Quasi-dynamic model for dissolution coupled with reaction and precipitation of sodium bicarbonate in fed-batch reactive crystallization

A quasi-dynamic model is proposed for fed-batch reactive crystallization of sodium bicarbonate (SBC) in a heterogeneous stirred tank reactor. SBC is one of the chemicals produced during recovery of ammonium perchlorate (AP), from rejected brine in AP manufacture. The mathematical model assimilates the dissolution of ammonium bicarbonate (ABC), reactions of bicarbonate, and crystallization of SBC. Since the process undergoes coupled dissolution, reaction and crystallization phenomena, the complex entwined aspects of hydrodynamics, kinetics, mass transfer rates, etc., are addressed individually. A holistic quasi-dynamic model was built by combining mass balances coupled with population balance model and CFD simulations. Model predicts temporal change of concentration of species, particle size distribution of sodium bicarbonate, and corroborate quite well with experimental results. It is a quasi-dynamic in nature owing to its dependency on bicarbonate species. After the short burst of nucleation during initial period of process, a steady concentration of bicarbonate species is achieved by a dynamic equilibrium between supply and depletion of bicarbonate through dissolution, precipitation, and dissociation. The mechanistic study reveals that the rate-controlling step would be "dissolution of ammonium bicarbonate", and the particles are formed through a burst of nucleation, followed by secondary nucleation and growth.