Reaction engineering of continuous crystallization of β-ammonium tetramolybdate in concentric structure reactor and its application

Abstract β-ammonium tetramolybdate [β-(NH4)2Mo4O13] is an important product of molybdenum metallurgy because of its uniform crystal structure and excellent thermal stability. The yield of molybdenum strip produced with β-(NH4)2Mo4O13 as raw material and various processing properties have been significantly improved. However, the crystallization process of β-(NH4)2Mo4O13 is very complex, including neutralization, polymerization, nucleation, and crystal growth stages, resulting in a variety of polymerization morphology. In this work, a concentric structure reactor was used to segment these stages with directional regulation of each stage. Residence time distribution (RTD) was used to evaluate the simulation of flow field characteristics in the concentric structure reactor. Determination of the influence of inlet-outlet positions, size and position of paddle, and baffle setting on the fluid behavior in a single tank suggested measures to improve the abnormal flow condition and reduce the dead zone volume fraction. In the concentric structure reactor, the dead zone volume fraction was only 2.36% when the clapboards were arranged alternately in an up-down design, using an inlet flow rate of 100 mL/min. β-(NH4)2Mo4O13 was prepared continuously by adding aqueous ammonia and product slurry for crystallization in the concentric structure reactor.