Preparation and characterisation of carbon-coated monoliths for catalyst supports

Carbon coated monoliths have been prepared by dipcoating cordierite monoliths in a polymer mixture and subsequent carbonisation and activation. Preparation parameters that were varied were viscosity of the dipcoating mixture, carbon precursor and carbonisation temperature. Two different polymers have been used as carbon precursors, Novolac and Furan resins. Also monoliths have been coated with slurry of these resins and a commercial activated carbon, CP-97. The features of the final carbon that have been optimised are carbon loading, carbon layer thickness, coverage and mesoporosity. Coverage has been tested by leaching tests in acid media and SEM analysis. Both coverage and mesoporosity are considerably enhanced when the dipcoating mixture was a slurry of Furan resin and activated carbon. Leaching of the cordierite was considerably reduced but not completely eliminated. The morphology of the activated carbon could be transferred to the coating layer.     

Preparation and characterisation aspects of carbon-coated monoliths

Carbon-coated monoliths have been prepared by dipcoating cordierite monoliths in a polymer solution and subsequent carbonisation. Parameters of preparation that were varied were viscosity of the dipcoating solution, carbon precursor and carbonisation temperature. Two different commercial polymers have been used as carbon precursors, Novolac and Furan resins. Also monoliths have been coated with slurry of such resins and a commercial mesoporous activated carbon (CP-97).

The features of the final carbon that have been optimised are carbon loading, carbon layer thickness, coverage and mesoporosity. Coverage has been tested by leaching test in acid media. Both coverage and mesoporosity are considerably enhanced when the dipcoating mixture was a slurry of Furan resin and a commercial activated carbon. These features makes carbon-coated monoliths very suitable for their use as catalyst support in three-phase reactions.     

Preparation of carbon-coated monolithic supports

This paper describes the development of preparation methods for carbon-coated monolithic supports starting from furfuryl alcohol-based polymers. Furfuryl alcohol with or without pyrrole and/or poly(ethylene glycol) mono methyl ether was polymerized using nitric acid under ambient conditions. Cordierite monolithic supports were dipcoated using the partially polymerized furfuryl alcohol mixtures. After solidification of the polymer, the coating was carbonized to obtain a carbon-coated monolithic support. The carbonized polymer is a microporous material. When coated onto a cordierite monolithic support, macropores are formed due to coating of the cordierite pores and carbonization. The polymer tends to shrink during carbonization, which is prohibited by the monolithic support, and then cracks. An oxidizing treatment prior to carbonization in combination with the use of a pore former yields mesopores. Due to shrinkage of the polymer, the carbon coating does not cover the ceramic monolithic support completely. Carbonization at temperatures up to 1000 °C increased the carbon content of the coating, which finally adopts an aromatic character and becomes electrically conducting.     

Preparation, characterisation of thermally treated Algerian dolomite powders and application to azo-dye adsorption

Dolomite powder from Ouled Mimoun, Tlemcen (western region of Algeria) was thermally treated within the temperature range 450-1000 °C. The modifications undergone by dolomite, inherent to thermal treatment, were investigated from X-ray diffraction patterns. The results were also discussed using scanning electronic microscopy and nitrogen adsorption. The XRD data, analysed from X Pert Plus program, showed that the dolomite phase ceases at 700 °C and is relayed by the formation of in situ calcite and periclase. The crystallographic parameters of these two phases tend towards that of pure periclase and calcite at 1000 and 900 °C, respectively. SEM analysis indicated that the morphological properties were profoundly affected. SEM images of D-1000 (sample treated at 1000 °C) indicated that the original particle shape of dolomite (presence of discrete grains having sharp edges with presence of cleavages) was totally destroyed, leading to small spherical particles with a diameter of 0.1 μm. The specific surface area value of D-1000 increased more than 6 times against that of the raw dolomite. Adsorption of azo-dye Orange I from aqueous solutions onto untreated and treated dolomites was also reported. The isotherms were of L-type. The interaction was explained by electrostatic considerations between sulfonate groups of the dye (D-SO₃Na), which are dissociated in the aqueous system, and positively charged adsorption sites. The affinity of orange I for the dolomitic solids follows the sequence D-900 > D-1000 > D-800 > > D-600 > raw dolomite. The maximum retention capacity shown by D-900 was explained and correlated with its crystallographic properties.     

Adsorption and breakthrough performance of carbon-coated ceramic monoliths at low concentration of n-butane

Carbon-coated ceramic monoliths have been studied for the dynamic adsorption of low-concentration n-butane. They exhibit a very sharp breakthrough performance, especially in the low-concentration regime, that illustrates the better breakthrough performance of monoliths with respect to shallow carbon packed beds. The low pressure drop of the monolithic system and its excellent performance under discontinuous flow conditions make it an attractive option for gas mask canister applications. A simulation model is presented, including terms of adsorption, diffusion and mass transfer. A parametric analysis has been carried out to study the influence of different variables on the breakthrough profile. The breakthrough performance is best described by considering a gas velocity distribution over the monolith cross-section. Stacking of the monolithic pieces, increasing cell density, and gas redistribution between pieces reduced this distribution and improved the breakthrough performance.     

Characterization of adsorbent materials supported on polyurethane foams by nitrogen and toluene adsorption

Different composite adsorbent materials were obtained by supporting three activated carbons, one zeolite and one pillared clay, in a polyurethane foam. Adsorption isotherms of nitrogen and toluene were determined to evaluate the influence of the supporting process in the adsorption capacity of the different adsorbent materials. The results indicate that the activated carbons in form of pellets presented the best results with a decrease of about 20% in the nitrogen adsorption capacity but maintaining the same toluene adsorption capacity. The inorganic adsorbents presented a decrease of about 73% for the zeolite and 97% for the pillared clay in the nitrogen adsorption capacity and also a pronounced decrease in the toluene adsorption capacity. Two materials, one activated carbon and one zeolite, with different particle sizes were supported in the polyurethane foam. The decrease in the adsorption capacity of nitrogen and toluene was more pronounced when solids with smaller particles were used. This was an indication that the decrease in the adsorption capacity is related to the impregnation of the surface of the solid particles by the polyurethane during the synthesis of the composite material, which was observed by scanning electron microscopy. Nevertheless, the supporting method, in a one step procedure, presented itself with good possibilities for applications with activated carbons in the form of pellets.     

Sintering behaviour and characterisation of low-cost ceramic foams from coal gangue and waste quartz sand

New ceramic foams have been successfully synthesised with coal gangue and waste quartz sand, which supply a feasible way to recycle these hazardous solid wastes. An objective of this research was to investigate the sintering behaviour and effects of sintering conditions on the crystalline phase change, microstructure and main properties of final ceramic foams. Good correlations among porosity, thermal conductivity, water absorption, bulk density, mechanical properties were studied. Results indicated that increasing sintering temperature or time had similar effects on the physical–mechanical properties. Samples sintering at 1140°C for 1 hour exhibited the highest porosity (87.5%), lowest bulk density (0.39?×?10^?3?kg?m^?3), lowest thermal conductivity (0.085?W·(m?K)^?1), moderate water absorption (9.38%) and adequate flexible strength (2.4?MPa). Combined with excellent properties and low-cost characteristics, the new development for ceramic foams preparation will be widely used in building insulation materials for no-load bearing walls.     

Preparation of ultra-light ceramic foams from waste glass and fly ash

Ultra-light ceramic foams were successfully prepared by a green spheres technique, which used waste glass powder and fly ash as the main material. Besides, borax and SiC were introduced as fluxing agent and foaming agent, respectively. The effects of fly ash content, borax content and sintering temperature on the microstructures and properties of ceramic foams were systematically investigated. The optimum composition is 30?wt-% fly ash, 70?wt-% waste glass, 15?wt-% borax and 0.5?wt-% SiC. Ultra-light ceramic foams sintered at 680–780°C possess bulk density of 0.14–0.41?g?cm^?3, porosity of 82.9–94.1%, compressive strength of 0.91–6.37?MPa and thermal conductivity of 0.070–0.121?W?m^?1?K^?1, respectively. This method is convenient, low-cost and environment friendly, which makes it a promising way for recycling solid wastes.     

The synthesis of humic acids graft copolymer and its adsorption for organic pesticides

humic acid graft copolymer (PSt-g-HA) was prepared by graft copolymerization of Humic acid (HA) with styrene and the sorption of three selected organic pesticides, parathion-methyl, carbaryl and carbofuran by PSt-g-HA acid and untreated humic were also examined, respectively. The PSt-g-HA had relatively high aromatic carbons content because the grafted copolymerization of polystyrene entered into condensed domains in HA, whereas the removal of the polar function groups, such as carboxyl and phenolic hydroxyl group, was performed. For above reasons, the sorption capacity of three organic pesticides (parathion-methyl, carbaryl and carbofuran) on PSt-g-HA increased by 64.1% to 95.2%.     

Effects of carbonisation on pore evolution and gas permeation properties of carbon membranes from Kapton polyimide

Carbon membranes were prepared by carbonisation of Kapton^® polyimide at different temperatures under vacuum and nitrogen flow. Pore structure development of the membranes during carbonisation was studied. Carbonisation temperature was critical in the modification of membrane structure. At the same temperature, the carbon membranes fabricated under nitrogen atmosphere had higher gas permeances than those fabricated under vacuum. During heat treatment, the value of d-spacing for the carbon membranes decreased with increasing temperature, however, vacuum and nitrogen atmosphere had different influences on the changes in the d-spacing. CO₂ adsorption showed that the carbon membranes prepared at 1273 K under vacuum had the highest micropore volume whilst the membranes prepared at 1073 K under vacuum had the highest characteristic adsorption energy. N₂ adsorption showed that the samples obtained at 873 K under vacuum had the highest nitrogen uptake. Mesopores were deemed to be connected through micropores and narrow channels between meso- and/or micropores were supposedly present. The micropores predominantly controlled the transport properties of the carbon membranes. The membrane samples obtained at 1173 K under vacuum yielded ideal separation factors of 558.27, 60.87, 19.69 and 138.53 for He/N₂, CO₂/N₂, O₂/N₂ and CO₂/CH₄, respectively, with permeances of 7.26, 0.79, 0.26, 0.13 and 0.006 mol/(m² s Pa) for He, CO₂, O₂, N₂ and CH₄, respectively.     

Removal of volatile organic compounds by cryogenic condensation followed by adsorption

Removal of volatile organic compounds (VOCs) from gaseous effluents by cryogenic condensation and adsorption has been studied. Mathematical models have been developed to predict the extent of removal of a binary mixture of VOCs in air by these two methods under a wide range of operating conditions. The model results are verified with the published work. A model parametric study carried out in this work suggests that if the concentrations of VOCs in the effluent stream vary over a wide range, condensation followed by adsorption is an effective technique to control the emissions. Condensation is found to be suitable if the VOCs emission levels are high (>1%). On the other hand, if the emission levels are low i.e. parts per millions (ppm) or sub ppm, adsorption is a preferred technique for removing the VOCs from the effluent stream. The model results in this work have significance from the perspective of understanding the mechanism of removal of VOCs by these two methods, determining the key operating parameters that control the removal process and also, defining an effective VOC control strategy.     

PVC-MnO2的制备及其对锂离子的吸附行为

MnCO3和Li2CO3经高温煅烧合成Li4Mn5O12,再与聚氯乙烯(PVC)和N,N-二甲基甲酰胺溶液混合,干燥、酸洗后制得粒径3?4 mm的多孔球形PVC?MnO2锂离子筛,用其吸附Li离子. 结果表明,PVC?MnO2吸附Li离子的反应符合Langmuir方程和拟二级动力学方程,吸附焓变为0.358 kJ/mol,吸附反应为吸热反应,Li离子最高吸附量可达23.4 mg/g.     

Estimation of activated carbon adsorption efficiency for organic vapours: I. A strategy for selecting test compounds

Strategies for developing quantitative structure–affinity relationships (QSAfR) for the prediction of break-through performance of 31 chlorinated hydrocarbons on activated carbon have been studied. Two different approaches for the selection of a limited set of compounds for modelling were evaluated through the predictive power of the resulting QSAfR models. When the model was based on a training-set selected without a rational strategy, the developed QSAfR model showed poor predictive performance. Accordingly, such models have a limited capability to produce information concerning the important adsorbate related parameters influencing adsorption. By using a strategy where multivariate data analytical techniques are used in conjunction with statistical experimental design to select a balanced set of compounds for break-through performance evaluation, it was possible to develop QSAfR models with high predictive capability.     

Preparation and characterisation of LiFePO4 ceramic powders via dissolution method

Various LiFePO₄ (LFP) powders with natural ironstone as a base material were prepared using the dissolution method. They were synthesised using different (a) calcination temperatures, (b) milling times, and (c) Cu doping concentrations. X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) were conducted to determine the purity, grain and crystallite morphology, and crystalline and local structure of the phases formed, respectively. According to the XRD data, LFP can be produced using the aforementioned variations, and no other phases were found. The TEM images showed that the LFP size can be reduced from 200 nm to 60 nm by milling. The SEM images confirmed the nanometric characteristics of the milled powder and also the effect of calcination temperature on growing the particle sizes. The EDX analysis further reinforced that the samples’ atomic fractions were relatively compatible with LFP to explain the synthesised products’ purity. Analysis of the Fe K-edge XANES data showed that the samples’ oxidation number of Fe for all samples was 2+ with 6 coordination numbers, which corresponded to the oxidation and coordination number of Fe in LFP. The EXAFS Fe K-edge analysis demonstrated that slightly increasing the temperature increased the distance between the absorbing Fe atom and its nearest neighbouring atom but milling reduced it. The XAS analyses, therefore, confirm that all synthesised samples contain only LFP. A preliminary electro-chemistry test showed that these materials are promising candidates for cathodes in LFP-based batteries.     

Synthesis and characterisation of organo-silica hydrophobic clay heterostructures for volatile organic compounds removal

Mesostructured materials belonging to a new class of solid acids known as porous clay heterostructures (PCHs) have been prepared by chemical modification of a natural clay, by using a cationic surfactant, a neutral amine, and an equimolar mixture of bis(triethoxysilyl)benzene (BTEB) and tetraethyl orthosilicate (TEOS). The effect of different polymerisation times of the silica sources and of the hydrocarbon chain length of the neutral amine was studied. The materials retained their layered structure after the formation of stable pillars by the polymerisation of hydrolysed TEOS and BTEB. All materials were characterised by low temperature nitrogen adsorption isotherms, ¹³C CP MAS, ²⁹Si MAS and CP MAS NMR spectroscopy, thermal analyses and infrared spectroscopy. The specific surface BET areas of the materials were in the range 550–800 m² g⁻¹ and the corresponding microporous volume were near 0.2–0.3 cm³ g⁻¹. The reduction of the reaction time from 12 to 4 h avoids the extra-gallery polymerisation, contributing for a larger specific surface area. The increase of two carbon atoms in the neutral amine chain does not show much effect on the available surface area.

These materials were very effective as adsorbents of volatile organic compounds (VOCs), according to tests on methanol, methyl ethyl ketone, toluene and trichloroethylene. The water adsorption isotherms proved the hydrophobicity of the materials, suggesting their capabilities for VOC adsorption in the presence of water.     

Surface area and pore structure of stannic oxide gel from organic vapour adsorption

Surface area measurements were performed on stannic oxide gel and its thermal dehydration products obtained both in vacuo and in presence of air in the temperature range 100–600°C by benzene and carbon tetrachloride adsorption at 35°C. The presence or absence of air is found to impose changes in the surface area and consequently vary the pore structure of the solid material. Pore size analyses for both micro- and mesopores are performed. The low temperature samples are characterised by the presence of micropores only. At 350°C widening of pores commences and at higher temperatures the results indicate the existence of pores of “submicro” dimensions together with the mesopores. These changes in pore structure go in parallel with the gradual development of the crystalline cassiterite structure.     

Preparation and microstructure evolution of novel ultra-low thermal conductivity calcium silicate-based ceramic foams

In this study, municipal solid waste incineration fly ash (MSWI FA) was used as a new raw material for the ceramics industry and a novel ultra-low thermal conductivity calcium silicate-based foams (CSFs) was prepared by the direct foaming method. The effects of the addition of foam and borax on the sintering behavior and microstructural evolution of the CSFs were investigated. With the optimal amount of foam, the CSFs had an apparent porosity of 63.43%–67.49%, bulk density of 0.75–0.84 g/cm³, compressive strength of 1.83–3.21 MPa, and room-temperature thermal conductivity of 0.213–0.235 W/(m·K). Notably, the whisker morphology, pore structure, and sintering behavior of the samples can be controlled by changing the amount of borax. The prepared ceramic foams can be applied in the fields of thermal insulation, filtration, and catalyst carriers.