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Research area 09 - ENGINEERING SCIENCES, 09-201 - Heat and mass exchange processes

KeywordsMembranes: ion-exchange, reverse osmosis, nanofiltration, ultrafiltration, track; electrodialysis; baromembrane processes; separation

Annotation
Development and active use of membrane technologies is a necessary condition for the safe and sustainable development of society, in particular, for providing the population with water and energy [Elimelech M., Phillip W.A. The future of seawater desalination: energy, technology, and the environment // Science. – 2011. – V. 333. – P. 712-717; Logan B.E., Elimelech M. Membrane-based processes for sustainable power generation using water // Nature. – 2012. – V. 488. – P. 313-319]. Currently, one of the most important problems of membrane technologies, which hinder their wider use for a sea and other natural waters desalination, neutralization and processing industrial and domestic wastewater, obtaining chlorine and soda etc., is salt deposition on the surface and in the volume of membranes. An effective solution to this problem can be the use of an approach (metathesis electrodialysis, selective electrodialysis), where processing of solutions is organized in such a way as to avoid the concentration of multiply charged cations and anions in the same solution. The most important step in this approach is the separation of singly and multiply charged ions during their transport through membranes. Note that the solution of this problem is also necessary for the removal of lithium from sea and industrial waters. The cardinal problem here is that an increase in the selectivity of membrane separation is accompanied by a decrease in their permeability/productivity and vice versa. The aim of the project is to develop a new process for separating single and multiply charged ions, providing significant selectivity with sufficiently high productivity. The idea is to apply an electric potential and pressure gradient to the membrane simultaneously. The electric force should act on the competitive ions in the direction opposite to their convective transport. Since the electric force acting on an ion is proportional to its charge, the transport of a multiply charged ions will be more impeded. Taking into account the fact that in membranes with nanoscale pores with charged walls the retention rate of multiply charged ions is essentially greater (due to electrostatic interaction and dielectric exclusion), it is expected that in electro-baromembrane processes it will be possible to achieve almost complete elimination of multiply charged ions transport through the membrane. In the literature, the use both of ion-exchange and nanofiltration/ultrafiltration membranes is known in electrodialysis as a way to effective separation of organic acids and nutrients; as well, the application of an electric field during the transport of ions and water under the action of a pressure drop is known as a way to increase the productivity and selectivity of baromembrane processes. However, the process proposed in this project, where the electric field is used to reduce the rate of transport of multiply charged ions under the action of a pressure drop, is novel. It is planned to consider several promising schemes based on the simultaneous application of electric potential and pressure gradients. Commercially available ion-exchange, reverse osmosis, nanofiltration, ultrafiltration and track membranes will be used. In recent publications, the high efficiency of track-etched membranes with cylindrical pores for electrodialysis separation of ions depending on their charge and ion size has been proven [Wang P., Wang M., Liu F., Ding S., Wang X., Du G., Liu J., Apel P., Kluth P., Trautmann C., Wang Y. Ultrafast ion sieving using nanoporous polymeric membranes // Nature Communications. – 2018. – V. 9 (1). – Art. № 569; Wen Q., Yan D., Liu F., Wang M., Ling Y., Wang P., Kluth P., Schauries D., Trautmann C., Apel P., Guo W., Xiao G., Liu J., Xue J., Wang Y. Highly selective ionic transport through subnanometer pores in polymer films // Advanced Functional Materials. – 2016. – V. 26 (32). – P. 5796-5803]. For the first time, in this project, track-etched membranes with cone-shaped pores with charged walls will be used for competitive ions separation purposes. The narrow part of the pore will represent only an insignificant barrier for the transport of singly charged ions, but very significant for multiply charged ones. The project involves experimental and theoretical studies to clarify the details of the separation mechanism (in particular, the effect of simultaneous application of potential and pressure gradients, coupling of ion transport through the membrane and the diffusion layer) and to search for the optimal combination of pore parameters to achieve efficient ion separation by charge. Mathematical models based on the Nernst-Planck-Poisson and Navier-Stokes equations will be developed for each type of processes. Simulation will allow one to find theoretical optimal parameters of the pores, which ensures efficient ion separation with high process productivity. The obtained results will be verified using the experiment.

Expected results
A new hybrid electro-baromembrane process will be developed to separate single- and multiply charged ions. It is expected that the degree of separation of ions will be higher than in standing alone electrodialysis or baromembrane processes, and the separation performance (values of ion and water fluxes) should remain sufficiently high. The effect is based on the fact that the external electric field produces a significantly greater force on multiply charged ions as compared to singly-charged ones. The proposed process is not described in the literature. In the course of the project, a series of membranes will be investigated including ion-exchange, reverse osmosis, nanofiltration, ultrafiltration and track membranes. For the first time, this study will reveal the relationships, which govern the transport of ions and water through a membrane under conditions of simultaneous application of an external electric field and a pressure drop. Mathematical modeling performed on the basis of the fundamental Nernst-Planck-Poisson-Navier-Stokes equations will provide a tool for theoretical optimization of the process under consideration and allow obtaining the parameters of an “ideal” pore (pore radius, its geometry, charge density of the pore walls) and the optimal ratio between the applied electrical field and pressure gradient. After that, several membranes with parameters close to the theoretical ones will be prepared, and the model predictions will be verified. The proposed process can be used as one of the stages of complex processing of natural waters or industrial solutions. The application of the proposed electro-baromembrane process will allow one to obtain a dilute solution containing only singly charged ions and a more concentrated solution with predominantly doubly and triply charged ions. The absence of multiply charged ions in a dilute solution (softened water) greatly facilitates its further processing (for example, using reverse osmosis, electrodialysis, and/or electrodeionization) in order to obtain pure/highly pure water and a concentrate. In some cases, the obtained softened water may be the final product (drinking water, water for feeding boilers). A more concentrated solution (the volume of which will be several times less than the volume of the initial solution) can be processed by metathesis electrodialysis/selectrodialysis for separation of salts and their possible crystallization and evaporation (zero liquid discharge (ZLD) systems). Possible applications of this kind of processes are as follows: production of drinking water from sea and other natural waters, sanitation and processing of industrial, domestic wastewater and mine water, extracting valuable components (Li+, nutrients, biologically active substances, heavy and rare earth metals etc.), preparing water for power plants and irrigation systems. Such a process may be of considerable interest for the technology of lithium extraction from seawater and industrial solutions at the stage of singly charged ions separation from the initial solution. It is also possible that the process being developed will be effective in the separation of sodium and lithium ions from their mixed solutions, since the mobility of these ions in an electric field differs by a factor of 1.3. In the course of the project, studies on the lithium separation efficiency from mixed solutions containing this ion together with sodium and potassium ions will be conducted. During the project, publication of 9 articles in peer-reviewed journals indexed in the Web of Science Core Collection or Scopus databases is expected. Among them 4 articles will be published in Q1 journals, including one review article.

Annotation of the results obtained in 2021
The idea of the electro-baromembrane method of ion separation is that the competing ions (K+ and Li+ cations in the considered cases) are transported through the membrane pores under the action of two driving forces: the electric potential gradient and the pressure gradient. The forces are directed in opposite directions. It is possible to choose such values of the driving forces at which the sum of these forces is zero for one of the competing ions. Then the transport of this ion becomes zero, while the other competing ion continues to be transported through the membrane at a high speed. Very high selectivity for the separation of two ions can be achieved. In this process, membranes with a pore size of 30-100 nm are mainly used. In most of the experiments, we used track-etched membranes, which have pores of almost the same size and shape (close to cylindrical). However, for the separation of certain types of ions, auxiliary membranes are also required. At the stage of 2021, an auxiliary anion exchange membrane was added to the electrochemical cell. Experiments on the K+ and Li+ ions separation were carried out using a track-etched membrane (conventionally named as No. 811, JINR, Dubna) with a pore diameter of 40 nm and using the two above-described configurations of an electro-baromembrane cell. It was found that the values of the competing ions flux densities, the selective permeability coefficient and energy consumption for the two configurations do not differ within the experimental error. However, as indicated above, the new configuration has the advantage – the anion exchange membrane prevents the loss of the target product (separated cations). It was found that the three modes of cell operation, differing in the ratio of driving forces, may be the most effective. Mode 1 corresponds to the case where the electric driving force is dominant and the pressure gradient is relatively small. In this case a minimum (ideally - zero) flux of a less mobile ion (Li+) is achieved, and a more mobile one is transported in the direction of the electric force action. This case is characterized by the highest separation rate (the fast ion (K+) is separated) and by the maximum coefficient of selective permeability P. Mode 2 corresponds to the case where both driving forces are close in absolute value: for a more mobile ion, electromigration transport, and for a less mobile ion, convective transport prevails. The fluxes of cations to be separated have opposite signs: one solution can be simultaneously enriched in ion 1 and the second solution in ion 2. Mode 3 – is the case where the flux of a more mobile ion (K+) has a minimum (zero) value, and a less mobile ion is selectively transported through the membrane (Li+). In this case, the most valuable ion (Li+) can be separated from the mixture, but the value of the coefficient P is less than in the case of Mode 1. The question of which of the modes is the most cost-effective requires additional research. A series of experiments were carried out using track-etched membranes (conventionally named as M100; JINR, Dubna) with a nominal pore diameter of 100 nm, the porosity of about 8%, as well as using membranes made of porous anodic aluminum oxide with a pore diameter of 25-30 nm, the porosity of about 13% (Krasnoyarsk Scientific Center RAS). The values of ion fluxes through the M100 membrane turned out to be close to the corresponding fluxes through membrane No. 811 with a pore diameter of 40 nm, in the case where the same modes of the separation process were used. However, the sum of the cation transport numbers turned out to be noticeably lower than in the case of membrane No. 811: 0.75 and 0.93, respectively, for M100 and No. 811. This result was expected due to the larger pore diameter in M100. Thus, the current efficiency in the case of a membrane with a pore diameter of 40 nm turned out to be higher, which determines lower energy consumption when using this membrane. The study of membranes made of porous anodic alumina showed that under experimental conditions this membrane exhibits anion-exchange properties. Thus, the membrane of porous anodic alumina turned out to be unsuitable for the separation of cations, but it is very likely that it can effectively separate anions, since the transport number of Cl– ions in the membrane is about 0.98. The task of separating anions was not set in the application for this project; however, this task is of scientific and practical interest and will be completed by us in the event of a continuation of the project. The separation of a mixture simulating natural mine water with a relatively high content of lithium ions (0.05 M LiCl, 0.06 M KCl, 0.05 M NaCl, and 0.04 M CaCl2 solution) was carried out at a voltage of 0.5 V and at three values of the pressure drop. It was found that, under the chosen experimental conditions, the flux density of lithium ions through the track-etched membrane was about 0.91±0.16 mol/(m2∙h). However, trace amounts of calcium, potassium and sodium were also found in the receiving chamber; the coefficient of selective permeability of lithium with respect to other cations was close to 10 for each of them. Thus, the separation of lithium ions from a mixed solution occurs at a sufficiently high rate and selectivity and with low energy consumption (about 0.03 kW∙h/mol, excluding the contribution of auxiliary membranes). A two-dimensional steady-state model has been developed based on the Navier-Stokes, Nernst-Planck, and Poisson equations. The model makes it possible to describe the transport of ions (K+, Li+, Cl−) and water in the pore of the track-etched membrane, taking into account the surface charge on the pore walls. Two pore geometries are considered: cylindrical pore and hourglass geometry. The model qualitatively correctly describes the dependence of the fluxes of competing ions on pressure and voltage; however, it gives underestimated values of the transport numbers of cations in the membrane: the sum of the transport numbers of potassium and lithium is 0.55 in the case of a cylindrical pore and 0.59 in the case of an hourglass geometry. Accordingly, the contribution of the electromigration ion transport turns out to be underestimated in comparison with the experiment. A possible reason is that the electroosmotic transport of ions is not taken into account in the solution of the problem. This effect will be taken into account in 2022 if the project is continued. The improvement of the one-dimensional steady-state model (of the “solution-diffusion model” type) of competitive ion transport, developed at the stage of 2019, was also carried out. It was shown that the type of space charge distribution inside the surface layer not only affects the selectivity of similarly charged cations separation, but also the onset of precipitation (for example, CaSO4) at the membrane surface: the higher the selectivity of the membrane with respect to the transport of sodium ions, the higher the risk of precipitation with the participation of calcium ions. Using the model, it will be possible to further optimize the charge distribution in the surface layer in such a way as to obtain a sufficiently high selectivity with respect to the transport of singly charged cations and, at the same time, avoid precipitation at the surface. The obtained experimental and theoretical results show that the values of the selectivity coefficient for the separation of K+ and Li+ cations and the flux of a preferably permeable ion are at the level of the best world achievements. At the same time, the energy consumption for the separation process turned out to be unprecedentedly low. These results can be assessed as significantly superior to the world level in the field of separation of similarly charged ions. To this, we can add that (as is known) the separation of singly charged ions is a much more difficult task in comparison to the separation of singly and multiply charged ions, where researchers have already made significant progress both when using the method of electrodialysis and nanofiltration. The low energy consumption in the developed method can be explained by the fact that both in the electro- and in the baromembrane processe the selectivity to ions of a certain type is achieved due to a thin layer deposited on the membrane surface – a barrier for both competing ions, and this barrier is higher for the ion to be retained. In the electro-baromembrane process, a fundamentally different principle of retention is used: no barriers are placed in the path of ions, they move through relatively large pores (20-100 nm, not 1-5 nm as in ion-exchange and nanofiltration membranes); ions are retained by equalizing absolute values of two oppositely directed driving forces - electrical and mechanical. In addition, the intense selective transport of ions is associated with the appearance of significant concentration gradients (concentration polarization). In the case of the developed electro-baromembrane method with oppositely directed electromigration and convective fluxes, the concentration polarization is much lower, since the impediment in coion transport is not so significant, and the convective transport through the membrane mixes the depleted diffusion layer adjacent to the membrane. The electro-baromembrane method seems extremely promising to use in technologies for the extraction of valuable/harmful components from natural and industrial solutions. One such technology is the separation of lithium from natural brines (mine waters). High selectivity and significant flux densities of the extracted components at an unprecedented low energy consumption make the electromembrane method very attractive. The rapidly growing demand and rising prices for lithium make it possible to predict the demand for new efficient methods of its extraction. The above information was, in particular, brought to the attention of the participants of the conference "Diversification and cooperation of defense industry enterprises in the interests of the mineral resource complex" within the framework of the International military-technical forum "Army-2021", chaired by V. Yazev, President of the Nonprofit Partnership for mining industries of Russia, Chairman of the National Committee of the World Petroleum Council. The results of the project were published in two articles in the highly-rated journal J. Membr. Sci. (Q1, IF =8.742), which formally corresponds to the 4 publication indexed in Scopus/WoS. The results are also presented at 3 conferences. A patent for an invention and a certificate of registration of a computer program were granted. Scientific designs carried out within the framework of the project were awarded four medals at international forums, exhibitions and salons of inventions. Information about the project is posted in the mass media (https://www.youtube.com/watch?v=nqQ7w9GApYE, http://rusmembrane.net/Files_to_dw/Proekt-19-19-00381.pdf; https://www.kubsu.ru/ru/fhivt/proekt-rossiyskogo-nauchnogo-fonda-19-19-00381-konkurentnyy-perenos-ionov-v-elektro).

Publications

1. Butylskii D.Yu., Pismenskaya N.D., Apel P.Yu., Sabbatovskiy K.G., Nikonenko V.V. Highly selective separation of singly charged cations by countercurrent electromigration with a track-etched membrane Journal of Membrane Science, Том 635, номер статьи 119449 (year - 2021) https://doi.org/10.1016/j.memsci.2021.119449

2. Evdochenko Е., Kamp J., Dunkel R., Nikonenko V.V., Wessling M. Charge distribution in polyelectrolyte multilayer nanofiltration membranes affects ion separation and scaling propensity Journal of Membrane Science, Том 636, номер статьи 119533 (year - 2021) https://doi.org/10.1016/j.memsci.2021.119533

3. Butylskii D.Yu., Nikonenko V.V., Mareev S.A. Высокоселективное разделение однозарядных катионов методом противоточной электромиграции Физико-химические процессы в конденсированных средах и на межфазных границах (ФАГРАН-2021): материалы IX Всероссийской конференции с международным участием, посвященной 100-летию со дня рождения Я.А. Угая, 4-7 октября 2021 г., г. Воронеж, с. 444-446 (year - 2021)

4. Kislyi A., Butylskii D., Mareev S., Nikonenko V. Modeling of selective separation of singly charged cations by countercurrent electromigration International conference "Ion transport in organic and inorganic membranes-2021": Conference Proceedings, 20-25 сентября 2021 г., г. Сочи, с. 143-144 (year - 2021)

5. Nikonenko V., Butylskii D., Mareev S., Gil V., Chuprynina D., Apel P. Selective extraction of lithium from aqueous solutions by countercurrent electromigration International conference "Ion transport in organic and inorganic membranes-2021": Conference Proceedings, 20-25 сентября 2021 г., г. Сочи, c. 222-223 (year - 2021)

6. - Способ разделения компонентов раствора -, 2753404 (year - )

7. - Моделирование электробаромембранного процесса разделения однозарядных ионов -, 2021613415 (year - )

8. - Проект Российского научного фонда 19-19-00381 «Конкурентный перенос ионов в электро-баромембранных процессах» Официальный сайт ФГБОУ ВО "Кубанский государственный университет", - (year - )

9. - Проект РНФ № 19-19-00381, руководитель В.В. Никоненко. Конкурентный перенос ионов в электро-баромембранных процессах Официальный сайт Российской мембранной сети, - (year - )

10. - Утро.Кубань, выпуск от 03.03.2021, 06:35. Телеканал "Россия. Кубань", см. с 1:30. (year - )

Annotation of the results obtained in 2019
The project is aimed at developing a new process for the separation of singly and multiply charged ions, which provides significant selectivity with high performance. The idea is to simultaneously apply gradients of electric potential and pressure across the membrane, and the electric force should act on the ions to be separated in the direction opposite to their convective transport. The separation is achieved due to the fact that the rate of electric transport of the ion is proportional to its mobility, and the rate of convective transport is the same for all ions. An additional factor is that, in membranes with nano-sized pores having charged walls, the concentration of a particular type of ion is strongly dependent on its charge. It is expected that it will be possible to achieve significantly higher separation parameters compared with those known in the literature by controlling the separation of ions by using the above-mentioned levers (potential and pressure gradients, pore size and charge). In accordance with the plan presented in the Application, the first year of the project is mainly devoted to the characterization of membranes of different nature (ion-exchange, track, nano- and / or ultrafiltration) in order to determine their ability to selectively separate singly and doubly charged ions. 16 membranes are selected for characterization: ion-exchange membranes [domestic heterogeneous MK-40 and MA-41; Japanese homogeneous membranes Neosepta, cation-exchange CMX and anion-exchange AMX (Astom company), as well as cation-exchange membrane CIMS selective for the transfer of singly charged cations (also manufactured by Astom)]; Chinese cation-exchange CJMC-3 and CJMC-5 and anion-exchange CJMA-3 and CJMA-7 (manufactured by Hefei Chemjoy Polymer Material Co. Ltd); nanofiltration membranes manufactured by Vladipor (porous polymer films on a polyamide (OPMN-P) or cellulose (ANM-P) basis), as well as a series of track membranes produced by the Joint Institute for Nuclear Research in Dubna. Nanofiltration membranes are kindly provided by Prof. S.I. Lazarev, track membranes are kindly provided by Prof. P.Yu. Apel. Selected membranes are thoroughly characterized. The study of the surface (SEM and optical microscopy) and structure (IR-spectroscopy) is conducted; the pore size is estimated; the concentration dependences of electrical conductivity, diffusion permeability and transport numbers in binary NaCl, CaCl2, Na2SO4 solutions and, for some cases, in ternary (mixture NaCl + CaCl2) solutions were obtained; current-voltage characteristics and chronopotentiograms of membranes were measured; estimates of the selective transport of Na+ and Ca2+ counterions across cation-exchange, as well as Cl– and SO42– across anion-exchange membranes are made. It is shown that surface modification can effectively influence the transport selectivity. The modification of the Chinese anion-exchange membranes CJMA-7 with a perfluorocarbon polymer film can decrease the transport of Na+ ions twofold and the transport of Ca2+ ions fourfold. In addition to characterizing the above-mentioned membranes, preliminary experiments to separate ions of the same charge sign using a track membrane are carried out under conditions when two forces act on the ions in membrane pores simultaneously: electrical (due to the imposed electric potential gradient) and mechanical (caused by the applied pressure gradient). Potassium and rhodamine ions were chosen as competing ions, whose diffusion coefficients differ fivefold. It is shown that at high voltages and the absence of a pressure drop, both cations are transferred through the pores of the track membrane. However, with an increase in the pressure gradient directed opposite to the cation flux in the electric field, the rhodamine transport rate decreases faster than the potassium transport rate. It is possible to choose such pressure gradient that the transport of potassium ions takes place, but the rhodamine transport is absent. These works were not planned in the Application, but since the project is aimed specifically at achieving the effective separation of ions by simultaneously applying potential and pressure gradients, we considered it appropriate to start these studies as early as possible in order to get significant results before the project ends. Another part of the research includes theoretical estimates of the velocities of ions in the membrane pores under the influence of potential and pressure gradients. Theoretical estimates of the rates of electric and convective transport of cations and anions through the membranes pores with a radius of tens of nanometers to tens of microns when applying gradients of the electric potential and pressure are carried out. Close to optimal pore sizes, voltages and pressure drops across the membranes, at which high separation coefficients and flows are achieved, are found. A one-dimensional stationary model of ion transport has been developed within the framework of the Theorell-Meyer-Sivers concept of a membrane as a homogeneous system containing a porous matrix with charged fixed groups and an aqueous solution with mobile ions, whose charge compensates for the charge of the matrix. The Nernst-Planck and Poisson equations, as well as the Navier-Stokes equations, are used. The model is realized within COMSOL. It is theoretically shown that the deposition of several polymer layers with an alternating charge of fixed ions on a large porous slightly charged substrate (ultrafiltration membrane) leads to a slight increase in the retention of singly charged ions (Na+), but to a multifold retention of doubly charged Ca2+ ions. It is established that with an increase in the number of layers, the separation coefficient of singly and doubly charged ions increases, but the hydraulic resistance of the membrane also increases. The model allows theoretically optimizing the number of alternating surface layers. It is shown that if the number of alternating layers exceeds four, a further increase in their number hardly causes an increase in the degree of separation. One article is published in the journal Membranes MDPI (Q2, IF = 3.28). One article is submitted to Journal of Membrane Science (Q1, IF = 7.015). The results of the project are presented at 4 conferences: 3 international and 1 Russian conferences (including 1 keynote lecture and 2 oral presentations).

Publications

1. Evdochenko Е., Kamp J., Femmer R., Xu Y., Nikonenko V., Wessling M. Unraveling the effect of charge distribution in a polyelectrolyte multilayer nanofiltration membrane on its ion transport properties Journal of Membrane Science, Том 611, номер статьи 118045 (year - 2020) https://doi.org/10.1016/j.memsci.2020.118045

2. Sarapulova V., Shkorkina I., Mareev S., Pismenskaya N., Kononenko N., Larchet C., Dammak L., Nikonenko V. Transport characteristics of Fujifilm ion-exchange membranes as compared to homogeneous membranes AMX and CMX and to heterogeneous membranes MK-40 and MA-41 Membranes, Том 9, выпуск 7, номер статьи 84 (year - 2019) https://doi.org/10.3390/membranes9070084

3. Butylskii D., Chuprynina D., Xu T., Pismenskaya N. Membrane specific permselectivity in mixed solutions Ion transport in organic and inorganic membranes-2019: Conference Proceedings, Sochi, 20-25 May 2019, с. 75 (year - 2019)

4. Butylskii D., Mareev S., Chuprynina D., Xu T., Jiang C., Pismenskaya N., Nikonenko V. Competitive transport of sodium and calcium ions through cation-exchange membranes International conference PERMEA 2019 Membrane Conference of Visegrád Countries, 26-29 августа 2019 года, Венгрия, Будапешт, с. 96 (year - 2019)

5. Lemay N., Mikhaylin S., Mareev S., Butylskii D., Nikonenko V., Bazinet L. How demineralization by electrodialysis under high frequency pulsed electric field can be more efficient than in continuous current condition? International conference PERMEA 2019 Membrane Conference of Visegrád Countries, 26-29 августа 2019 года, Венгрия, Будапешт, с. 97 (year - 2019)

6. Nikonenko V. Electroconvection in membrane systems: experiment, modelling and applications to electrodialysis 13th International Symposium on Electrokinetics, Cambridge, MA, United States, June 12-14, 2019, - (year - 2019)

7. Nikonenko V.V., Mareev S.A., Butylskii D.Yu., Chuprynina D., Lemay N., Bazinet L., Mikhaylin S. Конкурентный перенос ионов натрия и кальция через катионообменные мембраны. Влияние параметров электрического поля Мембраны-2019: Сборник тезисов докладов, 21-25 октября, г. Сочи, с. 101-102 (year - 2019)

8. Shkorkina I., Sarapulova V., Pismenskaya N. Study of transport properties of Fujifilm ion exchange membranes fabricated via electrospinning method International conference PERMEA 2019 Membrane Conference of Visegrád Countries, 26-29 августа 2019 года, Венгрия, Будапешт, с. 55 (year - 2019)

9. Skolotneva E., Mareeva D., Mareev S., Larchet C., Dammak L., Nikonenko V. Applicability of approximate equations for calculation of the chronopotentiometric transition time in membrane systems with a diffusion layer of finite length Ion transport in organic and inorganic membranes-2019: Conference Proceedings, Sochi, 20-25 May 2019, с.320-321 (year - 2019)

10. - Конкурентный перенос ионов через ионообменную мембрану при протекании постоянной плотности тока -, 2019660025 (year - )

11. - Расчет транспортных и электрохимических характеристик ионообменных мембран -, 2019661281 (year - )

Annotation of the results obtained in 2020
The project is aimed at developing a fundamentally new method for separating ions of the same charge sign. This task is very relevant today: the extraction of valuable ionic components (such as Li+ ions) or harmful impurities (for example, heavy metal ions) from natural and industrial wastewater requires the creation of effective and inexpensive methods. Membrane methods have proven to be environmentally and economically viable. Currently, two groups of membrane methods are used to separate ions: in one of them, the driving force is a gradient of an external electric field and mainly ion-exchange membranes (IEM) are used. In the second group, the driving force is set by the imposition of a pressure gradient and nanofiltration (NF) membranes are used. In both cases, using membranes whose surface is modified by layer-by-layer method with layers carrying oppositely charged fixed ions is considered very promising. Membranes of this structure make it possible to effectively separate ions of the same charge sign and different valence: singly charged ions more easily overcome the barriers created by fixed ions in separate layers. At the same time, such membranes are ineffective in separating ions of the same valence, for example, Li+ and K+. In this project, a new method is being developed. In this method, for the first time, separation occurs under the action of two simultaneously superimposed driving forces - an electrical force and a hydrostatic pressure force. The forces are directed oppositely. For example, if a pressure force is applied to a mixed solution containing Li+ and K+ ions, this will cause convective transport of the solution through the pores of the membrane, with both ions moving through the membrane at the same velocity. Then, if an electric field is applied to the membrane acting on the ions in the direction opposite to their convective transfer the movement of both ions will slow down. In this case, the velocity of potassium ions with a higher electrical mobility will slow down to a greater extent than lithium. One can choose such an electric field voltage at which potassium ions will stop completely, and lithium ions will continue to move. The aim of the project is the practical implementation of the above idea by creating and researching a laboratory setup that executes the separation process for several specific cases. At the first stage (2019), theoretical and experimental evaluations were carried out. Based on them, it was shown that the mentioned electro-baromembrane separation process can be carried out using membranes with both narrow and wide pores. Moreover, membranes with relatively wide pores should have the advantage expressed in ions experiencing less resistance from the matrix when being transferred through them. Based on this, in 2019, the characterization of large-pore IEM, NF and track membranes in NaCl, Na2SO4 and CaCl2 solutions was carried out. On this basis, the most promising samples for the implementation of the electro-baromembrane ion separation were selected. Trial tests have confirmed the possibility of the efficient separation of ions of the same charge sign and equal valence (for example, potassium and rhodamine). In 2020, experimental and theoretical study on the process of the electro-baromembrane separation of ions was continued. The main attention was paid to the separation of two pairs of cations (potassium and rhodamine, as well as potassium and lithium). Such choice was made due to the fact that the separation of ions occurs due to the difference in the values of their electrical mobility. The mobility of rhodamine cations is almost 10-fold less than the mobility of potassium cations. In the case of potassium and lithium, the difference in mobility is not so significant (the mobility of potassium is approximately 2 times as great), but this pair is of great practical interest. Based on the studies carried out in 2019, a track membrane was picked for futher investigation. The membrane was produced at our request at the Joint Institute for Nuclear Research (Dubna) by the group of Professor P.Yu. Apel and kindly provided to us for research. The membrane is made of polyethylene terephthalate (PET), the pore diameter estimated by SEM imaging of the surface is 40 nm, the thickness is 10 μm. The pore shape is close to cylindrical; the walls of the pores carry a small (compared to ion-exchange membranes) negative fixed charge, the ion-exchange capacity is 0.064 mmol/g of wet membrane due to the presence of the carboxyl groups. The separation cell and measuring system have been improved. In particular, Luggin capillaries connected to silver chloride electrodes were built into the cell to measure the potential drop across the track membrane together with adjacent diffusion layers. This makes it possible to correlate the achieved separation parameters with the characteristics of the track membrane without taking into account the phenomena occurring on auxiliary ion-exchange membranes and polarizing electrodes. The effective transfer numbers of competing counterions were measured by measuring the rate of change in the concentration of competing ions in one of the chambers of the cell (Hittorff method). The measurements were carried out at different set potential drops across the membrane and different pressure drops. In one of the series of measurements, the voltage across the track membrane was fixed and the pressure drop changed; in another series, the pressure was fixed and the voltage changed. The highest ever values of the permselectivity coefficient for different ions, P12, of two like charged ions (indicated by indices 1 and 2) and the flux density of the predominantly transfered ion, j1, were achieved. The P12 coefficient was defined as the ratio of fluxes (transport numbers) of competing ions divided by the ratio of their concentrations. In the case of the potassium and rhodamine separation, two pairs of values were obtained: P12=200 and j1=7.2 mol/m2/h, as well as P12=150 and j1=22.7 mol/m2/h; the first pair was obtained at 1 V and 0.12 bar, the second pair at 2 V and 0.1 bar. In the case of the potassium and lithium separation: P12=36 and j1=4 mol/m2/hour, as well as P12=5 and j1=11 mol/m2/hour; the first pair was obtained at 0.5 V and 0.28 bar, the second pair was obtained at 1 V and 0.12 bar. In separation technology, there is a principle, first proposed by Robeson [Robeson, L.M. The upper bound revisited. J. Membr. Sci. 2008, 320, 390–400] for the separation of gases and further extended to the separation of ions in solution [Park, H.B.; Kamcev, J.; Robeson, L.M.; Elimelech, M.; Freeman, B.D. Maximizing the right stuff: The trade-off between membrane permeability and selectivity, Science 2017, 356, eaab0530]. According to this principle, there is a permselectivity - ionic flux trade-off: the persuit to increase selectivity inevitably leads to a decrease in the flux density of the preferentially transfered component. T. Xu's group has published a graph based on well-known experiments [Ge, L .; … Xu, T. Monovalent cation perm-selective membranes (MCPMs): New developments and perspectives. Chin. J. Chem. Eng. 2017, 25, 1606–1615], in which the straight line limits the region where the values of the pairs (Р12, j1) found experimentally are located. Above this line lies the “attractive” region, which did not yet contain experimental pairs at the time of publication. Three of the four pairs we obtained by our group (P12, j1) fall into the "attractive" area, the fourth pair lies near the upper border. Two mathematical models to describe the electro-baromembrane process of ion separation have been developed. One of them is one-dimensional, the other is two-dimensional. The models are based on the Nernst-Planck equations with a convective term. The convective transfer rate is determined using the Hagen-Poiseuille equation. Since the pore radius is much larger than the double layer thickness (about 2 nm for the used solutions with the concentration of about 0.1 mol/L), the models used the condition of local electroneutrality and neglected the electroosmotic transfer as compared to the forced flow. It is shown that the 2D model can be with high accuracy replaced by the 1D model. It was found that, in a first approximation, the cation flux density through the track membrane linearly depends on the applied voltage and pressure drop. Satisfactory quantitative agreement between the calculations and experimental data was established using three adjustable parameters: the transport numbers of competing counterions (T1 and T2) and the pore diameter d. In all cases, the effective pore diameter was defined as 22 nm, which is less than the 40 nm pore diameter found from SEM images, but rather close to the d=29 nm value found from the experimentally determined membrane hydraulic permeability. As calculations show, concentration polarization at the track membrane is insignificant, since the electromigration transport numbers in the membrane only slightly differ from their values in the external solution. Thus, the transport number of potassium in the membrane in the case of the potassium-rhodamine system found by fitting calculations to the experiment is 0.65. Such slight exceeding as compared to the external solution (where this value is about 0.50) is explained by the presence of a weak negative charge of the pore walls. At the same time, the highest values of current densities used in the experiment are close to the limiting current density on auxiliary ion-exchange membranes used in the cell. Thus, it is precisely the achievement of the limiting current density on the auxiliary ion-exchange membranes that determines the maximum values of the flux densities of the selectively transferred ion in the proposed method. A further increase in the current density will lead to the same undesirable effects as in the case of electrodialysis: an increase in the resistance of the membrane system and energy consumption, as well as an increase in water splitting at the IEM/solution interface. An important difference between the electro-baromembrane method and electrodialysis is that in electrodialysis, when the limiting current density is applied, the selectivity of the transfer of individual ions is completely lost. In the proposed method, the coefficient of selective permeability depends on the ratio between the electric force and the force of pressure applied to the ions, but does not depend on the values of the forces themselves. Thus, the main result of the second year of the project is the proof of viability and high competitiveness of the new electro-baromembrane separation process. It is shown that the new method allows achieving the highest ever values of the selective permeability coefficient and the flux density of a selectively transferred ion. At the same time, energy consumption per 1 mole of the transferred ion turned out to be unprecedentedly low. The main course of work during the 3rd and last stage of the project is preliminary optimization of the electro-baromembrane process of the ion separation, as well as an attempt to solve the specific problem of extracting lithium ions from a model solution of natural water enriched with this ion. The nature of the influence of the most important factors on the characteristics of the process (coefficient of selective permeability, flux density of predominantly transfered ion and energy consumption) will be clarified. These factors include (1) the membrane pore diameter, (2) the nature of the dominant driving force, and (3) the configuration of the electro-baromembrane cell. The results obtained at the 2020 stage were published in 3 articles (Q1 and Q2 journals). One article has been submitted to the Journal of Membrane Science (Q1, IF 7.183); a patent application for an invention has been filed. Результаты выполнения проекта доложены на 3 международных конференциях: ICOM 2020 (Лондон), MELPRO 2020 (Прага) и международной конференции «Membrane Process Modeling», посвященной 60-летию профессора А.Н. Филиппова (Москва) (представлены 2 устных доклада и 1 ключевая лекция). The results of the project were reported at three international conferences: ICOM 2020 (London), MELPRO 2020 (Prague) and International web conference «MEMBRANE PROCESS MODELING» in celebration of the 60th anniversary of Professor A.N. Filippov (Moscow) (2 oral presentation and 1 keynote lecture).

Publications

1. Kislyi A.G., Butylsky D.Yu., Mareev S.A., Nikonenko V.V. Model of competitive ion transfer in an electro-baromembrane system with track-etched membrane Membranes and membrane technologies, Том 3, выпуск 2, стр. 131-138 (year - 2021) https://doi.org/10.1134/S2517751621020062

2. Sarapulova V., Pismenskaya N., Butylskii D., Titorova V., Wang Y., Xu T., Zhang Y., Nikonenko V. Transport and electrochemical characteristics of CJMCED homogeneous cation exchange membranes in sodium chloride, calcium chloride, and sodium sulfate solutions Membranes, Том 10, выпуск 8, номер статьи 165 (year - 2020) https://doi.org/10.3390/membranes10080165

3. Sarapulova V.V., Pasechnaya E.L., Titorova V.D., Pismenskaya N.D., Apel P.Yu., Nikonenko V.V. Electrochemical properties of ultrafiltration and nanofiltration membranes in solutions of sodium and calcium chloride Membranes and Membrane Technologies, Том 2, выпуск 5, стр. 332-350 (year - 2020) https://doi.org/10.1134/S2517751620050066

4. Butylskii D.Y., Ignatenko V., Mareev S.A., Kisly A., Pismenskaya N.D., Apel P.Y., Nikonenko V.V. Selective extraction of singly charged ions using a new method of electrobaromembrane separation On-line International Conference on Membrane Processes MELPRO: Book of Abstracts, 8-11 ноября 2020 года, Прага, Чешская Республика, с. 99 (year - 2020)

5. Butylskii D.Y., Mareev S.A., Gorobchenko A., Ignatenko V., Pismenskaya N.D., Apel P.Y., Nikonenko V.V. A new approach to the membrane separation of the ions of the same sign of charge by simultaneously applying electric and pressure fields International Congress on Membranes & Membrane Processes 2020 Online ICOM: 7-11 December 2020, O2E.01 (year - 2020)

6. Nikonenko V., Butylskii D., Mareev S., Kislyi A., Pismenskaya N., Apel P. Higly selective separation of cations with the same charge by a new membrane method using simultaneosly applied electric and pressure fields International web conference «Membrane Process Modeling»: Book of abstracts, 3-4 December 2020, Stavropol, Russia, с. 14-15 (year - 2020)