Polymorph selection and process intensification in a continuous crystallization-milling process: A case study on L-glutamic acid crystallized from water

The continuous crystallization of l-glutamic acid from water in a single-stage mixed-suspension mixed-product-removal crystallizer coupled to a milling loop is studied. We show that the stable β polymorph can be obtained in the presence of milling under operating conditions that would lead to the metastable α polymorph without milling. The effect is first shown through a series of experiments carried out at different residence times and feed concentrations in the absence or presence of milling. The experimental observations are rationalized through the use of a population balance equation model. We conclude that the observed effects result from fines generation and the corresponding increase in crystal surface area. Using the model, we obtain a map of polymorphic outcomes and process productivity in dependence on the operating conditions. It is shown that the combined crystallization–milling process exhibits higher productivity and an enlarged region of operating conditions where the stable polymorph of l...