Supercritical Fluids at Pacific Northwest National Laboratory
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    Review date: July 24, 2003
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    About Supercritical Fluid

    A supercritical fluid is any substance above its critical temperature and critical pressure. In the supercritical area there is only one state-of-the-fluid and it possesses both gas- and liquid-like properties.

    Critical point of a substance A supercritical fluid exhibits physicochemical properties intermediate between those of liquids and gases. Characterisitics of a supercritical fluid are

    • Dense gas
    • Solubilities approaching liquid phase
    • Diffusivities approaching gas phase.
    Mass transfer is rapid with supercritical fluids. Their dynamic viscosities are nearer to those found in normal gaseous states. In the vicinity of the critical point, the diffusion coefficient is more than ten times that of a liquid. As is the case for density, both the viscosity and diffusivity are dependent on temperature and pressure. Changes in viscosity and diffusivity are more pronounced in the region of the critical point. Even at high pressures (300-400 atm) viscosity and diffusivity are on order-of-magnitude less than a liquid. Therefore, the properties of gas-like diffusivity, gas-like viscosity, and liquid-like density combined with pressure-dependent solvating power have provided the impetus for applying supercritical fluid technology to various problems.

    This is not new technology. The phenomena of enhanced solubilities in supercritical fluids has been known since the late 1800s. For decades it has been used in food processing industries to extract compounds such as caffeine and hop oil. Parts cleaning is a new application with increasing interest in this area of established technology. Recent breakthroughs at PNNL have dramatically increased the potential applications. Additional information is available about our capabilities from links to the left.

    The role of carbon dioxide (CO2). Carbon dioxide is extremely attractive in industrial applications because it is the second most abundant and the second least expensive solvent on earth. It is non-flammable, non-toxic, and its use does not contribute to the net global warming effect.

    For information about supercritical fluid capabilities at PNNL,
    please contact Clement Yonker, at (509) 372-4748, clem.yonker@pnl.gov.