Study on the structure and association of asphaltene derived from liquefaction of lignite by fluorescence spectroscopy

Asphaltene (AS) is one of important heavy intermediates of direct coal liquefaction (DCL). It has significant influences on the technology of liquefaction, such as the coking property and the liquefaction efficiency. In this paper, the structure of AS derived from the liquefaction of Xiaolongtan lignite (XLT, a Chinese lignite) was characterized by element analysis, FTIR, UV and fluorescence spectroscopy, and its association was studied by the fluorescence spectroscopy. Results indicate that the aromatic system of AS derived at different liquefaction temperatures mainly consists of 2–3 rings aromatic nucleuses. With the increase of liquefaction temperature, the aliphatic structure is gradually cracked, and the aromaticity of AS and the proportion of large size aromatic nucleus increase. AS molecules easily form the nano-aggregates in a certain concentration of THF solution. The size of the nano-aggregates is independent of the liquefaction temperature and the AS concentration. The associations of ASs, which including intermolecular association and intramolecular association, originate mostly from the π–π interactions between aromatic nucleuses of AS rather than the hydrogen bonding interaction.