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

Abstract

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 CA_m (43% of total absolute energy) in the total energy [0–700 KHz] is much more than that of CA_a (3% of total absolute energy).

Keywords:

• Solution crystallization
• acoustic emission
• monitoring and control
• batch processes
• process analytical technology

Disclosure statement

No potential conflict of interest was reported by the authors.

Funding

This work was supported by the National Natural Science Foundation of China (grant number 41790443 and 41525010), the Building Project in Geological Disaster Emergency Capacity for the Department of land and resource of Gansu Province, China (grant number GSZYTC-ZC-18005), the overseas students science and technology activities project merit funding ([2016] 176) and the fundamental research funds for the central universities.