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CuO/γ-Al 2 O 3 and CuO–MnO 2 –Fe 2 O 3 /γ-Al 2 O 3 catalysts were synthesized by impregnation method. Their performances for selective catalytic reduction (SCR) were explored in a 200 MW coal-fired power plant boiler tail flue. The effects of catalyst amounts, NH 3 /NO molar ratios, abrasion resistance, catalyst regeneration and the catalytic efficiencies for Hg 0 oxidation were also discussed here. The optimum temperature range for the SCR of NO over fresh catalysts was 300 ~ 400 °C. In the optimum temperature range, the efficiencies of the two catalysts were over 80%, with a maximum efficiency of nearly 90% obtained at 350 °C. Reducing the catalyst amounts to half did not change the efficiency dramatically. The highest SCR activity was obtained with NH 3 /NO molar ratios ranging from 1.0 to 1.2. Abrasion resistance test indicates that the mechanical strength of the catalysts can bear the industrial scale and long-term erosion of fly ash. The activities of the catalysts remained constant during a 200 h test. Meanwhile, the catalysts were able to maintain excellent NO reduction efficiency after three times recycling. CuO/γ-Al 2 O 3 and CuO–MnO 2 –Fe 2 O 3 /γ-Al 2 O 3 achieved 40% and 80% Hg 0 oxidation efficiency, respectively. The present study provides a promising catalyst for NO and Hg 0 removal for coal-fired power plants. [ABSTRACT FROM AUTHOR]

Mn–Ce/γ-Al 2 O 3 granular catalyst was modified by adding silver and then developed in the low temperature selective catalytic reduction (SCR) of NO with NH 3 . It showed outstanding SCR activity in low and middle temperature region and achieved 95% NO conversion at 250 °C. It also performed excellent space velocity tolerance in a wide range. The characterization results showed that silver mainly existed in the form of Ag and Ag 2 O, which could promote the migration of surface active oxygen and increase the weak Brønsted and strong Lewis acid sites. NO adsorption benefited from the addition of silver and mainly existed as the bridged nitrite and bidentate nitrate species. Introducing O 2 could create more oxidized surfaces and promote the NO oxidation, which prompted NO to be adsorbed as unstable monodentate nitrate, bridged nitrite and nitrate species. NH 3 could be adsorbed mainly on the Lewis acid sites as coordinated NH 3 and − NH 2 species, which also could be promoted by the introduction of O 2 . The mechanism of SCR reactions was also explored. It showed that most NO could be adsorbed as the unstable nitrates or nitrites firstly and then reacted with the adsorbed ammonia species. The most possible reaction pathway followed the Langmuir–Hinshelwood mechanism. [ABSTRACT FROM AUTHOR]

This study aims to investigate the importance of aromatic structures in tar to the destruction of tar itself during the volatile–char interactions. The same nascent char was subjected to interactions with two distinctly different volatiles (e.g. coal volatiles and biomass volatiles) at 700–900 °C. The results indicate that the aromatic structures in tar are more reactive with char than the non-aromatic structures, especially at high temperature (e.g. 900 °C). At lower temperatures (< 800 °C), the more aromatic coal tar can form coke on the char surfaces more easily than the more aliphatic biomass tar. At higher temperatures (≥ 800 °C), the aromatic structures in tar are cracked and/or reformed into gases through interaction with the char; the aromatic structures from biomass can be reformed over char more easily than those from coal. [ABSTRACT FROM AUTHOR]

Abstract: An experimental study was performed on a 36 kWth down-fired furnace in order to obtain a wider and more detailed knowledge of the influence of the key parameters on the gaseous fuel reburning process when typical Chinese coals served as the primary fuel. The experimental results show that both above 50% nitric oxide reduction and low carbon loss can be obtained when reburn zone residence time is about 0.6 s–0.9 s, gaseous reburn fuel percent is about 10%–15% and average excess air coefficient of reburn zone is about 0.8–0.9. According to the optimizational reburning operating parameters, a 350 MWe coal-fired boiler was retrofitted for reburning application. The retrofitted boiler had about 0.7 s reburn zone residence time and about 2 s residence time after the burnout air was injected. The results of the demonstration on the full-scale boiler showed that the nitric oxide emission was about 235 mg/Nm3 (O2 =3%, dry) from the retrofitted boiler and above 60% nitric oxide reduction efficiency could be achieved with no adverse effects on the boiler operability when the coke-oven gas used as the reburn fuel. This successful demonstration project filled the gaps in the gaseous fuel reburning application on 300 MWe grade unit boiler in China and showed that the values of the optimizational reburning parameters obtained from experiments could be successfully applied to the designing, retrofitting and optimizing for the gaseous fuel reburning process. [Copyright &y& Elsevier]

Abstract: In the present study, one process was selected for a fundamental study of structural evolution during rapid pyrolysis, as well as for the study of the influence of such evolution on char reactivity. Chars were prepared at different situations from rice husk. The reactivity of resultant chars was measured using non-isothermal thermogravimetric analysis. The structure of fresh and partly reacted chars was characterized using proximate and ultimate analyses, physical adsorption/desorption measurements of N2 (−196 °C), mercury intrusion porosimetry (414 MPa), FTIR, Helium pycnometer as well as samples visualization by scanning electronic microscopy (SEM). Appreciable differences in the physical characteristics, depending markedly on the pyrolysis stage, were observed. SEM observation showed that surface of pore in char particle became increasingly rough in the middle of pyrolysis. Micropore characteristics obtained from adsorption/desorption measurement were complex. Release of volatile material led to the development of pores with different changing trends. The surface area of char increased with pyrolysis process to a maximum value of 56.95 m2/g at pyrolysis reaction ratio (R p =0.90). Macropores in char particles which were evaluated by mercury intrusion porosimetry indicated that the porosity increases continually. Combined the analysis result of density with porosity data, it was showed that particle shrinkage happened at the first stage of rapid pyrolysis. The H/C, O/C and N/C ratios of the char changed with different trends when the pyrolysis reaction ratio increased. Furthermore, FTIR studies indicated a gradual decrease in the intensities of OH, C–H and C–O stretches with pyrolysis process. At the end of reaction, most bands disappeared, resulting in a char that was mainly an aromatic polymer of carbon atoms. [Copyright &y& Elsevier]

Using Fe 2 O 3 , Fe 2 O 3 /Al 2 O 3 , and Fe 2 O 3 –NiO/Al 2 O 3 as oxygen carriers (OCs) on chemical looping combustion with CO was investigated in this study. All the modified iron-based OCs were prepared by sol–gel method, and the samples were characterized by X-ray diffraction (XRD), N 2 adsorption/desorption, and scanning electron microscope/energy dispersive X-ray spectroscopy. The temperature-programmed reduction showed that loading on Al 2 O 3 will promote the reduction of Fe 2 O 3 to Fe 3 O 4 , but further reduction will be inhibited, and the addition of NiO can effectively reduce this inhibition. Thermogravimetric analysis also revealed that NiO addition can improve the maximum reaction rate of iron-based OCs in the oxidation stage. Mixing with NiO will also decrease the oxygen capacity of iron-based OCs. The XRD data of the reduced samples showed that both Al 2 O 3 and NiO have an isomorphous replacement effect on Fe 3 O 4 . The isomorphous replacement effect of NiO is much stronger than that of Al 2 O 3 . Thus, NiO introduction can effectively inhibit the formation of FeAl 2 O 4 and promote the further reduction of Fe-oxides to Fe. However, Ni 2 + will replace part of the Fe 2 + in Fe 3 O 4 to form NiFe 2 O 4 and slightly decrease the oxygen capacity of iron-based OCs. [ABSTRACT FROM AUTHOR]

Serious coking from the bio-oil polymerisation is a bottle-neck challenge for bio-oil thermal upgrading. Probing the mechanism of bio-oil coking is the first step to achieve high carbon conversion efficiency. In this study, in-situ electron paramagnetic resonance (EPR) spectroscopy was used to characterise the stable free radical generation during bio-oil pyrolysis at 250–350 °C with reaction time of 2–10 min, which identify the coking process of bio-oil. The liquid and solid products were characterised using gas chromatography-mass spectrometer (GC–MS), ultraviolet fluorescence (UV-F) and Raman spectroscopy. The results indicate that the coking of bio-oil in pyrolysis can be divided into three stages of varied characteristics. The coke formation precedes with an initial induction period that lasts for 2–8 min and shortens with increasing pyrolysis temperature. In the period, light components polymerise into heavy ones, including polycyclic aromatics as the essential coke precursors. After the induction period, significant amounts of stable free radicals are generated with coke formation, and the content increases from 0.2 to 1.6–7.8 μmol/g bio-oil in the early stage of coking. Meanwhile, the coke precursors, polycyclic aromatics, are rapidly depleted. Afterwards, in the late stage, the nascent coke gradually condenses and the stable free radical content increases slowly. • In-situ EPR detection was used to identify the coke formation in bio-oil pyrolysis. • Coke formation and stable radicals generation are simultaneous during pyrolysis. • Coke formation is preceded by an induction period at the start of bio-oil pyrolysis. • In induction period, polycyclic aromatics accumulate due to bio-oil polymerisation. [ABSTRACT FROM AUTHOR]

Bio-oil has a high tendency towards coking upon heating, which can be the feedstock for production of carbonaceous materials with particular morpholpgy. Herein, production of carbon nanospheres via bio-oil pyrolysis at 800–1100 °C was conducted. The results revealed that the increasing temperature promoted the formation of carbon-rich structures of the nanospheres. The primary precursors for carbon spheres were identified as small gas-phase molecules. The competitive production of carbon spheres and flake carbon was observed, while carbon spheres gradually became the main product at higher pyrolysis temperature (>1000 °C). Furthermore, the abundance of aromatic organics was a critical factor for carbon nanosphere formation. Among the typical model components, the yields of carbon nanosphere at 1100 °C followed the order: guaiacol (38.2 wt%) > furfural (36.6 wt%) > heavy components (28.5 wt%). While acetic acid, acetone, and methanol as model compounds showed a yield of 0 wt%. The degree of interactions among bio-oil components also influenced the yield and properties of the produced carbon nanospheres. The addition of guaiacol to bio-oil facilitated the production of carbon spheres and graphitization, achieving a substantial yield of 12.7 wt% at 900 °C. However, the addition of methanol leads to a decrease in yield of carbon nanospheres. • Carbon nanospheres can be produced via bio-oil pyrolysis. • Interactions among bio-oil components influenced the yield and properties of carbon nanospheres. • The order of carbon nanosphere yields was as follows: guaiacol > furfural > heavy components. • Adding guaiacol to bio-oil improved the yields and graphitization of carbon nanospheres. [ABSTRACT FROM AUTHOR]

Terrestrial and aquatic biomasses can theoretically be used as feedstocks for producing activated carbon (AC). However, their differences in composition and biological structure would affect pore characteristics of resulting AC. In this work, activation of poplar and spirulina with H 3 PO 4 at medium to high temperatures (400, 550 and 700 °C) was conducted, which was followed by detailed characterization of the produced AC. The results showed that the presence or absence of sugary structures in poplar and spirulina made marked difference in evolution of pore structures of AC. The oligomers derived from cellulose/hemicellulose in poplar crosslinked with phosphates via esterification/polycondensation and further aromatized with temperature. This turned H 3 PO 4 -derivatives into skeleton of the poplar-derived AC, which served as the base for creating the AC obtained at 400 °C with highest specific surface area (1380.9 m2g−1) and capability for adsorption of tetracycline (68.8 mg/g). In comparison, low content of carbohydrate together with thermal melting and agglomeration of proteins/lipids in spirulina produced the AC with sponge-like morphology and maximum specific surface area of only 157.1 m2g−1. H 3 PO 4 efficiently catalyzed conversion of -OH and C O in sugary structures of poplar, forming stable C O bonds, which, however, did not work in activation of spirulina. [Display omitted] • Esterification of phosphate and sugars in poplar yields more activated carbon (AC). • Phosphate esters linking aromatic fragments create rich micropores in poplar-AC. • Pore development is inhibited by abundance of lipid/alkanes in spirulina. • H 3 PO 4 not effectively converted -OH/C=O in spirulina to P-O-C/C-O-C bonds. • H 3 PO 4 becomes part of skeleton of poplar-AC but reacts mainly with SiO 2 in algae. [ABSTRACT FROM AUTHOR]

Heavy components in bio-oils pose significant challenges for their utilisation through thermal conversion, as they are highly reactive and prone to polymerisation upon heating. This study investigates the formation and reduction of heavy components during ex-situ and in-situ catalytic pyrolysis of bio-oil over Ni/Al 2 O 3. The heavy components present in the volatile products from bio-oil pyrolysis can be cracked for ex-situ catalysis. In contrast, in-situ catalysis results in catalyst deactivation due to the polymerisation of bio-oil components. However, at temperatures >700 °C, as thermal cracking reactions dominate during bio-oil pyrolysis, in-situ catalysis can further suppress the polymerisation among bio-oil components. As a result, the tar and coke yields decrease by 9.8 wt% and 2.7 wt% at most. • Evolution of heavy components during in−/ex- situ catalysis were investigated. • Tar and coke were decreased by in-situ catalytic pyrolysis of bio-oil. • O-containing groups in heavy components tend to be cracked over Ni/Al 2 O 3. • Ni leads to more C−C- cross-linkage structures in heavy components. [ABSTRACT FROM AUTHOR]

Torrefaction of biomass is a well-known pretreatment method that can remarkably influence evolution of property of pyrolytic products in subsequent pyrolysis. Automobile shredder residue (ASR) is an important product in car recycling and it needs to be pretreated before recycling via pyrolysis. Nevertheless, how torrefaction impacts the composition and pyrolysis behaviours of ASR is still unknown, as ASR has a distinct composition from biomass. Thus, this study investigates the effect of torrefaction on the formation of heavy components in pyrolysis oil. ASR samples were torrefied from 240 °C to 330 °C and subsequently pyrolyzed from 600 °C to 800 °C with varied heating rates (ca. 80 °C /s and 0.17 °C /s). Results indicate that compared to raw ASR pyrolysis oil, torrefaction enhances the interaction between the volatile and semi-char, promoting the polymerization to form precursors of heavy components, thus the relative content of heavy components increases by >50% and heavy components containing heteroatoms decrease by >30% in the torrefied ASR pyrolysis oil, with the release of volatile heteroatom-containing compounds during torrefaction. More aliphatic heavy components are generated, reducing the overall aromaticity and degree of unsaturation of heavy components in the pyrolysis oil. [Display omitted] • Torrefaction promotes the formation of heavy components in ASR pyrolysis oil. • Torrefaction reduce the heteroatomic content in ASR pyrolysis oil. • The unsaturation degree of heavy components was reduced after torrefaction. • A proposed formation mechanism of heavy components in ASR's oil is provided. [ABSTRACT FROM AUTHOR]

Volatile-char interaction has been well documented in co-pyrolysis of varied feedstocks, which might also exist in activation process and impact pore evolution of activated carbon (AC). This was investigated herein in activation of mixed sawdust and spirulina with K 2 C 2 O 4 at 800 °C in two scenarios: one-step direct activation or two-step activation with an intermediate pre‑carbonization. The results showed that volatile-char interaction via cross-polymerisation of the volatiles was more significant in the pre‑carbonization step, forming more biochar/bio-oil while less gases. However, volatile-char interaction was not that important in impacting product yields and evolution of pore structures of AC in activation. This was due to the dominance of gasification/cracking with presence of K 2 C 2 O 4 , minimizing the chances for volatile-char interaction. The in-situ DRIFTS characterization of the activation process showed that removal of oxygen-containing species like C O with K 2 C 2 O 4 was important for generating pore structures. Comparing with two-step activation, one-step activation of sawdust, spirulina and their mixture without pre‑carbonization all generated the ACs of more developed pore structures and showed higher environmental impact. The pre‑carbonization removed a significant portion of thermally unstable aliphatic structures, enhancing aromatic degree and creating difficulty for generating pores via gasification/cracking in subsequent activation. [Display omitted] • Volatile-char interaction in pre‑carbonization forms more biochar while less gases. • Dominance of gasification/cracking weakens volatile-char interaction on activation. • Abundant aliphatic structures develop more pores in direct activation of feedstock. • Pre‑carbonization enhance aromatic degree, negatively impacting pore development. • Activation with K 2 C 2 O 4 cracks O-containing species, suppressing aromatization. [ABSTRACT FROM AUTHOR]

Stable free radicals are the long-lived macromolecule radicals formed in pyrolysis, and their reactions play an essential role in biochar formation. The alkali and alkaline earth metals (AAEMs) in biomass might be involved in the radical reactions during pyrolysis. Figuring out the effect of AAEMs on the reactions of stable free radicals can further understand the radical reaction mechanism and the formation of biochar in pyrolysis. In this paper, the in-situ electron paramagnetic resonance (EPR) spectroscopy was used to detect the stable free radicals in cocoanut pyrolysis, and the effect of AAEMs was analysed by the comparative experiments. The results indicate that the stable free radicals in nascent chars, which are generated from the thermal decomposition of biomass, could react and couple with each other. The AAEMs in biomass improve the activity of stable free radicals and promote the radical-radical coupling during high-temperature pyrolysis above 400 °C, which inhibits the condensation of aromatic structure and generates more weak bonds in hot nascent char. After stopping the heating, the weak bonds will be broken by cooling stress, thus inducing radical reactions and further changing the char structure. • In-situ EPR detection was used to study stable radicals during biomass pyrolysis. • Effect of alkali and alkali earth metals on stable radical reactions was analysed. • Nascent char formed in pyrolysis has secondary reaction after volatiles releasing. • Alkali and alkali earth metals promote coupling of stable radicals during pyrolysis. • Unstable structures formed by stable radicals coupling can be broken during cooling. [ABSTRACT FROM AUTHOR]

Bio-oil as a carbon source can be used to prepare hybrid metal@carbon material while the polymerization of which generally prevents metals from exposure. In this study, melamine was used as a structural regulating agent for preparing Co/N/C catalyst via heating the mixture of cobalt nitrate, melamine and bio-oil for hydrogenation of o-chloronitrobenzene (o-CNB). The results showed that the Co species was encapsulated in the carbon structure from cross-polymerization of melamine and bio-oil at 600 °C. The further heating to 900 °C led to decomposition of melamine-derived substance, and meanwhile cobalt oxide was reduced and confined in the resulting carbon structure. The formed metallic Co catalyzed the growth of long carbon nanotube with cobalt on the tip, forming the Co/N/C catalyst of higher specific surface area (128.2 m2/g) and metallic Co dispersion (3.7%), rendering the superior activity for hydrogenation of o-CNB with the yield of o-chloroaniline up to 90.2%. The encapsulation or exposure of Co species was closely related to relative ratio of bio-oil and melamine in the catalyst precursors. Additionally, leaching of cobalt, due to dechlorination of o-CNB, was found to be an issue of Co/N/C catalyst but not for that of Ni/N/C catalyst. [Display omitted] • Heating mixture of CoNO 3 , bio-oil and melamine produces pin-like Co/N/C catalyst. • Bio-oil acts as a source of carbon skeleton to confine Co from aggregation. • Complexation with Co is essential for dispersion of Co in Co/N/C. • Balance of bio-oil and melamine determines exposure and access of metallic Co. • Catalyst obtained at 900 °C minimizes Co encapsulation, rendering superior activity. [ABSTRACT FROM AUTHOR]

The formation of resultant volatiles is closely related with chemical structure of char during the pyrolysis process. In this study, all-components, that are semi-char, tar and gas product obtained by Shenfu coal pyrolyzed under various residence time at 435 °C were comprehensively analyzed at molecular level, aiming to reveal the reaction pathways responsible for the evolution of chemical structure of coal/char. The results showed that CO 2 and CO were the predominant pyrolysis gas product which inferred high content of organic oxygen species in low-rank Shenfu coal. At the initial stage of pyrolysis, cracking of bridged bonds, especially heteroatom bridged bonds, such as O, N and S, would produce relatively stable radicals in semi-char. Phase change of light components and decomposition of asphaltene in mobile phase can be strongly related with light tar aliphatic compounds formation. At the middle and later stage of pyrolysis, thermal cracking of polar radicals and decomposition of solvent extracted metaplast materials made predominant contribution to tar formation. In addition, the cracking of peripheral aromatic structures of coal/char skeleton structure, through which secondary reaction (such as methylation and dehydrogenation reaction) took place, would result in tar (light tar and heavy tar) and H 2 formation. [ABSTRACT FROM AUTHOR]

Microwave heating is different from furnace heating in terms of heat transfer direction and heating mechanism. The torrefaction with microwave or furnace heating might further impact evolution of the pyrolytic products in further pyrolysis. This was investigated herein via thermal pretreatment of sawdust at 150 to 250 °C and the subsequent pyrolysis at 600 °C. The results showed that the microwave pretreatment led to more pronounced pyrolysis at 200/250 °C, which enhanced aromatic degree of semi-char and created difficulty for its further cracking in pyrolysis at 600 °C but not affected gasification. This led to the formation of more biochar and much more gases but less bio-oil with less heavy components than that from furnace heating plus pyrolysis. Additionally, the microwave pretreatment could enhance deoxygenation but the enhanced aromatic degree of the semi-char created difficulty for creating micropores and development of the pore structures (176.2 m2g−1 with 67.3% micropores from microwave pretreatment versus 441.1 m2g−1 with 78.5% micropores from furnace pretreatment). The characterization of the pyrolysis of semi-char with in-situ IR technique confirmed that the microwave pretreatment substantially removed the aliphatic structures and made the biochar with more fragmented morphology. [Display omitted] • Microwave pretreatment (MP) at 200/250 °C induces aromatization of semi-char. • MP forms more biochar/gases but less bio-oil than furnace pretreatment (FP) in semi-char pyrolysis. • MP at 250 °C hinders formation of micropores in pyrolysis but forms more mesopores. • In-situ DRIFTS measurement indicates less aliphatic structures in semi-char from MP. • MP plus pyrolysis lead to biochar of more fragmented morphologies. [ABSTRACT FROM AUTHOR]

The effects of catalyst supports (γ-Al 2 O 3 and α-Al 2 O 3 ) on hydrogen yield and carbon nanotubes formation were studied during steam reforming of toluene over Ni-based catalysts. Hydrogen yield and CNTs quality over Ni/γ-Al 2 O 3 were better than those over Ni/α-Al 2 O 3 at S/C ratio of 1 due to the high Ni dispersion of Ni/γ-Al 2 O 3 . With the increasing of steam addition, CNTs production remarkably increased over Ni/α-Al 2 O 3 , while it decreased over Ni/γ-Al 2 O 3 . The CNTs on Ni/γ-Al 2 O 3 were corroded at S/C ratio of 3 by excess steam. Toluene conversion and hydrogen yield over Ni/α-Al 2 O 3 were significantly larger than those over Ni/γ-Al 2 O 3 , which was attributed to the different effects of CNTs on catalytic activity. The strong interaction between Ni particle and γ-Al 2 O 3 led to the base-growth mechanism of CNTs on Ni/γ-Al 2 O 3 in which Ni particles located at the bottom of CNTs, thus the growth of CNTs covered Ni active sites and decreased catalytic activity of Ni/γ-Al 2 O 3 . By contrast, owing to weak interaction, CNTs grown on Ni/α-Al 2 O 3 followed tip-growth mechanism that would increase Ni dispersion and promote reforming reaction. [ABSTRACT FROM AUTHOR]

Heavy components affect conversion behaviors of sludge-derived pyrolytic liquids during their utilization and contribute significantly to the formation of the notorious tar and soot during sludge gasification and combustion. Understanding the evolution of heavy components during pyrolysis is vital for developing a reliable sewage sludge utilization technology. This study investigates the compositions of oils from the pyrolysis of sewage sludge using an electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT ICR-MS). Hundreds of compounds with molecular mass higher than 400 Da were detected from the pyrolytic oil obtained at 450 and 650 °C. Higher pyrolysis temperatures promoted decomposition and polycondensation of large molecules and increased the amount of nitrogen-containing compounds in the liquid. Aromatic structured molecules consisting of carbon, hydrogen and nitrogen were the predominant compounds at 850 °C. From the results of this study, the evolution routes of heavy components in the pyrolytic liquid are proposed. [ABSTRACT FROM AUTHOR]

Microwave-assisted extractions (MAEs) were carried out on Shenfu (SF) low-rank coal using four types of solvent, namely tetrahydrofuran, methanol, dichloromethane and ethyl acetate. Comparison with the traditional thermal extractions (TEs) indicated that MAEs were much more efficient in extracting organic components of SF coal. A large amount of aromatic compounds with 2–3 rings and rich branched alkanes could be extracted from coal by MAE. The results also showed that solvent polarity and the interaction between solvent and functional groups abundant in the extracts were the two main factors leading to differences of their MAE. Among the studied solvents, tetrahydrofuran could extract much more amount of polar compounds and its solution was rich in highly-condensed polycyclic aromatic compounds (PACs) with ≥ 4 rings. And this feature had relationship with its strongest interaction with the C O bond. Ethyl acetate, in contrast, showed strong interaction with the C O bonds and had good potential for the extraction of low-polarity compounds especially PACs with two aromatic rings and aliphatic compounds with long alkane chains. And for methanol and dichloromethane, their solvent polarity played dominant roles during the MAE procedures. The results provided more detailed mechanistic influences of different solvents on MAE of coal, and would help for the identification of a suitable solvent for efficient detection of components in organic substances, especially the extraordinary complex compounds in coal. [ABSTRACT FROM AUTHOR]

This work aimed to evaluate the detailed chemical structures of the asphaltenes in the tetrahydrofuran-microwave-extracted portions from two Chinese coals, namely, Shenfu and Zhundong coal (SF, ZD) and to clarify their characteristics on chemical composition at molecular level. Based on the analyses of diffuse reflectance Fourier transform infrared spectroscopy (DRIFT) and Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS), the detailed chemical structure of a series of basic and non-basic nitrogen- and oxygen-containing class species in the asphaltenes were clarified. The results revealed that condensed nitrogen-containing alkylaromatic structures with amidogens (1–3) were the main structure units in N 4 O y (y = 0–2) class species due to the high double bond equivalent (DBE) values for both the asphaltene from SF (A SF ) and the asphaltene from ZD (A ZD ). Acidic O 2 –O 7 class species with two or three aromatic rings were the main structure units, among which O 4 and O 2 class species had the highest relative abundances (RAs) in A SF and A ZD , respectively. Acidic oxygen-containing components in A ZD had narrower range of DBE and carbon number and mainly consisted of aromatic structure units with two rings. On the contrary, the average DBE values of O 4 –O 7 class species in A SF had positive relationship with oxygen atom number which could be attributed to the introduction of phenol groups. The results provided more detailed information on the structural characteristics of polar and aromatic-rich components of mobile phase in coal. [ABSTRACT FROM AUTHOR]

Photocatalytic oxidation removal of elemental mercury (Hg 0 ) by Ag@AgCl/Ag 2 CO 3 hybrids was carried out in a wet scrubbing reactor under fluorescent light. The photocatalysts synthesized via a modified coprecipitation method were characterized by using SEM-EDS, HRTEM, N 2 adsorption-desorption, XRD, XPS, DRS, and ESR. Effects of operational parameters on Hg 0 removal, including AgCl content, fluorescent light (FSL) irradiation, pH value, reaction temperature, and flue gas components (O 2 , SO 2 and NO) were studied in detail. Furthermore, simultaneous removal of Hg 0 and SO 2 was investigated and the possible mechanism of highly enhanced Hg 0 removal efficiency was proposed. The results showed that AgCl amount, fluorescent light irradiation, reaction temperature, SO 2 and NO had notable impact on Hg 0 removal efficiency. Simultaneous removal efficiencies of 98% for SO 2 and 80% for Hg 0 were obtained by coupling Ag@AgCl(0.3)/Ag 2 CO 3 with Ca(OH) 2 under FSL. The trapping studies of reactive radicals exhibited that holes (h + ) were one of the main reactive species for Hg 0 removal. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the changes in iron phase, crystal size, surface area, and char structure/reactivity of the char-supported iron catalysts after them being used for bio-oil reforming. The catalysts were prepared under different conditions (varying in temperatures, gasification agents and iron concentrations) and then used to reform bio-oil under a fixed experimental condition at 800 °C. The results show that the catalysts prepared from the steam gasification of Fe-loaded coal were preferred in terms of catalytic performance. The X-ray diffraction analysis indicates that the iron phases in the fresh catalysts varied while the used catalysts nearly showed identical iron phase of magnetite (Fe 3 O 4 ). The crystal iron particle in the catalysts would apparently increase after reforming when the initial iron phase was carbides (γ-Fe and/or α-Fe). The char structure of the catalysts was significantly affected by the ‘volatile-char interactions’ during reforming process. And the catalysts' surface area and reactivity in air were both reduced mainly due to the coke formation. [ABSTRACT FROM AUTHOR]

The catalytic pyrolysis of flame retarded high impact polystyrene (Br-HIPS) was performed in the presence of five different solid acid catalysts in order to remove the bromine from the derived pyrolysis oil. The catalysts were three zeolite materials (HY, Hβ and HZSM-5) and two mesoporous solids (all-silica MCM-41 and active Al 2 O 3 ). The results showed that in the presence of HY and Hβ zeolites, a reduction of approximate 50 wt.% in oil yield and a corresponding increase in wax and gas yields were obtained compared to thermal degradation. The addition of HZSM-5 showed less impact on product distribution and produced more oil compared with the other zeolites. The mesoporous catalyst of all-silica MCM-41 obtained the highest oil yield of 67.9 wt.% and reduced the wax yield to 8.73 wt.%. In terms of the composition of the pyrolysis oil, HZSM-5 and all-silica MCM-41 were favorable to produce more valuable single ring aromatics, such as toluene, ethylbenzene and cumene. Moreover, the catalysts exhibited pronounced debromination performance, especially the Hβ catalyst, achieving the debromination efficiency of 70.47%. The results confirmed the catalytic pyrolysis of Br-HIPS and debromination performance was well related to the textural properties of catalysts. [ABSTRACT FROM AUTHOR]

Lignocellulosic biomass can be converted to biochar, bio-oil and gas through reactions of non-volatile stabilised free radicals (SFRs) and volatile radicals during thermal conversion. In the process, the interactions between radicals from different biomass components play an essential role. Figuring out the interactions of radicals during pyrolysis holds the key to revealing the interaction mechanism of biomass components. In this study, the evolution of SFRs during the co-pyrolysis of cellulose and lignin was explored using in-situ electron paramagnetic resonance (EPR) detection. The interactions of cellulose- and lignin-derived radicals were analysed based on the variation of SFRs, thermogravimetric behavior and Raman spectrum measurement. The results indicate that the interactions of radicals influence char yield, char structure and the SFRs evolution during pyrolysis. The interaction of volatile radicals and SFRs increases the char yield and promotes the condensation of aromatic structure in biochar. At temperatures above 400 °C, the interaction between cellulose- and lignin-derived SFRs leads to the coupling of radicals, which forms an unstable structure in the hot nascent biochar. In the subsequent cooling process, the weak bonds from interactions may break due to the structure shrinkage, which promotes radical reactions and further changes the char structure. • Interactions during co-pyrolysis improve char yield and stabilised radicals content. • The relationship between stabilised radicals and char carbon skeleton was studied. • The interaction of stabilised radicals in nascent char causes the radicals coupling. • The weak bonds from interaction break to promote radical reactions during cooling. [ABSTRACT FROM AUTHOR]

In pyrolysis of biomass pellet, heterogeneity in char is almost inevitable, due to the intra-particle mass/heat transfer limitation. In this study, the effects of temperature (350–600 °C) and aspect ratio of a cylindrical sawdust pellet (Diameter = 6, 8, 12, or 16 mm) on the heterogeneity of char structure at radial and axial directions were investigated with a micro-Raman spectroscopy. Based on the spatial distribution of Raman band area ratios, heterogeneity index was proposed to quantify the degree of heterogeneity in char structures. Results show that the heterogeneity exists in both radial and axial directions and could be weakened by the increase of temperature or enlarging the variance between radius and height of the pellet through enhancing the average heat and mass transfer inside the pellet. The heterogeneity index of different biochar decreased with increasing surface-area-to-volume ratio. The char structures was the most heterogeneous (HI(A D /A G) = 5.399 × 10−5, HI(A D /A (Gr+Vr+Vl)) = 2.359 × 10−5) for the pellet with a diameter of 8 mm. • Effects of temperature and aspect ratio on heterogeneity in char were investigated. • The heterogeneity of char structure at radial and axial directions was quantified. • A heterogeneity index was proposed to reflect heterogeneous structure in char. • The heterogeneity of pellet char could be weakened by the increase of temperature. [ABSTRACT FROM AUTHOR]

The influence of calcination temperature (200–800 °C) on the activity and structure of MnO x /TiO 2 adsorbent prepared by a deposition–precipitation method is investigated by using an elemental mercury (Hg 0 ) removal setup and a variety of techniques such as N 2 adsorption/desorption, SEM, XRD, H 2 -TPR, FTIR, TG-DSC, and XPS. The results exhibit that the Hg 0 removal activity of MnO x /TiO 2 adsorbent is closely related to the calcination temperature. The Hg 0 removal activity firstly increases below 400 °C and then decreases with the increase of calcination temperature. Calcination at various temperatures may cause several successive structural changes such as the evaporation of water, decomposition of manganese compounds, enhancement of MnO x crystallization, and the crystal phase transformation of MnO x and TiO 2 . Some agglomerations of MnO x /TiO 2 occur at higher calcination temperature, resulting in the drastic decreases of BET surface area and pore volume. Meanwhile, the particle sizes greatly increase. With an increase in calcination temperature, the oxidation state of manganese would convert from Mn 4 + to Mn 3 + , and the surface chemisorbed oxygen decreases due to the removal of surface chemisorbed oxygen. Excessively higher calcination temperature would lead to the deactivation of MnO x /TiO 2 . [ABSTRACT FROM AUTHOR]

Pyrolysis of high impact polystyrene (HIPS), containing decabromodiphenyl oxide as brominated flame retardant (BFR) with Sb 2 O 3 as a synergist (Br–Sb–HIPS), often leads to high concentrations of toxic brominated organic compounds in the pyrolysis oils which would detrimentally impact the reuse of these pyrolysis oils. In this work, the pyrolysis of Br–Sb–HIPS in the presence of polypropylene (PP) at different blending mass ratios using a fixed bed reactor at 410 °C was performed to investigate what the effect of PP has on the pyrolysis of Br–Sb–HIPS. The thermal decomposition characterization of Br–Sb–HIPS and PP was investigated using thermogravimetry analysis (TGA). The pyrolysis oils were analyzed using Fourier transform infrared spectroscopy (FTIR) and gas chromatography–mass spectrometry (GC–MS). TGA revealed that there was a synergistic interaction between Br–Sb–HIPS and PP during co-pyrolysis process. More wax/oil and less gas were produced and the yields of toluene, ethylbenzene, styrene and many other compounds in the pyrolysis oil reversely increased in the presence of PP. Moreover, PP was found to be effective to reduce bromine in the pyrolysis oil. When 30 wt.% PP was blended into Br–Sb–HIPS, it could reduce the amount of bromine in pyrolysis oil to 38% of the original value. [ABSTRACT FROM AUTHOR]

This study focused on the interaction between organic solid waste (OSW) components on the formation and chemical composition of heavy components (>150 m / z) in OSW-oil. Rice husk (RH) and polypropylene (PP) as typical biomass and plastic fractions in OSW, were co-pyrolyzed at different blend ratios and different temperatures. The heavy components were characterized by FT-ICR MS, UV-F and GC MS. The results indicated that the yield of heavy components in PP-oil was higher than in RH-oil under the same temperature. Heavy hydrocarbons were found in PP-oil, while heavy phenols and heavy lipids existed in RH-oil. Significant interactions occurred at high temperatures (>600 °C). The interactions promoted the heavy components in all the blend-oils, corresponding to an increase of 20–35% compared to the calculated value of the content in PP-oil and RH-oil. At low PP ratio (25PP + 75RH), PP provided hydrogen to the reactive O-containing species in RH, leading to promoted heavy phenols and heavy lipids. At high PP ratio (50PP + 50RH and 75PP + 25RH), large aromatics (>3 rings) increased of 48–111% with respect to the calculated values. Plenty of PP‑hydrogen and a rich oxygen environment provided by RH radicals enhanced the formation of heavy aromatics and heavy PAH. • Interactions between OSW components affect the formation of heavy components in the oil. • Temperature and blending ratio change the interaction effects on the heavy component formation. • Hydrogen provided by PP enhanced the recombination of heavy O-containing species. • Rich oxygen environment provided by RH enhanced the formation of heavy PAH. [ABSTRACT FROM AUTHOR]

The vapor-/solid-phase interactions are the inevitable phenomenon in biomass pyrolysis process, which significantly affects the formation of heavy components (molecular weight > 200 Da) in bio-oil (HCO). In this study, to deeply understand the mechanism of the formation of HCO during biomass pyrolysis, the effects of the vapor-/solid-phase interactions among cellulose, hemicellulose, and lignin (biomass three components) on the formation of HCO during pyrolysis were studied in a fixed-bed reactor system. The HCO were analyzed by the FT-ICR MS spectrometer and the UV-F spectrometer. The results showed that the vapor-phase interactions mainly promoted the formation of heavy phenolic compounds at a slow heating rate, and the total content of HCO was increased. The vapor-phase interactions decreased the total content and the O content of HCO obviously at a fast heating rate; meanwhile, the highly reactive compounds (e.g., furans, acids, and ketones) generated from the pyrolysis of cellulose and hemicellulose could interact with the phenol monomers. Thus the phenolic compounds were transformed into large aromatic compounds via the vapor-phase interactions. The solid-phase interactions facilitated the transformation of O-containing structures of the HCO into the char via cross-condensation reaction, decreasing the yield of HCO, especially the phenolic compounds and the saccharides. • Vapor-/solid-phase interactions affect the heavy components formation in bio-oil. • Effects of vapor-/solid-phase interactions vary with the changes in heating rate. • Vapor-/solid-phase interactions affect the primary and secondary reaction pathways. • Interactions are hard to bring new O-/H-structures into the heavy components. [ABSTRACT FROM AUTHOR]

The electrochemical method has emerged as a novel option for bio-oil upgrading due to the advantages of having mild reaction conditions, control convenience and carbon neutrality. Bio-oil is easy to form coke even at low current densities during electrochemical upgrades of bio-oil. Unveiling the coke evolution during the electrochemical processing of bio-oil is essential to enable both oil-to-material and oil-to-fuel strategies. Here, we investigate the coke formation behaviors during the electrochemical processing of bio-oil. The coke comes primarily from the polymerization of aromatic components. The reaction time and current density have a promoting effect on the coke yields. The current density has an accelerating influence on the morphological evolution of the coke. The O-containing groups increases slightly with the increasing reaction time and current density. The large to small ring ratio of the coke is similar under different reaction time and current densities. The potential applications as carbon materials of the coke formed from bio-oil via electrochemical polymerization are discussed based on its physical morphology and chemical structure. [Display omitted] • Coke yields increase with the increasing reaction time and current density. • Coke typically contains small aromatic clusters connected by ether and C-C bonds. • Time and current density slightly affect chemical structural evolution of the coke. • Increasing current density accelerates morphological evolution of the coke. [ABSTRACT FROM AUTHOR]

Biomass pellet is a popular fuel, and pyrolytic char can be a promised carbon material, further understanding char structural evolution can promote its utilization. To deeply investigate the evolution of char chemical structure and its heterogeneity during biomass pellet pyrolysis process, a new method was developed to fragment the char in space, and the chemical structures of the fragmented sections were analyzed by a micro-Raman spectroscopy (equipped with a 532 nm laser). The first-order Raman spectra (800–1800 cm−1) of varied positions of sawdust pellet pyrolytic char were curve-fitted with 10 Gaussian bands to reveal the temporal and spatial evolutions. The results indicate that pyrolysis of sawdust pellet can be divided into two stages: i) the decomposition of raw biomass (temperature heterogeneity in pellet remains); ii) the condensation reactions of aromatic ring systems (temperature in pellet becomes uniform). The axial and radial heterogeneity of char chemical structure is mainly caused by heat transfer when the whole pellet temperature is uniform during heating. While mass transfer, in accordance with volatile diffusion, can eliminate the heterogeneity of char chemical structure by volatile-char interaction. The combined effects of heat and mass transfer lead to a heterogeneity in pellet char chemical structure. • An expanded Raman method by combining micro positioning and analysis was developed. • Chemical structure heterogeneity of sawdust pellet pyrolytic char was quantified. • Temporal and spatial evolutions of pyrolytic char chemical structure were revealed. • Combined effects of heat and mass transfer on char chemical structure were found. [ABSTRACT FROM AUTHOR]

Heavy components (molecular weight > 200 Da) in bio-oil affect the thermal conversion of bio-oil significantly. The inherent alkali/alkaline earth metal species (AAEMs) in biomass affect the formation of heavy components in bio-oil due to its catalytic effects. In order to investigate the effects of AAEMs on the formation of heavy components in bio-oil during biomass pyrolysis, the heavy components in bio-oil were characterized with the Fourier transform ion cyclotron resonance mass (FT-ICR MS) spectrometer and the ultraviolet fluorescence (UV-F) spectroscopy. The roles of K and Ca were also investigated. The results showed that AAEMs promoted the breakage of active oxygen-containing functional groups in heavy phenolics and inhibited their formation during pyrolysis, as well as the formation of heavy carbohydrates. The total content of heavy components decreased due to the catalytic effects of AAEMs. The catalytic effects of K on the decomposition of large molecular weight compounds (> 500 Da) in heavy components were stronger than those of Ca. K increased the content of single ring aromatic components in bio-oil for 1.5 times, while Ca decreased the content of the 2–3 rings aromatic components in bio-oil for more than 50%, compared to the bio-oil generated from the pyrolysis without AAEMs. • AAEMs inhibit the formation of heavy components in bio-oil during pyrolysis. • AAEMs promote the breakage of O-containing structures of heavy components. • Ca promotes formation of heavy lipids and inhibits formation of heavy sugars. • Both Ca and K can inhibit formation of pyrolysis lignin in heavy components. [ABSTRACT FROM AUTHOR]

Revealing the pyrolysis reaction pathway related to coal structure evolution under different temperatures is important for the industry to design reactors and process operations. In this study, all the pyrolysis products obtained under different pyrolysis temperatures were comprehensively analyzed by multiple techniques. The results showed that the aromatic nucleus were inclined to react with methyl radicals, forming char with abundant methyl substitution aromatic structure at low pyrolysis temperature. At medium pyrolysis temperature, dramatically condensation reaction occurred, resulting in the formation of aromatic protonated carbon and abundant polycyclic aromatic hydrocarbons (PAHs) containing benzenoid rings joined by a carbon‑carbon single bond remaining in char. The concentration of aliphatic hydrocarbons in light tar decreased dramatically and converted into light hydrocarbon gas compounds (especially H 2 and CH 4). At high pyrolysis temperature, severe carbonation of char led to the formation of abundant PAHs with reduced aliphatic side chain in light tar. Tar precursors preferred to form larger PAHs due to occurrence of drastic secondary reaction. The contents and diversity of oxygen−/nitrogen-containing heteroatom compounds in heavy tar were significantly reduced with the increase of temperature. Finally, the devolatilization mechanism responsible for the evolution of chemical structure of Shenfu coal pyrolyzed at elevated temperatures was proposed. Unlabelled Image • Low temperature leads to char with abundant methyl substitution aromatic structure. • Medium temperature results in aromatic protonated carbon and single-bond PAHs in char. • Tar precursors prefer to form larger PAHs at high pyrolysis temperature. • Contents and diversity of heteroatom compounds in heavy tar decreased with elevated temperature. • Evolution pathways of coal chemical structure at elevated temperature was proposed. [ABSTRACT FROM AUTHOR]

Ignition of large size coal was the basis of the design and application of Fluidized Bed (FB) and Circulating Fluidized Bed (CFB) combustion technologies. The strongly coupled gas-phase and solid-phase temperature fields in existing experimental apparatus provoked obstacles for the determination of the influence of volumetric reactions on large size coal ignition. In this study, a gas-phase temperature adjustable concentrating photothermal reactor (GTA-CPR) was developed, and the gas-phase temperature could be effectively regulated by the preheated gas flow while the solid-phase temperature was determined by the irradiation voltage. 25 experimental conditions corresponded to 5 levels of solid-phase temperatures with 5 levels of gas-phase temperatures. Enhanced volumetric reactions (by higher gas-phase temperature) led to significant decrease in ignition delay (≥50%) and prolongation of flame duration (≥1.1 times). Real-time CH 4 concentration in volumetric reaction boundary was detected with Mass Spectrometry (MS), which exhibited double peaks. The first CH 4 peak height decreased dramatically while the second CH 4 peak height increased with the gas-phase temperature, indicating the advanced ignition and enhanced volumetric reactions. Ultimately, an ignition delay prediction model was proposed through Backward induction and the indispensable importance of volumetric reactions to coal ignition was evidenced. • Ignition of large size coal were experimentally investigated in the GTA-CPR. • Independent regulation of gas-phase and solid-phase temperature was realized. • Volumetric reactions significantly reduced ignition delay and enhanced flame intensity. • The 1st CH 4 peak decreased, the 2nd CH 4 peak increased with gas-phase temperature. • Ignition delay prediction model with form of τ i = a × (f(T) - b) -c was proposed. [ABSTRACT FROM AUTHOR]

Co-combustion of biomass offers a great potential to reduce CO 2 emissions but rarely mentioned co-combustion behavior of pelletized coal-biomass mixtures and inconclusive results based on single determinants formed obstacle for industrial application. In this study, ignition and flame characteristics, reaction and kinetic parameters and pollutant generation path were comprehensively investigated. Intrinsic combustion experiments were carried with the gas phase maintaining at room temperature in a concentrating photothermal reactor at heating rate over 200 °C/s. Same "homogeneous" ignition was evidenced while advanced devolatilization but more intense slagging behaviors were identified with the increase of biomass proportion. With the biomass proportion increased from 0% to 40%, the activation energies during devolatilization to ignition decreased non-linearly from 47.44 kJ/mol to 8.03 kJ/mol, indicating the existence of synergistic effect. CO exhibited relative high generation rates and the generation rate increased with the biomass content. Three fitted CO peaks were identified during co-combustion, which were contributed by devolatilization of coal and biomass, and combustion of char, respectively. First increased and then decreased NO emission with the increase of biomass proportion was evidenced for the higher N content in biomass but enhanced reduction by char and NH radicals with higher biomass proportion. • Co-combustion behaviors (ignition, slagging, kinetic and pollutant) were studied • The Ea decreased non-linearly from 47.44 kJ/mol to 8.03 kJ/mol with biomass addition • CO exhibited high intrinsic generation rate and biomass formed an independent CO peak • Biomass enhanced primary fuel-N emission and NO reduction by char and NH radical • Synthetic effects were proved by combustion characteristics and kinetic analysis [ABSTRACT FROM AUTHOR]

The certain challenge for the utilization of bio-oil is to investigate the nature and formation of reactive large molecular (heavy) components (>200 Da) in bio-oil. In order to investigate the chemical composition of the heavy components in the bio-oils from the pyrolysis of cellulose, hemicellulose and lignin, the molecular formulas of the heavy compounds and the large aromatic structures were obtained based on the results from the Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) and the ultraviolet fluorescence (UV-F) spectrometer. The results indicated that both the oxygen content and yield of the heavy components showed the highest in the cellulose-oil and the lowest in the lignin-oil. The large molecular compounds were formed mainly via the recombination of the O-containing species, which could be changed at different temperatures and heating rates. Large amount of heavy saccharide and phenolic species existed in cellulose-oil and hemicellulose-oil, while almost no saccharide species and little phenolic species were detected in the lignin-oil. The main heavy components in the lignin-oil were lipids rather than the phenolic species. The heavy components in the bio-oil from the biomass should be mainly derived from the pyrolysis of the cellulose individually or the interactions among the three components. • Main heavy components (>200 Da) in lignin-oil are lipids instead of the phenols. • Heavy components content is highest in cellulose-oil and lowest in lignin-oil. • Methyl groups of the heavy components are easier to be cracked than the O-groups. • High temperature and fast heating rate promote formation of the heavy components. • Heavy components are formed mainly via recombination of O-containing species. [ABSTRACT FROM AUTHOR]

Coal breakage characteristics have significant effects on the clean utilization of coal. The mechanical properties of Shenmu (SM) coal, Hongshaquan (HSQ) coal and Wucaiwan (WCW) coal under uniaxial compression were tested by a self-designed bench at 90 °C, 120 °C, 150 °C and 180 °C. The results show that the mechanical parameters overall decrease with the increase of temperature (T, °C) except that SM coal has an increasing trend from 120 °C to 180 °C due to thermal expansion of coal matrix and moisture inside closed pores. The compressive strength (σ m , MPa) of SM coal at 120 °C decreased by 43% compared with it in 90 °C. By means of fractal theory, these mechanical properties can be reflected by the meso-structural characteristics of coal surface. The fractal dimension (D) generally possesses a positive correlation with the stress (σ, MPa). In initial segments, the curves of some coal samples are relatively stable due to compaction and compressive resistance. Two dimensionless parameters, relative fractal dimension (D r) and relative stress (σ r), were introduced to represent the relationship of meso-structural and mechanical properties quantitatively. It is shown that the relative fractal dimension rises quickly when the relative stress is above 0.75, and the relationship of the two dimensionless parameters can be described. • Mechanical properties of three kinds of coals at different temperatures were studied. • The evolution of coal surface during the loading process was calculated with the help of high speed camera and fractal theory. • The nonlinear relationship between meso-structural and mechanical properties was formulated. [ABSTRACT FROM AUTHOR]