Phase behavior of arbutin/ethanol/supercritical CO₂ at elevated pressures

Abstract

The phase behavior of a ternary system containing arbutin, which is effective for skin lightening, in a solvent mixture of ethanol and supercritical carbon dioxide (CO₂) was investigated. A high-pressure phase equilibrium apparatus equipped with a variable-volume view cell was used to measure the phase equilibrium loci of the ethanol+CO₂ binary mixture from 298.2 K to 313.2 K and pressures between 2MPa and 9MPa. The solubility of arbutin in the mixed solvent comprising ethanol and CO₂, which equivalently represents the critical locus of T-x, was determined as a function of temperature, pressure, and solvent composition by measuring the cloud points under various conditions. Throughout, the arbutin loading was maintained at 1.5 wt% on a CO₂-free basis in the solvent mixture and the pressure and temperature were varied up to 14 MPa and 334 K, respectively. For a CO₂ loading less than 34wt% on ethanol basis, the cloud point was not observed. However, the solid remained undissolved when the CO₂ loading exceeded 54 wt%. Between these loadings, steep and almost pressure-insensitive solubility curves, which extended downward to the vaporization boundary, were found.