An e.s.r. study of some coals under rapid passage condition at high temperatures and pressure

The e.s.r. spectra of Miike and Taiheiyo coals were measured under rapid passage conditions in the temperature range 150–450 °C. A parameter, R, was defined by a ratio of out-of-phase and in-phase spectral amplitudes and the ratios for Miike and Taiheiyo coals were estimated in this temperature range. It was found that the temperature dependence for R was different for the two coals examined, and the reason for the difference was discussed. Further, the ratios for those coals mixed with pyrene were estimated in the temperature range 150–400 °C at atmospheric and 1.1 MPa nitrogen pressure. Based on the temperature dependence of the ratio the coal liquefaction ability of pyrene for those coals was discussed.     

Measurement of anisotropic development in a low-rank coal using e.s.r. spectroscopy and optical texture

Anisotropic development in a low-rank coal (Cerrejón coal) has been induced using natural heavy oil or anthracene oil as additives in a cocarbonization system at 500 °C. The heavy oil showed better modifying activity. To monitor the anisotropic development optical microscopy and e.s.r. spectroscopy have been used. The concentration of stabilized free radicals, measured at room temperature (trapped free radicals) increased with anisotropic development. The concentration of stabilized free radicals allows interaction in the carbonization system to be followed even when the microcrystallinity of the anisotropic phase is too small to be observed under the microscope.     

E.s.r. spectra of eastern oil shales

E.s.r. spectra of several oil shales from eastern and western USA have been measured at 9 and 25 GHz. The spectra of the western shales were similar to previously reported spectra and consist of a Mn²⁺ signal and a featureless organic signal. The eastern spectra consist of a V⁴⁺ signal and a complex and unusual organic signal consisting of at least four component signals. The organic signal has been characterized in terms of g factor, line-width and saturation characteristics. The effect of oxygen on the signal has also been examined. Electron nuclear double resonance (ENDOR) signals have been obtained from the organic signals of the eastern oil shales.     

Structural characterization of pitch feedstocks for coke making: Use of 13C coupled 1H n.m.r. spectroscopy

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.     

SEM study of binder coke in electrode carbon

As part of a study on the use of coal-tar pitches as binders in electrode carbons for the aluminium industry, the object of the present work was to attempt to identify textural components in electrode binder cokes. Accordingly, four experimental carbons, made using the same petroleum coke as filler and four coal-tar pitches of differing characteristics as binders, were examined in a scanning electron microscope (SEM) after embedding in resin, polishing and etching in atomic oxygen. Binder cokes could be distinguished from the filler particles and could be characterized in terms of the content of three components, termed lamellar, intermediate and granular. The textural composition of the binder cokes was dependent upon the character of the pitch and the type of quinoline-insoluble components present. Pitch cokes, made by carbonizing the pitches alone, differed markedly from the corresponding binder cokes. The findings are considered in terms of current ideas on pitch carbonization.     

E.s.r. study of pyrolysis vapour of coal

Wyodak and Heatburg subbituminous coals were pyrolysed in-situ in an e.s.r. microwave cavity at ≈510 °C in an evacuated sealed tube. At least two kinds of radicals are detected; first, phenalenyl-like radicals and then, polymerized radicals from the initial ones.     

Quench solvent evaluation: An e.s.r. study

An in-situ radical-quenching experiment was performed in an e.s.r. microwave cavity by using a solution flow system. Diphenylmethyl radicals produced from pyrolysis of 1,1,2,2-tetraphenylethane were quenched by several H-donor solvents. Among the solvents used, indan was the fastest in quenching, followed by hydrophenanthrene, tetralin, mesitylene and cumene in decreasing order of quenching rate.     

E.p.r. study of molecular phases in coal

E.p.r. spectra from coals of various carbon content are reported. The e.p.r. signal from coals in a vacuum consists of two lines with different widths. The results are interpreted using the Larsen-Kovac structural model (Am. Chem. Soc. Div. Fuel Chem. Preprints 1977, 22, 181). The paramagnetic centres, disposed in the macromolecular phase, give a narrow line whereas the spins of the molecular phase are responsible for the broad line. These results provide a good interpretation of the changes in e.p.r. signal-shape under the influence of various organic solvents observed by Yokokawa (Fuel 1968, 47, 273; Fuel 1969, 48, 29).     

A scanning electron microscope study of fractured and etched metallurgical coke surfaces

The object of this work was to attempt to link more closely coke strength and structure by establishing whether features visible on fracture surfaces could be identified with coke carbon textural constituents revealed either by polarized light microscopy of polished surfaces or by scanning electron microscopy of atomic oxygen-etched surfaces. The cokes used were produced in a laboratory furnace from coals covering the whole range or rank normally encountered in metallurgical coke production in the UK. Fracture surfaces were created by tensile fracture during diametral compression. In all three surfaces examined, the appearance of components derived from reactive coal constituents varied with the rank of the coal carbonized. A clear similarity was evident between features visible in the etched and fracture surfaces. The marked variation of fracture features imply that the textural composition of the coke carbon may make some contribution, as yet unquantified, to the variation in strength among cokes.     

High resolution solid state C n.m.r. of Canadian peats

Peat samples from three locations in Quebec, Canada, were characterized by ¹³C CP/MAS n.m.r. spectroscopy. The n.m.r. analysis indicates that the peats contain a significant amount of unaltered plant components including cellulose, hemicellulose, lignin, waxes and resins. Integration of specific regions of the spectra can give semi-quantitative estimates of some of these plant components and, in limited cases, information about the degree of decomposition can be obtained from the ¹³C CP/MAS n.m.r. spectrum. Dipolar dephasing experiments and difference spectroscopy were found to be valuable techniques for spectra assignments and enhancement of compositional differences.     

Quantitative aspects of solid state 13C n.m.r. of coals and related materials

The quantitative aspects of cross-polarization (CP), which is used in conjunction with dipolar decoupling and magic-angle rotation to obtain high resolution ¹³C n.m.r. spectra of coals, have been studied using a bituminous coal (82 wt% C, dmmf basis) and asphaltenes from an extract of the same coal. The condition for obtaining reliable quantitative data, that rotating frame ¹H relaxation times (T_1p′ these govern the extent of CP) are much longer than the time required to polarize the carbons present (≈1 ms), was met for the asphaltenes. In contrast, about half the protons in the coal have T_1p5 of ≈ ? 1 ms, these times being too short to allow CP of all the carbons. Although the aromaticities obtained for this coal were fairly constant (≈0.75) using (CP) contact times > 0.5 ms, the total peak intensity decreased markedly as the contact time was increased and was much less than that for the asphaltenes. These results indicate that not all the carbons in bituminous coals are observed by CP and, as a consequence, aromaticities reported in the literature for some bituminous coals appear to be low.     

Concerning the 1600 cm−1 region in the i.r. spectrum of coal

The assignment of the 1600 cm^?1 band in the i.r. spectra of coals has been a matter of controversy for some 20 years. The two most probable assignments of the band are to aromatic ring stretching or to highly conjugated, hydrogen-bonded carbonyl. In the present study, careful deconvolution of coal spectra obtained using a high resolution Fourier transform infrared spectrometer provides-additional support for the assignment of the band to an aromatic stretching mode.     

Application of high-field,high-resolution 13C CP/MAS n.m.r. spectroscopy to the structural analysis of Yallourn coal

High-field, high-resolution ¹³C cross-polarization and magic angle spinning nuclear magnetic resonance experiments are reported on Yallourn brown coal and on products obtained from the coal by heat treatment. The spectral resolution at 75 MHz is much improved over that previously reported for lower frequencies. A comparison of experimental and simulated spectra allowed the distribution of carbon types in Yallourn coal to be determined; the carbon aromaticity is 42%, and 30% of the carbon is present in methylene groups. The method was also used to determine structural changes during pyrolysis. At 773 K, aliphatic carbon structures are lost, but higher temperatures are necessary to decompose phenolic structures.     

Application of lanthanide n.m.r. shift reagents for functional group studies of shale bitumen asphaltenes

Ytterbium (fod)₃ was used as a shift reagent in conjunction with solution ¹H n.m.r. studies of asphaltene isolated from Devonian shale bitumen. Upon addition of the reagent, bands attributed to protons on alkyl groups alpha to oxygen atoms were shifted and separated from that attributed to protons alpha to two aromatic systems. Similar experiments with Green River bitumen asphaltene did not show any observable shift. The presence and absence of the ether formations in shale asphaltenes can be substantiated by ¹³C n.m.r.     

Application of FT-i.r. spectroscopy to the determination of COOH groups in coal

FT-i.r. studies of acid-demineralized and cation-loaded lignites demonstrate that exchange methods presently being used to determine carboxylic acid groups in coal produce systematic errors. An i.r. method based on intensity measurements of the 1710 cm^?1 carboxylic acid C = 0 stretching mode is reported.     

1H n.m.r. technique for characterization of polymerized petroleum pitches

A new proton n.m.r. technique has been developed for the chemical characterization of polymerized petroleum pitches with pyridine-insoluble contents as high as 80%. The polymerized pitches were completely solubilized for conventional ¹H n.m.r. evaluation in a mixed solvent system consisting of S₂Cl₂-SO₂Cl₂. Although solubilization occurs via the addition of chlorine to the polynuclear aromatic rings, the n.m.r. spectra can still be quantitatively interpreted. Several applications are discussed.     

An e.s.r. study of the motion of peroxy radicals in isotactic and atactic polypropylenes

E.s.r. spectra of peroxy radicals trapped in isotactic and atactic polypropylenes have been observed at various temperatures. The spectrum observed at 77 K was shown to be composed of one component by comparing it with that at 4 K. The spectra observed at higher temperatures comprised of two spectra arising from the rigid peroxy radicals and the mobile peroxy radicals. All of the observed spectra have been reconstructed by means of computer simulation and the changes in anisotropic g-values with temperature were estimated. The motion of the mobile fraction was shown to be rotation or rotatory vibration of the radicals around the chain axis both in the isotactic polypropylene and in the atactic polypropylene as well as in polyethylene and poly(tetrafluoroethylene) although the structures of the polymers are different, that is helical (polypropylene) or planar zigzag (polyethylene, poly(tetrafluoroethylene)).     

Free radical involvement in the oxidation of Victorian brown coal

Electron spin resonance spectroscopy has been used to investigate free radical involvement in the oxidation of Victorian brown coal. Fresh, wet Yallourn brown coal exhibits two superimposed e.s.r. signals due to organic free radicals. The free radicals responsible for the narrow signal interact reversibly with atmospheric oxygen while the broad signal changes intensity dramatically during prolonged exposure to air. Coal:oxygen complex formation may explain these observations. Results also suggest that the free radical content of brown coal increases as a consequence of vacuum drying.     

Characterization of needle coke feedstocks by magnetic resonance spectroscopy

Decant oil is the traditional petroleum-derived feedstock for the production of needle coke. However, with the dwindling supply of high-quality decant oil and potential availability of coal-derived liquids, alternative feedstocks are receiving attention. One of these is ethylene pyrolysis tar. The new materials are less suitable needle coke precursors and may need to be upgraded by structural alterations. Therefore, the structure of these materials is examined at the molecular level. The average molecular parameters for the aromatic and asphaltene fractions of decant oil and pyrolysis tar are reported, along with a method for calculating these parameters which is slightly different from the previously available procedures. These parameters indicate that the average molecule in the aromatic and asphaltene fractions of decant oil and pyrolysis tar differ in certain structural units. This difference possibly may be responsible for their different behaviour on pyrolysis.     

Preliminary studies on the aromaticity of Australian coals: Solid state n.m.r. techniques

The aromaticities of samples from nine Australian coal seams, including pairs of hand-picked vitrains and durains, have been determined by ¹³C cross-polarization n.m.r. spectroscopy with magic angle sample spinning. The results clearly show that the aromaticity (f_a) of the coals increases with increase in vitrinite reflectance and carbon content and decrease in atomic H/C ratio. For a given coal seam, durain (inertinite-rich coal) has a higher f_a value than vitrain (vitrinite-tich coal). The trends for carbon content and atomic H/C are in good agreement with results from North American coals, although the aromaticities of Australian coals obtained in this study appear to be slightly lower than some of those reported for North American coals of similar carbon content.