# Performance of Granulated Ti-Dopped Manganese Oxide Oxygen Carriers in Chemical Looping Processes
## 3 Results
### Batch Fluidized Bed Experiments
#### 3.3.2 Experiments with Combustion Gases
Tables 2 and 3 present the main properties of the used sample and the corresponding rate indexes calculated in TGA experiments at 950 \({}^{\circ}\)C in experiments with N\({}_{2}\)-air cycles and H\({}_{2}\) or CH\({}_{4}\). In Table 2, it can be observed that the crushing strength value of used particles decreased to values close to 1 N, the limit considered to operate in a fluidized bed. This corresponds with a slight increase in porosity. The H\({}_{2}\) and CH\({}_{4}\) rate indexes calculated in TGA for the used MnTi_20 oxygen carrier in Table 3 remain similar to \begin{table}
\begin{tabular}{l l l l} \hline \hline
**Sample** & **H\({}_{2}\)** & **CO** & **CH\({}_{4}\)** \\ \hline MnTi 20 granulation & 0.9 & 0.4 & 0.5 \\ \hline MnSA [27] & 1.6 & 0.7 & 0.5 \\ MnGBINE [27] & 1.5 & 0.4 & 0.5 \\ Mn-ZrSG [32] & - & - & 5.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Normalized rate index (%/min) obtained in the batch fluidized bed reactor for granulated MnTi_20 and other Mn-based oxygen carriers (T = 950 \({}^{\circ}\)C). those found for the calcined granulated particles, while the rate index for oxygen release seems to have slightly decreased. Figure 11 shows the SEM images of the MnTi_20 particles after their use in the batch reactor together with the fines collected in the hot filters after it. Similarly to Figure 8, Figure 11A-C show a general overview of the external morphology, while Figure 11D-F correspond to particles embedded in a resin and then cut. As it was the case after the TGA experiments, an increase in the porosity of the samples from the bed can be observed in Figure 11E compared to the calcined particles Figure 11D. Fines collected in the filters after the batch fluidized bed reactor are also shown in Figure 11C,F. Different types of fines are observed. On one hand, those with the smallest size are powder that could be attached to the granulated particles and be lost during the first hours of fluidization of the particles in the batch reactor. The fines with the largest size may correspond to the breakage of the particles during the reaction with the different gases. Based on the amount of fines collected from the bed, Figure 12 shows the time evolution of the attrition calculated for these experiments following Equation (8). Figure 11: SEM images of MnTi_20 (**A,D**) calcined and (**B,E**) after experiments in the batch fluidized bed reactor at 950 \({}^{\circ}\)C (**C,F**) fines collected in the hot filters after the batch fluidized reactor. Figure 12: Time evolution of the attrition rate in the batch fluidized bed experiments with granulated MnTi_20 (\(\Gamma=950\)\({}^{\circ}\)C). In Figure 12, the attrition rate increases at the beginning, probably due to the previously mentioned loss of fines attached to the fresh particles during the preparation of the granulated material. After then, the attrition rate decreases to low values, although an upward trend seems to initiate after 50 h of continuous fluidization. At this point, the estimated lifetime from the final value of the attrition rate measured would be around 2500 h. This value is better than those previously reported for manganese-based perovskites and minerals, which were frequently discarded for operation due to the low lifetime they presented [27, 34]. Nevertheless, to be confident in the durability of the particles, tens or hundreds of redox cycles would be required under a relevant environment and constant operating conditions, preferably in a CLC continuous unit.