Binary Diffusion in Dense Gases to 1360 atm by the Chromatographic Peak-Broadening Method

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Abstract
The chromatographic peak‐broadening method for measuring diffusion coefficients is applied to 11 binary gas pairs at pressures in the range 272–1360 atm. Operation is in the nonequilibrium mode, where it is shown that the small diffusive displacements characteristic of dense systems can be magnified to an arbitrary level, thereby increasing speed and accuracy. Since comparable data are not available, an attempt is made to estimate the level of accuracy; a 5% error is judged most probable. The results are compared with the Enskog–Thorne equation for binary diffusion in dense gases. The deviations become considerable at the higher pressures. When the trace species is larger than the carrier species, diffusivity exceeds the Enskog–Thorne value and, in a few cases, exceeds the ideal‐gas value. The opposite result is found for small trace species. These results are consistent with an explanation based on velocity correlations, the nature of which changes drastically with the relative size and thermal momentum of the trace and carrier species.

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