Magnesite-derived MgO promoted with molten salts and limestone as highly-efficient CO2 sorbent

Abstract

This study evaluated the CO2 capture performance of MgO obtained from mineral magnesite and doped with limestone and molten Li, Na and K nitrates under consecutive sorption/desorption cycles via thermogravimetric analysis. Increasing the molten promoter loading resulted in a higher CO2 sorption rate, while elevated CaCO3 amounts impeded CO2 diffusion. When exposed to a 30 % CO2 flow at 300 °C for 30 min, the sorbent with alkali salts and CaCO3 to MgO molar ratios of 0.20 and 0.05 respectively attained a capture of 7.2 mol CO2/kg of sorbent and a negligible activity loss (∼6%) after 50 cycles. This performance was promising, considering the mineral nature of precursors. In-situ X-ray diffraction revealed the growth of the MgO crystal after each desorption, proving the gradual MgO sintering. However, the morphological transformations occurring during cyclic operation and especially if high conversions of MgO are reached, trigger an alkali salt redistribution that grants high stability.