Exploration of coal tar asphaltene molecules based on high resolution mass spectrometry and advanced extraction separation method

Abstract

The structure of coal tar asphaltenes has been recognized as one of the most challenging research topics in coal chemistry. In this work, a stepwise extraction subfraction separation method is developed for coal tar asphaltenes to reveal the polar molecule distribution and structure information using (+) ESI FT-ICR MS coupled with collision induced dissociation (CID). It is found that the most easily ionized molecules are preferentially observed in unfractionated asphaltenes, while the strongly polar molecules are suffered with ionization suppression. The heteroatoms are more likely to be present in aromatic cores instead of substituent chains, and this phenomenon grows more significantly with the increase of solvent polarity. The O/C increases with the increase in solvent polarity, and O plays an important role in the adsorption and desorption of asphaltenes on silica gel surface. The “atypical” asphaltenes molecules are rich in N, S and particularly O containing groups with low aromaticity and small aromatic structures, and tending to be island structures. Moreover, the coal tar asphaltenes has a significantly higher island/archipelago ratio than petroleum asphaltenes. The polar driving force has a great impact on archipelago molecules, the proportion of which is high in polar fractions.