PVT measurements of carbon-dioxide + methane mixtures and an equation of state development

A mixture apparatus has been constructed for preparing mixtures of accurately known composition using a gravimetric method and has been used to prepare mixtures needed in this study. Two experimental techniques have been used to measure accurately the densities of carbon dioxide + methane mixtures over wide ranges of temperature and pressure. A continuously weighed pycnometer which can provide one density measurement about every twenty minutes in an isothermal run has been used to measure densities of four carbon dioxide + methane mixtures from 225 to 350 K up to 35 MPa. The Burnett apparatus can provide the best low density measurements and the best determinations of the virial coefficients; it has been used to obtain the densities and virial coefficients for four carbon dioxide + methane mixtures and pure methane at 300 and 320 K up to 10 MPa. The accuracy of the density measurements using the pycnometer is 0.1 kg/m;An innovative approach to the reference system of an EOS has been developed. It consists of three parts: (1) the choice of a proper pair potential and its division into reference and perturbation potentials; (2) the method used to calculate the effective hard-sphere diameter; and (3) different forms for the hard-body equations. We have investigated step-ramp and Born (exponential) pair potentials, and Carnahan-Starling and random closest packing basis hard-body equations. The random closest packing basis hard-body equation plus Born pair potential provides the best representation of the experimental saturated liquid densities and vapor pressures of argon.