An inverse gas chromatographic study of the adsorption of alkanes on hydroxyapatite
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Saturated alkanes adsorption on synthetic well-crystallized hydroxyapatite was studied by the inverse gas chromatography method, at zero coverage. Hydroxyapatite was prepared from Ca(OH)(2) and H3PO4 aqueous solutions by a slow titration technique. The powder was characterized by XR diffraction, surface area measurement, and chemical analysis. Adsorption of saturated alkanes was investigated in the temperature range 338-353 K, using a flame ionization detector, and nitrogen as a carrier gas. The gas/solid partition coefficients were calculated from the retention data as well as the standard thermodynamic functions of adsorption, Delta H-d(0), Delta S-a(0) and Delta G(a)(0). Linear relationships between lnK and 1/T and between Delta G(a)(0) and the number of carbon atoms in saturated alkanes were observed. The dispersive component of the surface free energy was calculated for the investigated temperature region. A possible analytical application of hydroxyapatite to n-alkanes separation... is given. (C) 2000 Kluwer Academic Publishers.