Ultrasonic crystallization monitoring technique for simultaneous in-line measurement of liquid and solid phase

The mean crystal size, the suspension density and the liquid concentration are the three most important process parameters to quantify the progress of industrial crystallization processes. It will be shown that these parameters can be in-line monitored simultaneously by means of an ultrasonic crystallization monitoring technique (UCM), which will be introduced here in a proof of concept. This process analytical technology (PAT) differs from the known ultrasonic attenuation spectroscopy (UAS). For the UCM the ultrasonic velocity and attenuation were correlated and related to characteristic events during a crystallization process measured at only one frequency (no spectra of frequencies as it is used for UAS). The results shown in this study prepare the ground to establish the UCM as a simple, less complex, robust, universal applicable, inexpensive and, therefore, a winning alternative PAT to monitor and control in-line the solid as well as the liquid phase in the industrial crystallization by means of only one measuring device with two sensors.

► An ultrasonic crystallization monitoring technique (UCM) is introduced.
► The mean crystal size can be measured by UCM.
► The suspension density can be measured by UCM.
► The liquid concentration can be measured by UCM.
► Only one device and two sensors are required for the measurements.