Gas chromatographic study of hydrocarbon adsorption on platinum/alumina catalyst

Abstract

The adsorption of three normal paraffins (n-pentane, n-hexane and n-heptane) and one isoparaffin (i-octane) on the commercial 0.3 %. wt PtJAI03 reforming catalyst were investigated using the elution (or the pulse) technique in a gas-solid chromatograph in the temperature range 185-235 °C. Adsorption isotherms were constructed from chromatographic data at various temperatures using helium as carrier. Average heats of adsorption were determined using the isosteres obtained from the adsorption isotherms, and the values were found to be 28.6 kJ/gmol for n-heptane, 36.4 kJ/gmol for n-hexane, 42.0 kJ/gmol for n-heptane and 41.6 kJ/gmol for i-octane. The experiments for n-pentane and n-hexane were repeated using hydrogen carrier, and the average heats of adsorption were determined to be 23.8 kJ/gmol and 36.7 kJ/gmol respectively. It was found that. the heat of adsorption increases linearly with increasing carbon number for normal paraffins, and that all the hydrocarbons studied were chemically adsorbed under the operating condilions used.