•DCLR and its components have different pyrolysis behaviors.•THFI formed by the condensation of oxygen containing functional groups.•THF soluble is more prone to form the THFI at lower temperature.The stability of direct coal liquefaction residue (DCLR) has significant effects on the DCL technology and the utilization of DCLR. In this paper, the pyrolysis behaviors of the DCLR from 6 t/d Shenhua BDU technology and its components including tetrahydrofuran soluble (THFS) and insoluble (THFI) were investigated by thermogravimetric analysis (TGA). Then, its thermal stability and THFS hydrogenation activity were studied by thermal treatment and hydrogenation treatment, respectively. Results show that DCLR and its components have different pyrolysis behaviors. Inorganic components existed in DCLR and THFI show a catalytic effect on the pyrolysis of organic matrix, but THFS inhibits the decomposition of carbonates in DCLR. The weight loss of THFI mainly results from the decomposition of carbonates and the dehydrogenation rather than the cracking of organic matrix. The thermal stability of DCLR mainly depends on the hydrogen donating ability and the solvency of solvent, and THFI formed in the thermal treatment mainly originates from the condensation between oxygen containing functional groups. The spent catalyst in DCLR can inhibit the condensation of THFS, which is more prone to form THFI at lower temperature.

•Fluorophors distributions of AS and PA mainly depend on original coal.•PA has significantly larger average size and stronger aggregation than AS.•Archipelago structure is valid molecular architecture of PA derived from coal.The heavy organic components in the direct coal liquefaction residue (DCLR), such as asphaltene (AS) and preasphaltene (PA) have significant influence on the direct coal liquefaction (DCL) technology. In this paper, the molecular structure and size of two types of AS and PA from the DCLR of 6 t/d Shenhua process developing unit and a batch hydro-liquefaction in laboratory were characterized. Results indicated that two types of AS and PA from different liquefaction technologies respectively display similar distribution of fluorophors. 3 ~ 4 rings fused aromatic nucleus (ANs) and/or more rings peri-condensed ANs are the predominating structures in the AS and PA. The scale of PA molecule is significantly larger than that of AS molecule. The molecular model, in which several ANs linked by bridge bonds or hydrogenated aromatic rings, is valid at least for the PA. Both AS and PA from direct coal liquefaction can form aggregates while the PA exhibits stronger aggregation than the AS.

Preasphaltene (PA) defined as tetrahydrofuran (THF) soluble and toluene insoluble is an important intermediate product of direct coal liquefaction (DCL). Investigating the structure of PA not only can improve the DCL technology but also can help us understand the structure of coal. In this paper, two types of PAs from the DCL residue of 6 t/d Shenhua process developing unit (PDU) and the products of a batch hydroliquefaction in an autoclave were first separated into different subfractions by the column chromatography. Then, the obtained subfractions were characterized by Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV) and fluorescence spectroscopy (FL), matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) and gel permeation chromatography (GPC), respectively. The results indicate that the PA from DCL mainly exists in the form of aggregates. Two different PAs show similar distribution of subfractions, but the PA(B) obtained by the batch liquefaction displays larger molecular weight than the PA(A) from Shenhua PDU technology. A molecule of PA contains two or more aromatic nuclei (fluorophors). Subfractions I–III consist of smaller fused aromatic nucleus than the other subfractions. In general, their intermolecular aggregations increase from subfraction I to VII, and the aggregation of PA(A) subfractions is stronger than that of corresponding PA(B) subfractions.

The investigation of hydro-conversion behavior of the heavy intermediate products derived from coal direct liquefaction is advantageous to optimize the technological conditions of direct coal liquefaction and improve the oil yield. In this paper, the hydro-conversion of preasphaltenes catalyzed by SO42−/ZrO2 solid acid was investigated based on the structural characterization of preasphaltenes and its hydro-conversion products, and the determination of products distribution and the kinetics of preasphaltenes hydro-conversion. The results indicated that the content of condensed aromatic rings increased, and the contents of hydrogen, oxygen and aliphatic side chains of preasphaltenes decreased with the increase of coal liquefaction temperature. The preasphaltenes showed higher hydro-conversion reactivity while SO42−/ZrO2 solid acid was used as catalyst. Higher temperature and longer time were in favor of increasing the conversion and the oil + gas yield. The conversion of preasphaltenes hydro-conversion under 425 °C, for 40 min reached 81.3% with 51.2% oil + gas yield. SO42−/ZrO2 solid acid was in favor of the catalytic cracking rather than the catalytic hydrogenation in the hydro-conversion of preasphaltenes. The activation energy of preasphaltenes conversion into asphaltenes was 72 kJ/mol. The regressive reactions were only observed at a higher temperature.Research Highlights► Preasphaltenes shows higher hydro-conversion reactivity catalyzed by SO42-/ZrO2. ► SO42-/ZrO2 mainly catalyzed the hydro-cracking of preasphaltenes. ► Some regressive reactions were found in the process of preasphaltenes conversion.

Catalysis and deactivation of SO42−/ZrO2 solid acid on the alkylation of benzene and 1-dodecene were studied by the characterization of XRD, BET, IR, TG/DTA, and NH3-TPD techniques and the determination of the 1-dodecene conversion, the yield of dodecylbenzene and the selectivity of linear alkylbenzene respectively. In addition, some treatment methods, such as the extraction with benzene or THF as solvent, and the calcinations with or without the dipping of H2SO4 in air, were respectively used to recover the activity of deactivated catalyst. The results indicate that SO42−/ZrO2 solid acid shows higher catalytic activity for the alkylation of benzene and 1-dodecene with nearly 100% of 1-dodecene conversion and more than 80% of dodecylbenzene yield, and higher selectivity of 2-LAB. The activity of catalyst for the alkylation of benzene is in proportion to the content and the strength of medium acid site. However, the distinct deactivation of catalyst was also obversed in the alkylation. According to the characterization of deactivated catalyst, the accumulation of hydrocarbon fragment and the removal of are mainly reasons of SO42−/ZrO2 deactivation. The SO42−/ZrO2 calcinated at higher temperature is apt to deactivate. The treatment by extraction with solvent or calcinations can recover the catalytic activity of spent catalyst at a certain extent, especially calcination with the dipping of H2SO4.

In order to study the catalysis of SO42-/ZrO2 solid acid for the liquefaction of coal, a series of SO42-/ZrO2 solid acids were synthesized by the method of precipitation–impregnation. The catalytic behaviours of the SO42-/ZrO2 solid acids for the hydro-liquefaction of Shenhua coal and model compounds, such as diphenylmethane, bibenzyl and phenyl ethyl ether, were investigated. In addition, non-catalytic liquefaction and the catalytic liquefaction under N2 were further compared with the catalytic liquefaction under H2 in order to understand the catalytic mechanism of SO42-/ZrO2 solid acid. The results indicate that hydro-liquefaction conversions of coal and model compounds are related to the strength, amount and nature of acid sites on the surface of SO42-/ZrO2, and the strong acid site responds to their catalytic activities. The SO42-/ZrO2 solid acid catalyzes mainly the hydro-cracking, ring-opening and hydrogenation reactions of coal to produce oil and gas during the coal liquefaction. The hydro-cracking reactions in the liquefaction of model compounds and coal catalyzed by SO42-/ZrO2 involved via carbenium ion intermediate instead of traditional radicals intermediate.

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

Catalyst plays an important role in direct coal liquefaction. This paper focuses on the catalytic behavior of a novel SO42-/ZrO2 superacid catalyst in coal hydro-liquefaction. A series of hydro-liquefaction experiments were conducted under mild conditions – 400 °C, 30 min and H2 initial pressure 4 MPa in a batch autoclave with a volume of 100 ml. The catalytic property of SO42-/ZrO2 was compared with FeS and FeS + S by Shenhua coal. The liquefaction products catalyzed by different catalysts were analyzed by FTIR spectrum, 1H NMR spectrum and element analysis. In addition, the SO42-/ZrO2 solid superacid was characterized. The results indicated that the SO42-/ZrO2 solid superacid shows outstanding catalytic property for direct liquefaction of coal and gives the highest coal conversion and gas + oil yield compared to other two catalysts. The THF conversion and the extraction yield of CS2/NMP mixed solvent of liquefied coal catalyzed with SO42-/ZrO2 are 76.3%, daf and 81.2%, daf respectively, and the yield of gas + oil is 62.5%, daf under the condition used in this study. The pyrolysis of coal macromolecular clusters can be promoted by catalysts such as FeS, FeS + S and SO42-/ZrO2. There may be only the pyrolysis of volatile matter and the relaxation of the structure of coal macromolecular clusters in non-catalytic liquefaction at 400 °C. Added sulfur in FeS can improve the catalytic activity of hydrogenation. SO42-/ZrO2 is a notable catalyst in the study of coal direct liquefaction because it shows excellent catalytic activities for the pyrolysis and the hydrogenation. In addition, it has been found that the C–O bond is the most stable group in coal liquefaction reaction except for the covalent bond between carbon and carbon.

High-temperature thermal extraction (TE) of Xianfeng lignite by different solvents was carried out, and FT-IR spectra of extracts and residues were determined. The results indicate that Xianfeng lignite shows the macro-molecular network structure by chemical bond cross-linking, in which some low molecular compounds are associated by non-covalent bond interaction. The TE can distinctly increase the extraction yields, which are up to 20.7% and 21.3% at 300°C in toluene and tetralin, respectively. The extracts result from the release of low molecular compounds by thermal rupture of non-covalent bonds at high temperature. Meanwhile, there is no obviously pyrolysis in the process of thermal extraction at 300°C. So the hydrogen donor solvent and hydrogen bond solvent can not increase the thermal extraction yield. The thermal extracts of Xianfeng lignite contain a great of aliphatic alkyl and carbonyl ester, a little of hydroxyl and aromatic structure. The solvent of thermal extraction shows distinctly influences on the constitution and structure of extracts.

Effects of liquefaction conditions, including temperature, time, initial hydrogen pressure, and catalyst dosage on direct liquefaction were investigated by batch hydro-liquefaction of Shenhua coal catalyzed by SO42–/ZrO2 solid acid. The mechanism and catalysis of Shenhua coal liquefaction catalyzed by SO42–/ZrO2 solid acid were also discussed by distribution and IR analysis of the products. The results indicate that increase in temperature is favorable for catalytic hydrocracking of coal, an increase in liquefaction conversion, and yields of oil plus gas. Raising the initial hydrogen pressure facilitates coal conversion into asphaltene and preasphaltene, but depresses the formation of oil and gas. The increase of liquefaction time is beneficial to the hydrocracking of preasphaltene with an increase in yields of oil plus gas. SO42–/ZrO2 solid acid mainly catalyzes the hydrocracking of coal macromolecular structure so that the conversion and yields of oil plus gas increase with increasing catalyst dosage. In addition, the conversion of the oxygen-containing structures such as hydroxyl needs high liquefaction temperature and initial hydrogen pressure.