Thermodynamic Analysis of Aluminum Oxide Chlorination

Abstract

A thermodynamic analysis of the chlorination of aluminum oxide was performed for the main possible reactions of interaction with chlorine. The process can only proceed in the direction of decreasing Gibbs energy (ΔG). The condition ΔG < 0 determines the fundamental possibility of carrying out the process under the given conditions and is determined only by the initial and final state of the system. The calculated Gibbs energy and the equilibrium constant in the temperature range of 400–1000 K show that, in the presence of a reducing agent, the reaction equilibrium is shifted towards the formation of aluminum chloride. It has been established that changes in the Gibbs energy of the chlorination reactions of Al₂O₃ polymorphs increase in the series γ-Al₂O₃, amorphous Al₂O₃, δ-Al₂O₃, and α-Al₂O₃. It is possible to assess efficiently the main principles of obtaining anhydrous aluminum chloride in a reacting system by assessing the change in the ratio of the starting components. A thermodynamic analysis of the Al–O–C–Cl and Al–O–C–Cl–Si–Na systems was performed at different component ratios. The latter system is a rough alumina containing sodium aluminosilicate. It has been shown that 100% yield of target products with the complete use of chlorine corresponds to the stoichiometry of their chemical interaction. The possibility of selective chlorination of Al₂O₃ and SiCl₄ has been determined. Sodium oxide, as demonstrated by calculations, is completely converted into chloride, which makes it possible to use the residue from chlorination to produce aluminum silicon alloys without sodium impurities.