Using Mn-Si oxygen carriers supported with CaO or Al2O3 for converting methane and syngas in chemical-looping with oxygen uncoupling (CLOU)

Journal article, 2020

Facing increasingly severe environmental problems and substantial energy demand, chemical-looping with oxygen uncoupling (CLOU) is regarded as a highly promising technique to facilitate the application of carbon capture storage and utilization (CCS & U) due to its inherent gas separation. Thus, feasible oxygen carriers for continuous operation on the industry scale are essential. A combination of Mn and Si, which is not only economic but also has few adverse effects on the environment, has been tested and found to provide satisfactory CLOU behavior. But the results are relevant for several oxygen carrier applications. However, the mechanical properties of these Mn-Si oxygen carriers require further improvement. Thus, two kinds of support materials are chosen in this study, CaO and Al2O3, to enhance the physical strength of the Mn-Si oxides. Twelve samples with a CaO content ranging from 2 wt% to 41 wt% and twelve samples with an Al2O3 content, ranging from 2 wt% and to 36 wt%, were produced using spray-drying at three sintering temperatures, 1100 °C, 1150 °C, and 1200 °C. The aim is to identify oxygen carriers, which exhibit high reactivity and strong mechanical properties. The oxygen release ability and gas-fuel conversion of these oxygen carriers are examined. In general, the particles with a lower content of support materials (≤5 wt%) calcined from lower temperatures (≤1150 °C) show better CLOU behavior and higher reactivity, regardless of the support material. Attrition resistance was assessed with surprisingly good results for an oxygen carrier with a low content of support materials (≤5 wt%). The material with 74% Mn 24% Si and 2% Al was further tested in a continuous 300 W. This was done to test the oxygen carrier capability under more conditions closer to a real circulating CLOU unit. In the 300 W unit the material release oxygen in inert atmosphere and converted up to 99.98%, of the syngas and 70% of the methane. However, under certain conditions with syngas as fuel the physical structure of the oxygen carriers were destroyed as the particles degraded to fines.