Supercritical Fluid Injection coupled with the continuous twin screw extrusion process opens many opportunities for new engineered processing techniques for the development of new products and new product concepts. This supercritical fluid extrusion technology has already resulted in new developments in cereals, confectioneries, pastas, flavorings, pharmaceuticals, and anything left to the imagination.

A definition and some background of the term supercritical related to fluids and gases is important to understand the terminology and concepts related to this fascinating technology.

"Supercritical" seems to be an eye-catching phrase for many researchers when they read or hear about using CO₂ to expand extruded products. It is useful, therefore, to define supercritical fluids and to understand the properties of supercritical CO₂. Fluids become supercritical when their temperature and pressure are above the critical temperature and pressure. The critical temperature (TC) is unique for every fluid and is defined as the temperature above which a gas cannot be liquefied by simply increasing its pressure. The critical pressure (PC), also unique for every fluid, is the gas-liquid equilibrium pressure which corresponds to the critical temperature. The triple point is the point at which the gas, liquid, and solid phases all exist in equilibrium.

Carbon dioxide has been selected as the solvent of choice for extrusion processing and may be used as the solvent for supercritical deposition techniques. In many cases supercritical CO₂ may be used as an alternative to water as an expansion agent simply because of its physical properties

Wenger manufactures a total Super/Subcritical Fluid Injection and Control System, which may be used in a broad range of applications.

For additional information, E-mail:  Brad Strahm Process Engineer