Chapter 3.2 - Investigation and Modelling of the Gas-Antisolvent Process

Abstract

This chapter discusses the investigation and modeling of the gas-antisolvent process. Gas-antisolvent micronization procedures seem to offer new and prospective chances for a more detailed and successful particle design. The study was aimed at investigating the influence that process parameters take on the mechanisms of particle growth and the resulting particle size distributions. Based on a simplified single-droplet model, statistical population densities could be derived that describe the behavior of an ensemble of droplets present in the real process, and are in reasonable agreement with experimental results obtained from gas-antisolvent crystallization investigations. As the model does not consider effects such as particle agglomeration, the agreement cannot be expected to be very accurate. The gas-antisolvent process is characterized by high amounts of supersaturation and, therefore, by high concentrations of primary nuclei and narrow particle size distributions due to a rather low tendency to agglomeration steps. As could be shown by detailed model calculations based on phase equilibria, mass transport equations, and population balances—the supersaturation required for the crystal formation process can be achieved within fractions of seconds, and does not significantly differ across the radial coordinate of the solution droplet.