Process for the production of hydrocarbons with low sulfur and mercaptan content

Abstract

Process for desulfurization of a cut containing hydrocarbons comprising sulfur compounds and olefinic compounds comprising at least the following successive steps: a first desulfurization in the presence of hydrogen and a hydrodesulfurization catalyst under conditions leading to a desulfurization rate of said cut strictly higher than 90%; separation of most of the hydrogen sulfide from the effluents resulting from the first desulfurization; a second desulfurization of the effluents, with the hydrogen sulfide removed, resulting from the separation step, in the presence of hydrogen and a hydrodesulfurization catalyst, and under conditions leading to a desulfurization rate of said effluents less than that of the first desulfurization.

Description

[0001] This invention relates to a process for the production of hydrocarbons with low sulfur content. This fraction of hydrocarbons contains an olefin fraction generally higher than 5% by weight and most often higher than 10% by weight. The process makes it possible notably to valorize an entire gasoline cut containing sulfur by reducing the sulfur and mercaptan content of said gasoline cut to very low levels, without reducing the gasoline yield, and while minimizing the reduction in the octane rating during said process. The invention is applicable particularly when the gasoline to be processed is a gasoline from catalytic cracking with a sulfur content greater than 500 ppm by weight or even higher than 1000 ppm by weight, even 2000 ppm by weight, and when the desired sulfur content in the desulfurized gasoline is less than 50 ppm by weight, even 20 ppm by weight or even 10 ppm by weight.PRIOR ART[0002] Future specifications for automobile fuels are expected to show a great reduct...

AI Technical Summary

Benefits of technology

[0033] According to the preferred but nonobligatory embodiment of the invention that follows, the batch to be desulfurized is preferably processed optionally in a series of reactors for selective hydrogenation of the diolefins (step a) and of making the light sulfurous compounds heavy (step b). The batch thus pre-processed is then distilled and fractionated into at least two cuts (step c): a light gasoline low in sulfur and high in olefins and a heavy gasoline high in sulfur and low in olefins. The light fraction resulting from the three preceding steps generally contains less than 50 ppm of sulfur, preferably less than 20 ppm of sulfur, very preferably less than 10 ppm of sulfur, and generally does not require subsequent processing before being used as a base gasoline. The heavy fraction resulting from the three preceding steps in which most of the sulfur is concentrated is processed according to the process that is the object of this invention. This preferred embodiment offers the advantage of further minimizing the loss of octane because the light olefins with 5 carbon atoms, easily hydrogenated, are not sent to the hydrodesulfurization section.

[0061] Surprisingly, it was found by the applicant that such constraints on the respective desulfurization rates of steps d) and f) make it possible to minimize the mercaptan content of the gasoline produced and thus to make any subsequent step of sweetening the gasoline optional or less constraining.

Problems solved by technology

The preservation of the octane rating of these gasolines thus requires that the transformation reactions of olefins into paraffins, which are inherent to hydrodesulfurization processes, be limited.

Further, gasolines have corrosive properties because of the presence of mercaptans.

However, for the reasons already described, this hydrogenation results in a latent octane loss in gasolines from catalytic cracking.

But such a process does not make it possible to expect to achieve desulfurization rates higher than 99% at industrial scale.

To reach a more extensive desulfurization, it would appear necessary to add at least one supplemental step, which greatly limits the economic attractiveness of the process.

The diolefins are precursors of gums that polymerize in hydrotreatment reactors and thus limit their lifetime.