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Volume 58 (2004)
- Issue 6 Pages 547-
- Issue 5 Pages 448-
- Issue 4 Pages 337-
- Issue 3 Pages 242-
- Issue 2 Pages 142-
- Issue 1 Pages 3-
Volume 58, Issue 5
Displaying 1-6 of 6 articles from this issue
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Ken-Ichiro SOTOWA2004 Volume 58 Issue 5 Pages 448-454
Published: 2004
Released on J-STAGE: February 19, 2013
JOURNAL FREE ACCESSSustained oscillation of crystal size distribution is frequently observed in operation of continuous crystallizers. This gives rise to variation in qualities of product crystals, and also periodic burst of fines increases the operation cost of filtration, whic is usually employed in the downstream of a crystallizer. There are a number of studies on application of advanced control systems to suppression of the oscillation. However, there are only a few examples of successful application of such techniques to industrial crystallizers. A recent study revealed that controllability of a crystallizer strongly depends on its design and operating conditions. This manuscript describes “indices of ease of control”, which can be used to evaluate the controllability of crystallizer very conveniently. They can also be used to design a crystallizer by taking the controllability into consideration.View full abstractDownload PDF (6351K) -
Hiroshi TAKIYAMA2004 Volume 58 Issue 5 Pages 455-461
Published: 2004
Released on J-STAGE: February 19, 2013
JOURNAL FREE ACCESSIn order to obtain NaCl product crystals at high efficiency, high suspension density conditions are indispensable in crystallization. However, under those conditions the nucleation rate which determines the number of product crystals becomes high, and crystal size distribution becomes broad. Therefore, it is necessary to control the excess number of micro-crystals in a crystallizer.
The following techniques were proposed and used as a method of controlling the number of micro-crystals: (1) Addition of micro-crystal dissolution equipment.(2) Application of Ostwald-ripening phenomena.(3) The design method of a supersaturation profile.(4) The design of the amount of seed crystals.(5) The design of undersaturation operation. However, since operations are experiential, many researches of micro-crystal control are still investigated.
In this review, some examples were introduced about these techniques. In particular, the previous research on removal of a micro-crystal was explained. The concept about producing at the high efficiency of NaCl crystallization was summarized.View full abstractDownload PDF (5515K) -
Kaoru OGAWA, Kenji SHIMIZU2004 Volume 58 Issue 5 Pages 462-474
Published: 2004
Released on J-STAGE: February 19, 2013
JOURNAL FREE ACCESSSeveral methods to control the crystal morphology and structure have been attempted to improve itsfunctionality. In recent years, a magnetic field has been applied to crystal growth to control the orientation andhabit of the crystals as well as to grow crystals of high quality for structural determinations.
In order to clarify this mechanism, a systematic investigation of the magnetic field effect on the crystallization of L-alanine crystal from aqueous solution was actually carried out in this study dealing with the magnetic field effect on the crystal orientation and surface topography. We prepared an optical microscope system for in situ observation, which could be used under a high magnetic field. It was found that the c-axes of small nucleated L-alanine crystals moving in the solution were parallel to the direction of the magnetic field.
At a homogenous magnetic field from 0 to 5 T, a clear inhibition in the growth rate of the (120) and (011) faces of an L-alanine crystal was observed. The growth inhibition induced by the magnetic field was attributed to a lower mass transfer, which was assumed to be caused by a decreased flow velocity of buoyancy convection and crystal orientation in suspending state in solution. Then we measured crystal growth rate when it experienced magnetic force in inhomogeneous magnet.
Also the effect of L-methionine additive on the crystal growth of L-alanine crystal was investigated by atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS) and time of flight-secondary ion mass spectrometry (TOF-SIMS).View full abstractDownload PDF (8301K) -
Masakazu MATSUMOTO, Mari ISAGO, Kaoru ONOE2004 Volume 58 Issue 5 Pages 475-486
Published: 2004
Released on J-STAGE: February 19, 2013
JOURNAL FREE ACCESSThe micro-bubble technique, which can be used to supply ions uniformly to the liquid phase, was applied to the crystallization and dissolution of calcium carbonate (CaCO3). CO2, NH3, and N2 gases were used as gas sources for the micro-bubbles. In addition to distilled water, three types of solution were used: Tris-HCl (pH 7.8), Ca(NO3)2, and Ca(NO3)2/Tris-HCl (pH 7.8). By continuously feeding various types of micro-bubblesinto each of the four liquids, the physical properties of the liquid phase were controlled in order to crystallize, dissolve and re-crystallize CaCO3. At the same time, the physical properties of the solutions (pH and electric conductivity) were determined and the generated solids were physico-chemically analyzed by means of SEM and XRD. The effects of the micro-bubbles on gas solubility in gas-liquid reactions and also on the crystallization, dissolution and re-rystallization of CaCO3 in gas-liquid-solid reactions were studied. The experimental results indicate the following; 1) in the gas-liquid reaction, the gas absorption rate of CO2 increases with decreasing bubble size, irrespective of the type of solution; 2) by controlling the pH of solutions containing Ca2+ ions over pH 7 with a mixture of CO2 and NH3 micro-bubbles or with Tris-HCl, then CaCO3 precipitates; 3) when the pH is higher than 7, vaterite is generated in high-selectivity with an increase of CO2 supply; 4) in the crystallization reaction induced by CO2/NH3 micro-bubbles (CO2/NH3=1/2, FCO2=0.28mmol/l/min, QCO2=4.2 mmol/l), micro-bead-shaped vaterite (2.4μm) is generated; 5) when CO2 micro-bubbles are used, CaCO3 dissolves with lowered pH owing to the dissolution of CO2 gases; and 6) when NH3 micro-bubbles are used, CaCO3 re-crystallizes at higher pH owing to the dissolution of ammonia gas.View full abstractDownload PDF (8466K) -
Development of Inline Particle Size Measurement EquipmentMasami HASEGAWA, Koji MASAOKA, Tomohiko KARUBE2004 Volume 58 Issue 5 Pages 487-493
Published: 2004
Released on J-STAGE: February 19, 2013
JOURNAL FREE ACCESSThe measuring method for particle size distribution was examined based on turbidity changes in the crystals which had been classified in the settling leg. The time needed for the largest particle existing in the classified sample to reach the turbidity sensor was assumed to equal the standup time of turbidity, and the elapsed time in turbidity changes was converted into particle size. The summation of turbidity taken over the whole range of the classified particle size was expressed in terms of weight, and a calibration curve was made for each particle size range. Application of these calibration curves to the samples of various particle size distributions and measurements of those particle size distributions resulted in, good measured values. Equipment applicable to an industrial crystallizer was designed and actually applied. Continuous operation of equipment for 24 hours revealed measurement with good precision was possible in real time.View full abstractDownload PDF (4384K) -
Masahiro KAMEKURA2004 Volume 58 Issue 5 Pages 494-505
Published: 2004
Released on J-STAGE: February 19, 2013
JOURNAL FREE ACCESSDownload PDF (11094K)
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