Characterization and morphology of spray dried kaolin particles

Abstract

In this study, the relationship between the physicochemical properties of kaolin slurries and their particles produced by spray drying to obtain FCC matrices was discussed. Eight aqueous slurries were prepared with 40 wt.% solids using two types of kaolin (K1 and K2) and sodium silicate solution as the dispersant. Additionally, nitric acid at 5.0 wt.% was used to adjust the pH in the range between 6 and 8. Both kaolin sources were characterized by X-ray diffraction and scanning electron microscopy. The K2 kaolin had a higher crystallinity of kaolinite and smaller particle size in comparison with K1. Likewise, while K2 showed 4 well defined bands of hydroxyl groups in the infrared spectrum at 3688, 3666, 3653 and 3620 cm−1, the K1 IR spectrum consisted of two sharp signals at 3692 cm−1 and 3620 cm−1 and two poorly developed bands at 3666 cm−1 and 3653 cm−1. These features intimately related to their structure were shown to have an effect on the morphology of the particles obtained during the drying process; in the case of the K1 slurries, these led to the formation of microspheres, and on the contrary, from K2 slurries mushroom head shape particles were formed. Furthermore, the average diameter (D50) of the particles increased with the increase of the amount of the binder in the slurry. Thus, the results show that a less crystalline kaolin favors the formation of microspherical particles during the spray drying process that allows a better control of the FCC matrix produced to be used in in-situ zeolite Y crystallization on kaolin particles.