Supercritical Fluids (SCFs) are compounds at temperatures and pressures above the compound’s critical temperature and critical pressure. SCFs are tunable and green solvents, provide interesting reaction environments and unique energy transfer opportunities.
Carbon dioxide is the most widely used and explored SCF owing to its critical conditions (304 K and 74 bar), low cost and that it is not flammable or toxic.
SCFs are a single phase with properties that lie between the properties of typical gases and that of typical liquids. Gaseous carbon dioxide (at 298 K and 1 atm) has a density of 1.8 kg/m3. Liquid carbon dioxide (at 298 K and 100 bar) has a density of 818.88 kg/m3. Supercritical carbon dioxide’s density can be tuned (at 350 K and 80 bar it is 164 kg/m3 while it is 941 kg/m3 at 305 K and 300 bar). This density shift over narrow temperature and pressure changes is key to many of the opportunities associated with SCF applications. SCF Properties for more.
SCF property tunability extends well beyond density. Density, enthalpy, entropy, diffusivity, viscosity, solubility and more depend on the selected SCF and on the operating conditions of temperature and pressure. This tunability presents an opportunity for the development of a wide range of applications. However, exploration of potential opportunities requires considerable data and is aided by models to bridge gaps.