Supercritical fluids-assisted micronization techniques. Low-impact routes for particle production*

Micronized powders are of interest in many industrial fields; pharmaceuticals, catalysts, pigments, and biopolymers, for example, are some categories of products that can be used as micro-sized particles. Traditional techniques used to produce micronic powders are based on high-temperature reactions that require high energies, on jet milling that is characterized by low efficiencies and mechanical stress, and on liquid solvents precipitation that has a poor control on particle size and can pollute the product. Generally, the control of the powder size and the span of its distribution are still very approximate. In the last few years, several supercritical fluids-based techniques have been proposed for the production of micronic and nanometric particles. These processes try to take advantage of some specific properties of gases at supercritical conditions such as enhanced solubilization power and its modulation, large diffusivities, solventless or organic solvent reduced operation, and the connected possibility of controlling powder size and distribution. Techniques like the rapid expansion of supercritical solutions (RESS), supercritical antisolvent precipitation (SAS), particle generation from gas-saturated solutions (PGSS), and new atomization processes have been critically reviewed in this work.