On the crystal polymorphic forms of L-glutamic acid following temperature programmed crystallization in a batch oscillatory baffled crystallizer

L-Glutamic acid exhibits two polymorphs: the metastable a form that is prismatic in nature and the stable ß form that is needle shaped. In this paper, the effects of mixing intensity, cooling rate, and temperature on the polymorphism and crystal characteristics in a solution crystallization of L-glutamic acid are investigated in a relatively new oscillatory baffled crystallizer. The prevalence of a preseeding effect was identified during the experiments, whereby traces of a specific polymorph were retained between experiments and acted as seeding for subsequent batches despite rigorous cleaning procedures. Under those conditions, the variations in mixing, cooling rate, and temperature seemed to have little effect on the polymorphic forms of the crystals prepared. Potential mechanisms for the preseeding effect are discussed. Examination of the role of seeding on the crystal morphology reveals its function to decouple the effect of preseeding, allowing the selected polymorph to be produced.