Extraction and Destruction of Hazardous Materials by Supercritical Fluids

EXTRACTION AND DESTRUCTION OF HAZARDOUS MATERIALS BY SUPERCRITICAL FLUIDS 

Under supercritical conditions, a gas, such as carbon dioxide, possesses liquid-like density and solubility, and gas-like diffusivity and viscosity, along with zero surface tension. Thus, supercritical fluids work extremely well as a processing media for a wide variety of chemical, biological, and polymer extractions. This solvent power of supercritical fluid has been known since 1879. Nevertheless, its application was not considered until recently when the sharp increases in energy cost, environmental regulations, and performance demands on materials have caused industry to consider alternative 

In addition to its high dissolution efficiency, another powerful aspect to SFE is its ability to precisely control which component(s) of a complex matrix are extracted and which ones are left behind. This is accomplished through precise control of several key operating parameters such as temperature, pressure, flow rates, and processing time. Yields are much greater with SFE than extractions performed by traditional techniques, and product purity is usually high. Decomposition of materials almost never occurs due to the relatively mild processing temperatures. 

Solid-vapor (SV) equilibria are often adopted for the estimation of solubihty under SFE conditions. This case is relatively simple because the solubility of gas in solid can almost always be ignored, and the solid solute can be considered pure. Under SV equilibrium, the fugacity of the pure solid, or component 2, is equal to the fugacity of the solute in the solution, i.e.. 

For a LV system under equilibrium, the fugacity of solid on the left-hand side of Eq. (23) will be replaced by the fugacity of the solute in the liquid phase, f-i. This quantity, in turn, can be estimated through, where y = activity coefficient of the 

---