After investigations were done under several conditions, a recovery cycle of hydrating agent (dichloromonofluoromethane, R-21) was established. In this cycle, R-21 was desorbed from the solution produced by gas hydrate process, and it was absorbed into raw sea water, by means of carrier gas and packed towers. Results obtained were as follows: 1) A test plant (packed volume in each tower was 0.0327m3) could be operated for a long time without any trouble and showed very stable results. 2) When 0.8-1.5m3/hr of carrier gas was applied in the both desorbing and absorbing towers, 0.2-0.4m3/hr of liquid could be charged. Channelling occured in the both towers at liquid flow rate of 0.1m3/hr, and flooding in the desorbing tower at 0.5m3/hr. 3) On the desorption, the optimum conditions for operating the tower were such as liquid flow rate was 0.2m3/hr, gas-liquid molar flow ratio was about 200 and in higher operating temperature (20-25°C). Under these conditions, desorbing ratio for R-21 was about 99%. 4) On the absorption, the tower could be most effectively operated at the liquid flow rate of 0.2-0.4m3/hr, but gas-liquid molar flow ratio which influenced the absorbing ratio was not defined. Under these conditions, absorbing ratio for R-21 was more than 99% at an average value. 5) The operating temperature of the tower during the desorption was so influential that it exerted an influence even upon the adsorption. 6) Theoretical tower heights for desorpton and absorption were calculated under various conditions by over-all volumetric mass transfer coefficient, which were lower than 10m.
Concentration and its distribution at and near the concentrating side surface (interfaces) of ion exchange membranes were estimated. Electrodialysis was carried out at 2 or 4 A/dm2 and 25°C, and 0.5 N-NaCl solution was used as raw solution. The estimation was done by Schlieren-Diagonal method previously reported. A process of concentration change in the interfaces during the concentrating process from O.5 N-NaCl to equilibrated concentration was shown by photographs. Concentration distributions in the interfaces under the equilibrium were observed to be a straight line in the Schlieren patterns, which showed that concentration differences in the interfaces from that of bulk solution could be expressed by quadratic equations of distance from membrane surface. Cencentration at membrane surfaces increased with current density increased. Concentration difference there between anion and cation exchange membrane, however, increased at increased current density. Concentration at membrane surface Ci, on the other hand, could be expressed by a linear equation of that of bulk solution Cb as Ci=αCb+Co. Both of constants α and Co were characteristic to membrane species and particularly,α was independent of current density. This relationship was seemed to be useful for a “dynamic characterization” of membranes which had previously been proposed.
As a fundamental experiment intended to examine a high caking tendency of refined salt, the authors studied a crystallizing process of two types of brine (A type was sulfate ion-rich, while B type was magnesium ion-rich) by concentrating them at 25°C and 55°C. Results were discussed from the viewpoints of changes in chemical composition, solid phase during crystallization, changes in the density of mother liquid and the ratio of sodium ion crystallized to total sodium ion. As a consequence, the following results were obtained: 1. In concentrating A type brine at 25°C, Na2SO4 crystallized, and the crystallizing process agreed with calculated process. During the concentration of B type brine, astrakanite crystallized, and the process agreed fairly well with calculated process. In case of B type brine, the mother liquid had a tendency to super-saturate with sulfate ion. 2. In concentrating A type brine at 55°C, Na2SO4 and vanthoffite crystallized. The process did not agree with calculated process because the concentrated solution super-saturated with sulfate ion. During the concentration of B type brine, astrakanite and loeweite crystallized. However, the process did not agree with calculated process. 3. During the crystallization, the density of mother liquid of B type brine increased more rapidly than that of A type brine. 4. During the crystallization, the sodium ion crystallized from B type brine was larger in ratio than that crystallized from A type brine.
In their previous paper (This Journal 20, 254-263 (1967)), the authors reported on the graphical calculations of the process of isothermal evaporation at 25°C of ion-exchange membrane brines by means of equilibrium diagrams of the five-component system. In the present paper, it was studied on the concentration of the brine belonging to NaCl-KCl-MgCl2-MgSO4-CaSO4-H2O type at 25°C. Two kinds of synthetic brines without calcium sulphate were prepared and evaporated to various concentrations. The compositions of the solutions were chemically analyzed and those crystals deposited were identified by X-ray diffraction. The authors tried to verify the validity of the graphical calcuations experimentally, and concluded as follows; 1) The compositions of the solutions were found to be fairly good coincidence with the calculated values, and the kinds of deposited crystals also were found to be in complete coincidence with that of crystals on the diagram. 2) For the simplicity's sake, all points on the diagram were combined with straight lines and all surfaces were assumed to be planes. But in fact, it was found that the surfaces to be curved one, and to be convex toward the origin, and the deviation to be the more marked at the higher concentration. 3) In the calculation of the evaporation of the brine, the presence of calcium sulphate may be neglected, as in the case of sea-water concentration. 4) It was found that the specific gravity (d254=1.21-1.33) of the solutions to increase linearly with the chloride ion conceatration, and under the simple conditions as the case of this experiment, chloride ion concentration or specific gravity etc. may be used as the degree of concentration.