The impurities in the CO2 sources could have a significant influence on DFMs performance. There is relatively little research on this topic. The presence of oxygen and steam is the most commonly studied. It is noted that the influence of impurities can be affected by the capacity of sorbent. However, more research should be done on other pollutants, such as SOx and NOx, which are present in power plant flue gas.
The following sentences are copied from this reference (https://doi.org/10.1016/j.ccst.2022.100052) regarding the influence of O2 and moisture on Ru-based DFMs for ICCU-methanation.
“It was found that, even with the presence of high concentration of O2 (∼18%), the Ru-CaO/γ-Al2O3 showed relatively stable CO2 uptake capacity and methanation capacity, and the average CO2 conversion was 76% (Duyar et al., 2015). With the presence of 20% steam, the CH4 yield decreased by 10% to 0.27 g-mol/kg over 19 cycles of operation. The CaO dispersion was found to be greatly reduced by 87% after the cyclic test in the presence of steam, yet the methanation capacity did not decrease significantly (Duyar et al., 2015). The decrease in the capacity was mainly attributed to the oxidation of some Ru, causing the loss of active sites (Duyar et al., 2015; Zheng et al., 2016). Nonetheless, this deactivation can be restored by extending the H2 exposure time or using a higher H2 concentration stream during the methanation stage (Wang et al., 2017). It was shown that a concentration of 15% H2 was sufficient for the oxidized Ru (5% Ru-6.1Na2O/γ-Al2O3) to be reduced in the methanation stage (Wang et al., 2018). This property makes the Ru a more suitable DFMs candidate than Ni in the ICCC-Met of real industrial flue gas containing both oxygen and steam (Arellano-Treviño et al., 2019a).”
“However, different observations for the effect of H2O and O2 were also reported. The storage capacity of 0.8%Ru-BaO/Al2O3 was inhibited by H2O and O2, which could be ascribed to the competition of hydrates and carbonates for the same sorption sites (Porta et al., 2021b). CO2 TPD result indicated that the weaker CO2 ad-species reduced in the presence of H2O and O2. The detrimental effect was also found for CH4 yield (0.153 vs. 0.08 mol/kg), which was possibly due to the sintering of Ru upon oxidation, as supported by the significant decrease of the metallic surface area (1/5 of the fresh sample) (Porta et al., 2021b). On the alkali and alkaline earth metals (Li, Na, K, Mg, Ca, and Ba) modified 1%Ru/γ-Al2O3, the addition of 2.5% H2O and 3% O2 during the capture stage (1%CO2/He) caused the uptake capacity as well as the CH4 yield to decrease significantly for all of the studies DFMs at 350°C (Porta et al., 2021a) (data shown in the below figure). For Ru-Li, Ru-Na, Ru-Mg, almost no CH4 was generated in the methanation stage due to the poor sorption of CO2, and a reduction in CH4 yield of 84%, 65%, and 47% for Ru−K, Ru−Ca, and Ru−Ba, respectively, were observed. This is quite different from other studies, however, where Na-Ru-Al DFMs (5%Ru-6.1%Na2O/Al2O3 (Arellano-Treviño et al., 2019a; Wang et al., 2018) and 0.5%Ru-6.1%Na2O/Al2O3 (Jeong-Potter and Farrauto, 2021)) were reported to still have considerable CO2 uptake and methanation capacity with the co-presence of H2O and O2. This contradiction could possibly stem from the different Na precursors used (carbonates vs. acetates), CO2 concentrations (7.5% vs. 1%), or impregnation sequence of sorbents and Ru on Al2O3 etc. used in these studies.”
Figure result – CH4 formation during the hydrogenation step with (A) and without O2 and H2O (B). (https://doi.org/10.1021/acs.iecr.0c05898)