In
the present contribution, diffusivities of binary mixtures of
propane (C3H8), carbon dioxide (CO2), and methane (CH4) were investigated between T = (293 and 353) K, p = (0.5 and 12) MPa,
and mole fractions x = (0.0833 and 0.917) by dynamic
light scattering (DLS). Which diffusivities are accessible by DLS
depends on the location of the thermodynamic state points studied
relative to the phase envelopes of the mixtures, the mixture density,
and the derivatives of the refractive index with respect to temperature
and concentration. A simultaneous determination of thermal and mutual
diffusivity was possible in the liquid phases and at some higher-density
states in the supercritical phase. For the gaseous and most of the
supercritical state points, only a thermal, mutual, or effective diffusivity
could be obtained and was identified with the help of Rayleigh ratios
and temperature-, pressure-, and concentration-dependent trends. The
reported diffusivities clearly improve the data situation for the
mixtures studied above atmospheric pressure. The average expanded
uncertainty (k = 2) for all presented mutual diffusivities
is 5.8%. For the thermal diffusivity, these uncertainties are 22%
and 3.0% for the cases where it was determined simultaneously with
the mutual diffusivity or alone.