Study on the molecular structure model of tar-rich coal and its pyrolysis process

With the continuous consumption of medium/high-rank coal and increasing energy shortage, the conversion and utilization of low-rank coal is gaining attention. A rational molecular model of coal combined with reaction molecular dynamics (ReaxFF MD) is becoming a promising way to explore coal conversion processes at the molecular level. In this work, a molecular structure model of tar-rich coal from northern Shaanxi, China, with the molecular formula C355H332O57N4S was proposed by combining experimental characterization tests and theoretical computational analysis. In addition, the molecular model was validated by calculating FTIR and 13C NMR spectra with quantum chemistry. Furthermore, complex multi-molecule systems were constructed based on the single-molecule model, the effect of heating rates on the pyrolysis process was investigated by ReaxFF MD simulations, and the evolution of pyrolysis process and products were analyzed in detail. The results show that a slower heating rate helps to obtain more gas products, inhibit the condensation reaction between tar fragments, and promote their cracking, more light tars could be obtained. The combination of experimental characterization and theoretical calculations provides a comprehensive understanding of the molecular structure and pyrolysis processes of tar-rich coal, and provides a basis for an in-depth study of the structure of low-rank coal and its clean utilization technologies.