RESS process in coating applications in a high pressure fluidized bed environment: Bottom and top spray experiments

Fluidized bed combined with RESS process in supercritical carbon dioxide (SC-CO2) is a promising technology for coating heat-sensitive materials of high added value. This work presents a study of the most influencing operation parameters (temperature, pressure and flow) of the two steps of the process (saturation and coating).As a model system, glass beads particles (dp,s = 176 μm) were encapsulated with paraffin (Tm = 52–54 °C). Two different ways of injecting the coating solution of paraffin in the SC-CO2 in the fluidized bed were tested, bottom and top spray. The operation variables were kept in the following ranges for the saturation step: pressure from 18 to 22 MPa and temperature from 35 to 55 °C. In the coating process the pressure range from 8 to 10 MPa and temperature from 35 to 50 °C. Yields of the global process up to 70% were achieved. SEM-images of the achieved coatings show complete coating films with no agglomeration in the top spray experiments.