Reduction Kinetics of Low-Cost Cu/Fe-Based Oxygen Carriers in Chemical Looping Mode

Abstract

Cu–Fe bimetallic oxides have been proposed as promising OC candidates in chemical looping combustion (CLC) due to their high reactivity and resistance to sintering, and the reduction kinetics of the Cu–Fe composite OCs is significantly essential. In this article, several low-cost Cu/Fe-based OCs are prepared using fine natural ores or red mud as raw materials. Among these OCs, the composite OC with thermal neutrality is determined by reduction investigation within the typical CLC temperature range. The heat flow curves indicate that the autothermal balance could be achieved when the mixing ratio of copper ore to hematite is 20:80 (i.e., Cu20Fe80@C), which further guides the design of the copper ore/red mud composite OC (i.e., Cu10.9Red89.1@C). Subsequently, 50 cyclic redox tests are performed to evaluate the reaction stability of these OCs, and the results show that the composite OCs (i.e., Cu20Fe80@C and Cu10.9Red89.1@C) exhibit a better cyclic stability as well as a higher oxygen transfer rate than those of pure Fe-based materials (i.e., red mud and Fe100@C). Moreover, the reduction kinetics of these OCs is studied in detail at both high- and low-temperature conditions. It is found that the OC reduction data obtained from high temperatures (750–950 °C) are inappropriate for analyzing the kinetic parameters, whose process is likely to be dominated by gas diffusion in the particle boundary layer. At low temperatures (400–610 °C), the reduction of all targeted OCs can be described by the shrinking core model, and the pure Fe-based OCs correspond to the mechanism function of G(X) = 1 – (1 – X)1/3, while that is G(X) = 1 – (1 – X)1/2 for the composite OCs. Additionally, it should be noted that the composite OCs present lower activation energy than their corresponding pure Fe-based OCs. In summary, this study shows the superiority of composite OCs in terms of cyclic reactivity and kinetic parameters, which will further guide and optimize the design of low-cost OCs.

Red Mud As the Catalyst for Energy and Environmental Catalysis: A Review

“…Carbon dioxide from the combustion of fossil fuels is a primary factor contributing to the current rise in greenhouse gas concentrations. − Capturing carbon dioxide from the atmosphere to reduce the greenhouse effect and enhance the efficiency of fossil fuels has sparked interest. CO 2 capture and storage (CCS) schemes are considered one of the few options to reduce emissions from small and mobile sources, which accounts for about 40% of total anthropogenic CO 2 emissions. − Chemical looping combustion (CLC) is an energy conversion system that can simultaneously achieve fuel efficient step utilization and low-cost CO 2 separation.…”