Ignacio Medina

Diffusion coefficients in supercritical fluids: available data and graphical correlations

The methods for obtaining reliable data on diffusion coefficients at high pressure have received great attention over the last 15 years. This interest has been due to the importance that supercritical fluids have assumed in some industrial areas, mainly in emerging separative operations based on mass transfer mechanisms. This review includes all the available data of diffusion coefficients in supercritical fluids at infinite dilution. Revised literature includes references until 1998. Frequent types of graphical correlation were analyzed.

Determination of binary diffusion coefficients of benzene and derivatives in supercritical carbon dioxide

Abstract The Taylor—Aris method is applied to calculate binary diffusion coefficients in supercritical carbon dioxide under quasi-infinite dilution conditions by means of the Giddings and Seager chromatographic technique. Benzene, toluene, ethylbenzene, n -propylbenzene and cumene have been tested at 40, 50 and 60°C in the pressure range 150–350 bar. The data have been correlated with temperature, pressure, density and viscosity, obtaining significant dependences and useful equations for obtaining new data by interpolation.

Determination of diffusion coefficients for supercritical fluids.

A review of the diffusion coefficients for solutes in supercritical fluids as reported in the literature is presented together with the correlation methods applied by the authors for modeling the experimentally determined data. Supercritical carbon dioxide has been the preferred solvent in most of the systems investigated, although other solvents at elevated pressure have also been used. The influence of pressure, temperature, density, and viscosity on the binary diffusion coefficients is discussed, and some general trends have been established. A number of experimental methods for determining diffusion coefficients in supercritical fluids have been reported in the literature. The methods are described, their advantages and disadvantages are discussed and some examples of their application are given. Predictive equations based on the Stokes-Einstein model, the Rough-Hard-Sphere theory, and other methods for the calculation of diffusion coefficients in supercritical fluids at infinite dilution are reviewed. The review also looks at the ternary systems reported in the literature. The latter are discussed in terms of temperature, pressure, the type of modifier employed, amount of modifier, and solute-modifier interactions. Several equations have been proposed for correlating and predicting the diffusion coefficients in ternary systems.

Measurement of diffusion coefficients for 2-nitroanisole, 1,2-dichlorobenzene and tert-butylbenzene in carbon dioxide containing modifiers

The molecular diffusion coefficients of 2-nitroanisole, 1,2-dichlorobenzene and tert-butylbenzene in supercritical carbon dioxide and carbon dioxide containing modifiers were determined by using the Taylor–Aris dispersion technique. Experimental values are reported for temperatures ranging from 313 to 333 K and pressures between 15.0 and 35.0 MPa. The influence of pressure, temperature, density and viscosity on the binary diffusion coefficients was examined. The addition of low proportions of methanol and n-hexane as modifiers had an important effect on the diffusion coefficient of the three solutes.

Dealcoholisation of Cider by Supercritical Extraction with Carbon Dioxide

A study of cider dealcoholisation by supercritical extraction with carbon dioxide using pilot-plant-scale equipment has been carried out. The effects of pressure, temperature and solvent to feed ratio have been examined. Supercritical and liquid carbon dioxide have been used to extract ethanol and aromas from cider at pressures of 80-250 bar and temperatures of 20 and 40°C.

Viscosities and densities for binary mixtures of cresols

This work reports the measured density and viscosity values of mixtures of 2-, 3- and 4-methylphenol (o-, m- and p-cresol), at temperatures in the range 313.15–333.15 K over a range of mole fractions. Viscosities were fitted to the McAllister three-body interaction model and to the Auslander equation. The results showed mixtures containing o-cresol to be more fluid when compared to the pure liquids and positive viscosity deviations for m- and p-cresol mixtures. The results indicated an increase in the average degree of cross-association of mixtures containing o-cresol. The activation energy, enthalpy and entropy of flow were determined by applying Eyring’s theory of rate processes.

Thermodynamic properties of solutions by gas chromatography using a liquid crytal compound 4,4-bis(heptyloxy)azoxybenzene as solvent

SummaryThermodynamic properties of 22 solutes at infinite dilution have been determined in the smectic, nematic and isotropic mesophases of 4,4′-bis(heptyloxy)azoxybenzone. The thermodynamic properties are discussed in relation to the solute-solvent (liquid crystal) interactions as conditioned by the degree of order in the liquid crystal.

Experimental binary diffusion coefficients of benzene and derivatives in supercritical carbon dioxide and their comparison with the values from the classic correlations

Abstract Experimental data for diffusion coefficients obtained by supercritical fluid chromatography (SFC) according to the Taylor–Aris dispersion method are compared with results from predictive equations for dense fluids. The goodness of fit and the bias of the correlation only suggest a slight empirical correction in these equations not specifically formulated for supercritical fluids (SCFs) and justify a persevering effort in experimentation oriented to the development of generalized models.

Thermodynamic properties of solution by gas chromatography using a liquid crystal as solvent: cholesteryl myristate

Abstract Thermodynamic properties of several organic compounds at infinite dilution in the three phases exhibited by cholesteryl myristate were determined from gas chromatographic data. Activity coefficients for the solutes are reported for the smectic A (74°C), cholesteric (80°C) and isotropic (86°C) phases of the liquid crystal. Excess solution thermodynamic properties are calculated and the results discussed in relation to solute-solvent interactions and orientations of the liquid crystal.

Purification of Zopiclone by Preparative High Performance Liquid Chromatography

Abstract The zopiclone was obtained in a 99.5% pure form, and in good yield by preparative scale high performance liquid chromatography. Purification was from a complex reaction mixture. A reversed phase preparative scale HPLC column is used. This work demonstrates how kilogram quantities of pure material can be conveniently obtained using preparative HPLC, even when the components in a mixture are difficult to resolve.