Abstract: The hydrofining catalyst FF-66 and combined hydrocracking catalysts FC-16B/FC-14 were used in the sixth cycle of the hydrocracking unit of SINOPEC Jinling Company. After 36 months of operation，the oxidation stability of the product transformer oil reduced, pour point increased，and the viscosity index of tail oil could no longer meet the demand of lube base oil. In order to improve the product quality and enhance the hydrogenation ability，FF-66 grading the bulk phase catalyst FTX-1 were used for refining catalyst and FC-16B/FC-14 grading the bulk phase catalyst FTXC-1 were used for cracking catalyst in the seventh cycle. The calibration data of the unit showed that compared with the sixth cycle, the sulfur content of heavy naphtha in the seventh cycle decreased from 4.0 μg/g to 1.3 μg/g，the smoke point of aviation kerosene increased from 25.4 mm to 26.8 mm, and the pour point of transformer oil decreased from －9 ℃ to －12 ℃. The high content of aromatics was the main reason for the poor oxidation stability of transformer oil. The aromatics content of transformer oil decreased from 10% to 0.5% by hydrosaturation treatment of further low temperature aromatics and the oxidation stability was improved. The viscosity index of tail oil in the seventh cycle was 91, which could not meet the requirement of the lube base oil. It can be increased by blending paraffin base oil and improving aromatics ring-opening ability of hydrocracking catalyst.

Key words: hydrocracking, bulk phase catalyst, transformer oil, oxidation stability, viscosity index