The existent gum content of the Fisher-Tropsch synthetic crude exceeded the standard seriously, affecting its transportation and use. To determine the structure of the existent gum extracted from the Fisher-Tropsch synthetic crude, elemental analysis, Fourier transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR), and X-ray photoelectron spectroscopy (XPS) were employed to determine the chemical structure of the gum. The Brown-Ladner method is used to calculate the average structural parameters and the average molecular formula of the existent gum. The results show that the existent gum of the Fisher-Tropsch synthetic crude is composed of heterocyclic aromatic hydrocarbons and short-carbon paraffins. Compared with petroleum gums and coal tar gums, the existent gum content of the Fisher-Tropsch synthetic crude has the characteristics of high aromaticity, short side chains, and nitrogen-containing heterocycles. After being oxidized, its aromaticity further increases, more closed loops are formed, and the side chain is further shortened. This is caused by a complex oxidation reaction during the oxidation process. Molecular dynamics simulation calculations were performed to reveal the T-stacked morphology of the existent gum of the Fisher-Tropsch synthetic crude in a mixed solvent of acetone and toluene.
Copyright © 2020 American Chemical Society.