Coal tar asphaltene (CT-asp) is one of the important heavy components of coal tar. It has significant influences on the conversion efficiency of slurry-phase hydrocracking. The reactivity and structure changes of CT-asp in a slurry-phase process were investigated. Experimental results showed that the conversion of CT-asp reached 66.5 wt % with a significant decrease of sulfur and oxygen contents as the reaction time increased. The CT-asp obtained from the hydrocracking reaction carried out for different time has been analyzed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and 1H/13C nuclear magnetic resonance. The chemical structural analysis results confirmed that CT-asp was mainly composed of more aromatic rings with oxygen functional groups and possessed a higher aromaticity and shorter aliphatic chains after hydrocracking. Moreover, the effective cracking of carbonyl groups, pyrrolic nitrogen, and alkyl sulfides in CT-asp was found during the slurry-phase hydrocracking. It was considered that a structure with an average of two aromatic rings per aromatic sheet existed in the average molecule of CT-asp, and the aromatic sheets were condensed with each other through diphenyl-like structures or oxo-bridged linkages. In addition, a free radical reaction pathway of CT-asp in slurry-phase hydrocracking was proposed on the basis of the main detected products and the molecular structural changes.

•This study investigates the impact of hydrocracking on the structure and composition of coal tar toluene insoluble.•The concentrations of toluene insoluble initially decreased and then increased as the increase of reaction temperature.•The decrease involved decomposition along with the removal of heteroatoms groups at low temperatures.•The increase was induced by coke formation via the stacking of rich-oxygen compounds at high temperatures.•The Fe1−xS was formed by self-sulfurized from inorganic matters and was studied.Toluene insoluble (TI) is an important heavy components of coal tar. It significantly affects on residues upgrading and coke formation during slurry-phase hydrocracking. The structural and compositional evolution of TI were investigate in hydrocracking experiments with oil-soluble catalysts. Experiment results showed that the concentrations of TI after hydrocracked initially decreased and then increased as the increase of reaction temperature. And TI consisted organic aromatic compounds and inorganic species. At low temperatures, the TI evolution involved the thermal decomposition along with the elimination of heteroatoms groups. The Fe1−xS was formed by self-sulfurized from inorganic matters and was studied. At relatively high temperatures, the TI evolution included both mesophase and coke formation through the aromatic sheet stacking of rich-oxygen compounds. On the basis of experimental studies, the pathway of the TI evolution was proposed for slurry-phase hydrocracking.

The coking behavior of coal tar atmospheric residue (CTAR) during slurry-bed hydrocracking was studied. The CTAR hydrocracking was performed in the autoclave at 430 °C with H2 pressure of 13 MPa, comparing with that of the Merey atmospheric residue (MRAR). The properties of C7-asphaltene and toluene-insoluble in feedstocks and products were analyzed respectively to describe the CTAR coking behavior during slurry-bed hydrocracking. The experimental results showed that CTAR with higher asphaltene content (30 wt%) produced less amount of coke than MRAR with asphaltene content (9.29 wt%), and little coke on the inner surface of reactor was found. The toluene-insoluble in the feedstock contained the larger carbonaceous particles (about 7 μm) and the inorganic fine particles (about 1 μm). Both sulfurized catalyst particles and inorganic fine particles in CTAR provided independent condensation nuclear or growth nuclear for macromolecular radicals during slurry-bed hydrocracking. These particles promoted the dispersion of spherical coke precursor and inhibited the coalescence of coke precursor. The larger carbonaceous particles in CTAR carried spherical coke particles as coke-carrier.

2,6-Diisopropylnaphthalene (2,6-DIPN), 1-methylnaphthalene (1-MN), and biphenyl (BP) were selected as model compounds to investigate the hydrogenation behavior of bicyclic aromatics. The experiments were conducted in a micro-autoclave in the presence of a dispersed catalyst at a temperature from 380 to 430 °C and pressure from 3 to 15 MPa. Through the analysis of the reaction products by gas chromatography–mass spectrometry (GC–MS) and gas chromatography (GC), the results revealed that hydrogenation of aromatics can be promoted significantly in the presence of a dispersed catalyst. A high selectivity toward monocyclic aromatic products was observed in hydrogenation of these model compounds, and its behavior was affected by the presence of substituents and a π-conjugated bridge on an aromatic ring. The yield of hydro-bicyclic aromatics increased with the temperature and hydrogen pressure, while sometimes, ring hydrogenation was influenced by thermodynamic properties of aromatics. Reaction pathways for hydrogenation of 2,6-DIPN, 1-MN, and BP in the presence of a dispersed catalyst were proposed.

Asphaltenes play a key role in the stability of the residue during processing. When asphaltenes reach their solubility limit in the residue, they would begin to aggregate, so that a new phase, called the mesophase, would separate from the oil phase, which eventually leads to coke formation. To relate coking characteristics, the changes in stability of the residue were studied during a slurry-phased hydrocracking reaction. The results indicated that the coke formation is obviously restrained by H2 and a catalyst such that the coke induction period is prolonged and the coke content is also reduced significantly compared to the coke content only in the presence of H2. The colloidal stability parameters (CSPs) determined by means of flocculation onset titration and the colloidal stability function (CSF) calculated on the basis of saturate, aromatic, resin, and C7-asphaltene (SARA) composition of the residue have a similar variation trend, which could be related to coking characteristics. First, the coking onset and the maximum asphaltene content in the residue were in correspondence with the turning point in the downward trend of the stability of the residue. The stability of the residue deteriorated significantly during the coke induction period, and the decreased trend tended to smooth after the coking onset point. Second, it is confirmed that the downward trend of stability is inhibited effectively in the presence of H2 and a catalyst, so that the ability of the residue against thermal disturbance is enhanced to reduce the coke formation. The changes in structure parameters of asphaltenes also showed that the catalyst could inhibit or delay the excessive condensations of asphaltenes to reduce the coke formation.