Structural Characterization Of Heavy Fractions From Coal Liquefaction And Their Reactivities To Catalytic Hydrogenation

In order to explore catalytic liquefaction mechanism, the liquefaction experiments of Shenfu sub-bituminous (SF), Shengli lignite (SL) and Xiaolongtan lignite (XLT) were carried with tetralin as hydrogen-donor solvent in a batch autoclave in the paper. The effects of reaction temperature, catalysts and initial hydrogen pressure on the liquefaction property and the distribution of liquefied fractions were investigated. The structural characterizations of the liquefied fractions were examined by elemental, FTIR and acidic oxygen-containing functional group analyses. The heavy fractions i.e. asphaltene (AS) and preasphaltene (PA), which were obtained by the liquefaction of different raw coal under different conditions, were separated by column chromatography. The application of hydrogen storage materials in hydrogenation of asphaltene or preasphaltene was also probed. In addition, the kinetics of the hydroliquefaction of preasphaltene, from liquefied fractions of different coal rank, was studied and a suitable kinetic model was proposed.The results indicated that the accuracy of the determination results of the content of acidic oxygen-containing functional group in coal and its derivates were distinctly improved by ultrasonic treatment under constant temperature water bath. Compared to the three catalysts, the THF extraction yield and oil+gas yield without catalyst is the lowest in XLT hydroliquefaction experiments. Noteworthily, although the THF extraction yield from XLT hydroliquefaction over FeS+S is much lower than that over FeS, the oil+gas yield obtained over FeS+S is appreciably higher than that obtained over FeS.The content of sub-component I and II obtained by column chromatography with toluene/tetrahydrofuran mixed solvent as the eluents in preasphaltene were higher, and the component IV obtained with methanol as the eluent in preasphaltene was lower. The content of carbon of the sub-component in preasphaltene lowered and the content of oxygen increased with the increasing of polarity of the eluent. The content of polar component, separated from asphaltenes and preasphaltenes of lignite liquefaction, was evidently higher than that of polar component from asphaltenes and preasphaltenes of subbituminous liquefaction. The sub-components in preasphaltene were compounds with wide molecular weights. The retention time of sub-components in preasphaltene were longer than that of asphaltene.The feedstock AS THF extraction yield and the yield of oil+gas increased from 30.8% to 53.9% and from 6.0% to 38.4%, respectively, but retrogressive condensation was reduced by 9 percent with the addition of sulfur into FeS in the hydroliquefaction experiments of asphaltenes from XLT liquefied products. Under the above two catalysts, both the THF extraction yields of feedstock AS increased with the increasing of reaction temperature, however, the THF extraction yield increment of 15.2% without sulfur addition was distinctly lower than 23.8% of sulfur addition. MgH₂ was stronger than NaBH₄ in hydrodeoxygenation of PA under the same conditions. The hydrogen-donating property of MgH₂ in XLT liquefied product preasphaltene (XLTPA) hydrogenation was better than that of SF liquefied product preasphaltene (SFPA). The studies of hydrogenation kinetics of SFPA and XLTPA indicated that the proposed kinetic model was suitable to describe the hydrogenation process of the two PAs between 380℃and 440℃. The apparent activation energies in XLTPA and SFPA hydrogenation were in the range of 50²45 kJ/mol^-1 and 165²25 kJ·mol^-1, respectively.There were 40 figures, 54 tables and 228 references in the paper.