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

In this work, nucleation and growth kinetics parameters for the acetylsalicylic acid (ASA) -ethanol system were determined from experimental data obtained in a batch crystallization process at different operating conditions. Saturated solutions, between 293.15 K and 313.15 K, were prepared and cooled following linear profiles in the range of 5 to 15 K/h. Measurements online of temperature, density and crystal size distribution were registered every 30 seconds. In addition, an algorithm was developed in Matlab to solve the mathematical model of the crystallization process. The model included the population and mass balances and power-law equations for nucleation and growth. The algorithm allowed optimizing the kinetic parameters by minimizing the sum of the square of the difference between the experimental and calculated profiles for the concentration of ASA in solution. The results showed that increasing the cooling rate increased the growth rates but decreased the nucleation rates. Besides, the average value of g supported that diffusional effects dominate crystal growth and the value of b suggested that secondary nucleation promoted the creation of new nuclei. The global error in the estimation of the kinetic parameters was less than 3%.

Keywords: acetylsalicylic acid, batch crystallization, crystallization kinetics, nucleation, parameter optimization.