Kinetics of chlorination and oxychlorination of chromium (III) oxide

Thermogravimetric analysis (TGA) is used to study the kinetics of chlorination of Cr2O3 with Cl-2 + N-2 and Cl-2 + O-2 gas mixtures in the temperature range of 550 degrees C to 1000 degrees C. The reactivity of Cr2O3 toward the chlorine-oxygen gas mixture is higher than that toward the chlorine-nitrogen one. Chlorination of Cr2O3 proceeds with an apparent activation energy of about 86 kJ/mol between 550 degrees C and 1000 degrees C, The apparent reaction order with respect to chlorine is about 1.23 at 800 degrees C. At temperatures lower than 650 degrees C, the shrinking sphere model is the most appropriate for describing the reaction kinetics. Oxychlorination of Cr2O3 is characterized by an apparent activation energy of about 87 and 46 kJ/mol for temperatures lower than 650 degrees C and higher than 700 degrees C, respectively. At 800 degrees C and using a Cl-2 + O-2 gas mixture, the maximum reaction rate is obtained when the Cl-2/O-2 molar ratio is equal to 4, confirming the formation of chromium oxychloride. At this temperature, the reaction orders with respect to chlorine, oxygen, and Cl-2 + O-2 are about 1.08, 0.23, and 1.29, respectively. Mathematical fitting of the experimental data is discussed.