Abstract:
This study aims to compare iso-rank vitrinite-rich and inertinite-rich coal samples to understand the impact of
coal-forming processes on pyrolysis chemistry. A medium rank C bituminous coal was density-fractionated to create a
vitrinite-rich and an inertinite-rich sub-sample. The vitrinite-rich sample has 83 vol% total vitrinite (mineral-matter-free
basis), whereas the inertinite-rich counterpart has 66 vol% total inertinite. The vitrinite-rich sample is dominated by
collotelinite and collodetrinite. Fusinite, semifusinite, and inertodetrinite are the main macerals of the inertinite-rich
sample. Molecular chemistry was assessed using a pyrolysis gas chromatograph (py-GC) equipped with a thermal desorption
unit coupled to a time of flight mass spectrometer (MS) (py-GC/MS) and solid-state nuclear magnetic resonance
(13C CP-MAS SS NMR). The pyrolysis products of the coal samples are generally similar, comprised of low and high
molecular weight alkanes, alkylbenzenes, alkylphenols, and alkyl-subtituted polycyclic aromatic hydrocarbons, although
the vitrinite-rich sample is chemically more diverse. The lack of diversity exhibited by the inertinite-rich sample upon
pyrolysis may be interpreted to suggest that major components were heated in their geologic history. Based on the 13C CPMAS
SS NMR analysis, the inertinite-rich sample has a greater fraction of phenolics, reflected in the py-GC/MS results as
substituted and unsubstituted derivatives. The greater abundance of phenolics for the inertinite-rich sample may suggest a
fire-related origin for the dominant macerals of this sample. The C2-alkylbenzene isomers (p-xylene and o-xylene) were
detected in the pyrolysis products for the vitrinite-rich and inertinite-rich samples, though more abundant in the former.
The presence of these in both samples likely reflects common source vegetation for the dominant vitrinite and inertinite
macerals.
