Study on Organosulfur Compounds in a Chinese High-Sulfur Bituminous Coal

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A Chinese high-sulfur bituminous coal (HSBC) was firstly extracted with CS₂, and then the corresponding extract was subject to gradient elution to obtain a fraction enriched in organosulfur compounds. A total of 29 organosulfur compounds were identified in this fraction using an Agilent 7890A/5975C GC/MS system. The results revealed that the organosulfur species in the HSBC predominantly exist in thiophenic forms, specifically as thiophene rings fused with benzene and/or naphthalene rings and their alkyl-substituted derivatives. The presence of thiophenic structures in HSBC facilitates the pyrolysis of its macromolecules and promotes the formation of light component, and their potential transformation behaviors during coal processing were also discussed. Physical sciences/Chemistry Earth and environmental sciences/Environmental sciences High-Sulfur Coal Organosulfur compounds Thiophenic mode Figures Figure 1 Figure 2 1. Introduction Over the past few decades, high-sulfur coals (HSCs) have faced significant criticism due to their high content of organosulfur compounds (OSCs), which lead to excessive emissions of sulfuric pollutants during coal processing [ 1 ] . Meanwhile, the substantial global reserves of HSCs in our plant necessitate dedicated efforts toward their clean utilization, encompassing strategies for sulfur release, removal, and/or transformation before, during, and after coal conversion processes [ 2 – 7 ] . The foundation of these efforts hinges on a comprehensive understanding of the existing forms of organosulfur in coal [ 1 ] . Previous studies have demonstrated that sulfur in coal and coal-related materials exists as aliphatic sulfur, aromatic sulfur, sulfoxides, sulfones, and sulfates [ 8 – 9 ] , with aromatic sulfur comprising the predominant fraction of organosulfur [ 10 – 11 ] . Solvent extraction combined with gas chromatography/mass spectrometry (GC/MS) has been pivotal in unraveling detailed insights into coal OSCs [ 12 – 15 ] , and providing critical data for HSC research and technology. However, due to the inherent heterogeneity and structural complexity of coals, characterizing the specific organosulfur profiles of individual coal remains quite a hard work. In this study, a Chinese high-sulfur bituminous coal (HSBC) from Pingdingshan coal field was extracted with carbon disulfide (CS₂), and the resulting extract was subjected to sequential elution through a silica column to isolate a fraction enriched in organosulfur compounds (OSCs). The obtained fraction was analyzed by a gas chromatography/mass spectrometry (GC/MS) to characterize the structural features of the sulfur-containing species, with the findings intended to provide valuable insights for the utilization of the HSBC. 2. Materials and Experiments 2.1 Coal Sample and Solvents The coal sample was collected from the No.2 Colliery in the Pingdingshan Coal Field, Henan Province, China, and washed at the Pingdingshan Tianzhuang Coal Washery to remove part inorganic impurities in it, which includes inorganic sulfur such as pyrite, and some organic sulfur, Etc. The sample was pulverized to pass through a 200-mesh sieve (< 75 µm), air-dried at room temperature for 24 hours, and stored in a glass desiccator prior to experimentation. Permission has been obtained to collect coal samples from this coal mine and to use the samples. The above coal samples are from the research partner organization and do not involve any disputes over rights and interests. The use of these samples for scientific analysis complies with all relevant regulations, and the study did not involve any endangered or protected species. Analytical-grade solvents including CS₂, n-hexane, methanol, and ethyl acetate were used in the experiments. All solvents were redistilled before use to ensure purity. 2.2 Coal Extraction of the Coal Sample with CS 2 The coal sample (approximately 5 g) was accurately weighed and ultrasonically extracted with 600 mL of CS₂ in a 1000-mL conical flask for 2 hours. Following 4 hours of sedimentation, the supernatant was decanted and filtered through a quantitative filter paper (pore size 1–3 µm) using a Buchner funnel under vacuum at room temperature. The filtrate was concentrated via a Hei-VAP Precisio rotary evaporator to recover CS₂ and obtain the extract. The recycled CS₂, supplemented with fresh CS₂ to a total volume of 600 mL, was reinjected into the flask containing the extracted coal residue. This extraction procedure was repeated over 10 times until the extracting solution became visually colorless. All concentrated filtrates were combined in a 100-mL beaker, and residual CS₂ and moisture were removed using a previously reported method [ 16 ] to determine the extract weight (F₁). 2.3 Isolation of organosulfur Compounds by column chromatography The extract (F₁) obtained above was completely dissolved in an appropriate amount of CS₂, and mixed with silica gel (SG, 60 mesh) in a 100-mL round-bottom flask under ultrasonic irradiation; and then the mixture was concentrated using a Hei-VAP Precisio rotary evaporator to remove CS₂, yielding a free-flowing particle-supported sample [ 17 ] for elution use. After that, the prepared sample was loaded onto the top of a silica gel-packed column (3 cm diameter, 80 cm height). The column was first eluted with n-hexane until no visible color band migration was observed, followed by sequential elution with n-hexane/ethyl acetate (EA) binary mixtures. The EA concentration was increased in 10% (v/v) gradients per 1000 mL of eluent. The eluates were collected in 150 ml sub-fractions, and similar sub-fractions, judged by a Agilent 7890A-5975C GC/MS were combined as one fraction. By this way a fraction enriched in organosulfur compounds (F₂) was obtained from the 600–900 mL elution volume, corresponding to the combined fifth and sixth sub-fractions. 2.4 GC/MS Analysis of organosulfur compounds in F 2 The F₂ fraction was analyzed using an Agilent 7890A/5975C GC/MS system equipped with a DB-35MS capillary column and quadrupole analyzer. The instrument was operated in electron impact (EI) mode at 70 eV with helium as the carrier gas. Key operational parameters included: a carrier gas flow rate of 1.0 mL/min, split ratio of 20:1, injector temperature of 300°C, and mass scanning range from 30 to 500 amu. The column oven temperature program was as follows: initial heating from 100°C to 200°C at a rate of 5°C/min, followed by heating from 200°C to 300°C at 10°C/min, and then maintaining at 300°C until no further peaks eluted. Data acquisition and processing were performed using Agilent ChemStation software. Compound identification was achieved by matching mass spectra against the NIST 2014 library; compounds absent from the library were identified by referencing published literature data [ 18 ] . 3. Results and Discussion 3.1 Extraction of HSBC The extract yield ( Y F₁ ) of 3.66% from the washed HSBC via CS₂ extraction was calculated as the weight ratio of the extract ( W extract ) to the coal sample on a dry ash-free (daf) basis ( W coal,daf ), i.e., Y F₁ = W extract / W coal,daf . CS₂ is widely used for coal extraction [ 19 – 21 ] due to strong π-π interactions between CS₂ molecules and coal aromatic structures. In this study, CS₂ was chosen for isolating organosulfur compounds from HSBC based on the similarity-intermiscibility theory, which suggests that CS₂ molecules may exhibit affinity for organosulfur compounds in coal. The Y F₁ obtained under mild extraction conditions with a conventional solvent represents a relatively high yield, demonstrating the strong extraction capability of CS₂ for coal matrices. Proximate and ultimate analyses of the raw, washed, and extracted HSBC samples are presented in Table 1 . Table 1 Proximate and Ultimate Analyses of the Raw, Washed and Extracted HSBC Samples a coal samples proximate analysis (wt %) ultimate analysis (wt %) M ad A d V daf FC daf C daf H daf N daf S t,daf Raw coal 1.22 16.67 24.38 75.62 82.00 4.310 1.170 4.098 Washed Coal 0.76 10.56 24.71 75.29 82.54 4.319 1.330 2.412 Extracted coal 0.57 10.80 25.64 74.36 82.91 4.278 1.380 2.373 a Data for proximate and ultimate analyses were obtained with a Ruixiang WS-G400-808 proximate autoanalyzer and a Elementar Macocube CHNS elemental determinator, respectively. According to Table 1 , the sulfur content (S t,daf ) decreased from 4.098% in the raw HSBC to 2.412% in the washed HSBC. This indicates that a significant portion of the sulfur in the tested HSBC are in inorganic forms such as pyrites, marcasites, and sulfates, and can be removed through coal washing. However, over about half of the original sulfur remains in the washed coal, presumably consisting primarily of organic sulfur with minor residual inorganic sulfur. The marginal reduction in S t,daf from washed HSBC to extracted HSBC suggests that little to no significant difference in sulfur content between the macromolecular and small-molecular phases, if such a distinction exists. 3.2 Analysis of organosulfur compounds from the HSBC by GC/MS The fraction mainly of organosulfur compounds, F 2 , was achieved through CS 2 extraction to the HSBC and then gradual elution to the extract obtained on a silica gel column as described above, but the yield of F 2 ( Y F2 ) could not be reached because the F 2 became very sticky when concentrated at end and the complete removal of CS 2 inside it is quite difficult. Figure 1 shows the total ion chromatography (TIC) of F 2 by GC/MS, and the correspounding organosulfur compounds detected are listed in Table 2 . As shown in Table 2 , a total of 29 aromatic sulfur compounds were detected in F 2 , including dibenzothiophene, naphthothiophene, benzonaphthothiophene, and their alkyl-substituted derivatives, with dibenzothiophene and its alkyl derivatives being the dominant components. Other compounds in F 2 identified by GC/MS, which are of 2–4 ring aromatic hydrocarbons, are not listed or discussed herein due to space constraints here. Considering the thiophene ring may fuse with benzene and naphthalene rings in different configurations and undergo alkyl substitution at various positions, the proposed structures of the compounds detected in F 2 are deduced in Fig. 2 . These isomers cannot be fully distinguished by GC/MS alone, and precise structural determination may require combined use of advanced analytical techniques. Table 2 Organosulfur compounds detected in F 2 No. Compounds No. Compounds 1 dibenzothiophene 16 trimethyldibenzothiophene 2 methyldibenzothiophene 17 C 4 -dibenzothiophene 3 methyldibenzothiophene 18 benzonaphthothiophene 4 methyldibenzothiophene 19 methylbenzonaphthothiophene 5 Ethyldibenzothiophene 20 methylbenzonaphthothiophene 6 dimethyldibenzothiophene 21 methylbenzonaphthothiophene 7 dimethyldibenzothiophene 22 methylbenzonaphthothiophene 8 dimethyl-naphthothiophene 23 methylbenzonaphthothiophene 9 dimethyldibenzothiophene 24 methylbenzonaphthothiophene 10 dimethyldibenzothiophene 25 methylbenzonaphthothiophene 11 trimethyldibenzothiophene 26 dimethylbenzonaphthothiophene 12 trimethyldibenzothiophene 27 dimethylbenzonaphthothiophene 13 trimethyldibenzothiophene 28 dimethylbenzonaphthothiophene 14 trimethyldibenzothiophene 29 dimethylbenzonaphthothiophene 15 trimethyldibenzothiophene It should be noted that no other species of organosulfur compounds—such as thiazoles, aliphatic sulfides, or thiols—were detected in F 2 . Notably, these species were also absent in other fractions obtained in this experiment. This result suggests that the organosulfur moieties in HSBC predominantly reside in pentacyclic thiophene rings fused with other aromatic systems (e.g., benzene and naphthalene). It can be guessed that in the insoluble fraction of HSBC, organosulfur groups are embedded within thiophene rings fused to larger aromatic frameworks. The absence of aliphatic organosulfur species (e.g., thiols, thioethers) isolated or detected in this HSBC can be attributed to its relatively high rank. Previous studies [ 8 – 10 ] have confirmed that organosulfur in coals exists in both aliphatic and aromatic forms, with aromatic sulfur compounds dominating as carbon content increases. Aliphatic organosulfur compounds are typically found in lower-rank coals. In contrast, the HSBC tested in this study is a relatively high-rank coal, explaining why earlier aliphatic organosulfur compounds (OSCs) likely diminished as aromatic species increased during coalification. 3.3 Discussion on Thiophene Sulfur Release of the Coal Macromolecules The predominant occurrence of organosulfur within thiophenic rings in HSBC attributed to the stability of the aromatic sextet electron structure [ 22 ] . In the pentacyclic thiophene ring, all four carbon atoms and one sulfur atom are sp²-hybridized. The sulfur atom donates a pair of unshared electrons from an sp² orbital orthogonal to the ring plane, combining with four π electrons from the four carbon atoms to create a closed conjugate π-system. This electron configuration satisfies a benzene-like aromatic sextet according to Hückel’s rule and endows aromatic stability to thiophenic sulfur structures, which has a significant influence on the release and conversion of organosulfur during coal processing. Thermal conversion is the primary pathway for coal processing, and also the primary pathway for the release of sulphur in coals. The conversion of sulphuric structures in coal requires energy, and it is temperature-dependent. The stablity of thiophenic forms in the HSBC implies higher energy barrier fthan that of aliphatic sulphur structures. Aliphatic sulfur compounds typically decompose at temperatures above 300℃, which are a relatively low temperature. As the temperature rises higher than 500℃, the alkyl-substituted groups on thiophenic rings may cleave first and release volatile sulfur-containing small molecules with the core thiophenic structures—especially those in more complex fused-ring systems—remaining stable until much higher pyrolysis temperatures, i.e., above 800℃. Several studies use thiophene as a model compound for desulfurization purposes in coal or other fossil fuels [ 23 – 28 ] , and the results showed that the conversion products of thiophenic sulphur include sulfur dioxide (SO 2 ), hydrogen sulfide (H 2 S), carbon disulfide (SO 2 ), as well as some unstable intermediates such as thioketene (CH 2 CS) and thioformaldehyde (CH₂S), etc. The thiophenic structures may begin to decompose above from 500℃ to 800℃, but the relative mechanism failed to reach full agreement by far because of the complexity of coal structure and coal conversion. Xian [ 28 ] et al investigated the decomposition and generation paths of thiophene by using the density functional theory (DFT), and reached a conclusion as: the hydrogen transfer between the C − C bond rather than the C − S bond promote the ring opening of thiophene, and thiophene is decomposed at 800 K mainly through the hydrogenation reaction that occurs at para carbons and the C − S bond, the H 2 S elimination reaction, and the generation of ethane. However, when thiphenic ring fused with benzene and/or naphthelene in coal macromolecules, the decomposition of thiophenic structure during coal pyrolysis needs to be further investigated. For example, could it be that hydrogen or small molecular free radicals generated from coal pyrolysis attack sulfur or C-S bonds, thereby resulting in ring opening? Anyway it can certain that the presence of thiophenic structures in HSBC facilitates its pyrolysis and promotes the formation of light components, because the C − S bond exhibits significantly lower stability compared to the C-C bond. However, when thiophenic ring is fused with benzene and/or naphthalene in coal macromolecules, the decomposition of thiophenic structures during coal pyrolysis requires further investigation. For instance, could it be that hydrogen radicals or small molecular free radicals generated from coal pyrolysis attack sulfur or C-S bonds, and lead to ring opening? Furthermore, the primary products may undergo secondary reactions with higher temperatures and more residence time, such as condensation or hydrogenation, which can either retain sulfur within the char or transform it into different sulfur-containing gaseous products like H 2 S or COS (Carbonyl Sulfide). These questions will be discussed in detail elsewhere. In any case, it is certain that the presence of thiophenic structures in HSBC facilitates the pyrolysis of its macromolecules and promotes the formation of light components, as the C-S bond exhibits significantly lower stability compared to the C-C bond. This is important to thermal conversion for coal processing. 4. Conclusions A Chinese HSBC was subjected to CS₂ extraction, followed by gradual elution of the obtained extract to prepare a fraction enriched in organosulfur compounds. A total of 29 organosulfur compounds were detected via Agilent 7890A/5975C GC/MS, all of which were thiophenic rings fused with benzene and/or naphthalene and their alkyl-substituted derivatives. Dibenzothiophene and its alkyl derivatives were the dominant species. The prevalence of organosulfur in thiophenic form in HSBC can be attributed to the stability of the aromatic sextet electron structure, while the absence of aliphatic organosulfur species, if any, is likely due to the relatively high rank (maturity) of the HSBC. The presence of thiophenic structures in HSBC can facilitate the pyrolysis of its macromolecules and promote the formation of light components. Declarations Funding : The Open Fund Project of the National Key Laboratory for Green Development of Coking Coal Resources(Grant No. 41040220201132T)and the Key Science and Technology Project of Henan Province (Grant No. 212102311070). Author Contribution Ding Mingjie, Han qunliang, Yin Jia’nan and Song Chengjian: Experimental investigations, Data collection; Ding Mingjie and Yin Jia’nan: Writing original draft; Ding Mingjie, Han qunliang, Yin Jia’nan, Jin Peng, Li Yinfeng , Song Chengjian, Zhang Yanbing, Wang Yuhong, Luo qing: Writing – review & editing, Advising; Ding Mingjie: Initial idea, Funding acquisition, Project administration, Resources, Conceptualization, Writing – review & final editing, Supervision. Acknowledgements This work was supported by the Open Fund Project of the National Key Laboratory for Green Development of Coking Coal Resources(Grant No. 41040220201132T)and the Key Science and Technology Project of Henan Province (Grant No. 212102311070). Data Availability The raw data supporting the findings of this study are presented as part of this article, and are directly accessible from the figures and tables within the paper. 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17:18:37","extension":"html","order_by":15,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":97545,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7828168/v1/6a57abe047397dff06f124bd.html"},{"id":96206033,"identity":"e35cba41-c25d-4b7f-a575-995aa6f87c83","added_by":"auto","created_at":"2025-11-18 17:18:36","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":31973,"visible":true,"origin":"","legend":"\u003cp\u003eTotal ion chromatography of F\u003csub\u003e2\u003c/sub\u003e by GC/MS\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7828168/v1/4e59c02d414e18dbbba3bffe.png"},{"id":96253229,"identity":"29617ceb-880e-4fe0-95d1-a2983efbf4d8","added_by":"auto","created_at":"2025-11-19 07:42:11","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":41918,"visible":true,"origin":"","legend":"\u003cp\u003eThe possible structures of organosulfur compounds detected in F\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7828168/v1/adf5bc257aeaa7c73a594d00.png"},{"id":98437430,"identity":"747ea371-ba19-44bd-ae9a-f3ca70c20cca","added_by":"auto","created_at":"2025-12-17 16:57:19","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":777002,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7828168/v1/2099f595-2737-44dc-9c5f-2154739c55de.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Study on Organosulfur Compounds in a Chinese High-Sulfur Bituminous Coal","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eOver the past few decades, high-sulfur coals (HSCs) have faced significant criticism due to their high content of organosulfur compounds (OSCs), which lead to excessive emissions of sulfuric pollutants during coal processing\u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]\u003c/sup\u003e. Meanwhile, the substantial global reserves of HSCs in our plant necessitate dedicated efforts toward their clean utilization, encompassing strategies for sulfur release, removal, and/or transformation before, during, and after coal conversion processes \u003csup\u003e[\u003cspan additionalcitationids=\"CR3 CR4 CR5 CR6\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eThe foundation of these efforts hinges on a comprehensive understanding of the existing forms of organosulfur in coal\u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]\u003c/sup\u003e. Previous studies have demonstrated that sulfur in coal and coal-related materials exists as aliphatic sulfur, aromatic sulfur, sulfoxides, sulfones, and sulfates \u003csup\u003e[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]\u003c/sup\u003e, with aromatic sulfur comprising the predominant fraction of organosulfur\u003csup\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e. Solvent extraction combined with gas chromatography/mass spectrometry (GC/MS) has been pivotal in unraveling detailed insights into coal OSCs \u003csup\u003e[\u003cspan additionalcitationids=\"CR13 CR14\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/sup\u003e, and providing critical data for HSC research and technology. However, due to the inherent heterogeneity and structural complexity of coals, characterizing the specific organosulfur profiles of individual coal remains quite a hard work.\u003c/p\u003e\u003cp\u003eIn this study, a Chinese high-sulfur bituminous coal (HSBC) from Pingdingshan coal field was extracted with carbon disulfide (CS₂), and the resulting extract was subjected to sequential elution through a silica column to isolate a fraction enriched in organosulfur compounds (OSCs). The obtained fraction was analyzed by a gas chromatography/mass spectrometry (GC/MS) to characterize the structural features of the sulfur-containing species, with the findings intended to provide valuable insights for the utilization of the HSBC.\u003c/p\u003e"},{"header":"2. Materials and Experiments","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Coal Sample and Solvents\u003c/h2\u003e\u003cp\u003eThe coal sample was collected from the No.2 Colliery in the Pingdingshan Coal Field, Henan Province, China, and washed at the Pingdingshan Tianzhuang Coal Washery to remove part inorganic impurities in it, which includes inorganic sulfur such as pyrite, and some organic sulfur, Etc. The sample was pulverized to pass through a 200-mesh sieve (\u0026lt;\u0026thinsp;75 \u0026micro;m), air-dried at room temperature for 24 hours, and stored in a glass desiccator prior to experimentation. Permission has been obtained to collect coal samples from this coal mine and to use the samples. The above coal samples are from the research partner organization and do not involve any disputes over rights and interests. The use of these samples for scientific analysis complies with all relevant regulations, and the study did not involve any endangered or protected species.\u003c/p\u003e\u003cp\u003eAnalytical-grade solvents including CS₂, n-hexane, methanol, and ethyl acetate were used in the experiments. All solvents were redistilled before use to ensure purity.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Coal Extraction of the Coal Sample with CS\u003csub\u003e2\u003c/sub\u003e\u003c/h2\u003e\u003cp\u003eThe coal sample (approximately 5 g) was accurately weighed and ultrasonically extracted with 600 mL of CS₂ in a 1000-mL conical flask for 2 hours. Following 4 hours of sedimentation, the supernatant was decanted and filtered through a quantitative filter paper (pore size 1\u0026ndash;3 \u0026micro;m) using a Buchner funnel under vacuum at room temperature. The filtrate was concentrated via a Hei-VAP Precisio rotary evaporator to recover CS₂ and obtain the extract.\u003c/p\u003e\u003cp\u003eThe recycled CS₂, supplemented with fresh CS₂ to a total volume of 600 mL, was reinjected into the flask containing the extracted coal residue. This extraction procedure was repeated over 10 times until the extracting solution became visually colorless. All concentrated filtrates were combined in a 100-mL beaker, and residual CS₂ and moisture were removed using a previously reported method \u003csup\u003e[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e to determine the extract weight (F₁).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Isolation of organosulfur Compounds by column chromatography\u003c/h2\u003e\u003cp\u003eThe extract (F₁) obtained above was completely dissolved in an appropriate amount of CS₂, and mixed with silica gel (SG, 60 mesh) in a 100-mL round-bottom flask under ultrasonic irradiation; and then the mixture was concentrated using a Hei-VAP Precisio rotary evaporator to remove CS₂, yielding a free-flowing particle-supported sample \u003csup\u003e[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e for elution use.\u003c/p\u003e\u003cp\u003eAfter that, the prepared sample was loaded onto the top of a silica gel-packed column (3 cm diameter, 80 cm height). The column was first eluted with n-hexane until no visible color band migration was observed, followed by sequential elution with n-hexane/ethyl acetate (EA) binary mixtures. The EA concentration was increased in 10% (v/v) gradients per 1000 mL of eluent.\u003c/p\u003e\u003cp\u003eThe eluates were collected in 150 ml sub-fractions, and similar sub-fractions, judged by a Agilent 7890A-5975C GC/MS were combined as one fraction. By this way a fraction enriched in organosulfur compounds (F₂) was obtained from the 600\u0026ndash;900 mL elution volume, corresponding to the combined fifth and sixth sub-fractions.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4 GC/MS Analysis of organosulfur compounds in F\u003csub\u003e2\u003c/sub\u003e\u003c/h2\u003e\u003cp\u003eThe F₂ fraction was analyzed using an Agilent 7890A/5975C GC/MS system equipped with a DB-35MS capillary column and quadrupole analyzer. The instrument was operated in electron impact (EI) mode at 70 eV with helium as the carrier gas. Key operational parameters included: a carrier gas flow rate of 1.0 mL/min, split ratio of 20:1, injector temperature of 300\u0026deg;C, and mass scanning range from 30 to 500 amu. The column oven temperature program was as follows: initial heating from 100\u0026deg;C to 200\u0026deg;C at a rate of 5\u0026deg;C/min, followed by heating from 200\u0026deg;C to 300\u0026deg;C at 10\u0026deg;C/min, and then maintaining at 300\u0026deg;C until no further peaks eluted. Data acquisition and processing were performed using Agilent ChemStation software. Compound identification was achieved by matching mass spectra against the NIST 2014 library; compounds absent from the library were identified by referencing published literature data \u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Extraction of HSBC\u003c/h2\u003e\u003cp\u003eThe extract yield (\u003cem\u003eY\u003c/em\u003e\u003csub\u003e\u003cem\u003eF₁\u003c/em\u003e\u003c/sub\u003e) of 3.66% from the washed HSBC via CS₂ extraction was calculated as the weight ratio of the extract (\u003cem\u003eW\u003c/em\u003e\u003csub\u003e\u003cem\u003eextract\u003c/em\u003e\u003c/sub\u003e) to the coal sample on a dry ash-free (daf) basis (\u003cem\u003eW\u003c/em\u003e\u003csub\u003e\u003cem\u003ecoal,daf\u003c/em\u003e\u003c/sub\u003e), i.e., \u003cem\u003eY\u003c/em\u003e\u003csub\u003e\u003cem\u003eF₁\u003c/em\u003e\u003c/sub\u003e = \u003cem\u003eW\u003c/em\u003e\u003csub\u003e\u003cem\u003eextract\u003c/em\u003e\u003c/sub\u003e/\u003cem\u003eW\u003c/em\u003e\u003csub\u003e\u003cem\u003ecoal,daf\u003c/em\u003e\u003c/sub\u003e. CS₂ is widely used for coal extraction \u003csup\u003e[\u003cspan additionalcitationids=\"CR20\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]\u003c/sup\u003e due to strong π-π interactions between CS₂ molecules and coal aromatic structures. In this study, CS₂ was chosen for isolating organosulfur compounds from HSBC based on the similarity-intermiscibility theory, which suggests that CS₂ molecules may exhibit affinity for organosulfur compounds in coal. The \u003cem\u003eY\u003c/em\u003e\u003csub\u003e\u003cem\u003eF₁\u003c/em\u003e\u003c/sub\u003e obtained under mild extraction conditions with a conventional solvent represents a relatively high yield, demonstrating the strong extraction capability of CS₂ for coal matrices. Proximate and ultimate analyses of the raw, washed, and extracted HSBC samples are presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003e\u003cb\u003eProximate and Ultimate Analyses of the Raw, Washed and Extracted HSBC Samples\u003c/b\u003e \u003csup\u003e\u003cem\u003ea\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"10\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003ecoal samples\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"4\" nameend=\"c5\" namest=\"c2\"\u003e\u003cp\u003eproximate analysis (wt %)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colspan=\"4\" nameend=\"c10\" namest=\"c7\"\u003e\u003cp\u003eultimate analysis (wt %)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eM\u003csub\u003ead\u003c/sub\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eA\u003csub\u003ed\u003c/sub\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eV\u003csub\u003edaf\u003c/sub\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eFC\u003csub\u003edaf\u003c/sub\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eC\u003csub\u003edaf\u003c/sub\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003eH\u003csub\u003edaf\u003c/sub\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003eN\u003csub\u003e\u003cb\u003edaf\u003c/b\u003e\u003c/sub\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c10\"\u003e\u003cp\u003eS\u003csub\u003et,daf\u003c/sub\u003e\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eRaw coal\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1.22\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e16.67\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e24.38\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e75.62\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e82.00\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e4.310\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e1.170\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e4.098\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eWashed Coal\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.76\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e10.56\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e24.71\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e75.29\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e82.54\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e4.319\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e1.330\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e2.412\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eExtracted coal\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.57\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e10.80\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e25.64\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e74.36\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e82.91\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e4.278\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e1.380\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e2.373\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003csup\u003e\u003cem\u003ea\u003c/em\u003e\u003c/sup\u003e Data for proximate and ultimate analyses were obtained with a Ruixiang WS-G400-808 proximate autoanalyzer and a Elementar Macocube CHNS elemental determinator, respectively.\u003c/p\u003e\u003cp\u003eAccording to Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, the sulfur content (S\u003csub\u003et,daf\u003c/sub\u003e) decreased from 4.098% in the raw HSBC to 2.412% in the washed HSBC. This indicates that a significant portion of the sulfur in the tested HSBC are in inorganic forms such as pyrites, marcasites, and sulfates, and can be removed through coal washing. However, over about half of the original sulfur remains in the washed coal, presumably consisting primarily of organic sulfur with minor residual inorganic sulfur. The marginal reduction in S\u003csub\u003et,daf\u003c/sub\u003e from washed HSBC to extracted HSBC suggests that little to no significant difference in sulfur content between the macromolecular and small-molecular phases, if such a distinction exists.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.2 Analysis of organosulfur compounds from the HSBC by GC/MS\u003c/h2\u003e\u003cp\u003eThe fraction mainly of organosulfur compounds, F\u003csub\u003e2\u003c/sub\u003e, was achieved through CS\u003csub\u003e2\u003c/sub\u003e extraction to the HSBC and then gradual elution to the extract obtained on a silica gel column as described above, but the yield of F\u003csub\u003e2\u003c/sub\u003e (\u003cem\u003eY\u003c/em\u003e\u003csub\u003eF2\u003c/sub\u003e) could not be reached because the F\u003csub\u003e2\u003c/sub\u003e became very sticky when concentrated at end and the complete removal of CS\u003csub\u003e2\u003c/sub\u003e inside it is quite difficult. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the total ion chromatography (TIC) of F\u003csub\u003e2\u003c/sub\u003e by GC/MS, and the correspounding organosulfur compounds detected are listed in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e\u003cp\u003eAs shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, a total of 29 aromatic sulfur compounds were detected in F\u003csub\u003e2\u003c/sub\u003e, including dibenzothiophene, naphthothiophene, benzonaphthothiophene, and their alkyl-substituted derivatives, with dibenzothiophene and its alkyl derivatives being the dominant components. Other compounds in F\u003csub\u003e2\u003c/sub\u003e identified by GC/MS, which are of 2\u0026ndash;4 ring aromatic hydrocarbons, are not listed or discussed herein due to space constraints here. Considering the thiophene ring may fuse with benzene and naphthalene rings in different configurations and undergo alkyl substitution at various positions, the proposed structures of the compounds detected in F\u003csub\u003e2\u003c/sub\u003e are deduced in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. These isomers cannot be fully distinguished by GC/MS alone, and precise structural determination may require combined use of advanced analytical techniques.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eOrganosulfur compounds detected in F\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNo.\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCompounds\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eNo.\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eCompounds\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003edibenzothiophene\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003etrimethyldibenzothiophene\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003emethyldibenzothiophene\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eC\u003csub\u003e4\u003c/sub\u003e-dibenzothiophene\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003emethyldibenzothiophene\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003ebenzonaphthothiophene\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003emethyldibenzothiophene\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e19\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003emethylbenzonaphthothiophene\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eEthyldibenzothiophene\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003emethylbenzonaphthothiophene\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003edimethyldibenzothiophene\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e21\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003emethylbenzonaphthothiophene\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003edimethyldibenzothiophene\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e22\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003emethylbenzonaphthothiophene\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003edimethyl-naphthothiophene\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e23\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003emethylbenzonaphthothiophene\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003edimethyldibenzothiophene\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e24\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003emethylbenzonaphthothiophene\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003edimethyldibenzothiophene\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003emethylbenzonaphthothiophene\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003etrimethyldibenzothiophene\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e26\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003edimethylbenzonaphthothiophene\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003etrimethyldibenzothiophene\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e27\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003edimethylbenzonaphthothiophene\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003etrimethyldibenzothiophene\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003edimethylbenzonaphthothiophene\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e14\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003etrimethyldibenzothiophene\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e29\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003edimethylbenzonaphthothiophene\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003etrimethyldibenzothiophene\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIt should be noted that no other species of organosulfur compounds\u0026mdash;such as thiazoles, aliphatic sulfides, or thiols\u0026mdash;were detected in F\u003csub\u003e2\u003c/sub\u003e. Notably, these species were also absent in other fractions obtained in this experiment. This result suggests that the organosulfur moieties in HSBC predominantly reside in pentacyclic thiophene rings fused with other aromatic systems (e.g., benzene and naphthalene). It can be guessed that in the insoluble fraction of HSBC, organosulfur groups are embedded within thiophene rings fused to larger aromatic frameworks.\u003c/p\u003e\u003cp\u003eThe absence of aliphatic organosulfur species (e.g., thiols, thioethers) isolated or detected in this HSBC can be attributed to its relatively high rank. Previous studies \u003csup\u003e[\u003cspan additionalcitationids=\"CR9\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/sup\u003e have confirmed that organosulfur in coals exists in both aliphatic and aromatic forms, with aromatic sulfur compounds dominating as carbon content increases. Aliphatic organosulfur compounds are typically found in lower-rank coals. In contrast, the HSBC tested in this study is a relatively high-rank coal, explaining why earlier aliphatic organosulfur compounds (OSCs) likely diminished as aromatic species increased during coalification.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Discussion on Thiophene Sulfur Release of the Coal Macromolecules\u003c/h2\u003e\u003cp\u003eThe predominant occurrence of organosulfur within thiophenic rings in HSBC attributed to the stability of the aromatic sextet electron structure \u003csup\u003e[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]\u003c/sup\u003e. In the pentacyclic thiophene ring, all four carbon atoms and one sulfur atom are sp\u0026sup2;-hybridized. The sulfur atom donates a pair of unshared electrons from an sp\u0026sup2; orbital orthogonal to the ring plane, combining with four π electrons from the four carbon atoms to create a closed conjugate π-system. This electron configuration satisfies a benzene-like aromatic sextet according to H\u0026uuml;ckel\u0026rsquo;s rule and endows aromatic stability to thiophenic sulfur structures, which has a significant influence on the release and conversion of organosulfur during coal processing.\u003c/p\u003e\u003cp\u003eThermal conversion is the primary pathway for coal processing, and also the primary pathway for the release of sulphur in coals. The conversion of sulphuric structures in coal requires energy, and it is temperature-dependent. The stablity of thiophenic forms in the HSBC implies higher energy barrier fthan that of aliphatic sulphur structures. Aliphatic sulfur compounds typically decompose at temperatures above 300℃, which are a relatively low temperature. As the temperature rises higher than 500℃, the alkyl-substituted groups on thiophenic rings may cleave first and release volatile sulfur-containing small molecules with the core thiophenic structures\u0026mdash;especially those in more complex fused-ring systems\u0026mdash;remaining stable until much higher pyrolysis temperatures, i.e., above 800℃.\u003c/p\u003e\u003cp\u003eSeveral studies use thiophene as a model compound for desulfurization purposes in coal or other fossil fuels\u003csup\u003e[\u003cspan additionalcitationids=\"CR24 CR25 CR26 CR27\" citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]\u003c/sup\u003e, and the results showed that the conversion products of thiophenic sulphur include sulfur dioxide (SO\u003csub\u003e2\u003c/sub\u003e), hydrogen sulfide (H\u003csub\u003e2\u003c/sub\u003eS), carbon disulfide (SO\u003csub\u003e2\u003c/sub\u003e), as well as some unstable intermediates such as thioketene (CH\u003csub\u003e2\u003c/sub\u003eCS) and thioformaldehyde (CH₂S), etc.\u003c/p\u003e\u003cp\u003eThe thiophenic structures may begin to decompose above from 500℃ to 800℃, but the relative mechanism failed to reach full agreement by far because of the complexity of coal structure and coal conversion. Xian\u003csup\u003e[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]\u003c/sup\u003e et al investigated the decomposition and generation paths of thiophene by using the density functional theory (DFT), and reached a conclusion as: the hydrogen transfer between the C\u0026thinsp;\u0026minus;\u0026thinsp;C bond rather than the C\u0026thinsp;\u0026minus;\u0026thinsp;S bond promote the ring opening of thiophene, and thiophene is decomposed at 800 K mainly through the hydrogenation reaction that occurs at para carbons and the C\u0026thinsp;\u0026minus;\u0026thinsp;S bond, the H\u003csub\u003e2\u003c/sub\u003eS elimination reaction, and the generation of ethane.\u003c/p\u003e\u003cp\u003eHowever, when thiphenic ring fused with benzene and/or naphthelene in coal macromolecules, the decomposition of thiophenic structure during coal pyrolysis needs to be further investigated. For example, could it be that hydrogen or small molecular free radicals generated from coal pyrolysis attack sulfur or C-S bonds, thereby resulting in ring opening? Anyway it can certain that the presence of thiophenic structures in HSBC facilitates its pyrolysis and promotes the formation of light components, because the C\u0026thinsp;\u0026minus;\u0026thinsp;S bond exhibits significantly lower stability compared to the C-C bond.\u003c/p\u003e\u003cp\u003eHowever, when thiophenic ring is fused with benzene and/or naphthalene in coal macromolecules, the decomposition of thiophenic structures during coal pyrolysis requires further investigation. For instance, could it be that hydrogen radicals or small molecular free radicals generated from coal pyrolysis attack sulfur or C-S bonds, and lead to ring opening? Furthermore, the primary products may undergo secondary reactions with higher temperatures and more residence time, such as condensation or hydrogenation, which can either retain sulfur within the char or transform it into different sulfur-containing gaseous products like H\u003csub\u003e2\u003c/sub\u003eS or COS (Carbonyl Sulfide). These questions will be discussed in detail elsewhere.\u003c/p\u003e\u003cp\u003eIn any case, it is certain that the presence of thiophenic structures in HSBC facilitates the pyrolysis of its macromolecules and promotes the formation of light components, as the C-S bond exhibits significantly lower stability compared to the C-C bond. This is important to thermal conversion for coal processing.\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eA Chinese HSBC was subjected to CS₂ extraction, followed by gradual elution of the obtained extract to prepare a fraction enriched in organosulfur compounds. A total of 29 organosulfur compounds were detected via Agilent 7890A/5975C GC/MS, all of which were thiophenic rings fused with benzene and/or naphthalene and their alkyl-substituted derivatives. Dibenzothiophene and its alkyl derivatives were the dominant species. The prevalence of organosulfur in thiophenic form in HSBC can be attributed to the stability of the aromatic sextet electron structure, while the absence of aliphatic organosulfur species, if any, is likely due to the relatively high rank (maturity) of the HSBC. The presence of thiophenic structures in HSBC can facilitate the pyrolysis of its macromolecules and promote the formation of light components.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFunding :\u003c/h2\u003e\u003cp\u003eThe Open Fund Project of the National Key Laboratory for Green Development of Coking Coal Resources(Grant No. 41040220201132T)and the Key Science and Technology Project of Henan Province (Grant No. 212102311070).\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eDing Mingjie, Han qunliang, Yin Jia\u0026rsquo;nan and Song Chengjian: Experimental investigations, Data collection; Ding Mingjie and Yin Jia\u0026rsquo;nan: Writing original draft; Ding Mingjie, Han qunliang, Yin Jia\u0026rsquo;nan, Jin Peng, Li Yinfeng , Song Chengjian, Zhang Yanbing, Wang Yuhong, Luo qing: Writing \u0026ndash; review \u0026amp; editing, Advising; Ding Mingjie: Initial idea, Funding acquisition, Project administration, Resources, Conceptualization, Writing \u0026ndash; review \u0026amp; final editing, Supervision.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e\u003cp\u003eThis work was supported by the Open Fund Project of the National Key Laboratory for Green Development of Coking Coal Resources(Grant No. 41040220201132T)and the Key Science and Technology Project of Henan Province (Grant No. 212102311070).\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe raw data supporting the findings of this study are presented as part of this article, and are directly accessible from the figures and tables within the paper. Any supporting datasets not presented in the main article are available in the Supplementary Materials. Accordingly, there are no separate datasets associated with this manuscript that require archiving.All datasets generated and analysed during the current study are included in this published article (and its Supplementary Information files).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBrockway, P. E., Owen, A., Brand-Correa, L. I. \u0026amp; Hardt, L. Estimation of global final-stage energy-return-on-investment for fossil fuels with comparison to renewable energy sources. \u003cem\u003eNat. 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Mechanism insight into the conversion between H₂S and thiophene during coal pyrolysis: A theoretical study. \u003cem\u003eACS Omega\u003c/em\u003e. \u003cb\u003e8\u003c/b\u003e (37), 33982\u0026ndash;33996. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/acsomega.3c04245\u003c/span\u003e\u003cspan address=\"10.1021/acsomega.3c04245\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2023).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"High-Sulfur Coal, Organosulfur compounds, Thiophenic mode","lastPublishedDoi":"10.21203/rs.3.rs-7828168/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7828168/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe clean utilization of high-sulfur coals depends on a comprehensive understanding of the occurrence forms of organosulfur compounds and their behaviors during coal processing at the molecular level. A Chinese high-sulfur bituminous coal (HSBC) was firstly extracted with CS₂, and then the corresponding extract was subject to gradient elution to obtain a fraction enriched in organosulfur compounds. A total of 29 organosulfur compounds were identified in this fraction using an Agilent 7890A/5975C GC/MS system. The results revealed that the organosulfur species in the HSBC predominantly exist in thiophenic forms, specifically as thiophene rings fused with benzene and/or naphthalene rings and their alkyl-substituted derivatives. The presence of thiophenic structures in HSBC facilitates the pyrolysis of its macromolecules and promotes the formation of light component, and their potential transformation behaviors during coal processing were also discussed.\u003c/p\u003e","manuscriptTitle":"Study on Organosulfur Compounds in a Chinese High-Sulfur Bituminous Coal","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-18 17:18:31","doi":"10.21203/rs.3.rs-7828168/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"09e29350-1119-41c2-9d34-0f897ddad100","owner":[],"postedDate":"November 18th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":58118079,"name":"Physical sciences/Chemistry"},{"id":58118080,"name":"Earth and environmental sciences/Environmental sciences"}],"tags":[],"updatedAt":"2025-12-16T16:09:18+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-18 17:18:31","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7828168","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7828168","identity":"rs-7828168","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}