The Phase and Volumetric Behavior of Natural Gases at Low Temperatures and High Pressures

The phase and volumetric properties of 10 very volatile mixtures are presented for temperatures from - 200 degrees F to above the critical points. These mixtures consisted of natural gases and of mixtures of natural gases with methane and nitrogen. Existing correlations of compressibility factors have been extended to apply to these mixtures. Existing correlations of critical pressures and temperatures do not apply to these mixtures. Methods have been developed for estimating critical temperatures of these mixtures to +/- 4 degrees F and critical pressures to +/- 5 per cent. These methods apply to other volatile and very volatile mixtures. The results of this work are particularly applicable to the separation of nitrogen from hydrocarbons by low-temperature distillation. Introduction Knowledge of the low-temperature phase and volumetric properties of natural gases and of other mixtures of the light hydrocarbons is becoming increasingly important as interest in low-temperature separation processes increases. Low-temperature distillation has been used to separate ethane and ethylene from natural gas and from refinery gases for petrochemical uses. Removal of nitrogen from natural gas by low-temperature distillation has been proposed as a means of increasing the capacity of existing gas transmission lines and of improving the marketability of the gas. Further application of low-temperature separation processes has been retarded by lack of data on the phase and volumetric behavior of mixtures at low temperatures and at high pressures. This paper presents the results of determination of the phase and volumetric properties of 10 very volatile mixtures at temperatures from - 200 degrees F to above the critical point. These mixtures consisted of natural gases with methane and nitrogen. Generalized methods are presented for estimating the critical temperatures, critical pressures, and the densities of such mixtures.