Process for reducing content of sulphur compounds and poly-aromatic hydrocarbons in a hydrocarbon feed

Abstract

A process for reducing content of sulphur compounds and polyaromatic hydrocarbons in a hydrocarbon feed having a boiling range between 200° C. and 600° C., which process comprises in combination contacting the feed and hydrogen over a hydrotreating catalyst and hydrotreating feed at hydrotreating conditions, cooling the hydrotreated effluent and hydrogen-rich gas from the hydrotreating reactor contacting said effluent and hydrogen gas over a hydrotreating catalyst in a post-pretreatment reactor at a temperature sufficient to lower the polyaromatic hydrocarbon content.

Description

[0001] The present invention relates to a process for removal of sulphur and polyaromatic compounds in vacuum gas oil by hydrotreatment of FCC hydrocarbon feed stock.[0002] Many countries are tightening specifications for the sulphur content in diesel and gasoline fuels. The fluid catalytic cracking (FCC) units are a major source of gasoline, but also the major source of sulphur in gasoline and diesel fuels. Lower sulphur content in fuel requests either treating the FCC feed or treating its products.[0003] Treating the FCC products involves multiple process solutions: naphtha treating, light-cycle oil (LCO) treating and flue gas treating to control the SO.sub.x emissions. Treating feed to the FCC unit can increase yields and at the same time lower sulphur levels in gasoline, and diesel fuels and reduces SO.sub.x emissions. The increased conversion in the FCC unit resulting from feed treatment may improve refinery margins. Product treatment, however, offers no yield benefits.[0004] I...

AI Technical Summary

Benefits of technology

[0022] By the inventive process, a low PAH content is achieved in FCC feeds with only slight additional investment in reactor volume and without reduction in run length. The essences of the inventive process consists of cooling the effluent exiting the hydrotreating reactor and passing the cooled product through a small posttreat reactor containing a suitable catalyst. The PAH content of the product existing in the hydrotreating reactor is reduced in the posttreatment reactor owing to the more favourable equilibrium conditions at the lower temperature. Consequently, the end of run temperature in the main hydrotreating reactor is not limited by the PAH content of the product exiting the main reactor, and a small overall reactor volume (main hydrotreater plus post treat reactor) is required for a given run length. In another embodiment of the process, the final bed of the main hydrotreating reactor is operated at lower temperature instead of using a post treatment reactor. The process can be used to lower the content of poly-aromatic hydrocarbons and thereby improve the performance of the FCC unit because of improved crackability of the FCC feed as well as the FCC product qualities.

Problems solved by technology

Nitrogen compounds poison the active sites in the FCC catalyst and increase coke-making propensity of the catalyst and reduce the yield of valuable products.

A shorter run length means high costs due to a higher rate of catalyst replacement, and relative more downtime (i.e. time off-stream) for catalyst change-out with a resultant loss of revenue due to reduced production of high quality FCC gasoline products.

The reactions are reversible and at high reaction temperatures and low hydrogen pressure the conversion of the PAH compounds is thermodynamically limited by equilibrium.

This will result at some point in an increase in the PAH content in the effluent of the hydrotreater reactor due to equilibrium limitations.

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