Molecular model and ReaxFF molecular dynamics simulation of coal vitrinite pyrolysis

Abstract

Vitrinite in coal, the mainly generating methane maceral, plays an important role in hydrocarbon generation of coal. This study aims at obtaining products formation mechanism of vitrinite pyrolysis, and hence determining the chemical bond, molecular liquefaction activity, and reactions mechanism of methane and C2-4 during pyrolysis. The ReaxFF molecular dynamics (MD) simulation was carried out at temperature of 1500 K in order to investigate the mechanism of vitrinite pyrolysis. Initially, a minimum energy conformational structure model was constrained by a combination of elemental and carbon-13 nuclear magnetic resonance ((13)C NMR) literature data. The model analysis shows the chemical and physical parameters of vitrinite pyrolysis are broadly consistent with the experimental data. Based on the molecular model, ReaxFF MD simulations further provide information of unimolecule such as bond length, and chemical shift, and hence the total population and energy of main products. Molecules bond and pyrolysis fragments, based on active bond analyzed, revealed pyrolysis products of single vitrinite molecule with aliphatic C-C bond, especially ring and chain aliphatic as liquefaction activity. The molecular cell whose density is 0.9 g/cm(3) with lowest energy accords with the experimental density 1.33 g/cm(3). The content of main products after pyrolysis, classifying as CH4, H2O, and H2, was changed along with the increasing temperature. The gas molecule, fragments and generation pathways of CO2, H2, CH4, and C2H6 were also elucidated. These results show agreement with experimental observations, implying that MD simulation can provide reasonable explanation for the reaction processes involved in coal vitrinite pyrolysis. Thus the mechanism of coal hydrocarbon generation was revealed at the molecular level.

Molecular Model Construction and Study of Gas Adsorption of Zhaozhuang Coal

“…Accurately constructing the molecular structure model of coal and the appropriate adsorption description model are the basis of understanding the interaction of coal and coalbed methane, , and these models also provide more accurate information for coalbed methane resource evaluation and capacity prediction. The real coal molecular model was constructed ,− by analyzing the properties of coal samples, which provides a theoretical basis for constructing molecular model of Zhaozhuang coal.…”

Structures of Aromatic Clusters of Different Coals Based on Benzene Carboxylic Acids from Coal via Oxidation

“…In addition, many structural models of coals based on the analyses of structural characters were constructed. − In 1942, Fuchs et al proposed the first coal structural model based on the pyrolysis products. In 1984, the classic Shinn model was proposed based on the products of liquefaction combined with the results of elemental analysis, aromaticity analysis, and the analysis of chemical functional groups .…”

Graphite and Graphite Oxide: New Models to Analyze the Calcium Catalytic Effect on Steam Gasification of Lignite and Char

“…The Peak fitting may be used to determine the structure changes of coal samples during pyrolysis process. The curve of the chemical shift was separated into 11 peaks, which may be assigned to different carbon configuration Figure also shows the carbon and oxygen distribution in the coal.…”

“…The curve of the chemical shift was separated into 11 peaks, which may be assigned to different carbon configuration. 45 Figure 3 also shows the carbon and oxygen distribution in the coal. The carbon and oxygen may be assigned to different functional groups in the coal, and the carbon and oxygen distribution may be determined from the spectral data.…”