Selective Adsorption Of CO2 Research Articles

Significance of fluid properties, pore structure, and surface chemistry in CMK series mesoporous carbon materials for N2/CH4/CO2 separation

We employed a combination of macroscopic approaches (Ideal Adsorption Solution Theory, IAST, and Two-Dimensional Equation of State, 2D-EOS) and microscopic molecular simulations to explore the adsorption and separation of N2, CH4, and CO2 in mesoporous materials CMK-1, CMK-3, and CMK-5. Our findings reveal that these behaviors are intricately linked to the material's structure, surface properties, and the adsorbed fluid type. For nonpolar N2/CH4 supercritical fluid, both macroscopic theories align remarkably well with molecular simulations. For gas mixtures with a supercritical gas (N2 or CH4) and a subcritical gas (CO2), the impact of material structure on adsorption and separation varies. While both adsorption theories perform well for CMK-3, with excellent agreement to simulations, only IAST accurately predicts CMK-1. This discrepancy indicates that 2D-EOS has a less satisfactory predictive accuracy for CMK-1 compared to CMK-3 due to structural differences. The hexagonal arrangement of nanorods in CMK-3 leads to a more uniform adsorption site, while CMK-1's diverse adsorption sites, including nanorod surfaces and inter-rod grooves, contribute to a more complex adsorption behavior. In CMK-5, a unique jump in the CO2 adsorption selectivity is observed, attributed to a phase transition within the pores. Interestingly, this transition-induced jump defies accurate prediction by common theoretical models, except for IAST, which correctly predicts trends in selectivity and adsorption amounts. This phenomenon is specific to CMK-5's dual-pore structure, where most CO2 adsorption occurs inside the pipes until saturation, followed by adsorption on the external surface. Examining the impact of –COOH and –OH functional groups on adsorption behavior, we find minimal influence on separation in nonpolar N2–CH4 fluid, independent of the material type. However, in CO2-containing systems, the –COOH functional group has a substantial impact, highlighting its significance in influencing adsorption behavior.

A novel preparation of microporous nanosilica derived from aluminum-extracted residue of coal fly ash for highly selective CO2 adsorption

Currently, the poor adsorption performance caused by the unsatisfactory pore size seriously restricts the further development of microporous nanosilica (MS). Herein, an excellent microporous nanosilica was constructed by preparing calcium silicate hydrate (CSH) support from the aluminum-extracted residue of coal fly ash and modifying it with different activating agents (H2SO4, HNO3, HCl, CH3COOH, KOH, NaOH and Na2CO3). The results indicated that CH3COOH at 30 wt% was the optimal modifier, achieving a CO2 uptake of 1.42 mmol/g at 298 K and 1.0 bar. Then the effects of synthesis parameters including mass fraction, liquid–solid ratio, temperature, and time on the adsorption capacity of CO2 were further investigated. The obtained MSCp exhibited a high specific surface area (up to 505.71 m2/g), well-developed microporosity (0.085 cm3/g), and excellent CO2 uptake (2.12 mmol/g at 273 K, 1.41 mmol/g at 298 K). Based on the study of kinetics, isosteric heat of adsorption (Qst), and situ diffuse reflectance infrared Fourier transformation spectroscopy (DRIFTS), the adsorption mechanism of MSCp was determined to be mainly physical adsorption. Besides, the excellent CO2/CH4 selectivity of 20.91 (15/85, v/v) and 30.75 (50/50, v/v), CO2/N2 selectivity of 53.79 (15/85, v/v) and 163.76 (50/50, v/v) were obtained from MSCp at 298 K and 1.0 bar. Finally, the binary gas breakthrough experiments and eight adsorption–desorption cycles confirmed the MSCp was suitable for selective adsorption of CO2 in practical applications.

Treatment of Waters Having Different Ionic Composition and pH with Natural Zeolites from Bulgaria

The migration of 32 elements from natural zeolitized tuffs from the Beli Plast and Golobradovo deposits (Bulgaria) was determined in ultrapure, tap, mineral, and coal mine waters in order to evaluate their desorption and adsorption properties. The tuffs are Ca-K-Na and contain clinoptilolite (90 and 78wt.%, respectively), plagioclase, sanidine, opal-CT, mica, quartz, montmorillonite, goethite, calcite, ankerite, apatite, and monazite. The desorption properties are best revealed during the treatment of ultrapure, tap, and mineral water, whereas the adsorption properties are best manifested in coal mine water treatment. The concentrations of Al, Si, Fe, Na, Mn, F, K, Pb, and U increase in the treated ultrapure, tap, and mineral water, while the content of K, Be, Pb, and F increase in the treated mine water. The tuffs show selective partial or complete adsorption of Na, Mg, Sr, Li, Be, Mn, Fe, Co, Ni, Cu, Zn, Al, Pb, U, and SO42−. They demonstrate the ability to neutralize acidic and alkaline pH. Sources of F are presumed to be clinoptilolite and montmorillonite. The usage of zeolitized tuffs for at-home drinking water treatment has to be performed with caution due to the migration of potentially toxic and toxic elements.

Impregnation of nanoclay montmorillonite by choline chloride-urea for selective CO2, N2, and O2 adsorption: Experimental and modeling

In this study, we successfully utilized a green chemistry approach to prepare an adsorbent by functionalizing Montmorillonite with Choline Chlroride: Urea (a Deep Eutectic Solvent) to compare CO2, O2, and N2 adsorption. We conducted studies on the adsorption mechanism using a volumetric system at temperatures ranging from 25 to 55 °C under pressures of up to 9 bar. We assessed the effects of acid activation concentration, solvent concentration, and adsorbent mass on the CO2/O2 and CO2/N2 adsorption ratios (mg/mg). Characterization analyses confirmed that modification of interlayer spaces, ion exchange content, and Al/Si occurred through acid treatment and solvent impregnation. The CO2 adsorption mechanism demonstrated a heterogeneous multilayer and chemophysical sorption nature, which was in agreement with the Hill isotherm and Ellovich kinetic model. In contrast, the O2 and N2 mechanisms were in agreement with a monolayer nature, which matched the Langmuir isotherm and first-order kinetic model. We achieved the optimum adsorption ratio of CO2/O2 and CO2/N2 at 35 °C, while the highest individual adsorption for all three gases was obtained at 25 °C. At 35 °C, 5 bar, and 0.5 g, the highest uptake adsorption was 208.6 mg/g for CO2, 72.6 mg/g for O2, and 39.3 mg/g for N2. Thermodynamic parameters showed that the adsorption nature of CO2, O2, and N2 was exothermic (ΔH < 0) with values of −14.49 Kj/mol, −7.74 Kj/mol, and −4.09Kj/mol, respectively. The study's experimental and modeling results showed a corresponding interpretation, which was remarkable. The adsorbent exhibited desirable renewability at adsorption/desorption cycles with remarkable uptake capacity, making it a highly potential adsorbent for CO2 capture from flue gases. The selectivity of CO2 towards O2 and N2 was almost 2.1 and 3.9, respectively.

CO2 selective adsorption over O2 on N−doped activated carbon: Experiment and quantum chemistry study

Utilizing flue gas as feedstock for CO2 electro−reduction systems is a promising technology to address problems caused by excessive CO2 emissions. However, the O2 contained in the flue gas has a significant adverse effect on the CO2 reduction. Herein, a facile strategy was proposed to suppress the influence of O2 by constructing a CO2−enriched region. N−doping was demonstrated to be an efficient way to enhance CO2 adsorption selectivity over O2 on activated carbon. The N−doped activated carbon achieved 3.7 times increase in CO2 adsorption selectivity over O2 than that before modification under simulated flue gas atmosphere (75 %N2 + 15 %CO2 + 10 %O2). The distinction in adsorption mechanism between CO2 and O2 was revealed by quantum chemistry study. The increased polarity of the carbon materials favored CO2 adsorption and had less impact on O2 adsorption. The electrostatic interaction between CO2 and carbon material was demonstrated to be enhanced after the introduction of pyridinic N and pyrrolic N, which led to an improvement in the CO2 adsorption capacity. The dispersion interaction, which fully regulated O2 adsorption, was weakened due to the deviation of the O2 adsorption position. This study provided a reference for the subsequent development of CO2 selective adsorption materials.

Fabrication of Bamboo-Based Activated Carbon for Low-Level CO2 Adsorption toward Sustainable Indoor Air

This study fabricated a low-cost activated carbon (AC) adsorbent from readily available bamboo trees to control indoor CO2 levels and reduce energy costs associated with sustaining clean indoor air. Bamboo is naturally high in potassium content and has narrow fibrous channels that could enhance selective CO2 adsorption. The prepared bamboo-based activated carbon (BAC) exhibits predominantly micropores with an average pore size of 0.17 nm and a specific surface area of 984 m2/g. Upon amination, amine functionalities, such as pyridine, pyrrole, and quaternary N, were formed on its surface, enhancing its CO2 adsorption capacity of 0.98 and 1.80 mmol/g for low-level (3000 ppm) and pure CO2 flows at the ambient condition, respectively. In addition, the 0.3% CO2/N2 selectivity (αs,g) of the prepared sorbents revealed a superior affinity of CO2 by BAC (8.60) over coconut shell-based adsorbents (1.16–1.38). Furthermore, amination enhanced BAC’s CO2αs,g to 13.4. These results exhibit this sustainable approach’s potential capabilities to ensure the control of indoor CO2 levels, thereby reducing the cost associated with mechanical ventilation systems. Further research should test the new sorbent’s adsorption properties (isotherm, kinetics, and thermodynamics) for real-life applicability.

Regulating the Si/Al ratio of GIS zeolite with bulky primary particles for selective CO2 capture from hydrocarbons

Carbon dioxide (CO2) capture from hydrocarbons using low-energy adsorption separation techniques is a promising alternative to conventional low-temperature distillation, but limited by the shortness of low-cost and efficient physical adsorbent, especially for the direct acetylene (C2H2) purification because of their very similar size and physiochemical properties. In this work, GIS zeolites with tunable Si/Al ratio were synthesized in an unusual acid co-hydrolysis route to enable the formation of large-sized primary particles, which greatly reduce the outside surface adsorption to enhance the sieving effect of 8-membered ring microchannels. The obtained GIS zeolites afforded high CO2 uptake (3.5 mmol g-1 and 128 cm3 cm-3) while negligible adsorption towards other gases including C2H2, N2, CH4, C2H4, and C2H6, showing the remarkable selective CO2 adsorption from a CO2-C2H2(N2 or CH4) mixture with the CO2/C2H2 (50/50 v/v) selectivity up to 8.5 × 1010. Breakthrough experiments revealed the favorable dynamic separation behavior with better performance on the sample with the comparatively high Si/Al ratio of 3.1. The CO2 adsorption at 195 K and structural refinement results demonstrated that the excellent separation performance was attributed to the less Na+ ions inside the microchannels providing more inner space for the accommodation of guest molecules.

Influence of functional groups on the microporous development and CO2-CH4 adsorption: A molecular simulation investigation

In this study, the influence of different functional groups (carbonyl, ether, carboxyl, and hydroxyl) on microporous development and competitive adsorption for CO2-CH4 was investigated using Connolly potential theory, molecular mechanics, molecular dynamics, and grand canonical Monte Carlo based on the macromolecular representation of coal vitrinite (CV). Results indicated that microporous diameter induced from the carboxyl (COOH) and hydroxyl (OH) was more sensitive to increasing temperature than carbonyl (CO) and ether (C2O). The COOH and OH could induce more micropores than the other functional groups. The adsorption capacities of OH-CV and COOH-CV were significantly higher than C2O-CV, CO-CV, and C-CV (coal vitrinite purified by carbon atoms) and they all decrease with the decreasing temperature. Both the calculation results of Locate- and Isotherm task suggested that OH and COOH have a significantly higher adsorption amount than other coal macromolecules and the others have a close adsorption amount. The adsorption selectivities of CO2 over CH4 ( SA/B) for all the functional groups were higher than 1 here, indicating the adsorption preference of CO2 over CH4. For the pressure dependence, the SA/B first decreases significantly for the pressure of &lt; 4 MPa and then slightly for the pressures of &gt;4 MPa with the increasing pressure, indicating that high pressure was not conductive to the replacement of CH4 by CO2. For almost all the pressures here, the SA/B follows the order of COOH-CV &gt; OH-CV≈C2O-CV≈Ori-CV≈CO-CV≈C-CV, indicating the highest adsorption preference of CO2 over CH4 for COOH, and OH-CV.

Y decorated B40 fullerene as a promising candidate for CO2 efficient storage and Separation: A DFT study

Using the Density functional theory, the adsorption and storage of CO2 molecules on Yttrium coated B40 fullerene are considered. The obtained results report that Y atoms are placed only in the heptagonal active sites on B40 external surface, and the formation of Y crystals does not occur. According to the findings, B40 fullerene decorated with 4 Y atoms may adsorb up to 28 CO2 molecules, which has a maximum density of 61 % wt. The results show that the addition of the eighth CO2 is practically not possible due to the excessive distance from the Surface, which is the result of the lack of higher valency of the Y atoms. Moreover, the average adsorption energy of the final structure is −0.68 eV which is in the suggested range for CO2 optimal adsorption (0.40–0.80 eV). In addition, the B40Y4 shows high selectivity for CO2 adsorption from CO2/CH4 and CO2/H2 natural gas mixtures.

New insight into impact of humidity on direct air capture performance by SIFSIX-3-Cu MOF.

Removal of CO2 from air is one of the key human challenges in battling global warming. SIFSIX-3-Cu is a promising metal-organic framework (MOF) suggested for carbon capture even at low CO2 concentrations. However, the impact of humidity on its performance in direct air capture (DAC) is poorly understood. To evaluate the MOF performance for DAC application under humid conditions, we investigate the adsorption of H2O, CO2, and N2 using density functional theory (DFT), grand canonical Monte Carlo (GCMC), and molecular dynamics (MD) simulations. The simulation results show a higher tendency of SIFSIX-3-Cu towards H2O adsorption rather than CO2 (and N2). The results agree with the adsorption isotherms for the pure compounds from the Sips model. The extended Sips model shows 1.34 mmol g-1 CO2 adsorption at the atmospheric pressure and 298 K for the CO2/N2 mixture containing 400 ppm CO2, and low CO2 adsorption (less than 0.75 mmol g-1) at a low relative humidity (RH) of 20%. This finding highlights the efficiency of SIFSIX-3-Cu for DAC in dry air and the negative impact of humidity on the CO2 selective adsorption. Therefore, we suggest to consider the impairing of humidity effects when designing a SIFSIX-3-Cu-based CO2 separation process and removal of any water vapor before introduction of the air to SIFSIX-3-Cu.

A (4,6)-c copper–organic framework constructed from triazole-inserted dicarboxylate linker with CO2 selective adsorption

An unusual (4,6)-c copper–organic framework was solvothermally isolated by virtue of a triazole-inserted dicarboxylate ligand concomitant with CO2 selective adsorption over N2 and CH4.

A copper-functionalized zirconium metal–organic framework for catalytic oxidative carboxylation of olefins and CO2

A Cu incorporation by post-metalation of a Zr-based metal–organic framework (MOF) produces a robustly bimetallic MOF that is suitable for selective CO2 adsorption and efficient conversion of CO2 and olefins into cyclic carbonates.

Modification of ZnO gas-diffusion-electrodes for enhanced electrochemical CO2 reduction: optimization of operational conditions and mechanism investigation

Amino-functionalized ZnO exhibits enhanced CO2 adsorption capacity and selectivity for electrochemical conversion of CO2 to CO.

Binding of carbon dioxide and acetylene to free carboxylic acid sites in a metal-organic framework.

The functionalisation of organic linkers in metal-organic frameworks (MOFs) to improve gas uptake is well-documented. Although the positive role of free carboxylic acid sites in MOFs for binding gas molecules has been proposed in computational studies, relatively little experimental evidence has been reported in support of this. Primarily this is because of the inherent synthetic difficulty to prepare MOF materials bearing free, accessible -COOH moieties which would normally bind to metal ions within the framework structure. Here, we describe the direct binding of CO2 and C2H2 molecules to the free -COOH sites within the pores of MFM-303(Al). MFM-303(Al) exhibits highly selective adsorption of CO2 and C2H2 with a high selectivity for C2H2 over C2H4. In situ synchrotron X-ray diffraction and inelastic neutron scattering, coupled with modelling, highlight the cooperative interactions of adsorbed CO2 and C2H2 molecules with free -COOH and -OH sites within MFM-303(Al), thus rationalising the observed high selectivity for gas separation.

A mechanochemical process to capture and separate carbon dioxide from natural gas using boron nitride nanosheets.

Addressing climate change is a critical and pressing matter that requires immediate attention to mitigate its severe repercussions. In order to enhance the capture and separation of carbon dioxide from natural gas and nitrogen gas, it is imperative to develop new capture materials and more efficient storage processes. In this study, we introduce an innovative environmentally friendly storage and separation technique. Through a controlled mechanochemical process, a substantial amount of carbon dioxide (103.6 wt%) was successfully captured within boron nitride. This process also excels at effectively isolating carbon dioxide from a gas mixture containing natural gas (CH4) or nitrogen due to its superior adsorption selectivity for CO2 over the other two gases. The stored carbon dioxide can be released upon heating, and this procedure can be repeated several times (minimum four times), indicating a game changing process in CO2 gas capture and separation technology with the advantages of green, low cost and efficiency.

Polymers of intrinsic microporosity with internal dihedral lock for efficient gas separation

Polymers of intrinsic microporosity (PIMs) stand out as promising membrane materials with exceptional separation performance. In this study, we crafted a highly efficient gas separation membrane using an emerging material, called cyclohexyl-fused spirobiindane-based PIM (CCS-PIM). The CCS-PIM features a robust and rigid microporous structure with a high specific surface area (SBET ​= ​704.6 ​m2/g), exhibiting excellent CO2-selective adsorption capacity. The CO2 adsorption uptake is 0.78 ​mmol/g at 273 ​K and 0.15 ​bar, leading to IAST selectivity of 25.2 for CO2/N2 (15/85 v/v) and 16.7 for CO2/CH4 (50/50 v/v) at 298 ​K. The precisely tuned pore size of the CCS-PIM membrane leads to an enhanced molecular sieving effect, showcasing superior selectivity across various gas pair separations. It demonstrates an O2/N2 selectivity of 6.03 and a CO2/CH4 selectivity of 26.1, surpassing the 2008 Robeson upper bounds. This study suggests a strategic method to improve gas separation efficiency by customizing a locked PIM structure with precise molecular sieving through the insertion of variously sized rings.

Importance of Bridging Molecular and Process Modeling to Design Optimal Adsorbents for Large-Scale CO2 Capture.

ConspectusCarbon capture, utilization, and storage have been identified as key technologies to decarbonize the energy and industrial sectors. Although postcombustion CO2 capture by absorption in aqueous amines is a mature technology, the required high regeneration energy, losses due to degradation and evaporation, and corrosion carry a high economic cost, precluding this technology to be used today at the scale required to mitigate climate change. Solid adsorbent-based systems with high CO2 capacities, high selectivity, and lower regeneration energy are becoming an attractive alternative for this purpose. Conscious of this opportunity, the search for optimal adsorbents for the capture of CO2 has become an urgent task. To accurately assess the performance of CO2 separation by adsorption at the needed scale, adsorbents should be synthesized and fully characterized under the required operating conditions, and the proper design and simulation of the process should be implemented along with techno-economic and environmental assessments. Several works have examined pure CO2 single-component adsorption or binary mixtures of CO2 with nitrogen for different families of adsorbents, primarily addressing their CO2 adsorption capacity and selectivity; however, very limited data is available under other conditions and/or with impurities, mainly due to the intensive experimental (modeling) efforts required for the large number of adsorbents to be studied, posing a challenge for their assessment under the needed conditions. In this regard, molecular simulations can be employed in synergy with experiments, reliably generating missing adsorption properties of mixtures while providing understanding at the molecular level of the mechanism of the adsorption process.This Account provides an outlook on strategies used for the rational design of materials for CO2 capture from different sources from the understanding of the adsorption mechanism at the molecular level. We illustrate with practical examples from our work and others' work how molecular simulations can be reliably used to link the molecular knowledge of novel adsorbents for which limited data exist for CO2 capture adsorption processes. Molecular simulation results of different adsorbents, including MOFs, zeolites, and carbon-based and silica-based materials, are discussed, focusing on understanding the role of physical and chemical adsorption obtained from simulations and quantifying the impact of impurities in the performance of the materials. Furthermore, simulation results can be used for screening adsorbents from basic key performance indicators, such as cycling the working capacity, selectivity, and energy requirement, or for feeding detailed dynamic models to assess their performance in swing adsorption processes on the industrial scale, additionally including monetized performance indicators such as operating expenses, equipment sizes, and compression cost. Moreover, we highlight the role of molecular simulations in guiding strategies for improving the performance of these materials by functionalization with amines or creating hybrid solid materials. We show how integrating models at different scales provides a robust and reliable assessment of the performance of the adsorbent materials under the required industrial conditions, rationally guiding the search for best performers. Trends in additional computational resources that can be used, including machine learning, and perspectives on practical requirements for leveraging CO2 capture adsorption technologies on the needed scale are also discussed.

Two Ln-MOFs containing abundant Lewis acid sites as the efficient and heterogeneous catalyst to activate epoxides for cycloaddition of CO2

The burning of a large number of fossil fuels leads to the increase of CO2 content in the air, causing environmental problems such as greenhouse effect and ocean acidification, which has attracted wide attention. It is of great significance to utilize microporous metal-organic frameworks (MOFs) for carbon dioxide conversion and utilization. Herein, two MOFs {[Ln(dppa)(H2O)2·2H2O]·dima·H2O·0.5O} (1: Sm-MOF; 2: Gd-MOF; H4dppa = 5-(3′ 4′-dicar- boxylphenoxy) isophthalic acid, dima = dimethylamine, which is decomposed by DMF hydrothermal reaction), and its structural characterization and CO2 catalytic conversion performance were studied. The BET test of MOFs 1–2 shows that it has good microporosity. At 273 K and 298 K, MOFs 1–2 showed lower adsorption capacity for CH4, but higher adsorption capacity for CO2. The adsorption enthalpy of CO2 was calculated by Virial equation, and the adsorption selectivity of CO2 at different separation ratios was discussed respectively. The heterogeneity of MOFs 1–2 was proved by thermal filtration experiments. The reproducibility test shows that the catalyst structure is still intact after five cycles, indicating that the catalyst still has good repeatability. In addition, the catalytic mechanism of cycloaddition reaction was discussed.

Designing Carbon‐Based Porous Materials for Carbon Dioxide Capture

AbstractRapid industrialization and urban development around the world have significantly increased carbon dioxide emissions, adversely affecting climate and ecosystems. Therefore, carbon capture and storage emerged as a promising route to reduce environmental CO2 concentration. Among various CO2 capture technologies, adsorption through carbon‐based porous materials has attracted particularly strong attention. This is primarily due to their high specific surface area, selective CO2 adsorption, moderate heat of adsorption, tunable morphology, and reduced degradation in moisture. This review critically examines carbon‐based CO2 sorbents derived from diverse sources. The key factors controlling adsorption performance, including the impact of structural and functional properties are discussed. The future research directions in this rapidly emerging field, contributing to the decarbonization of the global economy and society, are highlighted.

A Data-Driven Approach to Molten Salt Synthesis of N-Rich Carbon Adsorbents for Selective CO2 Capture.

Applying a design of experiments methodology to the molten salt synthesis of nanoporous carbons enables inverse design and optimization of nitrogen (N)-rich carbon adsorbents with excellent CO2 /N2 selectivity and appreciable CO2 capacity for carbon capture via swing adsorption from dilute gas mixtures such as natural gas combined cycle flue gas. This data-driven study reveals fundamental structure-function relationships between the synthesis conditions, physicochemical properties, and achievable selective adsorption performance of N-rich nanoporous carbons derived from molten salt synthesis for CO2 capture. Taking advantage of size-sieving separation of CO2 (3.30 Å) from N2 (3.64 Å) within the turbostratic nanostructure of these N-rich carbons, while limiting deleterious N2 adsorption in a weaker adsorption site that harms selectivity, enables a large CO2 capacity (0.73mmol g-1 at 30.4Torr and 30 °C) with noteworthy concurrent CO2 /N2 selectivity as predicted by the ideal adsorbed solution theory(SIAST = 246) with an adsorbed phase purity of 91% from a simulated gas stream containing only 4% CO2 . Optimized N-rich porous carbons, with good physicochemical stability, low cost, and moderate regeneration energy, can achieve performance for selective CO2 adsorption that competes with other classes of advanced porous materials such as chemisorbing zeolites and functionalized metal-organic frameworks.