EP2886629B1 - Process for the hydrodesulfuration of hydrocarbon fractions - Google Patents

Description

The present invention relates to a process for the simultaneous production of two cuts of hydrocarbons with low sulfur contents. In particular, the process makes it possible to desulfurize jointly (as a mixture) a gasoline cut containing olefins and a cut heavier than the gasoline cut so as to subsequently produce a desulfurized gasoline cut with a limited loss of octane number and a heavy cut also desulfurized.

The present invention is particularly interesting for producing two desulfurized cuts which can be sent respectively to the gasoline pool and to the diesel, kerosene and/or fuel oil pool.

State of the art

Sulfur in fuels is an undesirable impurity because it is converted to sulfur oxides when these products are burned. Sulfur oxides are unwanted air pollutants that can further deactivate most catalysts that have been developed for catalytic converters used in cars to catalyze the conversion of harmful exhaust gases. Therefore, it is desirable to reduce the sulfur content of products used in gasoline and diesel fuel compositions to the lowest possible levels.

Catalytic cracking gasoline is the essential product of FCC (FCC "Fluid Catalytic Cracking" according to Anglo-Saxon terminology) obtained with a yield of around 50% and represents approximately 25 to 30% of the gasoline pool of refineries. 'Western Europe. The main negative characteristic of these FCC gasolines compared to commercial fuels is their high sulfur contents and thus constitute the main vector of the presence of sulfur in fuels.

To meet the constraints of sulfur specifications, hydrocarbons produced from catalytic cracking processes are conventionally treated by hydrotreating. The hydrotreating process includes contacting the hydrocarbon feed with hydrogen in the presence of a catalyst so as to convert the sulfur contained in the impurities into hydrogen sulfide, which can then be separated and converted in elemental sulfur. Hydrotreating processes can result in partial destruction of feedstock olefins by converting them to saturated hydrocarbons through hydrogenation. This destruction of olefins by hydrogenation is not desirable in the case of cracked gasolines because it results in costly hydrogen consumption and a significant reduction in the octane number of hydrodesulfurized gasolines.

The residual sulfur compounds generally present in desulfurized gasoline can be separated into two distinct families: the non-hydrodesulfurized sulfur compounds present in the feed and the sulfur compounds formed in the hydrodesulfurization 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 to the mono-olefins present in the feed. Reducing the content of recombinant mercaptans can be achieved by catalytic hydrodesulphurization but at the cost of saturation of a significant part of the mono-olefins, which then leads to a sharp reduction in the octane number of the gasoline. as well as overconsumption of hydrogen.

Nowadays, in many countries and particularly in Europe, the fuel market has mainly shifted towards that of diesel and kerosene, which has the effect that many European refiners are faced with overcapacity problems for their units dedicated to the production of desulphurized gasoline cuts and undercapacity vis-à-vis hydrodesulphurization units which process intermediate distillate cuts used in the composition of diesel and/or kerosene fuel.

There is therefore a need today for processes that allow the refiner to better respond to market demand by using existing excess capacity at the hydrodesulphurization units for gasoline cuts.

• une étape de distillation atmosphérique du pétrole afin de séparer un distillat comprenant du gasoil et des fractions dont le point d'ébullition est inférieur à celui du gasoil;
• une première étape d'hydrodésulfuration du distillat;
• une seconde étape d'hydrodésulfuration du distillat partiellement désulfuré qui est réalisée à une température inférieure à celle de la première étape d'hydrodésulfuration; et
• une étape de séparation du distillat désulfuré en des fractions de gasoil, de kérosène, de naphta lourd et de naphta léger.

We know in the state of the art the document EP 902 078 which discloses a process for processing crude oil which comprises the following steps:

• an atmospheric petroleum distillation step in order to separate a distillate comprising gas oil and fractions whose boiling point is lower than that of the gas oil;
• a first step of hydrodesulfurization of the distillate;
• a second step of hydrodesulfurization of the partially desulfurized distillate which is carried out at a temperature lower than that of the first hydrodesulfurization step; And
• a step of separating the desulphurized distillate into fractions of diesel, kerosene, heavy naphtha and light naphtha.

The document process EP 902 078 thus treats a distillate resulting from an atmospheric distillation step. This type of distillate contains practically no compounds olefinic hydrocarbons unlike the feed treated in the present invention, one of the cuts which compose it contains a significant content of olefins, typically greater than 20% by weight relative to the total weight of said cut. The majority of recombinant sulfur compounds encountered in the process of the document EP 902 078 are therefore not mercaptans resulting from the addition of the H ₂ S formed in the reactor to the mono-olefins present in the feed, but probably the result of the addition of the H ₂ S formed to olefins resulting cracking reactions induced by the high temperature necessary for very deep desulphurization of the feed. Indeed, heavy naphtha from atmospheric distillation is generally intended to be converted in a catalytic reforming unit and must therefore be extensively desulfurized (the total sulfur content is typically less than 1 ppm by weight). On the other hand, the admissible sulfur specification in a gasoline pool is less strict (around 10 ppm weight). Those skilled in the art therefore seek, in the case of the hydrodesulfurization of a distillate comprising gas oil and fractions whose boiling point is lower than that of gas oil resulting from atmospheric distillation, to maximize the hydrodesulfurization reaction. while avoiding reactions (in particular cracking reactions) likely to form olefins.

The solution recommended by the patent EP 902 078 consists of carrying out extensive hydrodesulfurization at high temperature in a first reactor followed by gentler hydrodesulfurization in a second reactor which makes it possible to eliminate any recombination mercaptans and/or olefins which would have been produced in the first reactor. This way of operating is unsuitable for a feed containing gasoline from a conversion unit with a high olefin content because it risks causing significant hydrogenation of said olefins during the first step, thus inducing a loss of octane number. unwanted.

The document US 2013/0087484 describes a process for producing p-xylene from a mixture of naphtha and light cutting oil (LCO, “Light Cycle Oil” according to Anglo-Saxon terminology) from a catalytic cracking unit. The process comprises a step of hydrodesulfurization of said mixture followed by fractionation of the desulfurized effluent into three cuts, namely, a light C ₂ -C ₄ cut, a naphtha cut and a heavy cut. The intermediate naphtha cut is processed in a catalytic reforming unit to produce aromatics and the heavy cut is hydrocracked to give an aromatics-rich effluent which is recycled to the fractionation column.

• une première étape d'hydrodésulfuration de ladite coupe essence;
• une étape de séparation de la majeure partie de l'H₂S de l'effluent issu de la première hydrodésulfuration;
• une seconde étape d'hydrodésulfuration de ladite coupe essence débarrassée de l'H₂S.

The document FR 2837831 describes a process for hydrodesulfurization of a gasoline cut resulting from catalytic cracking or coking of a heavy hydrocarbon feed involving:

• a first step of hydrodesulfurization of said gasoline cut;
• a step of separating the majority of the H ₂ S from the effluent resulting from the first hydrodesulfurization;
• a second step of hydrodesulfurization of said gasoline cut freed of H ₂ S.

According to this document, the second hydrodesulfurization step is carried out at a temperature lower by at least 10°C, preferably by at least 20°C, than that of the first hydrodesulfurization step.

The prior art also includes the document FR 2811328 which teaches a process for hydrodesulfurization of a gasoline cut which can be a mixture of gasolines coming from different conversion processes such as steam cracking, coking or visbreaking processes or even gasolines directly resulting from the atmospheric distillation of petroleum.

An aim of the invention is to propose a hydrodesulfurization process which can respond to the problems of overcapacity of gasoline hydrodesulfurization units.

Summary of the invention

• une première fraction comprenant des hydrocarbures ayant une gamme de températures d'ébullition comprise entre la température d'ébullition initiale du mélange et 160°C et dont la teneur en oléfines est comprise entre 20 et 80% poids de ladite première fraction et la première fraction étant choisie parmi une coupe essence oléfinique issue d'une unité de craquage catalytique, de vapocraquage, de cokéfaction, de viscoréduction, la première fraction représentant entre 30 et 70 % poids du mélange, et
• une seconde fraction comprenant des hydrocarbures ayant une gamme de températures d'ébullition comprise entre 160°C et la température d'ébullition finale du mélange, ladite seconde fraction comprenant au moins 10% poids d'hydrocarbures ayant une gamme de températures d'ébullition comprise entre 220°C et la température d'ébullition finale du mélange, la seconde fraction étant une huile légère issue d'une unité de craquage catalytique,

le procédé comprenant les étapes suivantes:

1. a) on traite dans un premier réacteur ledit mélange constitué de ladite première fraction et de ladite seconde fraction dans une première étape d'hydrodésulfuration en présence d'hydrogène et d'un catalyseur comprenant au moins un métal du groupe VIII, au moins un métal du groupe VIB et un support, la teneur en métal(ux) du groupe VIII étant comprise entre 1,5 et 9% poids d'oxyde(s) de métal(ux) du groupe VIII et la teneur en métal(ux) du groupe VIB étant comprise entre 4 et 40% poids d'oxyde(s) de métal(ux) du groupe VIB, le rapport molaire métal(ux) du groupe VIII sur métal(ux) du groupe VIB dans le catalyseur sous forme oxyde est compris entre 0,1 et 0,8, la première étape d'hydrodésulfuration étant réalisée à une température comprise entre 200 et 400°C, à une pression comprise entre 1 et 10 MPa, avec une vitesse spatiale liquide comprise entre 0,1 et 10 h^-1 et avec un ratio (volume d'hydrogène / volume de mélange d'hydrocarbures) compris entre 50 et 500 Nlitre/litre;
2. b) on élimine le sulfure d'hydrogène de l'effluent partiellement désulfuré issu de l'étape a);
3. c) on traite dans un second réacteur le mélange partiellement désulfuré issu de l'étape b) dans une seconde étape d'hydrodésulfuration en présence d'hydrogène et d'un catalyseur comprenant au moins un élément du groupe VIII, au moins un élément du groupe VIB et un support, la teneur en métal(ux) du groupe VIII étant comprise entre 0,5 et 15% poids d'oxyde(s) de métal(ux) du groupe VIII et la teneur en métal(ux) du groupe VIB étant comprise entre 1,5 et 60% poids d'oxyde(s) de métal(ux) du groupe VIB, la seconde étape d'hydrodésulfuration étant réalisée à une température comprise entre 205 et 500°C, à une pression comprise entre 1 et 3 MPa, avec une vitesse spatiale liquide comprise entre 1 et 10 h^-1 et avec un ratio (volume d'hydrogène / volume de mélange) compris entre 50 et 500 Nlitre/litre, la température de la seconde étape d'hydrodésulfuration c) étant supérieure à celle de la première étape d'hydrodésulfuration a); et
4. d) on fractionne le mélange désulfuré issu de l'étape c) en au moins deux coupes d'hydrocarbures légère et lourde désulfurées, la coupe d'hydrocarbures légère ayant une température d'ébullition initiale comprise entre 35°C et 100°C et une température d'ébullition finale comprise entre 160°C et 220°C et dont la teneur en soufre total est inférieure à 50 ppm poids et la coupe d'hydrocarbures lourde ayant une température d'ébullition initiale comprise entre 160°C et 220°C et une température d'ébullition finale comprise entre 260°C et 340°C.

The invention therefore relates to a process for the simultaneous production of two cuts of hydrocarbons with low sulfur contents from a mixture of hydrocarbons having an initial boiling temperature of between 35°C and 100°C and a temperature of final boiling point of between 260°C and 340°C and having a total sulfur content of between 30 and 10,000 ppm by weight, said mixture of hydrocarbons consists of:

• a first fraction comprising hydrocarbons having a range of boiling temperatures between the initial boiling temperature of the mixture and 160°C and whose olefin content is between 20 and 80% by weight of said first fraction and the first fraction being chosen from an olefinic gasoline cut from a catalytic cracking, steam cracking, coking, visbreaking unit, the first fraction representing between 30 and 70% by weight of the mixture, and
• a second fraction comprising hydrocarbons having a boiling temperature range between 160°C and the final boiling temperature of the mixture, said second fraction comprising at least 10% by weight of hydrocarbons having a boiling temperature range between between 220°C and the final boiling temperature of the mixture, the second fraction being a light oil from a catalytic cracking unit,

the process comprising the following steps:

1. a) said mixture consisting of said first fraction and said second fraction is treated in a first reactor in a first hydrodesulfurization step in the presence of hydrogen and a catalyst comprising at least one metal from group VIII, at least one metal of group VIB and a support, the content of metal(s) of group VIII being between 1.5 and 9% by weight of oxide(s) of metal(s) of group VIII and the content of metal(s) of the group VIB being between 4 and 40% by weight of oxide(s) of metal(s) of group VIB, the molar ratio metal(s) of group VIII to metal(s) of group VIB in the catalyst in oxide form is between 0.1 and 0.8, the first hydrodesulfurization step being carried out at a temperature between 200 and 400°C, at a pressure between 1 and 10 MPa, with a liquid space velocity between 0.1 and 10 h ^-1 and with a ratio (volume of hydrogen / volume of hydrocarbon mixture) of between 50 and 500 Nliter/liter;
2. b) the hydrogen sulphide is removed from the partially desulphurized effluent resulting from step a);
3. c) the partially desulfurized mixture resulting from step b) is treated in a second reactor in a second hydrodesulfurization step in the presence of hydrogen and a catalyst comprising at least one element from group VIII, at least one element from group VIII, group VIB and a support, the content of metal(s) of group VIII being between 0.5 and 15% by weight of oxide(s) of metal(s) of group VIII and the content of metal(s) of group VIB being between 1.5 and 60% by weight of metal oxide(s) from group VIB, the second hydrodesulphurization step being carried out at a temperature between 205 and 500°C, at a pressure between 1 and 3 MPa, with a liquid space velocity between 1 and 10 h ^-1 and with a ratio (volume of hydrogen / volume of mixture) between 50 and 500 Nliter/liter, the temperature of the second hydrodesulfurization stage c) being greater than that of the first hydrodesulfurization step a); And
4. d) the desulfurized mixture resulting from step c) is fractionated into at least two desulfurized light and heavy hydrocarbon cuts, the light hydrocarbon cut having an initial boiling temperature of between 35°C and 100°C and a final boiling temperature of between 160°C and 220°C and whose total sulfur content is less than 50 ppm by weight and the heavy hydrocarbon cut having an initial boiling temperature of between 160°C and 220° C and a final boiling temperature of between 260°C and 340°C.

In the context of the invention, the boiling temperatures can fluctuate by plus or minus 5°C compared to the values mentioned.

The inventors have surprisingly observed that it is possible to jointly hydrodesulfurize a mixture containing a gasoline cut and a distillate cut loaded with sulfur and with a low olefin content in order to produce a gasoline cut with a low sulfur content, in particular in mercaptans, without significant loss of octane number and a cut of distillate depleted in sulfur which can then be upgraded to the diesel and/or kerosene pool or as fuel for maritime use.

In particular, the treatment in the first hydrodesulfurization step of the hydrocarbon mixture leads surprisingly to limit the formation of recombinant mercaptans, reaction products of the addition of H ₂ S with the olefins, and thus to obtain at the end of the process a gasoline cut having a very low mercaptan content. The second hydrodesulfurization step is carried out under conditions which then favor the hydroconversion of the more refractory sulfur compounds which essentially come from the distillate cut.

The process according to the invention responds well to the problem of overcapacity of gasoline hydrodesulphurization units to the extent that these same units can now be used to jointly desulphurize gasoline cuts and middle distillate cuts which are bases for the formulation of fuels. diesel and/or kerosene or usable as fuels for maritime use with low sulfur content.

Detailed description of the invention

The invention therefore relates to a process implementing at least two successive hydrodesulphurization stages of a mixture of hydrocarbons consisting of a first and a second hydrocarbon fraction with an intermediate stage of elimination of the hydrogen sulfide (H ₂ S) formed in the first hydrodesulfurization step and with a reaction temperature in the second hydrodesulfurization step which is higher than that in the first hydrodesulfurization step.

In a preferred embodiment, the catalyst of step a) is a hydrodesulfurization catalyst which comprises a Group VIII metal chosen from nickel and cobalt and a Group VIB metal chosen from molybdenum and tungsten.

Preferably the catalyst of step c) is also a hydrodesulfurization catalyst which comprises a metal from group VIII chosen from nickel and cobalt and a metal from group VIB chosen from molybdenum and tungsten.

The first fraction of hydrocarbons containing olefins is an olefinic gasoline cut from a catalytic cracking, steam cracking, coking, visbreaking unit.

The second hydrocarbon fraction of the mixture treated by the process according to the invention is a light oil cut from a catalytic cracking unit (LCO or "Light Cycle Oil" according to Anglo-Saxon terminology).

The feed for the process according to the invention is a mixture containing a catlaytic cracked gasoline cut and an LCO light oil cut. Advantageously, said mixture is the product of a distillation of an effluent from a catalytic cracking unit.

The light fraction of the LCO, i.e. the compounds having a boiling point lower than 300°C, and very preferably lower than 265°C, is used in mixture with the catalytic cracking gasoline.

The first fraction or hydrocarbon cut represents between 30 and 70% by weight of the mixture.

According to an alternative embodiment, the first fraction of the mixture is a heavy fraction of a catalytic cracked gasoline and the second fraction is a cut of light LCO oil. The heavy fraction of catalytically cracked gasoline is obtained by distillation of a catalytically cracked gasoline cut into two fractions, a light C5- fraction comprising hydrocarbons having a number of carbon atoms of between 2 and 5 atoms and a heavy C6+ fraction comprising hydrocarbons having a number of atoms of carbon greater than or equal to 6.

In a very preferred embodiment, before the step of separating the catalytically cracked gasoline cut into two fractions, said gasoline cut is treated in a step of selective hydrogenation of the diolefins.

• la figure 1 qui montre un schéma de principe du procédé selon l'invention.

Other characteristics and advantages of the invention will appear on reading the description which follows, given for illustrative and non-limiting purposes only, and to which is appended:

• there figure 1 which shows a block diagram of the process according to the invention.

In reference to the figure 1 , the first cut of hydrocarbons treated by the process according to the invention is sent via line 1 to a first hydrodesulphurization reactor 2. This first cut of hydrocarbons is combined (mixed) with a second cut of hydrocarbons supplied by line 3. The mixture, which is made up of two fractions, is then treated in the first hydrodesulfurization reactor 2.

The first hydrocarbon cut, an olefinic gasoline cut from a catalytic cracking, steam cracking, coking, visbreaking unit. Preferably, the gasoline cut is a catalytic cracked gasoline. Typically, the gasoline cut has an initial boiling temperature of between 35°C and 100°C and a final boiling temperature of between 130 and 200°C, preferably between 150 and 170°C and more preferably between 155 and 165°C. Generally the olefin content of the first cut (or first fraction making up the mixture) is between 20 and 80% by weight of said cut.

The second hydrocarbon cut has an initial boiling temperature of approximately 160°C and the final boiling temperature of between 260 and 340°C and comprises a fraction of at least 10% by weight of hydrocarbons having a temperature boiling temperature between 220°C and its final boiling temperature.

This second hydrocarbon cut is a light oil cut from a catalytic cracking unit (LCO or “Light Cycle Oil” according to Anglo-Saxon terminology).

This second cut has an olefin content lower than that of the first cut and a total sulfur content higher than that of the first cut.

• une première fraction comprenant des hydrocarbures ayant une gamme de températures d'ébullition comprise entre la température d'ébullition initiale du mélange et 160°C et dont la teneur en oléfines est comprise entre 20 et 80% poids de ladite première fraction, la première fraction étant choisie parmi une coupe essence oléfinique issue d'une unité de craquage catalytique, de vapocraquage, de cokéfaction, de viscoréduction, la première fraction représentant entre 30 et 70 % poids du mélange, et
• une seconde fraction comprenant des hydrocarbures ayant une gamme de températures d'ébullition comprise entre 160°C et la température d'ébullition finale du mélange, la seconde fraction étant une huile légère issue d'une unité de craquage catalytique.

Thus the treated hydrocarbon mixture has an initial boiling temperature of between 35°C and 100°C and a final boiling temperature of between 260°C and 340°C and a total sulfur content of between 30 and 10,000. ppm weight. The treated mixture consists of:

• a first fraction comprising hydrocarbons having a boiling temperature range between the initial boiling temperature of the mixture and 160°C and whose olefin content is between 20 and 80% by weight of said first fraction, the first fraction being chosen from an olefinic gasoline cut from a catalytic cracking, steam cracking, coking, visbreaking unit, the first fraction representing between 30 and 70% by weight of the mixture, and
• a second fraction comprising hydrocarbons having a boiling temperature range between 160°C and the final boiling temperature of the mixture, the second fraction being a light oil from a catalytic cracking unit.

According to the invention, said second fraction comprises at least 10% by weight of hydrocarbons having a boiling temperature range between 220°C and the final boiling temperature of the mixture.

The first hydrodesulfurization step converts part of the sulfur present in the mixture into hydrogen sulfide (H ₂ S). It consists of passing the mixture of hydrocarbons to be treated in the presence of hydrogen (supplied via line 4), over a hydrodesulphurization catalyst, at a temperature between 200°C and 400°C, preferably between 250°C. C and 340°C and at a pressure of between 1 and 10 MPa, preferably between 1.5 and 4 MPa. The liquid space velocity is generally between 1 and 10 h ^-1 , preferably between 2 and 5 h ^-1 and the H ₂ /HC ratio is between 50 Nliters/liter (l/l) and 500 Nliters/liter, preferably between 100 Nliters/liter and 450 Nliters/liter, and more preferably between 150 Nliters/liter and 400 Nliters/liter. The H ₂ /HC ratio is the ratio between the volume flow rate of hydrogen under 1 atmosphere and at 0°C and the volume flow rate of hydrocarbons.

The effluent resulting from this hydrodesulfurization step withdrawn by line 5 comprises the mixture of partially desulfurized hydrocarbons, the residual hydrogen and the H ₂ S produced by decomposition of sulfur compounds. This hydrodesulfurization step is carried out for example in a fixed bed or moving bed reactor.

The catalyst used during the first hydrodesulfurization step of the hydrodesulfurization process according to the invention comprises an active metal phase deposited on a support, said active phase comprising at least one metal from group VIII of the periodic table of elements (groups 8, 9 and 10 according to the new notation of the periodic classification of the elements: Handbook of Chemistry and Physics, 76th edition, 1995-1996 ) and at least one metal from group VIB of the periodic table of elements (group 6 according to the new notation of the periodic table of elements: Handbook of Chemistry and Physics, 76th edition, 1995-1996 ). Preferably, the active phase of said catalyst further comprises phosphorus. The catalyst of the first hydrodesulfurization step may also additionally contain one or more organic compounds.

Generally, the content of metal(s) from group VIB in said catalyst of the first hydrodesulfurization step is between 4 and 40% by weight of oxide(s) of metal(s) from group VIB, preferably between 8 and 35% by weight of metal oxide(s) from group VIB, very preferably between 10 and 30% by weight of metal oxide(s) from group VIB relative to the total weight of the catalyst. Preferably, the Group VIB metal is molybdenum or tungsten or a mixture of these two elements, and more preferably the Group VIB metal consists solely of molybdenum or tungsten. The Group VIB metal is most preferably molybdenum.

In general, the content of metal(s) from Group VIII in said catalyst of the first hydrodesulfurization step is between 1.5 and 9% by weight of oxide(s) of metal(s) from Group VIII, of preferably between 2 and 8% by weight of oxide(s) of metal(s) from Group VIII relative to the total weight of the catalyst. Preferably, the group VIII metal is a non-noble metal from group VIII of the periodic table of elements. Very preferably, said Group VIII metal is cobalt or nickel or a mixture of these two elements, and more preferably the Group VIII metal consists solely of cobalt or nickel. The Group VIII metal is most preferably cobalt.

The molar ratio of metal(s) from group VIII to metal(s) from group VIB in the catalyst in oxide form is between 0.1 and 0.8, very preferably between 0.2 and 0.6, and so even more preferred between 0.3 and 0.5.

When the catalyst contains phosphorus, the phosphorus content of the catalyst of the first hydrodesulfurization step is preferably between 0.1 and 20% by weight of P ₂ O ₅ , more preferably between 0.2 and 15% by weight of P ₂ O ₅ , very preferably between 0.3 and 10% by weight of P ₂ O ₅ relative to the total weight of the catalyst.

The molar ratio of phosphorus to metal(s) of group VIB in the catalyst of the first hydrodesulfurization step is greater than or equal to 0.05, preferably greater than or equal to 0.1, more preferably between 0.15 and 0.6, even more preferably between 0.15 and 0.5.

The support of the catalyst of the first hydrodesulfurization step on which the active phase is deposited is advantageously formed of at least one porous solid in oxide form chosen from the group consisting of aluminas, silicas, silica-alumina or even titanium or magnesium oxides used alone or mixed with alumina or silica-alumina. It is preferably chosen from the group consisting of silicas, transition aluminas and silica-alumina. More preferably, said support consists solely of a transition alumina or of a mixture of transition aluminas. The specific surface area of the catalyst is generally between 100 and 400 m ² /g, preferably between 150 and 300 m ² /g. The catalyst of the first hydrodesulfurization step is advantageously in the form of beads, extrudates, pellets, or irregular and non-spherical agglomerates whose specific shape can result from a crushing step. Very advantageously, said support is in the form of balls or extrudates.

The catalyst of the first hydrodesulfurization step is preferably used at least partly in its sulfurized form. Sulfurization consists of passing a charge containing at least one sulfur compound, which once decomposed leads to the fixation of sulfur on the catalyst. This charge can be gaseous or liquid, for example hydrogen containing H ₂ S, or a liquid containing at least one sulfur compound. The sulfurization step can be carried out in situ, that is to say within the process according to the invention, or ex situ, that is to say in a unit dedicated to the sulfurization of catalysts.

According to the invention, the process comprises a step where the H ₂ S is at least partly eliminated from the effluent obtained at the end of the first hydrodesulfurization step. This step can be carried out using any techniques known to those skilled in the art. It can be carried out directly in the conditions in which the effluent is found at the end of this step or after the conditions have been changed in order to facilitate the elimination of at least part of the H ₂ S. As possible technique, we can for example cite a gas/liquid separation (where the gas concentrates in H ₂ S and the liquid is depleted in H ₂ S), an effluent stripping step, an amine washing step, a capture of H ₂ S by an absorbent mass operating on the gaseous or liquid effluent, separation of H ₂ S from the gaseous or liquid effluent through a membrane. A combination of one or more of the possibilities presented previously is also possible, such as for example a gas/liquid separation following which the liquid effluent is sent to a stripping column while the gaseous effluent is sent to a stage of amine wash.

In reference to the figure 1 , the effluent from the reactor of the first hydrodesulphurization stage is sent via line 5 to a stripping column 6 which makes it possible to separate at the top of the column a gaseous flow 7 containing hydrogen and H ₂ S and at the bottom an effluent containing a mixture of hydrocarbons 8 partially desulfurized and freed of H ₂ S.

Surprisingly, the inventors have found that the presence of a distillate cut mixed with a gasoline cut has a positive effect on reducing the formation of recombination mercaptans in the partially desulfurized effluent.

Generally, at the end of the H ₂ S separation step, a mixture of hydrocarbons is obtained having a total sulfur content of between 100 and 1000 ppm by weight, preferably between 200 and 500 ppm by weight.

In reference to the figure 1 , the effluent comprising the partially desulfurized hydrocarbon mixture is treated in an additional hydrodesulfurization step (HDS) aimed at improving the final desulfurization rate. This second step aims to transform the refractory sulfur compounds present in the mixture and which are essentially provided by the second cut implemented in the process according to the invention. To this end, the effluent is sent via line 8 to a hydrodesulfurization reactor 9 and is brought into contact with a hydrodesulfurization catalyst in the presence of hydrogen supplied by line 10.

• une température comprise entre 205°C et 500°C, de préférence entre 250°C et 320°C ;
• une pression comprise entre 1 et 3 MPa, de préférence entre 1,5 et 2,5 MPa
• une vitesse spatiale liquide est généralement comprise entre 1 et 10 h^-1, de préférence entre 2 et 5 h^-1,
• un rapport H₂/HC est compris entre 50 Nlitres/litre (l/l) et 500 Nlitres/litre, de préférence entre 100 Nlitres/litre et 450 Nlitres/litre, et de façon plus préférée entre 150 Nlitres/litre et 400 Nlitres/litre. Le rapport H₂/HC est le rapport entre le débit d'hydrogène sous 1 atmosphère et à 0°C et le débit d'hydrocarbures.

The operating conditions for the second hydrodesulfurization step are as follows:

• a temperature between 205°C and 500°C, preferably between 250°C and 320°C;
• a pressure between 1 and 3 MPa, preferably between 1.5 and 2.5 MPa
• a liquid space velocity is generally between 1 and 10 h ^-1 , preferably between 2 and 5 h ^-1 ,
• an H ₂ /HC ratio is between 50 Nliters/liter (l/l) and 500 Nliters/liter, preferably between 100 Nliters/liter and 450 Nliters/liter, and more preferably between 150 Nliters/liter and 400 Nliters /liter. The H ₂ /HC ratio is the ratio between the hydrogen flow rate under 1 atmosphere and at 0°C and the hydrocarbon flow rate.

According to the invention, the temperature of the second HDS stage is higher than that of the first HDS stage, preferably higher by at least 5°C and even more preferably by at least 10°C. Advantageously, the second hydrodesulfurization step uses a catalyst having a selectivity in hydrodesulfurization with respect to the hydrogenation of olefins greater than the catalyst of the first hydrodesulfurization step.

The catalyst suitable for this second hydrodesulfurization step comprises at least one metal from group VIII (groups 8, 9 and 10 according to the new notation of the periodic classification of the elements: Handbook of Chemistry and Physics, 76th edition, 1995-1996 ) and at least one metal from group VIB (group 6 according to the new notation of the periodic classification of the elements: Handbook of Chemistry and Physics, 76th edition, 1995-1996 ) on an appropriate support.

The Group VIII metal content expressed as oxide is generally between 0.5 and 15% by weight, preferably between 1 and 10% by weight relative to the total weight of catalyst.

The metal content of group VIB is generally between 1.5 and 60% by weight, preferably between 3 and 50% by weight per contribution to the total weight of catalyst.

The Group VIII metal is preferably cobalt and the Group VIB metal is generally molybdenum or tungsten.

Preferably, the catalyst for the second hydrodesulfurization step further comprises phosphorus. The phosphorus content of said catalyst is preferably between 0.1 and 20% by weight of P ₂ O ₅ , more preferably between 0.2 and 15% by weight of P ₂ O ₅ , very preferably between 0.3 and 10% by weight of P ₂ O ₅ relative to the total weight of the catalyst.

Preferably, the catalyst further comprises one or more organic compounds.

The catalyst support is usually a porous solid, such as for example alumina, silica-alumina or other porous solids, such as for example magnesia, silica or titanium oxide, alone or in combination. mixture with alumina or silica-alumina.

To minimize the hydrogenation of the olefins present in heavy gasoline, it is advantageous to preferably use a catalyst in which the density of molybdenum, expressed in weight% of MoOs per unit surface area of catalyst, is greater than 0.07 and preferably greater than 0.10. The catalyst according to the invention preferably has a specific surface area less than 200 m ² /g, more preferably less than 180 m ² /g, and very preferably less than 150 m ² /g.

• CoO comprise entre 1 et 6% poids par rapport au poids total de catalyseur;
• MoOs comprise entre 3 et 15% poids par rapport au poids total de catalyseur;
• P₂O₅ comprise entre 0 et 3 % poids par rapport au poids total de catalyseur;
• une surface spécifique de catalyseur inférieure à 150 m²/g, de préférence comprise entre 50 et 150 m²/g.

In a preferred embodiment, the selective catalyst for the second hydrodesulfurization step comprises cobalt, molybdenum and optionally phosphorus deposited on an alumina support and having the following contents:

• CoO between 1 and 6% by weight relative to the total weight of catalyst;
• MoOs between 3 and 15% by weight relative to the total weight of catalyst;
• P ₂ O ₅ between 0 and 3% by weight relative to the total weight of catalyst;
• a specific catalyst surface area of less than 150 m ² /g, preferably between 50 and 150 m ² /g.

The catalyst of the second hydrodesulfurization step is preferably used at least partly in its sulfurized form. Sulfurization consists of passing the charge containing at least one sulfur compound, which once decomposed leads to the fixation of sulfur on the catalyst. This charge can be gaseous or liquid, for example hydrogen containing H ₂ S, or a liquid containing at least one sulfur compound. The sulfurization step can be carried out in situ, that is to say within the process according to the invention, or ex situ, that is to say in a unit dedicated to the sulfurization of catalysts.

After the second hydrodesulfurization step, the desulfurized effluent has a total sulfur content generally less than 50 ppm by weight, preferably less than 30 ppm by weight and has a mercaptan content generally less than 10 ppm by weight.

In accordance with the invention and as shown in figure 1 , the effluent which is withdrawn from the second hydrodesulfurization reactor 9 is sent via line 11 to a separation unit 12. Preferably, before being separated, the effluent from the reactor is first sent to a balloon gas/liquid separation allowing the separation of a gas rich in H ₂ S from the liquid effluent. This liquid effluent is then sent to a stabilization column in order to eliminate the last traces of solubilized H ₂ S and produce a stabilized column bottom product, that is to say whose vapor pressure has been corrected by elimination of the lightest hydrocarbon compounds. The gas/liquid separation and stabilization steps are classic steps for those skilled in the art and are not shown on the figure 1 .

The separation or distillation step consists of separating the stabilized effluent containing the mixture of hydrocarbons into at least two hydrocarbon cuts, namely a cut light hydrocarbons and a heavy hydrocarbon cut both desulfurized. Preferably, the cutting point is generally between 160°C and 220°C, limits included. In reference to the figure 1 , the separation unit used is a distillation column configured to separate at the top of the column a light desulphurized cut 13, equivalent to a gasoline cut and at the bottom a heavy desulphurized cut 14 equivalent to a distillate cut. The gasoline cut is sent to the gasoline pool and the desulfurized distillate cut is sent to the diesel, kerosene or fuel oil pool.

Preferably, the sulfur content in the desulfurized light cut (or gasoline cut) is less than 50 ppm by weight, preferably less than 30 ppm by weight and even more preferably less than 10 ppm by weight. Preferably, the sulfur content in the desulfurized heavy cut (or distillate cut) is less than 50 ppm by weight, optionally less than 30 ppm by weight or even less than 10 ppm by weight.

It is also possible to carry out stabilization and distillation concomitantly in a column with side withdrawal and total external reflux. The distillate cut is recovered at the bottom, the gasoline cut is withdrawn laterally several trays below the top tray while the lightest compounds are eliminated at the top of the column in the gaseous effluent.

Alternatively, the effluent from the stabilization column containing the desulfurized hydrocarbon mixture is separated into three cuts. In this case, the two cutting points will generally be around 160°C and around 220°C. The three hydrocarbon cuts have a total sulfur content of less than 50 ppm by weight, preferably less than 30 ppm by weight and even more preferably less than 10 ppm by weight.

Surprisingly, the inventors have found that the implementation of two successive stages of hydrodesulfurization with an intermediate stage of elimination of H ₂ S on a mixture of a gasoline cut and middle distillate ultimately makes it possible to provide a desulphurized gasoline with a low mercaptan content and without significant loss of octane number and this without requiring particularly severe hydrodesulphurization conditions which are generally accompanied by significant hydrogenation of the mono-olefinic hydrocarbon compounds. Indeed it is known that the loss of octane linked to the hydrogenation of mono-olefins during the hydrodesulfurization stages is all the greater as the targeted sulfur content is low, that is to say when the we seek to thoroughly eliminate the sulfur compounds present in the load.

According to an alternative embodiment of the method according to the invention also represented in figure 1 , a first cut of gasoline type hydrocarbons is sent to a pretreatment reactor 15 before being mixed with a second cut of hydrocarbons. As indicated above, the hydrocarbon feedstock is preferably a catalytically cracked gasoline cut which generally contains diolefins at a content of between 0.1 and 3% by weight. The pretreatment consists of a step of selective hydrogenation of the diolefins into corresponding mono-olefins, which is carried out in the presence of a catalyst and hydrogen. The catalyst for selective hydrogenation of diolefins suitable for pretreatment comprises at least one metal from group VIB and at least one metal from group VIII deposited on a porous support described in the patent applications FR 2 988 732 And EP 2 161 076 of the plaintiff. The catalytic selective hydrogenation reaction is generally carried out in the presence of hydrogen, at a temperature between 80°C and 220°C, and preferably between 90°C and 200°C, with a liquid space velocity (LHSV) comprised between 1 and 10 h ^-1 , the unit of liquid space velocity being the liter of charge per liter of catalyst and per hour (l/lh). The operating pressure is between 0.5 MPa and 5 MPa, preferably between 1 and 4 MPa.

Generally, the gasoline produced contains less than 0.5% by weight of diolefins, and preferably less than 0.25% by weight of diolefins.

Advantageously and as indicated on the figure 1 , the first pretreated hydrocarbon cut is directed via line 16 to a separation column 17 (splitter according to Anglo-Saxon terminology) which is designed to split said pretreated charge respectively into a light fraction C5 ^- and a heavy fraction C6+. The light fraction is advantageously sent to the gasoline pool via line 18, while the heavy C6+ fraction entering line 1 is hydrodesulfurized by the process described above, that is to say mixed with a cut of middle distillate at low olefin content.

Examples Example 1 (comparative)

An α hydrodesulfurization catalyst is obtained by impregnation “without excess solution” of a transition alumina in the form of beads with a specific surface area of 130 m ² /g and a pore volume of 0.9 ml/g, by a aqueous solution containing molybdenum and cobalt in the form of ammonium heptamolybdate and cobalt nitrate. The catalyst is then dried and calcined in air at 500°C. The cobalt and molybdenum content of the α catalyst is 3% by weight of CoO and 10% by weight of MoOs.

50 ml of the α catalyst are placed in a tubular fixed-bed hydrodesulfurization reactor. The catalyst is first sulfurized by treatment for 4 hours under a pressure of 3.4 MPa at 350°C, in contact with a charge consisting of 2% by weight of sulfur in the form of dimethyldisulfide in n-heptane.

The treated feed C is a catalytic cracked gasoline whose initial boiling point is 61°C and the final point is 162°C. Its sulfur content is 765 ppm by weight and its bromine index (IBr) is 75.9 g/100 g, which corresponds approximately to 42% by weight of olefins.

This charge C is treated with the catalyst α, under a pressure of 2 MPa, a volume ratio of hydrogen to charge to be treated (H ₂ /HC) of 300 NI/l and a VVH of 4 h ^-1 . After treatment, the effluent is cooled and the hydrogen rich in H ₂ S is separated from the liquid gasoline, and the gasoline is subjected to a stripping treatment by injection of a flow of hydrogen in order to eliminate the residual traces of H ₂ S dissolved in the desulfurized gasoline.

Table 1 shows the influence of the temperature involved on the desulfurization rates and the RON index of the desulfurized effluents. Table 1 Analysis of desulfurized gasoline Temperature in the hydrodesulfurization reactor, 285 °C Temperature in the hydrodesulfurization reactor, 295 °C Mercaptans, ppm weight 16 7 Total sulfur, ppm weight 25 12 Desulfurization rate, % 96.7 98.4 RON loss 6.9 8.4

It is noted that when the temperature used increases, the rate of desulfurization is improved but at the cost of an increase in the rate of hydrogenation of the olefins.

Example 2 (comparative)

50 ml of a β hydrodesulfurization catalyst in the form of extrudates with a specific surface area of 180 m ² /g whose content (weight of oxide(s) relative to the total weight of the catalyst) in cobalt, molybdenum and phosphorus are respectively 4.4% by weight of CoO and 21.3% by weight of MoO ₃ and 6.0% by weight of P ₂ O ₅ are placed in a fixed bed tubular hydrodesulfurization reactor. The catalyst is first sulfurized by treatment for 4 hours under a pressure of 2 MPa at 350°C, in contact with a filler consisting of 2% by weight of sulfur in the form of dimethyldisulfide in n-heptane.

The treated feed D has an initial boiling point of 160°C and an end point of 269°C. Its sulfur content is 5116 ppm by weight and its bromine index (IBr) is 19.5 g/100 g which corresponds approximately to 10% by weight of olefins. The fraction of charge D having a boiling point between 220°C and 269°C is 26.3% by weight.

Charge D is treated with catalyst β, at a temperature of 300°C, under a pressure of 2 MPa, with a volume ratio of hydrogen to charge to be treated (H ₂ /HC) of 300 NI/I and a VVH of 4 h ^-1 . After treatment, the effluent is cooled, the hydrogen rich in H ₂ S is separated from the liquid effluent, and the effluent is subjected to a stripping treatment by injection of a flow of hydrogen in order to eliminate the residual traces of dissolved H ₂ S before being analyzed. Table 2 shows the desulfurization rate and the sulfur and mercaptan content of the desulfurized effluent. Table2 Analysis Mercaptans, ppm weight 12 Total sulfur, ppm weight 34 Desulfurization rate, % 99.3

Example 3 (comparative)

A charge E tested in Example 3 is a mixture containing 50% by weight of charge C and 50% by weight of charge D. The initial boiling point of the mixture is 61°C and the final point is 269°C. vs. Its sulfur content is 2512 ppm by weight and its bromine index (IBr) is 53.4 g/100 g which corresponds approximately to 29.2% by weight of olefins.

This charge E is first treated on the catalyst α, at a temperature of 330°C, under a pressure of 2 MPa, with a volume ratio of hydrogen to charge to be treated (H ₂ /HC) of 300 NI/I and a VVH from 4 a.m. ^-1 . After treatment, the effluent is cooled, the hydrogen rich in H ₂ S is separated from the liquid effluent, and the effluent is subjected to a stripping treatment by injection of a flow of hydrogen in order to eliminate the residual traces of dissolved H ₂ S.

The effluent is then separated into two cuts: a first cut (petrol cut) with a final boiling point of 160°C and a second cut with an initial point of 160°C. Table 3 Analysis ^1st cut ^2nd cut 61°C-160°C 160°C-269°C Mercaptans, ppm weight 6 8 Total sulfur, ppm weight 6 49 Desulfurization rate, % 99.2 99 RON loss 9.8 Not applicable

Example 4 (according to the invention)

The feed E used in Example 3 is treated in a first hydrodesulfurization step on the catalyst β, at a temperature of 260°C, under a pressure of 2 MPa, with a volume ratio of hydrogen to feed to be treated (H ₂ /HC) of 300 NI/I and a VVH of 4 h ^-1 . After treatment, the effluent from the first hydrodesulfurization step is cooled, the hydrogen rich in H ₂ S is separated from the liquid effluent, and the effluent is subjected to a stripping treatment by injection of a flow of hydrogen in order to eliminate residual traces of dissolved H ₂ S. The stripped effluent constitutes the feedstock F treated in the second hydrodesulfurization step.

The feedstock F is then treated in a second hydrodesulfurization step on the α catalyst, at a temperature of 280°C, under a pressure of 2 MPa, with a volume ratio of hydrogen to feedstock to be treated (H ₂ /HC) of 300. l/l and a VVH of 4 h ^-1 . After treatment, the effluent from the second hydrodesulfurization step is cooled, the hydrogen rich in H ₂ S is separated from the liquid effluent, and the effluent is subjected to a stripping treatment by injection of a flow of hydrogen in order to eliminate residual traces of dissolved H ₂ S.

The effluent from the second hydrodesulfurization stage is then separated into two cuts: a first cut (petrol cut) with a final boiling point of 160°C and a second cut with an initial point of 160°C. Table 4 References ^1st cut ^2nd cut 61°C-160°C 160°C-269°C Mercaptans, ppm weight 7 11 Total sulfur, ppm weight 9 42 Desulfurization rate, % 98.8 99.2 RON loss 5.9 Not applicable

Example 4 shows that it is possible, from a mixture of hydrocarbons comprising at least a first cut of hydrocarbons having a boiling temperature of between 61° and 160°C and whose olefin content is of 42% by weight and a second cut of hydrocarbons having a boiling point between 160° and 269°C of which the fraction having a boiling point greater than 220°C is 26.3%, to obtain two desulphurized cuts whose sulfur content are respectively less than 10 ppm by weight of sulfur for the desulphurized cut having a boiling temperature between 61°C and 160°C and less than 50 ppm by weight of sulfur for the desulphurized cut having a temperature of boiling between 160° and 269°C while limiting the loss of RON index linked in particular to the hydrogenation of part of the olefins present in the mixture.

Claims (12)

1. Process for the concomitant production of two hydrocarbon cuts having low sulfur contents starting from a mixture of hydrocarbons having a starting boiling point of between 35°C and 100°C and a final boiling point of between 260°C and 340°C and having a total sulfur content of between 30 and 10 000 ppm by weight, said mixture of hydrocarbons consists of:

   • a first fraction comprising hydrocarbons having a range of boiling points of between the initial boiling point of the mixture and 160°C and the content of olefins of which is between 20% and 80% by weight of said first cut, the first fraction being chosen from an olefinic petrol cut resulting from a catalytic cracking, steam cracking, coking or visbreaking unit, the first fraction representing between 30% and 70% by weight of the mixture, and

   • a second fraction comprising hydrocarbons having a range of boiling points of between 160°C and the final boiling point of the mixture, said second fraction comprising at least 10% by weight of hydrocarbons having a range of boiling points of between 220°C and the final boiling point of the mixture, the second fraction being a light oil resulting from a catalytic cracking unit, the process comprising the following stages:

   a) in a first reactor, said mixture consisting of said first fraction and of said second fraction is treated in a first hydrodesulfurization stage in the presence of hydrogen and of a catalyst comprising at least one metal from group VIII, at least one metal from group VIB and a support, the content of metal(s) from group VIII being of between 1.5% and 9% by weight of oxide(s) of metal(s) from group VIII and the content of metal(s) from group VIB being of between 4% and 40% by weight of oxide(s) of metal (s) from group VIB, the molar ratio of metal(s) from group VIII to metal(s) from group VIB in the catalyst in oxide form is between 0.1 and 0.8, the first hydrodesulfurization stage being carried out at a temperature of between 200°C and 400°C, at a pressure of between 1 and 10 MPa, with a liquid space velocity of between 0.1 and 10 h^-1 and with a volume of hydrogen/volume of mixture of hydrocarbons ratio of between 50 and 500 Slitre/litre;

   b) the hydrogen sulfide is removed from the partially desulfurized effluent resulting from stage a);

   c) in a second reactor, the partially desulfurized mixture resulting from stage b) is treated in a second hydrodesulfurization stage in the presence of hydrogen and of a catalyst comprising at least one element from group VIII, at least one element from group VIB and a support, the content of metal(s) from group VIII being of between 0.5% and 15% by weight of oxide(s) of metal(s) from group VIII and the content of metal (s) from group VIB being of between 1.5% and 60% by weight of oxide(s) of metal(s) from group VIB, the second hydrodesulfurization stage being carried out at a temperature of between 205°C and 500°C, at a pressure of between 1 and 3 MPa, with a liquid space velocity of between 1 and 10 h^-1 and with a volume of hydrogen/volume of mixture ratio of between 50 and 500 Slitre/litre, the temperature of the second hydrodesulfurization stage c) being greater than that of the first hydrodesulfurization stage a); and

   d) the desulfurized mixture resulting from stage c) is fractionated into at least two light and heavy cuts of hydrocarbons, the light cut of hydrocarbons having an initial boiling point of between 35°C and 100°C and a final boiling point of between 160°C and 220°C and the total sulfur content of which is less than 50 ppm by weight and the heavy cut of hydrocarbons having an initial boiling point of between 160°C and 220°C and a final boiling point of between 260°C and 340°C.
2. Process according to Claim 1, in which the catalyst of stage a) comprises a metal from group VIII chosen from nickel and cobalt and a metal from group VIB chosen from molybdenum and tungsten.
3. Process according to Claim 2, in which the catalyst of stage a) comprises phosphorus.
4. Process according to one of the preceding claims, in which the catalyst of stage c) comprises a metal from group VIII chosen from nickel and cobalt and a metal from group VIB chosen from molybdenum and tungsten.
5. Process according to Claim 4, in which the catalyst of stage c) additionally comprises phosphorus.
6. Process according to one of the preceding claims, in which the first fraction of hydrocarbons is a petrol cut resulting from a catalytic cracking unit.
7. Process according to Claim 6, in which the first fraction of hydrocarbons is a cut of C6⁺ hydrocarbons obtained by distillation of a petrol cut resulting from a catalytic cracking unit.
8. Process according to Claim 7, in which, before the distillation stage, the petrol cut was subjected to a stage of selective hydrogenation of the diolefins present in said petrol cut.
9. Process according to one of the preceding claims, in which the temperature of stage c) is greater by at least 5°C than the temperature of stage a).
10. Process according to one of the preceding claims, in which the temperature of stage c) is greater by at least 10°C than the temperature of stage a).
11. Process according to Claims 6 and 8, in which, before stage a), a stage of mixing the first and second cuts of hydrocarbons is carried out upstream of the reactor of the first hydrodesulfurization stage.
12. Process according to Claims 6 and 8, in which a mixing of the first and second cuts of hydrocarbons is carried out in the reactor of the first hydrodesulfurization stage.

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