Application of a novel hexagonal ultrasonic reactor for intensified crystallization of adipic acid

Abstract

Application of hexagonal ultrasonic reactor for improved crystallization of adipic acid was investigated with response surface methodology (RSM) based parameter optimization to obtain minimum particle size with possible narrow particle size distribution (PSD). Optimized settings were elucidated as 150 W ultrasonic power, 30 min as irradiation time, a duty cycle of 50 %, and an ultrasonic frequency of 22 kHz. The mechanism of particle size reduction under sonication was elucidated to be governed by cavitation-induced shear forces coupled with acoustic streaming and microjet formation. X-ray diffraction analysis indicated minimal structural changes following sonication, suggesting that the primary effect of ultrasound is on particle size modification rather than crystal lattice alteration. FTIR analysis also confirmed unchanged functional groups after the ultrasonic treatment and SEM images show smaller round crystals of adipic acid. Under the optimized ultrasonic conditions, the particle size decreased to approximately 37.4 % of that observed in conventional samples, with a significantly lower energy consumption of roughly 0.00208 kWh per gram of solids. Overall, intensification benefits of the ultrasound were demonstrated in terms of lower size of crystals with better morphology and no adverse effects on the crystal quality.