Yaroshchuk, Andriy
Total activity: 26
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Department of Chemical Engineering
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andriy.yaroshchukupc.edu
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1 to 26 of 26 results
  • Characterization and modelling of micro and nanofluídic systems

     Licon Bernal, Edxon Eduardo
    Department of Chemical Engineering, Universitat Politècnica de Catalunya
    Theses

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    La miniaturización de los análisis químicos y bioquímicos está cada vez utiliza más utilizada. Todas las manipulaciones de transporte de las muestras, la separación, la mezcla con los reactivos y la detección se integren y apliquen a escala de un microchip de varios centímetros de tamaño. Esto hace posible una reducción dramática en las cantidades requeridas de muestra y reactivos, así como en el tiempo del análisis. Además de eso, las operaciones de automatización y de alto rendimiento se vuelven mucho más fáciles que en los entornos convencionales "macro-laboratorio".De acuerdo con el gran interés en el desarrollo de nuevos materiales porosos incluyendo su posterior integración en dispositivos biomédicos y aplicaciones industriales, la descripción de las particularidades de los medios nanoporosos (por ejemplo membranas) y el desarrollo de técnicas de caracterización son cruciales para controlar el comportamiento de los sistemas que incluyen procesos de separación y purificación con dichas tecnologías.En esta tesis se han llevado a cabo diferentes avances en el campo de la microfluídica, la separación y purificación de sustancias: Para el campo de la microfluídica, este estudio puede ser útil para la descripción de las primeras etapas de la polarización en los sistemas microfluídicos que acoplan tecnología de membranas o micro/nano interfaces. Por otro lado, se demostró que para tales sistemas, la teoría de Taylor-Aris es aplicable localmente dentro de microcanales abiertos en una amplia gama de números de Péclet. Además, fue posible derivar una aproximación analítica sencilla para el gradiente de concentración interno dentro de canales largos en términos de sólo unos pocos parámetros, determinados numéricamente. Esta aproximación es útil para desarrollar futuros estudios experimentales. En algunos equipos usados para la medición del potencial zeta de medios porosos, la variación de la altura del canal es técnicamente posible. En esta tesis se muestra que en estas condiciones, el flujo de fluido puede llegar a ser de transición a turbulento y los enfoques convencionales para la interpretación de las mediciones electrocinéticas debe modificarse en consecuencia. Se definió un modelo matemático que permite describir de manera sencilla, fenómenos de transporte que ocurren en diversos procesos de separación osmóticos, para mezclas de electrolitos arbitrarias. El número limitado de parámetros ajustables que contiene este modelo hace factible su determinación inequívoca a partir de un conjunto limitado de datos experimentales. De acuerdo con los resultados de esta tesis, los contactores de membrana con fibras huecas son útiles como etapa de pulido para la eliminación de bajos niveles de amonio en agua. Se ha determinado y validado experimentalmente un modelo matemático el cual ha ayudado a describir la influencia de las condiciones de funcionamiento, tales como flujo, concentraciones de amonio y pH del sistema para ambas configuraciones, de lazo cerrado y abierto. Dichos resultados son útiles para el diseño de sistemas de producción de agua ultra pura que puede ser usada en la producción de hidrogeno por electrolisis. La aplicación de las tecnologías de microfluidos a escala industrial es uno de los principales retos que enfrentar en este campo del conocimiento; sin embargo, existen algunos dispositivos que ya se están utilizando de forma sistemática a nivel industrial para fines de separación que cumplen criterios necesarios para considerarlos dentro del grupo de las tecnologías de microfluídica. Acotando a los resultados presentados en microfluídica, con este trabajo se han establecido patrones y definido conceptos básicos, dentro de este campo de la ciencia, que pueden servir como bases en la caracterización y la descripción de versiones en miniatura de procesos de separación bien conocidos, los cuales se pueden usar para el desarrollo de procesos en nuevas aplicaciones bioquímicas.

  • Electrophoresis and stability of nano-colloids: History, theory and experimental examples

     Felix, C.; Yaroshchuk, Andriy; Pasupathi, S.; Pollet, B. G.; Bondarenko, M.P.; Kovalchuk, V.I.; Zholkovskij, Emiliy K.
    Advances in colloid and interface science
    Vol. 211, p. 77-92
    DOI: 10.1016/j.cis.2014.06.005
    Date of publication: 2014-09-01
    Journal article

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    The paper contains an extended historical overview of research activities focused on determining interfacial potential and charge of dispersed particles from electrophoretic and coagulation dynamic measurements. Particular attention is paid to nano-suspensions for which application of Standard Electrokinetic Model (SEM) to analysis of experimental data encounters difficulties, especially, when the solutions contain more than two ions, the particle charge depends on the solution composition and zeta-potentials are high. Detailed statements of Standard Electrokinetic and DLVO Models are given in the forms that are capable of addressing electrophoresis and interaction of particles for arbitrary ratios of the particle to Debye radius, interfacial potentials and electrolyte compositions. The experimental part of the study consists of two groups of measurements conducted for Pt/C nano-suspensions, namely, the electrophoretic and coagulation dynamic studies, with various electrolyte compositions. The obtained experimental data are processed by using numerical algorithms based on the formulated models for obtaining interfacial potential and charge. While analyzing the dependencies of interfacial potential and charge on the electrolyte compositions, conclusions are made regarding the mechanisms of charge formation. It is established that the behavior of system stability is in a qualitative agreement with the results computed from the electrophoretic data. The verification of quantitative applicability of the employed models is conducted by calculating the Hamaker constant from experimental data. It is proposed how to explain the observed variations of predicted Hamaker constant and its unusually high value. (C) 2014 Elsevier B.V. All rights reserved.

  • Phosphate recovery from tertiary treatment effluents using nanofiltration membranes

     Licon Bernal, Edxon Eduardo; Reig i Amat, Monica; Marín, Miguel; Valderrama Angel, Cesar Alberto; Yaroshchuk, Andriy; Gibert Agullo, Oriol; Cortina Pallas, Jose Luis
    Ibero-American Conference on Membrane Science and Technology
    p. 382-383
    Presentation's date: 2014-05-28
    Presentation of work at congresses

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    Phosphate recovery will become more important within the next decades due to depletion ofmineral phosphorus resources [1]. Waste water has been identified as a secondary resource of this substance and nanofiltration (NF) is an attractive membrane process for selective phosphate recovery, since high rejections of NaCl are not required. This technique has similar performance as reverse osmosis (RO). However, NF membranes allow higher salt passage than RO membranes, which decreases osmotic pressure. Furthermore, the high permeability of NF membranes also reduces the pressure needed for phosphate recovery making NF a more cost effective process. Experimental studies evaluated the recovery of phosphate, however scare data on the description of the rejections could be found. Although those studies have obtained interesting results under several conditions, they do not explain the rejections of the phosphate under the extent of a rigorous transport model [2,3]. In this work the Solution-Diffusion-Film Model (SDFM) was used, to describe the phosphate transport through a planar NF membrane in the separation process of tertiary treatment effluents (TTEs) [4]. Experimental data was obtained with synthetic aqueous solutions of different major salts, present in TTEs, with phosphate as ion trace. The experiments were carried out with a polyamide thin-film composite NF membrane NF270 (Dow Chemical Company, Midland (USA)). A cross-flow set-up equipped with a test cell (GE SEPA™ CF II) with a spacer-filled feed channel and the possibility of independent variation of transmembrane pressure and cross-flow velocity was used. A flat sheet membrane with an effective filtration surface of 0.014 m2 was used (See Figure 1). The SDFM performed a good prediction of the behavior of species in solution, and rejection streams, with small deviations between mesured and predicted values. Then, it can be considered as a suitable model for design and calculations. According to Figure 2, high performance in the separation of phosphate in solution was observed (above 90%), demonstraiting that NF is an appropriate membrane process for phosphate recovery. In turn, the phosphate rejection is not considerably affected by the different major salt used in the solution.

  • Evaluation of electrolyte mixtures rejection behavior using nanofiltration membranes using spiral wound and flat sheet configurations

     Reig i Amat, Monica; Licon Bernal, Edxon Eduardo; Valderrama Angel, Cesar Alberto; Gibert Agullo, Oriol; Yaroshchuk, Andriy; Cortina Pallas, Jose Luis
    Ibero-American Conference on Membrane Science and Technology
    p. 391-392
    Presentation's date: 2014-05-26
    Presentation of work at congresses

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    Nanofiltration (NF) is a growing separation technology for water treatment processes at different industrials lands. It can be used in different membrane configurations, such as flat sheet (FS) or spiral wound (SW). Usually, FS configuration is used at lab-scale test membrane. On the other hand, SW membrane configuration is used at industrial scale, due to the need for more active membrane area and the space optimization. For this reason, the aim of this study is to determine the reliability of the data obtained in a FS lab-scale set up when they are implemented at industrial scale level using SW configuration. Two different pilot plants were used to evaluate the ion rejection of mixed feed salt solutions, based on a dominant and a trace salt. The membrane used in both pilot plants was the NF270 membrane, supplied by Dow Chemical, with an active membrane area of 0.014m2 and 2.6m2 for the FS and SW configuration, respectively. The membrane used has a negative superficial charge. Experimental conditions in both membrane configurations were the same: different synthetic salt mixture feed solutions were used working at constant temperature while the trans-membrane pressure (TMP) varied from the osmotic pressure to 20 bars with increments of approximately 2 bars. For each sample taken at different pressures, a trans-membrane flux was obtained. The concentrate and the permeate streams were recirculated in both cases to maintain constant the feed solution concentration during the experiment. Different parameters such as, pH, conductivity, temperature, TMP and flow rate were measured and monitored along the experiment. Synthetic solutions were prepared representing brackish waters of Catalonian rivers, such as Llobregat and Ebre. For this reason, NaCl, MgSO4 and MgCl2 were used as dominant salts, and Br-, NH4 +, K+ and I- were used as ion traces. This experimental design was used to study the effect of different electrolyte mixtures to a trace ion rejection. Trace salt concentration was set from 0.5 to 2% of the dominant one. The results of each experiment were modelled using the Solution-diffusion-film model (SDFM) [1] and compared taking into account the membrane configuration. By means of the SDFM the ion permeability of each ion can be calculated. This value depends on the capacity of the ion to cross the membrane. Figure 1 shows the measured and predicted ion rejection data as a function of transmembrane flux for each feed salt solution using both membrane configurations. Results showed that the most rejected ions were divalent ones in both configurations, in which SO4 2- was the most rejected one followed by Mg2+. NaCl is rejected moderately and K+ has shown a negative rejection. This phenomena was previously explained by Pages et al. [2] Comparing both membranes configurations, it is observed that fairly similar results are been obtained. However, for the same operation conditions, more trans-membrane flux was obtained working with FS configuration. Besides, the ion permeability order for each experiment was the same in both membrane configurations.

  • Rejection of trace ionic solutes in nanofiltration: Influence of aqueous phase composition

     Pages Hernando, Neus; Yaroshchuk, Andriy; Gibert Agullo, Oriol; Cortina Pallas, Jose Luis
    Chemical engineering science
    Vol. 104, p. 1107-1115
    DOI: 10.1016/j.ces.2013.09.042
    Date of publication: 2013-12-18
    Journal article

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    The use of nanofiltration (NF) in water treatment has been proposed to improve the quality of the produced water and extend the options of concentrate valorization, taking the benefit of its different ions selectivity patterns. However, there is a need to understand and optimize the rejection not only of major components (e.g. NaCl or MgSO4) but also of minor components specially in brackish waters. The selectivity of ion rejection by NF membranes has been studied theoretically and experimentally. Theoretical analysis has been carried out within the scope of the solution-diffusion-film model (SDFM) recently extended to electrolyte mixtures. In this study, experimental ion rejection data of typical cationic and anionic species present in surface waters at various trans-membrane pressures and cross-flow velocities have been obtained with a NF membrane (NF270). Several combinations of dominant salts (NaCl, MgCl2, MgSO4, Na2SO4) with trace ions (Na+, Cl-, Mg2+, SO42-) have been used. The rejection of ions crucially depends on their environment. The dramatic differences in the rejections can be explained by the spontaneously arising electric fields generated in the membrane phase. Their effect gives rise to negative rejections of singly charged inorganic ions present as small additions to well-rejected dominant salts. As a result of theoretical interpretation the intrinsic membrane permeabilities to ions have been estimated for different aqueous solutions compositions. © 2013 Elsevier Ltd.

    The use of nanofiltration (NF) in water treatment has been proposed to improve the quality of the produced water and extend the options of concentrate valorization, taking the benefit of its different ions selectivity patterns. However, there is a need to understand and optimize the rejection not only of major components (e.g. NaCl or MgSO4) but also of minor components specially in brackish waters. The selectivity of ion rejection by NF membranes has been studied theoretically and experimentally. Theoretical analysis has been carried out within the scope of the solution-diffusion-film model (SDFM) recently extended to electrolyte mixtures. In this study, experimental ion rejection data of typical cationic and anionic species present in surface waters at various trans-membrane pressures and cross-flow velocities have been obtained with a NF membrane (NF270). Several combinations of dominant salts (NaCl, MgCl2, MgSO4, Na2SO4) with trace ions (Na+, Cl−, Mg2+, SO42−) have been used. The rejection of ions crucially depends on their environment. The dramatic differences in the rejections can be explained by the spontaneously arising electric fields generated in the membrane phase. Their effect gives rise to negative rejections of singly charged inorganic ions present as small additions to well-rejected dominant salts. As a result of theoretical interpretation the intrinsic membrane permeabilities to ions have been estimated for different aqueous solutions compositions

  • Solution-Diffusion-Electro-Migration model and its uses for analysis of nanofiltration, pressure-retarded osmosis and forward osmosis in multi-ionic solutions

     Yaroshchuk, Andriy; Bruening, Merlin L.; Licon Bernal, Edxon Eduardo
    Journal of membrane science
    Vol. 447, p. 463-476
    DOI: 10.1016/j.memsci.2013.07.047
    Date of publication: 2013-11
    Journal article

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    This work presents an analytical solution to the differential equations that govern the electrically coupled transport of three different ions through membrane barrier layers in which the Solution-Diffusion–Electro-Migration model applies. This model disregards convective coupling between the trans-membrane flows of ions and solvent and uses composition-independent single-ion permeances to quantify ion transfer through the membrane. The limited number of adjustable parameters should make their unambiguous determination feasible from a limited set of experimental data. The solution presented here enables rapid calculations that explore the effects of spontaneously arising electric fields on rejections in nanofiltration (NF), volume flows in pressure-retarded osmosis (PRO) through NF membranes, and NaCl rejections in forward osmosis (FO). For NF, ion flux simulations confirm that large differences in the permeances of mono and divalent ions, e.g. Mg2+ and Cl- or Na+ and View the MathML source, can lead to negative rejections or enhanced rejections of trace monovalent ions, depending on the ion charge. Calculations also show that rejection of divalent ions by NF membranes can lead to significant osmotic flow, even in the presence of some excess of NaCl. Osmotic flow first decreases and then increases as the NaCl concentration increases in a draw solution containing MgCl2 or Na2SO4. In FO using MgCl2 as a draw solution and NF membranes, modeling reveals 3- to 4-fold enhancements in NaCl rejection relative to a pressure-driven process under similar conditions. These results demonstrate the importance of modeling coupled ion transport when designing membrane-based ion separations.

    This work presents an analytical solution to the differential equations that govern the electrically coupled transport of three different ions through membrane barrier layers in which the Solution-Diffusion–Electro-Migration model applies. This model disregards convective coupling between the trans-membrane flows of ions and solvent and uses composition-independent single-ion permeances to quantify ion transfer through the membrane. The limited number of adjustable parameters should make their unambiguous determination feasible from a limited set of experimental data. The solution presented here enables rapid calculations that explore the effects of spontaneously arising electric fields on rejections in nanofiltration (NF), volume flows in pressure-retarded osmosis (PRO) through NF membranes, and NaCl rejections in forward osmosis (FO). For NF, ion flux simulations confirm that large differences in the permeances of mono and divalent ions, e.g. Mg2+ and Cl− or Na+ and View the MathML source, can lead to negative rejections or enhanced rejections of trace monovalent ions, depending on the ion charge. Calculations also show that rejection of divalent ions by NF membranes can lead to significant osmotic flow, even in the presence of some excess of NaCl. Osmotic flow first decreases and then increases as the NaCl concentration increases in a draw solution containing MgCl2 or Na2SO4. In FO using MgCl2 as a draw solution and NF membranes, modeling reveals 3- to 4-fold enhancements in NaCl rejection relative to a pressure-driven process under similar conditions. These results demonstrate the importance of modeling coupled ion transport when designing membrane-based ion separations.

  • Electrokinetics in undeveloped flows

     Yaroshchuk, Andriy; Licon Bernal, Edxon Eduardo; Luxbacher, Thomas
    Journal of colloid and interface science
    Vol. 410, p. 195-201
    DOI: 10.1016/j.jcis.2013.08.021
    Date of publication: 2013-11
    Journal article

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    For the correct interpretation of results of tangential electrokinetic measurements with porous materials, in particular, composite/asymmetric membranes on porous supports, it is necessary to have the data available for various channel heights. In some kinds of equipment, the variation of channel height is technically possible only for a range of relatively large heights. This communication shows that under these conditions, the fluid flow can become undeveloped and the conventional approaches to the interpretation of electrokinetic measurements should be modified accordingly. In particular, the dependence of streaming-current coefficient on the channel height becomes sub-linear. If the experimental data are available only for larger channel heights, this can be mistakenly taken for the manifestation of contribution of porous sub-structure to the streaming current.In this communication, we investigate electrokinetic phenomena in undeveloped flows both numerically and experimentally. We confirm that the aforementioned sub-linearity occurs for nonporous as well as porous substrates. We also demonstrate that the channel heights estimated from the volume flow rate by using numerical simulations of undeveloped flows are in very good agreement with the reference values obtained from the electrical conductance (in contrast to the values estimated by using the conventional approach of Hagen-Poiseuille equation). The numerical fitting of channel-height dependences of streaming-current coefficient enables us to separate the contributions of external surface and porous sub-structure (in case of porous substrates) and obtain quite reasonable values of (effective) zeta-potentials in both cases. Nonetheless, the accuracy of experimental data deteriorates with increasing channel height, so it is generally advisable to vary the heights within a range below 100-150. µm.

    For the correct interpretation of results of tangential electrokinetic measurements with porous materials, in particular, composite/asymmetric membranes on porous supports, it is necessary to have the data available for various channel heights. In some kinds of equipment, the variation of channel height is technically possible only for a range of relatively large heights. This communication shows that under these conditions, the fluid flow can become undeveloped and the conventional approaches to the interpretation of electrokinetic measurements should be modified accordingly. In particular, the dependence of streaming-current coefficient on the channel height becomes sub-linear. If the experimental data are available only for larger channel heights, this can be mistakenly taken for the manifestation of contribution of porous sub-structure to the streaming current. In this communication, we investigate electrokinetic phenomena in undeveloped flows both numerically and experimentally. We confirm that the aforementioned sub-linearity occurs for nonporous as well as porous substrates. We also demonstrate that the channel heights estimated from the volume flow rate by using numerical simulations of undeveloped flows are in very good agreement with the reference values obtained from the electrical conductance (in contrast to the values estimated by using the conventional approach of Hagen–Poiseuille equation). The numerical fitting of channel-height dependences of streaming-current coefficient enables us to separate the contributions of external surface and porous sub-structure (in case of porous substrates) and obtain quite reasonable values of (effective) zeta-potentials in both cases. Nonetheless, the accuracy of experimental data deteriorates with increasing channel height, so it is generally advisable to vary the heights within a range below 100–150 μm.

  • Broadening of neutral analyte band in electroosmotic flow through slit channel with different zeta potentials of the walls

     Zholkovskij, Emiliy K.; Masliyah, Jacob H.; Yaroshchuk, Andriy
    Microfluidics and nanofluidics
    Vol. 15, num. 1, p. 35-47
    DOI: 10.1007/s10404-012-1118-0
    Date of publication: 2013-07
    Journal article

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    The study is concerned with addressing hydrodynamic dispersion of an electroneutral non-adsorbed solute being transported by electroosmotic flow through a slit channel formed by walls with different zeta potentials. The analysis is conducted in terms of the plate height which, using the Van Deemter equation, can be expressed through the cross-sectional mean flow velocity, the solute molecular diffusion coefficient and a length scale parameter having meaning of the minimum achievable plate height and depending on the velocity distribution within the channel cross-section. The minimum plate height is determined by substituting distribution of electroosmotic velocity into the preliminary derived integral expression that is valid for any given velocity distribution within a slit channel cross-section. The electroosmotic velocity distribution within the slit channel cross-section is obtained by solving one-dimensional version of the Stokes equation accounting for electric force exerted on the local equilibrium electric space charge. The major obtained result is an analytical expression which represents the minimum plate height normalized by half of channel width as a function of two dimensionless parameters, namely, half of channel width normalized by the Debye length, and the ratio of the wall zeta potentials. The obtained result reveals a substantial increase in the minimum plate height compared with the case of equal wall zeta potentials. Different limiting cases of the obtained relationships are analyzed and possible applications are discussed

    The study is concerned with addressing hydrodynamic dispersion of an electroneutral non-adsorbed solute being transported by electroosmotic flow through a slit channel formed by walls with different zeta potentials. The analysis is conducted in terms of the plate height which, using the Van Deemter equation, can be expressed through the cross-sectional mean flow velocity, the solute molecular diffusion coefficient and a length scale param- eter having meaning of the minimum achievable plate height and depending on the velocity distribution within the channel cross-section. The minimum plate height is determined by substituting distribution of electroosmotic velocity into the preliminary derived integral expression that is valid for any given velocity distribution within a slit channel cross-section. The electroosmotic velocity distri- bution within the slit channel cross-section is obtained by solving one-dimensional version of the Stokes equation accounting for electric force exerted on the local equilib- rium electric space charge. The major obtained result is an analytical expression which represents the minimum plate height normalized by half of channel width as a function of two dimensionless parameters, namely, half of channel width normalized by the Debye length, and the ratio of the wall zeta potentials. The obtained result reveals a sub- stantial increase in the minimum plate height compared with the case of equal wall zeta potentials. Different lim- iting cases of the obtained relationships are analyzed and possible applications are discussed.

  • Voltammetry on nanoporous charged classes membranes

     Reig i Amat, Monica; Mareev, Semyon; Yaroshchuk, Andriy; Nikonenko, Victor
    Annual International Conference Ion Transport in Organic and Inorganic Membranes
    p. 211-212
    Presentation's date: 2013-06-05
    Presentation of work at congresses

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    Porous glasses are leaching products of phase-separated alkali borosilicates. The first phase is an alkali-rich borate phase, soluble in hot mineral acids, water or alcohols. The second phase is almost pure silica. The pores can be formed during the phase separation process in a wide size range from 0.3 to 1000 nm in diameter, depending on glass composition, time and temperature of phase separation and leaching conditions. A quenching of the initial glass melt followed by a short-time treatment at lower temperatures results in microporous materials. Their surface is characterized by hydroxyl groups with concentration between 4 and 8 OHs nm-2. This kind of membranes possesses, in comparison with other porous inorganic solids, high thermal stability, chemical resistance, high optical transparency, very flexible geometric forms, very reactive surface and good accessibility to eventually available active sites inside the porous structure. Moreover, this type of membranes are characterized by low permeability of air, a low surface acidity caused by very weakly acidic silanol and weakly acidic boranol groups. They are of interest for molecular sieve applications. Porous glasses are applied in biotechnology, membrane technology, micro-reaction engineering, dental industry, in heterogeneous catalysis between others applications. Nanoporous glass membranes properties are studied with help of an electrodialysis cell. There are 4 different porous sizes available: 15, 30, 50 and 100 nm. The cell includes 4 compartments: 2 electrode rinse ones, 1 dilute and 1 concentrate stream compartments. There is a cathode and an anode in each of the ends of the cell followed by an anionic and a cationic membrane; the nanoporous glass membrane is placed in the middle of the cell. Two Luggin capillaries are used for measuring the potential difference across the glass membrane. In a 0.01 M NaCl solution, no limiting current was observed in the case of 100 nm and 15 nm porous glass membranes. In a 0.001 M NaCl solution, the limiting current for all studied membranes was detected. This behaviour was predicted by Yaroshchuk A. (2012) model for nanoporous membranes: the limiting current may occur in more dilute solutions and may not occur in more concentrated ones. However, in a 0,0001 M NaCl solution no limiting current was observed due to high resistivity of the system. In the graph below the experimental I-V curves 0.001 M NaCl solutions are shown for a 15, 30, 50 and 100 nm porous glasses membranes and also for a CMX-SB homogeneous membrane to comparison. Generally, it can be seen that the highest limiting current is observed for the 50 nm membrane, it decreases in the range: 50 > 30 > 15 > CMX-SB. This range may be explained by increasing membrane permselectivity: lower pore size reduces the fraction of pore space filled with uncharged solution. The case of 100 nm membrane presents an exception to the rule.

  • Fundamentals of selective ion transport through multilayer polyelectrolyte membranes

     Cheng, Chao; Yaroshchuk, Andriy; Bruening, Merlin L.
    Langmuir
    Vol. 29, num. 6, p. 1885-1892
    DOI: 10.1021/la304574e
    Date of publication: 2013-02-12
    Journal article

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    Membranes composed of multilayer poly(4-styrenesulfonate) (PSS)/protonated poly(allylamine) (PAH) films on porous alumina supports exhibit high monovalent/divalent cation selectivities. Remarkably, the diffusion dialysis K(+)/Mg(2+) selectivity is >350. However, in nanofiltration this selectivity is only 16, suggesting some convective ion transport through film imperfections. Under MgCl(2) concentration gradients across either (PSS/PAH)(4)- or (PSS/PAH)(4)PSS-coated alumina, transmembrane potentials indicate Mg(2+) transference numbers approaching 0. The low Mg(2+) transference numbers with both polycation- and polyanion-terminated films likely stem from exclusion of Mg(2+) due to its large size or hydration energy. However, these high anion/cation selectivities decrease as the solution ionic strength increases. In nanofiltration, the high asymmetry of membrane permeabilities to Mg(2+) and Cl(-) creates transmembrane diffusion potentials that lead to negative rejections (the ion concentration in the permeate is larger than in the feed) as low as -200% for trace monovalent cations such as K(+) and Cs(+). Moreover, rejection becomes more negative as the mobility of the trace cation increases. Knowledge of single-ion permeabilities is vital for predicting the performance of polyelectrolyte films in the separation and purification of mixed salts.

    Membranes composed of multilayer poly(4-styrenesul- fonate) (PSS)/protonated poly(allylamine) (PAH) fi lms on porous alumina supports exhibit high monovalent/divalent cation selectivities. Remarkably, the di ff usion dialysis K + /Mg 2+ selectivity is >350. However, in nano fi ltration this selectivity is only 16, suggesting some convective ion transport through fi lm imperfections. Under MgCl 2 concentration gradients across either (PSS/PAH) 4 - or (PSS/ PAH) 4 PSS-coated alumina, transmembrane potentials indicate Mg 2+ transference numbers approaching 0. The low Mg 2+ transference numbers with both polycation- and polyanion-terminated fi lms likely stem from exclusion of Mg 2+ due to its large size or hydration energy. However, these high anion/cation selectivities decrease as the solution ionic strength increases. In nano fi ltration, the high asymmetry of membrane permeabilities to Mg 2+ and Cl − creates transmembrane di ff usion potentials that lead to negative rejections (the ion concentration in the permeate is larger than in the feed) as low as − 200% for trace monovalent cations such as K + and Cs + . Moreover, rejection becomes more negative as the mobility of the trace cation increases. Knowledge of single-ion permeabilities is vital for predicting the performance of polyelectrolyte fi lms in the separation and puri fi cation of mixed salts.

  • Over-limiting currents and deionization “shocks” in current-induced polarization: Local-equilibrium analysis

     Yaroshchuk, Andriy
    Advances in colloid and interface science
    Vol. 183-184, p. 68-81
    DOI: 10.1016/j.cis.2012.08.004
    Date of publication: 2012-11-15
    Journal article

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    The problem is considered theoretically of dynamics of current-induced concentration polarization of interfaces between ideally perm-selective and non-ideally perm-selective (“leaky”) ion-exchange media in binary electrolyte solutions under galvanostatic conditions and at negligible volume flow. In contrast to the previous studies, the analysis is systematically carried out in terms of local thermodynamic equilibrium in the approximation of local electric neutrality in virtual solution. For macroscopically homogeneous media, this enables one to obtain model-independent results in quadratures for the stationary state as well as an approximate scaling-form solution for the transient response to the step-wise increase in electric-current density. These results are formulated in terms of such phenomenological properties of the “leaky” medium as ion transport numbers, diffusion permeability to salt and specific chemical capacity. An easy-to-solve numerically 1D PDE is also formulated in the same terms. A systematic parametric study is carried out within the scope of fine-pore model of “leaky” medium in terms of such properties as volumetric concentration of fixed electric charges and diffusivities of ions of symmetrical electrolyte. While previous studies paid principal attention to the shape and propagation rate of the so-called deionization “shocks”, we also consider in detail the time evolution of voltage drop and interface salt concentration. Our analysis confirms the previously predicted pattern of propagating deionization “shocks” within the “leaky” medium but also reveals several novel features. In particular, we demonstrate that the deionization-shock pattern is really pronounced only at intermediate ratios of fixed-charge concentration to the initial salt concentration and at quite high steady-state voltages where the model used in this and previous studies is applicable only at relatively early stages of concentration-polarization process.

    Concentration polarization; Over-limiting current; Ion-exchange medium; Deionization shock; Propagation; Local equilibrium

  • Current-induced concentration polarization of interfaces between non-ideally perm-selective ion-exchange media and electrolyte solutions

     Yaroshchuk, Andriy
    Journal of membrane science
    Vol. 396, num. April, p. 43-49
    DOI: 10.1016/j.memsci.2011.12.029
    Date of publication: 2012-04-01
    Journal article

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    In non-ideally perm-selective ion-exchange media and/or nano-porous/nano-channel systems, ion transport numbers depend on the salt concentration. Under conditions of current-induced polarization, this concentration changes considerably close to the membrane surface or nano-/micro-interface. It is well known that the value of limiting current is controlled (among other things) by the difference of counter-ion transport numbers between the membrane and solution. Thus, a natural question arises about what value of concentration has to be used in the estimates of the difference of transport numbers and, thus, of limiting current. At first glance, it appears that one should use the value of salt concentration occurring at the polarized interface. If this were correct, there would be a positive feedback in the process of concentration polarization making the latter self-sustaining. This communication shows that, rather surprisingly, the limiting current is controlled by the counter-ion transport number taken at the salt concentration occurring at the “opposite” membrane side where the salt concentration goes up (in the limiting case of dominant diffusion resistance of membrane as compared to the unstirred layer). Accordingly, the positive feedback does not occur. Besides, the limiting current can considerably depend on the stirring conditions close to the “back” membrane surface, which has not been generally recognized previously and can be important for the experimental practice. This result has been obtained via explicit solution of the ion-transport problem in the membrane phase.

  • REGENERABLE ACTIVE POLYELECTROLYTR NANOFILTRATION MEMBRANES FOR WATER REUSE AND METAL ACID RECOVERY

     Cortina Pallas, Jose Luis; Florido Pérez, Antonio; Valderrama Angel, Cesar Alberto; Yaroshchuk, Andriy
    Competitive project

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  • Integración de procesos de membranas, intercambio iónico y precipitación química en la valorización de concentrados de tratamientos

     Yaroshchuk, Andriy; Oliva Moncunill, Josep; Farran Marsa, Adriana; Valderrama Angel, Cesar Alberto; Gibert Agullo, Oriol; Cortina Pallas, Jose Luis
    Competitive project

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  • Nanofiltration as pretreatment for scale prevention in seawater reverse osmosis desalination

     Llenas Argelaguet, Laia; Yaroshchuk, Andriy; Rovira Boixaderas, Miguel Arcangel; Martínez Lladó, Xavier; Pablo Ribas, Joan de
    Desalination and water treatment
    Vol. 36, num. 1-3, p. 310-318
    DOI: 10.5004/dwt.2011.2767
    Date of publication: 2011-12
    Journal article

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  • Transport properties of long straight nano-channels in electrolyte solutions: A systematic approach

     Yaroshchuk, Andriy
    Advances in colloid and interface science
    Vol. 168, num. 1-2, p. 278-291
    DOI: 10.1016/j.cis.2011.03.009
    Date of publication: 2011-10-14
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  • Coupled concentration polarization and electroosmotic circulation near micro/nanointerfaces: Taylor-Aris model of hydrodynamic dispersion and limits of its applicability

     Yaroshchuk, Andriy; Zholkovskiy, Emiliy; Pogodin, Sergey; Baulin, Vladimir
    Langmuir
    Vol. 27, num. 18, p. 11710-11721
    DOI: 10.1021/la201354s
    Date of publication: 2011-09-20
    Journal article

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    Mismatches in electrokinetic properties between micro- and nanochannels give rise to superposition of electroosmotic and pressure-driven flows in the microchannels. Parabolic or similar flow profiles are known to cause the so-called hydrodynamic dispersion, which under certain conditions can be formally assimilated to an increase in the solute diffusivity (Taylor-Aris model). It is demonstrated theoretically that taking into account these phenomena modifies considerably the pattern of current-induced concentration polarization of micro/nanointerfaces as compared to the classical model of unstirred boundary layer. In particular, the hydrodynamic dispersion leads to disappearance of limiting current. At essentially "over-limiting" current densities, the time-dependent profiles of salt concentration in microchannels behave like sharp concentration "fronts" moving away from the interface until they reach the reservoir end of the microchannel. Under galvanostatic conditions postulated in this study, these "fronts" move with practically constant speed directly proportional to the current density. The sharp transition from a low-concentration to a high-concentration zone can be useful for the analyte preconcentration via stacking. The pattern of moving sharp concentration "fronts" has been predicted for the first time for relatively broad microchannels with negligible surface conductance. The Taylor-Aris approach to the description of hydrodynamic dispersion is quantitatively applicable only to the analysis of sufficiently "slow" processes (as compared to the characteristic time of diffusion relaxation in the transversal direction). A posteriori estimates reveal that the condition of "slow" processes is typically not satisfied close to current-polarized micro/nanointerfaces. Accordingly, to make the description quantitative, one needs to go beyond the Taylor-Aris approximation, which will be attempted in future studies. It is argued that doing so would make even stronger the dampening impact of hydrodynamic dispersion on the current-induced concentration polarization of micro/nanointerfaces.

  • COUPLED ION AND VOLUME TRANSFER PHENOMENA IN HETEROGENEOUS SYSTEMS: MODELLING,EXPERIMENT AND APPLICATIONS IN CLEAN ENERGY MICRO-ANAL

     Casas Garriga, Sandra; Licon Bernal, Edxon Eduardo; Yaroshchuk, Andriy
    Competitive project

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  • Solution-diffusion-film model for the description of pressure-driven trans-membrane transfer of electrolyte mixtures: One dominant salt and trace ions

     Yaroshchuk, Andriy; Martínez Lladó, Xavier; Llenas Argelaguet, Laia; Rovira Boixaderas, Miguel Arcangel; Pablo Ribas, Joan de
    Journal of membrane science
    Vol. 368, num. 1-2, p. 192-201
    DOI: 10.1016/j.memsci.2010.11.037
    Date of publication: 2011-02-15
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  • Interpretation of electrokinetic measurements with porous films: role of electric conductance and streaming current within porous structure

     Yaroshchuk, Andriy; Luxbacher, Thomas
    Langmuir
    Vol. 26, num. 13, p. 10882-10889
    DOI: 10.1021/la100777z
    Date of publication: 2010-07-06
    Journal article

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    It is shown that in tangential electrokinetic measurements with porous films the porous structure makes contribution not only to the cell electric conductance (as demonstrated previously) but also to the observed streaming current. Both of these contributions give rise to dependences of streaming-potential and streaming-current coefficients on the channel height. However, due to the combined contribution of two phenomena, the dependence of streaming-potential coefficient on the channel height may be rather complicated and not allow for simple extrapolation. At the same time, the dependences of streaming-current coefficient and cell electric conductance on the channel height turn out linear and can be easily extrapolated to zero channel heights. This enables one to determine separately the contributions of external surface of porous film and of its porous structure to the streaming current and of the channel and porous structure to the cell electric conductance. This procedure is illustrated by the measurements of tangential electrokinetic phenomena and electric conductance with Millipore mixed-cellulose membrane filters of various average pore sizes (from 0.025 to 5 μm) in the so-called adjustable-gap cell of SurPASS electrokinetic instrument (Anton Paar GmbH). The design of this cell allows for easy and quasi-continuous variation of channel height as well as accurate determination of cell electric conductance, streaming-current coefficient, and channel height (from the cell hydraulic permeability). The quality of linear fits of experimental data has been found to be very good, and thus, the extrapolation procedures were quite reliable and accurate. Zeta-potentials could be determined of both external film and internal pore surfaces. It is demonstrated that the porous structures make considerable contributions to both streaming-current coefficient and cell electric conductance especially in the case of filters with larger pores. It is also found that, rather surprisingly, in filters with smaller pores the reduction in the filter electric conductivity turns out essentially stronger than could be expected proceeding from the filter porosity.

  • Influence of osmosis on the diffusion from concentrated solutions through composite/asymmetric membranes: Theoretical analysis

     Yaroshchuk, Andriy
    Journal of membrane science
    Vol. 355, num. 1-2, p. 98-103
    DOI: 10.1016/j.memsci.2010.03.013
    Date of publication: 2010-06-15
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  • Broadening of neutral solute band in electroosmotic flow through submicron channel with longitudinal non-uniformity of zeta potential

     Zholkovskij, Emilij K.; Yaroshchuk, Andriy; Masliyah, Jacob H.; Pablo Ribas, Joan de
    Colloids and surfaces A: physicochemical and engineering aspects
    Vol. 354, num. 1-3, p. 338-346
    DOI: 10.1016/j.colsurfa.2009.09.043
    Date of publication: 2010-02
    Journal article

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    The present study is concerned with broadening of neutral solute band in electrically driven flow through a straight channel with longitudinally varying zeta potential. The present analysis takes into account effects that are important for submicron channels, namely, variation of the excess conductivity in the diffuse part of the electric Double Layer and the non-uniformity of the velocity profile within the Double Layer. Initially, the combined, electroosmotic and pressure driven flow through a straight channel is addressed for the case of longitudinal variation of zeta potential. Using the obtained distribution of the hydrodynamic velocity, the plate height for a non-electrolyte neutral solute is interrelated with the longitudinal distribution of the electrokinetic potential. Several examples of cross-section geometry and electrolyte composition are discussed.

  • INTEGRACIÓN DE PROCESOS DE EXTRACCION REACTIVA Y PROCESOS DE MEMBRANAS EN LA ELIMINACIÓN DE COMPUESTOS INDESADOS EN ETAPAS DE POTABI

     Farran Marsa, Adriana; Gibert Agullo, Oriol; Valderrama Angel, Cesar Alberto; Yaroshchuk, Andriy; Cortina Pallas, Jose Luis
    Competitive project

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  • Mechanisms of transfer of ionic solutes through composite polymer nano-filtration membranes in view of their high sulfate/chloride selectivities

     Yaroshchuk, Andriy; Rovira Boixaderas, Miguel Arcangel; Pablo Ribas, Joan de; Llenas Argelaguet, Laia
    Desalination and water treatment
    Vol. 6, p. 48-53
    Date of publication: 2009
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  • Tracer diffusion in sintered stainless steel filtres: Measurement of effective diffusion coefficients and implications for diffusion studies with compacted clays

     Glaus, Martin A.; Rossé, Roger; Van Loon, Luc R.; Yaroshchuk, Andriy
    Clays and clay minerals
    Vol. 56, num. 6, p. 677-685
    DOI: 10.1346/CCMN.2008.0560608
    Date of publication: 2008-12
    Journal article

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