Electrodialysis System Research Articles

Enhancement of the current efficiency for sodium hydroxide production from sodium sulphate in a two-compartment bipolar membrane electrodialysis system

Abstract Sodium sulphate, a by-product of chlorine dioxide generators and probably of most totally chlorine free (TCF) pulp bleaching sequences, was split into sodium hydroxide and sulphuric acid by using a two-compartment bipolar membrane electrodialysis (BME) system employing WSI4010/1030 bipolar membranes and Nafion417 cation-selective membranes. The current efficiency was enhanced by using the buffering effect of divalent anions such as sulphate to reduce the free hydrogen ion concentration in the feed compartment. In the optimized experiment, sodium hydroxide (1.08 M at 46 ml min−1) and sodium sesquisulphate (0.74 M at 68 ml min−1) were produced at a current efficiency of 78% for the production of both acid and base. The power requirement was 1986 kWh t−1 of sodium hydroxide at a current density of 142.9 mA cm−2 and with an effective membrane area of 728 cm'. Under the conditions of this experiment, it was possible to extract 25% of the sodium content of sodium sulphate in the form of sodium hydroxide.

Salt extraction from hydrogen‐sulfide scrubber solution using electrodialysis

AbstractThe buildup of undesirable sulfur compounds(sulfates and thiosulfates) reduces the scrubbing effectiveness of the LO‐CAT I autocirculation sulfur recovery process from acid‐gas stream. Among various processes, withdrawing and disposing of a portion of the scrubber solution and replacing this “blowdown” with fresh solution have been the practice in the industry. The application of the electrodialysis system to recycle the blowdown is presented. Experiments were carried out using electrodialysis to separate salts (sulfates and thiosulfates) from the LO‐CAT I autocirculation scrubber solution containing organic chelating agents, iron, and various alkali‐metal inorganic salts. The results indicated that the electrodialysis was successful in removing 50% of the salts from the scrubber solution with less than 8% loss of organic and 8% loss of carbonates. The fluxes of the undesired salt species were high even at low current densities (200 to 400 A/m2).

Modelling electrodialysis using the Maxwell-Stefan description

The Maxwell-Stefan mass transfer description is applied to two electrodialysis systems. Firstly, a model system involving NaCl and HCl is investigated. For this system, all the model parameters are obtained either from separate experiments or existing correlations. Although it is not possible to determine all the parameters accurately, the values found are all within the ranges expected. Secondly, a two amino acid system is investigated. The separation of two amino acids using electrodialysis is found to be feasible. Unfortunately, it is too difficult to obtain sufficient data for a proper quantitative description of the process. In both cases, the Maxwell-Stefan description appears to provide a thorough model of the electrodialysis process.

The development of a new electrodialysis system for brackish water

This paper describes a new high-performance electrodialyzer using ion exchange membranes which can be used for potable water production, water reuse, and production of table salt.

Theoretical studies on the separation of different ionic species of the same charge sign using cascaded electrodialysis with reflux

A feasibility study is carried out theoretically for the separation of different ionic species of the same charge sign via repeated permeation through ion-exchange membranes in multi-stage electrodialysis systems. In order to avoid excessive depletion and accumulation of ionic species in the cascade, reflux lines on both sides of the system return the recycle streams from each stage to the previous stage. Two types of cascades are considered. In the first type, called the ‘Cross type’, there are two center compartments over two units, and the reflux streams from the second set of these units are mixed and fed jointly to the two center compartments. In the second type, the ‘Straight type’, there is one center unit, and the depleted and concentrated reflux streams from the second units are mixed and fed to the center unit. A set of generalized equations for the concentration of each ionic species at each stage is derived for both cascade types. For ion-exchange membranes with perm-selective coefficients for ionic species 2 compared to ionic species 1, T 2 1 , of 2.0, numerical calculations are carried out for systems with 6, 10, 14 and 18 total cell compartments. The separation is predicted for two ionic species of the same charge and identical concentration. For the case of a mole fraction of ionic species 1 equal to 0.80 in the depleted withdrawal stream, the total recovery in a cross-type, multi- staged, electrodialysis system with reflux and 18, 14, 10 and 6 compartments is 0.27, 0.25, 0.24, and 0.23, respectively. And that for a straight-type system is 0.31, 0.30, 0.28 and 0.23, respectively. Hence, both the cross-type and straight-type system benefit from the addition of reflux. The former exhibited recoveries of 1.5 ∼ 1.8 times that of a unit electrodialysis cell, while the latter exhibited recoveries of 1.5 ∼ 2.1 times that of a unit electrodialysis cell.

Improved spacer design and cost reduction in an electrodialysis system

In electrodialysis using thin membranes and spacers, the compactness of the membrane cell-pairs leads to a small potential drop, and hence to energy saving. The spacer design itself has a great effect on the cost of the plants, since spacers act as turbulence promoters. A careful design, to increase the mass transfer coefficients, can reduce the membrane surface area required for a given application. Limiting current measurements, cell-pair resistance and pressure losses are presented for several thin spacers, for different flow-velocity values and feed water concentrations. It was possible to find an advantageous geometry of the separating mesh leading to substantial savings on investment and operation costs.

Production of 6-Aminopenicillanic Acid in Immobilized Enzyme Reactor with Electrodialysis.

Phenylacefic acid, an inhibitory product, was formed through the hydrolysis of penicillin G by immobilized penicillin acylase. In this study, electrodialysis was applied to remove phenylacetic acid continuously from the reaction mixture and to enhance the efficiency of the reaction.The permeation rate of phenylacetic acid, in this electrodialysis system was found to be much faster than those of two other compounds, penicillin G and 6-aminopenicillanic acid. Therefore, the membranes selected here might be suitable for continuous removal of phenylacefic acid from the reaction mixture for penicillin G hydrolysis. However, the permeation rate of phenylacetic acid was significantly influenced by the penicillin G concentration; it decreased with increasing penicillin G concentration. A theoretical model was developed to describe this phenomenon and was applied to the hydrolysis of penicillin G by means of a combination of immobilized penicillin acylase and electro dialysis. The experimental data were compared to those predicted by a model using independently determined parameters such as the Michaelis constant, inhibition constants and permeation rate constants. Fairly good agreement was found between the theoretical and experimental data. When a 100 mol·m–3 penicillin G solution was used as the substrate, the time required to reach 98% conversion could be reduced to 24.7% by using the combination with electrodialysis.

イオン交換膜電気透析系を活用した実用的な飲料水用新殺菌法（ＩＩ）工学的解析

イオン交換膜電気透析系を活用した実用的な飲料水用新殺菌法（ＩＩ）工学的解析

Continuous production of acetic acid by electrodialysis bioprocess with a computerized control of fed batch culture

The technique of electrodialysis bioprocess, in which acetic acid is continuously removed from the reaction mixture, was applied to the production of acetic acid by Acetobacter aceti. The continuous supply of ethanol and concentrated nutrient solution to the reaction mixture allowed the production of acetic acid to continue for 30 d, while production continued for only 2 d without the electrodialysis system, with or without pH control. During electrodialysis bioprocess, 2221.9 g of acetic acid was produced from 1991.6 g of ethanol during the course of a single culture run of 30 d. The maximum rate of production of acetic acid obtained by electrodialysis bioprocess under the improved electrodialysis conditions was 5.5 g h −1, which was about 1.7 times higher than the rates obtained by bioprocesses without the electrodialysis system. The improvement in the rate of production and yield of acetic acid resulted from the alleviation of the inhibitory effect, on metabolism of the microbe, of the acetic acid that is produced, by maintaining a favorable pH and a low level of acetic acid in the reaction mixture by electrodialysis.

Bactericidal effect of an electrodialysis system on E. coli cells

Using a new electrodialysis system with both cation- and anion-exchange membranes, the bactericidal effect on Escherichia coli has been investigated in detail from the standpoint of electrochemistry. Various electrolyte solutions containing E. coli (10 5 cells/cm 3) were passed through a desalting chamber at a flow rate of 3 cm 3/min under varying current densities, and the viability of the cell (%) and the pH changes in the effluents were measured. When a 0.1 M NaCl aqueous suspension was used, a disinfection effect emerged in the vicinity of the limiting current density (LCD 0.81 A/dm 2) and increased with an increase in the current density. The pH value of the suspensions decreased owing to the dissociation of water to H + and OH − ions by the well-known “neutrality disturbance phenomenon” in the region beyond the LCD. These tendencies were also observed when other electrolyte suspensions were used. Concerning the effect of the various species on the disinfection of E. coli cells, ionic systems in which a LCD was easily attained were found to have a strong effect. The germicidal effect may be due to a synergistic effect of acidic H + and basic OH − ions which are produced on the anion-exchange membrane and cation-exchange membrane, respectively, of the desalting chamber.

Bactericidal effect of an electrodialysis system on E. coli cells

Using a new electrodialysis system with both cation- and anion-exchange membranes, the bactericidal effect on Escherichia coli has been investigated in detail from the standpoint of electrochemistry. Various electrolyte solutions containing E. coli (10 8 cells/cm 3) were passed through a desalting chamber at a flow rate of 3 cm 3/min under varying current densities, and the viability of the cell (%) and the pH changes in the effluents were measured. When a 0.1 M NaCl aqueous suspension was used, a disinfection effect emerged in the vicinity of the limiting current density (LCD 0.81 A/dm 2) and increased with an increase in the current density. The pH value of the suspensions decreased owing to the dissociation of water to H + and OH − ions by the well-known “neutrality disturbance phenomenon” in the region beyond the LCD. These tendencies were also observed when other electrolyte suspensions were used. Concerning the effect of the various species on the disinfection of E. coli cells, ionic systems in which a LCD was easily attained were found to have a strong effect. The germicidal effect may be due to a synergistic effect of acidic H + and basic OH − ions which are produced on the anion-exchange membrane and cation-exchange membrane, respectively, of the desalting chamber.

ふっ素系イオン交換膜を用いた電気透析法による大腸菌の殺菌

Disinfection effects of electrodialysis systems using a cationic type fluorinated membrane (Nafion-415) on E. coli cells have been investigated.E. coli suspended in various electrolyte solution (108 cells/cm3) were passed through a desalting chamber at a flow rate of 3 cm/min at different current densities, and viability (%) in the effluents was determined.Remarkable disinfection effects were observed for the Nafion-415 system compared with the system of a usual cation-exchange membrane (CMV). For example, the E. coli cells suspended in 0.1 mol⋅dm-3 NaCl solution were perfectly devitalized after 20 min of the electrodialysis at the current density of 1.63 A/dm2.

Ion conducting spacer for improved ed

Polarization in electrodialysis systems can be suppressed by suitably shaped ion-conducting spacers. Cation- and anion-exchange fibers were used for the preparation of such spacers. In a laboratory cell pair, performance of the conducting spacer was compared to that of a geometrically similar inert one. High coulombic efficiency, stable pH, and low resistance were found with the conducting spacer at low dialysate concentration, high current density and low flow rate. With the inert spacer, water splitting was evident in this region, shown by acidification of diluate, and decrease of efficiency. The effective thickness of the dialysate cell containing the conducting spacer was found to be smaller than the actual geometrical one.

ELECTRODIALYSIS OF RAW WHEY AND WHEY FRACTIONATED BY REVERSE OSMOSIS AND ULTRAFILTRATION

ABSTRACTElectrodialysis is a unit operation which removes ionic species from a solution through the use of an imposed voltage and ion‐selective membranes. The temperature, flow rate, and composition of the feed, and the applied voltage all influence the rate of ionic transport in electrodialysis systems. The effects of the aforementioned process parameters on the performance of an electrodialysis system were investigated using cottage cheese whey as the process feed. Increasing the flow rate proved to be of little value in decreasing the membrane stack resistance for a given run, but it significantly retarded the rate at which the stack resistance increased in repeated runs. The effect of increasing the total solids concentration of the whey without altering the solute composition was to increase the potential rate of demineralization through an increase in conductivity. Prefractionation of the feed by ultrafiltration enhanced the value of the whey solids by increasing the protein concentration and decreasing the ash concentration. However, the electrodialytic process was less efficient in removing the remaining ash in this case than it was in demineralizing other feeds.

Sherwood Number and Friction Factor Correlations for Electrodialysis Systems, with Application to Process Optimization

Sherwood Number and Friction Factor Correlations for Electrodialysis Systems, with Application to Process Optimization

The aqueous extraction of protein from plant tissue with the use of electrodialysis

An electrodialysis system was used for the aqueous extraction of protein from frozen tissue of mung bean (Phaseolus aureus Roxb.) hypocotyl followed by gel electrophoresis and assay of polyphenol oxidase, esterase, and fungal glucose oxidase isozymes. The isozymes tested showed a consistent increase in activity with the increase in current, between 0 and 100 mA, suggesting that current application can overcome, in part, alterations in protein fraction during the aqueous extraction of plant tissue. Details of the extraction procedure and the construction of the electrodialysis system are described.

Membrane fouling in electrodialysis: a model and experiments

Membrane fouling is a common cause for poor performance in electrodialysis systems, usually because it reduces the limiting current. Fouling may be caused by deposits of either neutral matter or colloidal matter with ion exchange properties. In the present paper a model for membrane fouling is developed and expressions are derived for the reduction in limiting current caused by both neutral fouling films and films having ion exchange properties. The effect of fouling is shown to depend not only on the properties of the fouling film, but also on the hydrodynamic conditions in the channels and in the case of ion exchange fouling films on the salt concentration in the dialysate channel. Ion exchange fouling films are shown to be much more effective in reducing the limiting current than neutral films. Some experimental data are presented which confirm the trend of the theory for fouling with ion exchange films.

Experimental study of the effects of hydrodynamics and membrane fouling in electrodialysis

Experimental data are presented for the performance of a multicompartment electrodialysis system with laminar flow in plane, unobstructed channels. The data include current-voltage characteristics, current density distributions, and pH in the brine and dialysate effluents, for a wide range of operating conditions. The results are shown to be in good agreement with the theory of Sonin and Probstein ( Desalination, 5(1968) 293), provided that the membranes are relatively free of surface contamination. Fouling of the membrane surfaces, induced in these experiments by iron oxide in the feed water, is shown to bring about a reduction of the limiting current by as much as a factor of two below the theoretical value. The magnitude of the decrease depends on flow speed and other operating conditions.

Concentration polarization in electrodialysis—III. Practical electrodialysis systems

Concentration overpotential has been measured in systems having mass transfer by forced convection caused by flow through a compartment bounded by ion- between the bulk solution concentration and the apparent interfacial concentration derived from the measured overpotential is found to be non-linear. T increasing current, together with the presence of a diffusion layer of varying thickness. Interposition of a perforated corrugated spacer between the m thicknesses to an extent which increases with increasing flow velocity. Systems with mass transfer by stirring are briefly reported upon.