Characterization of nitrogen-containing compounds in coal tar and its subfractions by comprehensive two-dimensional GC x GC-TOF and ESI FT-ICR mass spectrometry based on new separation method

The molecular composition and structure of heavy oil and the subfraction have always been one of the most controversial topics despite the continuous improvement of detection and analytical methods. In this contribution, the composition and structure of nitrogen-containing compounds (NCs) in middle and low temperature coal tar (MLCT) and the subfractions are studied by GC x GC-TOF MS and ESI FT-ICR MS coupled with collision-induced dissociation (CID) through isolating a narrow window of mass-defined ions based on the developed MLCT subfraction separation method. It is found that the new separation subfraction method combined with high resolution mass spectrometry is efficient to detect the characteristics of each fraction at the molecular level. Eighty nitrogen compounds, dominant of quinolines, carbazoles and pyridines are identified in MLCT. The distribution laws of compound classes, carbon numbers, DBE are obtained with reasonable representative molecules for aromatic, resin and asphaltene. The qualitative analysis shows the island and archipelago structural motifs coexist in MLCT and the island-type is the predominant structure in aromatic (94%), resin (86%) and asphaltene (80%). The archipelagic structures in large molecules are more abundant. Meanwhile, the heterolysis mode is the predominant bond cleavages path for MLCT molecules and the proton transfers reactions occur during CID process.

Automated summary

The study utilized GC x GC-TOF MS and ESI FT-ICR MS with CID to analyze the nitrogen compounds in MLCT. It found that the new separation subfraction method combined with high resolution mass spectrometry efficiently detected the molecular characteristics of each fraction. The research revealed the presence of 80 nitrogen compounds in MLCT, with dominant quinolines, carbazoles and pyridines, and identified island and archipelago structural motifs coexisting in MLCT.