J. Chem. Phys. 144, 134304 (2016)

http://dx.doi.org/10.1063/1.4944984

Concentration dependent refractive index of CO2/CH4 mixture in gaseous and supercritical phase

Cédric Giraudet, Laurent Marlin, Didier Bégué, Fabrizio Croccolo and Henri Bataller

Carbon dioxide (CO2)/methane (CH4) binary mixtures are investigated at pressure values up to 20 MPa at 303 K in order to investigate the pressure dependence of the optical concentration contrast factor, (∂n/∂c)P,T, through gaseous and supercritical phase. Refractive index is measured by means of a Michelson interferometer. Refractivities of the mixtures are found in good agreement with Lorentz-Lorenz predictions after density calculations by means of the AGA8-DC92 equation of state. Experimental polarizabilities of pure fluids are compared to quantum calculations of monomers and dimers for each pressure; it results that the quantity of dimers is small in the investigated thermodynamic conditions. Finally, by extending our experimental database with numerical simulations, we evidence that (∂n/∂c)P,T presents a critical enhancement similar to heat capacity.