Particle Breakage: Limiting Conditions for Crystal-Crystallizer Collisions

Rory Tyrrell, Brian De Souza, Patrick J. Frawley

Research output: Contribution to journalArticlepeer-review

Abstract

Two prominent theories surround the origin of secondary nuclei in batch crystallization experiments. Traditionally, the generation of secondary nuclei has been attributed to attrition breeding, resulting from collisions between crystals, impeller, and vessel geometry. Mechanistically, it is assumed that the collision of crystals leads to the generation of fine particles and nucleation sites. More recently, an alternative mechanism has received considerable attention, namely, cluster breeding secondary nucleation whereby the source of fine particles is attributed to clusters in solution. In the present work, a detailed experimental investigation of particle wall collisions of active pharmaceutical ingredient crystals is conducted. A pressurized test rig was developed whereby crystals in suspension were fired through a nozzle perpendicular to a stainless steel target. Using shadowgraphy, direct imaging particle-plane collisions are captured for crystals between 100-400 μm as they approach a target surface with initial velocities of up to 10 m/s. Crystals approaching a target surface are seen to be cushioned by a squeeze film boundary layer, greatly reducing their impact velocities. Furthermore, below a critical freestream particle Reynolds number, complete particle arrest was observed, preventing contact with the target surface entirely. This work provides further evidence to suggest that indeed secondary nucleation cannot be accounted for through particle-impeller breakage events. The alternative crystal breeding ideology is therefore further supported.

Original languageEnglish
Pages (from-to)617-622
Number of pages6
JournalCrystal Growth and Design
Volume18
Issue number2
DOIs
Publication statusPublished - 7 Feb 2018

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