Construction and verification of vitrinite-rich and inertinite-rich Zhundong coal models at the aggregate level: new insights from the spatial arrangement and thermal behavior perspective

Abstract

To explore the thermal behavior of Zhundong coal from the perspective of maceral, it is essential to conduct molecular simulations based on constructing a realistic aggregate model of coal. Here, two Zhundong coal samples ZD-V (vitrinite-rich) and ZD-I (inertinite-rich) were collected, and coal models were constructed using elemental analysis, solid-state ¹³C-nuclear magnetic resonance (¹³C-NMR), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectrometry (FTIR). The chemical formulas of 2D vitrinite-rich coal and inertinite-rich coal constructed are C₁₅₂H₁₆₇NO₃₆ and C₁₅₅H₁₁₉NO₂₈, respectively. The chemical structure information matches well with that determined by those analysis results, including elemental analysis, structural composition, and ¹³C-NMR spectra. The final aggregate models show that the dimension of the unit cell is 2.785 × 2.785 × 2.785 nm for ZD-V and 2.743 × 2.743 × 2.743 nm for ZD-I, including six macromolecules respectively. The final aggregate structure models were verified by comparing experiments and simulation results. In addition to the verification with He density, the spatial arrangement of the aggregate model was verified by simulated XRD spectrum. And moreover, the thermal behavior was verified by ReaxFF MD, and the simulated trend of thermal weight loss and cumulative total molecules released were consistent with TG-MS. The final models show the visual difference between ZD-V and ZD-I, whether the 2D molecular structure or aggregation state. ZD-V is dominated by chain hydrocarbons, while ZD-I is dominated by cyclic hydrocarbons with linked aromatic rings. The aromatic substitution of oxygen atoms is different, ZD-V is mainly composed of ortho-disubstituted arenes, and ZD-I is mainly composed of meta-disubstituted arenes. In addition, ZD-V has a lower ultra-micropore size distribution and porosity than ZD-I. This study presents a comprehensive approach to construct and verify aggregate models from the spatial arrangement and thermal behavior perspective, and the constructed Zhundong coal models can provide a foundation for further exploration of the thermal reactivity (e.g. combustion, liquefaction, etc.) of coal from maceral aspects.