2.5. Coating with the RESS-BFB
This coating method is similar to the RESS-WTS but utilizes a fluidized MCC bed in a cylindrical container operating as a bubbling fluidized bed. It uses no air but only RESS CO2 to fluidize the bed. A nozzle heater (nozzle 1) and temperature controller were installed and heated to approximately 60 °C to minimize dry ice formation and nozzle blockage. Prior to passing CO2 through the cylindrical fluidized bed, 40–60 g of MCC particles were added to give respective bed heights of either 70 or 110 mm that were 25 mm in diameter. Valve V1 was opened to fluidize the MCC using pure CO2. The coating was then started by opening valve V2 and closing V1 simultaneously, so as to switch the flow from CO2 to the solute-laden CO2 solution. In a similar manner to the RESS-WTS, the solution carried the active through the nozzle, forming a high speed jet into the MCC fluidized bed. The particles of active precipitated from the solution and were collected on the surface of the MCC. After a designated coating time (10 min), the flow of the CO2 solution reverted to pure CO2 to purge the pipeline for a further 10 min. The coated MCC particles were stored in the same way as described above in 2.4 for further characterization and analysis.