Mutual diffusivity in n-heptane + n-hexane isomers

Abstract

A preliminary study of the effect of branching in the binary diffusion of hexane isomer + n-heptane systems is presented.Measurements have been performed with an instrument modeled for the Taylor dispersion technique, at several compositions, at 297 K, for the n-hexane + n-heptane and 2,2-dimethylbutane + n-heptane binary mixtures.The accuracy is estimated to be 1%.The influence of branching is discussed. It was found that the rough hard sphere model for binary diffusion can reproduce the experimental data within 6%. This model was used to predict the binary diffusion coefficients in the 2-methylpentane + n-heptane and 3-methylpentane + n-heptane mixtures, with an estimated accuracy of 5%.I.

Mutual diffusivity in binary mixtures of n-heptane with n-hexane isomers

“…27. The value of Vo for 2,3-dimethylbutane is consistent with the trend observed earlier [4], as it is smaller than for the 2,2 isomer. Also, the value obtained for B (1.11 ___ 0.03) agrees with the average value for the other isomers (1.08 +0.02), showing that the collisional processes that determine viscosity in the liquid hexanes are essentially the same.…”

“…A quantitative description of the present result can be attempted by means of the rough hard-spheres model. In a previous paper [4], this theory was applied to the systems X+n-heptane, where X=n-hexane, 2-methylpentane, 3-methylpentane, and 2,2-dimethylbutane, for which there were density and viscosity data available for the pure components [26,28]. Table IV shows the values of the fluid hard-core volume, V o, the hard-sphere diameter, a, and the rotational coupling constant for viscosity, B, for those systems as well as for n-heptane+2,3-dimethylbutane, for which the density was taken from Ref.…”

“…For comparison, this result was corrected to 297 K, assuming a linear dependence [ 8,9 ] of the logarithm of O~ with reciprocal temperature in the interval 283 to 298K. The value obtained, 3.68x10-9mZ-s -1 agrees within the experimental accuracy with the value 3.66 x 10 -9 m 2. s -1 previously reported [4]. Figure 1 shows the binary diffusion coefficients for the four systems studied at 298 K as a function of the molar fraction of n-heptane.…”

“…It is estimated that the overall accuracy of the measurements is better than 1%. Tables I to III display the results obtained for the different systems. In a previous paper [4] the infinite dilution diffusion coefficients of n-heptane in n-hexane at 297 K were compared with available data obtained by other authors. The measurements were repeated at a slightly higher temperature (298 K) and a value of (3.72_+ 0.04) 10 -9 m 2. s -1 was obtained.…”

“…The transport of mass in binary systems depends either on the molecular energies involved in the motion of molecules and on the mass differences of the diffusing species. In order to try to separate these two effects, a study on the influence of branching in the diffusion coefficients of n-alkane liquid mixtures was initiated in this laboratory and results obtained for the system 2,2-dimethylbutane+n-heptane at 297 K have been presented [4], together with the application of the van der Waals model of transport in binary liquid systems [5][6][7].…”