Crystallization and precipitation from solutions are responsible for 70% of all solid materials produced by the chemical industry. Competing with distillation as a separation and purification technique, their use is widespread. They operate at low temperatures with low energy consumption and yield with high purifications in one single step. Operational conditions largely determine product quality in terms of purity, filterability, flowability and reactivity. Producing a material with the desired quality often requires a sound knowledge of the elementary steps involved in the process: creation of supersaturation, nucleation, crystal growth, aggregation and other secondary processes. Mathematical models coupling these elementary processes to all particles in a crystallizer have been developed to design and optimize crystallizer operation. For precipitation, the spatial distribution of reactants and particles in the reactor is important; thus the tools of computational fluid dynamics are becoming increasingly important. For crystallization of organic chemicals, where incorporation of impurities and crystal shape are critical, molecular modeling has recently appeared as a useful tool. These theoretical developments must be coupled to experimental data specific to each material. Theories and experimental techniques of industrial crystallization and precipitation from solutions are reviewed, and recent developments are highlighted

The synthesis of solution crystallization processes is a complex task that often leads to multiple process options. In order ensure design reproducibility and reliability, a hierarchical design procedure has been proposed. The procedure has compared favorably to the currently accepted procedure because the number of design decisions is more evenly distributed throughout the design levels. The procedure is based on the work of Bermingham (A design procedure and predictive models for solution crystallization processes. Ph.D. thesis, Delft University of Technology, 2003), but recourse to sophisticated phenomenological models is avoided. Instead, experimental information, heuristics and qualitative theoretical considerations are used to cope with systems for which fragmentary information is available, since such is the situation most commonly found in industrial practice. Its applicability has been demonstrated in the design of a sodium chloride crystallization process on a 1 m3 scale. Analysis of the pilot unit operation has led to the identification of improved design criteria related to process control, temperature elevation in the recirculation loop, and crystals washing.

In the present work two 3‐D models, for the catalytic layer, were employed in order to simulate the responses of a PBI high temperature polymeric membrane fuel cell. The simulations made use of an agglomerate model and a pseudo‐homogenous model, both implemented taking into account the temperature influence over their parameters. The overall simulation was performed also as two models, linked by the variable pressure, one for the whole graphite plate simulating the distribution channels, and the other dealing with the MEA and thereof the catalytic layer. A discussion over the two models was done and the experimental results demonstrated that the pseudo‐homogeneous obtained the better fits.

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Static mixers with improved performance were developed from CFD simulations in a stepwise approach. The relevant geometric features of simple mixer designs and the corresponding mixing mechanisms-laminar shear, elongational flow, and distributive mixing-were identified first. This information was used to formulate guidelines for the development of new geometries. The solid elements of the static mixer should: (a) provide restrictions to the flow; (b) deflect the flow; (c) be sequentially rotated around the flow direction to provide symmetry; (d) extend from the center of the pipe to the vicinity of the walls to avoid short-circuiting; and (e) distribute and remix the flow. Based on these guidelines, two improved mixer designs were developed: the DS A-I mixer has a good mixing efficiency and an acceptable pressure drop; the Fins 35 • mixer is more efficient and compact, but requires a larger pressure drop. Their performance indicates that their use is possible on industrial applications.Des mélangeurs statiquesà rendement accru ontété créésà partir de simulations de dynamique numérique des fluides dans une approche progressive. Les caractéristiques géométriques pertinentes des conceptions de mélangeur uniques et les mécanismes de mélange correspondants-cisaillement d'unécoulement laminaire,écoulementélongationnel et mélange par distribution-ontété déterminés en premier. Ces renseignements ontété utilisés pour formuler des lignes directrices pour la création de nouvelles géométries. Leséléments solides du mélangeur statique doivent: (a) fournir des restrictionsà l'écoulement; (b) détourner l'écoulement; (c)être tournés séquentiellement autour de la direction de l'écoulement dans le but de fournir une symétrie; (d) s'étendre du centre du tuyauà la proximité des parois pouréviter le court-circuitage; et (e) distribuer et remélanger l'écoulement. Conformémentà ces lignes directrices, deux conceptions de mélangeur améliorées ontété créées : le mélangeur DS A-I présente une bonne efficacité de mélange et une perte de charge acceptable; le mélangeur Fins 35o est plus efficace et compact, mais nécessite une perte de charge plus grande. Leur rendement indique que l'on peut les utiliser pour des applications industrielles.