point of the vapor pressure curve is known as the gas liquid critical point where the distinction between gas and liquid disappears the temperature and the pressure at the critical point are known as the critical temperature t c and the critical pressure p c no gas can be liquefied above its t c no matter how great the pressure the shaded region in fig1 is known as the supercritical fluid state and a substance existing in that region i e a substance which has been heated above its t c and compressed beyond its p c is termed a supercritical fluid scf in the supercritical state substances behave partly as a gas and partly as a liquid their densities are liquid like but in respect of diffusivity or penetration capability they resemble gases the density of a supercritical fluid may be continuously changed without phase separation by changes in pressure and or temperature density dependent properties such as solvent power also undergo corresponding changes for example when water is in the supercritical state t c 374 u00b0 c and p c 218 atm it tends to lose its hydrogen bonding characteristics its dielectric constant tends to suffer a dramatic decline and it tends to become miscible with certain hydrocarbons such as benzene as discussed above the present invention uses supercritical or near supercritical carbon dioxide to.