The viscosity of the binary vapor mixture methanol–triethylamine at low densities and in the saturated vapor phase of the vapor–liquid equilibrium

For the first time, results of precision measurements of the viscosity coefficient of the binary vapor mixture methanol–triethylamine at low densities are reported. The relative measurements with an all-quartz oscillating-disk viscometer were carried out for nearly equimolar mixtures along five isochores at densities from 0.010 to 0.033 mol dm−3 as well as for a mixture of the mole fraction ymeth = 0.3322 at a density 0.016 mol dm−3 in the temperature range between 298 and 498 K. The uncertainty is estimated to be ±0.2% at ambient temperature, increasing to ±0.3% at higher temperatures. Isothermal values of a mixture with the averaged mole fraction ymeth = 0.5002 were recalculated from the original experimental data and evaluated with a first-order expansion for the viscosity, in terms of density. A so-called individual correlation on the basis of the extended theorem of corresponding states was employed to describe the interaction viscosity in the limit of zero density. Some data points at low temperatures had to be excluded from this calculation, since the measurements were performed in the saturated vapor phase. For these data points the vapor–liquid equilibrium had to be evaluated to assign the correct mole fraction in the vapor to the measured viscosity.