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

Abstract

This study investigates CO 2 capture on in house prepared Li 4 SiO 4 , a commercial Li 4 SiO 4 and a commercial derived CaO under the same experimental conditions in order to compare their performance, with emphasis on the in house prepared Li 4 SiO 4 . The selected commercial Li 4 SiO 4 resulted unsuitable for CO 2 absorption emission due to the insignificant CO 2 uptake after regeneration. The commercial derived CaO absorbs 41 wt.%, which was the highest CO 2 uptake among the studied samples. However, this sample underwent a severe decay after 12 carbonation regeneration cycles, despite the mild regeneration conditions used (700 ºC under N 2 ), reaching an almost constant CO 2 uptake value (10 wt.% after 18 cycles). The in house prepared Li 4 SiO 4 absorbs 30 wt.%, which was near the theoretical CO 2 uptake for Li 4 SiO 4 . After an initial loss of CO 2 uptake from near 30% to 26 %, the performance of in house prepared Li 4 SiO 4 was maintained after 16 cycles, under the same conditions that those used for CaO. The effect of CO 2 concentration on CO 2 uptake was to obtain the inversion temperature for practical CO 2 concentrations. Due to the significant differences amongst inversion temperatures from different equilibrium plots, experimental inversion temperatures were obtained by Temperature Programmed technique for absorption under a CO 2 concentration of 4% and for emission under a CO 2 concentration of 70%, giving 525 ºC and 660 ºC, respectively. A cyclic test was conducted with in house prepared Li 4 SiO 4 : absorption at 520 ºC under a CO 2 concentration of 4% and regeneration at 675 ºC under a CO 2 concentration of 70%. Under these mild thermal conditions the sample did not exhibit a CO 2 uptake decay, indicating that this sorbent could be efficiently used for high temperature CO 2 capture from power plant flue gas. Keywords: Li 4 SiO 4 ; sorbent; CO 2 capture; regeneration; cycles; thermodynamics; temperature programmed technique.

Conceptual Design for Integrating Lithium-Based Carbon Capture Looping Systems into Natural Gas Combined Cycle Power Plants

“…The sorbent is then regenerated at the required temperature in the regenerator (C-2) following the reverse of reaction . Sorbent absorption and regeneration working temperatures of 525 and 700 °C, respectively, were chosen based on previously obtained experimental data on Li 4 SiO 4 under NGCC flue gas conditions . The best operating temperature for each reactor was selected after performing temperature-programmed adsorption/desorption lab tests under the operational conditions of each reactor, respectively.…”

“…The conceptual design of the HTCC plant is done with the following assumptions: The make up flow rate is very small (0.01 kg fresh Li 4 SiO 4 / kg circulated Li 4 SiO 4 ), so there is no need to use heat exchangers with spent sorbent. That was decided based on the high stability of the sorbent observed during cyclic test of the sorbent under NGCC flue gas absorption condition and oxy-fuel combustion desorption condition as observed by Izquierdo et al The final CO 2 stream before the compression train is bypassed to another heat exchanger (E-9) to heat up the makeup stream before being fed to the absorber. That helps to improve the secondary steam cycle efficiency by transferring part of the hot CO 2 stream heat to the absorber through the sorbent make up flow which is being recovered in turn in the in-bed heat exchangers. Heat integration with the CO 2 compression excess heat has not been considered.…”

“…The make up flow rate is very small (0.01 kg fresh Li 4 SiO 4 / kg circulated Li 4 SiO 4 ), so there is no need to use heat exchangers with spent sorbent. That was decided based on the high stability of the sorbent observed during cyclic test of the sorbent under NGCC flue gas absorption condition and oxy-fuel combustion desorption condition as observed by Izquierdo et al…”

Sorbents for the Capture of CO2 and Other Acid Gases: A Review

“…As with single metal oxides, performance improvement strategies, such as the use of reaction mediators, have also been applied to mixed metal oxides. Mixtures of calcium and magnesium oxide, , calcium oxide-based mixtures, − and magnesium oxide-based mixtures , typically display improvements in performance over single metal oxides, as do a number of alkali metal-based oxides such as silicates, − ziconates, − cuprates, , borates, aluminates, and others. − The improvement in cyclic capacity achieved with synthetic mixed metal oxides increases sorbent cost, particularly when lithium is used . In some situations, this trade-off is reasonable, but only if performance under realistic conditions can be demonstrated. , Contamination with SO x will generally require disposal of the sorbent, , which becomes more significant an issue as sorbent cost increases.…”

New Catalytic and Sorption Bifunctional Li6CoO4 Material for Carbon Monoxide Oxidation and Subsequent Chemisorption

“…Carbon oxides (CO and CO 2 ) separation, capture, and catalytic conversion from different composition gas flows have become some of the most important issues from the environmental point of view. , Within this context, in the last two decades, different alkaline and alkaline earth ceramics have been proposed as possible CO 2 capture materials . Calcium oxide (CaO), lithium silicates (Li 4 SiO 4 and Li 8 SiO 6 ), ,− and alkaline zirconates (Li 2 ZrO 3 and Na 2 ZrO 3 ) ,− were proposed as CO 2 chemisorbents at high temperatures, presenting different advantages and disadvantages. However, in recent years, new alkaline ceramics have been proposed for this application. − Some examples include lithium cuprate (Li 2 CuO 2 ), − as well as lithium and sodium ferrites (Li 5 FeO 4 , LiFeO 2 , and NaFeO 2 ), ,− which have shown great properties, mainly due to the redox capacity of the transition metals present in these samples.…”