Examination of structural models and bonding characteristics of coals

More than 100 graphical coal structural models have proposed in the literature but their suitability has not been studied. All the coal models are in essence conceptual images, which are not very useful in quantitative analyses. This article analyzes the validity of 25 models selected from 134 models reported in the literature using the carbon content (C%) and aromaticity (fa) data of coals reported in the literatures. Eighteen of the models are found to be reasonably good because they meet the C%-fa relation within ±10% in fa. The concentrations of 9 covalent bonds in the 18 models are compared with those calculated by a method established in the paper based on ultimate analysis and 13C NMR data of coals. The pros and cons of the models are discussed and a matrix computation is proposed to represent the bonding structure of coals in a C% range of 59-91%.