Clara Blanco

On the pyrolysis of sewage sludge: the influence of pyrolysis conditions on solid, liquid and gas fractions

Abstract The pyrolysis of a sewage sludge, produced by a Spanish urban wastewater treatment plant, was carried out in a laboratory furnace. Pyrolysis conditions, like heating rate and final pyrolysis temperature, were varied so that their influence on the characteristics of the resulting gases, liquids and solid residues could be studied. It was found that increasing the pyrolysis temperature decreases the solid fraction yield and increases the gas fraction yield while that of the liquid fraction remains almost constant. Furthermore, the effect of the heating rate was found to be important only at low final pyrolysis temperatures. Independently of the pyrolysis conditions, all the solid products obtained were of a basic nature and highly macroporous, the meso- and micro-pore volumes being relatively low. Both oils and gases produced in the pyrolysis showed relatively high overall heating values, comparable to some conventional fuels, revealing the potential application of these products as fuel.

Towards a Further Generation of High‐Energy Carbon‐Based Capacitors by Using Redox‐Active Electrolytes

This work was supported by MICINN (Project MAT2007-61467). S.R. thanks MICINN for an FPI doctoral grant.

Chemical and physical properties of carbon as related to brake performance

Abstract The two objectives of this paper are: (a) to review the literature relevant to the structure, properties and applications of carbon-carbon (C/C) disc brakes, and (b) to present aspects of carbon science relevant to an understanding of the operational behaviour of such brakes. The literature describes numerous studies relating structure and composition of (C/C) disc brakes to wear mechanisms and performance. C/C brakes are manufactured from carbon fibres and a matrix carbon, usually an isotropic carbon from a resin, an anisotropic carbon from coal-tar pitch, or an isotropic carbon from pyrolysis of methane (CVD or CVI). Coefficients of friction depend upon the weave of the fibres, the matrix carbon, heat treatment temperatures, ambient gases such as air, water vapour and carbon dioxide, the testing conditions used (low- or high-speed), and the generation of wear dust. Wear generates debris (wear dust) from the surface which is then further comminuted during braking. Wear rates are also associated with gasification of both the brakevsurface and of wear dust. Mechanisms of generation of wear dust are summarised, and dull and lustrous wear dust surfaces are reported. Structures in the various forms of carbons are described and the special characteristics of C/C disc brakes are set out. The physical properties of graphite of dominant importance to brake performance are cleavage of the graphite crystal, and its thermal conductance and thermal capacity. Operational changes to braking performance are modelled. Carbon gasification reactions are explained, as well as the role of surface oxygen complexes and their influence on the absorption of water vapour which then, as a film, acts as a lubricant. The roles of wear dust during braking are elaborated upon.

Gas chromatographic study of the volatile products from co-pyrolysis of coal and polyethylene wastes.

The aim of this study was to determine the volatile products distribution of co-processing of coal with two plastic wastes, low-density polyethylene from agriculture greenhouses and high-density polyethylene from domestic uses, in order to explain the observed decrease in coal fluidity caused by polyethylene waste addition. Polymeric materials, although they are not volatile themselves, may be analysed by gas chromatography through the use of pyrolysis experiments. In this way, a series of pyrolysis tests were performed at 400 and 500 degrees C in a Gray-King oven with each of the two plastic wastes, one high-volatile bituminous coal and blends made up of coal and plastic waste (9:1, w/w, ratio). The pyrolysis temperatures, 400 and 500 degrees C, were selected on the basis of the beginning and the end of the coal plastic stage. The organic products evolved from the oven were collected, dissolved in pyridine and analysed by capillary gas chromatography using a flame ionization detector. The analysis of the primary tars indicated that the amount of n-alkanes is always higher than that of n-alkenes and the formation of the alkenes is favoured by increasing the pyrolysis temperature. However, this effect may be influenced by the size of the hydrocarbon. Thus, the fraction C17-C31 showed a higher increase of n-alkenes/n-alkanes ratio than other fractions. On the other hand, the difference between the experimental and estimated values from tars produced from single components was positive for n-alkanes and n-alkenes, indicating that co-pyrolysis of the two materials enhanced the chemical reactivity during pyrolysis and produced a higher conversion than that from individual components.

A comparative study of air-blown and thermally treated coal-tar pitches

Abstract A commercial impregnating coal-tar pitch was thermally treated at 430°C for times varying between 2 and 6 h and the same pitch was air-blown at 275°C for between 10 and 30 h. Both series of pitches were characterized and their properties compared. The pitches from the thermal treatments contained mesophase, the amount increasing from 10 vol.% to 65 vol.% with increasing time of treatment, whereas those from the air-blowing were completely isotropic. The study of the pitches revealed that the thermally treated pitches still contained a considerable amount of light compounds together with the large planar molecules generated. On the contrary, light components polymerized to a considerable extent during air-blowing to form cross-linked molecules. Evidence of cross-linked structures is provided by a decrease in the iodine uptake and also by the X-ray diffraction results. Furthermore, extensive removal of aliphatic hydrogen took place during pitch air-blowing, as confirmed by the increase in the aromaticity indices of the pitches.

Influence of fibre–matrix interface on the fracture behaviour of carbon-carbon composites

Abstract This paper studies the fracture behaviour of unidirectional carbon fibre reinforced carbon matrix composites and its relation with the type of fibre–matrix interface developed in the composite. Model unidirectional carbon–carbon composites were prepared using the same type of fibre and different pitches as matrix precursors. These included both commercial pitches and synthesized in the laboratory ones. The chemical composition of the matrix precursor determined the type of microstructure developed in the composite, this microstructure seems to govern the fibre-matrix bonding and in turn controls the fracture behaviour of the composite. In general, a matrix texture of mosaic (small size) seems to yield a good fibre-matrix bonding, making the materials to have higher interlaminar shear strength but having at the same time brittle fracture behaviour. On the other hand, composites where larger textures were developed in the matrix seem to have a poorer fibre-matrix bonding. This made the composites to have lower strength, but it allowed debonding of fibre and matrix during fracture. As a result, these materials showed pseudo-plastic failure behaviour. Other examples of both types of fracture behaviour associated with the change in microstructure and fibre–matrix interface are discussed.

A study of pitch-based precursors for general purpose carbon fibres

Abstract The isotropic phase isolated from a thermally treated coal-tar pitch was studied as a possible precursor for carbon fibres. Extraction with different solvents was performed in order to increase its softening point and so enable higher stabilisation temperatures to be used, with a significant reduction in time. The extraction conditions were selected studying the softening temperatures of the residues, the results of their thermogravimetric analysis and reactivity in air studied by means of differential scanning calorimetry. The residue obtained with a mixture of 40% acetone–60% acetonitrile was found to be the most suitable precursor for the fibres. The carbonised fibres showed a homogeneous surface and diameter, and had tensile properties comparable to other isotropic fibres described in the literature.

Graphite Felt Modified with Bismuth Nanoparticles as Negative Electrode in a Vanadium Redox Flow Battery

A graphite felt decorated with bismuth nanoparticles was studied as negative electrode in a vanadium redox flow battery (VRFB). The results confirm the excellent electrochemical performance of the bismuth modified electrode in terms of the reversibility of the V(3+) /V(2+) redox reactions and its long-term cycling performance. Moreover a mechanism that explains the role that Bi nanoparticles play in the redox reactions in this negative half-cell is proposed. Bi nanoparticles favor the formation of BiHx , an intermediate that reduces V(3+) to V(2+) and, therefore, inhibits the competitive irreversible reaction of hydrogen formation (responsible for the commonly observed loss of Coulombic efficiency of VRFBs). Thus, the total charge consumed during the cathodic sweep in this electrode is used to reduce V(3+) to V(2+) , resulting in a highly reversible and efficient process.

High performance activated carbon for benzene/toluene adsorption from industrial wastewater

A coal-tar-derived mesophase was chemically activated to produce a high surface area (~3200 m(2)/g) carbon with a porosity made up of both micropores and mesopores. Its adsorption capacities were found to be among the highest ever reported in literature, reaching values of 860 mg/g and 1200 mg/g for the adsorption of benzene and toluene, respectively, and 1200 mg/g for the combined adsorption of benzene and toluene from an industrial wastewater. Such high values imply that the entire pore system, including the mesopore fraction, is involved in the adsorption process. The almost complete pore filling is thought to be due to the high relative concentrations of the tested solutions, resulting from the low saturation concentration values for benzene and toluene, which were obtained by fitting the adsorption data to the BET equation in liquid phase. The kinetics of adsorption in the batch experiments which were conducted in a syringe-like adsorption chamber was observed to proceed in accordance with the pseudo-second order kinetic model. The combined presence of micropores and mesopores in the material is thought to be the key to the high kinetic performance, which was outstanding in a comparison with other porous materials reported in the literature.

Tailored graphene materials by chemical reduction of graphene oxides of different atomic structure

Graphene materials with different characteristics in terms of sheet size and defects (structural and/or functional groups) were obtained by the reduction with hydrazine of two graphene oxides with similar oxygen content, but with functional groups of different type and location. The oxides were prepared from two synthetic graphites with distinct crystalline structure. Our research has obtained experimental evidence of a greater reactivity of the oxygen functional groups located in the interior of the aromatic domains on the basal planes (mainly epoxy) and a lower reactivity of oxygen functional groups located at the edges (mainly carboxyl and OH). Furthermore, these edge-located groups were found to be responsible for hydrogen bonding lateral interactions between sheets (these occur through the residual OH groups), which cause a substantial increase in the size of the reduced graphene oxide with respect to that of the parent graphene oxide. These results offer a way to tailor the characteristics of graphene materials for diverse applications.