Supercritical Fluids

Abstract

A supercritical fluid is characterized as a gas that is pressurized and heated to a compressed fluid state, which is above both the critical pressure and temperature. In this state, density and subsequently solvent strength and transport properties are highly adjustable by modest changes in temperature and pressure. Complex phase behavior and interactions with materials can occur. This behavior can be examined experimentally and described successfully by molecular thermodynamics. Carbon dioxide and water are two substances used frequently as supercritical fluids. The former, which may be used independently or in the presence of various cosolvents, is predominantly used because of its environmentally benign nature and low cost. The latter is used because of its efficiency in destroying hazardous aqueous pollutants and hydrothermal synthesis. Numerous supercritical fluid processes have been commercialized, including coffee and tea decaffeination, supercritical water oxidation, and supercritical fluid chromatography. Process research and development involving supercritical fluids are progressing in many diverse areas, including extraction, membrane filtration, polymerization, particle formation, cleaning and drying, and applications in microelectronic engineering.

Polystyrene foams with inter-connected carbon particulate network

“…1,3,5,6–11 For most polymer nanocomposite foams, the nanoparticles are pre-compounded into the polymer matrix to form a dispersed phase and then extrusion or batch foamed into the foam products by employing blowing agents such as hydrogen-containing chlorofluorocarbons (HCFCs), fluorocarbons (HFCs), and carbon dioxide (CO 2 ). 5,12–17 Consequently, the properties of polymer nanocomposite foams are still dominated by the continuous polymer matrix because it is difficult to let the nanoparticles form a continuous structure unless the particle concentration is very high. It would be highly desirable to develop new materials and new methods such that nanoparticles, even at a very low concentration, may form an inter-connected structure in the polymer nanocomposite foams.…”

CO2Permeability of Polystyrene Nanocomposites and Nanocomposite Foams

“…CO 2 has better solubility in polymers than the other two. Of all these potential alternatives, CO 2 is the most preferable because it is nonflammable, inexpensive, essentially nontoxic, and environmentally friendly . The foaming process can be carried out in a batch or continuous system.…”

“…Of all these potential alternatives, CO 2 is the most preferable because it is nonflammable, inexpensive, essentially nontoxic, and environmentally friendly. 6 The foaming process can be carried out in a batch or continuous system. Batch foaming is widely used in research because it is simple and easy to control.…”