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In aim to study the influence of circulating ash used as heat carrier and dolomite used as catalyst on mercury transition during the step conversion of coal pyrolysis and combustion, five experiments with different operating conditions were conducted in this study, including four pyrolysis experiments of raw coal, coal/ash, coal/dolomite, coal and ash/dolomite, and combustion experiment of pyrolysis solid product. By changing the experimental conditions including final pyrolysis temperature, heating rate, coal-ash ratio and dolomite type, the transition path and final mercury distribution in the step conversion process were comprehensively analyzed. Experiments results indicated that mercury completely released out from coal when the final pyrolysis temperature was 600 °C. The individual addition of ash could promote the mercury release from coal at lower temperature. Dolomite could catalyze the oxidation of Hg0 in gas phase, and the modified dolomite had better catalytic capacity for Hg0 oxidation than natural dolomite. The addition of circulating ash and natural dolomite both had a certain catalytic effect on Hg0 emission peaks during the coal pyrolysis. Increasing the coal-ash ratio was conducive to the oxidation of Hg0 in pyrolysis gas. During the direct combustion of coal, the content of Hg0 released into the gas phase could reach to 69.97%. By adding ash, ash/natural dolomite and ash/modified dolomite to the coal pyrolysis process, the content of Hg0 in pyrolysis gas decreased to 58.99%, 34.77% and 31.30%, respectively. The research is able to offer the theoretical foundation for mercury contaminants' removal and process optimization of the step conversion technology. • Ash heat carrier can promote the release of mercury in coal at lower temperatures. • Fe 2 O 3 has the strongest catalysis ability towards Hg0. • Dolomite and circulating ash have a synergistic effect on Hg0 oxidation. • The step conversion process greatly reduces the treatment pressure of mercury. [ABSTRACT FROM AUTHOR]

To realize the high value-added utilization of low-rank coal and elucidate the selectivity of solvent structure and oxygen-containing compounds in low-rank coal, Zhaotong (ZT) lignite and Naomaohu (NMH) sub-bitumite were subjected to thermal dissolution in three types of oxygen-containing solvents with different properties, namely ethanol (ET), tetrahydrofuran (THF) and ethyl acetate (EA). The soluble portions (SPs) obtained were separated by column chromatography into three types of fractions: hydrocarbon (HY), non-hydrocarbon (NHY) and asphaltene (ASP). The results indicated that the yields of SPs in all three solvents for each coal was ET > THF > EA, and the ratios of column chromatographic fractions of SPs of the two coals were significantly different, with lower asphaltene content in the SPs of NMH. The thermal dissolution process of the three solvents significantly reduced the oxygen content of low-rank coal, and the deoxygenation capacity was in the order of ET > THF > EA. More medium or low polarity compounds could be obtained from NMH than from ZT through thermal dissolution process. ET showed excellent selectivity for the generation of both phenols and esters, where the phenols were mainly alkylphenols. THF could release highly condensed polycyclic compounds from coal thus more naphthalenols containing substituent groups were detected in phenols. And it was more selective to COO bonds in NMH than ZT from the results of XPS. More esters were detected in the SPs of NMH compared with ZT. EA had a strong selectivity for C O in low-rank coals, and the thermal dissolution process released a large number of esters, which could be divided into alkanoates and aromatic acid esters. This study can provide a theoretical basis for extracting high value-added chemicals from low-rank coal under mild conditions. [Display omitted] • Thermal dissolution can obtain oxygenated chemicals and upgrading coals. • Ethanol has the strongest deoxygenation capacity. • Ethyl acetate shows selective dissociation ability for esters. • Tetrahydrofuran dissociates highly condensed polycyclic compound such as naphthols. [ABSTRACT FROM AUTHOR]

To explore the sulfur transformation in the grading utilization of coal, the forms and distributions of sulfur at different operation parameters and foreign minerals were investigated in coal pyrolysis with solid heat carrier and combustion, respectively. The results show that the increasing pyrolysis temperature increases the sulfur content in the gaseous phase. For the coal with larger particle size, more sulfur will residue in char. The change of the mass ratio of quartz sand to coal and heating rate have little effect on the sulfur distribution in gas, tar and char products. After 3 wt% CaO is introduced to the raw coal, sulfur in gas and tar decreases from 29.68 and 12.16 wt% of the raw coal to 22.31 and 10.66 wt%, respectively. Fe 2 O 3 mainly affects the migration of gaseous sulfur to solid phase sulfur during coal pyrolysis. MgO, NaOH, and KOH have no sulfur fixation effect. The sulfur-fixed efficiencies for 3 wt% CaO and 3 wt% Fe 2 O 3 are 17.17 and 38.16 wt%, respectively. When the contents of CaO and Fe 2 O 3 increase, the sulfate sulfur and sulfide sulfur in the char increase, and the sulfur fixed in ash which obtained from the combustion of char increases. The inhibitory effect of CaO on the secondary release of SO 2 in the combustion stage is stronger than that of Fe 2 O 3 . This paper provides a basic reference for the removal of sulfur during the step conversion of coal pyrolysis and combustion. [ABSTRACT FROM AUTHOR]

To understand the bond cleavage behavior of the oxygen-containing structure during lignite pyrolysis, the pyrolysis experiments of Zhaotong (ZT) lignite were carried out at 300–600 °C. The main focuses are the form and the migration behavior of oxygen elements at different temperatures. The C-O content in ZT exceeds that of C O and COOH. In temperature region below 450 °C, the C O, COOH in ZT are cleaved, generating a large amount of CO 2 and CO, while at 450 °C, the structure containing C al -O, C O are cleaved with the formation of oxygenated liquid components, such as phenols, acids, as well as ketones, resulting in an increase of oxygen in the tar from 1.32 wt% at 300 °C to 4.12 wt% at 450 °C. With the increasing temperature, the demethoxy, dealkylation reaction, and ester bond cleavage are significant, resulting in the reduction of alkylphenols and ester compounds. At high temperatures, the cleavage and rearrangement of the methoxy group to form phenol and methylphenol, and the cleavage of C ar -O with higher bond dissociation energy leads to a decrease in phenols of tar, and O of char. The pyrolysis upgrading could change the oxygen distribution of the products and significantly reduce the oxygen content of ZT. [Display omitted] • The C O group in ZT is more likely to form ketones than oxygen-containing gases. • The bond cleavage number for CO 2 , CO formation is higher than hydrocarbon gases. • The structure containing C al -O, C O are cleaved with more O-tar at 450 °C. • The C ar -O cleavage leads to a decrease in phenols, and still exists at 600 °C. • Higher temperatures result in more oxygen in gas and less oxygen in char. [ABSTRACT FROM AUTHOR]

Gas chromatography-mass spectrometry (GC-MS) was used to analyze the soluble portions (SPs) of eight lignites which were obtained by extracting using cyclohexane, methanol and ethanol, respectively, as the solvent. For thermal dissolution at 300 °C using cyclohexane, the intermolecular interactions between mobile phase and macromolecules in coal were weakened. Consequently, non- and low-polar compounds such as alkanes and aromatics were well dissolved. Methanol and ethanol were more likely to closely interact with oxygen-containing functional groups and promoted the breakage of hydrogen bonds and weak covalent bonds. Hierarchical cluster analysis classified all the 24 SPs, and the SPs from cyclohexane and ethanol solvents exhibited more similarity. Partial least squares discriminant analysis was established to reproduce the classification results of SPs entirely and accurately. The SPs were further classified by combining a small number of geochemical characteristic compounds rather than massive GC-MS data. • Three low-rank coals retain the biological properties of numerous aquatic plants. • Data mining provides convenient and accurate classification for coal samples. • PLS-DA classification is determined by differential geochemical characteristic compounds. [ABSTRACT FROM AUTHOR]

Investigating the oxygen bond cleavage and its migration mechanisms during the pyrolysis process of sub-bituminous coals is essential for their classification utilization. The present study employed a fixed-bed pyrolysis technique (temperature range: 350–600 °C) to explore the cleavage of oxygen-containing bonds and subsequent behavior of oxygen migration and transformation during the pyrolysis process of Naomaohu sub-bituminous coal (NSBC). X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy results reveal that the organic oxygen in NSBC predominantly exists as the form of C–O bonds, accounting for 22.81 wt% of the total composition, mainly encompassing hydroxyl, carbonyl, ester, and ether groups. The organic oxygen in the light tar is mainly in the form of phenols, reaching 1.71 wt%, of which methyl substituted phenols is predominant at a final pyrolysis temperature of 600 °C. This can be attributed to the presence of more aryl ether bonds and hydroxyl groups in NSBC, which are prone to cleavage at higher temperatures, resulting in the formation of phenoxyl radicals. Additionally, the higher temperature facilitates the weakening of hydrogen bonds between phenolic hydroxyl groups, thereby enhancing the yield of phenolic compounds. The ester compounds present a decreasing trend with increasing temperature, primarily associated with the cleavage temperature of ester linkers being 350 °C, suggesting that an increase in temperature favors the cleavage of ester bonds. In addition, the cleavage of C–O bonds begins to accelerate significantly during the pyrolysis temperature range of 450–500 °C, subsequently accounting for the pronounced proliferation of phenols within this specific thermal interval. The oxygen content in semi-coke decreased with the increase of temperature, from 85.27 wt% at 350 °C to 37.17 wt% at 600 °C, while the oxygen content in the pyrolysis gas increases from 11.63 wt% at 350 °C to 47.53 wt% at 600 °C, indicating that a significant migration of organic oxygen to the pyrolysis gas during the pyrolysis of NSBC. This study can deepen the understanding of the transformation mechanism of oxygen-containing structure in NSBC pyrolysis process, and provide a theoretical basis for high-grade utilization of low-rank coals. [Display omitted] • Elevated temperatures promote the migration of organic oxygen into volatile products. • The breaking of organic oxygen bonds depends mainly on temperature. • High temperatures favor the breaking of aryl ether bonds to form phenols. • Cleavage of aryl alkyl ethers at 350–450 °C leads to a large increase in alcohols. • The release of volatile oxygenates leads to a reduction in the oxygen content of the coke. [ABSTRACT FROM AUTHOR]

The compositional distribution of pyrolysis products is related to the molecular structure of coal and pyrolysis parameters. In this study, gaseous products generated from the pyrolysis of two low-rank coals were analyzed by an online home-built infrared detection system. The effect of heating rate and temperature on compositional distribution was considered and evaluated. Fourier transform infrared (FTIR), gas chromatograph/mass spectrometry (GC/MS), and Orbitrap-MS were employed to analyze other pyrolysis products such as raw coals, chars, and tars. In the pyrolysis process, oxygen-containing compounds in coal were the first species to participate in pyrolysis reactions. With the enhancement of temperature, the content of aromatic hydrocarbons showed an increasing trend, and the contents of aliphatic hydrocarbons and oxygenates decreased. In the four major pyrolysis gases, the yield of H 2 was the highest and the lowest for CO 2. In addition, dynamic curves of the main pyrolysis gas were obtained, and the activation energies of pyrolysis gases were calculated by Ozawa-Flynn-Wall's (OFW) method. The possible generation pathways of gaseous products were proposed. • Online infrared device was used to study the release behavior of pyrolysis gas. • The transformation path of pyrolysis products is proposed. • The effect of secondary reaction on the product was investigated. [ABSTRACT FROM AUTHOR]

• The content of H 2 S is positively correlated with that of H 2. • Fe 2 O 3 , CaO, and MgO are main components for sulfur fixation and tar catalysis. • CFB ash and dolomite have the ability to promote the removal of sulfur from tar. • Ash and dolomite can improve the cleavage reactions of thiopyrans and thiazoles. For investigating the effectiveness of ash and dolomite on the migration of sulfur from coal pyrolysis volatiles, pyrolysis experiments of Xinzhou high-sulfur bitumite were executed in a self-designed reactor. The influences of heat carrier species, mass ratios of ash to coal, and ash particle sizes on the sulfur content in products were investigated. More importantly, the composition of sulfur-containing compound in tar was analyzed. The effect of different heat carriers on the volatiles was in the order of ash > fresh dolomite > deactivated dolomite. With ash and dolomite as heat carriers, H 2 and CO decreased, and CO 2 increased. In addition, H 2 S content was positively correlated with H 2 content. The deactivated dolomite contains a large amount of CaS and MgS, and its influence on pyrolysis volatiles was weaker than that of fresh dolomite and CFB ash. When fresh and deactivated dolomites were used as heat carriers, the sulfur contents in tar and in heat carrier were higher than that in ash. Fe 2 O 3 , CaO, and MgO were the main components for sulfur fixation and tar catalysis in heat carriers. Mercaptan was easily oxidized by metal oxides. Ash and dolomite heat carriers had a certain catalytic effect on the cleavage reactions of thiopyrans and thiazoles. This research is worth for the purification of sulfur-containing pollutants in coal pyrolysis process by ash and dolomite. [ABSTRACT FROM AUTHOR]

Highlights • Oxygenated compounds could be selectively extracted by tetrahydrofuran. • Pyridine was able to selectively extract nitrogen-containing compounds. • Solvent pretreatment increased the oil yield from high-sulfur coal pyrolysis. • The relative contents of phenols from residues tar were higher than raw coal tar. • Solvent pretreatment decreased the high carbon number components in residues tar. Abstract In this study, high-sulfur bituminous coal was extracted with n-hexane, acetone, carbon disulfide, tetrahydrofuran and pyridine, respectively. The effect of solvent pretreatment on pyrolysis characteristic of high-sulfur coal was studied in a fixed-bed reactor. The heterocyclic aromatic hydrocarbons such as tetrahydrofuran and pyridine got higher extraction yields than other solvents. Oxygenated compounds could be selectively extracted by tetrahydrofuran with a maximum relative content of 9.09%, and nitrogen-containing compounds by pyridine with its content of 5.61%. However, all the solvents did not exhibit the selective extraction ability of sulfur-containing compounds. Compared with raw coal, the phenols content in pyrolysis tar from residues of pyridine and tetrahydrofuran increased significantly, and the sulfur compounds all exhibited lower content tendency. The solvent pretreatment can inhibit the radical condensation reaction effectively, and result in the reduction of high carbon number tar components, which is beneficial to the upgradation of pyrolysis tar. In addition, solvent pretreatment can be able to increase the oil yield, especially pyridine of 17.63%. [ABSTRACT FROM AUTHOR]

Semicoke derived from lignite and biomass has been utilized in soil remediation and activated sludge treatment. Nitrogen-doping treatment has been utilized to improve adsorption capacity of semicoke for phenols (such as humic acids). Known as nitrogen-rich biomass residue, spent coffee grounds (SCG) may serve as nitrogen resources when co-pyrolyzed with lignite. But impacts of SCG on structure and adsorption capacity of semicoke in co-pyrolysis have not been confirmed. In consideration of proteins in SCG, nitrogen fixation and the impacting mechanism have not been sufficiently confirmed. In this work, nitrogen fixation between lignite and SCG during co-pyrolysis were investigated by thermogravimetric analysis (TG) and pyrolysis experiments. Corresponding mechanism were speculated and confirmed by in-situ diffuse reflectance infrared Fourier transformation spectra (DRIFT) and mass spectrum (MS). Impacts of nitrogen fixation on adsorption of phenols on semicoke were investigated by X-ray photoelectron spectroscopy (XPS), adsorption kinetics analysis and density functional theory (DFT) calculations. Compared to theoretical values, higher contents of N have been obtained in co-pyrolyzed semicoke (N: 2.89%; pyridinic N: 44.86%), which implied N fixation and cyclization reactions. Fixation mechanism can be explained by formation of Amadori/Heyns intermediates in Maillard reactions. Release of volatiles and capture of NH 3 are crucial in 340–440 °C range, which result in nitrogen fixation. Then formation of pyrrolic and pyridinic N can be explained by cyclization reactions and decomposition of Amadori/Heyns intermediates in 550 °C pyrolysis. Enrichment of pyridinic N, pyrrolic N and C O might enhance adsorption of phenols by offering binding sites for formation of hydrogen bonds. Both C, N fixation and improved adsorption capacity (27.80 mg/g) have been realized for 7:3–550 semicoke. Consequently, doping treatment with typical nitrogen-rich biomass (SCG) may be feasible to enhance adsorption of phenols onto semicoke, based on selection of raw materials and pyrolysis conditions. • N-rich biomass residue and lignite were co-pyrolyzed for nitrogen fixation. • Role of Maillard reactions in nitrogen fixation was emphasized. • Co-pyrolysis conditions can be selected based on structure-activity relationship. [ABSTRACT FROM AUTHOR]

To investigate the effects of circulating ash heat carriers and dolomite catalysts on sulfur migration in the coal pyrolysis/circulating fluidized bed combustion staged conversion process, five experiments of coal pyrolysis, ash/coal co-pyrolysis, coal pyrolysis catalyzed by dolomite, ash/coal co-pyrolysis catalyzed by dolomite and combustion of pyrolysis solid products were designed and carried out. By examining the effects of pyrolysis temperature, heating rate, coal-ash ratio and dolomite species on sulfur migration, the final distribution of sulfur-containing pollutants throughout the staged conversion process was systematically analyzed. The results showed that the separate mixing of ash heat carrier at final pyrolysis temperature of 600 °C increased the residual sulfur in solid phase from 79.29 % of raw coal pyrolysis to 90.00 %. When dolomite catalyst was added individually, the sulfur released into gas phase and tar was reduced from 18.28 % and 2.43 % of the raw coal to 13.14 % and 1.94 %, respectively. And Fe additive significantly improved sulfur resistance of the dolomite catalyst. The regeneration process has little effect on the sulfur fixation capacity of natural dolomite. When ash heat carrier and dolomite catalyst were simultaneously added to the system, the sulfur fixed in ash increased from 79.29 % of the raw coal to 91.27 %, and the sulfur fixed in natural dolomite and modified dolomite accounted for 4.32 % and 4.46 % of the total sulfur, respectively. In the combustion experiments of pyrolysis solid phase products, 43.57 %, 65.57 % and 61.44 % of sulfur was retained in the solid phase residue after combustion with circulating ash, circulating ash/natural dolomite and circulating ash/modified dolomite were added, respectively. Compared with direct combustion of coal, the staged conversion process resulted in a 55 % reduction of sulfur in the boiler flue gas. This study provides a theoretical basis for the purification of sulfur-containing pollutants in the staged conversion process. [Display omitted] • The staged conversion process reduces 55 % sulfur in combustion boiler flue gas. • CFB ash and dolomite promote the residual sulfur in solid phase. • Fe additives improve the sulfur resistance ability of dolomite. • Regeneration process has little effect on sulfur fixation capacity of dolomite. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ionic liquids exhibited higher extraction efficiency than organic solvents. • Ionic liquids extract was more abundant components than organic solvents. • The yield of liquid increased and the highest yield was 60.51 % after pretreatment. • The distribution of pyrolysis products and nitrogen changed significantly. • The oxygen content was reduced and the oxygen was converted to phenols in bio-oil. As an important renewable bioresource, it is extremely important to find an efficient utilization approach for microalgae. During the main utilization method of pyrolysis process, a large number of high value-added products are wasted. In this article, extract-pyrolysis cascading utilization technical scheme was proposed and explored. The extract characteristic of microalgae using different solvents under mild condition were investigated. The selected solvents include conventional organic solvents and green solvent ionic liquids (ILs).The organic solvents were ethyl alcohol (EA), tetrahydrofuran (THF), pyridine (Py) and ILs were 3-dimethylamine propylamine formate (DMAPAF), diethylamine formate (DEAF), triethylamine formate (TEAF). ILs obtained higher extraction yields and wider varieties of compounds than organic solvents. Among them, TEAF possessed highest extraction yield of 22.97 % and oxygen-containing compounds account for 47.24 % of the extracts. The cross-linking bonds between the macromolecular structures of chlorella were destroyed after extraction. The product distribution of the subsequent pyrolysis process changed significantly. Compared with RAWC, the relative content of aromatic compounds and phenols in pyrolysis bio-oil increased, while the relative content of aliphatic compounds and nitrogen-containing compounds decreased. The total liquid yields increased through extract-pyrolysis cascading utilization, with the highest value of 58.51 % for TEAF. [ABSTRACT FROM AUTHOR]