PVTx and thermal-pressure coefficient measurements of the binary CO2 + n-decane mixtures in the critical and retrograde regions

Abstract

Abstract PVTx and temperature derivative of pressure (thermal-pressure coefficient), γ VX = ( ∂ P / ∂ T ) VX , of binary CO2 + n-decane mixtures have been measured in the critical, supercritical, and retrograde condensation regions (near the critical and cricondenterm points). Most measurements were made in the immediate vicinity of the dew-, bubble, and the critical point curves (in the single – and two-phase regions) to precisely determine the phase boundary properties, T S , P bub , P dew , ρ S ′ , ρ S ″ , ( ∂ P / ∂ T ) VX ′ , and ( ∂ P / ∂ T ) VX ″ .The measurements have been made using a high-temperature, high-pressure, nearly constant-volume adiabatic piezo-calorimeter for three concentrations of 0.095, 0.178, and 0.263 mol fraction of n-decane over the temperature range: (for mixture-1, x = 0.095) from (292 to 567) K along the liquid and vapor densities between (89 and 659) kg·m−3 at pressures up to 28.3 MPa; (for mixture-2, x = 0.178) from (302 to 557) K along the liquid and vapor densities between (85 and 467) kg·m−3 at pressures up to 24.3 MPa; and (for mixture-3, x = 0.263) from (361 to 568) K along the liquid and vapor densities between (298 and 520) kg·m−3 at pressures up to 25.4 MPa. The combined expanded uncertainty of the density, ρ , pressure, P, temperature, T, concentration, x, and the thermal-pressure coefficient, γ VX , measurements at the 68% confidence level with a coverage factor of k = 2 is estimated to be (0.2–0.5)%, (0.5–1.0)%, 15 mK, 0.01 mol%, and (0.2–2.0)% (depending on temperature and pressure), respectively. The critical (the critical temperature, T C , the critical pressure, P C , and the critical density, ρ C ), cricondentherm, and cricondenbar point data of CO2 + n-decane mixture were derived as a function of concentration from phase boundary properties studied. The Krichevskii parameter and isomorphism of the critical behavior of the mixture were studied using the critical curve data for the mixture and vapor pressure data for the pure solvent (CO2). Features of the P S - T S phase boundary diagram and thermodynamic behavior of the mixture near the critical and cricondentherm points and in the retrograde region were observed.