Viscosity for Eight Gaseous and Vapor Mixtures: Revisited from Experiment between 297 K and 638 K. Final and Preliminary Values for the Interaction Viscosity and for the Product of Molar Density and Diffusion Coefficient in the Limit of Zero Density

Abstract

Low-density viscosity measurements on eight gaseous and vapor mixtures between 297 K and 638 K, originally performed using oscillating-disk viscometers, were re-evaluated after improved re-calibration. The relative combined expanded (k=2) uncertainty of the re-evaluated data is 0.2 % near room temperature and increases to 0.3 % at higher temperatures. The re-evaluated data were converted into quasi-isothermal viscosity data. Those for carbon dioxide-ethane, propane-isobutane, and methanol-triethylamine could be used to determine the zero-density and initial density viscosities, etamix(0) and etamix(1). The etamix(0) data for carbon dioxide-ethane agree almost perfectly with viscosity values theoretically computed for the nonspherical potential of the intermolecular interaction. Three procedures were applied to determine the interaction viscosity, etaij(0), and the product of molar density and diffusion, (rho Dij)(0), both in the limit of zero density. In a first procedure only applicable for the three mentioned mixtures, etaij(0) values were derived from the etamix(0) data additionally requiring Aijast values (ratio between effective cross sections of viscosity and diffusion). This procedure should provide the best results when it is possible to use Aijast values computed for the nonspherical potential. This was only feasible for carbon dioxide-ethane, for which the experimentally based etaij(0) and (rho Dij)(0) data perfectly agree with theoretically calculated values. For the seven other mixtures, the resulting data represent only preliminary ones. The second and third procedures were applied to the six vapor mixtures methanol with triethylamine, benzene, and cyclohexane and benzene with toluene, p-xylene, and phenol. The resulting data showed a density dependence and were extrapolated to zero density.