Evaluation of Mn-Fe mixed oxide doped with TiO2 for the combustion with CO2 capture by Chemical Looping assisted by Oxygen Uncoupling

Abstract

Bimetallic manganese-iron materials have been identified as suitable oxygen carriers for Chemical Looping Combustion (CLC) and Chemical Looping with Oxygen Uncoupling (CLOU) processes. These materials allow the combustion of a fuel with inherent CO2 capture according to two parallel mechanisms: reaction with lattice oxygen and oxygen uncoupling. This work is focused on the evaluation of the reactivity and physicochemical characterization of oxygen carrier particles consisting of a manganese-iron mixed oxide with manganese to iron molar ratio of 66:34 and doped with titanium (7 wt% TiO2) with the objective of determining suitable conditions to be used in CLC and CLOU processes. Particles were prepared by spray drying and the sintering procedure was optimized in order to achieve particles with high reactivity and mechanical strength. In addition, suitable magnetic properties were also sought in order to allow oxygen carrier recover and reuse in a chemical looping unit burning solid fuels. Optimum operating conditions for the fuel combustion and regeneration stages were determined in order to promote the oxygen uncoupling mechanism. Thus, temperature during the fuel combustion must be as high as possible to enhance the oxygen transference; but conditions for oxygen carrier regeneration by air must be carefully selected in order to take advantage of the oxygen uncoupling capability of this material. An oxidizing temperature interval of 1123–1173 K maximized the regeneration, while an air excess higher than 20% would be recommended in order to guarantee oxygen uncoupling capability.