CO2 Sorbent Research Articles

Efficient Selective CO2 Composite Sorbent from Amino Acid Ionic Liquids and Silica Gel: 2H NMR Spectroscopy Provides Insight on the CO2-Binding Mechanism and in-Pore Microscopic Viscosity.

A promising CO2 sorbent based on the [Emim][Gly] (1-ethyl-3-methylimidazolium glycinate)/silica gel composite has been studied. CO2 sorption experiments have shown that the optimum loading of [Emim][Gly] ionic liquid in silica gel is 40 wt.%. The 2-step process CO2 binding mechanism in [Emim][Gly] has been proposed based on the results of sorption experiments, 2H NMR spectroscopy and ab-initio calculations. The impact of CO2 on the microscopic viscosity and the dynamical melting of ionic liquid has been thoroughly investigated. 2H NMR spectroscopy has revealed that CO2 strongly binds cation and anion in [Emim][Gly], forcing them to move in a correlated fashion.

Molecule‐level Design to Form Pocket Structures for Improving Amine Efficiency in CO2 Capture

AbstractSolid amine adsorbents represent a promising class of CO2 sorbents, but their amine efficiency is limited by the inaccessibility of peripheral amines. The surface of mesocellular silica foam (MCF) is functionalized with the mixture of short‐chain 3‐Glycidyloxypropyl) triethoxysilane (GPTES) and long‐chain Octadecyltrimethoxysilane (OTMS), forming pocket structures on the support surface, thereby exposing more amine sites and enhancing the amine efficiency of polyethylenimine (PEI). The resulting adsorbent demonstrates a high CO2 adsorption capacity (5.02 mmol g−1 at 50 °C, 10 vol.% CO2, and 50%RH), high amine efficiency (0.43 at the dry condition), outstanding cyclic stability (0.5% performance decline per cycle under the conditions of dry CO2 regeneration), and fast adsorption kinetics (15 min for adsorption saturation at 50 °C). First‐principles calculations and CO2 temperature‐programmed desorption (TPD) experiments demonstrate that the introduction of GPTES and OTMS is beneficial to decreasing adsorption energy and forming paired carbamic acid states and ammonium carbamate states.

Synthesis of highly stable Li4SiO4-based CO2 sorbents using polysilicon by-product SiCl4 as raw material

With the rapid development of the photovoltaic industry, the demand for polysilicon has been continuously increasing. In the production of polysilicon, a large amount of SiCl4 will inevitably be produced as a by-product. Proper treatment of this SiCl4 is crucial for reducing environmental pollution and controlling the production costs of polysilicon. In this study, a by-product of polysilicon production SiCl4 was utilized as a silicon source to synthesize the high-temperature CO2 sorbent Li4SiO4. The effects of SiCl4 content in the precursor solution and CO2 volume concentration on the adsorption performance of the sorbents were thoroughly investigated. The results showed that Li4SiO4-x (x = 0.5, 1.5, and 2.5) exhibited excellent adsorption performance and cyclic stability under 100 vol% CO2 atmosphere, with adsorption capacities of 26.29, 29.66, and 34.04 wt% after 15 cycles, respectively. Additionally, the study found that as the CO2 concentration decreased from 100 vol% to 50 vol% and 15 vol%, the adsorption equilibrium temperature showed a slight shift to the left, and the adsorption capacity also decreased to varying degrees, but the material maintained good cycle stability throughout the process. In summary, the synthesis of Li4SiO4 from SiCl4 has broad application prospects.

Aluminum-enhanced Ca-based CO2 sorbents: Core-shell assembly and the impact of stabilizer precursors

Lately, Ca-based sorbents with a core–shell structure have been effectively produced to augment the sorbent’s capabilities. However, modifying the pristine core of Ca-based pellets with a core–shell structure notably influences the performance of the synthesized sorbent, and research in this domain remains scarce. Here, two categories of Al-stabilized, Ca-based pristine cores were produced using Ca(OH)2 mixed with Al-based stabilizer precursors of insoluble aluminum oxide and soluble aluminum nitrate, respectively, through the extrusion-spheronization technique. Due to the impact of mechanical extrusion, soluble aluminum nitrate can accumulate in-homogeneously in the Ca-based pristine core, leading to its expansion and rupture during the high-temperature calcination stage because of the decomposition of aluminum nitrate. The oxide-form aluminum stabilizer precursor can be uniformly distributed throughout the Ca-based pristine core pellets, demonstrating notably superior cyclic CO2 sorption capability and mechanical strength. The Al-fortified, core–shell structured Ca-based sorbent pellets demonstrated a peak CaO carbonation conversion rate of 54.8 % after 100 cycles when the Ca:Al molar ratio was precisely set to 85:15, which is about 2.1 times higher compared to the core–shell Ca-based sorbent pellets composed of a pure CaO core. This is primarily due to the formation of an evenly distributed inert Ca12Al14O33 within the pristine core, which effectively reduces high-temperature sintering. Hence, core–shell Ca-based sorbent pellet assembled with an Al-stabilized pristine core, could be a promising candidate for application in the CaL process for CO2 capture.

Study on the arrangement of CO2 sorbent and catalyst for integrated CO2 capture and methanation

Integrated CO2 capture and utilization (ICCU) is an emerging technology to reduce CO2 emissions by greatly simplifying the processes of conventional CO2 capture and utilization. In particular, ICCU-methanation could directly convert the low-concentration CO2 into CH4 using hydrogen from new energy electricity, representing an efficient Power-to-Gas route. CO2 adsorption/catalytic materials play a crucial role for the operation of ICCU-methanation, and it is more feasible to scale up material production and avoid components interference by directly combining the sorbent and catalyst. However, it is necessary to reveal the effect of different arrangements of sorbent and catalyst on reaction characteristics of ICCU-methanation. In the work, the matching of K2CO3-doped Li4SiO4 sorbent with various supported Ni-based catalyst was tested and four arrangements of sorbent and catalyst particles in a fixed-bed were investigated to understand the influences on ICCU-methanation. Results show that the presence of catalyst accelerates CO2 supply by sorbent and achieves quicker methanation, and the promotion effect becomes more obvious with a closer contact between the sorbent and catalyst. Under optimized conditions, ICCU-methanation of uniformly mixed K-Li4SiO4 and Ni/Al2O3 shows an excellent performance with very stable CO2 conversion of 95.58% and CH4 selectivity of 93.29% during cyclic reactions.

Comprehensive performance evaluation of HVAC systems integrated with direct air capture of CO2 in various climate zones

Direct Air Capture (DAC) is a rapidly evolving technology that extracts CO2 directly from ambient air. This study presents a comprehensive performance evaluation of integrating DAC in HVAC systems, which can reduce indoor CO2 concentration and improve energy efficiency of HVAC systems. The DAC equipment is modeled in Modelica based on isotherm and thermodynamic equations, and pressure drop curves of the CO2 sorbent described in literature. The model is validated with data from the literature, and then integrated into a typical HVAC system available in Modelica Buildings library. The HVAC system is a Variable Air Volume (VAV) with reheater system for a one-floor office building with standard ASHRAE 2006 control sequences. Demand control ventilation strategies are designed to reduce the outdoor air flowrates when indoor CO2 concentrations are lower than the threshold, which is to maximize the benefits of integrating DAC. Four cases are proposed to assess the impacts of integrating DAC and DCV in HVAC systems in 8 different ASHRAE climate zones in the USA. The results show that by integrating DAC unit into the HVAC system, the average indoor CO2 concentration can be significantly reduced by over 45 % against the baseline without a DAC unit. By integrating DCV, 0.39–21.66 % of annual energy savings and 226–9539 kg carbon emissions reduction are observed across different climate zones. The highest energy savings are found to be achieved with cold climatic conditions while the lowest energy savings occur with favorable weather.

Enhanced CO2 capture by functionalization of SBA-15 with APTES and l-lysine

In this study, amine-based CO2 sorbents were synthesized after functionalizing SBA-15 mesoporous materials. Mesoporous SBA-15 was characterized and functionalized by APTES as an alkanolamine, L-lysine as an amino acid and a combination of both. CO2 adsorption tests were performed at 1.6 and 2 bar to estimate the carbon dioxide (CO2) uptake on the sorbents. As expected, CO2 adsorption capacity (mmol/g) increases with pressure. Based on the elemental analysis of the sorbents and the results of Fourier transform infrared spectroscopy (FTIR), a proposal was made of the possible chemical reactions that may occur in order to describe the experimental results. It is important to mention that the pretreatment prior to the CO2 adsorption tests plays a key role for the application of amine-functionalized mesoporous silica. The presence of water conditions the formation of carbonic acid and carbonate adsorbed on the surface and, consequently, the CO2 adsorption capacity of the sorbent. APTES and l-lysine loaded onto mesoporous SBA-15 exhibited the highest CO2 adsorption capacity (4.53 mmol/g) at 2 bar and room temperature. After reloading the sorbents with APTES and Lysine, no improvements in the CO2 absorption capacity were observed.

Completely sealed direct carbon solid oxide fuel cell with in situ steam-carbon gasification reaction

Direct carbon solid oxide fuel cells (DC-SOFCs) offer the potential for clean and efficient conversion of chemical energy in carbon fuels into electricity. However, the reverse Boudouard gasification of carbon requires a high operating temperature (≥800 °C), which hinders the development of DC-SOFCs. We present a completely sealed DC-SOFC with in situ steam-carbon gasification. The cells have a symmetrical cell structure (Ag–Ce0.8Gd0.2O1.9/La0.9Sr0.1Ga0.8Mg0.2O3−δ/Ag–Ce0.8Gd0.2O1.9) and are loaded with K-loaded activated carbon fuel. Ca(OH)2 and Li4SiO4 are loaded into the anode chamber as the steam feedstock and CO2 sorbent, respectively. Completely sealed DC-SOFCs with Ca(OH)2–C of 0 %, 5 %, 10 %, 15 %, and 20 % have been tested at 700 °C. Compared with a cell with a conventional structure and a completely sealed cell without Ca(OH)2 loading, the electrochemical performances of all the completely sealed cells with Ca(OH)2 loading are significantly enhanced. The cell with Ca(OH)2 to C of 15 % obtained the highest maximum power density of 75 mW cm−2, which is approximately two-fold that of the conventional DC-SOFC. The mechanism for improving the performance of the cell is the introduction of steam. This study offers a new method to develop high-performance DC-SOFCs and reduce their operating temperatures.

Thermodynamic and CO2 sorption investigations on improved Li3BO3-based sorbents by NaOH addition

The development of new solid sorbents with high carbon capture capacity and good reversible sorption properties is considered a key factor for mitigating CO2 emissions. Tri-lithium borate (Li3BO3) has shown to be a high-capacity CO2 sorbent adequate for an intermediate temperature range (500–650 °C). However, the performance of this sorbent has been little studied in particular at low CO2 concentrations, requiring the introduction of changes in Li3BO3 to make it competitive. Here, highly efficient NaOH-modified Li3BO3 sorbents were synthesized by a simple two-step mechano-thermal method at low temperature using different amounts of NaOH. For the first time, the influence of increasing amounts of an additive on the standard enthalpy change of Li3BO3 as well as on the relation between CO2 pressure and temperature equilibrium was determined. A progressive rise in the standard enthalpy change and a decrease in the equilibrium CO2 pressure at a fixed temperature were observed with the increase in the amount of additive. Moreover, the NaOH addition to Li3BO3 improves its CO2 capture capacity, CO2 absorption rate and stability during carbonation/regeneration cycles. The CO2 capture capacity ranges between 50 wt% and 35 wt% at pure CO2 and 15 % CO2, respectively, for low amounts of NaOH added. Further studies showed that CO2 capture/desorption efficiency is kept high after 20 cycles at 525 °C and 15 % CO2. The improved performance of NaOH-modified Li3BO3 sorbents and the changes in the thermodynamic properties were associated with two factors: the partial substitution of boron by carbon in the Li3BO3 structure, and the formation of Li2CO3-Na2CO3 molten carbonates. Therefore, these NaOH-modified Li3BO3 materials represent attractive CO2 sorbents for moderate temperatures, applicable for post-combustion industrial processes.

Encoding CO2 Adsorption in Sodium Zirconate by Neutron Diffraction.

Recent research into sodium zirconate as a high-temperature CO2 sorbent has been extensive, but detailed knowledge of the material's crystal structure during synthesis and carbon dioxide uptake remains limited. This study employs neutron diffraction (ND), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) to explore these aspects. An improved synthesis method, involving the pre-drying and ball milling of raw materials, produced pure samples with average crystal sizes of 37-48 nm in the monoclinic phase. However, using a slower heating rate (1 °C/min) decreased the purity. Despite this, the 1 °C/min rate resulted in the highest CO2 uptake capacity (4.32 mmol CO2/g Na2ZrO3) and CO2 sorption rate (0.0017 mmol CO2/g) after 5 min at 700 °C. This was attributed to a larger presence of microstructure defects that facilitate Na diffusion from the core to the shell of the particles. An ND analysis showed that the conversion of Na2ZrO3 was complete under the studied conditions and that CO2 concentration significantly impacts the rate of CO2 absorption. The TGA results indicated that the reaction rate during CO2 sorption remained steady until full conversion due to the absorptive nature of the chemisorption process. During the sorbent reforming step, ND revealed the disappearance of Na2O and ZrO2 as the zirconate phase reformed. However, trace amounts of Na2CO3 and ZrO2 remained after the cycles.

Understanding Electrochemical and Mechanical Durability of Bipolar Membranes Used in Electrodialysis

Using renewable energy to drive direct carbon capture systems is a powerful way to contribute to net negative emissions. When using liquid alkaline sorbents for CO2 direct air capture, it is critical to reduce the energy demand for CO2 concentration and sorbent regeneration. Electrodialysis is an ideal candidate technology to integrate renewable energy into this process, however, to enable this ion-exchange membrane separators that can operate at high ion flux and low voltage are needed. Bipolar membranes (BPMs), that generate protons and hydroxide ions from the dissociation of water when operated in reverse bias, are the enabling component to generate acid and base in electrodialysis systems. Bipolar membrane electrodialysis (BPMED) uses a BPM to create acidifying and basifying chambers which are well suited to concentrate and release CO2 and concentrate the remaining alkaline effluent to cycle back to the capture process. Current BPM durability, however, sufferers at high current density (ion flux) and physical scale. BPMs have several known degradation mechanisms including chemical breakdown of ion exchange polymers, loss of junction adhesion, or physical breakdown due to shearing force and pressure swings in an electrodialysis cell.To assess the electrochemical and mechanical durability of BPMs under operational conditions, we investigated how fabrication conditions (including preconditioning, hot pressing, and catalyst loading) impact the adhesion of custom made BPMs. T-peel studies were performed ex-situ to quantify adhesive forces of BPMs made of different compositions and prepared under different conditions, and BPMED experiments were performed to assess the electrochemical performance of the corresponding BPMs. The BPMED results show that, while adhesion is necessary to physically maintain the BPM junction, mechanical adhesion alone cannot overcome poor ion and water transport management at the water dissociation junction. The results of this systematic comparison indicate that in order for BPMs to operate at high current densities, high adhesion forces made during fabrication of BPMs will need to be balanced with water dissociation kinetics and ion/water transport through the individual membrane layers.

(Invited) Nanowire Catalysts and Adsorbents

The unique properties of nanowire materials like fast charge transport, short diffusion length, controlled surface sites and single crystal nature make them ideal for designing high performance catalysts, adsorbents and electrocatalysts by design. To realize any of these applications, one would need either large quantities of nanowire powders or nanowire arrays on large areas. In this presentation, we will highlight our group’s efforts with scalable methods for continuous manufacturing of nanowire powders and arrays for oxides1 and III-nitride materials.2 The process for producing metal oxide nanowires has been scaled up to ton-scale. The resulting nanowire powders can be used to formulate unique catalyst and adsorbent products.Zinc oxide nanowires alloyed with catalytically active metals and have been formulated into ultra-deep desulfurization catalytic adsorbents.3,4 These materials exhibited ultra-deep desulfurization with sulfur removal down to 1 ppm or below for liquid hydrocarbons (diesel, gasoline and naphthalene) and to less than 1 ppb for natural gas. The desulfurization mechanism does not involve formation of H2S species unlike that typically observed with hydro-desulfurization process involving sulfided catalysts.Titania nanowires supported with nickel and molybdenum clusters have also shown to exhibit high activity and durability as hydro-desulfurization catalysts for removal of sulfur from hydrocarbons by forming H2S.5 The synergistic activity with MoS2 and titania are expected to contribute to enhanced activity with desulfurization.Alloying of nanowires with other elements is also studied to produce compound and alloyed nanowires. Fundamental studies have shown that alloying process occurs at much lower temperatures than decomposition temperatures for precursors used. Alloying studies have clearly shown that the solubility in nanowires to be much more than that expected for bulk materials systems. This presentation will provide several examples in which nanowires were alloyed with elements at compositions more than that expected for thermodynamic solubility.In the case of CO2 sorbents, alkali metal oxide nanowires have shown high capacity for CO2 sorption as high as 75% by wt. The alkali metal oxide nanowires have been alloyed with alkali hydroxides to produce alkali metal oxide compound nanowires. These solid sorbents showed selective CO2 sorption from a variety of streams including air, exhausts containing CO2 at various concentrations. Nanowire geometry for these nanowires allow for non-sinterability, and smaller length scales for rapid diffusion of alkali ions allow for fast kinetics and regenerability. 6,7 Acknowledgements: Authors also acknowledge contributions from Drs. Juan He, Sivakumar Vasireddy, Vivekanand Kumar, Veerendra Atla and Tu Nguyen. Partial support from National Science Foundation (NSF) and US Department of Energy (DOE) EPSCOR programs and full support from NSF and DOE SBIR programs and Kentucky Cabinet for Economic Development for Advanced Energy Materials, LLC are highly appreciated.

Effect of Li-Na sorbent phase in Ru/Al2O3 dual function materials for the Integrated CO2 capture and methanation

The design of highly performing dual functional materials (DFMs) is the key to the successful deployment of Integrated Carbon Capture and Methanation (ICCM) process that combines both steps into a single unit operation with high energy efficiency. Intending to enhance the CO2 working capacity while preserving high catalytic methanation activity, herein we set out to investigate the effect of combining Li and Na as the CO2 sorbent phase in Ru/Al2O3 DFMs. ICCM tests in a fixed bed reactor operated with alternate feeds indicated that combining Na with Li (or partially substituting it for Li) effectively increases the CO2 capture capacity and methane production of the DFM. However, this generally requires higher temperatures to properly activate the catalytic methanation and to regenerate the DFM compared to a pure Li-based formulation. Transient operando DRIFTS and catalytic kinetic experiments provided mechanistic insights into the activation/inhibition of different reaction paths on those DFMs containing only Li and/or Na.

A comprehensive thermodynamic analysis of hydrogen and synthesis gas production from steam reforming of propionic acid: Effect of O2 addition and CaO as CO2 sorbent

A thermodynamic analysis was performed for the production of synthesis gas and hydrogen gas from steam reforming of propionic acid, one of the constituents of the bio-oil, using ASPEN Plus v8.8. The aim of the study was to perform a global analysis on steam reforming of propionic acid focusing on several parameters such as steam-to-propionic acid ratio, reaction temperature, addition of O2 in the feed stream and presence of CaO as a CO2 sorbent in the reaction environment. The results showed that higher amounts of steam/propionic acid ratio resulted in higher H2 and CO2 yields. It was also observed that high H2O/PA molar ratios led to reduced coke production as WGS reaction was favored with excess steam, causing CO in the reaction mixture to be consumed through the WGS reaction rather than the Boudouard reaction. Addition of O2 in the reaction environment was observed to negatively affect yield of H2. Yet, coke formation was deprived and increasing the O2 amount in the feed stream decreased the energy required for the process. Furthermore, the presence of CaO enhanced H2 yield and energy requirements of the process compared to conventional steam reforming process. 100 % yield of H2 production with a heat generation of −83.4 MJ/kmol of PA and almost zero formation of CO2, CO, CH4 and coke is achieved at 600 °C for sorption enhanced steam reforming of propionic acid.

All-solid-waste-derived CaO-based sorbents for simultaneously enhanced calcium looping CO2 capture and thermochemical energy storage

Calcium looping (CaL) process relying on CaO as high-temperature CO2 sorbents is a prospective alternative technology for simultaneously cyclic CO2 capture and thermochemical energy storage. However, the cyclic stability and the energy storage density of the CaO-based sorbents decay drastically over repeated carbonation-calcination cycles. Herein, we yielded CaO-based sorbents derived from all industrial solid wastes with carbide slag (CS) as precursor and coal fly ash (CFA) as stabilizer featuring superior carbonation characteristics, stable CO2 cyclic uptake and high thermochemical energy storage density over multiple operation cycles. The optimal sorbent (CCS–H-G-CFA-D) exhibited a high initial CO2 uptake of 0.38 gCO2/gsorbent, superior cyclic stability with an average decay rate of 1.05% per cycle and remarkably stable energy storage density of 1375 kJ/kg, retaining 89.5% after 10 repeated cycles. Thereby, the simultaneously enhanced cyclic CO2 capture and thermochemical energy storage are attributed to adding CFA stabilizers in CS-derived CaO-based sorbents, forming stable skeleton to alleviate sintering, improving the uniform mixing degree between sorbent particles and promoting the carbonation reaction via synergistic effect. This simple and eco-friendly approach of cost-effective sorbents totally derived from industrial solid wastes provides a new avenue for large-scale practical CO2 capture and energy storage processes.

Glycidyl Ether-Functionalized Poly(ethylenimine)-Impregnated Sorbents for CO2 Capture from Ultradilute Sources

Glycidyl Ether-Functionalized Poly(ethylenimine)-Impregnated Sorbents for CO₂ Capture from Ultradilute Sources

Use of building wastes and red mud as CO2 sorbent and catalyst for the production of hydrogen

Use of building wastes and red mud as CO2 sorbent and catalyst for the production of hydrogen

Experimental and DFT study of Na4SiO4 doped with oxysalts for high-temperature CO2 capture

Eutectic doping has been considered as one of the most efficient ways to modify the Na4SiO4-based CO2 sorbent. Nevertheless, the effects of different acid radical ions and alkali metal cations of the oxysalts on the CO2 capture performances of Na4SiO4 have never been explored. In this study, Na4SiO4-based CO2 sorbents were prepared using four kinds of oxysalts as the dopants. The effects of acid radical ions/alkali metal cations, doping ratios and sorption/desorption temperatures on the CO2 capture performances of sorbents were investigated. The results showed that the promotion effects of CO32− and Li+/K+ ions were stronger than others, the maximum CO2 sorption capacity of Na4SiO4-30Li2CO3 and Na4SiO4-30K2CO3 at 700 °C reached 20.6 wt% and 19.5 wt%, respectively. The cyclic sorption capacity of Na4SiO4-30Li2CO3 was 8.5 wt%, which was 40.0% higher than that of Na4SiO4. Further, the oxysalt dopants could enhance the CO2 adsorption energy on the Na4SiO4 surfaces and reduce the energy level of the systems using density functional theory calculation, which were consistent with the experimental values. Finally, the effects of water vapor on the sorption of Na4SiO4 and Na4SiO4-K2CO3 were simulated, which could enhance the activity of O atoms on sorbent surfaces and promote rapid carbonization during the sorption progress. Thus, Na4SiO4 doped with oxysalts exhibit promising potential for high-temperature CO2 capture application.

Hydrated carboxylate ionic liquids as chemical CO2 sorbents of high capacity and moderate enthalpy of absorption

Tetralkylphosphonium carboxylate ionic liquids are herein presented as efficient carbon dioxide chemisorbents in the presence of water. The ionic liquids tetrabutylphosphonium formate and acetate, tributylmethylphosphonium formate and a series of triethylalkylphosphonium formates and acetates, have been prepared by various synthetic procedures either from hydroxide or methylcarbonate precursors, or via multiple steps starting from the parent triethylphosphine. Their physicochemical properties, namely melting or glass transition temperatures, thermal decomposition behaviour, densities and viscosities have been determined. As dry substances, they are viscous liquids or low-melting solids, whereas they show little tendency to solidify in their hydrated forms. They were used mostly as monohydrates in CO2 solubility measurements, exhibiting highest capacities (3 mol L−1, i.e. ≈ 0.9 molCO2 molIL−1, at 5 bar, 25 °C) at equimolar H2O/ionic liquid ratios, approaching those of commercial aqueous amine sorbents. Carbon dioxide chemisorption into hydrogencarbonate takes place, as demonstrated by infrared spectroscopy with isotopic labelling. CO2 absorption isotherms were recorded at various temperatures and the data used to estimate the heat of absorption according to three different thermodynamic models. Enthalpies of CO2 absorption depended heavily on the model used. Rationalisation of this was done on the grounds of the expected relevance of physical and chemical sorption processes. Average heats of CO2 absorption lie between −40 and −45 kJ mol−1, in accordance with mild chemical absorption albeit significantly lower than those for typical chemical sorbents such as amines. This reinforces the feasibility of hydrated carboxylate ionic liquids for CO2 capture technologies of low regeneration energies.

Demonstration of CO2 capture with CaO and Ca(OH)2 in a countercurrent moving bed carbonator pilot

Decoupling the carbonation and calcination stages of Calcium Looping (CaL) facilitates the capture of CO2 from small point sources, or even the atmosphere, by transporting CO2 as CaCO3 to centralized calcination plants to obtain pure CO2 and regenerate the Ca-sorbent. In this work, we provide the experimental proof of a novel countercurrent moving bed carbonator particularly suited for such applications. We conducted experiments in a 3-meter-long moving bed reactor with an internal diameter of 0.15 m, using Ca-sorbent particles of varying sizes (in the mm and cm scale). Simulated flue gases with varied concentrations of CO2 (up to 8.5 %v), superficial gas velocities (0.5–2 m/s) and inlet gas temperatures (250–630 °C) have been tested. The temperature profiles we observed along the axial direction confirm the formation of a carbonation zone at optimum temperatures (i.e., 550–700 °C), together with a CO2 polishing region towards the gas exit that leads to CO2 capture rates over 99 % in some cases. Using Ca(OH)2 as a CO2 sorbent, we achieved a molar conversion to CaCO3 of approximately 0.7.