Comparison of Benedict-Webb-Rubin and back equations of state for use in P-V-T calculations

By means of the available experimental gas and liquid state volumetric data, the relative predictive accuracy of the Benedict-Webb-Rubin and BACK equations was compared at the low, intermediate and critical state range of temperatures and pressures for methane, ethane and ethylene. The average absolute volumetric deviation percent values calculated over the T-P range studied, showed that for both the BACK equation and the simpler Benedict-Webb-Rubin equation their accuracy levels increase when both pressure and temperature decrease; but the BACK equation proves superior for calculations performed at the critical and in the liquid states.