Caffeine metastable zone width and induction time in anti-solvent crystallization

Abstract

In this study, the anti-solvent approach was used to investigate caffeine's induction time and metastable zone width (MSZW). Chloroform is used as a solvent, and carbon tetrachloride is used as an anti-solvent. Initially, caffeine solubility data is gathered in the chloroform/carbon tetrachloride mixture at various chloroform mass fractions. Caffeine solutions with various concentrations were then created to determine the MSZW. The anti-solvent (carbon tetrachloride) was injected into the solution to achieve supersaturation. The metastable zone limit was obtained by adding the anti-solvent at a constant rate and using turbidity changes in the system. The time of induction in various supersaturations was also investigated. In this section, various concentrations of solutions were created. Then, the system was instantly supersaturated with an anti-solvent. The period between the addition of the anti-solvent and the change in the turbidity of the solution was known as the induction time. The visual technique is compared to the use of an online turbidimeter before starting induction time measurements, and it is shown that the induction times obtained with the online turbidimeter are shorter and more accurate. Additionally, the induction time was investigated by various supersaturations, and it was discovered that as the supersaturation approaches the metastable zone border, the induction time decreases. Furthermore, in the same supersaturations, the influence of mixing on induction time was explored, and it was revealed that the higher the stirring speed, the shorter the induction time. Finally, the interfacial energy of solid–liquid phase was calculated for two systems with different initial chloroform mass fractions. It was shown that a reduction in polarity of medium increases the interfacial energy.