Environmentally friendly diesel fuels produced from middle distillates generated by conversion processes

Some diesel fuels specifications already in use or proposed for the near future are concerning with a 500 ppm sulphur content and a total aromatics content limited to 35 vol. % or even less. A new process aimed to meet the proposed diesel fuels specifications has been developed by Research Institute for Petroleum Processing and Petrochemistry Ploiesti. The pilot plant studies have been carried out to establish the best solution for revamping existing gas oil hydrotreating plants to reach both deep hydrodesulphurization (HDS) and aromatics content reduction. It was found that a two stage hydrotreating process at medium pressure is the best approach for middle distillates higher in sulphur and aromatics content such as blends of straight run gas oil with thermally cracked gas oil. In the first stage the sulphur removal to very low levels is achieved combining the high HDS activity of a new type of promoted NiMo catalyst with variation of the process conditions. Aromatics hydrogenation is much more challenging than sulphur removal as requires additional hydrotreating capacity. A moderate pressure hydrogenation stage using a specific noble metal catalyst appears to be sufficient to reach a deep aromatics reduction ifa feed desulphurization less than 150 ppm is performed. Tests of aromatics saturation at moderate pressure performed with a special high nickel containing catalyst have also been reported.