Effect of Pressure On a Budesonide-Ethanol Spray During the Supercritical Anti-Solvent Precipitation Process

This study seeks to understand the effects of pressure on the creation of micron sized steroid particles through a supercritical anti-solvent precipitation process. A 1 weight % budesonide in ethanol solution was sprayed through a 100 μm inner diameter capillary nozzle into a high pressure vessel containing supercritical CO2. The spray characteristics were visualized by a high magnification video system, which captured images through viewing windows on the sides of the vessel. The supercritical CO2 temperature was held constant at 323 K, and particles were produced for operating pressures of 84, 89, and 94 bar. Images were taken at three distances from the nozzle. Images taken from the nozzle tip were used to measure the jet break up length, which decreased with increasing operating pressure. The average droplet diameters were measured at 3 and 14 mm distances away from the nozzle at each operating pressure. The droplet diameters increased from 3 to 14 mm and decreased with increased operating pressure. The collected budesonide particles were analyzed under a scanning electron microscope. The particles were spherical and about 1 μm in diameter for each operating pressure. The visualization methods allow particle properties to be related to process and jet properties.