Correlação entre dados calorimétricos, espectroscópicos e de imagem na precipitação do ácido adípico: efeito da taxa de resfriamento na distribuição de tamanho dos cristais

Abstract

Crystallization is an essential step in chemical and pharmaceutical processes, as it affects physicochemical properties and the quality of the final product. This work investigated the influence of cooling rate on the crystallization of adipic acid in aqueous solution through a multi-technique approach integrating calorimetry, ATR-FTIR spectroscopy, and real-time image analysis (PVM and RGB), complemented by scanning electron microscopy (SEM). Calorimetry proved to be the most sensitive technique for detecting nucleation, enabling the determination of the total heat released during crystallization, thermal conversion curves, desupersaturation, supersaturation, and the width of the metastable zone (MSZ). Supersaturation derived from these data confirmed that higher cooling rates favor nucleation, whereas lower cooling rates hinder it. ATR-FTIR spectroscopy tracked the decrease in solute concentration, corroborating the calorimetric data. Imaging techniques provided real-time visual monitoring, revealing turbidity changes, the prismatic morphology of the crystals, and possibly subcritical aggregates. SEM quantitatively confirmed the effects of MSZ, supersaturation, and cooling rate: at 2.0 °C/min, smaller particles with narrower distributions were formed, whereas at 0.2 °C/min, larger and more heterogeneous crystals were obtained. Overall, the integration of calorimetry, ATR-FTIR, PVM, RGB, and SEM enabled a comprehensive characterization of crystallization, consolidating itself as a robust tool for studying and controlling crystalline processes of industrial and pharmaceutical relevance.