HYDROTHERMAL CRACKING OF HEAVY OILS AND ITS MODEL-COMPOUND

Liquid-phase cracking of vacuum gas oil (VGO) was performed over NiMo supported nonacidic catalysts under 713 K and 8.0 MPa of hydrogen in a batch reactor, which is termed hydro-thermal cracking. Compared with VGO thermal cracking under the same reaction conditions the new proces s showed the suppressed naphtha yield (from 22.4 to 13.5 wt. %) and VG O conversion (from 65.7 to 64.0 wt. %) and increased the middle distil late yield (from 44.3 to 49.3 wt. %). At the same conversion level, th e yield ratio of middle distillates to naphtha for this new process wa s two times higher than that for VGO hydrocracking. The VGO hydrocrack ing over USY-supported NiMo proceeded at much lower temperatures but g ave higher naphtha yields. Both the thermal cracking and the hydro-the rmal cracking of n-dodecyl benzene (C6H5(CH2)(11)CH3) yielded toluene as the major aromatic product, whereas its hydrocracking over NiMo/USY yielded benzene as the major aromatic product. The reaction mechanism of this new process was assumed to consist of thermal cracking of hyd rocarbon molecules via the free radical chain mechanism and the cataly tic hydroquenching of free radicals. (C) 1998 Elsevier Science B.V. Al l rights reserved.