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

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 degrees 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 degrees 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.

Automated summary

This study explores the advantages of Cu/Fe-based composite oxygen carriers in terms of cyclic reactivity and kinetic parameters, providing guidance and optimization methods for the design of low-cost oxygen carriers.