Monitoring of Copper(II) Sulfate Pentahydrate Crystallization Using Ultrasound

Abstract

Ultrasound is beginning to be used to characterize many types of industrial two-phase dispersions, both suspensions and emulsions. It also has great potential as a process-monitoring tool alongside the well-established techniques of conductivity, pH, optical turbidity, tomography, and so forth. This paper describes a small volume test cell that has been developed to ultrasonically monitor the batch crystallization of a hydrated salt from saturated solution. The interaction of low-power, low-frequency (2− 7 MHz) ultrasound with a two-phase dispersion is discussed, and a series of experiments are outlined that have been carried out on a crystallizing 24% w/w (anhydrous) solution of copper(II) sulfate. The nucleation and growth of the crystals have been successfully monitored ultrasonically. Crystal size distributions of the final crystallized product have been obtained using light scattering and are used to model the effects that crystallization has on the ultrasonic data. It is shown that the Allegra and Hawley model of ultrasonic propagation in a two-phase dispersion, in a form modified to account for time dependent changes in the continuous phase, gives reasonable correlation with experimental data.