Chromatography theory: Application to supercritical fluid extraction

Abstract

The adsorption equilibrium constants for naphthalene on alumina have been measured in the presence of subcritical and supercritical carbon dioxide by the dynamic tracer response technique. The equilibrium constants decrease with increases in density, and the isochoric temperature dependency is very small at supercritical conditions. Through chromatography theory, an expression has been developed for the density dependency of the capacity factor, a quantity related to the adsorption equilibrium constant by the porosity and density of the particle and the porosity of the bed, in terms of the partial molar volume of the solute at infinite dilution in the fluid phase. The partial molar volumes extracted from the data agree well with the published data. Investigation of the dynamics of the bed shows that a model, including axial dispersion and effective diffusion into the pores, successfully represents the data. The effective diffusivities and the axial dispersion coefficients were also extracted from the second central moments of the response curves at each condition.

Fischer-Tropsch synthesis in supercritical fluids. Final report

“…The system pressure was set by a back pressure regulator placed after the UV detector. A second back pressure regulator at 54.4 atm reduced pulsations in the system by utilizing the double expansion technique developed in our laboratories (Erkey and Akgerman, 1990). The system pressure was measured by an internal pressure transducer in the syringe pump calibrated to a precision of +1 bar.…”

Coking and activity of porous catalysts in supercritical reaction media

“…Implicit is the assumption that K, values for 1-hexene are similar to that for CO, at similar reduced densities and reduced temperatures. The K, values reported by Erkey and Akgerman (1990) at a reduced C02 temperature of 1.01 was correlated with reduced density as follows:…”

“…A similar correlation was employed by Erkey and Akgerman (1990) to describe the effective diffusivity of naphthalene dissolved in supercritical carbon dioxide in alumina pores and by Biswas and Do (1987) to describe the effective diffusivity of gases in porous reforming catalysts that are subject to coke formation upon reaction.…”

“…Due to a lack of sufficient data o n the solubility and effective desorption constants for supercritica1 hexene-naphthalene-Pt/ y-Al,03 systems, the adsorption equilibrium constant ( K A ) data of Erkey and Akgerman (1990) for the CO,-naphthalene-AI20, system were used to obtain the effective desorption coefficient k,. Implicit is the assumption that K, values for 1-hexene are similar to that for CO, at similar reduced densities and reduced temperatures.…”

Influence of adsorption on the measurement of diffusion coefficients by Taylor dispersion

“…These rate constants are usually determined in packed column chromatography by superimposing an axial dispersion parameter on a radially uniform velocity [18][19][20][21]. However, in the case of Taylor dispersion with adsorption in an empty column, the rate constants will be evaluted by solving the two-dimensional Taylor dispersion model in which the radial velocity profile is exactly maintained.…”