Coating of Particles in a Fluidized Bed operated at Supercritical Fluid Conditions

摘要

The combination of fluidized bed technology with supercritical carbon dioxide as fluidizing gas and as a solvent for the coating material enables the production of thin,even and solvent-free coatings[1-4].The solubility of the supercritical carbon dioxide can be affected easily by changing pressure or temperature or can be reduced to practically zero by the decrease of pressure to ambient conditions.Beyond that the reduction of the surface tension at high pressures makes the production of thin and smooth coatings possible.Because of the comparatively low critical temperature of carbon dioxide of 304 K,low temperatures can be realized for the coating process.In particular this enables the coating of temperature-sensitive substances.Therefore,the combination of the advantages of the fluidized bed technology(good solids mixing,reduced risk of agglomerate formation)with the possibilities of a supercritical fluid seems to be a very promising process for the production of coatings on "high value" products.However,the successful operation of such a coating process requires detailed knowledge of fluidi-zation at supercritical fluid conditions.