Improved crystallization of ammonium sulphate using ultrasound assisted approach with comparison with the conventional approach

In chemical processing industries, crystallization is one of the most important operations to obtain solid products with desired purity and characteristics. With distinct processing problems for the conventional approaches for crystallization, research into alternate approaches such as ultrasound assisted crystallization has been on the forefront. The present work deals with comparison of the conventional approach and ultrasound assisted approach for crystallization of ammonium sulphate followed by detailed understanding into the effect of important operating parameters (initial concentration, pH, agitation speed, depth of horn, and cooling approach) on the metastable zone width and average crystal size. Ultrasound assisted crystallization has been investigated using both ultrasonic bath and ultrasonic horn to understand the effect of type of irradiation. It has been observed that the maximum reduction in the MSZW was obtained using ultrasonic horn under conditions of optimized initial concentration. The order of average crystal size obtained for ammonium sulphate was conventional cooling crystallization > ultrasonic bath > ultrasonic horn. The average crystal size obtained was in the range of 411-450 µm for conventional approach of cooling crystallization, 350-400 µm using ultrasonic bath and 200-250 µm using ultrasonic horn. The analysis of crystal size distribution and surface characteristics using the SEM analysis was also performed under set of optimized parameters established using the particle size analysis. Overall the work has clearly established that the ultrasound assisted crystallization gave better results as compared to the conventional cooling crystallization in terms of reduced metastable zone width, better crystal characteristics and less agglomeration.