Abstract: The hydrotreating experiment of medium-temperature coal tar was carried out on the pilot plant of ebullated bed, the hydrogen nuclear magnetic resonance spectroscopy (1H-NMR) of the medium-temperature coal tar feedstock pitch and hydrotreated tail oil were measured, and the structural changes of the medium-temperature coal tar heavy fraction during the ebullated bed hydrotreating process were investigated. The results showed that the total carbon number and the average side chain length of the average molecular structure of the hydrotreated tail oil decreased, the number of aromatic rings decreased and the number of naphthenic rings increased due to the saturation of aromatic rings to naphthenic rings. Because of the partial hydrogenation-ring-opening cracking of aromatic rings and ring-opening of naphthenic rings, the average total number of rings of the hydrotreated tail oil decreased. The higher the reaction temperature was, the more significant the structural change trend of the heavy fraction became. Within the range of experimental temperature, the aromatic ring condensation parameter (HAU/CA) of the hydrotreated tail oil increased firstly and then decreased with the increase of reaction temperature. It was suggested that the reaction temperature should be strictly controlled below (base+20 ℃) in order to avoid macromolecular condensation and reduce the generation of light hydrocarbons.

Key words: medium-temperature coal tar, ebullated bed, nuclear magnetic resonance, molecular structure