Two-Phase Isochoric Heat Capacity, Phase Transition, and Theoretically Important Physical Parameters of Methyl Dodecanoate

The two-phase isochoric heat capacity ( C_V2 VT), liquid–gas phase transition ( T_S , ρ_s^' ), vapor-pressure ( P_S , T_S ), and thermal -pressure coefficient ( dP_S /dT) of methyl dodecanoate, a key biofuels component, have been measured along nine liquid isochores between (180.90 and 845.31) kg·m−3 and three near-critical liquid and vapor (180.90, 234.52, and 374.11) kg·m−3 isochores. The temperature range covers the liquid–vapor phase transition temperature T_S( ρ) for each measured isochore to near the thermal decomposition temperature, 450 K. The measurements were performed using a high-temperature and high-pressure, nearly constant-volume adiabatic calorimeter previously used for the measurements of the C_V VT relationship of biofuel components in the two- and single-phase region. The combined expanded uncertainty of the density (ρ), temperature (T), and isochoric heat capacity ( C_V2 ) measurements at the 95 T_S . For each experimental liquid isochore, most measurements were concentrated in the immediate vicinity of the liquid–gas phase transition temperature ( T_S ) to precisely determine the phase boundary properties ( ρ_S , T_S , C_V1 , and C_V2 ) using an isochoric heat -capacity abrupt-behavior technique. For nine liquid isochores between (745.16 and 845.31) kg·m−3 the phase transition temperatures ( T_S ) were experimentally determined. For two vapor (180.90 and 234.52) kg·m−3 and liquid near-critical (374.11) kg·m−3 isochores, for which the transition temperatures are very high (above the thermal decomposition temperature, 473 K), we failed to reach the phase-transition temperatures, T_S , because for these isochores the thermal decomposition of methyl dodecanoate occurs before reaching the phase transition temperature (above 673 K). The measured two-phase ( C_V2 ) isochoric heat capacities as a function of specific volume (V) along the various isotherms (below 473 K) were used to accurately estimate the values of the second temperature derivatives of chemical potential, d^2μ/dT^2 , and vapour-pressure, d^2 P_S/dT^2 , based on the Yang–Yang theoretical relation. The contributions of the vapour-pressure, C_VP = VTd^2 P_S/dT^2 , and the chemical potential, C_Vμ = - Td^2μ/dT^2 , to the heat capacities of the measured total two-phase C_V2 were estimated as a function of temperature. In addition, measured C_V2 and phase boundary ( ρ_S , T_S , P_S ) property data were used to calculate key thermodynamic property data C_P , C_sat , K_TS , W_S , Δ H_V , ( ∂ P/∂ T)_V^sat. , ( ∂ V/∂ T)_P^sat. along the saturation curve. The measured vapor-pressure ( P_S − T_S ) and saturated liquid densities ( ρ_S − T_S ) were used to develop extended theoretically based scaling -type correlations and to estimate the critical property data ( T_C , P_C , and ρ_C ), asymptotical critical amplitudes, and asymmetric parameter.