Ultrasound assisted size reduction of DADPS based on recrystallization

The present study investigates the use of ultrasound in size reduction based on recrystallization of a commercially important compound, 3,3'-diaminodiphenyl sulfone, popularly known as DADPS. Typically the applications of DADPS depends on the size distribution, more importantly on the mean size and hence the ultrasound assisted recrystallization has been applied for controlling the size as an alternative to energy intensive mechanical size reduction. For the size reduction studies, DADPS was dissolved in methanol and irradiated with ultrasound during the anti-solvent crystallization operation using water. Effect of different operating parameters such as temperature, rate of addition of antisolvent and its nature (whether neutral, acidic or basic) and ultrasonic parameters such as time of irradiation, power dissipation and duty cycle on the mean size and overall distribution has been studied. The particle characteristics of the original sample and processed samples have been analyzed using particle size analyzer, optical microscopy and X-Ray Diffraction (XRD). The positive effect of ultrasound for size reduction was clearly established from particle size analysis with reduction in the mean size to almost one-third the initial value under optimum conditions of 100 W as the power dissipation, 70% as the duty cycle and 60 min as the time of operation. In terms of the trends of the operating parameters, an increase in the rate of addition of antisolvent yielded the best results in terms of lower size and also alkaline conditions for antisolvent gave better size reduction. The microscopic images revealed a uniform and well-defined crystal shape on processing using ultrasound while XRD analysis established that ultrasound did not alter the crystalline structure. Ultrasound was overall established as an effective approach for size reduction without any changes in the crystalline structure.