CO2 isn’t a liquid at normal room temperature and pressure. It is a gas. When temperature and pressure are increased over the critical point, we have supercritical fluid. The CO2 is at the same time a liquid and a gas at every point along the Equilibrium Curve.
The cleaning procedure is an important practice: it has the same importance as the extraction process. Any extraction system needs to be cleaned periodically: this period depends on many factors, including the type, quality and pre-treatment of raw materials, use of a co-solvent, and the number of extractions between cleanings.
Traditional technologies in many cases do not offer a satisfactory solution to a specific problem. Furthermore, there is a continuous search to reduce production costs. Pilot scale studies may show that, despite initial high capital costs, operating costs would be lower and the overall feasibility can be proven at certain scale of operation.
We say that a liquid is in equilibrium with its gas when the same mass is exchanged from the gas to liquid and from liquid to gas. This happens continuously, and this point is strongly dependent on pressure and temperature. Any change in temperature produces a change in the pressure.
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.