Effect of polymorphism on the purity of l-glutamic acid

The effect of polymorphism on the purity of l-glutamic acid (l-Glu) is investigated by combining experiments and molecular simulations using l-aspartic acid (l-Asp) as an impurity. The results show that the content of l-Asp in β form is higher than that in α form, and the purity of l-Glu decreases with the increase of the amount of β form in the final product. Molecular simulation is employed to account for the different contents of l-Asp in different polymorphs of l-Glu. It reveals that l-Asp is mainly incorporated into the (011) surface of α form and the (020) surface of β form. Because the area for α (011) is much smaller than that for β (020), β crystal can accommodate more l-Asp than does α crystal.

► Crystal purity is influenced by polymorphism during solvent crystallization.
► l-glutamic acid in β form adsorbs more l-aspartic acid than in α form.
► β form l-glutamic acid has large (020) surface and adsorbs more l-aspartic acid.