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

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 hetematoms 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.

Automated summary

The structure of coal tar asphaltenes is a challenging topic in coal chemistry. This study developed a stepwise extraction method to analyze the polar molecules and structure information using mass spectrometry. The results showed that the polarity of the molecules increased with solvent polarity, and oxygen played a crucial role in the adsorption and desorption of asphaltenes.