Influence of temperature on ICCU-DRM using K-Li4SiO4 -Ni/Al2O3

Dual functional materials, containing K-Li₄SiO₄ sorbent as the sorbent and 10 wt% Ni/Al₂O₃ as the catalyst, were investigated for ICCU-DRM, and the influence of temperature (600, 625 and 650 °C) was focused (https://doi.org/10.1016/j.seppur.2021.119476). The following content was copied from the above reference.

“As CO₂ desorption velocity is seriously affected by temperature, the duration of pre-breakthrough stage is different under various temperatures. At 650 °C as shown in Fig. 4(c), there is almost no pre-breakthrough stage in the in-situ conversion due to the rapid decrease of CO₂ desorption velocity. At the beginning of the conversion, the amount of CO₂ is much higher than CH₄, causing the occurrence of a significant side reaction (CO2+H2→CO+H2O) and making the mount of produced H₂ is less than that of CO. Gradually, the content of CO₂ becomes lower due to the dramatic reduction of CO₂ release velocity, resulting in methane decomposition (CH4→C+2H2) and a H₂/CO ratio bigger than 1. When reaction temperature is set at 625 °C, as presented in Fig. 4(a), the release velocity of CO₂ decreases gently, and the pre-breakthrough time is about 7 min in the in-situ conversion process. Within this stage, the ratio of H₂/CO in product is stable in the range of 0.95–1.05 and the conversion of CH₄ and CO₂ is 95% and 81%, respectively. It should be noted that the continuous consumption of CO₂ by in-situ DRM accelerates the desorption of CO₂ from K-Li₄SiO₄ following Le Chatelier’s principle, and results in a much more release of CO₂ in the pre-breakthrough stage during ICCU-DRM than that without the presence of catalyst. Therefore, the actual ratio of CO₂/CH₄ is higher than the pre-set value, which reduces the CO₂ conversion rate significantly. Further decreased reaction temperature into 600 °C, the release of CO₂ becomes more gradual, and the time of pre-breakthrough stage extends to 15 min. However, as the temperature is too low to efficient conversion of CH₄, the conversion of CH₄ and CO₂ during the pre-breakthrough stage is only 75% and 85%, respectively. In conclusion, the optimal operating temperature of K-Li₄SiO₄ and Ni/Al₂O₃ is 625 °C in ICCU-DRM. When the temperature is at 650 °C, CO₂ release velocity of K-Li₄SiO₄ drops too fast to be integrated with the reforming. On the other side, Ni/Al₂O₃ catalyst cannot efficiently convert CO₂ and CH₄ at 600 °C.”

“Fig. 4. ICCU-DRM at (a) 625 °C; (b) 600 °C; (c) 650 °C.” https://doi.org/10.1016/j.seppur.2021.119476