Temperature and density dependence of the self-diffusion coefficient of n-hexane from 223 to 333 K and up to 400 MPa

Abstract

Self-diffusion coefficients for liquid n-hexane measured by the n.m.r. spin-echo technique are reported at 223, 248, 273, 298 and 333 K at pressures up to 400 MPa. Owing to a marked non-linear volume dependence, the results could not be directly fitted to the rough hard-sphere model of diffusion, but reduced diffusion coefficients were fitted as a function of a reduced volume, expressed as the ratio of the molar volume to a ' hard-core volume '. The temperature dependence of an equivalent hard-sphere diameter calculated from this hard-core volume was found to be adequately represented by an equation origmally proposed by Protopapas, Andersen and Parlee for liquid metals: CT = a, [l -B(T/T,):]. The constant B, 0.072, is of similar magnitude to that found to fit CH, and C,H, self-diffusion data, 0.069, and is consistent with diameters derived from the viscosity measurements of Brazier and Freeman. Between 273 and 333 K where the diffusion and viscosity results overlap, the group Dvt is constant, at a given temperature, with t = 0.97: consequently the Stokes-Einstein equation is not obeyed.

Pressure‐Temperature‐Dependence of Mass Density and Self‐Diffusion Coefficients in the Binary Liquid System n‐Hexane/Benzene

“…The molar volume-results agree with the literature data [2,4,5, Table 4 Activation energies E,D and preexponential factors Do of the self-diffusion in binary liquid mixtures (C6H6)r(n-C6H14)1--x according to Eqs. (2) and (5).…”

“…The molar volume-results agree with the literature data [2,4,5, Table 4 Activation energies E,D and preexponential factors Do of the self-diffusion in binary liquid mixtures (C6H6)r(n-C6H14)1--x according to Eqs. (2) and (5). The first number is Ef in kJ mol-' and the second in brackets is Do in lo-' mz s-' E,D (kJ mol-'); (Do ( which leads to the activation energies E ; of the self-diffusion Process given in Table 4.…”

Temperature and Density Dependence of the Viscosity of Cyclopentane

“…For cyclopentane, this correlation is superior to those based on reduced viscosities employed in earlier studies. 8,[20][21][22] The viscosity of cyclopentane has been measured under high pressure by Brazier and Freeman 12 using a rolling ball viscometer at the single temperature of 303.15 K to 400 MPa pressure and by Assael and Dalaouti 2 using a vibrating wire technique over the temperature range of (210 to 310) K but to only 25 MPa pressure. Figure 3 shows a comparison with the results of this work.…”

Size-dependent diffusion in cycloalkanes

“…C 6 and C 16 are solutes in each other; unique to C 6 C 5 , 2-methylbutane, 2,2-dimethylbutane, tetralin, 2,2,4-trimethylpentane, phenanthrene, toluene, benzo(a)pyrene, CS 2 , C 10 and C 18 . The value of 10 9 D s ¼ 4.22 AE 0.10 m 2 s À1 for C 6 is the average of seven determinations [40][41][42][43] while 10 9 D s ¼ 0.378 m 2 s À1 for C 16 is from [44].…”