Chapter 2 - Particle Formation Using Sub- and Supercritical Fluids

Abstract

Applying supercritical fluids may overcome the drawbacks of several conventional processes for formulation of products. For production of particles with micron and submicron size, several methods using supercritical fluids like rapid expansion of supercritical solution and gas antisolvent recrystallization, gas antisolvent precipitation, supercritical antisolvent/precipitation with a compressed fluid antisolvent/solution-enhanced dispersion of solids, Supercritical assisted atomization (SAA), particle formation from gas-saturated solutions (PGSS™) were studied. Powders and composites with special characteristics can be produced. Up to 2013, the applications of the high-pressure micronization processes using subcritical and supercritical fluids have been investigated for polymers, waxes and resins, natural products, fats and fat derivatives, pharmaceuticals, synthetic and natural antioxidants, surface-active compounds, UV stabilizers, composites of the mentioned substances, etc. The powders produced show narrow particle-size distribution, and have improved properties compared to the conventional produced powders. The structure of the substance to be micronized (crystalline amorphous, pure, or composite), the process parameters (pre-expansion pressure, temperature, gas-to-substance ratio, and viscosity of melt/solution/dispersion) of the high-pressure micronization process, and geometry of the process equipment influence particle size, particles size distribution, bulk density, the morphology (particle shape), and ratios of crystalline to amorphous of the processed substances. In detail, PGSS™ process will be presented. In the process, melts, solutions, emulsions, or suspensions are intensively mixed with compressed gas—most frequently the gas is carbon dioxide. Also other highly compressible fluids have been used: propane, butane, dimethyl ether, freons, nitrogen, alcohols, esters, ethers, ketones, and mixtures of above-mentioned gasses and solvents.