Molecular model construction and structural characteristics analysis of Wucaiwan coal in Eastern Junggar Coalfield based on quantum chemistry theory

Quantum chemistry theory is one important method to study the energy change and heat release of coal oxidation and combustion process. In this paper，the molecular structure of Wucaiwan coal was established by using computer⁃aided software(Chemdraw，Chem3D，and Materials Studio)which is based on a series of experiments data，then， its stable 3D model was obtained by optimizing and minimizing its molecular energy. Coal samples were heated from 20 °C(room temperature)to 100，200，300，400，500，600，700，and 800 °C respectively. Then some tests and experi⁃ ments were conducted， such as the test of coal proximate and ultimate analysis， the X - ray photoelectron spectroscopy，the X-ray diffraction(XRD)，the Fourier transform infrared spectroscopy(FTIR)，the nuclear magnetic resonance spectrum(13CNMR)，etc.，which aim to investigate the macro and micro change of coal samples. Results show that the aromatic carbon dominates within coal molecular structure，the aliphatic carbon exists in the form of a branch chain or linked aromatic ring，and the side chain length of alkanes is longer. The ether oxygen group(C—O) is the major type of oxygen within coal molecular structure. The pyrrole(N-5)and the pyridine are the major type of nitrogen. The sulfone is the major type of sulfur. The major type of benzene ring is replaced by three and four， and the molecular formula of coal sample is C206 H128 O3 6 N2 . After a geometry optimization and annealing simulation op⁃ timization of molecular structure，the aromatic lamellar in the model tends to be oriented，so the van der Waals ener⁃ gy takes up a large part of energy proportion for keeping the structure stable. The heating process was divided in⁃ to three stages，i.e.，the low⁃temperature stage(20-300 °C)，the mid⁃temperature stage(300-600 °C)，and the high⁃temperature stage(600-800 °C). At the low⁃temperature stage，the carbon participates in the reaction mainly in the form of C—C and C—H，which produces a little amount of C—OH，C—O—C，C