An online strategy to increase the average crystal size during organic batch cooling crystallization

In situ attenuated total reflectance Fourier transform infrared (FTIR) measurements were shown to allow the online monitoring of supersaturation during solution crystallization processes, thus opening up new monitoring and control possibilities. With this aim in view, the monitoring of unseeded batch cooling solution crystallizations of two agrochemical products was investigated. The FTIR measurements of solute concentrations were used to develop a fines dissolution technique, based on a controlled heating-up procedure after primary nucleation. The strategy only requires the knowledge of the solubility curve and was deliberately designed to be robust and easy to implement. Two organic solute/solvent systems were studied. It is clearly demonstrated that the technique allows one to improve both the reproducibility of the final crystal size distribution and the mean crystal size. For Isoproturon, a well-known pesticide, the average final size is increased up to 90%. The efficiency of the monitoring procedure is also shown to depend on the solute/solvent system in question.