(583b) Solvents for Crystallization

In many industrial crystallization processes the control of crystal size and shape is very important since such control affects the ease of separating, washing, drying, packaging, handling and storage of crystals. The crystal morphology can influence properties such as the packing density, agglomeration and re-dissolution characteristics. Certain solutes crystallized from different classes of solvents exhibit different crystal size and morphology. For example carboxylic acids such as succinic acid and ibuprofen are known to exhibit varying morphologies from solvents. In this context it will be extremely valuable to study the influence of solvents on the size and morphology of crystals formed from them. The insights gained form these studies will help us understand the solvent property - solute morphology link. These results will aid us in solvent selection and solvent design strategies for crystallization processes. This work presents a comprehensive study of size and shape of 5 different carboxylic acids in 3 solvents ranging from non polar to highly polar. Crystallization experiments we carried out and size and morphology were analyzed through optical microscope and SEM pictures. The results suggest that for carboxylic acids non-polar solvents tends to give smaller size and higher aspect ratio (ratio between two major dimensions) crystals while polar solvents tend to give larger size and lower aspect ratio crystals. It is our view that hydrogen bonding between the solute carboxylic groups and the solvent plays an important role in the crystal morphology. Another interesting observation is that solutes having higher solubility parameter values tend to form larger size and lower aspect ratio crystals in a given solvent. This observation is consistent to both non-polar and polar solvents. We believe this comprehensive experimental study and the subsequent analysis will help us better understand this phenomenon.