Role of co-solvents in the SCFE process

Co-solvents play a crucial role in carbon dioxide (CO2) supercritical extraction in India or elsewhere in that they enable the supercritical fluid (CO2 in this case) to extract those materials that it is not naturally good with. What this does is expand the range of compounds (called target molecules) that the CO2 supercritical fluid extraction system in India or the rest of the world can extract. With the range of the equipment so expanded, it acquires considerable versatility which boosts its utility.

In the supercritical fluid extraction process, the fluid is taken into its supercritical state by raising its pressure and temperature respectively above its critical pressure and critical temperature. In this state, changes in density modify its solvent power i.e. its capacity to dissolve. Closely controlled pressure fluctuations are a great way to alter density of the supercritical fluid.

At a certain pressure, the supercritical fluid will dissolve only one particular compound from the raw material while not extracting other compounds. This particular compound is called target molecule. SCFE systems in India and abroad are calibrated to extract one target molecule at a certain pressure. When the process pressure is changed, another target molecule gets separated.

For example, the supercritical extraction of Acai palm (Euterpe oleracea) separates phenolic phytochemicals at a higher pressure and anthocyanin from the same pulp at lower pressure. The point is, supercritical extraction in India or abroad benefits from having equipment with a broad range as the same equipment can be used to obtain different molecules, even from the same raw material. It always makes greater financial sense to have an equipment that can extract a variety of target molecules. 

Co-solvents take this feature forward. When in its supercritical state, carbon dioxide is naturally good at extracting non-polar target molecules. CO2 supercritical extraction in India and the rest of the world benefits from co-solvents such as ethanol, water, and methanol as it also extracts polar molecules.

During the CO2 SCFE of phytochemicals, this limitation makes its presence felt. Supercritical CO2 (sCO2) is able to extract polar phytochemicals located outside the cell wall, but not those positioned inside the cell wall. The capacity of sCO2 to extract volatile phytochemicals and those with low molecular weight is greater than those that fall outside these groups.

The function of co-solvent pumps is to add one of the mentioned co-solvents in the required proportion during the process of CO2 supercritical fluid extraction.  Because otherwise, SCFE systems in India or anywhere else cannot harness the full benefits of co solvents. Optimal yield and efficiency are possible with the correct relative flow rates between the supercritical fluid and the co-solvent. Suppose 2% co-solvent is necessary for the process. If the extractor volume is 50 liters, 1 liter of co-solvent is added in the extractor before the process begins. Now, if the mass flow rate of supercritical carbon dioxide is 100 liters per hour, then the pump will add co-solvent at the rate of 2 liters per hour.

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