Excess enthalpy for the (benzene + cyclohexane) mixture over a wide range of temperature and pressure

•A twin flow type calorimeter for high temperature and pressure was constructed.•HmE of (benzene + cyclohexane) were measured in wide range of temperature and pressure.•The method with only 5 constants for estimating HmE of this mixture was proposed.

A twin flow type of mixing calorimeter was constructed for measuring excess enthalpies of fluid mixtures over wide temperature and pressure ranges. The precision of the calorimeter was tested with (water + ethanol) mixture. The excess molar enthalpies HmE for the (water + ethanol) mixture at temperatures T = (423.2 and 523.2) K and pressure p = 5.00 MPa and at T = 523.2 K and p = 15.00 MPa are in good agreement with the literature values. The HmE values for the (benzene + cyclohexane) mixture were measured using this calorimeter over the temperature range from T = 298.2 K to T = 573.2 K and the pressure range from p = 5.00 MPa to p = 25.00 MPa. All HmE values are positive and all mole fraction dependencies of HmE are almost symmetrically parabolic. The maximum values of the mole fraction dependence of HmE decrease with increasing temperature and are independent of the pressure, except for the conditions at T = (498.2 and 523.2) K and p = 5.00 MPa whose states are near the critical point of benzene. The maximum values of HmE of these states were greater than the values expected from the curve representing the temperature dependence of other maximum values of the mole fraction dependence of HmE.

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