(664b) Solid Fuel Conversion Via Chemical-Looping With Oxygen Uncoupling (CLOU) Using Co-Precipitation Derived Cu-Mn Oxygen Carriers

Chemical-looping combustion (CLC) is an emerging CO₂
capture and storage (CCS) technology. In CLC oxygen derived from a solid oxygen
carrier is used to completely combust a (hydro-) carbonaceous fuel to CO₂
and H₂O. Thus, in CLC CO₂ is inherently separated from
the nitrogen in air. Conventional CLC for solid fuels requires a prior,
relatively slow gasification step to produce a synthesis gas containing mostly CO
and H₂. An alternative strategy is chemical-looping with oxygen
uncoupling (CLOU) [1]. Here, oxygen is released via a decomposition reaction, with the combustion reaction of the
solid fuel with molecular oxygen being very fast.

A suitable oxygen carrier for CLOU, typically a transition
metal oxide, must possess a high oxygen storage capacity, thermal stability and
fast decomposition kinetics at typical operating temperatures (800-1000 ˚C). In addition,
resistance to attrition and agglomeration, cost and environmental impact have
to be taken into account. With regards to equilibrium thermodynamics CuO and Mn₂O₃ are arguably the most
attractive oxygen carriers for CLOU [1]. However, both copper and manganese
have some drawbacks. For the CuO/Cu₂O
system, agglomeration and a comparatively low oxygen partial pressure (at
temperatures below 850 ˚C) are the main disadvantages, whereas Mn₂O₃/Mn₃O₄
has a low oxygen storage capacity and at temperatures above 900 ˚C Mn₃O₄
is thermodynamically stable and cannot be re-oxidized back to Mn₂O₃
using air.

In this study, mixed metal oxide oxygen carriers
containing manganese and copper oxides were synthesized using a
co-precipitation technique. The synthesized oxygen carriers were fully
characterized and assessed with regards to solid fuel conversion under CLOU conditions.
A comparison with the performance of the individual metal oxides revealed that
the optimized Cu-Mn mixed oxides possessed an
improved resistance to agglomeration, a higher oxygen carrying capacity, a high
solid fuel conversion and an improved physical and chemical stability. These favorable
characteristics make the newly developed Cu-Mn mixed
oxides promising oxygen carriers for CLOU.

Reference

[1] Mattisson, T., Lyngfelt,
A., Leion, H., Int. J. Greenhouse Gas Control 2009, 3
(1), 11-19