On-line control of crystal properties in nonisothermal antisolvent crystallization

The issues regarding the design and implementation of on-line optimal control strategies of crystal properties in noniso- thermal antisolvent crystallization processes to control particles’ mean size and standard deviation are dealt. The one- dimensional Fokker–Planck equation is used to represent the dynamic characteristics of the crystal growth and generate iso-mean and iso-standard deviation curves. Using controllability tools it is demonstrated that the system is ill condi- tioned in the whole operational range, posing limitations on the achievable control performance. To circumvent the problem, a control strategy is formulated by pairing crystals’ mean size with antisolvent feed rate and manipulating temperature to control the standard deviation. A novel digital image-texturing analysis approach is discussed and imple- mented to track crystals’ size distribution along the experiment and providing the on-line information for further feed- back control action. Subsequently, alternative control strategies are implemented and tested to achieve a desired crystal size distribution.