Isochoric heat capacity measurements for a CO2+n-decane mixture in the near-critical and supercritical regions

The isochoric heat capacity of a (0.7367 mole fraction) CO2 + (0.2633 mole fraction) n-decane mixture was measured in a range of temperatures from 362 to 577 K, at nine near-critical liquid and vapor densities between 298 and 521 kg m(-3) by using a high-temperature, high-pressure, nearly constant volume adiabatic calorimeter. The measurements were performed in both one- and two-phase regions including the vapor + liquid coexistence curve. Uncertainties of the heat capacity measurements are estimated to be 2% (in this work we use a coverage factor k = 2). The uncertainty in temperature is 10 mK and that for density measurements is 0.15%. The liquid and vapor one- (C'(V1), C"(V1)) and two-phase (C'(V2), C"(V2)) isochoric heat capacities, temperatures (T-S) and densities (rho(S)) at saturation were extracted from the experimental data for each filling density. The critical temperature (Tc = 509.71 0.2 K), the critical density (pc = 344.7 5 kg m(-3)), and the critical pressure (P-C = 15.37 +/- 0.5 MPa) for the (0.7367 mole fraction) CO2 + (0.2633 mole fraction) n-decane mixture were extracted from isochoric heat capacity measurements using the well-established method of quasi-static thermograms. The observed isochoric heat capacity along the critical isochore of the CO2 + n-decane mixture exhibits a renormalization of the critical behavior of C-V unlike that of the pure components. The ranges of conditions were defined, on the T-x plane for the critical isochore and the p-x plane for the critical isotherm, for which we observed renormalization of the critical behavior for isochoric heat capacity. The Krichevskii parameter for this mixture was calculated by using the critical loci for the mixture and vapor pressure data for the pure solvent (CO2), and the results are compared with published values. (C) 2004 Elsevier B.V. All rights reserved.