(137d) Application of Psychrometric Principles for Predicting the Bulk Density of Spray Dried Dispersions

A closed-loop spray drying process may be deconstructed into a thermodynamic cycle comprising evaporative cooling, sensible cooling, dehumidification, and sensible heating. Consequently, its outcomes may be predicted through application of psychrometric principles. Here, we present psychrometric analyses of the spray drying process of a pharmaceutical product at large pilot scale. In this approach, the thermophysical properties of the vapor and gas are modeled using the Redlich-Kwong equation of state. The gas-vapor mixture properties are evaluated assuming ideal behavior (Raoult’s law), and the saturation vapor pressure of each mixture component is computed using the Clausius-Clapeyron relation. Vapor-liquid phase equilibria are approximated through the Van-Laar activity model. Through the resulting model, an algebraic, semi-empirical relation that describes factors governing droplet evaporation, namely the Sherwood, Reynolds, and Spalding thermal and mass numbers, is derived. We demonstrate that such a relation trends with the bulk density of the spray dried dispersion, and may provide key process insights beyond those achieved from a conventional empirical QbD approach.