Adsorptive Properties of Decationated Zeolite for Some Aromatic Hydrocarbons as Observed by Gas Chromatography

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The adsorptive properties of decationated zeolite for simple aromatic hydrocarbons, such as benzene, toluene, ethylbenzene, and xylenes were investigated by means of gas chromatography at 270–330°C. The specific retention volumes of these alkylbenzenes increased with the increase in the sodium ion content and the rise in the pretreatment temperature of zeolite. The adsorption heat was substantially independent of the sodium content, but slightly increased with the rise in pretreatment temperature above 550°C. A linear relationship was found between the decrease in the ionization potential of aromatic hydrocarbons and the increase in the heat of adsorption. For comparison, the adsorption of ethylene was also examined. With the rise of pre treatment temperature of zeolite, the retention volume of ethylene decreased. On introduction of water to the system, the retention volume of ethylene reversibly increased, whereas that of aromatic hydrocarbons decreased. In accordance with the decationation process of zeolite proposed by Hall <I>et al.</I>, these aromatic hydrocarbons are adsorbed preferably on tricoordinated aluminum site as well as on sodium ion to form the charge transfer complex, while ethylene interacts with hydroxyl group to form the carbonium ion or hydrogen-bonded complex.
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