Masakuni Matsuoka

Determination of solid-liquid phase equilibria of binary organic systems by differential scanning calorimetry

Abstract A differential scanning calorimetry (DSC) and personal computer system to determine binary solid-liquid equilibria (SLE) was developed. The validity of the system was demonstrated using three organic binary systems having different types of SLE involving a simple eutectic, complete solid solutions and solid solutions woth miscibility limits. It was shown that this system is useful and ready to use to give accurate SLE in a short time for binary mixtures having any type of the SLEs noted above.

Preparation and characterization of alumina-supported molybdenum carbide

Abstract Molybdenum carbide on alumina was studied by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and temperature-programmed surface reaction (TPSR) with hydrogen. The molybdenum carbide was prepared by nitridation of 12.5 wt% MoO 3 /Al 2 O 3 in a flow of NH 3 at 700°C, followed by carburization in a flow of 20% CH 4 /H 2 also at 700°C for 3 h. The sample was compared to an unsupported material prepared from MoO 3 in the same manner. The CH 4 formation profile during TPSR was deconvoluted into three peaks with maxima at 490°C, 690°C, and 810°C. The peak at 490°C was assigned to reduction of carbidic carbon, and the peaks at 690°C and 810°C were assigned to the removal of pyrolytic and graphitic carbon, respectively, as indicated by XPS and XRD measurements. Overall, the results suggest that molybdenum carbide was formed on the alumina supported by the carburization treatment at 700°C, in the same manner as with an unsupported reference sample. Prenitridation before carburization resulted in the formation of a carbide with a larger surface area and less free carbon, compared to the carbide formed by direct carburization.

Morphology of NaCl Crystals in Drowning-Out Precipitation Operation

The drowning-out precipitation of sodium chloride was carried out to observe nucleation phenomena by mixing two saturated aqueous ethanol solutions having different concentrations. The shape of the crystals was found to differ with the operating conditions. Crystals with hollow surfaces that may lead to a decrease in purity were observed only when the initial supersaturation ratio σ 0 was high. From the induction time, primary nucleation was found to be predominant, with homogeneous nucleation becoming significant at σ 0 > 0.7. The number of crystals generated increased slightly with increasing initial supersaturation ratio, but started to decrease after a certain supersaturation, where the crystals were agglomerated from the early stages of crystallization. The ‘hollow’ crystals were generated in such high supersaturations. The crystals generated by homogeneous nucleation agglomerated readily. Since the number of crystals depended on the ethanol concentration in aqueous solution and/or the agitation condition, nucleation was strongly influenced by local mixing.

Selection of solvents for organic crystal growth from solution

The influence of organic solvents on the habit of organic crystals was examined experimentally. The differences in two physical properties such as heats of crystallization between the solution and the crystallizing component and dipole moments between the solvent and the crystallizing components were proposed as measures of the discrepancy from ideal behavior of the mixtures. The crystal shapes of m-chloronitrobenzene and 2-methyl-4-nitroaniline were classified into three types: one-dimensional (needle-like), two-dimensional (plate-like) and three-dimensional (prismatic) crystals. It was found that well defined three-dimensional crystals were formed from the solutions with solvents which provide ideal solubilities and possess similar values of dipole moments.

Processes and phenomena of purity decrease during the optical resolution of dl-threonine by preferential crystallization

Abstract In order to elucidate the phenomena of purity decrease in the later stages of the batchwise preferential crystallization process resolving racemic mixtures of dl -Threonine ( dl -Thr), changes both in the purity and surface structures of threonine crystals were measured and observed. It was found that the onset of purity decrease was strongly related to the consumption of the supersaturation of the crystallizing enantiomer ( l -Thr) and to the surface morphology changes of the seed crystals. Based on the observations the mechanism of purity decrease was concluded to be the surface nucleation of the unseeded enantiomer ( d -Thr) during the resolution, phenomenon responsible for the start of the deposition of d -Thr. The relative rates of deposition of l - and d -Thr were found to determine the start of the purity decrease.

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.

Purification of organic solid solutions by melt crystallization: comparison between layer and suspension crystallization

Abstract In order to compare the degrees and rates of purification achieved by layer and suspension melt crystallization operations, purification by “sweating” of naphthalene-benzothiophene solid solution crystals was carried out after they were formed either on a cold surface (layer crystallization) or in supercooled melts (suspension crystallization). The purification rate coefficients obtained for the suspension system crystals were found to always be larger than those for the layer system, furthermore, the amount of impurities unable to be removed by “sweating” from the layer was higher than that from the particles. These two facts lead to the conclusion that the overall efficiency for the purification by sweating is higher for the suspension crystallization than the layer one.

Growth rates and compositions of organic solid solution crystals from binary melts — Experimental study

Abstract Linear growth rates and compositions of m-chloronitrobenzene-m-fluoronitrobenzine solid solution crystals were investigated experimentally. By extrapolating to zero growth rate, the equilibrium temperature and the equilibrium composition of the solid solution were determined for a given melt, and then the equilibrium phase diagram was constructed. The growth rates were found to vary with the square of the supercooling and the compositions were dependent on the growth rates. The growth rates and the compositions were quantitatively analyzed and were correlated with the supercoolings and the growth rates respectively. The growth rates of the pure and solid solution crystals, were shown to be comparative and this suggested a common similar growth mechanism.

Polymorphism, morphologies and bulk densities of DL-methionine agglomerate crystals

To explain the experimentally determined operation conditions to produce DL-methionine (DL-Met) crystalline particles having high bulk density from reaction crystallization, the morphologies of DL-Met agglomerated crystals in addition to the crystallographic structures were investigated. The existence of the third polymorph, the γ-form, was confirmed. Both the observed and predicted morphologies for the elementary particles were plate-like and were strongly affected by the crystal structures. The effect of polymorphism and morphology of resulting particles from reaction crystallization on the bulk density of the product agglomerates was discussed. The bulk density was strongly affected by the agglomeration and the morphology of the constituent elementary crystals. The morphology change with pH of the solution was also experimentally found. Local pH during the reaction crystallization is concluded essential to determine the morphology of the elementary particle, and hence the bulk density of the agglomerates.

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.