Isochoric heat capacity, phase transition and derived key thermodynamic properties of methyl decanoate

Abstract In the present work single – and two–phase isochoric heat capacity ( C V ) and liquids-gas phase transition temperature ( T S ) and density ( ρ S ) of methyl decanoate as component of biodiesel derived from coconut oil or babassu oil have been studied. The 15 liquid and vapor isochores between (152 and 834) kg·m−3 at temperatures from (300 to 463) K and at pressures up to 16 MPa were determined using high-temperature and high-pressure nearly constant-volume adiabatic calorimeter. For each experimental isochores the measurements were conducted in the two-phase region in the immediate vicinity of the phase-transition temperatures ( T S ) to precisely determine the phase boundary density, one-phase and two-phase isochoric heat capacities ( ρ S , C V1 , and C V2 ) using isochoric heat -capacity discontinuity behavior technique. For ten liquid isochores, the T S was experimentally determined using C V discontinuity method (irregular behaviour of C V ). For vapor (152.09 and 204.55) kg·m−3 and near-critical (235.13 and 300.83) kg·m−3 isochores we have never reached isochoric heat-capacity discontinuity temperatures T S due to thermal decomposition of the methyl decanoate at high temperatures (above 473 K). The measured C V2 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 and vapour-pressure using theoretically based Yang-Yang relation. The contributions of the vapour-pressure and the chemical potential to the measured total two-phase C V2 of methyl decanoate were estimated. The measured C V2 ρ S , and T S were used for determination many key thermodynamic properties of methyl decanoate along the saturation curve as well as the critical property data ( T C =669.5 ± 5 K and ρ C  = 287 ± 5 kg·m−3).