**2. Supercritical CO2**

A supercritical fluid is defined as whatever substance above its critical temperature and pressure. In **Figure 1** a typical pressure-temperature phase diagram is shown where a singular region is shaded. Supercritical fluids have special properties as solvent power similar to liquids, but diffusivities two orders of magnitude larger than those of typical liquids, resulting in higher mass transfer rates. Moreover, solvent power and selectivity can be tuned with the modification of the density of this fluid. This one can be adjusted continuously by altering the experimental conditions of temperature and pressure.

Singularities in compressibility and viscosity, diminishing difference in liquid and vapor phases, are other exceptional characteristics that are present in this state.

CO2 is the fluid more used in supercritical conditions due to its low danger and relative low cost. CO2 is a solvent generally recognized as safe (GRAS), nonflammable, non-toxic, gaseous at room temperature, and easily removed from the process. Moreover, it presents relative mild conditions of its critical point (31.1°C and 71.8 bar) permitting the processing of thermolabile solutes which are primordial in pharmaceutical, cosmetic, and functional food industries.
