Prediction and Characterization of the Microcrystal Structures of Coal with Molecular Simulation

The characterization of coal structures is challenging due to their broad distribution of molecular structures including large-scale entities. Previously, the microcrystal structure of coal has been extensively observed with the XRD analysis and its features were found to be closely correlated with the carbon/oxygen content. In this work, Polymorph Predictor, a Monte Carlo method, was applied to predict the most favorable microcrystal structures formed by simplistic coal models and to study the effect of carbon content on the density and interlayer spacing (d(002)) of coal. The valence or nonbond interactions existing in predicted crystal structures were analyzed by calculating the energy contributions based on the classical molecular dynamics (MD) simulation theory. The calculation from density functional theory of coal fragments was conducted to study the relationship between carbon content and electronic properties of coal. Additionally, the MD simulation of water contact angle was conducted to examine the wetting properties of the coal surface. This research is expected to provide insight in understanding the characteristics of coal from the molecular level. It demonstrates that molecular simulation should be a reliable alternative in the absence of the related laboratory measurements, which require complex experimental equipment and procedure, and are sometimes expensive and time-consuming.