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 β-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 β polymorph was retained. However, when the bulk supersaturation exceeded this range to values of 3–8, primary nucleation of the metastable α 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.
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