Study On The Structure And Composition Of Heavy Intermediate Products From The Direct Liquefaction Of Coal

In order to study the conversion behaviors of heavy intermediate products of coal direct liquefaction and the mechanism of coal direct liquefaction, the heavy products of coal liquefaction such as asphaltene and preasphaltene, which are obtained by the liquefaction of different raw coal under different liquefaction conditions, are separated by column chromatography in this paper. The structures of all sub-components are characterized by ultimate analyses, FTIR, UV/Vis, fluorescence spectrum and GPC. The influence of each factor on the composition and distribution of liquefied products is also explored. In addition, the aggregation behavior of preasphaltene is discussed preliminarily by fluorescence photometry.The results indicate that the content of component I and II, which are obtained by column chromatography with a mixture solvent (toluene and tetrahydrofuran) as the eluents, are higher than that of component IV obtained with methanol as the eluent in preasphaltene. Ultimate analyses show that element components of I, II and III are very similar, in which the content of carbon is high but the content of oxygen is low. The component IV is mainly strong polarity compound containing oxygen which consists in preasphaltene through aggregation of the non-covalent bonds. The primary component of all asphaltenes is weak polarity component obtained with toluene or toluene/ tetrahydrofuran (4:1) as the eluent. The higher the polarity of the eluent is, the content of carbon of the sub-component is lower, but the content of oxygen is higher, especially the component E obtained with methanol as the eluent is evidently higher than other components. The hydrogenation and removal of heteroatom for the asphaltene and preasphaltene can be promoted by increasing the liquefaction temperature, time and atmosphere with strong supply hydrogen (H2 atmosphere and FeS+S catalyst), so that the content of weak polarity components increase and the content of oxygen decreases. The content of strong polarity component separated from asphaltenes and preasphaltenes of lignite liquefaction is evidently higher than that of subbituminous liquefaction, in which the content of carbon is higher than raw coal but the content of oxygen is lower. The oxygen-containing functional groups are extremely complicated. They not only contain large numbers of phenolic hydroxyl group, ether bond and aromatic ketone carbonyl group, but also carboxylic ester, carboxylic acid, acid anhydride and aliphatic alcohol hydroxyl group. The oxygen-containing functional groups such as aromatic ketone carbonyl group and phenolic hydroxyl group is show comparatively low reactivity and are difficult to remove. There are two different fluorophores with different energy state in all sub-components of asphaltene and prasphaltene. The difference of fluorescence characteristic of different components is mainly originated from different distribution of energy state and fluorescence efficiency. Fluorescence efficiency of sub-component is evidently lower than its parent asphaltene and prasphaltene. Aromatic ring of preasphaltene is mainly single ring structure. Meanwhile, there is few 2-3 aromatic fused ring structures in preasphaltene. Except for single ring structure, asphaltene shows abundant 2-3 aromatic fused ring structures which are mainly existed in weak polarity component. Non-covalent bond aggregation exists extensively in asphaltene and preasphaltene of heavy intermediate products of coal liquefaction. It can influence the separation performance and apparent molecular weight of heavy intermediate products. The aggregation of preasphaltene in solution is a progressive process.