Comparison between Open-Loop Temperature Control and Closed-Loop Supersaturation Control for Cooling Crystallization of Glycine

Consistent particle properties are an important goal for industrial batch crystallizations. Several control strategies, from unseeded linear cooling to seeded supersaturation control, were evaluated for the cooling crystallization of glycine. Particle properties were assessed in-line, facilitating investigations of process consistency. Seeding was by far the most effective strategy. Changing the preset cooling profile or the preset supersaturation limit showed limited benefits. Crystal growth rates matched the rate of supersaturation increase for all cooling rates, so that seeded processes operated entirely within the metastable zone. No secondary nucleation was observed.