Hydrotreatment of Light Cycle Oil over Pt-Pd Supported Catalyst Combined with Ni-Mo Supported Catalyst

摘要

Virgin light cycle oil (LCO) derived from the FCC process containing 6090 mass ppm sulfur and 76.1 mass% aromatics, and with cetane index of 26 was refined by hydrotreatment over Ni-Mo supported catalysts in a down flow fixed-bed reactor, and the resulting LCO was hydrotreated over Pt-Pd supported catalyst in a down flow fixed-bed reactor. Ni-Mo supported silica-alumina (Ni-Mo/SA) and Ni-Mo supported alumina containing USY zeolite (Ni-Mo/USY-Al_2O_3) were used for the first hydrotreatment reaction. The double layer system of Ni-Mo/ SA and Ni-Mo/USY-Al_2O_3 showed slightly better nitrogen removal activity and cetane index improvement activity at the same sulfur removal activity than the single layer system of Ni-Mo/SA, so the double layer system of Ni-Mo/SA and Ni-Mo/USY-Al_O_3 was used for the first hydrotreatment reaction. Hydrotreated LCO using the double layer system which contained 137 mass ppm sulfur and cetane index of 32 underwent hydrotreatment over Pt-Pd supported alumina containing USY zeolite (Pt-Pd/USY-Al_2O_3). The second hydrotreatment over Pt-Pd/USY-Al_2O_3 resulted in 5 mass ppm sulfur and cetane index of 47 at hydrogen pressure 4.9 MPa, LHSV 1.0 h~(-1), hydrogen/oil ratio 400 Nl/l and reaction temperature 320℃, which confirmed the high hydrotreatment ability of Pt-Pd/USY-Al_2O_3. Catalytic life of Pt-Pd/USY-Al_2O_3 was tested for 266 days using first hydrotreated LCO containing 137 mass ppm sulfur and cetane index of 32. Throughout the life test, sulfur content were around 10 mass ppm and and cetane index was 40. Under the same reaction conditions as the life test, another test for 42 days was carried out to examine coke deposition on Pt-Pd/USY-Al_2O_3. Coke deposition on the catalyst greatly increased towards the reactor outlet, mainly due to hydrogen reduction.