Kinetic studies on the influence of temperature and growth rate history on crystal growth

Abstract

Crystallization experiments of sucrose were performed in a batch crystallizer to study the effect of temperature and growth rate history on the crystal growth kinetics. In one of the growth methods adopted, the isothermal volumetric growth rate (R V ) is determined as a function of supersaturation (S) at 35, 40 and 45 ºC. In the other, crystals are allowed to grow at constant supersaturation by automatically controlling the solution temperature as the solute concentration decreased. Using the latter method R V is calculated as the solution is cooled. The obtained results are interpreted using empirical, engineering and fundamental perspectives of crystal growth. Firstly, the overall activation energy (E A ) is determined from the empirical growth constants obtained in the isothermal method. The concept of falsified kinetics, widely used in chemical reaction engineering, is then extended to the crystal growth of sucrose in order to estimate the true activation energy (E T ) from the diffusion-affected constant, E A . The differences found in the isothermal and constant supersaturation methods are explained from the viewpoint of the spiral nucleation mechanism, taking into account different crystal surface properties caused by the growth rate history in each method. Finally, the crystal growth curve obtained in the batch crystallizer at 40 ºC is compared with the one obtained in a fluidized bed crystallizer at the same temperature. Apparently divergent results are explained by the effects of crystal size, hydrodynamic conditions and growth rate history on the crystallization kinetics of sucrose.

Kinetics and thermodynamics of sucrose crystallization from pure solution at different initial supersaturations

“…4 and the obtained results are presented in Table 1. The effect of growth rate history [6,[19][20][21][22] is clearly shown in both Figs. 2 and 3, when all runs are compared with the run of highest initial supersaturation.…”

Unsteady-state inhibition of crystal growth caused by solution impurities

“…3, 4 and 5 Fig. demonstrated using kinetic data [35][36][37][38] and high-resolution microscopy, 39,40 the crystallization kinetics of sucrose is significantly affected by the growth rate history and by the alteration of surface roughness. Simulation II was performed using the CAMUS parameters chosen to fit the experimental data.…”

Growth Rate Measurements of Organic Crystals in a Cone‐Shaped Fluidized‐Bed Cell

“…Furthermore, the authors assumed that the surface roughness acts in the manner of a strong impurity, which they underlined by treating the mechanism as being equivalent to the surface adsorption of an impurity using the Kubota‐Mullin model . Martins et al as well as Flood speak of strains or interfacial tensions on the crystal surface, which likely cause an increase in the energetic barrier for growth and thus decrease the crystal growth rate. Another example for reduced growth rates due to an increase in surface roughness is given by Garside who found that milled seed crystals of potassium chloride grew more slowly on average than unmilled crystals.…”

“…With respect to the surface quality of the crystals, there exist two opinions that are discussed controversially in the literature. On the one hand, some authors claim that the growth rate decreases with an increase in surface roughness , , . On the other hand, there are authors who found that crystal‐growth rates increase with an increase in surface roughness , .…”

“…Furthermore, the authors assumed that the surface roughness acts in the manner of a strong impurity, which they underlined by treating the mechanism as being equivalent to the surface adsorption of an impurity using the Kubota-Mullin model [34]. Martins et al [29] as well as Flood Figure 7. Crystal growth rate G of L-alanine (primary axis, green circles) and Sherwood number Sh (secondary axis, blue squares) with respect to the seed crystal size d 50.…”