Supercritical carbon dioxide separation of fish oil ethyl esters by means of a continuous countercurrent process with an internal reflux

The continuous countercurrent fractionation of fish oil ethyl esters using supercritical carbon dioxide is studied, modelling a process with internal reflux generated by a thermal gradient at the top stage. A methodology for process design is proposed and applied to determine the relationships between the temperature at the top stage (T1), the number of theoretical stages (N), and the solvent to feed ratio (S/F), with the aim of providing a quantitative comparison with the external reflux process. The internal reflux process is viable and, for stated process specifications (mass fraction and recovery of C20 + C22 ethyl esters of 95%), provides comparable or better results than the external reflux process. For example, operating at 13.3 MPa and 50 °C, and keeping T1 in the range (66–70) °C, the specifications are attained with N and S/F in the range 16–30 and 88–120, respectively.