Peter H. Given

The concept of a mobile or molecular phase within the macromolecular network of coals: A debate

Abstract The question addressed here is whether coals contain a substantial fraction of relatively small molecules clathrated within the macromolecular network and requiring long time or extra thermal energy for release. The debate primarily hinges on the interpretation of 1 H n.m.r. data, but some other relevant findings reported in the literature are recapitulated. Cases are made out by the original authors for two different interpretations of the n.m.r. data (it should be emphasized that there is no dispute about the actual data, only about its interpretation). It appears that there are two (or possibly three) populations of protons in coals, which exhibit appreciably different free induction decay times and hence have quite different levels of rotational mobility. This is a fact of considerable interest in its own right, but the possession of high mobility does not necessarily mean that the mobile protons must be in relatively small molecules which are free to tumble in cages within the macromolecular network. Taking into account evidence from extractability and other experiments, it is possible to draw the conclusion that the content of relatively small molecules held within coal is larger than has been supposed and is essentially equal to the content of substances containing highly mobile protons, though a substantial proportion of these substances can probably be extracted only under various special conditions. However, it should be stated that there is disagreement between the authors on the admissibility of evidence from solvent extraction experiments. There is certainly evidence that the very high extractability of lignites with ethylenediamine is due to chemical reaction, and it is argued that this may be true also of higher-rank coals.

Dependence of coal liquefaction behaviour on coal characteristics. 4. Cluster analyses for characteristics of 104 coals

Abstract In an extension of earlier work, the conversion of 104 high volatile bituminous coals at 400 °C with tetralin has been determined in duplicate with the aid of a new reactor system. For the whole set of coals, volatile matter and vitrinite reflectance have the highest correlation coefficients with conversion (0.85 and −0.84, respectively). However, tests showed that the sample set contained more than one population. Cluster analysis partitioned the set into three reasonably homogeneous populations. A factor representing sulphur content was the major contributor from a set of variables in separating the coals into groups, with smaller contributions from factors related to rank and petrographic composition. Each of the groups contained samples mostly from one geological province, but 11 coals of relatively high sulphur content from the Eastern province were clustered in a group that contained also 25 coals from the Interior province. The ranges of conversion are distinctly different for the three groups, and the three regression equations developed for correlating conversion each require a different set of coal properties. The possible general significance of the clustering of coals into groups as a novel basis for classification is discussed.

Dependence of coal liquefaction behaviour on coal characteristics. 2. Role of petrographic composition

Abstract The techniques used were the same as those used in Part 1 (p 34). Comparison of the liquefaction behaviour of two lithotypes from a Kentucky bituminous coal indicated that in this process pseudovitrinite is a reactive maceral. The hydrogenation of sets of maceral concentrates obtained from a New Mexico sub-bituminous and a Kentucky bituminous coal showed fair correlations between conversion and the total concentration of the presumed reactive macerals (vitrinite, pseudovitrinite and sporinite). Similar concentrates from a Montana lignite showed no such correlation; the one sample that showed a high conversion was a high-density fraction that had a high mineral-matter content and in which nearly all the pyrite in the coal had accumulated. Two samples that have boghead and cannel characteristics gave quite different results on hydrogenation. Both were highly aliphatic in structure and had unusually high hydrogen contents and volatile matter. One, which contained appreciable proportions of sporinite, alginite and resinite, gave essentially no conversion to oil. The other, predominantly vitrinitic but containing alginite as the second most abundant maceral, gave an excellent yield of an oil of low viscosity and aromaticity. It was concluded that although rank, petrographic composition and perhaps geological history are important factors determining liquefaction behaviour, there are other characteristics of coals that may at times override these basic parameters, and the composition of the inorganic matter may be the most significant of these other characteristics.

Dependence of coal liquefaction behaviour on coal characteristics. 1. Vitrinite-rich samples

Abstract The liquefaction behaviour of a number of vitrinite-rich coals has been determined in batch autoclaves at temperatures of 385–425 °C and pressures of about 8.6 MPa (85 atm) of hydrogen. In one set of experiments, impregnated ammonium molybdate was used as catalyst, with no added liquid as vehicle. In a second set, a proprietary catalyst was used and anthracene oil served as vehicle. Lignites, sub-bituminous, medium-volatile and low-volatile bituminous coals gave relatively poor conversions. However, a lignite sample that had been subjected to ion-exchange treatments gave high conversion, and the viscosity and structural parameters of the products varied with the nature of the treatment. In general the highest conversions were observed for coals in the high-volatile bituminous range, but within this broad range and for the comparatively small set of samples studied neither these data nor the structural characteristics of the products show any very evident correlation with rank parameters or with the geological history of the sample. Two geologically young bituminous coals from the Pacific Coal Province gave excellent conversions; both had very high mineral-matter contents, a fact that may be very relevant.

An Essay on the Organic Geochemistry of Coal

Publisher Summary It is the geoscience of coals, that is, their geochemistry of origin and postburial geological history, that suggests that coals are a very diverse set of materials. This chapter discusses the relations between the chemistry of coal macerals and reviews the biochemistry of their precursors and the biological markers in coals that are indicative of their origins. The content of carboxyl groups in coals is commonly determined by an ion-exchange reaction with barium acetate. Values of 1–4 milliequivalents per gram have been found for lignites and lower-rank subbituminous coals—decreasing with increasing rank and essentially zero for coals of higher rank—except that HVC coals of the Rocky Mountain province may contain some carboxyl. The cations in the carboxylates of low-rank coals can give rise to calcite deposits in liquefaction reactors, can promote liquefaction, and can give rise to catalysts for the gasification of lignite chars.

Determination of the mineral-matter contents of coals by low-temperature ashing

Abstract A new method is described for determining the mineral-matter content of coals, based on low-temperature ashing in an oxygen plasma. Unwanted side-reactions can occur during ashing, particularly oxidation of pyrite to haematite and fixation of organic sulphur as sulphate. These effects cannot be totally eliminated, but procedures are offered that minimize them, and are presented as accurate and rapid means of determining the mineral-matter content of bituminous coals. Data are presented to illustrate the magnitude of the effects under the recommended conditions of ashing. Duplicate determinations of the mineral-matter contents of 13 coals by acid demineralization and low-temperature ashing are reported in support of the new procedures. Statistical analysis of the data shows that the precision (± 2 standard deviations) of the LTA procedure under the defined conditions is 0.20. Acceptance of the procedure is suggested for routine use with most coals of bituminous or anthracite rank. The procedure as proposed is unsuitable for use with HVC coals from Western provinces of the USA or with lignites and subbituminous coals.

The fate of cellulose and lignin in peats: an exploratory study of the input to coalification

Abstract The plant organs that give rise to preserved tissue in peats are often composed chiefly of cells with cellulosic (unlignified) walls, which frequently retain the birefringence characteristic of cellulose. Yet unaltered polymeric cellulose is present in very low concentration and, if inserted into peat as cotton, is rapidly destroyed. Our objective is to resolve this paradox and also identigy chemical changes undergone by any lignin that escapes depolymerization. Cores of peat from four environments in the Florida Everglades and one in Okefenokee Swamp (Georgia) are being studied. Size separation of peat from various depths by slurrying in water and passing through an 80 mesh sieve is an effective method of segregating rootlets and other plant tissue from fine-grained humic matter. In most cases, the various plant tissue fragments seem to consist chiefly of the principal plant polymers (cellulose and lignin), though these are somewhat oxidized and cellulose tends to decrease with depth. The fine-grained humic matter contains more or less the same structural features as the plant polymers, but shows bands of different shapes and relative intensities. In the case of the Cypress peat (only), the spectra of coarse and fine materials are quite similar. Thus there is evidence that cellulose does survive in some peats and that the polymers can be somewhat altered without destruction of cellular morphology.

Determination of aromatic and aliphatic CH groups in coal by FT-i.r.: 1. Studies of coal extracts

Abstract A set of coal extracts have been characterized by FT-i.r. and proton n.m.r. spectroscopy. The n.m.r. measurements of aliphatic and aromatic hydrogen allow a direct calibration of the absorption coefficients of appropriate i.r. bands. This allows methods for calculating these coefficients based on relating i.r.-band intensities to elemental hydrogen to be tested directly. Reasonable agreement was obtained.

Dependence of coal liquefaction behaviour on coal characteristics. 3. Statistical correlations of conversion in coal-tetralin interactions

Abstract The liquefaction behaviour of coals can vary over a wide range depending on both their chemical and petrographic characteristics. Sixty-eight coals have been studied under standard liquefaction conditions, in the presence of tetralin but with no added catalyst or molecular hydrogen. Simple correlations between conversion and individual coal parameters proved unsatisfactory. A novel approach utilizing a stepwise multiple regression analysis led to a number of linear equations relating conversion simultaneously to several coal characteristics. Such linear equations provide a basis for accurately predicting liquefaction behaviour and confirm that wise selection of appropriate feedstocks will have an important economic value. It seems permissible to infer that the behaviour of coals in any processing conditions can only be adequately accounted for by consideration of at least three coal properties; attempts to correlate coal properties solely with a rank parameter, such as carbon content, can no longer be considered adequate.

Characterization and classification of Rocky Mountain coals by Curie-point pyrolysis mass spectrometry

A set of 102 coal samples from the Rocky Mountain coal province, selected from the Penn State Coal Sample Bank, was analysed by Curie-point pyrolysis mass spectrometry in combination with computerized pattern recognition techniques. The spectra obtained were shown to be quite representative for the coal seams with characteristic differences often present between different seams, fields or regions within the Rocky Mountain Coal province. In general, the spectra were found to be dominated by homologous ion series, e.g., representing dihydroxybenzenes, phenols, naphthalenes, benzenes, alkenes, dienes, alkyl fragments and sulphur compounds with varying degrees of alkyl substitution. The relative abundances of dihydroxybenzenes and naphthalenes were shown to correlate closely with differences in rank, whereas those of phenols, aliphatic hydrocarbons and sulphur compounds appeared to correlate more closely with differences in depositional environment. Different spectra -dominated by aliphatic compound series -were obtained from several samples of a boghead coal (Cannel King seam). Moreover, spectra of two of these boghead coal samples, known to be severely weathered, showed markedly increased CO2+ and C6H6+ signals, indicating the presence of benzenecarboxylic acids. Factor analysis of pyrolysis m.s. data revealed the two main underlying chemical tendencies to be a shift from heteroatomic compounds to hydrocarbon series with increasing rank and a difference in degree of aromaticity corresponding primarily to differences in depositional environment. The dominant rank-related factor exhibited a clear coalification break between the ASTM hvC bituminous and hvB bituminous ranks and appears to represent a significant shift in coalification mechanisms. It was demonstrated that rank-dependent differences in the pyrolysis mass spectra enable correct classification of the spectra into four ASTM rank classes (subbituminous, hvC, hvB and hvA bituminous) in 90% of all cases. Moreover, the discovery of a marked aliphaticity/aromaticity factor in the data could be useful for the direct measurement of aromaticity (fa) from pyrolysis mass spectra of whole coals.