CO2 Sorption Capacity Research Articles

The Influence of Mg, Na, and Li Oxides on the CO2 Sorption Properties of Natural Zeolite

This study presents a comparative analysis of the CO2 sorption properties of natural zeolites sourced from the Tayzhuzgen (Tg) and Shankanay (Sh) deposits in Kazakhstan. The Tayzhuzgen zeolite was characterized by a Si/Al ratio of 5.6, suggesting partial dealumination, and demonstrated enhanced specific surface area following mechanical activation. Modification of the Tayzhuzgen zeolite with magnesium oxide significantly improved its CO2 sorption capacity, reaching 8.46 mmol CO2/g, attributed to the formation of the CaMg(Si2O6) phase and the resulting increase in basic active sites. TPD-CO2 analysis confirmed that MgO/Tg exhibited the highest basicity of the modified samples, further validating its potential for CO2 capture applications.

Enhanced carbon dioxide capture through composite of polyamide 6 nanofibers and zeolites: Preparation and performance evaluation

The increasing concentration of atmospheric carbon dioxide (CO2) demands innovative solutions for its capture and sequestration. Composite and nanocomposite materials have gained attention for their high surface area, adjustable properties, and improved adsorption capabilities. This manuscript explores the preparation, characterization, and performance assessment of a novel composite material consisting of polyamide 6 nanofibers combined with two types of zeolites, designed for CO2 capture. We detail the fabrication process, as well as the structural, chemical, and morphological characterization of the composites. The results confirmed the successful modification of polyamide 6 nanofibers with both types of zeolites. CO2 sorption measurements revealed that the composite with zeolite Y exhibited a notably high sorption capacity, with a maximum of 35.8 cm³/g, significantly surpassing the performance of amine-modified nanofibers, which demonstrated sorption capacities approximately three times lower. These findings highlight the potential of this composite for efficient CO2 capture, providing valuable insights into its practical application for reducing greenhouse gas emissions. While the CO2 sorption capacities of the composite are lower than those of pure zeolites, the composite offers practical advantages, such as easier handling and simplified application.

PH-controlled-ion-mobility of Laponite-phosphate dispersion for physical hydrogel with improved mechanical properties and sensitivity to CO2

Self-assembled physical nanocomposite hydrogels based on bio-based poly(itaconic acid) and Laponite® nanoclays were prepared and tested as possible CO2 sensors in smart food packaging. The structure and mechanical properties of the fabricated hydrogels were controlled by changing the initial pH of the aqueous Laponite® dispersions stabilised by tetrasodium pyrophosphate. The dispersions were studied by SAXS and analysed using circular disc and fractal model to determine clay agglomeration tendency. Sodium and pyrophosphate ions mobility was investigated by 23Na and 31P 1D as well as spin-spin relaxation times T2 NMR measurements. The rheological behaviour of the produced hydrogels was studied by oscillatory shear measurements. It was found that decreasing the pH of the Laponite® nanodispersions up to 8 increases the strength of the physical interactions between the nanoclays, dispersant, and polyelectrolyte chains, which enables production of dimensionally stable and mechanically robust hydrogels. Their potential application as the CO2-sensitive matrix for construction of environmentally friendly colorimetric sensors was demonstrated showing the CO2 sorption capacity of 0.07 mmol CO2/g. A prototype device of hydrogel sensor was built and tested in a food packaging application to monitor the plum fruit respiration processes.

Synthesis and optimization of 3D porous polymers for efficient CO2 capture and H2 storage

In this study, a new porous organic polymer (KFUPM-CO2) with intrinsic nitrogen atoms as active sites for CO2 capture was optimized and synthesized via Friedel-Crafts alkylation of triptycene and 2,2-bipyridine. The porous polymer shows a high surface area of 1100 m2/g with a tuned microporosity of less than 1.2 nm, confirmed by NLDFT. KFUPM-CO2 showed a remarkable CO2 sorption capacity of 5.6 mmol/g at 273 K, 3.2 mmol/g at 298 K, and a pressure of 760 mmHg KFUPM-CO2 showed a high enthalpy of adsorption of 43.7 kJ/mol for CO2 with IAST selectivity of CO2/N2 of 127 at 273 K and 97 at 298 K on simulated flue gas composition. Additionally, KFUPM-CO2 exhibited an H2 storage capacity of 1.5 wt. % at 77 K and 860 mmHg Grand Canonical Monte Carlo (GCMC) simulations further revealed that KFUPM-CO2 was mainly stabilized by π-π intra-molecular interactions, and exhibited strong van der Waals attractions to CO2 molecules via the pyridyl nitrogen atoms, resulting in the rapid uptake. The combined advantages of binding 2,2-bipyridine with triptycene provided a robust porous polymer with abundant nitrogen sites, permanent porosity, and thermal stability, rendering KFUPM-CO2 an excellent candidate for CO2 capture and H2 storage technologies.

Lithium-Containing Sorbents Based on Rice Waste for High-Temperature Carbon Dioxide Capture

This article studies the influence of the nature of the carrier from rice wastes on the sorption properties of lithium-containing sorbents, and also considers the impact of the modifying additive (K2CO3) and adsorption temperature on their characteristics. It has been shown that the sorption capacity of 11LiK/SiO2 at 500 °C reached 36%, which is associated with the formation of lithium orthosilicate in the sorbent composition, as well as with an increase in the specific surface area of the sorbent. After 12 cycles of sorption–desorption, it was found that the sorption capacity of 11LiK/SiO2 for CO2 decreased by only 8%. Rice waste-based sorbents have a high sorption capacity for CO2 at high temperatures, which allows them to be used for carbon dioxide capture. The results of this study indicate the prospects of using agricultural residues to create effective adsorbents that contribute to reducing environmental pollution and combating global warming.

CO2 sorption of elastomer poly(ionic liquid)s with imidazolium cations having different alkyl chains: Structure-morphology-property relationships and thermodynamic modelling by the PC-SAFT equation of state

In this work related to Carbon Capture and Storage (CCS), the CO2 sorption capacities of a new family of elastomer poly(ionic liquid)s (PILs) with imidazolium cations having different alkyl chains were studied. These PILs were synthesized by chemical modification of polyepichlorohydrin (polyECH) obtained by living anionic polymerization. PolyECH was quaternized with different 1-alkylimidazoles (alkyl = methyl, n-butyl, and n-hexyl) and followed by anion exchange to obtain three PILs: PIL-Me, PIL-nBu, and PIL-nHex. They were analyzed by NMR (1H, 13C, 2D 1H/13C HSQC, APT 13C) and characterized by SEC, DSC, calorimetry, rheology, and XRD SAXS/WAXS. The influence of the alkyl chain on the PIL CO2 sorption was studied with a magnetic suspension balance (MSB) at 35 °C and CO2 pressures varying from 1 to 10 bar. The best results were obtained with PIL having methyl chains (9.60 mg CO2/g PIL at 1.1 bar and 159.28 mg CO2/g PIL at 10.0 bar at 35 °C). Finally, the CO2 sorption properties of these PILs were modeled with the PC-SAFT equation of state (EoS). The pure-component parameters were obtained from model regression of the PILs densities calculated by the Bondi's and Van Krevelen's methods. The binary interaction parameters of the systems CO2/PIL were optimized with average absolute deviations (AAD) lower than 6.3 % for the three PILs. The PC-SAFT modelling of their sorption properties opens interesting prospects for modelling the CO2 sorption process for CCS facilities.

Cationic Imidazolium-Urethane-Based Poly(Ionic Liquids) Membranes for Enhanced CO2/CH4 Separation: Synthesis, Characterization, and Performance Evaluation.

The escalating emissions of CO2 into the atmosphere require the urgent development of technologies aimed at mitigating environmental impacts. Among these, aqueous amine solutions and polymeric membranes, such as cellulose acetate and polyimide are commercial technologies requiring improvement or substitution to enhance the economic and energetic efficiency of CO2 separation processes. Ionic liquids and poly(ionic liquids) (PILs) are candidates to replace conventional CO2 separation technologies. PILs are a class of materials capable of combining the favorable gas affinity exhibited by ionic liquids (ILs) with the processability inherent in polymeric materials. In this context, the synthesis of the IL GLYMIM[Cl] was performed, followed by ion exchange processes to achieve GLYMIM variants with diverse counter anions (NTf2-, PF6-, and BF4). Subsequently, PIL membranes were fabricated from these tailored ILs and subjected to characterization, employing techniques such as SEC, FTIR, DSC, TGA, DMA, FEG-SEM, and CO2 sorption analysis using the pressure decay method. Furthermore, permeability and ideal selectivity assessments of CO2/CH4 mixture were performed to derive the diffusion and solubility coefficients for both CO2 and CH4. PIL membranes exhibited adequate thermal and mechanical properties. The PIL-BF4 demonstrated CO2 sorption capacities of 33.5 mg CO2/g at 1 bar and 104.8 mg CO2/g at 10 bar. Furthermore, the PIL-BF4 membrane exhibited permeability and ideal (CO2/CH4) selectivity values of 41 barrer and 44, respectively, surpassing those of a commercial cellulose acetate membrane as reported in the existing literature. This study underscores the potential of PIL-based membranes as promising candidates for enhanced CO2 capture technologies.

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.

Pressure swing adsorption of Li exchange hierarchical X zeolite for pure hydrogen from binary gas mixture

This study reports the separation of pure hydrogen (H2) employing pressure swing adsorption (PSA). The Li-X and Li-hierarchical X (Li–H-X) zeolite were prepared by an ion exchange process. The sorbents were evaluated through several experiments including, breakthrough, empty bed contact time (EBCT), single-bed, and two-bed PSA with different steps. The effect of pressure, purity, and recovery relationship was developed. The high-pressure PSA study was performed at 4, 6, and 10 bar with varying feed flow rates to assess their efficacy in pure H2 separation using binary gas stream (H2/CO2, 75/25 vol.%). The breakthrough adsorption capacity of Li–H-X exhibited 3.4 mmol g−1 and 0.212 mmol g−1 of CO2 and H2, respectively. Li–H-X shows ∼8% higher CO2 sorption capacity than the Li-X sorbent at 1 bar and 300 K due to the large meso-microporous structure of the sorbent. The two-bed PSA purity and recovery were found higher than single-bed PSA. Using two-bed PSA, the Li–H-X achieved a 99.5% of purity, 92.9% of recovery, and 10.4 mL min−1 g−1 of productivity, which was ∼16% higher recovery and productivity than single-bed PSA at a flow rate of 1200 mL min−1 at 6 bar. With increasing the pressure and flow rate, the recovery of Li–H-X was enhanced up to 93.7% with 99.1%–99.9% H2 purity. The long-term PSA was run using Li–H-X sorbent for 7.5 h with 230 cycles with H2 purity between 98.5 and 99.5% at 6 bar. Interestingly, the adsorbent shows the scalability of PSA for efficient H2 separation for a binary mixture of H2/CO2.

Sorption of Soil Carbon Dioxide by Biochar and Engineered Porous Carbons.

CO2 is 45 to 50 times more concentrated in soil than in air, resulting in global diffusive fluxes that outpace fossil fuel combustion by an order of magnitude. Despite the scale of soil CO2 emissions, soil-based climate change mitigation strategies are underdeveloped. Existing approaches, such as enhanced weathering and sustainable land management, show promise but continue to face deployment barriers. We introduce an alternative approach: the use of solid adsorbents to directly capture CO2 in soils. Biomass-derived adsorbents could exploit favorable soil CO2 adsorption thermodynamics while also sequestering solid carbon. Despite this potential, previous study of porous carbon CO2 adsorption is mostly limited to single-component measurements and conditions irrelevant to soil. Here, we probe sorption under simplified soil conditions (0.2 to 3% CO2 in balance air at ambient temperature and pressure) and provide physical and chemical characterization data to correlate material properties to sorption performance. We show that minimally engineered pyrogenic carbons exhibit CO2 sorption capacities comparable to or greater than those of advanced sorbent materials. Compared to textural features, sorbent carbon bond morphology substantially influences low-pressure CO2 adsorption. Our findings enhance understanding of gas adsorption on porous carbons and inform the development of effective soil-based climate change mitigation approaches.

Synergistic effects of CeO2 and Al2O3 on reactivity of CaO-based sorbents for CO2 capture

The calcium looping (CaL) process, comprising reversible calcination and carbonation reactions with CO2 and CaO-based sorbents, stands out as a highly promising industrial approach for CO2 capture. A significant challenge, however, is the swift degradation of the reactivity of CaO-based sorbents. In this study, CeO2-stabilized and CeO2/Al2O3 co-stabilized CaO-based sorbents were produced via a Pechini technique. Results indicated that incorporating CeO2 enhanced the CO2 sorption performance of CaO-based sorbents. The most effective CeO2-stabilized CaO-based sorbents (a CeO2/CaO mass ratio of 15:85) demonstrated an initial sorption capacity of 0.479 gCO2/gmaterial, undergoing a 41% reduction in its initial reactivity by the 20th cycle. To enhance CO2 sorption stability and reduce the high cost linked with the expensive cerium precursor, Al2O3 was introduced as the second stabilizer into the CeO2-stabilized CaO-based sorbents. When the CeO2/Al2O3/CaO mass ratio was adjusted to 5:10:85, the CO2 sorption capacity of CeO2/Al2O3 co-stabilized CaO-based sorbents reached 0.354 gCO2/gmaterial in the 20th cycle. This represented only a 17.7% reduction in its initial performance, surpassing the CeO2-stabilized counterpart by 26.3%. Comprehensive characterizations, including scanning electron microscopy (SEM), X-ray photoelectron spectrometry (XPS), and electron paramagnetic resonance (EPR), revealed that incorporating Al2O3 into the CeO2-stabilized CaO-based sorbents served a dual purpose: acting as a stable framework to inhibit pore structure deterioration and increasing the concentration of oxygen vacancies. In consequence, the synergistic effect of CeO2 and Al2O3 improved both structural stability and oxygen vacancy concentration of the sorbents, ultimately leading to superior CO2 sorption performance.

Scalable and Highly Porous Membrane Adsorbents for Direct Air Capture of CO2.

Direct air capture (DAC) of CO2 is a carbon-negative technology to mitigate carbon emissions, and it requires low-cost sorbents with high CO2 sorption capacity that can be easily manufactured on a large scale. In this work, we develop highly porous membrane adsorbents comprising branched polyethylenimine (PEI) impregnated in low-cost, porous Solupor supports. The effect of the PEI molecular mass and loading on the physical properties of the adsorbents is evaluated, including porosity, degradation temperature, glass transition temperature, and CO2 permeance. CO2 capture from simulated air containing 400 ppm of CO2 in these sorbents is thoroughly investigated as a function of temperature and relative humidity (RH). Polymer dynamics was examined using differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS), showing that CO2 sorption is limited by its diffusion in these PEI-based sorbents. A membrane adsorbent containing 48 mass% PEI (800 Da) with a porosity of 72% exhibits a CO2 sorption capacity of 1.2 mmol/g at 25 °C and RH of 30%, comparable to the state-of-the-art adsorbents. Multicycles of sorption and desorption were performed to determine their regenerability, stability, and potential for practical applications.

CO2 capture using silica-immobilized dicationic ionic liquids with magnetic and non-magnetic properties

The need to find alternative materials to replace aqueous amine solutions for the capture of CO2 in post-combustion technologies is pressing. This study assesses the CO2 sorption capacity and CO2/N2 selectivity of three dicationic ionic liquids with distinct anions immobilized in commercial mesoporous silica support (SBA- 15). The samples were characterized by UART-FTIR, NMR, Raman, FESEM, TEM, TGA, Magnetometry (VSM), BET and BJH. The highest CO2 sorption capacity and CO2/N2 selectivity were obtained for sample SBA@DIL_2FeCl4 [at 1 bar and 25 °C; 57.31 (±0.02) mg CO2/g; 12.27 (±0.72) mg CO2/g]. The results were compared to pristine SBA-15 and revealed a similar sorption capacity, indicating that the IL has no impact on the CO2 sorption capacity of silica. On the other hand, selectivity was improved by approximately 3.8 times, demonstrating the affinity of the ionic liquid for the CO2 molecule. The material underwent multiple sorption/desorption cycles and proved to be stable and a promising option for use in industrial CO2 capture processes.

Application of lithium modified ZIF-90 in a hybrid absorption-adsorption method for carbon capture

Herein, a lithium modified Zeolitic Imidazolate Framework-90 (ZIF-90-OLi) was used in a slurry with its organic ligand Imidazole Carboxaldehyde (ICA) water, and glycol to improve the process conditions for the capture system and enhance the sorption ability. The performance of this slurry was compared to two other slurries, one based on the parent ZIF-90 nanoporous material with ICA/water/glycol and another based on ZIF-8, its organic ligand Methylimidazole (MIm) and water/glycol. The comparison to ZIF-8 was done because of its use as a ZIF of reference in carbon capture. The maximum sorption capacity for CO2 by the alkali containing slurry was 7.19 mol/L and the maximum CO2/N2 selectivity was 222.93 compared to 2.72 mol/L and 121.63 for the ZIF-8/water/glycol/mlm slurry.

Dual synergistic effect of the amine-functionalized MIL-101@cellulose sorbents for enhanced CO2 capture at ambient temperature

The development of high carbon dioxide (CO2) sorption capacity materials is necessary for the deployment of the CO2 capture and storage strategy. Metal-organic frameworks (MOFs) have emerged as promising substitutes for traditional liquid and solid CO2 capture sorbents due to their high surface area, tunable pore size, diverse composition, and various physical and chemical properties. However, MOFs feature the intrinsic limitations of powder agglomeration, weak binding affinity, and sluggish diffusion kinetics, thus hindering their industrial application in CO2 capture. Herein, we design an amine-functionalized MIL-101@cellulose (NH2-MIL-101@BM) composite sorbent by anchoring NH2-MIL-101 nanoparticles onto the BM matrix through hydrogen bonding interaction. The dual synergistic effect, origin from the physical sorption synergistic effect and chemisorption synergistic effect proposed between NH2-MIL-101 and BM, not only facilitates the mass transfer of CO2 by reducing the diffusion resistance through hierarchical-pore structure but also offers stronger sorption sites with CO2 by increasing the adsorption energy of metal-CO2 or amine-CO2, which are confirmed by series of characterizations and theory functional calculations. Benefiting from the above merits, the NH2-MIL-101@20 %BM sorbent delivers a superior initial CO2 sorption capacity of 13.4 mmol/g when the BM doping amount is 20 wt% at 25 °C, and also shows good recycle stability even after 15 runs with maintainable structure. This work displays the in-depth mechanism understanding for enhanced CO2 capture, providing value inspiration for future MOF-based composite sorbent construction for CO2 capture at ambient temperatures.

Modulated synthesis of hcp MOFs for preferential CO2 capture.

We herein show that the μ2-OH bridging groups in the double M12O8(OH)14 clusters of hcp UiO-66 could act as a preferential CO2 sorption site, compared to fcu UiO-66. As such, hcp-UiO-66-0.015 shows a high binary CO2 sorption capacity of 0.31 mmol g-1 and CO2/N2 (15/85) mixture selectivity of 87 at 298 K and 1 bar, which holds great potential for post-combustion CO2 capture.

Mg2-xCaxAl layered double hydroxide-derived mixed metal oxide porous hexagonal nanoplatelets for CO2 sorption.

Porous hexagonal nanoplatelets of mixed metal oxide (MMO) derived from the calcination of MgAl layered double hydroxide exhibits a CO2 sorption capacity of 1.99 mmol g-1 at 30 °C, with a retention of 87% sorption capacity over 10 carbonation-decarbonation cycles and a CO2 sorption capacity of 1 mmol g-1 at 200 °C with a 40% increase in capacity over 10 cycles. The high sorption capacity is attributed to the porous nanoplatelet structure of the MMO with a BET surface area of 115 m2 g-1, which enables increased CO2 diffusion. Upon partially replacing magnesium with calcium (33, 50 and 66 mol%), the CO2 sorption capacity of the MMO increases with an increase in temperature. MMO derived from LDH, in which 66% of magnesium is replaced by calcium (MgCaAl-66), delivers CO2 sorption capacities of 1.38, 1.31, 2.50, 4.85 and 7.75 mmol g-1 at 200, 300, 350, 400 and 600 °C, respectively, which is significant for application in the sorption-enhanced water gas shift (SEWGS) process. MgCaAl-66 MMO exhibits a sorption capacity of 1 mmol g-1, which is stable over 10 cycles at 200 °C, and a sorption capacity of 3.68 mmol g-1 at 400 °C with 85% capture efficiency retention over 10 cycles. While the incorporation of Ca2+ serves multiple purposes such as increasing basic defect sorption sites and improving stability to repress the sintering-induced limitation of MMO over sorption cycles, the porous nanoplatelets act as individual sorbent units resisting volume changes through carbonation-decarbonation cycles.

Performance of Li exchange hierarchical X zeolite for CO2 adsorption and H2 separation

Li exchange hierarchical X zeolite (Li-H-X) was prepared by decationization of X zeolite by NH4Cl solution followed by Li exchange and subsequent calcination. NH4-X and Li-X were prepared to compare the results of Li-H-X. XRD, FE-SEM, EDS, N2 adsorption–desorption, and micro-/mesoporous volume were performed. The higher mesoporosity was confirmed in Li-H-X due to the framework dealumination during decationization. Static and dynamic sorption capacity of sorbents was evaluated to identify the performance of sorbent. The CO2 and H2 equilibrium adsorption capacity of Li-H-X was found to be 9.6 mmol g−1 and 0.78 mmol g−1, respectively, at 298 K and 20 bar, which was 25 % (CO2) and 30 % (H2) higher than Li-X. Static experimental data were validated using the Langmuir, Freundlich, and Sips models. The CO2 & H2 dynamic sorption capacity of Li-H-X sorbent for binary gas (CO2/H2, 25/75 %) was 4.145 mmol g−1 and 0.258 mmol g−1 at 303 K and 10 bar. The higher sorption capacity of Li-H-X was obtained due to large micro-/mesoporous volume of sorbent, which may allow to access unoccupied sites at higher pressure. This result reveals that micro-/mesoporous structure of zeolite adsorbs significantly higher CO2 from binary gas stream, which can use to separate pure H2 from gas stream.

Low-Temperature Composite CO2 Sorbents Based on Amine-Containing Compounds

The use of technologies based on combustion of carbon-containing fossil fuel leads to emission of large amounts of CO2, one of the main greenhouse gases, into the atmosphere. To reduce the CO2 level in the atmosphere, systems for CO2 sorption from various gas sources are being developed. The systems allowing the CO2 sorption and desorption at low temperatures (25–200°С) are of most interest. Most frequently, such systems are composite materials consisting of a porous support and a CO2 chemisorbent dispersed on it. Low-volatile amine-containing compounds are the most promising among organic chemisorbents. Classification of the amine-containing sorbents with respect to the preparation procedure is discussed. The procedures include impregnation, covalent grafting, and in situ polymerization on the support surface. The impregnation procedure is simple and cheap in implementation. The sorption characteristics of materials prepared by impregnation depend on the efficiency of the dispersion of the active component, which is determined by the characteristics of the support pore structure, in particular, by the ability of the pore surface for chemical or electrostatic interaction with the supported amine-containing compound. The covalent grafting is based on immobilization of alkoxyaminosilanes on the surface of porous silica materials. The supports for implementing this approach should contain a large amount of silanol groups on the surface and should have the pore size sufficient for the efficient transport of CO2 molecules to amino groups. The main drawback of the grafting method is low thickness of the amine-containing component layers obtained. In situ polymerization is used for preparing materials with high content of grafted functional groups. Provided that the blocking of support pores is excluded in the course of in situ polymerization, materials of this type exhibit the highest sorption capacity for CO2.

Carbon capture from low CO2 concentration stream through ternary alkali metal nitrates promotion of MgO sorbents at intermediate temperature and low space velocity

Many MgO sorbents exhibit high CO2 uptake in the presence of high concentration CO2 and aided by high space velocity, which unfortunately leads to low CO2 capture efficiency from the gas stream. This study investigates the effect of Li/Na/K ratio on sorption performance in dilute CO2 streams (15% CO2) using alkali metal nitrates-promoted MgO sorbents at a low space velocity of 20 ml/g·min in fixed bed reactor. Study shows that the ratio of Li/Na/K in ternary alkali nitrate salt mixture significantly affects the induction periods for the second phase CO2 sorption, which is a key contributor to high CO2 uptake. High LiNO3 content in ternary mixture leads to long induction period, and therefore lower CO2 capacity during the 4 h period. Conversely, high ratios of NaNO3 and KNO3 leads to shorter induction periods. Among the samples, MgO with 9 mol% (Li0.18Na0.52K0.3) exhibits the highest CO2 sorption capacity of 5.56 mmol/g at 240°C in 4 h (20.6% CO2 capture efficiency) and 3.18 mmol/g after 5 cycles (10.8% CO2 capture efficiency). Comparative studies show that optimal temperatures for CO2 sorption are higher when using pure CO2 (280 to 320°C) than when using 15% CO2 (240°C) due to the thermodynamic equilibrium. CO2-TPD results indicate that CO2 desorption proceeds in two phases similar to CO2 sorption, and the presence of alkali salt in MgO also promotes the decomposition of bulk carbonate to CO2. It is shown that molten salt migration and agglomeration of MgO particles are likely the factors that lead to decline in CO2 uptake over the sorption-desorption cycles.