Unravelling the role of alkaline earth metal carbonates in intermediate temperature CO2 capture using alkali metal salt-promoted MgO-based sorbents

Abstract

Alkali metal salt (AMS)-promoted MgO sorbents are promising for intermediate temperature CO₂ capture due to their high capacity, but suffer from slow sorption kinetics and poor stability which hinder their applications. Herein, we report that incorporation of alkaline earth metal carbonates (CaCO₃, SrCO₃ or BaCO₃) into AMS-promoted MgO can improve the CO₂ capture performance of the sorbent in multiple sorption/desorption cycles. Experimental studies reveal that CaCO₃ and BaCO₃ participate in MgO carbonation with fast and reversible formation of dolomite and norsethite, respectively, thus resulting in a rate enhancement, while SrCO₃ is inert for CO₂ sorption but acts as a stabilizer to prevent sintering of MgO particles and in turn improve the sorbent stability. Kinetic studies show that the activation enthalpy of sorption at the surface reaction-controlled stage is 36.9, 28.1, 35.3, and 30.6 kJ mol⁻¹ for AMS-MgO and AMS-MgO doped with CaCO₃, SrCO₃ and BaCO₃, respectively, which agrees well with the rate enhancement of the CaCO₃- or BaCO₃-doped sorbent. This discovery offers new opportunities to develop high-performance MgO-based CO₂ sorbents by doping with alkaline earth metal carbonates.