Thermal Dissolution And Structure Simulation Of Upper Freeport Coal And Shenfu Coal

In this work, Upper Freeport(UF) coal and Shenfu coal(SC) were subjected to thermal dissolution(TD) and the thermal dissolution soluble factions(TDSFs) obtained were further sequential extracted with acetone and pyridine. Then the TDSFs were characterized to obtain the related structural parameters of coal, and the macromolecular structural models of coal were constructed. Based on the results, the macromolecular structural model of UF coal and SC were optimized in molecular mechanics and molecular dynamics using the Materials Studio7.0, and the energy dependence between the density and molecular structure model was explored, and the swelling behavior of the UF coal was simulated.The results suggest that the TD yields of solvents to UF coal follow the order as 1-methylnaphthalene(1-MN)/ N-methyl-2-pyrrolidone(NMP)(v:v/1:1) > NMP > 1-MN at the same temperature. The effect of temperature on the TDs of UF coal and SC is greatly. With the rising of temperature the TD yield increased, and the highest TD yields for UF coal and SC were 93.21% and 47.1% respectively at 360?.The content of acetone soluble factions(AS) in the TD soluble fraction(TDSF) of UF coal in 1-MN/NMP was significantly higher than that of TDSFs in 1-MN and NMP. When using 1-MN as the solvent, the content of AS in the TDSF at 360? was significantly lower than that of the TDSF in 300?. While using NMP or 1-MN/NMP as the solvent, the result was opposite. However, the content of AS in the TDSF at 360? was significantly higher than that of TDSF at 300? for SC. More aliphatic compounds and oxygenal derivatives including esters, ketones and carboxylic acids in TDSF were transferred into AS in acetone extraction process.Under the same conditions, the content of pyridine insoluble fractions(PI) in the TDSF of UF coal in 1-MN was less than those of TDSFs in NMP and 1-MN/NMP. Pyridine mainly interacts on the side chains and bridge bonds of aromatic nuclears in the basic structural unit of coal. The number and weighted average molecular weights of pyridine soluble fractions(PS) obtained at 360? were significantly higher than those of PS obtained at 300?. In the meantime the index of dispersion increased, and the distribution of molecular weight became wider. TDSFs of SC were almost completely dissolved in pyridine.The main forms of oxygen-comtaining functional groups in the coal structure are the ether, hydroxyl and carbonyl. The fatty chains mainly exist as methyl and methylene. Sulfur element mainly exists in the form of alkyl sulfide and thiophene sulfide. Nitrogen mainly exists in the form of pyridinic and pyrrolic types.Through the energy analysis of two kinds of coal structure model, the results show that potential energy is mainly composed by non bonding energy, and the non bonding energy is much higher than valence electron energy. Van der Waals energy is dominant in the potential energy of the structure model. After optimization by molecular dynamics, it is found that the torsion of the chemical bonds in the structural model, especially fatty chain and bridge bond torsions make the different aromatic sheets to be layered nearly parallel arrangement; and the ?-? interaction between the different aromatic sheets maintains the stability of structure model.The aromatic structure of SC coal is smaller, when the coal rank increase, the layer of parallel aromatic sheet in aggregation molecular chain enlarge, and the ? bond structure formed in molecules. After the optimization of the molecular dynamics, Van der Waals is obvious changed for the non-bond energy, and it become stronger as the higher coal rank.The density of minimum energy geometries of UF coal and SC in the periodic boundary conditions were 1.3 g·cm-3 and 1.2 g·cm-3 respectively, which is consistent with the relationship between the coal density of the macromolecular structure and its rank.The simulations of UF coal swelling behavior show that polar solvents interact with the polar position of UF coal macromolecular structural model through electrostatic interaction and hydrogen bonding, and weak polar solvent mainly interact with aromatic ring in the macromolecular structural model of UF coal through electrostatic interaction. With the continuous addition of the swelling solvent molecules into macromolecular structural model of UF coal, the volume of unit cell increases, and the energy of the system decreases till to the state of swelling equilibrium. The results have a good agreement with the experimental values.