Monitoring the Dynamics of a Continuous Sonicated Tubular Cooling Crystallizer

Abstract

For the first time, continuous ultrasound-assisted tubular crystallizer dynamics has been studied in pilot scale operation. It is vital to understand the process dynamics for continuous crystallizers as robust crystallization processes are developed. The mixing time using tracer impulses and experimental continuous crystallization runs to understand the performance of process variables, with focused beam reflectance measurement (FBRM), process video microscope measurements, and off-line particle size analytics, is reported. The model system was phthalic acid crystallization from water. The effects of ultrasound power and residence time on the crystallization dynamics and on the product crystal size distribution (CSD) were studied. The use of ultrasound was found to be vital in the crystallization operations in order to prevent pipe clogging. It was shown that an increase in ultrasound power improves mixing in tubular reactors, and it decreases the product CSD, most probably due to nucleation. Also, an increase in residence time decreases the CSD due to an increase in ultrasound irradiation time during crystal growth. The video-microscope-based relative backscatter index signal was more sensitive to crystallization startup in this system in comparison to FBRM chord lengths. The continuous crystallization process dead time was found to follow fluid mixing dynamics by monitoring relative backscatter index signals as the flow rate and US power were increased. The steady-state crystallization conditions were found to take more than 2 reactor residence times on the basis of continuous crystallization experiments.

Nucleation in continuous flow cooling sonocrystallization for coiled capillary crystallizers

“…They also found that supersaturations that are punctual high and not uniformly distributed lead to clogging. In the case of Ezeanowi et al [60], no clogging was observed at similar average velocities of 5-9 cm s − 1 and an internal diameter of 250 mm. The observed duration per experiment was also 3-4 residence times [60].…”

“…In the case of Ezeanowi et al [60], no clogging was observed at similar average velocities of 5-9 cm s − 1 and an internal diameter of 250 mm. The observed duration per experiment was also 3-4 residence times [60].…”

“…Another research group has recently released a patent, it comprises the inlet of a substance to be crystallized into a tubular crystallizer which is sonicated (20 to 40 kHz) by an ultrasonic source and includes a temperature control structure for cooling the process fluid [59]. Studies on this patent were made by Han et al and Ezeanowi et al [52,60].…”

“…Ezanowi et al investigated a bigger version of the setup in pilot scale with an inner diameter twice as large and approximately equal length. They found out that with increasing residence time the CSD decreased and that ultrasound prevented pipe clogging [60].…”

Flow-driven crystal growth of lithium phosphate in microchannels

“…Ultrasound assistance in mixing during tubular crystallization, besides eliminating pipe clogging, helps to control crystal size as well. 22 The production of active pharmaceutical ingredients via flow chemistry has led to the syntheses of many promising compounds. 23 Metal ions in the form of sparingly soluble salts can also be spatially separated from their homogeneous solution mixture by the appropriate choice of precipitation.…”