Solubility of oxygen in n-hexane and in n-perfluorohexane. Experimental determination and prediction by molecular simulation

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The solubility of oxygen in n-hexane and in n-perfluorohexane was determined experimentally and calculated by computer simulation. A precision apparatus based on a saturation method at constant pressure was used to measure the solubility at temperatures from 288 to 313 K and close to atmospheric pressure. Henry's law coefficients, H2,1(T,psat1), were obtained from the experimental data and their temperature dependence was represented by appropriate correlations. The precision of the results was characterised by average deviations of H2,1 from these smoothing equations and is of ±0.5% and ±0.8% for oxygen in n-hexane and in n-perfluorohexane, respectively. From the temperature variation of the Henry's law coefficients, partial molar solvation quantities such as the variation of the Gibbs energy, enthalpy and entropy were derived. Molecular dynamics simulations with all-atom force fields, associated with Widom's test particle insertion method, were used to calculate the residual chemical potential of oxygen in the two solvents studied leading to Henry's law coefficients which were then compared to the experimental values. The difference between oxygen solubility in the two solvents was interpreted on the basis of solute–solvent interactions and structural properties such as solute–solvent radial distribution functions.