Solubility in supercritical carbon dioxide: Importance of the poynting correction and entrainer effects

Gibbs ensemble Monte Carlo simulations were used to investigate the effect of pressure and of entrainers on the solubility of low-volatility species in CO₂. Two entrainers were examined, n-octane and methanol, as well as two solutes, hexamethy!benzene and benzoic acid. For the three pressures studied (12, 20, and 28 MPa), the simulations demonstrate that the increase in the solubility with increasing pressure is mostly due to an increase in the solute's chemical potential (as expressed by the Poynting correction) and not due to an increase in the solvent strength of supercritical CO₂. The presence of an entrainer enhances solubility, particularly when the solute and entrainer can form hydrogen bonds. The solubility of benzoic acid is enhanced by an order of magnitude upon addition of methanol entrainer, whereas the enhancements are less than 2 for the other systems.