Identification of the structural characteristics of the asphaltenes in the tetrahydrofuran-microwave-extracted portions from two Chinese coals

- N4Oy (y = 0-2) class species dominated in the detected basic components.
- Acidic Oy class species with two/three aromatic rings enriched in the asphaltenes.
- OCC structure size in the asphaltenes had different relationship with O atom number.

This work aimed to evaluate the detailed chemical structures of the asphaltenes in the tetrahydrofuran-microwave-extracted portions from two Chinese coals, namely, Shenfu and Zhundong coal (SF, ZD) and to clarify their characteristics on chemical composition at molecular level. Based on the analyses of diffuse reflectance Fourier transform infrared spectroscopy (DRIFT) and Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS), the detailed chemical structure of a series of basic and non-basic nitrogen- and oxygen-containing class species in the asphaltenes were clarified. The results revealed that condensed nitrogen-containing alkylaromatic structures with amidogens (1-3) were the main structure units in N4Oy (y = 0-2) class species due to the high double bond equivalent (DBE) values for both the asphaltene from SF (ASF) and the asphaltene from ZD (AZD). Acidic O2-O7 class species with two or three aromatic rings were the main structure units, among which O4 and O2 class species had the highest relative abundances (RAs) in ASF and AZD, respectively. Acidic oxygen-containing components in AZD had narrower range of DBE and carbon number and mainly consisted of aromatic structure units with two rings. On the contrary, the average DBE values of O4-O7 class species in ASF had positive relationship with oxygen atom number which could be attributed to the introduction of phenol groups. The results provided more detailed information on the structural characteristics of polar and aromatic-rich components of mobile phase in coal.

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