Investigation of barium sulfate mixing-precipitation processes

Most of sparingly soluble crystals are produced through precipitation, which is the rapid crystallization of a substance induced either by physical changes or a chemical reaction in a solution upon mixing of the solution with another fluid.

The course of a precipitation process can be strongly affected by mixing when some of the precipitation sub-processes as chemical reaction and subsequent nucleation are fast compared to mixing.

The aim of this project is to gain a better understanding of the interaction mechanisms between hydrodynamics, mixing and precipitation. Precipitation process carried out in stirred tank reactors are investigated experimentally and through modeling. New mixing-precipitation models are formulated, which can be used to predict effects of process parameters on the product properties. Simple short-cut models characterizing the main mixing mechanisms are developed as well as detailed CFD based closure models that can capture the process characteristics in detail. The modeling tools are applied to the precipitation of the substance barium sulfate upon mixing of aqueous Na2SO4 and BaCl2 solutions in a stirred vessel. The effect of the key operating parameters, e.g. agitation rate, feed point position and reactant concentrations, on the mean particle size is investigated. Simulation results are compared with experimental data, thus highlighting the strength of the different models for particle size prediction [1].

The performance of different mixing models is evaluated by applying them to the yield prediction of competitive chemical reactions carried out in a stirred tank under various operating conditions [2].



[1] Vicum, L., Mazzotti, M., Baldyga, J.: Applying a thermodynamic model to the non-stoichiometric precipitation of barium sulfate, Chem. Eng. & Tech., 26, (2003), 325-333.

[2] Vicum, L., Mazzotti, M., Ottiger, S., Makowski,L., Baldyga, J.: Multi-scale modeling of a reactive mixing process in a semibatch stirred tank, Chem. Eng. Sci. (2004), in press.


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