Supercritical carbon dioxide isn’t just an efficient solvent for apolar compounds. In fact, if it’s combined with fluid modifiers like water, it becomes a very efficient solvent for medium polar and polar substances (caffeine for coffee decaffeination). The extraction efficiency is better than conventional technologies based on chemical solvents.
The Supercritical CO2 extraction process is “geometrically variable.” A supercritical fluid is any compound at a temperature and pressure above its Critical Point. It can diffuse through solids like a gas, and it can dissolve materials like a liquid. For any pure compound, there is a transition state called “critical” state: for temperatures below the critical temperature (Tc), two phases — liquid and vapor — coexist; for temperatures above Tc, there is only one phase: supercritical fluid.
After the extraction process, the mixture composed of CO2 and solutes leaves the extraction vessel(s) and it is directed to the separation vessels. By varying the pressure, flow and temperature of these vessels, it is possible to induce the selective precipitation of different chemical compounds as a function of their different saturation conditions in the supercritical fluid.