CaO‐Based CO₂ Sorbents: From Fundamentals to the Development of New, Highly Effective Materials

Abstract

The enormous anthropogenic emission of the greenhouse gas CO2 is most likely the main reason for climate change. Considering the continuing and indeed growing utilisation of fossil fuels for electricity generation and transportation purposes, development and implementation of processes that avoid the associated emissions of CO2 are urgently needed. CO2 capture and storage, commonly termed CCS, would be a possible mid-term solution to reduce the emissions of CO2 into the atmosphere. However, the costs associated with the currently available CO2 capture technology, that is, amine scrubbing, are prohibitively high, thus making the development of new CO2 sorbents a highly important research challenge. Indeed, CaO, readily obtained through the calcination of naturally occurring limestone, has been proposed as an alternative CO2 sorbent that could substantially reduce the costs of CO2 capture. However, one of the major drawbacks of using CaO derived from natural sources is its rapidly decreasing CO2 uptake capacity with repeated carbonation-calcination reactions. Here, we review the current understanding of fundamental aspects of the cyclic carbonation-calcination reactions of CaO such as its reversibility and kinetics. Subsequently, recent attempts to develop synthetic, CaO-based sorbents that possess high and cyclically stable CO2 uptakes are presented.

CaO‐Based CO2 Sorbents Effectively Stabilized by Metal Oxides

“…However,C aO-based sorbents suffer from poor cyclic stabilityover multiple carbonation/calcination (i.e.,C O 2 capture andr egeneration) cycles,w hich is believed to stem from the severe sintering of CaCO 3 .T he Ta mmann temperature (T T )o fC aCO 3 ( % 533 8C) is significantly below the operating temperatures (i.e., % 650 8Cf or carbonation, and % 900 8Cf or regeneration) of the process. [4,5] To improve the CO 2 capture performance of limestone-derived sorbents, various methodsi ncluding hydration [6] and thermalt reatment [7] have been proposed.A lthough these approachesi mprovet he CO 2 uptake performance of limestonederived CaO, the materials still undergo as ignificant degree of deactivation with cycle number.A na lternative to enhance the cyclic stabilityo fC aO-based CO 2 sorbents relies on the incorporationo fs tabilizers with high T T ,s uch as the oxides of Al, Mg, Yo rZ r, intot he CaO framework. [5] The main purpose of the addition of ah igh-T T material is to increase the overall thermals tability of the sorbenta nd thus, minimize the sintering-induced loss of the CO 2 capturec apacity under the harsh operating conditions.…”

“…[4,5] To improve the CO 2 capture performance of limestone-derived sorbents, various methodsi ncluding hydration [6] and thermalt reatment [7] have been proposed.A lthough these approachesi mprovet he CO 2 uptake performance of limestonederived CaO, the materials still undergo as ignificant degree of deactivation with cycle number.A na lternative to enhance the cyclic stabilityo fC aO-based CO 2 sorbents relies on the incorporationo fs tabilizers with high T T ,s uch as the oxides of Al, Mg, Yo rZ r, intot he CaO framework. [5] The main purpose of the addition of ah igh-T T material is to increase the overall thermals tability of the sorbenta nd thus, minimize the sintering-induced loss of the CO 2 capturec apacity under the harsh operating conditions. However,t he stabilizers are typically inactive for CO 2 capture under the operating conditions of the process and reduce, thus, the maximal CO 2 uptake capacity of the material on aw eight basis.…”

“…[5,[8][9][10][11] Turning to materials ynthesis techniques, in most of the works reported so far," conventional" approaches including mechanical mixing, wet impregnation, or co-precipitation have been used to introduce the stabilizer into the CaO matrix. [12][13][14] The main issue associated with these preparation techniques is that they do not provide materials with enhanced structural properties, such as high pore volume and surface area, which are criticalt oo btain high CO 2 uptakes.F urthermore, most conventional techniques can only provide al imited degree of homogeneity in terms of mixing between the active materiala nd the stabilizer.A saresult, larger quantities of the stabilizer are Calcium looping( i.e.,C O 2 captureb yC aO) is ap romising second-generation CO 2 capture technology.C aO, derived from naturallyo ccurring limestone, offersa ni nexpensives olution, but due to the harsh operating conditions of the process, limestone-derived sorbents undergo ar apid capacity decay induced by the sintering of CaCO 3 .H ere, we report aP echini methodt os ynthesize cyclically stable, CaO-based CO 2 sorbents with ah igh CO 2 uptake capacity.T he sorbents synthesized feature compositional homogeneity in combination with an anostructured and highly porous morphology.…”

Energy and exergy pertaining to solid looping cycles

“…Thus, intensive research has been focused on the reactivation of CaO and the development of routes to obtain more stable CaO-based CO 2 sorbents. The development of methods and modified CaO precursors to mitigate the decay of capture capacity is desired to facilitate the scale-up of this technology (Arias, Grasa, Alonso, & Abanades, 2012;Kierzkowska, Pacciani, & M€ uller, 2013;Manovic & Anthony, 2008;Valverde, Sanchez-Jimenez, & Perez-Maqueda, 2014). Those techniques more widely presented in literature are steam reactivation (Arias, Grasa, & Abanades, 2010;Fennell, Davidson, Dennis, & Hayhurst, 2007;Hughes, Lu, Anthony, & Wu, 2004;Manovic & Anthony, 2007), preactivation (Blamey et al, 2010), selfreactivation effect (Manovic & Anthony, 2008), sorbent doping (Al-Jeboori, Nguyen, Dean, & Fennell, 2013), synthetic sorbents (Abanades et al, 2004;Blamey et al, 2010;Manovic & Anthony, 2008) and recarbonation (Arias et al, 2012;Valverde et al, 2014).…”

In situstudies of materials for high-temperature CO2capture and storage

“…Cycling studies of natural limestone show its capacity to reduce by as much as 90 mol% aer only the rst 20 cycles owing to sintering. 5 While one focus of recent research has been to alter the properties of CaO through synthetic methods with different additives such as Al 3 O 3 , Ca 12 Al 14 O 33 , or SiO 2 , [6][7][8] there is still a fundamental lack of understanding regarding how the carbonation reaction proceeds and what parameters control the function of absorbent materials.…”