High pressure phase equilibria of ethyl esters in supercritical ethane and propane

The high pressure phase equilibria of ethyl esters (ethyl decanoate/caprate, ethyl dodecanoate/laurate, ethyl tetradecanoate/myristate and ethyl hexadecanoate/palmitate) in supercritical ethane and propane have been measured in the temperature ranges 311–358 K (TR = 1.02–1.17) and 376–409 K (TR = 1.02–1.11), respectively. The measurements were conducted in a high pressure view cell for ethyl ester mass fractions between 0.015 and 0.65. The results show a generally linear relationship between the phase transition temperature and pressure. No temperature inversions or three phase regions were observed. An increase in hydrocarbon backbone length leads to an increase in phase transition pressure. For ethane as supercritical solvent, this increase is linear. For propane as supercritical solvent, the nature of the increase was not quantified as the magnitude of the increase would be significantly influenced by the experimental measurement error as the observed increase is not very large. Comparison of the phase behaviour of ethyl esters with methyl esters shows very little difference, yet the phase transition pressure of ethyl esters in supercritical ethane and propane is significantly lower than those of the corresponding acids. The phase transition pressure of ethyl esters in ethane and propane is also lower than those in carbon dioxide.