Membranes

41 pages, 2259 KiB

Open AccessArticle

Modeling Fixed Bed Membrane Reactors for Hydrogen Production through Steam Reforming Reactions: A Critical Analysis

by Maria Anna Murmura, Stefano Cerbelli and Maria Cristina Annesini

Membranes 2018, 8(2), 34; https://doi.org/10.3390/membranes8020034 - 19 Jun 2018

Cited by 21 | Viewed by 6959

Membrane reactors for hydrogen production have been extensively studied in the past years due to the interest in developing systems that are adequate for the decentralized production of high-purity hydrogen. Research in this field has been both experimental and theoretical. The aim of [...] Read more.

Membrane reactors for hydrogen production have been extensively studied in the past years due to the interest in developing systems that are adequate for the decentralized production of high-purity hydrogen. Research in this field has been both experimental and theoretical. The aim of this work is two-fold. On the one hand, modeling work on membrane reactors that has been carried out in the past is presented and discussed, along with the constitutive equations used to describe the different phenomena characterizing the behavior of the system. On the other hand, an attempt is made to shed some light on the meaning and usefulness of models developed with different degrees of complexity. The motivation has been that, given the different ways and degrees in which transport models can be simplified, the process is not always straightforward and, in some cases, leads to conceptual inconsistencies that are not easily identifiable or identified. Full article

(This article belongs to the Special Issue Modeling and Design of Membrane Reactors)

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16 pages, 6345 KiB

Open AccessFeature PaperArticle

Application of Novel Anion-Exchange Blend Membranes (AEBMs) to Vanadium Redox Flow Batteries

by Hyeongrae Cho, Henning M. Krieg and Jochen A. Kerres

Membranes 2018, 8(2), 33; https://doi.org/10.3390/membranes8020033 - 19 Jun 2018

Cited by 14 | Viewed by 6095

Abstract

Both cation-exchange membranes and anion-exchange membranes are used as ion conducting membranes in vanadium redox flow batteries (VRFBs). Anion-exchange membranes (AEMs) are applied in vanadium redox flow batteries due to the high blocking property of vanadium ions via the Donnan exclusion effect. In [...] Read more.

Both cation-exchange membranes and anion-exchange membranes are used as ion conducting membranes in vanadium redox flow batteries (VRFBs). Anion-exchange membranes (AEMs) are applied in vanadium redox flow batteries due to the high blocking property of vanadium ions via the Donnan exclusion effect. In this study, novel anion-exchange blend membranes (AEBMs) were prepared, characterized, and applied in VRFBs. Bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide), poly[(1-(4,4′-diphenylether)-5-oxybenzimidazole)-benzimidazole] (PBI-OO) and sulfonated polyether sulfone polymer were combined to prepare 3-component AEBMs with 1,2,4,5-tetramethylimidazole (TMIm) for quaternization. 3-component AEBMs showed significantly enhanced chemical and mechanical properties compared with those of 2-component AEBMs, resulting in an improved performance in VRFBs. The compositions of the anion-exchange polymers in 3-component AEBMs were systematically varied to optimize the AEBMs for the redox-flow battery application. While the 3-component AEBMs showed comparable efficiencies with Nafion^® 212 membranes, they displayed improved vanadium ions cross-over as was confirmed by open circuit voltage tests and capacity fade tests conducted in VRFBs. In addition, one of the synthesized 3-component AEBM had a superior coulombic efficiency and capacity retention in a charging–discharging test over 300 cycles at a current density of 40 mA/cm². It can thus be concluded that 3-component AEBMs are promising candidates for long-term operation in VRFBs. Full article

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15 pages, 4209 KiB

Open AccessFeature PaperArticle

Estimating CO₂/N₂ Permselectivity through Si/Al = 5 Small-Pore Zeolites/PTMSP Mixed Matrix Membranes: Influence of Temperature and Topology

by Clara Casado-Coterillo, Ana Fernández-Barquín, Susana Valencia and Ángel Irabien

Membranes 2018, 8(2), 32; https://doi.org/10.3390/membranes8020032 - 16 Jun 2018

Cited by 10 | Viewed by 4014

Abstract

In the present work, the effect of zeolite type and topology on CO₂ and N₂ permeability using zeolites of different topology (CHA, RHO, and LTA) in the same Si/Al = 5, embedded in poly(trimethylsilyl-1-propyne) (PTMSP) is evaluated with temperature. Several models [...] Read more.

In the present work, the effect of zeolite type and topology on CO₂ and N₂ permeability using zeolites of different topology (CHA, RHO, and LTA) in the same Si/Al = 5, embedded in poly(trimethylsilyl-1-propyne) (PTMSP) is evaluated with temperature. Several models are compared on the prediction of CO₂/N₂ separation performance and then the modified Maxwell models are selected. The CO₂ and N₂ permeabilities through these membranes are predicted with an average absolute relative error (AARE) lower than 0.6% taking into account the temperature and zeolite loading and topology on non-idealities such as membrane rigidification, zeolite–polymer compatibility and sieve pore blockage. The evolution of this structure–performance relationship with temperature has also been predicted. Full article

(This article belongs to the Special Issue Mixed Matrix Membranes)

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15 pages, 2312 KiB

Open AccessFeature PaperArticle

Membrane Distillation Trial on Textile Wastewater Containing Surfactants Using Hydrophobic and Hydrophilic-Coated Polytetrafluoroethylene (PTFE) Membranes

by Jesús Villalobos García, Noel Dow, Nicholas Milne, Jianhua Zhang, Leslie Naidoo, Stephen Gray and Mikel Duke

Membranes 2018, 8(2), 31; https://doi.org/10.3390/membranes8020031 - 15 Jun 2018

Cited by 58 | Viewed by 8088

Abstract

Treating wastewater from textile plants using membrane distillation (MD) has great potential due to the high-salinity wastes and availability of waste heat. However, textile wastewaters also contain surfactants, which compromise the essential hydrophobic feature of the membrane, causing membrane wetting. To address this [...] Read more.

Treating wastewater from textile plants using membrane distillation (MD) has great potential due to the high-salinity wastes and availability of waste heat. However, textile wastewaters also contain surfactants, which compromise the essential hydrophobic feature of the membrane, causing membrane wetting. To address this wetting issue, a custom-made membrane consisting of a hydrophilic layer coated on hydrophobic polytetrafluoroethylene (PTFE) was tested on textile wastewater in a pilot MD setup, and compared with a conventional hydrophobic PTFE membrane. The test was carried out with a feed temperature of 60 °C, and a permeate temperature of 45 °C. The overall salt rejection of both membranes was very high, at 99%. However, the hydrophobic membrane showed rising permeate electrical conductivity, which was attributed to wetting of the membrane. Meanwhile, the hydrophilic-coated membrane showed continually declining electrical conductivity demonstrating an intact membrane that resisted wetting from the surfactants. Despite this positive result, the coated membrane did not survive a simple sodium hydroxide clean, which would be typically applied to a membrane process. This brief study showed the viability of membrane distillation membranes on real textile wastewaters containing surfactants using hydrophilic-coated hydrophobic PTFE, but the cleaning process required for membranes needs optimization. Full article

(This article belongs to the Section Polymeric Membranes)

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23 pages, 2998 KiB

Open AccessReview

Progress on Incorporating Zeolites in Matrimid^®5218 Mixed Matrix Membranes towards Gas Separation

by Roberto Castro-Muñoz and Vlastimil Fíla

Membranes 2018, 8(2), 30; https://doi.org/10.3390/membranes8020030 - 14 Jun 2018

Cited by 65 | Viewed by 7260

Abstract

Membranes, as perm-selective barriers, have been widely applied for gas separation applications. Since some time ago, pure polymers have been used mainly for the preparation of membranes, considering different kinds of polymers for such preparation. At this point, polyimides (e.g., Matrimid^®5218) [...] Read more.

Membranes, as perm-selective barriers, have been widely applied for gas separation applications. Since some time ago, pure polymers have been used mainly for the preparation of membranes, considering different kinds of polymers for such preparation. At this point, polyimides (e.g., Matrimid^®5218) are probably one of the most considered polymers for this purpose. However, the limitation on the performance relationship of polymeric membranes has promoted their enhancement through the incorporation of different inorganic materials (e.g., zeolites) into their matrix. Therefore, the aim of this work is to provide an overview about the progress of zeolite embedding in Matrimid^®5218, aiming at the preparation of mixed matrix membranes for gas separation. Particular attention is paid to the relevant experimental results and current findings. Finally, we describe the prospects and future trends in the field. Full article

(This article belongs to the Special Issue Zeolitic Membranes: Advances and Applications)

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16 pages, 3951 KiB

Open AccessArticle

“Modified” Liquid–Liquid Displacement Porometry and Its Applications in Pd-Based Composite Membranes

by Lei Zheng, Hui Li, Haijun Yu, Guodong Kang, Tianying Xu, Jiafeng Yu, Xinzhong Li and Hengyong Xu

Membranes 2018, 8(2), 29; https://doi.org/10.3390/membranes8020029 - 8 Jun 2018

Cited by 6 | Viewed by 5186

Abstract

For H₂ separation by Pd-based composite membranes, the pore mouth size distribution of the porous support immediately affects the quality of the deposited layer, including continuity and defect/pinhole formation. However, there is a lack of convenient and effective methods for characterization of [...] Read more.

For H₂ separation by Pd-based composite membranes, the pore mouth size distribution of the porous support immediately affects the quality of the deposited layer, including continuity and defect/pinhole formation. However, there is a lack of convenient and effective methods for characterization of pore mouth size of porous supports as well as of defect distribution of dense Pd-based composite membranes. Here we introduce a novel method by modifying conventional liquid–liquid displacement porometry. When the pore tunnels are filled with Liquid B and the outer surface is occupied by Liquid A, the reopening of the pore mouth depends on the pressure of Liquid B and the interfacial tension at the position of the pore mouth, from which the pore mouth size can be determined according to the Young–Laplace equation. Our experimental tests using this method with model samples show promising results, which are well supported by those obtained using FESEM (fild emission scanning electron microscope), AFM (atomic force microscope), and conventional liquid–liquid displacement porometry. This novel method can provide useful information for not only surface coatings on porous substrates but also for modification of dense membrane defects; thus, broad utilizations of this technique can be expected in future study. Full article

(This article belongs to the Special Issue Pd-based Membranes: Overview and Perspectives)

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Graphical abstract

17 pages, 4624 KiB

Open AccessArticle

CO₂ Separation in Nanocomposite Membranes by the Addition of Amidine and Lactamide Functionalized POSS^® Nanoparticles into a PVA Layer

by Gabriel Guerrero, May-Britt Hägg, Christian Simon, Thijs Peters, Nicolas Rival and Christelle Denonville

Membranes 2018, 8(2), 28; https://doi.org/10.3390/membranes8020028 - 8 Jun 2018

Cited by 17 | Viewed by 4333

Abstract

In this article, we studied two different types of polyhedral oligomeric silsesquioxanes (POSS^®) functionalized nanoparticles as additives for nanocomposite membranes for CO₂ separation. One with amidine functionalization (Amidino POSS^®) and the second with amine and lactamide groups functionalization [...] Read more.

In this article, we studied two different types of polyhedral oligomeric silsesquioxanes (POSS^®) functionalized nanoparticles as additives for nanocomposite membranes for CO₂ separation. One with amidine functionalization (Amidino POSS^®) and the second with amine and lactamide groups functionalization (Lactamide POSS^®). Composite membranes were produced by casting a polyvinyl alcohol (PVA) layer, containing either amidine or lactamide functionalized POSS^® nanoparticles, on a polysulfone (PSf) porous support. FTIR characterization shows a good compatibility between the nanoparticles and the polymer. Differential scanning calorimetry (DSC) and the dynamic mechanical analysis (DMA) show an increment of the crystalline regions. Both the degree of crystallinity (

X_{c}

) and the alpha star transition, associated with the slippage between crystallites, increase with the content of nanoparticles in the PVA selective layer. These crystalline regions were affected by the conformation of the polymer chains, decreasing the gas separation performance. Moreover, lactamide POSS^® shows a higher interaction with PVA, inducing lower values in the CO₂ flux. We have concluded that the interaction of the POSS^® nanoparticles increased the crystallinity of the composite membranes, thereby playing an important role in the gas separation performance. Moreover, these nanocomposite membranes did not show separation according to a facilitated transport mechanism as expected, based on their functionalized amino-groups, thus, solution-diffusion was the main mechanism responsible for the transport phenomena. Full article

(This article belongs to the Special Issue Mixed Matrix Membranes)

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12 pages, 3884 KiB

Open AccessArticle

Applicability of PolyActive™ Thin Film Composite Membranes for CO₂ Separation from C₂H₄ Containing Multi-Component Gas Mixtures at Pressures up to 30 Bar

by Karina Schuldt, Jan Pohlmann, Sergey Shishatskiy and Torsten Brinkmann

Membranes 2018, 8(2), 27; https://doi.org/10.3390/membranes8020027 - 5 Jun 2018

Cited by 15 | Viewed by 6962

Abstract

The PolyActive™ thin film composite membrane (TFCM) has already been successfully applied for CO₂ separation tasks at feed pressures up to 10 bar. To investigate the applicability at higher pressures, measurements were undertaken with C₂H₄ containing gas mixtures with [...] Read more.

The PolyActive™ thin film composite membrane (TFCM) has already been successfully applied for CO₂ separation tasks at feed pressures up to 10 bar. To investigate the applicability at higher pressures, measurements were undertaken with C₂H₄ containing gas mixtures with a composition comparable to the product stream of the oxidative coupling of methane process, as well as single gases up to a feed pressure of 30 bar. Furthermore, the permeances of the conducted gas mixture experiments were simulated. The results show a strong swelling influence of CO₂ on the used membrane depending on the CO₂ fugacity. This swelling effect leads to a pronounced decrease in selectivity. The observed membrane behavior at high pressures could not be predicted by the Free Volume Model (FVM). Two different simulations were conducted: one based on parameters calculated from single gas data measured at pressures up to 2 bar; and a second based on parameters calculated from single gas data measured at pressures from 2 to 30 bar. The two simulations differ in their prediction accuracy. However, they confirm that it is possible to predict the measured permeances in the pressure range up to an average CO₂ fugacity of 6 bar. Full article

(This article belongs to the Special Issue Composite Membranes: Synthesis and Characterization)

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12 pages, 7242 KiB

Open AccessFeature PaperArticle

TEM Tomography of Pores with Application to Computational Nanoscale Flows in Nanoporous Silicon Nitride (NPN)

by Gregory Madejski, Kilean Lucas, Flavius C. Pascut, Kevin F. Webb and James L. McGrath

Membranes 2018, 8(2), 26; https://doi.org/10.3390/membranes8020026 - 2 Jun 2018

Cited by 7 | Viewed by 5001

Abstract

Silicon nanomembrane technologies (NPN, pnc-Si, and others) have been used commercially as electron microscopy (EM) substrates, and as filters with nanometer-resolution size cut-offs. Combined with EM, these materials provide a platform for catching or suspending nanoscale-size structures for analysis. Usefully, the nanomembrane itself [...] Read more.

Silicon nanomembrane technologies (NPN, pnc-Si, and others) have been used commercially as electron microscopy (EM) substrates, and as filters with nanometer-resolution size cut-offs. Combined with EM, these materials provide a platform for catching or suspending nanoscale-size structures for analysis. Usefully, the nanomembrane itself can be manufactured to achieve a variety of nanopore topographies. The size, shapes, and surfaces of nanopores will influence transport, fouling, sieving, and electrical behavior. Electron tomography (ET) techniques used to recreate nanoscale-sized structures would provide an excellent way to capture this variation. Therefore, we modified a sample holder to accept our standardized 5.4 mm × 5.4 mm silicon nanomembrane chips and imaged NPN nanomembranes (50–100 nm thick, 10–100 nm nanopore diameters) using transmission electron microscopy (TEM). After imaging and ET reconstruction using a series of freely available tools (ImageJ, TomoJ, SEG3D2, Meshlab), we used COMSOL Multiphysics™ to simulate fluid flow inside a reconstructed nanopore. The results show flow profiles with significantly more complexity than a simple cylindrical model would predict, with regions of stagnation inside the nanopores. We expect that such tomographic reconstructions of ultrathin nanopores will be valuable in elucidating the physics that underlie the many applications of silicon nanomembranes. Full article

(This article belongs to the Section Membrane Analysis and Characterization)

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10 pages, 2326 KiB

Open AccessCommunication

Low-Energy Membrane Process for Concentration of Stick Water

by Jinxiang Zhou and Scott M. Husson

Membranes 2018, 8(2), 25; https://doi.org/10.3390/membranes8020025 - 27 May 2018

Cited by 4 | Viewed by 4207

Abstract

This communication describes the application of forward osmosis (FO) to concentrate stick water, a nutrient-rich water byproduct of meat rendering operations. The objectives of the study were to carry out a set of batch FO runs in concentration mode to determine the maximum [...] Read more.

This communication describes the application of forward osmosis (FO) to concentrate stick water, a nutrient-rich water byproduct of meat rendering operations. The objectives of the study were to carry out a set of batch FO runs in concentration mode to determine the maximum achievable stick water concentration and to perform a preliminary cost analysis for operating a FO/reverse osmosis membrane separation process for comparison to an evaporative concentration process. The study examined the roles of feed and draw solution stir rates, temperature, feed concentration, and draw solution ionic strength on flux using commercial cellulose triacetate membranes. Results show that FO could concentrate the stick water up to 45 wt %; however, concentrations above about 30 wt % would be difficult to process through conventional membrane configurations. Preliminary operating cost estimations show that the energy cost of the FO process is about 5.3% of the energy costs for a single-effect thermal evaporation process; and, assuming a 2-year membrane lifetime, the total operating cost using FO membranes was estimated to be about 23.1% of the operating cost using such a thermal evaporation process. Full article

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35 pages, 4223 KiB

Open AccessReview

Performance of Nanocomposite Membranes Containing 0D to 2D Nanofillers for CO₂ Separation: A Review

by Saravanan Janakiram, Mahdi Ahmadi, Zhongde Dai, Luca Ansaloni and Liyuan Deng

Membranes 2018, 8(2), 24; https://doi.org/10.3390/membranes8020024 - 14 May 2018

Cited by 65 | Viewed by 8087

Abstract

Membrane technology has the potential to be an eco-friendly and energy-saving solution for the separation of CO₂ from different gaseous streams due to the lower cost and the superior manufacturing features. However, the performances of membranes made of conventional polymers are limited [...] Read more.

Membrane technology has the potential to be an eco-friendly and energy-saving solution for the separation of CO₂ from different gaseous streams due to the lower cost and the superior manufacturing features. However, the performances of membranes made of conventional polymers are limited by the trade-off between the permeability and selectivity. Improving the membrane performance through the addition of nanofillers within the polymer matrix offers a promising strategy to achieve superior separation performance. This review aims at providing a complete overview of the recent advances in nanocomposite membranes for enhanced CO₂ separation. Nanofillers of various dimensions and properties are categorized and effects of nature and morphology of the 0D to 2D nanofillers in the corresponding nanocomposite membranes of different polymeric matrixes are discussed with regard to the CO₂ permeation properties. Moreover, a comprehensive summary of the performance data of various nanocomposite membranes is presented. Finally, the advantages and challenges of various nanocomposite membranes are discussed and the future research and development opportunities are proposed. Full article

(This article belongs to the Special Issue Membranes for Carbon Dioxide Separation)

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17 pages, 2277 KiB

Open AccessArticle

Investigation of the Use of a Bio-Derived Solvent for Non-Solvent-Induced Phase Separation (NIPS) Fabrication of Polysulfone Membranes

by Xiaobo Dong, Amna Al-Jumaily and Isabel C. Escobar

Membranes 2018, 8(2), 23; https://doi.org/10.3390/membranes8020023 - 7 May 2018

Cited by 113 | Viewed by 21984

Abstract

Organic solvents, such as N-methyl-2-pyrrolidone (NMP) and dimethylacetamide (DMAc), have been traditionally used to fabricate polymeric membranes. These solvents may have a negative impact on the environment and human health; therefore, using renewable solvents derived from biomass is of great interest to [...] Read more.

Organic solvents, such as N-methyl-2-pyrrolidone (NMP) and dimethylacetamide (DMAc), have been traditionally used to fabricate polymeric membranes. These solvents may have a negative impact on the environment and human health; therefore, using renewable solvents derived from biomass is of great interest to make membrane fabrication sustainable. Methyl-5-(dimethylamino)-2-methyl-5-oxopentanoate (Rhodiasolv PolarClean) is a bio-derived, biodegradable, nonflammable and nonvolatile solvent. Polysulfone is a commonly used polymer to fabricate membranes due to its thermal stability, strong mechanical strength and good chemical resistance. From cloud point curves, PolarClean showed potential to be a solvent for polysulfone. Membranes prepared with PolarClean were investigated in terms of their morphology, porosity, water permeability and protein rejection, and were compared to membranes prepared with traditional solvents. The pores of polysulfone/PolarClean membranes were sponge-like, and the membranes displayed higher water flux values (176.0 ± 8.8 LMH) along with slightly higher solute rejection (99.0 ± 0.51%). On the other hand, PSf/DMAc membrane pores were finger-like with lower water flux (63.1 ± 12.4 LMH) and slightly lower solute rejection (96 ± 2.00%) when compared to PSf/PolarClean membranes. Full article

(This article belongs to the Section Polymeric Membranes)

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15 pages, 3596 KiB

Open AccessArticle

Effect of DS Concentration on the PRO Performance Using a 5-Inch Scale Cellulose Triacetate-Based Hollow Fiber Membrane Module

by Masahiro Yasukawa, Daisuke Shigefuji, Masafumi Shibuya, Yuki Ikebe, Ryuto Horie and Mitsuru Higa

Membranes 2018, 8(2), 22; https://doi.org/10.3390/membranes8020022 - 1 May 2018

Cited by 8 | Viewed by 5104

Abstract

In this study, pressure-retarded osmosis (PRO) performance of a 5-inch scale cellulose triacetate (CTA)-based hollow fiber (HF) membrane module was evaluated under a wide range of operating conditions (0.0–6.0 MPa of applied pressure, 0.5–2.0 L/min feed solution (FS) inlet flow rate, 1.0–6.0 L/min [...] Read more.

In this study, pressure-retarded osmosis (PRO) performance of a 5-inch scale cellulose triacetate (CTA)-based hollow fiber (HF) membrane module was evaluated under a wide range of operating conditions (0.0–6.0 MPa of applied pressure, 0.5–2.0 L/min feed solution (FS) inlet flow rate, 1.0–6.0 L/min DS inlet flow rate and 0.1–0.9 M draw solution (DS) concentration) by using a PRO/reverse osmosis (RO) hybrid system. The subsequent RO system for DS regeneration enabled the evaluation of the steady-stated module performance. In the case of pilot-scale module operation, since the DS dilution and the feed solution (FS) up-concentration had occurred and was not negligible, unlike the lab-scale experiment, PRO performance strongly depended on operating conditions such as inlet flow rates of both the DS and FS concentration. To compare the module performance with different configurations, we proposed a converted parameter in which a difference of the packing density between the spiral wound (SW) and the HF module was fairly considered. In the case of HF configuration, because of high packing density, volumetric-based performance was higher than that of SW module, that is, the required number of the module would be less than that of SW module in a full-scale PRO plant. Full article

(This article belongs to the Special Issue Mass Transfer in Membranes)

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11 pages, 2133 KiB

Open AccessArticle

Applicability of a Supported Liquid Membrane in the Enrichment and Determination of Cadmium from Complex Aqueous Samples

by Núria Pont, Victòria Salvadó and Clàudia Fontàs

Membranes 2018, 8(2), 21; https://doi.org/10.3390/membranes8020021 - 23 Apr 2018

Cited by 17 | Viewed by 5066

Abstract

A supported liquid membrane is developed for the separation of Cd from either high in salinity or acidity aqueous media. The membrane consisted of a durapore (polyvinylidene difluoride) polymeric support impregnated with a 0.5 M Aliquat 336 solution in decaline. The effect of [...] Read more.

A supported liquid membrane is developed for the separation of Cd from either high in salinity or acidity aqueous media. The membrane consisted of a durapore (polyvinylidene difluoride) polymeric support impregnated with a 0.5 M Aliquat 336 solution in decaline. The effect of carrier concentration, organic solvent and feed and receiving solutions on the metal permeability is studied. This system allows the effective transport of trace levels of Cd through the formation of CdCl₄²⁻, which is the predominant species responsible for the extraction process, in both NaCl and HCl solutions. The supported liquid membrane system in a hollow fibre configuration allows the enrichment and separation of trace levels of Cd from spiked seawater samples, facilitating the analytical determination of this toxic metal. Full article

(This article belongs to the Special Issue Advances in Liquid Membrane-Based Separation)

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13 pages, 5213 KiB

Open AccessArticle

Effective Conversion of Amide to Carboxylic Acid on Polymers of Intrinsic Microporosity (PIM-1) with Nitrous Acid

by Wei-Hsuan Wu, Paul Thomas, Paul Hume and Jianyong Jin

Membranes 2018, 8(2), 20; https://doi.org/10.3390/membranes8020020 - 18 Apr 2018

Cited by 22 | Viewed by 8099

Abstract

Carboxylate-functionalised polymers of intrinsic microporosity (C-PIMs) are highly desirable materials for membrane separation applications. The recently reported method to afford C-PIMs was via an extensive base hydrolysis process requiring 360 h. Herein, a novel and effective method to convert PIM-CONH₂ to C-PIM [...] Read more.

Carboxylate-functionalised polymers of intrinsic microporosity (C-PIMs) are highly desirable materials for membrane separation applications. The recently reported method to afford C-PIMs was via an extensive base hydrolysis process requiring 360 h. Herein, a novel and effective method to convert PIM-CONH₂ to C-PIM using nitrous acid was studied. The chemical structure of C-PIM was characterised by ¹H NMR, ¹³C NMR, FTIR, elemental analysis, UV-Vis, TGA and TGA-MS. Complete conversion from amide to carboxylic acid groups was confirmed. Decarboxylation of C-PIM was also successfully studied by TGA-MS for the first time, with a loss of m/z 44 amu (CO₂) observed at the first degradation stage. TGA also revealed decreased thermal stability of C-PIM relative to PIM-CONH₂ under both N₂ and air atmosphere_. Gel permeation chromatography (GPC) analysis showed continuous molecular weight degradation of C-PIM with extended reaction time. Aromatic nitration was also observed as a side reaction in some cases. Full article

(This article belongs to the Special Issue Polymeric Membranes for Gas Separation)

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10 pages, 2837 KiB

Open AccessArticle

Liquid Membranes as a Tool for Chemical Speciation of Metals in Natural Waters: Organic and Inorganic Complexes of Nickel

by Cristina Vergel, Carolina Mendiguchía and Carlos Moreno

Membranes 2018, 8(2), 19; https://doi.org/10.3390/membranes8020019 - 15 Apr 2018

Cited by 4 | Viewed by 4149

Abstract

The different species of nickel present in natural waters exhibit different transport behaviour through bulk liquid membranes (BLMs). This fact has been used to design and optimise a separation/pre-concentration system applicable to separate labile and non-labile nickel fractions. A hydrazone derivative—1,2-cyclohexanedione bis-benzoyl-hydrazone (1,2-CHBBH) [...] Read more.

The different species of nickel present in natural waters exhibit different transport behaviour through bulk liquid membranes (BLMs). This fact has been used to design and optimise a separation/pre-concentration system applicable to separate labile and non-labile nickel fractions. A hydrazone derivative—1,2-cyclohexanedione bis-benzoyl-hydrazone (1,2-CHBBH) dissolved in toluene/dimethyl formamide (2% DMF)—was used as a chemical carrier of nickel species, from an aqueous source solution (sample) to a receiving acidic solution. Both chemical and hydrodynamic conditions controlling the transport system were studied and optimised. Under optimum conditions, variations in the transport of nickel ions as a function of organic (humic acids) and inorganic (chloride ions) ligands were studied. Relationships between the permeability coefficient (P) or recovery efficiency (%R) and the concentrations of ligands and nickel species were analysed using Winhumic V software. A negative correlation between P and the concentration of organic nickel complexes was found, suggesting that only labile nickel species are transported through the liquid membrane, with non-labile complexes remaining in the water sample; allowing for their separation and subsequent quantification in natural waters. Full article

(This article belongs to the Special Issue Advances in Liquid Membrane-Based Separation)

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40 pages, 47726 KiB

Open AccessReview

Progress of Nanocomposite Membranes for Water Treatment

by Claudia Ursino, Roberto Castro-Muñoz, Enrico Drioli, Lassaad Gzara, Mohammad H. Albeirutty and Alberto Figoli

Membranes 2018, 8(2), 18; https://doi.org/10.3390/membranes8020018 - 3 Apr 2018

Cited by 218 | Viewed by 16232

Abstract

The use of membrane-based technologies has been applied for water treatment applications; however, the limitations of conventional polymeric membranes have led to the addition of inorganic fillers to enhance their performance. In recent years, nanocomposite membranes have greatly attracted the attention of scientists [...] Read more.

The use of membrane-based technologies has been applied for water treatment applications; however, the limitations of conventional polymeric membranes have led to the addition of inorganic fillers to enhance their performance. In recent years, nanocomposite membranes have greatly attracted the attention of scientists for water treatment applications such as wastewater treatment, water purification, removal of microorganisms, chemical compounds, heavy metals, etc. The incorporation of different nanofillers, such as carbon nanotubes, zinc oxide, graphene oxide, silver and copper nanoparticles, titanium dioxide, 2D materials, and some other novel nano-scale materials into polymeric membranes have provided great advances, e.g., enhancing on hydrophilicity, suppressing the accumulation of pollutants and foulants, enhancing rejection efficiencies and improving mechanical properties and thermal stabilities. Thereby, the aim of this work is to provide up-to-date information related to those novel nanocomposite membranes and their contribution for water treatment applications. Full article

(This article belongs to the Special Issue Membrane Preparation and Characterisation and Their Application in Environmental Field)

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13 pages, 1245 KiB

Open AccessCommunication

Comparison of NF-RO and RO-NF for the Treatment of Mature Landfill Leachates: A Guide for Landfill Operators

by Sreenivasan Ramaswami, Joachim Behrendt and Ralf Otterpohl

Membranes 2018, 8(2), 17; https://doi.org/10.3390/membranes8020017 - 21 Mar 2018

Cited by 24 | Viewed by 8498

Abstract

Reverse osmosis (RO) and nanofiltration (NF) are among the state-of-the-art technologies for treating landfill leachates. Due to the complexity and variance in the composition of leachates, numerous combinations of multiple technologies are used for their treatment. One process chain for the treatment of [...] Read more.

Reverse osmosis (RO) and nanofiltration (NF) are among the state-of-the-art technologies for treating landfill leachates. Due to the complexity and variance in the composition of leachates, numerous combinations of multiple technologies are used for their treatment. One process chain for the treatment of raw leachate is RO followed by further concentration of RO-retentate using NF (RO-NF scheme). The aptness of this process train used by some landfill sites around the world (usually with the aim of volume reduction so as to re-inject the concentrate into the landfill) is questionable. This study investigated two schemes RO-NF and NF-RO (nanofiltration of raw leachate followed by reverse osmosis of NF permeate) to identify their merits/demerits. Experiments were conducted in bench scale using commercial membranes: DOW Filmtec NF270 and SW30HR. Filtration trials were performed at different pressures to compare the water and solute transports in the individual stages of the two schemes. Based on the water fluxes and compositions of retentates and permeates; osmotic pressures, energy demands, and other possible operational advantages were discussed. NF-RO offers some advantages and flexibility for leachate treatment besides being energy efficient compared to RO-NF, wherein osmotic pressure steadily increases during operation in turn increasing operation and maintenance costs. Full article

(This article belongs to the Special Issue Advanced Nanofiltration Membranes)

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Membranes, Volume 8, Issue 2 (June 2018) – 18 articles

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