Viscosities of some n-alkane liquid mixtures

Abstract

The viscosities and densities of selected non-electrolyte liquid mixtures was measured and the results compared with various theoretical models. The following mixtures were prepared: (1) a binary mixture of n-hexadecane + n-octane; and (2) a "pseudo-ternary" mixture of (n-tetra-cosane + n-octane) + n-octane; and (3) a quaternary mixture of (n-tetra-cosane + n-octane) + (n-decane + n-hexane). Five intermediate compositions as well as several pure component viscosities and densities were measured at 45°C, 55°C, and 65°C. Rather than yielding values of mixture viscosities and densities which were similar because of the similarities in mixture composition, experimental results showed different viscosity values. At each of the experimental temperatures a stronger dependence of viscosity on chemical composition, rather than temperature, was noted. Three major classes of predictive mixture equations were tested using the data measured in this study. They were the following categories of mathematical averages: arithmetic, logarithmic/arithmetic and reciprocal. The arithmetic average was shown to most closely predict values of mixture viscosities for all mixtures. Two theoretical models, the Principle of Congruence and the Method of Corresponding States, were tested with the experimental data. The Principle of Congruence was supported as a prediction method for the three systems studied; although the binary system showed reasonable agreement, the ternary and quaternary systems gave results which were independent of temperature. The Principle of Corresponding States was seen to give reasonable agreement for the binary systems viscosities but was not useful for the ternary or quaternary systems. Both theoretical models require further testing with extensive experimental data before recommendations for improvement to the models can be considered.