Hirohisa Uchida

Determination of solid-liquid phase equilibria by using measured DSC curves

Abstract Solid–liquid phase equilibria (SLE) data are essential in designing apparatus and operation of industrial crystallization because they determine the possibility of separation and predict purification limits. In this study, a SLE determination system by using differential scanning calorimetry (DSC) was improved and applied not only to eutectic systems but also to partial solid solution systems. This method is different from conventional techniques that use onset and peak temperatures to determine SLE. A classification method of phase diagram types is proposed. This determination system was applied to the naphthalene (naph)– p -chloronitrobenzene ( p -CNB) and naph–catechol (cate) systems (eutectic systems) and the indole–naph system (partial solid solution system). From the calculated results, the determined SLE was in good agreement with the literature data.

Analysis of nucleation of zeolite A from clear solutions

Abstract It is recently reported that the preparation of zeolite membranes from clear solutions with low concentrations of Si 4+ and Al 3+ could prevent secondary nucleation and hence results in tight structures. Therefore, it is essential to study the phenomena of nucleation and crystal growth of zeolites from low concentration and clear solutions. In this study, the dependence of induction periods for nucleation of zeolite A on solution compositions and temperatures was analyzed. The induction periods of nucleation were found to decrease with the saturation ratios. The dependence of induction periods on saturation ratios was represented by two straight lines and the lines intersected at critical points that corresponded to the points of changing the types of precipitate structures. In the range of the saturation ratio above the critical point, precursors precipitated, while zeolite A precipitated in the rest of the range. This suggests that the induction periods are related to the type of precipitate structures.

Crystallization phenomena in ternary systems: nucleation of KCl during dissolution of NaCl

Abstract Spontaneous nucleation of potassium chloride crystals onto the surfaces of dissolving sodium chloride substrate crystals was observed in the ternary system of NaCl–KCl–H2O. The phenomena were understood being controlled by the local conditions of the mother liquor adjacent to the dissolving surface of the sodium chloride substrate and are specific to ternary systems or systems having more than two components, since the local supersaturations are created by the equilibrium conditions. When sodium chloride crystals are dissolving in either aqueous potassium chloride solutions or NaCl–KCl–H2O solutions, the solution adjacent to the dissolving surface is assumed to be saturated with respect to sodium chloride, and this can cause local high supersaturation with respect to potassium chloride enough to induce its nucleation. The mechanism of nucleation of potassium chloride is discussed on the basis of ternary phase equilibrium and kinetics of dissolution.

Mechanism of growth rate enhancement by micro-crystals for the potash alum–water system

Abstract Phenomenon of growth rate enhancement (GRE) caused by newly born micro-crystals was experimentally measured and quantitatively analyzed for the system of potash alum and water. Micro-crystals were prepared by mixing stoichiometric amounts of aqueous solutions of aluminum and potassium sulphates, and were fed as slurry. The size and number were controlled by the age and volume of the slurry, respectively. The age showed a substantial effect on the growth enhancement in such a way that the younger the age greater the effect. The degree of enhancement was found to be proportional to the square of the slurry volume added to the mother liquor. An empirical correlation was obtained among the degree of GRE, the slurry age and the slurry volume added. The size and number of micro-crystals were then estimated from the analysis based on a simple nucleation – growth model. Although the maximum effective size of micro-crystals could not be to determined due to the lack of reliable values of surface tension for the present system, it was estimated to be several micrometers from the experimental observations. In addition, the growth rate of such micro-crystals was found to be much slower than that of coarse ones.

Influences of reflux ratio on separation and purification of acrylic acid by inclined column crystallizer

Using an inclined column crystallizer that enhances settling velocities of crystalline particles, the continuous operation to separate and to purify organic compounds is established and the influences of reflux ratios on the separation and purification of acrylic acid are discussed. The locations of feeding and of withdrawing product and waste streams, were determined from the distributions of the melt composition in the purification section in the steady state under total reflux conditions. The number of theoretical steps increased with the reflux ratio. The operations of the crystallizer became unstable and the product purity was lower for the case of lower reflux ratios. The suspension density was controlled by reflux ratios. It is found that the reflux ratio is the most effective variable for the separation and purification of acrylic acid in an inclined column crystallizer.

Morphological changes and local purities of m-CNB crystals

Abstract Local purities of crystal faces of m-chloronitrobenzene (m-CNB) growing from its binary melts containing p-chloronitrobenzene (p-CNB) were measured and were correlated with the local linear growth rates. The local purity is determined from composition of the part of the crystal related to the growth of a certain crystal face. As the result of the experiments, the growth rates in the directions of y -axis and + z -axis are controlled by the presence of p-CNB, and p-CNB was detected in most crystal faces at a variety of levels depending on the crystallographic faces. The existence of the noncrystallizing component (p-CNB) in the crystal was attributed to the inclusion of mother liquor during the growth of crystals. The fractional amounts of inclusions, calculated from the local concentration of p-CNB, were defined as the inclusion factors of each crystal face and were correlated with the local linear growth rates. From the experimental results of local purity, it was found that the faster the crystal face grows the more the purity of m-CNB decreases. With the crystal structure of m-CNB to analyze the molecular arrangements, each face has different characteristic functional group. The linear growth rates of (0xa02xa00) and rounded faces which have the same functional group were slower than (0 2 1 ) face.