Journal
CRYSTAL RESEARCH AND TECHNOLOGY
Volume 57, Issue 1, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/crat.202100102
Keywords
continuous crystallization; direct contact cooling; impurity distribution; phosphoric acid
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This study performed batch crystallization and continuous crystallization of phosphoric acid hemihydrate, showing differences in crystal shape and impurity concentration under different processes. By utilizing the equipment and approach elaborated in this study, the correlation between operating conditions and crystal quality can be assessed.
In this study, batch crystallization via indirect cooling and continuous crystallization via direct and indirect cooling of phosphoric acid hemihydrate (H3PO4.1/2H(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.
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