(84a) Precipitation of Nanostructured & Ultrafine Powders: Process Intensification Using the Segmented Flow Tubular Reactor - Still in Search of the Perfect Powder? | AIChE

(84a) Precipitation of Nanostructured & Ultrafine Powders: Process Intensification Using the Segmented Flow Tubular Reactor - Still in Search of the Perfect Powder?

Authors 

Bowen, P. - Presenter, Swiss Federal Institute of Technology
Testino, A. - Presenter, Ecole Polytechnique Fédérale de Lausanne (EPFL)
Legagneur, V. - Presenter, Ecole Polytechnique Fédérale de Lausanne (EPFL)
Hofmann, H. - Presenter, Ecole Polytechnique Fédérale de Lausanne (EPFL)
Donnet, M. - Presenter, Ecole Polytechnique Fédérale de Lausanne (EPFL)
Cobut, N. - Presenter, TechPowder S.A


The synthesis of powders with controlled shape, narrow particle size distributions, desired stoichiometry and crystal polymorph is still a major concern for many industries. The Segmented Flow Tubular Reactor (SFTR) has been developed and overcomes many of the problems often encountered when using batch reactors with respect to product quality. The SFTR is composed of a mixer-segmenter and a tubular reactor. A supersaturation is created in the mixing chamber inducing the precipitation of particles. The precipitating suspension is then segmented into identical small volumes by a non-miscible fluid. The SFTR achieves a quasi-plug flow when compared to large batch volumes, the micro-volumes created in the SFTR are more homogeneous. The precipitated product is consequently more homogeneous with narrower particle size distributions, enhanced control of particle morphology, polymorph selectivity and better stoichiometry control; all these features have been demonstrated[1]. To increase productivity for commercial application the SFTR can be ?scaled-out? by multiplying the number of tubes running in parallel instead of scaling-up by increasing their size. This "scaling-out" approach means that the pilot scale and production scale are identical reactors. This cuts out a whole step in the normal scale-up development thus intensifying the process, a key factor in reducing time to market. A multi-channel SFTR was developed in the European Community Fifth Framework Programme involving seven partners. The results demonstrate, at a pilot scale, the adaptability and promise of the SFTR. The versatility of the SFTR concept allows changes in type of precipitation chemistry with a minimum of new investment as the new chemistry can be; researched, developed and optimized on a small batch scale (25 -50 ml), transferred to a single channel unit and then scaled-out. Examples for calcium carbonate and barium titanate, produced using the technology will be presented illustrating a scaling-out factor of 5000 with no change in product quality and the robustness of ultrafine barium titanate powder quality. Process intensification and indeed control of any precipitation reaction strongly depends on our knowledge of the precipitation mechanism. Recent results on the kinetics and growth mechanisms for the both the nanostructured calcite [2] and nanosized barium titanate [3] will be presented. Modelling of the dominant complexes in solution along with experimental determination of the kinetics during precipitation provide data for a population balance model which helps elucidate the growth mechanisms. Combining modelling of the solution chemistry, crystal growth and aggregation with cryogenic electron microscopy, particle size measurement and post precipitation microscopy, further insights into the growth mechanisms have been gained.[1] Jongen N., et al, Chem.Eng.Technol. 26(3) 303-305 (2003). [2] M. Donnet, P. Bowen, N Jongen, J. Lemaître, H. Hofmann, Langmuir 21 (1) 100-108 (2005)[3] A. Testino, V. Buscaglia, M. T. Buscaglia, M. Viviani, P. Nanni, in press Chem. Mater. (2005).

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