Development of CaMn0.775Mg0.1Ti0.1Ti0.125O3-delta oxygen carriers produced from different Mn and Ti sources

Journal article, 2016

Perovskite CaMa(0.775)Mg(0.1)Ti(0.125)O(3-delta) has attracted great interest as an oxygen carrier. To apply this material to a commercial scale chemical-looping unit, one key challenge is to find raw materials which are cheap and available in large quantities for production. Considering the content and price, Mn- and Ti-oxides are likely the raw materials having the major effect. Twelve Mn-oxide sources and four different TiO2 powders were evaluated for production of CaMa(0.775)Mg(0.1)Ti(0.125)O(3-delta) in this work. Particles with perovskite structure were successfully spray dried. All oxygen carriers showed oxygen uncoupling characteristics and most of them had a high reactivity, i.e. over 90% methane conversion already at 950 degrees C with a bed mass corresponding to 57 kg/MW, when examined in a batch fluidized-bed system at 900-1050 degrees C. Furthermore bulk density, crushing strength and resistance against attrition were studied. Although the attrition index varied, materials with good attrition resistance were identified. The rates of reaction were analyzed using two pseudo-first order apparent rate constants. The rates varied in a wide range, and are generally lower than with optimized Ni-based materials, but higher than with ilmenite. Still, the added oxygen uncoupling likely has a large positive effect at high degrees of solid conversion, something not seen with Ni-based materials.