L'oxydation du dioxyde de soufre dans les nitrates alcalins fondus

Université Catholique de Louvain, Laboratoire d'Electrochimie des Liquides Ioniques et de Chimie des Radiations. Bâtiment Lavoisier, Place Louis Pasteur, 1 B-1348 Louvain-la-Neuve, Belgique.

Résumé

L'étude du rendement de la réaction hétérogène : SO₂ + 2 MN0₃ [math] M₂SO₄ + 2 NO₂ (M : alcalin) vise à préciser le comportement chimique des nitrates alcalins fondus. L influence de l'oxoacidobasicité sur le pouvoir oxydant des nitrates est mise en évidence en modifiant la composition cationique du solvant. Aux environs de 275 °C, les rendements augmentent brutalement suite à l'intervention d'un processus autocatalytique lié a la dissociation du dioxyde d’azote.

Abstract

The heterogeneous reaction : SO₂ + 2 MNO₃ [math] M₂SO₄ + 2 NO₂ (M : alkali metal) was carried out to contribute to the study of the chemical behavior of molten nitrates. The influence of some physical parameters (flow and dilution of the gas, volume off the solvent) was first determined. A mixture of sulfur dioxide and nitrogen was bubbled through the melt in order to better control the rate of the reaction. The modification of the cationic composition of the melt allowed to define the influence of the oxoacidobasicity on the oxidation properties of nitrates. The efficiency of the chosen reaction increases following the sequence K^- < Na^- < Li^- A partial substitution off alkali nitrates by Mg (NO₁)₂ confirms this evolution. The dependence of the reactivity with respect to the temperature was also determined. An other oxidation mechanism was detected beyond 275 °C. The decomposition of nitrogen dioxide (NO₂ [math] NO + 1/2 O₂) is not negligible in this temperature range and the resulting gaseous mixture catalytically oxidizes sulfur dioxide.