The present work investigates the hydrotreating process of a diesel in order to achieve lower sulphur and
aromatics content. The entire work was performed in a Hydrodesulphurization (HDS) pilot plant unit
located in Chemical Process Engineering Research Institute (CPERI). For the tests, a commercial HDS
catalyst (CoMo) was used while the feed was provided by the deep desulphurization unit of a Greek
refinery (Motor-Oil refinery). For the determination of diesel aromatics, a method based on the ASTM D-
2549-85 was applied. The objective of the work was to investigate the ability of a typical HDS catalyst for
aromatics saturation. The effect of the main hydrotreating operating parameters (T, P, WHSV, H2/Oil
ratio) on sulphur and aromatics removal was also investigated. In general, the data showed that the product
density and the aromatic and sulphur content of diesel decreased as the temperature or pressure increased
or space velocity decreased. It was concluded that with the present catalyst an aromatics saturation
degree of up to 40% could be achieved, giving a diesel product with aromatics content of about 20-25%
wt. However, high temperatures (>370°C) were required in order to achieve 500 ppmw sulphur in this
feedstock.