WO2021013525A1

WO2021013525A1 - Process for treating a gasoline by separation into three cuts

Info

Publication number: WO2021013525A1
Application number: PCT/EP2020/069031
Authority: WO
Inventors: Sophie COUDERC; Adrien Gomez
Original assignee: IFP Energies Nouvelles
Priority date: 2019-07-23
Filing date: 2020-07-06
Publication date: 2021-01-28
Also published as: FR3099172A1; FR3099172B1

Abstract

The present invention relates to a process for desulphurising a gasoline, comprising at least the following steps: a) fractionating the gasoline so as to recover a light gasoline cut LCN and a first heavy gasoline cut HCN, b) carrying out a first step of desulphurising the first heavy gasoline cut HCN, c) fractionating the effluent from step b) so as to produce a gas phase consisting essentially of hydrogen and H₂S, an intermediate gasoline cut MCN and a second heavy gasoline cut HHCN, wherein the fractionation of the intermediate gasoline cut MCN and the second heavy gasoline cut HHCN is carried out with a cutting point between 100 and 140°C, d) a second step of desulphurising the second heavy gasoline cut HHCN, e) separating H₂S from the intermediate gasoline cut MCN of step c) and from the heavy gasoline cut HHCN of step d).

Description

PROCESS FOR TREATMENT OF A GASOLINE BY SEPARATION IN THREE CUTS Technical field

The present invention relates to a process for the production of gasoline with low sulfur and mercaptan content. State of the art

The production of gasolines meeting the new environmental standards requires that their sulfur content be significantly reduced to values generally not exceeding 50 ppm (mg / kg), and preferably less than 10 ppm.

It is also known that the conversion gasolines, and more particularly those originating from catalytic cracking, which can represent 30 to 50% of the gasoline pool, have high olefin and sulfur contents.

The sulfur present in gasolines is for this reason attributable, to nearly 90%, to gasolines resulting from catalytic cracking processes, which will hereinafter be called FCC gasoline (Fluid Catalytic Cracking according to Anglo-Saxon terminology, which the 'one can translate by catalytic cracking in a fluidized bed). FCC gasolines therefore constitute the preferred feedstock for the process of the present invention.

Among the possible ways of producing fuels with a low sulfur content, the one which has been very widely adopted consists in specifically treating the sulfur-rich gasoline bases by hydrodesulfurization processes in the presence of hydrogen and of a catalyst. Traditional processes desulphurize gasoline in a non-selective manner by hydrogenating a large part of the mono-olefins, which generates a high loss in octane number and a high consumption of hydrogen. The most recent processes, such as Prime G + process (trademark), allow desulfurization of cracked gasolines rich in olefins, while limiting the hydrogenation of mono-olefins and consequently the loss of octane and the resulting high consumption of hydrogen. Such processes are for example described in patent applications EP 1077247 and EP1174485. The residual sulfur compounds generally present in desulphurized gasoline can be separated into two distinct families: the unconverted refractory sulfur compounds present in the feed on the one hand, and the sulfur compounds formed in the reactor by secondary reactions known as recombination. Among this last family of sulfur compounds, the majority compounds are the mercaptans resulting from the addition of the H ₂ S formed in the reactor on the mono-olefins present in the feed.

Mercaptans with the chemical formula R-SH, where R is an alkyl group, are also called recombinant mercaptans. Their formation or decomposition obeys the thermodynamic equilibrium of the reaction between mono-olefins and hydrogen sulfide to form recombinant mercaptans. An example is illustrated according to the following reaction:

The sulfur contained in the recombinant mercaptans generally represents between 20% and 80% by weight of the residual sulfur in the desulfurized gasolines.

The formation of recombinant mercaptans is in particular described in patent US Pat. No. 6,231,754 and patent application W001 / 40409 which teach various combinations of operating conditions and catalysts making it possible to limit the formation of recombinant mercaptans. Other solutions to the problem of the formation of recombinant mercaptans are based on a treatment of partially desulfurized gasolines to extract said recombinant mercaptans therefrom. Some of these solutions are described in patent applications WO02 / 28988 or WO01 / 79391. Still other solutions are described in the literature for desulfurizing cracked gasolines using a combination of hydrodesulfurization steps and removal of recombinant mercaptans by reaction to thioethers or disulfides (also called sweetening or sweetening according to English terminology) (see for example US7799210, US6960291, US2007114156, EP2861094). Publication US2017 / 0101591 in particular describes a process for the production of hydrocarbons with a low sulfur and mercaptan content comprising a stage of selective hydrogenation by catalytic distillation making it possible to recover a light fraction and a heavy fraction, the heavy fraction then being subjected to hydrodesulfurization by catalytic distillation making it possible to recover a second light fraction which is subjected to a stripping section, then to a finishing hydrodesulfurization step, and a heavy fraction which is subjected to a hydrodesulfurization step. The second desulfurized light fraction and the desulfurized heavy fraction are then subjected to a step of removing the H ₂ S in a stabilization column.

The publication EP3299441 describes a process for desulphurizing a gasoline cut comprising a fractionation of the gasoline so as to recover a light gasoline cut and a first heavy gasoline cut; then a first step of desulphurizing the first heavy gasoline cut. The effluent is then condensed and the first gasoline cut is separated into an intermediate gasoline cut and a second heavy gasoline cut. A second step of desulfurization of the second heavy gasoline cut is carried out. The separation steps are carried out by stripping with a gas or by an adsorption method.

Obtaining a gasoline with a very low sulfur content, typically at a content of less than 10 ppm by weight, therefore requires the elimination of at least part of the recombinant mercaptans. Almost all countries have a very low specification for mercaptans in fuels (typically less than 10 ppm sulfur from SHRs (measurement of mercaptan content by potentiometry, ASTM D 3227 method). Other countries have adopted a measurement of "Doctor Test" to quantify the mercaptans with a negative specification to be respected (method ASTM D4952).

Thus in some cases, it appears that the most restrictive specification, because the most difficult to achieve without harming the octane number, is the specification in mercaptans and not that of total sulfur.

An object of the present invention is to provide a process for the desulfurization of an olefinic gasoline comprising a fractionation in three cuts which is capable of producing, by limiting the loss of octane number, a gasoline with a low total sulfur content, typically less than 30 ppm, or even preferably less than 10 ppm by weight and with a very low content of recombinant mercaptans.

In the remainder of the text, the following terms usually used in this technical field will be used for better readability:

LCN for "light cracked naphtha" according to Anglo-Saxon terminology for a light petrol cut - MCN for "medium cracked naphtha" according to Anglo-Saxon terminology for an intermediate petrol cut

- HCN for "heavy cracked naphtha" according to the Anglo-Saxon terminology for a heavy gasoline cut - H HCN for "heavy heavy cracked naphtha" according to the English terminology for a very heavy gasoline cut resulting from the HCN cut.

- FRCN for "full range cracked naphtha" according to English terminology for a petrol cut including all cuts.

Summary of the invention The present invention relates to a process for desulphurizing a gasoline containing sulfur compounds, olefins and diolefins, comprising at least the following steps:

a) the gasoline is split so as to recover a LCN light gasoline cut and a first HCN heavy gasoline cut,

b) in at least one reactor, the first heavy gasoline HCN cut is brought into contact with hydrogen and a hydrodesulfurization catalyst comprising an oxide support and an active phase comprising a metal from group VI B and a metal from group VIII, at a temperature between 210 and 320 ° C, at a pressure between 1 and 4 MPa, with a space velocity between 1 and 10 h and a ratio between the hydrogen flow rate expressed in normal m ³ per hour and the flow rate of the first cut of heavy HCN gasoline to be treated, expressed in m ³ per hour at standard conditions of between 100 and 600 Nm ³ / m ³ , so as to convert at least part of the sulfur compounds into H2S and to produce a first desulphurization effluent, c) the effluent from step b) is fractionated so as to produce a gas phase consisting essentially of hydrogen and H ₂ S, a MCN intermediate gasoline cut and a second HHCN heavy gasoline cut, the fractionation of the cut MCN intermediate gasoline and the second heavy gasoline HHCN cut being performed with a cut point between 100 and 140 ° C,

d) in at least one reactor, the second HHCN heavy gasoline cut is brought into contact with hydrogen and a hydrodesulfurization catalyst comprising an oxide support and an active phase consisting of at least one metal from group VIII, at a temperature between 260 and 420 ° C, at a pressure between 0.5 and 5 MPa, with a space velocity between 1 and 10 h and a ratio between the hydrogen flow rate expressed in normal m ³ per hour and the flow rate of the second HHCN heavy gasoline cut to be treated expressed in m ³ per hour at standard conditions of between 25 and 600 Nm ³ / m ³ , said temperature of step d) being higher than the temperature of step b ), so as to produce a second desulphurized HHCN heavy gasoline cut, e) a step of separation of the H2S formed and present in the MCN intermediate gasoline cut resulting from step c) and in the second HHCN heavy gasoline cut is carried out desulphurized from step d).

The process according to the invention responds to the problem of desulfurizing an olefinic gasoline while limiting the hydrogenation of the olefins and reducing the content of recombinant mercaptans in the desulfurized effluents, by virtue of the combination of the steps mentioned above.

Thus step a) is carried out so as to separate a light gasoline cut with a high octane number and a reduced content of sulfur compounds without involving a reaction. hydrodesulphurization catalytic which would hydrogenate some of the olefins. Step b) carries out partial desulfurization of the HCN gasoline cut (complementary to the LCN cut) during which recombinant mercaptans are formed resulting from the reaction of olefins with the H ₂ S formed. Step c) contributes to the efficiency of the process thanks to the separation of the partially desulfurized HCN gasoline cut, judiciously carried out at high temperature, into an intermediate MCN gasoline cut with low sulfur content and a second heavy HHCN gasoline cut containing organic sulfur compounds including recombinant mercaptans which have higher boiling temperatures than those of the olefins from which they are derived. Step d) of desulfurization of the second heavy HHCN gasoline cut, which is carried out under more severe conditions than that of step b) insofar as the fractions richest in olefins have been separated beforehand, makes it possible to produce deep treatment to provide an effluent with a low sulfur content. The fact of using a very selective hydrodesulfurization catalyst in step d) makes it possible to hydrogenate the olefins very little or not and therefore maintain the octane number. The method according to the invention further comprises a step of separating the H2S (step c)) which is produced during the desulfurization step b) and which allows a rebalancing of the thermodynamic equilibrium of the formation of the mercaptans of recombination towards decomposition and therefore elimination of recombinant mercaptans.

The separation of the HCN liquid hydrocarbon phase of step c) into an intermediate MCN gasoline cut and a second HHCN heavy gasoline cut is carried out with a cut point between 100 ° C and 140 ° C. The operating conditions are adjusted so as to obtain an MCN fraction with a low sulfur content and a low mercaptan content, in particular a content of less than 10 ppm sulfur. The choice of a point of cut between 100 ° C and 140 ° C makes it possible to obtain an intermediate MCN gasoline cut substantially free of most of the recombinant mercaptans contained in the effluent which formed during hydrodesulphurization step b). In general, the recombinant mercaptans have higher boiling temperatures than those of the olefins from which they are derived. This property is thus used in step c) to produce an intermediate MCN gasoline cut with a low content of sulfur and of recombinant mercaptans insofar as said recombinant mercaptans, the boiling point of which is higher than that of the gasoline cut intermediate MCN are entrained in the second cut heavy gasoline HHCN. Another advantage of the process according to the invention comes from the fact that it makes it possible to achieve a very low mercaptan content (eg less than 10 ppm by weight of sulfur) in the final desulfurized gasoline with operating conditions for step a) much less severe hydrodesulphurization (for example significant reduction in temperature and / or operating pressure), which has the effect of limiting the loss of octane, increasing the lifetime of the catalyst of the step hydrodesulfurization and also reduce energy consumption.

Another advantage of the method according to the invention comes from the fact that it can easily be installed on existing units (remodeling or revamping according to the English terminology). According to one variant, the fractionation of the MCN intermediate gasoline cut and of the second HHCN heavy gasoline cut of step c) is carried out with a cut point between 110 and 130 ° C. According to one variant, in step c), the first desulfurization effluent from step b) is partially condensed so as to produce a gas phase consisting essentially of hydrogen and H ₂ S and a desulfurized HCN liquid phase. , then the said desulfurized HCN liquid phase is separated with a cut point of between 100 and 140 ° C. in an intermediate MCN gasoline cut and a second heavy gasoline H HCN cut.

According to one variant, in step c), the effluent from step b) is separated with a cut point of between 100 and 140 ° C. into an MCN intermediate gasoline cut containing a gas phase containing hydrogen and H2S and in a second heavy gasoline H HCN cut, then a gas phase consisting essentially of hydrogen and H2S is separated by condensation from said MCN intermediate gasoline cut.

Alternatively, the temperature of step d) is at least 5 ° C higher than the temperature of step b).

According to one variant, step e) is carried out in a stabilization column configured to separate a C4- hydrocarbon phase containing H2S from a stabilized gasoline cut. Alternatively, in step e) the second desulfurized HHCN heavy gasoline cut from step d) and the MCN intermediate cut from step c) are mixed in a stabilization column.

According to one variant, the catalyst of step a) comprises alumina and an active phase comprising cobalt, molybdenum and optionally phosphorus, said catalyst containing a content by weight relative to the total weight of oxide catalyst of cobalt, in CoO form, between 0.1 and 10%, a content by weight relative to the total weight of molybdenum oxide catalyst, in M0O ₃ form, between 1 and 20%, a cobalt / molybdenum molar ratio between 0.1 and 0.8, a content by weight relative to the weight total phosphorus oxide catalyst in P2O5 form of between 0.3 and 10% when phosphorus is present, said catalyst having a specific surface area of between 30 and 180 m ² / g.

According to one variant, the catalyst of step d) consists of alumina and nickel, said catalyst containing a content by weight relative to the total weight of catalyst of nickel oxide, in NiO form, of between 5 and 20 %, said catalyst having a specific surface area between 30 and 180 m ² / g.

According to a variant, before step a), the gasoline is treated in the presence of hydrogen and a selective hydrogenation catalyst so as to at least partially hydrogenate the diolefins and carry out a reaction to weigh down a portion. sulfur compounds, step a) being carried out at a temperature between 50 and 250 ° C, at a pressure between 0.4 and 5 MPa, with a space velocity between 0.5 and 20 h and with a ratio between the hydrogen flow rate expressed in normal m ³ per hour and the feed rate to be treated expressed in m ³ per hour at standard conditions of between 2 Nm ³ / m ³ and 100 Nm ³ / m ³ .

Alternatively, the gasoline is obtained from a catalytic cracking unit.

In the following, groups of chemical elements are given according to CAS Classification (CRC Handbook of Chemistry and Physics, CRC press publisher, editor DR Lide, 81 ^th Edition, 2000-2001). For example, group VIII according to the CAS classification corresponds to the metals of columns 8, 9 and 10 according to the new IU PAC classification.

The metal content is measured by X-ray fluorescence. Description of figures

Figure 1 illustrates an embodiment according to the invention.

Figure 2 illustrates another embodiment according to the invention.

Figure 3 illustrates a method according to the prior art. Detailed description of the invention

The other characteristics and advantages of the invention will become apparent on reading the description which follows, given by way of illustration only and not as limitation, and with reference to the appended figures. In the figures, similar elements are generally designated by identical reference signs. Description of the load

The process according to the invention makes it possible to treat any type of gasoline cut containing sulfur compounds, olefins and diolefins, such as for example a cut obtained from a coking unit (coking according to the English terminology), visbreaking (visbreaking according to Anglo-Saxon terminology), steam cracking (steam cracking according to Anglo-Saxon terminology) or catalytic cracking (FCC, Fluid Catalytic Cracking according to Anglo-Saxon terminology). This gasoline can optionally be composed of a significant fraction of gasoline from other production processes such as atmospheric distillation (gasoline resulting from direct distillation (or straight run gasoline according to the English terminology) or from gasoline processes. conversion (coking or steam cracking gasoline) Said feed is preferably constituted by a gasoline cut obtained from a catalytic cracking unit. The feed is a gasoline cut containing sulfur compounds, olefins and diolefins, the boiling point range of which typically extends from the boiling points of hydrocarbons with 2 or 3 carbon atoms (C2 or C3) up to at 260 ° C, preferably from the boiling points of hydrocarbons with 2 or 3 carbon atoms (C2 or C3) up to 220 ° C, more preferably from the boiling points of hydrocarbons with 5 atoms of carbon up to 220 ° C. The method according to the invention can also treat feeds having end points lower than those mentioned above, such as for example a C5-180 ° C cut.

The sulfur content of gasoline cuts produced by catalytic cracking (FCC) depends on the sulfur content of the feed treated by the FCC, the presence or not of a pretreatment of the feed from the FCC, as well as the end point of the feed. chopped off. Generally, the sulfur contents of an entire gasoline cut, especially those from the FCC, are greater than 100 ppm by weight and most of the time greater than 500 ppm by weight. For gasolines having end points greater than 200 ° C., the sulfur contents are often greater than 1000 ppm by weight, they can even in certain cases reach values of the order of 4000 to 5000 ppm by weight.

In addition, gasolines from catalytic cracking units (FCC) contain, on average, between 0.5% and 5% by weight of diolefins, between 20% and 50% by weight of olefins, between 10 ppm and 0.5% weight of sulfur, generally less than 300 ppm of mercaptans. Description of the selective hydrogenation step (optional)

With reference to FIG. 1 which represents a particular embodiment of the invention, an olefinic gasoline feedstock, for example a catalytic cracked gasoline described above, is treated in an optional step which carries out the selective hydrogenation of the diolefins and the conversion (weighting) of part of the mercaptan compounds (RSH) present in the feed into thioethers, by reaction with mono-olefins. Typically the mercaptans which can react during the optional selective hydrogenation step are the following (non-exhaustive list): methyl mercaptan, ethyl mercaptan, n-propyl mercaptan, isopropyl mercaptan, iso-butyl mercaptan, tert-butyl mercaptan, n-butylmercaptan, secbutyl mercaptan, iso-amyl mercaptan, n-amyl mercaptan, alpha-methyl-butyl mercaptan, alpha-ethylpropyl mercaptan, n-hexyl mercaptan, 2-mercapto-hexane.

To this end, the FRCN gasoline feed is sent via line 1 to a selective hydrogenation catalytic reactor 2 containing at least one fixed or mobile bed of catalyst for the selective hydrogenation of the diolefins and the weighting of the mercaptans.

The reaction for the selective hydrogenation of the diolefins and the weighting down of the mercaptans is preferably carried out on a sulfurized catalyst comprising at least one element from group VIII and optionally at least one element from group VII and a support. The element of group VIII is preferably chosen from nickel and cobalt and in particular nickel. The element of group VI B, when it is present, is preferably chosen from molybdenum and tungsten and very preferably molybdenum. The catalyst support is preferably chosen from alumina, nickel aluminate, silica, silicon carbide, or a mixture of these oxides. Alumina is preferably used and even more preferably high purity alumina is used. According to a preferred embodiment, the selective hydrogenation catalyst contains nickel with a content by weight of nickel oxide (in NiO form) of between 4 and 12%, and molybdenum with a content by weight of molybdenum oxide. (in M0O ₃ form) of between 6% and 18% and a nickel / molybdenum molar ratio of between 1 and 2.5, the metals being deposited on a support consisting of of alumina and in which the degree of sulfurization of the metals constituting the catalyst is greater than 80%.

During the optional selective hydrogenation step, the gasoline to be treated is typically brought into contact with the catalyst at a temperature between 50 ° C and 250 ° C, and preferably between 80 ° C and 220 ° C, and even more preferably between 90 ° C and 200 ° C, with a liquid space velocity (or LHSV for “liquid hourly space velocity” according to the English terminology) of between 0.5 h and 20 h, the unit the liquid space velocity being the liter of feed per liter of catalyst and per hour (l / l / h). The pressure is between 0.4 MPa and 5 MPa, preferably between 0.6 and 4 MPa and even more preferably between 1 and 3 MPa. The optional selective hydrogenation step is typically carried out with a ratio between the hydrogen flow rate expressed in normal m ³ per hour and the feed rate to be treated expressed in m ³ per hour at standard conditions of between 2 and 100 Nm ³ / m ³ , preferably between 3 and 30 Nm ³ / m ³ .

The entire charge is generally injected at the inlet of the reactor. However, it may be advantageous, in certain cases, to inject a fraction or all of the feed between two consecutive catalytic beds placed in the reactor. This embodiment makes it possible in particular to continue to operate the reactor if the inlet to the reactor is blocked by deposits of polymers, particles or gums present in the charge.

After selective hydrogenation, the diolefin content, determined by means of the maleic anhydride number (MAV or Maleic Anhydride Value according to the English terminology), according to the UOP 326 method, is generally reduced to less than 6 mg maleic anhydride / g, or even less than 4 mg AM / g and more preferably less than 2 mg AM / g.

In some cases it can be obtained less than 1 mg AM / g. Description of the fractionation of step a) in LCN and HCN sections

As shown in Figure 1, the gasoline feed is sent via line 1 to the selective hydrogenation reactor 2. An effluent with a low content of diolefins and mercaptans is withdrawn from reactor 2 via line 3 and is sent, according to the step a), in a fractionation column 4 (or splitter according to English terminology) configured to separate the gasoline into two cuts: an LCN 5 light gasoline cut (or light gasoline) and a (first) heavy gasoline HCN cut 6 which consists of the additional heavy fraction of LCN light gasoline. The cut point of the light cut is usually performed at a temperature below 100 ° C, and the cut point of the heavy cut is usually performed at a temperature above 65 ° C. The final boiling point of the light cut is chosen so as to provide a low sulfur LCN light gasoline cut (total sulfur content typically less than 30 ppm by weight and preferably less than 10 ppm by weight) without requiring a step. subsequent hydrodesulfurization. Thus preferably the LCN light gasoline cut is a C5- hydrocarbon cut (ie containing hydrocarbons having 5 and less than 5 carbon atoms per molecule). The first HCN heavy gasoline cut, which is preferably a C6 ⁺ cut (ie containing hydrocarbons which may have 6 and more than 6 carbon atoms per molecule), is treated in a stage b) of selective hydrodesulfurization (selective H DS). The purpose of this step b) is, using a catalyst described below and hydrogen, to convert part of the sulfur compounds of the heavy gasoline HCN cut into H2S and hydrocarbons. Description of the hydrodesulfurization step b) of the HCN cut

The first HCN heavy gasoline cut 6 is thus brought into contact with the hydrogen supplied by line 7 and a selective HDS catalyst in at least one hydrodesulfurization unit 8 which comprises at least one fixed or moving bed reactor of catalyst. Hydrodesulfurization step b) consists of contacting the first heavy gasoline HCN cut to be treated with hydrogen, in one or more hydrodesulfurization reactors, containing one or more catalysts suitable for carrying out the hydrodesulfurization.

According to a preferred embodiment of the invention, step b) is carried out with the aim of carrying out a hydrodesulfurization selectively, that is to say with a degree of hydrogenation of the mono-olefins of less than 80%, preferably less than 70% and very preferably less than 60%.

The temperature is generally between 210 and 320 ° C and preferably between 220 and 290 ° C. The temperature used must be sufficient to maintain the gasoline to be treated in the vapor phase in the reactor. In the case where the hydrodesulfurization step b) is carried out in several reactors in series, the temperature of each reactor is generally higher by at least 5 ° C, preferably by at least 10 ° C and very preferably at least 30 ° C at the temperature of the reactor preceding it.

The operating pressure for this step is generally between 1 and 4 MPa and preferably between 1, 5 and 3 M Pa.

The quantity of catalyst used in each reactor is generally such that the ratio between the gasoline flow rate to be treated expressed in m ³ per hour at standard conditions, per m ³ of catalyst (also called space velocity) is between 1 and 10 h and preferably between 2 and 8 h.

The hydrogen flow rate is generally such that the ratio between the hydrogen flow rate expressed in normal m ³ per hour (Nm ³ / h) and the flow rate of the heavy HCN gasoline cut to be treated, expressed in m ³ per hour under standard conditions (15 ° C, 0.1 MPa) is between 100 and 600 Nm ³ / m ³ , preferably between 200 and 500 Nm ³ / m ³ . Normal m ³ is understood to mean the quantity of gas in a volume of 1 m ³ at 0 ° C. and 0.1 MPa.

It should be noted that the hydrogen supplied by line 7 can be either fresh hydrogen (make-up according to Anglo-Saxon terminology), or so-called "recycled" hydrogen coming from a step of the process, in particular steps c) and / or d), or else a mixture of fresh hydrogen and recycled hydrogen. Preferably the hydrogen in line 7 is fresh hydrogen.

Preferably, the mixture of the first HCN heavy gasoline cut with the hydrogen contacted with the catalyst in step b) is entirely in the vapor phase. The degree of desulfurization of step b), which depends on the sulfur content of the feed to be treated, is generally greater than 50% and preferably greater than 70% so that the product resulting from step a) contains less than 100 ppm by weight of sulfur and preferably less than 50 ppm by weight of sulfur.

The catalyst used in step b) must exhibit good selectivity with respect to hydrodesulfurization reactions with respect to the reaction of hydrogenation of olefins. The hydrodesulfurization catalyst of step b) comprises an oxide support and an active phase comprising a metal from group VI B and a metal from group VIII and optionally phosphorus and / or an organic compound as described below. .

The metal from group VIB present in the active phase of the catalyst is preferably chosen from molybdenum and tungsten. The group VIII metal present in the active phase of the catalyst is preferably chosen from cobalt, nickel and a mixture of these two elements. The active phase of the catalyst is preferably chosen from the group formed by the combination of the elements nickel-molybdenum, cobalt-molybdenum and nickel-cobalt-molybdenum and very preferably the active phase consists of cobalt and molybdenum.

The group VIII metal content is between 0.1 and 10% by weight of oxide of the group VIII metal relative to the total weight of the catalyst, preferably between 0.6 and 8% by weight, preferably between 2 and 7% by weight, very preferably between 2 and 6% by weight and even more preferably between 2.5 and 6% by weight. The metal content of group VIB is between 1 and 20% by weight of oxide of the metal of group VIB relative to the total weight of the catalyst, preferably between 2 and 18% by weight, very preferably between 3 and 16 % weight.

The group VIII metal to group VIB metal molar ratio of the catalyst is generally between 0.1 and 0.8, preferably between 0.2 and 0.6. In addition, the catalyst has a group VIB metal density, expressed as the number of atoms of said metal per unit area of the catalyst, which is between 0.5 and 30 atoms of group VIB metal per nm ² of catalyst, preferably between 2 and 25, even more preferably between 3 and 15. The metal density of group VIB, expressed as the number of atoms of metal of group VIB per unit area of the catalyst (number of atoms of metal of group VIB per nm ² of catalyst) is calculated for example from the following relation:

with:

X =% by weight of metal from group VIB;

N _A = Avogadro number equal to 6,022.10 ²³ ;

S = Specific surface area of the catalyst (m ² / g), measured according to standard ASTM D3663;

M _M = Molar mass of the metal of group VIB (for example 95.94 g / mol for molybdenum).

By way of example, if the catalyst contains 20% by weight of molybdenum oxide M0O ₃ (i.e. 13.33% by weight of Mo) and has a specific surface area of 100 m ² / g, the density d (Mo) is equal at :

Optionally, the catalyst may also have a phosphorus content generally between 0.3 and 10% by weight of P2O5 relative to the total weight of catalyst, preferably between 0.5 and 5% by weight, very preferably between 1 and 3% by weight. For example, the phosphorus present in the catalyst is combined with the metal of group VIB and optionally also with the metal of group VIII in the form of heteropolyanions. Furthermore, the phosphorus / (metal of group VIB) molar ratio is generally between 0.1 and 0.7, preferably between 0.2 and 0.6, when phosphorus is present. Preferably, the catalyst is characterized by a specific surface area of between 5 and 400 m ² / g, preferably between 10 and 250 m ² / g, preferably between 20 and 200 m ² / g, very preferably. between 30 and 180 m ² / g. The specific surface is determined in the present invention by the BET method according to the ASTM D3663 standard, as described in the work Rouquerol F .; Rouquerol J .; Singh K. “Adsorption by Powders & Porous So / ids; Princip / e, methodology and applications ”, Academie Press, 1999, for example by means of an Autopore III ™ model apparatus of the brand Microméritics ™.

The total pore volume of the catalyst is generally between 0.4 cm ³ / g and 1.3 cm ³ / g, preferably between 0.6 cm ³ / g and 1.1 cm ³ / g. The total pore volume is measured by mercury porosimetry according to standard ASTM D4284 with a wetting angle of 140 °, as described in the same book.

The packed fill density (DRT) of the catalyst is generally between 0.4 and 0.7 g / mL, preferably between 0.45 and 0.69 g / mL. The DRT measurement consists in introducing the catalyst into a test tube whose volume has been determined beforehand and then, by vibration, in compacting it until a constant volume is obtained. The bulk density of the packed product is calculated by comparing the introduced mass and the occupied volume after packing.

Advantageously, the hydrodesulphurization catalyst, before sulphurization, has an average pore diameter greater than 20 nm, preferably greater than 25 nm, or even 30 nm and often between 20 and 140 nm, preferably between 20 and 100 nm, and very preferably between 25 and 80 nm. The pore diameter is measured by mercury porosimetry according to ASTM D4284 with a wetting angle of 140 °. The catalyst can be in the form of extrudates of small diameter, cylindrical or multilobed (trilobes, quatrefoils, etc.), or spheres.

The catalyst oxide support is usually a porous solid chosen from the group consisting of: aluminas, silica, alumina silicas or even titanium or magnesium oxides used alone or as a mixture with alumina or silica alumina . It is preferably chosen from the group consisting of silica, the family of transition aluminas and alumina silicas, very preferably, the oxide support consists essentially of alumina, that is to say that it comprises at least 51% by weight, preferably at least 60% by weight, very preferably at least 80% by weight, or even at least 90% by weight of alumina. It preferably consists solely of alumina. Preferably, the oxide support of the catalyst is a “high temperature” alumina, that is to say which contains theta, delta, kappa or alpha phase aluminas, alone or as a mixture, and an amount of less than 20. % of gamma, chi or eta phase alumina.

A very preferred embodiment of the invention corresponds to the implementation for step b) of a catalyst comprising alumina and an active phase comprising cobalt, molybdenum and optionally phosphorus, said catalyst containing a content by weight relative to the total weight of cobalt oxide catalyst, in CoO form, of between 0.1 and 10%, a content by weight relative to the total weight of molybdenum oxide catalyst, in M0O ₃ form , between 1 and 20%, a cobalt / molybdenum molar ratio of between 0.1 and 0.8, a content by weight relative to the total weight of phosphorus oxide catalyst in P2O5 form between 0.3 and 10 % when phosphorus is present, said catalyst having a specific surface area between 30 and 180 m ² / g.

According to one embodiment, the active phase consists of cobalt and molybdenum. According to another embodiment, the active phase consists of cobalt, molybdenum and phosphorus.

Description of the fractionation step c)

According to step c) of the process of the invention, the effluent from step b) is fractionated so as to produce a gas phase consisting essentially of hydrogen and H ₂ S, an intermediate MCN gasoline cut and a gas phase. second HHCN heavy gasoline cut, the fractionation of the MCN intermediate gasoline cut and of the second HHCN heavy gasoline cut being carried out at a cut point between 100 and 140 ° C. The cut point is defined as the arithmetic mean between the temperature corresponding to 95% of the distilled mass of an intermediate hydrocarbon cut and the temperature corresponding to 5% of the distilled mass of the heavy cut. The cut point is therefore defined by the equation:

The method used to determine the temperatures corresponding to 5% and 95% of the distilled mass is described in the document OU Gas Sci. Technol. Flight. 54 (1999), No. 4, pp. 431-438 under the name “CSD method” (abbreviation of “Conventional Simulated Distillation” according to Anglo-Saxon terminology) and which can be translated as “Conventional Simulated Distillation”.

According to a first embodiment, a gaseous phase is first separated from the effluent from step b) so as to obtain a partially desulfurized HCN liquid phase, then the desulfurized HCN liquid phase is separated in MCN intermediate gasoline cut and secondly HHCN heavy gasoline cutter. More particularly, the first desulfurization effluent resulting from step b) is partially condensed so as to produce a gas phase consisting essentially of hydrogen and H ₂ S and a partially desulfurized HCN liquid phase. The condensation is generally carried out by cooling to a temperature between 40 and 60 ° C, preferably between 45 and 55 ° C. Then, in a separation column, with a cut point of between 100 and 140 ° C., said desulfurized HCN liquid phase is separated into an MCN intermediate gasoline cut and a second HHCN heavy gasoline cut.

According to this mode, illustrated in FIG. 1, the first desulphurization effluent from step b) discharged via line 9 then is cooled and partially condensed so as to produce two phases in separator 10 (step c)): one gas phase 1 1 rich in hydrogen and containing part of the H S produced by the desulfurization in step b) and a desulfurized HCN liquid phase 12 containing dissolved H S, unconverted sulfur compounds and mercaptans of recombination.

This condensation step essentially aims to eliminate most of the H S formed during step b).

As shown in FIG. 1, the HCN 12 desulfurized liquid phase withdrawn from separator 10 is then subjected to separation with a cut point of between 100 and 140 ° C.

The desulfurized HCN liquid phase 12 which is preferably a C6 ⁺ cut (ie containing hydrocarbons which may preferably have 6 and more than 6 carbon atoms per molecule) is sent to a separation means 13 configured to separate at the top. an MCN intermediate petrol cut which is withdrawn via line 14 and at the bottom of a second HHCN heavy gasoline cut withdrawn via line 15. This separation means can be a fractionation column (or splitter according to English terminology).

Since step b) is carried out so as to ensure a high conversion of the light thiophenic sulfur compounds (mainly thiophene and methyl thiophenes), the MCN intermediate gasoline cut obtained after the fractionation of step c) contains only low contents of unconverted thiophenic sulfur compounds. The MCN intermediate gasoline cut is, thanks to the high-temperature fractionation step c), also freed of most of the recombinant mercaptans contained in the effluent which formed during the hydrodesulfurization step b). In general, recombinant mercaptans have higher boiling temperatures than those of the olefins from which they are derived. For example 2-methyl-2-pentene (pure boiling point under normal conditions: 67 ° C) can form a recombinant mercaptan with 5 carbon atoms such as 2-methyl-2-penthanethiol (point d pure substance boiling under normal conditions: 125 ° C). This property is thus used in step c) to produce an intermediate MCN gasoline cut with a low content of sulfur and of recombinant mercaptans insofar as said recombinant mercaptans, the boiling point of which is higher than that of the gasoline cut intermediate MCN are entrained in the second cut heavy gasoline HHCN. The operating conditions of the separation are adjusted so as to obtain a low sulfur content MCN fraction and in particular a low content of recombinant mercaptans.

To obtain the MCN intermediate gasoline cut low in sulfur and in particular low in recombinant mercaptan, the operating conditions of the separation are adjusted so as to obtain a cut of hydrocarbons whose difference in temperature (DT) between the temperatures corresponding to 5% and to 95% of the distilled mass which is less than or equal to 75 ° C, preferably which is between 20 ° C and 65 ° C. The temperature corresponding to 5% of the distilled mass of the MCN intermediate gasoline cut is preferably between 50 ° C and 80 ° C and the temperature corresponding to 95% of the distilled mass of the MCN intermediate gasoline cut is preferably between 88 ° C and 125 ° C. For example, the MCN intermediate gasoline cut has a temperature corresponding to 5% of the distilled mass which is equal to 65 ° C ± 2 ° C, or equal to 60 ° C ± 2 ° C or equal to 55 ° C ± 2 ° C . Preferably, the MCN intermediate gasoline cut has a temperature corresponding to 95% of the distilled mass which is equal to 110 ° C ± 10 ° C. In a preferred embodiment, the MCN intermediate gasoline cut essentially contains hydrocarbons having 6 to 7 carbon atoms and predominantly hydrocarbons with 6 carbon atoms.

Typically the total organic sulfur content in the MCN intermediate gasoline cut recovered at the top of the fractionation column of step c) is less than 30 ppm by weight, preferably less than 15 ppm by weight and more preferably less than 10 ppm weight of total sulfur. The sulfur content from the mercaptans in the MCN intermediate gasoline cut recovered at the top of the fractionation column in step c) is less than 10 ppm by weight.

According to a second embodiment of step c), the effluent from step b) is first separated into an MCN intermediate gasoline cut containing a gas phase containing hydrogen and H ₂ S and into a second HHCN heavy gasoline cut, then a gas phase consisting essentially of hydrogen and H ₂ S is separated from the intermediate gasoline cut

MCN. More particularly, the effluent from step b) is separated into a gasoline cut. MCN intermediate containing a gas phase containing hydrogen and H ₂ S and in a second heavy gasoline HHCN cut in a separation means, then a gas phase consisting essentially of hydrogen and H ₂ S is condensed. the MCN intermediate gasoline cut, so as to obtain a cut point between the MCN cut and the HHCN cut of between 100 ° C and 140 ° C. The condensation is generally carried out by cooling to a temperature between 40 and 60 ° C, preferably between 45 and 55 ° C.

According to this mode, illustrated in FIG. 2, the first desulphurization effluent from step b) discharged via line 9 is separated in a separation means 25, for example in a separation flask, in an MCN intermediate gasoline cut. containing a gas phase containing hydrogen and H S 24 and in a second heavy gasoline HHCN 15 cut containing unconverted sulfur compounds and recombinant mercaptans. Then the MCN intermediate gasoline cut containing a gas phase containing hydrogen and H S 24 is cooled and partially condensed so as to produce in the separator 10 two phases: a gas phase 11 rich in hydrogen and containing part of the H S produced by the desulfurization in step b) and the MCN intermediate gasoline cut 14. This condensation step essentially aims to eliminate most of the HS formed during step b) and can be carried out in a gas / liquid separator flask. Description of the hydrodesulfurization step d) of the HHCN cut

In accordance with step d) of the process, the second HHCN heavy gasoline cut is treated by hydrodesulfurization. Said gasoline cut, withdrawn from the bottom of the splitter 13 in Figure 1 or from the bottom of the separation flask 25 in Figure 2 via line 15, is brought into contact with hydrogen supplied via line 16 in at least one hydrodesulfurization unit 17. This selective hydrodesulfurization step d) thus makes it possible to convert the sulfur-containing compounds of the heavy HHCN gasoline cut (including the major part of the recombinant mercaptans formed in the hydrodesulfurization step b)) in H2S and hydrocarbons. The hydrodesulphurization step d) is carried out at a higher temperature than that of step b) and in the presence of a very selective catalyst. By using a higher temperature in this step compared to the temperature of step b) the formation of olefins and H ₂ S will be favored by the thermodynamic equilibrium of the recombinant mercaptans which allows even more to eliminate the recombinant mercaptans. The hydrodesulfurization step d) consists in bringing the second HHCN heavy gasoline cut into contact with hydrogen, in one or more hydrodesulfurization reactors, containing one or more catalysts suitable for carrying out the hydrodesulfurization.

Hydrodesulfurization step d) is performed without significant hydrogenation of the olefins. The degree of hydrogenation of the olefins in this stage is generally less than 5% and preferably less than 2%.

The temperature of this step is generally between 260 and 420 ° C, more preferably between 290 and 400 ° C, and very preferably between 290 and 350 ° C. The temperature of this step d) is generally at least 5 ° C, preferably at least 10 ° C and very preferably at least 30 ° C above the temperature of step b). The operating pressure of this step is generally between 0.5 and 5 MPa and preferably between 1 and 3 MPa. The quantity of catalyst used in each reactor is generally such that the ratio between the gasoline flow rate to be treated expressed in m ³ per hour at standard conditions, per m ³ of catalyst (also called space speed) is between 1 and 10 tr ¹ and preferably between 2 and 8 h -. The hydrogen flow rate is generally such that the ratio between the hydrogen flow rate expressed in normal m ³ per hour (Nm ³ / h) and the flow rate of the HHCN cut to be treated expressed in m ³ per hour at standard conditions is included between 25 and 600 Nm ³ / m ³ , preferably between 200 and 500 Nm ³ / m ³ .

The hydrogen required for this step and supplied via line 16 can be fresh hydrogen or recycled hydrogen, preferably free of H ₂ S.

Preferably, fresh hydrogen will be used. This makes it possible to reduce the partial pressure of H ₂ S at the inlet of step d) and therefore promotes the elimination of the mercaptans in olefins and H ₂ S.

According to one embodiment, the hydrogen can come from a hydrogen supply dedicated to this step, for example a hydrogen compressor.

In another embodiment, the hydrogen can also be withdrawn directly from the fresh hydrogen feed to unit 8 through line 18, saving a hydrogen compressor.

The catalyst of step d) is of a different nature and / or composition from that used in step b). The catalyst of step d) is in particular a very selective hydrodesulfurization catalyst: it makes it possible to hydrodesulfurize without hydrogenating the olefins and therefore to maintain the octane number. The catalyst which may be suitable for this step d) of the process according to the invention, without this list being limiting, is a catalyst comprising an oxide support and an active phase consisting of at least one metal from group VIII, and of preferably chosen from the group formed by nickel, cobalt, iron. These metals can be used alone or in combination. Preferably, the active phase consists of a metal from group VIII, preferably nickel. Particularly preferably, the active phase consists of nickel.

The group VIII metal content is between 1 and 60% by weight of oxide of the group VIII metal relative to the total weight of the catalyst, preferably between 5 and 30% by weight, very preferably between 5 and 20. % weight. Preferably, the catalyst is characterized by a specific surface area of between 5 and 400 m ² / g, preferably between 10 and 250 m ² / g, preferably between 20 and 200 m ² / g, very preferably. between 30 and 180 m ² / g. The specific surface is determined in the present invention by the BET method according to the ASTM D3663 standard, as described in the work Rouquerol F .; Rouquerol J .; Singh K. “Adsorption by Powders & Porous So / ids; Princip / e, methodology and applications ”,

Academie Press, 1999, for example by means of an Autopore III ™ model apparatus of the brand Microméritics ™.

The pore volume of the catalyst is generally between 0.4 cm ³ / g and 1.3 cm ³ / g, preferably between 0.6 cm ³ / g and 1.1 cm ³ / g. The total pore volume is measured by mercury porosimetry according to standard ASTM D4284 with a wetting angle of 140 °, as described in the same book.

The packed fill density (DRT) of the catalyst is generally between 0.4 and 0.7 g / mL, preferably between 0.45 and 0.69 g / mL. The DRT measurement consists in introducing the catalyst into a test tube, the volume of which has been determined beforehand, then, by vibration, in compacting it until a constant volume is obtained. The bulk density of the packed product is calculated by comparing the introduced mass and the occupied volume after packing. Advantageously, the catalyst of step d), before sulfurization, has an average pore diameter greater than 20 nm, preferably greater than 25 nm, or even 30 nm and often between 20 and 140 nm, preferably between 20 and 100 nm, and very preferably between 25 and 80 nm. The pore diameter is measured by mercury porosimetry according to ASTM D4284 with a wetting angle of 140 °. The catalyst can be in the form of extrudates of small diameter, cylindrical or multilobed (trilobes, quatrefoils, etc.), or spheres.

The catalyst oxide support is usually a porous solid chosen from the group consisting of: aluminas, silica, alumina silicas or even titanium or magnesium oxides used alone or as a mixture with alumina or silica alumina . It is preferably chosen from the group consisting of silica, the family of transition aluminas and alumina silicas, very preferably, the oxide support consists essentially of alumina, that is to say that it comprises at least 51% by weight, preferably at least 60% by weight, very preferably at least 80% by weight, or even at least 90% by weight of alumina. It preferably consists solely of alumina. Preferably, the oxide support of the catalyst is a “high temperature” alumina, that is to say which contains theta, delta, kappa or alpha phase aluminas, alone or as a mixture, and an amount of less than 20. % of gamma, chi or eta phase alumina. A very preferred embodiment of the invention corresponds to the implementation for step d) of a catalyst consisting of alumina and nickel, said catalyst containing a content by weight relative to the total weight of catalyst of Nickel oxide, in NiO form, between 5 and 20%, said catalyst having a specific surface area between 30 and 180 m ² / g. The catalyst of the hydrodesulfurization step d) is characterized by a catalytic activity generally between 1% and 90%, preferably between 1% and 70%, and very preferably between 1% and 50% of the catalytic activity of the catalyst for hydrodesulfurization step b).

At the end of step d) is withdrawn from the selective hydrodesulfurization unit, via line 19, a second desulfurized HHCN heavy gasoline cut which typically has a sulfur content of less than 30 ppm by weight, preferably less than 15 ppm by weight and even more preferably less than 10 ppm by weight, of which respectively less than 10 ppm by weight of sulfur, preferably less than 8 ppm by weight and even more preferably less than 5 ppm of sulfur derived from recombinant mercaptans relative to to the total weight of the load. The degree of hydrogenation of the olefins in this stage is generally less than 2%.

Description of the stabilization step e)

According to step e) of the process according to the invention, a step is carried out for separating the H ₂ S formed and present in the MCN intermediate gasoline cut resulting from step c) and the second desulfurized HHCN heavy gasoline cut resulting from of step d). Preferably, the separation step comprises a stabilization step in order to separate therefrom a fraction of light C4- hydrocarbons mixed with the H2S formed and the hydrogen which has not reacted. According to the embodiment of FIG. 1 or 2, the MCN intermediate gasoline cut from line 14 and the second desulphurized HHCN heavy gasoline cut from line 19 are sent as a mixture via line 20 into a stabilization column 21 of which there is withdraw at the top via line 22 the C4- hydrocarbon fraction mixed with H2S and hydrogen and at the bottom, a mixture of desulphurized MCN and HHCN gasolines, stabilized, via line 23.

The LCN light gasoline cuts, and the mixture of desulfurized MCN and HHCN gasolines, produced by the process according to the invention, are advantageously used as bases for the formulation of a gasoline fuel.

Description of the preparation of the catalysts and of the sulfurization The preparation of the catalysts of stages b) or d) is known and generally comprises a stage of impregnation of the metals of group VIII and of group VI B when it is present, and optionally of the phosphorus and / or of the organic compound on the oxide support, followed by drying, then by optional calcination making it possible to obtain the active phase in their oxide forms. Before its use in a hydrodesulfurization process of an olefinic gasoline cut containing sulfur, the catalysts are generally subjected to sulfurization in order to form the active species as described below.

The impregnation step can be carried out either by slurry impregnation, or by excess impregnation, or by dry impregnation, or by any other means known to those skilled in the art. The impregnation solution is chosen so as to be able to dissolve the metal precursors in the desired concentrations.

By way of example, among the sources of molybdenum, use may be made of oxides and hydroxides, molybdic acids and their salts, in particular ammonium salts such as ammonium molybdate, ammonium heptamolybdate, phosphomolybdic acid (H ₃ PM0 ₁₂ O ₄₀ ), and their salts, and optionally silicomolybdic acid (HUSiMo ^ CUo) and its salts. The sources of molybdenum can also be any heteropolycompound such as Keggin, Lacunar Keggin, substituted Keggin, Dawson, Anderson, Strandberg, for example. Molybdenum trioxide and heteropolycoms of the Keggin, lacunar Keggin, substituted Keggin and Strandberg type are preferably used.

The tungsten precursors which can be used are also well known to those skilled in the art. For example, among the sources of tungsten, it is possible to use oxides and hydroxides, tungstic acids and their salts, in particular ammonium salts such as ammonium tungstate, ammonium metatungstate, phosphotungstic acid and theirs. salts, and optionally silicotungstic acid (hUSiW ^ Cho) and its salts. The sources of tungsten can also be any heteropolycompound such as Keggin, Lacunar Keggin, substituted Keggin, Dawson, for example. Oxides and ammonium salts, such as ammonium metatungstate or heteropolyanions of the Keggin, lacunar Keggin or substituted Keggin type, are preferably used. The cobalt precursors which can be used are advantageously chosen from oxides, hydroxides, hydroxycarbonates, carbonates and nitrates, for example. Cobalt hydroxide and cobalt carbonate are preferably used.

The nickel precursors which can be used are advantageously chosen from oxides, hydroxides, hydroxycarbonates, carbonates and nitrates, for example. The preferred phosphorus precursor is orthophosphoric acid H3PO4, but its salts and esters such as ammonium phosphates are also suitable. The phosphorus can also be introduced at the same time as the element (s) of group VI B in the form of heteropolyanions of Keggin, lacunar Keggin, substituted Keggin or of Strandberg type. After the impregnation step, the catalyst is generally subjected to a drying step at a temperature below 200 ° C, advantageously between 50 ° C and 180 ° C, preferably between 70 ° C and 150 ° C, of very preferably between 75 ° C and 130 ° C. The drying step is preferably carried out under an inert atmosphere or under an atmosphere containing oxygen. The drying step can be carried out by any technique known to those skilled in the art. It is advantageously carried out at atmospheric pressure or at reduced pressure. Preferably, this step is carried out at atmospheric pressure. It is advantageously carried out in a crossed bed using air or any other hot gas. Preferably, when the drying is carried out in a fixed bed, the gas used is either air or an inert gas such as argon or nitrogen. Very preferably, the drying is carried out in a crossed bed in the presence of nitrogen and / or air. Preferably, the drying step has a duration of between 5 minutes and 15 hours, preferably between 30 minutes and 12 hours.

According to a variant of the invention, the catalyst has not undergone calcination during its preparation, that is to say that the impregnated catalytic precursor has not been subjected to a heat treatment step at a higher temperature. at 200 ° C under an inert atmosphere or under an atmosphere containing oxygen, in the presence of water or not.

According to another variant of the invention, which is preferred, the catalyst has undergone a calcination step during its preparation, that is to say that the impregnated catalytic precursor has been subjected to a heat treatment step at a temperature between 250 and 1000 ° C and preferably between 200 and 750 ° C, for a period typically between 15 minutes and 10 hours, under an inert atmosphere or under an atmosphere containing oxygen, in the presence of water or not. Before coming into contact with the feed to be treated in a gasoline hydrodesulfurization process, the catalysts of the process according to the invention generally undergo a sulfurization step. The sulphurization is preferably carried out in a sulforreducing medium, that is to say in the presence of H ₂ S and hydrogen, in order to convert the metal oxides into sulphides such as, for example, M0S ₂ , Co _g S ₈ or Ni ₃ S ₂ . Sulfurization is carried out by injecting onto the catalyst a stream containing H ₂ S and hydrogen, or else a sulfur compound capable of decomposing into H2S in the presence of the catalyst and hydrogen. Polysulfides such as dimethyldisulfide (DM DS) are precursors of H ₂ S commonly used to sulfide catalysts. Sulfur can also come from the charge. The temperature is adjusted so that the H ₂ S reacts with the metal oxides to form metal sulphides. This sulfurization can be carried out in situ or ex situ (inside or outside the reactor) of the reactor of the process according to the invention at temperatures of between 200 and 600 ° C, and more preferably between 300 and 500 ° C.

The degree of sulfurization of the metals constituting the catalysts is at least equal to 60%, preferably at least equal to 80%. The sulfur content in the sulfurized catalyst is measured by elemental analysis according to ASTM D5373. A metal is considered to be sulphurized when the overall sulphurization rate defined by the molar ratio between the sulfur (S) present on the catalyst and said metal is at least equal to 60% of the theoretical molar ratio corresponding to the total sulphurization of the (s) metal (s) considered. The overall sulfurization rate is defined by the following equation:

in which : (S / metal) _catalyst is the molar ratio between sulfur (S) and metal present on the catalyst

_Theoretical (S / metal) is the molar ratio between sulfur and metal corresponding to the total sulphurization of the metal to sulphide. This theoretical molar ratio varies according to the metal considered:

-

When the catalyst comprises several metals, the molar ratio between the S present on the catalyst and all the metals must also be at least equal to 60% of the theoretical molar ratio corresponding to the total sulphurization of each metal to sulphide, the calculation being carried out in proportion to the relative mole fractions of each metal. For example, for a catalyst comprising molybdenum and nickel with a respective molar fraction of 0.7 and 0.3, the minimum molar ratio (S / Mo + Ni) is given by the relation:

Examples

Example 1: Pretreatment of the FCC gasoline feed by selective hydrogenation (according to the prior art)

Table 1 gives the characteristics of an FCC gasoline treated by the method according to Figure 3 of the prior art (EP1077247).

The FCC gasoline (line 1) is treated in the selective hydrogenation reactor (2) in the presence of a catalyst A (optional step). Catalyst A is a catalyst of the NiMo type on gamma alumina. The metal contents are respectively 7% by weight NiO and 11% by weight MoO3 relative to the total weight of the catalyst, ie an Ni / Mo molar ratio of 1, 2. The specific surface of the catalyst is 230 m ² / g. Prior to its use, catalyst A is sulfurized at atmospheric pressure in a sulfurization bench under an H2S / H2 mixture consisting of 15% by volume of H ₂ S at 1 L / gh of catalyst and at 400 ° C. for two hours. This protocol makes it possible to obtain a sulfurization rate greater than 80%.

FRCN gasoline (line 1) is brought into contact with hydrogen in a reactor which contains catalyst A. This stage of the process carries out the selective hydrogenation of the diolefins and the conversion (weighting down) of part of the mercaptan compounds. (RSH) present in the load. The diolefin content is directly proportional to the value of the MAV (maleic anhydride index or Maleic Anhydrid Value according to English terminology). Diolefins are undesirable compounds because they are precursors of gums in gasolines.

The operating conditions implemented in the selective hydrogenation reactor are: Temperature: 140 ° C, Total pressure: 2.5 MPa, volume ratio H2 added / FRCN petrol charge: 5 normal liters of hydrogen per liter of petrol ( vol / vol), hourly volume speed (VVH): 3 h-1.

Table 1: Characteristics of the FRCN feed (1) and of the selective hydrogenation effluent (3).

The effluent from the selective hydrogenation stage (3) with a low content of conjugated diolefins (MAV = 0.6 mg / g) and low content of light sulfur compounds (weighed down in the selective hydrogenation stage) is sent in a fractionation column (4) according to step a) of the present invention in order to separate a light LCN gasoline at the top (line 5) and at the bottom of the column a first heavy gasoline HCN cut (line 6). The characteristics of LCN light gasoline and the first cut heavy gasoline HCN are shown in Table 2. As shown in Table 2, the LCN gasoline obtained (row 5) has a low sulfur content (10 ppm). The first cut of heavy HCN gasoline, which corresponds to approximately 72% by mass of FRCN gasoline, has a high sulfur content (600 ppm) and requires additional treatment before being incorporated into the gasoline pool.

Table 2: Cut characteristics: LCN light gasoline and first cut HCN heavy gasoline

Example 2 (comparative): Hydrodesulfurization of the first heavy gasoline HCN cut This example refers to the prior art (patent EP 1077247) and to FIG. 3. The first heavy gasoline HCN cut (line 6) obtained in Example 1 is mixed with hydrogen and treated in a selective hydrodesulfurization unit (8) which corresponds to a first hydrodesulfurization step. The first hydrodesulfurization step is carried out in the presence of a CoMo catalyst supported on alumina. The temperature is 268 ° C, the pressure is 2 MPa, the space velocity of the liquid (expressed in volume of liquid per volume of catalyst and per hour) is 3 h, the H2 / HCN cut ratio is 250 normal m ³ per m ³ under standard conditions. The reactor effluent (line 9) is then reheated in an oven (not shown in the figure) and then introduced into a second reactor (27) containing a so-called finishing catalyst. This second finishing step is carried out in the presence of an Ni catalyst supported on alumina. The pressure is 1.8 MPa, the space velocity of the liquid (expressed as volume of liquid per volume of catalyst and per hour) is 3 h.

The effluent from reactor 27 (line 20) is sent to a stabilization column (21), in order to recover at the top of the column the hydrogen and H2S (line 22), optionally with light hydrocarbons and at the bottom of the column. the column (line 23) is a desulphurized and HCN stabilized heavy gasoline cut from the second Polishing reactor. Characteristics of the HCN obtained after the second hydrodesulfurization step and stabilized, are illustrated in Table 3. The loss of olefins is presented in Table 4.

Table 3: Characteristics of heavy HCN gasoline after the first and second hydrodesulfurization stages

Table 4: Loss of olefins between the first cut of heavy HCN gasoline (line 6) and the gasoline obtained after the second hydrodesulfurization step (line 20)

The process according to Example 2 makes it possible to obtain an HCN gasoline with a low sulfur content (10 ppm by weight). The loss of olefins between the first cut of heavy HCN gasoline and the stabilized gasoline obtained after the second hydrodesulfurization step is 27.3% by mass (in absolute).

Example 3: (according to the present invention) with Splitter

This example refers to the present invention, according to Figure 1. The first heavy gasoline HCN cut (line 6) obtained in Example 1 is mixed with hydrogen and treated in a selective hydrodesulfurization unit (8) which corresponds to step b) of the present invention. The first hydrodesulfurization step (step b)) is carried out in the presence of a CoMo catalyst supported on alumina. The temperature is 260 ° C, the pressure is 2 MPa, the space velocity of the liquid (expressed in volume of liquid per volume of catalyst and per hour) is 3 h, the H2 / HCN cut ratio is 200 normal m ³ per m ³ under standard conditions. The effluent from the reactor (line 9) is then reheated in an oven and then introduced into a second reactor (not shown in the figure) containing a so-called finishing catalyst. Neither supported on alumina. The pressure is 1.8 MPa, the space velocity of the liquid (expressed as volume of liquid per volume of catalyst and per hour) is 3 h.

The effluent from the finishing reactor is partially condensed to be introduced into the gas / liquid separator (10). The gas phase produced (line 1 1) essentially contains hydrogen and H2S, possibly with light hydrocarbons. The bottom of the separator (10) contains a partially desulfurized HCN hydrocarbon cut.

The characteristics of the HCN obtained after step b) of the present invention are shown in Table 5. The loss of olefins after step b) is shown in Table 6.

Table 5: Characteristics of the first HCN heavy gasoline cut after hydrodesulfurization step b) according to the invention

Table 6: Loss of olefins between the first cut of heavy HCN gasoline (line 6) and the gasoline obtained after step b) according to the invention

The conditions of step b) are less severe than in Example 2: the loss of olefins at the end of step b) is reduced by 5.3% by weight in this example according to the invention. In step c) according to the invention, the effluent from step b) (line 12) is fractionated in a distillation column (13) so as to produce an MCN intermediate gasoline cut (line 14) and a second H HCN heavy gasoline cutter (line 15). The fractionation of the intermediate MCN gasoline cut and of the second H HCN heavy gasoline cut being carried out at a temperature of 120 ° C. so as to obtain an MCN cut at less than 10 ppm sulfur. The operation of the fractionation column is adjusted so as to obtain an MCN cut whose temperature at 95% of the distilled mass of the MCN intermediate gasoline cut is 120 ° C ± 5 ° C (temperatures measured according to the CSD method described in Oil Gas Sci. Technol, Vol 54 (1999), No. 4, pp. 431-438). The operation of the fractionation column is also adjusted so as to obtain at the bottom of the column, a second heavy gasoline H HCN cut whose temperature at 5% of distilled mass is 120 ° C ± 5 ° C (temperatures measured according to the CSD method described in Oil Gas Sci. Technol, Vol. 54 (1999), No. 4, pp. 431-438).

The characteristics of the MCN and of the second heavy gasoline H HCN cut obtained after step c) of the present invention are illustrated in Table 7.

Table 7: Characteristics of MCN intermediate gasoline and heavy gasoline cuts

HHCN obtained after step c) according to the invention

In step d) according to the invention, the second HHCN heavy gasoline cut is brought into contact in the reactor (17) with hydrogen and a Ni catalyst supported on so-called polishing alumina. The temperature is 300 ° C, the pressure is 2 MPa, the space velocity of the liquid (expressed in volume of liquid per volume of catalyst and per hour) is 3 h. The ratio between the hydrogen flow rate expressed in normal m ³ per hour and the flow rate of the second HHCN heavy gasoline cut to be treated, expressed in m ³ per hour at standard conditions, is 80 Nm ³ / m ³ . Under these operating conditions, the hydrogenation of the olefins is negligible.

The characteristics of the HHCN obtained after step d) of the present invention are shown in Table 8.

Table 8: Characteristics of the second HHCN heavy gasoline cut after hydrodesulfurization step d) according to the invention The desulfurized HHCN cut (line 19) is mixed with the MCN cut (line 14) and the mixture is sent (line 20) to a stabilization column (21), in order to recover the hydrogen and the hydrogen at the top of the column. H2S (line 22), optionally with light hydrocarbons and at the bottom of the column (line 23) a desulfurized HCN hydrocarbon cut. The characteristics of the HCN obtained after stabilization (21) according to the present invention are illustrated in Tables 9 and 10.

Table 9: Characteristics of the mixture of MCN and HHCN gasoline after

hydrodesulfurization and stabilization according to the invention

Table 10: Loss of olefins between the first cut of heavy HCN gasoline (6) and gasoline

(line 23) obtained after hydrodesulfurization according to the invention

Very advantageously, the process according to the invention makes it possible to produce a gasoline with a low sulfur content (10 ppm S) while reducing the absolute loss of olefins compared to the heavy gasoline HCN desulfurized after the second desulfurization step

(presented in comparative example 2). In example 2, the loss of olefins (in% by mass) between the first cut of heavy HCN gasoline (line 6) and the gasoline obtained after the second hydrodesulphurization step is 6.8% and in the example 3 according to the invention, the loss of olefins between the first heavy gasoline HCN cut (line 6) and the gasoline mixture of intermediate gasoline cut MCN and second heavy gasoline cut H HCN desulfurized and stabilized (line 23) is 5, 3%. Thus, Example 3 according to the invention makes it possible to preserve 19% relative of the olefins present in the first cut of heavy HCN gasoline while producing gasoline with the same low sulfur content (10 ppm). The preservation of the olefins present has a positive impact on the octane numbers of the gasoline produced. The process according to the invention thus makes it possible to obtain, after stabilization, an HCN gasoline cut with a low organic sulfur content (10 ppm). This gasoline can, with the light LCN gasoline obtained in Example 1, be upgraded in the gasoline pool for the formulation of fuel for vehicles.

Example 4: (according to an alternative mode of the present invention) with an MCN balloon This example refers to an alternative mode of the present invention, according to Figure 2. The first HCN heavy gasoline cut (line 6) obtained in Example 1 is mixed with hydrogen and treated in a selective hydrodesulfurization unit (8) which corresponds to step b) of the present invention.

The conditions of step b) are strictly identical to those described in Example 3 according to the invention.

According to a second mode of step c), the first desulphurization effluent from step b) discharged via line 9 is separated in a separation means (25), for example in a separation flask at a controlled temperature of 140 ° C, in an MCN intermediate gasoline cut containing a gas phase containing hydrogen and H S (line 24) and in a second heavy HHCN gasoline cut (line 15) containing unconverted sulfur compounds and recombinant mercaptans. Then the MCN intermediate gasoline cut containing a gaseous phase containing hydrogen and H S (line 24) is cooled and partially condensed so as to produce in the separator (10) two phases: a gas phase (line 1 1 ) rich in hydrogen and containing part of the H S produced by the desulphurization in step b) and the MCN intermediate gasoline cut (line 14). This condensation step is essentially aimed at eliminating most of the HS formed during step b).

The characteristics of MCN and HHCN obtained after step c) of the present inventions are shown in Table 7.

Table 1 1: Characteristics of MCN intermediate gasoline and heavy gasoline cuts

HHCN after step c). In step d) according to the invention, the second HHCN heavy gasoline cut is contacted in the reactor (17) with hydrogen and a Ni catalyst supported on so-called finishing alumina. The temperature is 400 ° C, the pressure is 1.8 MPa, the space velocity of the liquid (expressed in volume of liquid per volume of catalyst and per hour) is 3 h.

The ratio between the hydrogen flow rate expressed in normal m ³ per hour and the flow rate of the second cut of heavy HHCN gasoline to be treated expressed in m ³ per hour at standard conditions is 50 Nm ³ / m ³ . To ensure a high conversion of the RSHs, the reactor (17) is operated at a temperature higher than that of the same reactor in Example 3.

Under these operating conditions, the hydrogenation of the olefins is negligible. The characteristics of the HHCN obtained after step d) of the present invention are shown in Table 12.

Table 12: Characteristics of the second HHCN heavy gasoline cut after step d) of hydrodesulfurization according to the invention

The second desulfurized HHCN heavy gasoline cut (line 19) is mixed with the MCN intermediate gasoline cut (line 14) then the mixture is sent (line 20) to a stabilization column (21), in order to recover at the top of column 1 'hydrogen and H2S (line 22), optionally with light hydrocarbons and at the bottom of the column (line 23) a stabilized desulphurized HCN hydrocarbon cut. The characteristics of the HCN obtained after stabilization (23) according to the present invention are illustrated in Tables 13 and 14

Table 13: Characteristics of heavy gasoline after hydrodesulfurization and stabilization according to the invention

Table 14: Loss of olefins between the first HCN heavy gasoline cut (line 6) and gasoline (line 23) obtained after hydrodesulphurization and stabilization according to the invention Very advantageously, the process according to the alternative mode of the invention makes it possible to produce a gasoline with a low sulfur content (10 ppm S) while reducing the absolute loss of olefins compared to the heavy gasoline HCN desulfurized after the second desulfurization step (presented in comparative example 2).

The advantage of this alternative mode over the separation step c) is to carry out the MCN / HHCN separation using a liquid and gas phase separation drum. In this alternative mode, the proportion of HHCN sent to the reactor 17 is 77%, against 44% in example 3. The temperature imposed on the reactor 17 is higher in this alternative mode, because the rate of elimination of the RSH is higher than that of Example 3. In Example 2, the loss of olefins (in% by mass) between the first cut of heavy HCN gasoline (line 6) and the gasoline obtained after the second hydrodesulphurization step is 6.8%, and in the example 4 according to the invention, the loss of olefins between the first heavy gasoline HCN cut (line 6) and the gasoline mixture of intermediate gasoline cut MCN and second heavy gasoline H HCN desulfurized and stabilized cut (line 23) is 5, 5% (identical to Example 3). Thus, Example 4 according to an alternative embodiment of the invention makes it possible to preserve 19% relative of the olefins present in the first heavy HCN gasoline cut while producing gasoline with the same low sulfur content (10 ppm). The preservation of the olefins present has a positive impact on the octane numbers of the gasoline produced.

The method according to the invention thus makes it possible to obtain, after stabilization, a petrol cut

HCN with a low organic sulfur content (10 ppm) which can be used in the gasoline pool for the formulation of vehicle fuel.

Claims

1. Process for desulphurizing a gasoline containing sulfur compounds, olefins and diolefins, comprising at least the following steps: a) gasoline is fractionated so as to recover an LCN light gasoline cut and a first HCN heavy gasoline cut , b) in at least one reactor, the first heavy gasoline cut is brought into contact

HCN, hydrogen and a hydrodesulfurization catalyst comprising an oxide support and an active phase comprising a group VI B metal and a group VIII metal, at a temperature between 210 and 320 ° C, at a pressure between 1 and 4 MPa, with a space velocity between 1 and 10 h and a ratio between the hydrogen flow rate expressed in normal m ³ per hour and the flow rate of the first heavy HCN gasoline cut to be treated, expressed in m ³ per hour at standard conditions between 100 and 600 Nm ³ / m ³ , so as to convert at least part of the sulfur compounds into H2S and to produce a first desulphurization effluent, c) the effluent from step b) is fractionated so as to produce a gas phase consisting essentially of hydrogen and H ₂ S, an intermediate gasoline cut MCN and a second heavy gasoline H HCN cut, the fractionation of the intermediate gasoline MCN cut and the second heavy gasoline H HCN cut being performed with a point d e cut between 100 and 140 ° C, d) in at least one reactor, the second heavy gasoline H HCN cut is brought into contact with hydrogen and a hydrodesulphurization catalyst comprising an oxide support and an active phase consisting of at least one metal from group VIII, to a temperature between 260 and 420 ° C, at a pressure between 0.5 and 5 MPa, with a space velocity between 1 and 10 tr ¹ and a ratio between the hydrogen flow rate expressed in normal m ³ per hour and the flow rate of the second HHCN heavy gasoline cut to be treated expressed in m ³ per hour at standard conditions of between 25 and 600 Nm ³ / m ³ , said temperature of step d) being higher than the temperature of step b) , so as to produce a second desulfurized HHCN heavy gasoline cut, e) a step of separation of the H S formed and present in the MCN intermediate gasoline cut resulting from step c) and in the second HHCN heavy gasoline cut is carried out desulphurized from step d).

2. Method according to claim 1, wherein in step c), the first desulfurization effluent from step b) is partially condensed so as to produce a gas phase consisting essentially of hydrogen and H S and a desulfurized HCN liquid phase, then the said desulfurized HCN liquid phase is separated with a cut point of between 100 and 140 ° C. in an intermediate MCN gasoline cut and a second HHCN heavy gasoline cut.

3. The method of claim 1, wherein in step c), separating with a cut point between 100 and 140 ° C the effluent from step b) in an intermediate gasoline MCN cut containing a gas phase. containing hydrogen and H S and in a second heavy HHCN gasoline cut, then a gas phase consisting essentially of hydrogen and H S is separated by condensation from said MCN intermediate gasoline cut.

4. Method according to one of the preceding claims, wherein step c) is carried out with a cut point between 110 and 130 ° C.

5. Method according to one of the preceding claims, wherein the temperature of step d) is at least 5 ° C higher than the temperature of step b).

6. Method according to one of the preceding claims, wherein step e) is carried out in a stabilization column configured to separate a C4 ^~ hydrocarbon phase containing H ₂ S from a stabilized gasoline cut.

7. Method according to one of the preceding claims, wherein in step e) the second desulphurized HHCN heavy gasoline cut from step d) and the MCN intermediate cut from step c) are mixed into a stabilization column.

8. Method according to one of the preceding claims, wherein the catalyst of step a) comprises alumina and an active phase comprising cobalt, molybdenum and optionally phosphorus, said catalyst containing a content by weight relative to to the total weight of cobalt oxide catalyst, in CoO form, between 0.1 and 10%, a content by weight relative to the total weight of molybdenum oxide catalyst, in M0O ₃ form, between 1 and 20%, a cobalt / molybdenum molar ratio of between 0.1 and 0.8, a content by weight relative to the total weight of phosphorus oxide catalyst in P2O5 form of between 0.3 and 10% when the phosphorus is present, said catalyst having a specific surface area between 30 and 180 m ² / g.

9. Method according to one of the preceding claims, wherein the catalyst of step d) consists of alumina and nickel, said catalyst containing a content by weight relative to the total weight of nickel oxide catalyst, in NiO form, between 5 and 20%, said catalyst having a specific surface area between 30 and 180 m ² / g.

10. Method according to one of the preceding claims, wherein before step a), the gasoline is treated in the presence of hydrogen and a selective hydrogenation catalyst so as to at least partially hydrogenate the diolefins and achieve a reaction to make some of the sulfur compounds heavier, step a) being carried out at a temperature between 50 and 250 ° C, at a pressure between 0.4 and 5 MPa, with a space speed between 0 , 5 and 20 h and with a ratio between the hydrogen flow rate expressed in normal m3 per hour and the feed rate to be treated expressed in m ³ per hour at standard conditions of between 2 Nm ³ / m ³ and 100 Nm ³ / m ³ .

11. Method according to one of the preceding claims, wherein the gasoline is obtained from a catalytic cracking unit.