Carbon dioxide adsorption on the microporous ACC carbon adsorbent

Adsorption isotherms of carbon dioxide on the microporous ACC carbon adsorbent and the adsorption deformation of the adsorbent were measured. The heats of adsorption at temperatures raising from 243 to 393 K and pressures from 1 to 5⋅10⁶ Pa were measured. In the low-temperature region (243 K), an increase in the amount adsorbed is accompanied by adsorbent contraction, and at high micropore fillings (a > 10 mmol g⁻¹) the ACC carbon adsorbent expands. At high temperatures, adsorbent expansion is observed in the whole region of micropore filling. At 243 K in the low filling region (a < 1 mmol g⁻¹), the heat of adsorption decreases smoothly from 27 to 24 kJ mol⁻¹. The heat of adsorption remains virtually unchanged in the interval 2 mmol g⁻¹ < a < 11 mmol g⁻¹ and then decreases to 8 kJ mol⁻¹ at a = 12 mmol g⁻¹. Taking into account the nonideal character of the gas phase and adsorbent deformation the heats of adsorption are strongly temperature-dependent in a region of high pressures. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1331–1335, June, 2005.     

Carbon dioxide and methane adsorption at high pressure on activated carbon materials

Granular and monolith carbon materials were prepared from African palm shell by chemical activation with H₃PO₄, ZnCl₂ and CaCl₂ aqueous solutions of different concentrations. Adsorption capacity of carbon dioxide and methane were measured at 298 K and 4,500 kPa, and also of CO₂ at 273 K and 100 kPa, in a volumetric adsorption equipment. Correlations between the textural properties of the materials and the adsorption capacity for both gases were obtained from the experimental data. The results obtained show that the adsorption capacity of CO₂ and CH₄ increases with surface area, total pore volume and micropore volume of the activated carbons. Maximum adsorption values were: 5.77 mmol CO₂ g^?1 at 273 K and 100 kPa, and 17.44 mmol CO₂ g^?1 and 7.61 mmol CH₄ g^?1 both at 298 K and 4,500 kPa.     

Classical atomistic simulations of protein adsorption on carbon nanomaterials

Carbon nanomaterials are receiving an increasingly large interest in a variety of fields, including also nanomedicine. In this area, much attention is devoted to investigating and modeling the behavior of these nanomaterials when they interact with biological fluids and with biological macromolecules, in particular proteins and oligopeptides. The interaction with these molecules is in fact crucial to understand and predict the efficacy of nanomaterials as drug carriers or therapeutic agents as well as their potential toxicity when they occupy the active site of a protein or severely affect the secondary and tertiary structure, or even the local dynamics, thus inhibiting their biological function. In this review, therefore, we describe the most recent work carried out in the last few years to model the interaction between carbon nanomaterials, either pristine or functionalized, and proteins or oligopeptides using classical atomistic methods, mainly molecular dynamics simulations. The attention is focused on 0-dimensional fullerenes, mainly C₆₀, on 1-dimensional carbon nanotubes, mostly the single-walled armchair and some chiral ones, and on 2-dimensional graphene and graphyne, the latter containing also sp hybridized atoms in addition to the sp² ones common to the other carbon nanomaterials.     

Dihydrogen adsorption isotherms (77 K) on carbon nanomaterials

Dihydrogen adsorption at 77 K on a number of fine-particle carbon materials, activated carbons, and carbon nanotubes has been investigated. The micropore structure parameters of these materials have been determined using a volumetric comparative method and nonlocal density functional theory (NLDFT). These data processing methods lead to different values of textural parameters. This difference is attributed to the presence of specific sorption sites on the surface of real carbon materials. The pore size range in which the NLDFT method is applicable to the C-H₂ system has been determined. A comparison between the hydrogen sorption properties of different carbon nanotubes is presented.     

Zr doping on one-dimensional titania nanomaterials synthesized in supercritical carbon dioxide

The growth mechanism of one-dimensional metal oxide nanotubular structures is of tremendous current interest to tailor materials using "green" synthetic procedures for emerging industries in alternative energy and biomaterials. In this study, ZrO(2)-modified TiO(2) nanorods and tubular structures were successfully synthesized via a surfactant-free sol-gel route using supercritical carbon dioxide (scCO(2)) as the solvent/drying agent. The effect of metal alkoxide concentration (0.35-1.4 mol/L), acid/metal alkoxide ratio (R = 3-7), and Zr ratio (0-20%) was examined on the morphology and crystallinity of the resulting nanostructures as measured by electron microscopy (SEM and TEM), EDX, XPS, and XRD. The electron microscopy results showed that the crystal growth of the synthesized binary Ti-Zr nanomaterials could be tailored by changing the operating variables with nanotubular structure formed at metal alkoxide concentration of 1.2 mol/L, R = 5-6, and Zr ratio between 4% and 20%. Gelation kinetics for this new system was also studied and revealed that increasing alkoxide concentration and R value enhanced the gelation kinetics. In situ and powder FTIR results revealed that this Ti-Zr binary system follows a similar reaction scheme to that of either single-component system, showing the flexibility of this approach for tailoring nanotubular production.     

Carbon dioxide-methane mixture adsorption on activated carbon

In this work, we report new experimental data of pure and binary adsorption equilibria of carbon dioxide and methane on the activated carbon RB2 at 273 and 298 K. The pressure range studied were 0–3.5 MPa for pure gases and 0–0.1 MPa for mixtures. The combination of the generalized Dubinin model to describe the pure CO₂ and CH₄ isotherms with the IAST (Ideal Adsorbed Solution Theory) for the mixtures provide a method for the calculation of the binary adsorption equilibria. This formulation predicts with acceptable accuracy the binary adsorption data and can easily be integrated in general dynamic simulation of PSA (pressure swing adsorption process) adsorption columns. It involves only three parameters, independent of the temperature, and directly determined with only one adsorption isotherm of CO₂.     

Study of carbon dioxide adsorption on a Cu-nitroprusside polymorph

A careful structural characterization was carried out to unequivocally determine the structure of the synthesized material. The TGA, DRIFTS and a Pawley fitting of the XRD powder profiles indicate that the hydrated and in situ dehydrated polymorph crystallizes in the orthorhombic space group Pnma. Meanwhile, the CO₂ isosteric heat of adsorption appears to be independent of loading with an average value of 30 kJ/mol. This translates to a physisorption type interaction, where the adsorption energy corresponding to wall and lateral interactions are mutually compensated to produce, an apparently, homogeneous adsorption energy. The somewhat high adsorption energy is probably due to the confinement of the CO₂ molecules in the nitroprusside pores. Statistical Physics and the Dubinin theory for pore volume filling allowed model the CO₂ equilibrium adsorption process in Cu-nitroprusside. A DRIFTS test for the adsorbed CO₂ displayed a peak at about 2338 cm⁻¹ that was assigned to a contribution due to physical adsorption of the molecule. Another peak found at 2362 cm⁻¹ evidenced that this molecule interacts with the Cu²⁺, which appears to act as an electron accepting Lewis acid site. The aim of the present paper is to report a Pnma stable Cu-nitroprusside polymorph obtained by the precipitation method that can adsorb carbon dioxide.     

Engineering electronic structures of nanomaterials toward carbon dioxide electroreduction

The electroreduction of CO₂ into valuable products holds the prospect for the shortage of fossil fuels and global warming. For the design of catalysts, manipulating the electronic structures of catalysts plays a vital role in the adsorption, activation, and desorption behaviors during the catalytic process. Here, we summarize recent progress in CO₂ electroreduction from the perspective of engineering electronic structures of catalysts. The strategies include vacancy engineering, heteroatom substitution, atomic layer regulation, sharp-tip effect, and interlayer bond length regulation. Particularly, combining with the experimental and theoretical results reported previously, we provide an atomic-level insight into the effect of electronic structure on CO₂ activation.     

Modeling carbon dioxide adsorption on polyethylenimine-functionalized TUD-1 mesoporous silica

Samples of porous, foam-like TUD (Technische Universit?t Delft)-1 mesoporous silica were functionalized with polyethylenimine and were used as a substrate for CO(2) adsorption. Produced solids were characterized by means of electron microscopy, thermogravimetric analysis, and N(2) adsorption/desorption at 77K, in order to prove that polymer chains efficiently filled the pores of functionalized samples. CO(2) adsorption isotherms on polyethylenimine-containing TUD-1 were evaluated at T=298, 313, 328, and 348 K for pressures up to 100 kPa by means of a volumetric technique. The CO(2) adsorption capacity proved to be significantly dependent on temperature, with the highest capacity encountered at T=348 K. The experimental data for CO(2) adsorption were satisfactorily described by means of the Langmuir isotherm, and the dependence of the isosteric heat on the fractional coverage of the adsorbent was evaluated by means of the van't Hoff equation, showing values in the order of 80 kJ/mol for a fractional coverage of about 50%.     

Carbon dioxide adsorption by synthetic mordenite isotherms and differential heat of adsorption

Carbon dioxide adsorption isotherms by synthetic mordenite are determined over the ranges 10^?5 atm<P<50 atm and ?77°C<T<+160°C, differential heats of adsorption calorimetrically measured over 10^?5atm<P<l atm and ?77°C< T< + 120°C.Differential heat curves show two adsorption ranges with different energetic characteristics. At the transition a very marked maximum appears.The integral molar entropy and specific heat of adsorbed phase are calculated.Two methods for adsorbed phase density determination are proposed:(i) The first, straight from maximal adsorbed amount at 50 atm. where adsorption isotherms level out.(ii) The second, based on adsorption potential theory with an elementary graphical determination.When the adsorbed phase density is so determined, Dubinin's equation can be successfully applied.     

Trapping adsorption of carbon monoxide located between carbon dioxide adsorbed on magnesium oxide

Carbon monoxide adsorbed on MgO is strongly trapped by the adsorbed carbon dioxide, increasing the heat of adsorption from 85.4 to 184.1 kJ/mol. The trapped CO is thought to be captured by two or three adsorbed CO₂ and becomes less active to react with oxygen.

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, MgO, , 85,4 184,1 /. , CO CO₂ .

     

Influence of MgO template on carbon dioxide adsorption of cation exchange resin-based nanoporous carbon

In this work, porous carbons with well-developed pore structures were directly prepared from a weak acid cation exchange resin (CER) by the carbonization of a mixture with Mg acetate in different ratios. The effect of the Mg acetate-to-CER ratio on the pore structure and CO(2) adsorption capacities of the obtained porous carbons was studied. The textural properties and morphologies of the porous carbons were analyzed via N(2)/77K adsorption/desorption isotherms, SEM, and TEM, respectively. The CO(2) adsorption capacities of the prepared porous carbons were measured at 298 K and 1 bar and 30 bar. By dissolving the MgO template, the porous carbons exhibited high specific surface areas (326-1276 m(2)/g) and high pore volumes (0.258-0.687 cm(3)/g). The CO(2) adsorption capacities of the porous carbons were enhanced to 164.4 mg/g at 1 bar and 1045 mg/g at 30 bar by increasing the Mg acetate-to-CER ratio. This result indicates that CER was one of the carbon precursors to producing the porous structure, as well as for improving the CO(2) adsorption capacities of the carbon species.     

Fixed-bed adsorption of carbon dioxide/methane mixtures on silicalite pellets

The adsorption of carbon dioxide and methane on silicalite pellets packed on a fixed bed has been studied. Equilibrium and kinetic measurements of the adsorption of carbon dioxide and methane have been performed, and a binary adsorption isotherm for carbon dioxide/methane mixtures has been obtained. A model based on the LDF approximation for the mass transfer has been used to describe the breakthrough curves obtained experimentally. A PSA cycle has been proposed for obtaining methane with purity higher than 98% from carbon dioxide/methane mixtures containing 38% and 50% methane, and its performance has been simulated using the proposed model. The simulation results show that silicalite can be a suitable adsorbent for employment in a PSA separation process for carbon dioxide removal from coalseam and landfill gases.     

Carbon deposition in methane reforming with carbon dioxide

Coke formation in the dry reforming of methane was studied using a thermobalance (TG) and with a catalytic microreactor in the temperature range 800–950 K. Silica-supported and lanthana-supported nickel catalysts were examined. The effects of process variables such as temperature and gas composition (He dilution, CH₄/CO₂ ratio) on the coke formation rate were determined. The reactivity of H₂ on several kinds of carbon was also investigated. The morphology of the coke was studied by scanning electron microscopy (SEM). The induction times for coke formation were significantly affected by temperature and by the CO content in the feed gas. The results of catalytic tests were consistent with the TG measurements. The behaviour of SiO₂ and La₂O₃ supported Ni catalysts agree with a mechanism in which the lanthana support plays an important role in the carbon deposition.     

Carbon dioxide capture-related gas adsorption and separation in metal-organic frameworks

Reducing anthropogenic CO₂ emission and lowering the concentration of greenhouse gases in the atmosphere has quickly become one of the most urgent environmental issues of our age. Carbon capture and storage (CCS) is one option for reducing these harmful CO₂ emissions. While a variety of technologies and methods have been developed, the separation of CO₂ from gas streams is still a critical issue. Apart from establishing new techniques, the exploration of capture materials with high separation performance and low capital cost are of paramount importance. Metal-organic frameworks (MOFs), a new class of crystalline porous materials constructed by metal-containing nodes bonded to organic bridging ligands hold great potential as adsorbents or membrane materials in gas separation. In this paper, we review the research progress (from experimental results to molecular simulations) in MOFs for CO₂ adsorption, storage, and separations (adsorptive separation and membrane-based separation) that are directly related to CO₂ capture.     

Endothermic character of toluene adsorption from supercritical carbon dioxide on activated carbon at low coverage

Recasens, P., Velo, E., Larrayoz, M.A. and Puiggené, J., 1993. Endothermic character of toluene adsorption from supercritical carbon dioxide on activated carbon at low coverage. Fluid Phase Equilibria, 90: 265-287.

Heat effects and volumetric properties are analyzed for the adsorption of toluene from supercritical carbon dioxide onto activated carbon at the limit of zero coverage, based on existing data for the system. Using values of the adsorption equilibrium constant at different temperatures as a function of fluid density, large, negative partial molar volumes for toluene in the fluid were obtained, which were previously unavailable.

Numerical integration of the differential equation that expresses the isobaric temperature dependence of the equilibrium constant, coupled with parameter optimization, enabled us to estimate the differential enthalpy of toluene adsorption onto the surface from the ideal gas at the same pressure and temperature, in addition to the enthalpy of transfer from the fluid to the surface. This is found to be large and positive near the critical conditions. Using the thermodynamic analysis of Kelley and Chimowitz, our results show that in terms of the enthalpy of transfer, the isothermal adsorption from a supercritical fluid is an endothermic process, thus explaining the retrograde behavior experimentally observed for the regeneration of carbon with supercritical CO₂ at conditions not far from the solvent's critical point.     

Surface chemistry of polymers. The adsorption of carbon dioxide and sulfur dioxide on polyvinylidene chloride

Isotherms for the adsorption of nitrogen (77 K), carbon dioxide (195–247 K) and sulfur dioxide (254–293 K) on polyvinylidene chloride have been measured volumetrically. The B.E.T. cross-sectional areas of 18 Ų (CO₂) and 24 Ų (SO₂) are comparable to liquid density values. The isosteric heat of adsorption of CO₂ is constant for 0.2 < θ < 0.4 and is lower than the latent heat of condensation. For SO₂, the two are practically identical up to the monolayer. Entropy calculations show ‘supermobility’ in the case of CO₂.     

Effect of chemical modification on carbon dioxide adsorption property of mesoporous silica

Three adsorbents were prepared by different modification methods, which were grafting silica gel with (3-aminopropyl) trimethoxysilane, grafting silica gel with acrylamide polymer, and impregnating silica gel with acrylamide polymer, respectively. The characterization of materials was carried out by N(2) adsorption experiments, Fourier transform infrared spectroscopy, scanning electron microscopy, thermo-gravimetric analysis, and elemental analyses. The results showed that the amine group was successfully loaded on all three modified adsorbents; among that, the polymer-modified silica adsorbents had higher amine content and larger surface area than the aminopropyl-grafted silica adsorbent and displayed higher thermal stability than the other polymer-modified silica materials previously reported. The CO(2) adsorption/desorption experiments performed at 25°C by TGA-DSC method showed that the highest CO(2) adsorption capacity (0.98 mmol/g) was observed for the polymer-impregnated silica adsorbent. CO(2) adsorbed on all samples was completely desorbed by purging with inert gas at 60°C except for the aminopropyl-grafted silica material, which showed the highest enthalpy of CO(2) adsorption.