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

Carbon dioxide capture and storage technologies are short to mid‐term solutions to reduce anthropogenic CO2 emissions. CaO‐based sorbents have emerged as a viable class of cost‐efficient CO2 sorbents for high temperature applications. Yet, CaO‐based sorbents are prone to deactivation over repeated CO2 capture and regeneration cycles. Various strategies have been proposed to improve their cyclic stability and rate of CO2 uptake including the addition of promoters and stabilizers (e. g., alkali metal salts and metal oxides), as well as nano‐structuring approaches. However, our fundamental understanding of the underlying mechanisms through which promoters or stabilizers affect the performance of the sorbents is limited. With the recent application of advanced characterization techniques, new insight into the structural and morphological changes that occur during CO2 uptake and regeneration has been obtained. This review summarizes recent advances that have improved our mechanistic understanding of CaO‐based CO2 sorbents with and without the addition of stabilizers and/or promoters, with a specific emphasis on the application of advanced characterization techniques.ISSN:1864-564XISSN:1864-563

Analysis of the structural dynamics in a NaNO3-promoted MgO-based CO2-sorbent during cyclic operation: an in situ time-resolved X-ray powder diffraction study

ISSN:0021-8898ISSN:1662-534XISSN:1662-535

Experimental data supported techno-economic assessment of the oxidative dehydrogenation of ethane through chemical looping with oxygen uncoupling

Ethylene is an essential building block in the petrochemical industry and it is almost exclusively produced via ethane steam cracking, a well-established albeit highly energy and carbon dioxide intensive process. The oxidative dehydrogenation of ethane is a promising alternative to steam cracking reactions due to its exothermic nature, which decreases the overall energy requirements and carbon footprint. The need of a capital intensive air separation unit for producing oxygen limits its potential for industrial application. The current study investigates an alternative route, i.e. the production of oxygen via chemical looping, where oxygen is released in-situ by suitable oxygen carriers. The chemical looping oxidative dehydrogenation, supported by original experimental data, and the steam cracking processes are simulated with ASPEN Plus®. A comprehensive analysis of the energy requirements and an economic assessment are carried out for both processes. Compared with state-of-the-art ethane steam cracking, the proposed process provides ~28% energy savings per tonnes of ethylene produced and ~21% reduction in the resulting ethylene price. Sensitivity analysis show that the economy of the chemical looping oxidative dehydrogenation process is strongly sensitive to the feedstock price.ISSN:1364-032

Deciphering the structural dynamics in molten salt–promoted MgO-based CO2 sorbents and their role in the CO2 uptake

The development of effective CO2 sorbents is vital to achieving net-zero CO2 emission targets. MgO promoted with molten salts is an emerging class of CO2 sorbents. However, the structural features that govern their performance remain elusive. Using in situ time-resolved powder x-ray diffraction, we follow the structural dynamics of a model NaNO3-promoted, MgO-based CO2 sorbent. During the first few cycles of CO2 capture and release, the sorbent deactivates owing to an increase in the sizes of the MgO crystallites, reducing in turn the abundance of available nucleation points, i.e., MgO surface defects, for MgCO3 growth. After the third cycle, the sorbent shows a continuous reactivation, which is linked to the in situ formation of Na2Mg(CO3)2 crystallites that act effectively as seeds for MgCO3 nucleation and growth. Na2Mg(CO3)2 forms due to the partial decomposition of NaNO3 during regeneration at T ≥ 450°C followed by carbonation in CO2.ISSN:2375-254

Yolk-shell-type CaO-based sorbents for CO2 capture: assessing the role of nanostructuring for the stabilization of the cyclic CO2 uptake

ISSN:2040-3364ISSN:2040-337

Structure of Na Species in Promoted CaO-Based Sorbents and Their Effect on the Rate and Extent of the CO2 Uptake

To advance CaO-based CO2 sorbents it is crucial to understand how their structural parameters control the cyclic CO2 uptake. Here, CaO-based sorbents with varying ratios of Na2CO3:CaCO3 are synthesized via mechanochemical activation of a mixture of Na2CO3 and CaCO3 to investigate the effect of sodium species on the structure, morphology, carbonation rate and cyclic CO2 uptake of the CO2 sorbents. The addition of Na2CO3 in the range of 0.1–0.2 mol% improves the CO2 uptake by up to 80% after 10 cycles when compared to ball-milled bare CaCO3, while for Na2CO3 loadings >0.3 mol% the cyclic CO2 uptake decreases by more than 40%. Energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy, X-ray absorption spectroscopy (XAS), and 23Na MAS NMR, reveal that in sorbents with Na2CO3 contents 100 nm, and enhance the diffusion of CO2 through CaCO3. For Na2CO3 contents >0.3 mol%, the accelerated deactivation of the sorbents via sintering is related to the formation of crystalline Na2Ca(CO3)2 and the high mobility of Na.ISSN:1616-3028ISSN:1616-301