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A new insight for quantitative determination of the complex interaction of kinetics of reactive crystallization is gained by a study of the acidification of monosodium glutamate with hydrochloric acid in a semibatch reactor. The dynamic equilibrium of the L-glutamic acid ions, their simultaneous presence in the solution, and the effect on the crystal size and size distribution are simulated using a mathematical model based on integration of the population balance equation with the crystallization kinetics and thermodynamics of the process. The model includes equations of chemical reactions, pH, nucleation, size-independent growth, and population balance. This allows a precise determination of the driving force for the reactive crystallization and the parameters of the nucleation and crystal growth rate expressions. The model considers the effect of the controlling parameters such as the rate of addition of the acid and the initial concentrations of ionic species and can be used to predict the concentrations in the solution, the pH, and the crystal mass. The effect of process conditions on the crystal size, crystal size distribution, and morphology is studied.

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A new tomographic technique, based on synchrotron X-ray diffraction, has been used to chart polymorphic content and crystallite alignment inside a model pharmaceutical reactor. This reveals complex behavior according to crystallite shape/size characteristics; in particular, stirring induces pronounced crystal zonation marked by a boundary “alignment band” in which the crystallites adopt a “stand on edge” orientation.

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