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Christian Werner Scholz, Roland Span

• Densities in the homogeneous liquid phase of (mono-)ethanolamine (MEA) and diethanolamine (DEA) were investigated using a commercially available high-pressure vibrating-tube densimeter (VTD). Due to the melting point of the experimental materials, the setup of the VTD had to be modified by an insulated housing of the entire piping including the pressure pump. The insulated housing could be heated up by a temperature-controlled heating fan. The liquid samples with a purity of (0.9994 or 0.9950) mole fraction, respectively, were decanted within an inert protective argon atmosphere and further degassed by several freeze–pump–thaw cycles. Density measurements were carried out at temperatures between (293, respectively, 313 and 423) K and at pressures between (5 and 90) MPa. The resulting 140, respectively, 120 \(\textit {(p, ρ, T)}\) data points, explicitly extend the published database for MEA and DEA, with regards to pressure. A comparison with the currently used equations of state for MEA and DEA revealed a maximum relative deviation of – 0.18 % for MEA and – 0.41 % for DEA, each at the highest investigated temperature and pressure. Considering the measurement uncertainties in temperature, pressure, and oscillation period, as well as uncertainties resulting from the calibration and from the impurities of the sample, the combined expanded relative uncertainty (\(\it k\) = 2) in density varied from (0.1027 to 0.1038) % and from (0.1104 to 0.1130) %, respectively. The VTD was previously calibrated by comprehensive measurements of water and helium and had been further validated by measurements with pure propane.