Fractionation technologies for liquid mixtures using dense carbon dioxide

Supercritical Fluid Extraction of liquid mixtures with dense CO₂ is an end-of-line process that is typically used to fractionate materials extracted by conventional methods. Because continuous countercurrent packed columns are the devices most commonly applied to fractionate liquid mixtures (lipid mixtures, essential oils, and alcoholic beverages), this review offers general background on the use of CounterCurrent Supercritical Fluid Fractionation (CC-SFF) in packed columns. Additionally, the manuscript characterizes in detail packed column facilities in leading institutions, and describes different modes of operation of countercurrent packed columns. The manuscript also discusses less common SFF technologies for liquid mixtures such as membrane contactors, mixer-settler arrangements, and spray processes. When appropriate, the review includes extensions of these topics (e.g., special uses of static mixers in SFF of liquid mixtures). In all cases, applications, future perspectives, and developments are included. Main fractionation applications include lipid mixtures, essential oils, and alcoholic beverages. Available phase equilibrium data and relevant physical properties of mixtures that are common to all technologies are also discussed. Even though a comparison between technologies is not straightforward, considerable effort has been made to identify the characteristics that make a technology more suitable for each application. In general, mixtures with low separation factors are associated with packed columns. Mixer-settler arrangements are limited to mixtures with high separation factors and when a small number of stages (≤5) are required for separation. An immobile interface at the pores mouth makes aqueous systems ideal for membrane contactors, and spray processes are used when handling with high viscosity mixtures.