Acoustic emission detection of crystallization in two forms: monohydrate and anhydrous citric acid

Reliable monitoring of solution crystallization processes is important to provide further insight into process dynamics and to improve process control in the regimen of Process Analytical Technology (PAT), e.g. as the case studied here: detection of crystallization of the anhydrous and monohydrate forms of Citric Acid (CA). To set up the relationship between acoustic emission (AE) and crystallization form, two experiments (monohydrate and anhydrous citric acid) were carried out to specify the features and origins of the different acoustic signals emitted during batch cooling solution crystallization processes. Two kinds of AE experimental variables convey information about the development of crystallization processes: frequency and acoustic energy variables. The experimental results show notably that though it has less acoustic bursts, the acoustic activity generated by the crystallization of the monohydrate form of CA actually releases more acoustic energy than the crystallization of anhydrous form. It is also shown that the form of the crystallization is associated with the percentage of absolute energy. The proportion of the absolute energy [150–700 KHz] released by CAm (43% of total absolute energy) in the total energy [0–700 KHz] is much more than that of CAa (3% of total absolute energy).