PVT, saturated liquid density and vapor-pressure measurements of main components of the biofuels at high temperatures and high pressures: Methyl palmitate

摘要

PVT, saturated liquid density and two-phase (vapor-pressure) properties of one of the main component of the biofuel (methyl palmitate), produced from a soybean, have been measured. One-phase PVT measurements were made for ten liquid and four vapor isochores between (85.2 and 811.7) kg.m(-3) over the temperatures range from (300 to 443) K using a constant-volume piezometer technique. The vapor-pressures (P-S, T-S) of the methyl palmitate were measured in the temperature range from (300 to 501) K. The combined expanded uncertainty of the density, rho, pressure, P, and temperature, T, measurements at 95% confidence level with a coverage factor of k = 2 is estimated to be 0.1%, (0.15-0.5)% depending on temperature and pressure ranges, and 15 mK, respectively. We have critically assessed all of the reported density data at atmospheric pressure and at high-pressures and vapor-pressures together with the present results for their internal thermodynamic consistence to carefully select primary data to fit reference correlations for rho(0) (T) and vapor-pressure P-S(T). The measurements were concentrated in the two-phase region to accurately determine vapor-pressures and in the immediate vicinity of the phase-transition temperatures to precisely determine the phase boundary properties (P-S, T-S, rho(S)) on the liquid + gas equilibrium curve. The liquid-gas phase transition temperatures (T-S) for seven liquid isochores of (711.9, 766.8, 774.5, 782.3, 795.00, 803.40, and 811.70) kg.m(-3) were accurately obtained using the isochoric (P-T) break point technique. The measured values of the vapor-pressures and saturated liquid densities were fitted to Wagner-type vapor-pressure equation and complete scaling model, respectively. The values of the critical parameters (P-C, T-C, rho(C)) were estimated using vapor-pressure and liquid-gas coexistence curve data. The correlation for the density at atmospheric pressure, rho(0)(T), together with the present and reported high-pressure density measurements (rho, P, T) were used to develop two-parametric (c and B) and theoretically based Tait-type equation of state.