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 (CV) and liquids-gas phase transition temperature (TS) and density (ρS) 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 (TS) to precisely determine the phase boundary density, one-phase and two-phase isochoric heat capacities (ρS,CV1, and CV2) using isochoric heat -capacity discontinuity behavior technique. For ten liquid isochores, the TSwas experimentally determined usingCVdiscontinuity method (irregular behaviour of CV). 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 TSdue to thermal decomposition of the methyl decanoate at high temperatures (above 473 K). The measured CV2 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 CV2 of methyl decanoate were estimated. The measured CV2ρS, and TS were used for determination many key thermodynamic properties of methyl decanoate along the saturation curve as well as the critical property data (TC=669.5 ± 5 K andρC = 287 ± 5 kg·m−3).