Fluid Catalytic Cracking of Coal Liquids(Part 2). Catalytic Cracking of Coal Derived Middle Distillates and Related Model Compounds.

Effect of prehydrotreating on the yield of naphtha and middle fraction, as well as on the behavior of coke formation in the catalytic cracking of coal derived middle distillate, has been investigated. Hydrotreating of Battle River coal-derived middle distillate was carried out over Ni-Mo/Al₂O₃catalyst, using a high pressure continuous apparatus equipped with a fixed bed reactor of 20ml in volume at 370?, H2 pressure of 50–150kg/cm²G and LHSV of 1h⁻¹. Fluid catalytic cracking, which is outlined below, was carried out using a specially designed small apparatus at 482°C under atmospheric pressure, WHSV of 16wt/wt/h and FCC catalyst/feed oil weight ratio of 3.0. The hydrogen content and H/C atomic ratio of the hydrotreated oils rose from 10.2 to 11.6wt% and from 1.4 to 1.6, respectively, with increasing hydrogen pressure (Table 1). Removal of hetero atom, especially, denitrogenation of middle distillate, proceeded much effectively in comparison with that of heavy distillate (Fig. 1). Lowest nitrogen content of 300ppm was observed under higher hydrogen pressure of 150kg/cm²G at 370°C. 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) also increased with increasing hydrogen pressure (Fig. 2). The reactivities of aromatic rings toward hydrogenation are higher for middle distillate than those for heavy distillate. But there were no significant differences in distillation properties of the hydrotreated oils (Table 2, Fig. 3). On the other hand, the hydrogen contents and the H/ C atomic ratios of the cracked oils dropped to a level comparable with those of crude distillates (Table 1). The cracked oil from crude middle distillate did not show a big difference in distillation characteristics but gave higher coke formation of 2.8wt%. But the distillation characteristics of the cracked oils from the hydrotreated oils changed drastically with the degree of hydrotreatments (Table 2, Fig. 4). Naphtha fraction increased 2.5–5 fold with respect to the original crude oil base. Conversely, middle and heavy fraction decreased by 20–45wt% and 24–67wt%, respectively. The production of C₃and C₄hydrocarbon gases increased up to 2wt% and the formation of coke decreased to 1.3wt% with the degree of hydrotreatment. T/N, OHP/PH and DHP/PY ratios in the cracked oil decreased to almost the same level, in spite of the different severity of hydrotreatment. This suggests that hydrogenated portions in aromatic molecules have been cracked selectively to low molecules, yielding C₃and C₄gases. Catalytic cracking of model compounds, paraffinic hydrocarbons, hydroaromatic and aromatic compounds, etc., has also been carried out to discuss the reactivity of coal liquids (Tables 3, 4, 5, Fig. 5).