Desulfurization of naphtha blends

Abstract

A process for desulfurizing a delayed coker naphtha in a catalytic naphtha desulfurization process in which the feed comprising the delayed coker naphtha is passed over a silicon trap comprising a high surface area inert alumina of low metals content prior to being hydrodesulfurized in an olefin-retentive, catalytic naphtha hydrodesulfurization process. Unpromoted (no intentional metals content), inert alumina is preferred for the silicon trap since it will not affect the olefin-retentive qualities of the hydrodesulfurization catalyst and for maximal silicon capture, a high surface area alumina is employed.

Description

FIELD OF THE INVENTION[0001]This invention relates to a method of using thermally cracked naphtha feedstocks effectively in the refinery gasoline pool by catalytic desulfurization in a naphtha blend.BACKGROUND OF THE INVENTION[0002]A large proportion of the gasoline pool in the United States, Europe and elsewhere is filled by naphtha from fluid catalytic cracking units. While this naphtha has good octane as a result of a relatively high olefin content resulting from the catalytic cracking process, it also tends to have an unacceptably high sulfur content under the regulatory standards for motor gasoline, the United States currently sets a standard with a maximum of 30 ppm sulfur but in 2017 the Tier 3 standard of not more than 10 ppm which has been the European standard since 2009. Over the same time period, the progressive decreases in permitted sulfur content have been accompanied by a requirement to reduce mobile source emissions, especially carbon monoxide, by the addition of ox...

AI Technical Summary

Benefits of technology

[0009]We have now found that it is possible to process coker naphthas as a naphtha blend component in the feedstocks for olefin retentive selective catalytic naphtha hydrodesulfurization processes if a suitably selected silicon trap is used. To minimize the octane loss which occurs in the process a high surface area inert alumina with a controlled low metal content is required. In particular, the levels of metals with hydrogenation capability such as the base metals Ni, Co and Mo should be held at low levels and preferably should be absent.

Problems solved by technology

While the octane retention afforded by the SCANfining process would be useful if the process were applied to the desulfurization of the olefinic coker naphthas, the difficulty encountered in many cases results from the fact that coker naphthas frequently contain silicon which has been found to have a deleterious effect on the SCANfining catalyst.

Once the silicon is bound to the alumina surface, it cannot be removed by regeneration or other means.

It is a more moderate poison compared to contaminants like sodium or arsenic, but it nonetheless results in activity loss of the order of 5-10° F.

For these reasons, coker naphthas coming from the delayed coking process have not usually been considered suitable feedstocks for the process even though their desulfurization in this way and subsequent incorporation into the gasoline pool would be desirable.

While alternative desulfurization processes for coker naphthas are, of course, at hand, they are generally hydrogenative with a high hydrogen consumption resulting from olefin saturation.

Thus, the refiner is faced with a true dilemma, he may use SCANfining and retain olefins but inhibit the catalyst or he may use other hydrodesulfurization methods and spend money on hydrogen.