Calibration of dielectric constant measurements to improve the detection of cloud and clear points in solution crystallization

Abstract

Metastable zone width, which can be approximated as the gap between the loci of cloud and clear points is an important control parameter for successful operations of solution crystallization processes. This study attempts to improve the accuracy of cloud point determination in paracetamol-ethanol solution using dielectric constant measurements and a special calibration technique. A suitable calibration model based on logarithm-polynomial expansion is developed using adjusted R2 and Akaike Information Criterion as model selection guides. The model, which decouples the effects of temperature and solute concentration on solution dielectric constant, is utilized to transform the dielectric constant profile into a solute concentration profile. The results show that the cloud points determined from the solute concentration profile are more accurate than those determined directly from the dielectric constant profile. The former are shown to be in good agreement with those obtained from the turbidity measurements, which are used as benchmarks in this study. Consequently, a more accurate metastable zone width could also be obtained using this calibration technique. © 2011 The Institution of Chemical Engineers.