Performance Enhancement of Calcium Oxide Sorbents for Cyclic CO₂ Capture—A Review

Abstract

While calcium oxide has been identified to be the best candidate for capturing CO 2 at high temperature, it suffers a well-known problem of loss-in-capacity; that is, its capacity for carbon capture decays dramatically during cyclic carbonation/ calcination processes. Recently, extensive research work has been conducted on the enhancement of the cyclic performance of calcium oxide through either improving the performance of natural minerals, such as water/steam hydration and pretreatment or modification of calcium oxide sorbents by some techniques such as doping and synthesis. This work summarizes the state-of-theart research in the literature aiming to identify potential solutions to the loss-in-capacity problem. It is found that hydration during or after calcination is effective in recovering the capacity of natural minerals and mixing can produce highly effective synthetic sorbents. Periodic hydration of synthetic sorbents could be a good strategy to overcome the technical issues associated with loss-in-capacity while meeting the requirements of the physical properties of sorbents in many potential applications.

Multicyclic conversion of limestone at Ca-looping conditions: The role of solid-sate diffusion controlled carbonation

“…Current directions of research aimed at this goal are the modification/synthesis of Ca-based sorbents [16,17] and reactivation of natural limestone either by steam [18,19] or heat pretreatment [20][21][22][23][24][25][26][27][28]. Lysikov et al…”

CO2 multicyclic capture of pretreated/doped CaO in the Ca-looping process. Theory and experiments

“…CaO sintering causes a decrease of the available surface area for fast carbonation, which leads to a decrease of short-timed conversion in the successive carbonation. The addition of dopants, with higher thermal stability, is a direction of research to improve the regenerability of limestones (see [14,15] for recent reviews). CaO synthetic sorbents have been also formulated by using dopants that increase the affinity towards CO 2 such as alkali metals [16].…”

CO2 capture by calcium aluminate pellets in a small fluidized bed

“…This is the result of a combination of high temperature and reactive sintering processes, side reactions with sulphurous gases and ash, as well as loss from reaction systems (typically fluidized beds) through attrition. As a result, several methods of sorbent enhancement, including synthetic sorbents, have been proposed [2][3][4], which may offer reduced decay rates in reactivity or increased resistance to attrition. Use of synthetic sorbents may have an initial energy penalty in production, with long-term benefits in terms of reduction of sorbent requirement.…”

“…One of the most studied supports is Al2O3, which thermodynamically will form the inert-to-CO2 mayenite (Ca12Al14O33) upon reaction with CaO [12,13], though there are kinetic reasons why this may not form rapidly -or, e.g., in the first few cycles of carbonation and calcination [14]. Other proposed supports include: MgO [15,16], in analogy with enhancements seen with natural dolomite over natural limestone [17], which does not form mixed metal oxides with CaO [3]; SiO2, which forms mixed metal oxides with CaO [18], has a relatively low sintering temperature, but phase change materials have the potential to increase the porosity upon calcination [19]; amongst others such as ZrO2, CeO2, TiO2/CaTiO3, CuO, CoO, BaO and Cr2O3 [3,4].…”