New insights into Mn2O3 based metal oxide granulation technique with enhanced chemical and mechanical stability for thermochemical energy storage in packed bed reactors

High temperature thermochemical energy storage still requires a significant research effort. Most of the research has been carried out with materials at lab-scale, and proper material fabrication techniques need to be developed in order to make feasible the upscaling of the technology. Agglomeration, abrasion, or low volumetric energy density are some negative consequences observed when trying to pass from the powder state to the material shape and amount required for a thermochemical reactor. In this work, an established granulation technique is investigated, using a Si-doped manganese oxide as active material to determine the critical parameters that provide the best chemical and mechanical stability of the granules. The granulation process uses a polymeric binder to give consistency to the granules and later, it is removed to create a porous structure to facilitate the oxygen diffusion in and out of the granule. We identified the positive effect of decreasing the bath temperature to increase the volumetric energy density of the granules. Furthermore, it was observed that increasing the mechanical stability through a high temperature treatment did not decrease the chemical stability of the material. In order to provide the first insights into the scalability of the solution, the chemical and mechanical stability of the granules have been satisfactorily checked during 100 redox cycles, out of which 50 were carried out in a homemade lab-scale packed bed reactor with an inner diameter of 13 mm and another 50 redox cycles in a simultaneous thermal analyzer.

Automated summary

This study investigated an established granulation technique using Si-doped manganese oxide as the active material to determine critical parameters for achieving the best chemical and mechanical stability of the granules. The positive effect of decreasing the bath temperature on increasing the volumetric energy density of the granules was identified.