Selective naphtha hydrodesulfurization with high temperature mercaptan decomposition

Abstract

A process for the selective hydrodesulfurization of olefinic naphtha streams containing a substantial amount of organically bound sulfur and olefins. The olefinic naphtha stream is selectively desulfurized in a first hydrodesulfurization reaction stage. This effluent stream is then contacted with a stripping agent in a H2S removal zone, such as steam or an amine solution, to remove H2S from the effluent stream, thereby reducing the H2S partial pressure of the process stream. The process stream is then subjected to a second desulfurization reaction stage followed by a mercaptan decomposition stage to reduce the content of mercaptan sulfur in the final product stream. In a second embodiment, the effluent stream from the first hydrodesulfurization reaction stage, after being subjected to the H2S removal zone, is fed directly to the mercaptan decomposition stage where total sulfur content and mercaptan sulfur content are reduced in the final product stream.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a multistage process for the selective hydrodesulfurization and mercaptan removal of an olefinic naphtha stream containing a substantial amount of organically bound sulfur and olefins. BACKGROUND OF THE INVENTION [0002] Environmentally driven regulatory pressure concerning motor gasoline (“mogas”) sulfur levels have resulted in the widespread production of less than 50 wppm sulfur mogas in 2004, and levels below 10 wppm are being considered for later years. In general, this will require deep desulfurization of refinery naphtha streams. The largest target of naphtha streams for such processes are those resulting from cracking operations, particularly those from a fluidized catalytic cracking unit which comprise a large volume of the available refinery blending stock as well as generally higher sulfur content than the “non-cracked” refinery naphtha streams. Naphthas from a fluidized catalytic cracking unit (“cat naphthas”)...

AI Technical Summary

Benefits of technology

[0022] In still another preferred embodiment, the total sulfur content of said mercaptan decomposition reactor product stream is less than about 1 wt. % of the total sulfur content of said olefinic naphtha feedstream.

[0023

Problems solved by technology

Hydrodesulfurization of cracked naphthas using conventional naphtha desulfurization catalysts under conventional startup procedures and under conventional conditions required for sulfur removal, typically leads to an undesirable loss of olefins through hydrogenation.

Such additional refining, or course, adds significantly to production costs.

Although selective hydrodesulfurization processes have been developed to avoid significant olefin saturation and loss of octane, such processes have a tendency to liberate H2S that reacts with retained olefins to form mercaptan sulfur by reversion.

While economics of such strategies may appear favorable compared to a single processing technology, the complexity of overall refinery operations is increased and successful mogas production is dependent upon numerous critical sulfur removal operations.

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