Industrial crystallization for the production of desired products, as expressed by produced crystal size and production rate, is discussed theoretically, and effective secondary nucleation and crystal growth rate are shown to be important. Recent studies on secondary nucleation rates are reviewed that involve complicated mechanisms and considered for application in design of crystallizers. Sticking phenomenon of suspended fines on growing crystals is discussed with regards to the population density of fines on the surface of growing seed. New mechanisms of crystal growth in an industrial crystallizer are also reviewed that involve breakage of growing crystal and sticking of suspended fines, and crystal growth rates available to calculate scaling up of a crystallizer is discussed. Two kinds of design theories of continuous crystallizers are reviewed. One is proposed on an ideal models of states of crystal and solution in a crystallizer and the dimensionless characteristic factors defined by dimensionless crystal size and supersaturation, can be used, independently of system and product crystal size and shape. Another theory is proposed on product crystal, and is shown to be applicable to operational line, independently of size of a crystallizer under some restricted conditions. Finally, industrial crystallization is becoming more and more important not only in conventional mass chemical processes, but also in fine chemical ones, and progressive studies on industrial crystallization will answer to the needs of the chemical industries in future.
A new model that considers both the electrostatic and steric-hindrance effects based on the space-charge model and the steric-hindrance pore model has been proposed to evaluate the transport phenomena of an organic electrolyte across a nanofiltration membrane. The dependence of the membrane parameters, reflection coefficient and solute permeability on the electrostatic and steric-hindrance effects has been analyzed in the system of an organic electrolyte and a negatively charged nanofiltration membrane. This model has been verified in the system of a tracer organic electrolyte (sodium benzenesulfonate), a supporting salt (sodium chloride) and commercial nanofiltration membranes (Desal-5, NF-40, NTR7450 and G-20); the theoretical values of the membrane reflection coefficients agreed very well with the experimental results of them.
A TVD (Total Variation Diminishing) scheme based on a compressible Navier-Stokes equation was applied to axisymmetric flow in a low pressure impactor with a circular nozzle. This TVD scheme was a type combined to a two-step MacCormack scheme. The shock was clearly observed at the half distance between the outlet of jet and the impaction plate. The critical stagnation pressure ratio of the impactor designed by Hering et al. was found to be about 0.40. The separation efficiency curve of the impactor was not dependent on the stagnation pressure ratio, nor the distance between the jet and the plate when the stagnation pressure ratio was less than 0.70.
The dynamics of adsorption of benzene dissolved in supercritical carbon dioxide on activated carbon were studied by analysis of breakthrough curves in the nonlinear region of the adsorption isotherm. The column was long enough to ensure constant pattern conditions, and the shapes of the experimental breakthrough curves were used for identification of the controlling mass transfer processes. The effects of intraparticle diffusion and external mass transfer were investigated by numerical solution of the corresponding differential equations. Surface diffusion was found to be the main transport mechanism inside the adsorbent particles. No considerable variation of the effective surface diffusivity was observed in the range of experimental conditions, and the measured values are in the order 10–10 m2/s.
We clarified experimentally that a Ni-Al2O3 catalyst is active for steam reforming of methanol at 450–750°C, and that it results in a different reaction to that obtained when using a CuO-ZnO catalyst. We also analyzed the characteristics of Ni-Al2O3-catalyzed steam reforming in a reformer when switching fuel from methane to methanol or propane, and vice versa. The flow rates of hydrogen and carbon monoxide in the steam-reformed gas can be kept almost constant by controlling the supply rates of fuel and steam. The methanol decomposition reaction and the propane steam reforming reaction occur mostly near the gas inlet of the catalyst bed, unlike the methane steam reforming reaction. We demonstrated experimentally that by regulating the rates of fuel and steam supplied to a reformer and by using a Ni-Al2O3 reforming catalyst. a phosphoric acid fuel cell power plant generates a continuous constant power of 9.6 kW or 26 kW when the pipeline gas 13A fuel is switched to methanol or propane respectively, and vice versa.
Previously published data of three-phase fluidization were correlated to develop a new empirical correlation for predicting bed voidage in gas-liquid-solid fluidized beds. The proposed correlation model, when used in conjunction with any suitable two-phase model for bed voidage, can serve as a correlation for bed voidage in both two- and three-phase fluidized beds. It describes the bed expansion and contraction phenomena observed during fluidization and is valid even as the superficial gas velocity approaches zero. A new criterion for quantifying the bed expansion and contraction phenomena based on this empirical model is derived and is also discussed in this paper.
Experiments on the condensation of binary vapor mixtures of methanol-steam and acetone-ethanol systems on a short horizontal tube were made for a wide range of vapor flow rates and concentrations. The observed vapor phase sensible heat and diffusion fluxes showed good agreement with the authors’ previous numerical correlation for heat and mass transfer on a cylinder with high mass flux effect. The effect of vapor flow rates and cooling water temperatures on partial condensation, where the concentration of condensate is lower than that of vapor free stream, was discussed. A new method for predicting the concentrations of condensate of binary vapor mixtures on a short horizontal tube was proposed, and compared with the experimental data under total and partial condensation.
Liquid-liquid equilibria of three ternary systems—methanol-heptane-1,3-dioxolane, methanol-heptane-1,4-dioxane, and methanol-heptane-tetrahydropyran—were measured at 253.15, 273.15, 283.15, 293.15 and 303.15 K for the first and third systems, and at 273.15, 283.15, 293.15 and 303.15 K for the second system. 1,3-Dioxolane, 1,4-dioxane and tetrahydropyran are cyclic ether compounds. We found expanses of the two liquid phase areas of the systems on the phase diagram were proportional to the ratio of the number of oxygen atoms to that of carbon atoms (O/C) in the molecules of the cyclic ethers. The distribution ratio of the ethers in methanol/heptane phases was related to the O/C ratio as well. Results were also successfully correlated using the NRTL equation.
The binding constants of immobilized Cu(II) on PEG-IDA with imidazole and histidine at various solution pH values, salt concentrations and temperatures were determined by differential UV spectrophotometer. The bimodal binding behavior of basic solute was observed by the study of the salt effect. However, the formation of the coordinated compound is the dominated binding mechanism at the pH value higher than pKa of the deprotonation of imidazole nitrogen. There was no obvious effect of temperature on binding constant because of the complexity of binding mechanism. The binding behavior of several dipeptides and tripeptides with histidine at C- or N-terminal was also investigated and the results were explained by the “metal ion transfer” (MIT) hypothesis. Furthermore, the binding constants of synthetic heptapeptides with two histidine residues separated by different number of glycine residues were investigated to demonstrate the effect of histidine residues distance on the binding affinity. This study provides basic information of binding behavior of protein to immobilized metal ion.
The phase control (phase transition, hydrophobic-hydrophilic balance) of a thermosensitive polymer gel was performed by an electrochemical method at constant temperature. The relationships of the amount of charge supplied to induce the phase transition of gel, ionic content and electrolyte content were examined. The mechanism of electrochemical phase control of gel was clarified in terms of ionic transport in the gel.
The precipitation of ammonium perchlorate (AP) from methanol solutions of AP by a salting out method has been studied. The organic solvents studied as precipitants were: chloroform, ether, isobutyl alcohol and methylene chloride. The characteristics of the precipitated AP crystals were investigated by means of scanning electron micrograph, X-ray diffraction, differential scanning calorimetry and thermogravimetric analysis. When ether, chloroform and methylene chloride were the precipitants, the product crystals had a particle size less than 5 μm. On the other hand, the crystals obtained with isobutyl alcohol as the precipitant had a orthorhombic shape and the mean crystal size was larger than 10 μm. Diffraction angles for AP crystals obtained with isobutyl alcohol as the precipitant coincided with those obtained with other precipitants used in this work, though the intensity in the X-ray diffraction changed.
The effects of alcohols, column dimensions, gas velocity, physical properties of liquids, and gel particles on the gas holdup εG and the volumetric liquid-phase mass transfer coefficient kLa in a gel-particle-suspended bubble column under liquid-solid batch operation were studied experimentally. It was shown that addition of alcohols to water generally increases εG. However, kLa values in aqueous solutions of alcohols became larger or smaller than those in water, according to the kind and concentration of the alcohol added to water. It was also shown that the presence of suspended gel-particles in the bubble column reduces values of εG and kLa. Based on these observations, empirical equations for εG in the transition regime in an ethanol solution, for εG in the heterogeneous flow regime applicable to various alcohol solutions and for kLa in both flow regimes were proposed.
Phenylacetic acid, a strong acid, was formed from the enzymatic hydrolysis of penicillin G to 6-amino-penicillanic acid. Because of the difficulty of maintaining the pH constant inside the reactor, the reaction mixture was circulated at a high flow rate between the packed bed reactor and the vessel for adjusting pH. The reactor and the vessel were connected via a pump. When an immobilized enzyme made of compressible fibers was packed in the packed bed reactor, the hydrolytic efficiency of the immobilized enzyme was approximately 0.5. The low efficiency of the immobilized enzyme was assumed to be caused by the aggregation of the immobilized enzyme due to the pressure generated by flow of the reaction mixture. Therefore, the aggregation in the packed bed reactor was analyzed experimentally using Kozeny-Carman’s equation in order to estimate the distribution of the aggregation in the reactor. Furthermore, a new column devised specially to prevent aggregation of the compressible fibrous support was developed. A reaction time required for completing the hydrolysis (98% of conversion) was adopted to estimate the efficiency of the entire immobilized enzyme packed in the reactor throughout the entire period of reaction. The efficiency of the immobilized enzyme packed in the new column of the reactor was concluded to be increased by approximately 1.8 times, compared with that of conventional packed bed columns.
For the purpose of wet separation of particles differing in shape, particle settling characteristics have been investigated in a stationary liquid simultaneously subjected to centrifugal and gravitational forces. Several kinds of irregularly shaped particles were settled through viscous silicone oil at rest in a closed rectangular vessel rotated at low speeds. The settling trajectories of the particles in the liquid were measured in the laminar flow region. When the initial settling orientation of each particle was set in a given and appropriate direction, the radial settling displacement of the particle depended approximately on the particle shape, regardless of the size. By devising a simple feeding method, it was possible to make the initial settling orientation of particles automatically uniform. Continuous shape separation of particles in the liquid could be expected by applying a feeding method to the separation field receiving both centrifugal and gravitational forces as used in this paper.
A dynamic model combining molecular kinetic theory and classical nucleation theory was used to simulate the heterogeneous vapor-to-crystal phase transition in a closed vacuum chamber at low substrate temperature. The governing equations for the motes of molecules adsorbed to the substrate, the pressure in the chamber, and the number and mass of the crystals formed were simultaneously integrated. The model showed that the heterogeneous phase transition changed from one controlled by crystal growth to one controlled by heterogeneous nucleation as the condensation coefficient decreased. On the basis of the observation and the assumption for the adherence between the crystals and the substrate surface to be incomplete, the substrate temperature and the crystal surface temperature, respectively, were raised by 0.4 K and by 1 K at the onset of nucleation in the model computation. The changes in vapor pressure with elapsed time in the computed results agreed reasonably well with the experimental ones.
Dependencies of effective diffusivity of glucose in Ca-alginate gel beads and mechanical compression strength of the gel on alginate composition, viscosity, concentration, temperature and pH of the alginate solution were systematically investigated. Diffusional and mechanical properties of Ca-alginate gel beads depended on alginate composition and the gelling conditions. The results were discussed in relation to get structure and conformation of alginate molecule. Differences in reported diffusivities of glucose could be explained by the differences in alginate composition and the gelling conditions such as alginate concentration, temperature and pH. Furthermore, selection guidelines for preparation of Ca-alginate gel having low diffusional obstruction and large compression strength were presented.
Ultrafine PbS particles were prepared using AOT/isooctane reverse micellar systems as reaction media. On the basis of the change in UV-visible absorption spectra expressing the change in the size of semiconductor particles, the mechanism of the particle formation was studied. Because of the relatively large solubility of PbS, the growth of particles by Ostwald ripening was significant at low reactant concentration. When an excess amount of lead ion or sulfide ion was used, ultrafine PbS particles having stable spectra could be prepared. Particle coagulation was found to be controlled by the statistical distribution of particles among the reverse micelles. By irradiating a reverse micellar solution containing PbS particles stabilized by an excess amount of sulfide ion using a Xenon lamp, hydrogen was generated by the photocatalytic reduction of water.