Na2CO3 and K2CO3 based sorbent for ICCU-methanation

As ICCU-methanation happens at relatively lower temperatures compared to syngas production, medium-temperature sorbent should be used. Na₂CO₃ and K₂CO₃ based DFMs were investigated at temperature around 320 °C. It is noted that CaO should not be used around this temperature due to the low capacity of CO₂ capture and slow reaction.

The following sentences are copied from this reference (https://doi.org/10.1016/j.ccst.2022.100052) regarding the reaction mechanism of Ni-based DFMs for ICCU-RWGS.

“Due to the greater CO₂ uptake capacity of 10%K₂CO₃/γ-Al₂O₃ and 10%Na₂CO₃/γ-Al₂O₃ than 10%CaO/γ-Al₂O₃ at low temperatures (e.g., 320 °C), the methanation capacity of Ru loading on K₂CO₃ and Na₂CO₃ were also found to be higher. The CH₄ yield of 5%Ru-10%Na₂CO₃/γ-Al₂O₃ (1.05 g-mol CH₄/kg) was about two times that of the 5%Ru-10%CaO/γ-Al₂O₃ (0.50 g-mol CH₄/kg) at 320°C.”

“This indicated that Na₂CO₃ could be an attractive sorbent component for DFMs development in the ICCC-Met process (Duyar et al., 2016). When using Na₂CO₃ as a CO₂ sorbent in Ru-based DFMs, the carbonates decomposition and the subsequent hydrogenation happen at lower temperatures than using CaO due to the stability of the formed carbonates on CaO (Bermejo-López et al., 2019a).”

“At a lower operation temperature of 310°C, a comparable yield of 380 mmol/kg can be achieved for the 4%Ru-15Na₂CO₃/Al₂O₃, as shown in Fig. 14, due to the higher Ru dispersion coupled with lower stability of the formed carbonates. ”

Fig. 14. Evolution of CO₂ storage and CH₄ and CO production with temperature for Ru-CaO/Al₂O₃ (a, b, and c, respectively) and Ru-Na₂CO₃/Al₂O₃ (d, e, and f, respectively) with different sorbent contents (Bermejo-López et al., 2019a).

“By using the mixed NaCO₃ and CaO as sorbents, the basicity of the Ru-based DFMs could be modulated (Bermejo-López et al., 2022). It was found that Ru-8Na/8Ca DFM, the optimum selection, showed a higher CH₄ yield in the whole temperature range tested (280 – 400°C) compared to the DFMs with the single sorbent, which was suggested to be caused by the highly dispersed Ru and the promoted basic sites with medium strength on the Na-Ca combined sorbent surface.”