Crystallization of Glycine in a Dual-Zone Continuous Slug-Flow Crystallizer to Improve Crystal Size Distribution

A common objective of various crystallization procedures is to produce polymorphic pure crystals that have a narrow size distribution and a specific average crystal size. A cooling continuous slug-flow crystallizer with silicone oil as the continuous phase and with separate nucleation and growth zones is developed for glycine crystallization. A supersaturation of 1.5–2.75, residence times of 8 and 11 min, and two crystallizer configurations were utilized for crystal production. The crystallizer can produce crystals with an average crystal size ranging from 70 to 350 μm, with up to 83% yield. The residence time, feed concentration, and temperature of the nucleation and growth zones are the major operational parameters regulated to produce the desired crystals without the need for crystal seeding. Experimental and computational validation confirmed that increasing the temperature in the growth zone resulted in the formation of crystals with a narrow size distribution. Consistent and continuous operation for several hours was achieved using the crystallizer. Thus, pure α-glycine crystals of the desired crystal size with narrow size distribution can be produced continuously using the slug-flow crystallizer design presented in this study.