Diffusion of benzene, toluene, naphthalene, and phenanthrene in supercritical dense 2,3‐dimethylbutane

Abstract

The conditions under which the Taylor-Aris dispersion phenomenon can be employed to generate accurate tracer diffusion data in supercritical dense fluids are established. The technique is used to determine the diffusivities of benzene, toluene, naphthalene, and phenanthrene in supercritical dense 2,3-dimethylbutane as a function of temperature and pressure. A molecular theory incorporating the Sung-Stell formulation of molecular dynamic correlations in smooth-hardsphere fluids and the Baleiko-Davis molecular roughness for polyatomics with the Enskog-Thorne dense gas diffusivity relationship is found to represent our experimental data to within f4%. The values of the effective hard-sphere diameters involved in the present theory can be predicted fairly accurately from the critical volumes of the solutes and solvent considered here. C. K. J. SUN and S. H. CHEN Department of Chemical EngineeringUnlverslty of Rochester Rochester, NY 14627 SCOPEBinary diffusivity is an important property in correlating and predicting the mass transfer coefficient for the design of separation processes. Separation using supercritical dense gases has proven to be advantageous over conventional methods such as liquid extraction or distillation, and yet there exist no consistent binary diffusion data for application under such conditions. This study is aimed at providing a reliable experimental method on the basis of the Taylor-Aris dispersion phenomenon. The measured values of the tracer diffusivities of a series of aromatic hydrocarbons in supercritical dense 2,3-dimethylbutane are used to furnish a fundamental understanding of binary diffusion within the framework of a molecular theory. CONCLUSIONS AND SIGNIFICANCEWe have analyzed the experimental conditions under which the Taylor-Aris dispersion phenomenon can be reliably employed in practice to determine the tracer diffusion coefficient in supercritical dense fluids. On the basis of the EnskogThorne dense gas theory, the Sung-Stell formulation of molecular dynamic correlations in smooth spheres, and the BaleikoDavis theory of rough spheres, the present theory is shown to represent to within f4% the observed diffusivities of benzene, toluene, naphthalene, and phenanthrene in supercritical dense 2,3-dimethylbutane at temperatures from 523.2 to 548.2 K and pressures from 5.352 X los to 1.590 X lo7 N/m2. The fact that the effective solute and solvent molecular diameters can be fairly accurately predicted from critical volumes verifies the practical application of the present theory. The theory is also used to reveal the inconsistency and probable lack of accuracy of the existing data for tracer diffusion in supercritical dense carbon dioxide.

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.…”

Concentration dependency of dispersion coefficient of aqueous solutions of urea and ethyl acetate in porous media

“…This method has been extensively received attention due to its advantages, including relative simplicity and a wide range of applications using a refractive index detector for standard high‐performance liquid chromatography (HPLC), which has created the conditions for rapid and accurate measurements of the diffusion coefficients in liquids 22,23 . This method has been widely used for the measurement of diffusion coefficients in a wide range of fluids and conditions, particularly organic mixtures and in supercritical fluids 24–26 . Taylor dispersion technique involves the measurement of the dispersion of a pulse of a solute in a fluid flowing in laminar flow of solvent in a tube of circular cross‐section, that is, the combined action of convection along the axis of the column and molecular diffusion in the radial direction 25,26 …”

“…22,23 This method has been widely used for the measurement of diffusion coefficients in a wide range of fluids and conditions, particularly organic mixtures and in supercritical fluids. [24][25][26] Taylor dispersion technique involves the measurement of the dispersion of a pulse of a solute in a fluid flowing in laminar flow of solvent in a tube of circular cross-section, that is, the combined action of convection along the axis of the column and molecular diffusion in the radial direction. 25,26 Ethyl acetate is the ester from ethanol and acetic acid 27 that is primarily used as a diluent and solvent for cleaning, paint removal, and coatings.…”

“…[24][25][26] Taylor dispersion technique involves the measurement of the dispersion of a pulse of a solute in a fluid flowing in laminar flow of solvent in a tube of circular cross-section, that is, the combined action of convection along the axis of the column and molecular diffusion in the radial direction. 25,26 Ethyl acetate is the ester from ethanol and acetic acid 27 that is primarily used as a diluent and solvent for cleaning, paint removal, and coatings. 28 Usually, the esterification reaction of acetic acid with ethanol in the presence of an acidic catalyst is used to produce ethyl acetate and water.…”

Measurements of Binary Diffusion Coefficients in Supercritical Carbon Dioxide

“…Although many studies have been paid to the measurements of diffusion coefficients in SC CO 2 , there are still few works on the diffusion coefficients for polar compounds, drug compounds, metal complexes, and in the regions near to critical point, at higher temperatures (>100°C) and higher pressures (>40 MPa) region in SC CO 2 . In addition, the solvents such as 2,3-dimethylbutane [36], chlorotrifluoromethane, [37], ethane [38][39][40], ethanol [41], hexane [40][41][42], propane, [40][41][42][43] 2-propanol [44] and water [45] are also used as SCFs, in which the binary diffusion coefficients have been measured for various organic compounds with lower MWs such as 1,3,5-trimethylbenzene, 1-octene, 1-tetradecene, acetone, benzene, m-cresol, naphthalene, n-decane, n-tetradecane, phenanthrene, phenol, p-xylene and toluene.…”