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Carbon dots are zero‐dimensional carbon nanomaterials with quantum confinement effects and edge effects, which have aroused great interests in many disciplines such as energy, chemistry, materials, and environmental applications. They can be prepared by chemical oxidation, electrochemical synthesis, hydrothermal preparation, arc discharge, microwave synthesis, template method, and many other methods. However, the raw materials' high cost, the complexity and environmental‐unfriendly fabrication process limit their large‐scale production and commercialization. Herein, we review the latest developments of coal‐based carbon dots about selecting coal‐derived energy resources (bituminous coal, anthracite, lignite, coal tar, coke, etc.) the developments of synthesis processes, surface modification, and doping of carbon dots. The coal‐based carbon dots exhibit the advantages of unique fluorescence, efficient catalysis, excellent water solubility, low toxicity, inexpensive, good biocompatibility, and other advantages, which hold the potentiality for a wide range of applications such as environmental pollutants sensing, catalyst preparation, chemical analysis, energy storage, and medical imaging technology. This review aims to provide a guidance of finding abundant and cost‐effective precursors, green, simple and sustainable production processes to prepare coal‐based carbon dots, and make further efforts to exploit the application of carbon dots in broader fields. [ABSTRACT FROM AUTHOR]

Thermal extraction (TE) of low rank coal with low boiling point solvent is an important approach to obtain organic chemicals, but it remains a great deal of thermal extraction residue (TER) due to low extraction yield. In this paper, Xilinguole lignite (XL) and Shenfu sub-bituminous coal (SF) were extracted by toluene and toluene/methanol mixed solvents at 250–350 °C to obtain TERs. Then the obtained TERs were hydro-liquefied to investigate their hydro-liquefaction property under mild conditions. By combination with the structural characterizations of TER and its liquefied products, it was found that TE can separate small molecular compounds, and improve the hydro-liquefaction performance of TER. Rising TE temperature and adding appropriate methanol to toluene can increase the TE yield and the oil + gas (O + G) yield of TER hydro-liquefaction, especially for XL which containing abundant oxygen functional groups. The effects of heat-induced relaxation of non-covalent bonding associated structure and solvent-induced cleavage of covalent bonds on the TE and the hydro-liquefaction of TER were discussed. [ABSTRACT FROM AUTHOR]

The thermolysis of biomass-related model compounds was carried out and its promotion on the thermal dissolution of coal was probed in this study. Benzyl phenyl ether was easily to pyrolyze than dibenzyl ether, and the thermolysis conversions of benzyl phenyl ether and dibenzyl ether were 98.3 and 32.4% at 360 °C respectively. The product analysis of the thermolysis suggests that the pyrolysis of the biomass-related model compounds follows the radical reaction route and some phenyl oxygen free radicals are formed in the process. Addition of 2% phenol could obviously increase the thermolysis conversion of dibenzyl ether, suggesting that the free radicals formed from phenol can promote the pyrolysis of dibenzyl ether. Addition of 10% benzyl phenyl ether could obviously promote the thermal dissolution of Shenfu sub-bituminous coal, and the thermal dissolution yield of Shenfu sub-bituminous coal could be increased by 20.8% at 360 °C. The enhancement of thermal dissolution of Shenfu coal by benzyl phenyl ether can be attributed to that the benzyloxy and phenoxy radicals formed from the thermolysis of benzyl phenyl ether attack the coal molecules, thus promoting the depolymerization of coal. [ABSTRACT FROM AUTHOR]

• A low carbon footprint method for converting low-rank coals to chemicals was proposed. • Large amount of oxygenated chemicals such as phenols, esters, and RHAs were obtained. • SF has poorer TE and oxy-cracking reactivity than XLT and XLGL. • More than 40.6% RHA yield with neglectable CO 2 emission can be obtained from XLT-TER and XLGL-TER at 300 °C. • Average sizes of aromatic rings in RHAs are between benzene and naphthalene. Due to the urgent need to reduce CO 2 emission and the shortage of petroleum, using coals especially low-rank coals as raw materials for producing chemicals has attracted much attention. Thermal extraction and oxidation in aqueous solution are efficient approaches for obtaining oxygen-containing chemicals from low-rank coals. However, yield of chemicals is limited and/or large amount of CO 2 is released solely using either of the two technologies for converting low-rank coals. In this paper, a low carbon footprint method combining thermal extraction (TE) and oxy-cracking in dilute alkali aqueous solution for efficiently depolymerizing three low-rank coals, i.e., Xiaolongtan lignite (XLT), Xilinguole lignite (XLGL), and Shenfu sub-bituminous coal (SF), was proposed. The results indicate that considerable oxygen-containing compounds such as phenols, esters, and humic acids along with little CO 2 emission can be obtained via the two-step depolymerization process. TE temperature significantly effects the dissolution of small molecular compounds. Comparing with XLT and XLGL, SF has lower TE and oxy-cracking activity. A good correlation between the oxy-cracking conversion of TE residues and their DTG peak temperature for the low-rank coals can be found. Therefore, the aforementioned approach is promising for high-value and low-carbon utilization of low-rank coals. [ABSTRACT FROM AUTHOR]

Abstract: In order to study the catalysis of solid acid for the liquefaction of coal, a series of solid acids were synthesized by the method of precipitation–impregnation. The catalytic behaviours of the solid acids for the hydro-liquefaction of Shenhua coal and model compounds, such as diphenylmethane, bibenzyl and phenyl ethyl ether, were investigated. In addition, non-catalytic liquefaction and the catalytic liquefaction under N2 were further compared with the catalytic liquefaction under H2 in order to understand the catalytic mechanism of solid acid. The results indicate that hydro-liquefaction conversions of coal and model compounds are related to the strength, amount and nature of acid sites on the surface of , and the strong acid site responds to their catalytic activities. The solid acid catalyzes mainly the hydro-cracking, ring-opening and hydrogenation reactions of coal to produce oil and gas during the coal liquefaction. The hydro-cracking reactions in the liquefaction of model compounds and coal catalyzed by involved via carbenium ion intermediate instead of traditional radicals intermediate. [Copyright &y& Elsevier]

Abstract: Effects of pre-swelling of coal on solvent extraction and liquefaction properties were studied with Shenhua coal. It was found that pre-swelling treatments of the coal in three solvents, i.e., toluene (TOL), N-methyl-2-pyrrolidinone (NMP) and tetralin (THN) increased its extraction yield and liquefaction conversion, and differed the liquefied product distributions. The pre-swollen coals after removing the swelling solvents showed increased conversion in liquefaction compared with that of the swollen coals in the presence of swelling solvents. It was also found that the yields of (oil+gas) in liquefaction of the pre-swollen coals with NMP and TOL dramatically decreased in the presence of swelling solvent. TG and FTIR analyses of the raw coal, the swollen coals and the liquefied products were carried out in order to investigate the mechanism governing the effects of pre-swelling treatment on coal extraction and liquefaction. The results showed that the swelling pre-treatment could disrupt some non-covalent interactions of the coal molecules, relax its network structure and loosened the coal structure. It would thus benefit diffusion of a hydrogen donor solvent into the coal structure during liquefaction, and also enhance the hydrogen donating ability of the hydrogen-rich species derived from the coal. [Copyright &y& Elsevier]

Abstract: In this paper, the hydrothermal treatment of Shenhua coal was carried out under 0.1MPa (initial pressure) nitrogen and different temperature. Effects of hydrothermal treatment on the structure and the hydro-liquefaction activity of Shenhua coal were investigated by the ultimate and proximate analyses, the FTIR measurements and TG analyses of hydrothermally treated coals, and the characterizations of extraction and swelling properties, and the batch hydro-liquefaction of treated coal were also carried out. The results indicate that hydrothermal treatment above 200°C can increase the hydrogen content of treated coal and decrease the yield of volatiles and the content of ash, especially a large amount of CO and CH4 are found in gas products obtained by the hydrothermal treatment above 250°C. Hydrothermal treatment disrupts the weak covalent bond such as ether, ester and side-chain substituent by hydrolysis and pyrolysis, and changes the distribution of H-bond in coal. The swelling ratio and the Soxhlet extraction yield of treated coal decrease with the increase of hydrothermal treatment temperature. The conversion of liquefaction and the yield of CS2/NMP mixed solvent extraction at ambient temperature are enhanced by hydrothermal treatment at 300°C. Therefore hydrogen donation reactions and the rupture of non-covalent bond and weak covalent bonds present in the process of hydrothermal treatment resulting in the changes of structure and reactivity of Shenhua coal. The results show that the hydro-liquefaction activity of Shenhua coal can be improved by hydrothermal pretreatment between 250°C and 300°C. [Copyright &y& Elsevier]

Abstract: The roles of CS2 in the CS2/NMP mixed solvent to coal extraction and solubilization were investigated in this study. There was little effect of removing of CS2 from the solutions on the solubilities of UF coal extract and pyridine insoluble (PI) of the extract in the NMP/CS2 mixed solvent, suggesting that NMP has high enough solubilities to the UF coal extract and PI. Six Argonne different rank coals were extracted with the CS2/NMP mixed solvent and NMP, respectively. It was found that the extraction yield difference between NMP and CS2/NMP mixed solvent for UF coal is largely deviated from the curve obtained for the other 5 coals, suggesting that the pre-swelling of CS2 in the mixed solvent may be one of important roles for high extraction yield of UF coal in the CS2/NMP mixed solvent. FTIR indicated that there was a strong interaction between CS2 and NMP in the CS2/NMP mixed solvent of 1:1 volume ratio, which made the strong absorbance at 2156 cm−1 in the FTIR spectra, and this interaction may disrupt the dipole based association of NMP thus making the CS2/NMP mixed solvent lower viscosity, to penetrate more quickly into the network structure of coal, resulting in the larger solvent partner (NMP) to enter and break the stronger coal–coal interactions. [Copyright &y& Elsevier]

• Sodium in ashes promotes liquid phase formation and increases its content. • Ash melting temperatures notably increased through co-combustion. • The ashes from co-firing exhibits reduced fouling and slagging propensity. • The appropriate co-firing ratio of coal gangue should be lower than 30%. Fouling and slagging are major challenges that impede the clean and efficient use of high-sodium coals (HC) for power generation. To address these persistent issues, this study examined the impact of sodium (Na) on ash-melting behaviors and assessed the feasibility of mitigating fouling and slagging through the co-combustion of HC with coal gangue (CG). The mineral transformation mechanisms were analyzed through experimental and thermodynamic calculations using the FactSage software. The potential for inhibiting slagging through the co-firing of HC with CG rich in silica (SiO 2) and alumina (Al 2 O 3) was also investigated. The presence of Na-containing species led to the formation of more flexible minerals and lowered the ash fusion temperatures (AFTs). Na not only decreased the initial temperature required for the formation of the liquid phase but also increased the proportion of the liquid phase during high-temperature ash-melting processes. Co-firing with CG rich in silica and alumina significantly improved the AFTs of HC. Furthermore, this approach effectively reduced the propensity for fouling and slagging. In practice, it is recommended to control the co-firing ratios of CG within 10–30% to inhibit slagging and fouling issues while maintaining a smooth boiler operation. [ABSTRACT FROM AUTHOR]

Thermal dissolutions (TDs) of Xilinguole lignite (XL) and coking coal (CC) with different solvents were performed, and feasibility of applying TD soluble fractions (TDSFs) to coke-making was evaluated. The results show that the TDSFs yield of XL (< 30%) is lower than that of CC (> 40%) in both polar and non-polar solvents at 360 °C. Methanol remarkably enhances TDSF yield of XL from 30% to 45.3% with 10% addition to 1-methylnaphthalene (1-MN) due to methanolysis. All TDSFs prepared show better caking property, lower softening temperatures, and greater caking indexes (G R.I) than the commonly used fat coals for coke-making. Using 5 wt.% TDSFs to substitute equivalent amount of fat coal in coal blends effectively improves the quality of the resultant coke, verifying the feasibility of using TDSFs from low rank coals for coke-making. • Thermal dissolution (TD) performed for using low-rank coal in coke-making. • TD of coal produced soluble fractions (TDSFs) with coking application potentials. • Methanolysis during TD effectively increased TDSFs yield from low-rank coals. • TDSFs exhibited superior caking and coking properties compared to raw coals. • Feasibility of using TDSFs from low-rank coals for coke-making was verified. [ABSTRACT FROM AUTHOR]

• Co-pyrolysis of high-sulfur coal with fat/lean coals to examine sulfur migration. • Suldifies and pyrite easily decomposed and removed during coal pyrolysis. • Thiophene and sulfone are recalcitrant during pyrolysis. • Release of volatile matters favors sulfur migration into gas phase in pyrolysis. Desulfurization remains a critical yet challenging aspect of producing high-quality metallurgical coke through pyrolysis. Previous studies have suggested that introducing hydrogen-rich gases may improve sulfur removal efficiency. To further explore this approach, we investigated the effects of volatile matter on sulfur migration during co-pyrolysis of high-sulfur coal (SC) with both fat coal (FC) and lean coal (LC). Our findings indicate that most sulfur is transferred into the coke during pyrolysis, with sulfide and pyrite being relatively easy to decompose, while thiophenes and sulfones tend to be thermally stable. Co-pyrolysis with FC significantly decreased sulfur content in the final coke product, while co-pyrolysis with LC resulted in higher sulfur content. The comparative analysis points to the beneficial influence of volatile matter in promoting desulfurization through enhanced sulfur transfer into the gas phase and reduced sulfur fixation with nascent coke. These findings offer practical guidance for coke-making industries to optimize coal blending scheme and to achieve efficient desulfurization during coke-making. [ABSTRACT FROM AUTHOR]

Abstract: The effects of pre-swelling treatment of Shenhua coal at mild temperatures (less than 160 °C) on its hydro-liquefaction properties were determined in this paper. It was found that with the increase of pre-swelling temperature in tetralin (THN) up to 120 °C, the liquefaction conversions of swollen coals increased. However, when N-methyl-2-pyrrolidinone (NMP) was used as swelling solvent, the liquefaction conversion decreased with the increase of pre-swelling temperature. The liquefied product distributions were very much dependent on the pre-swelling pretreatment conditions, and the mechanism was discussed. Based on the results obtained, a new swelling-liquefaction combining technology (SLCT) was advanced, in which the liquefaction conversion and oil+gas yield were enhanced. [Copyright &y& Elsevier]

Abstract: Three cokemaking bituminous coals were extracted by the CS2/NMP mixed solvents with different content of NMP, and the effect of the amount and the component of coal soluble constituents on the caking property of the extracted residues of coals were investigated in this study. The CS2/NMP mixed solvent (1:1 by volume) was found to give the maximal extraction yields for the three coals, and the fat coal gave the highest extraction yield of 78.6% (daf) corresponding to its highest caking index of 101. It was found that for coking coal, when the extraction yield got to the maximum of 25.3% in the 1:1 by volume of CS2/NMP mixed solvent, the residue extracted still had caking property with the caking index of 19. This means parts of the caking constituents of coal are un-extractible because of covalent bonding or strong associative cross-links. The soluble components extracted by the CS2/NMP mixed solvent and their effects on the caking indexes of the residues at a similar extraction yield quite differed depending on the NMP content in the mixed solvent. The coal solubles extracted by the CS2/NMP mixed solvent with NMP less than 50% contained less light constituents with less of oxygen groups. This may lead to the decrease in the caking indexes for the residues obtained at the similar extraction yields compared to those of the CS2/NMP mixed solvent with NMP more than 50%. [Copyright &y& Elsevier]

Understanding the sulfur migration during pyrolysis of coals especially high-sulfur coals is important. However, structural complexity and diversity of coals make it face huge challenge. In this study, a predictive model for morphological sulfur migration was developed using machine learning based on proximate analysis, ultimate analysis, sulfur forms of raw coal, ash composition, and blending ratio of coal. Three algorithms, i.e., Random Forest, XGBoost, and LightGBM were introduced and compared. The results show that six features are sufficient to accurately predict the products (R2 > 0.9, RMSE < 3.01%). LightGBM model has the advantages of better accuracy, generalization, efficiency, and performance, and Hyperopt has a higher upper limit than Grid-search. H content has a significant effect on S content in chars (St,d char) and increasing H content from 5.0–5.3 wt% facilitates desulfurization. In addition, CaO, K 2 O and Fe 2 O 3 also have remarkable effects on St,d char. Higher H and volatile contents have a greater effect on thiophene removal in char. This work can provide a new approach to explore the sulfur migration in coal blending for coking. [Display omitted] • Prediction of pyrolytic sulfur migration using Random Forest, XGBoost and LightGBM. • High prediction performance with reduced features (R2 > 0.9, RMSE < 3.01%). • The importance of different features on pyrolytic sulfur form was determined. • LightGBM was used to analyze the influence of sulfur migration from various angles. • Clearer investigation of morphological sulfur migration and new ideas for desulfurization. [ABSTRACT FROM AUTHOR]

• Ni-Mo-S/Al 2 O 3 is active and reusable for hydro-liquefaction of SDP. • Ni-Mo-S/Al 2 O 3 promotes hydrogenation of SDP into hexane soluble fraction. • Hydrogen donor favors formation of light product during hydro-liquefaction. • SDP converts into 1–3 rings aromatics and their derivatives after hydrogenation. This work performed de-polymerization of Shengli lignite (SL) to remove minerals, and the resultant product (denoted as SDP) was subjected to hydro-liquefaction to prepare value-added aromatic products, especially n-hexane soluble fractions (HS for abbreviation). Compared with raw lignite, SDP is easily converted to light products (HS) with low H 2 consumption due to its small molecular weight and less free radicals generated during hydro-liquefaction. Appropriate temperatures (e.g., 400 °C) are required for efficient conversion of SDP into HS fractions. Ni-Mo-S/Al 2 O 3 catalyst effectively promotes hydrogenation of SDP into HS during the reaction, moreover, the condensation reaction is effectively reduced. The yield of HS (Y HS) reaches to 73.7% and the yield of THFI (Y THFI) is only 2% with the use of Ni-Mo-S/Al 2 O 3 at 400 °C. The Aromatic fractions in the solvent effectively reduce Y THFI through suppression of condensation reaction, and the hydrogen donor solvents remarkably increase Y HS. The HS fractions primarily consist of aromatic hydrocarbons with 1–3 rings and aromatic derivatives containing alkyl as well as various oxygen-containing functional groups. [ABSTRACT FROM AUTHOR]

[Display omitted] • Interactions during co-firing high sodium coal and coal gangue examined. • AAEM are responsible for synergistic combustion of the blended fuel. • N O is reduced while S O 2 is enhanced during co-firing at 1000 °C. • CaO particpates competitive reactions with both minerals and desulfurization. • Formation and emission mechanism of NO and S O 2 is proposed. To promote the utilization of coal gangue (CG) as alternative fuels for heat or power generation, this work investigated the interactions between a CG (denoted as XJG) and a high sodium coal (HSQ) during co-combustion as well as the evolution behaviors of gaseous pollutants (S O 2 and N O). Results show that co-firing HSQ with less than 30 % XJG does not deteriorate its combustion performance. Synergistic conversion is observed due to the complementarity of the fuels in volatile matter, fixed carbon, ash content and reactivity. Moreover, alkali and alkaline-earth metals promote co-firing and lower activation energy of combustion from 100 to 70 kJ/mol. Both S O 2 and N O are evolved in two stages during co-combustion as described by the shrinking core model and 3D-diffusion model. N O is reduced by char and C O and the reduction is catalyzed by the alkaline species(especially CaO) in ash. S O 2 emission behavior is significantly varied by the competitive reactions of calcium oxide with silica/alumina species. Overall, N O is decreased by about 10 % relatively at 900–1100 °C while S O 2 is notably enhanced at 1000 °C by 23 %. The mechanism of formation and reaction of S O 2 and N O are proposed. These results provide useful reference for clean utilization of CG and controlling of polluting gas emission, thus boosting sustainable development of energy, ecology and environment. [ABSTRACT FROM AUTHOR]

Thermal dissolution (TD) of coal and hydro-liquefaction of the thermal dissolution soluble fraction (TDSF) with a high activity catalyst is one of effective high efficient hydro-liquefaction of coal techniques. In this study, a Chinese Shenfu (SF) sub-bituminous coal was thermally dissolved, and the TDSF obtained was further hydro-liquefied with Ni–Mo-S/Al 2 O 3 catalyst. Based on the hydro-liquefaction results, a model including series and parallel reactions was established for the hydro-liquefaction of TDSF catalyzed by Ni–Mo-S/Al 2 O 3 , and the regressive reactions were ruled out in the model. From the kinetic parameters calculated, it suggested that the regressive reactions including the char formation reactions were negligible in the hydro-liquefaction of TDSF catalyzed by Ni–Mo-S/Al 2 O 3 . The reactions of TDSF to preasphaltene and preasphaltene to oil + gas predominated the formation of oil + gas. Ni–Mo-S/Al 2 O 3 could decrease the activation energy of preasphaltene to oil + gas reaction, thus promoting the formation of oil and gas in the catalytic hydro-liquefaction of TDSF. [ABSTRACT FROM AUTHOR]

The fast-increasing demand for high-performance carbon conductive paints has motivated the use of inexpensive precursors and easy-to-manufacture methods to scale up production. The performance of carbon conductive paints highly depends on the precursor types, carbonization conditions and the coordination between carbon pigment and binder. This work investigated the effect of precursors (by-products of coking industry including coal tar pitch, anthracene oil, naphthalene oil, and washing oil) on the structure and properties of carbon pigment, as well as the influences of binders polyvinylidene fluoride (PVDF), styrene-butadiene emulsion, and acrylic emulsion on the electrothermal properties and adhesion of carbon paint coating. The conductive pigment prepared from coal pitch has nano-sheet structure, high sp2 content, large sp2 cluster size and high disordered structure, resulting high carrier concentration and mobility, and low volume resistivity. The carbon conductive coating fabricated from coal pitch-based pigment and PVDF (PC-PVDF) has good electrothermal properties, excellent stability, low volume resistivity, good adhesion and corrosion resistance. The electrical conductivity of carbon-PVDF composites prepared from coal tar pitch, anthracene oil, naphthalene oil, and washing oil as precursors were 15.7, 3.0, 4.4, and 4.0 S/m, respectively. Coal pitch-derived conductive pigment-PVDF carbon coating exhibits excellent Joule heating performance, i.e., up to 147 °C at 20 V when heating at 122 °C/min, uniform temperature distribution, and excellent reusability. This work demonstrates the potential application of coal pitch-based pigment-PVDF coating for Joule heating. [Display omitted] • The effects of precursor and binder types on the properties of conductive coating were investigated. • Coal pitch-based conductive pigment has nano-sheet structure, high sp2 content, large sp2 cluster size. • PVDF is an ideal binder for highly conductive coal tar-based carbon pigments. • Coal pitch-based conductive coating has good electrothermal properties, excellent stability, and good adhesion and corrosion resistance. [ABSTRACT FROM AUTHOR]

[Display omitted] • N,O,S-multidoped porous carbon was fabricated using a widely available high-sulfur coal. • HNO 3 oxidation increases specific surface area, pore volume, and the defects of NOSTPC. • The S@NOSTPC(O) delivers a high capacity of 645 mAh g−1 at 2C after 200 cycles. • HNO 3 oxidation increases chemical adsorption and conversion of polysulfides together with the catalytic oxidation of Li 2 S. Heteroatoms-doped carbon materials have received increasing interest as promising sulfur hosts for lithium-sulfur (Li-S) batteries. Herein, high-sulfur coal was selected as the low cost and earth-abundant precursor and HNO 3 pre-oxidation was adopted to tune the microstructure of N,O,S-multidoped three-dimensional porous carbon (NOSTPC) to facilitate affinity and conversion toward polysulfides. HNO 3 pretreatment significantly increases the specific surface area, pore volume, and the content of pyrrolic nitrogen and the defects in NOSTPCs. HNO 3 pre-oxidation increases the specific capacity of Li-S battery with NOSTPC as the sulfur host from 559.3 to 860.4 mAh g−1 at 1C, and the capacity retention from 67% to 81% after 200 cycles. The satisfying performance benefits from that oxidation pretreatment improves the chemical adsorption of polysulfides by NOSTPC(O), and accelerates the kinetic conversion of polysulfides together with the catalytic oxidation of Li 2 S. Accordingly, the good performance of high-sulfur coal-based NOSTPCs can not only promote practical application of Li-S batteries, but also facilitate the efficient utilization of high-sulfur coal. [ABSTRACT FROM AUTHOR]

The co-thermal dissolution (CTD) behavior of Shenmu–Fugu subbituminous coal (SFSBC) and sawdust was investigated in this study. The synergic effect between SFSBC coal and sawdust in CTD was probed. The individual thermal dissolution (TD) of SFSBC and sawdust showed that sawdust gave much higher thermal dissolution yield (TDY) and lower thermal soluble yield (TSY) than SFSBC. This resulted in much lower difference of (TDY–TSY) for SFSBC compared to that of sawdust at the same condition. CTDs of SFSBC and sawdust in 1-methylnaphthalene (1-MN) at different temperatures were carried out. The results suggested that there existed a negative synergic effect for TDY in the whole range of temperatures studied, but a positive synergic effect for TSY at 320 and 340 °C. The largest enhancements in TSY of 33.6% comparing with the corresponding calculated weighted mean values of the individual TD of SFSBC and sawdust were obtained at 320 °C. The positive synergic effect can be attributed to that the thermal depolymerization of lignin at relatively low temperatures produces lots of intermediates such as phenoxy radicals, which then attack the coal, causing scission of aliphatic carbon–carbon bonds in the coal and promoting the TD of coal. [ABSTRACT FROM AUTHOR]

• TDSF is rich in arenes and suitable for saturated hydrogen to prepare jet fuel. • BF 3 /SBA-15 is effective in enhancing TDSF yield during TD of lignite. • CH 3 OH greatly increases TDSF yield and BF 3 /SBA-15 promotes TD of lignite. • Tetralin dramatically increases cyclanes content during TDSF hydro-liquefaction. • Hydro-liquefaction of TDSF prepared at low temperatures favors cyclanes formation. This work proposes a promising means for jet fuel production using lignite as feedstock, which is of great significance for resource utilization of low rank coals (LRCs). Thermal dissolution soluble fractions (TDSFs) were prepared and the ensuing hydro-liquefaction of the TDSFs was performed to obtain liquefied oil, which can be upgraded and refined into jet fuels. The effects of different catalysts on the catalytic thermal dissolution (TD) properties of Xilinguole (XLGL) lignite were studied. The structure of the TDSFs was analyzed and characterized. The results suggested that the catalytic TD could notably enhance TDSFs yield compared to non-catalytic TD, and the activity of the four catalysts used was in order of BF 3 /SBA-15＞FeS + S＞SO 4 2-/ZrO 2 ＞Fe 2 O 3. The oil yield and composition, especially cyclanes content, varied with the hydro-liquefaction conditions, i.e., technical parameters including temperature, catalyst, solvent and TDSF type significantly changed the oil yield and cyclanes content, thus affecting the potential for jet fuel production. The Ni-Mo-S/γ-Al 2 O 3 catalyst effectively promoted TDSFs hydro-liquefaction, and both conversion and oil yield increased with rising temperatures during catalytic and non-catalytic hydro-liquefaction. On the other hand, the cyclanes content in liquefied oil decreased with rising hydro-liquefaction temperatures. The TDSFs prepared at low temperatures are more suitable for jet fuel production due to its higher cyclanes content through hydro-liquefaction. [ABSTRACT FROM AUTHOR]

The thermal dissolution (TD) behaviors of Shenfu (SF) coal, a kind of Chinese sub-bituminous coal at different temperatures in different solvents were investigated in this study. The results show that almost all of the ash in the raw coal was transferred into the TD residue. The TD soluble yield (TDSY) of SF coal increased with the raising of TD temperatures from 300 to 360°C for 60min with 1-methylnaphthalene (1-MN) as solvent, and the highest TDSY of 56% was obtained at 360°C. Further raising temperature to 380°C, the TDSY decreased rapidly. The highest TDSY obtained at 360°C can be attributed to the partial pyrolysis of SF coal. When N-methyl-2-pyrrolidinone (NMP) or methanol was added into 1-MN, the TDSY greatly increased. Especially, when 20% NMP was added, the TDSY reached up to 75%. Since NMP is a strongly polar solvent, it can dissociate the strong cross-links in the coal, resulting in the increase of the TDSY. However, when both of NMP and methanol were added into 1-MN, the TDSY dramatically decreased, indicating that there are some interactions between the two solvents. Crude methyl naphthalene oil (CMNO) was a more effective solvent for the TD of SF coal than 1-MN, and its TDSY achieved 66% at 360°C for 60min. Addition of various polar solvents into CMNO, the TDSY decreased, especially for the addition of methanol, the TDSY decreased by about 15%. The result indicated that methanol may react with some active fractions in CMNO, resulting in the decrease of the TD effect. When both of NMP and methanol were added into CMNO, the TDSY dramatically decreased due to the interaction between them. The TD soluble fractions (TDSFs) obtained from various solvents were characterized by elemental and FTIR analyses. [ABSTRACT FROM AUTHOR]

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

• Structural features of sub-fractions of liquefaction residues were analyzed. • Isothermal CO 2 gasification rate decreased as Coal ≥ Res ≫ DeR > PAA. • Enriched minerals improved but condensed aromatics reduced gasification reactivity. • USC was superior to UR for analyzing isothermal CO 2 gasification of residues. Coal hydro-liquefaction is important means for producing liquid fuel thus ensuring energy security for countries lacking crude oil reserves such as China. Liquefaction residues account for one third of feeding coal and its utilization is crucial for reducing the cost of hydro-liquefaction. Residues can be gasified to produce H 2 thus eliminate the hazardous solid waste. Liquefaction residues are complex mixture of unreacted coal, heavy components, inherent mineral matters in coal and used catalysts. This work investigated the structural features and gasification reactivity of the sub-fractions of residues (Res) including preasphaltene and asphaltene (PAA), deashed residues (DeR), and raw coals were also used for comparison. The results showed that the enriched minerals in the residues significantly accelerated gasification while the compact and condensed aromatic structures remarkably inhibited the reaction. The gasification rate decreased in the order Coal ≥ Res ≫ DeR > PAA during isothermal CO 2 gasification. Kinetic analysis of gasification was performed with the uniform reaction (UR) and unreacted shrinking core (USC) model, and the kinetic parameters (E α and A) obtained with the two models were well correlated. Comparatively, USC model was superior to UR model in describing the gasification behaviors of both the coals and the sub-fraction of the residues. These results are potentially helpful for optimizing gasification conditions and realizing clean and efficient utilization of the residues. [ABSTRACT FROM AUTHOR]

• Carajás hematite can be moderately reactive oxygen carrier in CF-CLC. • K 2 CO 3 promotes carbon conversion but lowers CO 2 selectivity in CF-CLC. • CuO effectively and stably enhances CF-CLC performance of the hematite. • CuO is superior to K 2 CO 3 for hematite decoration in CF-CLC. Coal fuelled-chemical looping combustion (CF-CLC) is a novel and promising technology for CO 2 mitigation. Reactive, cheap and environmental-friendly oxygen carriers (OC) are crutial for the development of CF-CLC. Carajás hematite is high grade iron ore with the largest reserve in the world, and its CF-CLC performance is examined in this work. Modifications of the Carajás hematite with K 2 CO 3 and CuO were performed and the effects of the modifications were evaluated. The results show that Carajás hematite was moderately reactive and could be potential OC for CF-CLC. Decoration of the Carajás hematite with K 2 CO 3 effectively improved carbon conversion but lowered CO 2 selectivity. K 2 CO 3 was gradually lost thus reducing the performance of the decorated hematite. In addition, hematite particles were sintered after adding K 2 CO 3. CuO remarkably enhanced carbon conversion, reaction rate as well as CO 2 selectivity, and the Cu-modified hematite remained stable and highly reactive although agglomeration occurred in CF-CLC cycles. Overall, CuO is superior to K 2 CO 3 for modification of Carajás hematite, and the CuO-decorated hematite is suitable and promising OC for CF-CLC. [ABSTRACT FROM AUTHOR]

• Aromatic layers are condensed and crystallites grow but graphitized during coalification. • Aliphatic fractions increased and aromatics decreased with rising coal metamorphism. • Aromatic clusters grow while the side-chains are lost with the rise of coal rank. • Consistent results of molecular structures are obtained with multi-spectral techniques. In-depth understanding of coal molecular structures is crucial to the clean and efficient coal conversion, as they are the dominant factors determining the reactivity and reaction behaviors of coals in thermal conversions such as combustion, pyrolysis, gasification and liquefaction. However, the molecular structures of coals are still far from clear due to the intrinsic complexity and heterogeneity of coals. This work probes the molecular structures of eight coals of various metamorphic grades with combined spectral techniques of X-ray diffraction (XRD), solid state 13C NMR and FTIR spectra. The structural parameters were correlated with the coalification indicator R o to investigate the structural evolutions during coal metamorphism. Consistent results concerning the structural evolution during coalification were obtained with different techniques. From the parameters of proximate and ultimate analysis, the increasing aromaticity and decreasing aliphatic fractions with rising coalification degree are observed. XRD patterns show the ubiquitous presence of amorphous carbon, the gradually condensing aromatic layers, and the size-growing but graphitizing crystallites during coalification. 13C NMR spectra reveal different types of carbons presented, the increasing aromatic and decreasing aliphatic components, the growing size and weight but reducing number of side-chains of the aromatic clusters. FTIR spectra indicate shortening and reducing of aliphatic chains, as well as enhancing aromaticity with the deepening metamorphism. These findings shed light on the structure features of coals and are potentially useful to the clean and efficient coal utilization. [ABSTRACT FROM AUTHOR]

Hydro-liquefaction of an asphaltene from thermal dissolution of Xinlinguole lignite (XLAS) was carried out, and the effects of catalyst, temperature and reaction time on oil yield and cyclanes content in oil for the potential jet fuel were probed in this study. Comparing the hydrogenation activities of three catalysts i.e. Cu-Ni/γ-Al 2 O 3 , Ni/ZSM-5 and Ni-Mo-S/γ-Al 2 O 3 , it was found that Ni-Mo-S/γ-Al 2 O 3 was the most beneficial for jet fuel production from coal liquefied oil due to it contained a continuous distribution of weaker to stronger acidic sites. It gave the highest oil yield of 68.8%, and cyclanes content of 20.5% in the oil, which displayed the highest hydrogenation activity for arenes saturated hydrogenating among the three catalysts used in the hydro-liquefactions of XLAS at 360 °C for 90 min. For Cu-Ni/γ-Al 2 O 3 , it only contained weak acidic sites therefore it gave the lowest saturated hydrogenating activity. With rising of temperature, oil yield increased, but cyclanes content in oil decreased in the hydro-liquefactions of XLAS under Ni-Mo-S/γ-Al 2 O 3 catalyst. The highest content of cyclanes (29.3%) in oil was obtained at 280 °C for 90 min. Reaction time remarkably affected cyclanes content in oil. With the reaction time prolonging from 30 to 60 min, oil yield and cyclanes content in oil increased. Further prolonging reaction time to 90 min, oil yield hardly increased, but cyclanes content in oil decreased from 23.6% to 20.5% at 360 °C with Ni-Mo-S/γ-Al 2 O 3 catalyst. Some oxygen-containing compounds (OCs) may convert into cyclanes by hydro-deoxygenation (HDO) with increasing of reaction time. [ABSTRACT FROM AUTHOR]

A deep understanding of coal pyrolysis behaviors is essential for the clean and efficient coal utilization. Detailed structural characterization and kinetic analysis could provide valuable information about coal pyrolysis. This work deals with structural analysis and pyrolysis kinetics of four low-medium rank coals with the distributed activation energy model (DAEM). The carbon structures, pyrolysis characteristic and kinetic parameters were correlated to gain some updated insights into coal pyrolysis. The results show that aliphatic carbons gradually convert into aromatic ones, and the aromatic clusters grow in both size and weight with the rise of coal rank. The side-chains of aromatic clusters are shortened and eliminated thus aromaticity is increased. Characteristic temperatures of pyrolysis are closely related to coal properties and carbon types. Both initial and peak temperatures increase with FC ar and C daf while decrease with VM ar and H / C. Meanwhile, the initial temperature is related to the aliphatic carbon (f al ) and aliphatic carbon bonded oxygen (f al o) due to their low bonding energies, while the peak temperature is linked to the aromatic carbon (f a) and aromatic bridgehead carbon (f a B) because of their higher bonding energy. DAEM model is reliable for analyzing pyrolysis kinetics of bituminous coals. The range of activation energy gradually narrows down with the increase of coal rank, corresponding to the concentrating distribution of different carbon types. Moreover, DAEM could accurately predict the pyrolysis behavior of bituminous coals at very high heating rates, but the effectiveness of DAEM in modeling and predicting pyrolysis of lignite is less satisfying. [ABSTRACT FROM AUTHOR]