In short, supercritical fractionation is the process of extracting compounds from a liquid. If one would perform this in a single vessel it would be the same. However, Supercritical Fractionation should be performed in a packed column applying a counter current flow. It can best be compared with distillation defining rectifying section and a stripping section. The column has several equilibrium stages, which will make it possible to separate a liquid mixture into two fractions with designed purity. One of the applications that was commercially applied was the purification of lubricants for hard discs by
It is especially suitable for temperature sensitive compounds. For Supercritical Fractionation the thermodynamics and the subsequent selectivity of the compound are extremely important. Increasing the solubility will decrease the selectivity. The solubility is related to the diameter of the column, while the selectivity determines the number of stages and therefore the height of the column. While the thermodynamics are already complex, the hydrodynamics of supercritical fractionation are even more complicated. This is due to the fact that in supercritical fractionation the top of the column will have the highest supercritical density. The gas will have a tendency to flow downwards in the column, and subsequently destroy the performance of the column.
When designing the process the engineer will to try to minimize the carbon dioxide flow, the volume of the equipment and the pressure. All to ensure the lowest capital costs and operational costs.
Although complex, supercritical fractionation is an alternative for processes that uses short path distillation. The reason is that short path distillation has only one theoretical stage, while supercritical fractionation will have as many stages as required for the purity.
Some examples of feasible processes are: polymers, esterified fatty acid separation (fish oil, algae oil, etc), squalene separation, purification of pure compounds from botanical extracts and trace removal.