Experimental Investigation and Modeling of Thermophysical Properties of Pure Methyl and Ethyl Esters at High Pressures

Densities, speeds of sound, and refractive indices of methyl laurate, ethyl laurate, ethyl myristate, and ethyl oleate in the temperature range 288.15-343.15 K and viscosities from 288.15 to 373.15 K were measured at atmospheric pressure. The measured properties were in good agreement with several available literature data, finding an overall absolute average percentage deviation (AAD) of 0.04%, 0.07%, 3%, and 0.1% for density, speed of sound, viscosity, and refractive index, respectively. The densities of mentioned esters were also measured along 15 isotherms from 293.15 to 413.15 K and at pressures up to 60 MPa using an Anton Paar DMA HP densimeter. Based on the literature data selected for comparison, in the studied ranges of temperature and pressure, the AADs of high-pressure densities were 0.08% for methyl laurate, 0.06% for ethyl laurate, and 0.05% for ethyl myristate. The obtained density values were correlated through the modified Tammann-Tait equation with an AAD lower than 0.009% for all the studied esters. The adjusted parameters were used to calculate the isothermal compressibility, isobaric thermal expansivity, internal pressure, and difference in isobaric and isochoric heat capacities. It was found that methyl laurate has higher density, speed of sound, and refractive index than ethyl laurate of the same fatty acid, while viscosities for the ethyl are slightly higher than those of the methyl laurate. The values of the isothermal compressibility and the isobaric thermal expansivity for ethyl laurate are slightly higher than those for methyl.