The crystallization of aspirin from ethanol

Abstract

The rate of growth of aspirin crystals has been examined in a circulatory crystallizer in which the crystals are held in suspension as a fluidized bed. The deposition rate was measured, as a function of both the degree of supersaturation and the solution temperature, by observing the rate of weight increase and the change in particle size distribution of the crystals. The dependence of the mass transfer coefficient for the process upon the temperature was of the Arrhenius type, the activation energy being 21·8 kcal/mole. This indicates that the surface reaction step is rate-controlling, diffusional transport to the crystal surface being rapid. The density of aspirin solutions in alcohol has also been measured as a function of temperature and concentration.