Coal Pyrolysis Research Articles

Coal Petrography and Rock-Eval Pyrolysis of Coals of Barakar Formation of Kothagudem and Godavari Sub-Basins, Pranhita-Godavari Basin, India: Implication to Depositional Environment

ABSTRACT Understanding the depositional environment of coals is crucial for determining the geological history and potential resource assessment. This study employs coal petrography and Rock-Eval pyrolysis to analyse the coals of the Barakar Formation in the Kothagudem and Godavari Sub-Basins, within the Pranhita-Godavari Basin, India. By interpreting the organic composition and thermal maturity of these coals, this study aims to provide valuable insights into their depositional conditions and hydrocarbon potential. The physicochemical and reflectance (0.30% and 0.44%) investigations indicate that the coal samples are sub-bituminous and of low rank. In the Kothagudem and Godavari sub-basins, vitrinite (26.7–70.6%) is the predominant maceral, followed by liptinite (10.7–14.7%) and inertinite (5.3–30.0%). The materials have a high total organic carbon (TOC) content (43.37 to 68.43%) and the capacity to generate hydrocarbons, as indicated by the results of Rock-Eval pyrolysis and analysis. Tmax interpretations (415°C to 427°C) suggest that the samples are primarily immature for oil production. The type II and type III kerogens that make up the majority of the coals in the sub-basins are produced mostly by terrestrial plants, which are the main source of organic matter. This kerogen is typically gas-prone and has minimal potential for oil generation. However, the primary phase was wet moor with intermittent moderate to severe floods and a few alternative dry spells that resulted in oxic and anoxic moor conditions.

Mechanistic exploration of tar-rich coal pyrolysis through ReaxFF MD simulation coupled with experimental validation

Mechanistic exploration of tar-rich coal pyrolysis through ReaxFF MD simulation coupled with experimental validation

Physicochemical and combustion characteristics of pyrolyzed coal and biocoal briquettes via thermogravimetric analysis

ABSTRACT Pyrolysis is highly regarded as a means to produce smokeless briquettes. This study investigated the effects of torrefaction and fast pyrolysis on the physicochemical and combustion characteristics of coal and biocoal briquettes. Biocoal briquettes were prepared with coal dust and rice husks using cassava starch gel as a binder, whereas no biomass was used for coal briquettes. The feedstocks were compacted in a briquetting machine and then dried in a solar dryer before pyrolysis in a muffle furnace fitted with a vacuum system. The proximate compositions were derived from thermogravimetric analysis (TGA), and the calorific values were calculated. The combustion characteristics were determined through thermogravimetry (TG-DTG) analysis. The functional groups were analyzed via Fourier transform infrared (FTIR) spectroscopy. The results revealed that biocoal briquettes with coal-to-rice husk ratios of 50:50 and 60:40, which were subjected to torrefaction for 30 min at 200°C, had the same volatile matter content (12%), but differed in other properties. The pyrolyzed coal briquette exhibited the highest flammability and combustion indices. Furthermore, some transmittance peaks shifted to lower or higher frequencies. This study demonstrates that the the properties of pyrolyzed briquettes are influenced by the pyrolysis temperature, feedstock and blending ratio.

Molecular Simulation of Graphene Growth Reactions at Various Temperatures Derived from Benzene in Coal Tar Aromatic Hydrocarbons

Coal tar, a by-product of the pyrolysis of coal, is rich in aromatic compounds that have the potential to facilitate the synthesis of graphene, a high-quality carbon material, via low-temperature chemical vapor deposition (CVD). This approach offers a promising avenue for the cost-effective and large-scale industrial production of graphene while minimizing energy consumption. Nevertheless, there is a paucity of research focused on the low-temperature synthesis mechanisms of graphene derived from aromatic compounds in the context of graphene growth. To achieve high-quality graphene synthesis from coal tar and its aromatic constituents at reduced temperatures, a comprehensive investigation into the reaction pathways of these aromatic compounds is essential. In this study, we meticulously simulate the pyrolysis of benzene, a key aromatic component of coal tar, across various temperature settings utilizing reactive force field (ReaxFF) methodology. Furthermore, we apply density functional theory (DFT) calculations, executed through the Vienna Ab initio Simulation Package (VASP), to assess the dehydrogenation energy associated with the adsorption of benzene on vapor-deposited copper foils. Our molecular dynamics simulations, enhanced by a mixed force field approach, revealed that the dehydrogenated benzene ring (C6 intermediate) acts as a critical precursor for graphene synthesis. This research significantly elucidates the reaction pathways of aromatic benzene in coal tar through molecular simulations conducted at different temperatures, both in the gas phase and on solid copper foil substrates.

Molecular Insights into the Pyrolysis of Bituminous Coals through Various Spectroscopy, Thermogravimetric-Mass Spectrometry Experiments and ReaxFF Molecular Dynamics Simulations

Molecular Insights into the Pyrolysis of Bituminous Coals through Various Spectroscopy, Thermogravimetric-Mass Spectrometry Experiments and ReaxFF Molecular Dynamics Simulations

Study on molecular structural heterogeneity of tar-rich coal based on micro-FTIR.

The coal molecular structure in micro-areas plays a critical role in matrix thermal conduction and volatile generation during the pyrolysis of tar-rich coal. However, as a major maceral contributing to hydrocarbon generation, the molecular structures of different micro-areas in vitrinite show heterogeneity, which still lacks research. Micro-FTIR technology was used in this study to characterize the molecular structure in different micro-areas of tar-rich coal with varying tar yields. It exhibits a significant advantage in obtaining the molecular structure of the coal surface at the micrometer scale compared to transmission FTIR. The results have shown: Even within the homogeneous vitrinite under a microscope, the molecular structural heterogeneity in different micro-areas is also marked. Specifically, the functional groups in the 1100-1800cm-1 band show a greater heterogeneity than the 2800-3000cm-1 and 700-900cm-1 bands. In the former, the variation of the C=C, C-O, and -CH2- contents is particularly pronounced, indicating that aromatic structures, ether bonds, and alkyl structures are the key factors leading to heterogeneity. Furthermore, samples with higher tar yields exhibit weaker molecular structural heterogeneity. The above research provides theoretical guidance for analyzing the pyrolysis behavior of tar-rich coal.

Experimental and simulated analysis for nitrogen migration behavior during coal rapid pyrolysis under Ar/CO2 atmospheres using a free-fall reactor

Experimental and simulated analysis for nitrogen migration behavior during coal rapid pyrolysis under Ar/CO2 atmospheres using a free-fall reactor

Multilevel screening and mechanism analysis of ionic liquids for separating pyridine from coal pyrolysis model oil

Multilevel screening and mechanism analysis of ionic liquids for separating pyridine from coal pyrolysis model oil

Exploring Pyrolysis Gaseous Tar Distribution and Combustion Temperature Identification in Coal Fire

ABSTRACT This paper establishes correlations between various pyrolysis products collected from the vicinity of the fire zone and the prevailing temperature using substance identification via GC-MS analysis. Further experimental comparisons among multiple substances reveal a strong correlation between phenols and temperature. This leads to the identification of temperature-specific products primarily composed of phenols, ultimately enhancing the accuracy of fire area temperature recognition. This experiment utilized a self-built fixed bed and GC-MS technology to qualitatively and quantitatively study the release characteristics of gaseous tars from lignite, long-flame coal, and gas coal at different temperatures (300°C, 350°C, 400°C, 450°C, 500°C) under pyrolysis conditions. The experimental results showed that there are significant differences in the tar components produced during pyrolysis among coals with different degrees of metamorphism. The composition ratios are all in the order of oxygen-containing organic compounds > aromatic hydrocarbons > aliphatic hydrocarbons, and the three most abundant organic compounds are phenol, o-cresol, and p-cresol. The types and quantities of organic compounds in coal pyrolysis tars are positively correlated with reaction temperature. Based on a third-order polynomial fitting of the total amount of compounds in pyrolysis tars and the corresponding temperature under pyrolysis conditions, the representative subclasses of each type of substance were further fitted. The results of the temperature correlation show that the fitting trend of phenols with temperature is similar to the overall trend and far superior to naphthalene organics and saturated alkanes. In the vertical comparison of phenolic content at different temperatures, common identifiable substances such as C8H10O and C23H32O2 are selected, and specific substance identification was provided for coal samples of different ranks of coal metamorphism. This ultimately provides a new approach for establishing a method to identify the combustion state of coal fires at 300–500°C.

Experimental investigation and ReaxFF simulation on pore structure evolution mechanism during coalification of coal macromolecules in different ranks

This analysis revealed the alterations in the pore structure of large organic molecules in coal during the process of coal pyrolysis. Nine models of macromolecular structures in coals, representing distinct coal ranks, have been built. The research results show that along with the increasing coal rank, the average microporous volume of medium rank coal is 0.0287 cm3/g. The average microporous volume of high-grade coal is 0.0662 cm3/g. The micropore volume and specific surface area of coal samples decrease in the order of high rank, low rank, and middle coal. The experimental measurements align with the ReaxFF pyrolysis simulation calculations, indicating a decrease in the hydrogen to carbon ratio and oxygen to carbon ratio of all coal molecules. Additionally, the pore volume and specific surface area exhibit a pattern of initially decreasing and then increasing. The simulation results of gas probes indicate that a majority of the pores with a diameter larger than that of CH4 molecules are found in the macromolecular structure models of low rank coal and medium to high rank coal. The conclusions are useful for us to understand the formation and development process of pores in coal reservoir. A two-dimensional representation of coal’s macromolecular structure was constructed using ChemDraw software. The Forcite module in Materials Studio software was used to perform geometric optimization and annealing kinetics simulation of a two-dimensional macromolecular structure model. The ReaxFF-MD module in Amsterdam Modeling Suite (AMS) 2020 software to model the pyrolysis of XJ coal macromolecules.

Two-dimensional spectroscopic analysis of sulphur group and pyrite transformations in coal coking

An accurate description of the sulphur migration process and mechanism is essential for guiding the selection and development of desulphurisation technology during the coking process, to increase the desulphurisation efficiency in the use of high-sulphur coking coal and decrease the sulphur content in the produced coke. However, the identified sulphur transformation mechanism in coal pyrolysis is not entirely applicable to the coking process due to variations in atmosphere, temperature and pressure. This work used numerous characterisation techniques in conjunction with experiments to quantitatively evaluate the transformation mechanism of both organic and inorganic sulphur throughout the coking process. The bond-breaking order of functional groups in sulphur during coking was obtained by the two-dimensional correlation spectroscopy analysis. The results show that desulphurisation in the coking process mainly occurs below 600 °C and 72.8% of sulphur in coal is retained in coke. Among them, FeS2 and sulphoxide are completely removed while sulphides are reduced by 67.9%. The content of sulphone increases by 46.1% because of the transformation of sulphoxide. Thiophenes and sulphates increase by 32.5% and 33.9%, respectively, as a result of the inorganic sulphur transformation and secondary reactions of sulphur-containing gases above 500 °C. Through Noda's theorem, the bond-breaking sequence of sulphur-containing functional groups in coal during the coking process is obtained as follows: Fe–S bond → thiol C–S bond → alkyl sulphide C–S bond → thiol–SH → aliphatic C–S bond → thioether C–S bond → sulphoxide S=O bond → sulphone, sulphoxide C–S bond. By clarifying the desulphurisation characteristics of different sulphur forms, suggestions and ideas for the development of desulphurisation technology of coking coal are put forward, which is helpful for the wide utilisation of high-sulphur coal.

Effect of Oxygen Concentration on Volatile Precipitation and Critical Ignition Point.

The purpose of this study was to investigate the impact of the oxygen concentration on the ignition of bituminous coal. Different oxygen concentrations and temperatures were used in the large-scale oxidation experiments to collect oxidized coals, which were then extracted with chloroform. And compare the critical ignition temperature of different mass samples. The liquid samples obtained were analyzed by using GC-MS and Fourier transform infrared spectroscopy. Fourier transform infrared spectroscopy was also used to characterize extracted oxidized coal. The results revealed that the critical ignition point of bituminous coal decreases by 229.4 °C when the mass sample increases from 5 to 300g. Furthermore, at the same temperature, an increase in the oxygen concentration in the atmosphere was found to enhance the pyrolysis of bituminous coal. The oxidation activity of coal initially decreased and then increased with the temperature rise. The ether bond formed below 150 °C is oxidized and decomposed above 175 °C, which is closely related to the ignition of the coal seam.

Mechanical and Microstructural Properties of Cement-Stabilized Soft Clay Improved by Sand Replacement and Biochar Additive for Subgrade Applications

Biochar (BC) is an eco-friendly material produced through coal pyrolysis and can improve the mechanical properties of cement-based construction and building materials. This research study explored the effects of BC and natural sand (Sand) replacement on the improved static and cyclic response of blended hydraulic cement (BHC) stabilized soft clay (SC) as a greener subgrade material. Unconfined compressive strength (UCS), indirect tensile stress (ITS), and indirect tensile fatigue life (ITFL) of the BHC-stabilized SC-BC-Sand samples were examined. Adding 10% BC to the BHC-stabilized samples was found to enhance cementitious products due to its porous structure and high water absorbability. The UCS, ITS and ITFL at this optimum ingredient were improved up to 315%, 347% and 862%, respectively, compared to the BHC-stabilized SC. Fourier transform infrared spectrometer, thermogravimetry differential thermal analysis and a scanning electron microscope with energy-dispersive -ray spectroscopy analyses the BHC-stabilized sample at the optimum ingredient showed the highest C-S-H and Ca(OH)2 in the pores. This investigation will encourage the utilization of BC to create both environmentally friendly and durable stabilized subgrade material.

Staged evolutionary features of the aromatic structure in high volatile A bituminous coal (hvAb) during gold tube pyrolysis experiments

Low-temperature pyrolysis of coal is a crucial step in the coal thermal conversion process and involves very complex physical and chemical reactions that can have different effects on the coal's structure. The thermal evolution behavior and transformation mechanism of the coal microstructure are not yet fully understood, which also limits the efficient utilization of coal to a certain extent. The aromatic structural features (including size, molecular ordering, nematic symmetry, stacking, and curvature) of the char produced from low-temperature pyrolysis of high volatile A bituminous coal (hvAb) from the Xutuan coal mine, China, were quantitatively assessed via high-resolution transmission electron microscopy (HRTEM) image processing and analytical techniques. The thermal transformation process and the mechanisms controlling it were explored. The results show that, except for the unexpected slight growth of aromatic sheets at 440 °C, the lower pyrolysis temperature (< 521 °C) contributed weakly to their size growth, whereas at higher temperatures (561–600 °C), it significantly increased their size. The aromatic molecular ordering tended to gradually change in three stages: increasing between 340 and 440 °C, decreasing between 440 and 521 °C and increasing again between 521 and 600 °C. The nematic symmetry strength of aromatic fringes also followed a similar pattern with temperature at different scales. Additionally, in addition to a very minor development trend at 440 °C, the stacking did not significantly change at temperatures below 521 °C but developed appreciably further with increasing temperatures at 561–600 °C; however, the average spacing of the stacks did not appear to be significantly reduced at all temperatures. The curvature of the aromatic sheets also varied in different temperature stages, i.e., initially slightly increasing (340–380 °C), then gradually decreasing (380–480 °C), later increasing again (480–521 °C), and eventually decreasing (521–600 °C). The properties of the chemical composition and structure of the initial coal play important roles in the thermal reaction behavior, and the physical and chemical reactions that dominate at the different temperature stages may be responsible for such wiggly trends in the evolution of the aromatic structure. Notably, the properties of the mesophase (approximately 440 °C) strongly influence the subsequent structural transformation. These findings could provide useful information for the microstructure–property relationships and preparation of coal-based carbon materials.

Tar formation characteristic of integrated process of coal pyrolysis with dry reforming of low carbon alkane over Ni/La2O3-ZrO2

Tar formation characteristic of integrated process of coal pyrolysis with dry reforming of low carbon alkane over Ni/La2O3-ZrO2

Investigation on steam co-gasification of torrefied biomass and coal: Thermal behavior, reactivity, product characteristic and synergy

The steam gasification of rice straw torrefied at 200–300 °C and its co-gasification with coal were examined in this study. The effect of torrefaction temperature on thermal behavior, reactivity, product characteristic, and synergy were investigated. The results showed that torrefaction temperature influenced the pyrolysis and char gasification stages by shifting them to higher temperature ranges. As torrefaction temperature increased, the H2 content increased while the CO and CH4 contents decreased, with H2/CO molar ratio increasing from 1.8 to 2.4. The total gas yield also increased from 0.95 to 1.30 Nm3/kg, especially with a large increase up to 27.4 %. As for the co-gasification, stages of biomass pyrolysis and coal pyrolysis overlapped at torrefaction temperature of 300 °C. The pyrolysis reactivity decreased while the char gasification reactivity increased with the torrefaction temperature increasing. The H2/CO molar ratio decreased slightly from 3.55 to 3.40, while the total gas yield increased from 1.87 to 1.96 Nm3/kg as well as the cold gas efficiency from 75 % to 77 %. The strongest synergistic effect on the reactivity occurred at torrefaction temperature of 250 °C. The increased torrefaction temperature enhanced the synergistic effect on the total gas yield but weakened it on the H2 yield.

Study on the enhancement of oxidation activity of heated coal in closed fire area and mechanism of reignition by opening seal

Residual heat following the closure of a coal mine fire area induces alterations in the physical and chemical structure of coal, which not only interfere with the opening time but also engenders potential catastrophic incidents upon the reopening of the fire area. Therefore, the structural changes in coal before and after pyrolysis were first analyzed by SEM, BET, XPS, 13C NMR and ESR. Second, the crossing-point temperature and constant-temperature differential heat methods were employed to investigate the process and characteristics of alkyl radical oxidation heat production. Quantum chemistry was integrated to analyze the mechanism of coal oxidation activity enhancement when the fire area was unsealed. The experimental results revealed that the residual heat could induce physicochemical structural changes in coal at varying distances. Upon exposure to oxygen, cracks facilitate oxygen migration and water evaporation mitigates heat consumption. The low-energy barrier of the alkyl radical oxidation reactions intensifies the oxidation activity of pyrolyzed coal, which can react with oxygen at room temperature to release heat. Under heat storage conditions, the active groups in coal are stimulated to further react. As a corollary, the substantial release of heat occurs, heightening the risk of coal re-ignition upon reopening of the fire area. The research results are helpful in performing accurate targeted treatment for different temperature gradients in underground fire areas to prevent the reignition of heated coal in closed fire areas.

Distribution of volatile composition from co-pyrolysis of NMH coal and dealkaline lignin

Experimental studies on co-pyrolysis of coal and lignin are carried out on a fixed-bed reactor to investigate composition and transformation of the co-pyrolysis products. The results show that co-pyrolysis reduces yield of char and promotes yield of gas, the maximum pyrolysis gas yield increases by 33.1%. Co-pyrolysis has a significant promotion effect on generation of CH4 and CO. The interaction between the pyrolyzed volatile fractions of coal and lignin shows the most pronounced interaction at a coal to lignin mixing ratio of 1:1, and the pyrolysis tar yield shows a positive synergistic effect. Guaiacols are converted to monophenols and bisphenols during the co-pyrolysis process. Content of monophenols and bisphenols increase by 2.9% and 9.8%, respectively, while content of guaiacols decreases by 5.1% compared with the theoretically calculated values. The breakage of carbonyl and carboxyl groups, and the interaction with volatile components are enhanced, which inhibits formation of ethers, aldehydes and acids, and promotes generation of phenols, release of oxygenated gases and stabilization of pyrolysis tar. The introduction of lignin into coal pyrolysis also significantly promotes the upgrading of tar in which light components is nearly 90%.

Response of nano-pores and heterogeneity of tar-rich coal to microwave pyrolysis

ABSTRACT In-situ pyrolysis of tar-rich coal can alleviate the external dependence of oil and gas in China, and achieve efficient and safe exploitation of tar-rich coal. In fact, the nano-pores and heterogeneity of tar-rich coal undergo significant changes during pyrolysis, but there is currently limited research, which seriously restricts the efficient utilization of tar-rich coal. In this study, the pore and heterogeneity characteristics of tar-rich coal were studied by microwave pyrolysis experiment, gas adsorption results and multifractal theory, and the pyrolysis evolution mechanism of pores of tar-rich coal was proposed. The results show that microwave pyrolysis significantly promoted the development of nano-pores in tar-rich coal. The nano-pore size distribution of tar-rich coal after pyrolysis showed obvious multifractal characteristics, and the influence of sparse area on nano-pore size distribution was more obvious, while the nano-pore distribution heterogeneity increases initially and subsequently drops with temperature. Moreover, the development of nano-pores in tar-rich coal occurred in three stages. Stage I, the total pore volume changed little, increasing only from 0.06851 to 0.09463 ml/g, and thermal cracking is the main reason for pore development. Stage II, numerous pores were produced as a result of the pyrolysis products’ generation, and total pore volume grew rapidly increased to 0.331 ml/g. Stage III, liquid hydrocarbons and precipitated volatile products blocked nano-pores, so that the total PV began to decrease. The total pore volume was only 0.19967 ml/g at 1000°C. This study provides guidance for the investigation of pore evolution during pyrolysis and enriches the theory of in-situ pyrolysis of tar-rich coal.

Preparation and growth mechanism of high-quality multilayer graphene from simulated coal pyrolysis gas via chemical vapor deposition

Chemical vapor deposition (CVD) of graphene from coal pyrolysis gas provides new ways for both large-scale graphene preparation and high value-added utilization of coal. However, green, efficient and continuous preparation of high-quality multilayer graphene with both good uniformity and ideal structure characteristic remains a great challenge. Herein, we first investigated the influence of main carbonaceous species (CH4, C2H6, C3H8, CO2, and CO) in coal pyrolysis gas on the quality of CVD graphene products. The experimental results indicated that CO2 and CO have little effect on the growth of graphene, while methane as carbon source is conducive to obtain ideal graphene materials, propane and ethane could also influence structural defects and layer number of graphene products remarkably. On this basis, we designed a mixed gas of methane, ethane, and propane with optimized ratio as simulated coal pyrolysis gas, and successfully prepared high-quality multilayer graphene products on nickel foam from the as-designed simulated coal pyrolysis gas by CVD method. Notably, with a CH4:C2H6:C3H8 ratio of 2:1:1, the graphene products prepared from simulated coal pyrolysis gas outperformed that of raw coal pyrolysis gas in terms of physical structure, layer number, and quality uniformity. The corresponding I2D/IG value reached 0.97. The graphene growth process and mechanism were investigated and discussed macroscopically and microscopically. This work is of great significance for the intrinsic understanding of CVD growth of graphene from coal pyrolysis gas, and also inspires an efficient and environmentally friendly avenue for high-throughput, uniform production of high-quality graphene materials.