Heat Of CO2 Adsorption Research Articles

Activated carbons prepared by the KOH activation of a hydrochar from garlic peel and their CO2 adsorption performance

Biomass is regarded as a promising low-cost precursor for the preparation of activated carbons. However, direct carbonization of biomass usually produces a low-surface-area or even non-porous carbons that are useless for CO2 capture. In this work, garlic peel was first transformed to a hydrochar by hydrothermal carbonization and then chemically activated by KOH to obtain activated carbons with high-surface-areas and large pore volumes. The microstructure and morphology of the activated carbons were characterized by N2 adsorption, SEM and XRD. Results indicate that their surface area and pore volume are mainly determined by the activation temperature and KOH/hydrochar mass ratio. Activated carbon (AC-28) obtained by KOH activation with a KOH/hydrochar ratio of 2 at 800 °C has a well-developed porosity with a surface area and pore volume of 1 262 m2/g and 0.70 cm3/g, respectively, while a reduction of the activation temperature to 600 °C (AC-26) results in a material whose corresponding values are 947 m2/g and 0.51 cm3/g. Although AC-26 exhibits a much lower surface area and pore volume compared with AC-28, it has the larger CO2 uptake of up to 4.22 mmol/g at 25 °C and 1 bar due to its higher microporosity of up to 98% and abundant narrow micropores, implying that the microporosity is one of the main factors for CO2 capture besides the traditionally-believed surface area and pore volume. The isosteric heat of CO2 adsorption indicates that the affinity between the activated carbon and CO2 molecules increases with the volume of narrow micropores less than 0.8 nm and the number of surface oxygen-containing functional groups.

Carbon foams from sucrose employing different metallic nitrates as blowing agents: Application in CO2 capture

Carbon foams were prepared employing sucrose as the carbon source. The porosity of the materials as well as the morphology was controlled using different metallic nitrates during the synthesis, such as aluminum (obtaining EsAl foam), iron (obtaining EsFe foam) and silver (obtaining EsAg foam) nitrate. The samples have interconnecting pores with a turbostratic structure, where the EsFe foam shows a more ordered structure. The addition of the chemical agents promotes improvements in the porosity of the foams, highlighting those obtained with the aluminum nitrate nonahydrate - EsAl (98%) and iron nitrate nonahydrate - EsFe (90%), as well as a greater control of pore growth avoiding collapse. All carbon foams presented a microporous nature, but EsFe foam also present mesoporosity (with pore sizes between 2.2 to 3.5 nm). The high specific surface area values for EsAl and EsFe carbons (600 and 380 m2/g) were attributed to in situ activation during carbonization of the foams. All carbon foams present ultramicropores with pore sizes less than 0.6 nm. The synthesized carbon foams have interesting CO2 adsorption capacities, mainly the EsAl foam that reach CO2 adsorption capacities (at 1000 kPa) of 4 and 4.4 mmol/g at 50 °C and at 35 °C, respectively. These capacities of the carbon foams obtained were similar to those reported in the bibliography for other carbon materials, shows their great potential as CO2 adsorbents. The isosteric heat of CO2 adsorption show that the CO2 capture with the carbon foams synthesized is associated with a physisorption process.

Preparation and evaluation of nitrogen-tailored hierarchical meso-/micro-porous activated carbon for CO2 adsorption

ABSTRACT In this study, nitrogen-tailored hierarchical meso-/micro-porous activated carbons were successfully fabricated from cypress sawdust by H3PO4 activation with further nitrogen modification using three kinds of nitrogen source (i.e. nitic acid, urea and melamine). The produced carbons were used as adsorbents for CO2 capture. The physic-chemical properties of the produced carbons were characterized by N2 adsorption-desorption, fourier-transform infrared spectroscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. The effects of pore structure and nitrogen content on CO2 adsorption were investigated. It was found that H3PO4 activation would turn cypress sawdust into mesoporous carbon (AC), nitrogen doping could induce the development of microporosity and also increase the basicity of the carbon framework, which favoured for CO2 adsorption. Among the nitrogen-tailed carbons, HNO3-treated activated carbon (AC–N) showed the highest V mic (0.127 cm3/g), the largest CO2 adsorption capacity (2.8 mmol/g at 273 K, 1 bar) and the best CO2/N2 selectivity as compared to urea and melamine treated ones. The adsorption experiments showed that the presence of microporosity and pyrrolic-N on the carbons were responsible for CO2 adsorption, the oxygen functional groups on AC–N might also contribute to higher CO2 uptake, and the mesoporous structure could favour for the fast mass transfer of CO2. The results of CO2 adsorption heat confirmed the high affinity of the prepared carbons to CO2. This study provides a strategy to produce hierarchical meso-/micro-porous activated carbons with enriched nitrogen functional groups, which favoured for CO2 adsorption.

Improved CO2 recovery from flue gas by layered bed Vacuum Swing Adsorption (VSA)

Performance of a two column five-step vacuum swing adsorption cycle is tested for CO2 enrichment and recovery from a simulated ternary flue gas mixture containing 13% CO2, 82% N2, and balance O2. The results are compared when a layered bed of commercial activated carbon (AC) (F-400, Calgon) and 13X zeolite (Z10-04, Zeochem) is employed with reference to an only single layer of AC and 13X adsorbent. With the layered bed, in which the first layer at the feed entry end is AC followed by 13X, the CO2 recovery obtained is 84% which is 42% more than that of pure 13X bed and the purity of CO2 is almost at the same level as that with 13X bed (∼90 mol%). The VSA is compared at same adsorption time, set as a 70% of CO2 breakthrough time. The CO2 purity obtained with the activated carbon bed was 76 mol% which is considerably lower compared to the bed with only zeolite 13X layer (90 mol%). The result can be explained due to higher CO2/N2 selectivity of the zeolite than activated carbon. The recovery of CO2 with activated carbon is, however, higher (97%) than zeolite (59%) due to its lower heat of CO2 adsorption compared to that with 13X. The lower heat of CO2 adsorption on the activated carbon surface implies weaker interaction and thus better desorption characteristics than 13X. VSA performance of the layered bed are also compared under different adsorption/evacuation time, bed temperature and evacuation level.

Amine functionalized mesoporous hybrid materials: influence of KCl and xylene on the textural characteristics and CO2 sorption

Amine-functionalized mesoporous silica materials were prepared by sol–gel method in the system tetraethylortosilicate: bis[(3- trimethoxysilyl)propyl]amine (TEOS: BTPA). The hybrid amine functionalized silica materials were synthesized by co-condensation reaction between TEOS and BTPA precursors in acidic media. Soft template approach for pore formation was applied and as a structural directing agent was used surfactant Pluronic P123. For improving of pore ordering and textural characteristics xylene and KCl were used and their influence on the structural and morphological characteristics was investigated by FTIR, 13C CP MAS NMR, 29Si MAS NMR, BET, PSD and XRD techniques. CO2 adsorption properties of the synthesized amine functionalized hybrid materials were investigated. The simultaneous presence of xylene and KCl leads to improvement of the pore ordering, increasing of the textural characteristics values and formation of cylindrical pores. The determined heats of CO2 adsorption evidenced chemisorption process between CO2 and the amine groups of the hybrid materials.

Preparation of pineapple waste-derived porous carbons with enhanced CO2 capture performance by hydrothermal carbonation-alkali metal oxalates assisted thermal activation process

The pineapple waste-derived porous carbons with enhanced CO2 adsorption performance were successfully prepared by a facile hydrothermal carbonation and followed thermal activation using facile alkali metal oxalates instead of KOH or K2CO3 for chemical activation. Compared with macroporous-mesoporous carbons activated by Li2C2O4 and Na2C2O4, the microporous carbon activated by K2C2O4 at 700 °C with a relatively high specific surface area of 1076.3 m2 g−1 and big pore volume of 0.92 cm3 g-1 for narrow micropores (<1 nm)for narrow micropores (<1 nm) shows the highest adsorption capacities of 5.32 mmol g-1 at 0 °C, and 4.25 mmol g-1 at 25 °C under 1 bar, respectively. Furthermore, all the samples show high selectivities from 18.24 to 38.42 for CO2/N2 separation, stable cyclic capability with adsorption loss of 12.6–17.8% after twelve cycles at 25 °C and reasonable isosteric heat of CO2 adsorption. Especially, the microporous carbon activated by facile K2C2O4 at 700 °C shows speedy adsorption dynamics and excellent dynamic adsorption performance for simulated flue gas based on its breakthrough curve. In combination with the low-cost carbon source, the above advantages make the pineapple waste-derived porous carbons exceptionally potential sorbent to capture and separate CO2 under real conditions.

Experimental and theoretical demonstration of the relative effects of O-doping and N-doping in porous carbons for CO2 capture

Will the CO2 capture be affected by the N-doping? This question remains conflict due to the effect of oxygen content in N-doped porous carbons on CO2 uptake has not been systematically investigated. Herein, the effects of N-free and N-doped porous carbons on CO2 uptake were investigated by experiments and theoretical calculations. To elucidate the relative influences of nitrogen functional groups, we synthesized a series of carbons without or with N-doping (2.73–9.44% N) by varying the synthesis conditions. Experimental results show that the introduction of oxygen and nitrogen into carbon framework improves CO2 capture in porous carbons (PCs) and N-doped porous carbons (NPCs). Among these samples, the NPC600 exhibits an exceptionally high CO2 adsorption capacity (5.01 mmol g−1 at 1 bar and 25 °C). Based on the theoretical calculations, the introduction of nitrogen into carbon framework with high oxygen content further enhances electrostatic interaction for CO2 adsorption. Moreover, the doping of nitrogen to carbon framework also has a greater effect on both the selectivity for CO2/N2 and the isosteric heat of CO2 adsorption. It is predicted that this investigation will eliminate any ambiguities and better explain the influence of N-doping on CO2 capture.

CO2 capture using three-dimensionally ordered micromesoporous carbon

Adsorption of CO2 on three-dimensionally ordered micromesoporous carbon with a spherical pore structure has been studied using gravimetric and manometric analyses. Adsorptive properties were compared with activated carbon and nanostructured carbon materials such as carbon nanotubes, zeolitic-imidazolate framework-derived carbon, carbon nanohorns and ordered mesoporous carbon materials. The regular spherical pores of 14–15 nm diameter with a large pore volume of 3.4 cm3 g−1 provided a very high CO2 adsorption capacity exceeding the compared carbon materials at high gas pressures (≥4 MPa and room temperature). A strong increase in the isosteric heat of CO2 adsorption with increasing surface coverage indicates that high pressure adsorption was predominantly controlled by strong quadrupole moment interactions between CO2 molecules and less intensive interactions of CO2 with the mesoporous surface. Micropores in the walls of the main spherical mesopores, with a pore volume of 0.17 cm3 g−1, provided good CO2 adsorption properties at atmospheric pressure, characterized by rectilinear isotherms and a predominant surface coverage mechanism. Analysis of the strength of CO2 interaction with the carbon adsorbent and a kinetic study of CO2 adsorption revealed excellent CO2 adsorption-desorption reversibility.

A metal-organic framework with suitable pore size and dual functionalities for highly efficient post-combustion CO2 capture.

Capturing carbon dioxide (CO2) from flue gases with porous materials has been considered as a viable alternative technology to replace traditional liquid amine adsorbents. A large number of microporous metal-organic frameworks (MOFs) have been developed as CO2-capturing materials. However, it is challenging to target materials with both extremely high CO2 capture capacity and gas selectivity (socalled trade-off) along with moderate regeneration energy. Herein, we developed a novel porous material, [Cu(dpt)2(SiF6)] n (termed as UTSA-120; dpt = 3,6-di(4-pyridyl)-1,2,4,5-tetrazine), which is isoreticular to the net of SIFSIX-2-Cu-i. This material exhibits simultaneously high CO2 capture capacity (3.56 mmol g-1 at 0.15 bar and 296 K) and CO2/N2 selectivity (~600), both of which are superior to those of SIFSIX-2-Cu-i and most other MOFs reported. Neutron powder diffraction experiments reveal that the exceptional CO2 capture capacity at the low-pressure region and the moderate heat of CO2 adsorption can be attributed to the suitable pore size and dual functionalities (SiF62- and tetrazine) which not only interact with CO2 molecules but also enable the dense packing of CO2 molecules within the framework. Simulated and actual breakthrough experiments demonstrate that UTSA-120a can efficiently capture CO2 gas from the CO2/N2 (15/85, v/v) and CO2/CH4 (50/50) gas mixtures under ambient conditions.

Synthesis of Nitrogen and Sulfur Codoped Nanoporous Carbons from Algae: Role in CO2 Separation.

Nitrogen and sulfur codoped and completely renewable carbons were synthesized from two types of algae, Spirulina Platensis and Chlorella Vulgaris, without any additional nitrogen fixation reaction. The type of activation agents, char-forming temperature, activation agent-to-char ratio, and activation temperature were all varied to optimize the reaction conditions for this synthesis. The maximum Brunauer–Emmett–Teller surface area and total pore volumes of the carbons were 2685 m2/g and 1.4 cm3/g, respectively. The nitrogen and sulfur contents of the carbons were in the range of 0.9–5.69 at. % and 0.05–0.2 at. %, respectively. The key nitrogen functionalities were pyridinic, amino, and pyridonic/pyrrolic groups, whereas the key sulfur functionalities were S–C, O–S–C, and SOx groups. CO2 adsorption isotherms were measured at 273, 298, and 313 K, and the ideal adsorbed solution theory was employed to calculate the selectivity of adsorption of CO2 over N2 and simulate binary adsorption isotherms. The adsorption results demonstrated that the CO2 adsorption amount and the heat of CO2 adsorption were higher for carbons with higher nitrogen content, confirming the influence of nitrogen functionality in CO2 adsorption. The overall results suggested that these algae-derived renewable carbons can serve as potential adsorbents for CO2 separation from N2.

CO2 Adsorption on Premodified Li/Al Hydrotalcite Impregnated with Polyethylenimine

In this study, Li/Al hydrotalcite (HT) was treated with calcination and potassium hydroxyl-ethanol to form bcHT (basic-modified calcined hydrotalcite). This material was then polyethylenimine (PEI)-functionalized to create a new sorbent that has ultralow energy consumption. Various methods were applied to characterize the sorbent, including N2 adsorption–desorption, Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. CO2 adsorption capacity, which was affected by PEI loadings and adsorption temperatures, was assessed with the CO2 adsorption isotherms and cyclic CO2 adsorption–desorption performance. Results showed that the optimal CO2 adsorption capacity of 1.723 mmol/g was reached when operating with temperature of 323 K and PEI loading of 40%. The Freundlich model was applied to provide optimal correlations with the experimental data, and the correlation coefficients reached 0.997. The average isosteric heat of CO2 adsorption was calculated to be 67.492 kJ/mol. ...

Application of Industrial Wastes from Chemically Treated Aluminum Saline Slags as Adsorbents.

In this study, industrial wastes, which remain after aluminum extraction from saline slags, were used as adsorbents. The aluminum saline slags were treated under reflux with 2 mol/dm3 aqueous solutions of NaOH, H2SO4, and HCl for 2 h. After separation by filtration, aqueous solutions containing the extracted aluminum and residual wastes were obtained. The wastes were characterized by nitrogen adsorption at −196 °C, X-ray diffraction, scanning electron microscopy, and ammonia pulse chemisorption. The chemical treatment reduced the specific surface area, from 84 to 23 m2/g, and the pore volume, from 0.136 to 0.052 cm3/g, of the saline slag and increased the ammonia-adsorption capacity from 2.84 to 5.22 cm3/g, in the case of acid-treated solids. The materials were applied for the removal of Acid Orange 7 and Acid Blue 80 from aqueous solutions, considering both single and binary systems. The results showed interesting differences in the adsorption capacity between the samples. The saline slag treated with HCl rapidly adsorbed all of the dyes present in solution, whereas the other materials retained between 50 and 70% of the molecules present in solution. The amount of Acid Orange 7 removed by the nontreated material and by the material treated with NaOH increased in the presence of Acid Blue 80, which can be considered as a synergistic behavior. The CO2 adsorption of the solids at several temperatures up to 200 °C was also evaluated under dry conditions. The aluminum saline slag presented an adsorption capacity higher than the rest of treated samples, a behavior that can be explained by the specific sites of adsorption and the textural properties of the solids. The isosteric heats of CO2 adsorption, determined from the Clausius–Clapeyron equation, varied between 1.7 and 26.8 kJ/mol. The wastes should be used as adsorbents for the selective removal of organic contaminants in wastewater treatment.

Paddlewheel SBU based Zn MOFs: Syntheses, Structural Diversity, and CO₂ Adsorption Properties.

Four Zn metal–organic frameworks (MOFs), {[Zn2(2,6-ndc)2(2-Pn)]·DMF}n (1), {[Zn2(cca)2(2-Pn)]·DMF}n (2), {[Zn2(thdc)2(2-Pn)]·3DMF}n (3), and {[Zn2(1,4-ndc)2(2-Pn)]·1.5DMF}n (4), were synthesized from zinc nitrate and N,N′-bis(pyridin-2-yl)benzene-1,4-diamine (2-Pn) with naphthalene-2,6-dicarboxylic acid (2,6-H2ndc), 4-carboxycinnamic acid (H2cca), 2,5-thiophenedicarboxylic acid (H2thdc), and naphthalene-1,4-dicarboxylic acid (1,4-H2ndc), respectively. MOFs 1–4 were all constructed from similar dinuclear paddlewheel {Zn2(COO)4} clusters and resulted in the formation of three kinds of uninodal 6-connected non-interpenetrated frameworks. MOFs 1 and 2 suit a topologic 48·67-net with 17.6% and 16.8% extra-framework voids, respectively, 3 adopts a pillared-layer open framework of 48·66·8-topology with sufficient free voids of 39.9%, and 4 features a pcu-type pillared-layer framework of 412·63-topology with sufficient free voids of 30.9%. CO2 sorption studies exhibited typical reversible type I isotherms with CO2 uptakes of 55.1, 84.6, and 64.3 cm3 g−1 at 195 K and P/P0 =1 for the activated materials 1′, 2′, and 4′, respectively. The coverage-dependent isosteric heat of CO2 adsorption (Qst) gave commonly decreased Qst traces with increasing CO2 uptake for all the three materials and showed an adsorption enthalpy of 32.5 kJ mol−1 for 1′, 38.3 kJ mol−1 for 2′, and 23.5 kJ mol−1 for 4′ at zero coverage.

Developing hierarchically ultra-micro/mesoporous biocarbons for highly selective carbon dioxide adsorption

Activated carbons represent one of the important categories of the adsorbent materials for CO2 capture currently under development. However, the low adsorption capacity and selectivity at low CO2 partial pressure and/or relatively high flue gas temperatures is the main barrier for carbons to be applied in post-combustion CO2 capture under practical conditions. Here, we report the successful preparation of hierarchical ultra-micro/mesoporous bio-carbons from using a facile one-step method with a low-grade biomass waste as the feedstock. The bio-carbons exhibit high adsorption capacities (1.90 mmol/g) and record-high Henry’s law CO2/N2 selectivities up to 212 at ambient temperature and low CO2 partial pressure. Unlike conventional chemical activation process for manufacturing carbon materials, the integrated compaction-carbonization-activation method proposed endows the biowaste-derived carbons with unique hierarchical bio-modal pore structures, which are highly characterised by their high mesoporosity and high ultra-microporosity with narrow pore size distributions. The results demonstrated that the unique surface textural properties along with the enhanced surface chemistry due to the simultaneously achieved potassium intercalation created favourable conditions for CO2 adsorption with high CO2/N2 selectivity at low CO2 partial pressures, whilst the presence of mesoporosity greatly increased the CO2 adsorption kinetics. Measurements of CO2 adsorption heat confirmed the strong surface affinity of the prepared bio-carbons to CO2 molecules.

Molecular simulation of coal-fired plant flue gas competitive adsorption and diffusion on coal

Better understanding the microcosmic mechanism of CO2, O2, and N2 competitive adsorption can benefit the effective CO2 storage and fire prevention by injecting coal-fired flue gas into the goaf. Toward this aim, macromolecular coal model was established. Grand Canonical Monte Carlo and Molecular Dynamics simulation were carried out at single, binary, and ternary component systems under the conditions of 298.15–318.15 K and up to 10000 kPa. Simulation results demonstrate that the absolute adsorption amount decreases with the increase of temperature and water content in coal, and increases with the pressure increasing and corresponding bulk mole fraction. The competitiveness is CO2 > O2 > N2 basing on the ternary adsorption selectivity of CO2/O2 (5.6–24.2), CO2/N2 (8.4–29.3), and O2/N2 (1.2–1.5). The isosteric adsorption heat of CO2 (about 29.1–30.9 kJ/mol) is nearly double of O2 or N2 (about 16.6–17.3 kJ/mol), and CO2 occupies stronger adsorption sites without being affected by O2 or N2. The interaction energy between CO2 and coal is greater than O2 or N2 due to the electrostatic energy and much larger van der Waals energy. The adsorbed molecules swell the coal and the trend of self-diffusion coefficients with pressure is consistent with loading and volumes. So the flue gas injecting into the goaf is better than pure N2, and can store large amounts of CO2 (0.406 mmol/g), meanwhile inhibit the coal spontaneous combustion, visually displayed by density distributions. The findings provide essential evidence for injection parameters such as temperature, pressure, gas concentration, injectivity, moisture, and so on.

Influence of temperature and high-pressure on the adsorption behavior of scCO2 on MCM-41 and SBA-15

Actually there is a growing interest in various so-called adsorption precipitation processes. Thereby, an organic molecule is dissolved in supercritical CO2, followed by the adsorption of the molecule onto a substrate (e.g. MCM-41, SBA-15) and subsequent solute precipitation due to pressure decrease. For the design of such processes it is essential to understand the complex nature of the multicomponent adsorption behavior. Thus as a first step, there is a need for studying the adsorption behavior of the particular CO2-substrate system at the respective process conditions. Due to a lack of experimental data adsorption isotherms of CO2 on MCM-41 and SBA-15 were measured at temperatures from T = 298 to 353 K and pressures up to p = 25 MPa. Based on these results, the absolute amount adsorbed was calculated from the surface excess amount. Finally, the isosteric heat of adsorption for CO2 was calculated by using the Clausius - Clapeyron equation.

Improving isosteric heat of CO2 adsorption by introducing nitro moieties into jungle-gym-type porous coordination polymers

Four types of novel jungle-gym-type porous coordination polymers, [Zn2(bdc)2(dabco)]n (Zn, bdc = 1,4-benzenedicarboxylate, dabco = 1,4-diazabicyclo[2.2.2]octane), [Zn2(bdc-NO2)2(dabco)]n (Zn-NO2, bdc-NO2 = nitro-terephthalate), [Cu2(bdc)2(dabco)]n (Cu) and [Cu2(bdc-NO2)2(dabco)]n (Cu-NO2), were synthesised and characterised using gas adsorption measurements to estimate the affinity between CO2 and nitro moieties. N2 adsorption measurements at 77 K for four compounds show type-I isotherms, indicating the permanent porosities, where the BET surface areas are 1417 m2 g−1 (Zn), 1076 m2 g−1 (Zn-NO2), 1688 m2 g−1 (Cu), and 759 m2 g−1 (Cu-NO2). The adsorption capacity of CO2 at 195 K obeys the amount of surface area, whereas the isosteric heat of CO2 adsorption in both Zn-NO2 and Cu-NO2 are higher than the original compounds. The enthalpies at zero coverage of CO2 adsorption are 19 kJ mol−1 (Zn), 27 kJ mol−1 (Zn-NO2), 17 kJ mol−1 (Cu), and 27 kJ mol−1 (Cu-NO2), which may be attributed to the quadruple interaction between CO2 and nitro moieties.

Improved CO2 capture and separation performances of a Cr-based metal–organic framework induced by post-synthesis modification of amine groups

A composite adsorbent based on a metal–organic framework MIL-101 (Cr3F(H2O)2O(BDC)3; BDC: terephthalic acid) loaded with N,N′-dimethylethylenediamine (dmeda) was synthesized by post-synthesis modification method, and the crystal structure and thermal stability of MIL-101 were maintained. The composite is shown to enhance capacity and selectivity for post-combustion carbon dioxide capture, even if its BET specific surface area decreases by 52% compared to MIL-101. At 273 K and 298 K under 1 bar, dmeda-MIL-101 exhibited 8.7% and 18.7% increase in CO2 capacity respectively (from 2.30 mmol/g of MIL-101 to 2.50 mmol/g at 273 K, and from 1.35 mmol/g of MIL-101 to 1.59 mmol/g at 298 K). At 273 K and 298 K under a 0.15 bar CO2/0.75 bar N2 mixture, the CO2/N2 selectivities of MIL-101 and dmeda-MIL-101 were calculated by Ideal Adsorbed Solution Theory (IAST), according to single-component gas sorption experiment data. The improved capacity and selectivity are consequences of the higher isosteric heat of CO2 adsorption (33.9 kJ/mol at zero coverage), which is due to the interaction between amines and CO2.

An amine functionalized carbazolic porous organic framework for selective adsorption of CO2 and C2H2 over CH4

Abstract A new microporous organic polymer (PCB NH2) has been synthesized based on amine functionalized carbazole derivative by oxidative coupling polymerization with anhydrous FeCl3. Polymer PCB-NH2 exhibits microporous nature with a BET surface area of 542.4 m2 g−1, and shows moderately high CO2 and C2H2 adsorption capacities, 51.6 cm3 g−1 (10.3 wt%), 58.4 cm3 g−1 (7.5 wt%) at 278 K, 1 atm, respectively. Remarkably, at 278 K, the predicted IAST selectivities of PCB-NH2 are 16.7–5.8 for a CO2/CH4 (5:95 v/v) gas mixture and 34.3–21.0 for a C2H2/CH4 (50:50 v/v) gas mixture at pressures varying from 0 to 1 atm, respectively. More interesting, PCB-NH2 displays higher CO2/CH4 selectivity than its matrix polymer PCB. The isosteric heats of CO2 adsorption (Qst) for PCB-NH2 and PCB further indicate that the amine group may facilitate the interaction between the polarizable CO2 molecules and the polymer by local dipole−quadrupole interactions, subsequently favors selective gas separation for these gas molecules. The high selectivity of CO2/CH4 and C2H2/CH4 makes PCB-NH2 possible candidate for future natural gas upgrading and acetylene purification.

In Situ Synthesis of Nitrogen-Enriched Activated Carbons from Procambarus clarkii Shells with Enhanced CO2 Adsorption Performance

Highly microporous nitrogen-enriched activated carbons were in situ synthesized by using K2C2O4·H2O as an activating agent and Procambarus clarkii shells as a carbon and nitrogen (N) source. The obtained samples exhibit good CO2 adsorption performance at 1 bar ranging from 4.99 to 6.48 mmol/g at 0 °C, and from 2.55 to 4.51 mmol/g at 25 °C, respectively. In particular, a high CO2 adsorption capacity of 4.51 mmol/g at 25 °C was achieved for the sample prepared by using the K2C2O4·H2O/precursor mass ratio of 3 and activated at 700 °C. The high CO2 uptake was achieved because of a unique microporous structure and high N content. Furthermore, the CO2/N2 selectivity and CO2 adsorption heat of this carbon are as high as 52 and 33 kJ/mol, respectively. In addition, this carbon exhibits excellent reusable stability and a high dynamic CO2 capture capacity of 0.79 mmol/g under conditions mimicking aflue gas environment. The aforementioned advantages demonstrate that the obtained N-enriched activated carbon can be a ...