High-temperature CO2 Adsorption Research Articles

Preparation of Li4SiO4 from lithium-ion battery cathode waste and diamond wire saw silicon powder using a two-step process

Li4SiO4 materials have excellent high-temperature CO2 adsorption properties. In this thesis, Li4SiO4 was produced by a two-step process by using Li+ from waste lithium-ion battery cathodes as a partial lithium source. The diamond wire saw silicon powder generated by the photovoltaic industry, was used as the silicon source. The reduction melting process of LiMeO2 (Me = Ni, Co, or Mn) in the battery cathode material was analyzed, and the effect of the Li: Si molar ratio in the melting system on the reduction of metal oxides was investigated. The effects of roasting temperature and roasting time on the adsorption properties of Mn-doped Li4SiO4 were also studied. The results showed that the maximum adsorption capacity of Mn-doped Li4SiO4 reached 29.44 wt% under a pure CO2 atmosphere, which was about 2.6 times higher than that of pure Li4SiO4. The saturated adsorption capacity reached 34.2 wt%. This study achieved the resource utilization of solid waste and may reduced the preparation costs of Li4SiO4 adsorbent, which may promote carbon capture technologies.

Density functional theory study of high-temperature CO2 adsorption by Li2ZrO3: Effect of typical flue gas components on adsorption energy and electronic properties

Lithium zirconate (Li2ZrO3) is one of the best-performing high-temperature CO2 adsorbents, but the effect of flue gas on its mutual mechanism of action is not clear. The adsorption mechanism of CO2 and flue gas components on the Li2ZrO3 (111) surface is investigated theoretically through density functional theory (DFT), where the selected flue gas components are O2, H2O, and SO2. Theoretical calculations show that O2 exhibits physical adsorption and CO2, H2O, and SO2 exhibit chemisorption on the Li2ZrO3 surface. The energy potential barrier for CO2 adsorption on the Li2ZrO3(111) surface is 0.3 eV. CO2 is gradually desorbed at temperatures above 870 K. When there are flue gas atmospheres present, the desorption temperature of CO2 decreases, to a certain extent. All selected flue gas components inhibit the adsorption of CO2, O2, and H2O, weakening the interaction forces between the surface and CO2 and making it less stable. SO2 has the same adsorption sites as CO2, while SO2 has much higher adsorption energy than CO2. SO2 is more likely to adsorb onto and occupy the active sites of CO2.

In-Situ observation and quantitative analysis on sintering process of Li4SiO4 sorbents

High-temperature CO2 adsorption has an attractive prospect in reducing CO2 emissions efficiently. As the core of CO2 adsorption technology, sorbents suffer from a well-known problem of capacity degradation as a result of sintering during cyclic CO2 adsorption and desorption at high temperatures. This work aims to understand the microstructural evolution of Li4SiO4, one of the most typical and promising sorbents, during CO2 capture. In-situ Transmission Electron Microscopy was used to directly capture the morphological variation of Li4SiO4 sorbents. Comprehensive characterization techniques were adopted to quantify microstructural parameters of Li4SiO4 under different conditions. The real-time shrinkage of Li4SiO4 particles was demonstrated and equations on grain growth, specific surface area reduction, and pore volume evolution were established. The work can not only reveal the reason for the reduction of CO2 capacity, but provide a theoretical guidance for the development of sintering-resistant CO2 sorbents.

Understanding the competition between carbonation and sulfation of Li4SiO4-based sorbents for high-temperature CO2 capture

High-temperature CO2 adsorption is an important method in reducing the excessive CO2 emissions for the mitigation of global climate change. As a potential high-temperature CO2 sorbent, Li4SiO4 attracted extensive concern due to its high CO2 capacity with excellent stability. However, gas impurities in industrial flue gas, especially SO2 affect the CO2 adsorption process, and the competition between SO2 and CO2 during the adsorption process by Li4SiO4 is lack of understanding. This work studied the competitive behavior between carbonation and sulfation through experimental tests, characterizations, and DFT calculations. Results show that carbonation can slightly inhibit the proceeding of sulfation while sulfation almost prevents the occurrence of carbonation for both Li4SiO4 and K-Li4SiO4. In addition, the doping of K2CO3 in Li4SiO4 is observed to significantly promote both the carbonation and sulfation process. Furthermore, stable adsorption structures of CO2 and SO2 on Li4SiO4 were obtained via DFT calculation, which verifies the mutual inhibition between carbonation and sulfation. These results provide a well understanding of the competition between carbonation and sulfation of Li4SiO4-based sorbents, and are helpful for the design and optimization of CO2 adsorption process.

Kinetic study and modeling on the regeneration of Li4SiO4-based sorbents for high-temperature CO2 capture

Li4SiO4 is acknowledged as a promising sorbent candidate in high-temperature CO2 adsorption. However, reaction kinetics for the regeneration process of Li4SiO4, especially its dependence on CO2 pressure is lack of understanding. This work designed and carried out a series of isothermal tests on the regeneration of pure Li4SiO4 and K-Li4SiO4 under CO2 partial pressure of 0–0.5 atm and temperature of 625–725 °C. For the first time, the expression of (Peq − PCO2)n is introduced into the regeneration rate equation so as to reveal its dependence on CO2 pressure. The reaction order (n) is found to grade according to the value of (Peq − PCO2), and the apparent activation energy is calculated as 284.42 kJ•mol−1 and 146.31 kJ•mol−1 for the regeneration of Li4SiO4 and K-Li4SiO4, respectively. Furthermore, this work proposes that power law model with m = 4/3 is the most probable mechanism function for the regeneration of Li4SiO4-based sorbents.

Reaction Mechanism and Kinetics of the Sulfation of Li4SiO4 for High-Temperature CO2 Adsorption

Reaction Mechanism and Kinetics of the Sulfation of Li₄SiO₄ for High-Temperature CO₂ Adsorption

High-temperature CO2 adsorption by one-step fabricated Nd-doped Li4SiO4 pellets

High-temperature CO2 capture by using Li4SiO4-based adsorbent has been considered as an efficient approach to alleviate the global warming problem. However, the relatively low conversion and lake of suitable pelletization approach still limit the applications of Li4SiO4 in practical looping system. In this work, high-performance Nd-doped Li4SiO4-based adsorbent pellets were one-step fabricated conveniently by combining the synthesis, the pelletization and the doping processes. The physico-chemical properties as well as the CO2 capture performance of doped pellets were systematically investigated. Especially, the modification effects and mechanisms of Nd-doping were also studied in depth. The results show that triple positive effects including the pore-forming, the formation of inert sintering-resistant frameworks and the occurrence of Li4SiO4 lattice defects were introduced by Nd-doping. All of above effects lead to a stable capacity of Nd-doped pellet as high as ~0.2 g/g within 20 ad-desorption cycles, which is promising for its future applications.

Atomic Layer Deposited Ni/ZrO2-SiO2 for Combined Capture and Oxidation of VOCs.

This work reports on the development of novel Ni nanoparticle-deposited mixed-metal oxides ZrO2-SiO2 through atomic layer deposition (ALD) method and their application in combined capture and oxidation of benzene, as a model compound of aromatic VOCs. Concentrating ppm-level VOCs in situ, before their oxidation, offers a practical approach to reduce the catalyst inventory and capital cost associated with VOC emissions abatement. The benzene vapor adsorption isotherms were measured at 25 °C and in the pressure range of 0 to benzene saturation vapor pressure thereof (0.13 bar). In the combined capture-reaction tests, the materials were first exposed to ca. 86 100 ppmv benzene vapor at 25 °C, followed by desorption and catalytic oxidation while raising the bed temperature to 250 °C. The textural properties revealed that ALD of Ni or ZrO2 on SiO2 decreased surface area and pore volume, while sequential doping with ZrO2 and then Ni caused the otherwise. The benzene vapor adsorption isotherms followed the type-IV isotherm classification, revealing a combination of monolayer-multilayer and capillary condensation adsorption mechanisms in sequence. At saturation vapor pressure, an average equilibrium adsorption capacity of 15 mmol/g was obtained across the materials. However, the dynamic adsorption capacities were up to 50% less than the corresponding equilibrium uptake for the materials. Benzene desorption temperature was observed around 90 °C, and conversion of 85-95% and TOF of 1.28-16.42 mmolC6H6/molNi/s were obtained over the materials, with 3Ni/ZrO2-SiO2, prepared with 3 ALD cycles, exhibiting the maximum conversion and TOF indicating synergistic effects of Ni nanoparticles and ZrO2 support based on the number of ALD cycles. However, the yields of CO2 and H2O were about 5% and 40%, respectively. The small value of the CO2 yield was hypothesized to be due to simultaneous high-temperature adsorption of CO2 as the catalytic reaction progressed. The high adsorption affinity, low desorption temperature, and high catalytic activity of the materials investigated in this study made these materials as promising candidates for the abatement of BTX.

Bubbling synthesis and high-temperature CO2 adsorption performance of CaO-based adsorbents from carbide slag

Carbide slag used as low-cost adsorbents for high-temperature CO2 capture has widely researched; however, the sintering at high calcination temperature often resulted in an obvious decay of CO2 capture performance after multiple CO2 capture cycles. In this work, a new strategy of synthetic CaO-based adsorbents from carbide slag via the bubbling approach was reported to stabilize the pore structure of adsorbents, to improve the sintering resistance of adsorbents and to boost the CO2 adsorption capacity. Therefore, the influences of bubbling rate, stirring rate, reaction temperature, and carbide slag dosage on CO2 adsorption capacity of CaO-based adsorbents were systemically investigated at 750 °C for 1 h. The synthetic CaO-based adsorbent from carbide slag on the basis of following conditions: 200 sccm of CO2 bubbling, 1100 rpm/stirring, 40 °C of reaction temperature and 5 g of carbide slag dosage, presented the highest CO2 adsorption capacity of 619.8 mg/g and 542.6 mg/g in the 1st and 15th cycles, which were about 6.6% and 33.9% higher than that of original carbide slag (CS). This significant improvement in CO2 uptake capacity is due to more stable interconnected and 2–5 nm porous structure in the as-prepared CaO-based adsorbent, which outstandingly lowered down the sintering of adsorbents and stabilized the CO2 adsorption capacity during multiple CO2 capture cycles.

Promoting CO2 hydrogenation to methanol by incorporating adsorbents into catalysts: Effects of hydrotalcite

CO2 hydrogenation, in which CO2 conversion to methanol plays a key role, is of increasing importance in mitigating the climate crisis. However, high reaction pressures are required to conduct methanol synthesis because of poor catalytic performance of conventional catalysts, leading to high energy consumption. In this study, a novel strategy was applied to promote methanol synthesis by adsorption-enhanced CO2 hydrogenation. Catalysts made from Cu-ZnO-Al2O3 mixed with different hydrotalcite contents (named CZA-HT) were prepared by physically mixing a commercial copper-based catalyst for methanol synthesis with hydrotalcite for high temperature CO2 adsorption. In these catalysts, only the commercial copper-based component contains the active part for CO2 hydrogenation and its copper surface area is 48.1 m2 g−1 with an optimal reaction temperature of 523 K. Hydrotalcite exhibits no catalytic activity, yet the catalytic performance of the CZA-HT catalysts were clearly facilitated by CO2 adsorption on HT. The sample containing 40 wt% hydrotalcite and 60 wt% CZA showed the highest methanol selectivity of 73.4% and a methanol yield of 4.4% among all samples. The reaction was conducted at a low reaction pressure of 30 bar (much lower than conventional pressure), so that the methanol yield was not high. However, it is observed that the methanol formation rate based on a unit mass of active CZA always increases as the hydrotalcite content in CZA-HT increases, confirming the promotion effects of CO2 adsorption on HT on catalytic performance. The mechanism of adsorption enhanced catalytic reaction was also analysed and discussed, in which the well mixed finer particles of CZA and HT perform better than CZA alone with a 73.9% higher methanol yield.

Al-Stabilized Double-Shelled Hollow CaO-Based Microspheres with Superior CO2 Adsorption Performance

Novel, double-shelled hollow Al-stabilized CaO-based microspheres were successfully prepared through a facile, green method using carbonaceous microspheres as sacrificial templates. Both the morphological and adsorption performance differences, between employing organic and inorganic calcium salt as calcium precursors, to fabricate the double-shelled hollow microspheres were exhibited. Derived from calcium acetate, the Al-stabilized double-shelled hollow microspheres with denser shells showed excellent stability. This was ascribed to the shells that were composed of small CaCO3 nanocrystallite (grain size of <50 nm) and homogeneously distributed stabilizer, Al2O3. Well-spherical, porous hollow structures facilitated CO2 diffusion and buffered mechanical stresses generated by volume change during the calcium looping. The sorbent, CaA40Al1, exhibited a favorable high-temperature CO2 adsorption performance with the capacity of 0.40 g of CO2/g of ads over 60 carbonation/calcination cycles.

Calcium precursor from stirring processes at room temperature for controllable preparation of nano-structure CaO sorbents for high-temperature CO2 adsorption

Nano-structure CaO crystals with an average size of 480 nm × 255 nm (length and width) were prepared by simply roasting CaCO3 precursors at 900 °C for 2 h. The CaCO3 precursors with a pure vaterite crystalline phase were readily synthesized by a room temperature stirring method using Ca(NO3)2 and CO2 storage material (CO2SM). The CO2SM played an important role in providing CO32− source and structure controlling. The effects of CO2SM dosage, Ca2+ concentration, and stirring time on the crystallization of CaCO3 precursors were investigated. In addition, the CO2SM was successfully regenerated by simply exposing the filtrate from the preparation process to CO2 for further preparing CaCO3 precursor. The as-obtained CaO crystals exhibited a strong CO2 adsorption capacity up to 17.18 mmol g-1 under 0.1 MPa at 700 °C.

Synthesis of Metal-Oxide/Carbon-Fiber Heterostructures and Their Properties for Organic Dye Removal and High-Temperature CO2 Adsorption

One-dimensional metal-oxide/carbon-fiber (MO/CF) heterostructures were prepared by a facile two-step method using the natural cotton as a carbon source the low-cost commercial metal salts as precursors. The metal oxide nanostructures were first grown on the cotton fibers by a solution chemical deposition, and the metal-oxide/cotton heterostructures were then calcined and carbonized in nitrogen atmosphere. Three typical MO/CF heterostructures of TiO2/CF, ZnO/CF, and Fe2O3/CF were prepared and characterized. The loading amount of the metal oxide nanostructures on carbon fibers can be tuned by controlling the concentration of metal salt in the chemical deposition process. Finally, the performance of the as-obtained MO/CF heterostructures for organic dye removal from water was tested by the photocatalytic degradation under a simulated sunlight, and their properties of high-temperature CO2 adsorption were predicted by the temperature programmed desorption. The present study would provide a desirable strategy for the synthesis of MO/CF heterostructures for various applications.

Fabrication of multi-shelled hollow Mg-modified CaCO3 microspheres and their improved CO2 adsorption performance

Novel multi-shelled hollow Mg-modified CaCO3 microspheres were successfully prepared through a facile, green method by using carbonaceous microsphere as a template with controllable Ca/Mg molar ratio, size and shells number. The triple-shelled hollow microspheres structure facilitated CO2 diffusion and buffered mechanical stresses of volume change during the carbonation/calcination process. Connected with sintering-resistance of inert Mg-modification, the Mg-doped CaCO3 triple-shelled hollow microspheres had collapse resistance, fast adsorption kinetics, improved CO2 adsorption capacity and calcium looping stability. The sorbent exhibited a favorable high temperature CO2 adsorption performance with the capacity of 0.51g-CO2/g-ads after 50 carbonation/calcination cycles and 92.4% of the initial maximal sorption in only 3min.

Enhancement in CO2 Adsorption on Hydrotalcite-based Material by Novel Carbon Support Combined with K2CO3 Impregnation

In recent years, a great deal of interest has been shown for high-temperature adsorption of CO2 on hydrotalcite-like compounds (HTlcs). Numerous efforts have been undertaken to enhance the CO2 capture property of HTlcs, including alkali-metal impregnation, use of support materials, and modification of chemical composition. The present work demonstrates the applicability of coal-derived graphitic material (CGM) as an effective support for neat as well as K2CO3-promoted Mg–Al HTlc, enhancing the CO2 adsorption capacity. Both surface area and basic site density affect the adsorption capacity. The K2CO3-promoted CGM-supported Mg–Al HTlc exhibited a fresh adsorption capacity of 1.10 mmol g–1 at 300 °C under a total pressure of 1 bar. After the initial drop, it maintained an average working capacity of 0.42 mmol g–1 during nine cycles of adsorption–desorption in the temperature range of 300–400 °C. The Yoon–Nelson kinetic model fit well with the experimental data.

High temperature CO2 adsorption by mesoporous silica supported magnesium aluminum mixed oxide

Magnesium aluminum mixed oxide (Mg–Al–O) was deposited in various weight percentages into SBA-15 mesoporous silica through excess solution impregnation of magnesium and aluminum nitrate salts and subsequent high temperature calcination. In all the syntheses the Mg:Al mole ratio was fixed at 2. High temperature CO2 uptake capacity of these composites were measured in the temperature range 300–400°C and were compared with the capacity of the unsupported mixed oxide phase with same Mg:Al mole ratio of 2. An improvement in the specific equilibrium capacity as well as uptake kinetics for CO2 was observed in the composite adsorbent after an optimum loading of the mixed oxide. The result could be explained on the basis of better accessibility of the active sites for CO2 adsorption following dispersion of the mixed oxide on to the high surface area SBA-15 support. The CO2 adsorption capacity is higher than recent reports of Mg–Al–O supported on graphene oxide and CNT where there is additional complication of support degradation during thermal decomposition of Mg/Al salt precursors to corresponding metal oxides during adsorbent preparation.

Comprehensive investigation of CO2 adsorption on Mg–Al–CO3 LDH-derived mixed metal oxides

Layered double hydroxides (LDHs) have been intensively studied for high-temperature CO2 capture. However, big differences in the CO2 capture capacity, ranging from 0.28 to 0.6 mmol g−1, have often been reported for the same Mg–Al–CO3 LDH. Furthermore, how the active Mg–O species that are responsible for CO2 adsorption are formed is still unclear. In this work, we have performed a comprehensive investigation on the CO2 adsorption characteristics of Mg–Al–CO3 LDH-derived mixed metal oxides. Based on these results we proposed the possible adsorption sites and the mechanisms for CO2 adsorption. Initially, the effects of synthesis method, Mg : Al ratio, pretreatment conditions, adsorption conditions, and thermal stability on the CO2 adsorption capacity were systematically studied. By carefully examining the structural changes during thermal treatment using X-ray diffraction and solid state NMR, we suggest that the active Mg–O species could be induced either by the substitution of Mg2+ by Al3+ in the periclase MgO lattice, or by the diffusion of Al3+ out of the octahedral brucite layers. This work not only suggests the optimal testing conditions for LDH-derived CO2 adsorbents, but also provides a clearer understanding of the CO2 adsorption sites and mechanisms on LDH-derived mixed oxides and sheds light on the synthesis and utilization of LDH-derived high-temperature CO2 adsorption materials.

High temperature adsorption of carbon dioxide on Cu–Al hydrotalcite-derived mixed oxides: kinetics and equilibria by thermogravimetry

The effect of Cu/Al molar ratio on the high-temperature adsorption characteristics of CO2 on the mixed oxides of Cu–Al hydrotalcite skeletal structure has been studied by thermogravimetry. The Cu/Al molar ratio of the hydrotalcites synthesized was varied between 1.0 and 3.0, and the adsorption temperature ranged from ambient to 600 °C. The hydrotalcite with Cu/Al molar ratio of 2.0 was found to be the most suitable adsorbent for high-temperature CO2 adsorption, in both the capacity and the rate of adsorption. The activation energy values suggested that the physical adsorption dominates at low temperatures ( 400 °C).

High temperature adsorption of CO2 on various hydrotalcite-like compounds

A study was conducted to describe and quantify how substitution of the divalent cation and interlayer charge compensating anions affect the CO2 adsorptive capacity of various hydrotalcite-like compounds (HTlcs). Physical and chemical properties of the HTlcs were evaluated using a number of methods and the CO2 adsorption rate and capacity were measured at elevated temperature (603 K). The results showed that the synthetic analogue of the naturally occurring hydrotalcite mineral, [Mg0.73Al0.27(OH)2](CO3)0.13⋅xH2O, had the best overall adsorption capacity and kinetics. The stability of the adsorption capacity was tested by subjecting the model HTlc to 10 equilibrium adsorption and desorption cycles. At the end of the cycle, the HTlc had maintained approximately sixty-five percent of its initial capacity. Temperature programmed desorption of CO2 was used to quantify the surface basicity of the various HTlcs. The results showed that the reversible physisorption portion of the CO2 isotherm was correlated to the number of surface basic sites on the HTlcs.

Structural Effects on the High Temperature Adsorption of CO2 on a Synthetic Hydrotalcite

Hydrotalcite-like compounds (HTlcs) are solid sorbents that may potentially be used for high-temperature separation and capture of CO2. The high-temperature adsorption of CO2 on Mg−Al−CO3 HTlc is affected by structural changes that take place upon heating of the material. The structural changes of a synthetic HTlc upon heating to 200 and 400 °C in a vacuum were characterized using various analytical techniques. These structural changes were then related to observed behavior with respect to the physisorption and chemisorption of CO2 at 200 °C. Upon heating to 200 °C, the material retains its layered structure, though the interlayer spacing is decreased by ∼0.6 A due to loss of interlayer water. Chemisorption of CO2 at 200 °C represents more than half of the total adsorption capacity (at 107 kPa) due to increased availability of the framework Mg2+ cation and the subsequent formation of MgCO3. There is no significant increase of surface area or pore volume after heating to 200 °C. Upon heating to 400 °C the ...