CO2 Sorption Research Articles

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.

Potassium nickel hexacyanoferrate–polyacrylonitrile composite for removing cobalt, strontium, and cesium from radioactive laundry wastewater

AbstractThe applicability of potassium nickel hexacyanoferrate–polyacrylonitrile (KNiFC–PAN) for the sorption of Co2+, Sr2+, and Cs+ from radioactive laundry wastewater generated in nuclear power plants was investigated. Competitive sorption of Co2+, Sr2+, and Cs+ onto KNiFC–PAN was studied for single, binary, and ternary solutions. The Langmuir, Freundlich, Kargi–Ozmıhci, Koble–Corrigan, and Langmuir–Freundlich models predicted the single‐sorption data (R2 ≥ 0.942, sum of squared error ≤ 0.105). The sorption isotherms were nonlinearly favorable (Freundlich coefficient, NF = 0.288–0.842). According to the Langmuir, Freundlich, Kargi–Ozmıhci, Koble–Corrigan, and Langmuir–Freundlich models, at pH 5 (C0 = 20 mM), KNiFC−PAN exhibited the highest maximum sorption capacity (qmL) for Cs+ among the investigated cations, wherein the primary mechanism was physical sorption. The competition between the metal ions in the binary and ternary systems reduced the respective sorption capacities. Binary and ternary sorption models, such as the ideal adsorbed solution theory (IAST) model coupled with Freundlich (IAST–Freundlich), IAST–Langmuir, and IAST–Langmuir–Freundlich models, were fitted to the experimental data; among these, the IAST–Freundlich model was the most accurate for the binary and ternary systems. The presence of sodium 4‐n‐octylbenzenesulfonate and dodecylbenzene–sulfonic acid sodium salt as anionic surfactants strongly affected the sorption capacity on KNiFC–PAN owing to increased distribution coefficients (Kd) of Cs+, Sr2+, and Co2+. Thus, KNiFC–PAN is promising for removing Cs+, Sr2+, and Co2+ from radioactive laundry wastewater.

Modeling of methane and carbon dioxide sorption capacity in tight reservoirs using Machine learning techniques

The viability of enhanced coalbed methane recovery (ECBM) and enhanced shale gas recovery (ESGR) are abundantly explored in various studies since they present a solution for ongoing energy demand and environmental crisis. As a matter of challenge, the prediction of the gas sorption profile poses a significant obstacle in the development of such resources. In this regard, mathematical models, numerical simulations, empirical correlations, and experimental measurements suffer from over-simplification, computationally extensive calculations, time-consuming, and costly processes. This work examines different machine learning methods, from shallow to deep learning, to investigate their capability to model 3804 data points of methane (CH4) and/or carbon dioxide (CO2) sorption capacity in shale and coal at different thermodynamic conditions. Percentage of CO2 in injection gas, rock type, total organic carbon (TOC), moisture, temperature, and pressure were taken as input. Hyperparameter tuning was executed by Optuna optimizer. According to the results, the random forest (RF) was the most proficient predictor for both test subsets of CH4 (MAE = 0.0864, MSE = 0.0231, RMSE = 0.1520) and CO2 (MAE = 0.0529, MSE = 0.0533, RMSE = 0.2308) sorption capacity. Based on the trend prediction simulation, RF predictors were able to properly capture the single and binary sorption capacities. More importantly, they successfully predict the abnormal descending behavior of CO2 sorption in high pressures. In addition, a sensitivity analysis was carried out to acquire the importance of input features and model hyperparameters in the training process. Input feature impacts were consistent with technical expectations of geology and reservoir engineering aspects. Both models are capable of being applied to lab scale and further developed for their application in reservoir scale simulators.

Functional Activated Biocarbons Based on Biomass Waste for CO2 Capture and Heavy Metal Sorption.

Inexpensive porous activated biocarbons were prepared from biomass and agriculture waste following the method of thermal and hydrothermal carbonization and activation with superheated water vapor. The activated biocarbons were characterized by nitrogen adsorption-desorption at 77 K, SEM, XRD, Raman spectrometry, FTIR spectroscopy, determination of particle size, and elemental composition by XRF. The specific surface area was in the range of 240-709 m2/g, and the total pore volume was from 0.12 to 0.43 cm3/g. The percentage of microporosity in activated biocarbons was 89-92%. These activated biocarbons have been used for CO2 and heavy metal sorption. Activated biocarbons based on pine cones and birch prepared by thermal carbonization and activation with superheated water vapor had the highest ability to capture CO2 and amounted to 6.43 and 6.00 mmol/g at 273 K, as well as 4.57 and 4.22 mmol/g at 298 K, respectively. The best activated biocarbon was characterized by unchanged stability after 30 adsorption and desorption cycles. It was proved that the adsorption of CO2 depends on narrow micropores (<1 nm). Activated biocarbons have also been analyzed as effective adsorbents for removing Cu2+, Zn2+, Fe2+, Ni2+, Co2+, and Pb2+ ions from aqueous solutions. Activated biocarbons are effective adsorbents for the removal of lead and zinc ions from aqueous solutions.

Amino acid-based ionic liquid as a promising CO2 sorption increasing agent by aqueous MDEA solution

The present study aims to enhance the efficiency of CO2 absorption by aqueous MDEA solutions and reduce the energy consumption of the process by designing combined absorbent systems. For this, a novel ionic liquid based on the amino acid glycine, known as bis(2-hydroxyethyl)dimethylammonium glycinate ([M2E2A][Gly]), was synthesized and investigated as a carbon dioxide sorbent. The composition was confirmed using 1H NMR. The sorption capacity of neat [M2E2A][Gly], its aqueous solutions and amine + IL aqueous mixtures was evaluated gravimetrically at different temperatures and concentrations of comprising components. The study observed an increase in both the sorption capacity and the rate of chemical reaction with carbon dioxide when using this compound as an additive. The H2O/MDEA/[M2E2A][Gly] absorbent (50/30/20 wt%) exhibited the highest sorption capacity of 2.98 mol CO2·kg-1solution. Furthermore, a mechanism of CO2 interaction with the H2O/MDEA/[M2E2A][Gly] absorbent was suggested and confirmed using FTIR spectroscopy. To assess the effect of the IL concentration on the absorbent’s viscosity behavior, studying rheological properties of absorbent with different contents of [M2E2A][Gly] were studied.

Discovery and In Situ Crystallization Studies of Cerium-Based Metal-Organic Frameworks with V-Shaped Linker Molecules.

We report the discovery and characterization of two porous Ce(III)-based metal-organic frameworks (MOFs) with the V-shaped linker molecules 4,4'-sulfonyldibenzoate (SDB2-) and 4,4'-(hexafluoroisopropylidene)bis(benzoate) (hfipbb2-). The compounds of framework composition [Ce2(H2O)(SDB)3] (1) and [Ce2(hfipbb)3] (2) were obtained by using a synthetic approach in acetonitrile that we recently established. Structure determination of 1 was accomplished from 3D electron diffraction (3D ED) data, while 2 could be refined against powder X-ray diffraction (PXRD) data using the crystal structure of an isostructural La-MOF as the starting model. Their framework structures consist of chain-like inorganic building units (IBUs) or hybrid-BUs that are interconnected by the V-shaped linker molecules to form framework structures with channel-type pores. The composition of both compounds was confirmed by PXRD, elemental analysis, as well as NMR and IR spectroscopy. Interestingly, despite the use of (NH4)2[CeIV(NO3)6] in the synthesis, cerium ions in both MOFs occur exclusively in the + III oxidation state as determined by X-ray absorption near edge structure (XANES) and X-ray photoelectron spectroscopy (XPS). Thermal analyses reveal remarkably high thermal stabilities of ≥400 °C for the MOFs. Initial N2 sorption measurements revealed the peculiar sorption behavior of 2 which prompted a deeper investigation by Ar and CO2 sorption experiments. The combination with nonlocal density functional theory (NL-DFT) calculations adds to the understanding of the nature of the different pore diameters in 2. An extensive quasi-simultaneous in situ XANES/XRD investigation was carried out to unveil the formation of Ce-MOFs during the solvothermal syntheses in acetonitrile. The crystallization of the two Ce(III)-MOFs presented herein as well as two previously reported Ce(IV)-MOFs, all obtained by a similar synthetic approach, were studied. While the XRD patterns show time-dependent MOF crystallization, the XANES data reveal the presence of Ce(III) intermediates and their subsequent conversion to the MOFs. The addition of acetic acid in combination with the V-shaped linker molecule was identified as the crucial factor for the formation of the crystalline Ce(III/IV)-MOFs.

Ionic Conjugated Microporous Polymers for Cycloaddition of Carbon Dioxide to Epoxides

AbstractAlong the development of ionic porous organic polymers, simple and efficient synthetic methods are actively pursued. Herein, the Debus–Radziszewski reaction is applied to synthesize ionic conjugated microporous polymers (iCMPs) in one step. A series of imidazolium‐linked iCMP‐X (X = 1, 2, 3) are developed for CO2 sorption and in situ conversion with epoxide into cyclic carbonates. The as‐synthesized iCMPs are characterized in detail by scanning electron microscope, solid‐state nuclear magnetic resonance, X‐ray photoelectron spectroscopy, X‐ray diffraction analysis, N2/CO2 sorption, and more. Among all synthesized iCMPs, iCMP‐1 possesses the highest specific surface area and in turn the strongest CO2 sorption capacity. Moreover, through a simple anion ion exchange reaction with halide, iCMP‐1 is transformed to iCMP‐1@Cl that embodies significant catalytic capability for converting CO2 into cyclic carbonates.

Converting Nanoflower-like Layered Double Hydroxides into Solvent-Free Nanofluids for CO2 Capture.

Due to the flexibility and versatility of the layered crystal structure of layered double hydroxides (LDHs), they have shown great potential in various fields. However, LDH nanosheets (LDH-NSs) are easy to agglomerate, leading to the problem of accumulation, which hinders their further application. Accordingly, once LDHs are combined with solvent-free nanofluids (SFNs), the advantages of LDHs and SFNs could be combined to achieve an extraordinary performance. However, the stacked structure of traditional LDHs is not conducive to the exposure of hydroxyl functional groups, and hydroxyl sites are key to the conversion of LDHs to SFNs. Therefore, in this work, nanoflower-like LDHs (NFLs) with abundant exposed hydroxyl groups were prepared and combined with organic oligomers to achieve a solid-to-liquid transition. The formation mechanism of NFLs and the grafting mechanism of OS-PEA on their surface were identified. The prepared NFL-F3 still has good fluidity and dispersion stability in different solvents after storage for 100 days. The high-saturated grafting density on the surface of NFLs increased the steric hindrance effect of the nanoparticles, thereby improving the dispersion stability and reducing the viscosity of NFL-F3. Notably, the CO2 sorption performance of NFL-F3 is significantly improved, which is attributed to the voids between polymers, physical sorption, and good fluidity caused by high-saturation grafting on the surface of NFL-F3. Finally, by combining the sorption behavior and model fitting, it was confirmed that the physical effect was dominant in CO2 sorption by the NFL-F, which saved energy for the sorption-desorption process of its industrial application. Moreover, NFL-F3 has a good CO2/N2 separation performance and cycle stability. We envision that this general strategy will open up new insights into the construction of innovative low-viscosity LDH-based SFNs with high CO2 capacity and facilitate CO2/N2 selectivity and offer new directions for LDH utilizations.

Elucidating influences of defects and thermal treatments on CO2 capture of a Zr-based metal–organic framework

Carbon capture and storage (CCS) technology is currently an essential response to the global warming problem caused by excessive CO2 emissions. Efficient and reproducible adsorbents for flue gas treatment play an important role in CCS technology, and metal–organic frameworks (MOFs) are considered to be ideal candidates by virtue of their designable CO2 sorption sites. However, carbon capture performance evaluation and reproducibility of MOFs still hinder their application promotion in industrial production. In this work, an extended UiO-66-type MOF based on 1,4-naphthalenedicarboxylate, was successfully synthesized in both a near defect-free form (UiO-66N) and a defect-rich form (DUiO-66N), for exploring the influence of crystalline defects and thermal treatments on carbon capture performance. Although powder X-ray diffraction showed that UiO-66N and DUiO-66N possessed the same crystalline phase, transmission electron microscopy, thermalgravimetric analyse and gas/dye sorption confirmed the presence of crystalline defects and the variation of porosity in DUiO-66N. CO2 sorption isotherms and flue gas breakthrough experiments revealed the defect-induced improved carbon capture performance, which was also supported by density functional theory. Meanwhile, the metastability of defects required low thermal treatment temperatures for activation and regeneration thus maintaining the superior carbon capture performance. These findings suggested that in reproducing and evaluating the carbon capture performance of MOFs, it cannot rely only on the global crystalline phase judgment, but needs to identify the local fine structure as well as optimize activation and regeneration conditions.

Highly Selective CO2 Hydrogenation to Methanol over Complex In/Co Catalysts: Effect of Polymer Frame

The growing demand for new energy sources governs the intensive research into CO2 hydrogenation to methanol, a valuable liquid fuel. Recently, indium-based catalysts have shown promise in this reaction, but they are plagued by shortcomings such as structural instability during the reaction and low selectivity. Here, we report a new strategy of controlling the selectivity and stability of bimetallic magnetically recoverable indium-based catalysts deposited onto a solid support. This was accomplished by the introduction of a structural promoter: a branched pyridylphenylene polymer (PPP). The selectivity of methanol formation for this catalyst reached 98.5%, while in the absence of PPP, the catalysts produced a large amount of methane, and the selectivity was about 70.2%. The methanol production rate was higher by a factor of twelve compared to that of a commercial Cu-based catalyst. Along with tuning selectivity, PPP allowed the catalyst to maintain a high stability, enhancing the CO2 sorption capacity and the protection of In against sintering and over-reduction. A careful evaluation of the structure–activity relationships allowed us to balance the catalyst composition with a high level of structural control, providing synergy between the support, magnetic constituent, catalytic species, and the stabilizing polymer layer. We also uncovered the role of each component in the ultimate methanol activity and selectivity.

Developing High-Capacity Solid "Molecular Basket" Sorbents for Selective CO2 Capture and Separation.

ConspectusSince carbon-based energy continues to dominate (over 80%) the global primary energy supply, carbon dioxide capture, utilization, and sequestration (CCUS) is deemed to be a promising and viable option to mitigate greenhouse gas emissions and climate change, for which CO2 capture is critical to the overall success of CCUS. Although liquid amine scrubbing is a mature technology for carbon capture, it is energy-intensive and costly due to energy consumption in solvent heating and water evaporation apart from the energy needed to break amine-CO2 bonding. To address this challenge, Song's group developed a new design approach for adsorptive CO2 capture and separation, namely, "molecular basket" sorbents (MBS), without the need for dealing with solvent heating and water evaporation. The solid MBS consisting of polymeric amines (such as PEI) immobilized into nanoporous materials (such as SBA-15) possesses a high capacity for CO2 capture with high selectivity, fast kinetics, and good regenerability. Consequently, MBS can greatly reduce energy consumption and carbon capture cost. Conventional adsorbents such as zeolites, activated carbon, alumina, and silica have low adsorption capacities, and their use of CO2 adsorption requires prior removal of moisture and cooling of flue gas (∼35 °C). On the contrast, the CO2 sorption capacity of MBS can even be promoted by the presence of moisture/steam and reaches the best performance closer to flue gas temperature (∼75 °C). This Account presents an overview of our research progress in the material development and fundamental understanding of MBS for CO2 capture and the separation of CO2 from various gas streams. It begins with an illustration of the MBS concept, followed by efforts to improve the performance and pilot-scale demonstration of MBS for CO2 capture. With the systematic characterization of MBS by various ex situ and in situ techniques, a better understanding is developed for the CO2 sorption process mechanistically. Furthermore, this Account demonstrates how the fundamental understanding of the CO2 sorption mechanism promotes the further development of more robust and advanced sorbent materials with improved CO2 sorption capacity, kinetics of sorption and desorption, and cyclic stability. Finally, an outlook is provided for the future design and development of novel sorbent materials and the CO2 sorption process for various gas streams including flue gas, biogas, air, and hydrogen streams.

Long Time CO2 Storage Under Ambient Conditions in Isolated Voids of a Porous Coordination Network Facilitated by the "Magic Door" Mechanism.

A coordination network containing isolated pores without interconnecting channels is prepared from a tetrahedral ligand and copper(I) iodide. Despite the lack of accessibility, CO2 is selectively adsorbed into these pores at 298K and then retained for more than one week while exposed to the atmosphere. The CO2 adsorption energy and diffusion mechanism throughout the network are simulated using Matlantis, which helps to rationalize the experimental results. CO2 enters the isolated voids through transient channels, termed "magic doors", which can momentarily appear within the structure. Once inside the voids, CO2 remains locked in limiting its escape. This mechanism is facilitated by the flexibility of organic ligands and the pivot motion of cluster units. In situ powder X-ray diffraction revealed that the crystal structure change is negligible before and after CO2 capture, unlike gate-opening coordination networks. The uncovered CO2 sorption and retention ability paves the way for the design of sorbents based on isolated voids.

Sorption of Cs, Sr, and Co from a solution by a composite sorbent (ClSZ) based on zeolite depending on the activation temperature

Sorption of Cs, Sr, and Co from a solution by a composite sorbent (ClSZ) based on zeolite depending on the activation temperature

Minimizing Carbon Dioxide Emissions with Clinoptilolite Zeolite in Moris Pineapple Cultivation on Drained Sapric Soils

Drained tropical peat soils for agriculture emit more carbon dioxide (CO2) into the atmosphere from their stored carbon compared with their pristine state. Field and laboratory experiments were conducted to assess whether the natural zeolite of the clinoptilolite (ZeoC) species could be included in the pineapple fertilization program to decrease the CO2 emissions from tropical sapric soils. The static closed-chamber and laboratory incubation methods were used to determine the effects of ZeoC on the CO2 emitted from a drained sapric soil planted with Moris pineapple. The treatments assessed were as follows: (a) suggested ratio of ZeoC (5 g, 10 g, 14 g, and 20 g of ZeoC) and 20 g compound NPK 30:1:32 fertilizer, enumerated based on the pineapple plant requirement; (b) 20 g of compound NPK 30:1:32 fertilizer only; and (c) unfertilized sapric soils. The drained sapric soils amended with ZeoC (rate of 5 g to 20 g/plant) minimized the CO2 emissions compared with those without the ZeoC, because of the physical and chemical sorption of organic compounds and polar CO2 onto the lattices of ZeoC, which inhibited organic matter decomposition. ZeoC fertilization reduces sapric soil acidity and improves Moris pineapple fruit quality attributes and yield. Monthly pineapple fertilization with ZeoC at the vegetative and flowering phases is an alternative agronomic strategy to reduce CO2 emissions. This approach does not reduce pineapple yield on drained tropical sapric soils.

Peering into the mechanisms of granulation and CO2 capture on alginate-assisted Li2CaSiO4-decorated Li4SiO4 sorbents

In recent years, high-temperature CO2 capture technology based on Li4SiO4-based sorbents has received widespread attention. However, powder elutriation and low sorption performance of Li4SiO4 hinder its practical application. In this work, these two obstacles have been solved in one step via a novel alginate-assisted route, via which the granulation and performance enhancement of Li4SiO4 sorbents were simultaneously achieved. The obtained Li4SiO4 pellets exhibited good mechanical strength (i.e., anti-attrition ability), demonstrating the suitability for the realistic application in circulating fluidized bed systems. In addition, Li2CaSiO4 phase was formed in the synthesis process and well dispersed in the sorbent. Meanwhile, the produced Li4SiO4 pellets (especially the pellets derived from lithium acetate) were featured with wrinkled surfaces. As a result, Li2CaSiO4-decorated Li4SiO4 sorbents displayed satisfactory CO2 sorption capacity reaching 0.24 g CO2/g sorbent. To clarify the mechanism of Li2CaSiO4 decorating, Li2CaSiO4-Li4SiO4-CO2 sorption model based on the double-shell reaction mechanism was proposed. Following this model, Li2CaSiO4 functioned as a ‘catalyst’ layer that greatly promoting the diffusion of Li+ and O2–, thus improving the cyclic CO2 sorption performance of Li4SiO4 sorbent. In conclusion, two main problems (elutriation and poor sorption performance) of Li4SiO4-based CO2 sorbent have been well mitigated in one step via alginate-assisted technique, which surely helps pave the way for the practical application of Li4SiO4 sorbents for CO2 capture.

Amine-functionalized MIL-101(Cr) fibers for direct air capture at cold temperatures using rapid temperature vacuum swing adsorption

Given that most of the world shows annual temperatures lower than 25 °C and some regions exhibit a large diurnal temperature difference in a single day, it is desirable to explore the CO2 sorption behavior of materials not only at ambient (25 °C) but also at cooler, “sub-ambient” conditions (defined here as < 25 °C). These cold temperatures may offer advantages for DAC such as higher gas adsorption capacities and lower absolute humidity, reducing concomitant water adsorption. Here, amine-functionalized MIL-101(Cr) fibers are evaluated at cold temperatures using rapid temperature vacuum swing adsorption (RTVSA). MIL-101(Cr)/cellulose acetate fibers loaded with macromolecular amines are evaluated as practical gas–solid contactors. As spun MIL-101(Cr) fibers show desirable properties for use as structured contactors such as high permeance and low pressure drop. Breakthrough and RTVSA experiments are conducted in the presence of humidity at sub-ambient temperatures to understand the CO2 adsorption and desorption behavior of the sorbent/contactor under conditions approaching practical operation. With optimized amine loading, the PEI-MIL-101(Cr) fibers give CO2 capacities comparable to the powder form of the sorbent, as well as sharp breakthrough curves at fast flow rates (1.4 m/s superficial velocity) suggesting the system is not limited by additional mass transfer resistances under the tested conditions. RTVSA shows fast desorption kinetics (14.4 mmol of CO2/g of fiber/h) at moderate desorption conditions, at 0.1 bar vacuum with temperatures below 80 °C. The entire cycle during RTVSA finishes in ∼ 25 min with ∼ 76 mol% CO2 purity as the product in this initial, modestly optimized study.

Separation of CO2 using biochar and KOH and ZnCl2 activated carbons derived from pine sawdust

Due to the CO2 emissions and greenhouse effect, reducing its harmful impacts on climatic conditions is necessary. CO2 adsorption in a microporous carbon structure is one of the more effective separation techniques to avoid this type of emissions. In this work, one biochar (BC) and five activated carbons (ACs) were produced from Pinus radiata sawdust by chemical activation with potassium hydroxide (KOH) or zinc chloride (ZnCl2). Characterization was performed by scanning and transmission electron microscopy (SEM and TEM), surface area and pore size distribution by volumetric N2 and CO2 adsorption experiments using the Brunauer-Emmet-Teller (BET) and Barret-Joyner-Halenda (BJH) methods, respectively, X-ray diffraction (XRD), elemental analysis and X-ray photoelectron spectroscopy (XPS). The performance efficiency of the carbons was analyzed in terms of CO2 adsorption capacity at an absolute pressure range of 0–760 mmHg and at different temperatures (0, 25 and 50 ºC). The apparent and IAST selectivity of CO2 over N2 were determined and all carbons showed preferential sorption for CO2. Langmuir, Freundlich and Toth isotherms were employed to analyze pure CO2 and N2 adsorption data and the Toth isotherm gave the best fit. The carbon activated at 600ºC with KOH at a ratio of 1:4 w/w achieved the largest CO2 uptake (5.79 mmol/g at 0 °C and 750 mmHg) due to a combination between high microporosity (89 %) and surface area (2437 m2/g). This carbon also reached a relatively high selectivity.

Effects of alkali-metal nitrate salts on hydrotalcite-based sorbents for enhanced cyclic CO2 capture at high temperatures

CO2 capture using solid-based adsorbents at high temperatures has been in the spotlight as a CO2 capture and storage (CCS) technology for solving global warming and climate change problems. Hydrotalcite is an anionic clay that is widely used as a CO2 sorbent at temperatures of 200–400 °C. In various methods to improve the relatively low CO2 uptake of hydrotalcite, the hydrotalcites with a high Mg/Al molar ratio achieved significantly increased CO2 sorption uptake. This was because the preparation method allowed incorporation of NaNO3 in the hydrotalcite structure; the maximum CO2 sorption uptake was measured as 28.4 wt% when the Mg/Al molar ratio was 30. The different degrees of NaNO3 melting, depending on the sorption temperature, led to different CO2 sorption kinetics and uptakes at 250, 275, and 300 °C. Over the repeated sorption-desorption cycles, the CO2 cyclic capacity continuously decreased under sorption at 250 and 275 °C, whereas it increased at 300 °C, regardless of the Mg/Al molar ratio. The partial melting of NaNO3 at 250 and 275 °C, below its melting temperature, provided insufficient rearrangement of molten NaNO3. This further caused sintering of the MgO structure, which also increased its crystallite size. Conversely, the accelerated rearrangement of molten NaNO3 at 300 °C, near its melting temperature, and the low CO2 uptake at the initial step inhibited sintering. Different changes in the strength of CO2 sorption on the hydrotalcite-based sorbents also appeared as the cycle number increased.

Natural Products Derived Porous Carbons for CO2 Capture.

As it is now established that global warming and climate change are a reality, international investments are pouring in and rightfully so for climate change mitigation. Carbon capture and separation (CCS) is therefore gaining paramount importance as it is considered one of the powerful solutions for global warming. Sorption on porous materials is a promising alternative to traditional carbon dioxide (CO2 ) capture technologies. Owing to their sustainable availability, economic viability, and important recyclability, natural products-derived porous carbons have emerged as favorable and competitive materials for CO2 sorption. Furthermore, the fabrication of high-quality value-added functional porous carbon-based materials using renewable precursors and waste materials is an environmentally friendly approach. This review provides crucial insights and analyses to enhance the understanding of the application of porous carbons in CO2 capture. Various methods for the synthesis of porous carbon, their structural characterization, and parameters that influence their sorption properties are discussed. The review also delves into the utilization of molecular dynamics (MD), Monte Carlo (MC), density functional theory (DFT), and machine learning techniques for simulating adsorption and validating experimental results. Lastly, the review provides future outlook and research directions for progressing the use of natural products-derived porous carbons for CO2 capture.