Molecular Structure Characterization of CS_2-NMP Extract and Residue for Malan Bituminous Coal via Solid-State ~(13)C NMR, FTIR, XPS, XRD, and CAMD Techniques

摘要

The extract and residue were acquired by CS2-NMP (1:1, v/v) ultrasonic extraction of Malan No. 8 coking coal. The chemical structure models were constructed based on elemental and structural analyses of C-13 NMR, Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) using C-13 chemical shift calculations. The formula of the extract model is C178H154N2O5S at a molecular weight of 2435.2, and the formula of the residue is C181H149N3O5S at a molecular weight of 2478.2. The elemental compositions and aromaticity values of the constructed model match well with those determined by the ultimate analysis and C-13 NMR. The energy-minimum conformations of the extract and residue were determined through molecular mechanics (MM) and molecular dynamics (MD) methods. The optimized three-dimensional (3D) structural models were enclosed into the periodic boundary conditions (PBC) in an amorphous cell to perform density calculation. The simulated density values of the extract (1.37 g/cm(3)) and residue (1.40 g/cm(3)) were slightly lower than the true relative density (1.39 and 1.43 g/cm(3), respectively) because the singular model construction does not consider the presence of small molecules, moisture, and minerals. Moreover, the X-ray diffraction (XRD) spectra were simulated at the determined density values to further validate the molecular model. Good agreement between the analytical data and the structure model was obtained. In addition, intermolecular interactions were investigated. The interactions are dominated mainly by E-B (bond length torsion energy) and secondarily by E-van (van der Waals energy), the former making the rings between the aromatic rings, aliphatic rings, and side chains stacked, and the aromatic layers tended to be parallel by pi-pi interaction. These findings revealed the structural features of the coking coal and were potentially useful to investigate the coal coking mechanism and beneficial for improving its utilization efficiency.