Carbon dioxide at temperatures higher than the critical temperature Tc = 31.26 ℃, the pressure is higher than the critical pressure (Pc) = 72.9, under the condition of ATM properties change, its close to liquid density, viscosity to gas, liquid diffusion coefficient for 100 times, and therefore has the amazing ability to dissolve. Use it can dissolve various substances, and then extract the effective components, has wide application prospects. Supercritical carbon dioxide is one of the most widely studied nowadays fluid, because it has the following features:

(1) CO2 critical temperature of 31.26 ℃, the critical pressure is 72.9 ATM, easy to achieve critical conditions.

(2) the chemical property of CO2 is inert, colorless, odorless, non-toxic and safe.

(3) low price, high purity and easy access

Carbon dioxide extraction