(660a) Particle Imaging in Dense Suspensions Enabled By a Novel Dilution Technique

Crystallization plays an important role in the production of essential chemicals such as active pharmaceutical ingredients, food additives, and agrochemicals, serving as a key purification technique. Despite its widespread application, the fundamental phenomena occurring during crystallization remain poorly understood, especially under real-world industrial conditions. Deeper insight into crystallization phenomena could be gained by studying the evolution of the particle size and shape distribution (PSSD) during crystallization. However, in situ measurement tools like FBRM and imaging probes provide particle characterization with limited accuracy. Therefore, these tools can be supplemented by more precise ex situ offline imaging techniques. Advanced imaging techniques like the DISCO [1] have successfully been used in an online fashion in lab-scale R&D environments for process modeling and control, where low suspension densities allow for undiluted measurements [2; 3]. However, these techniques cannot provide a time-resolved evolution of the PSSD under industrial conditions, where the suspension densities exceed the acceptable particle density level for characterization by several orders of magnitude. The issue of high suspension densities has been tackled to some extent through automated dilution with filtered mother liquor, [4; 5] but they suffer from severe practical difficulties.

In this work, we introduce a novel continuous and automated device to dilute dense suspensions, with particle density exceeding 20 w/w%, using mother liquor from the crystallizer. The device is coupled with a state-of-the-art stereoscopic imaging device, the DISCO, to accurately measure the PSSD of ensembles of equant, needle-like, and plate-like particles. [6] Through a thorough experimental campaign, we show the ability of the dilution device to robustly operate for long periods (exceeding 24 hours) and to autonomously adapt to changes in particle density (e.g. induced by milling, seeding, or dissolution) by manipulating the dilution factor. Through wet milling and cooling crystallization experiments, we demonstrate the device’s capabilities to monitor the evolution of the PSSD, under conditions that mimic an industrial setting. Crucially, in all these experiments, we show that the dilution device does not change the PSSD.

By enabling accurate, time-resolved observations of the PSSD in high particle density suspensions, this technology paves the way for an enhanced understanding of crystallization processes. This has the potential to facilitate the development of robust modeling and control of crystallization processes under real industrial conditions, which was previously not feasible.

References

[1] Rajagopalan, A. K.; Schneeberger, J.; Salvatori, F.; Bötschi, S.; Ochsenbein, D.R.; Oswald, M.R.; Pollefeys, M.; Mazzotti, M. Powder Technol. 2017, 321, 479-493

[2] Rajagopalan, A. K.; Bötschi, S.; Morari, M.; Mazzotti, M Cryst. Growth Des. 2018, 18, 10, 6185-6196

[3] Bötschi, S.; Rajagopalan, A. K.; Rombaut, I.; Morari, M.; Mazzotti, M. From needle-like toward equant particles: A controlled crystal shape engineering pathway. Comput. Chem. Eng. 2019, 131, 106581

[4] Jager, J.; Kramer, H.J.M.; De Jong, E.J.; De Wolf, S. Powder Technol. 1990, 62, 2, 155-162

[5] Schorsch, S.; Vetter, T.; Mazzotti, M. Chem. Eng. Sci. 2012, 77 130-142

[6] Binel, P.; Jain, A.; Jaeggi, A.; Biri, D.; Rajagopalan, A. K.; deMello, A. J.; Mazzotti, M. Online 3D Characterization of Micrometer-Sized Cuboidal Particles in Suspension. Small Methods 2023, 7, 2201018