H. Takenaka

The effects of temperature on the spherical crystallization of salicylic acid

Abstract The effects of temperature on the spherical crystallization of salicyclic acid were investigated. An ethanolic solution of salicylic acid held at 40 °C was introduced into a well-dispersed mixture of chloroform and water at 5 to 30 °C. By increasing the temperature, larger agglomerates with less spherical forms composed of larger crystals were obtained. The mass growth rate of the agglomerated crystals was described by the mass transfer-controlled kinetics. The growth rate coefficient at 30 °C was significantly smaller than those at 10 and 20 °C. The linear growth rate of the agglomerated crystals increased with increasing temperature, but did not depend upon the solute bulk concentration.

Spherical agglomeration of calcium carbonate dispersed in aqueous medium containing sodium oleate

Abstract It was found that calcium carbonate particles dispersed in aqueous medium with sodium oleate were agglomerated spherically by adding and agitating a small amount of organophilic liquid, termed bridging liquid, e.g. benzene, kerosene and amyl acetate, whereas the agglomeration was not accomplished in the system without sodium oleate. This phenomenon was explained by the preferential wetting of the sodium oleate-treated calcium carbonate by the bridging liquid. Sodium oleate concentration in the medium determined the settling velocity and the sedimentation volume of agglomerates or flocs of calcium carbonate. The size distribution of agglomerates was dependent on both the concentration of sodium oleate and the type of bridging liquid used. The residual concentration of calcium carbonate particles in the supernatant separated from the system was also controlled by the above two factors.

An experimental study of the kinetics of the spherical crystallization of aylline sodium theophylline monohydrate

Abstract Direct agglomeration of sodium theophylline monohydrate crystals produced by salting out in a liquid was carried out in a stirred vessel. Addition of aqueous ethylenediamine solution of theophylline and sodium chloride solution to a mixture of chloroform and ethanol (mixing ratio of chloroform:ethanol = 0.1 to 0.505:1) with agitation yielded spherically agglomerated crystals of sodium theophylline monohydrate. The diameter of the spherical agglomerate decreased with increase in agitation speed of the chloroform fraction in the mixture. The spherical crystallization process was described by first-order kinetics. The rate constant was a function of the agitation speed of the system and the difference between the residual concentration of theophylline in the solvent in the initial and the equilibrium state.