METHOD FOR THE PRODUCTION OF LOW-SULFUR AND MERCAPTANE GASOLINE

Abstract

The present application relates to a method for treating a gasoline containing sulfur-containing compounds and olefins, comprising the following steps: a) a step of hydrodesulfurization in the presence of a catalyst comprising an oxide support and an active phase comprising a group VIB metal and a group VIII metal, b) a step of hydrodesulfurization at a higher temperature than that of step a) and in the presence of a catalyst comprising an oxide support and an active phase constituted of at least one group VIII metal, c) a step of separating the H2S formed, d) a step of hydrodesulfurization with a low hydrogen / feedstock ratio and in the presence of a hydrodesulfurization catalyst comprising an oxide support and an active phase comprising a group VIB metal and a group VIII metal or an active phase constituted of at least one group VIII metal, e) a step of separating the H2S formed.

Description

[0001] PROCESS FOR PRODUCING A LOW-SULFUR AND LOW-SPOIL GASOLINE

[0002] MERCAPTANS

[0003] technical field

[0004] The present invention relates to a process for producing gasoline with a low sulfur and mercaptan content.

[0005] State of the art

[0006] The production of fuels that meet new environmental standards requires a significant reduction in their sulfur content.

[0007] It is also known that conversion fuels, and more particularly those from catalytic cracking, which can represent 30 to 50% of the fuel pool, have high levels of mono-olefins and sulfur.

[0008] The sulfur present in gasoline is therefore attributable, to the tune of nearly 90%, to gasoline produced by catalytic cracking processes, which will be referred to hereafter as FCC gasoline (Fluid Catalytic Cracking, according to Anglo-Saxon terminology, which can be translated as fluidized bed catalytic cracking). FCC gasoline thus constitutes the preferred feedstock for the process of the present invention.

[0009] Among the possible methods for producing low-sulfur fuels, the one that has been most widely adopted involves specifically treating high-sulfur gasoline base oils using catalytic hydrodesulfurization processes in the presence of hydrogen. Traditional processes desulfurize gasoline non-selectively by hydrogenating a large portion of the monoolefins, resulting in a significant loss of octane rating and high hydrogen consumption. More recent processes, such as the process

[0010] Prime G+ (trademark) allows for the desulfurization of olefin-rich cracked gasoline while limiting the hydrogenation of monoolefins and consequently the resulting octane loss and high hydrogen consumption. Such processes are described, for example, in patent applications EP1077247 and EP1 174485.

[0011] The residual sulfur compounds generally present in desulfurized gasoline can be separated into two distinct families: unconverted refractory sulfur compounds present in the feedstock, and sulfur compounds formed in the reactor by secondary reactions known as recombination reactions. Among this latter family of sulfur compounds, the major compounds are mercaptans resulting from the addition of hydrogen sulfide (H₂S) formed in the reactor to the monoolefins present in the feedstock. Mercaptans, with the chemical formula R-SH, where R is an alkyl group, are also called recombination mercaptans. Their formation or decomposition is governed by the thermodynamic equilibrium of the reaction between monoolefins and hydrogen sulfide to form recombination mercaptans. An example is illustrated by the following reaction:

[0012] The sulfur contained in recombination mercaptans generally represents between 20% and 80% by weight of the residual sulfur in desulfurized gasoline.

[0013] The formation of recombination mercaptans is described in particular in US patent 6231754 and patent application W001 / 40409, which teach various combinations of operating conditions and catalysts for limiting the formation of recombination mercaptans. Other solutions to the problem of recombination mercaptan formation are based on the treatment of partially desulfurized gasoline to extract these recombination mercaptans. Some of these solutions are described in patent applications WO02 / 28988 and WO01 / 79391. Other solutions are described in the literature for desulfurizing cracking fuels using a combination of hydrodesulfurization steps and removal of recombination mercaptans by reaction to thioethers or disulfides (also called sweetening or sweetening according to Anglo-Saxon terminology) (see for example US7799210, US6960291, US2007114156, EP2861094).Document WO2018 / 096063 describes a process for producing low sulfur and mercaptan hydrocarbons using a high gas flow / feed ratio.

[0014] Obtaining ultra-low sulfur gasoline, typically below 10 ppm by weight, therefore requires the removal of at least some of the recombination mercaptans. Almost all countries have a very low mercaptan specification for fuels (typically below 10 ppm sulfur from RSH (mercaptan content measured by potentiometry, ASTM D3227 method)). Other countries have adopted a "Doctor Test" measurement to quantify mercaptans with a negative specification to be met (ASTM D4952 method).

[0015] Thus, in some cases, it appears that the most restrictive specification, because it is the most difficult to achieve without harming the octane rating, is the mercaptan specification and not the total sulfur specification.

[0016] When gasoline is treated by a two-stage reactor sequence without hhS removal between the two stages, as described in document EP1077247, the first stage, also called the selective HDS stage, generally aims to achieve deep desulfurization of the gasoline with minimal olefin saturation (and no aromatic loss), leading to maximum octane retention. The catalyst used is generally a C0M0 type catalyst. During this stage, new sulfur compounds are formed by recombination of the hhS from the desulfurization and the olefins: the recombination mercaptans.

[0017] The second stage generally aims to minimize the amount of recombination mercaptans. To achieve this, the gasoline is treated in a hydrodesulfurization reactor, also called a finishing reactor, using a catalyst typically based on nickel. This catalyst exhibits virtually no olefin hydrogenation activity and is capable of reducing the amount of recombination mercaptans. The temperature is generally higher in the finishing reactor to thermodynamically promote mercaptan removal. In practice, a furnace is therefore placed between the two reactors to raise the temperature of the second reactor higher than that of the first. Another way to reduce recombination mercaptans in the second reactor is to increase the ratio between the hydrogen flow rate and the feed flow rate, also referred to as the H2 / HC ratio.Increasing the H2 / HC ratio in the finishing step allows, through dilution, a decrease in the partial pressure of hhS (pphhS) formed by hydrodesulfurization during the selective HDS step. This reduction in the partial pressure of H2S promotes the elimination of recombination mercaptans through the reaction between olefins and H2S (thermodynamic equilibrium).

[0018] Therefore, increasing the temperature and / or the H2 / HC ratio can reduce the content of recombination mercaptans in the finishing stage. However, the temperature and / or the H2 / HC ratio cannot be increased indefinitely. Indeed, excessively high temperatures in the finishing stage cause gasoline cracking and catalyst coking, thus reducing the catalyst cycle time. Similarly, a very high hydrogen injection rate relative to the feed rate represents an additional hydrogen cost for the refiner. Furthermore, olefin hydrogenation reactions can occur. Therefore, other methods must be found to reduce the amount of recombination mercaptans, particularly when the original gasoline has a high sulfur content.

[0019] Summary of the invention

[0020] One aim of the present invention is to propose a process for treating gasoline, which makes it possible to reduce the mercaptan content of said gasoline while limiting as much as possible the loss of octane and the consumption of reagents such as hydrogen.

[0021] The present invention proposes a process for treating gasoline containing sulfur compounds using a sequence of two reactors without removing hhS between the two stages, followed by a separation step of the hhS formed during these stages and an additional hydrodesulfurization step carried out under very mild conditions. More particularly, the invention relates to a process for treating gasoline containing sulfur compounds, olefins, and diolefins, the process comprising at least the following steps:

[0022] a) In at least one reactor, gasoline, hydrogen, and a hydrodesulfurization catalyst comprising an oxide support and an active phase comprising a metal from group VIB and a metal from group VIII are brought into contact 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 1 and a ratio between the hydrogen flow rate expressed in normal m 3 per hour and the flow rate of the load to be processed expressed in m 3 per hour under standard conditions between 100 Nm 3 / m 3 and 600 Nm 3 / m 3, in order to convert at least part of the sulfur compounds into H2S, b) the effluent from step a) without removal of the hhS formed, hydrogen, and a hydrodesulfurization catalyst comprising an oxide support and an active phase consisting of at least one metal from group VIII are brought into contact in at least one reactor, at a temperature between 280 and 400°C, at a pressure between 0.5 and 5 MPa, with a space velocity between 1 and 10 h 1 and a ratio between the hydrogen flow rate expressed in normal m 3 per hour and the flow rate of the load to be processed expressed in m 3 per hour under standard conditions between 100 and 600 Nm 3 / m 3 said temperature of step b) being higher than the temperature of step a),

[0023] c) a separation step is carried out for the h₂S formed and present in the effluent from step b), d) the H₂S-depleted effluent from step c) is contacted in at least one reactor 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 or an active phase consisting of at least one metal from group VIII, at a temperature between 150 and 330°C, at a pressure between 0.5 and 5 MPa, with a space velocity between 0.5 and 10 fr 1and a ratio between the hydrogen flow rate and the feed flow rate to be treated lower than that of step a), e) a separation step of the h^S formed and present in the effluent from step d) is carried out. It has in fact been found surprisingly that a specific sequence of different hydrodesulfurization steps using specific operating conditions for each in combination with specific catalysts for each hydrodesulfurization step combined with hhS separation steps allows operation under conditions which are thermodynamically favorable to the elimination of recombination mercaptans, and therefore leads to a sufficient conversion of recombination mercaptans.

[0024] Indeed, implementing hydrodesulfurization steps a) and b), with step b) being carried out under more severe operating conditions and in the presence of a catalyst based solely on a Group VIII metal, allows for a high overall level of hydrodesulfurization. The residual sulfur compounds in the effluent from step b) are essentially recombination mercaptans. From a thermodynamic equilibrium perspective, separation step c) favors the decomposition of recombination mercaptans and thus their removal in step d). In fact, the recombination mercaptans remaining in the effluent after step c) are relatively easy to hydrodesulfurize compared to the more refractory compounds removed in step b). The remaining recombination mercaptans can therefore be hydrodesulfurized in step d) under relatively mild operating conditions.Thus, the process according to the invention makes it possible to produce a gasoline with a specification of low sulfur and mercaptan content without requiring a severe and costly hydrodesulfurization finishing step while limiting the loss of octane.

[0025] Another advantage of the process according to the invention is that it allows for a very low mercaptan content (e.g., less than 10 ppm sulfur by weight) in the final desulfurized gasoline with much less stringent operating conditions for step b) of hydrodesulfurization (e.g., a significant reduction in temperature and / or operating pressure) than those described for the finishing step of the process according to

[0026] EP1077247, which has the effect of limiting octane loss, increasing the lifespan of the hydrodesulfurization catalyst, and also reducing energy consumption. Another advantage of the process according to the invention is that it can easily be implemented on existing units (remodeling or revamping, according to Anglo-Saxon terminology).

[0027] According to one embodiment of the invention, the catalyst in step a) comprises alumina and an active phase comprising cobalt, molybdenum, and optionally phosphorus, said catalyst containing a cobalt oxide content, in the form of CoO, by weight relative to the total weight of the catalyst, of between 0.1 and 10%, a molybdenum oxide content, in the form of M0O3, by weight relative to the total weight of the catalyst, of between 1 and 20%, a cobalt / molybdenum molar ratio of between 0.1 and 0.8, and a phosphorus oxide content, in the form of P2O5, by weight relative to the total weight of the catalyst of between 0.3 and 10% when phosphorus is present, said catalyst having a specific surface area of ​​between 30 and 180 m² 2 / g.

[0028] According to one variant, the catalyst in step b) consists of alumina and nickel, said catalyst containing a nickel oxide content, in the form of NiO, by weight relative to the total weight of catalyst, of between 5 and 20%, said catalyst having a specific surface area of ​​between 30 and 180 m² 2 / g.

[0029] According to one variant, the catalyst in step d) consists of alumina and a cobalt-molybdenum active phase, said catalyst containing a cobalt oxide catalyst content, in the form of CoO, by weight relative to the total weight of between 0.1 and 10%, a molybdenum oxide catalyst content, in the form of M0O3, by weight relative to the total weight of between 1 and 20%, a cobalt / molybdenum molar ratio of between 0.1 and 0.8, said catalyst having a specific surface area of ​​between 30 and 180 m² 2 / g.

[0030] According to another variant, the catalyst in step d) consists of alumina and nickel, said catalyst containing a nickel oxide content, in the form of NiO, by weight relative to the total weight of catalyst, of between 5 and 20%, said catalyst having a specific surface area of ​​between 30 and 180 m² 2 / g.

[0031] According to one variant, the temperature of step b) is at least 5°C higher than the temperature of step a). According to another variant, the temperature of step d) is at least 5°C lower than the temperature of step b).

[0032] According to one variant, the ratio of the hydrogen flow rate to the feed flow rate to be treated at the reactor inlet of step a) / ratio of the hydrogen flow rate to the feed flow rate to be treated at the reactor inlet of step d) is greater than or equal to 1.05. According to one variant, the separation steps c) and e) are carried out in a starter or stripping section.

[0033] According to one variant, before step a) a distillation step of the gasoline is carried out so as to fraction said gasoline into at least two cuts, light gasoline and heavy gasoline, and the heavy gasoline cut is treated in steps a), b), c), d) and e). According to another variant, before step a) and before any possible distillation step, the gasoline is contacted with hydrogen and a selective hydrogenation catalyst to selectively hydrogenate the diolefins contained in said gasoline into olefins.

[0034] According to one variant, the gasoline is a catalytically cracked gasoline. In the following, the chemical element groups are given according to the CAS classification.

[0035] (CRC Handbook of Chemistry and Physics, publisher CRC Press, editor-in-chief DR Lide, 81 èmeedition, 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 IUPAC classification.

[0036] The metal content is measured by X-ray fluorescence.

[0037] Description of the figures

[0038] Figure 1 illustrates an embodiment according to the invention.

[0039] Figure 2 illustrates a process according to the prior art.

[0040] Detailed description of the invention

[0041] Description of the load

[0042] The process according to the invention makes it possible to treat any type of gasoline fraction containing sulfur compounds and olefins, such as, for example, a fraction from a coking, visbreaking, steam cracking, or fluid catalytic cracking (FCC) unit. This gasoline may optionally be composed of a significant fraction of gasoline from other production processes such as atmospheric distillation (straight-run gasoline) or conversion processes (coking or steam cracking gasoline). This feedstock preferably consists of a gasoline fraction from a catalytic cracking unit.

[0043] The feedstock is a gasoline fraction containing sulfur compounds and olefins whose boiling point range typically extends from the boiling points of 2- or 3-carbon hydrocarbons (C2 or C3) up to 260°C, preferably from the boiling points of 2- or 3-carbon hydrocarbons (C2 or C3) up to 220°C, and more preferably from the boiling points of 5-carbon hydrocarbons up to 220°C. The process according to the invention can also process feedstocks having endpoints lower than those mentioned above, such as, for example, a C5-180°C fraction.

[0044] The sulfur content of gasoline fractions produced by fuel catalytic cracking (FCC) depends on the sulfur content of the feed processed by FCC, whether or not the FCC feed undergoes pretreatment, and the endpoint of the fraction. Generally, the sulfur content of an entire gasoline fraction, particularly those from FCC, is greater than 100 ppm by weight and most often greater than 500 ppm by weight. For gasolines with endpoints above 200°C, sulfur content is often greater than 1000 ppm by weight and can even reach values ​​of 4000 to 5000 ppm by weight in some cases. The feed processed by the method according to the invention can be a feed containing sulfur compounds with a sulfur content greater than 1000 ppm by weight, and often greater than 1500 ppm.

[0045] Furthermore, gasoline produced by fuel catalytic cracking (FCC) units contains, on average, between 0.5% and 5% by weight of diolefins, between 20% and 50% by weight of olefins, and between 10 ppm and 0.5% by weight of sulfur, of which generally less than 300 ppm of mercaptans. Description of the hydrodesulfurization step a)

[0046] The hydrodesulfurization step a) is implemented to reduce the sulfur content of the gasoline to be treated by converting the sulfur compounds into H2S which is then removed in step c). The hydrodesulfurization step a) consists of bringing the gasoline to be treated into contact with hydrogen, in one or more hydrodesulfurization reactors, containing one or more catalysts adapted to carry out hydrodesulfurization.

[0047] According to a preferred embodiment of the invention, step a) is implemented in order to carry out hydrodesulfurization in a selective manner, that is to say with a degree of hydrogenation of mono-olefins less than 80%, preferably less than 70% and most preferably less than 60%.

[0048] 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 within the reactor. If step a) of hydrodesulfurization is carried out in several reactors in series, the temperature of each reactor is generally at least 5°C higher, preferably at least 10°C higher, and most preferably at least 30°C higher than the temperature of the preceding reactor.

[0049] The operating pressure of this stage is generally between 1 and 4 MPa, and preferably between 1.5 and 3 MPa. The amount of catalyst used in each reactor is generally such that the ratio between the gasoline flow rate to be treated, expressed in m³, and the catalyst volume is such that the ratio of the fuel flow rate to be treated, expressed in m³, is approximately 1.5 to 3 MPa. 3 per hour under standard conditions, per m 3 The catalyst velocity (also called space velocity) is between 1 and 10 fr 1 and preferably between 2 and 8 am 1 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 load 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 By normal m 3 the quantity of gas in a volume of 1 m 3 at 0°C and 0.1 MPa.

[0050] The hydrogen required for this step can be fresh hydrogen or recycled hydrogen, preferably free of h₂S, or a mixture of fresh and recycled hydrogen. Fresh hydrogen is preferred.

[0051] The desulfurization rate of step a), 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 from step a) contains less than 100 ppm by weight of sulfur and preferably less than 50 ppm by weight of sulfur.

[0052] The catalyst used in step a) must exhibit good selectivity for hydrodesulfurization reactions compared to the hydrogenation reaction of olefins. The hydrodesulfurization catalyst in step a) comprises an oxide support and an active phase comprising a metal from group VIB and a metal from group VIII, and optionally phosphorus and / or an organic compound as described below.

[0053] The group VIB metal in the catalyst's active phase is preferably chosen from molybdenum and tungsten. The group VIII metal in the catalyst's active phase is preferably chosen from cobalt, nickel, and mixtures of these two elements. The catalyst's active phase is preferably chosen from the group formed by the combination of nickel-molybdenum, cobalt-molybdenum, and nickel-cobalt-molybdenum, and most preferably the active phase consists of cobalt and molybdenum.

[0054] The Group VIII metal content is between 0.1 and 10% by weight of Group VIII metal oxide relative to the total weight of the catalyst, preferably between 0.6 and 8% by weight, preferably between 2 and 7% by weight, most preferably between 2 and 6% by weight and even more preferably between 2.5 and 6% by weight.

[0055] The content of Group VI B metal is between 1 and 20 wt% of Group VI B metal oxide relative to the total weight of the catalyst, preferably between 2 and 18 wt%, and most preferably between 3 and 16 wt%. The molar ratio of Group VIII metal to Group VI B metal in the catalyst is generally between 0.1 and 0.8, preferably between 0.2 and 0.6.

[0056] Furthermore, the catalyst has a group VI B metal density, expressed as the number of atoms of said metal per unit area of ​​the catalyst, which is between 0.5 and 30 group VI B metal atoms per nm 2 of catalyst, preferably between 2 and 25, even more preferably between 3 and 15. The group VI B metal density, expressed as the number of group VI B metal atoms per unit area of ​​the catalyst (number of group VI B metal atoms per nm²). 2 of catalyst) is calculated, for example, from the following relationship: d (metal of the group

[0057] with :

[0058] X = % weight of metal from group VI B;

[0059] N A = Avogadro's number equal to 6.022 x 10 23 ; S = Specific surface area of ​​the catalyst (m 2 / g), measured according to ASTM D3663;

[0060] MM = Molar mass of the metal in group VIB (for example 95.94 g / mol for molybdenum).

[0061] For example, if the catalyst contains 20% by weight of molybdenum oxide M0O3 (i.e., 13.33% by weight of Mo) and has a specific surface area of ​​100 m² 2 / g, the density d(Mo) is equal to: ,

[0062] 8.4 Mo / iim atoms of catalyst

[0063]

[0064] Optionally, the catalyst may also contain phosphorus, generally between 0.3 and 10 wt% of P₂O₅ relative to the total catalyst weight, preferably between 0.5 and 5 wt%, and most preferably between 1 and 3 wt%. For example, the phosphorus in the catalyst is combined with Group VIB metal and possibly also with Group VIII metal in the form of heteropolyanions.

[0065] Furthermore, the phosphorus / (VIB group metal) molar ratio is generally between 0.1 and 0.7, preferably between 0.2 and 0.6, when phosphorus is present.

[0066] Preferably, the catalyst is characterized by a specific surface area between 5 and 400 m² 2 / g, preferably between 10 and 250 m 2 / g, preferably between 20 and 200 m 2 / g, preferably between 30 and 180 m 2 / g. The specific surface area is determined in the present invention by the BET method according to ASTM D3663, as described in the book Rouquerol F.; Rouquerol J.; Singh K. "Adsorption by Powders & Porous Soils; Principle, Methodology and Applications", Academy Press, 1999, for example using a Micromeritics™ Autopore III™ apparatus. The total pore volume of the catalyst is generally between 0.4 cm³ 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 ASTM D4284 with a wetting angle of 140°, as described in the same publication. The packed fill density (PLD) of the catalyst is generally between 0.4 and 0.7 g / mL, preferably between 0.45 and 0.69 g / mL. The PLD measurement consists of introducing the catalyst into a predetermined volumetric cylinder and then, by vibration, compacting it until a constant volume is obtained. The apparent density of the compacted product is calculated by comparing the introduced mass with the volume occupied after compaction.

[0067] Advantageously, the hydrodesulfurization catalyst, prior to sulfidation, 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 most preferably between 25 and 80 nm. The pore diameter is measured by mercury porosimetry according to ASTM D4284 with a wetting angle of 140°.

[0068] The catalyst can be in the form of small diameter extrudates, cylindrical or multilobed (trilobed, quadrilobed,...), or spheres.

[0069] The catalyst oxide support is usually a porous solid chosen from the group consisting of: aluminas, silica, silica-alumina, or titanium or magnesium oxides used alone or in mixtures with alumina or silica-alumina. It is preferably chosen from the group consisting of silica, the family of transition aluminas, and silica-alumina. Most preferably, the oxide support is essentially composed of alumina, that is, it comprises at least 51% by weight, preferably at least 60% by weight, most preferably at least 80% by weight, or even at least 90% by weight of alumina. It is preferably composed solely of alumina. Preferably, the catalyst oxide support is a "high temperature" alumina, i.e., one that contains theta, delta, kappa or alpha phase aluminas, alone or in mixtures, and less than 20% gamma, chi or eta phase alumina.

[0070] The catalyst may also further comprise at least one organic compound containing oxygen and / or nitrogen and / or sulfur before sulfidation.

[0071] A highly preferred embodiment of the invention involves implementing, in step a), a catalyst comprising alumina and an active phase comprising cobalt, molybdenum, and optionally phosphorus. The catalyst contains a cobalt oxide content (CoO) by weight relative to the total catalyst weight of between 0.1% and 10%, a molybdenum oxide content (MOO3) by weight relative to the total catalyst weight of between 1% and 20%, a cobalt / molybdenum molar ratio of between 0.1 and 0.8, and a phosphorus oxide content (P2O5) by weight relative to the total catalyst weight of between 0.3% and 10% when phosphorus is present. The catalyst has a specific surface area of ​​between 30 and 180 m². 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 final hydrodesulfurization step b)

[0072] During the hydrodesulfurization step a), a large part of the sulfur compounds are transformed into H2S. The remaining sulfur compounds are essentially refractory sulfur compounds and recombination mercaptans resulting from the addition of the hhS formed in step a) to the mono-olefins present in the feed.

[0073] The so-called finishing hydrodesulfurization step (b), which is carried out at a higher temperature than step a) and in the presence of a specific catalyst, is primarily used to reduce the content of recombination mercaptans. Indeed, by using a higher temperature in this step compared to step a), the formation of olefins and h₂S is favored by thermodynamic equilibrium. Step b) also allows for the hydrodesulfurization of more refractory sulfur compounds.

[0074] The hydrodesulfurization step b) consists of contacting the effluent from step a) optionally with an addition of hydrogen, in one or more hydrodesulfurization reactors, containing one or more catalysts suitable for carrying out hydrodesulfuration.

[0075] The hydrodesulfurization step b) is carried out without significant hydrogenation of the olefins. The hydrogenation level of the olefins in the catalyst for the hydrodesulfurization step b) is generally less than 5% and even more commonly less than 2%.

[0076] The temperature of this stage is generally between 280 and 400°C, more preferably between 290 and 380°C, and most preferably between 300 and 360°C. The temperature of this stage (b) is generally at least 5°C higher, preferably at least 10°C higher, and most preferably at least 30°C higher than the temperature of stage (a). The operating pressure of this stage is generally between 0.5 and 5 MPa, and preferably between 1 and 3 MPa.

[0077] The amount of catalyst used in each reactor is generally such that the ratio between the gasoline flow rate to be treated, expressed in m³ 3 per hour under standard conditions, per m 3The catalyst (also called space velocity) is between 1 and 10 hours 1 and preferably between 2 and 8 am 1 .

[0078] Preferably, the hydrogen flow rate is constant and equal to the quantity injected in step a) minus the hydrogen consumed in step a). 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 load 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 .

[0079] The desulfurization rate 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 from step b) contains less than 60 ppm by weight of sulfur and preferably less than 40 ppm by weight of sulfur.

[0080] Hydrodesulfurization steps a) and b) can be carried out either in a single reactor containing both catalysts or in at least two different reactors. When steps a) and b) are carried out using two reactors, these two reactors are connected in series, with the second reactor treating all of the effluent from the first reactor (without separating the liquid and gas between the first and second reactors).

[0081] The catalyst in step b) is of a different nature and / or composition than that used in step a). The catalyst in step b) is in particular a very selective hydrodesulfurization catalyst: it allows hydrodesulfurization without hydrogenating the olefins and therefore maintains the octane number.

[0082] The catalyst suitable for this step (b) of the process according to the invention, without this list being exhaustive, is a catalyst comprising an oxide support and an active phase consisting of at least one metal from Group VIII, preferably chosen from the group formed by nickel, cobalt, and iron. These metals may be used alone or in combination. Preferably, the active phase consists of a metal from Group VIII, preferably nickel. Most preferably, the active phase consists of nickel. The Group VIII metal content is between 1 and 60% by weight of the oxide of the Group VIII metal relative to the total weight of the catalyst, preferably between 5 and 30% by weight, and most preferably between 5 and 20% by weight.

[0083] Preferably, the catalyst is characterized by a specific surface area between 5 and 400 m² 2 / g, preferably between 10 and 250 m 2 / g, preferably between 20 and 200 m 2 / g, preferably between 30 and 180 m 2 / g. The specific surface area is determined in the present invention by the BET method according to ASTM D3663, as described in the book Rouquerol F.; Rouquerol J.; Singh K. “Adsorption by Powders & Porous So / ids; Principle, methodology and applications”, Academy Press, 1999, for example using an Autopore III™ model apparatus from the Microméritics™ brand.

[0084] The porous 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 ASTM D4284 with a wetting angle of 140°, as described in the same publication. The packed filling density (PTD) of the catalyst is generally between 0.4 and 0.7 g / mL, preferably between 0.45 and 0.69 g / mL.

[0085] The DRT measurement involves introducing the catalyst into a test tube of predetermined volume and then, by vibration, compacting it until a constant volume is obtained. The apparent density of the compacted product is calculated by comparing the mass introduced and the volume occupied after compaction.

[0086] Advantageously, the catalyst in step b), before sulfidation, 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 most preferably between 25 and 80 nm. The pore diameter is measured by mercury porosimetry according to ASTM D4284 with a wetting angle of 140°.

[0087] The catalyst can be in the form of small-diameter extrudates, cylindrical or multilobed (trilobed, quadrilobed, etc.), or spheres. The catalyst oxide support is usually a porous solid chosen from the group consisting of: aluminas, silica, silica-alumina, or titanium or magnesium oxides used alone or in mixtures with alumina or silica-alumina. It is preferably chosen from the group consisting of silica, the family of transition aluminas, and silica-alumina. Most preferably, the oxide support is essentially composed of alumina, that is, it comprises at least 51% by weight, preferably at least 60% by weight, most preferably at least 80% by weight, or even at least 90% by weight of alumina. Preferably, it is composed solely of alumina.Preferably, the catalyst oxide support is a "high temperature" alumina, i.e., one that contains theta, delta, kappa or alpha phase aluminas, alone or in mixtures, and less than 20% gamma, chi or eta phase alumina.

[0088] A highly preferred embodiment of the invention involves the use in step b) of a catalyst consisting of alumina and nickel, said catalyst containing a nickel oxide content, in the form of NiO, by weight relative to the total weight of the catalyst, of between 5 and 20%, said catalyst having a specific surface area of ​​between 30 and 180 m². 2 / g.

[0089] The catalyst for the hydrodesulfurization step b) is characterized by a hydrodesulfurization catalytic activity generally between 1% and 90%, preferably between 1% and 70%, and most preferably between 1% and 50% of the catalytic activity of the catalyst for the hydrodesulfurization step a).

[0090] Description of the hhS separation step (step c)

[0091] This step is implemented to separate the excess hydrogen and the h₂S formed during steps a) and b). Any method known to those skilled in the art may be used. According to a first embodiment, after the hydrodesulfurization steps a) and b), the effluent is cooled to a temperature generally below 80°C and preferably below 60°C to condense the hydrocarbons. The gas and liquid phases are then separated in a separation flask. The liquid fraction, which contains the desulfurized gasoline and a fraction of the dissolved h₂S, is sent to a stabilization or starter column. This column separates a top section consisting mainly of residual h₂S and hydrocarbon compounds with a boiling point lower than or equal to that of butane, from a bottom section free of h₂S, called stabilized gasoline, containing compounds with a boiling point higher than that of butane.According to a second embodiment, after the condensation step, the liquid fraction containing the desulfurized gasoline and a fraction of the dissolved H₂S is sent to a stripping section, while the gaseous fraction, consisting mainly of hydrogen and H₂S, is sent to a purification section. Stripping can be carried out by heating the hydrocarbon fraction alone, or with the injection of hydrogen or steam, in a distillation column to extract, at the top, the light compounds that have been carried along by dissolution in the liquid fraction, as well as the residual dissolved H₂S. The temperature of the stripped gasoline recovered at the bottom of the column is generally between 120°C and 250°C.

[0092] Preferably, the separation step c) is carried out in a stabilization or starter column. Indeed, a stabilization column allows for more efficient separation of h⁻¹S than a stripping section.

[0093] Step c) is preferably implemented so that the sulfur in the form of hhS remaining in the desulfurized gasoline, before the mild hydrodesulfurization step d), represents less than 30%, preferably less than 20% and more preferably less than 10% of the total sulfur present in the treated hydrocarbon fraction.

[0094] Description of the mild hydrodesulfurization step d)

[0095] This hydrodesulfurization step consists of contacting, under relatively mild operating conditions in at least one reactor, the H2S-depleted effluent from step c) with hydrogen and a hydrodesulfurization catalyst. Indeed, the recombination mercaptans remaining in the effluent after step b) are relatively easy to hydrodesulfurize compared to the more refractory compounds removed in step b). Mild conditions are defined, in particular, as a flow rate / feed rate ratio lower than that of steps a) and b), preferably combined with a temperature lower than that of step b) and possibly lower than that of step a). This low flow rate / feed rate ratio allows for the hydrodesulfurization of residual mercaptans without hydrogenating the olefins.Just like the previous hydrodesulfurization steps a) and b), step d) is implemented with the aim of achieving selective hydrodesulfurization, i.e. with a degree of hydrogenation of mono-olefins less than 80%, preferably less than 70% and most preferably less than 60%.

[0096] The operating pressure of this step is generally between 0.5 and 5 MPa and preferably between 1 and 3 MPa. The temperature is generally between 150 and 330°C and preferably between 180 and 300°C. The temperature of this step (d) is generally at least 5°C lower, preferably at least 10°C lower, and most preferably at least 15°C lower than the temperature of step (b).

[0097] The quantity of catalyst used in step d) is generally such that the ratio between the flow rate of gasoline to be treated, expressed in m 3 per hour under standard conditions, per m 3The catalyst velocity (also called space velocity) is between 1 and 10 fr 1 and preferably between 2 and 8 francs 1 The ratio between the hydrogen flow rate and the feed flow rate, also called the H2 / HC ratio of step d), is less than the H2 / HC ratio of step a). The ratio between the hydrogen flow rate and the feed flow rate is defined as the ratio at the reactor inlet of the step in question. The ratio or adjustment factor defined by F = (h2 / HC centered in the reactor of step a)) / (H2 / HC centered in the reactor of step d)) is greater than or equal to 1.05, preferably greater than 1.1, and preferably between 1.1 and 6, and preferably between 1.2 and 4.

[0098] The hydrogen flow rate in step d) 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 load to be treated expressed in m 3per hour under standard conditions is between 25 and 400 Nm 3 / m 3 preferably between 40 and 250 Nm 3 / m 3 , and particularly preferably between 50 and 150 Nm 3 / m 3 .

[0099] The hydrogen required for this step can be fresh hydrogen or recycled hydrogen, preferably free of hhS, or a mixture of fresh and recycled hydrogen. Fresh hydrogen is preferred. This reduces the partial pressure of hhS at the inlet of step d) and thus promotes the removal of mercaptans into olefins and H2S.

[0100] In one embodiment, the hydrogen can be supplied from a dedicated hydrogen supply for this step, for example, a hydrogen compressor. In another embodiment, and thanks to the low required flow rate / charge flow rate ratio in step d), the hydrogen can be supplied from the hydrogen supply in step a), thus saving the need for a hydrogen compressor.

[0101] Suitable hydrodesulfurization catalysts for this step (d) are catalysts exhibiting good selectivity for hydrodesulfurization reactions compared to the hydrogenation of olefins under mild operating conditions. The catalyst comprises an oxide support and an active phase consisting of a metal from Group VIB and a metal from Group VIII, or an active phase consisting of at least one metal from Group VIII.

[0102] According to a first variant, the catalyst comprises an oxide support and an active phase comprising a metal from group VI B and a metal from group VIII. According to this variant, the hydrodesulfurization catalyst of step d) is a catalyst such as the catalyst described for hydrodesulfurization step a). The catalyst of step d) may be identical or different from the catalyst of step a). Preferably, the catalyst of step d) does not contain phosphorus. Indeed, the presence of phosphorus in the catalyst, known among other things to stabilize the support at high temperature, is not mandatory under the mild operating conditions of step d).

[0103] A highly preferred embodiment of the invention involves implementing, in step d), a catalyst consisting of alumina and a cobalt-molybdenum active phase, said catalyst containing a cobalt oxide content (CoO) by weight relative to the total catalyst weight of between 0.1 and 10%, a molybdenum oxide content (MOO3) by weight relative to the total catalyst weight of between 1 and 20%, and a cobalt / molybdenum molar ratio of between 0.1 and 0.8, said catalyst having a specific surface area of ​​between 30 and 180 m². 2 / g. According to a second embodiment, the catalyst comprises an oxide support and an active phase consisting of at least one Group VIII metal. According to this embodiment, the hydrodesulfurization catalyst of step d) is a catalyst such as the catalyst described for hydrodesulfurization step b). The catalyst of step d) may be identical or different from the catalyst of step b). A highly preferred embodiment of the invention involves the use, for step d), of a catalyst consisting of alumina and nickel, said catalyst containing a nickel oxide content, in the form of NiO, by weight relative to the total weight of the catalyst, of between 5 and 20%, said catalyst having a specific surface area of ​​between 30 and 180 m². 2 / g.

[0104] The mercaptan removal rate is generally greater than 50% and preferably greater than 70%, so that the product from step d) contains less than 10 ppm sulfur, and preferably less than 5 ppm sulfur from recombination mercaptans, relative to the total feed weight. The olefin hydrogenation rate from step d) is generally less than 5% and preferably less than 2%.

[0105] Description of catalyst preparation and sulfidation

[0106] The preparation of catalysts for steps a), b), or d) is known and generally comprises an impregnation step with Group VIII and Group VIB metals (when present), and optionally with phosphorus and / or the organic compound, onto the oxide support, followed by drying and then optional calcination to obtain the active phase in its oxide forms. Before use in a hydrodesulfurization process of a sulfur-containing olefinic gasoline fraction, the catalysts are generally subjected to sulfidation to form the active species as described below.

[0107] The impregnation step can be carried out either by slurry impregnation, excess impregnation, dry impregnation, or any other method known to those skilled in the art. The impregnation solution is chosen so as to be able to solubilize the metal precursors in the desired concentrations.

[0108] For example, sources of molybdenum include oxides and hydroxides, molybdic acids and their salts, particularly ammonium salts such as ammonium molybdate, ammonium heptamolybdate, and phosphomolybdic acid (H3PM0). 12 O 40 ), and their salts, and possibly silicomolybdic acid (H4SNVI0 12 O 40 ) and its salts. Sources of molybdenum can also be any heteropolycompound of the Keggin type, lacunary Keggin, substituted Keggin, Dawson, Anderson, Strandberg, for example.

[0109] Molybdenum trioxide and heteropolycompounds of the type preferred are molybdenum trioxide and heteropolycompounds.

[0110] Keggin, vacancy Keggin, substituted Keggin, and Strandberg. The tungsten precursors that can be used are also well known to those skilled in the art. For example, tungsten sources include oxides and hydroxides, tungstic acids and their salts, particularly ammonium salts such as ammonium tungstate, ammonium metatungstate, phosphotungstic acid and their salts, and possibly silicotungstic acid (hUSiW^Cho) and its salts. Tungsten sources can also be any heteropolycompound of the Keggin, vacancy Keggin, substituted Keggin, or Dawson type, for example. Ammonium oxides and salts such as ammonium metatungstate or heteropolyanions of the Keggin, vacancy Keggin, or substituted Keggin type are preferred. Cobalt precursors that can be used are advantageously chosen from among oxides, hydroxides, hydroxycarbonates, carbonates and nitrates, for example.Cobalt hydroxide and cobalt carbonate are preferred.

[0111] Nickel precursors that can be used are advantageously chosen from among 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. Phosphorus can also be introduced along with the Group VI B element(s) in the form of Keggin, lacunar Keggin, substituted Keggin, or Strandberg-type heteropolyanions.

[0112] 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, most preferably between 75°C and 130°C.

[0113] The drying step is preferably carried out under an inert atmosphere or 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 reduced pressure. Preferably, this step is carried out at atmospheric pressure. It is advantageously carried out in a flow bed using air or any other hot gas. Preferably, when drying is carried out in a fixed bed, the gas used is either air or an inert gas such as argon or nitrogen. Most preferably, drying is carried out in a flow bed in the presence of nitrogen and / or air. Preferably, the drying step has a duration of between 5 minutes and 15 hours, and more preferably between 30 minutes and 12 hours.

[0114] According to one variant of the invention, the catalyst did not undergo calcination during its preparation, i.e. the impregnated catalytic precursor was not subjected to a heat treatment step at a temperature above 200°C under an inert atmosphere or under an atmosphere containing oxygen, in the presence of water or not.

[0115] According to another preferred embodiment of the invention, the catalyst underwent a calcination step during its preparation, i.e. the impregnated catalytic precursor was 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.

[0116] Before contacting the feedstock in a gasoline hydrodesulfurization process, the catalysts of the process according to the invention generally undergo a sulfidation step. Sulfuration is preferably carried out in a sulfur-reducing medium, i.e., in the presence of H₂S and hydrogen, in order to transform the metal oxides into sulfides such as, for example, M₂S₂, CogSs, or N₁₃S₂. Sulfuration is performed by injecting a stream containing hhS and hydrogen, or a sulfur compound capable of decomposing into H₂S in the presence of the catalyst and hydrogen, onto the catalyst. Polysulfides such as dimethyl disulfide (DM₂DS) are commonly used hhS precursors for sulfiding catalysts. The sulfur can also be obtained from the feedstock. The temperature is adjusted so that the hhS reacts with the metal oxides to form metal sulfides.This sulfidation 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 between 200 and 600°C, and more preferably between 300 and 500°C.

[0117] The sulfidation level of the metals constituting the catalysts is at least 60%, preferably at least 80%. The sulfur content in the sulfided catalyst is measured by elemental analysis according to ASTM D5373. A metal is considered sulfided when the overall sulfidation level, defined by the molar ratio between the sulfur (S) present on the catalyst and that metal, is at least 60% of the theoretical molar ratio corresponding to the total sulfidation of the metal(s) in question. The overall sulfidation level is defined by the following equation:

[0118] (S / lTiet3l) C analyzer 0.6 X (S / lTlStaJ)th orM|ue in which:

[0119] (S / metal) Cataiyseur is the molar ratio between sulfur (S) and metal present on the catalyst

[0120] (S / metal) théorique is the molar ratio between sulfur and the metal corresponding to the total sulfidation of the metal into sulfide.

[0121] This theoretical molar ratio varies depending on the metal in question:

[0122] - (S / Fe)theoretical — 1

[0123] - (S / Co)theoretical — 8 / 9 - (S / N Î)theoretical — 2 / 3

[0124] - (S / Mo)theoretical—2 / 1

[0125] - (S / W)theoretical = 2 / 1

[0126] 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 sulfidation of each metal into sulfide, the calculation being carried out in proportion to the relative molar fractions of each metal.

[0127] For example, for a catalyst comprising molybdenum and nickel with respective mole fractions of 0.7 and 0.3, the minimum mole ratio (S / Mo + Ni) is given by the relation:

[0128] (S / Mo+Ni)catalyst = 0.6 x {(0.7 x 2) + (0.3 x (2 / 3)}

[0129] Description of the hhS separation step (step e)

[0130] At the end of step d), the gasoline treated under the conditions described above therefore has a reduced mercaptan content. This is because the mercaptans have been converted by hydrodesulfurization to form hhS.

[0131] According to the invention, a separation step e) is carried out of the h^S formed and present in the effluent from step d). Any method known to a person skilled in the art may be considered.

[0132] According to a first embodiment, after the hydrodesulfurization step (d), the effluent is cooled to a temperature generally below 80°C and preferably below 60°C in order to condense the hydrocarbons. The gas and liquid phases are then separated in a separation vessel. The liquid fraction, which contains the desulfurized gasoline as well as a fraction of the dissolved hhS, is sent to a stabilization column or starter column.

[0133] This column separates a top section consisting mainly of residual hhS and hydrocarbon compounds having a boiling point less than or equal to that of butane and a bottom section free of hhS, called stabilized gasoline, containing compounds having a boiling point higher than that of butane.

[0134] According to a second embodiment, after the condensation step, the liquid fraction containing the desulfurized gasoline and a fraction of the dissolved H₂S is sent to a stripping section, while the gaseous fraction, consisting mainly of hydrogen and H₂S, is sent to a purification section. Stripping can be carried out by heating the hydrocarbon fraction alone, or with the injection of hydrogen or steam, in a distillation column to extract, at the top, the light compounds that have been carried along by dissolution in the liquid fraction, as well as the residual dissolved H₂S. The temperature of the stripped gasoline recovered at the bottom of the column is generally between 120°C and 250°C. Preferably, the separation step e) is carried out in a stabilization or starter column. Indeed, a stabilization column allows for more efficient separation of H₂S than a stripping section.

[0135] Step e) is preferably implemented so that the sulfur in the form of hhS remaining in the effluent from step d) represents less than 30%, preferably less than 20% and more preferably less than 10% of the total sulfur present in the treated hydrocarbon fraction.

[0136] It should be noted that the hydrodesulfurization step d) and the separation step e) of h₂S can be carried out simultaneously using a catalytic column equipped with a catalytic bed containing the hydrodesulfurization catalyst. Preferably, the catalytic distillation column has two hydrodesulfurization catalyst beds, and the effluent from step c) is fed into the column between the two catalyst beds.

[0137] Schemes that can be implemented within the framework of the invention

[0138] Several methods can be implemented to produce desulfurized gasoline with reduced mercaptan content at a lower cost. The choice of the optimal method depends on the characteristics of the gasoline to be processed and produced, as well as the specific constraints of each refinery.

[0139] The diagrams described below are given as illustrations and are not exhaustive.

[0140] According to a first variant, the gasoline to be treated is distilled to separate two cuts (or fractions), namely a light cut and a heavy cut, and the heavy cut is then treated according to the process of the invention. The light cut generally has a boiling point range below 100°C, and the heavy cut a boiling point range above 65°C. This first variant has the advantage of not hydrotreating the light cut, which is rich in olefins and generally low in sulfur, thus limiting the loss of octane through olefin hydrogenation.

[0141] According to a second variant, the essence to be treated is subjected before the process according to the invention to a preliminary step consisting of a selective hydrogenation of the diolefins present in the charge, as described in patent application EP 1077247.

[0142] The gasoline to be treated is pre-treated in the presence of hydrogen and a selective hydrogenation catalyst to at least partially hydrogenate the diolefins and induce a weighting reaction of some of the light mercaptan (RSH) compounds present in the thioether feedstock, by reaction with olefins. For this purpose, the gasoline is fed into a selective hydrogenation catalytic reactor containing at least one fixed or moving bed of a catalyst for the selective hydrogenation of diolefins and the weighting of light mercaptans. The selective hydrogenation of diolefins and the weighting of light mercaptans is preferably carried out on a sulfide catalyst comprising at least one element from Group VIII and optionally at least one element from Group VI B and an oxide support. The Group VIII element is preferably chosen from nickel and cobalt, and in particular nickel.The group VIB element, when present, is preferably selected from molybdenum and tungsten, and most preferably from molybdenum. The oxide support for the catalyst is preferably selected from alumina, nickel aluminate, silica, silicon carbide, or a mixture of these oxides. Alumina is preferred, and even more preferably, high-purity alumina is used. In a preferred embodiment, the selective hydrogenation catalyst contains nickel with a weight content of nickel oxide, in the form of NiO, of between 1 and 12%, and molybdenum with a weight content of molybdenum oxide, in the form of M0O3, of between 6 and 18%, and a nickel / molybdenum molar ratio of between 0.3 and 2.5, the metals being deposited on a support made of alumina. The sulfidation rate of the metals constituting the catalyst is preferably greater than 60%.

[0143] During the optional selective hydrogenation step, the gasoline is brought into contact with the catalyst at a temperature between 50 and 250°C, and preferably between 80 and 220°C, and even more preferably between 90 and 200°C, with a liquid space velocity (LHSV) of between 0.5 h 1 and 8 p.m. 1 The unit of liquid space velocity is liters of feed per liter of catalyst per hour (L / L / h). The pressure is between 0.4 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 normals m 3 per hour and the flow rate of the load to be processed expressed in m 3 per hour under standard conditions, between 2 and 100 Nm 3 / m 3 , preferably between 3 and 30 Nm 3 / m 3After selective hydrogenation, the diolefin content, determined by the Maleic Anhydride Value (MAV) according to UOP 326, is generally reduced to less than 6 mg maleic anhydride / g, or even less than 4 mg MA / g, and more preferably less than 2 mg MA / g. In some cases, it can be reduced to less than 1 mg MA / g. The selectively hydrogenated gasoline is then distilled into at least two cuts: a light cut and a heavy cut, and optionally an intermediate cut. In the case of two-cut fractionation, the heavy cut is processed according to the method of the invention. In the case of three-cut fractionation, the intermediate and heavy cuts can be processed separately according to the method of the invention.It should be noted that it is possible to carry out the hydrogenation steps of diolefins and fractionation into two or three cuts simultaneously using a catalytic distillation column which includes a distillation column equipped with at least one catalytic bed.

[0144] Other features and advantages of the invention will now become apparent from the following description, given for illustrative purposes only and not as a limitation, and with reference to the attached Figure 1.

[0145] With reference to Figure 1 and according to one embodiment of the process according to the invention, the gasoline to be treated is sent via line 1 and hydrogen via line 3 to a selective hydrogenation unit 2 (optional step) in order to selectively hydrogenate the diolefins and increase the weight of the light mercaptans. The effluent with a low diolefin and mercaptan content is withdrawn from reactor 2 via line 4 and sent to a fractionation column 5 (or splitter) configured to separate the gasoline into two cuts: a light gasoline cut 6 (or light gasoline) and a (first) heavy gasoline cut 7, which consists of the heavy fraction complementary to the light gasoline. The cut point for the light cut is generally made at a temperature below 100°C, and the cut point for the heavy cut is generally made at a temperature above 65°C.The final boiling point of the light cut is chosen so as to provide a low sulfur light gasoline cut (total sulfur content typically less than 30 ppm by weight and preferably less than 10 ppm by weight) without requiring a subsequent hydrodesulfurization step.

[0146] The heavy gasoline fraction is then sent via line 7 and hydrogen via line 8 to the hydrodesulfurization unit 9 of step a). The hydrodesulfurization unit 9 of step a) is, for example, a reactor containing a supported hydrodesulfurization catalyst based on a metal from group VIII and VIB, in a fixed bed or fluidized bed configuration; preferably, a fixed-bed reactor is used. The reactor is operated under the operating conditions and in the presence of a hydrodesulfurization catalyst as described above to decompose the sulfur compounds and form hydrogen sulfide (H₂S). During hydrodesulfurization in step a), recombination mercaptans are formed by the addition of H₂S to the olefins. The effluent from the hydrodesulfurization unit 9 is then introduced into the so-called finishing hydrodesulfurization unit 11 via line 10 without removal of the hhS formed.The hydrodesulfurization unit 11 of step b) is, for example, a reactor containing a hydrodesulfurization catalyst in a fixed bed or fluidized bed configuration; preferably, a fixed-bed reactor is used. Unit 11 is operated at a higher temperature than unit 9 and in the presence of a selective catalyst comprising an oxide support and an active phase consisting of at least one metal from group VIII to decompose, at least partially, the recombination mercaptans into olefins and H2S. It also allows for the hydrodesulfurization of more refractory sulfur compounds.

[0147] An effluent (gasoline) containing h₂S is drawn from the hydrodesulfurization reactor 11 via line 12. The effluent then undergoes an h₂S removal step (step c), which, in the embodiment shown in Figure 1, consists of treating the effluent by condensation. This involves introducing the effluent from step b) via line 12 into a separation vessel 13 to draw off a gas phase containing h₂S and hydrogen via line 14, and a liquid fraction. The liquid fraction, containing the desulfurized gasoline and a fraction of the dissolved h₂S, is sent via line 15 to a stabilization or starter column 16 to separate, at the top of the column via line 17, a stream containing C₄ hydrocarbons. ~ and the residual hhS and at the bottom via line 18 of the column a so-called stabilized essence containing compounds having a boiling point higher than that of butane.

[0148] The stabilized gasoline is sent via line 18 to a hydrodesulfurization unit 19 in step d) to reduce the residual mercaptan content of the hydrodesulfurized gasoline under mild operating conditions. As mentioned above, unit 19 implements mild operating conditions, including a low flow rate (hh) to load flow rate ratio, in the presence of a suitable hydrodesulfurization catalyst. Fresh hydrogen can be supplied via line 20. Due to the low required flow rate (hV) to load flow rate ratio in step d), the hydrogen needed for step d) in unit 19 can also be drawn directly from the hydrogen supply of unit 9 via line 21. This saves the need for a hydrogen compressor.The effluent from step d) then undergoes an hhS removal step (step e) which, in the embodiment of Figure 1, consists of treating the effluent by condensation by introducing the effluent from step d) via line 22 into a separation vessel 23 in order to draw off a gas phase containing hhS and hydrogen via line 24 and a liquid fraction via line 25. The liquid fraction which contains the desulfurized gasoline as well as a fraction of the dissolved hhS is sent via line 25 to a stabilization column or starter column 26 in order to separate at the top of the column via line 27 a stream containing C4- hydrocarbons and residual h^S and at the bottom of the column via line 28 a gasoline which has mercaptan and total sulfur contents respectively less than 5 ppm wt and 10 ppm wt.

[0149] Examples

[0150] Example 1: Pretreatment of FCC gasoline feed by selective hydrogenation (according to the prior art) Table 1 gives the characteristics of an FCC gasoline treated by the process according to Figure 2 of the prior art (EP1077247).

[0151] The FCC gasoline (line 1) is treated in the selective hydrogenation reactor 2 in the presence of catalyst A (optional step). Catalyst A is a NiMo-gamma alumina catalyst. The metal contents are 7% NiO by weight and 11% M0O3 by weight, respectively, relative to the total catalyst weight, resulting in a Ni / Mo molar ratio of 1.2. The catalyst's specific surface area is 230 m². 2 / g. Prior to its use, catalyst A is sulfided at atmospheric pressure in a sulfidation test bench under mixture

[0152] H2S / H2 consists of 15% hhS by volume at 1 L / gh of catalyst and is heated to 400°C for two hours. This protocol achieves a sulfidation level exceeding 80%. The gasoline (line 1) is contacted with hydrogen (line 3) in a reactor containing catalyst A. This step of the process performs the selective hydrogenation of diolefins and the conversion (weighting) of some of the light mercaptans (RSH) present in the feedstock. The diolefin content is directly proportional to the MAV (Maleic Anhydride Value). Diolefins are undesirable compounds because they are gum precursors in gasoline.

[0153] The operating conditions implemented in the selective hydrogenation reactor are: Temperature: 140°C, Total pressure: 2.5 MPa, Volumetric ratio of added H2 / gasoline charge: 5 normal liters of hydrogen per liter of gasoline under standard conditions (volume / volume), Volumetric rate per hour (WH): 3 h 1 .

[0154]

[0155] Table 1: Characteristics of the feedstock (1) and the selective hydrogenation effluent (4). The effluent from the selective hydrogenation step (line 4), with a low content of conjugated diolefins (MAV = 0.6 mg / g) and low content of light sulfur compounds (which become heavier in the selective hydrogenation step), is sent to a fractionation column (5) to separate a light gasoline (line 6) at the top and a heavy gasoline first cut (line 7) at the bottom. The characteristics of the light gasoline and the heavy gasoline first cut are shown in Table 2. As shown in Table 2, the light gasoline obtained (line 6) has a low sulfur content (10 ppm wt). The heavy gasoline first cut, which corresponds to approximately 72% wt of the gasoline, has a high sulfur content (600 ppm) and requires further treatment before being added to the gasoline pool.

[0156]

[0157] Table 2: Characteristics of the cuts: Light gasoline and first cut heavy gasoline

[0158] Example 2 (comparative analysis according to the prior art): Hydrodesulfurization of the first heavy gasoline cut

[0159] This example refers to the prior art (EP1077247) and Figure 2. The first heavy gasoline fraction (line 7) obtained in Example 1 is mixed with hydrogen (line 8) and processed in a selective hydrodesulfurization unit (9), which corresponds to a first hydrodesulfurization step. The first hydrodesulfurization step is conducted in the presence of an alumina-supported CoMo catalyst. The temperature is 268°C, the pressure is 2 MPa, and the space velocity of the liquid (expressed as liquid volume per catalyst volume per hour) is 3 h⁻¹ 1 The ratio between the hydrogen flow rate and the charge flow rate is 250 normal m 3 by m 3under standard conditions, the reactor effluent (line 10) is then heated in a furnace (not shown in the figure) and then introduced into a second reactor (11) containing a finishing catalyst. This finishing step is carried out in the presence of a Ni catalyst supported on alumina. The temperature is 316°C, the pressure is 1.8 MPa, and the liquid velocity (expressed as liquid volume per catalyst volume per hour) is 3 h⁻¹. 1 .

[0160] The effluent from reactor 11 (line 12) is sent to a separation vessel (13) to separate a gas phase containing hhS and hydrogen via line 14 from a liquid fraction. The liquid fraction, which contains desulfurized gasoline and a fraction of dissolved hhS, is sent via line 15 to a stabilization or starter column (16) to separate, at the top of the column via line 17, a stream containing C4- hydrocarbons and residual hhS, and at the bottom of the column, via line 18, a stabilized heavy gasoline from the second reactor (11), the characteristics of which are illustrated in Table 3. The olefin loss is shown in Table 4.

[0161]

[0162] Table 3: Characteristics of heavy gasoline after the first and second hydrodesulfurization stages

[0163] Table 4: Loss of olefins between the first heavy gasoline cut (row 7) and the gasoline obtained after the second hydrodesulfurization step (row 12)

[0164] The process according to example 2 makes it possible to obtain a heavy gasoline with a low sulfur content (10 ppm wt). The loss of olefins between the first heavy gasoline cut and the stabilized heavy gasoline obtained after the second hydrodesulfurization step is 27.3% wt (absolute).

[0165] Example 3: (according to the present invention)

[0166] This example refers to the present invention, according to Figure 1. The first heavy gasoline cut (line 7) obtained in Example 1 is mixed with hydrogen and treated in a selective hydrodesulfurization unit (9) which corresponds to step a) of the present invention.

[0167] The first hydrodesulfurization step (step a)) is carried out in the presence of a CoMo catalyst supported on alumina. The temperature is 260°C, the pressure is 2 MPa, and the space velocity of the liquid (expressed as volume of liquid per volume of catalyst per hour) is 3 h 1 The ratio between the hydrogen flow rate and the charge flow rate is 200 normal m 3 by m 3 under standard conditions. The reactor effluent (line 10) is then heated in a furnace (not shown in the figure) and then introduced into a second reactor (11) containing a finishing catalyst, corresponding to step b). This selective hydrodesulfurization step is carried out in the presence of a Ni catalyst supported on alumina. The temperature is 306°C, the pressure is 1.8 MPa, and the liquid velocity (expressed as liquid volume per catalyst volume per hour) is 3 h⁻¹ 1 .

[0168] The characteristics of the heavy gasoline obtained after step b) of the present invention are illustrated in Table 5. The loss of olefins after step b) is shown in Table 6.

[0169]

[0170] Table 5: Characteristics of heavy gasoline after step b) of hydrodesulfurization according to the invention

[0171]

[0172] Table 6: Loss of olefins between the first heavy gasoline cut (line 7) and the heavy gasoline (line 12) obtained after step b) according to the invention

[0173] The conditions of step b) are less severe than in example 2: the olefin loss at the end of step b) is reduced by 5.3% by weight in that example according to the invention. In step c) according to the invention, a step is carried out to remove the hhS present in the effluent from step b).

[0174] The reactor effluent (11) is partially condensed before being introduced into the gas / liquid separator (13). The resulting gas phase (line 14) consists primarily of hydrogen and hhS, possibly with light hydrocarbons. The bottom of the separator contains a partially desulfurized heavy hydrocarbon fraction. After condensation of the effluent from step b) (line 15), separation is carried out in a stabilization column (16) to produce a stabilized heavy gasoline fraction (line 18) and a gas phase containing C4- hydrocarbons and residual hhS (line 17). The characteristics of the stabilized heavy fraction obtained after step c) of the present invention are illustrated in Table 7.

[0175]

[0176] Table 7: Characteristics of the stabilized heavy gasoline (line 18) after step c) according to the invention. In step d) according to the invention, the stabilized heavy gasoline cut, depleted in H2S, is contacted in the hydrodesulfurization reactor (19) with hydrogen and in the presence of a Ni catalyst supported on alumina, referred to as the finishing catalyst. The temperature is

[0177] At 240°C, the pressure is 2 MPa, and the spatial velocity of the liquid (expressed as volume of liquid per volume of catalyst per hour) is 3 h 1 The ratio between the hydrogen flow rate expressed in normal m 3 per hour and the flow rate of the load to be processed expressed in m 3 per hour under standard conditions is less than that of step a), i.e., 80 Nm 3 / m 3Under these operating conditions, the hydrogenation of olefins is negligible. The characteristics of the effluent (22) obtained after step d) of the present invention are illustrated in Table 8.

[0178]

[0179] Table 8: Characteristics of the heavy gasoline (line 22) after step d) of hydrodesulfurization according to the invention. The desulfurized heavy fraction (line 22) is sent, via a separation flask (23), to a stabilization column (26) in order to recover hydrogen and hhS (line 27), possibly with light hydrocarbons, at the top of the column, and a desulfurized hydrocarbon fraction (step e) at the bottom of the column (line 28). The characteristics of the heavy gasoline fraction obtained after stabilization (28) of the present invention are illustrated in Tables 9 and 10.

[0180] Table 9: Characteristics of stabilized heavy gasoline (line 28) after step e) according to the invention

[0181]

[0182] Table 10: Loss of olefins between the first heavy gasoline cut (line 7) and the stabilized heavy gasoline (line 28) after step e)

[0183] Advantageously, the process according to the invention makes it possible to produce low-sulfur gasoline (10 ppm S) while reducing the absolute loss of olefins compared to heavy gasoline desulfurized after the second desulfurization step (shown in comparative Example 2). Indeed, in Example 2, the olefin loss (as a mass percentage) between the first heavy gasoline cut (7) and the gasoline obtained after the second hydrodesulfurization step (12) is 6.8%, and in Example 3 according to the invention, the olefin loss between the first heavy gasoline cut (7) and the desulfurized and stabilized heavy gasoline (28) is 5.5%. Thus, Example 3 according to the invention makes it possible to preserve 19% of the olefins present in the first heavy gasoline cut (7) while producing gasoline with the same low sulfur content (10 ppm). Preserving olefins has a positive impact on the octane ratings of the gasoline produced.

[0184] The process according to the invention thus makes it possible to obtain, after stabilization, a heavy gasoline fraction with a low organic sulfur content (10 ppm) and very little mercaptans. This gasoline, along with the light gasoline obtained in Example 1, can be used in the gasoline pool for the formulation of vehicle fuel.

Claims

DEMANDS 1. A process for treating gasoline containing sulfur compounds, olefins, and diolefins, the process comprising at least the following steps: a) in at least one reactor, the gasoline, hydrogen, and a hydrodesulfurization catalyst comprising an oxide support and an active phase comprising a metal of Group VIB and a metal of Group VIII are contacted 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 1 and a ratio between the hydrogen flow rate expressed in normal m 3 per hour and the flow rate of the load to be processed expressed in m 3 per hour under standard conditions between 100 and 600 Nm 3 / m 3, in order to convert at least part of the sulfur compounds into H2S, b) the effluent from step a) without removal of the hhS formed, hydrogen, and a hydrodesulfurization catalyst comprising an oxide support and an active phase consisting of at least one metal from group VIII are brought into contact in at least one reactor, at a temperature between 280 and 400°C, at a pressure between 0.5 and 5 MPa, with a space velocity between 1 and 10 h 1 and a ratio between the hydrogen flow rate expressed in normal m 3 per hour and the flow rate of the load to be processed expressed in m 3 per hour under standard conditions between 100 and 600 Nm 3 / m 3 , said temperature of step b) being higher than the temperature of step a), c) a separation step is carried out of the h^S formed and present in the effluent from step b), d) In at least one reactor, the H2S-depleted effluent from step c) is contacted 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 or an active phase consisting of at least one metal from group VIII, at a temperature between 150 and 330°C, at a pressure between 0.5 and 5 MPa, with a space velocity between 0.5 and 10 fr 1and a ratio between the hydrogen flow rate and the feed flow rate to be treated lower than that of step a), e) a separation step is carried out for the h^S formed and present in the effluent from step d).

2. A process according to claim 1, wherein the catalyst of step a) comprises alumina and an active phase comprising cobalt, molybdenum, and optionally phosphorus, said catalyst containing a cobalt oxide catalyst content, in the form of CoO, by weight relative to the total weight of between 0.1 and 10%, a molybdenum oxide catalyst content, in the form of M0O3, by weight relative to the total weight of between 1 and 20%, a cobalt / molybdenum molar ratio of between 0.1 and 0.8, and a phosphorus oxide catalyst content, in the form of P2O5, by weight relative to the total weight of between 0.3 and 10% when phosphorus is present, said catalyst having a specific surface area of ​​between 30 and 180 m² 2 / g.

3. A process according to any one of the preceding claims, wherein the catalyst in step b) consists of alumina and nickel, said catalyst containing a nickel oxide content, in the form of NiO, by weight relative to the total weight of the catalyst, of between 5 and 20%, said catalyst having a specific surface area of ​​between 30 and 180 m². 2 / g.

4. A process according to any one of the preceding claims, wherein the catalyst in step d) consists of alumina and a cobalt-molybdenum active phase, said catalyst containing a cobalt oxide catalyst content, in the form of CoO, by weight relative to the total weight of between 0.1 and 10%, a molybdenum oxide catalyst content, in the form of M0O3, by weight relative to the total weight of between 1 and 20%, and a cobalt / molybdenum molar ratio of between 0.1 and 0.8, said catalyst having a specific surface area of ​​between 30 and 180 m². 2 / g.

5. A process according to any one of claims 1 to 3, wherein the catalyst in step d) consists of alumina and nickel, said catalyst containing a nickel oxide content, in the form of NiO, by weight relative to the total weight of the catalyst, of which is between 5 and 20%, said catalyst having a specific surface area between 30 and 180 m² 2 / g.

6. A method according to any one of the preceding claims, wherein the temperature of step b) is at least 5°C higher than the temperature of step a).

7. A method according to any one of the preceding claims, wherein the temperature of step d) is at least 5°C lower than the temperature of step b).

8. A method according to any one of the preceding claims, wherein the ratio of the hydrogen flow rate to the feed flow rate at the inlet of the reactor in step a) to the ratio of the hydrogen flow rate to the feed flow rate at the inlet of the reactor in step d) is greater than or equal to 1.

05.

9. A method according to any one of the preceding claims, wherein the separation steps c) and e) are carried out in a starter or stripping section.

10. A method according to any one of the preceding claims, wherein prior to step a) a distillation step of the gasoline is carried out so as to fraction said gasoline into at least two cuts, light and heavy gasoline, and the heavy gasoline cut is treated in steps a), b), c), d) and e).

11. A method according to any one of the preceding claims, wherein prior to step a) and prior to any possible distillation step, the gasoline is contacted with hydrogen and a selective hydrogenation catalyst to selectively hydrogenate the diolefins contained in said gasoline into olefins.

12. A method according to any one of the preceding claims, wherein the gasoline is a catalytic cracking gasoline.