Vapor pressure measurements on saturated biodiesel fuel esters by the concatenated gas saturation method

The purpose of this work was to determine vapor pressures for saturated biodiesel esters at the low-temperature end of their liquid range. A “concatenated” gas saturation apparatus capable of simultaneous measurements on 18 samples was used for measurements on methyl palmitate, ethyl palmitate, methyl stearate, ethyl stearate, and eicosane (C20H42) over the temperature range 323.15 K–343.15 K. Eicosane, a linear alkane with a well known vapor pressure curve (in the same range as the biodiesel esters), was included as a control compound. Importantly, the measured vapor pressures for eicosane are in excellent agreement with reference values, which is good evidence of the low uncertainty of the measurements on the biodiesel esters. Over this temperature range, the measured vapor pressure ranges were 0.145 Pa–1.11 Pa for methyl palmitate, 0.0687 Pa–0.616 Pa for ethyl palmitate, 0.0159 Pa–0.183 Pa for methyl stearate, and 0.00704 Pa–0.0912 Pa for ethyl stearate. The combined standard uncertainty in the vapor pressure measurements ranged from 8% to 15%.