Facile synthesis of hierarchically porous MgO sorbent doped with CaCO₃ for fast CO₂ capture in rapid intermediate temperature swing sorption

For CO₂ sorbents, a fast sorption rate is as important as the sorption capacity in order to enable efficient CO₂ capture in the treatment of large amounts of emission gas, where the contact time between the sorbent and gas is limited. A facile and environmentally benign method of fabricating advanced sorbents with fast CO₂ sorption for pre-combustion capture was developed by incorporating CaCO₃ into triple salt-promoted MgO sorbents (LiNO₃, NaNO₃, and Na₂CO₃) using salt-controllable coprecipitation. The incorporation of Ca into the salt-promoted MgO (MgCa) was effective for controlling the lattice parameter, textural properties, and basicity. The salt-promoted MgCa sorbents had a bi-disperse pore distribution with different range, which contributed to the fast sorption. When 5 mol.% of Ca was doped into the triple salt-promoted MgO, the CO₂ sorption capacity within 10 min was significantly improved (from 6 wt% (MgO) to 43 wt% (MgCa-5%)) at 325 °C. For CO₂ sorption for 10 min at 325 °C and N₂ regeneration for 5 min at 400 °C, the working capacity of MgCa-5% was approximately 30 wt% at the 30 th cycle. Under the same rapid cycling conditions, the sorption capacity was 12 wt% when a wet CO₂ mixture (29 vol% CO₂, 3 vol% H₂O, and balance N₂) and pure CO₂ was used for sorption and regeneration, respectively. When the regeneration gas contained water vapour, the cyclic sorption capacity decreased to 1–2 wt%. The MgCa sorbents prepared via salt-controllable coprecipitation exhibited high working capacities during the rapid cyclic temperature swing operation at intermediate temperature.