Utilization of micro-mixers for supercritical fluid fractionation: Influence of the residence time

The utilization of micro-mixers for supercritical fluid fractionation (SFF) was investigated in this work. Two different mixing principles were tested: multi-lamination and T-type lamination. The extraction of ethanol from aqueous solutions by supercritical carbon dioxide (scCO₂) was chosen as the model system. The influence of the average residence time on the extraction results was studied by varying the capillary length as well as the overall flow rate. Experimental results proved that thermodynamic equilibrium is reached in the micro-mixer and therefore the extraction cannot be enhanced by increasing the capillary length. On the other hand, in the experiments with different overall flow rate but same solvent-to-feed ratio (S/F), changes in the K-factor were observed when having a feed of 50 wt.% ethanol: the K-factor decreased as the total volumetric flow rate increased. Nevertheless, for the feed concentrations of 10 wt.% and 90 wt.% of ethanol, no significant changes were observed when the total flow rate was increased.