Separation and characterization of C5-asphaltene from low temperature coal tar

The asphaltene was obtained from the low temperature coal tar heavy fraction by solvent precipitation with three kinds of solvents; n-pentane, n-pentane with 5% ethanol and n-pentane with 5% isopropanol. The properties such as structure parameters and hetero atom distribution were analyzed by ¹H-NMR, ¹³C-NMR, FT-ICR MS, elemental analysis and average molecular weight determination (GPC). Some possible average molecular structures containing hetero atoms were constructed and discussed. The results show that after adding polar solvent, the yield of C5-asphaltene is significantly reduced, while the aromaticity and average molecule weight are enhanced. The average molecular structure of the C5-asphaltene exhibits shorter side-chains and higher condensation degree. Though the type of heteroatom compounds in the asphaltene is barely changed by the addition of polar solvents, the relative abundance of O3-O6 class species is increased. Meanwhile, some O1-O2 class species with low condensation degree are transferred into maltene, indicating that the mixed solvent has a larger solubility with these compounds.