Macromolecular Structure Of Coal Research Articles

Changes in the macromolecular structure of coals with pyrolysis temperature

This paper describes a study of the effect of pyrolysis temperature on the macromolecular structure of coal, using solvent swelling techniques. Heat treatment initially dissociates the intermolecular interactions in the coal and cleaves some cross-links, leading to increase in the solvent swelling of the coal, which indicates a decrease in the cross-link density. The solvent swelling reaches a maximum before cross-linking reactions predominate, causing a progressive increase in cross-link density and a decrease in solvent swelling. For lower-rank coals there appears to be an overlap (near the temperature of minimum cross-link density) of the dissociation of intermolecular interactions and thermal decomposition. Appreciable decrease in the apparent cross-link density of high-rank coals as indicated by increase in solvent swelling was observed only after thermal decomposition had commenced. Major decomposition involves cross-linking reactions leading to the formation of chars. However, the solvent swelling characteristics continue to change above the resolidification temperature, eventually ceasing at ∼600°C. The results are discussed in relation to measurements of thermoplastic properties and devolatilization characteristics.

96/03520 Viscoelastic property and macromolecular structure of coal

96/03520 Viscoelastic property and macromolecular structure of coal

96/03772 Changes of macromolecular structure of coals in the processes of reduction and reductive alkylation in liquid ammonia

96/03772 Changes of macromolecular structure of coals in the processes of reduction and reductive alkylation in liquid ammonia

Some aspects of the generation of coking pressure during coal carbonization

The relations between the gas pressure developed during carbonization in coke ovens, the changes in the coal macromolecular structure, thermoplastic properties, devolatilization with respect to temperature and coke porosity were investigated. The macromolecular structure, i.e. the apparent cross-link density, was characterized by the solvent swelling technique using pyridine as solvent for coals carbonized in the temperature range 300–600°C. The thermoplastic properties were assessed using constant-shear-rate and Gieseler plastometry and dilatometry. The thermal decomposition of the coal macromolecular structure starts prior to the softening of coal and the development of thermoplasticity. The temperature at which the apparent cross-link density reaches a minimum is close to the plastometry caking temperature, at which the maximum particle cohesion occurs. After the cross-link density reaches a minimum, primary decomposition of the coal macromolecular structure occurs, resulting in the development of thermoplasticity and the formation of new cross-links. The changes in microporosity with temperature correlate with the changes in the macromolecular structure, thermoplasticity and devolatilization. Initially, the microporosity increases as the cross-link density decreases, due to the opening up of the structure caused by the cleavage of cross-links. As carbonization proceeds, the microporosity decreases due to the blocking of the micropores by plastic material and the formation of new cross-links, until a minimum is reached in the thermoplastic phase. Thereafter it increases again due to the opening up of microporosity associated with devolatilization and the development of the semicoke microporous structure. The gas pressure in the plastic layer 100 mm from the oven wall (halfway between the oven wall and the oven centre) starts to rise at the caking temperature and reaches a maximum close to the resolidification temperature of maximum weight loss rate. In contrast, the gas pressure in the oven centre reaches a maximum at the caking temperature. This difference is discussed from the viewpoint of the existence of the zones of low gas permeability and the migration of the plastic layer. For dangerously swelling coals, the maximum rate of weight loss with respect to temperature occurs in a temperature range where the cross-link density of the macromolecular structure is high. A qualitative model based on the comparison of the rate of release of volatiles in relation to the cross-link density of the macromolecular structure is proposed.

Use of 2,2-Dimethoxypropane and 1H NMR To Distinguish and Quantify the External and Internal Sorbed Water in Coals

Physisorbed and chemisorbed water in coal can be effectively removed by the use of 2,2-dimethoxypropane (DMP) which reacts with the water to form methanol and acetone. This reaction is rapid and endothermic. An 1H NMR method, based on this reaction, was developed to measure the amount of water in coals of different rank. Integrations of the methyl resonances from acetone and the methylene resonances of cycloheptane, an internal hydrogen standard, were used to determine the number of moles of water reacted. The method was also used to determine the diffusion kinetic parameters and type of diffusion associated with the chemical dehydration of coals. The initial mechanism for the diffusion of the solvent−reactant into the macromolecular structure of coal can be either Fickian or Case II depending on the coal. From the kinetic study, it was found that external and internal sorbed water were removed sequentially. Free or surface sorbed water is nearly instantaneously removed followed by the water in the intern...

96/01202 Some aspects of changes in the macromolecular structure of coals in relation to thermoplastic properties

96/01202 Some aspects of changes in the macromolecular structure of coals in relation to thermoplastic properties

Some aspects of changes in the macromolecular structure of coals in relation to thermoplastic properties

The development of coal thermoplasticity during the primary devolatilization region is critical in determining coke structures. The solvent swelling technique was used to study the changes in macromolecular structure of four coals of different rank (902 to 203 in the British Coal classification scheme) during carbonization to temperatures up to 600°C. The results were compared with the thermoplastic characteristics of the coals. The dilatometric and gas permeability properties are discussed in terms of changes in macromolecular structure. The study of the macromolecular structure provides new insight into the development of thermoplasticity and coke structure.

95/05642 Pretreatment of coal. Potentiality of microwave and gamma-ray pretreatments in the desulfurization, demineralization, and comminution

The effect of γ-irradiation on the extractability of lignite and coal has been investigated. The solubility of Kutch lignite and sub-bituminous Samla coal irradiated in aerial, aqueous, and CCl4 media at varying γ-doses (50, 100, and 150 Mrad) in different solvents, i.e., benzene, ethanol, azeotropic 1:1 ethanol-benzene mixture, and pyridine was determined. The radiation dose of up to 100 Mrad was found to be most effective in increasing the solubility, after which it either decreased or levelled off. Maximum solubility upon CCl4 irradiation was observed in all solvents in comparison to aerial and aqueous irradiation. The increase or decrease in solubility has been attributed to either degradation or cross-linking of polyaromatic groups - or possibly an interplay of both, in the macromolecular structure of coal and lignite during γ-irradiation, wherein the former, i.e. degradation, gives rise to weakening or breakdown of cohesive secondary forces rather than primary linkages, whilst the constancy or decrease in solubility might be due to polymerisation or cross-linking. The increase in solubility as a consequence of CCl4 irradiation is ascribable to radiation chlorination of coal and lignite during the radiolysis of CCl4.

95/03254 The effects of oxidation on the macromolecular structure of coal

95/03254 The effects of oxidation on the macromolecular structure of coal

The effects of oxidation on the macromolecular structure of coal

The effect of oxidation on the macromolecular structure of four coals of rank 902 to 204 in the British Coal classification scheme was investigated. Various particle size ranges of the coals were oxidized in air at 200°C for 24 h. Oxidation led to an increase in the extent of swelling in pyridine, which indicates a decrease in the covalent cross-link densities of the coals. Unlike that of the initial coals, which can be described by Fickian diffusion and relaxation processes, the swelling of the oxidized coals occurred by a two-stage process. This behaviour was attributed to the differences in extent of oxidation with increasing depth in the coal particles. A two-stage swelling process was observed regardless of whether a well-defined oxidation front was observed by optical microscopy. FT-i.r. spectra indicated that oxidation reduced the aliphatic:aromatic ratio, increased the hydroxyl:aromatic ratio and increased the carbonyl functionality in the coals. The results are consistent with breaking of the cross-links in the coal by severe oxidation.

95/01135 Coal macromolecular network structure analysis: Solvent swelling thermodynamics and its implications

95/01135 Coal macromolecular network structure analysis: Solvent swelling thermodynamics and its implications

Chemical Structure of Organic Sulfur Compounds in Extracted Oils and Hydrogenated Oils Derived from Coals Examined by Means of GC-FPD and GC-LVEI MS.

The purpose of this study is to elucidate the bonding types of organic sulfur compounds in macromolecular coal structure. High sulfur containing coals, Illinois No. 6 (C: 77.7, S: 2.4wt%) and Miike coal (C: 84.5, S: 1.1wt%, Japan) were examined. It consisted of study on the chemical structure of sulfur containing compounds in extracted oils which are n-hexane soluble, and hydrogenated oil derived from pyridine insoluble residue by hydrogenation. Capillary column GC equipped with FPD detector, which enables to determine specifically the sulfur element, and for this purpose, GC-LVEI MS analyses were provided. Species of organic sulfur compounds in extracted oil and hydrogenated oils were determined, to compare between those of lower rank Ilinois No. 6 coal and bituminous Miike coal. The 2-4 ring aromatic thiophenes consisting of C1-C5 benzothiophenes, C0-C4 dibenzothiophenes and benzonaphthothiophene were found in the higher ranking Miike coal, whereas the lower ranking Illinois No.6 coal contained 2-3 ring aromatic thiophenes with C1-C6 benzothiophene and C0-C6 dibenzothiophene. Species and alkyl carbon distribution of organic sulfur compounds for both extracted oil and hydrogenated oil were found to be approximately similar with each other.

95/00051 Study of relation between electric conductivity and coal macromolecular structure

95/00051 Study of relation between electric conductivity and coal macromolecular structure

Dynamic Detection of a Phase Transition for Illinois No. 6 Coal in Pyridine by Nuclear Magnetic Resonance Imaging (NMRI) and NMR Spectroscopy

An Illinois No. 6 coal preswollen in pyridine was allowed to undergo slow deswelling by solvent evaporation. The process was monitored by NMR and NMRI techniques in order to better understand coal's macromolecular structure and mobility of solvent within the coal. Pyridine concentration profiles and spin-spin relaxation times measured by conventional 1 H NMR suggest that pyridine diffusion in the coal network during the initial stages of the deswelling process is Fickian and that the pyridine exists within two regimes of molecular mobility. NMR imaging perpendicular to and parallel to the coal bedding plane shows that the deswelling process follows nearly isotropic behavior. Once the pyridine concentration decreases to approximately 0.5 of the initial equilibrium concentration, a dramatic increase in the deswelling rate and decrease in pyridine concentration are observed, implying that a phase transition occurs at this point in the coal-pyridine system

Observation of first- and second-order transitions during the heating of Argonne Premium coals

With the recent advent of the ability to separate coal into maceral concentrates of high purity, the individual constituents of coal can now be analyzed separately, without their mutual interference, giving a much better understanding of the macromolecular structure of coal. The sporinites from two Pennsylvanian age coal samples (Illinois Basin, U.S.A.) were studied, one from a vitrinite-rich high-volatile bituminous coal, the other from a liptinite-rich high-volatile butuminous coal of slightly higher rank. Sporinites were isolated from each coal by density gradient centrifugation. The sporinite of the vitrinite-rich coal was compared chemically and petrographically with the parent coal and with the sporinite of the liptinite-rich coal. The fluorescence spectrum of the sporinite from the liptinite-rich coal is shifted to the red end of the spectrum, which may be accounted for by the somewhat higher rank of the sample and/or by differences in the original assemblage of spores. The lack of chemical differences between the extracts of the sporinite and its whole coal reinforce the concept of bitumen as an homogeneous mobile phase pervading the coal. Thus, extract chemistry seems an unsuitable technique for distinguishing between macerals from the same coal. Hopane and sterane distributions in the sporinite and parent coal pyrolyzates are very similar, but the two materials can be readily distinguished by the distribution of tetracyclic diterpanes of the phyllocladane type, which are biological marker compounds derived from higher plant material. Overall, the sporinite is considerably more paraffinic in character and has a greater preponderance of straight-chain alkane moieties than the coal as a whole. In the case of the vitrinite-rich coal, the whole-coal structure appears significantly more polyaromatic than the sporinite. The distributions of thiophenic compounds differ in the pyrolyzates of the two materials. The sporinite from the liptinite-rich coal is even less polycondensed than the sporinite from the vitrinite-rich sample. The chemical and petrographic differences of the two sporinites probably reflect the different assemblages of spores in the original peats and their different diagenetic histories.

New applications of differential scanning calorimetry and solvent swelling for studies of coal structure: Prepyrolysis structural relaxation

Differential scanning calorimetry and solvent swelling have been applied for identifying physical transition temperatures in the macromolecular structure of coals. The transition processes seem to be associated with physical relaxation of the coal structure and are irreversible processes. In Pittsburgh no. 8 coal, one physical transition was noted at 250–300 °C (at 8 °C min −1) without any significant accompanying weight loss. Illinois no. 6 coal does not exhibit such a relaxation process at these temperatures. Coals of higher rank than high volatile bituminous i.e. Upper Freeport and Pocahontas no. 3 coals, exhibit structural relaxation just before the major thermal decomposition process and a sharp increase in solvent swellability accompanies this relaxation. In the case of both the Pittsburgh no. 8 and the Upper Freeport coal, structural relaxations at around 360 °C seem to coincide with release of ‘guest molecules’. In addition, significant shifts in transition temperatures have been observed with heating rate. In coals of higher rank than high volatile bituminous, pyridine exposure prior to thermal treatment does not influence the transition temperatures, indicating that heat is more effective than pyridine in relaxing the macromolecular structure, as suggested by Sakurovs et al. On the other hand, CS 2 pyridine mixtures are effective at relaxing the structure of the Upper Freeport coal, even at room temperature.

The dynamic nature of coal's macromolecular structure: viscoelastic analysis of solvent-swollen coals

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe dynamic nature of coal's macromolecular structure: viscoelastic analysis of solvent-swollen coalsGeorge D. Cody, Alan Davis, and Patrick G. HatcherCite this: Energy Fuels 1993, 7, 4, 463–468Publication Date (Print):July 1, 1993Publication History Published online1 May 2002Published inissue 1 July 1993https://doi.org/10.1021/ef00040a004RIGHTS & PERMISSIONSArticle Views74Altmetric-Citations13LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (722 KB) Get e-Alerts Get e-Alerts

The relation between coal macromolecular structure and solvent diffusion mechanisms

The mechanisms of solvent diffusion into coal of a set of substituted pyridine molecules and a set of straight-chain amine molecules were determined using dynamic volumetric swelling. The diffusion mechanism varies with the extent to which the diffusing solvent reacts with the coal, changing the viscoelastic properties. For basic solvents this is related to the number of hydrogen bonds disrupted by the diffusing solvent. In turn, this is a function of the coal structure; in particular, the hydrogen bonding is related to the effective cross-link densities before and after solvent interaction.

THE EFFECT OF TEMPERATURE TREATMENT ON PENETRANT TRANSPORT IN COAL

Abstract The macromolecular structure of coals thermally treated at 35°C, 100°C and 150°C was investigated by dynamic penetrant transport in thin coal sections. The effects of temperature, carbon content in coal, and penetrant type on the transport mechanism were investigated. Dynamic swelling studies showed that penetrant transport into coal is a function of the average molecular weight between crosslinks, Mc. The penetrant transport mechanism at low activity is Fickian diffusion. The transport mechanism deviates from Fickian diffusion to anomalous transport, when the carbon content in coal and penetrant activity increase. Variations of the diffusion coefficients and relaxation constants were determined using a diffusion/relaxation coupled model.

Interpretation of high temperature second order phase transitions for coal/solvent systems

Letter to the editor. An understanding of the physical properties of coal macromolecular structure is fundamental to understanding the processes that take place during coal processing such as liquefaction.