Powder processing using supercritical fluids

Abstract : Particulate solids attract a lot of industrial interest as they are used so widely, particularly in the agro-food, pharmaceutical, cosmetics and mineral industries. However they are also the focus of a lot of scientific attention while their generation, their formulation and the control of their usage properties are still not well understood and mastered. In the domain of particle formation, processes using crystallisation from a supercritical medium constitute a new route to obtain finely divided solids. By using pressure as an operating parameter, these processes lead to the production of fine and monodisperse powders. Previously to the study of the processes, it is necessary to know the solubility of the studied solids in supercritical phases which require the knowledge of the behaviour of the different fluid and solid phases involved. There exist two families of processes, according to whether supercritical fluid - usually carbon dioxide - is used as a solvent or an anti-solvent: RESS or SAS. In the first case it is the drop in density due to the sudden decompression of the fluid, which is the driving force of nucleation. Because of its simplicity, RESS remains the first process to be tested and a large amount of different materials have been processed through RESS and its derivatives. Its main limitation lies in the rather poor solubility of several families of molecules in carbon dioxide. In the SAS process, it is the reciprocal dissolution of an organic solvent in the supercritical fluid which leads to the particle precipitation. The universality of SAS (there is always a proper solvent-antisolvent couple for the studied solute) will ensure future developments for very different type of materials. Very often, semi-continuous SAS process and RESS process can compete for pre-industrial particle generation Supercritical-assisted particle formation has made a lot of progress in the recent years. Both RESS and SAS processes continue to undergo fundamental and applied research and have benefited from the recent years’ advances. Even if several controversial issues are still in debate in the scientific community, industrial applications are expected soon in many sectors, though it is the pharmaceutical industry which seems best equipped to gather a majority of its developments.
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Jacques Fages. Powder processing using supercritical fluids. Supercritical fluids and materials, Jul 2003, Biarritz, France. p.33-85. ⟨hal-01781679⟩

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