CO2 Sorption Capacity Research Articles

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.

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.

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.

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.

Performance improvement of Na4SiO4 doped with Li2CO3-K2CO3 for high-temperature CO2 capture and thermochemical energy storage

Na4SiO4 is regarded as a new candidate of high-temperature CO2 sorbent. However, the sorption/desorption temperature of Na4SiO4 is high, and cyclic sorption capacity is low. In this study, Na4SiO4 sorbents doped with Li2CO3-K2CO3 (LiKCO3) were synthesized, and the dynamic, isothermal, and cyclic CO2 capture performances were investigated to improve the performance. The maximum CO2 sorption capacity of Na4SiO4-20LiKCO3 reached 20.64 wt% at 725 °C, and the cyclic sorption capacity was about 50 % higher than that of pure Na4SiO4. The results indicated that LiKCO3 doping could efficiently decrease the optimal sorption/desorption temperature of Na4SiO4. Furthermore, the maximum conversion efficiency and energy storage density of Na4SiO4-20LiKCO3 reached high levels of 95.7 % and 788 kJ/kg, respectively. Finally, the CO2 chemisorption mechanisms on the Na4SiO4 and Na4SiO4-LiKCO3 co-adsorption surfaces were studied via density functional theory calculations. LiKCO3 doping could enhance CO2 adsorption energy and C–OS covalent interaction on the sorbent surface and the energy levels of the CO2/Na4SiO4-LiKCO3 system were reduced. These changes were beneficial to CO2 chemisorption and agreed well with the experimental values. Thus, Na4SiO4 doped with LiKCO3 had high potential for high-temperature CO2 capture and thermochemical energy storage.

Exploiting monoterpenoids in type V deep eutectic solvents: A combined high-pressure experiments and theoretical approach for enhanced carbon dioxide and nitrogen absorption

This comprehensive study investigates the development, characterization, and application of natural hydrophobic deep eutectic solvents (HDES) in high-pressure gas capture, focusing specifically on carbon dioxide (CO2) and nitrogen (N2). Two binary HDES systems were formulated, using LnA as a hydrogen bond donor (HBD) and CAR and CIN as hydrogen bond acceptors (HBA). The HDES materials were thoroughly characterized, examining properties such as density, viscosity, conductivity, acidity, surface tension, and hydrophobicity across varying temperature ranges using state-of-the-art equipment. High-pressure gas solubility experiments were conducted to assess CO2 and N2 sorption capacities, demonstrating promising results. Simultaneously, an integrated computational approach was applied: COSMO-RS was used to predict solid–liquid equilibria (SLE) and the eutectic point of the NADES, while Density Functional Theory (DFT) calculations aided in optimizing molecular geometries and understanding the dispersion interactions. Furthermore, molecular dynamics (MD) simulations were employed to evaluate solubility of CO2 and N2 in the NADES and their interaction energies. The results from this dual experimental and computational approach show the potential of these HDES systems in high-pressure gas capture. This study represents a significant addition to the knowledge of deep eutectic solvents, their synthesis, characterization, predictive modeling, and practical applications.

Distribution and Mobility of Amines Confined in Porous Silica Supports Assessed via Neutron Scattering, NMR, and MD Simulations: Impacts on CO2 Sorption Kinetics and Capacities.

ConspectusSolid-supported amines are a promising class of CO2 sorbents capable of selectively capturing CO2 from diverse sources. The chemical interactions between the amine groups and CO2 give rise to the formation of strong CO2 adducts, such as alkylammonium carbamates, carbamic acids, and bicarbonates, which enable CO2 capture even at low driving force, such as with ultradilute CO2 streams. Among various solid-supported amine sorbents, oligomeric amines infused into oxide solid supports (noncovalently supported) are widely studied due to their ease of synthesis and low cost. This method allows for the construction of amine-rich sorbents while minimizing problems, such as leaching or evaporation, that occur with supported molecular amines.Researchers have pursued improved sorbents by tuning the physical and chemical properties of solid supports and amine phases. In terms of CO2 uptake, the amine efficiency, or the moles of sorbed CO2 per mole of amine sites, and uptake rate (CO2 capture per unit time) are the most critical factors determining the effectiveness of the material. While structure-property relationships have been developed for different porous oxide supports, the interaction(s) of the amine phase with the solid support, the structure and distribution of the organic phase within the pores, and the mobility of the amine phase within the pores are not well understood. These factors are important, because the kinetics of CO2 sorption, particularly when using the prototypical amine oligomer branched poly(ethylenimine) (PEI), follow an unconventional trend, with rapid initial uptake followed by a very slow, asymptotic approach to equilibrium. This suggests that the uptake of CO2 within such solid-supported amines is mass transfer-limited. Therefore, improving sorption performance can be facilitated by better understanding the amine structure and distribution within the pores.In this context, model solid-supported amine sorbents were constructed from a highly ordered, mesoporous silica SBA-15 support, and an array of techniques was used to probe the soft matter domains within these hybrid materials. The choice of SBA-15 as the model support was based on its ordered arrangement of mesopores with tunable physical and chemical properties, including pore size, particle lengths, and surface chemistries. Branched PEI─the most common amine phase used in solid CO2 sorbents─and its linear, low molecular weight analogue, tetraethylenepentamine (TEPA), were deployed as the amine phases. Neutron scattering (NS), including small angle neutron scattering (SANS) and quasielastic neutron scattering (QENS), alongside solid-state NMR (ssNMR) and molecular dynamics (MD) simulations, was used to elucidate the structure and mobility of the amine phases within the pores of the support. Together, these tools, which have previously not been applied to such materials, provided new information regarding how the amine phases filled the support pores as the loading increased and the mobility of those amine phases. Varying pore surface-amine interactions led to unique trends for amine distributions and mobility; for instance, hydrophilic walls (i.e., attractive to amines) resulted in hampered motions with more intimate coordination to the walls, while amines around hydrophobic walls or walls with grafted chains that interrupt amine-wall coordination showed recovered mobility, with amines being more liberated from the walls. By correlating the structural and dynamic properties with CO2 sorption properties, novel relationships were identified, shedding light on the performance of the amine sorbents, and providing valuable guidance for the design of more effective supported amine sorbents.

Tuning basic poly(ionic liquid) solutions towards atmospheric pressure CO2 capture

Ionic liquids and poly(ionic liquid)s are interesting materials for CO2 capture, however, the deployment of their industrial application has been delayed on account of economic and technical issues that demand further optimization. The control over viscosity has serious consequences over the process, therefore, this work is focused on the study of imidazolium and pyrrolidinium-derived ILs and PILs with basic anions, such as acetate, hydroxide, and imidazolate that were synthesized and characterized by NMR, ATR-FTIR, TGA, and DSC. Different solvents and concentrations were tested in the preparation of PIL and IL solutions, which were used to capture CO2 by bubbling this gas at room temperature and atmospheric pressure (1 atm). The evaluation of the CO2 sorption capacity of each sample was carried out through the analysis of quantitative 13C NMR. The poly(1-vinyl-3-ethylimidazolium) acetate showed and sorption capacity of 5.68 mmol CO2/g PIL, and also the capacity to capture CO2 from exhaust gas mixture and the possibility to be recycled at least 5 times.

Basic Properties of MgAl-Mixed Oxides in CO2 Adsorption at High Temperature.

The increase of consciousness towards global warming and the need to reduce greenhouse gas emissions lead to the necessity of finding alternative applications based on easy-to-use materials in order to control and reduce global CO2 emissions. Layered Double Hydroxides (LDHs) and LDH-derived materials are potentially good adsorbents for CO2, thanks to their low cost, easy synthesis, high sorption capacity, and surface basicity. They have been intensively studied in CO2 capture at high temperature, presenting variable sorption capacities for MgAl LDHs with the same composition, but prepared under different synthesis conditions. The ambient temperature coprecipitation synthesis method is an attractive one-step procedure to synthesize LDHs under mild conditions, with low energy consumption and short synthesis time. The present study is based on the synthesis and characterization of hydrotalcites by a mild-conditions coprecipitation process and the production of derived mixed oxides to be used as CO2 adsorbents. A critical comparison to similar materials is reported. Moreover, the effect of the surface basicity of the derived mixed oxides (measured by adsorption calorimetry) and the CO2 sorption capacity are discussed, showing a linear correlation between the amount of weak and very strong basic sites and the CO2 adsorption behavior.

Upcycling plastic waste: Rapid aqueous depolymerization of PET and simultaneous growth of highly defective UiO-66 metal-organic framework with enhanced CO2 capture via one-pot synthesis

UiO-66(Zr) MOF was synthesized rapidly via one-pot synthesis in an acidic aqueous media starting with waste polyethylene terephthalate (PET) plastic flakes and Zr metal salt. Complete depolymerization of PET into BDC (benzene dicarboxylic acid) linkers and coordination with Zr metal clusters occurred in 30 mins under microwave irradiation. PET-derived UiO-66 showed a large micron-sized cuboctahedron crystal structure with high microporosity. The use of acetic acid as a modulator helps to increase the reo-topology defect within the MOFs improving CO2 uptake. PET-derived UiO-66 exhibited intense reo-defects than UiO-66 synthesized using a pristine BDC linker. This was likely due to the one-pot reaction of PET depolymerization with simultaneous MOF growth that results in an enhanced competition of modulator and byproducts formed during PET digestion along with the BDC to bind with Zr clusters inducing more defects in the structure. Heat treatment of the PET-derived UiO-66 with the optimal mole ratio of 1Zr:1PET yields UiO-66 with the highest BET surface area of 1200 m2g−1 and a total pore volume of 0.57 cm3g−1. The highest CO2 uptake of 2.06 mmolg−1 was shown by 1Zr:1PET, due to their high microporosity and profound reo-structure which demonstrated superior CO2 uptake than the UiO-66 synthesized using commercial BDC. The selectivity of the CO2 over N2 was over 25.3 times and exhibited excellent regeneration stability and recyclability over 5 cycles with 99% of persistent CO2 sorption capacity. This study demonstrated the utilization and recycling of PET waste to BDC linkers with simultaneous MOF growth which have a high potential to capture CO2 effectively.

CaAlFe–mixed metal oxides prepared from an aluminum salt–cake and their evaluation as CO2 sorbents at moderate temperature

Potentially–CO2 adsorbing solids at moderate temperature have been prepared by calcination at 400 °C and 750 °C of CaAlFe hydrocalumites (a sort of Ca2+–layered double hydroxide), which had been prepared using a salt cake as aluminum source. The characterization of the obtained solids was carried out by powder X–ray diffraction, FT–infrared spectroscopy, thermal analysis, N2 adsorption–desorption isotherms at –196 °C and electron microscopy. After calcination, different crystalline phases were identified as a function of the amount of Fe3+ incorporated. Static sorption equilibrium experiments were performed at 300 °C and pCO2 = 0.3 bar. The CO2 sorption capacity was affected by the presence of different phases in the CaAlFe–mixed oxides (MMOs), being maximum when the amount of Fe3+ was 40 mol % of the trivalent positions. No differences in CO2 sorption capacities were observed between CaAlFe–MMOs–400 and CaAlFe–MMOs–750 (materials calcined respectively at 400 and 750 °C), suggesting that CO2 sorption capacity was not related to SBET. Experiments under dynamic conditions at 400 °C and pCO2 = 0.15 bar showed good behaviors for CaAl–400, CaAl0.60Fe0.40–400 and CaFe–400. In addition, CaAl0.60Fe0.40–400 was evaluated in several CO2 sorption–desorption cycles in the presence of water vapor, finding that the steam presence enhanced the CO2 capture.

Development of high capacity moisture-swing DAC sorbent for direct air capture of CO2

Direct air capture (DAC) of CO2 complements traditional carbon capture technologies to achieve zero- or negative-carbon emissions. One of the most promising DAC technologies is moisture-swing adsorption due to its low regeneration costs and easiness of operation, particularly when using amine-based anion-exchange resins (AER) as sorbents, but the limited CO2 sorption capacity and desorption efficiency of current AERs are still critical challenges hindering the large-scale implementation of DAC. For the first time, this work developed a novel diamine-based double quaternary ammonium anion-exchange resins (Diamine-DQ-AER) by modifying commercial resins with tertiary diamines. The significantly improved quaternary ammonium content in Diamine-DQ-AER (68–81 %) compared to diamine-based single quaternary ammonium anion-exchange resins (Diamine-SQ-AER) resulted in an unprecedented moisture-swing DAC capacity of 3.41 mmol/g under DAC conditions, nearly doubled that of Diamine-SQ-AER. Diamine-DQ-AER also showed a stable capacity in the 6-cycle test, outperforming most moisture-swing DAC sorbents reported in the literature. Moreover, a complete desorption kinetic curve was obtained using an optimized testing protocol. It found that the CO2 adsorption/desorption process involves two stages, and the material exhibited fast desorption kinetics in the 1st stage.

Measured CO2 sorption isotherms with 25 Bakken Petroleum System rock samples from the Lower and Upper Shales, Middle Bakken, and Three Forks formations

Isotherms were measured with 25 Bakken Petroleum System (BPS) rock samples using a magnetic suspension balance at reservoir conditions of 110 °C and pressures up to 345 bar. Samples from four wells represented the Middle Bakken (MB) and Three Forks (TF) production zones, and the Upper Bakken Shale (UBS) and Lower Bakken Shale (LBS) source shales. UBS and LBS CO2 sorption capacities at 345 bar averaged 12–14 g/kg rock compared to 1.3 to 2.5 g/kg rock for MB and TF. Increasing pressure from 150 to 345 bar resulted in only small increases in CO2 sorption for all lithofacies. For the UBS and LBS source shales, the higher average total organic carbon (TOC) values (14.7 and 11.4 wt.%) and clay values (25 and 28 wt.%) corresponded to their higher CO2 sorption values while for the MB and TF samples, lower TOCs (0.3 and 0.5 wt.%) and clay values (8.2 and 18.2 wt.%) corresponded to lower CO2 sorption values. When all 25 samples (from all lithofacies) were evaluated as a group, sorption capacities were highly correlated with TOC (Spearman's rho values +0.84 to +0.85), with rock density (rho values -0.75 to -0.76), and clay content (rho values +0.66). However, correlations with porosity and thermal maturity (Tmax) were weak. Measured sorption capacities and rock porosities showed that sorption accounted for about 10-times as much CO2 storage as the available pore space for the UBS and LBS lithofacies. In contrast, the pore space dominated the storage resource of the TF and MB lithofacies.

Structure-Property Relationships of CO2 Absorbing Core-Shell Microparticles with Encapsulated Ionic Liquid.

The demand for new ionic liquid (IL)-based systems to selectively sequester carbon dioxide from gas mixtures has prompted the development of individual components involving the tailored design of IL themselves or solid-supported materials that provide excellent gas permeability of the overall material as well as the ability to incorporate large amounts of ionic liquid. In this work, novel IL-encapsulated microparticles comprising a cross-linked copolymer shell of β-myrcene and styrene and a hydrophilic core of the ionic liquid 1-ethyl-3-methylimidazolium dicyanamide ([EMIM][DCA]) are proposed as viable materials for CO2 capture. Water-in-oil (w/o) emulsion polymerization of different mass ratios of β-myrcene to styrene (i.e. 100/0, 70/30, 50/50, 0/100) yielded IL-encapsulated microparticles, where the encapsulation efficiency of [EMIM][DCA] was dependent on the copolymer shell composition. Thermal analysis using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) revealed that both thermal stability and glass transition temperatures depend on the mass ratio of β-myrcene to styrene. Images from scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to observe the microparticle shell morphology as well as measure the particle size perimeter. Particle sizes were found to be between 5 and 44 μm. CO2 sorption experiments were conducted gravimetrically using TGA instrumentation. Interestingly, a trade-off between CO2 absorption capacity and ionic liquid encapsulation was observed. While increasing the β-myrcene content within the microparticle shell increases the amount of encapsulated [EMIM][DCA], the observed CO2 absorption capacity did not increase as expected due to reduced porosity compared to microparticles with higher styrene content in the microparticle shell. [EMIM][DCA] microcapsules with a 50/50 weight ratio of β-myrcene/styrene showed the best synergistic effect between spherical particle diameter (32.2 μm), pore size (0.75 μm), and high CO2 sorption capacity of ∼0.5 mmol CO2/g sample within a short absorption period of 20 min. Therefore, core-shell microcapsules composed of β-myrcene and styrene are envisioned as a promising material for CO2 sequestration applications.

Probing the Morphology and Mobility of Amines in Porous Silica CO2 Sorbents by 1H T1–T2 Relaxation Correlation NMR

Molecular and oligomeric amines supported in porous oxide supports are a promising class of CO2 sorbent materials studied for CO2 removal from diverse streams such as flue gas and ambient air. Among the various amines investigated, low molecular weight, hyperbranched poly(ethyleneimine) (PEI), and tetraethylenepentamine (TEPA) are among the most extensively studied. While macroscopic structure–performance relationships relating the support structure, amine loading, and other factors affecting CO2 sorption capacities and kinetics have been developed, structural and dynamic information about the organic amine phase in the porous support is less plentiful. The structure and mobility of amines impregnated in the pores of porous supports directly impact gas sorption, as the accessibility of amine sites in the pores directly relates to amine distribution in the pores and overall pore filling as well as the dynamics of the amine chains. Here, we prepare a family of mesoporous silica SBA-15 materials containing varying loadings of oligomeric (PEI) and molecular (TEPA) amines. 1H T1–T2 relaxation correlation solid-state NMR experiments are used to characterize the structural and dynamic properties of the confined amines. Both TEPA and PEI are shown to form multiple different domains in the pores, each with distinguishable dynamic properties. TEPA and PEI form more rigid layers around the silica support walls at lower organic loading fractions, characterized by lower mobilities, followed by the formation of more mobile domains less engaged in pore wall interactions at higher loadings. TEPA shows faster mobilities than PEI because of its lower molecular weight. TEPA also appears to more easily transfer between domains within the pores, leading to generally faster CO2 uptake rates with higher sorption capacities, while PEI located closer to the pore walls remained much less mobile and is thus less engaged in CO2 capture.

Fruit waste (pomelo peels)-derived activated carbons for biogas upgradation and capture of green house gases from flue gas and low concentration coalbed methane

Rising emissions of greenhouse gases, such as CO2 and CH4, due to anthropogenic activities cause several adverse environmental impacts and encourage technological development for their effective capture and separation. The present work addresses a facile hydrothermal approach to impregnate K2CO3 and K2C2O4 into pomelo peels (fruit waste), followed by thermochemical activation for preparing activated carbons, i.e., PKC and PKOX, respectively, as adsorbents for biogas upgradation (CO2/CH4) and capture of greenhouse gases from flue gas (CO2/N2) and low concentration coalbed methane (CH4/N2). The high CO2 sorption capacity of PKC (4.67 mmol.g-1) and PKOX (3.96 mmol.g-1) at 298 K and 1 bar is attributed to their high surface area (1224–1371 m2.g-1), excellent microporosity, nitrogen-based functionalities, and turbostratic structural features. The ideal adsorbed solution theory (IAST) model is applied to estimate separation selectivity for binary gas mixtures, i.e., CO2/N2 (15:85), CO2/CH4 (45:55), and CH4/N2 (30:70) using PKC and PKOX adsorbents. The adsorption selectivity of PKC and PKOX for CO2/CH4 is found to be 143% and 296% higher compared to a widely used commercial activated carbon, signifying the potential of PKOX for biogas upgradation via adsorptive separation of CO2. The adsorption selectivity of PKC and PKOX for CO2/N2 is estimated to be 124% and 119% higher than commercial activated carbon, revealing the potential of both PKC and PKOX for capturing CO2 from flue gas to minimize its release in the atmosphere.

Effect of wire and needle spinning on the direct manufacturing PAN/amine nanofibrous membranes for CO2 sorption

Manufacturing of membranes for carbon dioxide (CO2) capture is a significant research topic. Achieving maximum CO2 sorption capacity while maintaining air permeability with a minimum number of technological steps was the main motivation of this work. The greatest advantages of this approach are its simplicity, low cost and easy transition to industrial scale. Electrospun nanofibrous membranes polyacrylonitrile (PAN)/triethylenetetramine (TETA) and polyacrylonitrile (PAN)/tetraethylenepentamine (TEPA) were prepared by one-step technology (modifying amines TETA, TEPA in different weight concentrations dissolved directly in spinning solution) using two different spinning conditions: needle spinning (electric field attached to a hollow needle through which a polymer solution is extruded under pressure) and wire spinning (electric field connected to a thin wire that is coated with a layer of polymer solution, and the spinning thus takes place from the free surface). Wire electrospinning turns out to be more suitable for a one-step technology with a modifying substance in the spinning solution. The best result as to the CO2 sorption capacity has been obtained for wire spinning PAN_TEPA_2% 11.7 ± 1.3 cm3/g with air permeability 53 ± 5 L/m2/s, which gives a good chance for the design of a sandwich functional unit for practical use. In addition to studies of CO2 adsorption, the article also deals with the comparison of both spinning methods for the PAN polymer, which have not yet been compared for this polymer in the literature, not only from the point of view of the possibility of preparing PAN nanofibers, but also their functional use precisely for CO2 capture.

Catalyst-free upcycling of crosslinked polyethylene foams for CO2 capture

Recycling of crosslinked plastics is an intractable challenge due to their very limited amenability to mechanical reprocessing. While a variety of chemical recycling methods have been recently reported, these systems primarily focus on deconstructing or depolymerizing plastics to monomers and liquid fuels, which their subsequent use likely involves additional energy consumption and greenhouse gas emission. In this work, we present a simple, scalable, and catalyst-free method for directly converting crosslinked polyethylene (PE) foams into porous carbon materials. This process is enabled by sulfonation-based crosslinking, allowing the conversion of PE to become efficient carbon precursors, while retaining the high porosity feature from the foam precursors. Through two steps of sulfonation and carbonization, derived carbons contain a relatively high surface area and sulfur-doped framework. As a result, these materials can exhibit high CO2 sorption capacity and CO2/N2 selectivity. This work presents a viable pathway to address two grand-scale environmental challenges of plastic wastes and greenhouse gas emissions.Graphical abstract

Enhancing the CO2 capture capacity of natural macroporous carbonized fibers by growing carbon nanotubes on their surface

In this study, a new hybrid material with superior CO2 sorption capacity was prepared by the growth of carbon nanotubes (CNT) into the macroporous structure of acid carbonized fibers (ACF). The growth of CNT was carried out by chemical vapor deposition using acetylene as a carbon source for 3.5 min at 700 °C. Selected materials were characterized by N2 physisorption, FTIR, potentiometric titrations, acid digestions, Raman spectroscopy, scanning and transmission electron microscopy. The CO2 capture was measured in static mode at pressure up to 10 atm in a sorptometer and in dynamic mode in a thermogravimetric analyzer at pressure of 1 atm. CNTs were homogeneously grown on the entire surface of ACF. The surface area of carbonized fibers increased from 2 to 452 m2/g after CNT growth and treatment at 300 °C for 1 min in air. The CO2 capture capacity of the ACF increased from 2.30 to 3.51 mmol/g at 25 °C and 10 atm after CNTs growth and air treatment (ACF3-CNT-AT1). The CO2 capture rate was also higher, from 0.023 to 0.032 mmol/g·min for ACF and ACF3-CNT-AT1 at 25 °C and 1 atm, respectively. These results were mainly attributed to the increase in basic groups and highly reactive edge sites. In addition, regeneration capacities of 99% and 95% were obtained for the first 3 sorption-desorption cycles and an apparent selectivity (QCO2/QN2) of 1.65 and 2.48 for ACF and ACF3-CNT-AT1, respectively. The rapid sorption-desorption kinetics, coupled with the high reversibility of CNT-modified ACFs, makes this hybrid material viable for use in CO2 capture systems.