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Etude expérimentale et modélisation par bilans de populations des cinétiques de nucléation de croissance d’opérations discontinues de cristallisation par refroidissement en absence et en présence d’impuretés.

Abstract : Hindering effects of impurities on crystal growth are usually assumed to result in the adsorption of impurity species on the crystal surface. In the presence of impurities the growth rate does not depend on supersaturation only, but also on the concentration in impurities and on the contact time of a given particle with inhibiting species (unsteady-state adsorption mechanisms). Few kinetic models describe such phenomena. Indeed, for process engineering purposes, the available kinetic inhibition models accounting for the effect of impurities (e.g. Kubota-Mullin’s approaches), have to be evaluated in industrial situations where complex and distributed features of the crystallizing suspensions are involved (e.g. during batch solution crystallization). Population Balance Equations (PBE) modeling offers an invaluable simulation tool for such evaluation.With this aim in view, a comprehensive modeling approach based on in situ continuous and dispersed phase measurements, and specific PBE simulation was developed to represent and better understand the effect of impurities on the development of batch crystallization processes.Cooling solution crystallization of Ammonium Oxalate (AO) in water in the absence and presence of Nickel Sulphate at different concentrations was selected as a model system during this study. In situ measurements of supersaturation were performed using ATRFTIR spectroscopy and the CSD was assessed thanks to in situ image acquisition. The experimental results were simulated after estimating crystallization kinetic parameters, including parameters of models describing the inhibiting adsorption of impurity on the growing crystal surfaces. Primary and secondary surface nucleation mechanisms as well as growth of the main crystal dimension (length) were described in pure and impure media. The model roughly represents the effects of different cooling rates and impurity concentration on the supersaturation profiles and the CSD of the final particles.
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Nesrine Gherras. Etude expérimentale et modélisation par bilans de populations des cinétiques de nucléation de croissance d’opérations discontinues de cristallisation par refroidissement en absence et en présence d’impuretés.. Autre. Ecole Nationale Supérieure des Mines de Saint-Etienne, 2011. Français. ⟨NNT : 2011EMSE0637⟩. ⟨tel-00721835⟩

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