Comparison of CaO-Based Synthetic CO₂Sorbents under Realistic Calcination Conditions

Abstract

Several concepts to capture CO 2 in power plants and hydrogen generation plants are under development using CaO as regenerable sorbent. The drastic decay in sorbent capture capacity of CaO obtained through calcination of natural sources of CaCO 3 (limestones or dolomites) justifies the search of synthetic sorbents that aim to overcome this decay in capture capacity. We have reviewed some of the recent literature on the subject and tested some of the proposed sorbents under comparable conditions. Our results confirm the good performance of some of these synthetic sorbents under mild conditions and/or long carbonation times used in the original references. However, we show that these sorbents deactivate also very quickly when realistic regeneration conditions (high temperatures for calcination at high partial pressures of CO 2 ) are used in the laboratory test. We conclude that none of the reviewed sorbents have a chance to compete with the performance of natural limestones, of much lower cost.

Adsorbent Materials for Carbon Dioxide Capture from Large Anthropogenic Point Sources

“…The direction of these research efforts can be categorized into four different strategies, (1) techniques using rigid supports, (2) use of additives (3) preparation of nanoparticles, and (4) use of different synthetic precursors. [131] The first method is based on the concept of employing a rigid porous material as a carrier or a matrix for the calcium oxide species. For example, Feng prepared very fine calcium oxide particles in an inert porous alumina support that preserved a high conversion of over 90 % after 9 cycles of carbonation and decarbonation ( Figure 25).…”

“…[141] Similarly, Grassa indicated that synthetic precursors including CaA C H T U N G T R E N N U N G (CH 3 COO) 2 , CaC 2 O 4 , and Ca(OH) 2 , produced adsorbents with little differences in adsorbent regenerability from natural limestones, if tested under realistic calcination conditions ( Figure 26). [131] 2.2.1.6. Magnesium oxides Besides calcium oxide, other alkaline earth metal oxides such as magnesium oxide have been investigated as adsorbents for CO 2 .…”

“…[129][130][131] It was also suggested that since physisorption of H 2 O on the surface is unlikely to happen at these temperatures, adsorption of H 2 O by LDO can be attributed to chemisorption by the production of hydroxides in the following manner:…”

“…[130] The utility of calcium oxide based adsorbents in high temperature applications has lead to a wide array of reports of these materials for other CO 2 separations, such as capture from flue gas. [131,132] In large-scale CO 2 capture applications, these materials are thought to be advantageous compared to other adsorbents on account of the low cost and wide availability of precursors such as limestones or dolomites. [130] 2.2.1.2.…”

CO2 capture by calcium aluminate pellets in a small fluidized bed

“…These precursors have been shown to give a CaO of a very high porosity and surface area [8,9]. Grasa et al [10] reported that the benefit of many of these type of sorbents was significantly reduced under realistic conditions, i.e., higher temperatures and CO2 concentration in the calcination stage, over many cycles. This is likely a result of a very rapid reduction in surface area and porosity, as CaO sinters significantly more rapidly above 900 °C [11].…”