Microfluidic supercritical CO2 applications: Solvent extraction, nanoparticle synthesis, and chemical reaction

Abstract

Supercritical CO2, known for its non-toxic, non-flammable and abundant properties, is well-perceived as a green alternative to hazardous organic solvents. It has attracted considerable interest in food, pharmaceuticals, chromatography, and catalysis fields. When supercritical CO2 is integrated into microfluidic systems, it offers several advantages compared to conventional macro-scale supercritical reactors. These include optical transparency, small volume, rapid reaction, and precise manipulation of fluids, making microfluidics a versatile tool for process optimization and fundamental studies of extraction and reaction kinetics in supercritical CO2 applications. Moreover, the small length scale of microfluidics allows for the production of uniform nanoparticles with reduced particle size, beneficial for nanomaterial synthesis. In this perspective, we review microfluidic investigations involving supercritical CO2, with a particular focus on three primary applications, namely, solvent extraction, nanoparticle synthesis, and chemical reactions. We provide a summary of the experimental innovations, key mechanisms, and principle findings from these microfluidic studies, aiming to spark further interest. Finally, we conclude this review with some discussion on the future perspectives in this field.