INTRODUCTION OF SUPERCRITICAL FLUIDS PARTICLE PROCESSING
Abstract
Several conventional methods are currently in use for producing fine powders, including jet and ball milling, spray drying, and recrystallization using solvent evaporation or liquid anti-solvent. But all these techniques have in common the disadvantage of poor control of the size distribution of the particles, i.e., a wide range of particle sizes is usually produced. In addition, each method has its own specific disadvantages. For example, spray drying usually requires high operating temperatures, which may cause thermal degradation of sensitive materials such as the majority of food ingredients and pharmaceuticals. Solvent evaporation and liquid antisolvent recrystallization face solvent and anti-solvent residual problems.
In the past two decades, many researchers have tried to solve these shortcomings of conventional techniques of particle design by investigating the potential of supercritical fluids (SF). Since the size and size distribution and sometimes even the morphology of particles produced in different industries are usually not appropriate for the subsequent use of those materials, particle design has been gaining increasing importance in manufacturing advanced ceramic materials, dyes, explosives, catalysts, coating materials, microsensors, polymers, pharmaceuticals, and many other chemicals. The most attractive features of SCF in this respect include enhanced solubility power compared to regular gases, sensitivity to small changes in either temperatures or pressures and fairly mild operating conditions. Until now, carbon dioxide (CO2) has been the most common supercritical fluid, due to its unique characteristics such as having low critical temperature and pressure, good solubility in organic solvents, good transport properties, and being inflammable, non-toxic, and inexpensive.