Fluid Catalytic Cracking of Coal Liquids (Part 1) Effect of Prehydrotreating on the Properties of Cracked Oils

Effects of prehydrotreating of coal-derived liquids over Ni-Mo/Al₂O₃ on catalytic cracking have been investigated. Hydrotreating of Battle River coal-derived heavy distillate (Table 1) was carried out in a conventional flow apparatus equipped with a fixed bed reactor of 20 ml in volume at 350—390° C under hydrogen pressure of 50—150 kg/cm²·G with LHSV of 0.5—2 hr^-1. The Ni-Mo/Al₂O₃ catalyst was presulfided, using a commercial gas oil containing 1% CS₂, in the same apparatus at 300° C under hydrogen pressure of 40 kg/cm²·G with LHSV of 1 hr^-1 for 15 hrs. Hydrotreating of coal liquid was started after presulfiding by elevating the temperature and hydrogen pressure. The hydrogen content and H/C atomic ratio of the hydrotreated oils rose from 9.9 to 10.8 wt% and from 1.33 to 1.44, respectively, by elevating the temperature, hydrogen pressure, and lowering LHSV (Table 2). The nitrogen and oxygen contents decreased with increasing severity of reaction conditions. The nitrogen content, however, did not decrease lower than 0.1 wt% under our reaction conditions. This is considered to be caused by high concentrations of carbazole derivatives measured by GC analysis with a NPD detector (Figs. 2 and 3). The weight ratios of tetralin/naphthalene (T/N), 1,2,3,4,5,6,7,8-octahydrophenanthrene/phenanthrene(OHP/PH), and dihydropyrene/pyrene(DHP/PY) increased also with increasing severity of hydrotreating conditions, but there were no significant differences in the distillation properties of the hydrotreated oils (Fig. 4). Catalytic cracking was carried out using a FCC catalyst in a small apparatus, specially designed in conformity with the ASTM standards (Fig. 1), at 452—502° C with WHSV of 8—32 wt/wt/hr under atmospheric pressure of nitrogen. The levels of hydrogen content and H/C atomic ratio of the cracked oils dropped to those of the crude liquid (Table 2). Yields of gases, especially C₃, C₄ gases, increased, and conversely, the formation of coke decreased with highly hydrotreated reactant oils. According to the degree of severity of hydrotreatment, conversion of the 350° C⁺ fraction rose to 30wt% at the cracking temperature of 482° C with WHSV of 16 wt/wt/hr. Production of light fraction with a b.p. lower than 216° C also increased from 1 wt% up to 20wt% during the two-stage reaction of prehydrotreating and catalytic cracking (Table 3, Figs. 5, and 6). Similar cracking behavior was observed with the elevation of cracking temperature and WHSV (Table 4). The weight ratio of T/N, OHP/PH, and DHP/PY dropped to the lowest level in every case (Figs. 4, 7, and 8). It seems reasonable that the naphthenic rings produced by hydrogenation of aromatic rings in the coal liquid are effectively cracked.