Abstract: The high-pressure hydroprocessing unit for production of paraffin base oil in CNOOC is a key unit for company`s benefit. The CLG proprietary catalysts, process package were used. The problems of low yield of base oil, and unqualified heavy product in some indicators appeared in operation. This paper analyzes the causes of the problem. The results showed that the presence of large nitrogen compounds in the feed, which are difficult to remove, increases the cracking reaction and reduces the base oil yield. The high content waxes with rings in the feed add the difficulty for isomerization, and aggravate the cracking reaction, leading to a low base oil yield, and a higher pour point and turbidity point. Some short-term improvement measures, such as reducing space velocity, processing more No.3 VGO time and lowering the dry point of No.4 VGO were proposed. The measures of using appropriate crude oils, blending feeds and adopting more efficient catalyst grading are suggested for medium and long term production.

Key words: high-pressure hydrotreating unit, paraffin base oil, analysis, measure