Composition and structure analysis of products from the sequential ex-traction process of medium temperature coal tar pitch

According to the results of Hansen solubility parameter calculated by software HSPiP,anhydrous ethanol,npentane,isopropanol,toluene,the tetrahydrofuran and Nmethylpyrrolidone were selected as extractants for medium temperature coal tar pitch soxhlet extraction to analyze the composition and structure.The results of highresolutionmassspectrometry analysis show that more than 3 000 compounds are detected and the molecular weight is in the range of 100 to 400,wherein,the content of compounds containing carbon and hydrogen is up to 60%.It can be observed that the relative content of 20 compounds is higher,among which 9 compounds mainly contain heteroatoms and oxygen.In addition,the content of Nn species,consisting by pyridine and pyrrole,is 4.3%-12.9%,while it is 10.1%-12.0% for ONS compounds.The unsaturation double bond equivalent (DBE) values of the extracts range from 15 to 19,and the carbon number is between 21 and 28.Meanwhile,the residues were characterized by XPS,FTIR,TG-DTG and 13C NMR.The XPS results show that the aromatic carbon is the major form of carbon and its content is up to 80%.For nitrogen element,it exists in pyridine and pyrrole,and the latter is more easily to be extracted by solvent,thus leading to the gradual decrease of relative content with the raising extraction series.The thiophene is the main form of sulfur.According to the analysis of 13C NMR,the Xb of coal tar pitch and all residues is 0.7,indicating that the average number of aromatic rings is about 5.It is noted that the content of aromatic bridge carbon faB is 65%,suggesting the highly condensed aromatic structure.As the extraction proceeds,the weak bonds and side chain groups in the residues gradually decrease,while the condensation of aromatics and molecular weight increases,resulting in an enhancement of the thermal stability of the samples.Correspondingly,saturated chain and aromatic sheet spacing in residues gradually reduce,however,the diameter,stacking height and number of aromatic lamellar present an increase tendency