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Yoshinobu Tanaka - One of the best experts on this subject based on the ideXlab platform.

  • computer simulation of ion exchange membrane electrodialysis for salt concentration and reduction of ro discharged brine for salt production and marine environment conservation
    Desalination, 2015
    Co-Authors: Yoshinobu Tanaka, M Reig, S Casas, C Aladjem, J L Cortina
    Abstract:

    Abstract The salt discharged from reverse osmosis is concentrated by ion-exchange membrane electrodialysis to produce salt for industrial use and the salt concentration is reduced to seawater level for preventing environmental impact on marine ecosystems. The technology was evaluated experimentally and discussed with a computer simulation program of the electrodialysis system incorporated with U shape cells. The algorithm computes mass transport, energy consumption, electric Current leakage, concentrate NaCl purity, pressure drop and Limiting Current Density. The seawater reverse osmosis discharged brine was supplied to the electrodialysis pilot plant and it was operated changing Current Density and temperature taking benefit of seasoning variations. The computed energy consumption ENaCl and NaCl concentration in concentrated solutions C″NaCl using developing algorithms provided a good description of the experimentally measured values with correlation coefficients of R(r) = 0.9 for ENaCl and R(r) = 0.6 for C″NaCl. Then the reasonability of the developed algorithms is supported by the experimental set of data. The Current leakage is nearly 3% for any electric Current. The pump driving force is very low. The Limiting Current Density is very high. In order to decrease salt concentration at the outlets of desalting cells to seawater level, it is necessary to increase desalting ratio to 0.5. This technique however increases ENaCl and decrease C″NaCl. In spite of this operating circumstance, ENaCl and C″NaCl are comparable to the data in the salt manufacturing plant operation to produce edible salt. NaCl produced from in the reverse osmosis discharged brine electrodialysis is competitive in the edible salt market.

  • ion exchange membranes fundamentals and applications
    2015
    Co-Authors: Yoshinobu Tanaka
    Abstract:

    Fundamentals Chapter 1 Preparation of ion exchange membranes Chapter 2 Membrane property measurement Chapter 3 Membrane characteristics and transport phenomena Chapter 4 Theory of Teorell, Meyer and Sievers (TMS theory) Chapter 5 Irreversible thermodynamics Chapter 6 Overall mass transport Chapter 7 Concentration polarization Chapter 8 Water dissociation Chapter 9 Current Density distribution Chapter 10 Hydrodynamics Chapter 11 Limiting Current Density Chapter 12 Leakage Chapter 13 Energy consumption Chapter 14 Membrane deterioration Applications Chapter 1 Elecreodialysis Chapter 2 Electrodialysis reversal Chapter 3 Bipolar membrane electrodialysis Chapter 4 Electro-deionization Chapter 5 Electrolysis Chapter 6 Diffusion dialysis Chapter 7 Donnan dialysis Chapter 8 Energy conversion

  • Limiting Current Density
    Ion Exchange Membranes, 2015
    Co-Authors: Yoshinobu Tanaka
    Abstract:

    When an electric Current passes through an ion exchange membrane, salt concentration on the desalting surface of the membrane decreases because of concentration polarization and reduces to zero at the Limiting Current Density. In this circumstance, there are no more salt ions available to carry the electric Current; as a result, the voltage drop across the boundary layer increases drastically and causes higher energy consumption and the generation of water dissociation. The Limiting Current Density of an ion exchange membrane i lim is measured using the Current–voltage relationship. The mechanism of i lim can be understood from the Nernst diffusion model and analyzed with chemical engineering techniques. When the Current Density reaches i lim at the outlet of a desalting cell at its lowest linear velocity and electrolyte concentration, the average Current Density applied to an electrodialyzer is defined as Limiting Current Density ( I / S ) lim . The solution velocity distribution in an electrodialyzer strongly influences ( I / S ) lim .

  • a computer simulation of batch ion exchange membrane electrodialysis for desalination of saline water
    Desalination, 2009
    Co-Authors: Yoshinobu Tanaka
    Abstract:

    Abstract A computer simulation program including the principle of ① mass transport, ② Current Density distribution, ③ energy consumption and ④ Limiting Current Density is developed for predicting desalinating performance of a continuous (one-pass flow) electrodialysis process. In this simulation the following parameters are inputted; ① membrane characteristics such as overall transport number, overall solute permeability, overall electro-osmotic permeability, overall hydraulic permeability, direct Current electric resistance etc. ② electrodialyzer specifications such as flow-pass thickness, flow-pass width and flow-pass length of a desalting cell etc. and ③ electrodialytic conditions such as Current Density, electrolyte concentration in a feeding solution, linear velocity in desalting cells, standard deviation of normal distribution of solution velocity ratio etc. In a practical-scale electrodialyzer, electrolyte concentration in a desalting cell is decreased along a flow-pass and it gives rise to electrolyte concentration distribution. It causes electric resistance distribution and Current Density distribution. Solution velocities in desalting cells vary between the cells, and give rise to solution velocity distribution. In this simulation, these distributions are taken into account assuming that the frequency distribution of solution velocity ratio is equated by the normal distribution. Further, the influences of electrodialyzer specifications and elctrodialysis conditions described above on the performances of an electrodialyzer (desalting ratio, Current efficiency, electrolyte concentration at the outlets of desalting cells, cell voltage, energy consumption, electrolyte concentration distribution, Current Density distribution, and Limiting Current Density) are predicted. The simulation model is developed on the basis of the experiments and its reasonability is supported by the performance of electrodialyzers operating in salt-manufacturing plants.

  • Chapter 11 Limiting Current Density
    Membrane Science and Technology, 2007
    Co-Authors: Yoshinobu Tanaka
    Abstract:

    Publisher Summary This chapter discusses the Limiting Current Density. When an electric Current is passed through an ion exchange membrane, salt concentration on a desalting surface of the membrane is decreased due to concentration polarization, and reduced to zero at the Limiting Current Density. The chapter derives the Limiting Current Density equation introduced from the Nernst–Planck equation. The chapter discusses the dependence of Limiting Current Density on electrolyte concentration and solution velocity of a solution. Concentration polarization occurs in a boundary layer formed on the desalting surface of an ion exchange membrane. The Limiting Current Density is influenced by the solution flow in a desalting cell and ionic transport in the boundary layer. Limiting Current Density of an electrodialyzer is influenced by the distribution of solution flow in desalting cells. The chapter explains Limiting Current Density of an electrodialyzer based on the Limiting Current Density equation.

Denise Crocce Romano Espinosa - One of the best experts on this subject based on the ideXlab platform.

  • Determination of Limiting Current Density, Plateau Length, and Ohmic Resistance of a Heterogeneous Membrane for the Treatment of Industrial Wastewaters with Copper Ions in Acid Media
    Energy Technology 2019, 2019
    Co-Authors: Kayo Santana Barros, Jorge Alberto Soares Tenório, Valentín Pérez-herranz, Denise Crocce Romano Espinosa
    Abstract:

    In the last years, the electrodialysis process has been considered as an alternative to the chemical precipitation for the treatment of wastewaters from electroplating industries due to some limitations involved in the precipitation, as the sludge formation. For the success of the electrodialysis, some membranes properties have to be evaluated and the chronopotentiometry technique can be used. Hence, the present paper aimed at using chronopotentiometry for determining the Limiting Current Density, plateau length, and ohmic resistance of the cationic heterogeneous HDX100 membrane by constructing Current–voltage curves. The synthesized solution of the effluent from the electroplating industry evaluated was prepared with copper sulfate and sulfuric acid (2 g Cu2+/L and pH 2). The chronopotentiometric curves were also evaluated for the study of the precipitate formation. According to the results, typical curves of monopolar membranes were obtained and the properties could be effectively determined by chronopotentiometry.

  • chronopotentiometry of an anion exchange membrane for treating a synthesized free cyanide effluent from brass electrodeposition with edta as chelating agent
    Separation and Purification Technology, 2018
    Co-Authors: Kayo Santana Barros, Denise Crocce Romano Espinosa
    Abstract:

    Abstract The promising substitution of cyanide by EDTA as chelating agent in brass electrodeposition has been evaluated by many researchers in the last few years. This is very interesting for treating the effluent generated, since the presence of EDTA facilitates the recovery of the metals using electrodialysis, for example. Hence, using chronopotentiometry, our aim was to investigate the transport properties of the chelates involved in the potential treatment by electrodialysis of the effluent generated in the free-cyanide brass electrodeposition. We assessed the Limiting Current Density, ohmic resistance, plateau length, concentration polarization and the undesirable precipitate formation in function of the solution pH, Cu2+/Zn2+ proportion and EDTA/Cu2+ molar ratio using the anionic HDX200 membrane. The pH solution showed a strong relation with all the properties and under higher pH, precipitate formation by the curves behavior was verified. Besides, the precipitate formation was also observed for the lower proportion of Cu2+, while no unexpected behavior was verified for Cu2+ concentrations ≥ Zn2+. Finally, the EDTA concentration altered only the Limiting Current Density, since similar typical chronopotentiograms and Current-voltage curves were obtained. It was found that the better conditions of the effluent to be treated may be pH 9/10, Cu2+ proportion = 50% and EDTA/Cu2+ = 2.5.

  • Determination of Limiting Current Density of a Solution with Copper, Zinc and EDTA from the Effluent of Brass Electrodeposition
    Energy Technology 2018, 2018
    Co-Authors: Kayo Santana Barros, J. A. S. Tenório, Denise Crocce Romano Espinosa
    Abstract:

    In the last decades, authors have been focused in the development of a cyanide-free bath for the electroplating industry of brass due to the risks that involves the use of cyanide and they have been evaluated the electrodialysis as an alternative method for the treatment of the effluent generated in this type of industry because of the limitations caused by the chemical precipitation. Hence, the present paper aimed to determine the Limiting Current Density of the effluent generated in the free-cyanide electrodeposition of copper and zinc using EDTA as chelating agent for the treatment of the effluent by electrodialysis. The synthesized solutions were prepared with copper sulfate and zinc sulfate in different conditions of pH (10–12) and proportion of cupric ions (30%, 50%, 70%). According to the results, the increase of pH and the cupric ions proportion caused an increase in the Limiting Current Density because of the larger amount of anionic species in solution and the consequent difficult to achieve the concentration polarization phenomenon.

  • Evaluation of the transport properties of copper ions through a heterogeneous ion-exchange membrane in etidronic acid solutions by chronopotentiometry
    Journal of Membrane Science, 2017
    Co-Authors: Tatiana Scarazzato, Zehbour Panossian, M. García-gabaldón, E. Ortega, Jorge Alberto Soares Tenório, Valentín Pérez-herranz, Denise Crocce Romano Espinosa
    Abstract:

    Abstract The transport properties of copper chelates across an anion-exchange membrane were investigated by means of chronopotentiometry. Several solutions containing etidronic acid, copper sulfate and potassium chloride were evaluated. Tests were accomplished in a three-compartment reactor using a heterogeneous membrane containing quaternary ammonium functional groups. Results showed a strong relation between the amount of chelated anions and the Limiting Current Density, the electrical resistance and the concentration polarization. An increase in the anionic equivalent charge of the solutions modified the three regions of the Current-voltage curves. The acid medium was found to be less favorable because of the possibility of the formation of non-charged species in overLimiting regions. The presence of chloride anions increased the Limiting Current Density, especially when the chloride concentration exceeded the etidronic acid concentration.

Yoshihiko Sano - One of the best experts on this subject based on the ideXlab platform.

  • Numerical Estimation of Limiting Current Density by Focusing on Mass Transfer within Porous Spacers in an Electro-Dialysis.
    Membranes, 2019
    Co-Authors: Yoshihiko Sano, Kosuke Fukagawa, Fujio Kuwahara
    Abstract:

    Estimating and increasing Limiting Current Density (LCD) levels is of fundamental importance for the development of electrodialysis (ED) systems, and it is becoming clear that the use of porous spacers can significantly increase such LCD levels. In this study, a three-dimensional numerical simulation was proposed for evaluating the mass transfer within a porous spacer unit cell and for estimating LCD levels. It was found that our proposed method is effective for estimating the minimum value of an LCD, which is a significant factor related to the safe operation of ED systems. Furthermore, it was found that increasing the minimum effective Sherwood number provides a key to increasing LCD levels. Porous spacer design guidelines were proposed based on the numerical simulation results, after which a new spacer was introduced, designed according to those guidelines. It was found that flow disturbances on the membrane caused by porous spacer structures can lead to increases in effective Sherwood numbers and that LCD levels could be increased by eliminating the flow stagnation behind the structures on the membrane. The LCD of our new spacer was found to be higher than that of the spacers with the highest LCD levels in use at present. Therefore, we can conclude that the proposed design guidelines are effective for increasing LCD levels.

  • Effect of a porous spacer on the Limiting Current Density in an electro-dialysis desalination
    Desalination, 2018
    Co-Authors: Yoshihiko Sano, Xiaohui Bai, Shuzen Amagai, Akira Nakayama
    Abstract:

    Abstract A series of experiments have been carried out to examine the performance of porous spacers proposed for increasing the Limiting Current Density, since it is of fundamental importance to find an optimal operate condition in an electro-dialysis. The fluid mixing in the porous material can play an important role to suppress the concentration polarization and achieve a high Limiting Current Density. The effect of porous spacers filled in both dilute and concentrate channels on the stack voltage and the Limiting Current Density has been investigated by comparing the cases with and without porous spacers. It has been found that the Limiting Current Density with porous spacers is 1.8 to 3.3 times higher than that without a porous spacer as a result of mechanical dispersion caused by fluid mixing in porous materials. Furthermore, the increase ratio of Limiting Current Density with the present spacers to that without spacer is higher than that of conventional mesh spacers. Moreover, it was found that the electrical resistance does not increase even when inserting the present porous spacers by comparing that of conventional mesh spacers, since the present porous spacer can suppress the concentration polarization concerned with electrical resistance. On the other hand, the increase in the pumping power turns to be negligible small by comparing the electrical power for an electro-dialysis since permeability of the present spacers is sufficiently high. In this study, it has been proven that the insertion of porous spacers is quite useful in terms of Limiting Current Density, electrical resistance and pumping power.

  • A boundary layer analysis for determination of the Limiting Current Density in an electrodialysis desalination
    Desalination, 2017
    Co-Authors: Akira Nakayama, Yoshihiko Sano, Xiaohui Bai, Kenji Tado
    Abstract:

    Abstract A general ion-transport equation has been derived eliminating the electrophoresis term from the set of Nernst-Planck equations for cations and anions, under the local electro-neutrality assumption. Boundary layer solutions were obtained for the two asymptotic cases of sufficiently short and long channels, respectively, when the electric Current is applied uniformly across the channels. A local volume averaging theory for porous media was also introduced to describe the cases of electrodialysis stacks with spacers. The results obtained for both with and without spacers are compared against available experimental data. The predicted Limiting Current Density and stack voltage based on the asymptotic solutions for sufficiently short channels agree well with those of measurements for both cases with and without spacers, revealing the validity of the present analysis based on the local electro-neutrality assumption. It has been clearly shown that the spacers work to delay possible depletion of the ions on the dilute side of the membrane, thus increasing the Limiting Current Density.

Heiner Strathmann - One of the best experts on this subject based on the ideXlab platform.

  • determination of the Limiting Current Density in electrodialysis desalination as an empirical function of linear velocity
    Desalination, 2006
    Co-Authors: Heiner Strathmann, Seung-hyeon Moon
    Abstract:

    Electrodialysis is known to be a useful membrane process for water desalination. The Limiting Current Density (LCD) in the electrodialysis process is an important parameter which determines the electrical resistance and the Current utilization. Usually, LCD depends on membrane and solution properties as well as on the electrodialysis stack construction and various operational parameters such as the flow velocity of the diluate solution. Therefore, a reliable determination of LCD is required for designing an efficient electrodialysis plant. In this study, LCD was measured in an electrodialysis flow cell system of given geometry and spacer configuration as a function of the linear velocity. The coefficients a and b of an equation describing LCD as a function of the linear flow velocity of the diluate solution, ilim=aCub, were determined from a plot of the measured LCD over the electrolyte concentration versus the linear velocity on a double logarithmic scale. It was found that the coefficient b was related to the hydrodynamic conditions, while the coefficient a was affected by the cell geometry, electrolyte concentration and the membrane properties.

  • determination of the Limiting Current Density in electrodialysis desalination as an empirical function of linear velocity
    Desalination, 2006
    Co-Authors: Heiner Strathmann, Seung-hyeon Moon
    Abstract:

    Electrodialysis is known to be a useful membrane process for water desalination. The Limiting Current Density (LCD) in the electrodialysis process is an important parameter which determines the electrical resistance and the Current utilization. Usually, LCD depends on membrane and solution properties as well as on the electrodialysis stack construction and various operational parameters such as the flow velocity of the diluate solution. Therefore, a reliable determination of LCD is required for designing an efficient electrodialysis plant. In this study, LCD was measured in an electrodialysis flow cell system of given geometry and spacer configuration as a function of the linear velocity. The coefficients a and b of an equation describing LCD as a function of the linear flow velocity of the diluate solution, ilim=aCub, were determined from a plot of the measured LCD over the electrolyte concentration versus the linear velocity on a double logarithmic scale. It was found that the coefficient b was related to the hydrodynamic conditions, while the coefficient a was affected by the cell geometry, electrolyte concentration and the membrane properties.

  • Limiting Current Density and water dissociation in bipolar membranes
    Journal of Membrane Science, 1997
    Co-Authors: Heiner Strathmann, J.j. Krol, H.-j Rapp, Gerhart Eigenberger
    Abstract:

    The behaviour of bipolar membranes in NaCl and Na2SO4 solutions is discussed. The membranes are characterized in terms of their Limiting Current densities. Below the Limiting Current Density the electric Current is carried by salt ions migrating from the transition region between the anion and the cation exchange layer of the bipolar membrane. In steady state these ions are replaced by salt ions transported from the bulk solutions into the transition region by diffusion and migration due to the fact that the ion-exchange layers are not strictly permselective. When the Limiting Current Density is exceeded, the salt transport from the transition region can no longer be compensated by the transport into the region and a drastic increase in the membrane resistance and enhanced water dissociation is observed. This water dissociation is described as being a combination of the second Wien effect and the protonation and deprotonation of functional groups in the membrane. The Limiting Current Density is calculated from a mass balance that includes all components involved in the transport. The parameters used in the mathematical treatment are the diffusion coefficients of salt ions and water, the ion mobilities in the membrane, the fixed charge densitiy of the membrane, the pKb values of the functional groups and the solution bulk concentrations.

Akira Nakayama - One of the best experts on this subject based on the ideXlab platform.

  • Effect of a porous spacer on the Limiting Current Density in an electro-dialysis desalination
    Desalination, 2018
    Co-Authors: Yoshihiko Sano, Xiaohui Bai, Shuzen Amagai, Akira Nakayama
    Abstract:

    Abstract A series of experiments have been carried out to examine the performance of porous spacers proposed for increasing the Limiting Current Density, since it is of fundamental importance to find an optimal operate condition in an electro-dialysis. The fluid mixing in the porous material can play an important role to suppress the concentration polarization and achieve a high Limiting Current Density. The effect of porous spacers filled in both dilute and concentrate channels on the stack voltage and the Limiting Current Density has been investigated by comparing the cases with and without porous spacers. It has been found that the Limiting Current Density with porous spacers is 1.8 to 3.3 times higher than that without a porous spacer as a result of mechanical dispersion caused by fluid mixing in porous materials. Furthermore, the increase ratio of Limiting Current Density with the present spacers to that without spacer is higher than that of conventional mesh spacers. Moreover, it was found that the electrical resistance does not increase even when inserting the present porous spacers by comparing that of conventional mesh spacers, since the present porous spacer can suppress the concentration polarization concerned with electrical resistance. On the other hand, the increase in the pumping power turns to be negligible small by comparing the electrical power for an electro-dialysis since permeability of the present spacers is sufficiently high. In this study, it has been proven that the insertion of porous spacers is quite useful in terms of Limiting Current Density, electrical resistance and pumping power.

  • A boundary layer analysis for determination of the Limiting Current Density in an electrodialysis desalination
    Desalination, 2017
    Co-Authors: Akira Nakayama, Yoshihiko Sano, Xiaohui Bai, Kenji Tado
    Abstract:

    Abstract A general ion-transport equation has been derived eliminating the electrophoresis term from the set of Nernst-Planck equations for cations and anions, under the local electro-neutrality assumption. Boundary layer solutions were obtained for the two asymptotic cases of sufficiently short and long channels, respectively, when the electric Current is applied uniformly across the channels. A local volume averaging theory for porous media was also introduced to describe the cases of electrodialysis stacks with spacers. The results obtained for both with and without spacers are compared against available experimental data. The predicted Limiting Current Density and stack voltage based on the asymptotic solutions for sufficiently short channels agree well with those of measurements for both cases with and without spacers, revealing the validity of the present analysis based on the local electro-neutrality assumption. It has been clearly shown that the spacers work to delay possible depletion of the ions on the dilute side of the membrane, thus increasing the Limiting Current Density.