Crystal Shape Control by Manipulating Supersaturation in Batch Cooling Crystallization

Abstract

This paper describes a study on the shape control of potassium dihydrogen phosphate (KDP) in batch cooling suspension crystallization by selecting the supersaturation as a media control variable. The effects of different cooling modes on the supersaturation level and hence on the crystal shape were investigated. The results clearly show that different shapes of crystals were obtained at the various supersaturation courses. When a specific shape of crystal is desired from suspension batch cooling crystallization, a suitable cooling mode should be selected and furthermore the optimal one can be found.

Measurement, modelling, and closed-loop control of crystal shape distribution: Literature review and future perspectives

“…There is some work regarding the methods to modify the crystal size by controlling the supersaturation level during crystal growth [18,155] or by using impurities to manipulate the shape of crystals for sodium chlorate, which also represents an important direction since the use of impurity is considered in industry as an effective handle for size control. Several studies were carried out to develop some robust closed-loop control strategies (for example [1,64,139,[156][157][158][159][160]) with the help of the advanced in-situ sensors developed in last decade.…”

“…Barrett et al [61] proposed an approach to use solute-specific ATR-FTIR absorption peak heights for solute solubility and dissolved concentration, in turn, supersatuation, for the optimization of cooling crystallisation processes. Louhi-Kultanen and co-workers [155,156,184,185] investigated the feedback control of a reactive semi-batch precipitation process of LGA, and proposed a control structure to control the driving force of the reactive crystallisation using the feeding rate of the added acid. The solution concentration, obtained from PAT instruments such as MID-IR and ATR-FTIR, and pH were used to calculate the feedback information in the closed-loop control of the process.…”

“…A multidimensional PB model was developed in their work, which used two characteristic size dimensions to represent the shape of a twelve-faceted crystal. For the same chemical, Yang et al [155] proved experimentally that the shape for a population of crystals was able to be tailored by manipulating the supersaturation profile. In addition to manipulating the temperature or supersaturation profile in cooling crystallisation, another means of influencing the shape of growing crystals is the introduction of impurities.…”

Model Predictive Control and Dynamic Operability Studies in a Stirred Tank: Rapid Temperature Cycling for Crystallization

“…Past work on shape control has mostly restricted itself to two specific methodologies (Yang et al, 2006). The first has involved the use of additional solvents and impurities in the growth process, thereby influencing, through the additives, the specific growth rates of the different crystal faces.…”

“…One study in particular has focused on the crystal habit of potassium dihydrogen phosphate (KDP) and how changes in the cooling profile resulted in crystals with different aspect ratios (Yang et al, 2006). Additionally, recent progress in the modeling of crystal growth (Zhang et al, 2006) and crystal dissolution mechanisms has postulated an interesting new approach, suggesting that it may be possible to change the shape of the crystal by running the growth and dissolution steps in cycles (Snyder and Doherty, 2007).…”