Experimental and Modeling Studies on High-Temperature Capture of CO2 Using Lithium Zirconate Based Sorbents

Shedding Light on Solid Sorbents: Evaluation of Supported Potassium Carbonate Particle Size and Its Effect on CO2 Capture from Air

Solid sorbents are essential for developing technologies that directly capture CO₂ from air. In solid sorbents, metal oxides and/or alkali metal carbonates such as potassium carbonate (K₂CO₃) are promising active components owing to their high thermal stability, low cost, and ability to chemisorb the CO₂ present at low concentrations in air. However, this chemisorption process is likely limited by internal diffusion of CO₂ into the bulk of K₂CO₃. Therefore, the size of the K₂CO₃ particles is expected to be an important factor in determining the kinetics of the sorption process during CO₂ capture. To date, the effects of particle size on supported K₂CO₃ sorbents are unknown mainly because particle sizes cannot be unambiguously determined. Here, we show that by using a series of techniques, the size of supported K₂CO₃ particles can be established. We prepared size-tuned carbon-supported K₂CO₃ particles by tuning the K₂CO₃ loading. We further used melting point depression of K₂CO₃ particles to collectively estimate the average K₂CO₃ particle sizes. Using these obtained average particle sizes, we show that the particle size critically affects the efficiency of the sorbent in CO₂ capture from air and directly affects the kinetics of CO₂ sorption as well as the energy input needed for the desorption step. By evaluating the mechanisms involved in the diffusion of CO₂ and H₂O into K₂CO₃ particles, we relate the microscopic characteristics of sorbents to their macroscopic performance, which is of interest for industrial-scale CO₂ capture from air.

CO2 Capture at Medium to High Temperature Using Solid Oxide-Based Sorbents: Fundamental Aspects, Mechanistic Insights, and Recent Advances

Carbon dioxide capture and mitigation form a key part of the technological response to combat climate change and reduce CO₂ emissions. Solid materials capable of reversibly absorbing CO₂ have been the focus of intense research for the past two decades, with promising stability and low energy costs to implement and operate compared to the more widely used liquid amines. In this review, we explore the fundamental aspects underpinning solid CO₂ sorbents based on alkali and alkaline earth metal oxides operating at medium to high temperature: how their structure, chemical composition, and morphology impact their performance and long-term use. Various optimization strategies are outlined to improve upon the most promising materials, and we combine recent advances across disparate scientific disciplines, including materials discovery, synthesis, and in situ characterization, to present a coherent understanding of the mechanisms of CO₂ absorption both at surfaces and within solid materials.

New approach to consecutive CO oxidation and CO2 chemisorption using Li2CuO2 ceramics modified with Na- and K-molten salts

The addition of alkali carbonates to Li₂CuO₂ improved the CO oxidation and the subsequent CO₂ with a high ratio of captured/released CO₂. Materials modified with a single carbonate presented the best enhancement for the removal of both CO_X.

Siderite Formation by Mechanochemical and High Pressure–High Temperature Processes for CO2 Capture Using Iron Ore as the Initial Sorbent

Iron ore was studied as a CO2 absorbent. Carbonation was carried out by mechanochemical and high temperature–high pressure (HTHP) reactions. Kinetics of the carbonation reactions was studied for the two methods. In the mechanochemical process, it was analyzed as a function of the CO2 pressure and the rotation speed of the planetary ball mill, while in the HTHP process, the kinetics was studied as a function of pressure and temperature. The highest CO2 capture capacities achieved were 3.7341 mmol of CO2/g of sorbent in ball milling (30 bar of CO2 pressure, 400 rpm, 20 h) and 5.4392 mmol of CO2/g of absorbent in HTHP (50 bar of CO2 pressure, 100 °C and 4 h). To overcome the kinetics limitations, water was introduced to all carbonation experiments. The calcination reactions were studied in Argon atmosphere using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis. Siderite can be decomposed at the same temperature range (100 °C to 420 °C) for the samples produced by both methods. This range reaches higher temperatures compared with pure iron oxides due to decomposition temperature increase with decreasing purity. Calcination reactions yield magnetite and carbon. A comparison of recyclability (use of the same material in several cycles of carbonation–calcination), kinetics, spent energy, and the amounts of initial material needed to capture 1 ton of CO2, revealed the advantages of the mechanochemical process compared with HTHP.

Evaluation of Fe-containing Li2CuO2 on CO2 capture performed at different physicochemical conditions

Li₂CuO₂ and different iron-containing Li₂CuO₂ samples were synthesized by solid state reaction. On iron-containing samples, atomic sites of copper are substituted by iron ions in the lattice (XRD and Rietveld analyses). Iron addition induces copper release from Li₂CuO₂, which produce cationic vacancies and CuO, due to copper (Cu²⁺) and iron (Fe³⁺) valence differences. Two different physicochemical conditions were used for analyzing CO₂ capture on these samples; (i) high temperature and (ii) low temperature in presence of water vapor. At high temperatures, iron addition increased CO₂ chemisorption, due to structural and chemical variations on Li₂CuO₂. Kinetic analysis performed by first order reaction and Eyring models evidenced that iron addition on Li₂CuO₂ induced a faster CO₂ chemisorption but a higher thermal dependence. Conversely, CO₂ chemisorption at low temperature in water vapor presence practically did not vary by iron addition, although hydration and hydroxylation processes were enhanced. Moreover, under these physicochemical conditions the whole sorption process became slower on iron-containing samples, due to metal oxides presence.

Ultrafast Carbon Dioxide Sorption Kinetics Using Morphology-Controllable Lithium Zirconate

It was reported that the main obstacle of Li₂ZrO₃ as high-temperature CO₂ absorbents is the very slow CO₂ sorption kinetics, which are ascribed to the gradual formation of compact zirconia and carbonate shells along with inner unreacted lithium zirconate cores; accordingly, the "sticky" Li⁺ and O^2- ions have to travel a long distance through the solid shells by diffusion. We report here that three-dimensional interconnected nanoporous Li₂ZrO₃ exhibiting ultrafast kinetics is promising for CO₂ sorption. Specifically, nanoporous Li₂ZrO₃ (LZ-NP) exhibited a rapid sorption rate of 10.28 wt %/min with an uptake of 27 wt % of CO₂. Typically, the k₁ values of LZ-NP (kinetic parameters extracted from sorption kinetics) were nearly 1 order of magnitude higher than the previously reported conventional Li₂ZrO₃ reaction systems. Its sorption capacity of 25 wt % within ∼4 min is 2 orders of magnitude faster than those obtained using spherical Li₂ZrO₃ powders. Furthermore, nanoporous Li₂ZrO₃ exhibited good stability over 60 absorption-desorption cycles, showing its potential for practical CO₂ capture applications. CO₂ adsorption isotherms for Li₂ZrO₃ absorbents were successfully modeled using a double-exponential equation at various CO₂ partial pressures.

Insights into the mechanism of the capture of CO2 by K2CO3 sorbent: a DFT study

The adsorption and reactions of CO₂ and H₂O on both monoclinic and hexagonal crystal K₂CO₃ were investigated using the density functional theory (DFT) approach.

Regeneration mechanisms of high-lithium content zirconates as CO2capture sorbents: experimental measurements and theoretical investigations

During absorption/desorption cycles, lithium-rich zirconates (Li₈ZrO₆and Li₆Zr₂O₇) will be consumed and will not be regenerated. Their primary regeneration product is in the form of Li₂ZrO₃. This result indicates that among known lithium zirconates, Li₂ZrO₃is the best sorbent for CO₂capture.