Density measurements of seven methane-rich binary mixtures over the temperature range from (100 to 180) K at pressures up to 9.7 MPa

Abstract

Densities of seven methane-rich binary mixtures were measured in the homogeneous liquid and supercritical regions at temperatures between (100 and 180) K using a low-temperature single-sinker magnetic-suspension densimeter. For each mixture, four to six isotherms were measured, and seven values were taken along each isotherm in the pressure range from (0.19 to 9.7) MPa. Molar compositions of the gravimetrically-prepared methane-rich binary mixtures were 0.25 ethane, 0.12 propane, 0.030 isobutane, 0.010 n-pentane as well as (0.30, 0.030 and 0.010) nitrogen with the balance being methane. The relative expanded combined uncertainty (k = 2) of the experimental densities was less than 0.020% in most cases. Due to a supercritical liquefaction procedure and the integration of a special VLE-cell, it was possible to measure densities in the homogeneous liquid phase without changing the composition of the mixture. Moreover, saturated-liquid densities were determined by extrapolation of the isothermal densities to the vapour pressure; their uncertainty is less than 0.05% in most cases. The new experimental results were compared with the GERG-2008 equation of state and two correlation methods. The results were already used as a reliable basis for the development of a new fundamental equation of state for liquefied natural gases (LNG).