Reactions of stearic acid, of n dodecanol and of cyclohexanol on the clay minerals illite, kaolinite and montmorillonite

(Chemistry Department, The Queen’s University Belfast, BT 9 5 AG), Northern Ireland.

Abstract

Stearic acid and n-dodecanol react between 400-550 K at the surfaces of the clay minerals illite, kaolinite and montmorillonite to yield mixtures of alkanes in which the 2- and 3- methyl isomers predominate and the n-alkanes are formed in smaller amounts. The mixtures of products obtained from all six reactant preparations are generally similar though small differences could be delected. Kinetic data for C₆ — C₈ hydrocarbon formation processes showed that reaction rates are comparable, within the temperature range studied, despite relatively large variations in the values of the Arrhenius parameters measured. The effective influence of these variations is largely offset by a pronounced compensation effect. The observed behaviour is ascribed to differences, for each reaction mixture, in the temperature dependencies of the effective concentrations of the surface-bonded intermediates which participate in the rate-limiting step for product desorp- tion. Since the same species participate in surface equilibria on each material, the product mixtures contain the same constituents.

Some observations for the reactions of cyclohexanol on montmorillonite are also reported.

Résumé

Les réactions entre l’acide stearic ou n-dodécanol 400-550 K et trois argiles (illite, kaolinite ou montmorillonite) rendent mélanges de hydrocarbures, dans lesquelles 2- et 3-méthyl alkanes prédominent. Quoique les produits des six mélanges réactionnels soient semblables, les paramètres d’Arrhenius sont très différents. Nous discutons ces résultats.