Seeded Crystallization of β-L-Glutamic Acid in a Continuous Oscillatory Baffled Crystallizer

A continuously seeded L-glutamic acid cooling crystallization process, in a continuous oscillatory baffled crystallizer, was designed and operated to deliver control over polymorphic form. Different feed solution concentrations and seed loadings of beta-L-glutamic acid crystals were examined. Steady-state operation, based on particle size distribution and polymorphic form, was demonstrated consistently after two residence times. Where bulk supersaturation remained in the range 2-3, the polymorphic phase purity of the thermodynamically stable beta polymorph was retained. However, when the bulk supersaturation exceeded this range to values of 3-8, primary nucleation of the metastable alpha polymorph was observed, and product crystals were a mixed phase. In the absence of seeding the system could not be operated without significant encrustation to the vessel surface thus leading to loss of control, whereas a continuously seeded approach allowed robust processing for at least 10 h.