Open Access

ARTICLE

CO₂ Capture Performance of CaO in Molten NaCl-CaCl₂: Effect of Operating Parameters and KCl Modification of Molten Salt

Yinan Li^1,#, Zhenyu Song ^2,#, Xing Xie¹, Dan Lin¹, Zhentao Wang^1,*, Bin Li^1,3,*
1 School of Energy and Power Engineering, Jiangsu University, Zhenjiang, China
2 Shunde Branch, Guangdong Institute of Special Equipment Inspection and Research, Shunde, China
3 School of Engineering, Anhui Agricultural University, Hefei, China
* Corresponding Author: Zhentao Wang. Email: ; Bin Li. Email:
# These authors contributed equally to this work

Energy Engineering https://doi.org/10.32604/ee.2026.082784

Received 23 March 2026; Accepted 13 May 2026; Published online 15 June 2026

Abstract

Dissolving CaO into molten salts can overcome its structural collapse and thermal sintering issues during CO₂ capture by constructing a homogeneous liquid reaction environment. Herein, a molten CaO/NaCl-CaCl₂ system was developed, and the effects of operating parameters and KCl addition on its CO₂ capture performance were systematically investigated. Compared with solid CaO, molten NaCl-CaCl₂ significantly boosted the CO₂ capture capacity of CaO. CaO was fully dissolved in molten NaCl-CaCl₂ at 600°C–700°C and dissociated into Ca²⁺ and mobile alkaline O²⁻, forming a uniform liquid ionic environment for CO₂ capture, where O²⁻ anions served as active sites for CO₂ conversion to CO₃²⁻. The marked enhancement of CO₂ capture of CaO in molten NaCl-CaCl₂ was attributed to eliminated sorbent sintering, accelerated interfacial O²⁻ transport, and bypassed CaCO₃ layer barrier, with the molten salt exhibiting high stability and uniform dispersion of CaO/CaCO₃ during the process. 650°C, 200 mL·min⁻¹ 10% CO₂/Ar gas, and 10 wt.% CaO relative to molten salt were identified as the favorable operating parameters under the testing conditions, achieving a CO₂ uptake of 14.42 mmol·g⁻¹ and CaO conversion rate of 80.73%. This condition balanced CO₂ capture kinetics, interfacial O²⁻/CO₂ transfer, and CO₃²⁻ stability in Molten salt; excess temperature aggravated carbonate decomposition, while improper gas flow rate or CaO loading reduced efficiency. The addition of 10 wt.% KCl further improved the capture performance by lowering molten salt viscosity and promoting O²⁻ migration, especially relieving O²⁻ depletion in the mid-late capture stage to sustain interfacial activity, lifting CO₂ uptake to 15.56 mmol·g⁻¹ and CaO conversion rate to 86.56%. This study demonstrates that molten NaCl-CaCl₂ integrated with compositional tuning is an effective strategy for enhancing CaO-based high-temperature CO₂ capture.

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Keywords

CO₂ capture; CaO; molten salt; NaCl-CaCl₂; KCl

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