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The Construction of Liulin3#Coal Supramolecular Structure and Molecular Simulation

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Tutor: ZengFanGui
School: Taiyuan University of Technology
Course: Mineral prospecting and exploration
Keywords: coal structure,LLR,asphaltenes,supramolecular structure,molecular simulation
CLC: TQ531
Type: Master's thesis
Year:  2012
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Abstract:
By the non-covalent research in coal, the interaction between coal molecule and solvent has a significant characterization that not only non-covalent interaction exists, but also the recognition interaction can be found. In terms of the supramolecular chemistry, these structures can be seen as supramolecular entity. They have the basic features of the supramolecuar structure, such as the fixed structure and configuration. The second coalification jump occurs on the condition of Cdat=87%,Vdaf=29%,Rm0=1.3%. With this coalification, the coal in this rank has the highest extraction. So in order to understand the relation between extraction and the second coalification, it is essential to insight into the microscopic structure of the coal.In recent years, computer-aided molecular design (CAMD) technology has been widely used in the coal macromolecular structure. It not only can easily build the model of a particular coal macromolecular structure, but also understand their three-dimensional structure. The microstructure parameters of the coal and the microstructure difference of different ranks coal also can be understood on the basis of reseach of molecular mechanics, molecular dynamics and quantum chemistry. Therefore, the pyridine extracted residue of vitrain from Linlin3#(Cdaf=88.18%,Vdaf=25.49%,Rm0=1-31%) and extraction are the objects of study. The coal samples are studied by13C CP/MAS NMR and XPS analysis. Macromolecular structure models are constructed based on the results of proximate and ultimate analysis.13C chemical shift of macromolecular structure is calculated by ACD/CNMR predictor, and the structure is corrected according to the calculation results. Finally the macromolecular structure which is consistent with the experimental results is gotten. On the basis of the two models, the supramolecule is constructed. The main conclusions are as follows:1In the LLR model, aromatic structure units are dominated by anthracene; Aliphatic C atoms exist in the form of side-chain, it connects the aromatic structure; O atoms mainly exist in the form of-OH and-O-, which contain a small amount of C=O.2In the asphaltenes, aromatic structure units are dominated by naphthalene and anthracene; Aliphatic C atoms exist in the form of side-chain, which are very long. Oxygen exists in the form of phenolic hydroxyl; meanwhile there is a small amount of carbonyl and carboxyl.3The order of main energy for stable LLR model is van der waals energy> torsion energy> angle energy>bond energy. The simulation results also showed the aromatic layer structure tend to be parallel occupies a small proportion, this may be the structure factors that the physical and chemical properties of the coal whose vitrinite reflectance is1.3%take a new turn. LLR density is1.22g/cm3by enclosing coal model into the (PBC) periodical boundary condition. Semi-empirical quantum chemistry methods (AM1) simulation indicates that the C-C bonds adjacent to aliphatic side chain C atoms exhibit a higher activity and terminal C atoms have more negative charge, which therefore prone to undergo oxidation reactions while aromatic C atoms are characterized by fewer charges and very high stability. Also in the asphaltenes model, the aromatic layer structure tend to be parallel occupies a small proportion, and its density is1.15g/cm3.4Due to the difference of the combination of the residual coal and asphaltenes, the aromatic layer structure has different proportion in the supramolecular structure. In particular, the model (asphaltenes+asphaltenes+residual coal+residual coal) is disorganized, while the model (asphaltenes+asphaltenes and residual coal+residual coal) is terse. So the presence of the asphaltenes effects the Linlin3#supramolecular configuration. The molecular mechanical calculations of the supramolecular model show that the main drive interaction in the supramolecualr formation is the attraction between the aromatic planes. The molecular recognition is completed with the contribution from other atomic groups present in the molecule, such as the alkyl branches. These alkyl groups contribute to the formation of the supramolecular formation through the combined effect the steric repulsion and the van der Waals attraction. The side-chain in the asphaltenes affects the size of the supramolecular model and its density. The strong interaction between the aromatic layer of the two molecules and less interference of the aliphatic side-chain causes the supramolecular formation process easy relatively. It was also found that the alkyl branches limit the number of available active sites for H-bonding and other directional interactions.5The non-covalent bond in the molecular conformation plays a very important role, especially the Van der Waals force. In the medium-rank coal, the Van der Waals force is the driving interaction in the supramolecular formation. The electrostatic contribution arising mainly from the polar groups is small in all cases, showing that polarity does not seem to play an important role in the formation.6By the XRD analysis, the average values of the d002, La and Lc is3.50A,12.30A and12.40A, which are consistent with the theoretical result (3.5A,11.435A and12.20A).7Due to the etraction rate of9.93%in Liulin3#raw coal, the raw coal consists of five residual coal molecules and one asphaltene. The relative of the residual coal molecules and asphaltene affects the formation of the supramolecualr structure, besides the perpendicular geometry can be found.
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