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An in-depth investigation was carried out on five Chinese coals using a range of advanced analytical techniques focused specifically on extracting structural parameters. Detailed investigations were carried out using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and X-ray diffraction followed by peak deconvolution and data analysis. Correlations were established for parameters determined from different techniques. The FTIR data showed good linear relationships between the apparent aromaticity (f a(FTIR)) and (R/C)u with the H/C atomic ratio for all coals under investigation. These results indicate that FTIR spectroscopy coupled with appropriate data analysis can be successfully used to determine aromaticity and the coal rank. Raman spectroscopy data showed a negative linear relationship between the GL fraction and H/C ratio; no well-defined relationship was observed between other band fractions and the H/C ratio. The decrease of A D/A G with increasing H/C ratio indicates the growth of aromatic rings; i.e., the structure of the sample was closer to that of graphite. This result is in good agreement with the decrease of apparent aromaticity (f a(FTIR)) as determined by the FTIR spectroscopy. A good linear relationship was observed between the structural parameters (f a(X‑ray) and R X‑ray) determined with X-ray and coal rank (represented by the H/C ratio). Even though the correlations among parameters derived from three techniques showed a similar trend and were consistent with each other, FTIR, and X-ray diffraction techniques were found to be better than Raman spectra to characterize coal maturity. These findings have led to a simplified coal model based on the complementary information from different techniques on various aspects of the coal structure.

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A parametric study of ReaxFF for molecular dynamics simulation of graphitization of amorphous carbon was conducted. The responses to different initial amorphous carbon configurations, simulation time steps, simulated temperatures, and ReaxFF parameter sets were investigated. The results showed that a time step shorter than 0.2 fs is sufficient for the ReaxFF simulation of carbon using both Chenoweth 2008 and Srinivasan 2015 parameter sets. The amorphous carbon networks produced using both parameter sets at 300 K are similar to each other, with the first peak positions of pair distribution function curves located between the graphite sp bond peak position and the diamond sp bond peak position. In the graphitization process, the graphene fragment size increases and the orientation of graphene layers transforms to be parallel with each other with the increase of temperature and annealing time. This parallel graphene structure is close to the crystalline graphite. Associated with this graphitization is the presence of small voids and pores which arise because of the more efficient atomic packing relative to a disordered structure. For all initial densities, both potential parameter sets exhibit the expected behavior in which the sp fraction increases significantly over time. The sp fraction increases with increasing temperature. The differences of sp fraction at different temperatures are more obvious in lower density at 1.4 g/cm. When density is increased, the gap caused by different temperatures becomes small. This study indicates that both Chenoweth 2008 and Srinivasan 2015 potential sets are appropriate for molecular dynamics simulations in which the growth of graphitic structures is investigated.

The thermodynamics of possible reactions, including gasification and reduction reactions, in carbon–carbon dioxide–sodium or potassium carbonate systems was analyzed first. And then, the gasification reactions of graphite and coke with CO2 in this system were studied kinetically by temperature programmed thermogravimetry. The results showed that the carbon conversion curve shifted to a lower temperature zone after Na2CO3 or K2CO3 was added, and graphite was more susceptible than coke to be catalyzed by Na2CO3 or K2CO3. Ten kinetic equations were adopted to simulate the reaction process using the method of Coats–Redfern. The Avrami–Erofeev equation was found to be the most probable kinetic equation, with which the values of activation energy and frequency factor were calculated. The kinetic simulation indicated that the activation energy of coke carbon had been activated to the lowest level by its inner factors, thus it was difficult to be reduced by adding Na2CO3 or K2CO3. The kinetic compensation effect was confirmed to exist in both graphite gasification and coke gasification. X-ray diffraction and Raman spectra were used to characterize the inner difference between graphite and coke, which showed that coke carbon structure was greatly different from graphite structure because of its highly disordered and heterogeneous carbon structure.

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