Fuel

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Online ISSN: 0016-2361
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Article
This paper describes the application of matrix assisted laser desorption ionization (MALDI) to coals and coal-derived materials using sinapinic acid as the matrix. The mass range of molecules in coal and coal-derived materials has been extended by a factor 100 compared with prelaser desorption mass spectrometric measurements. A peak of intensity is observed for coals and coal-derived materials in the mass range 1000–5000 u which is sample dependent. The upper mass ranges of the spectra vary according to sample, ranging from over 260 000 u for Point of Ayr coal and 200 000 u for a coal tar pitch, to 20 000 u for a maceral concentrate liquefaction extract. These results confirm earlier results using laser desorption mass spectrometry and are in broad qualitative agreement with size exclusion chromatography results. Detailed quantitative agreement, however, requires further work. The implications of this work for the debate on coal structure and models of coal conversion are considerable.
 
Article
The use of cattle manure (referred to as feedlot biomass, FB) as a fuel source has the potential to both solve waste disposal problems and reduce fossil fuel based CO2 emissions. A co-firing technology is proposed where FB is ground, mixed with coal, and then fired in existing, pulverized coal-fired boiler burner facilities. A research program was undertaken in order to determine (i) fuel characteristics, (ii) combustion characteristics when fired along with coal in a small scale 30-kWt (100,000 BTU/h) boiler burner facility, and (iii) combustion and fouling characteristics when fired along with coal in a large pilot scale 150-kWt (500,000 BTU/h) DOE-NETL boiler–burner facility. Part I presented a methodology for fuel collection, fuel characteristics of the FB, its relation to ration fed, and the change in fuel characteristics and volatile oxides due to composting. Part II addresses the pyrolysis characteristics of coal, FB, and blend and presents results on the performance of 90:10 coal:FB (PC) blend as fired in a 30-kWt boiler–burner unit. The boiler–burner unit is made of steel and lined with a cast ceramic liner for long duration operation and a commercial feeding system is used for firing the coal and the blend. Thermogravimetric analyses (TGA) performed on coal, FB, and 90:10 coal:FB blend reveal that biomass will start releasing gases at 273 °C (523 °F) which is about 100 °C (212 °F) lower than that of coal. The maximum rate of volatile release is about 0.000669 kg/s kg for FB while that of coal is 0.000425 kg/s kg. The experiments revealed that the 90:10 blend burns more completely in the boiler, due to the earlier release of biomass volatiles and higher amount of volatile matter in FB. The NOx emission for coal was 290 ppm, 0.162 kg/GJ (0.3768 lb/mm BTU) and 260 ppm, 0.1475 kg/GJ (0.343 lb/mm BTU) for the 90:10 blend at 10% excess air. Even though the effective N content of the blend increased by 18%, compared to coal the NOx emission decreased which is attributed to the higher VM of FB and more N in the form of NH3. However, due to limited residence time and higher VM, the CO emission increased from 15,582 ppm, 5.29 kg/GJ (12.305 lb/mm BTU) to 22,669 ppm, 7.81 kg/GJ (18.16 lb/mm BTU) when fuel was switched from coal to 90:10 blend. Large scale pilot plant tests performed at the 150-kWt facility (DOE-NETL) reveal increased falling potential for the blend compared to coal (Part III), emissions were negligible.
 
Article
The cost of maintaining aeroplanes is still considerable. It concerns especially operation cost where fuel is a substantial part. At the moment the special 100LL gasoline is used to fuel aircraft piston engines. It is about 20% more expensive than ES95 gasoline featuring comparable properties.The article shows the results of test-bed research conducted on the radial piston aircraft engine fuelled by aircraft 100LL gasoline and automotive ES95 gasoline. The object of research was ASz-62IR engine by WSK PZL-Kalisz that was equipped with an experimental fuel injection system. Power, fuel consumption, head temperatures and indicated pressure in cylinders were analysed in the selected typical operating points. The testing was carried out in steady state. It was proved that it is possible to exchange fuels with no engine power loss and merely an insignificant increase of fuel consumption but with significant increase of IMEP cycle-to-cycle variation.
 
Article
Measurements were made of the reaction rate of three sizes (2.9, 0.9 and 0.22 mm) of petroleum-coke particles with carbon dioxide over the temperature range 1018–1178 K, and at carbon dioxide partial pressures between 26 and 118 kPa. A limited number of similar measurements were made on samples of a commercial aluminium-smelting anode, an experimental anode, and AGKSP graphite. The materials were all reacted under conditions of chemical rate control alone: there were no rate limitations due to transport processes without or within the carbon particles. The order of the rate with respect to carbon dioxide concentration was found to be close to 0.6 for the petroleum coke and anode carbons, and between 0.6 and 0.8 for the graphite. Activation energies in the range 203–237 kJ/mol were found for petroleum coke; 187–237 kJ/mol for electrode carbon; and 293 kJ/mol for the graphite. For the petroleum coke, the order was found to be constant up to 45% burn-off and the activation energy essentially constant between 21 and 45% burn-off. The reactivity ϱs, based on unit pore surface area of the petroleum coke at a carbon dioxide pressure of 101 kPa, can be represented by: . For the 2.9 and 0.9 mm particles, α = 6.1 /sx 106 g/m2 min and E = 215 kJ/mol; for the 0.22 mm particles the respective values are 1.8 /sx 107 and 222. The reactivity ϱ of the commercial electrode on a weight basis was within the range of those of the coke and experimental electrode. For AGKSP graphite, values of ϱs were close to those found by Walker and Raats14.
 
Article
The significant changes of surface texture in CaCO3 crystallites due to reaction in an equimolar SO2O2 mixture were examined by scanning electron microscopy. Surface modifications were extensive above 870 K, which is close to the temperature of CaCO3 dissociation and of CaSO3 oxidation. It appears that both rate processes participate in the conversion of calcite to CaSO4 by reaction with SO2 under oxidizing conditions. The results confirm the production of sulfate above 870 K, but this generation of product across the surfaces represents a barrier to gas-solid contact that prevents complete reaction of the CaCO3 particles. The observations show that potassium ions enhance CaSO4 formation, probably by promoting fusion of the barrier layer, and that rapid heating does not disrupt calcite crystals sufficiently to increase the reactant surface area. The product barrier layer is identified as controlling both rate and extent of the reaction of calcite in desulfurization processes.
 
Article
This paper presents the results obtained for the operation of a 10 kWth chemical-looping combustor using a South African coal as the solid fuel and an oxygen carrier of ilmenite, a natural iron titanium oxide. A chemical-looping combustor for solid fuels was designed and built. It consists of two interconnected fluidized beds, an air reactor where the oxygen carrier is oxidized and a fuel reactor where the coal is gasified by steam and the syn-gases react with the oxygen carrier. A constant coal flow corresponding to a thermal power of 3.3 kW was introduced into the fuel reactor. The tests were conducted at temperatures above 850 °C and for a total test duration of 22 h. The particle integrity of ilmenite and the particle circulation between the two reactors were investigated and verified. The effects of particle circulation on coal conversion, gas conversion of the fuel reactor and carbon separation or CO2 capture between the air and fuel reactors were investigated. The actual CO2 capture ranged between 82.5% and 96% while the gas conversion from the fuel reactor was in the range 78–81%, based on measurements of unconverted CO and CH4.
 
Article
The chemistry of tin added in various forms as catalyst in the liquefaction of Victorian brown coal was determined by 119Sn Mössbauer analysis. After 60 min hydrogenation at 380 °C and 6 MPa initial hydrogen pressure, tin was principally distributed between β-Sn, SnS and SnO2. No significant dependence of liquefaction yield on the initial tin compound was apparent. The results extend earlier work and support the previous conclusion that elemental tin is the important species for promoting hydroliquefaction in these systems.
 
Article
Boron and its compounds are environmentally hazardous substance and are well-known condensed products that appear in coal fly ash during combustion of coal in coal-fired electric power stations. In a previous study, we suggested that boron in coal fly ash obtained from Nantun coal in China, identified as Ash–N, may exist on the surface of relatively large coal fly ash particles or as very fine particles generated by homogeneous nucleation. Although the characterization of boron in coal fly ash is important for its effective stabilization or removal, its detection is quite difficult because of its low concentration in coal fly ash and its light atomic weight. In the present work, solid-state magic angle spinning nuclear magnetic resonance (MAS-NMR) technique has been applied to reveal the local chemical structures of boron in Ash–N. In the 11B MAS-NMR spectrum of Ash–N, two peaks which are attributed to a three-oxygen coordinated boron unit (BO3) and a four-oxygen coordinated boron unit (BO4) were observed with high resolution. We have estimated quadrupole parameters of the BO3 unit in Ash–N using computer simulation, and we have fingerprinted these moieties with the parameters of borates. The result of the present analysis shows that calcium- or magnesium-bearing orthoborate or pyroborate are the most likely forms of boron in Ash–N.
 
Article
The chemical characteristics of fly ash samples from combustion of three fuels: coal, peat and wood chips, have been studied. The ash materials were collected in the 12 MW CFB at Chalmers University of Technology during full load combustion with similar standard combustion parameters. The samples were characterized in terms of chemical composition, mineralogy and leaching behavior. The special characteristics of the mineral matter in each fuel were reflected in the leaching results. Upon reaction with moderate amounts of water secondary mineral phases such as ettringite and calcite, were formed. These compounds were shown to affect the leaching rates for calcium and sulfate as well as the pH of the leachates.
 
Article
Optimum experimental conditions for a quantitative n.m.r. analysis of oil products are given together with the expected degree of repeatibility and accuracy. Conclusions are drawn regarding the possibility of using characteristic shift ranges to recognize structural features of chemical importance. In this respect aromatic carbons may be subdivided into four categories: protonated, methyl-and alkyl-substituted, and condensed (polyaromatic and benzonaphthenic carbons). A method is suggested to estimate approximately the aliphatic and naphthenic saturated carbons.
 
Article
Carbon-13 Nuclear Magnetic Resonance Spectroscopy has been applied to coal-derived liquids in order to obtain additional information regarding molecular structure and composition. The data have demonstrated that, although the chemical structure is extremely complex, a significant amount of material is present in the form of normal paraffinic material both as free paraffins and alkyl substituents on aromatic and hydroaromatic materials. Semiquantitative estimates are made of the alkyl content of the liquids and the atom percentage of this material that must exist in the unprocessed coal.
 
Article
The n.m.r. methods described previously are tested upon a synthetic base oil made up of a mixture of alkylbenzenes, and are then applied to five heavy ends derived from the same Arabian Light crude oil. The computed structure parameters show a regular increase of the aromaticity factor and of the aromatic and naphthenic condensation degree from the middle distillate (gas oil) to the heavy residues (vacuum residue and asphalt).
 
Article
The gasification of carbon-13 doped with nitrogen was used as a model for coal char gasification. The nitrogen was inserted into the carbon-13 by treatment with ammonia at high temperatures. N2O and N2 could thus be distinguished from CO2 and CO respectively in a thermogravimetric analysis-mass spectrometry instrument. The results of temperature-programmed gasification in oxygen-argon mixtures showed that the nitrogen in the carbon matrix was gasified to nitric and nitrous oxides with clearly bimodal gas evolution profiles, whereas the corresponding carbon monoxide and carbon dioxide profiles were symmetrical. The results are interpreted in terms of the gasification of different types of nitrogen functionality.
 
Article
Carbon-13 chemical shifts are reported for tetralin, hydrophenanthrenes and hydropyrenes and their alkyl substituted derivatives. Mono- and di- plus tri-aromatic fractions of hydrogenated phenanthrene and pyrene were also examined by carbon-13 n.m.r. and, wherever possible, the components in them identified.
 
Article
13C n.m.r. spectra of kerogen concentrates isolated from several different subbituminous to high-volatile bituminous coal macerals have been obtained by a combined cross polarization/magic-angle spinning technique. The samples comprise three vitrinites, two sporinites, two alginites and one fusinite, all of Upper Paleozoic age. It is shown that this technique can be used to differentiate the maceral types by providing characteristic spectral fingerprints. Aromaticities decrease in the order fusinite vitrinite sporinite alginite, as expected with the rank range studied. Furthermore, fine spectral details provide general information on the nature and distribution of discrete structural moieties and their variations with both type and rank.
 
Article
Six crude oils from the North Sea and the corresponding silica-adsorbed fractions are analysed by 13C nuclear magnetic resonance spectroscopy and subsequent principal component analysis. Solvent shifts, integrals and peak heights are used as input in the principal component analysis. The silica-adsorbed fractions are enriched in condensed aromatics relative to the crudes. The individual crudes vary from being relatively naphthenic/aromatic to relatively paraffinic. The principal component loadings for the peak heights strongly indicate the presence of a long straight chain aliphatic compound containing a heteroatom substituent. The compound is particularly abundant in the paraffinic oils. It is believed that it may be active in the formation of stable water-in-crude oil emulsions.
 
Article
Solid state 13C n.m.r. analysis of the insoluble organic matter associated with the clay mineral, silica, and heavy metal minerals of heavy oils/bitumen is reported. The conditions under which these measurements can be made are related to the concentration of organic matter found, the nature and amount of paramagnetic constituents, and contact times. The data are related to changes in hydrophilic/hydrophobic surface properties of the solids. The relationship with bitumen losses in recovery processes is also discussed.
 
Article
The difficulties associated with obtaining quantitative results from 13C nuclear magnetic resonance spectroscopy are discussed. By careful choice of the experimental conditions quantitative results have been obtained for a mixture of model compounds, containing most of the types of carbon linkages present in coal-derived materials, and for an aromatic fraction of a coal extract.
 
Article
Three H-Coal liquids, ASO, ASB, and VSO, have been characterized by quantitative FT-n.m.r. spectroscopy. FT-parameters were chosen to allow determination of aromatic:aliphatic carbon ratios to within 1% and 2% error of the theoretical and the absolute number of aromatic and aliphatic carbons in a simulated coal liquid, respectively. The aromaticity, fa, the Car:Cal ratio and, the absolute number of both the aromatic and the aliphatic carbons on a per mol basis, have been derived for each H-Coal liquid using c.m.r. in combination with other physical data. By analysis of the chemical shifts of the c.m.r. spectra, the carbon distributions in the H-Coal liquids have been estimated and compared in terms of six structural types. The molecular parameters thus derived are reasonable correlated with the average molecular structures proposed as working hypothesis for the molecular characterization of the three H-Coal liquids.
 
Article
A sample of kerogen from Aleksinac oil shale was examined by high-resolution solid-state 13C n.m.r. spectroscopy. The presence and relative proportions of kerogen structural units were estimated using a combination of NQS and T1ϱC methods with a peak-synthesis technique applied to the 13C CP—MAS spectrum. Relaxation parameters from these experiments were used to estimate differences in relative ‘mobility’ of various structural units. The kerogen was found to be highly aliphatic and to contain ∼ 79% long-chain aliphatic plus alicyclic structures, as well as ∼ 9% aromatic structures. These findings are in good agreement with the characterization of the same kerogen from its oxidation products.
 
Article
Solid-state 13C n.m.r. (CP/MAS-13C n.m.r.) spectroscopy provides a direct method for estimating potential oil yields of oil shale formations. Relative aliphatic resonance areas correlate linearly with oil yield and provide a method for oil yield estimation that obviates the need to determine weight per cent organic carbon for each specimen. This direct measurement is performed using an internal area standard, the carbonyl resonance of N-(2-13C-propanonyl)-N,N,N-trimethylammonium chloride, to monitor spectrometer sensitivity. Oil shale samples obtained as a function of depth at a site in the Mahogany Zone of the Green River Formation show a near-constant aliphatic carbon fraction, fal ≡ (1−fa), and a twofold, nonlinear variation in oil yield over the vertical dimension of the sampling. Aliphatic carbon resonance band shape changes among these samples are interpreted qualitatively as reflecting a two component mixture composed of the condensed alicyclic structures which link together to form the kerogen matrix and an n.m.r.-distinct but not necessarily chemically distinct contribution from normal-long chain hydrocarbon residues.
 
Article
Biomass pyrolysis for the production of fuels and chemicals is certainly one of the most promising strategies to replace petro-chemical polymers. Generally the biomass is first pyrolysed using temperature up to 700 °C to obtained vapors that are further cracked using catalysts. The catalyst can be poisoned by tars that are formed during the pyrolysis step and that are entrained with the vapor. In order to understand and model the behaviour of the biomass during such a process, a complete structural study of the chars was performed with high-resolution solid-state 13C, EPR, and susceptibility measurements. The origin of biomass does not affect the nature of the solid residues that are formed during the thermal treatment. They all loose their ligno-cellulosic structure and are transformed to polycyclic material with a preponderance of aromatic structures with proton amounts that decrease drastically as the temperature of treatment increases. The presence of unpaired electrons is undoubtedly indicated with EPR spectroscopy. Most of metallic compounds found in the solid residues are easily removed by a mild acidic treatment. It indicates that they are not intercalated inside the polycyclic plans. The occurrence of ferri/ferromagnetic parts has been clearly shown. Their origin is probably exogenous. The study has revealed some non-classical and unexpected features of the NMR spectra that are presented and discussed in relation to the structural properties of the pyrolysed biomass.
 
Article
Selected, multiplet C n.m.r. spectra are obtained for three test samples deriving from petroleum and coal sources, by combining gated spin echo (GASPE) and conventional spin echo 13C n.m.r. procedures. Each selected multiplet spectrum contains resonances due to only one of the following groups: aromatic C or CH or aliphatic C, CH, CH2orCH3. In general artifacts contribute only minor intensity to individual spectra, with the separation between aliphatic CH and CH3 spectra being the most difficult to achieve. Each spectrum can be integrated to yield the relative abundances of CHn groups (n = 0 to 3). Selected multiplet 13C n.m.r. spectra provide a more detailed view of the component hydrocarbon groups in fossil-fuel derived materials than can be deduced from conventional 13C n.m.r. spectra.
 
Article
The use of TOSS spinning sideband suppression to obtain 13C n.m.r. spectra of a wide range of aromatic materials is discussed in relation to the spectra of the same materials obtained without sideband suppression. The 39 samples studied include polymers containing both aromatic and aliphatic carbon, asphaltenes, fossil fuels spanning the range in rank from pet to semianthracite, pitch, separated macerals, laboratory oxidized coals and naturally weathered, stockpiled bituminous coals. Despite the diversity in structure, it is found that sideband suppression can be used to obtain apparent aromaticity values consistent with the normal spectra in the majority of samples. The observation of inaccurate aromaticities due to destructive interference between the frequencies associated with magic angle spinning and slow molecular motions in some samples is illustrated.
 
Article
Coal-derived products of SRC-I liquefaction of Blacksville coal and vacuum tower bottoms (VTB) of SRC-II liquefaction of Powhatan mine coal (both bituminous and from the Pittsburgh Seam) were separated into fractions by solvent extraction. The SRC-I was first extracted with ethylacetate, and solubles were subsequently separated into oils and a mixture of asphaltenes and preasphaltenes (APA). The VTB was Soxhlet extracted with pentane to remove any residual oils, followed by tetrahydrofuran to recover APA. The APA portions were then separated by sequential elution solvent chromatography (SESC) into fractions differing in chemical functionality, and then examined by 13C n.m.r. and FT-i.r. spectroscopic techniques. APA are intermediates and end products of coal liquefaction. SRC-II APA are of higher molecular weight than the APA of SRC-I. The lower numbered fractions of APA of SRC-I in SESC separation have the same functional groups as the corresponding fractions of middle and heavy distillates. However, the higher numbered fractions are rich in oxygen, which is mainly in carbonyl groups. Part of the carbonyl groups are in esters which cross-link aromatic clusters. Therefore, APA and the coal itself are ‘oligomeric’ in structure, with aromatic clusters linked by carbon bridges with different functional groups. The nature of carbonyl groups in APA has been analysed in detail.
 
Article
A number of samples of shale oil prepared under various conditions have been examined by 13C n.m.r. using multiple-pulse techniques that allow carbon-type assignments. Previous assignments by Netzel et al. (Fuel 1981, 60, 307) are confirmed and several new ones made. Product chemistry is then examined as a function of heating conditions. New or verified observations are: 1.(1) isoprenoids are evolved in the early stages of oil generation, and the average length of normal hydrocarbons in the evolved oil is approximately independent of the extent of kerogen conversion;2.(2) alkene content depends strongly on the heating rate during pyrolysis but average normal chain length does not; and3.(3) the ratio of isoprenoid to normal carbons and the average normal chain length in bitumen are greater than in shale oil, but there are greater questions about the correct equation for calculating the average normal chain length of bitumen.
 
Article
A new theoretical model has been developed which explains the association between the molecular structure and the knock resistance of individual gasoline compounds convincingly. The constitutions of more than 300 individual gasoline components were correlated with their knock rating (Blending Research Octane Number, BRON) simultaneously. 13C NMR spectra of all compounds were binned in 28 chemical shift regions of different size. The number of individual carbon signals of the nearly 2500 carbons was counted in each shift region and was combined with the information about the presence or absence of the structure groups Oxygen, Rings, Aromatics, aliphatic Chains and oLefins (ORACL). These numbers were used for the encoding of the chemical structure. The relations between the structure information and the knock ratings were determined using an artificial neural network. For a validation data set of 50 individual chemical compounds from various substance classes consisting only of C, H and O a good agreement was found with their experimentally determined BRON (R=0.933).
 
Article
Ultralarge magic-angle spinning (MAS) systems (2.4–6.5 cm3) provide a sufficiently large increase in signal-to-noise ratio that 13C MAS experiments without cross-polarization (CP), as well as time-domain 13C CP/MAS studies, can be carried out expeditiously. The non-CP approach allows one to circumvent the uncertainties in quantitation by 13C CP/MAS techniques; however, a more direct determination of TH1ϱ values than by variable contact-time experiments yields promising results on 13C spin counting in coal. The 1H combined rotation/multiple-pulse spectroscopy technique, based on multiple-pulse dipolar line narrowing and MAS, provides a useful complement to 13C MAS techniques, typically yielding poorly resolved 1HCsp2 and 1HCsp3 peaks from which deconvolution nevertheless provides at least a semiquantitative assessment of amounts. A dipolar-dephasing approach and imbibing with perdeutero-pyridine, employed either separately or together, dramatically improve resolution and provide strategies for examining the mobilities of individual coal components.
 
Article
Sixty coal samples of different rank and origin have been investigated by means of e.s.r., 1H n.m.r. and 13C n.m.r., the last two in combination with dynamic nuclear polarization (DNP). The following parameters have been determined: the number of free radicals, the e.s.r. linewidth, the 1H Zeeman relaxation rate, the 1H relaxation rate in the rotating frame, the 1H DNP enhancement, the 13C DNP enhancement, the 13C Zeeman relaxation rate and the 13C aromaticity, observed via 1H13C cross-polarization (CP), both with and without magic-angle spinning (MAS). The relations between these parameters and coal rank have been investigated. Moreover, with DNP special experiments have been performed which provide information about the localization and the mobility of the unpaired electrons present in these coals. Finally, DNP has been used to investigate various features of the quantitative analysis of coal via 13C n.m.r. MAS was found to reduce the measured 13C aromaticity, and for three coals it was shown that even without MAS only ≈ 50% of the aromatic 13C nuclei are detected by the CP technique.
 
Article
Stable carbon isotope compositions of CH4 and CO evolved from a lignite of the Mahakam delta series are determined as a function of time and temperature. Variations in the trend of data are due to the diversity of sources for carbon monoxide and methane. Chemical kinetic laws for first-order reactions applied to these experiments suggest that values for activation energies and preexponential factors can be estimated from isotope data.
 
Article
Several pitches, used to make high-grade cokes, are characterized by 13C and 1H n.m.r. spectroscopy. Average molecular parameters of solvent fractions of the pitches indicate distinct differences in molecular structure. Principal differences between A-240 petroleum and medium coal-tar pitches are composition of fractions, aromaticity, degree of aromatic condensation and amount of naphthenic groups. The mild conditions of production of A-240 petroleum pitch leads to the formation of methylene bridges and biaryl linkages between two aromatic moieties in constituent molecules.
 
Article
The residues of hexane extraction of a highly volatile bituminous coal, pretreated under the conditions of the first stages of hydroliquefaction (T ≈ 350 °C), were studied by solid state high resolution 13C n.m.r. and FT-i.r. The catalysts used are non porous aerosols of Fe2O3, MoO3 and SnO2 with a very fine grain size (Φ ⩽ 0.05 μm), sulphided in situ in the course of the operation. The catalytic effect resides on the hydrogenolysis of bridging bonds, especially the ether type, between the polyaromatic units of the coal, as well as the hydrogenation of the latter, to give hydroaromatic structures (following the order of activity in tetralin solvent: Fe2O3 ≈ MoO3 ⪢ SnO2). The role of Fe2O3 as catalyst does not appear fundamentally different in a medium that is not a hydrogen donor (1-methylnaphthalene) as compared with a donor medium, even though the latter solvent is barely hydrogenated under conditions employed in this work.
 
Article
13C and 1H n.m.r. spectroscopy have been applied to benzene extracts of Polish coals to obtain additional information on their molecular structure. The data have shown that a considerable amount of the material can occur in the form of aliphatic carbon chains as paraffins and/or n-alkyl substituents on aromatic and hydroaromatic rings. Different types of branching both of alkane and alkyl groups were also indicated.
 
Article
13C n.m.r. spectral editing techniques have been used to determine the concentrations of aliphatic CH, CH2 and CH3 groups directly in aromatic fractions from a North Sea waxy heavy distillate (vacuum gas oil) and a hydrotreated sample of this distillate. To help resolve effective and poor hydrogen-donor naphthenic groups, these fractions were catalytically dehydrogenated and re-examined by 13C n.m.r.. The results indicate that naphthenic groups in the initial aromatic fraction account for a maximum of 40% of the total carbon but only 10% of the carbon is present in effective hydrogen donors and that, in contrast to earlier structural models for heavy petroleum fractions, the naphthenic groups are relatively small comprising no more than two rings on average.
 
Article
Bloch decay or single pulse excitation (SPE) 13C n.m.r., generally recognized as the best approach to obtain quantitatively reliable aromaticity values and other skeletal parameters for coals, was applied to partly carbonized coal samples, a biomass char and the toluene-insolubles from a coal tar and a corresponding pitch. As found previously for coals, the aromaticities and non-protonated carbon concentrations were generally higher than those estimated by cross-polarization (CP). Furthermore, in terms of accumulation times, the shorter 13C T1's of low-temperature chars makes SPE a more efficient technique than for coals. The higher concentrations of paramagnetic centres responsible for the shorter 13C T1's still result in observability of 75% of the carbon in the chars by the SPE technique. The ratios derived from the SPE measurements agree well with those obtained from elemental analysis.
 
Article
High resolution 13C n.m.r. spectroscopy of neat pitches was measured above their softening point to clarify their molecular structure, as well as molecular orientation of mesophases in the magnetic field. This method improved the ratio to a great extent, allowing the detection and identification of aliphatic carbons as well as aromatic ones in a hard coal-tar pitch. Carbonaceous mesophase was also measured in its liquid crystal phase by this method. The orientated molecules in the mesophase pitches were distinguished from non-orientated molecules. The discrepancy between the ratios of orientated/non-orientated molecules and anisotropic/isotropic areas is discussed.
 
Article
Magic-angle 13C n.m.r. spectra have been obtained for a series of vitrinite concentrates. Proper modification of the cross-polarization pulse sequence allows separation of protonated and nonprotonated carbon resonances. This technique is used to determine the relative fraction of nonprotonated aromatic carbons for each of the vitrinites, a parameter observed to decrease with increasing rank. Another parameter, related to the aromatic hydrogen content, is also calculated from these data and the results correlate with those from Fourier transform i.r. spectroscopy. The methods used for analysis of the vitrinite concentrates were then applied to the low-temperature oxidation of coal. The fractional aromaticity as determined by n.m.r. increases with longer oxidation times, indicating preferential attack on aliphatic structures. Here the FT-i.r. results are in quantitative agreement with those from n.m.r. Finally, the advantages of using various pulse sequences to extend the range of magic-angle n.m.r. and of combining FT-i.r. and n.m.r. results are discussed in the context of their potential for coal science.
 
Article
The cross-polarization/magic-angle spinning technique has been applied to obtain 13C n.m.r. spectra of samples produced by artificial oxidation of a type III humic coal of southern Utah. The oxygen is mainly incorporated in carboxylic acid and phenol functional groups. Results are confirmed by infra-red spectroscopy.
 
Article
The cross polarization technique combined with magic-angle spinning has been applied to obtain 13C n.m.r. spectra of a sedimentologically homogeneous series of peat, lignite and bituminous coal derived from higher plants. Despite some uncertainties on the quantitative aspects of the method, the structural information obtained was corelated with data from elemental analysis. Structural average parameters were also calculated by using the structural basic unit concept and relating it to the maturation stage of the organic matter.
 
Article
While solid state 13C n.m.r. has made a major contribution to the characterization of coal and other insoluble carbonaceous materials over the past decade, there has been considerable uncertainty concerning the quantitative reliability of the technique. This debate addresses this important topic and comprises six contributions from authors who are recognized experts in n.m.r. characterization of solid fuels. The principal issue discussed is the accuracy of aromaticity measurements on coals by cross-polarization — magic-angle spinning (CP/MAS) 13C n.m.r., together with additional problems posed by high field measurements and spectral editing, and with some discussion of emerging techniques. There is a consensus that significant errors can arise in CP/MAS 13C n.m.r. measurements of aromaticity due to the unfortunate spin-dynamics of coals, which typically result in only ≈50% of the carbon being observed for bituminous coals. There is clear discrimination against aromatic carbon, but differences of opinion exist over the magnitude of the errors (from 2 to 15 mole carbon %) and whether high field (⩾ 50 MHz) measurements are as accurate as those of low field (< 25 MHz) because either sideband suppression or extremely high speed MAS has to be employed to eliminate sidebands. From the evidence presented, it is suggested that a combination of low field, single pulse excitation with long relaxation delays and the use of a suitable reagent to quench paramagnetic centres is the most satisfactory, albeit time consuming, recipe for obtaining reasonably reliable results on unknown samples. An inter-laboratory exercise is being organized by Argonne National Laboratory to check the precision and to further investigate quantitative reliability of 13C n.m.r. measurements on coals from their Premium Coal Sample Bank.
 
Article
High-boiling (535–675 °C) distillate fractions of Wilmington (Calif. USA) and Gach Saran (Iran) crude oils were separated into saturate, monoaromatic, diaromatic and polyaromatic-polar fractions by passage through a silica-gel—alumina dual packed chromatography column. These fractions were further separated on the basis of molecular volume by gel-permeation chromatography (g.p.c.). Select g.p.c. fractions were then analyzed by 1H and 13C n.m.r. spectroscopy. The fraction of aromatic carbons (Ar-C) of the total carbon content of a given series of g.p.c. fractions, obtained directly from the 13C n.m.r. spectra, showed a significant range of values (e.g. 13.2% to 29.2%) within each series. Furthermore, the values of %Ar-C within a series of g.p.c. fractions showed a maximum in each case. No such maximum was observed in the 1H n.m.r. spectra for the fraction of aromatic proton (%Ar-H) content compared to the total proton content of any of the g.p.c. fraction series. Signals observed in the 13C n.m.r. spectra confirmed the presence of aliphatic chains attached to aromatic structures in the monoaromatic, diaromatic and polyaromatic-polar g.p.c. series of each distillate fraction. Well-defined signals, not attributable to straight-chain aliphatic material, were also observed in the 13C n.m.r. spectra. Comparison of the chemical shifts of these 13C n.m.r. signals with those spectra of model compounds obtained experimentally, and with appropriate systems in the literature, strongly suggested the presence of saturated terpenoid-like structures as well as the presence of methyl groups in sterically hindered positions on an aromatic ring system. Gated decoupling techniques and the use of a relaxation agent were used to overcome the deleterious effects of slow relaxation times and Nuclear Overhauser Enhancement (NOE) on the analytical quality of the 13C n.m.r. spectra.
 
Article
The application of experimental n.m.r. and chemical resolution enhancement techniques in cross-polarization/magic angle spinning (CP/MAS) 13C-n.m.r. spectroscopy yields spectra of coals and coalderived solids which contain structural information within the hybridization resonance envelopes. The sp2- and sp3-carbon resonance manifolds are partitioned into components arising from carbon centres bonded directly to oxygen, hydrogen and only other carbon atoms. The unique, observable chemical shift bands in the spectrum are increased from three (the relative areas of the sp2- and sp3-carbon resonance envelopes and a separate carbonyl band) to nine. This resolution permits the principal structural changes in chemically-modified coals to be mapped in unprecedented detail. The reductive alkylation of a typical bituminous coal has been examined by this method.
 
Article
Fused-state 13C n.m.r., which provides high-resolution spectra in a significantly shorter measuring time than the solution method, was used to obtain spectra of quaternary aromatic carbons in pitch. The spectra showed that the conventional shift ranges for inner and outer quaternary aromatic carbons postulated on the basis of model compounds were somewhat erroneous. Structural differences between coal-tar-derived and petroleum-derived mesophase pitches were elucidated in terms of their aromatic carbon distributions determined by this method.
 
Article
Coal-derived products of the SRC-II liquefaction of Powhatan Mine (Pittsburgh Seam) bituminous coal were separated into various fractions either by solvent extraction or by distillation. Subsequently, the middle and heavy distillates were separated by sequential elution solvent chromatography into fractions differing in chemical functionality. These fractions were examined by 13C n.m.r. and FT-i.r. spectroscopic techniques. In addition to developing the techniques, the work was undertaken to relate the product composition to the possible reactions occurring during the solvent-induced pyrolytic fragmentation of coal. The bulk of the SRC-II generated middle distillate is composed of two-ring nonpolar aromatic compounds, tetralins, one-ring phenols, indoles, and some alkanes. The heavy distillate contains three-and four-ring systems.
 
Article
Three Polish coal samples (flame coal, gas coal and orthocoking coal) and their macerals were studied in the solid state by means of 13C cross polarization/magic angle spinning n.m.r. and FT-i.r. spectroscopies. Several structural parameters derived from these analyses allow the characterization of the three macerals, vitrinite, exinite and fusinite, and their comparison with their parental coal. These structural data were compared with the solvent extraction yields of the same samples with N-methyl 2-pyrrolidone.
 
Article
Dry phase oxidation of a subbituminous coal with air was carried out in a fluidized bed reactor at 175, 200, 250 and 275 °C. Coal samples were withdrawn during the reaction at fixed intervals up to 12 h. Reaction pathways and chemical changes occurring in coal structure during oxidation were studied by 13C n.m.r. spectroscopy, elemental analysis and weights variation. By coupling 13C n.m.r. and carbon mass balance data it was possible to detect semiquantitatively the fate of aliphatic and aromatic carbon. The results show that, at each temperature, aliphatic carbon is more reactive than aromatic carbon, and that aromatic carbon does not seem to be affected by oxidation ⩽ 200 °C. A decrease in the aromatic carbon of 15% at 250 °C, and 20% at 275 °C was detected after 12 h of oxidation. The mass balance data and elemental analyses were used to examine the effect of reaction temperature on the relative importance of reaction pathways which lead to oxygen fixation or coal combustion. The weight losses at 250 and 275 °C are mainly due to combustion of the aliphatic structure.
 
Article
Four coals (bituminous, subbituminous, lignite and canneloid) are treated with tetralin-1,1,4,4,-d4 or — 1,1 -d2 or mixtures of tetralin-d4 and tetralin-d0 at 427 °C in degassed Pyrex vessels for times between 5 and 60 min. Deuterium depletion and scrambling in solvent-derived products are determined for degassed and air-saturated experiments. Deuterium distributions are determined for preasphaltene and asphaltene fraction (A + P) and light oils (LTO) by 2H FT-n.m.r., and solid coals and products are characterized by 13C CP/MAS and 13C FT-n.m.r. Illinois No. 6, PSOC 837 and PSOC 531 coals selectively consume tetralin-d0 over tetralin-d4 and exhibit isotope effects in the scrambling of deuterium from 1 — to 2-positions. Intersite deuterium scrambling in recovered tetralin is negligible at 10 min or shorter reaction times, but deuterium depletion from tetralin is significant at all reaction times. Deuterium is detected predominantly at benzylic-type and secondary aliphatic positions and to a lesser extent at aromatic positions of A + P and LTO fractions at reaction times of 5 min. The presence of air significantly enhances both the extent of deuterium scrambling and the rearrangement of tetralin to 1-methylindan at reaction times of 30–60 min.
 
Article
13C-1H heteronuclear dipolar dephasing n.m.r. techniques allow discrimination between different chemical species contributing to the 13C n.m.r. spectra of complex hydrocarbons. Model compound studies show significantly different effective transverse relaxation constants for carboxyl and quaternary carbon atoms (≈200 μs), secondary and tertiary (≈20 μs), and primary carbon atoms (≈80 μs). Use of these effective relaxation data, together with appropriately timed windows in the continuous wave decoupling applied in standard cross-polarization-magic-angle spinning experiments on anthracite coal allow discrimination between aromatic tertiary and aromatic quaternary ring carbon atoms in this coal. Within the accuracy of experimental error, and of the structural modelling experiments herein reported, the use of the dipolar dephasing technique together with results of X-ray diffraction on coals allows a reasonable estimate to be made of the average number of condensed polynuclear rings in an ‘average molecule’ in the anthracite studied. Based on a model of pericondensed aromatic rings, this number lies between 33 and 45.
 
Article
The chemical structure of Estonian kukersite kerogen is evaluated using a simulation of 13C MAS NMR spectrum. A reasonable fit to the experimental NMR spectrum is obtained by assuming a model of the geomacromolecule with empirical formula C421H638O44S4NCl and a set of structural elements comprising mainly alkylated phenolic structures particularly alkyl-1,3-benzenediols and condensed alicyclic rings. From the presented model new views are coming up on the carbon skeleton of kerogen and constraints on the phenol formation pathways in the retorting process, i.e. up to 80% of methylene groups in kerogen are located in aliphatic chains and the complicated mixture of phenols in the retort oil seems to result mainly from the thermal conversion of alkyl-1,3-benzenediol units originally present in kerogen.
 
Article
A dual circulating fluidized bed pilot plant was operated in chemical looping reforming conditions at a scale of 140 kW fuel power with natural gas as fuel. A nickel-based oxygen carrier was used as bed material. The pilot plant is equipped with an adjustable cooling system. Three experimental campaigns have been carried out at 747 °C (1020 K), 798 °C (1071 K) and 903 °C (1176 K), respectively. In each campaign, the global stoichiometric air/fuel ratio was varied step-wise between 1.1 and the minimum value possible to keep the desired operating temperature when the cooling is finally switched off. The results show that the fuel reactor exhaust gas approaches thermodynamic equilibrium. The residual amount of methane left decreases with increasing fuel reactor temperature. Further, the oxygen in the air reactor can be completely absorbed by the solids as soon as the air reactor operating temperature is higher than 900 °C (1173 K). Even though no steam was added to the natural gas feed no carbon formation was found for global excess air ratios larger than 0.4.
 
Top-cited authors
Stanislav Vassilev
  • Bulgarian Academy of Sciences
Yang Haiping
  • Huazhong University of Science and Technology
J.M. Jones
  • University of Leeds
Anders Lyngfelt
  • Chalmers University of Technology
R. Kandiyoti
  • Imperial College London