Ideal Adsorption Solution Research Articles

Waste biomass-derived activated carbons for selective oxygen adsorption

Activated carbons (ACs) derived from waste rice husk ash (RHA) exhibit remarkable potential for selective oxygen adsorption. The pore morphology of the prepared materials was characterized utilizing BET measurement, t-plot, and BJH-plot suggesting a linear relation between activation temperature and mesopore volume, whereas, micropore volume decreases at activation beyond 550 °C. FT-IR spectroscopy confirms their non-polar surface. Notably, AC-600 achieves an outstanding O2/N2 (0.21/0.78) of 152.7 at 0.01 bar at 25 °C, owing to the non-polar nature of the surface, favouring oxygen adsorption due to its low quadrupole moment. Additionally, the mixed micro and mesoporous structure of AC-600 significantly enhance the oxygen adsorption, showing an ∼18.4% (or 1.2-fold) increase compared to AC-500. However, a ∼32.3% decrease in oxygen uptake was observed for AC-800 due to excessive “burn-off”. Adsorption selectivity, assessed with Ideal Adsorption Solution Theory (IAST) and fitted to the Freundlich isotherm model, and adsorption kinetics, analysed using the pseudo-second-order Lagergren and Webber-Morris intraparticle diffusion models, highlighted the impact of activation temperature on the porosity of the material. Understanding the surface chemistry and pore morphology of activated carbon offers deeper insights to enhance oxygen uptake capacity, advancing the development of sustainable, industrially viable materials for oxygen production.

Exploring the potential of biomass-derived carbons for the separation of fluorinated gases with high global warming potential

The development of advanced and innovative biomaterials with porous structural characteristics for the capture of fluorinated gases (F-gases) is important to contribute to the reduction of emissions of these gases with very high global warming potential. In this work, four biocarbons (CC-1:3H3PO4, CC-1:1H3PO4, CC-K2CO3 and CC-CO2) were produced by chemical and physical activation of corn cob biomass (CC). The adsorption equilibria of difluoromethane (R-32), pentafluoroethane (R-125), 1,1,1-tetrafluoroethane (R-125), 1,1,2-tetrafluoroethane (R-134a), sulphur hexafluoride (SF6), and nitrogen (N2) on these biocarbons were determined at 303.15 K. The highest adsorption capacities were obtained for CC-K2CO3 and CC-CO2 and a full characterization was also performed for these biomaterials at 283.15 and 323.15 K. On the other hand, the selectivities of SF6/N2 and the commercial refrigerants R-410A, R-407C, and R-407F were estimated using the Ideal Adsorption Solution theory (IAST). The results obtained for SF6/N2 show that the biocarbon CC-K2CO3 stands out from the other materials. In addition, the CC-CO2 shows a preference for R-32 over R-125 for the separation of the R-410A. Finally, CC-K2CO3 has a greater preference for R-134a over R-32 and R-125 in the R-407C and R-407F blends. Overall, these novel biocarbons improve the separation and purification of the F-gases under study, facilitating their application on a pilot scale.

Adsorption study of CO2/CH4 and CO2/N2 binary mixtures on titanosilicates ETS-10 and SrETS-10; industrial application aspects

Despite the outstanding features of the titanosilicate ETS-10 and some studies done on CO2 adsorption so far, there is a lack of coherent information to evaluate its potential industrial application in CO2 separation from natural gas and flue gas. In this work, ETS-10 and SrETS-10 were synthesized and characterized by PXRD, SEM, DTA, EDX, and BET. Pure gas adsorption isotherms of CO2, CH4, and N2 at 298 K were obtained by the constant-volume method. The obtained adsorption data were fitted with Langmuir and UNILAN isotherm models. The CO2/CH4 selectivity (yCO2 = 0.05) predicted by Ideal Adsorption Solution Theory (IAST) was 67.54 and 35.65 for ETS-10 and SrETS-10, respectively, while the CO2/N2 selectivity (yCO2 = 0.04) was 94.64 and 99.94. The Pseudo-Nth-Order (PNO) and micropore diffusion model were used to evaluate the CO2 adsorption kinetics and diffusivity of the adsorbents. The results showed that both ETS-10 and SrETS-10 exhibited fast kinetics for CO2 adsorption, but SrETS-10 had a slightly smaller diffusion coefficient (DC/rC2 = 0.01494 and 0.01458 s−1 for ETS-10 and SrETS-10, respectively) resulting in a slower adsorption rate than ETS-10. The regenerability of ETS-10 and SrETS-10 was studied and it was found that for ETS-10 about 79.07% and 96.32% of the capacity can be regenerated by applying vacuum and heating, respectively and also 79.67% of the SrETS-10 capacity can also be regenerated by applying vacuum. From the results of this work with an approach of industrial application, it was concluded that ETS-10 and SrETS-10 can be used in a combined PSA and TSA process for CO2 separation.

Highly efficient separation of CO2/N2 and CO2/CH4 via metal-ion regulation in ultra-microporous metal-organic frameworks

Efficient separation of CO2 from CH4 and N2 is crucial for industrial processes. This study presents a novel approach to enhance CO2/N2 and CO2/CH4 separation using metal-ion regulation in ultra-microporous metal–organic frameworks (MOFs). Specifically, we synthesized ZSTU-8-M (M=Cd, Zn) by coordinating norfloxacin ligands with different metal ions, achieving precise modulation of the pore structure. Ideal adsorption solution theory (IAST) calculations demonstrated that ZSTU-8-Cd exhibited superior selectivity for CO2/N2 (952) and CO2/CH4 (369) mixtures compared to ZSTU-8-Zn. Grand canonical Monte Carlo (GCMC) simulations and in situ single-crystal X-ray diffraction (SCXRD) confirmed the presence of specific CO2 binding sites within the pore channels. The CO2 molecule shows a unique strong adsorption mechanism of hydrogen bonding sites in this structure, and thus achieves high adsorption capacity at low pressure. Dynamic breakthrough experiments further validated the practical separation efficiency of ZSTU-8-Cd, with high retention times and saturated adsorption capacities for CO2. These findings highlight the ability of metal-ion modulation to achieve simultaneous improvement in adsorption capacity and selectivity, demonstrating the potential of MOFs for advanced gas separation applications.

Experimental and theoretical study of multiple active site-functionalized Spirulina residue-based porous carbon as an economical adsorbent for NH3 and SO2 adsorption: Micro- and macro-mechanistic investigations

Here, we successfully synthesized a cost-effective (7.88 USD/kg) multi-active site (CuCl2, CuO and KCl) functionalized Spirulina residue-based porous carbon (MMBC). This innovative synthesis method utilizes Spirulina residue, a sustainable and low-cost biomass source, making the production of MMBC economically viable and environmentally friendly. Under ambient conditions, MMBC exhibits competitive adsorption capacities for NH3 and SO2 compared to other adsorbents, reaching 3.01 mmol/g (i.e., 51.26 mg/g) and 0.70 mmol/g (i.e., 44.85 mg/g), respectively, and tolerable recoverability. These values are significant improvements over many existing adsorbents, highlighting MMBC's efficiency in removing toxic industrial chemicals (TICs). Additionally, even at low molar fractions of NH3 or SO2, such as 0.001, MMBC demonstrates significant ideal adsorption solution theory (IAST) selectivity for NH3/N2 and SO2/N2, with values of 12.02 and 4.19, respectively. This high selectivity at low concentrations underscores MMBC's potential for applications in environments with trace amounts of pollutants. Furthermore, extensive research has been conducted in this study to elucidate the microscopic and macroscopic adsorption mechanisms of NH3 and SO2 on MMBC. Specifically, investigations in statistical physics models and statistical thermodynamics reveal that the adsorption of NH3 and SO2 on MMBC adhere to a non-aggregative, multilayer, multi-anchorage, and spontaneous exothermic physicochemical behavior. And the adsorption orientation occurs either horizontally or both horizontally and non-horizontally, contingent upon the system and temperature. These findings provide a deeper understanding of the adsorption processes and provide innovative insights into the adsorption mechanisms at the molecular level and at the macroscopic scale. Besides, the material characterization results reveal that the above adsorption process involves both physical interactions (pore diffusion and van der Waals forces) and chemical interactions (CuCl2 with NH3, CuO and KCl with SO2), indicating a physicochemical adsorption mechanism. This dual mechanism of adsorption offers a comprehensive explanation of the high performance of MMBC. In summary, this study developed a cost-effective Spirulina residue-based adsorbent, exhibiting high removal efficiency and selectivity for TICs, and providing deep insights into adsorption mechanisms. The innovative use of Spirulina residue addresses waste management issues and promotes the development of sustainable materials in the field of environmental remediation, contributing to cleaner production.

Ultramicroporous metal-organic framework for efficient carbon dioxide capture from flue gas and natural gas

Carbon dioxide capture from flue gas (CO2/N2) and natural gas (CO2/CH4) is a challenging and cost-effective task. In this paper, ultramicroporous metal-organic frameworks (MOFs) (Co-norf and Ni-norf) are synthesized to realize the efficient separation of CO2/N2 and CO2/CH4 by metal ion regulation. The Ideal Adsorption Solution Theory (IAST) was calculated to evaluate the adsorption selectivity of activated Co-norf and Ni-norf for CO2/N2 (v/v = 15/85) mixtures and CO2/CH4 mixtures. The CO2/N2 selectivity of Co-norf and Ni-norf at 100 kPa was 734 and 96, respectively, which corresponds to an almost 7.6-fold increase by metal ion modulation. The specific binding sites of CO2 molecules within the pore channels were obtained by grand canonical Monte Carlo simulation (GCMC). Dynamic breakthrough experiments respond to the actual separation in systems simulating flue gas and natural gas, where the higher saturation adsorption and longer retention time proved that Co-norf is an ideal material for CO2 capture and separation. The present work provides a feasible approach for the application of MOF in gas separation.

Preparation and characterization of UiO-66-(OH)2/MWCNTs composites for CO2/N2 adsorption separation

The increasing CO2 concentration in the atmosphere can lead to climate change, and CO2 capture technology is one of the most direct and effective means of reducing carbon emissions. In this study, a new composite was prepared in situ by loading multi-walled carbon nanotubes (MWCNTs) onto metal–organic frameworks (MOFs) to efficiently capture CO2 in flue gas. The morphological states and pore structures of the composites were analyzed using characterization methods. The CO2 adsorption properties of the composites were tested at 273 K and 298 K with different MWCNTs loadings. The optimal CO2 adsorption quantities of the composite material were measured to be 4.4 and 5.75 mmol/g, respectively, which increased the adsorption capacity by 66.7 % and 55 %, respectively, compared with the parent material at a pressure of 1 bar. The CO2/N2 separation performance of the composites was examined using ideal adsorption solution theory calculations and dynamic adsorption breakthrough experiments. The stability of the composites was investigated by thermogravimetric analysis, acidification experiments, and cyclical adsorption–desorption experimentation. The UiO-66-(OH)2/MWCNTs composites exhibited superior CO2 adsorption–separation performance, thermal stability, acid resistance, and cycling stability. Therefore, the composite has potential applications in CO2 capture separation technology.

Activation-free preparation of porous carbon fiber derived from phenolic resin for CO2 absorption

BackgroundIt is not uncommon to study the preparation of porous carbon materials for CO2 adsorption, but it is still a challenge to simultaneously achieve the good mechanical strength, porous structure, and efficient adsorption performance of porous carbon fibers. MethodsPorous carbon fibers with desirable morphology and selective CO2 adsorption were prepared using an activation-free method. The fibers were prepared through melt spinning of phenolic resin modified with polyvinyl butyral (PVB) and urea, followed by curing treatment, and then the pore structures were adjusted by controlling the carbonization temperature. Significant findingsThe porous carbon fibers prepared by carbonization at 900 °C not only had excellent CO2 adsorption (3.48 mmol/g) but also possessed desirable tensile strength (132 MPa). Those carbonized at 700 °C showcased CO2/N2 selectivity of 57 (Ideal adsorption solution theory (IAST), CO2: N2 =15:85), and tensile strength of 148 MPa, much higher than most fibers using other methods. The study revealed that the adsorption of CO2 was mainly performed by nitrogen-containing groups and physical function through pores ranging from 0.3 nm to 0.8 nm, and the micropores between 0.3 nm and 0.6 nm were conducive to the selective adsorption of CO2/N2.

Unveiling the power of defect engineering in MOF-808 to enhance efficient carbon dioxide adsorption and separation by harnessing the potential of DFT analysis

Defect engineering in metal–organic frameworks involves intentionally introducing defects to modify their properties. These defects create new active sites, increase surface area, and enhance overall performance in various applications. If properly designed, these intentional defects can create new active sites and increase the specific surface area and thus the overall performance in various applications. The defect engineering strategy in MOF-808 was evaluated using the second ligand agent in different ratios. The exceptional specific surface area obtained compared to the pristine MOF 808 indicates the realization of the improvement potential of MOFs and the increase of their performance capabilities, especially in adsorbing and sequestering carbon dioxide gas in order to achieve a carbon dioxide-free future. A comprehensive set of characterization tests was conducted on the synthesized compounds in order to determine their physical and chemical properties. The Langmuir isotherm and the Weber and Morris kinetic model were chosen as the most suitable models due to their consistent performance, with R2 values surpassing 0.95 across all linker concentrations. In MOF-808 with different linker ratios of 0 %, 5 %, 10 %, 15 %, and 20 %, adsorption capacities of 6.4, 5.9, 6.7, 8.3, and 6.4 mmol/g were determined at 25 °C and 110 kPa, respectively. Notably, MOF-808-15 % exhibited the highest adsorption capacity and a remarkable surface area of 3922 m2/g, indicating a substantial interaction between CO2 molecules and the available open metal sites. Also, MOF-808 variants showed great moisture stability after being exposed to moist air for 7 days. Furthermore, an assessment of this adsorbent’s performance under flue gas conditions, utilizing the Ideal Adsorption Solution Theory (IAST), underscored its outstanding selectivity, with a significant value of 760, representing a 115-fold increase compared to pristine MOF-808-0 %. Density Functional Theory (DFT) shows better adsorption energy for MOF-808-15 % compared to MOF-808-0 %, implying the effect of defects in CO2 adsorption. Isosteric heat of adsorption study shows chemisorption phenomenon for all MOF-808 variants. Lastly, an evaluation of the cyclic stability of these MOFs over ten adsorption–desorption cycles showcased their robust and enduring performance, offering promising prospects for industrial applications.

Effect analysis of temperature and initial water content on the adsorption and separation of VOCs by ZIF‐8 based on molecular simulation

AbstractVolatile organic compounds (VOCs) have seriously polluted the atmospheric environment and caused harmful effects on human beings, so it is imperative to control oil vapor emissions. Metal organic framework materials, as one of the porous materials, have a good application prospect in the field of gas adsorption separation. In this paper, the effects of temperature and initial water content (IWC) on the adsorption properties of methane (CH4), ethane (C2H6), ethylene (C2H4), propane (C3H8), and propylene (C3H6) by ZIF‐8 were studied by combining the large gauge Monte Carlo (GCMC) and ideal adsorption solution theory. The results show that the higher the temperature is, the lower the adsorption capacity is, the higher the threshold pressure is, and the single molecule interaction energy changes little with temperature. But pore volume is still the main influencing factor. The IWC also reduces the saturated adsorption capacity. Preloaded water molecules can enhance the electrostatic interaction at low pressure, thus affecting the adsorption heat and interaction energy of single molecules. Overall, these findings provide valuable mechanistic insights into the effects of temperature and IWC on the adsorption properties of ZIF‐8 for VOCs.

Simple synthesis of acyl coupling conjugated microporous polymers monolithic material for synergistic capture of PM and CO2 in flue gas and process simulation

Adsorption and separation technologies based on physical adsorbents have the advantages of simple operation, low heat of adsorption and easy regeneration. They have received much attention for the capture of CO2 and PM from flue gases. However, the inherent “trade-off” between adsorption capacity and adsorption selectivity, as well as the high gas permeation resistance after powder processing and shaping, severely limit the prospects for industrial applications. Here, acyl functional groups were strategically introduced into polymer frameworks to successfully synthesize monolithic adsorbents (AC-CMPs) with a hierarchical pore structure for PM capture and CO2/N2 selective adsorption. The three-dimensional network structure composed of aligned hollow nanotubes effectively enhances the dispersion and mass transfer of gas flow per unit volume. Based on the porous media, multiphase flow model and discrete phase model, the gas flow process of PM trapped by AC-CMPs was simulated using Fluent. The simulation dynamically revealed the relationship between permeability resistance and filtration efficiency. The highly delocalized π-π conjugated porous skeleton linked by continuous covalent bonds endowed AC-CMPs with good stability, which prevented them from degrading in humid and high-temperature environments, thus keeping the adsorption capacity unchanged. The high polarity environment generated by the open oxygen atoms within the AC-CMPs framework, along with a high micro/mesopore ratio, enable it to achieve a CO2 adsorption capacity of 2.07 mmol/g at 273 K and 1 bar. Ideal adsorption solution theory calculations (IAST) and CO2/N2 column breakthrough experiments confirmed the excellent CO2 selectivity of AC-CMPs under realistic carbon capture conditions.

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.

Introduction of functionality into a Tb(III)-organic framework via mixed-ligand strategy for selective C2H2 capture and ratiometric Cr(VI) detection

Introduction of porosity and fluorescent properties into lanthanide metal–organic frameworks (MOFs) with rational design to achieve multifunctional use is of great significance from the energy and environmental viewpoint. In this study, a microporous Tb(III)-based MOF with the formula of {[Tb2(oba)3(Phen)2](DMF)2(H2O)4}n (1) was solvothermally prepared via using the mixed ligands of 1,10-phenanthroline (Phen) and 4,4′-oxybis(benzoic acid) (H2oba) as organic connecters. The structural evaluation results indicate that complex 1 is composed of binuclear Tb2(CO2)6(Phen)2 clusters which are extended by the oba2− ligands to afford a two-fold interpenetrated framework with one-dimensional microporous channels along the b-axis. Gas sorption studies show that the activated 1 demonstrates a high ideal adsorption solution theory (IAST) sorption selectivity of 7.4 toward C2H2 in a C2H2/CO2 gas mixture, which are further supported by the dynamic breakthrough experiments. The grand canonical Monte Carlo (GCMC) simulation results indicate that the synergistic effects of the H-bond interactions of C2H2 with oba2− ligands and the C–H···π interactions with Phen ligand contribute to the strong binding of the framework toward C2H2 molecules. What's more, the luminescent measurements reveal that the emission of 1 features both the characteristic peaks of Phen ligand and Tb(III) ion, which could be further applied as a self-calibrating sensor for the Cr(VI) detection in water. To the best of our knowledge, complex 1 represents the first example of Tb-MOF holding such a high C2H2/CO2 selectivity together with ratiometric Cr(VI) detection performances.

N-rich chitosan-derived porous carbon materials for efficient CO2 adsorption and gas separation.

Capturing and separating carbon dioxide, particularly using porous carbon adsorption separation technology, has received considerable research attention due to its advantages such as low cost and ease of regeneration. In this study, we successfully developed a one-step carbonization activation method using freeze-thaw pre-mix treatment to prepare high-nitrogen-content microporous nitrogen-doped carbon materials. These materials hold promise for capturing and separating CO2 from complex gas mixtures, such as biogas. The nitrogen content of the prepared carbon adsorbents reaches as high as 13.08wt%, and they exhibit excellent CO2 adsorption performance under standard conditions (1 bar, 273K/298K), achieving 6.97mmol/g and 3.77mmol/g, respectively. Furthermore, according to Ideal Adsorption Solution Theory (IAST) analysis, these materials demonstrate material selectivity for CO2/CH4 (10 v:90 v) and CO2/CH4 (50 v:50 v) of 33.3 and 21.8, respectively, at 1 bar and 298K. This study provides a promising CO2 adsorption and separation adsorbent that can be used in the efficient purification process for carbon dioxide, potentially reducing greenhouse gas emissions in industrial and energy production, thus offering robust support for addressing climate change and achieving more environmentally friendly energy production and carbon capture goals.

High adsorption selectivity of activated carbon and carbon molecular sieve boosting CO2/N2 and CH4/N2 separation

High adsorption selectivity of activated carbon and carbon molecular sieve boosting CO2/N2 and CH4/N2 separation

Mixed matrix membranes based on NbOF52− anion-pillared porous MOFs for efficient CO2 separation

CO2 capture and storage technologies are crucial for environmental conservation and sustainable progress. To overcome the challenging trade-off between permeability and selectivity in polymeric CO2 separation membranes, we innovatively fabricated mixed matrix membranes (MMMs) by introducing three different NbOF52− anion-pillared porous metal–organic frameworks (MOFs), namely NbOFFIVE-2-Cu-i, NbOFFIVE-2-Ni-i, and NbOFFIVE-bpy-Ni. The CO2 capture performance of the three MOFs was investigated for the first time, and the ideal adsorption solution theory (IAST) method was used to predict the CO2 separation selectivity. Density functional theory (DFT) calculations confirmed that the interaction energy between NbOFFIVE-2-Cu-i and CO2 is the highest among the three MOFs. This is due to the optimal pore dimensions and strong Cδ+ … Fδ− electrostatic interaction between the C atoms in CO2 molecules and the F atoms in NOFFIVE-2-Cu-i. The introduction of the three MOFs into the MMMs led to an increase in CO2 solubility, resulting in enhanced CO2 permeability and selectivity. The MMM loaded with 2 wt% of NbOFFIVE-2-Cu-i exhibited exceptional CO2 permeability and CO2/N2 ideal selectivity values of 578 Barrer and 70, respectively, representing enhancements of 39 % and 29 % compared to neat membrane, and exceeding the upper bound established in 2019.

Simultaneous adsorption of malachite green, methyl orange, and rhodamine B with TiO2/macadamia nutshells-derived activated carbon composite

Abstract In this study, TiO2/activated carbon (TiO2/MAC) composite was synthesized from activated carbon prepared from macadamia nutshells and a water-soluble titanium complex, and it was used to simultaneously adsorb malachite green (MG), methyl orange (MO), and rhodamine B (RhB) from aqueous solutions. The kinetic studies show that the pseudo-second-order kinetic model describes the adsorption experimental data the best. The equilibrium data of the trinary system were analyzed via the ideal adsorption solution theory (IAST) and the Langmuir and P-factor-Langmuir extended models that combine the three single-component isotherms (Langmuir, Freundlich, and Sips). The AICs (Akaike Information Criterion) values indicate that IAST incorporating the Langmuir model is the most suitable to describe the removal of the dyes in the trinary solution. The TiO2/MAC composite exhibits a high dye adsorption capacity compared with those of the published adsorbents. The thermodynamic analysis reveals that the adsorption is spontaneous and endothermic. The high adsorption capacity and the recyclability through photocatalytic self-cleaning show that TiO2/MAC can be utilized as a sustainable alternative for the simultaneous elimination of textile dyes from effluents.

Effective adsorptive removal of trace CO2 from olefin using alkanolamine‐polyethylenimine‐functionalized fumed silica

AbstractThe purification of gaseous olefins, such as C2H4 and C3H6, requires the efficient removal of trace CO2 impurities. However, the development of ideal adsorbents with high CO2/olefin selectivity has remained a challenge. In this study, we synthesized a novel adsorbent, denoted as PEI/DEA@FS, by modifying fumed silica (FS) with a combination of polyethylenimine (PEI) and diethanolamine (DEA). At 298 K and 0.0004 bar, PEI/DEA@FS presented the highest CO2 adsorption capacity among previously studied adsorbents, with a value of 2.12 mmol/g. Notably, PEI/DEA@FS demonstrated very high ideal adsorption solution theory selectivity for CO2/C2H4 (>1010) and CO2/C3H6 (>107) at 298 K and 0.01 bar. Breakthrough experiments revealed its excellent separation performance, producing olefins (C2H4 and C3H6) with ultra‐high purity (>99.9%) from a CO2/olefin (1/99) mixture. Moreover, PEI/DEA@FS exhibited outstanding stability over 20 adsorption and desorption cycles, and its CO2 adsorption performance remained almost unchanged under 75% relative humidity in the feed stream.

3D ultra-micropore organic polymers with fixed group and thieno[3,2-b]thiophene to enhance adsorption and separation of Xe/Kr

The reduction of environmental pollution and the exploration of economic values require the efficient separation and purification of xenon (Xe) and krypton (Kr) from radioactive gases generated during nuclear fission processes. To address this issue, we have synthesized three thieno[3,2-b]thiophene-based porous organic polymers (POP-ch-ET, POP-ch-SP and POP-ch-ME) via high yield C–H direct arylation reaction, all of which exhibited excellent thermal and acid-base stability. Notably, the three-dimensional (3D) structures of POP-ch-SP and POP-ch-ME allowed higher Xe capacity compared to the two-dimensional (2D) structure of POP-ch-ET. Density functional theory (DFT) calculations confirmed that thieno[3,2-b]thiophene moieties contributed to a more negative adsorption energy for Xe than benzene. Among them, POP-ch-SP with fixed group showed superior Xe capacity (2.37 mmol/g) at 298 K and 1.0 bar and the highest ideal adsorption solution theory (IAST) selectivity (11.5). This superior performance is attributed to its 3D ultra-micropore structure, which enables closer proximity between aromatic rings, thereby enhancing Xe interaction. The DFT calculation further revealed that the adsorption energy of Xe in POP-ch-SP was more negative compared to other POPs, indicating a stronger interaction. In addition, POP-ch-SP exhibited the largest ΔQst (14.2 kJ/mol) between Xe and Kr, highlighting a marked affinity difference. In dynamic breakthrough experiments, POP-ch-SP demonstrated robust Xe/Kr separation efficiency under both low (400 ppm Xe and 40 ppm Kr in dry air) and high concentration scenarios (Xe/Kr, v/v, 20/80), underscoring its promising potential for practical applications in radioactive gas management.

Influence of competitive adsorption, diffusion, and dispersion of CH4 and CO2 gases during the CO2-ECBM process

The displacement mechanisms of adsorbed CH4 by injected CO2 at high pressures in CO2-enhanced coalbed methane (CO2-ECBM) processes involve competitive adsorption, diffusion, and dispersion. Inherent coal heterogeneity and the complexity of the CO2-CH4 displacement model make CO2-ECBM modelling and optimal process design challenging. The pure gas isotherms and Langmuir adsorptions constants for CO2 and CH4 were determined using the manometric method. Notably, CO2 shows higher adsorption capacity than methane, and Langmuir volume (VL) for CO2 is 2 to 2.3 times that of methane. High pressure adsorption isotherms and experimentally determined diffusion coefficients set the sorption kinetics. The diffusion coefficient of CH4 for all four samples was in the range between 1.35×10-12 and 7.42×10-12 m2/s, while for CO2, it varied from 10.9×10-12 to 15.48×10-12 m2/s. The new concept of caucus time was introduced in the sorption kinetics of CO2 and CH4. Each sample has distinct caucus time and was positively correlated with Langmuir volumes of CO2 and CH4 with R2 > 0.9. The critical desorption pressure above which CH4 exhibits retrograde adsorption behaviour is evaluated from co-adsorption isotherms adopting Ideal Adsorption Solution Theory (IAST). The critical desorption pressure for the four samples were 1220, 460, 575 and 740 psi respectively. IAST also predicts a critical mole fraction (∼30 %) in the gas phase above which CO2 becomes the dominant adsorbed phase on coal surfaces. The results of Advective-Dispersion modelling at a larger scale illustrate the value of the Dispersion coefficient in forecasting and screening. Since the time available for diffusion versus dispersion depends upon flowrate, high values of dispersion coefficient can negatively influence favourable competitive adsorption expectations through higher operational cost in CO2 separation. This work suggests the existence of both an optimal operational pressure and flowrate to maximize the potential of CO2-ECBM technology demonstrated in competitive adsorption modelling.