Adsorption of phosgene and chloroform by activated and impregnated carbons

Equilibrium adsorption and desorption isotherm data at room temperature have been obtained for phosgene and chloroform vapors on BPL grade activated carbon, ASC whetlerite and four ASB impregnated carbons. Isotherm data were plotted in the form of the Dubinin-Polanyi equation. Experimental affinity coefficients (β_ex) for phosgene with chloroform as a reference, were calculated for all the carbons except ASC whetlerite from the slopes (k) of the Dubinin-Polanyi plot, and were compared with the theoretical affinity coefficients (β_th) in order to assess the adsorption capabilities of different adsorbents. In the case of phosgene on ASC whetlerite carbon, significant chemisorption takes place along with physical adsorption and the resulting isotherm shows non-linear behavior. Attempts were made to separate the chemisorption contribution from the total adsorption and thus assess β_ex for the physical adsorption contribution.     

A novel reaction catalysed by active carbons: Production of dichloromethane from phosgene and formaldehyde

A variety of activated charcoals have been found to catalyse a previously unknown, highly selective, reaction between phosgene and formaldehyde. In a continuous flow fluidized bed reactor, the reaction rate reaches a broad maximum at ≈170 °C where the selectivity is consistent with the stoichiometry: COCl₂ + CH₂O → CH₂Cl₂ + CO₂. The reaction proceeds via a strongly adsorbed intermediate which has been identified as chloromethyl chloroformate. This ester is an adduct of formaldehyde and phosgene and forms rapidly above 100 °C in co-adsorption/desorption experiments. It decomposes rapidly at ≈170 °C without significant desorption of the intact molecule to give the observed products dichloromethane and carbon dioxide. Under steady-state conditions the rate-determining step is the formation of this ester so that it is normally only present on the surface at low coverages; hence it is not observable in the gas phase. The catalysis is probably due to the presence of polar acid or base sites on the surface of the activated charcoals.     

Effect of soil organic carbon on sorption and desorption of perchloroethylene in soils

The objective of this study was to elucidate the sorption and desorption behaviors of PCE (Perchloroethylene, C₂Cl₄) in seven soils with different organic carbon (OC) content. Sorption/desorption kinetic and serial dilution desorption experiments were conducted in batch slurries. The sorption distribution coefficient (K _d ) of PCE ranged from 0.60 to 4.66 L kg^?1. K _d tended to increase as the soil OC increased, but K _oc tended to decrease, suggesting that adsorption into the mineral surface was not negligible in soils with low OC. Desorption kinetic data were analyzed by the two-site desorption model. The sorption/desorption of PCE was not reversible over short incubation times due to the presence of a non-desorbable site. The desorbable site fractions of PCE increased and non-desorbable site fractions decreased as the soil OC increased. It is suggested that partition of PCE into soil organic carbon is more reversible than adsorption on soil minerals.     

A simple method to synthesize graphitic mesoporous carbon materials with different structures

Graphitic mesoporous carbon materials with different structure were synthesized by reversed replication method. SBA-15 was used as hard template and the synthesized aromatic polymers with different polymerization degree as the carbon sources. Adopting the impregnation method, the carbon source was assembled into the pore of the SBA-15. The silica/aromatic polymers system was carbonized under N₂ atmosphere (high polymerization degree aromatic polymers) and vacuum (low polymerization degree aromatic polymers) to produce the graphitic mesoporous carbon materials with structure of CMK-3 and CMK-5, respectively. It is a easy way to synthesize the graphitic mesoporous carbon materials, especial for the CMK-5 structure. The porous structure and composition of these carbon materials were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectrometry, and N₂ adsorption–desorption measurements.     

Synthesis and characterization of monolithic carbon/silicon carbide composite aerogels

Resorcinol–formaldehyde/silica composite (RF/SiO₂) aerogels were synthesized using sol–gel process followed by supercritical CO₂ drying. Monolithic carbon/silicon carbide composite (C/SiC) aerogels were formed from RF/SiO₂ aerogels after carbothermal reduction. X-ray diffraction and transmission electron microscopy demonstrate that β-SiC was obtained after carbothermal reduction. Scanning electron microscopy and nitrogen adsorption/desorption reveal that the as-prepared C/SiC aerogels are typical mesoporous materials. The pore structural properties were measured by nitrogen adsorption/desorption analysis. The resulting C/SiC aerogels possess a BET surface area of 564 m²/g, a porosity of 95.1 % and a pore volume of 2.59 cm³/g. The mass fraction of SiC in C/SiC aerogels is 31 %.     

Nano-CaCO3 templated mesoporous carbon as anode material for Li-ion batteries

Mesoporous hard carbon is obtained by pyrolyzing a mixture of sucrose and nanoscaled calcium carbonate (CaCO₃) particles. The microstructure of the carbon is characterized by N₂ adsorption/desorption, Hg porosimetry, field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and Raman spectroscopy. The electrochemical performances of the carbon as an anode material for lithium ion batteries are evaluated by galvanostatic charge/discharge and cyclic voltammetry tests. It is shown that this mesoporous carbon possesses high capacity, good cycling performance and rate capability, indicating the promising application of nano-CaCO₃ particle as template in massive fabrication of mesoporous carbon anode materials for lithium ion batteries.     

Preparation of bis(chloroformate)s for use in cyclization reactions

Cyclic oligomeric carbonates are prepared by a hydrolysis/condensation reaction from aromatic bis(chloroformate)s. Three methods for convenient preparation of bis(chloroformate)s have been developed: (1) use of diethylaniline to scavenge HCl, in a modification of an earlier procedure; (2) low pH, low temperature interfacial condensation of bisphenols with phosgene; and (3) use of Ca(OH)₂ in interfacial condensation with phosgene. Reaction parameters which control formation of monomeric bis(chloroformate)s versus higher oligomerization include temperature, pH, and rate of phosgene addition. For water-soluble bisphenols such as hydroquinone, the phase ratio of water to CH₂Cl₂ can also be important.     

Flue gas treatment by activated carbon obtained from oil-fired fly ash

The treatment of the solid particulates derived from the combustion of heavy oils (that is, oil-fired fly ash) with acidic solutions (HCl and HF) followed by activation at 900 °C with CO₂ and then with O₂ (1%) in N₂ at 800 °C, produces activated carbon having high surface area values (measured both by N₂ adsorption at 77 K and by CO₂ adsorption at 273 K) and surface basic characteristics. This carbon appears to be suitable for SO₂ and NO_X adsorption and hence for industrial flue gas treatment processes. By submitting the activated carbon thus obtained to some adsorption/desorption cycles of gaseous mixtures having a similar composition to that of flue gases, its general characteristics (surface areas, sorbent properties etc.) change as expected of a typical activated carbon. Based on the results obtained, these particulate materials, produced in large amounts by heavy oil combustion, are assumed to be fully exploitable for flue gas treatment.     

Comparative study of methylene blue dye adsorption onto activated carbon,graphene oxide,and carbon nanotubes

Three different carbonaceous materials, activated carbon, graphene oxide, and multi-walled carbon nanotubes, were modified by nitric acid and used as adsorbents for the removal of methylene blue dye from aqueous solution. The adsorbents were characterized by N₂ adsorption/desorption isotherms, infrared spectroscopy, particle size, and zeta potential measurements. Batch adsorption experiments were carried out to study the effect of solution pH and contact time on dye adsorption properties. The kinetic studies showed that the adsorption data followed a pseudo second-order kinetic model. The isotherm analysis indicated that the adsorption data can be represented by Langmuir isotherm model. The remarkably strong adsorption capacity normalized by the BET surface area of graphene oxide and carbon nanotubes can be attributed to π–π electron donor acceptor interaction and electrostatic attraction.     

改性蜂窝状活性炭吸附二氧化碳和氮气的热力学

蜂窝状活性炭具有较高的比表面积、多孔道、压降低、吸脱附速率快、不易堵塞等优点,因此被认为是捕集烟道气中CO₂重要吸附材料。选用蜂窝状煤基和椰壳两种活性炭吸附剂,采用磁悬浮热天平分别测定了CO₂和N₂的吸附等温线。采用1 mol·L^-1 K₂CO₃对蜂窝状活性炭材料进行浸渍改性,提高在低二氧化碳分压下的CO₂吸附性能。采用Langmuir、multi-site Langmuir和Virial 3种模型对吸附平衡数据进行拟合,得出热力学参数,为后续吸附工艺优化设计提供基础数据。结果表明在实验范围内3种模型均能对实验测量的等温线进行较好的拟合,Langmuir模型总体拟合效果最好。     

Effect of the nanostructure and surface chemistry on the gas adsorption properties of macroscopic multiwalled carbon nanotube ropes

The NO₂ adsorption properties of macroscopic multiwalled carbon nanotube (MWCNT) ropes and acid treated MWCNT ropes, obtained by the floating catalyst chemical vapour deposition process, have been examined. The structural characterisation shows that these ropes constitute bundles of MWCNTs. This bundled structure is found to control the electrical and gas adsorption properties of the material. The electrical resistance of these ropes decreases upon exposure to NO₂ with a high sensitivity even at room temperature. The adsorption of the NO₂ onto MWCNT bundles is found to be more stable with temperature in comparison to isolated MWCNTs revealing the complex nature of the adsorption process. These adsorption sites, which are created within the bundles of carbon nanotubes, are more stable requiring higher desorption energy. The surface of the MWCNT ropes is also modified with acid treatment, which increases the response to NO₂ by a factor 100% due to increased polar interactions between the gas molecules and the existing functionalised surface. These results suggest the possibility of using these macroscopic MWCNT ropes as low cost gas sensing materials.     

A direct synthesis of mesoporous carbon supported MgO sorbent for CO2 capture

Ordered mesoporous carbon supported MgO (Mg-OMC) materials were synthesized by the carbonization of sulfuric-acid-treated silica/triblock copolymer/sucrose/Mg(NO₃)₂ composites. In the current approach, triblock copolymer P123 and sucrose were employed as both structure-directing agents for the self-assembly of rice husk ash silica solution and carbon precursor. Sulfuric acid was used to cross-link P123 and sucrose in the as-synthesized composites in order to improve the carbon yield. The synthesized Mg-OMC was characterized by X-ray diffraction, N₂ adsorption-desorption isotherm method, X-ray photoelectron spectroscopy, scanning electron microscope equipped with energy dispersive X-ray analysis and transmission electron microscopy. The thermal stability of Mg-OMC was verified by CO₂-temperature programmed desorption, which confirmed the chemisorption of CO₂ on MgO. The CO₂ adsorption capacity of Mg-OMC-1 was observed to be 92 mg/g of sorbent which is comparable with that of the well established CO₂ sorbents.     

Amine modified mesocellular siliceous foam (MCF) as a sorbent for CO2

Adsorption is considered a promising method for carbon capture. CO₂ adsorbents take a variety of forms - but one approach is to fill mesoporous substrates with a polymeric CO₂ selective sorbent. SBA-15 and mesocellular siliceous foam (MCF) are high pore volume, high surface area ordered mesoporous materials for which modification with amine should result in high capacity, highly selective adsorbents. SBA-15 and MCF were separately loaded with approximately one pore volume equivalent of linear polyethyleneimine (PEI) (M_w = 2500) or branched PEI (M_n = 1200). CO₂ adsorption/desorption isotherms under dry CO₂ were obtained at 75, 105 and 115 °C. The CO₂ adsorption/desorption kinetics were improved with temperature, though the CO₂ capacities generally decreased. The adsorption capacity for MCF loaded with branched PEI at 105 and 115 °C were 151 and 133 mg/g adsorbent, respectively (in 50% CO₂/Ar, 20 min adsorption time). These are significantly higher than the adsorption capacity observed for SBA-15 loaded with branched PEI under same conditions, which were 107 and 83 mg/g adsorbent, respectively. Thus the results indicate that, on a unit mass basis, amine modified MCF's are potentially better adsorbents than amine modified SBA-15 for CO₂ capture at modestly elevated temperature in a vacuum swing adsorption process.     

Carbon dioxide capture under postcombustion conditions using amine-functionalized SBA-15: Kinetics and multicyclic performance

ABSTRACT

In this work, ordered mesoporous SBA-15 was synthesized and functionalized by polyethyleneimine (PEI). The morphological properties were characterized by N₂ adsorption/desorption, field–emission scanning electron microscopy (FE-SEM), high–resolution transmission electron microscopy (HR-TEM) and Fourier transform infrared (FTIR) spectroscopy methods. The carbon dioxide (CO₂) uptake on the sorbents, kinetics of CO₂ adsorption/desorption and long-term multicycle stability of PEI-impregnated sorbent were measured. An optimal amine loading of 50 wt.% showed a CO₂ adsorption capacity ~3.09 mmol g^?1 using 10% pre-humidified CO₂ at 75°C. The presence of moisture in flue gas showed a promoting effect in CO₂ sorption capacity. The temperature swing adsorption/desorption cycles showed excellent multicycle stability over 60 cycles during 65 h of operations under humid CO₂.     

Enhanced catalytic oxidation via nano Cu0.5Mg0.5Fe2O4 embedded in CNTs for adsorption–reduction of hexavalent chromium

A catalyst consisting of Cu_0.5Mg_0.5Fe₂O₄ (CMF) supported on carbon nanotubes (CNTs) which exhibits great potential as an adsorbent for treating Cr(VI)-contaminated wastewater has been successfully prepared. The ferrite possesses excellent magnetic properties, while CNTs have the advantage of a large surface area. This composite material not only prevents the aggregation of magnetic materials and enhances the exposure of active sites but also effectively solves the recycling problem of CNTs. Our results show that the adsorption capacity of Cu_0.5Mg_0.5Fe₂O₄–carbon nanotubes (CMF-CNTs) for Cr(VI) wastewater (45.60 mg/g) is 1.49 times higher than that of Cu_0.5Mg_0.5Fe₂O₄ (30.48 mg/g). Compared to a single catalyst, CMF-CNTs not only improve the dispersibility of magnetic materials but also exhibit synergistic effects between the composite materials, enhancing the chemical adsorption capacity. After five consecutive adsorption and desorption experiments, the adsorption capacity of CMF-CNTs remains at 88% of its initial value. Furthermore, the study of the catalyst before and after adsorption by XPS reveals that the valence state transition of Fe³⁺/Fe²⁺ and Cu²⁺/Cu⁺ plays a crucial role in the adsorption process. The results of this study demonstrate the potential of using waste materials for effective wastewater treatment and provide insights into the development of new adsorbents for pollutant removal.     

Synthesis and characterization of the SBA-15/carbon cryogel nanocomposites

The ordered mesoporous silica SBA-15 materials were synthesized using Pluronic P123 (non-ionic triblock copolymer, EO₂₀PO₇₀O₂₀), under acidic conditions. SBA-15/carbon cryogel composites were obtained by sol–gel polycondensation of resorcinol and formaldehyde followed by freeze drying, and subsequent pyrolysis, in the presence of different amounts of SBA-15. For comparison purpose, SBA-15/carbon composite was also prepared using sucrose as carbon source. These materials were characterized by room temperature nitrogen adsorption–desorption measurement, X-ray diffraction, scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. It was revealed that the samples have amorphous structure, high specific surface area (350–520 m² g^?1) and developed meso- as well as microporosity. The porosity of structure depends on the carbon source and Si/C ratio which can be easily controlled by varying concentration of starting solution.     

Study of SO2 adsorption and thermal regeneration over activated carbon-supported copper oxide catalysts

The mechanisms of SO₂ adsorption and regeneration over activated carbon-supported copper oxide sorbent/catalysts were analyzed. Studies were carried out in a fixed-bed reactor equipped with a non-dispersive infrared gas analyzer to detect the reaction products and by using X-ray powder diffraction (XRPD) and temperature-programmed desorption (TPD) experiments to characterize the nature of the sulfate species and surface oxygen complexes. The results indicate that SO₂ was catalytically oxidized to SO₃ over a copper phase in the presence of gaseous oxygen, and then reacted with a copper site to form a sulfate linked to copper without desorption into the gas phase. The activated carbon support did not participate in this sulfation reaction. After the adsorption of SO₂, the exhausted sorbent/catalysts could be regenerated by direct heat treatment in inert gas at temperatures between 260 and 480 °C, while the neighboring surface oxygen complexes on the carbon surface were acting as the reducing agents to reduce CuSO₄ to Cu. During the subsequent adsorption process, the copper is rapidly oxidized by oxygen in the flue gas.     

Why is aluminum-based lithium adsorbent ineffective in Li+ extraction from sulfate-type brines

Aluminum-based lithium adsorbent (Li/Al-LDH) is the only industrialized adsorbent for Li⁺ extraction from salt lake brines. The inherent mechanism of declined Li⁺ adsorption performance was revealed to explain the feebleness in sulfate-type brines. SO₄²⁻ in brines could replace interlayer Cl⁻ by a stronger electrostatic attraction with laminates, significantly altering the stacking structure and interlayer spacing, while Cl K-edge of XAFS showed intercalated SO₄²⁻ would not obviously change the chemical environment of interlayer Cl⁻. Experiments as well as DFT and FEM simulations indicated the intercalated SO₄²⁻ regulated Li⁺ adsorption of Li/Al-LDHs at different ionic strength under a combined effect of expanded interlayers, close packing, and electrostatic repulsion. Although sufficient SO₄²⁻ contents in brines might promote the single Li⁺ adsorption by offering ionic strength as a driving force, the long-term usability would be severely impaired as SO₄²⁻ intercalation in interlayers reduced the subsequent Li⁺ adsorption capacity and increased the desorption difficulty.     

CO2 capture efficiency in post‐combustion using MWNT‐PAA in a packed bed column

The adsorption capacity of polyaspartamide (PAA) and multi‐wall carbon nanotubes with polyaspartamide (MWNT‐PAA) was investigated through a packed bed column with the flowing of flue gas composed of 15 % CO₂, 5 % O₂ and the balance N₂. The adsorption performed at 25 °C, 110 kPa and inlet gas flow rate of 60 mL/min resulted in high CO₂ adsorption capacity of 5.70 and 10.20 mmol‐CO₂/g for PAA and MWNT‐PAA, respectively. The adsorption kinetics was very high, so 7 min were enough for the effluent gas to reach the breakthrough after saturation. The consistency of adsorbents in recurring regeneration was successful through a continuous TSA system of 10 cycle adsorption‐desorption with temperatures of 25–100 °C. The evaluation of heat through differential scanning calorimetry (DSC) resulted in exothermic adsorption with heat release of 45.14 kJ/mol and 124.38 kJ/mol for PAA and MWNT‐PAA, respectively. The heat release was found favourable to promote the desorption as the temperature could rise after adsorption. This is an advantage for energy efficiency, as it depicts the potential of energy recovery. Thus, both adsorbent PAA and MWNT‐PAA were demonstrated to be promising for CO₂ adsorption capture in post‐combustion.     

Surface properties of carbons obtained from hexachlorobenzene and hexachloroethane by combustion synthesis

The paper describes the combustion synthesis of carbon materials from hexachloroethane (C₂Cl₆), hexachlorobenzene (C₆Cl₆), and a mixture of these compounds. The chemical composition (elemental analysis), structural composition (XRD, Raman spectroscopy), microstructure (SEM), surface physicochemical properties (low-temperature nitrogen adsorption, XPS, FTIR) and electrochemical behavior (cyclic voltammetry) of the solid reaction products were investigated. Their unique structural and surface properties depend on the chemical composition of the starting compounds. The properties of the carbon samples tested are much like those of carbon black, but the material from hexachloroethane exhibits the most distinctly amorphous features. In contrast, the adsorptive properties (porous structure) of the sample obtained from hexachlorobenzene tend to resemble those of activated carbon.