Chemical looping integrated CO2 capture and utilisation

Chemical looping dry methane reforming provides a few advantages compared to conventional dry methane reforming. These include 1) the removal of deposited carbon in a separate oxidation process; 2) enhancing the concentration of the produced hydrogen by avoiding the direct contact between H₂ and CO₂. Therefore, integrating chemical looping dry methane reforming with CO₂ capture is promising to enhance process efficiency.

A simple Fe₂O₃/Al₂O₃ catalyst mixed with CaCO₃ was used for the ICCU-DRM (the schematic diagram is shown below) (https://doi.org/10.1021/acs.iecr.9b05783). The experiment was carried out at non-isothermal conditions, where the oxidation and carbonation happened at 600  °C and the reforming was carried out at 900 °C. The results showed that the combination of oxygen carrier and CO₂ sorbent could improve the reforming reactivity and reduce carbon deposition. However, the formation of FeAl₂O₄ resulted in a loss of oxygen storage capacity (as shown below).

Similar to this process, a novel concept combining ICCU with chemical looping RWGS was reported (https://doi.org/10.1016/j.cej.2022.135752).

Ca-Fe DFMs were prepared by a one-pot sol-gel method. The dual looping concept is shown below.

A significant enhancement of CO generation rate was observed using the DFMs compared to CaO. The work achieved 11.3 mmol g_DFM⁻¹ CO yield, 82.5% CO₂ conversion and 99.9% CO selectivity at 650 °C. In particular, when the molar ratio between Ni and Fe was 1:9, Notably, CO₂ conversion higher than 80% and CO selectivity >99.9% were obtained. In terms of the influence of Ni/Ca ratio, the authors commented below:

“Introducing a small amount of Ni contributes to the enhanced CO yield and cyclic stability by improving the reducibility of Ca₂Fe₂O₅ and stabilising the Fe size. However, increased Ni loading could negatively affect the performance of DFMs owing to the sintering of Ni and poorer CO selectivity. ”

It is suggested that Ca₂Fe₂O₅ acted as an oxygen carrier for in-situ chemical looping to produce CO and a thermally stable physical barrier to prohibit the sintering of CaO.

In addition, it is essential to introduce air or steam purge after RWGS to remove carbon and also avoid the formation of CO during the stage of CO₂ capture. The newly formed CO could be a new pollutant for flue gases.