Supercritical CO2 extraction of solids using aqueous ethanol as static modifier is a two-step mass transfer process

Abstract

This study re-analyzes literature data on S. platensis’ chlorophyll (CHL) extraction using 5-25 cm3 of 20–80% v/v ethanol in water (static modifier) and 82.5–62.5 cm3 of CO2 at 50 °C and 40 MPa. Under these conditions, a CO2-expanded aqueous ethanol (liquid) phase coexists with an aqueous-ethanol-modified CO2 (SCF) phase in the extraction vessel. Authors hypothesize the resulting extraction is a two-step process consisting of slow transfer of CHL from the substrate to the liquid phase, followed by fast (equilibrium) transfer of CHL to the SCF phase. For analysis, we described the ternary (CO2 + ethanol + water) system at 50 °C and 40 MPa using Peng-Robinson Equation of State and Wong-Sandler mixing rules with binary interaction parameters describing phase equilibrium of binaries (CO2 + ethanol), (ethanol + water), and (CO2 + water). Authors propose a simple mathematical model of the extraction process, and identify research needs to validate/refine it.