The extraction process using supercritical CO2 consists of the following three major process steps:
- Extraction process
- Separation of solvent (CO2) from extract
- Solvent make-up (recovery, purification of solvent…)
The liquid CO2 is usually supplied from a corresponding buffer tank where CO2 is present at its boiling point. The conditions of the buffer tank are usually at approx. 60bar and 22 ° C. In the first step the CO2 is cooled down before feeding it to the CO2 pump which pressurizes the CO2 up to extraction pressure and is responsible for feeding the desired amount of CO2 to the extractors. The cooling before the pump prevents possible cavitation inside the pump since the compression of CO2 induces heat thus partly evaporating the liquid CO2. After the pressurization, the CO2 is pre-heated before conveying it to the corresponding extractor. In this high pressure vessel the product is charged inside a corresponding handling basket and the CO2 flows through the product material. The solubility of certain compounds in the CO2 cause these organic components to dissolve in the CO2 and the loaded CO2-mixture is conveyed to the depressurization valve which keeps the pressure inside the extractor at a constant level. After the relaxation of the CO2 / extract mixture is routed through a pre-heater and is introduced into a separator. Since the solubility is strongly dependent on pressure and temperature of the CO2 the extract can be separated inside the separator since the pressure of the CO2 is lower than in the extractor. Depending on the actual product, several separation steps can be realized allowing a frationation of the extract by using different pressures and temperatures. The CO2 can be recovered to the buffer tank using a condenser which recombines the gaseous CO2 thus optimizing the loss of solvent.