04 By-products related to fuels pitch-based and coconut activated carbons, respectively. Comparatively, the micro-porous specific volume of a commercial coconut carbon molecular sieve was increased by 26% without modification of its mean pore size and therefore of its sieving effect. Those results have been used to test a simple textural model of activated carbon porosity proposed in the recent literature.
04•01268 An evaluation of thermal resistance as a measure of black carbon content in diesel soot, wood char, and sediment Nguyen, T. H. et al. Organic Geochemistry, 2004, 35, (3), 217-234. The time dependence and efficacy of pretreatment by chemothermal oxidation for estimating black carbon (BC) content was evaluated using 28 samples of wood char, soot, activated carbon, and sediment. For 19 wood chars, 24-h carbon survival under air (at 375°C) varied between 0 and 44%, with no survival in any char formed at _<850°C and even in some low H/C chars formed at 1000°C. Results depended not only on extent of carbonization, but also on physical attributes of particles. Because not all environmentally relevant BC is detected, the method is perhaps best considered as a semi-quantitative measure of soot content.
were pre-treated either in He, dry air or wet air flow at 623 K for 6 h. They were then characterized by X-ray photoelectron spectroscopy, Xray diffraction, measurements of the pH of the point of zero charge, and activity in the decomposition reaction of isopropanol. Turnover frequencies for the formation of propene were obtained. According to these results, the oxygen surface complexes of the support have a major influence on the total acidity of the tungsten oxide supported catalysts. In some supported catalysts, W(VI) was reduced to W(V) during the decomposition reaction of isopropanol as a consequence of the hydrogen evolution. The results indicate that oxygen surface complexes of the support may play an important role in this reduction process, which was inhibited when the support had high surface oxygen content.
04/01272 Mechanisms of surfactant adsorption on nonpolar, air-oxidized and ozone-treated carbon surfaces
Davini, P. Carbon, 2003, 41, (8), 1559-1565. Chars were obtained by the pyrolysis of mixtures of oil refining pitch and carbon-fired fly ash. These materials, after activation with CO2 at 900°C, produced activated carbons with high surface area, high content of oxygen, and surface sites with prevalent basic characteristics. The amount of SO2 adsorbed by the carbons produced increases with an increase in the amount of added ash. Subsequent leaching with water allows the distinction of three forms of SO2: (a) a portion that desorbs as SO2; (b) a portion that desorbs as SO3; and (c) a portion that cannot be recovered by leaching with water. The addition of ash favours the process by which SO2 can be desorbable as SO3 or cannot be desorbable. This behaviour is enhanced by the presence of NOx in the gaseous adsorption mixture.
Chert, X. et al. Carbon, 2003, 41, (8), 1489-1500. Ozone treatment of fly ash carbon has recently been reported to inhibit the adsorption of commercial surfactants in concrete paste, thus mitigating the known negative effects of carbon on ash utilization. This paper examines the general mechanism of surfactant adsorption on carbon and its suppression by surface oxidation. Experimental results are presented for two carbon types (carbon black, fly ash carbon), both raw and surface oxidized (by ozone and molecular oxygen) and several commercial anionic and non-ionic surfactants (Darex II, SDS, Tergitol). The treated carbon surfaces were characterized with XPS, FT-IR, thermal desorption in N2 and Hz/He, surface acidity, hygroscopic behaviour, interfacial energy and its components through contact angle measurement involving standard liquid probes. Surface oxidation is found to decrease surfactant adsorption in each of the carbon/oxidant/surfactant systems examined, and its effect correlates with the amount of surface oxides by XPS. The combined results suggest that surfactant adsorption primarily occurs on non-polar carbon surface patches where it is driven by hydrophobic interactions. The main mechanism of oxidative suppression is the destruction of this non-polar surface, though micropore blockage and increased negative surface charge may also contribute for some systems.
04•01270 Effect of carbon fiber surface functional groups on the mechanical properties of carbon-carbon composites with HTT
04/01273 Mesophase pitches for 3D-carbon fibre preform densification: rheology and processability
04/01269 Behaviour of activated carbons obtained from mixtures of oil-fired fly ash and oil refining pitch
Dhakate, S. R. and Bahl, O. P. Carbon, 2003, 41, (6), 1193-1203. The present investigation describes the quantitative measurement of surface functional groups present on commercially available different PAN based carbon fibres, their effect on the development of interface with resol-type phenol formaldehyde resin matrix and its effect on the physico-mechanical properties of carbon-carbon composites at various stages of heat treatment. An ESCA study of the carbon fibres has revealed that high strength (ST-3) carbon fibres possess almost 10% reactive functional groups as compared to 5.5 and 4.5% in case of intermediate modulus (IM-500) and high modulus (HM-45) carbon fibres, respectively. As a result, ST-3 carbon fibres are in a position to make strong interactions with phenolic resin matrix and HM-45 carbon fibres make weak interactions, while IM-500 carbon fibres make intermediate interactions. This observation is also confirmed from the pyrolysis data (volume shrinkage) of the composites. Bulk density and kerosene density more or less increase in all the composites with heat treatment up to 2600°C. It is further observed that bulk density is minimum and kerosene density is maximum upon heat treatment at 2600°C in case of ST-3 based composites compared to HM-45 and IM500 composites. It has been found for the first time that the deflection temperature (temperature at which the properties of the material start to decrease or increase) of flexural strength as well as interlaminar shear strength is different for the three composites (A, B and C) and is determined by the severity of interactions established at the polymer stage. Above this temperature, flexural strength and interlaminar shear strength increase in all the composites up to 2600°C. The maximum value of flexural strength at 2600°C is obtained for HM-45 composites and that of ILSS for ST-3 composites.
04101271 Influence of carbon-oxygen surface complexes on the surface acidity of tungsten oxide catalysts supported on activated carbons Moreno-Castilla, C. et al. Carbon, 2003, 41, (6), 1157 1167. Tungsten oxide catalysts supported on activated carbons were prepared by using tungsten hexacarbonyl, ammonium tungstate, and tungsten pentaethoxide as precursors. An activated carbon was obtained from olive stone by physical activation. A portion of this activated carbon was oxidized with ammonium peroxydisulfate in order to introduce different oxygen surface complexes. Subsequently, different portions of this oxidized activated carbon were heat treated in nitrogen flow at various temperatures to partially remove the oxygen surface complexes. In this way, activated carbons with different amounts of oxygen surface complexes were obtained, which were then used as supports for the tungsten oxide catalysts. Both the supports and the supported catalysts
Fuel and Energy Abstracts
Dumont, M. et al. Fuel, 2003, 82, (12), 1523-1529. Synthetic mesophase pitches, produced from naphthalene (ARA24, ARA24r), were examined in terms of fluidity and thermal stability in comparison with other mesophase, isotropic pitches, or mesophase pitch/softening molecules blends. Their interest for carbon/carbon (C/C) composites processing by liquid impregnation or vacuum transfer inside three-dimensional carbon preform is discussed. Viscosity versus reduced temperature plots is reported on the same graph to compare the studied pitches and to define a suitable C/C processing window. Methylnaphthalene-based pitch is a good candidate with viscosity and stability adapted to the processing temperature and high carbon yield.
04/01274 Phase-mineral and chemical composition of coal fly ashes as a basis for their multicomponent utilization. 1. Characterization of feed coals and fly ashes Vassilev, S. V. et al. Fuel, 2003, 82, (14), 1793-1811. The phase-mineral and chemical composition of feed coals and their fly ashes (FAs) produced in four large Spanish thermo-electric power stations was characterized as a basis for multi-component FA utilization. The feed fuels used are bituminous coals, semi-anthracites and anthracites with high detrital mineral abundance and mixed carbonate and sulphide-sulphate authigenic mineral tendency. Their mineral composition includes quartz, kaolinite, illite-muscovite, pyrite, chlorite, plagioclase, K-feldspar, gypsum, siderite, calcite, dolomite, marcasite, montmorillonite, jarosite, and ankerite. The FAs studied have aluminosilicate composition with higher concentrations of alkaline and alkaline-earth oxides than Fe oxide. Elements such as Ag, As, Ba, Cr, Cs, Li, P, Sb, Sc, Sn, St, Ti, V, Zn, and Zr are relatively enriched in these FAs in comparison with the respective mean values for bituminous coal ashes worldwide. The FAs consist basically of aluminosilicate glass, to a lesser extent of mineral matter (with high silicate abundance and dominant oxide tendency) and moderate char occurrence. The phase-mineral composition (in decreasing order of significance) of these FAs is normally glass, mullite, quartz, char, kaolinite-metakaolinite, hematite, cristobalite, plagioclase, K-feldspar, melilite, anhydrite, wollastonite, magnetite and corundum plus 42 important accessory minerals or phases. A scheme of conventional separation procedures was applied to recover sequentially six initial and potentially useful and/or hazardous products from FAs, namely: (1) a ceramic cenosphere concentrate; (2) a water-soluble salt concentrate; (3) a magnetic concentrate; (4) a char concentrate; (5) a heavy concentrate; and finally (6) an improved F A residue.