Particle Production Using Supercritical Fluids

I. Properties of Supercritical Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 642 II. Nanoscale Particle Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 646 A. Rapid Expansion of Supercritical Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . 646 B. SAS — Supercritical Anti-Solvent Precipitation and Related Processes . . . . . . 647 C. The Influence of Different Methods and Process Parameters . . . . . . . . . . . . . . 651 D. PGSS — Particles from Gas-Saturated Solutions/Suspensions . . . . . . . . . . . . 652 E. Other Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 654 F. Inorganic Particles Obtained Using Supercritical Fluids . . . . . . . . . . . . . . . . . 656 G. Polymer Solid Particles Obtained Using Supercritical Fluid Processing . . . . . . 657 H. Particles with Specific Drugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 660 I. Encapsulation and Coating Using Supercritical Fluids . . . . . . . . . . . . . . . . . . . 660 III. Aerogels and Sol-Gel Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 663 A. Preparation of Aerogels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 663 1. Sol-Gel Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 663 2. Supercritical Drying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 667 B. Application of Aerogels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 670 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 672 The unique characteristics of gases at supercritical conditions, which are between those for liquids (density) and gases (viscosity and diffusivity) enable that different processes could be realized as for example: the selective extraction of specific components from the complex mixtures, the particle micronization, the supercritical fractionation, the production of materials with unusual and specific structure, etc. Many similar processes, based on supercritical fluids use are today the part of intensive investigations, while others have already been patented and applied in the pilot-plant scale. Obviously, in the recent past there is not always the advantage for all investigated supercritical processes because of high financial investment necessary for their implementation in industry compared to other conventional methods. However, it is important to notice the substantial increase of scientific research published in many journals, which include the new potential use and application of supercritical fluids.