FIG. 3.

Supercritical ${\mathrm{CO}}_2$ extraction processes in microfluidics. (a) A schematic illustration of supercritical fluid extraction (SFE) in a microcapillary, where the valuable compound is extracted into the supercritical ${\mathrm{CO}}_2$ bubbles. The typical microchannel diameter is of the order of a few hundred $\mu$m. (b) Supercritical ${\mathrm{CO}}_2$ extracts astaxanthin from hydrothermally disrupted algae cells using a silicon-glass microfluidic device.^42,67 Reproduced with permission from Cheng et al., Green Chem. 19, 106–111 (2017). Copyright 2017 Royal Society of Chemistry. Reproduced with permission from Cheng et al., Bioresour. Technol. 250, 481-485 (2018). Copyright 2018 Elsevier. (c) A schematic illustration of supercritical fluid extraction of emulsion (SFEE) in a microcapillary, where the supercritical ${\mathrm{CO}}_2$ bubbles extract the solvent from the water/solvent/chemical compound mixture. (d) Supercritical ${\mathrm{CO}}_2$ extracts an organic solvent, ethyl acetate, from water plus solvent emulsions in a microcapillary.³⁶ Reproduced with permission from Luther and Braeuer, J. Supercrit. Fluids 65, 78–86 (2012). Copyright 2012 Elsevier.