Aromatic Structural Characterization of Different-Rank Vitrinites: Using HRTEM, XRD and AFM

Abstract

The aromatic structure of three different-rank vitrinites, V-YJL (R o =0.61%), V-AW (R o =1.13%), and V-JC (R o =2.22%), was investigated by X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), and atomic force microscope (AFM). Based on the HRTEM experimental results, it was found that with vitrinite reflectance increasing, the distributions of aromatic layers changed from disordered to well-aligned. The shapes of aromatic layers changed from twisted to more straight and parallel. In addition, there were more large-sized aromatic layers in vitrinite samples with larger vitrinite reflectance. XRD experimental data also showed that the sizes (L a, L c and N) of vitrinite crystallite structures increased and the inter-layer spacing (d 002) decreased with increasing the vitrinite reflectance, which was consistent with the HRTEM data. AFM images illustrated that the surface morphologies of V-YJL, V-AW, and V-JC vitrinite samples showed as granule-like structure, compact spherical clusters, and irregular network with granular structure. Through comprehensive analysis of HRTEM data, XRD data, and AFM data, it was found that the morphology of the vitrinite samples obtained by AFM was related to the aromatic structural features of vitrinite from HRTEM and XRD. Both the aromatic chemical structure and morphological structure were coal rank dependent, and greatly affected by the arrangement of heterogeneous atoms. This study can provide helpful information on aromatic structure of vitrinite, which is important for investigation of coal and coal clean utilization.