1 Introduction

Micronization processes based on the use of supercritical fluids have been suggested during the last few years as alternatives to traditional techniques. ^[1] Indeed, one of the most intriguing challenges in the development of supercritical fluid (SCF)-based applications is the micronization of solid compounds that can be precipitated at mild temperatures and with reduced or no solvent residue. Moreover, SCF-based techniques guarantee the control of particle size (PS) and distribution (PSD) in the micrometric and nanometric range. These expectations are based on the peculiar characteristics of gases at supercritical conditions: very fast mass transfer and the fast and complete elimination of the SCF at the end of the micronization process.

The first supercritical fluid-based micronization process has been the rapid expansion of supercritical solutions (RESS); it is based on the solubilization of the solid to be micronized in the SCF and its subsequent precipitation by fast depressurization of the solution. However, the use of this technique is largely limited by the low solubility in supercritical carbon dioxide (SC-CO ₂) of many of the solids of interest. ^{[2] - [8]}

Particles generation from gas saturated solutions (PGSS) has also been proposed. In this case the product to be micronized is liquefied by heating and addition of SC-CO ₂; then, the gas-liquid solution is sprayed in a low-pressure vessel, thus obtaining microparticles. This technique has been successfully used to process some polymers, but has limited applicability in the case of thermolabile compounds...