CA2440189C - Method for producing desulphurised petrol from a petroleum fraction containing cracked petrol - Google Patents

Abstract

The invention relates to a method for producing low-sulphur petrol from an initial petrol containing sulphur compounds comprising the following steps: a) the selective hydrogenation of the non-aromatic polyunsaturated compounds present in the initial petrol; b) increasing the molecular weight of the light sulphur products that were initially present in the petrol at the beginning of step b); c) the alkylation of at least part of the sulpur compounds present in the product resulting from step b); d) the fractionation of the petrol resulting from step c) into at least two fractions, one of said fractions being practically free of sulphur compounds and the other containing a larger proportion of sulphur compounds (heavy petrol); e) the catalytic treatment of the heavy petrol to transform the sulphur compounds in conditions that allow the, at least partial, decomposition or hydrogenation of said sulphur compounds.

Description

PROCESS FOR PRODUCING DESULFURIZED ESSENCE FROM A PETROL CUT
CONTAINING CRACKING GASOLINE
Technical field of the invention The invention relates to a scheme for the desulfurization of conversion species and to particularity of gasoline from catalytic cracking, cracking catalytic fluid bed (FCC), a coking process (coking in the tongue of Shakespeare), a process of visbreaking (visbreaking in the language of Shakespeare), a pyrolysis process. This process can also treat of the straight run species in a mixture with least one species listed above. The method of the present invention allows reaching high desulphurization rates by limiting the octane loss due to saturation of olefins observed during hydrodesulfurization reactions. The invention regards a process for producing low sulfur gasoline comprising a hydrogenation, a step of transformation of sulfur compounds, a step of alkylation of the unprocessed sulfur compounds in the previous step, a fractionation into a light fraction and into at least one heavy fraction and optionally one or more intermediate fractions, and a hydrodesulfurization a heavy fraction and / or an intermediate fraction. This process allows valorize a section containing optionally also hydrocarbons with two three or four carbon atoms, by reducing the total sulfur content of said cutting at very low levels compatible with current specifications or to come.
This desulfurization is moreover carried out without any appreciable decrease in yield gasoline and minimizing the decrease in the octane number Prior art The production of reformulated species meeting the new standards environment requires, in particular, that their concentration in olefins but significantly their concentration of sulfur. The essences of conversion and more particularly that resulting from catalytic cracking, who can represent 30 to 50% of the gasoline pool, have levels of olefins and in high sulfur. The sulfur present in the reformulated species is attributable to nearly 90%, with catalytic cracking gasoline (FCC, "Fluid Catalytic Cracking »
or catalytic cracking in a fluidized bed). Desulfurization (hydrodesulfurization) essences and mainly FCC essences is therefore of importance evident for the achievement of specifications.

2 The hydrodesulfurization of the feedstock sent to catalytic cracking leads to of the species typically containing 100 ppm sulfur. Hydroprocessing units of Catalytic cracking charges, however, operate under severe conditions of temperature and pressure, which implies significant consumption hydrogen and a high investment. In addition, the entire load must be desulfurized, which leads to the processing of very large load volumes.
The hydrodesulfurization of cracking gasolines, when carried out in conventional conditions known to those skilled in the art can reduce the content in sulfur of the cup. However, this process has the major disadvantage lead a very significant drop in the octane number of the cut, because of the saturation of all olefins during hydrotreatment.
The teaching of the prior art is extremely diffuse and very numerous solutions have been envisaged to obtain a desulphurised gasoline current standards and future predictable standards for years 2005-2010 both in terms of sulfur content and the point of view content aromatic compounds and value of the desired octane number. Therefore one can be cited for example the process described in US-A-4,131,537 which teaches the interest of splitting the essence into several cuts, preferably three, according to their boiling point, and desulphurize them under conditions that can be different and in the presence of a catalyst comprising at least one metal of the group VIB and / or group VIII. It is stated in this patent that the largest profit is obtained by splitting the gasoline into three cuts, and when cutting with intermediate boiling points are treated under mild conditions.
We can also mention the teaching of the patent application EP-A-0 725 126 which described a process for the hydrodesulfurization of a cracking gasoline in which the essence is separated into a plurality of fractions comprising at least a first rich fraction in compounds easy to desulphurize and a second fraction rich in compounds difficult to desulfurize. Before doing this separation, you must first determine the distribution of sulfur compounds by means of analyzes. These analyzes are necessary to select the equipment and the separation conditions.
In this application it is thus indicated that a light fraction of cracking its olefin content and octane number drop significantly when it is desulfurized without being fractionated. However, the splitting of said light fraction in 7 to 20 fractions followed by analyzes of the sulfur contents and in olefins of these fractions makes it possible to determine the richest fraction or fractions in compounds

3 sulfurized which are then desulfurized simultaneously or separately and mixed to the other fractions desulfurized or not. Such a procedure is complex and to be reproduced with each change in the composition of the gasoline to be treated.
It has also been proposed, for example in US Pat. No. 5,290,427, to processes hydrotreatment of gasolines consisting of splitting gasoline and then introduce the fractions at different levels of a hydrodesulfurization reactor and at convert desulfurized fractions on a zeolite ZSM-5, in order to compensate for the loss octane recorded by isomerization. This isomerization is accompanied a cracking gasoline towards lighter compounds.
In these processes, the species to be treated generally have a point initial above 70 ° C, and again it is necessary to treat separately light gasoline (fraction corresponding to the compounds of boiling point between hydrocarbons with 5 carbon atoms and 70 ° C), for example by means of a softening.
According to the teaching of US Pat. No. 5,599,441, the process of desulfurizing a chopped off naphtha comprising an olefinic gasoline comprises a weighing step of the sulfur compounds by alkylation followed by a fractionation step of the essence in two cuts, light petrol being depleted of sulfur.
According to the teachings of US Pat. No. 6,024,865, the process for the production of gasoline desulfurate includes a separation of gasoline into a light gasoline and a heavy gasoline. Light gasoline is sent to a ballast reactor of the sulfur compounds by alkylation. Heavy gasoline with added olefins reactive is sent to a reactor for increasing the sulfur compounds by alkylation.
Heavy gasoline and light gasoline are mixed and sent to a distillation which makes it possible to recover, at the head, an essence impoverished in sulfur.
According to the teaching of the applicant's patent document EP-A-1 077 247 gasoline to be desulfurized is treated in a process comprising a step a1) hydrogenation selective diolefinic compounds, optionally at least one step a2) aiming to increase the molecular weight of the light sulfur products present in gasoline initial step to desulfurize, at least one step b) of separation of the gasoline obtained at the leaving step a1) and / or a2) in two distinct sections, one of which is light virtually free of sulfur and containing the lightest olefins the initial essence and the other heavy cut containing the bulk of the compounds sulphides present in the initial gasoline and / or sulfur compounds from step a2), at least one c) processing step of the heavy cut allowing break down

4 or to hydrogenate the unsaturated sulfur compounds present in this section and cyclic or even aromatic sulfur compounds in terms of limited hydrogenation of the olefins present in this section and at least a step d) gasoline from step c) for decomposing the compounds sulfur unsaturated unsubstituted in step c) and saturated sulfur compounds linear and / or cyclic present in this essence from step c) with a limited hydrogenation of the olefins present. The application of this process leads to limiting the temperature at the top of the fractionation column for power obtain a fraction of head containing practically no sulfur and in particular not containing thiophene. This limitation is thus largely penalizing level of implementation of the whole process since the fraction recoverable at the top of the fractionation column is limited in temperature and therefore in quantity which, moreover, leads to an increase in the heavy fraction retreat then to reduce its sulfur content.
The present invention makes it possible to produce a desulfurized gasoline while limiting the octane loss by desulfurization. The scheme of the present invention distinguishes classical desulphurisation schemes that are based on desulfurization of gasoline total. In some cases these schemes provide for a separation of gasoline into at minus two cuts: a cup containing the light petrol and a cup containing heavy gasoline that is to say a gasoline of final boiling point superior to that of light essence.
The heavy gasoline is desulfurized, for example by treatment with hydrogen or by absorption of sulfur compounds. Schemes including treatment with hydrogen lead to significant saturation of the olefins, and by therefore, a strong loss of octane Light gasoline can be desulfurized under mild conditions by hydrodesulfurization, washing with a basic solution or adsorption on a solid, or softened by an oxidation process such as for example the Merox ~ process of the Universal Oil Product Company (UOP) that can be extractive.
Some schemes allow to desulphurize only heavy gasoline, compounds sulphides usually present in light petrol (mercaptans) having been previously weighed upstream of a distillation or fractionation zone (splitter in the language of Shakespeare).

With regard to the processes for increasing the weight of compounds sulfurized by alkylation presented above, they make it possible to produce a light desulfurized gasoline, heavy gasoline concentrating sulfur compounds heavy and weighed down by alkylation.
These processes therefore do not allow to desulfurize the entire cup essence of

Conversion and particularly that resulting from cracking units Catalytic. By Moreover, the processes for increasing the weight of sulfur compounds by alkylation are based on acid catalysis. The life of the catalyst can be limited by the presence of diolefins and basic compounds (mainly nitrogenous) in gasoline treat.
Summary of the invention The present invention relates to a process for the production of low-grade species content in sulfur, which makes it possible to valorize the whole of a petrol cut containing sulfur, preferably a gasoline catalytic cracking or coking fraction (coking according to English terminology), or pyrolysis, or visbreaking (visbreaking according to English terminology), possibly mixed with a straight-run gasoline, and to reduce sulfur levels in said cut at very low levels, with no appreciable decrease in gasoline while minimizing the decrease in octane number due to hydrogenation olefins.
The charge of the process according to the invention can also optionally understand in more than one petrol cut, a C4- cut comprising hydrocarbons with two, three or four carbon atoms.
The present invention relates to a process for the production of low-grade species content sulfur from an initial gasoline containing at least 150 parts by million in weight (ppm), often at least 200 ppm and most often at least 300 ppm sulfur compounds comprising at least the following steps a step a) of selective hydrogenation of non-polyunsaturated compounds aromatics present in the initial essence, at least one step b) to increase the molecular weight of the products sulfur mainly from those in the form of mercaptans having from 1 to 6 carbon atoms in their molecules and sulphides often having 2 to 6 carbon atoms in their molecules initially present in gasoline introduced in step a) and / or those contained in the product from step a), at least one step c) of alkylation of at least a part of the sulfur compounds mainly those in the form of thiophene compounds present

6 in the product from step b) to obtain sulfur compounds of weight higher molecular at least one step d) of fractionation of the gasoline resulting from step c) into at minus two fractions, a first fraction substantially free of sulfur and containing the lighter olefins of the original gasoline not converted to step (c), (light petrol), at least one other fraction, heavier than the said first fraction, enriched in sulfur compounds and preferably at least one fraction called heavy material containing most of the sulfur compounds present in gasoline from step c) (heavy gasoline), and at least one step e) of treating at least one of the heavier fractions outcome of step d) on a catalyst for decomposing at least partially sulfur compounds. Preferably during this step e) the fraction so-called heavy separated in step d) In steps (b) and (c), the term "mainly" means that during the step concerned, at least 50% of the sulfur compounds which are form compounds of the type indicated.
Often step e) is a step of treating at least one of the fractions more heavy material separated in step d) on a catalyst for decomposing less partially sulfur-containing compounds performed under conditions where hydrogenating olefins on this catalyst is limited.
According to a preferred embodiment of the invention, the treatment of at least one of heavier fractions from step d) and preferably heavy gasoline is realised in two stages at least one step e) of treating at least one of the fractions heavy and preference of heavy gasoline separated in step d) on a catalyst allowing to at least partially break down the sulfur compounds, under conditions where the hydrogenation of the olefins on this catalyst is limited, and at least one step f) of treating the product obtained in step e), without elimination H2S formed during this step e), on a catalyst and in terms allowing at least partial decomposition of non-sulfur compounds transformed during step e) with a limited hydrogenation of olefins, and preferentially to decompose the unsaturated sulfur compounds and the compounds

7 saturated saturated linear and / or cyclic unprocessed during the step e) with limited hydrogenation of olefins.
For the purposes of the present description, the term polyunsaturated compounds covers the diolefinic hydrocarbon compounds, that is to say containing two double links, hydrocarbon compounds containing more than two double bonds but not aromatics and hydrocarbon compounds containing at least one triple bond present in the initial essence. Most often the initial essence contains as polyunsaturated compounds essentially diolefinic compounds. Within the meaning of the this description the low sulfur gasoline that we get is a containing less than 150 ppm by weight, often less than 100 ppm and the more often less than 80 ppm by weight of sulfur.
Stage b) of transformation of the light sulfur compounds concerns habitually essentially the transformation of saturated sulfur compounds with a point boiling below 120 ° C. This step may be possibly conducted simultaneously with step a) on all or part of the initial essence, in the even reactor or in a different reactor. It can also be performed from way separated on all or part of the hydrogenated gasoline in step a). In this step b), the thiophene and thiophene compounds are poorly processed. So this step a) of hydrogenation of the unsaturated compounds and step b) to increase the weight molecular weight of the light saturated sulfur products initially present in gasoline introduced in step a) are possibly carried out simultaneously in a zone single reaction containing one or more beds of a single catalyst.
Step c) is an alkylation step of the sulfur compounds belonging to habitually the group comprising thiophene, thiophene compounds and mercaptans present in the product from step b). Mercaptans eventually present are those formed in step a) and / or b), or those present in gasoline initial and not converted to step a) and / or b). This step can be performed in one or many reactors in series or in parallel. In the case of a device comprising many series reactors, the first reactor can act as a guard bed intended to retain the basic compounds that may be present in the starting gasoline. These basic compounds may also be at least partly eliminated before the introduction of gasoline in step a) of hydrogenation of the compounds polyunsaturated.
This elimination is preferably carried out by treatment with a solution aqueous acid. The operating conditions can be adjusted in such a way a part of the olefins of the starting gasoline is converted to long olefins branched by addition reactions between olefins. Similarly, the conditions operating

8 can be adjusted so that some of the aromatics are weighed down by alkylation with olefins.
Step d) fractionation of the gasoline obtained at the end of step c) includes the fractionation into at least two fractions (or cuts), a slight fraction of preferably substantially free of sulfur and containing the most olefins light of the initial gasoline (light gasoline or light fraction), and a fraction heavy in which preferably the majority of the sulfur compounds initially present in the initial essence and / or formed during steps a), b) and c) is concentrated (gasoline or heavy fraction). It is also possible to separate the essence obtained at step c) in addition to two fractions, i.e. for example a fraction slight, minus an intermediate fraction and a heavy fraction. In this case, the fractions intermediates can be sent to a catalytic reforming unit usually after a thorough desulphurization step.
Stage e) of treatment of heavy gasoline and / or a fraction intermediate containing a proportion of sulfur compounds very much higher than that contained in the light fraction is a step of treatment of this fraction on a catalyst for at least partially decomposing the compounds sulfur, in particular cyclic or even aromatic sulfur compounds such as example thiophene compounds, placing themselves in conditions where hydrogenation of olefins on this catalyst is limited.
Step f) is a step of treating the product obtained in step e), without elimination H2S formed during this step e), on a catalyst and in terms at least partially decomposing or hydrogenating the compounds sulphides not transformed during step e), and preferentially break down or to hydrogenate unsaturated sulfur compounds and saturated sulfur compounds linear and / or cyclic non-transformed during step e) and in particular thiophene compounds and mercaptans, with limited hydrogenation of olefins.
Steps e) and f) are most often performed in at least two zones successive and distinct reactions. Catalytic treatments made during steps e) and f) can be carried out either in a single reactor containing both catalysts, or in at least two different reactors. When the treatment is two reactors, the latter two are placed in series, the second reactor preferably treating the effluent at the outlet of the first reactor, preferably without separation of liquid and gas between first and second reactor.

9 It is also possible to use several reactors in parallel or in series for one and / or the other of steps e) and / or f).
In addition, it is not necessary to eliminate the H2S formed during step e) before to send the effluent of this step e) to the inlet of the reactor (s) hydrodesulfurization of step f).
One of the advantages of the method according to the invention therefore lies in the fact that is not necessary to adjust the H2S content between step e) and step f).
Furthermore, a step g) is preferably performed after step f), this step consists in mixing the separated light petrol in step d) and at least one part of the heavy gasoline from step f) to form the overall desulfurized gasoline sought.
Preferably, all the heavy gasoline desulphurized from step f) is mixed with the light gasoline from step d), without separation of the liquid and some gas contained in heavy gasoline after desulfurization, possibly a simple stripping by at least one inert gas can be performed to remove the H2S from the gasoline heavy largely desulfurized, that is to say usually containing less than 50%
weight and often less than 20% by weight of residual sulfur compounds with respect to the content sulfur compounds of heavy gasoline leaving step d).
In certain specific cases, the valorization of light petrol and heavy gasoline desulphurized is carried out separately. It is then useless to realize step g).
For species with a boiling point greater than 130 ° C, two stages Additional information may be needed ~ an additional step of elimination of basic compounds that can be performed by washing with an acidic aqueous solution intended for eliminate basic compounds may be required before step c) a step of splitting the gasoline resulting from steps d), splitting or well of one of the steps e) or f) hydrodesulphurization to separate from gasoline produced a heavy fraction whose initial point would be by example of 210 ° C and a lighter fraction whose end point would be example of 210 ° C.
In the case where this splitting is carried out on the gasoline resulting from the step d), the light fraction is sent in step e).

The feedstock of the process according to the invention is a petrol cut containing sulfur, preferably a petrol cut from a cracking unit most often a catalytic cracking unit, the range of boiling points of which typically since about the boiling points of hydrocarbons with 2 or 3 atoms of carbon (C2 or C3) up to about 250 ° C, preferably from about boiling points hydrocarbons with 2 or 3 carbon atoms (C2 or C3) up to about 220 ° C, from most preferred way since about the boiling points of hjrdrocarbures to 5 carbon atoms (C5) up to about 220 ° C. The process of this invention more particularly applies to catalytic cracking gasolines whose

Final boiling temperatures are from about 120 ° C to about 230 ° C.
The advantages of this scheme over those of the prior art are the following 1 - Removal of diene compounds, and possibly acetylenic compounds, content in the initial gasoline to limit catalyst deactivation of alkylation of the subsequent step c) sulfur compounds and the formation of gums in the species.
2 - Elimination of light mercaptans to produce a softened light species born not requiring further purification or desulfurization.
3 - Increase in the production of light desulphurized gasoline recovered in head of fractionation column, which induces a minimization of the quantity from gas to treat by hydrodesulfurization 4 - Production, by fractionation of a heavy gasoline rich in olefins branched whose octane is not very sensitive to the saturation of olefins 5 - Selective desulphurization of heavy gasoline (or from rackings lateral) for limit the saturation of olefins and the octane loss of heavy gasoline.
6 - Overall decrease in the vapor pressure of gasoline produced by report to the initial essence.
Detailed description the invention It is described in the present invention a method for obtaining of a gasoline desulphurized from a conversion gasoline and preferably from a gasoline from a unit of catalytic cracking, coking, visbreaking or pyrolysis, possibly in mixture with a saturated gasoline and having a limited sulfur content in which gasoline is first treated of selective hydrogenation of the diolefins, then a stage of transformation of sulfur compounds of gasoline present in the form of mercaptans having from 1 to 6 carbon atoms in their molecule and sulphides often having 2 to 6 carbon of carbon that should after splitting be in the gasoline slight so that they are essentially in the heavy fraction after the stage of

11 fractionation of the process according to the invention, an alkylation step of compounds sulphides present as thiophenic compounds in the gasoline derived from the transformation stage of the sulfur compounds in the form of mercaptans and sulphides.
In this step the operating conditions can be adjusted in order to promote S alkylation reactions of olefins on olefins and aromatics who trains, in particular, a drop in the vapor pressure of gasoline. At least one fraction from the fractionation step, preferably the heavy fraction or a fraction intermediate, can be processed in a transformation step of these compounds sulfurous in H2S (hydrogen sulphide) with or without minimization of saturation of the olefins.
After said fractionation, the heavy gasoline or at least a fraction intermediate is treated in a hydrodesulfurization section, preferably in the presence a hydrodesulfurization catalyst or optionally an absorbent. Of preference, no desulfurization of the light fraction is necessary in the process according to the invention, since most of the sulfur compounds initially present in gasoline are found in the heavy fraction and possibly in the the intermediate fractions of the fractionation step d) which is carried out after the steps of hydrogenation, transformation of the sulfur compounds (step b), transformation of thiophene compounds and possibly mercaptans, in particular residual mercaptans not converted and / or formed in steps a) and b) (step c) by alkylation of at least a portion of the non-sulfur compounds converted in step b) (step c).
This sequence makes it possible to obtain in the end a desulfurized gasoline without decrease of the content of ofefines or of the octane number, even for rates high desulphurisation, and this without the need to deal with light gasoline means of a hydrodesulfurization or softening section, or to have recourse to processes for restoring the octane number of gasoline. Thanks to this process, significant desulfurization rates are achieved under operating specified below.
The sulfur species contained in the feeds treated by the process of the invention may be mercaptans, sulfides, disulfides and / or compounds heterocyclic compounds, such as, for example, thiophene or alkyl-thiophenes, or of the heavier compounds, such as, for example, benzothiophene and / or dibenzothiophene.

12 The splitting point of the gasoline is preferably limited in order to avoid the presence of sulfur compounds in light gasoline. In the absence of the reactor of alkylation of sulfur compounds, one could not ~ separate in gasoline light that C5 olefins and a small part of C6 olefins under pain to lead a too much thiophene fraction in this section. So the process according to the invention is advantageous by performing a step of transforming the thiophene and more generally thiophenic compounds, for example by means of a alkylation section upstream of the fractionation section or integrated with said section according to a detailed mode in the following description.
To recover a larger fraction of light gasoline all in limiting the sulfur content of this fraction without additional treatment, he is proposed in a preferred way to treat the feedstock in step b) in conditions and on catalysts that transform light sulfur compounds present in the form of mercaptans and sulphides having most often from 2 to 6 atoms of carbon in their molecule into sulfur compounds with higher boiling point high recovering after separation, possibly in at least a fraction intermediate or in heavy gasoline. These intermediate cuts and / or heavy can then be desulfurized. This desulfurization is carried out in terms defined and by means of a hydrodesulfurization catalyst eventually to limit the saturation of the olefins or according to a preferred embodiment of the invention, by means of a series of catalysts enabling the attainment of desulfurization while limiting the hydrogenation rate of olefins and so the octane loss.
The sulfur content of the gasoline fractions produced by catalytic cracking and fluid catalytic cracking (FCC) depends on the content of sulfur FCC-treated load, whether or not pre-treatment of the charge of FCC, as well as the end point of the cut. Generally, sulfur contents of the entirety of a petrol cut, including those from the FCC, are greater than 150 ppm by weight and most often greater than 500 ppm by weight. For species with end points greater than 200 ° C, the contents in sulfur are often greater than 1000 ppm by weight, they can even in some cases reach values of the order of 4000 to 5000 ppm by weight.
The process according to the invention applies especially when desulphurization high levels of gasoline are required, ie when the gasoline is desulphurised must contain not more than 10% of the sulfur of the initial gasoline and possibly not more than 5%
at most

13 2% of the sulfur of the initial gasoline which corresponds to desulphurization greater than 90% or even greater than 95% or 98%.
The method according to the invention comprises at least the following steps a) to e) Step a) selective hydrogenation of diolefins: this step is intended to eliminate diolefins which may lead to premature deactivation of the catalysts for increasing the weight of compounds sulfurized by alkylation during step c) below, and to form gums in the desulfurized gasolines. This step is performed by passing the load, preferably consisting of the set of the gasoline cut, on a catalyst allowing to selectively hydrogenate the diolefins gasoline without hydrogenating the olefins.
Step b) of increasing mercaptans and light sulfides on a catalyst base of supported metal: this reaction can be carried out in the reactor selective hydrogenation of diolefins. This step is to spend everything or part of the initial gasoline or hydrogenated gasoline in step a), preferably all of the initial or hydrogenated gasoline in step a), on a catalyst allowing of at least partially transform the light sulfur compounds (for example ethyl mercaptan, propyl mercaptan), by reaction with all or some of the olefins, in heavier sulfur compounds. This step is for example performed simultaneously to step a) by passing for example the initial essence on a catalyst capable at a time to hydrogenate the diolefins and to transform the light sulfur compounds, preferably with the olefins, in heavier sulfur compounds, or on a catalyst distinct but allowing to achieve this transformation in the same reactor that the one used to carry out step a) Step c) is a step of increasing the sulfur compounds by alkylation.
This This step makes it possible to eliminate most of the sulfur compounds present under form thiophenics by an addition reaction on the olefins. This step consists of passing all or part of the gasoline from step b) on a catalyst presenting a acid function that allows for the addition of sulfur compounds under made of mercaptans and sulfides on olefins and the alkylation reaction of the thiophene and thiophenic derivatives with these same olefins.
Step d) of splitting the gasoline obtained at the end of step c):
this step is intended to produce a light desulfurized gasoline at the head of a column of distillation. The recovered gasoline is low in sulfur and the most often do not requires no further treatment. This light, poor essence sulfur is most often directly sent to the gasoline storage area (pool essence according to the terminology most frequently used in the trade) of

14 preferably without additional post processing. Gasoline recovered in the bottom of column concentrates the sulfur compounds initially present in the load.
This column may comprise lateral withdrawals allowing for example to get a or more intermediate fractions.
In step e) the essence of the column bottom and / or that contained in a fraction intermediate resulting from step d) is desulfurized by hydrotreatment.
According to a preferred embodiment of the invention, the essence of the column bottom and / or contained in an intermediate fraction resulting from step d) is desulfurized in step e) on a catalyst and under conditions such that the saturation of olefins is partial to limit octane loss.
According to a more preferred embodiment of the invention, in the successive steps e) and f) the essence of column bottom and / or that contained in a fraction intermediate issue of step d) is desulphurized by hydrotreatment according to a process that allows to limit the saturation of olefins. Indeed, the implementation of a selective hydrodesulfurization limits the saturation of olefins and thus limits the loss of octane of gasoline. Heavy gasoline and / or at least one intermediate gasoline desulfurized can then optionally be stripped (i.e. a gaseous stream, of preferably containing one or more inert gases passed through this petrol) to remove any H2S produced during the desulphurization.
According to a variant of the method according to the invention, it is possible to associate with least one reaction section at the fractionation column. Said sections reactants then operate on at least one fraction taken from inside of the fractionation column and the effluent from the reaction section is returned to fractionation column. The reaction section or sections thus the fractionation column of step d) can be selected from the group consisting by the reaction sections of the following steps ~ transformation of sulfur compounds by alkylation such as for example the thiophene, thiophene compounds and optionally mercaptans (step vs) desulfurization of the intermediate fractions and / or desulfurization of the fraction heavy ((step e) and / or step f)) Such devices comprising a fractionation column associated with a reactor external and usable in the process according to the invention have been for example described for applications in the field of refining and petrochemistry in patents US 5,177,283, US 5,817,227 and US 5,888,355 According to other variants of the process according to the invention, it is also possible to use a reactive column instead of the fractionation column, that is to say move at least one of said reaction sections in the column of splitting (column internal reaction section), preferably in an area where the Reagent concentration is maximal. For example, in the case of step c) of transformation of the sulfur compounds by alkylation, such as, for example, compounds thiophenic, the reaction section will preferably be placed in a zoned having the maximum concentration of these compounds.
According to a preferred variant of the process according to the invention, the section reaction internal to the column is chosen from the group consisting of sections reaction following: transformation of sulfur compounds such as thiophene, compounds thiophenics and optionally mercaptans by alkylation (step c)), desulphurization intermediate fractions and / or desulfurization of the heavy fraction (( e) and / or

Step f).
In a very preferred embodiment of the process according to the invention, the section reactionary is placed in the middle of the fractionation column, so as to treat the compounds having the intermediate boiling points, that is to say the compounds up constitute an intermediate cut and which are recovered alone or with the fraction heavy at the bottom of the column, at the end of the fractionation step. Fraction heavy is then treated in an external reactor associated or not with the column of splitting.
Such reactive columns are known to those skilled in the art and have been example described in the patents or patent applications US 5,368,691, US 5, 523,062, FR 2,737,131, FR 2,737,132, EP-A-0 461 855.
Another variant of the method according to the invention consists of both using a column reactive composition comprising at least one reaction section and an external reactor couple or not to the said column. Such variants are for example described in the patent application WO00 / 15319.
The variants described above are only illustrations of variants possible of the method according to the invention. The method according to the invention can in effect be implemented by combining reaction sections (steps a), b), c), e) or f)) associated with) the fractionation column of step d), ie internal) to said column, external) and non-coupled) to said column in the sense that the effluent from said or of said reaction sections) is not recycled to the column of splitting.

16 One of the advantages of the process according to the invention lies in the fact that it is not most often not necessary to desulphurize the light fraction of gasoline from splitting. The transformation of sulfur and / or thiophene compounds (steps (b) and / or (c)) makes it possible to considerably reduce the content of compounds sulfur of the light cut and possibly at least one cut intermediate, and generally to recover most of these compounds in the heavy fraction, and optionally in the intermediate fraction or fractions.
Steps b) and c) are distinguished inter alia by the fact that the conversion of the Thiophene compounds are generally less than 60% by weight, lower than 40% weight in step b), whereas conversion is most often better than 80% by weight, preferably greater than 90% by weight, very preferably greater than 95% weight in step c). Step b) realizes indeed essentially the increase of light mercaptans and sulphides while step c) realized essentially the increase of the thiophene compounds.
This operation is carried out while maintaining most of the olefins in fraction slight, possibly in at least one intermediate fraction not requiring no advanced desulfurization. The content of sulfur compounds in the light fraction so obtained is usually less than 100 ppm, preferably less than 50 ppm, of more preferably less than 20 ppm and very preferably less than 10 ppm.
Another advantage lies in the fact that the residual content of compounds sulfur-containing the desulfurized gasoline by means of the process according to the invention is particularly low, and that the octane number of gasoline is maintained at a high level.
The steps of the process according to the invention are described in more detail below.
hydrogenation of diolefins (step a) Hydrogenation of dienes is a step that eliminates, before hydrodesulfurization, almost all the dienes present in the cup gasoline containing sulfur to be treated. It takes place preferentially in first step (step a) of the process according to the invention, generally in the presence of a catalyst comprising at least one Group VIII metal, preferably selected from group consisting of platinum, palladium and nickel, and a carrier. We will use by example a catalyst based on nickel or palladium deposited on a support inert,

17 such as, for example, alumina, silica or a carrier containing at least minus 50 alumina.
The pressure used is sufficient to maintain more than 60%, preferably 80%, and more preferably 95% by weight of the gasoline to be treated in phase liquid in the reactor; it is most generally between about 0.4 and about 5 MPa and preferably greater than 1 MPa, more preferably included enter 1 and 4 MPa. The hourly space velocity of the liquid to be treated is included between about 1 and about 20 h-1 (volume load per volume of catalyst per hour), preferably between 2 and 10 h -1, very preferably between 3 and 8 h -1.
temperature is most generally between about 50 and about 250 ° C, and preferably between 80 and 220 ° C, and more preferably between 100 and 200 ° C, to ensure a sufficient conversion of diolefins. In a very preferred way it is limited at 180 ° C. The hydrogen ratio on charge expressed in liter is generally between 1 and 50 liters per liter, preferably between 2 and 30 liters, more preferably between 3 and 25 liters per liter.
The choice of operating conditions is particularly important. We will operate most usually under pressure and in the presence of a low amount of hydrogen excess relative to the stoichiometric value needed to hydrogenate the diolefins.
The hydrogen and the feedstock to be treated are injected in ascending streams or progeny in a reactor preferably comprising a fixed bed of catalyst.
Another metal may be associated with the main metal to form a catalyst bimetallic, such as for example molybdenum or tungsten. Use such For example, catalytic formulas have been claimed in FR 2,764 299.
Catalytic cracking gasoline can contain up to a few percent (%) in diolefin weights. After hydrogenation, the diolefin content is usually reduced to less than 3000 ppm or even less than 2500 ppm and more favorite less than 1500 ppm. In some cases, it can be obtained less than 500 ppm. The diene content after selective hydrogenation can even if necessary be reduced to less than 250 ppm.
According to a particular embodiment of the method according to the invention, the step hydrogenation dienes takes place in a catalytic hydrogenation reactor which includes a catalytic reaction zone traversed by the entire charge and the quantity of hydrogen necessary to effect the desired reactions.

18 - transformation of light sulfur compounds (step b) This step consists of transforming the light compounds of sulfur. That is to say the compounds which, at the end of stage a) of hydrogenation of the dienes, would find (after fractionation in step d)) in the light gasoline, in sulfur compounds more heavy trained in heavy gasoline. Preferably, the sulfur compounds light are selected from the families of mercaptans of 1 to 6 carbon atoms and of the sulphides of 2 to 6 carbon atoms. This transformation takes place preferably on a catalyst comprising at least one element of group VIII of the classification Periodic Review of Elements (Handbook of Chemistry and Physics 45th edition 1964-1965) (groups 8, 9 and 10 of the new periodic table). The choice of catalyst is realized in particular to promote the reaction between mercaptans light and olefins, which leads to heavier sulphides or mercaptans. other compounds such that COS or CS2 may possibly also be converted.
This step may possibly be performed at the same time as step a).
By For example, it may be particularly advantageous to operate when hydrogenation of diolefins, under conditions such that at least some of the compounds form of mercaptan is transformed. So some reduction in the content of mercaptans is obtained. To do this, we can use the procedure hydrogenation dienes described in patent application EP-A-0 832 958, which uses advantageously a palladium-based catalyst, or that described in FIG.
patent FR 2,720,754.
Another possibility is to use an identical nickel-based catalyst or different the catalyst of step a), such as, for example, the catalyst recommended in the process of US-A-3,691,066, which makes it possible to transform the mercaptans (butyl mercaptan) to heavier sulfur compounds (sulphides).
Another possibility for achieving this step is to hydrogenate at less thiophene to thiophane whose boiling point is greater than that of thiophene (boiling point 121 ° C). This step can be done on a catalyst to base of nickel, platinum or palladium. In this case the temperatures are generally between 100 and 300 ° C and preferably between 150 and 250 ° C. The H2 / load ratio is adjusted between 1 and 20 liters per liter, preferably between 3 and 15 liters per liter, to favor, if possible, the desired hydrogenation compounds thiophenics and minimize the hydrogenation of the olefins present in the charge. The space velocity is generally between 1 and 10 h -1, preferably between 2 and 4 hr and the pressure between 0.5 and 5 MPa, preferably between 1 and 3 MPa.

19 transformation of sulfur compounds by alkylation (step c) This step consists in passing preferably the whole of the fraction from step b) on a catalyst having an acid function which makes it possible to achieve the addition of sulfur compounds in the form of mercaptans to olefins and the alkylation reaction of thiophene and thiophene derivatives by these same olefins. The operating conditions are adjusted to achieve the transformation desired with conversion rates of thiophene and / or compounds thiophene, greater than 80% by weight, preferably greater than 90% by weight, so very preferred greater than 95% weight. Other compounds such as COS or CS2 can possibly also be converted.
During this stage, some of the olefins of the starting gasoline can be converted long branched olefins, by addition reactions (oligomerization) enter olefins, and some of the aromatics increased by alkylation olefins.
To minimize the oligomerizing activity of the acid catalyst optionally used, the essence can be additive of a compound known to inhibit the activity oligomerizing acidic catalysts such as alcohols, ethers or water.
During alkylation, the thiophene compounds whose boiling point is about 60 ° C to about 160 ° C will react with conversion rates greater than 80 weight, preferably greater than 90% by weight, with the olefins to form alkyls thiophenes whose boiling point is well above that of the starting thiophene compounds.
Some or all of the benzene may also be removed by alkylation with olefins.
These compounds of higher molecular weight are mainly characterized by of the higher boiling temperatures than they had before alkylation. So the The theoretical thiophene boiling temperature of 84 ° C is finds it displaced at about 150 ° C for the thiophene alkyls. This reaction is coupled with reactions addition of the olefins which therefore most often lead to a increase in gasoline, in particular where the gasoline fraction and / or gasoline departure are light, and a decrease in its vapor pressure.
This alkylation step is carried out in the presence of an acid catalyst. This catalyst can be indifferently a resin, a zeolite, a clay, any silica functionalized or any silico-aluminate having acidity, or any grafted support of groups acid functional. The ratio of the volume of charge injected into the volume of catalyst is between 0.1 and 10 liter / liter / hour and preferably between 0.5 and 4 liter / liter / hour. More specifically, this alkylation step is carried out in presence at least one acid catalyst selected from the group consisting of of Bronsted (including phosphoric, sulfuric, boric acids, fluoridriques) 5 supported for example on silica, alumina or silica alumina, silicoaluminates titanosilicates, mixed titanium alumina, clays, resins, mixed oxides obtained by grafting at least one organo-metallic organosoluble compound or water-soluble (selected from the group consisting of alkyls and / or alkoxy.
metals at least one element such as titanium, zirconium silicon, germanium, tin, tantalum, Niobium ...) on at least one oxide such as alumina (gamma, delta, eta, only or in admixture) silica, silica aluminas, titanium silicas, zirconia silicas or any other solid having any acidity. A particular mode of the invention consist in implementing a physical mixture of at least two of the catalysts ci before in proportions ranging from 95/5 to 5/95, preferably from 85/15 to 15/85 and most preferably 70/30 to 30/70.
The temperature for this step is usually about 10 to about 350 ° C according to the type of catalyst or the strength of the acidity. So for a catalyst of acid type phosphoric acid, the temperature is usually around 50 to about 250 ° C

Preferably from about 100 to about 210 ° C
The molar ratio of olefins to thiophene compounds is greater than 10 mol / mol preferably greater than 100 mol / mol.
The operating pressure of this step is generally between 0.1 and 3 MPa and preferably such that the charge is in liquid form in the conditions of temperature and pressure, ie at a pressure greater than 0.5 MPa.
The effluent from step c) of transformation of the sulfur compounds is at less partially and preferably entirely sent to a unit of splitting (step d)) to be separated into at least two fractions, a light fraction and an heavy fraction which is preferably sent in full possibly after mixed with an intermediate fraction in a desulfurization zone operating in a (step e) or two successive desulfurization steps (step e) and step f)).

21 separation of the gasoline resulting from stage c) into at least two fractions (step d) According to a first variant of the process according to the invention, gasoline is split into two fractions ~ a light fraction containing a limited residual sulfur content, preference less than about 100 ppm, very preferably less than about 20 ppm and most often allowing to use this cup without making any other treatment to reduce its sulfur content, ~ a heavy fraction in which preferably most of the sulfur initially present in the charge is concentrated.
This separation is preferably carried out by means of a column of distillation classic also called splitter according to the English name. This column of splitting must allow to separate a light fraction of the gasoline containing a small fraction of sulfur and a heavy fraction preferably containing the major part of the sulfur initially present in the initial gasoline.
This column generally operates at a pressure of between 0.1 and 2 MPa and of preferably between 0.2 and 1 MPa. The number of theoretical plateaus of this column of separation is generally between 10 and 100 and preferably between 20 and and 60.
The reflux ratio, expressed as the ratio of liquid flow in the column divided by the distillate flow expressed in kg / h, is generally less than the unit and preferably less than 0.8.
The light gasoline obtained after the separation is usually consisting of hydrocarbon cuts with 5, 6 and 7 carbons. Generally, this fraction light has a low sulfur content, that is, it is not usually necessary treat the light cut before using it as fuel.
In this case, the gasoline is preferably fractionated into at least two slices having the following properties a so-called light cup (L cup) whose boiling points are preference below about 120 ° C. This temperature is given as indicative, she generally corresponds to the maximum temperature for which the sulfur is less than 20 ppm,

22 ~ at least one so-called heavy cup (H1 section) whose boiling points are greater than about 100 ° C.
The light cut L is preferably injected into a gas separation flask liquid in order to separate the unconsumed hydrogen and the H2S, formed during step a) and / or b) and / or c), olefins having generally from 5 to 7 carbon atoms.
The so-called heavy cut H1 that is to say the cut whose temperatures are greater than about 100 ° C is sent to the desulfurization zone step e) and way preferred steps e) and f).
According to a second variant of the process according to the invention, the gasoline is split into at least 3 fractions: a light fraction, a heavy fraction and at least a fraction intermediate.
The light fraction is identical to that described above. Fraction intermediate 12 whose boiling points as an example are at least 100 ° C and up about 140 ° C or about 160 ° C. This cut can be treated in step e) then optionally in step f) of the process according to the invention. The heavy fraction H2 is then a fraction whose boiling points are generally higher than about 160 ° C
or at about 140 ° C. In this case the whole intermediate fraction plus heavy fraction is equivalent to the heavy fraction H1 of the case where the fractionation is limited together fractions.
The heavy H2 cut whose boiling temperatures are generally greater than about 160 ° C or about 140 ° C is sent into the area of desulfurization.
In another version of the method according to the invention, it is also possible of fractionate the product from step c) into at least three cuts one cut slight (L), at least one intermediate cut (12) and at least one heavy cut (H2) with the properties described above.
The intermediate cut 12 whose boiling points are between about 100 ° C
and about 120 ° C or about 160 ° C can be sent in a processing unit sulfur compounds according to step c) or recycled in this step c).
After step d), the cut (s) 12 can again be split into cutting intermediate 13 and a heavy cut H3 The cut H3, thus obtained can optionally be mixed with the H2 cut, preferably before desulfurization and the

23 section 13 can be sent to a compound processing unit sulfur according to step c) or recycled in this step c).
In the rest of the description, the conditions given for step e) include that in which a single desulfurization step is carried out and those of a preferred embodiment of the invention in which the hydrodesulfurization is performed in two successive steps e) and f).
- Decomposition of sulfur compounds of heavy fractions and / or intermediates from step d) (step e) This step, which applies to heavy gasoline (heavy fractions and / or fractions intermediates) obtained at the end of step d) of fractionation consists in hydrogenolyser at least partially the sulfur compounds to form H2S. The fraction of the sulfur compounds thus transformed is a function of the rate of desulphurization research.
This step can for example be carried out by passing the heavy gasoline, in presence of hydrogen, on a catalyst comprising at least one element of group VIII and / or at least one element of group VIB at least partly in the form of sulphide, a temperature of between about 210 ° C and about 350 ° C, preferably between 220 ° C and 320 ° C, under a pressure generally between about 1 and about 4 MPa, preferably between 1.5 and 3 MPa. The space velocity of the liquid is range between about 0.5 and about 20 hours (expressed as volume of liquid by volume of catalyst and per hour), preferably between 0.5 and 10 h -1, in a very favorite between 1 and 8 h-1. The ratio H2 / HC is between 100 to 600 liters per liter and preferably between 200 and 500 liters per liter.
To achieve, at least in part, the hydrogenolysis of sulfur compounds unsaturated according to the process of the invention, at least one catalyst, comprising at least one group VIII element (metals of groups 8, 9 and 10 of the classification, that is iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium or platinum) and / or at least one element of group VIB
(Group 6 metals of the new classification, that is, chromium, molybdenum or tungsten), on a suitable support.
The metal content of group VIII expressed in oxide is generally understood enter 0.5 and 15% by weight, preferably between 1 and 10% by weight. Content metal of the group VIB is generally between 1.5 and 60% by weight, preferably between 3 and 50% weight. The element of group VIII, when present, is preference

24 cobalt, and the element of group Vlb, when present, is generally the molybdenum or tungsten. Combinations such as cobalt-molybdenum are preferred. The catalyst support is usually a porous solid, such by an alumina, a silica-alumina or other porous solids, such as by example of magnesia, silica or titanium oxide, alone or in mix with alumina or silica-alumina. To minimize the hydrogenation of olefins present in heavy gasoline, it is advantageous to use preferentially catalyst in which the molybdenum density, expressed as% Mo03 by unit area is greater than 0.07 and preferably greater than 0.10. The The catalyst according to the invention preferably has a specific surface area lower than 190 m 2 / g, more preferably less than 180 m 2 / g, and very favorite less than 150 m2 / g.
The catalyst is preferably used at least in part in its form sulphide.
The sulphurization step may be carried out by any known technique of the man of art, in-situ or ex-situ.
In the process according to the invention, the conversion of sulfur compounds is better than 50% and preferably greater than 90%.
Step e) is carried out under conditions such that the transformation of at least a part of unsaturated sulfur compounds such as the thiophenic compounds, saturated compounds, for example thiophanes (or thiacyclopentanes) or in mercaptans, or to hydrogenolyser at least partially unsaturated sulfur compounds to form H2S.
In the method according to this preferred embodiment of the invention the conversion of unsaturated sulfur compounds is greater than 15% and preferably greater than 50%.
At the same time, the degree of hydrogenation of the olefins is preferably less than 50%, more preferably less than 40%, and very preferably lower than %, during this step. The effluent from this first stage hydrogenolysis is then sent, preferably without any separation of the liquid and gas towards step f) which makes it possible to decompose saturated sulfur compounds into H2S.
35 - Decomposition of the sulfur compounds contained in the product from step e) (step f) In this step, the saturated sulfur compounds are transformed into the presence hydrogen, on a suitable catalyst. The decomposition of unsaturated compounds no hydrogenated during step e) can also take place simultaneously. This transformation is carried out, without significant hydrogenation of the olefins, that is, to say that during this stage the hydrogenation of the olefins is generally limited to 20 in volume relative to the olefin content of the initial gasoline, and preference, 5 limited to 10% by volume in relation to the olefin content of gasoline initial.
Catalysts which may be suitable for this stage of the process according to the invention without that this list is limiting, are catalysts generally comprising at least a basic element selected from group VIII and group VIB elements, and of Preferably selected from the group consisting of nickel, cobalt, iron, molybdenum, the tungsten. These metals can be used alone or in combination, they are of preferably supported and used in their sulfurized form. The catalyst of step f) is preferably of a different nature and / or composition from that used in step e). The base metal content of the catalyst according to the invention is generally Between about 1 and about 60% by weight, preferably between 5 and 30 % weight, and very preferably between 10 and 25% by weight. Preferably, the catalyst is generally shaped, preferably in the form of beads, pellets, extrusions, for example trilobes. The metal can be incorporated into the catalyst by deposit on the preformed support, it can also be mixed with the support before The shaping step. The metal is usually introduced in form a salt precursor, generally soluble in water, such as, for example, nitrates, the heptamolybdates. This mode of introduction is not specific to the invention.
Other introduction mode known to those skilled in the art may be suitable. We use very advantageously a catalyst containing at least one element of group VIII and in

Particularly nickel.
Catalyst supports used in this step of the process according to the invention are generally porous solids selected from refractory oxides, such as by for example, aluminas, silicas and silica-aluminas, magnesia and that oxide of titanium and zinc oxide, these latter oxides can be used alone or in mixture with alumina or silica-alumina. Preferably, the supports are transition aluminas or silicas whose specific surface area is included in 25 and 350 m2 / g. Natural compounds, such as, for example, kieselguhr or kaolin, may also be suitable as supports for the catalysts used in this step of the process.
The catalyst is preferably used at least in part in its form sulphide. This has the advantage of minimizing the risks of hydrogenation of compounds unsaturated such as olefins or compounds. aromatics during the phase of

26 start-up. The sulphurization step may be carried out by any technique known from the person skilled in the art, in situ or ex situ.
After sulfurization, the sulfur content of the catalyst is generally understood between 0.5 and 25% by weight, preferably between 4 and 20% by weight. and very favorite between 4 and 10% by weight. The hydrodesulfurization carried out during this stage goal convert to H2S the saturated sulfur compounds of gasoline that have already undergone at least a prior hydrogenation of unsaturated sulfur compounds during the step e). She allows to obtain an effluent that meets the desired specifications in terms of content in sulfur compounds. The gasoline thus obtained shows only a loss of octane low. The treatment to break down the saturated sulfur compounds of step e) of the process is carried out in the presence of hydrogen, with the catalyst comprising at least one base metal selected from the group consisting of nickel, the cobalt, iron, molybdenum, tungsten, at a temperature between about 280 ° C and about 400 ° C, preferably between about 290 ° C
and about 380 ° C, more preferably between 310 ° C and 360 ° C, and very preferred between 320 ° C
and 350 ° C, at a pressure generally between about 0.5 and about 5 MPa, preferably between 1 and 3 MPa, more preferably between 1,5 and 3 MPa. The space velocity of the liquid is between about 0.5 and about 10 am ~
(expressed in volume of liquid per volume of catalyst and per hour), preference between 1 and 8 h- ~. The ratio H2 / HC is adjusted according to the rates hydrodesulfurization desired in the range of from about 100 to about 600 liters per liters, of preferably between 100 and 300 liters per liter. All or part of this hydrogen can possibly from step e) (unconverted hydrogen) or from a recycling of hydrogen not consumed in steps a), b) or c). It has been found that implementation of this second catalyst in this step under conditions operating particular, allows the decomposition of saturated compounds contained in effluent from step c, in H2S. This implementation makes it possible to reach a level global hydrodesulfurization at the end of all the steps of the process according to the invention, while minimizing the octane loss resulting from saturation olefins, because the conversion of olefins during step e) is generally limited at most 20% by volume of the olefins, preferably at most 10% by volume.
In a particular form implemented, according to the characteristics of the charge of initial gasoline, the latter is rid of most of its compounds basic nitrogenous substances which are at least partially removed before step c) of alkylation of least a part of the sulfur compounds present in the product resulting from the step b).
In a preferred embodiment, the basic nitrogen compounds contained in gasoline initially at least partly eliminated before being introduced at)

27 hydrogenation of polyunsaturated compounds. Most often the elimination of basic nitrogen compounds is carried out by treatment (washing) using a acidic aqueous solution. So when the initial essence contains compounds nitrogen basic these are at least partly eliminated by a treatment using a acidic aqueous solution carried out before step c) of alkylation of at least one part of sulfur compounds present in the product from step b). This wash is usually performed before or after the selective hydrogenation treatment in step a) polyunsaturated compounds contained in the initial essence.
The catalysts used in steps e) and f) are most often catalysts separate sulphides.
Description of the single figure (schematically illustrating, in a non restrictive, an embodiment of the invention) Gasoline (a) containing sulfur compounds, diolefins and olefins is injected into the line (1). Hydrogen is injected into the line (2) quantity such as the hydrogen / diolefin molar ratio is greater than 1. The gasoline and hydrogen are contacted in a reactor (A) for selective hydrogenation of diolefins, in optimized conditions to limit the saturation of olefins while hydrogenating diolefins.
The reactor effluent (A) is sent via line (3) in a unit Ballast sulfur compounds (B). The reactions implemented in this reactor (B) are essentially mercaptan weighting reactions of 1 to 6 atoms of as well as sulphides of 2 to 6 carbon atoms. We observe also a partial conversion of compounds such as CS2 and COS. Gasoline produced is introduced by line (4) into a reactor (C) for increasing the weight of the compounds sulfur by addition to olefins. Sulfur compounds mainly weighed down in this reactor are the thiophene compounds. We also observe in this reactor (C), oligomerization reactions of olefins and partial alkylation compounds benzene. The gasoline produced in this reactor (C) is therefore both more heavy than gasoline (a) and depleted in light sulfur compounds. The produced essence in the reactor (C) is injected via line (5) into a fractionation column (D) who separates the essence into at least two cuts.
Light gasoline whose end point may be between 55 ° C and 160 ° C is recovered at the head of the column. This essence is desulfurized and does not require of

28 additional treatment. The final temperature of this light petrol is fixed by the maximum amount of sulfur allowed.
The heavy gasoline recovered at the bottom of the column by the line (7) is sent after mixture with hydrogen introduced via line (8) to a section of desulphurization (E + F). This species has an initial distillation point between 50 ° C and 130 ° C.
The hydrodesulfurization section (E + F) is designed to desulphurize gasoline all in limiting the hydrogenation of olefins, which makes it possible to limit the loss in octane. She is consisting of at least 2 reactors in series, the first of which (E) system catalytic optimized to saturate thiophene compounds and transform partially sulfur compounds in H2S. The second contains a catalyst who is optimized catalyst for converting mercaptans to H2S, limiting the hydrogenation of olefins present in gasoline. This scheme of desulfurization a has been described in patent application EP 1 077 247 The heavy gasoline recovered by the line (10) and the light gasoline recovered by line (6) can be blended to produce a total desulfurized gasoline recovered by the line (11).
Example 1 (comparative) A cracking gasoline is subjected to a hydrogenation treatment of diolefins under conditions where the light sulfur compounds saturated present in the charge are partly converted into heavier compounds.
This treatment is carried out in a reactor operating continuously. The catalyst is at base of nickel and molybdenum (catalyst marketed by the company Procatalyse under the reference HR945). The reaction is carried out at 180 ° C. under a total pressure of 2.6 MPa, with a space velocity of 6 h -1. The ratio H2 / load, expressed in liter of hydrogen per liter of charge is 10.
The characteristics of catalytic cracked gasoline and effluent after Hydrogenation of diolefins and conversion of light compounds are indicated in Table 1.

29 Table 1 Essence Gasoline after initial h law a and b density 15/4 0.7215 0.7237 Bromine index 78 74 Br / 100 Olefines GC% oids 43 40.5 MAV m / 10 0.2 93 92.5 octane number research Motor octane number 79.6 79.4 merca tans m 26 4 S Total m 350 350 DS neck points 0.5% 2 2 5% 23 24 10% 30 31 50% 86 87 g0% 141 143 g5% 152 151 gg, 5% 175 175 At the end of this treatment, the essence is separated into two fractions, one light fraction representing 65% by weight of the distilled gasoline whose cutting point corresponds to a temperature of 100 ° C and a heavy fraction. The separation is performed on a discontinuous distillation column composed of 30 theoretical plates. The characteristics of the two fractions obtained are given in Table 2.

Table 2 FractionFraction l heavy density 15/4 0.6826 0.7712 Bromine index Br / 10091 48 MAV m / <0.2 <0.2 ~

Research octane number93.4 91.8 Motor octane number79,9 79 merca tans m 3 4 S Total m 62 885 DS neck points 0.5% 4 93 5% 20 99 10% 22,108 50% 60 128 90% 96 145 95% 99,152 99.5% 110,177 The light fraction has diolefin, mercaptan and sulfur contents such 5 that it can be used directly, provided that the specification on the content sulfur is greater than 60 ppm.
Heavy gasoline must be desulphurized before use. In all cases, this schema does not produce a desulphurized gasoline containing less than 40 ppm sulfur, by recombination of light gasoline and heavy gasoline Example 2 (comparative) The catalytic cracking gasoline obtained in Example 1 after the treatment hydrogenation is separated into two fractions, a light fraction representing 20%
the weight of distilled gasoline whose cut point corresponds to a temperature of 55 ° C and a heavy fraction. The separation is carried out on the same column that in Example 1. The characteristics of the two fractions obtained are given in the table 3.

Table 3 FractionFraction l heavy density 15/4 0.65 0.77 Bromine index Br / 100130 65 Olefines GC 60 36 MAV m / <0.2 <0.2 Research octane number95 90.5 Motor octane number81,5 80 merca tans m <1 4 S Total m 2 437 DS neck points 0.5% 4 52 5% 20 54 10% 22 67 50% 36 102 90% 41,138 95% 54,151 99.5% 72 176 The light gasoline produced by distillation has mercaptan contents, diolefins and sulfur such that it can be used directly.
Heavy gasoline requires additional desulphurization.
Heavy gasoline is therefore subjected to hydrodesulfurization on a chain of catalysts in isothermal tubular reactor.
The first catalyst (catalyst A) is obtained by impregnation "without excess of solution of a transition alumina, in the form of beads, area specificity of 130 m2 / g and a pore volume of 0.9 ml / g, by a solution aqueous containing molybdenum and cobalt in the form of ammonium heptamolybdate and of cobalt nitrate. The catalyst is then dried and calcined under air at 500 ° C. The The cobalt and molybdenum content of this sample is 3% Co0 and 14%
of Mo03.
The second catalyst (catalyst B) is prepared from an alumina of transition from 140 m2 / g in the form of balls 2 mm in diameter. Volume porous is 1 ml / g of support. One kilogram of support is impregnated with 1 liter of solution nickel nitrate. The catalyst is then dried at 120.degree.
calcined under current of air at 400 ° C for one hour. The nickel content of the catalyst is 20% weight.
100 ml of catalyst A and 200 ml of catalyst B are placed in two reactors S series, so that the load to be processed (heavy fraction) meets, first of all the catalyst A and then catalyst B. A sampling zone for the effluent of the stage e is expected between catalysts A and B. The catalysts are first of all sulphured by treatment for 4 hours under a pressure of 3.4 MPa at 350 ° C., contact of a filler containing 2% by weight of sulfur in the form of dimethyldisulphide in of n-heptane.
The operating conditions of the hydrodesulfurization are as follows: VVH =
1.33 h ~~
relative to the entire catalytic bed H2 / HC = 300 I / I, P = 2.0 MPa. The temperature of the catalytic zone comprising catalyst A is 280 ° C., the temperature of the Catalytic zone containing catalyst B is 330 ° C.
The characteristics of the effluents thus obtained are presented in table 4.

Table 4.
Fraction Fraction heavy heavy the essence initial light sulfide and of gasoline heavy dsulfure density 15/4 0.7732 0.7696 0.7228 Bromine index 65 38.5 56.2 Br / 100 Olfins GC% oids 36 25 32 MAV m / <0.2 <0.2 <0.2 Octane number 90.5 85.4 88.9 research Motor octane number 80 76 78.2 merca tans m '4 12 10.4 S Total m 437 30 25 DS neck points 0.5% 52 2 5% 54 23 10% 67 30 50% 102 86 90% 138 141 95% 151,152 99.5% 176,175 This scheme as described in the patent application EP 1 077 247 makes it possible to produce a desulfurized gasoline, the mercaptan and diolefin contents of which are compatible with the qualities required for the essences.
In the particular case of this example, the desulfurization rate is 92.8 %, content residual sulfur is 25 ppm and the octane loss calculated by the formula (RON + MON) / 2 is 2.75 points.
Example 3 (according to the invention) The catalytic cracking gasoline obtained in Example 1 after the treatment of hydrogenation [steps a) and b) according to the invention] is sent to a reactor of sulfur compounds by alkylation with olefins (step c) according to the invention). This step is carried out in a tubular reactor containing phosphoric acid catalyst supported on silica containing 20%
weight phosphoric acid (catalyst C) under the following operating conditions : VVH =
1 h -1, pressure = 2.0 MPa, temperature = 180 ° C. Before injection into the reactor, the load is additivated in isopropanol up to 500 ppm, intended to moisturize the catalyst continuously in the reactor.
The effluent thus produced is separated into two sections using a column of distillation as described in Example 1. The cutting point of the distillation is set at 100 ° C, the light fraction represents 50% by weight of the starting gasoline.
The characteristics of the gasoline produced during stages c) alkylation and ~ d) fractionation are given in Table 5.
a water Essence after Fraction Fraction heavy weight pa (step d) (step d) alkylation ta density 15/4 0.7641 0.6921 0.8124 Bromine index 62 53 72 Br / 100 MAV m / <0.2 <0.2 <0.2 Octane number 91.4 86.2 93.6 Research Octane number 80.7 79.5 81.7 Moteu r merca tans m 5 4 S Total m 350 18 670 DS neck points 0.5% 6 6 94 5% 23 19 102 10% 30 24 108 50% 105 61 154 90% 206 97 210 95% 215 100 219 99.5% 240 111 238 T b1 5 The light gasoline recovered at the end of the fractionation stage has content diolefins, mercaptans and total sulfur as may be used without treatment additional. Heavy gasoline requires a desulfurization step.
Desulfurization of heavy gasoline (steps e) and f) of the process according to the invention) performed using the device described in Example 2. The conditions operating rooms are the following: VVH = 1.33 h- 'with respect to the entire catalytic bed H2 / HC = 300 I / I, P = 2.0 MPa. The temperature of the catalytic zone comprising catalyst A
is of 290 ° C, the temperature of the catalytic zone containing catalyst B
is 340 ° C.
10 The gasoline thus produced has only a sulfur content of 26 ppm. She can to be used without further treatment. This essence is recombined at gasoline light recovered in step d). .
The characteristics of desulphurised heavy gasoline and recombinant gasoline are given in Table 6.
Table 6 Essence Essence Heavy EssenceLight Essence initialelgre dsulfure and (tape (tapes e) heavy gasoline d) and recombinants f density 15/4 0.7215 0.6921 0.8134 0.7683 Bromine index Br / 100 80 53 37 45 Olfins GC% oids 44 MAV m / 12 <0.2 <0.2 <0.2 Research octane number93 86.2 90.4 88.8 Engine octane number 79.8 79.5 80.2 79.7 merca tans m 20 4 12 ~ 9 Sulfur non-merca tan 330 14 24 17 m S Total m 350 18 36 26 This scheme made according to the invention makes it possible to produce a desulfurized gasoline.
with a limited octane loss, whose mercaptan and diolefin contents are compatible with the qualities required for the species.
In the particular case of this example, the desulfurization rate is 92.6%.
%, content residual sulfur is 26 ppm and the octane loss calculated by the formula (RON + MON) / 2 is 2.15 points.

Claims (19)

1- Process for the production of gasolines with a low sulfur content from a essence initial containing at least 150 ppm by weight of sulfur compounds comprising at minus the following steps:
.cndot. a step a) of selective hydrogenation of the polyunsaturated compounds not aromatics present in the initial essence, .cndot. at least one step b) aimed at increasing the molecular weight of the sulfur products light mainly of those which are in the form of mercaptans having from 1 to 6 carbon atoms in their molecules and sulfides present initially in the essence introduced in step a) and/or those contained in the product from step a), .cndot. at least one step c) of alkylation of at least some of the compounds sulfur mainly of those which are in the form of thiophenic compounds present in the product resulting from step b) aimed at obtaining sulfur compounds of weight higher molecular, .cndot. at least one step d) of fractionating the gasoline resulting from step c) in au least two fractions, a first fraction substantially free of sulfur and containing the lightest olefins of the initial gasoline not converted to step c), (light gasoline), at least one other fraction, heavier than said first fraction, enriched in sulfur compounds, and .cndot. at least one step e) of processing at least one of the fractions heavier outcome of step d) on a catalyst making it possible to decompose at least partially sulfur compounds. 2- Process according to claim 1 wherein step e) of treatment of at less one of the heavier fractions separated in step d) over a catalyst allowing to at least partially decomposing sulfur compounds is carried out in conditions where the hydrogenation of olefins over this catalyst is limited. 3- Process according to claim 1 or 2 comprising at least one step f) of treatment of the product obtained in step e), without elimination of the H2S formed in the during this step e), on a catalyst and under conditions allowing decompose to less partially the sulfur compounds not converted during the step e) with limited hydrogenation of olefins. 4- Method according to one of claims 1 to 3 wherein the initial gasoline is a catalytic cracked gasoline whose final boiling temperatures are from about 120°C to about 230°C. 5- Process according to claim 3 or 4 wherein the conditions of step f) are chosen in such a way as to decompose the unsaturated sulfur compounds and the compounds linear and/or cyclic saturated sulfur compounds not transformed during the step e), with limited hydrogenation of olefins. 6- Method according to one of claims 1 to 5 wherein step a) hydrogenation unsaturated compounds and step b) aimed at increasing the molecular weight of the light sulfur products initially present in the gasoline introduced into step a) are carried out simultaneously in a single reaction zone containing a Where multiple beds of a single catalyst. 7- Method according to one of claims 1 to 6 wherein the initial essence contains basic nitrogen compounds which are at least partly eliminated before step c) alkylation of at least some of the sulfur compounds present in the resulting product of step b) 8- Process according to claim 7 wherein the basic nitrogen compounds contained in the initial essence are at least partly eliminated before its introduction in step a) of hydrogenation of the polyunsaturated compounds. 9- Process according to claim 6 or 7 wherein the elimination of nitrogen compounds bases is carried out by treatment with an aqueous solution acid. 10- Method according to one of claims 3 to 9 wherein the heavy gasoline desulfurized from step f) is subjected to a stripping treatment with means of a inert gas. 11- Method according to one of claims 3 to 10 wherein steps e) and f) are carried out in at least two successive and distinct reaction zones. 12- Method according to one of claims 3 to 11 wherein the light gasoline issue from step d) and at least part of the heavy gasoline from step f) are mixed to form the overall desired desulphurized gasoline. 13- Method according to one of claims 1 to 12 wherein the catalyst of step (e) contains at least one element from group VIII and at least one element from band VIB. 14- Method according to one of claims 3 to 13 wherein the catalyst of step f) comprises at least one element from group VIII. 15- Method according to one of claims 3 to 14 wherein the catalysts used in steps e) and f) are separate sulfur catalysts. 16- Method according to one of claims 3 to 15 wherein steps e) and f) are carried out in two reactors placed in series, the second reactor treating fully the effluent from the first reactor. 17- Method according to one of claims 1 to 16 wherein step c) of alkylation is carried out under conditions such that a part of the olefins of the gasoline departure is converted to long branched olefins by addition reactions between olefins and that part of the aromatics is made heavier by alkylation by the olefins. 18- Method according to one of claims 1 to 17 wherein wherein the fraction heavy from step d) is sent to a fractionation zone allowing to obtain a heavy fraction enriched in sulfur and a lighter fraction impoverished in sulfur. 19- Method according to one of claims 1 to 17 wherein the gasoline from of the hydrodesulfurization stage e) or f) is sent to a zone of splitting making it possible to obtain a heavy fraction enriched in sulfur and a fraction lighter depleted in sulphur.