E.s.r. study of formation of coke texture

The optical coke texture is a major factor in the high-temperature properties of metallurgical coke but the mechanism of formation of coke texture is not established yet. By studying the carbonization process during the formation of optically anisotropic coke with an e.s.r. spectrometer fitted with a high temperature cavity a relation between the concentration of the free-spins during carbonization and coke texture has been inferred for some organic compounds used as the model materials and for coals covering a range of coal rank.     

Pore distribution in high-volatile bituminous coal: An e.p.r. study using nitroxide spin labels

Nitroxide spin labels of different size were diffused into high-volatile bituminous coal from the Mary Lee and Black Creek Coal seams of Alabama in an effort to study the relative pore size and number distributions. The nitrogen coupling in the principal z direction of the incorporated spin label exhibits a temperature dependence above 250 K that is largely a result of librational motion of the nitroxide moiety about an N-C bond. Below 250 K, the temperature dependence of the nitrogen coupling behaves in the same manner as found for spin labels in solids that exhibit a hydrogen bond equilibrium at low temperatures. The distribution of pore sizes differs considerably between the Mary Lee and Black Creek coals. Similar studies of selected coal samples from the Penn State coal sample bank indicate that the spin-label doping method proposed is not applicable to all types of coal; however, it can be used to study selected samples of high-volatile bituminous coal.     

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.     

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.     

In-situ monitoring of the stabilization with hydrogen of free radicals thermally induced from coal using high pressure e.s.r., d.t.a. and p.d.a. equipment

High temperature, high pressure e.s.r. measurements of the hydrogenation reaction of Taiheiyo coal in the presence of catalysts were carried out to understand the stabilization of thermally and/or catalytically induced free radicals. A decrease in free radical concentration with increasing temperature was observed for ZnCl₂ and SnCl₂ · 2H₂O catalysts at 10MPa under hydrogen gas. High pressure modified single-cell d.t.a. and p.d.a. equipment augmented the uniquely designed high temperature, high pressure e.s.r. cell. The hydrogenation reaction was monitored under the same experimental conditions as for e.s.r. From the results of the combination of high temperature, high pressure e.s.r. with high pressure d.t.a. and p.d.a., it was established that H₂ molecules can react efficiently with free radicals from coal molecules created by the presence of ZnCl₂ and SnCl₂ · 2H₂O catalysts.     

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)).     

High temperature and high pressure H n.m.r. and e.s.r. studies on coal liquefaction reactions

Changes in chemical reactions during coal liquefaction of Yallourn brown coal and Akabira bituminous coal were monitored by using high temperature and high pressure ¹H n.m.r. A simple high temperature and high pressure e.s.r. cell was constructed and the variation in concentration of free radicals during coal liquefaction reactions was monitored under the same experimental conditions as for n.m.r. With the liquefaction and coking reaction, typical spectra of n.m.r. and e.s.r. were obtained and could distinguish the reaction steps: swelling; liquefaction; coking. The combination of high temperature and high pressure n.m.r. and e.s.r. is promising to the chemistry of coal liquefaction reactions.     

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.     

Rapid coal characterization by FT-i.r. spectroscopy

A method is described for the rapid characterization of bituminous coals based on factor analysis of the FT-i.r. spectra of a wide variety of coals from several countries. Correlations between the factor loadings and some significant coal properties are reported. Weaker, but in some cases still useful, correlations were made between coke properties and factor loadings from analysis of the FT-i.r. spectra of the corresponding coals or coal blends.     

E.p.r. studies of outburst-prone anthracite coal

Changes in the macroscopic structure of coal have been observed as an outburst-prone area is approached. Associated with this structural change was an increase in the concentration of paramagnetic centres. Initial results suggested that this increase was not due to variation in maceral content within the coal samples but to the mechano-chemical degradation of the coal as a result of tectonic forces applied over geological time.     

Study of the changes in i.r. spectra bands of coal after reductive alkylation

Depolymerization reactions of a Spanish bituminous coal, such as reductive hydrolysis and alkylation, and O-alkylation, were investigated by Fourier transform infrared spectroscopy (FT-i.r.). The spectra show that the reductive hydrolysis increases the phenolic hydroxyl groups, whereas these decrease by alkylation. These changes in the OH group content were studied in relation to variations in the absorbances at 3800–2000, 1700, 1600 and 1112 cm⁻¹, and some linear correlations were found, which seem to indicate a clear contribution of the OH groups to the intensity of the broad band near 1600 cm⁻¹. The influence of the phenolic OH groups on the C=O vibration frequency at 1700 cm⁻¹ was also studied.     

Disclinations in the optical texture of a high-rank vitrinite coke and a petroleum needle-coke

The microstructure of coke formed on carbonization of a low-volatile bituminous rank vitrinite (NCB Classification 204), at a heating rate of 60 °C min^?1, was found to consist largely of coarse-grained mozaic and domain type optical texture. The domain optical texture possessed a variety of optical structures, e.g. $\text{‘X’}$ and $\text{‘Y’-}\text{type}$ crosses and nodes, characteristic of it having passed through a nematic liquid crystal stage (mesophase) during carbonization. These structures are compared with, and found equivalent to, disclination structures found in the domains of a petroleum needle-coke, the surface of which had been gasified to reveal the underlying graphitic structure. The formation of disclination structures in the domains of the coal-coke is strong evidence for the formation and coalescence of mesophase during its carbonization as a result of the very high heating rate used.     

E.p.r. study of paramagnetic metal ions in Victorian brown coal

Electron paramagnetic resonance (e.p.r.) spectra of some Victorian brown coals in the raw state possess absorbances attributable to metal ion radicals. E.p.r. signals at g≈4.3 and g≈2 (multiplet) have been assigned to iron(III) and manganese(II), respectively. The g≈4.3 signal intensity does not appear to vary directly with the total iron content of the raw coal. The amplitudes of the metal ion signals were found to change with drying of the coal, and were reduced to zero on removal of the metal ions by acid washing. Ion exchange of the sodium form of brown coal with iron(III) reintroduced the g≈4.3 signal and produced an additional broad signal centred at g≈2. The intensity of the latter signal was related to the total iron content of the iron(III)-exchanged coal. The extent of iron(III) exchange was shown to be pH dependent. Other paramagnetic ions, such as oxovanadium(IV), manganese(II) and copper(II) when exchanged onto brown coal produced their characteristic metal ion spectra.     

E.p.r. study of organic free radicals in Victorian brown coal

The signals at g≈2 in the e.p.r. spectra of Victorian brown coals are attributed to organic free radicals. Mathematical lineshape analysis and variation of linewidth with frequency suggested that the observed signals at low power levels are mainly homogeneously broadened. Power saturation experiments, however, resolved the signals to show the presence of from one to three resonances due to different free radical types.     

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.     

Quantitative solid-state C n.m.r. measurements on cokes, chars and coal tar pitch fractions

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.     

Wide-line H n.m.r. study of perdeuterated pyridine imbibed in a premium coal

The motion of perdeuterated pyridine imbibed in Argonne premium high-volatile coal (no. 601) has been studied by wide-line ²H n.m.r. spectroscopy. The coal sample had been saturated with perdeuterated pyridine for several days, then evacuated until the pyridine reached a concentration of 3.5%. The entrapped pyridine molecules undergo two tyes of rotation about the twofold symmetry axis: rapid diffusional rotation with a correlation time of 1 × 10⁻⁷ s; and 180 ° jumps with a residence time of 6 × 10⁻⁶ s. It is estimated that roughly half of the pyridine molecules execute each kind of motion. There is no evidence for a pyridine fraction that executes rapid isotropic rotation. The anisotropic nature of the rotation indicates that the interaction between pyridine and the coal structure is strong enough to prevent isotropic rotation.     

1H n.m.r. relaxation in bituminous coal and semicoke

Temperature and frequency-dependent proton relaxation measurements, in conjunction with spin concentrations determined by e.s.r., have shown that for fresh and oxidized coal the relaxation mechanism involves spin-diffusion to paramagnetic centres and to rotating methyl groups on alkyl chains. ¹H relaxation in semicokes is more complex; probably both direct relaxation to paramagnetic centres as well as spin-diffusion contribute.     

E.p.r. spectroscopy of spin-labelled macromolecules as a tool for determining chain conformations in amorphous solid polymers

The feasibility of using e.p.r. spectrscopy in studying conformations of spin-labelled macromolecules in the amorphous solid state is examined. The algorithm for e.p.r. spectra computation is developed. It was assumed that molecular weights of labelled linear chains are high and their solid solution is diluted. It is shown that the scaling exponent which determines the dependence of mean-square end-to-end distance on molecular weight and stiffness parameter (mean-square length of monomer unit) may be extracted from the spectra. Computed spectra are compared with experimental ones, measured at 77 K, of diluted solutions of spin-labelled poly(4-vinyl pyridine) [P(4-VP)] of different molecular weights in methanol and non-labelled P(4-VP). The conformational state (Gaussian coil), parameter of stiffness, and radius of gyration of spin-labelled P(4-VP) macromolecule in frozen solutions are determined. A conclusion is drawn that e.p.r. spectroscopy may become a new tool for studying chain conformatin in solid polymers.     

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.