Experimental investigation of the reduction of liquid bismuth oxide with graphite

Abstract

We report an experimental demonstration of the chemical reactions for the chemical looping gasification process using molten bismuth oxide as the oxygen carrier. Cycling of the material without noticeable degradation was shown using a thermo-gravimetric analyser (TGA) furnace through both the reduction of bismuth oxide with carbon and its oxidation with air. The potential for any contamination of liquid bismuth oxide with the alumina container and of any agglomeration was assessed experimentally using x-ray diffraction (XRD) test. A kinetic model was also developed using Kissinger method to estimate the activation energy and the pre-exponential factor for the reduction and the oxidation reactions. It was found that the reduction and oxidation of bismuth and its oxide is feasible at temperatures of approximately 900 °C with the activation energies of 229.4 kJ/mol and 173.6 kJ/mol for the reduction and oxidation reactions, respectively at chemical conversion of 0.7. The chemical conversion of carbon in the presence of bismuth oxide was measured to reach 85% for the partial oxidation of carbon and to reach completion for the complete oxidation of bismuth. Furthermore, no containment challenges for liquid bismuth were identified in the alumina crucible at 900 °C. Hence, the proposed system offers potential to avoid the challenges of sintering and agglomeration that are associated with chemical looping systems using a solid oxygen carrier.