Investigation of organic structures in coal pitch based on separableselective destruction analysis method

Coal tar pitch (CTP) is abundant in China,but its utilization level is low.Investigating the organic structure and composition of CTP at the molecular level is essential for its efficient utilization.However,the structure of CTP is complex,and it is difficult to accurately understand its structural characteristics through a single direct characterization method.Herein,CTP produced by a tar processing plant in Shanxi was used as a sample.Based on the method of separable-selective destruction,the organic structural characteristics of CTP were explored at the molecular level.Considering the different solubility parameters and extraction effects on CTP of solvents,the methanol,cyclohexane and toluene were adopted for sequentially extracting CTP,which was divided into three extracts and residue.These components were systematically analyzed using modern instrument analysis methods combined with ruthenium ion catalytic oxidation methods.It was found that the sequential extraction could effectively realize the separation of soluble and insoluble components in CTP,and further separate the soluble components into three groups of components.From the methanol extract to the residue,the aromaticity increased gradually and the thermal stability increased successively.Furthermore,the methanol extract contained more nitrogen-containing compounds,whereas,the content of aromatic components in cyclohexane and toluene extracts gradually increased,and the residue had a condensed peri-condensed aromatic structure as its skeleton with the average number of aromatic rings was close to 7 in its structural unit.All components constituted the whole CTP through intermolecular force,and the soluble component existed in the macromolecular aromatic ring skeleton of the insoluble component in free or embedded form.Through extraction,the solvent destroyed these forces step by step,taking away the soluble components,and leaving the residue with more depressions and holes on the surface.