On‐line monitoring of a crystallization process

The application of ultrasonic spectroscopy for particle‐size measurements was investigated during the batch crystallization of (L)‐glutamic acid α‐polymorph from an aqueous solution. The technique, based on measurements of the attenuation of ultrasonic waves through the suspension, was applied using a prototype ultrasonic spectrometer with a flow‐through cell. High‐precision measurements of ultrasonic attenuation in the frequency range 7–110 MHz were performed, the deconvolution of which enabled in‐process measurement of crystal size distribution and solid concentration throughout the crystallization process. In addition to evincing secondary nucleation, growth and crystal breakage on‐line in real time, the experimental results were used to obtain kinetic parameters essential for process design, including secondary nucleation rate and growth rate.