Two-stage Hydrocracking of Long-chain Paraffins Contained in the Heavy Distillate in a Coal Liquid

Two-stage hydrocracking of heavy distillate in a coal liquid was studied to find a procedure to crack long-chain (C₁₈~C₃₀) paraffins contained in the distillate (the content: 23 wt%); under hydrogen pressure of 150 atm at 380°C of the first stage with a commercial Ni-Mo/ A1₂O₃ catalyst (HDN-30) and at 420°C of the second stage with HDN-30 and silica-alumina (low alumina) catalysts. A single-stage hydrocracking of the distillate at 420°C with HDN-30 alone or HDN-30 and silica-alumina cracked only 21 or 41%, respectively of C₂₅₊ paraffins. The two-stage reaction was very effective to crack their 61% principally into C₁₁~C₂₀ paraffins with least amount of dry gases (~3%). The first stage hydrogenated extensively polar and aromatic fractions in the distillate. Such fractions may be strongly adsorbed on the acidic sites of the catalyst to prohibit the interaction of paraffins with the catalyst. However, their hydrogenation, hydrodenitrogenation or hydrodeoxygenation weakens their adsorption to allow the cracking of long-chain paraffins on the acidic sites in the second stage. The reaction of model mixture of pentacosane and fluoranthene or tetrahydrofluoranthene under the same conditions confirmed the scheme of the single- and two-stage hydrocrackings described above. A better hydrogenation catalyst (KF-840, Nippon Ketjen Co., Ltd.) with the aid of silica-alumina increased the conversion of C25+ paraffins in the distillate up to 75% in the two-stage hydrocracking.