Effect of syngas constituents on CdO- and MgO-based sorbents for pre-combustion CO2 capture

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Abstract

Magnesium oxide/cesium carbonate composites as well as cadmium oxide/sodium halide mixtures have been previously described as potential candidates for pre-combustion carbon dioxide capture. Here, the effects of water and hydrogen alongside CO2 were examined in simulated partial pressure swing experiments analyzed by thermogravimetric means. It was shown that the magnesium/cesium sorbents are tolerant to hydrogen at a temperature of 370 °C and that their working capacities over 25 cycles are enhanced by the addition of water to the sorption gas stream. The cadmium/sodium iodide sorbent showed a stable working capacity for 23 sorption cycles at 285 °C, but tended to lose working capacity after that point. At 305 °C, a significant loss in capacity was observed during sorption cycling. As reduction in an inert gas/hydrogen mixture was not found to commence below 400 °C, a halide promoter disintegration mechanism is assumed to be the cause of the decay. The sorption of hydrogen sulfide was also examined. Both Cd- and Mg-based materials showed a significant uptake of H2S, which was hard to desorb. It appears that H2S sorption competes alongside CO2 sorption, causing a reduction in working capacities over multiple cycles. Powder X-ray diffraction showed that the Cd-based sorbent forms CdS upon H2S sorption, whereas the MgO phase of the Mg-based sorbent is not changed. A new Cs phase was formed from cesium carbonate with H2S, which is probably a previously unreported magnesium-cesium sulfide mixed phase
Original languageEnglish
Pages (from-to)5909-5918
Number of pages10
JournalEnergy and Fuels
Volume29
Issue number9
DOIs
Publication statusPublished - 2015

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