Tracer diffusion in dense ethanol: A generalized correlation for nonpolar and hydrogen‐bonded solvents

Abstract

Tracer diffusion coefficients were measured for benzene, toluene, mesitylene, naphthalene, and phenanthrene in dense ethanol at 0.56 5 TR 5 1.07 and pR 2 1.44. The results were used to examine the temperature dependence of the degree of association between ethanol molecules across the entire range of temperature. The hard-sphere tracer diffusion equation and the Stokes-Einstein equation were used to develop two engineering correlations. The former approach was found to be adequate for solvents of relatively compact molecules, and the latter to be more general in its applications. The absolute deviation of prediction from observed values of tracer diffusivities is 4%, with a maximum error of 13%. C. K. J. Sun and S. H. Chen Department of Chemical EngineeringUniversity of Rochester Rochester, NY 14627 SCOPEDiffusion coefficients are required for the design of separation processes involving interface mass transfer. The Taylor-Aris dispersion phenomenon was used in the present work to measure the tracer diffusion coefficients of benzene, toluene, mesitylene, naphthalene, and phenanthrene in dense ethanol (T, = 516.2 K; pc = 275.9 kg/m3) from 313.2 to 554.0 K. This was done particularly to meet the need for diffusion data for designing supercritical separation processes. The measured values of tracer diffusivity were employed first to investigate the degree of solvent molecular association as a function of temperature and then to develop an engineering correlation. An alternative correlation scheme was established by empirically modifying the Stokes-Einstein equation. In both correlations, the supercritical dense gases were treated essentially as expanded liquids. CONCLUSIONS AND SIGNIFICANCEUsing the measured values of the tracer diffusivity of a series of aromatic hydrocarbons (benzene, toluene, mesitylene, naphthalene, and phenanthrene) in both liquid and supercritical dense ethanol at 0.56 I T,, 5 1.07 and p, 2 1.44, we managed to gather information on the temperature dependence of solvent molecular association. The association number was found to decrease linearly from 2.82 at 293.2 K to 1.85 at 554.0 K. Based on the hard-sphere tracer diffusion equation, a generalized correlation was developed by including the temperature-dependent solvent molecular association.Correspondcna concerning this paper should bc addressed to S. H. Chen.The correlation was found to be adequate for solvents of relatively compact molecules. Alternatively, by empirically modifying the Stokes-Einstein equation we established the other correlation, which turned out to be more general in its applications. Both correlations predict tracer diffusivities that deviate from experimentally determined values to within ? 4% on the average, with a maximum error of 13%. In essence, the present work has provided a basis for correlating data for tracer diffusion in liquids and supercritical dense gases within a consistent framework. In other words, the supercritical dense gases can be treated as expanded liquids as far as molecular association and diffu...

Diffusion of aromatic compounds in nonaqueous solvents: A study of solute, solvent, and temperature dependences

“…The above experimental results are in agreement with the MCT study of Bhattacharyya and Bagchi,25(b) which found that the effect of solute mass on diffusion is generally quite weak; in particular, the solute-mass dependence can normally be considered as negligibly small when changes of solute mass are small within a factor of 2 or so. It should be pointed out that it 51,53,54 have reported tracer diffusivities of nonassociated aromatic solutes in cyclohexane, ethanol, and n-hexane at temperatures above 298.2 K. We have carried out linear regressions for their data at temperatures below the normal boiling point of solvent (but excluding those data at higher temperatures which were measured at different pressures above 1 atm). All data, except one of Dymond's 14 In view of the correlation coefficients and the average % deviations for the 13 sets of linear regressions in Table II, it is clear that Eq.…”

A Mathematical Model of Supercritical Methylamine (Scm) Delignification of Wood

“…Since the supercritical conditions from Pottinger were similar to the conditions used by Li and Kiran for methylamine delignification of wood (Li, 1989), mean specific volume values from Pottinger were used to estimate the critical molar volume for the complex. The methylamine viscosity and the complex critical molar volume were used with the correlation of Sun and Chen (Sun, 1986) to estimate the complex molecular diffusivity. Chang's method (Chang, 1982) was used to estimate the effective diffusivity based on molecular diffusivity.…”

Diffusion and thermodynamic measurements by supercritical fluid chromatography

“…Diffusion coefficients in propane were simply interpreted [43] in terms of the StokesEinstein coefficients [44]. In a series of papers, Sun and Chen measured diffusion coefficients of several aromatic and aliphatic hydrocarbons in near-or supercritical cyclohexane [45], 2,3-dimethylbutane [46], n-hexane 1471, ethanol [48], and methanol and 2propanol [49]. The results were represented by a rough-hard-sphere model, and the diffusivity data in the hydrogen-bonded fluids were used to obtain information on the degree of molecular association of the respective fluid.…”