On‐line control of crystal properties in nonisothermal antisolvent crystallization

Abstract

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

A novel hollow fiber membrane‐assisted antisolvent crystallization for enhanced mass transfer process control

“…In recent years, researchers have focused on improving the mixing efficiency by using various feed modes, the antisolvent‐solution contact approach, additional physical fields (electric, magnetic, etc. ), and novel feeding devices and crystallizers . However, because antisolvent transfer is based on the droplet or capillary mixing approach, the fundamental mixing mechanism is still limited by the mixing devices with a millimeter or submillimeter scale (10 −4 ‐10 −3 m).…”

Feedback Control for the Size and Shape Evolution of Needle-like Crystals in Suspension. II. Cooling Crystallization Experiments

“…Thus, for a different compound with a broader attainable region, the controller applied in this work might already be sufficient to achieve a significant shape change. In any other case, there is a need to integrate the growth step with more complex processes exhibiting increased actuation with respect to the crystal size and shape, such as milling, temperature cycling, ,,,, combined cooling and antisolvent crystallization, − cooling crystallization under the influence of additives, or a combination thereof. Despite the observed limitations in terms of shape change, we believe that this work provides a basis to develop and control such integrated crystallization processes in an entirely model-free framework, benefiting from the robust operation of the process enabled by feedback control.…”

Ethanol-free antisolvent crystallization of glycine by liquefied dimethyl ether

“…During crystallization processes, the physical properties of the final product, such as its chemical purity, crystal size distribution, and morphology, are changed by several factors, including temperature reduction and the antisolvent/solution ratio. In pharmaceutical industries these properties affect the bioavailability of materials [ 1 , 2 ].…”