An Assessment of the Use of Ultrasound in the Particle Engineering of Micrometer-Scale Adipic Acid Crystals

Adipic acid was crystallized via batch cooling from aqueous solution under continuous ultrasonic radiation. The product particle characteristics are compared first with those achieved at steady state in a continuous crystallization process operated under continuous insonation and second with the products of dry milling techniques, viz. hammer milling and micronization and high shear wet milling (HSWM) respectively, and of batch reverse antisolvent crystallization (RAS). off-line Malvern MasterSizer measurement, scanning electron microscopy (SEM), and atomic force microscopy (AFM), were used to compare particle size distributions and to investigate the difference in particle habit and to analyze the surface characteristics at sub-micrometer scale. The effect of ultrasonic waves applied to batch and continuous crystallization was found to be effective in producing particle sizes comparable with micronization. Continuous insonation during batch crystallization provides spherical particles, with increased and regular surface roughness and highly reproducible results.