Investigation on asphaltene compositions and structures during hydroprocessing of low-temperature coal tar at different reaction temperatures on Ni–Mo–W/γ–Al2O3 catalysts

Abstract

Hydroprocessing of low-temperature coal tar from Shanbei (SLCT) on Ni–Mo–W/γ–Al2O3 catalysts was carried out in an autoclave. The compositions and structures of asphaltenes obtained from hydrotreated products at temperatures of 350–410 °C have been characterized by elemental analysis, FTIR, 1H NMR and fluorescence spectroscopy (FL). Results indicate that temperature has significant influence on the hydrogenation and cracking functions of catalyst. At temperature 370 °C or below, the asphaltene conversions increase obviously while molecular weights are not evidently reduced as temperatures go up. Moreover, compared with asphaltene in SLCT, the asphaltene from hydrotreated products contains higher H/C ratio. It can be speculated that the hydrogenation reaction becomes dominant at lower temperature. In addition, the asphaltenes hydrotreated at higher temperature always contain lower H/C ratio and lower molecular weight. The results may be attributed to some cracking reactions. As for the heteroatoms (S, N and O) in asphaltenes, their removal efficiency is not only affected by temperature, but also the forms located in molecular structure. In addition, as the temperature increased, both the average side chain length and the number of naphthenic rings show a slight decrease. However, the aromatic degree (fA) increases and surprisingly the number of aromatic rings shows a slight increase. It indicates that higher reaction temperature is unfavorable to the hydrogenation of aromatic ring system.