Pressure dependence of excess enthalpy for (benzene + cyclohexane) mixture near the critical locus at T = (558.2, 563.2 and 573.2) K and p = (3 to 15) MPa

•The HmE of (benzene + cyclohexane) were measured near the critical locus.•The pressure dependence of HmE was obtained from the experimental results.•The composition dependence of HmE was obtained from the p  –HmE curves.•The relations of the behaviours of HmE with the phase of the mixture were discussed.

The pressure dependences of excess molar enthalpies HmE of the (benzene + cyclohexane) mixture at constant temperatures and compositions were measured near the critical locus, using a twin flow type mixing calorimeter. The measurement states are as follows; temperature T = (558.2, 563.2, and 573.2) K, mole fraction of benzene x = (0.119 to 0.916), and pressure range p = (3 to 15) MPa. The composition dependences of HmE at constant pressures and at each temperature were calculated from the pressure dependences of HmE. All pressure dependences of HmE have two peaks except at x = 0.916. The pressure dependences at x = 0.916 have one peak, and the curve at T = 573.2 K has a shoulder near p = 5 MPa. From the detailed consideration with respect to the phase behaviour near the critical locus for this mixture, two peaks should exist in the pressure dependences of HmE at T = 558.2 K and x = 0.916, but the second peak cannot be detected because the peak width is too narrow. The composition dependences of HmE near the critical locus were skewed or S-shaped ones, which are ascribed as the characteristic behaviour in the vicinity of the critical locus.

Graphical abstractThe pressure dependences of HmE for {x benzene + (1 − x) cyclohexane} mixtures.Figure optionsDownload full-size imageDownload as PowerPoint slide