Continuous Crystallization of Phosphoric Acid Using Suspension Crystallizer: Effect of Operating Conditions on Purity of Crystals

Abstract

In this study, batch crystallization via indirect cooling and continuous crystallization via direct and indirect cooling of phosphoric acid hemihydrate (H 3 PO 4 .1/2H 2 O) from the mixed acid solution of phosphoric acid and acetic acid are performed. In batch crystallization, needle-shaped crystals are obtained, and the impurity concentration of acetic acid in the crystals is 4.2 wt%. Primary nucleation occurred under a high degree of supersaturation, and the metastable zone width for secondary nuclei is narrow. In contrast, in continuous crystallization via indirect cooling, scaly crystals are obtained, and the acetic acid impurity concentration therein is 2.0 wt%. Additionally, continuous crystallization via direct contact cooling is performed, the crystal shape and impurity concentration under direct cooling are similar to those under indirect cooling, suggesting the possibility to downsize the apparatus. Through utilization of the equipment and approach elaborated herein, the correlation between the operating conditions and crystal quality can be assessed.

Development of a Novel Supersaturation Monitoring System in Continuous Crystallization of KAl(SO4)2·12H2O

“…For industrial applications, the purity of crystals has been investigated using methods such as adsorption crystallization [16] and continuous crystallization [17] to recover large amounts of phosphoric acid in semiconductor processes. Moreover, the inclusion of mother liquor in suspended crystals has been considered as a function of crystal size for the crystallization of potassium sulfate in both batch and continuous crystallization processes [18].…”

Inclusion of the Mother Liquor of Three Different Salt Crystals Formed via Industrial Crystallization Processes

“…1. This apparatus has been previously used to assess the purity and inclusion of the mother liquor in phosphoric acid and potassium sulfate crystals formed by continuous industrial crystallization [29,30].…”