Influence of fluid properties on the hydrodynamics and operability of a countercurrent supercritical packed column

•Liquid hold-up and pressure drop do not reliably indicate operability in SF fractionation columns.•No observable “loading” operating regime was found under SF conditions.•Changes in temperature had a significant impact on operability due to fluid property variation.•Column operability range decreased with an increase in liquid viscosity and density. The hydrodynamic operability and the influence of fluid properties on hydrodynamics under supercritical conditions were investigated in a 38mm diameter column packed with ¼” Dixon rings. The column was operated using 100cSt and 200cSt Poly[dimethylsiloxane] (PDMS), with supercritical CO2 at 14MPa and 333K, 328K and 323K respectively. The pressure drop, liquid hold-up, mass flow and mass fractions were measured. The column operability limits were determined for both systems over a range of liquid and supercritical fluid flow rates using the measured data. Three distinct types of inoperability were identified, namely liquid layer flooding, bubble column flooding and excessive entrainment. It was found that liquid hold-up and pressure drop are not reliable indicators of operability in supercritical systems. Further, no observable loading operating regime was found, with the column only operating in the pre-loading or inoperable (flooded/entrained) regimes. The influence of the density and dynamic viscosity on hydrodynamics was found to be complex, yet significant. Small changes in temperature caused substantial changes in fluid properties, having a significant impact on column operability. Column operability range reduced with an increase in liquid viscosity and SF density. Finally, the data are compared to available models.