High-Temperature CO₂ Capture by Li₄SiO₄ Sorbents: Effect of CO₂ Concentration and Cyclic Performance under Representative Conditions

This study investigates CO₂ capture on in-house-prepared Li₄SiO₄, a commercial Li₄SiO₄, and a commercial-derived CaO under the same experimental conditions in order to compare their performance with emphasis on the in-house-prepared Li₄SiO₄. The selected commercial Li₄SiO₄ was unsuitable for CO₂ absorption-emission due to the insignificant CO₂ uptake after regeneration. The commercial-derived CaO absorbs 41 wt %, which was the highest CO₂ uptake among the studied samples. However, this sample underwent a severe decay after 12 carbonation-regeneration cycles despite the mild regeneration conditions used (700 °C under N₂), reaching an almost constant CO₂ uptake value (10 wt % after 18 cycles). The in-house-prepared Li₄SiO₄ absorbs 30 wt %, which was near the theoretical CO₂ uptake for Li₄SiO₄. After an initial loss of CO₂ uptake from near 30% to 26%, the performance of in-house-prepared Li₄SiO₄ was maintained after 16 cycles under the same conditions as those used for CaO. The effect of CO₂ concentration on CO₂ uptake was to obtain the inversion temperature for practical CO₂ concentrations. Due to the significant differences among inversion temperatures from different equilibrium plots, experimental inversion temperatures were obtained by the temperature-programmed technique for absorption under a CO₂ concentration of 4% and for emission under a CO₂ concentration of 70%, giving 525 and 660 °C, respectively. A cyclic test was conducted with in-house-prepared Li₄SiO₄: absorption at 520 °C under a CO₂ concentration of 4% and regeneration at 675 °C under a CO₂ concentration of 70%. Under these mild thermal conditions the sample did not exhibit a CO₂ uptake decay, indicating that this sorbent could be efficiently used for high-temperature CO₂ capture from power plant flue gas.