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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).

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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.

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A significant enhancement of CO generation rate was observed using the DFMs compared to CaO. The work achieved 11.3 mmol gDFM−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.

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