From sulfite liquor to vanillin: effect of crystallization process on the yield, purity, and polymorphic form of crystals

Abstract

Different approaches for vanillin crystallization were performed using an aqueous solution, with low concentrations of this potential food and pharmaceutical phenolic compound, obtained from adsorption/desorption experiments applied to an oxidized solution of lignin isolated from softwood sulfite liquor. The process yield and purity of the vanillin crystals were determined, and the thermal stability of the two resulting polymorphic forms was analyzed by DSC. Crystallization processes by swift cooling and evaporation with heat favor the nucleation of metastable vanillin crystals (Form II) with lower yields than slow evaporative and cooling processes that crystallize vanillin into the stable polymorph (Form I) with yields around 80%. Moreover, the polymorphic form of vanillin, yield, and purity were found to be highly dependent on the conditions of the crystallization process, mainly the temperature and the range of temperature variation. The melting points of polymorphic Form I and II were found to be 82.6 and 81.0 degrees C, respectively, proving that Form I is the most thermodynamically stable vanillin crystal form. In conclusion, the process conditions for vanillin crystallization strongly affect the polymorphic form, the process yield, the contents, and the type of impurities in the final product, consequently, influencing its potential industrial applications.