Atypical crystal growth within the supercritical antisolvent process: Experimental and molecular modeling approach with sodium bicarbonate

Abstract

This paper presents the recrystallization of sodium bicarbonate (NaHCO3) using the Supercritical AntiSolvent process. The focus is pointed toward crystal habit and its modification induced by varying the solvent nature. The observed habit is uncommon with crystals exhibiting a “zigzag” shape. High Resolution Scanning Electron Microscopy observations refuted that this shape was due to particle attachment: those “zigzag” particles are likely monocrystals grown in a diffusion-limited media. Firstly, a molecular modeling study shed light on organic solvents that can interact strongly with NaHCO3 crystals. Such solvents were found to be ethylene glycol and glycine, in contrast to ethanol or water which likely interact weakly with NaHCO3 crystals. An experimental campaign confirmed the predicted interactions. Ethylene glycol interactions with NaHCO3 crystals led to the production of a different crystal salt. Alternatively, adding glycine as a growth inhibitor led to the initial polymorphic form, although with a modified growth mechanism.