INCA Method
Membranes 2019, 9(10), 134; https://doi.org/10.3390/membranes9100134 - 17 Oct 2019
Viewed by 112
Abstract
We investigated the possibility to increase the working temperature and endurance of proton exchange membranes for fuel cells and water electrolyzers by thermal annealing of short side chain perfluorosulfonic acid (SSC-PFSA) Aquivion® membranes. The Ionomer nc Analysis (INCA method), based on [...] Read more.
We investigated the possibility to increase the working temperature and endurance of proton exchange membranes for fuel cells and water electrolyzers by thermal annealing of short side chain perfluorosulfonic acid (SSC-PFSA) Aquivion® membranes. The Ionomer nc Analysis (INCA method), based on nc/T plots where nc is a counter elastic force index, was applied to SSC-PFSA in order to evaluate ionomer thermo-mechanical properties and to probe the increase of crystallinity during the annealing procedure. The enhanced thermal and mechanical stability of extruded Aquivion® 870 (equivalent weight, EW = 870 g·mol−1) was related to an increase of long-range order. Complementary differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) measurements confirmed the increase of polymer stiffness by the annealing treatment with an enhancement of the storage modulus over the whole range of temperature. The main thermomechanical relaxation temperature is also enhanced. DSC measurements showed slight base line changes after annealing, attributable to the glass transition and melting of a small amount of crystalline phase. The difference between the glass transition and melting temperatures derived from INCA plots and the ionic-cluster transition temperature derived from DMA measurements is consistent with the different experimental conditions, especially the dry atmosphere in DMA. Finally, the annealing procedure was also successfully applied for the first time to an un-crystallized cast membrane (EW = 830 g·mol−1) resulting in a remarkable mechanical and thermal stabilization. Full article
(This article belongs to the Special Issue Ionic Conductive Membranes for Fuel Cells)
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Open AccessArticle
Preliminary Study of Emulsion Liquid Membrane Formulation on Acetaminophen Removal from the Aqueous Phase
Membranes 2019, 9(10), 133; https://doi.org/10.3390/membranes9100133 - 16 Oct 2019
Viewed by 134
Abstract
The aim of this study is to develop an Emulsion Liquid Membrane (ELM) system for the extraction of acetaminophen (ACTP). Firstly, ELM was formulated by the screening of liquid membrane components where the compatibility of diluent with other membrane phase components was investigated. [...] Read more.
The aim of this study is to develop an Emulsion Liquid Membrane (ELM) system for the extraction of acetaminophen (ACTP). Firstly, ELM was formulated by the screening of liquid membrane components where the compatibility of diluent with other membrane phase components was investigated. The chosen carrier, diluent and stripping solution must comply with the reaction at the interface of the membrane to support the simultaneous processes of extraction and stripping. Therefore, parameters such as stripping agent concentration, volume ratio, initial concentration of feed phase and HCl concentration were investigated. A stable emulsion and maximum acetaminophen removal efficiency of 85% was achieved. Full article
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Open AccessFeature PaperArticle
Molecular Dynamics Simulation Study of Solid Vibration Permeation in Microporous Amorphous Silica Network Voids
Membranes 2019, 9(10), 132; https://doi.org/10.3390/membranes9100132 - 12 Oct 2019
Viewed by 164
Abstract
Microporous silica membranes have silica polymer network voids smaller than 3 Å where only small gas molecules such as helium (2.6 Å) and hydrogen (2.89 Å) can be transported. These silica membranes are highly expected to be available for H2 separation. In [...] Read more.
Microporous silica membranes have silica polymer network voids smaller than 3 Å where only small gas molecules such as helium (2.6 Å) and hydrogen (2.89 Å) can be transported. These silica membranes are highly expected to be available for H2 separation. In order to examine gas permeation mechanisms in the silica polymer network voids, factors such as membrane porous structures, gas diffusivity, and gas permeability were studied via membrane permeation molecular dynamics simulation. The thermal motions of silica membrane constituent atoms were examined according to classic harmonic oscillation potential using a suitable amorphous silica structure and non-equilibrium molecular dynamics (NEMD) simulations of gas permeation. The dynamic model successfully simulated the gas permeation characteristics in an amorphous silica membrane with a suitable Hooke’s potential parameter. The introduction of the oscillative thermal motion of the membrane atoms enhanced gas diffusivity. Helium and hydrogen diffusivity and permeability were analyzed using gas translation (GT) and solid vibration (SV) models. The diffusion distance of gas molecules between adsorption sites was around 5.5–7 Å. The solid-type vibration frequencies of gas molecules in the site were on the order of 1013 and were reasonably smaller for heavier helium than for hydrogen. Both the GT and SV models could explain the temperature dependency of helium and hydrogen gas diffusivities, but the SV model provided a more realistic geometrical representation of the silica membrane. The SV model also successfully explained gas permeability in an actual silica membrane as well as the virtual amorphous silica membrane. Full article
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Open AccessArticle
Inkjet Printed Y-Substituted Barium Zirconate Layers as Electrolyte Membrane for Thin Film Electrochemical Devices
Membranes 2019, 9(10), 131; https://doi.org/10.3390/membranes9100131 - 11 Oct 2019
Viewed by 156
Abstract
In this work, the inkjet printing of proton conducting Y-substituted barium zirconate (BZY) thin films was studied. Two different kinds of precursor inks, namely a rather molecular BZY precursor solution and a BZY nanoparticle dispersion, have been synthesized and initially investigated with regard [...] Read more.
In this work, the inkjet printing of proton conducting Y-substituted barium zirconate (BZY) thin films was studied. Two different kinds of precursor inks, namely a rather molecular BZY precursor solution and a BZY nanoparticle dispersion, have been synthesized and initially investigated with regard to their decomposition and phase formation behavior by thermal analysis, X-ray diffraction, and scanning electron microscopy. Their wetting behavior and rheological properties have been determined in order to evaluate their fundamental suitability for the inkjet process. Crystalline films have been already obtained at 700 °C, which is significantly lower compared to conventional solid-state synthesis. Increasing the temperature up to 1000 °C results in higher crystal quality. Permittivity measurements gave values of around 36 that are in good agreement with the literature while also proving the integrity of the materials. A modification of the as-synthesized BZY stock solution and nanoparticle dispersion by dilution with propionic acid improved the jetability of both inks and yielded homogeneous BZY coatings from both inks. In order to study the electrochemical properties of BZY films derived from the two printed inks, BZY coatings on sapphire substrates were prepared and characterized by electrochemical impedance spectroscopy. Full article
(This article belongs to the Special Issue Ceramic Membranes for Fuel Cell Applications and Hydrogen Production )
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Open AccessArticle
Channelized Substrates Made from BaZr0.75Ce0.05Y0.2O3−d Proton-Conducting Ceramic Polymer Clay
Membranes 2019, 9(10), 130; https://doi.org/10.3390/membranes9100130 - 09 Oct 2019
Viewed by 205
Abstract
A novel process for producing thick protonic ceramics for use in hydrogen separation membrane reactors is demonstrated. Polymer clay bodies based on polyvinyl acetate (PVA) and mineral oil were formulated, and they permitted parts with complex architectures to be prepared by simple, low-pressure [...] Read more.
A novel process for producing thick protonic ceramics for use in hydrogen separation membrane reactors is demonstrated. Polymer clay bodies based on polyvinyl acetate (PVA) and mineral oil were formulated, and they permitted parts with complex architectures to be prepared by simple, low-pressure molding in the unfired, “green” state. Ceramic proton conductors based on doped barium zirconate/cerate, made by solid-state reactive sintering, are particularly well-suited for the polymer clay process. In this work, the ceramic proton conductor, BZCY755 (BaZr0.75Ce0.05Y0.2O3−d) was fabricated into a variety of shapes and sizes. Test coupons were produced to confirm that the polymer clay route leads to a high-quality ceramic material suitable for the demanding environment of high-temperature membrane reactors. It has been demonstrated that protonic ceramic specimens with the requisite properties are easily prepared at the laboratory scale. The polymer clay fabrication route opens up the possibility of high-volume, low-cost manufacturing at a commercial scale, by a process similar to how dinnerware and sanitary porcelain are produced today. Full article
(This article belongs to the Special Issue Ceramic Membranes for Fuel Cell Applications and Hydrogen Production )
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Open AccessArticle
Simple and Precise Approach for Determination of Ohmic Contribution of Diaphragms in Alkaline Water Electrolysis
Membranes 2019, 9(10), 129; https://doi.org/10.3390/membranes9100129 - 04 Oct 2019
Viewed by 220
Abstract
A simple and low-cost alternating current (AC)-based method, without electrolyte correction, is proposed (Electrochemical Impedance Spectroscopy (EIS)-Zero Gap Cell) for the determination of ohmic contribution of diaphragms. The effectiveness of the proposed methodology was evaluated by using a commercial Alkaline Water Electrolysis (AWE) [...] Read more.
A simple and low-cost alternating current (AC)-based method, without electrolyte correction, is proposed (Electrochemical Impedance Spectroscopy (EIS)-Zero Gap Cell) for the determination of ohmic contribution of diaphragms. The effectiveness of the proposed methodology was evaluated by using a commercial Alkaline Water Electrolysis (AWE) diaphragm (Zirfon®). Furthermore, the results were compared with two conventional electrochemical methodologies for calculating the separator resistance, based on direct current (DC), and AC measurements, respectively. Compared with the previous techniques, the proposed approach reported more accurate and precise values of resistance for new and aged samples. Compared with the manufacturer reference, the obtained error values for new samples were 0.33%, 5.64%, and 41.7%, respectively for EIS-Zero gap cell, AC and DC methods, confirming the validity and convenience of the proposed technique. Full article
(This article belongs to the Special Issue Membranes for Electrolysis, Fuel Cells and Batteries)
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Open AccessReview
Progress and Perspectives on Ceramic Membranes for Solvent Recovery
Membranes 2019, 9(10), 128; https://doi.org/10.3390/membranes9100128 - 04 Oct 2019
Viewed by 191
Abstract
With the increase in demand for commodities in the world, it is advisable to conserve resources. In the case of liquid wastes generated from pharmaceutical and petroleum industries, an unconventional solution is provided for the regeneration of solvents. However, this solvent recovery can [...] Read more.
With the increase in demand for commodities in the world, it is advisable to conserve resources. In the case of liquid wastes generated from pharmaceutical and petroleum industries, an unconventional solution is provided for the regeneration of solvents. However, this solvent recovery can be carried out using various efficient methods. Recently, Mixed Matrix Membranes (MMM) obtained by the addition of nanoparticles into a polymer matrix as reinforcements, or using a material with a well-defined inorganic network as a membrane like zeolite, silica based, Zeolite imidazolate frameworks (ZIFs) and Metal organic frameworks (MOFs), were explored for a solvent recovery process. These membranes possess characteristics such as high selectivity, flux and stability at various environmental conditions for the solvent recovery process. In this review, we have covered the polymer, nanocomposites, and ceramic membranes for solvent recovery through the pervaporation and organic solvent nanofiltration processes. The key challenges faced by the materials such as MOFs, zeolite, silica, zeolite and ZIFs when they are fabricated (through in situ synthesis or secondary growth process) as membranes and separation of solvents to explore for the solvent recovery process are reviewed. Full article
(This article belongs to the Special Issue Catalytic Membranes and Their Applications)
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Open AccessArticle
Flower and Leaf Extracts of Sambucus nigra L.: Application of Membrane Processes to Obtain Fractions with Antioxidant and Antityrosinase Properties
Membranes 2019, 9(10), 127; https://doi.org/10.3390/membranes9100127 - 24 Sep 2019
Viewed by 315
Abstract
This study aimed at evaluating and comparing the chemical profile as well as the antityrosinase and antioxidant activities of ethanol (EtOH) and methanol (MeOH) extracts of Sambucus nigra L. (Adoxaceae) flowers and leaves in order to discover new candidates for food additives and [...] Read more.
This study aimed at evaluating and comparing the chemical profile as well as the antityrosinase and antioxidant activities of ethanol (EtOH) and methanol (MeOH) extracts of Sambucus nigra L. (Adoxaceae) flowers and leaves in order to discover new candidates for food additives and cosmetic and pharmaceutical products. For this purpose, a novel lower-melting-point ethylene-chlorotrifluoroethylene (LMP ECTFE) nanofiltration (NF) membrane was employed in order to produce the concentrated fractions of S. nigra. Floral extracts were richer in phytochemicals in comparison to the leaf extracts. The High-performance liquid chromatography (HPLC) profile revealed rutin, quercetin, protocateuchic acid, 3,5-dicaffeoylquinic acid, and neochlorogenic acid as the most abundant compounds. Ferric reducing antioxidant power (FRAP), 2,2’-diphenil-1-picrylhydrazil (DPPH) radical scavenging, and 2,2’-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) tests were used to investigate the antioxidant properties. NF retentate fractions of floral ethanol extracts exerted the highest tyrosinase inhibitory activity with an IC50 of 53.9 µg/mL and the highest ABTS radical scavenging activity (IC50 of 46.4 µg/mL). In conclusion, the present investigation revealed the potential benefits of NF application in S. nigra extracts processing, suggesting the use of retentate fractions as a promising source for antioxidant and tyrosinase inhibitory compounds which could pave the way for future applications Full article
(This article belongs to the Special Issue Functional Membranes for Biomedical and Environmental Applications)
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Open AccessArticle
Factors Limiting the Apparent Hydrogen Flux in Asymmetric Tubular Cercer Membranes Based on La27W3.5Mo1.5O55.5−δ and La0.87Sr0.13CrO3−δ
Membranes 2019, 9(10), 126; https://doi.org/10.3390/membranes9100126 - 24 Sep 2019
Viewed by 285
Abstract
Asymmetric tubular ceramic–ceramic (cercer) membranes based on La27W3.5Mo1.5O55.5−δ-La0.87Sr0.13CrO3−δ were fabricated by a two-step firing method making use of water-based extrusion and dip-coating. The performance of the membranes was [...] Read more.
Asymmetric tubular ceramic–ceramic (cercer) membranes based on La27W3.5Mo1.5O55.5−δ-La0.87Sr0.13CrO3−δ were fabricated by a two-step firing method making use of water-based extrusion and dip-coating. The performance of the membranes was characterized by measuring the hydrogen permeation flux and water splitting with dry and wet sweep gases, respectively. To explore the limiting factors for hydrogen and oxygen transport in the asymmetric membrane architecture, the effect of different gas flows and switching the feed and sweep sides of the membrane on the apparent hydrogen permeability was investigated. A dusty gas model was used to simulate the gas gradient inside the porous support, which was combined with Wagner diffusion calculations of the dense membrane layer to assess the overall transport across the asymmetric membrane. In addition, the stability of the membrane was investigated by means of flux measurements over a period of 400 h. Full article
(This article belongs to the Special Issue Ceramic Membranes for Fuel Cell Applications and Hydrogen Production )
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Open AccessArticle
On the Morphological Characterization Procedures of Multilayer Hydrophobic Ceramic Membranes for Membrane Distillation Operations
Membranes 2019, 9(10), 125; https://doi.org/10.3390/membranes9100125 - 23 Sep 2019
Viewed by 248
Abstract
The paper introduces some aspects of the characterization of hydrophobized multilayer ceramic membranes intended for use in membrane distillation (MD) operations. Four-layer hydrophobic carbon-based titania membranes, manufactured by the Fraunhofer Institute for Ceramic Technologies and Systems (IKTS, Hermsdorf, Germany), were tested according to [...] Read more.
The paper introduces some aspects of the characterization of hydrophobized multilayer ceramic membranes intended for use in membrane distillation (MD) operations. Four-layer hydrophobic carbon-based titania membranes, manufactured by the Fraunhofer Institute for Ceramic Technologies and Systems (IKTS, Hermsdorf, Germany), were tested according to the gas permeation technique. Gas permeance data were elaborated following the premises of the dusty gas model, to calculate the average pore size and the porosity-tortuosity ratio of each layer. Membrane testing was the opportunity to discuss which characterization method is more appropriate to obtain the membrane parameters necessary for the simulation of membranes in MD processes. In the case of multilayer membranes, the calculation of the morphological parameters should be performed for each layer. The “layer-by-layer gas permeation” method, previously introduced by other authors and completed in this work, is more appropriate for obtaining representative parameters of the membrane. Conversely, the calculation of morphological parameters, averaged over the entire membrane, might lead to heavy underestimations of the total membrane resistance and then to a heavy error on the transmembrane flux simulation. Full article
(This article belongs to the Section Fundamentals of Membrane Processes)
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Open AccessArticle
Synthesis, Transfer, and Gas Separation Characteristics of MOF-Templated Polymer Membranes
Membranes 2019, 9(10), 124; https://doi.org/10.3390/membranes9100124 - 20 Sep 2019
Viewed by 375
Abstract
This paper discusses the potential of polymer networks, templated by crystalline metal–organic framework (MOF), as novel selective layer material in thin film composite membranes. The ability to create mechanically stable membranes with an ultra-thin selective layer of advanced polymer materials is highly desirable [...] Read more.
This paper discusses the potential of polymer networks, templated by crystalline metal–organic framework (MOF), as novel selective layer material in thin film composite membranes. The ability to create mechanically stable membranes with an ultra-thin selective layer of advanced polymer materials is highly desirable in membrane technology. Here, we describe a novel polymeric membrane, which is synthesized via the conversion of a surface anchored metal–organic framework (SURMOF) into a surface anchored gel (SURGEL). The SURGEL membranes combine the high variability in the building blocks and the possibility to control the network topology and membrane thickness of the SURMOF synthesis with high mechanical and chemical stability of polymers. Next to the material design, the transfer of membranes to suitable supports is also usually a challenging task, due to the fragile nature of the ultra-thin films. To overcome this issue, we utilized a porous support on top of the membrane, which is mechanically stable enough to allow for the easy membrane transfer from the synthesis substrate to the final membrane support. To demonstrate the potential for gas separation of the synthesized SURGEL membranes, as well as the suitability of the transfer method, we determined the permeance for eight gases with different kinetic diameters. Full article
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Open AccessArticle
Fabrication and Evaluation of Trimethylmethoxysilane (TMMOS)-Derived Membranes for Gas Separation
Membranes 2019, 9(10), 123; https://doi.org/10.3390/membranes9100123 - 20 Sep 2019
Viewed by 216
Abstract
Gas separation membranes were fabricated with varying trimethylmethoxysilane (TMMOS)/tetraethoxy orthosilicate (TEOS) ratios by a chemical vapor deposition (CVD) method at 650 °C and atmospheric pressure. The membrane had a high H2 permeance of 8.3 × 10−7 mol m−2 s−1 [...] Read more.
Gas separation membranes were fabricated with varying trimethylmethoxysilane (TMMOS)/tetraethoxy orthosilicate (TEOS) ratios by a chemical vapor deposition (CVD) method at 650 °C and atmospheric pressure. The membrane had a high H2 permeance of 8.3 × 10−7 mol m−2 s−1 Pa−1 with H2/CH4 selectivity of 140 and H2/C2H6 selectivity of 180 at 300 °C. Fourier transform infrared (FTIR) measurements indicated existence of methyl groups at high preparation temperature (650 °C), which led to a higher hydrothermal stability of the TMMOS-derived membranes than of a pure TEOS-derived membrane. Temperature-dependence measurements of the permeance of various gas species were used to establish a permeation mechanism. It was found that smaller species (He, H2, and Ne) followed a solid-state diffusion model while larger species (N2, CO2, and CH4) followed a gas translational diffusion model. Full article
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