The principles of electrodialysis, electrolysis and their actual conditions have been introduced mainly for applications of ion preferential permselectivity. The perfluorinated cation exchange membrane mainly uses chlor-alkali. The essentian requirements for the chlor-alkali membrane are high current efficiency and high conductivity. The chlor-alkali membranes consist of a carboxylate polymer with high current efficiency and sulfonate polymer with high conductivity to fulfill the requirements. The chlor-alkali membranes usually have a two layer structure. Ion exchange membranes with preferential permselectivity for monovalent ions are used by necessity to avoid any scale formation when producing table salt. In the case of anion exchange membranes, preferential permselectivity for monovalent anions is achieved by covering the membrane surface with a very thin layer of polyanions. On the other hand,Ion exchange membranes with preferential permselectivity between monovalent anions have also been studied. A noble kind of membrane will be developed in a variety of fields.
The improvement in permeability of glutamic acid across anion ion exchange membrane was investigated. The permeability of glutamic anion across the anion exchange membrane depends greatly on the temperature and concentration of glutamate in the solution and it is highest at the 2mol/l of glutamate under the condition of the temperature over 40°C obtained from the measurement of limiting current density. The perm-selectivity coefficient (TAB) of various ions contained in the glutamate fermentation broth was calculated on the basis of the glutamic acid from the data of electrodialysis operated by the following conditions; current density 2A/dm2, concentration of glutamate 1.67mol/l pH 6.5, circulation rate 1.3cm/s. The order of relative selectivity was as follows; K>Na>Mg>Ca>color substance>Protein. More than 80% of the neutral amino acids remained in the feed solution through the electrodialysis operation. The effect of the temperature on the relative perm-selectivity coefficient of glutamate ion to sodium ion was measured and found to be 0.05 for 15°C and 0.54 for 55°C. The two stage operation of electrodialysis for recovery and purification of glutamate from fermentation was performed; first stage operated for demineralization at 15del.°C charged with 5.2 V for about 14 hours and the following stage operated for removal of weak or non electrolyte substances at 55°C charged constant current density of 2A/dm2 for 12 hours. The recovery of glutamate was 95% and more than 95% of salts were removed and colored substance was also removed about 80%. For the application of ion exchange membrane to glutamate industry, further innovation of membrane and the development of design technology of the process are necessary.
In order to maintain long term stable operation in an Electrodialyzer, it is necessary to pay careful attention to proper pretreatment, as well as to good design of the Electrodialyzer so that water decomposition is prevented. In particular, the purpose of the Electrodialyzer is to demonstrate a large desalination ratio. Therefore, the electrical resistance will show some distribution between the inlet and the outlet. Because of the difference in liquid resistance, there is membrane resistance and membrane potential between them. In this paper, the electrical current distribution in the Electrodialyzer is calculated using a number of assumptions. The purpose of this paper is to find the relationship between the current distribution and the water decomposition, using a calculation model. It may be useful for both the design and the operation of the Electrodialyzer.
Bipolar membranes consist of a layered structure involving a cation selective membrane joined to an anion selective membrane. This is of practical interest in terms of a new process for the commercial production of acids and bases. This study examines why water splitting is reduced in bipolar membranes. It has been suggested that water splitting occurrs due to the second Wien effect in the intermediate region, because the potential drop is very large. If amines exist in the intermediate region, water splitting is accelerated because protonation and deprotonation reactions occur between H2O and the amines. If space between the cation and anion exchange layers is produced, the water splitting effect is reduced. It was proved that if the anion exchange layer was composed of only binary or ternay amino groups, the water splitting effect was also reduced due to the low anion selectivity.
In this work, bipolar membrane (BPM) was prepared and membrane characteristics were studied. A novel bipolar membrane was prepared by forming polypyrrole from a pyrrole monomer in the presence of Fe3+ at the interface between commercial cation and anion exchange membranes. In an electrodialytic cell composed of four compartments with BPM fixed in the central portion, the current-voltage curve was measured under constant current supply. The current-voltage relation indicated an Ohmic change against the positive current, while the relation abruptly increased the current against the negative current. The increased current seems to be attributable to the proton and hydroxyl ions that were produced inside the bipolar membrane. According to the equation introduced by Mafe et al., these phenomena were interpreted as being due to the increased rate constant of water dissociation in the bipolar membrane. On the other hand, water splitting was also noticed because of pH changes in the KCl solution when dc current was supplied through a pair of Pt electrodes from the anion exchange layer to the cation exchange layer of BPM. When a reverse current (positive current) was applied to the same system, water splitting did not take place. Concentrations of protons or hydroxyl ions calculated from pH values changed linearly in relation to time and each flux was obtained from the slope of the relations. Furthermore, current efficiency was estimated as the ratio of flux to added current. It was indicated that the current efficiency is closely related to donnan salts in bipolar membrane.
A novel electrodialysis process has been developed for the recovery of rare-metal elements from their EDTA complexes. The electrodialyzer used for the experiments was composed of five compartments divided by a cation-exchange membrane, C, and an anion-exchange membrane, A. The compartments were set in the order of Anode, Feed, Reaction, Strip, and Cathode compartments, and were partitioned with the A, C, C and A membranes, respectively. The Feed solution, the Reaction solution, and the Strip solution, each of which flowed through the corresponding compartment, contained CuCl2, rare metal-EDTA complex, and HCl solution, respectively. The electrodialysis for the recovery of rare-metal elements was expected to proceed as follows: When voltage is applied to the electrodialyzer, Cu2+ should proceed from the Feed compartment to the Reaction compartment, and act as the substitute for rare-metal elements in the EDTA complexes. The resultant free ions of rare-metal elements move to the Strip compartment, and are recovered. In the experiments, Co, La, Gd, Y, and Ni were selected as rare-metal elements. In the electrodialysis experiment for the Co-EDTA system, Cu2+ from the Feed compartment was immediately substituted for Co, and part of the resultant Co2+ moved to the Strip compartment. No permeation of Cu-EDTA and free Cu2+ was observed during the dialysis. The flux of Co2+ increased with an increase in current density. For the systems of La-EDTA, Gd-EDTA, and Y-EDTA, the permeation behavior of metal ions was almost the same as that for the Co-EDTA system. For the Ni-EDTA system, however, Cu2+as well as Ni2+ proceeded to the Strip compartment: This suggests that for the Ni-EDTA system the metal substitution reaction is much slower than that for the other metal elements. Moreover, the substitution reaction rates of Cu for the rare-metal elements in the EDTA complexes were measured spectroscopically and analyzed with due consideration of dinuclear complex intermediates. The rate constants were smaller in decreasing order-La-EDTA, Gd-EDTA, Y-EDTA, and Ni-EDTA and were correlated with the stability constants for EDTA.
In order to prevent fouling of ion exchange membranes, the ionic transport and concentration polarization in the substance layer attached to the membrane surface was analyzed in an NaCl solution using the extended Nernst-Planck equation. The ionic diffusion coefficient in a non-infinitely diluted region withn the layer was obtained ushlg the diffusion coefficient equation taken from the Nernst-Einstein equation, and the same coefficient in an infinitely diluted region was expressed using the values in the infinitely diuted region. When the NaCl concentration in the substance layer is increased in the non-infinitely diluted region, the ionic concentration change is expressed linearly. This is because the effbct of convection on the ionic transport is neghgible. When the NaCl concentration is reduced in the non-infinitely diluted region, the ionic concentration is expressed by a curved line and the concentration polarization is moderated to some extent. This is because of the increase in the ionic diffusion codfficient in the low NaCl concentration. In the infinitely diluted region, the ionic diffhsion coefficient being co nstant, the concentration polarization is promoted by the sharp linear decrease of the NaCl concentration neaf the membrane surface. Accordingly, the possibility of trouble occurrhlg, such as water dissociation, increases as a result of the formation of the infinitely diluted region. The concentration polarization is promoted in the substance Iayer because the convection is less and the effect of the 3rd term (convection term) in the extended Nernst-Planck equation decreases. The convection in the layeroccur only as a result of the electro-osmotic flow and convection diffbrence osmotic flow in the membranes. It is important to remove the substance layer attached to the membrane surface in the electrodialysis, because of the cel voltage increase Qwing to the promotion of concentration polarization.
Sodium sulfate, sodium nitrate, ammonium lactate and sodium glycinate were converted to original acids and bases by means of Bipolar membrane electro-dialysis. Sodium sulfate and sodium nitrate were subjected to 3-compartment Bipolar membrane (BPM/CM/AM) electrodialysis. When the concentration of acid and base increased, the current efficiency decreased and the salt content increased. Energy consumption of NaOH production was 2300kwh/t-NaOH. In the case of sodium nitrate, the results were very similar to those for sodium sulfate. Ammonium lactate and sodium glycinate were subjected to 2-compartment Bipolar membrane (BPM/CM) electrodialysis. Ammonium lactate was converted to lactic acid by more than 99%. Energy consumption was 0.61kwh/kgLacH. Sodium glycinate was converted to glycine by 95%. Energy consumption was 0.78kwh/kg Glycine. Ammonium lactate was subjected to 2-compartment Bipolar membrane (BPM/AM) electrodialysis. Ammonium lactate was converted to Lactic acid by more than 98%. Concentration of lactic acid reached 3.5mol/l and energy consumption was 0.83kwh/kgLacH.
The elemental composition (Ca, Na, Sr, Mg, Fe, Mn, Zn, P) of sagittae (otoliths) taken from several species of teleost fish living under different salinities was analysed using Inductivity Coupled Atomic Emission Spectrometry (ICP) after ashing with HNO3 and HClO4 (5:1) in a Teflon vessel (Experiment 1). Concentrations of Na, Sr and Mg in otoliths were dependent on the salinity. The sodium concentration and Na/Ca ratio in the otoliths of freshwater fish, except for rainbow trout, were lower than those of brackish water and sea water fish. The strontium concentration and Sr/Ca ratio in the otoliths of freshwater fish were lower than those of brackish water and sea water fish. The magnesium concentration and Mg/Ca ratio in the otoliths of carp, goldfish and gobid fish were higher than those of eel, rainbow trout and sea water fish. The effect of environmental salinity on elemental composition (Ca, Na, Sr, Mg) in the otoliths of raibow trout and Japanese flounder reared for 3 months at 15±1°C and 20±1°C, respectively, was studied (Experiment 2). The element composition of the otolith portion formed during culturing was analysed using the method mentioned above. The otoliths of rainbow trout exposed to 100% sea water increased with regard to Sr concentration and Sr/Ca ratio, and decreased with regard to Mg concentration and Mg/Ca ratio compared to those for freshwater fish. In the otoliths of the Japanese flounder exposed to 50% sea water, lower values for Na, Sr, Na/Ca and Sr/Ca and higher values for Mg and Mg/Ca than those reared in 100% sea water were found. These results indicate that not only Sr concentration and Sr/Ca concentration ratio, but also Na and Mg concentrations and the ratios of each of these elements to Ca in otoliths may be effective indices for determinating the salinity of a past environment of a fish. It is recommended assessing the history of environmental salinity in fish by means of utilizing synthetically the indices found in this study.