Enhanced performance of red mud for chemical-looping combustion of coal by the modification of transition metal oxides

Red mud has been considered a promising candidate of low-cost oxygen carriers (OCs) for chemical looping combustion (CLC) technology due to its relatively high Fe2O3 content, but it shows poor stability during long-term redox cycling. In the present work, NiO, MnO2 and CuO are used as additives to tune the components of red mud used for the CLC of coal. The results show that the addition of NiO (e.g. 15 wt%) can significantly improve the reactivity of red mud for coal combustion, but it suffers a sharp decline after a chemical looping. In the case of MnO2, it significantly improves the selectivity for coal oxidation to CO2, which yields relatively high-purity CO2 in the combustion step. The presence of CuO in the red mud oxygen carriers obviously enhances the reactivity, selectivity and redox stability. The sample with 20 wt% CuO (20Cu-RM) shows a stable carbon capture rate with a CO2 purity higher than 90% during the long-term chemical looping process. The XRD and H-2-TPR characterization results for the cycled 20Cu-RM sample shows that part of Cu element was separated from CuFe2O4 spinel structure and may act as active phase for improving redox performance.

Automated summary

This study investigates the effects of NiO, MnO2, and CuO additives on red mud used in chemical looping combustion. The results show that NiO improves reactivity, MnO2 enhances selectivity for CO2, and CuO enhances reactivity, selectivity, and redox stability.