The objective of this study was to establish the reaction kinetics involved in redox cycles of the CaMn 0.9 Mg 0.1 O 3- material to be used as an oxygen carrier in the Chemical Looping Combustion process. The oxygen transport capacity and reactivity of this material during consecutive reduction and oxidation steps with gaseous compounds (CH 4 , H 2 , CO and O 2) were studied in a TGA apparatus. The oxygen uncoupling properties of this material were also analysed. It was found that material reactivity increased with the number of redox cycles, whereas oxygen transport capacity decreased with the cycle number until it was stabilized or "activated". Conversion vs. time curves at different temperatures (973-1273 K), and reacting gas

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The objective of this work was to determine the kinetic parameters for reduction and oxidation reactions of a highly reactive Fe-based oxygen carrier for use in chemical looping combustion (CLC) of gaseous fuels containing CH 4 , CO and/or H 2 , e.g. natural gas, syngas and PSA-off gas. The oxygen carrier was prepared by impregnation of iron on alumina. The effect of both the temperature and gas concentration was analysed in a thermogravimetric analyser (TGA).The grain model with uniform conversion in the particle and reaction in grains following the shrinking core model (SCM) was used for kinetics determination. It was 2 assumed that the reduction reactions were controlled by two different resistances: the reaction rate was controlled by chemical reaction in a first step, whereas the mechanism that controlled the reactions at higher conversion values was diffusion through the product layer around the grains. Furthermore, it was found that the reduction reaction mechanism was based on the interaction of Fe 2 O 3 with Al 2 O 3 in presence of the reacting gases to form FeAl 2 O 4 as the only stable Fe-based phase. The reaction order values found for the reducing gases were 0.25, 0.3 and 0.6 for CH 4 , H 2 and CO, respectively, and the activation energy took values of between 8 kJ mol -1 (for H 2 ) and 66 kJ mol -1 (for CH 4 ). With regard to oxidation kinetics, the reacting model assumed a reaction rate that was only controlled by chemical reaction. Values of 0.9 and 23 kJ mol -1 were found for reaction order and activation energy, respectively.Finally, the solids inventory needed in a CLC system was also estimated by considering kinetic parameters. The total solids inventory in the CLC unit took a minimum value of 150 kg MW -1 for CH 4 combustion, which is a low value when compared to those of other Fe-based materials found in the literature.

A synthetic Fe-based oxygen carrier prepared by impregnation using -Al 2 O 3 as support, successfully tested for gas CLC combustion, has been now evaluated with respect to gas combustion in a 500 W th CLC continuous unit when the fuel, CH 4 , contained variable amounts of H 2 S.Full gas combustion was reached at oxygen carrier-to-fuel ratio values higher than 1.5. The presence of sulfur in the fuel gas hardly affected the reactivity and combustion efficiency of the oxygen carrier, independently of the amount of sulfur in the gas stream. All the sulfur introduced as H 2 S in the fuel reactor (FR) was released in the same reactor as SO 2 . Furthermore, oxygen carrier particles extracted from the CLC unit after the experimental tests with H 2 S addition were 3 characterized by means of different techniques and no sulfur was detected in any case. The impregnated Fe-based oxygen carrier was highly reactive and sulfur resistant, and can be considered as a suitable material for CLC with gaseous fuels that contain sulfur.

Sour gas represents about 43 % of the world's natural gas reserves. The sustainable use of this fossil fuel energy entails the application of CO 2 Capture and Storage (CCS) technologies. The Chemical Looping Combustion (CLC) technology can join the exploitation of the energy potential of the sour gas and the CO 2 capture process in a single step without the need of a sweetening pre-treatment unit. In this work, a total of 60 hours of continuous operation with sour gas and H 2 S concentrations up to 15 vol. % has been carried out in a 500 W th CLC unit, from which 40 corresponded to a Cu-based oxygen carrier (Cu14Al) and 20 to a Fe-based material (Fe20Al). This is the first time that so high H 2 S concentrations are present in a fuel to be burnt in a CLC process. The Cu14Al oxygen carrier seems to be no recommendable for the combustion of sour gas because, although all the H 2 S is burnt to SO 2 , copper sulfides were formed at all combustion conditions. In contrast, the Fe20Al oxygen carrier presented an excellent behavior with no agglomeration problems and maintaining the reactivity of the fresh material. The sour gas (CH 4 , H 2 , and H 2 S) was completely burnt, and neither SO 2 was released in the AR nor iron sulfides were formed at usual CLC operating conditions. These tests demonstrated the possibility to use sour gas in a CLC process with 100% CO 2 capture without any SO 2 emissions to the atmosphere.