Extraction process

The extraction process using supercritical CO₂ consists of the following three major process steps:

• Solvent make-up (recovery, storage of solvent, pressurization,…)

• Extraction

• Separation of extract from solvent (CO₂)

Within the solvent make-up step the CO₂ is recycled, stored and conditioned to match the process specifications. If recycling of the CO₂ is considered, the amount of CO₂ needed to pressurize the plant is stored in a buffer tank. There the CO₂ is stored at boiling condition at around 60 bar and 22°C.

During the first step of the process the CO₂ is cooled down before going to the CO₂ pump which pressurizes the CO₂ up to the extraction pressure. Cooling the CO₂ before entering the CO₂ pump prevents possible cavitation inside the pump. After the pressurization, the CO₂ is pre-heated to the desired extraction temperature before entering the active extractor. Inside the extractor vessel there usually is a basket, charged with the product to ease the product exchange. The CO₂ flows through the basket and thuse the product material. The solubility of certain feed compounds in the CO₂ causes these (organic) components to dissolve in the CO₂. The CO₂ loaded with those extracts is transported to the depressurization valve which controls the pressure inside the extractor. After the relaxation of the loaded CO₂ it is routed through a pre-heater to reach the desired separation temperature and is introduced into the separator. Since the solubility of the extract in the CO₂ is strongly dependent on pressure and temperature, the extract is separated inside the separator. Depending on the product, additional separation steps can be realized  allowing a fractionation of the extract by using different pressure stages and temperatures. After leaving the separators the CO₂ can be recovered to the buffer tank using a condenser to liquify the (partially) gaseous CO₂ thus optimizing the loss of solvent.