Effect of ethanol on supercritical CO2 solvent densities

The development of new industrial applications in the pharmaceutical, food, and cosmetic fields uses supercritical carbon dioxide as a solvent or antisolvent in their processes for extracting non-polar molecules. Ethanol ($\text{EtOH}$) is added in small quantities to isolate a polar molecule during a unit operation by solubilization or precipitation. Density measurements in pure carbon dioxide (${\text{CO}}_2$) and in binary ${\text{CO}}_2$-$\text{EtOH}$ mixtures with mass compositions ($w_{{\text{CO}}_2}=0.99$ and $w_{{\text{CO}}_2}=0.98$) were carried out using a vibrating tube densimeter. The isotherms were determined at temperatures of 303, 308, and 313 K, above the critical temperature, and for a pressure range from 5 to 10 MPa. Fine modeling around the critical point was performed using cubic equations of state with two or three parameters (Peng–Robinson and Coquelet–El Abbadi–Houriez EoS). The Huron-Vidal mixing rule coupled with the NRTL model was employed. To enhance the prediction around the critical point of pure carbon dioxide and binary ${\text{CO}}_2$-$\text{EtOH}$ mixtures, White’s correction method was used. The results for pure supercritical carbon dioxide show modeling performance with a deviation of 5.8% around the critical point.