Acoustic Emission, a New Sensor for Monitoring Industrial Crystallization Processes

Abstract

The potential of Acoustic Emission (AE) for monitoring industrial crystallization processes is investigated through the monitoring of two typical crystallization systems. The sensing technology is successfully applied to monitoring the batch cooling solution crystallization of Citric Acid (CA) in water, which exhibits a anhydrous to monohydrate phase transition. The technique is also applied to monitoring the precipitation of salicylic acid from its sodium salt. A huge amount of acoustic data is recorded by the AE system, and the analysis of this data set is focused on the evaluation of AE as a new sensor for monitoring the basic steps of the crystallization process (i.e., nucleation, growth, phase transition, etc.) A time- and frequency domain analysis is presented which shows the wealth of the technique. It is finally concluded that AE allows a very early detection of nucleation events, provides a means of monitoring the development of the crystallization or precipitation process and allows monitoring solvent-mediated phase transition phenomena occurring under cooling. It is thus suggested that acoustic emission could be valuable in the development of new crystallization monitoring and control strategies: this is all the more interesting that the acoustic piezo-sensor is non-intrusive and does not require any sampling of the slurry, two features which are of tremendous importance in the field of cooling crystallization processes.