Coating Granulation by Rapid Expansion of Supercritical Fluid Solutions in a Fluidized Bed

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The coating granulation by the rapid expansion of supercritical CO_2 solutions of binder (paraffin) was performed to coat the surface of core particles (glass beads) with fine silica particles in a fluidized bed. The deposition of paraffin by rapid expansion of supercritical CO_2 solutions incorporated fine silica particles into the layers around core particles. Initially individual fine particles are attached to the core particles due to the adhesion force and then are bounded by solid bridging due to the deposition of binder. A stable coating granulation was achieved without the excess agglomeration. At low gas velocity the binder material was deposited on the coating layer of fine particles adhered to the core particle. This leads to the uniform coating granulation by layering fine particles. On the other hand, at high gas velocity small agglomerates and fine particles are found to be layered on the core particles.In addition, porous particles were coated with film masking for releasing control by the rapid expansion of supercritical CO_2 solution in a fluidized bed. The coating characteristics was examined by the measurements of releasing rate of red pigment and SEM observation. It was found that the releasing rate can be controlled by controlling the operation condition. All the particles in mono-dispersion in the coating process with out agglomeration in granules. The releasing rate and the coating surface analysis was analyzed in the experiment.