Research

18 pages, 4976 KiB

Open AccessArticle

On the Ionic Conductivity of Cation Exchange Membranes in Mixed Sulfates Using the Two-Phase Model

by Liansheng Wu, Haodong Jiang, Tao Luo and Xinlong Wang

Membranes 2023, 13(10), 811; https://doi.org/10.3390/membranes13100811 - 26 Sep 2023

Viewed by 1217

The concentration dependence of the conductivity of ion exchange membranes (IEMs), as well as other transport properties, has been well explained by the contemporary two-phase model (Zabolotsky et al., 1993) considering a gel phase and an inter-gel phase filled with electroneutral solution. Here, [...] Read more.

The concentration dependence of the conductivity of ion exchange membranes (IEMs), as well as other transport properties, has been well explained by the contemporary two-phase model (Zabolotsky et al., 1993) considering a gel phase and an inter-gel phase filled with electroneutral solution. Here, this two-phase model has been adopted and first applied in electrolytes containing mixed counter-ions to investigate the correlation between the membrane ionic conductivity and its microstructure. For three representative commercial cation exchange membranes (CEMs), the total membrane conductivity (

κ^{T}

) when in equilibrium with mixed MgSO₄ + Na₂SO₄ and H₂SO₄ + Na₂SO₄ electrolytes could be well predicted with the experimental composition of counter-ions in the gel and inter-gel phase, as well as the counter-ion mobility in the gel phase when the membrane is in a single electrolyte. It is found that the volume fraction of the inter-gel phase (

f_{2}

) has little impact on the predicted results. The accuracy of the model can be largely improved by calculating the inter-gel phase conductivity (

κ^{i n}

) with the ionic mobility being the same as that in the external solution (obtained via simulation in the OLI Studio), rather than simply as equivalent to the conductivity of the external solution (

κ^{s}

). Moreover, a nonlinear correlation between the CEMs’ conductivities and the counter-ion composition in the gel phase is observed in the mixed MgSO₄ + Na₂SO₄ solution, as well as for the Nafion117 membrane in the presence of sulfuric acid. For CEMs in mixed MgSO₄ + Na₂SO₄ electrolytes, the calculated conductivity values considering the interaction parameter

σ

, similar to the Kohlrausch’s law, are closer to the experimental ones. Overall, this work provides new insights into membrane conductivity with mixed counter-ions and testifies to the applicability of the contemporary two-phase model. Full article

(This article belongs to the Special Issue Ion Transport in Membranes and Membrane Systems: Modelling and Experiment)

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18 pages, 2857 KiB

Open AccessArticle

Modelling the Performance of Electrically Conductive Nanofiltration Membranes

by Alexey A. Kapitonov and Ilya I. Ryzhkov

Membranes 2023, 13(6), 596; https://doi.org/10.3390/membranes13060596 - 12 Jun 2023

Cited by 1 | Viewed by 1199

Abstract

Electrically conductive membranes are a class of stimuli-responsive materials, which allow the adjustment of selectivity for and the rejection of charged species by varying the surface potential. The electrical assistance provides a powerful tool for overcoming the selectivity–permeability trade-off due to its interaction [...] Read more.

Electrically conductive membranes are a class of stimuli-responsive materials, which allow the adjustment of selectivity for and the rejection of charged species by varying the surface potential. The electrical assistance provides a powerful tool for overcoming the selectivity–permeability trade-off due to its interaction with charged solutes, allowing the passage of neutral solvent molecules. In this work, a mathematical model for the nanofiltration of binary aqueous electrolytes by an electrically conductive membrane is proposed. The model takes into account the steric as well as Donnan exclusion of charged species due to the simultaneous presence of chemical and electronic surface charges. It is shown that the rejection reaches its minimum at the potential of zero charge (PZC), where the electronic and chemical charges compensate for each other. The rejection increases when the surface potential varies in positive and negative directions with respect to the PZC. The proposed model is successfully applied to a description of experimental data on the rejection of salts and anionic dyes by PANi–PSS/CNT and MXene/CNT nanofiltration membranes. The results provide new insights into the selectivity mechanisms of conductive membranes and can be employed to describe electrically enhanced nanofiltration processes. Full article

(This article belongs to the Special Issue Ion Transport in Membranes and Membrane Systems: Modelling and Experiment)

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12 pages, 2546 KiB

Open AccessArticle

Modified LIX^®84I-Based Polymer Inclusion Membranes for Facilitating the Transport Flux of Cu(II) and Variations of Their Physical–Chemical Characteristics

by Fang Hu, Yifa Huang, Yanting Huang, Junming Tang and Jiugang Hu

Membranes 2023, 13(6), 550; https://doi.org/10.3390/membranes13060550 - 24 May 2023

Cited by 1 | Viewed by 833

Abstract

A unique facilitation on the transport flux of Cu(II) was investigated by using modified polymer inclusion membranes (PIMs). LIX^®84I-based polymer inclusion membranes (LIX^®-based PIMs) using poly(vinyl chloride) (PVC) as support, 2-nitrophenyl octyl ether (NPOE) as plasticizer and Lix84I as [...] Read more.

A unique facilitation on the transport flux of Cu(II) was investigated by using modified polymer inclusion membranes (PIMs). LIX^®84I-based polymer inclusion membranes (LIX^®-based PIMs) using poly(vinyl chloride) (PVC) as support, 2-nitrophenyl octyl ether (NPOE) as plasticizer and Lix84I as carrier were modified by reagents with different polar groups. The modified LIX^®-based PIMs showed an increasing transport flux of Cu(II) with the help of ethanol or Versatic acid 10 modifiers. The metal fluxes with the modified LIX^®-based PIMs were observed varying with the amount of modifiers, and the transmission time was cut by half for the modified LIX^®-based PIM cast with Versatic acid 10. The physical–chemical characteristics of the prepared blank PIMs with different Versatic acid 10 were further characterized by using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), contract angle measurements and electro-chemical impedance spectroscopy (EIS). The characterization results indicated that the modified LIX^®-based PIMs cast with Versatic acid 10 appeared to be more hydrophilic with increasing membrane dielectric constant and electrical conductivity that allowed better accessibility of Cu(II) across PIMs. Hence, it was deduced that hydrophilic modification might be a potential method to improve the transport flux of the PIM system. Full article

(This article belongs to the Special Issue Ion Transport in Membranes and Membrane Systems: Modelling and Experiment)

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26 pages, 4379 KiB

Open AccessArticle

Donnan Dialysis for Recovering Ammonium from Fermentation Solutions Rich in Volatile Fatty Acids

by Kayo Santana Barros, Mónica Carvalheira, Bruno Costa Marreiros, Maria Ascensão M. Reis, João Goulão Crespo, Valentín Pérez-Herranz and Svetlozar Velizarov

Membranes 2023, 13(3), 347; https://doi.org/10.3390/membranes13030347 - 17 Mar 2023

Viewed by 1569

Abstract

For the production of polyhydroxyalkanoates (PHA) using nitrogen-rich feedstocks (e.g., protein-rich resources), the typical strategy of restricting cell growth as a means to enhance overall PHA productivity by nitrogen limitation is not applicable. In this case, a possible alternative to remove the nitrogen [...] Read more.

For the production of polyhydroxyalkanoates (PHA) using nitrogen-rich feedstocks (e.g., protein-rich resources), the typical strategy of restricting cell growth as a means to enhance overall PHA productivity by nitrogen limitation is not applicable. In this case, a possible alternative to remove the nitrogen excess (NH₄⁺/NH₃) is by applying membrane separation processes. In the present study, the use of Donnan dialysis to separate ammonium ions from volatile fatty acids present in the media for the production of PHA was evaluated. Synthetic and real feed solutions were used, applying NaCl and HCl receiver solutions separated by commercial cation-exchange membranes. For this specific purpose, Fumasep and Ralex membranes showed better performance than Ionsep. Sorption of ammonium ions occurred in the Ralex membrane, thus intensifying the ammonium extraction. The separation performances with NaCl and HCl as receiver solutions were similar, despite sorption occurring in the Ralex membrane more intensely in the presence of NaCl. Higher volumetric flow rates, NaCl receiver concentrations, and volume ratios of feed:receiver solutions enhanced the degree of ammonium recovery. The application of an external electric potential difference to the two-compartment system did not significantly enhance the rate of ammonium appearance in the receiver solution. The results obtained using a real ammonium-containing solution after fermentation of cheese whey showed that Donnan dialysis can be successfully applied for ammonium recovery from such solutions. Full article

(This article belongs to the Special Issue Ion Transport in Membranes and Membrane Systems: Modelling and Experiment)

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14 pages, 2262 KiB

Open AccessArticle

Lactose Mother Liquor Stream Valorisation Using an Effective Electrodialytic Process

by Arthur Merkel, Matej Vavro, Ladislav Čopák, Lukáš Dvořák, Lilia Ahrné and Christian Ruchti

Membranes 2023, 13(1), 29; https://doi.org/10.3390/membranes13010029 - 26 Dec 2022

Cited by 3 | Viewed by 1972

Abstract

The integrated electrodialysis (ED) process supports valorisation of a lactose-rich side stream from the dairy industry, creating an important source of milk sugar used in various branches of the industry. This work focuses on the optimization of the downstream processes before the crystallization [...] Read more.

The integrated electrodialysis (ED) process supports valorisation of a lactose-rich side stream from the dairy industry, creating an important source of milk sugar used in various branches of the industry. This work focuses on the optimization of the downstream processes before the crystallization of lactose. The process line includes a pre-treatment and desalination by ED of the industrial waste solution of the lactose mother liquor (LML). The LML was diluted to 25% total solids to overcome hydraulic issues with the ED desalination process. Two different levels of electrical conductivity reduction (70% and 90%) of the LML solutions were applied to decrease the mineral components and organic acids of the LML samples. The ED performance parameters such as ash transfer rate (J), the specific capacity (C_F) of the ED and specific electric energy consumption (E) were determined and the influence of the LML solution on the monopolar ion-exchange membranes has been investigated. A higher degree of desalination is associated with higher electric energy consumption (by 50%) and lower specific capacity (by 40%). A noticeable decrease (by 12.8%) in the resistance of the anion exchange membranes was measured after the trials whereas the resistance of the cation exchange membranes remained practically unchanged. Any deposition of the alkaline earth metals on the membrane surface was not observed. Full article

(This article belongs to the Special Issue Ion Transport in Membranes and Membrane Systems: Modelling and Experiment)

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15 pages, 2175 KiB

Open AccessArticle

Correlation between Nafion Morphology in Various Dispersion Liquids and Properties of the Cast Membranes

by Ekaterina Yu. Safronova, Daria Yu. Voropaeva, Dmitry V. Safronov, Nastasia Stretton, Anna V. Parshina and Andrey B. Yaroslavtsev

Membranes 2023, 13(1), 13; https://doi.org/10.3390/membranes13010013 - 22 Dec 2022

Cited by 5 | Viewed by 1885

Abstract

Nafion is a perfluorosulfonic acid polymer that is most commonly used in proton-exchange membrane fuel cells. The processes of pretreatment and formation of such membranes strongly affect their properties. In this work, dispersions of Nafion in various ionic forms and dispersing liquids (ethylene [...] Read more.

Nafion is a perfluorosulfonic acid polymer that is most commonly used in proton-exchange membrane fuel cells. The processes of pretreatment and formation of such membranes strongly affect their properties. In this work, dispersions of Nafion in various ionic forms and dispersing liquids (ethylene glycol, N,N-dimethylformamide, N-methyl-2-pyrrolidone and isopropyl alcohol–water mixtures in different ratios) were obtained and studied. Membranes fabricated by casting of the various dispersions were also studied. The effect of the nature of the dispersing liquid and the counterion on the properties of Nafion dispersions, the morphology of the polymer in the dispersions and the characteristics of the membranes obtained from them has been shown. Based on the overall results, it can be concluded that the use of perfluorosulfonic acid dispersions in aprotic polar solvents is advisable for obtaining membranes by the casting procedure. This is because it provides optimal polymer morphology in the dispersion, which leads to the formation of films with good selectivity, mechanical and transport properties. The performed investigations show the relationship between the composition of dispersions, the morphology of the polymer and the properties of the membranes formed from them by the casting procedure. Full article

(This article belongs to the Special Issue Ion Transport in Membranes and Membrane Systems: Modelling and Experiment)

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18 pages, 2844 KiB

Open AccessArticle

Modeling the Conductivity and Diffusion Permeability of a Track-Etched Membrane Taking into Account a Loose Layer

by Vladlen S. Nichka, Semyon A. Mareev, Pavel Yu. Apel, Konstantin G. Sabbatovskiy, Vladimir D. Sobolev and Victor V. Nikonenko

Membranes 2022, 12(12), 1283; https://doi.org/10.3390/membranes12121283 - 19 Dec 2022

Cited by 6 | Viewed by 1657

Abstract

The microheterogeneous model makes it possible to describe the main transport properties of ion-exchange membranes using a single set of input parameters. This paper describes an adaptation of the microheterogeneous model for describing the electrical conductivity and diffusion permeability of a track-etched membrane [...] Read more.

The microheterogeneous model makes it possible to describe the main transport properties of ion-exchange membranes using a single set of input parameters. This paper describes an adaptation of the microheterogeneous model for describing the electrical conductivity and diffusion permeability of a track-etched membrane (TEM). Usually, the transport parameters of TEMs are evaluated assuming that ion transfer occurs through the solution filling the membrane pores, which are cylindrical and oriented normally to the membrane surface. The version of the microheterogeneous model developed in this paper takes into account the presence of a loose layer, which forms as an intermediate layer between the pore solution and the membrane bulk material during track etching. It is assumed that this layer can be considered as a “gel phase” in the framework of the microheterogeneous model due to the fixed hydroxyl and carboxyl groups, which imparts ion exchange properties to the loose layer. The qualitative and quantitative agreement between the calculated and experimental concentration dependencies of the conductivity and diffusion permeability is discussed. The role of the model input parameters is described in relation to the structural features of the membrane. In particular, the inclination of the pores relative to the surface and their narrowing in the middle part of the membrane can be important for their properties. Full article

(This article belongs to the Special Issue Ion Transport in Membranes and Membrane Systems: Modelling and Experiment)

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19 pages, 2854 KiB

Open AccessArticle

Electrodialysis with Bipolar Membranes for the Generation of NaOH and HCl Solutions from Brines: An Inter-Laboratory Evaluation of Thin and Ultrathin Non-Woven Cloth-Based Ion-Exchange Membranes

by Tamara León, Syed Abdullah Shah, Julio López, Andrea Culcasi, Lluis Jofre, Andrea Cipollina, José Luis Cortina, Alessandro Tamburini and Giorgio Micale

Membranes 2022, 12(12), 1204; https://doi.org/10.3390/membranes12121204 - 29 Nov 2022

Cited by 12 | Viewed by 2885

Abstract

The SEArcularMINE project aims to recover critical raw materials (CRMs) from brines from saltworks, thus facing a CRM shortage within Europe. To promote a fully circular scheme, the project valorises concentrated brines using electrodialysis with bipolar membranes (EDBM) to generate the required amounts [...] Read more.

The SEArcularMINE project aims to recover critical raw materials (CRMs) from brines from saltworks, thus facing a CRM shortage within Europe. To promote a fully circular scheme, the project valorises concentrated brines using electrodialysis with bipolar membranes (EDBM) to generate the required amounts of reactants (i.e., acids and bases). Regarding the performances of new non-woven cloth ion-exchange membranes (Suez): (i) an ultra-thin non-woven polyester cloth and (ii) a thin polypropylene cloth acting as the support structures were assessed. Additionally, the anion layer includes a catalyst to promote the water dissociation reaction. The effect of current density (100, 200, and 300 A m⁻²) on the performance of two combinations of membranes in an inter-laboratory exercise using 2 M NaCl was evaluated. According to statistical analysis ANOVA, there was an agreement on the results obtained in both laboratories. NaOH/HCl solutions up to 0.8 M were generated working at 300 A m⁻² using both combinations of membranes. Regarding the performance parameters, stack set-ups incorporating thin polypropylene membranes showed lower specific energy consumption (SEC) and higher specific productivity (SP) than ultra-thin polypropylene ones. Hence, for ultra-thin polypropylene membranes, SEC was reported to be between 2.18 and 1.69 kWh kg⁻¹_NaOH and SP between 974 and 314 kg m⁻² y⁻¹. Full article

(This article belongs to the Special Issue Ion Transport in Membranes and Membrane Systems: Modelling and Experiment)

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15 pages, 4437 KiB

Open AccessArticle

Electric Potential Profiles in a Model Single-Path Electrodialysis Unit

by Jan Pagáč, Petr Kovář and Zdeněk Slouka

Membranes 2022, 12(11), 1136; https://doi.org/10.3390/membranes12111136 - 12 Nov 2022

Cited by 1 | Viewed by 1460

Abstract

Electrodialysis is an important electromembrane separation process anticipated to play a significant role in developing future technologies. It produces ion-depleted and ion-concentrated product streams, intrinsically suggesting the formation of spatial gradients of relevant quantities. These quantities affect local conditions in an electrodialysis unit. [...] Read more.

Electrodialysis is an important electromembrane separation process anticipated to play a significant role in developing future technologies. It produces ion-depleted and ion-concentrated product streams, intrinsically suggesting the formation of spatial gradients of relevant quantities. These quantities affect local conditions in an electrodialysis unit. To investigate the spatial distribution of electric potentials, we constructed a model electrodialysis system with a single diluate channel that included ports for inserting reference electrodes measuring potential profiles. We validated our system and measurement methods in a series of control experiments under a solution flow rate of 250 µL/min and current densities between 10 and 52 A/m². The collected data showed that the electric potential in the diluate channel did not change in the vertical direction (direction of gravity force), and only minimally varied in the diluate channel center in the flow direction. Although we could not reconstruct the potential profile within ion-depleted layers due to the resolution of the method, we found appreciable potential variation across the diluate channel. The most significant potential drops were localized on the membranes with the developed ion-depleted zones. Interestingly, these potential drops abruptly increased when we applied current loads, yielding almost complete desalination. The increase in the resistance accompanied by relatively large fluctuations in the measured potential indicated the system transition into limiting and overlimiting regions, and the onset of overlimiting convection. Full article

(This article belongs to the Special Issue Ion Transport in Membranes and Membrane Systems: Modelling and Experiment)

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21 pages, 5600 KiB

Open AccessArticle

Separation of Chromium (VI), Copper and Zinc: Chemistry of Transport of Metal Ions across Supported Liquid Membrane

by Saik Su Goh, Mohd Rafatullah, Norli Ismail, Mahboob Alam, Masoom Raza Siddiqui and Eng-Keng Seow

Membranes 2022, 12(7), 685; https://doi.org/10.3390/membranes12070685 - 01 Jul 2022

Cited by 8 | Viewed by 2200

Abstract

Prior to applying supported liquid membranes (SLM) with strip dispersion for separation of chromium (VI), copper and zinc, suitable chemical settings were determined through solvent extraction and stripping studies. More than 90% of copper and zinc could be simultaneously extracted with at least [...] Read more.

Prior to applying supported liquid membranes (SLM) with strip dispersion for separation of chromium (VI), copper and zinc, suitable chemical settings were determined through solvent extraction and stripping studies. More than 90% of copper and zinc could be simultaneously extracted with at least 3% (v/v) di-(2-ethylhexyl)phosphoric acid (D2EHPA) at a feed equilibrium pH in the range of 3.5–5.0. For stripping, theoretical model equations derived and experimental results revealed that suitable concentrations of lower acid strength reagents can strip metals that have weaker metal-extractant bond without significantly stripping metals that have a stronger metal-extractant bond. Therefore, in a setup comprising three compartments separated by two SLM, we propose to fill the three compartments in the following order: feed—strip dispersion containing low acid strength reagent—strong acid. An organic phase with 4% (v/v) D2EHPA was used. From stripping experiments, 0.2 mol/L pH 3 citrate buffer, which resulted in the highest copper recovery (88.8%) and solution purity (99.0%), was employed as the low acid strength reagent while the strong acid consisted of 1 mol/L sulfuric acid. In 26 h, 99.1% copper was recovered by citrate buffer with 99.8% purity and 95.1% zinc was recovered by sulfuric acid with 98.4% purity. Chromium (VI), copper and zinc could be separated effectively using this separation strategy. Full article

(This article belongs to the Special Issue Ion Transport in Membranes and Membrane Systems: Modelling and Experiment)

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19 pages, 14130 KiB

Open AccessArticle

Economic Benefits of Waste Pickling Solution Valorization

by Rosa Gueccia, David Bogle, Serena Randazzo, Alessandro Tamburini, Andrea Cipollina, Daniel Winter, Joachim Koschikowski and Giorgio Micale

Membranes 2022, 12(2), 114; https://doi.org/10.3390/membranes12020114 - 19 Jan 2022

Cited by 4 | Viewed by 1683

Abstract

An integrated hybrid membrane process, composed of a diffusion dialysis (DD), a membrane distillation (MD) and a reactive precipitation unit (CSTR), is proposed as a promising solution for the valorization and onsite recycling of pickling waste streams. An economic analysis was performed aiming [...] Read more.

An integrated hybrid membrane process, composed of a diffusion dialysis (DD), a membrane distillation (MD) and a reactive precipitation unit (CSTR), is proposed as a promising solution for the valorization and onsite recycling of pickling waste streams. An economic analysis was performed aiming to demonstrate the feasibility of the developed process with a NPV of about EUR 40,000 and a DPBP of 4 years. The investment and operating costs, as well as the avoided costs and the benefits for the company operating the plant, were analyzed with an extensive cost tracking exercise and through face-to-face contact with manufacturers and sector leaders. A mathematical model was implemented using the gPROMS modelling platform. It is able to simulate steady state operations and run optimization analysis of the process performance. The impact of key operating and design parameters, such as the set-point bath concentration and the DD and MD membrane areas, respectively, was investigated and the optimal arrangement was identified. Finally, operating variables and design parameters were optimized simultaneously in a nonlinear framework as a tradeoff between profitability and environmental impact. We show how the integration of new technologies into the traditional pickling industry could provide a significant benefit for the issues of process sustainability, which are currently pressing. Full article

(This article belongs to the Special Issue Ion Transport in Membranes and Membrane Systems: Modelling and Experiment)

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