Teiriki Tadaki

The desalination of a mixed solution of an amino acid and an inorganic salt by means of electrodialysis with charge-mosaic membranes

Abstract A new electrodialysis with charge-mosaic membranes was proposed to achieve efficient desalination of a mixed solution of an amino acid and an inorganic salt. For such a mixed solution, the conventional electrodialytic desalination with both cation-and anion-exchange membranes had resulted in a considerable loss of the amino acid through the membranes. In this method, however, the amino acid in the desalination channel of the electrodialyzer migrates away from the membranes so that the permeation loss of the amino acid through the membrane can be prevented. Batchwise desalination experiments by this method were carried out with a glutamic acid or arginine solution including NaCl under the condition of constant electric current density. Similar experiments by the conventional method were also carried out. As a result of comparing both methods, the amino acid loss in this method became much smaller than that in the conventional one. It was confirmed that this method was very useful for the desalination of an amino acid solution. The effects of operating conditions on the desalination process are also discussed.

Calculation of supercooling temperature for primary nucleation of potassium nitrate from aqueous solution by the two-kind active site model

This paper describes the calculation of the supercooling temperature, i.e., the degree of supercooling at which the first nucleation occurs during cooling at a constant rate. The calculation uses the two-kind active site model, a stochastic model in which primary nucleation is assumed to be induced heterogeneously by the active sites in a stochastic manner. The nucleation probability W per unit time cannot be expressed as a function of the degree of supercooling, since the variable p1, which is the number of the first kind active site, satisfies a Poisson distribution. Therefore, a Monte Carlo simulation has been used for its calculation. Analytical solutions, however, are also given for the two limiting cases in which W is given as a function of the degree of supercooling. The calculated average supercooling temperature is in good agreement with the experimental values. The parameter values used for the theoretical calculation were determined experimentally from the time distribution of the first nucleation which occurs at a constant degree of supercooling. The good agreement between theory and experiment proves that nucleation at constant temperature and at constant cooling rate is well understood. The effect of filtering the solution on the supercooling temperature is explained by the reduction of the number of the active sites.

THE DETERMINATION OF DIFFUSION COEFFICIENTS OF COUNTER-IONS IN THE ION-EXCHANGE MEMBRANE BY MEANS OF BATCHWISE DONNAN DIALYTIC EXPERIMENTS

Abstract A new method, based on the Nernst-Planck equation, has been proposed for determining diffusion coefficients of counter-ions in an ion-exchange membrane for bi-ionic Donnan dialysis. This method involves dialytic experiments in which both the solution concentration and the membrane potential are measured under the condition controlled by diffusion resistance in the membrane. It also involves mathematical optimization treatment of the experimental data. The K + −H + system with a cation-exchange membrane was studied, and the optimum diffusion coefficients of these counter-ions were obtained. The diffusion coefficients were found to vary with the ionic composition of the solution. The theoretical time courses of the concentration and membrane potential calculated by using the optimum diffusion coefficients agreed with the experimental results.

Continuous Synthesis of Titanium Dioxide Fine Particles Using a Slug Flow Ageing Tube Reactor

A continuous reactor system for titanium dioxide fine particle synthesis has been proposed, in which a packed bed for the nucleation of fine particles was connected in series with a slug flow ageing tube for growth of the particles. By injection of nitrogen gas into the inlet of the ageing tube, the continuous liquid feed was separated into small portions so that slug flow was formed. Spherical unagglomerated fine particles of titanium dioxide were obtained using this reactor system, and the effectiveness of using slug flow was elucidated. The effects of some operation variables such as liquid flow rate in the ageing tube and tube diameter were also examined. The particles obtained under the slug flow condition had narrower particle size distribution than those under a laminar flow condition at any flow rate. Particle geometric standard derivation (GSD) was found to be as small as that obtained in a batch process. No quality difference in particle GSD exists between ageing tubes of 2 mm i.d. and 3 mm i.d. for the slug flow. Chronomal analysis assuming diffusion-controlled growth was applied and was found to be effective for simulating a continuous particle synthesis process of titanium dioxide.

Modeling and Simulation of Continuous Rotating Annular Ion-Exchange Chromatography for Separation of Amino Acids

Abstract Separation of an amino acid mixture using continuous rotating annular ion-exchange chromatography is numerically simulated by a newly constructed mathematical model. Dissociation reactions of amino acids and eluent buffer components, Nernst-Planck-type intraparticle ionic transport, and a nonlinear ion-exchange equilibrium based on ion-exchange selectivity are considered in the model. The simulated and the experimental results agree well under various operation conditions. The effects of rotation speed of the annular bed and the interstitial liquid velocity on separation are studied experimentally and theoretically.

Effect of volume on the supercooling temperature for primary nucleation of potassium nitrate from aqueous solution

The supercooling temperature has been measured for the primary nucleation of potassium nitrate from aqueous solution at a fixed concentration (46.0 wt%) and at a constant cooling rate (1.87×10−3°C/s) over a range of sample volumes (1.19−13.7 cm3). The data are analyzed by using the two-kind active site model, in which the nucleation is assumed to be induced heterogeneously and in a stochastic manner by the active sites of two kinds of activities. The effect of volume on the supercooling temperature could be well explained by assuming that the number of active sites of each kind increases in proportion to the sample volume. Literature data on the effect of the volume on the supercooling temperature (or freezing temperature) of water and the supercooling temperature of ammonium chloride aqueous solution could also be explained theoretically by the two-kind active site model.

A Novel Continuous Rotating Annular Liquid Chromatograph with a Multichannel Peristaltic Pump for Variable Eluent Withdrawal

Abstract A novel continuous rotating annular chromatograph is proposed and used for the separation of amino acids. The system is equipped with a multichannel peristaltic pump to withdraw the eluent and to easily regulate its flow rate. The inlet of the annular chromatographic packed bed is divided into a number of chambers to prevent circumferential dispersion of the sample. The mass transfer characteristics of the apparatus were theoretically analyzed by using a two-dimensional transport model. The experimental results for solute elution are well simulated by the transport model. Solute dispersion in the annular column was found to be negligible. A shallower liquid depth in the inlet chamber gave sharper concentration peaks. An increase in the number of feed nozzles and the installation of inlet chambers were found to be preferable for multicomponent separation.

Origin of secondary nucleation as revealed by isotopic labelling

Abstract Isotopic measurement by mass spectroscopy was for the first time applied to the secondary nucleation products formed in a supersaturated H 2 O-alum solution in the presence of a seed crystal containing D 2 O. It was shown that fine particles were chipped off from the seed into the solution and act as centres for secondary nucleation.

Modelling of the isothermal oxidative stabilization of mesophase pitch fibre

Abstract Isothermal experiments were conducted to elucidate the rate process of stabilization for mesophase petroleum pitch fibre. The rate of oxygen consumption in the fibres was quantified by measuring the time course of the oxygen concentration in the effluent gas from the reactor. A mathematical model of the stabilization, in which the mass transfer of molecular oxygen and the autoxidation reaction with the active sites in the fibre were taken into account, was also constructed and a numerical simulation of the model equations was conducted. Physical parameters such as the effective diffusivity of molecular oxygen in the fibre, the reaction rate constant and the gas—solid equilibrium coefficient of molecular oxygen, which are included in the mathematical model, were determined by comparing the experimental values of oxygen concentration in the exit gas with theoretical values. Physicochemical processes of the stabilization were also discussed on the basis of the theoretical results. It was concluded that the stabilization is complete even when the reaction does not proceed deeply into the fibre.

Chemical absorption of dilute H2S by aqueous solution of NaOH in a wetted-wall column.

濡壁塔におけるHaOH水溶液による希釈H2Sガスの反応吸収現象を理論的に解析した.解析において, 液相逐次2段階可逆反応ならびにイオン泳動を考慮した液相基礎式を, 気相基礎式群と連立させ, 有限差分法により数値解を得た.そして種々条件下の計算結果が, 純および希釈H2Sガスを用いた吸収実験より得られた吸収速度を良好に表現することから, 本解析が妥当なものであることがわかった.さらに, 得られた理論計算結果に基づき, 吸収速度に及ほす諸因子の影響を明らかにするとともに, 液相におけるS2-分布などを定量的に示した.