Sorbents for CO(2) capture from flue gas--aspects from materials and theoretical chemistry

Applicability of linear polyethylenimine supported on nano-silica for the adsorption of CO2from various sources including dry air

Linear polyethylenimine impregnated on nano-silica as effective and easily regenerable CO₂adsorbents for fast adsorption/desorption cycles.

A first principles study of CO2 adsorption on α-SiO2(001) surfaces

CO₂ interaction with cleaved and reconstructed α-SiO₂(001) surfaces is studied using first principles calculations.

Estimating the binding ability of onium ions with CO2 and π systems: a computational investigation

The impact of increasing methyl substitution on onium ions in their complexes with CO₂ and aromatic systems has been analyzed using DFT calculations.

Poly(amide-imide)/silica supported PEI hollow fiber sorbents for postcombustion CO(2) capture by RTSA

Amine-loaded poly(amide-imide) (PAI)/silica hollow fiber sorbents are created and used in a rapid temperature swing adsorption (RTSA) system for CO2 capture under simulated postcombustion flue gas conditions. Poly(ethylenimine) (PEI) is infused into the PAI/mesoporous silica hollow fiber sorbents during fiber solvent exchange steps after fiber spinning. A lumen-side barrier layer is also successfully formed on the bore side of PAI/silica hollow fiber sorbents by using a mixture of Neoprene with cross-linking agents in a post-treatment process. The amine loaded fibers are tested in shell-and-tube modules by exposure on the shell side at 1 atm and 35 °C to simulated flue gas with an inert tracer (14 mol % CO2, 72 mol % N2, and 14 mol % He, at 100% relative humidity (RH)). The fibers show a breakthrough CO2 capacity of 0.85 mmol/g-fiber and a pseudoequilibrium CO2 uptake of 1.19 mmol/g-fiber. When tested in the temperature range of 35-75 °C, the PAI/silica/PEI fiber sorbents show a maximum CO2 capacity at 65 °C, owing to a trade-off between thermodynamic and kinetic factors. To overcome mass transfer limitations in rigidified PEI infused in the silica, an alternate PEI infusion method using a glycerol/PEI/methanol mixture is developed, and the CO2 sorption performance is improved significantly, effectively doubling the functional sorption capacity. Specifically, the glycerol-plasticized sorbents are found to have a breakthrough and equilibrium CO2 capacity of 1.3 and 2.0 mmol/g of dry fiber sorbent at 35 °C, respectively. Thus, this work demonstrates two PAI-based sorbents that are optimized for different sorption conditions with the PAI/silica/PEI sorbents operating effectively at 65 °C and the PAI/silica/PEI-glycerol sorbents operating well at 35 °C with significantly improved sorption capacity.

Molecular basis for the high CO2 adsorption capacity of chabazite zeolites

CO2 adsorption in Li-, Na-, K-CHA (Si/Al=6,=12), and silica chabazite zeolites was investigated by powder diffraction. Two CO2 adsorption sites were found in all chabazites with CO2 locating in the 8-membered ring (8MR) pore opening being the dominant site. Electric quadrupole-electric field gradient and dispersion interactions drive CO2 adsorption at the middle of the 8 MRs, while CO2 polarization due to interaction with cation sites controls the secondary CO2 site. In Si-CHA, adsorption is dominated by dispersion interactions with CO2 observed on the pore walls and in 8 MRs. CO2 adsorption complexes on dual cation sites were observed on K-CHA, important for K-CHA-6 samples due to a higher probability of two K(+) cations bridging CO2. Trends in isosteric heats of CO2 adsorption based on cation type and concentration can be correlated with adsorption sites and CO2 quantity. A decrease in the hardness of metal cations results in a decrease in the direct interaction of these cations with CO2.

The effect of pyridine modification of Ni–DOBDC on CO2 capture under humid conditions

The metal–organic framework Ni–DOBDC was modified with pyridine molecules to make the normally hydrophilic internal surface more hydrophobic.

New technology for post-combustion abatement of carbon dioxide via an in situ generated superoxide anion-radical

A novel chemistry for the efficient abatement of carbon dioxideviaswift nucleophilic attack by superoxide anions is disclosed.

Photodecomposition of ferrocenedicarboxylic acid in methanol to form an electroactive infinite coordination polymer and its application in bioelectrochemistry

Accurately characterizing the product of photodecomposition of ferrocene derivatives remains a longstanding challenge due to its structural complexity and strong dependence on the solvent and the substituent. Herein, photodecomposition of ferrocenedicarboxylic acid (FcDC) in methanol is found for the first time to form an electroactive infinite coordinate polymer (ICP) with uniform size, good water stability and photostability, and excellent electrochemical activity. The possible mechanism for the ICP formation is proposed based on the fission of the Fe-ring bond and deprotonation of FcDC under light irradiation. The dissociated Fe(2+) is first oxidized to Fe(3+) that consequently coordinates with the deprotonated ferrocene dicarboxylate to produce ICP nanoparticles. This work not only provides a new insight into the product formation of the photodecomposition of ferrocene derivatives but also offers a mild and simple route to the synthesis of electroactive ICPs.

Carbon dioxide and nitrogen adsorption on cation-exchanged SSZ-13 zeolites

Samples of high-silica SSZ-13, ion exchanged with protons and alkali-metal cations Li(+), Na(+), and K(+), were investigated using adsorption isotherms of CO(2) and N(2). The results show that Li-, Na-SSZ-13 have excellent CO(2) capacity at ambient temperature and pressure; in general, Li-SSZ-13 shows the highest capacity for N(2), CO(2) particularly in the low-pressure region. The effect of cation type and Si/Al ratio (6 and 12) on the adsorption properties was investigated through analysis of adsorption isotherms and heats of adsorption. The separation of CO(2) in a flue gas mixture was evaluated for these adsorbents in the pressure swing adsorption and vacuum pressure adsorption processes.

Synthesis of hierarchical porous carbon monoliths with incorporated metal-organic frameworks for enhancing volumetric based CO₂ capture capability

This work aims to optimize the structural features of hierarchical porous carbon monolith (HCM) by incorporating the advantages of metal-organic frameworks (MOFs) (Cu₃(BTC)₂) to maximize the volumetric based CO₂ capture capability (CO₂ capacity in cm³ per cm³ adsorbent), which is seriously required for the practical application of CO₂ capture. The monolithic HCM was used as a matrix, in which Cu₃(BTC)₂ was in situ synthesized, to form HCM-Cu₃(BTC)₂ composites by a step-by-step impregnation and crystallization method. The resulted HCM-Cu₃(BTC)₂ composites, which retain the monolithic shape and exhibit unique hybrid structure features of both HCM and Cu₃(BTC)₂, show high CO₂ uptake of 22.7 cm³ cm⁻³ on a volumetric basis. This value is nearly as twice as the uptake of original HCM. The dynamic gas separation measurement of HCM-Cu₃(BTC)₂, using 16% (v/v) CO₂ in N₂ as feedstock, illustrates that CO₂ can be easily separated from N₂ under the ambient conditions and achieves a high separation factor for CO₂ over N₂, ranging from 67 to 100, reflecting a strongly competitive CO₂ adsorption by the composite. A facile CO₂ release can be realized by purging an argon flow through the fixed-bed adsorber at 25 °C, indicating the good regeneration ability.

Controlling the adsorption enthalpy of CO(2) in zeolites by framework topology and composition

Zeolites are often investigated as potential adsorbents for CO(2) adsorption and separation. Depending on the zeolite topology and composition (Si/Al ratio and extra-framework cations), the CO(2) adsorption heats at low coverages vary from -20 to -60 kJ mol(-1), and with increasing surface coverage adsorption heats either stay approximately constant or they quickly drop down. Experimental adsorption heats obtained for purely siliceous porous solids and for ion-exchanged zeolites of the structural type MFI, FER, FAU, LTA, TUN, IMF, and -SVR are discussed in light of results of periodic density functional theory calculations corrected for the description of dispersion interactions. Key factors influencing the stability of CO(2) adsorption complexes are identified and discussed at the molecular level. A general model for CO(2) adsorption in zeolites and related materials is proposed and data reported in literature are evaluated with regard to the proposed model.

Computational study of adsorption and separation of CO2, CH4, and N2 by an rht-type metal-organic framework

In this work, a computational study is performed to evaluate the adsorption-based separation of CO(2) from flue gas (mixtures of CO(2) and N(2)) and natural gas (mixtures of CO(2) and CH(4)) using microporous metal organic framework Cu-TDPAT as a sorbent material. The results show that electrostatic interactions can greatly enhance the separation efficiency of this MOF for gas mixtures of different components. Furthermore, the study also suggests that Cu-TDPAT is a promising material for the separation of CO(2) from N(2) and CH(4), and its macroscopic separation behavior can be elucidated on a molecular level to give insight into the underlying mechanisms. On the basis of the single-component CO(2), N(2), and CH(4) isotherms, binary mixture adsorption (CO(2)/N(2) and CO(2)/CH(4)) and ternary mixture adsorption (CO(2)/N(2)/CH(4)) were predicted using the ideal adsorbed solution theory (IAST). The effect of H(2)O vapor on the CO(2) adsorption selectivity and capacity was also examined. The applicability of IAST to this system was validated by performing GCMC simulations for both single-component and mixture adsorption processes.

Fluorinated and nanoporous graphene materials as sorbents for gas separations

The physisorption of gases on surfaces depends on the electrostatic and dispersion interactions with adsorbates. The former can be tuned by introducing charge variations in the material, and the latter can be tuned by chemical substitution. Using atomistic Monte Carlo calculations, the Henry's law constants, and isosteric heats of adsorption of CH(4), CO(2), N(2), O(2), H(2)S, SO(2), and H(2)O on graphene, two-dimensional polyphenylene (2D-PP), fluorographene, and fluoro(2D-PP) surfaces are used to demonstrate the tunability of these two types of interaction. With the exception of H(2)O, fluorination and nanoporosity-induced charge variations reduce the binding of the adsorbates. Gas separations relevant for CO(2) sequestration, biogas upgrading, SO(2) pollution control, and air dehumidification are considered, and in most cases, the nanoporosity and fluorination reduce the selectivity of adsorption. The exceptions are separations involving adsorption of H(2)O and the SO(2)/N(2) separation, where the large dipole moments of the adsorbed species leads to enhanced binding relative to the nonpolar species.