Near-infrared and ultraviolet absorption of water–benzene mixtures has been measured at temperatures and pressures in the ranges of 323–673 K and 50–400 bar, respectively. Concentrations of water and benzene in both the water-rich phase and the benzene-rich phase of the mixtures were obtained from absorption intensities of near-infrared bands of water and benzene and ultraviolet bands of benzene. Mutual solubilities in molar fractions increase remarkably with increasing temperature at pressures in the two-liquid-phase coexistence region, and are consistent with previously reported values. It proves that the solubility of benzene in water is an order of magnitude smaller than that of water in benzene throughout the two-phase region. In addition, it is found that effect of pressure on the solubilities is opposite between water in benzene and benzene in water. These solubility properties are discussed on the basis of a cavity-based solvation model. It is suggested that the asymmetry in the mutual solubility and the opposite direction of the pressure effect are caused by difference in molecular size and difference in thermal compressibility, respectively, between water and benzene.
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