Na2CO3-doped CaO-based high-temperature CO2 sorbent and its sorption kinetics

Peering into buried interfaces with X-rays and electrons to unveil MgCO 3 formation during CO 2 capture in molten salt-promoted MgO

“…Owing to the impressive effect of molten AMS on the CO2 uptake of bare MgO, the elucidation of the underlying promoting mechanism(s) has been the aim of a series of studies that have led to the postulation of a number of working hypotheses (13,14,17,(19)(20)(21)(22)(23). For example, combining thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR) and X-ray powder diffraction (XRD), it has been proposed that the addition of AMS promotes the CO2 uptake of MgO through the following two effects.…”

Mechanistic Understanding of CaO‐Based Sorbents for High‐Temperature CO2 Capture: Advanced Characterization and Prospects

“…[15][16][17][18][19][20] A number of approaches have been proposed to improve the cyclic stability and residual CO 2 uptake capacity of CaO-based sorbents, including the addition of promoters or stabilizers as well as the micro-and nanostructuring of the sorbents. [16][17][18][21][22][23][24][25][26] Several reviews have summarized the engineering strategies to promote or stabilize the CO 2 uptake. [9,12,27] However, our fundamental knowledge of the underlying mechanisms that control the CO 2 uptake characteristics of CaO is limited.…”

“…(a) In-situ XRD of Na 2 CO 3 -wet-impregnated CaO between 25°C and 800°C (b) Proposed formation mechanism of Na 2 Ca(CO 3 ) 2 . Adapted with permission from Ref [22]…”

CO2 capture using solid sorbents: Fundamental aspects, mechanistic insights and recent advances

“…Importantly, single alkali metal carbonates (specifically Na2CO3 and K2CO3) readily react with CaO and CO2 under typical carbonation conditions, forming alkali metal-Ca double carbonates (e.g. Na2Ca(CO3)2 or K2Ca(CO3)2) [319]-[321]. The very fast formation of such Na/K-Ca carbonates (the double salts or double carbonates) appears to depend on surface area to a much lesser extent than does the formation of CaCO3 from CaO.Double carbonates have similar melting temperatures as the single alkali metal carbonates, butpossess different thermodynamic properties: in a N2 atmosphere, they decompose to CaO and the single alkali metal carbonate at temperatures similar to, or even lower than, CaCO3, whereas in a CO2 atmosphere, they do not decompose even when they reach their melting point (in contrast to many Mg-based double carbonates[322]-[325]).…”

“…The very fast formation of such Na/K-Ca carbonates (the double salts or double carbonates) appears to depend on surface area to a much lesser extent than does the formation of CaCO3 from CaO.Double carbonates have similar melting temperatures as the single alkali metal carbonates, butpossess different thermodynamic properties: in a N2 atmosphere, they decompose to CaO and the single alkali metal carbonate at temperatures similar to, or even lower than, CaCO3, whereas in a CO2 atmosphere, they do not decompose even when they reach their melting point (in contrast to many Mg-based double carbonates[322]-[325]). Double carbonates have therefore been used as sorbents for CO2 achieving higher cyclic CO2 uptake capacities than those that were observed for the reference CaO sorbent even at lower sorption temperatures[321],[326];the regeneration of the sorbents was always performed under N2. Other studies utilized the low eutectic temperatures of the carbonate mixtures to fabricate sorbents coated with molten salts under reaction conditions [327]a similar approach to what is typically employed to enable fast sorption rates for MgO-based sorbents (Section 3.2).The rate and extent of CO2 uptake under pure CO2 was found to be highest when the binary or ternary alkali metal carbonates were molten at the carbonation temperatures > 600 °C.…”