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Liuhuanggou bituminous coal (LBC) and its extraction residue (ER) were thermally dissolved sequentially in cyclohexane, toluene, and ethanol at 300 °C to obtain soluble portions (SPs) 1–3 (SP1-SP3) from the thermal dissolution (TD) In the total yield (TY) of 10.4% and SPs I-III (SPI-SPIII) from the TD in the TY of 4.9%, respectively. The SPs were analyzed by multiple analytical tools, including gas chromatograph/mass spectrometer (GC/MS), quadrupole exactive orbitrap mass spectrometer (QEOTMS), and Fourier transform infrared spectrometer. The analysis with GC/MS shows that normal alkanes are the most abundant in SPI, while arenes are predominant in SP1, SP2, and SPII. According to the analysis with QEOTMS, abundant heteroatom-containing organic species were concentrated into SP3 and SPIII with molecular masses of 150–750 u. The relative contents of N1 and N1O1 species are predominantly high in SPIII and SP3, respectively.

A highly active difunctional Ni-Mg2Si/γ-Al2O3 was prepared by thermally decomposing nickel tetracarbonyl onto γ-Al2O3 impregnated with Mg2Si. The non-catalytic hydroconversion (NCHC) and catalytic hydroconversion (CHC) of the extract (E) and extraction residue (ER) from Yinggemajianfeng lignite were investigated over Ni-Mg2Si/γ-Al2O3 at 240 °C in n-hexane. Benzyloxybenzene and oxybis(methylene)dibenzene were used as lignite-related model compounds to speculate the possible mechanisms for the catalytic hydrocracking and hydrogenation over Ni-Mg2Si/γ-Al2O3. As a result, more organic matter in ER was converted to soluble portion (SP) by the CHC than by the NCHC. The main SP from the CHC are chain alkanes and cyclanes, while that from the NCHC is rich in arenes and oxygen-containing organic compounds. The results indicate that Ni-Mg2Si/γ-Al2O3 effectively catalyze the hydrocracking of >Calk–O– linkages and the hydrogenation of aromatic rings in E and ER.

Zhundong subbituminous coal (ZSBC) and Shenmu-Fugu subbituminous coal (SFSBC) were oxidized in aqueous sodium hypochlorite solution at 30 °C for 10 h to produce valuable benzenecarboxylic acids (BCAs) and to understand structural characteristics of the 2 typical Chinese subbituminous coals. Fourier transform infrared spectrometer, gas chromatograph/mass spectrometer, and direct analysis in real time ionization source coupled to an ion trap mass spectrometer were used to characterize the resulting products from the oxidation. The results show that the distributions of functional groups, molecular masses, and group components of the products from ZSBC and SFSBC oxidation are largely similar. Non-chlorine BCAs are the dominant carboxylic acids (CAs) from the oxidation and the total yields of BCAs from ZSBC and SFSBC oxidation are 15.6 wt% and 16.5 wt% based on organic matter in ZSBC and SFSBC, respectively, suggesting that both coals contain abundant polycyclic or condensed aromatic rings (ARs). Various BCAs, including cata-condensed aromatics, polyaryls, and peri-condensed aromatics, were generated from different aromatic precursors (APs) via the oxidation. According to the distributions of BCAs, ZSBC is rich in polyaryl moieties with Car-Car bridged linkages between the ARs, while SFSBC contains much more highly condensed ARs. O2 − dissociated from NaOCl could play a crucial role in producing BCAs from the ARs in ZSBC and SFSBC. In addition, some nitrogen-containing CAs were produced and their possible APs in ZSBC and SFSBC were speculated.

Xilingol No. 6 lignite (XL) was subjected to thermal dissolution in methanol at 200 °C, 240 °C, 280 °C, and 320 °C, respectively. Each reaction mixture was sequentially extracted with methanol and isometric carbon disulfide/acetone mixed solvent in a modified Soxhlet extractor to afford extracts a and b, respectively. According to the analysis with a Curie-point pyrolyzer-gas chromatograph/mass spectrometer, the main products from the flash pyrolysis of Ea320, i.e., Ea obtained from XL methanolysis at 320 °C, are phenolic compounds. The analysis with a quadrupole-orbitrap mass spectrometer indicates that N3O2-N3O4 are predominant nitrogen- and oxygen-containing class species (NOCCSs) in Ea320. In the NOCCSs, nitrogen atoms mainly exist in the forms of pyridine, imidazole or pyrazole, and pyrazine or pyrimidine, while the main oxygen atoms exist in alkoxy, furan, ester or carbonyl group. In addition, possible pathways for the formation of the NOCCSs were speculated.

Converting lignite into soluble organic compounds (SOCs) under mild conditions is significant for both evaluating molecular structure and producing clean fuels/chemicals. A three-step dissociation, i.e., sequential extraction, sequential thermal dissolution (TD), and ruthenium-ion-catalyzed oxidation (RICO), was adopted to convert the organic matter (OM) in Xiaolongtan lignite (XL) into SOCs. The perspectives on chemicals, geochemical information, and structural characteristics of XL were evaluated based on the molecular compositions of SOCs. Much higher yields of SOCs were obtained from TD than from extraction, which could be attributed to the thermal dissociation of non-covalent interactions in XL. Normal alkanes, alkyl-substituted benzenes, alkyl-substituted phenols, ketones, and aliphatic esters are the main group components released from TD. A series of important biomarkers were released and their distributions and evolution pathways during XL-forming process imply that higher terrestrial plants could be the main input of the OM in XL. Benzenecarboxylic acids were produced from TD residue in high selectivity via the RICO. According to the results from the RICO, the insoluble macromolecular structures in XL are rich in peri-condensed aromatics along with some cata-condensed aromatics and polyaryls, and CH3 is the major alkyl side chain on the aromatic rings. Adjacent aromatic moieties are mainly connected each other directly by Car Car bridged bonds.

Natural gas burns cleaner than coal by reducing ∼50% of the carbon footprint and emission of toxic substances and particulates. Coalbed natural gas can be produced from coal by indigenous microorganisms. Hydrogen peroxide treatment to coal has been shown to enhance the production of biogenic coalbed natural gas. In this study, we investigated methane generation from a subbituminous coal pretreated by hydrogen peroxide and the changes of the organic composition during gas production. We demonstrate that there is a great potential to produce natural gas from hydrogen peroxide-treated coal by microorganisms. The organic composition of the coal-derived compounds and the bulk organic profiling were changed because of the microbial degradation. The liquid samples before and after gas production were characterized by fluorescence spectrometer, GC/MS, HPLC, GPC, and TOCs. The results indicated that the chemical treatment has produced both labile organic components and compounds that are recalcitrant to microbial degradation. Labile compounds including short-chain carboxylic acids (C1 to C6) were found to contribute to the gas production. HPSEC analysis has shown shifts of molecular weight distributions, confirming organic composition changes. In addition, the analyses suggested that the labile organic compounds were conducive to shorten the lag phase of the gas production, whereas the presumed-recalcitrant constituents were surprisingly slightly biodegraded. The analysis also showed that the chemical treatment and biotransformation could produce compounds that are toxic to the environment. Environmental impacts should be fully evaluated before field applications.

Trifluoromethanesulfonic acid supported on attapulgite powder (TFMSA/AP) and Mg2Si/γ-Al2O3 were facilely prepared by impregnating TFMSA onto AP and Mg2Si onto γ-Al2O3. The extraction residue from Yiwu lignite (YLER) was subjected to non-catalytic hydroconversion (NCHC) and catalytic hydroconversion (CHC) over TFMSA/AP and Mg2Si/γ-Al2O3, respectively. Detailed molecular compositions of the soluble portions from the NCHC (SPNCHC) and CHC over TFMSA/AP (SPCHC-A) and Mg2Si/γ-Al2O3 (SPCHC-B) were characterized with a gas chromatograph/mass spectrometer. As a result, the yields of SPCHC-A and SPCHC-B are 19.6% and 17.5%, respectively, which are much higher than that of SPNCHC (1.04%), suggesting that both TFMSA/AP and Mg2Si/γ-Al2O3 show excellent activity for the CHC of YLER. Arenes and arenols are predominant in SPCHC-A and SPCHC-B, respectively, while large amounts of alkanoates were detected in SPNCHC. The results indicate that TFMSA/AP effectively catalyzes the cleavage of Car–Calk and Calk–O bridged bonds (BBs) in YLER, while Mg2Si/γ-Al2O3 significantly promotes the cleavage of C–O BBs in YLER. Di(1-naphthyl)methane, 1-methylnaphthalene, oxydibenzene, and benzyloxybenzene were used as coal-related model compounds (CRMCs) for the CHC to further explore the catalysis of TFMSA/AP and Mg2Si/γ-Al2O3. The results show that TFMSA/AP not only releases mobile H+ but also heterolytically splits H2 to form an immobile H− and a mobile H+, leading to the cleavage of Calk–Car and Calk–O BBs in the CRMCs. In contrast, Mg2Si/γ-Al2O3 facilitates heterolytically splitting H2 to an immobile H+ and a mobile H−, resulting in the cleavage of C–O BBs in the CRMCs.

Unmineable coal accounts for over 90% of the world’s fossil fuel resources. Fortunately, many coal seams contain indigenous microorganisms capable of utilizing the coal as a carbon source to produce secondary biogenic coalbed natural gas. However, coal bioavailability has been shown to be a significant factor that limits the extent of bioconversion. In this study, we have analyzed the rate and yield of the biogas production and assessed the gas potential, carbon balance, stable carbon isotopes, microbial communities, and microbial pathways changes resulting from the hydrogen peroxide pretreatment with the Wyoming’s Powder River Basin subbituminous coal. The results showed that coal pretreated with hydrogen peroxide can significantly enhance the bioavailability of coal for enhancing the biogas production, with a peak yield of 552.6 μmol/g coal (437.1 Scf/ton coal) at the day 184. The stable carbon isotopic analysis indicated that the δ13C values of the methane and carbon dioxide were much less negative than the published field data. This suggested that the enrichment or depletion of the precursor 13C could contribute to the shift of the carbon isotopic composition in the subsequence processes. Therefore, the data should be used with cautions for interpreting genesis of the thermogenic/biogenic methane and the methanogenic pathways. The methanogenic pathways were also investigated with re-fed experiment and microbial community analysis. The results indicated that the hydrogenotrophic pathway was not active in the original inoculum became activated after the gas production. The microbial community analysis demonstrated that the obligate hydrogenotrophic methanobacterium was the most dominant methanogens in the microcosms after the gas production. This suggested that the chemical treatment of coal has impacts on the microbial structure during the subsequent methane production phase.

Coalbed methane (CBM) has great environmental and economic values in addition to its energy content. For years natural gas has been considered a transitional cleaner energy source as it emits less carbon dioxide and other pollutants than other fossil fuels. Due to thebiogenic origin of CBM in many reservoirs, microbial enhancement may also be used to stimulate gas production in coal seams; however, the CBM output is relatively low when compared to other sources of natural gas. Studies have shown that chemical pretreatment of coal prior to gas production can significantly increase the bioconversion rate of coal. This review summarizes and discusses the mechanisms of coal biotransformation and biodegradation in the context of CBM production using chemical pretreatment methods, as well as the latest development in the field, in order to promote the further development of CBM resources.

Catalyst Ni/attapulgite powder (AP) was facilely prepared by thermally decomposing nickel tetracarbonyl onto AP. Anthracene was used as a condensed arenes (CAs)-related model compound to evaluate the catalytic activity and selectivity of Ni/AP for hydrogenating CAs. The results show that anthracene can be completely converted to perhydroanthracenes (PHAs) at 175 °C and selectively converted to 9,10-dihydroanthracene (DHA, ca. 86.4%) at 300 °C by catalytic hydrogenation over Ni/AP. Ni/AP effectively promotes the formation and transfer (F & T) of biatomic active hydrogen (H⋯H) at 175 °C, resulting in the complete hydrogenation of anthracene to PHAs. The mechanism for the F & T of H⋯H is consistent with the observation from the higher selectivities of cis-PHAs than that of trans-PHAs. At 300 °C, the catalytically produced H⋯H over Ni/AP tends to be homolytically spitted to hydrogen radical (H ), inducing the partial hydrogenation of anthracene to DHA. Quantum chemical calculations based on density functional theory further confirmed the temperature-controlled hydrogenation of anthracene over Ni/AP. This finding is a conclusive proof that the active hydrogen species is crucially important for affecting the product selectivities from the catalytic hydrogenation of anthracene over Ni/AP. Our research also offers a novel strategy for highly selective conversion of CAs to polycyclic alkanes or hydroarenes.

High-temperature coal tar (HTCT) is an important raw material for obtaining value-added aromatics. However, effective utilization of HTCT is not optimistic because of backward processing technology and higher energy consumption, resulting in fewer product types and lower purity. Accordingly, value-added utilization (VAU) of HTCT should be paid urgent attention. In order to realize VAU of HTCT, deep processing methods were systematically discussed. This paper mainly discusses the source, composition, research status, separation method, and upgrading of HTCT along with the utilization of coal tar pitch. Subsequently, the comprehensive processing route for VAU of HTCT was proposed. HTCT research ideas are put forward in combination with future research directions. We hope that this review will add to the ongoing discussions on the VAU of HTCT.

The development of bio-processing low rank coal into fuels and non-fuel products has received growing interest in recent years, e.g., production of alternative chemical stock (i.e., humic acids) by the fungal transformation. Previous studies have demonstrated that fungal strains isolated from coal environments can play an important role in the coal-transformation processes with in vivo optimization and chemical pretreatments. In this study, the influence of chemical pretreatments (nitric acid and hydrogen peroxide) with a fungal isolate from coal on the depolymerization of Pakistani subbituminous coal was conducted. The chemical pretreatment exhibited enhanced production of humic acid from 13.5% to 54.2% for nitric acid and 45.7% for hydrogen peroxide. Nitric acid was more effective pretreatment in individual and combination with fungal-mediated depolymerization than hydrogen peroxide. The production of fungal-transformed liquid-derived humic acids were 36.4% and 31.1% for nitric acid and hydrogen peroxide pretreated coal. The results showed that the fungal-transformed humic acid has a high molecular weight, elevated aromatic condensation with mono and poly-substituted functional groups than the chemically treated and raw coal-derived humic acids. The fungal treatment also increased the nitrogen content in the resultant extract, which can be beneficial to the functionality of humic acids. By combining chemical and fungal treatment, it is possible to improve the quantity and quality of humic acids extracted from low rank coal. This is a promising approach in the development of more sustainable-cleaner products from Pakistan’s coal resources for the production of bio-active humic acid.

Structural features of Dahuangshan lignite (DL) and 4 derived residues (DRs) were analyzed to understand the internal correlation between the associative fragments and organic macromolecular structures in DL. The structural changes before and after DL extraction and degradation can be effectively understood through the combination of multiple tools. The results show that >C-OH and >C-O- moieties are dominated on all the sample surfaces, while pyrrolics and SSSs (i.e., SO42−, SO42−, and -SO3H) are the most abundant nitrogen- and sulfur-containing species, respectively, from X-ray photoelectron spectrometric analysis. According to thermogravimetric and Fourier transform infrared semi-quantitative analyses, the cleavage of weak and medium strength covalent bonds, i.e., >Cal-X bonds (X denotes H, Cal

Shengli lignite (SL) was pretreated in H 2 O 2 aqueous solution at 40 °C for 4 h to obtain pretreated SL (PTSL). Both the SL and PTSL were oxidized in NaOCl aqueous solution at 30 o C for 5 h to investigate the effect of pretreatment (PT) on SL oxidation with NaOCl. Gas chromatography/mass spectrometry analysis shows that the PT with H 2 O 2 significantly increased the yields of alkanoic acids, alkanedioic acids, and benzene carboxylic acids (BCAs), but substantially suppressed the formation of chloro-substituted alkanoic acids (CSAAs). The total yield (daf) of BCAs was 7.4% from SL and increased to 10.1% from PTSL, while that of CSAAs decreased from 5.4% for SL to 0.8% for PTSL. Direct analysis in real time ionization source coupled to mass spectrometry analysis exhibits that the PT with H 2 O 2 enhanced the formation of compounds with molecular from m/z 300 to 500. The possible mechanisms for the PT and subsequent oxidation are discussed according to the experimental results. The cleavage of covalent bonds and introduction of oxygen functional groups such as −COOH and −OH by the PT could be responsible for the increase in the yields of soluble species.

Structural features of Shengli lignite (SL) were investigated through ruthenium ion-catalyzed oxidation and oxidations in aqueous hydrogen peroxide (AHPO) and sodium hypochlorite (ASHC) under mild conditions. The results suggest that SL is rich in condensed aromatic species and hydroxyl-, methoxy-, and/or methyl-substituted benzene rings, and –CH 2 CH 2 – is a dominant bridged linkage connecting aromatic rings in SL. Aliphatic linkages connecting three aromatic rings also exist in SL. Most of the organic matter in SL was converted into soluble fractions in either AHPO or ASHC. The products from SL oxidation in AHPO are rich in hydroxyl- and/or methoxyl-substituted benzoic acids, alkanoic acids (AAs), and long-chain alkanedioic acids (ADAs), whereas those from SL oxidation in ASHC are mainly composed of benzene carboxylic acids, chloro-substituted short-chain AAs and ADAs. The nitrogen- or sulfur-containing species produced from SL oxidation provide important information on structural features of organic nitrogen and sulfur species in SL.

The products in the water-soluble portion from mild oxidation of Jincheng No. 15 anthracite in aqueous hydrogen peroxide were analyzed with a gas chromatograph/quadrupole time-of-flight-mass spectrometer (GC/QTOF-MS) along with theoretical calculation for the first time. A series of heteroatom(s)-containing components were identified by comparing their mass spectra with NIST11 library data. Moreover, two organosulfur compounds without matched library mass spectra were inferred according to their tandem mass spectra and the formation of their fragmental ions was convincingly explained by energy calculation based on density functional theory. The investigation suggests that GC/QTOF-MS analysis combined with theoretical calculation would be a powerful tool for identifying unknown compounds in complicated mixtures from coals or their derivates.