A grain model based on population balances for redox reactions of copper-based oxygen carriers is developed. It considers the effects of grain size distribution and sintering, and a new expression for the aggregation frequency, which takes into account the sintering mechanisms and synthesis method, is deduced. In order to validate the model, six copper -based oxygen carriers were synthesized by excess wet impregnation and by incipient impregnation. They were characterized by BET surface area, BJH porosimetry, and SEM microscopy. Model results were compared with experimental data acquired by thermogravimetry during several redox cycles and the model was able to predict the conversion drop over the course of redox cycles due to sintering. It was found that copper-based oxygen carriers synthesized by incipient impregnation are more strongly affected by sintering than those prepared via excess wet impregnation, and finally it is shown that metallic copper sinters during oxidation, resolving a controversy in this regard that has existed in the literature. (C) 2017 Elsevier Ltd. All rights reserved.