Effect of solvent composition on crystallization process of ascorbic acid

Abstract

The crystal growth kinetics of ascorbic acid in water and in the solvent systems water/ethanol, water/methanol, and water/propanol is determined by means of seeded isothermal batch crystallization experiments. The measurements are correlated by a power low equation of the form (G = kg σn). The composition of the solvent system is found to have a significant influence on the kinetic parameters of growth of ascorbic acid. An increase in growth rate in the presence of alcoholic solvents (20 wt %) is measured compared to experiments with pure water. The thermodynamic effect of the solvent on the growth kinetics is approached by the UNIFAC method. The kinetic effect of solvent composition is explained using the two-step model. Both thermodynamic and kinetic analyses give the same result: The addition of alcoholic solvents (20 wt % ethanol, methanol, and propanol) to the ascorbic acid/water system slightly reduces the diffusion rate and significantly accelerates the surface integration process. © 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.