Determination of kinetic parameters of nucleation and growth of acetylsalicylic acid crystals in ethanol

Abstract

In this work, nucleation and growth rates, as well as kinetics parameters, for the acetylsalicylic acid (ASA) -ethanol system were evaluated from experimental data and a nonlinear optimization model. Saturated solutions, between 298.15 K and 313.15 K, were prepared and cooled following linear profiles at 9, 12 and 15 K/h. Measurements online of temperature, density and crystal size distribution were registered every 30 seconds. At the end of each run, crystal dimensions were measured from images obtained with an optical microscope. The predicted results related to the concentration profile of ASA were in good agreement with the experimental data. They showed that an increment in cooling rate enhanced growth but inhibited nucleation. Similar results were obtained for an increment in the solution initial saturation concentration. The analysis of the kinetic exponents suggested crystal growth was dominated by surface diffusional effects and formation of new nuclei was dominated by primary nucleation. The images obtained with an optical microscope showed no morphological differences due to the different operation conditions. Specific shape factor evaluation confirmed the absence of morphological changes in the ASA crystals at the analyzed conditions in this study.