Salt-Composition-Controlled Precipitation of Triple-Salt-Promoted MgO with Enhanced CO₂ Sorption Rate and Working Capacity

Triple-salt-promoted MgO composites (NaNO_3, Na₂CO₃, and LiNO₃) for precombustion CO₂ capture were developed by a precipitation method with a controllable salt composition. MgO precursors were mixed and aged with salts to control the composition and morphology. The MgO composites exhibited a CO₂ sorption capacity of 73 wt % in pure CO₂ at 240 min and 300 °C and achieved a sorption capacity of 25 wt % within 10 min because of a high sorption rate. When a cyclic test was conducted with pure CO₂ sorption for 60 min at 325 °C and N₂ regeneration for 15 min at 425 °C (60/15 min cycle) as a reference, the cyclic capacity was 45 wt % after 30 cycles. On the other hand, considering the applicable capture processes, the sorption capacity during a fast cycle (10/5 min cycle) was 18 wt % under the same gas and temperature conditions. Finally, the working capacity of the MgO composite was evaluated under a simulated emission gas (29% CO₂, 3% H₂O, and balance N₂) at 300 °C for sorption and CO₂ at 450 °C for regeneration because of the importance of water vapor and CO₂ regeneration in the evaluation. The rearrangement of the salts and the MgO grains during the initial cycles led to an enhanced working capacity. However, the working capacity declined along the subsequent cycles due to sintering, and it was severe under CO₂ regeneration. However, the working capacity for the wet mixture sorption and CO₂ regeneration stabilized after 20 cycles at 23 and 4.6 wt % for 60/15 min and 10/5 min cycles, respectively. The results indicate that the as-synthesized MgO composites are feasible for the practical application of precombustion CO₂ capture.