Solubility of Betulin in Supercritical Carbon Dioxide and a Carbon Dioxide–Ethanol Mixture

The solubility of betulin in pure and modified supercritical carbon dioxide (SC-CO2) at 313.15–333.15 K and 8.0–30.0 MPa is experimentally studied by the dynamic method. It is found that betulin swells in pure SC-CO2 without being dissolved. The solubility of betulin increases upon the addition of 5% ethanol as a cosolvent. The pressures corresponding to the first and second crossover points are determined to be 7.7–8.3 and 27.1–27.6 MPa, respectively. The experimental data are described using a model based on the Peng–Robinson equation of state.