PVT measurements of carbon-dioxide + nitrogen and an equation of state development for natural and hydrocarbon gases

Densities of five mixtures of carbon dioxide + nitrogen (x;A flexible foil gravity mixer is described which has been developed to assist in the preparation of gas mixtures of accurately known composition without contaminating the mixtures. A new automated temperature measurement and control scheme is described which has been implemented on both the Burnett apparatus and the pycnometer. The new controller is capable of temperature control to ;A new equation of state has been developed for hydrocarbon gases based upon the truncated virial equation. The second and third virial coefficients are calculated from the specific gravity at temperatures between 220 and 360 K at pressures to 10 MPa yielding an average uncertainty in the compressibility factor of about 0.1 per cent. The new equation can be applied to natural gases containing hydrocarbons, nitrogen and carbon dioxide by treating the hydrocarbon fraction of the mixture as a single component and using simple combining rules to calculate the cross virial coefficients without introducing additional parameters.