Search

The technology of coal pyrolysis and conversion of high value-added aromatic chemicals is one of the important ways of coal efficient and clean utilization. To obtain high yield aromatic compounds and tar from coal pyrolysis process with high yield, analyse the influencing factors including pyrolysis atmosphere, catalyst, solvent pretreatment technology as well as reactor type on pyrolysis product distribution. The results show that, the development of pyrolysis technology and catalyst help to improve the BTX yield, meanwhile some secondary causes also should be payed attention. [ABSTRACT FROM AUTHOR]

[Display omitted] • Shendong coal macerals is swelled by acetic acid, ethanol and acetone, respectively. • Based on the coal structure and Py-GC/MS, pathways of phenols formation are proposed. • The reaction energy of phenols generation pathway is carried out by using DFT. • The PCXC yield derived from VD-AT and ID-EA is 43.63 g/kg and 34.19 g/kg, separately. • Among seven pathways of VD-AT, Path 3 exhibits the lowest energy of −148.38 kJ/mol. Phenols are the important high value-added chemical product of coal tar, and exploring the release behavior of phenols is crucial for clarifying the coal pyrolysis mechanism and regulating the product distribution. The aim of this paper is to investigate the effects of swelling on the pyrolytic properties of de-ashed vitrinite (VD) and de-ashed inertinite (ID). VD and ID prepared by Shendong coal were characterized by 13C NMR, XPS and FTIR to explore physicochemical properties. Acetic acid (AA), ethanol (EA) and acetone (AT) were employed to prepare the swelled VD (VD-AA, VD-EA and VD-AT) and swelled ID (ID-AA, ID-EA and ID-AT). Kinetic analysis was carried out using thermogravimetry, the pyrolysis characteristics and distribution of pyrolysis products were analyzed by fast pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS) and fast pyrolysis fixed bed. Combining with density functional theory (DFT), the possible pyrolysis pathways of phenols generation were proposed. As a result, the macromolecular structures of VD and ID are constructed. TG and kinetic analysis exhibit that swelling promotes the pyrolysis of VD and ID, and the activation energy of the second stage is VD > VD-EA > VD-AT > VD-AA and ID > ID-EA > ID-AT > ID-AA, respectively. Py-GC/MS analysis exhibits that the selectivity of phenol, cresol, xylenol and catechol decreases to 17.53 % (VD-AA) and 12.18 % (ID-AT). By analyzing and comparing the distribution of the full component of Py-GC/MS, seven possible pathways of cresol generation are proposed. DFT calculation exhibits that Path 3 of VD-AT, which produces cresol via sequential decarboxylation, ether bond cleavage, decarbonylation, aliphatic side chain removal and dehydroxylation, demonstrates the lowest reaction energy of −148.38 kJ/mol. [ABSTRACT FROM AUTHOR]

The original structural units of the coal can be deduced from the oxygen-containing macromolecules dropped in the low-temperature region during the multi-step pyrolysis of the de-ashed Shendong coal and its macerals by weak bonding, and their possible pyrolysis pathways were analyzed by DFT. [Display omitted] • The pyrolysis behavior of coal was investigated by TG, Py-GC/MS, and DFT analysis. • Low temperature pyrolysis can preserve the original O-containing structural units. • A strategy for building coal structure based on assembled O-compound. • The generated phenols energy of RD can be as low as −2167.4 kJ/mol. • Only VD (−2155.2 kJ/mol) and ID (−1670.79 kJ/mol) can generate phthalic anhydride. Most of the existing structural models of coal macromolecules are based on indirect characterization, which cannot reflect the real product structure of coal pyrolysis. This study focuses on the construction of the real structural units of de-ashed Shendong coal (RD) and its vitrinite (VD) and inertinite (ID). Two pyrolysis modes of fast pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS), Thermogravimetry (TG), Fourier transform infrared (FTIR) as well as rapid infrared heating (RIH) were used to obtain the pyrolysis properties and product composition distributions of each coal. A strategy for structural unit construction of coal, termed "Molecular Reorganization", is introduced to ensure that the original structure of the coal can be reproduced. Macromolecules produced by multi-step pyrolysis in the low-temperature region were used to assemble the real structural units of coal. The pyrolysis pathways of the oxygenated compounds in the constructed molecular unit models of RD-C 70 H 50 O 9 N, ID-C 101 H 62 O 13 N 2 , and VD-C 71 H 43 O 9 N were analyzed by density functional theory (DFT). The results showed that the reaction energy for the pyrolysis of ID fragments to phenol was higher, with fragments 1 and 2 being −4212.98 kJ/mol and −2190.83 kJ/mol, respectively. [ABSTRACT FROM AUTHOR]

• Coal was pretreated by CH 3 OH-THF swelling in-situ loading of metal ions. • The structures of coal samples were characterized by CP/MAS 13C NMR and FTIR. • The pyrolysis characteristics of coal were analyzed by TG-FTIR, Py-GC/MS, etc. • The swelling with loading of Cu2+ and Co2+ promotes the generation of benzene. • The activation energy of coal pyrolysis can be reduced by loading of metal ions. The effects of demineralization, CH 3 OH-THF mixed solvent swelling, CH 3 OH-THF swelling coupled with in-situ loading of metal ions (Ca2+, Mn2+, Cu2+ and Co2+) on pyrolysis reactivity and kinetic characteristics of Shendong low rank coal were investigated. The structure of coal samples was characterized by solid-state cross-polarization magic angle spinning carbon-13 nuclear magnetic resonance (CP/MAS 13C NMR) and Fourier transform infrared spectrometer (FTIR). The pyrolysis characteristics and distribution of pyrolysis products of coal were analyzed by thermogravimetric analyzer/Fourier transform infrared spectrometer (TG-FTIR), pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and the fixed bed reactor. The results show that solvent swelling coupled with in-situ loading of Ca2+, Mn2+, Cu2+ and Co2+ promotes coal pyrolysis, and their net weight losses increase by 2.14 wt%, 0.07 wt%, 6.31 wt% and 6.18 wt%, respectively. Py-GC/MS analysis shows that the treatment of solvent swelling coupled with in-situ loading of metal ions Ca2+, Mn2+, Cu2+, Co2+ can increase the content of aromatic hydrocarbons and decrease the content of acidic compounds in coal tar. The content of benzene increases under the action of solvent swelling coupled with in-situ loading of Cu2+ and Co2+ by 42.73 wt% and 40.98 wt%, respectively. The kinetic calculation shows that the activation energies of the first and second stages of coal pyrolysis are reduced and the reactivity of coal can be improved by swelling coupled with in-situ loading of metal ions. [ABSTRACT FROM AUTHOR]

Highlights • Low temperature solvent pretreatment experiments of vitrinite were carried out. • Sulfur composition and distribution of coal tars were analyzed by GC–MS. • Pretreatments of hot water, ethanol and alkaline ethanol solution show the ring opening. • Six types of thiophenes have been detected in coal tars. • Dibenzothiophene and benzo[b]naphthothiophene are relatively concentrated in coal tars. Abstract The low temperature solvent pretreated experiments of vitrinite sorted out from Permo-carboniferous high organic sulfur fine coal were performed to research the effects of solvent pretreatment on the characteristics of pyrolysis products and the composition and distribution of sulfur in the produced coal tar. Six solvents containing hot water, ethanol solution, 1, 2-propanediol solution, KOH solution, KOH-ethanol solution and KOH-1, 2-propanediol solution were employed. The results show that the solvent pretreatment method has little influence on the organic sulfur content of coal, but it results in the increase of coal tar yield and a great variation of volatiles during the pyrolysis of pretreated coals. Six types of thiophenes, containing benzothiophene, dibenzothiophene, naphthothiophene, benzo[b]naphthothiophene, dinaphthothiophene and phenanthro[9,10-b]thiophene, were detected in coal tars. The pretreatments of hot water, ethanol solution and alkaline ethanol solution show the ring opening to large aromatic structures in coal. The generation of benzothiophene, dinaphthothiophene and phenanthro[9,10-b]thiophene may be due to the ring opening effect. [ABSTRACT FROM AUTHOR]

Highlights • The transfer of hydrogen species effectively promoted the formation of light aromatics. • Hydrogen species prevent polymerization of molecules by stabilizing the radicals. • This hydrogen cycle process used the hydrogen existed in original system in the absence of external H 2. • Ga/HZSM-5 is a potential candidate in catalytic upgrading of pyrolysis volatiles. Abstract Coal tars produced by conventional low-temperature pyrolysis processes require further upgrading before being used as fuels or high valuable aromatic chemicals owing to a low yield of light aromatics and high oxygen contents. In this study, a set of metal-loaded HZSM-5 catalysts were evaluated in a fluidized bed reactor for improving tar quality via the in situ catalytic upgrading of the pyrolysis volatiles. The product yields of the three different phases, the gaseous composition, the char reactivity, and the chemical properties and composition of the coal tar were comprehensively studied. The use of metal-loaded catalysts increased the amounts of light aromatics while decreasing the amounts of aliphatics and oxygenated compounds. The products distribution was optimized from a complex mixture with different functional group compounds to a tar concentrated in aromatics after catalysis. The possible reaction pathways were depicted to illuminate the mechanism of catalytic reaction based on the variation of the volatile products distribution. Incorporation of metals promoted hydrogen transfer within the reaction system. Hydrogen species formed by dehydrogenation of chain hydrocarbons may stabilize the radicals generated from coal initial pyrolysis stages. Moreover, these species can efficiently promote hydrodeoxygenation of phenolic compounds to aromatic hydrocarbons by metal-acid catalysis. The present work effectively promoted the formation of light aromatics and further clarified the catalytic mechanism of pyrolysis volatiles over metal/HZSM-5 catalysts. [ABSTRACT FROM AUTHOR]

Solvent swelling and catalyst have significant effects on the volatile release behavior during coal pyrolysis process, not only affecting the total amount, but also affecting the release trend when the temperature rises. An accurate quantification of this relationship can promote the efficient utilization of pyrolysis volatiles. This work adopts machine learning (ML) methods to construct prediction models for four primary volatiles (CO, CH 4 , aromatic and aliphatic hydrocarbons) during the pyrolysis of coal samples treated by different metal loading and solvent swelling, to predict the instantaneous volatile content at any time in the pyrolysis process. The deep learning models constructed by Recurrent neural networks (RNN) were compared with traditional machine learning methods of artificial neuron network (ANN), random forest (RF) and support vector machine (SVM), and realized an obvious preponderance on prediction performance for hole release curve. The best long short-term memory (LSTM) models achieve the average R2 of 0.978, 0.900, 0.950 and 0.936 for the release curve prediction of CO, CH 4 , aromatic and aliphatic volatile. Further adjustments shown that the reduction of sampling points on curves has little effect on the model's performance, which makes it feasible to condense the models and decrease the dimensions of input. An easy signal processing of integral transformation had an obvious improvement on the predictive power of models, with a highest increase of R2 with 0.14 for aromatics predicting. All of these results provide a good method for real-time tracking of the conversion process. [Display omitted] • Machine learning were adopted to predict the release of pyrolysis volatiles. • RNN overperformed traditional ML algorithms when predicting time series. • Signal transform preprocessing can improve the result of time series prediction. • Optimal LSTM predicts CO, CH 4 , aliphatics and aromatics with R2 > 0.90. • Swelling ratio and temperature are the most critical factors. [ABSTRACT FROM AUTHOR]

• HTP hydrolyzes ether bonds to form phenolic hydroxyl groups. • SSP breaks hydrogen bonds and dissolves small molecule compounds. • Destruction of ether bonds facilitates the release of aromatic C C and light tar. • Destruction of hydrogen bond reduces the pyrolysis activation energy of oxygen-containing groups. Coal pyrolysis is one of the methods of clean and efficient utilization of coal. Coal has a complex structure, which has an important influence on its pyrolysis characteristics. In order to further explore the structure–activity relationship between the structure and pyrolysis characteristics of coal, the structure of coal can be artificially changed to investigate the influence of structural changes on its pyrolysis characteristics. In this study, hydrothermal pretreatment (HTP) and solvent swelling pretreatment (SSP) were used to artificially change the structure of Shengli (SL) lignite. The influence of each pretreatment on the physicochemical structure was analysed by Fourier-transform infrared (FT-IR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The evolution of functional groups and the pyrolysis characteristics of the SL/pretreated coal were investigated by using an in-situ FT-IR device and a fluidised bed reactor, respectively. The results showed: HTP could remove some oxygen-containing functional groups and aliphatic side chains, hydrolyze ether bonds and generate phenolic hydroxyl groups, thus destroying the cross-linking structure, promote the release of aromatic C C, the yield of pyrolysis tar increased from 9.4% to 10.6%, and the content of light tar increases from 43.1% to 49.1%. SSP mainly weakening the cross-linking structure by destroying hydrogen bonds and dissolving part of oxygen-containing functional groups, which reduces the pyrolysis activation energy of oxygen-containing functional groups and aliphatic groups, promotes the generation of tar. Accordingly, the yield of tar increases from 9.4% to 11.1%, and the content of light tar increases from 43.1 % to 49.8%. In particular, this research work reveals the structure–activity relationship between the structural changes of coal and the pyrolysis characteristics, which provides a theoretical basis for the directional pyrolysis of lignite. [ABSTRACT FROM AUTHOR]

[Display omitted] • TPOAC-directed mesoporous ZSM-5 is used for effective loading of Ga active species. • Designed regulation of Ga active species is achieved by post-treatments of reduction and redox. • Optimal Ga/MZ5_R/O catalyst exhibits a superior catalytic performance in coal pyrolysis volatile upgrading. • Factor evaluation including regulated gallium species, balance of BAS/LAS, and mesopore diffusion superiority. • Possible conversion pathway of high value-added BTEXN products is proposed. Quality improvement of pyrolysis tar with yield increasing of high value-added components is highly desired for coal utilization. Herein, Ga-impregnated mesoporous ZSM-5 (Ga/MZ5) directed by organosilane surfactant of [3-(trimethoxysilyl) propyl] octadecyldimethylammonium chloride (TPOAC) is used as a catalyst for the catalytic upgrading of coal pyrolysis volatiles. Effective regulation by reduction and reduction/reoxidation promotes a secondary dispersion of gallium species from external surface deposition to micropore permeation. The comprehensive evaluation of catalytic upgrading performance indicates that the designedly regulated gallium species (mainly Ga+, GaH 2 + and GaO+), feasible balance of Brønsted and Lewis active sites and mesopore diffusion superiority effectively contribute the yield increasing of both light-fraction (M LF / M Tar) and target products of BTEXN (benzene, toluene, ethylbenzene, xylene and naphthalene). The optimal catalyst of Ga/MZ5_R/O exhibited the highest value of M LF / M Tar (88 %) and highest yield of BTEXN (31.84 mg.g−1), which are 173 and 589 % higher than non-catalytic single pyrolysis and 133 and 280 % higher than those over the conventional Ga-impregnated ZSM-5 (Ga/Z5). Moreover, the possible reaction networks towards high value-added products of BTEXN based on the positive conversion of polycyclic aromatic hydrocarbons (PAHs), phenols, and other oxygen-containing compounds (abbreviated as PPO) is further proposed. [ABSTRACT FROM AUTHOR]

• The content of phenolic hydroxyl increased during hydrothermal pretreatment. • OH-ether O hydrogen bonds were newly formed during THF swelling pretreatment. • Reactions during methane thermal pretreatment were bond breaking and re-bonding. • Structure-activity relationship between coal structure and pyrolysis was revealed. Studying the relationship between the structure and pyrolysis of coal is useful for understanding the coal pyrolysis mechanism. In this study, three typical pretreatment methods (viz. hydrothermal pretreatment, tetrahydrofuran swelling pretreatment, and methane thermal pretreatment) were selected to artificially change the structure and composition of Shendong coal. Subsequently, the physicochemical structure and pyrolysis characteristics of the pretreated coals were systematically investigated. The results indicate that the three pretreatment methods had different influences on the pore modification and evolution of the functional groups in coal, thereby destroying the cross-linking structure in different ways. Correspondingly, these changes eventually altered the distribution and composition of the pyrolysis products. Based on these findings, the different mechanisms underlying the pyrolysis behavior, involving alteration of the structure and composition, were analyzed, and the structure–activity relationship between the coal structure and the pyrolysis characteristics was explored. [ABSTRACT FROM AUTHOR]

[Display omitted] • ZSM-5, HY and USY are evaluated on catalytic upgrading of CTA pyrolysis vapors. • The ratio of CTA to catalyst has an important influence on the product distribution. • Catalysts have a better ability to regulate products distribution and produce BTXN. • The catalytic mechanisms of "Hydrocarbon pool" and "Phenolic pool" were proposed. Coal tar asphaltene (CTA) is a low-grade fuel with a high content of oxygen, high-viscosity and high-toxicity. Three kinds of zeolite catalysts ZSM-5, HY and USY were used for catalytic fast pyrolysis (CFP) of CTA to upgrade its pyrolysis vapors by using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The effects of the heating rate (1 °C/ms, 5 °C/ms, 10 °C/ms and 20 °C/ms), the pyrolysis time (20 s, 50 s, 80 s and 100 s), the catalyst types and the mass ratio of CTA-to-catalyst (MRCTC, 4:1, 2:1, 1:1 and 1:2) on the pyrolysis product distribution were investigated. Results show that a higher heating rate (20 °C/ms) and a shorter pyrolysis time (20 s) are more beneficial to improve the selectivity of aromatic hydrocarbons (ArHs). Moreover, Compared with the non-CFP of CTA, ZSM-5, HY and USY promote the decomposition of organic oxygen compounds (OOCs) and the generation of light ArHs (L-ArHs, e.g. benzene, toluene, xylene and naphthalene (BTXN)) from polycyclic ArHs (P-ArHs). The highest yield of BTXN has been obtained at the MRCTC of 1:1 over HY, which is 23 times than that obtained from fast pyrolysis of CTA. Viewed as a whole, the catalysis over these catalysts are capable to convert these undesirable pyrolysis products (containing OOCs, P-ArHs or heteroatom compounds) into BTXN through various reactions, and thus to decrease the oxygen content, aromaticity and toxicity of CTA pyrolysis products. Furthermore, the catalytic mechanisms of "Hydrocarbon pool" and "Phenolic pool" were also proposed. [ABSTRACT FROM AUTHOR]

• Ion exchange of Na+, K+, Ca2+, Mg2+, Ca2+, Co2+ and Ni2+ on coal is performed. • Metal ion-exchanged coal pyrolysis and its char gasification were investigated. • The char decrease and the gas increase during metal ion-exchanged coal pyrolysis. • Ion exchange increases char gasification reactivity: K+ > Na+ > Mg2+ > Co2+ > Ni2+. • Mechanisms of coal pyrolysis and its char gasification are concluded. The effects of ion-exchanged metal cations (Na+, K+, Ca2+, Mg2+, Co2+ and Ni2+) on the pyrolysis reactivity of Shendong demineralized coal (SD-coal) and the gasification performance of pyrolysis chars were investigated by Py-GC/MS, TG-FTIR, FBR (the fixed-bed reactor), FTIR, SEM, XRD and CO 2 reactivity. The results show that the order of pyrolysis weight loss rates is SD-coal-Ni > SD-coal-Co > SD-coal-Mg > SD-coal-Na > SD-coal-Ca > SD-coal-K. The char yields decrease and the pyrolysis gas yields increase during the pyrolysis of metal ion-exchanged coals compared with those of SD-coal. Ion exchange of Co2+ and Ni2+ increases the coal tar yields, especially the yield of coal tar obtained from SD-coal-Co pyrolysis increases to 9.45 %. Ion exchange of alkali and alkaline earth metal cations is generally conducive to the formation of naphthalene and its derivatives in coal tar. The catalytic effect of these metal cations on coal pyrolysis is Na+ > K+ > Ni2+ > Ca2+ > Mg2+ > Co2+. The values of L c and N ave in chars derived from metal ion-exchanged coal pyrolysis are reduced compared with SD-coal char. The effect of ion-exchanged metal cations on the gasification reactivity of chars is K+ > Na+ > Mg2+ > Co2+ > Ni2+. And on this basis, the mechanisms of metal ion-exchanged coal pyrolysis and char gasification are concluded. [ABSTRACT FROM AUTHOR]

• Dual-templating synthesis of gallium-substituted mesoporous ZSM-5 (Ga-MZ5). • Ga-MZ5 exhibited superior performances with high aromatic-yield and effective phenol-reduction in CFP. • Dehydrogenation/cracking ratio decided by zeolite acidity. • Deoxygenation of phenols dominated by non-framework Ga x O y species. • Diffusion superiority contributed by hierarchical meso-/microporosity. Five MFI-type zeolite catalysts, which were aluminosilicate ZSM-5 (Z5), gallium-substituted silicalite-1 (Ga-S1), mesoporous ZSM-5 (MZ5), gallium-substituted mesoporous silicalite-1 (Ga-MS1) and gallium-substituted mesoporous ZSM-5 (Ga-MZ5), were hydrothermally synthesized with combined using of TPAOH and TPOAC as micropore and mesopore structure-directing agents respectively, followed by the application in the catalytic upgrading of volatiles from low-rank coal fast pyrolysis. The obtained results indicated that significant improvements with the yield of high value-added products of BTEXN (benzene, toluene, ethylbenzene, xylene and naphthalene) increased from 5.4 mg.g−1 to 11.9–26.4 mg.g−1, as well as the content of light fractions (<300 °C) in coal tars increased from 51% to 65–88% were realized by using the representative MFI-type zeolite catalysts in contrast to non-catalyst pyrolysis. Moreover, the possible mechanism for catalytic upgrading over the best-performing catalyst of gallium-substituted mesoporous ZSM-5 (Ga-MZ5) with the highest yield of aromatics and effective reduction of phenols was proposed on the basis of systematic comparison of structural features and catalytic performances of various MFI-type zeolite catalysts and fundamental study of the synergetic effects dominated by acidity, ratio of Brønsted/Lewis acid sites, intra-/extra-framework gallium species and hierarchical meso-/microporosity. [ABSTRACT FROM AUTHOR]