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.