Sur l’adsorption comparée de SO₂ et de CO₂

I. Application à l’étude des modifications texturales d’un charbon de saccharose au cours de sa carbonisation

¹ The Institute of Chemistry and Technology of Petroleum and Coal, Polytechnic of Wroclaw, Pologne.
² Laboratoire de Chimie des Gaz et des Combustibles, Bât. 414, Université Paris-Sud, 91405 Orsay, France.

Résumé

Nous avons étudié l’adsorption comparée du dioxyde de carbone et du dioxyde de soufre (domaine de température : entre 195 et 298 °K) sur quatre charbons de saccharose carbonisés entre 500 et 1 100 °C.

On montre notamment que SO₂ s’adsorbe volumétriquement dans les micropores du carbone tandis que CO₂ forme une couche monomoléculaire à leur surface. Nous précisons aussi, grâce aux résultats complémentaires d’adsorption d’azote à 77 °K, de benzène à 298 °K, d’une part, et de porosimétrie au mercure, d’autre part, l’influence de la température de traitement sur l’évolution de la texture capillaire de ce charbon actif.

Abstract

Saccharose char samples carbonized in the atmosphere of an inert gaz at temperatures between 500 and 1 100 °C have been studied in order to establish the influence of the heat treatment temperature on the chemical composition and capillary structure of the char. For the determination of the parameters of the porous structure, adsorption methods and mercury porosimetry were used. Results of SO₂ and CO₂ adsorption were compared.

In the evaluation of the carbon dioxide isotherms and the sulphur dioxide isotherms the manner of fixing of these two adsorbates on the carbon surface was considered, this problem being closely related with the density of CO₂ in the adsorbed state. Basing on experimental evidence of adsorption results of CO₂ and SO₂ obtained at different temperatures on samples whose properties were, to some extent, known, and considering the structure shape, polarity and polarizibility of the carbon dioxide molecule it was concluded that carbon dioxide, contrary to SO₂ and N₂ which get adsorbed by volume filling of the micropores, gets adsorbed by forming a monolayer on the surface of these micropores. This means that carbon dioxide is a special adsorbate permitting the determination of the surface area of microporous carbonaceous materials provided these micropores arc not too narrow to lose the physical significance of the concept of their surface area.