Transforming Industrial Crystallization by Sono-mechanical Manipulation of Crystal Surfaces

Crystallization is the principal purification technique in the pharmaceutical, fine chemical, paint, pigment and agrochemical sectors. Purification occurs by molecular recognition at the solution - lattice interface. At some sites on the crystal surface the mismatch between the impurity molecule and the lattice is so large that the impurity is rejected. At other sites the lattice mismatch is small enough for the impurity to attach to the crystal face where it disrupts and slows the subsequent growth on that crystal face, eventually the impurity is overgrown and incorporated into the product. Typical feed streams to industrial crystallizations contain several % of impurities so these interactions are very frequent and have serious consequences, for example product purity reduced, throughput is lowered and incomplete desupersaturation reduces yield. Intervening to remove impurities from the growing crystal surface during crystallization will overcome this problem increasing product purity and productivity, whilst reducing waste and delivering crystals with improved performance. Ultrasound is uniquely suited to this task as sound propagates through media by interaction with every molecule present. Frequencies in the KHz to MHz range are high enough to intervene as each molecular layer is added to the growing crystal. This research program sits alongside the EPSRC Centre for Innovative Manufacturing in Continuous Manufacturing and Crystallisation (CMAC) which provides access to a new dedicated facility within the £89M University of Strathclyde Technology and Innovation Centre (TIC) designed to promote continuous processing, particularly crystallization. This project is supported by GSK, AZ, Pfizer and Syngenta and will involve significant interactions with the industry partners.