Measurements and Reference Correlation of the Density and Speed of Sound and Derived Thermodynamic Properties of Methyl Laurate and Methyl Stearate

The density (ρ) and speed of sound (u) of two fatty acid methyl esters (FAMEs), methyl laurate and methyl stearate, were measured at temperatures from 283 to 353 K and from 313 to 353 K at atmospheric pressure, respectively. A commercial instrument, Anton Paar DSA 5000 M sound-speed analyzer (viscodensimeter), has been employed to the simultaneous measurements of the density and speed of sound of methyl laurate and methyl stearate as the primary components of biodiesel fuel. The measured values of density and speed of sound were used to calculate other derived key thermodynamic properties such as the adiabatic coefficient of bulk compressibility (βS), coefficient of thermal expansion (α P ), isothermal coefficient of bulk compressibility (βT), isochoric (C V ) and isobaric (CP ) heat capacities, enthalpy (ΔH) and entropy (ΔS) difference, partial temperature derivative of enthalpy (∂H/∂T) P and entropy (∂S/∂T) P , and the partial specific volume derivatives of internal energy (∂U/∂V) T (internal pressure) of methyl laurate and methyl stearate as a function of temperature. The measured values of density and speed of sound together with the reported data have been critically assessed for their accuracy and internal consistency and used to develop reference correlation models that are valid over a wide range of temperature (from the melting point to 353 K) and at an atmospheric pressure of 101.325 kPa. The overall uncertainties (at the 95% confidence level) of the reference correlations of the density and speed of sound of methyl laurate and methyl stearate are 0.025 and 0.045%, respectively.