Investigation On Structures And Aromatic Characteristics Of Heavy Oils

Laser desorption ionization mass spectrometry (LDI-MS) can be used to investigate molecular weight distributions and average molecular weights of residues accurately and rapidly. In order to understand the structural changes in the hydrogenation reactions of Lungu atmospheric residue (LAR), LDI-MS together with nuclear magnetic resonance (NMR) is employed to test the molecular weights and mean structural parameters of the LAR components involved in the reactions, e. g. NC/NH, fA, RA, and so on. Experimental results suggest that LDI-MS can efficiently desorb residue molecules. No dimer is observed in LDI-MS experiment, suggesting polymerization of the molecules doesn't occur. In the hydrogenation reactions, NC/NH is found to decrease and the side chains of aromatic ring are broken. The components of LAR are apparently lightened. Furthermore, in order to understand the aromatic contribution of model molecules of heavy oils, polyacene derivatives acenes (A1-A4), phenacenes (P3-P4), helicene (H4) and perinaphthalene derivatives are structurally optimized using DFT methods. On the basis of the optimizations, aromaticities of all the molecules are investigated by the indices of harmonic oscillator model of aromaticity (HOMA), independent nuclear chemical shift (NICS), and para-delocalization index (PDI). Aromaticity of center and outside rings in polyacenes as well as of substituted and unsubstituted rings for single substituted perinaphthalene derivatives are considered. The correlations of different aromatic indices, i.e., HOMA, NICS and PDI are discussed, the relationship between HOMO-LUMO GAP and aromaticity that shows molecules reactivity and aromaticity are also studied. With a view to suppling theory guidance for processing heavy oils, structures and aromaitcities of the model molecules are carefully investigated.