Process intensification of anti-solvent crystallization of salicylic acid using ultrasonic irradiations

Anti-solvent crystallization of salicylic acid has been investigated using conventional stirring approach and under the influence of ultrasound. During silent conditions, experiments have been conducted to study the effect of various parameters such as solution concentration, standing time, solvent–anti-solvent ratio, temperature, stirring speed and solution injection rate on the crystal characteristics. It was observed that the average particle size increased with an increase in the solution concentration and solvent/anti-solvent ratio while the change in temperature had marginal effect on the particle size. Ultrasound related variables such as irradiation time, moment of application, power and frequency of ultrasound and type of reactor have been varied to investigate the effect on the particle size distribution. It was observed that, the average particle size of salicylic acid crystals reduced with an increase in the irradiation time and power of ultrasound. The exact time of application of ultrasound altered the average particle size of crystals and significantly affected the agglomeration of crystals. The effect of ultrasound was more intense when horn was used for irradiation instead of ultrasonic bath. Use of ultrasonic irradiations also resulted in narrow distribution of the particles which is a distinct advantage especially considering the possible pharmaceutical applications of sonocrystallization.