Coal Molecular Structure Research Articles

The Effect of an Iron-based Catalyst on Coal Liquefaction at High Temperature

Quick coal liquefaction at high temperature is a novel method of coal direct liquefaction, which is based on the initial highly reactive characteristics at the beginning of coal liquefaction reaction and the different chemical bond energy in molecular structure of coal, so the essence of coal liquefaction can be essentially revealed by the method. The catalyst plays a key role in the coal liquefaction process. Taking Yanzhou coal as a case, this article studies the effect of homemade iron-based catalyst on quick coal liquefaction at high temperature in a micro autoclave for the first time.

Low Temperature Oxidation Effects on Lignite Molecular Structure

The paper studied the change of the coal characteristics based on the influence of lignite naturally oxidated in air. The original lignite and lignite naturally oxidated under different time were analyzed by the FTIR technology. The reason that metamorphism of lignite was vulnerable by oxygen was analyzed from the side of coal molecular structure. It indicates that lignite of a low rank coal easily oxidated is mainly because lignite has more active groups in coal molecular such as methyl, methylene, hydroxyl, aromatic ether, oxygen button and ether key. In lignite molecular, side chains of aromatic ring structure unit is firstly oxidized. The bridge button or side chains of coal molecular structure unit are easily oxidized at the same time with the structure of the bridge between units fracturing oxidation. Number of aromatic hydrocarbons remains stable after oxidation. General trend of cycloparafin hydrocarbon as well as aliphatic hydrocarbon are gradually reduced over the oxidized time.

Co-liquefaction behavior of a sub-bituminous coal and sawdust

The co-thermolysis and co-liquefaction properties of Shenhua coal and sawdust were investigated in this study. The synergistic effect between Shenhua coal and sawdust in co-liquefaction was probed. TG/DTG analysis suggests that the sawdust, which has lower pyrolysis temperature, can promote the thermolysis of Shenhua coal, resulting in more volatile matter to be released from coal molecular structure during the co-thermolysis process. This will result in the larger weight losses of their mixture compared to the corresponding weighted mean values of individual pyrolysis. The individual liquefaction of Shenhua coal and sawdust shows that sawdust has higher liquefaction activity compared to Shenhua coal. It gives much higher liquefaction conversion and oil yield than Shenhua coal at the same liquefaction conditions. Co-liquefactions of Shenhua coal and sawdust at different conditions were carried out. The results suggest that there exists an obviously synergistic effect during the co-liquefaction, and this synergistic effect is the function of liquefaction conditions. At high liquefaction temperatures and long reaction times, the synergistic effect decreases because of the increase of liquefaction activity of coal and lack of hydrogen donating ability of the system at the conditions, resulting in the increase of the rate of retrogressive condensed reactions. The largest enhancements in conversion of 16.8% and oil yield of 11.4% comparing with corresponding calculated weighted mean values of the individual liquefaction of Shenhua coal and sawdust were obtained at 400 and 380 °C, respectively in the co-liquefaction with 1/1 blending ratio of coal/sawdust.

Upgrading of Yi’an gas coal by low temperature pyrolysis under different atmospheres

The quality of Yi’an gas coal before and after low temperature upgrading under either a N 2 or H 2 atmosphere was examined by thermogravimetric and infrared analyses. The effect of upgrading on the prepared coke quality was analyzed. The results show that the carboxyl and phenolic hydroxyls in the coal molecular structure are removed after upgrading by low temperature pyrolysis under either N 2 or H 2 atmospheres. This improves coal caking properties to a certain extent. The upgrading effect under a H 2 atmosphere is remarkably better than the effect observed after upgrading under N 2. Compared to coke obtained from raw coal, the compressive- and micro-strength of the cokes obtained from upgraded coal are greatly improved. The effect on coke reactivity with CO 2 is not significant. The best upgrading temperature for Yi’an gas coal under either a N 2 or H 2 atmosphere is 250 or 275 °C respectively.

Research on the Mechanism of Quick Coal Liquefaction at High Temperatures

In this article, the mechanism of quick coal liquefaction at high temperatures is investigated theoretically and experimentally. Based on the bond energy of some model compounds in the coal molecular, it is pointed out that the bridge bonds of coal molecular structure during quick coal liquefaction at high temperatures can be broken. Taking Yanzhou bituminous coal as the research object, pyrolytic behavior of coal molecular and the mechanism of hydrogen-donor of quick coal liquefaction at high temperatures are studied. The reaction mechanism of quick coal liquefaction at high temperatures has been proposed.

Risk assessment of underground coal fire development at regional scale

Abstract Underground coal combustion is a phenomenon known worldwide. Coal fire monitoring and risk assessment provide important input data for the delineation of coal fire zones and planning of extinguishing activities. At present, research on coal fire risk focuses mainly on the probability assessment of spontaneous combustion at micro scale, based on laboratory investigations of coal molecular structure and composition, and their impact on the combustion process. Coal fire risk assessment at a larger scale, such as for mines, relies on geological factors and aspects of mining engineering and mine management. These scales, however, are insufficient when considering extinguishing activities in larger areas. In order to fill these gaps, we studied risk assessment of underground coal fire development (UCFD) at a regional scale. The factors impacting on coal fire development were analyzed under three different aspects: coal composition and structure which can influence the direction of underground coal combustion; topography and geology which determine the burning environment; and climatic conditions and human activities which trigger combustion processes. Based on this analysis, a regional underground coal fire risk assessment (UCF-RA) index system was established; it is predicated on the assumption that all indices contribute equally to coal fire risk. Data layers of 1 km × 1 km spatial resolution for each index were calculated and overlaid. Xinjiang Uygur Autonomous Region was selected as a validation area. In view of local conditions and the availability of relevant data, the index system was modified; the applied method, however, remained unchanged. Assessment results are generally satisfying and can be used for monitoring and extinguishing of underground coal fires (UCFs) in Xinjiang.

A newly proposed view on coal molecular structure integrating two concepts: Two phase and uniphase models

Concept of coal molecular structure was reexamined on the basis of detailed information concerning aliphatic moieties of coal and the reactions occurred during coalification process. Based on the observed similarity of the distribution of chain length between alkylene bridge bonds and alkyl pendant groups on coal aromatic cluster, the authors have already proposed [Nomura, M., Murata, S., Kidena, K. 2004a. Some view on the solubilities of coals toward solvents. Proceedings of 21st Annual International Pittsburgh Coal Conference, No. 12-4.] the presence of common intermediates in the coalification process which results in uniphase structure under reductive conditions and two phase structure under oxidative conditions, respectively. The present paper proposes, the concept that the reactivity of the coal aromatic moieties for common intermediates and/or the stability of common intermediates govern the reactions leading to a two phase structure or uniphase structure in more rationalized way as coalification is believed to proceed under reductive conditions, especially at its late stage. Brown and subbituminous coals have relatively many oxygen-containing functionalities on aromatic moieties so that their aromatic rings are activated for radical reactions. Common intermediate radicals, aryl alkyl radicals, from cleavage of alkyl pendant groups on aromatic rings and alkylene bridge bonds attack neighboring aromatics to form entanglement-like structure in an easy way. These structures are less soluble to organic solvents due to its entanglement character. Bituminous coals with high solubility toward CS2/NMP solvents tend to have carbon contents from 85 to 87% (daf. basis), their aromatic moieties being so stable that intermediate radicals cited above can attack more selectively the neighboring aromatic moieties: they have less tendency to make such bridge bonds to form cross linked structures, the resulting coal molecules being not entangled like uniphase. In the case of coals having more carbon than 87% or bituminous coals with less carbon than 85%, the resulting coal molecules become less soluble toward organic solvents: In the higher rank coals, the aromatic rings are so large and so stable that their solubility toward solvent are intrinsically low. In addition to this, it is supposed that bridge bonds are cleaved to make the structure with less cross linking. Their stacking tendency should be also considered as other reason for low solubility to solvent. On the other hand, less solubility of the lower ranked bituminous coals can be rationalized partly, in an analogy with the behavior that the brown and subbituminous coals show, despite of their relatively large aromatic clusters.

ＥＳＲによる急速加熱炭の石炭構造解析

Coal was heat-treated up to the softening temperature under the 2 types of heating conditions (10°C/min, 104°C/min). Spin concentration by high temperature Iusitu ESR, and the saturation behavior of the ESR spectrum were measured. Based on that result, effect of rapid preheating on coal molecular structure was examined.(1) Because the change in coal chemical structure by the cracking reaction is taking place, spin concen-tration of slow preheated coal is higher than that of rapidly preheated coal and raw coal. At 300°C or more, the spin concentration of rapidly preheated coal is same profile as raw coal. In the case of rapid preheating, it is indicated that the degree of coal structure change by cracking reaction is small.(2) The following results were obtained as the saturation power of ESR was measured. At 250°C or more, the saturation power of slow preheated coal declines as the temperature rises. One side, it confirmed that the saturation power of rapidly preheated coal became large at 370°C. The increase in saturation power indicates that the relaxation of coal structure progressed about coal molecular structure part that can be observed with ESR.

04/02657 Study of coal molecular structure and model compound reaction: Li, Y. and Wang, X.-H. Meitan Jishu, 2003, 22, (5), 100–102. (In Chinese)

Covalent organic frameworks (COFs) are a new class of porous materials receiving much attention due to their unique characteristics. However, COFs have been usually synthesized under harsh and complicated conditions, limiting their practical applications. We propose a surfactant-free strategy to controllably synthesize an imine-based covalent organic framework (COF) nanomaterial in water at room temperature. Introduction of tiny amounts of co-solvents not only achieves the morphology and size control of COFs but also ensures stability of COF nanomaterials in aqueous solution. Moreover, water as a solvent plays an important role in the size adjustment of COFs. The surface area of the obtained COFs was approximately 398 m2/g with a pore size distribution of about 2.8 nm. In addition, the COFs displayed a good crystallinity.

Coal structure studied by means of molecular acoustics methods

In this paper, a brief overview of our works on macromolecular network and molecular structure of coal via the elastic properties studies has been made. The recent investigations of raw, demineralized and solvent-treated coals, as well as coal extracts by means of molecular acoustics methods, have been described.

The measurement of coal porosity with different gases

Sorption processes can be used to study different characteristics of coal properties, such as gas content (coalbed methane potential of a deposit), gas diffusion, porosity, internal surface area, etc. Coal microstructure (porosity system) is relevant for gas flow behaviour in coal and, consequently, directly influences gas recovery from the coalbed. This paper addresses the determination of coal porosity (namely micro- and macroporosity) in relation to the molecular size of different gases. Experiments entailed a sorption process, which includes the direct method of determining the “void volume” of samples using different gases (helium, nitrogen, carbon dioxide, and methane). Because gas behaviour depends on pressure and temperature conditions, it is critical, in each case, to know the gas characteristics, especially the compressibility factor. The experimental conditions of the sorption process were as follows: temperature in the bath 35 °C; sample with moisture equal to or greater than the moisture-holding capacity (MHC), particle size of sample less than 212 μm, and mass ca. 100 g. The present investigation was designed to confirm that when performing measurements of the coal void volume with helium and nitrogen, there are only small and insignificant changes in the volume determinations. Inducing great shrinkage and swelling effects in the coal molecular structure, carbon dioxide leads to “abnormal” negative values in coal void volume calculations, since the rate of sorbed and free gas is very high. In fact, when in contact with the coal structure, carbon dioxide is so strongly retained that the sorbed gas volume is much higher than the free gas volume. However, shrinkage and swelling effects in coal structure induced by carbon dioxide are fully reversible. Methane also induces shrinkage and swelling when in contact with coal molecular structure, but these effects, although smaller than those induced by carbon dioxide, are irreversible and increase the coal volume.

00/02217 Computer simulation techniques for molecular structure of coal for advanced coal conversion technology

00/02217 Computer simulation techniques for molecular structure of coal for advanced coal conversion technology

Modelling the relationship of coal structure to char porosity

This paper investigates the ‘average’ coal molecular structure of Pittsburgh #8, and how that structure changes during pyrolysis to form char. Chars were prepared at different stages of pyrolysis in a heated wire mesh reactor, and analysed by FTIR spectroscopy of the C–H stretching regions. This yielded information on the aromaticities and the concentrations of aromatic and aliphatic hydrogen and carbon atoms within the coal and chars. From this, elemental analysis, and existing literature data on the structural properties of bituminous coals and chars, average molecular models were constructed which were geometry optimised by energy minimisation using a commercial molecular modelling package. The coal model structure has a molecular weight of 8189 amu, and an aromaticity of 0.79. Average char structures which are consistent with experimental data (aromaticities of 0.90 or higher) require large extended aromatic clusters and extensive Ar–Ar cross-linking The resulting molecular conformations exhibit microporosities and densities comparable to those expected from experimental measurement. The derived structures also have implications for predictions of char combustion behaviour.

遺伝的アルゴリズムを用いた石炭分子構造の構築

遺伝的アルゴリズムを用いた石炭分子構造の構築

98/00802 Computer-aided construction of coal molecular structure using construction knowledge and partial structure evaluation

98/00802 Computer-aided construction of coal molecular structure using construction knowledge and partial structure evaluation

Computer-Aided Construction of Coal Molecular Structure Using Construction Knowledge and Partial Structure Evaluation

A computer-aided construction of molecular structure model for coal organic materials is proposed in this paper. In this method, the chemical fragments of coal organic materials are obtained by using the structural data of typical Japanese bituminous Akabira coal. First, some partial structures are selected from candidates of the structure, which are constructed by connecting input fragments based on construction knowledge from basic chemical experiments and practical experiments. Next, the partial structures are narrowed down to an appropriate one in terms of three-dimensional conformation by using partial structure evaluation. We found that this method can derive molecular structures more scientifically and in more time-saving way than the handmade structures.

97/02488 Change in the associated molecular structure of coals in pyridine/carbon disulfide mixed solvents

97/02488 Change in the associated molecular structure of coals in pyridine/carbon disulfide mixed solvents

97/01571 Evolution of coal molecular structure in metamorphism and changes in coal thermal characteristics

97/01571 Evolution of coal molecular structure in metamorphism and changes in coal thermal characteristics

95/01128 Applications of molecular modeling in coal research

Over the past several years, molecular modeling has been applied to study various characteristics of coal molecular structures. Powerful workstations coupled with molecular force-field-based software packages have been used to study coal and coal-related molecules. Early work involved determination of the minimum-energy three-dimensional conformations of various published coal structures (Given, Wiser, Solomon and Shinn), and the dominant role of van der Waals and hydrogen bonding forces in defining the energy-minimized structures. These studies have been extended to explore various physical properties of coal structures, including density, microporosity, surface area, and fractal dimension. Other studies have related structural characteristics to cross-link density and have explored small molecule interactions with coal. Finally, recent studies using a structural elucidation (molecular builder) technique have constructed statistically diverse coal structures based on quantitative and qualitative data on coal and its decomposition products. This technique is also being applied to study coalification processes based on postulated coalification chemistry.

Direct observations on the interaction of coals with pitches and organic compounds during co-pyrolysis

Proton magnetic resonance thermal analysis (p.m.r.t.a.) was used to monitor the pyrolysis behaviour of a variety of coals, their mixtures with four different addivites, and each of the additives alone. A model was developed to quantify the effects of small quantities of an additive on the thermoplastic and other molecular properties of coal, by measuring the difference in behaviour of the mixture from that predicted assuming no interactions between the coal and additive. This model was used to define a solvation index, which was used in turn to estimate the capacity of an additive to destabilize or ‘solvate’ the molecular structure of coals. It was found that 1. (1) pitches — both coal-tar and petroleum-derived — ‘solvate’ bituminous coals at temperatures significantly below the coal fusion or ‘softening’ temperature but do not solvate subbituminous or brown coals; 2. (2) this capacity to solvate bituminous coals is shared by the two other aromatic additives tested — decacyclene and p-quaterphenyl; and 3. (3) the rates of coking of both pitch and decacyclene are greatly increased when they are co-pyrolysed with low-rank coals, this enhancement decreasing with increasing rank of the coal.