Abstract
Millimeter-sized α-glycine crystals were generated from continuous non-seeded cooling crystallization in slug flow. The crystallization process is composed of three steps in sequence: slug formation, crash-cooling nucleation, and growth. Stable uniform slugs of three different aspect ratios (slug length/tubing inner diameter) were formed, by adjusting the flow rates of both the solution and air streams. Besides supersaturation, the slug aspect ratio can also affect primary nucleation outcome. Stable slug flow can accommodate a relative supersaturation (C/C*) of up to 1.5 without secondary nucleation. Large glycine crystals can grow to millimeter size within 10 min, inside millimeter-sized slugs without reducing the slug quality.
Highlights
Continuous crystallization has received increasing research interests in both academia and industry for controlling crystal qualities, including polymorphic form, size, and morphology [1,2,3,4,5,6,7,8,9,10,11,12,13]
Primary nucleation is indicated by the existence of crystals in the slugs collected at the crystallizer exit
The specific process and physical setup were composed of slug formation, cooling nucleation, and growth zones in sequence
Summary
Continuous crystallization has received increasing research interests in both academia and industry for controlling crystal qualities, including polymorphic form, size, and morphology [1,2,3,4,5,6,7,8,9,10,11,12,13]. Stirred-tank based crystallizers (a) allow relatively longer residence time and spacious crystallization area. As with any other continuous crystallizer, it is interesting to explore more aspects of the slug flow crystallizer, including how slug flow properties affect the crystallization process and crystals inside and how to tune the flow to enhance crystallization in the desired direction. How does slug flow handle crash cooling, which tends to induce secondary nucleation and sometimes agglomeration as well, especially for non-seeded situations? This article provides additional aspects and understanding of the slug flow crystallizer, including using glycine cooling crystallization from water solvent as an example for the questions above. Even though it is impossible to cover all aspects of all compounds, the examples may provide useful information, such as generating large crystals from suppressing secondary nucleation
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