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Membranes, Volume 9, Issue 3 (March 2019)

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Cover Story (view full-size image) This outstanding research demonstrates the fabrication and transport properties of novel composite [...] Read more.
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Open AccessArticle Application of Ultrafiltration in a Swimming Pool Water Treatment System
Received: 14 February 2019 / Revised: 5 March 2019 / Accepted: 19 March 2019 / Published: 25 March 2019
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Abstract
Swimming pool water was treated using an ultrafiltration process using ceramic and polymer membranes for comparison. It was determined that the efficiency of the process depended on the type of membrane used. The polymer membrane decreased the absorbance and concentration of combined chlorine [...] Read more.
Swimming pool water was treated using an ultrafiltration process using ceramic and polymer membranes for comparison. It was determined that the efficiency of the process depended on the type of membrane used. The polymer membrane decreased the absorbance and concentration of combined chlorine in the pool water to a greater extent than the ceramic membrane. In the case of a ceramic membrane, the concentration of combined chlorine in the permeate exceeded the limit values. During the ultrafiltration process, the permeate flux decreased, causing the blockage of membrane pores. The extent of this phenomenon was similar for both tested membranes. In the case of the ceramic membrane, flushing it with water could significantly restore its initial performance. For both tested membranes, a high regeneration efficiency was observed during chemical treatment with an alkaline solution. SEM photos of the polymer membrane showed low resistance of this polymer to the chlorine present in the swimming pool water. Full article
(This article belongs to the Section Membrane Applications in Water Treatment)
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Open AccessCommunication Metastable State of Water and Performance of Osmotically Driven Membrane Processes
Received: 27 February 2019 / Revised: 18 March 2019 / Accepted: 19 March 2019 / Published: 22 March 2019
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Abstract
Semipermeable membranes play critical roles in many natural and engineering systems. The osmotic pressure is found experimentally much less effective than the hydraulic pressure to drive water through the membrane, which is commonly attributed to the internal concentration polarization (ICP) in the porous [...] Read more.
Semipermeable membranes play critical roles in many natural and engineering systems. The osmotic pressure is found experimentally much less effective than the hydraulic pressure to drive water through the membrane, which is commonly attributed to the internal concentration polarization (ICP) in the porous layer of the membrane. In this study, it has been shown that a necessary condition for the osmotic pressure to be effective is water continuity across the entire membrane thickness under negative pressure, i.e., the water inside the membrane remains in a metastable state. However, the metastable state of water cannot be maintained indefinitely, and cavitation will undoubtedly occur in the osmotically driven processes. Collapse of the water metastable state was suggested for the first time to be a more important and fundamental reason for the low water fluxes in the osmotically driven membrane processes. Full article
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Open AccessArticle Synthesis and Study of Gas Transport Properties of Polymers Based on Macroinitiators and 2,4-Toluene Diisocyanate
Received: 24 February 2019 / Revised: 14 March 2019 / Accepted: 17 March 2019 / Published: 20 March 2019
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Abstract
Nowadays, block copolymers hold great promise for the design of novel membranes to be applied for the membrane gas separation. In this regard, microporous block copolymers based on a macroinitiator with an anionic nature, such as potassium-substituted block copolymers of propylene oxide and [...] Read more.
Nowadays, block copolymers hold great promise for the design of novel membranes to be applied for the membrane gas separation. In this regard, microporous block copolymers based on a macroinitiator with an anionic nature, such as potassium-substituted block copolymers of propylene oxide and ethylene oxide (PPEG) and 2,4-toluene diisocyanate (TDI), were obtained and investigated as effective gas separation membranes. The key element of the macromolecular structure that determines the supramolecular organization of the studied polymers is the coplanar blocks of polyisocyanates with an acetal nature (O-polyisocyanate). In the present research, the influence of the content of peripheral polyoxyethylene (POE) blocks in PPEG on the supramolecular structure processes and gas transport characteristics of the obtained polymers based on PPEG and TDI was investigated. According to the study of polymers if the POE block content is 15 wt %, the polyoxypropylene segments are located in the internal cavity of voids formed by O-polyisocyanate blocks. When the POE block content is 30 wt %, the flexible chain component forms its own microphase outside the segregation zone of the rigid O-polyisocyanate blocks. The permeability for polar molecules, such as ammonia or hydrogen sulfide, significantly exceeds the permeability values obtained for non-polar molecules He, N2 and CH4. A relatively high permeability is also observed for carbon dioxide. At the same time, the content of POE blocks has a small effect on the permeability for all studied gases. The diffusion coefficient increases with an increase in the POE block content in PPEG for all studied gases. Full article
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Open AccessArticle Polymer of Intrinsic Microporosity (PIM-1) Membranes Treated with Supercritical CO2
Received: 19 December 2018 / Revised: 7 March 2019 / Accepted: 11 March 2019 / Published: 18 March 2019
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Abstract
Polymers of intrinsic microporosity (PIMs) are a promising membrane material for gas separation, because of their high free volume and micro-cavity size distribution. This is countered by PIMs-based membranes being highly susceptible to physical aging, which dramatically reduces their permselectivity over extended periods [...] Read more.
Polymers of intrinsic microporosity (PIMs) are a promising membrane material for gas separation, because of their high free volume and micro-cavity size distribution. This is countered by PIMs-based membranes being highly susceptible to physical aging, which dramatically reduces their permselectivity over extended periods of time. Supercritical carbon dioxide is known to plasticize and partially solubilise polymers, altering the underlying membrane morphology, and hence impacting the gas separation properties. This investigation reports on the change in PIM-1 membranes after being exposed to supercritical CO2 for two- and eight-hour intervals, followed by two depressurization protocols, a rapid depressurization and a slow depressurization. The exposure times enables the impact contact time with supercritical CO2 has on the membrane morphology to be investigated, as well as the subsequent depressurization event. The density of the post supercritical CO2 exposed membranes, irrespective of exposure time and depressurization, were greater than the untreated membrane. This indicated that supercritical CO2 had solubilised the polymer chain, enabling PIM-1 to rearrange and contract the free volume micro-cavities present. As a consequence, the permeabilities of He, CH4, O2 and CO2 were all reduced for the supercritical CO2-treated membranes compared to the original membrane, while N2 permeability remained unchanged. Importantly, the physical aging properties of the supercritical CO2-treated membranes altered, with only minor reductions in N2, CH4 and O2 permeabilities observed over extended periods of time. In contrast, He and CO2 permeabilities experienced similar physical aging in the supercritical treated membranes to that of the original membrane. This was interpreted as the supercritical CO2 treatment enabling micro-cavity contraction to favour the smaller CO2 molecule, due to size exclusion of the larger N2, CH4 and O2 molecules. Therefore, physical aging of the treated membranes only had minor impact on N2, CH4 and O2 permeability; while the smaller He and CO2 gases experience greater permeability loss. This result implies that supercritical CO2 exposure has potential to limit physical aging performance loss in PIM-1 based membranes for O2/N2 separation. Full article
(This article belongs to the Special Issue Mass Transfer in Membranes)
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Open AccessFeature PaperReview Nanomaterials: Solutions to Water-Concomitant Challenges
Received: 4 February 2019 / Revised: 5 March 2019 / Accepted: 11 March 2019 / Published: 14 March 2019
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Abstract
Plenty of fresh water resources are still inaccessible for human use. Calamities such as pollution, climate change, and global warming pose serious threats to the fresh water system. Although many naturally and synthetically grown materials have been taken up to resolve these issues, [...] Read more.
Plenty of fresh water resources are still inaccessible for human use. Calamities such as pollution, climate change, and global warming pose serious threats to the fresh water system. Although many naturally and synthetically grown materials have been taken up to resolve these issues, there is still plenty of room for enhancements in technology and material perspectives to maximize resources and to minimize harm. Considering the challenges related to the purification of water, materials in the form of nanofiber membranes and nanomaterials have made tremendous contributions to water purification and filtration. Nanofiber membranes made of synthetic polymer nanofibers, ceramic membranes etc., metal oxides in various morphologies, and carbonaceous materials were explored in relation to waste removal from water. In this review, we have discussed a few key materials that have shown effectiveness in removing pollutants from waste water, enabling solutions to existing problems in obtaining clean drinking water. Full article
(This article belongs to the Section Membrane Applications in Water Treatment)
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Open AccessArticle 2D Mathematical Modelling of Overlimiting Transfer Enhanced by Electroconvection in Flow-Through Electrodialysis Membrane Cells in Galvanodynamic Mode
Received: 20 February 2019 / Revised: 5 March 2019 / Accepted: 6 March 2019 / Published: 11 March 2019
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Abstract
Flow-through electrodialysis membrane cells are widely used in water purification and the processing of agricultural products (milk, wine, etc.). In the research and operating practice of such systems, a significant place is occupied by a galvanodynamic (or galvanostatic) mode. 2D mathematical modelling of [...] Read more.
Flow-through electrodialysis membrane cells are widely used in water purification and the processing of agricultural products (milk, wine, etc.). In the research and operating practice of such systems, a significant place is occupied by a galvanodynamic (or galvanostatic) mode. 2D mathematical modelling of ion transfer in the galvanodynamic mode requires solving the problem of setting the average current density equal to a certain value, while the current density distribution in the system is uneven. This article develops a 2D mathematical model of the overlimiting transfer enhanced by electroconvection in a flow-through electrodialysis cell in the galvanodynamic mode. The model is based on the system of Navier–Stokes, Nernst–Planck, Poisson equations and equations for the electric current stream function. To set the electric mode we use a boundary condition, relating the electric field strength and current density. This approach allows us to describe the formation of the extended space charge region and development of electroconvection at overlimiting currents. For the first time, chronopotentiograms and current–voltage characteristics of the membrane systems are calculated for the galvanodynamic mode taking into account the forced flow and development of electroconvection. The behaviors of the calculated chronopotentiograms and current–voltage characteristic coincide qualitatively with experimental data. The effects of the electrolyte concentration, forced flow velocity and channel size on the mass transfer at overlimiting currents are estimated. Full article
(This article belongs to the Section Membrane Transport Phenomena)
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Open AccessArticle Novel Composite Membranes Based on Chitosan Copolymers with Polyacrylonitrile and Polystyrene: Physicochemical Properties and Application for Pervaporation Dehydration of Tetrahydrofuran
Received: 7 February 2019 / Revised: 27 February 2019 / Accepted: 2 March 2019 / Published: 7 March 2019
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Abstract
Pervaporation has been applied for tetrahydrofuran (THF) dehydration with novel composite membranes advanced by a thin selective layer composed of chitosan (CS) modified by copolymerization with vinyl monomers, acrylonitrile (AN) and styrene, in order to improve the chemical and mechanical stability of CS-based [...] Read more.
Pervaporation has been applied for tetrahydrofuran (THF) dehydration with novel composite membranes advanced by a thin selective layer composed of chitosan (CS) modified by copolymerization with vinyl monomers, acrylonitrile (AN) and styrene, in order to improve the chemical and mechanical stability of CS-based membranes. Composite membranes were developed by depositing a thin selective layer composed of CS copolymers onto a commercially-available porous support based on aromatic polysulfonamide (UPM-20®). The topography and morphology of the obtained materials were studied by atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). Thermal properties and stability were determined by coupled evolved gas analysis (EGA-MS). Transport properties were estimated in pervaporation dehydration of THF. The effect of operating parameters for the pervaporation dehydration of THF such as feed compositions and temperatures (295, 308 and 323 K) was evaluated. It was shown that CS modification with different vinyl monomers led to a difference in physical and transport properties. The composite membrane with the thin selective layer based on CS-PAN copolymer demonstrated optimal transport properties and exhibited the highest water content in the permeate with a reasonably high permeation flux. Full article
(This article belongs to the Section Membrane Preparation and Characterization)
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Open AccessArticle Influence of Hydraulic Pressure on Performance Deterioration of Direct Contact Membrane Distillation (DCMD) Process
Received: 13 February 2019 / Revised: 27 February 2019 / Accepted: 1 March 2019 / Published: 6 March 2019
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Abstract
Direct contact membrane distillation (DCMD) is a membrane distillation (MD) configuration where feed and distillate directly contact with a hydrophobic membrane. Depending on its operating conditions, the hydraulic pressures of the feed and distillate may be different, leading to adverse effects on the [...] Read more.
Direct contact membrane distillation (DCMD) is a membrane distillation (MD) configuration where feed and distillate directly contact with a hydrophobic membrane. Depending on its operating conditions, the hydraulic pressures of the feed and distillate may be different, leading to adverse effects on the performance of the DCMD process. Nevertheless, little information is available on how hydraulic pressure affects the efficiency of DCMD. Accordingly, this paper investigates the effect of external hydraulic pressure on the process efficiency of DCMD. Gas permeabilities of MD membranes were measured to analyze the effect of membrane compaction by external pressure. Mass transfer coefficients were calculated using experimental data to quantitatively explain the pressure effect. Experiments were also carried out using a laboratory-scale DCMD set-up. After applying the pressure, the cross-sections and surfaces of the membranes were examined using a scanning electron microscope (SEM). Results showed that the membrane structural parameters such as porosity and thickness were changed under relatively high pressure conditions (>30 kPa), leading to reduction in flux. The mass transfer coefficients were also significantly influenced by the hydraulic pressure. Moreover, local wetting of the membranes were observed even below the liquid entry pressure (LEP), which decreased the rejection of salts. These results suggest that the control of hydraulic pressure is important for efficient operation of DCMD process. Full article
(This article belongs to the Special Issue State-of-the-art Membrane-based Desalination)
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Open AccessArticle Mussel-Inspired Surface Functionalization of AEM for Simultaneously Improved Monovalent Anion Selectivity and Antibacterial Property
Received: 14 January 2019 / Revised: 27 February 2019 / Accepted: 27 February 2019 / Published: 6 March 2019
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Abstract
A facile membrane surface modification process for improving permselectivity and antimicrobial property was proposed. A polydopamine (PDA) coating was firstly fabricated on pristine anion exchange membrane (AEM), followed by in situ reduction of Ag without adding any extra reductant. Finally, 2,5-diaminobenzene sulfonic acid [...] Read more.
A facile membrane surface modification process for improving permselectivity and antimicrobial property was proposed. A polydopamine (PDA) coating was firstly fabricated on pristine anion exchange membrane (AEM), followed by in situ reduction of Ag without adding any extra reductant. Finally, 2,5-diaminobenzene sulfonic acid (DSA) was grafted onto PDA layer via Michael addition reaction. The as-prepared AEM exhibited improved permselectivity (from 0.60 to 1.43) and effective inhibition of bacterial growth. In addition, the result of the long-term (90-h continuous electrodialysis) test expressed the excellent durability of the modified layer on membrane surface, because the concentration of Cl and SO42− in diluted chamber fluctuated ~0.024 and 0.030 mol·L−1 with no distinct decline. The method described in this work makes the full use of multifunctional PDA layer (polymer-like coating, in situ reduction and post-organic reaction), and a rational design of functional AEM was established for better practical application. Full article
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Open AccessFeature PaperArticle Separation of Carbon Dioxide from Real Power Plant Flue Gases by Gas Permeation Using a Supported Ionic Liquid Membrane: An Investigation of Membrane Stability
Received: 3 January 2019 / Revised: 13 February 2019 / Accepted: 15 February 2019 / Published: 4 March 2019
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Abstract
The separation of carbon dioxide from coal-fired power plant flue gases using a CO2/N2-selective supported ionic liquid membrane (SILM) was investigated and the performance and stability of the membrane during operation are reported. The membrane is composed of a [...] Read more.
The separation of carbon dioxide from coal-fired power plant flue gases using a CO2/N2-selective supported ionic liquid membrane (SILM) was investigated and the performance and stability of the membrane during operation are reported. The membrane is composed of a polyacrylonitrile (PAN) ultrafiltration membrane as a support and a selective layer of an ionic liquid (IL), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM Tf2N). The feasibility of large-scale SILM production was demonstrated by the formation of a square-meter-scale membrane and preparation of a membrane module. A flat-sheet envelope-type SILM module containing 0.67 m2 of the membrane was assembled. Prior to real flue gas operation, the separation behaviour of the membrane was investigated with single gases. The stability of the SILM during the test stand and pilot plant operation using real power plant flue gases is reported. The volume fraction of carbon dioxide in the flue gas was raised from approx. 14 vol. % (feed) to 40 vol. % (permeate). However, issues concerning the membrane stability were found when SO3 aerosols in large quantities were present in the flue gas. Full article
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Open AccessArticle Steady State and Dynamic Response of Voltage-Operated Membrane Gates
Received: 30 January 2019 / Revised: 19 February 2019 / Accepted: 25 February 2019 / Published: 2 March 2019
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Abstract
An electrochemical flow cell with Nafion 212, aqueous LiI/I2 redox solution, and carbon paper electrode was operated as an electro-osmotic gate based on the Electrokinetic Energy Conversion (EKEC) principle. The gate was operated in different modes. (i) In normal DC [...] Read more.
An electrochemical flow cell with Nafion 212, aqueous LiI/I 2 redox solution, and carbon paper electrode was operated as an electro-osmotic gate based on the Electrokinetic Energy Conversion (EKEC) principle. The gate was operated in different modes. (i) In normal DC pump operation it is shown to follow the predictions from the phenomenological transport equations. (ii) Furthermore, it was also demonstrated to operate as a normally open, voltage-gated valve for microfluidic purposes. For both pump and valve operations low energy requirements (mW range) were estimated for precise control of small flows ( μ L range). (iii) Finally, the dynamic response of the pump was investigated by using alternating currents at a range of different frequencies. Full article
(This article belongs to the Special Issue Development of Membranes in Battery & Membrane Based Devices)
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Membranes EISSN 2077-0375 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
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