Abstract: Using propane as solvent，the quality upgrading process for bright stock was researched by supercritical extraction to explore the relations between extraction conditions and product qualities. The results showed that the yield could reach above 90% under the appropriate conditions and could be adjusted according to the demand. Compared with feed，the color and the oxidation stability of the extracted oil were significantly improved with a reduction of acid value and an increased viscosity index. The viscosity index of the extracted oil (yield 30%) was 105 with a viscosity of 17.23mm2/s. After the further process of complexation-adsorption refining, the oxidation stability, viscosity and pour point of the product can meet SINOPEC HVI Ia 120BS requirements. The new process can achieve the goal of subdivision for high boiling point BS that is difficult by the other conventional separation methods and has a greater practical value to downstream lubricating oil blending.

Key words: base oil, bright stock, propane solvent, supercritical extraction