The neutral oil index was implemented from 1983, and three neutral oil standards, paraffin-based SN, intermediate ZN and cycloalkyl DN, were formulated. This standard plays an important role in improving the quality of lube base oil. In order to better meet the needs of oil adjustment, it is now revised to five levels and three categories.

Category Ultra High Viscosity Index Extremely High Viscosity Index High Viscosity Index Medium High Viscosity Index Low High Viscosity Index

Six "140"120 "90" 40 < 40

Ordinary petroleum UHVI VHVI HVI MVI LVI

Deep deoiling LVI

Deep refining ultra-high vacuum ultra-high vacuum HVIS MVIS LVIS

-Foreign paraffin-based base oils generally account for 80-90% of the total output, while domestic paraffin-based base oils only account for more than 55% of the total output, and intermediate base oils account for 40% of the total output. Therefore, a hydrotreating unit should be built, and the structure of base oil should be changed to produce high-quality lube base oil. From the quality analysis of paraffin-based base oil, some enterprises still have some problems, such as unqualified evaporation loss of 150SN base oil, unqualified oxidation stability of 500SN and so on.