FR3020373A1 - HYDROTREATING PROCESS IN ASCENDING CO-CURRENT REACTORS HAVING AN OVERCURRENT CURRENT - Google Patents

Abstract

A simulated countercurrent fixed bed hydrotreatment process comprising two upflow cocurrent hydrotreating zones and two separation zones in which the second hydrotreatment zone is disposed below the first separation zone so as to creating a hydrostatic head H of liquid in a liquid leg connecting said first separation zone to said second hydrotreatment zone, the height H generating a pressure difference allowing the flow of the first liquid fraction to flow to the second zone; hydrotreatment in a gravitational manner without the need for a pump.

Description

The present invention relates to the field of hydrocarbon feed hydrotreatment processes, preferably of diesel type. More particularly, the present invention relates to a simulated countercurrent fixed bed hydrotreatment process in which the feedstock and hydrogen are injected in upward flow. In general, the hydrotreatment process of a hydrocarbon feedstock, in particular a diesel fuel, is intended to improve its characteristics by reducing the presence of sulfur or other heteroatoms such as nitrogen, but also by decreasing the content of aromatic hydrocarbon compounds by hydrogenation to increase the cetane number. In particular, the hydrotreating process of hydrocarbon cuts is intended to eliminate the sulfur or nitrogen compounds contained therein in order, for example, to bring a petroleum product to the required specifications (sulfur content, aromatic content, etc.). for a given application (automotive fuel, gasoline or diesel, domestic fuel, jet fuel). The tightening of automobile pollution standards in the European community has forced refiners to drastically reduce the sulfur content in diesel fuels and gasoline (up to 10 parts per million weight (ppm) of sulfur as of 1 January 2009, compared with 50 ppm as of January 1, 2005). Conventional hydrotreating processes generally employ a fixed bed reactor, wherein one or more catalyst beds containing one or more hydrotreatment catalysts are provided. The feedstock and the hydrogen are generally introduced at the top of the reactor and pass through the reactor from top to bottom in co-downflow. When the feedstock and the hydrogen pass through the reactor, the hydrotreatment reaction makes it possible to decompose the impurities, in particular the impurities containing sulfur or nitrogen, and possibly to partially eliminate the aromatic hydrocarbon compounds and more particularly the hydrocarbon compounds. polyaromatics. The destruction of impurities leads to the production of a hydrorefined hydrocarbon product and an acid gas rich in H2S and NH3, gases known to be inhibitors and even in some cases poisons of hydrotreatment catalysts. The simplest hydrogenation reactions generally take place in the upper part of the reactor, then become increasingly difficult as the feedstock and hydrogen progressively pass through the reactor. This loss of efficiency is due not only to the fact that the hydrocarbon feed 5 comprises more and more sulfur compounds that are refractory to the hydrogenation reactions, but also to the fact that the gas phase comprising hydrogen is loaded with compounds inhibitors (NH3 and H2S) which consequently decreases the hydrogen partial pressure. Large quantities of catalysts must therefore be put in place in order to compensate for this drop in reactivity. To circumvent this difficulty, two main alternatives are generally proposed in the state of the art: The first alternative is a pure countercurrent hydrotreating process: In this type of process, hydrogen is introduced at the bottom of the reactor and the hydrocarbon feedstock at the head. Thus, the purest hydrogen is located in the finishing zones in which are the sulfur compounds most refractory to the hydrogenation reactions. The problem of this type of process is the risk of clogging due to the flow of countercurrent charge and hydrogen. Such a method is known from US 2002/0130063. The second alternative is a simulated counter-current hydrotreating process: this type of process makes it possible to avoid the hydrodynamic difficulties associated with waterlogging while taking advantage of the advantages of the pure countercurrent. This type of process sets up a succession of fixed bed co-current but with a global circulation of hydrogen and the countercurrent charge. In the case of two successive fixed beds, the fresh feed is introduced into the first reactor in cocurrent with non-pure hydrogen from the second reactor. The liquid effluent of the first hydrotreatment reactor is separated from the gas phase containing impurities (H25, NH3) by flash or stripping with hydrogen or by any other separation means known to those skilled in the art (for example a 30 sequence of flashes). This gas stream is purified before being reinjected with the liquid effluent of the first reactor into a second finishing hydrotreating reactor. The liquid effluent of the second reactor is separated from the gas phase containing unpurified hydrogen charged with impurities (H 2 S, NH 3), the non-pure hydrogen being subsequently recycled to the first reactor. Overall, the flow of hydrogen is against the flow of the charge. This process requires the addition of several equipment and internal often expensive that can make the process non-competitive. Simulated counter-current methods can operate in co-current down, which is the most conventional case, or upward co-current. In the first case, the continuous phase is generally the gas phase whereas in the second case the continuous phase may be the liquid with gas bubbles (bubble regime) or the gas with drops of dispersed liquids (said regime of fog ). EP1149142 discloses a multi-stage hydrotreatment process comprising at least two ascending co-current hydrotreating reaction stages. The flow of hydrogen and the hydrocarbon feed is in general countercurrent: the purest hydrogen is injected on the second stage to complete the hydrotreatment of the liquid effluent from the first stage and partially hydrotreated. The two catalytic stages are placed in one and the same ferrule also comprising two gas / liquid separation zones and a "washing" zone at the ferrule head. A pump allows the circulation of the liquid effluent from the first catalytic bed to the second catalytic bed. The disadvantage of such a scheme is that this pump will have to operate at high temperature and that its investment and operation cost will be high.

The present invention proposes to optimize the process described in EP1149142 by replacing the hot pump by a sufficiently high liquid leg between the two hydrotreating reaction zones to allow the liquid fraction from the first reaction zone of flow gravitationally into the second reaction zone. This makes it possible to suppress the hot pump and thus reduce the investment and operation costs associated with it while maintaining the hydrotreatment performance in order to produce a fuel with a high cetane number, deflavored and desulfurized. In general, the invention describes a process for the hydrotreatment in a fixed bed of a hydrocarbon feed comprising sulfur and nitrogen compounds, in which the following steps are carried out: a) a first hydrotreatment step is carried out by contacting at least a portion of the feedstock and a gaseous stream comprising hydrogen with a first hydrotreatment catalyst in a first reaction zone R1 to produce a first hydrotreated effluent E 1 comprising hydrogen, H 2 S and NH 3, said part of the feedstock and said gaseous flow circulating in upward co-current in said first reaction zone R1, b) and then separating the first effluent E1 into a first gaseous fraction G1 comprising hydrogen, from H2S and NH3, and a first liquid fraction Li in a first separation zone Si, c) and then optionally cooled, and then purifying the first gaseous fraction G1 to produce an enriched flow. d) then a second hydrotreating step is carried out by contacting the first liquid fraction Li obtained in step b) and at least a portion of said hydrogen-enriched stream with a second hydrotreating catalyst in 20 a second reaction zone R2 for producing a second hydrotreated effluent E2 comprising hydrogen, NH3 and H2S, said first liquid fraction Li and said enriched hydrogen stream circulating in ascending co-current in said second reaction zone; R2, said second hydrotreating step being carried out at a higher pressure than said first hydrotreating step, said second reaction zone R2 being disposed below said separation zone Si of step b) so as to create a hydrostatic head H of liquid in a liquid leg connecting said first separation zone Si to said second reaction zone R2, the height Ha g comprising a pressure difference making it possible to carry out the flow of said first liquid fraction Li resulting from said first separation zone Si towards the second reaction zone R2 in a gravitational manner, e) and then separating in a second separation zone S2 the second effluent E2 into a second gaseous fraction G2 comprising hydrogen, H2S and NH3 and a second liquid fraction L2, f) and then recycling at least a portion of the second gaseous fraction G2 comprising hydrogen, H2S and NH3 in step a) as a gaseous stream comprising hydrogen. According to one variant, the hydrostatic head H of liquid in the liquid leg lo connecting said first separation zone Si to said second reaction zone R2 is created by disposing said second reaction zone R2 below said separation zone Si of the step b) in such a way that a height called the available height H 'is created between the introduction zone of said effluent E1 in the separation zone Si and the mixing zone of said first fraction Li with said enriched flow. hydrogen, said available height H 'creating said liquid leg with a hydrostatic height H less than or equal to said available height H', said height H being such as to generate a static pressure difference equal to the sum of the pressure drops encountered between said mixing zone and said effluent introduction zone E1 in the direction of fluid flow. According to another variant, the first reaction zone R1 and the second reaction zone R2 are arranged in the same reactor or in two different reactors. According to another variant, the first separation zone Si and the second separation zone S2 are disposed inside or outside the reactor (s). According to one variant, the pressure of said second hydrotreating step is greater by a value of between 0.01 and 0.3 MPa relative to the pressure of said first hydrotreating step. According to one variant, a hydrogen booster is carried out so as to carry out the second hydrotreatment stage in the presence of said hydrogen booster, said hydrogen booster comprising at least 95% by volume of hydrogen.

According to one variant, the reaction zones are used under the following conditions: a temperature of between 300.degree. C. and 420.degree. C., a pressure of between 2 MPa and 15 MPa, a volumetric hourly velocity of between 0.degree. 5 and 5 h -1, the ratio of hydrogen to hydrocarbon compounds of between 150 and 1000 Nm 3 / Sm 3. Alternatively, step c) performs an amine wash step to produce said hydrogen enriched stream.

According to a variant, in stage c) prior to purification, said first gaseous fraction G1 is partially condensed by cooling and the first partially condensed fraction is separated into a second first liquid fraction L1 'and a second first gaseous fraction G1', and in step c) the second first gaseous fraction G1 'is brought into contact with an absorbent solution comprising amines to produce said hydrogen-enriched stream. According to a variant, before carrying out step d), said stream enriched with hydrogen is contacted with a capture mass to reduce the water content of said hydrogen-enriched stream. According to one variant, the first catalyst and the second catalyst are independently selected from catalysts composed of a porous mineral support, at least one metal element selected from group VIB and a metal element selected from group VIII. According to one variant, the first and second catalysts are independently selected from a catalyst composed of cobalt and molybdenum deposited on a porous support based on alumina and a catalyst composed of nickel and molybdenum deposited on a porous support based on alumina. According to one variant, the first catalyst and the second catalyst are independently chosen from catalysts composed of a porous mineral support and of at least one noble metal element chosen from group VIII. According to one variant, the diameter of the first and second catalysts is between 0.9 and 5 mm.

According to one variant, the hydrocarbon feedstock is composed of a section whose initial boiling point is between 80 ° C. and 250 ° C. and the final boiling point is between 260 ° C. and 600 ° C.

DETAILED DESCRIPTION The present invention relates to a simulated countercurrent fixed bed hydrotreating process for transferring the partially hydrotreated liquid phase from the first hydrotreating zone to the second hydrotreating zone in a gravitational manner.

"Gravity flow" is understood to mean a flow of liquid which takes place under the effect of gravity and therefore does not require the aid of a pump or any other equipment. The term "hydrotreatment" is understood to mean any reaction making it possible to eliminate impurities from the feedstock, and in particular hydrodesulfurization and hydrodenitrogenation reactions, but also hydrogenation reactions of unsaturations and / or aromatic rings (hydrodearomatization) as well as hydrocracking reactions that lead to naphthenic ring opening or fractionation of paraffins into several smaller molecular weight fragments.

Step a) First hydrotreatment step According to step a) of the process according to the invention, a first hydrotreating step is carried out by contacting at least a portion of the feedstock and a gaseous stream comprising hydrogen with a first hydrotreatment catalyst in a first reaction zone R1 for producing a first hydrotreated effluent E1 comprising hydrogen, H25 and NH3, said part of the feed and said gaseous flow circulating in upward co-current in said first reaction zone Ri. The hydrocarbon feed may be a kerosene and / or a gasoline and / or a gas oil and / or a vacuum gas oil (also called VGO for vacuum gas oil according to the English terminology). The hydrocarbon feed may be a cut whose initial boiling point is between 80 ° C and 250 ° C, preferably between 100 ° C and 200 ° C, and the boiling point is between 260 ° C and 600 ° C, preferably between 280 ° C and 580 ° C. The hydrocarbon feedstock may be chosen from an atmospheric distillation cut, a cut produced by a vacuum distillation, a cut resulting from catalytic cracking (commonly known as "LCO cut" for Light Cycle Oil according to the English terminology) or a cut resulting from a heavy charge conversion process, for example a coking, visbreaking, residue hydroconversion process. In a particularly preferred manner, the feedstock is a diesel fuel. The feedstock comprises sulfur compounds, generally at a content of at least 1000 ppm by weight of sulfur, or even more than 5000 ppm by weight of sulfur. The feedstock also comprises nitrogen compounds, for example the feedstock comprises at least 50 ppm by weight of nitrogen, or at least 100 ppm by weight of nitrogen. With reference to FIG. 1, which describes the process of the invention generally, the hydrocarbon feedstock to be treated arriving via line 1 is mixed with a stream comprising hydrogen arriving via line 3. optionally be heated before its introduction into the reaction zone R1. Alternatively, the mixture of hydrogen and the feed can be carried out in the reaction zone R1. The mixture of feedstock and hydrogen is fed through line 2 upwardly into reaction zone R1 to be contacted with a hydrotreatment catalyst. If necessary, before introduction into R1, the mixture can be heated and / or relaxed. The hydrotreatment reaction makes it possible to decompose the impurities, in particular the impurities containing sulfur or nitrogen, and possibly to partially remove the aromatic hydrocarbon compounds and more particularly the polyaromatic hydrocarbon compounds. The destruction of the impurities leads to the production of a hydrorefined hydrocarbon product and an acid gas rich in H25 and NH3. This hydrotreatment reaction also makes it possible to partially or completely hydrogenate the olefins, and partially the aromatic nuclei. This makes it possible to achieve a low polyaromatic hydrocarbon compound content, for example a content of less than 8% by weight in the treated gas oil.

The reaction zone R1 can be operated with the following operating conditions: - temperature between 300 ° C. and 420 ° C., - pressure between 2 and 15 MPa (20 and 150 bar), - Volumetric Speed Hourly VVH (that is, that is, the ratio between the volume flow rate of the liquid charge with respect to the volume of catalyst) of between 0.5 and 5 h -1, - volume ratio between hydrogen (in normal m3, that is to say in m3 at 0 ° C and 0.1 MPa (i bar)) and hydrocarbons (in Standard m3, that is to say in m3 at 15 ° C and 0.1 MPa (lbar)) in the reactor H2 / HC between 50 and 1000 (Nm3 / 5m3). The operating conditions of the reaction zone R1 and the catalyst contained in the zone R1 may be chosen to reduce the sulfur content so that the sulfur content in the effluent from the zone R1 is lowered to a content comprised between between 50 and 1000 ppm weight. Thus, the hydrogenation reactions of sulfur compounds the easiest to perform are carried out in the area Ri. Step b) First separation According to step b) of the process according to the invention, the first effluent E1 is separated into a first gaseous fraction G1 comprising hydrogen, H25 and NH3, and a first liquid fraction. Li in a first separation zone Si. With reference to FIG. 1, the effluent from the reaction zone R1 via the conduit 4 is introduced into the separation zone Si in order to separate a first liquid fraction Li and a gaseous fraction G1 rich in hydrogen, H25 and NH3. The separation described in the present description can be carried out by any technique known to those skilled in the art. For example, the separation zone Si may use one or more separation tanks between gas and liquid, possibly with heat exchangers for partially condensing the gas flows. When the hydrotreatment and separation zones are disposed in the same reactor, the separation zone may be an internal one. The liquid fraction L1 is removed from the separation zone Si by the duct 6. The gaseous fraction G1 is removed from Si by the duct 5. In the process according to the invention, the first liquid hydrocarbon fraction L1 discharged from Si is partially hydrotreated. and generally still includes sulfur compounds most refractory to hydrogenation reactions. According to the invention, this first liquid fraction L1 is sent via line 6 into reaction zone R2 in order to hydrogenate the most refractory sulfur compounds. Step c) Purification of the first gaseous fraction According to step c) of the process according to the invention, it is optionally cooled, and then the first gaseous fraction G1 is purified to produce a stream enriched with hydrogen. For this purpose, the first gas fraction G1 rich in H25 and NH3 circulating in the duct 5 is advantageously introduced into a purification unit LA, for example an LA amine washing unit. In the LA unit, the hydrogen-containing H25 and H3 first gas fraction G1 is contacted with an amine-containing absorbent solution. Ammonia NH3 can be removed before the amine wash. During contacting, the acid gases are absorbed by the amines, which makes it possible to produce a stream enriched in hydrogen. FR2907024 and FR2897066 disclose amine washing processes that can be carried out in the LA unit. The stream enriched with hydrogen may optionally be brought into contact with adsorbents to dry said gas stream (reduction of the water content). The stream enriched in hydrogen may comprise at least 95% by volume, or even more than 99% by volume, or even more than 99.5% by volume of hydrogen. The hydrogen-enriched stream is then discharged from the LA amine washing unit through line 7, optionally compressed by a compressor, and recycled to the reaction zone R2 mixed in line 8 with said first liquid fraction L1 arriving via the conduit 6. Alternatively, the mixture of hydrogen and the first liquid fraction L1 arriving via the conduit 6 can be produced in the reaction zone R2.

According to a variant, a supplement of fresh hydrogen can be provided by the conduit 23. The flow of hydrogen arriving via the conduit 23 can be produced by a process commonly called "steam reforming of natural gas" or "steam methane reforming" according to the Anglo-Saxon terminology for producing a flow of hydrogen from water vapor and natural gas. The hydrogen stream 23 may contain at least 95%, or even more than 98% by volume, or even more than 99% by volume, of hydrogen. The hydrogen stream can be compressed to be at the operating pressure of the reaction zone R2. Preferably, according to the invention, the hydrogen stream 23 comes from a source external to the process, that is to say that it is not obtained from a part of an effluent produced by the method. According to a preferred variant and with reference to FIG. 2, said first gaseous fraction G1 is cooled before being purified by an EC heat exchanger to be partially condensed. The first gaseous fraction G1 flowing in the conduit 5 is cooled by the heat exchanger EC to be partially condensed. Preferably, the exchanger EC is operated to condense the majority of hydrocarbons contained in the gaseous fraction G1 and retains the majority of hydrogen, NH3 and H2S in gaseous form. The partially condensed flow from EC is introduced into the separation zone Si ', for example a separator flask, in order to separate a second first liquid fraction L1' containing hydrocarbons and a second first hydrogen-rich gas fraction G1 ', in NH3 and in H25. The second first liquid fraction L1 'is discharged from Si' through line 24. The second first gaseous fraction G1 'is removed from Si' by line 26 and then purified to produce a stream enriched in hydrogen. The first liquid fraction L1 coming from the separation device Si (line 6) and the second first liquid fraction L1 'coming from the separation device Si' (line 24) are advantageously combined to be sent to the reaction zone R2. Optionally, a stream of water may be added through line 28 to the gaseous fraction flowing in line 5 to allow dissolution of the NH 3 present in the gaseous fraction in an aqueous fraction. In this case, an aqueous fraction containing dissolved NH 3, which is discharged via line 30, is also separated from the flask Si. Optionally, part or all of the hydrocarbon liquid fraction derived from Si 'through line 24 is discharged from the flask. process via line 32 as a hydrotreated cut, for example as a hydrotreated gas oil cut. Indeed, according to the operating conditions of the reaction zone Ri, this hydrocarbon liquid fraction may be at or near the specifications in terms of sulfur, nitrogen and content of aromatic hydrocarbon compounds. Step d) Second hydrotreatment step According to step d) of the process of the invention, a second hydrotreatment step is carried out by bringing the first liquid fraction Li obtained in step b) into contact with at least a portion said hydrogen enriched stream with a second hydrotreatment catalyst in a second reaction zone R2 to produce a second hydrotreated effluent E2 comprising hydrogen, NH3 and H2S. In this step d) said first liquid fraction Li and said hydrogen-enriched stream circulate in downward co-flow in said second reaction zone R2. Said second hydrotreating step is moreover carried out at a higher pressure than said first hydrotreating step. Said second reaction zone R2 is disposed below said separation zone Si of step b) so as to create a hydrostatic head H of liquid in a liquid leg connecting said first separation zone Si to said second reaction zone R2 . The height Ha is such that it generates a pressure difference making it possible to carry out the flow of said first liquid fraction Li resulting from said first separation zone Si towards the second reaction zone R2 in a gravity manner. More particularly, the hydrostatic head H of liquid in the liquid leg connecting said first separation zone Si to said second reaction zone R2 is created by disposing said second reaction zone R2 below said separation zone Si of step b ) in such a way that a height called the available height H 'is created between the introduction zone of said effluent E1 in the separation zone Si and the mixing zone of said first fraction Li with said hydrogen-enriched stream. Said available height H 'creating said liquid leg with a hydrostatic head H less than or equal to said available height H' is such that it generates a static pressure difference equal to the sum of the pressure losses encountered between said mixing zone and said zone for introducing the effluent E1 in the direction of circulation of the fluids. The available height Ha 'is a fixed height, defined by geometric parameters, and in particular by the position of the zone of introduction of the effluent Ela with respect to the position of the mixing zone of the first fraction Lia with the flow enriched with hydrogen.

The hydrostatic head Ha of the liquid leg is a fluctuating height, defined by physical parameters, and in particular by the sum of the head losses. With reference to FIG. 1, the available height H 'is defined by the height of the duct 4 (introduction zone of the effluent E1) at the height of the junction point of the duct 7 with the duct 6 (mixing zone of said first fraction Li has with said hydrogen enriched stream). The hydrostatic head H is the height of the liquid leg of said first liquid fraction Li up to the junction point of the duct 7 with the duct 6. It is meant by the sum of the pressure losses encountered between the mixing zone of said first fraction Li liquid and said stream enriched in hydrogen and the zone of introduction of said first effluent E1 into said separation zone Si in the direction of fluid flow, all the pressure losses encountered in the reaction zones R1 and R2, in the separating zones Si and S2 and in all conduits the binders. More particularly and with reference to FIG. 1, the sum of the pressure losses encountered between the mixing zone of said first liquid fraction Li and said stream enriched with hydrogen and the zone of introduction of said first effluent E1 into said separation zone Si in the direction of the circulation of the fluids is the sum of the losses of charges successively encountered in the second reaction zone R2, then in the conduit 9, then in the second separation zone S2, then in the ducts 3, then in the duct 2, then in the first reaction zone R1, then in the conduit 4. This height H of the liquid leg can be calculated as follows: DP = pxgxH with p the density of the liquid contained in the liquid leg of height H DP the sum of the pressure losses between the mixing zone of said first liquid fraction Li with the stream enriched in hydrogen and the zone of introduction of the effluent E1 into the separation zone Si in the direction of the circulation of fluids; - the acceleration of gravity on the surface of the Earth of 9.81 m.s-2 and - H the height of the liquid leg. By way of example, assuming a liquid density of 600 kg / m3, g = 9.81 ms-2, and pressure drops of DP = 0.04 MPa or 0.4 bar, the height H of the liquid leg is 7 meters to allow the transfer of the first liquid fraction Li from the first reaction zone R1 to the second reaction zone R2 without the aid of a pump. The available height H 'must therefore be at least equal to 7 meters. The pressure drop, whether at the level of a reaction zone, a separation zone or a duct, represents a pressure difference between two points that the person skilled in the art can easily measure; for example, the pressure difference (A p) between the outlet and the inlet of the reaction zone R1 gives the pressure drop of the zone Ri. The sum of all the pressure drops is thus measured by proceeding in the same manner for all the zones and conduits traversed by the fluids between the mixing zone of said first liquid fraction Li and said hydrogen-enriched stream and the introduction zone. said first effluent E1 in said first separation zone Si in the fluid flow direction. In order to limit the height H of the liquid leg, and therefore the available height H ', the pressure losses in the reaction zones R1 and R2 as well as in the separation zones Si and S2 are advantageously limited.

According to a preferred variant, the diameter of the first and second hydrotreatment catalysts is advantageously between 0.9 and 5 mm, preferably between 1.6 and 3.2 mm. Indeed, the use of larger diameter catalyst grains makes it possible to increase the void fraction in the reaction zone and thus reduce the pressure drop. Note that the name "diameter" refers not only to a ball shape or extruded, but more generally to any particle shape. The term "diameter" denotes the representative length of the particle on which the measurement is made. The first catalyst may have a diameter that is the same or different from the diameter of the second catalyst. With reference to FIG. 1, the first partially hydrotreated liquid fraction L1 arriving via line 6 is mixed with at least a portion of the stream enriched in hydrogen arriving via line 7. The first liquid fraction L1 can optionally be reheated before its introduction into the reaction zone R2. If necessary, before introduction into R2, the mixture can be heated and / or relaxed. Alternatively, the mixture of hydrogen and the first liquid fraction L1 arriving via line 6 can be produced in reaction zone R2. The mixing zone can thus be outside or inside the reaction zone R2. According to the invention, the mixture comprising the first liquid fraction L1 and the stream enriched in hydrogen is introduced in ascending cocurrent in the reaction zone R2 to be brought into contact with a hydrotreatment catalyst. The hydrotreatment reaction makes it possible to decompose the impurities, in particular the impurities containing sulfur or nitrogen, and possibly to partially remove the aromatic hydrocarbon compounds and more particularly the polyaromatic hydrocarbon compounds. The destruction of the impurities leads in particular to the production of a hydrorefined hydrocarbon product and an acid gas rich in H25 and NH3. The fact of sending purified hydrogen, that is to say without or without inhibiting compounds, in particular H25 and NH3, from the hydrogenation reaction in zone R2 makes it possible to maximize the hydrogen partial pressure. in the zone R2 in order to carry out the most difficult hydrogenation reactions there. The stream of purified hydrogen advantageously comes from the purification unit LA, for example an amine washing unit LA and optionally the hydrogen filling arriving via the pipe 23. Preferably, according to the invention, the entire flow from the purification unit LA is introduced into the zone R2. Preferably according to the invention, the hydrogen present in the zone R2 comes solely and directly from the hydrogen-rich stream coming from the unit LA and from the hydrogen filling coming through the pipe 23. The reaction zone R2 can operate with the following operating conditions: - temperature between 300 ° C. and 420 ° C., - pressure of between 2 MPa and 15 MPa (20 bar and 150 bar), - the pressure of R2 is greater than the pressure of R1, preferably, the pressure of R2 is greater by a value of between 0.01 MPa and 0.3 MPa (0.1 bar and 3 bar), preferably between 0.03 MPa and 0.1 MPa (0.3 bar and 1 bar) with respect to the pressure of R1, - hourly volumetric velocity VVH between 0.5 and 5 h -1, - ratio of hydrogen to H2 / HC hydrocarbons of between 50 and 1000 (Nm3 / Sm3 ). Step e) Second separation According to step e) of the process according to the invention, the second effluent E2 is separated in a second separation zone S2 into a second gaseous fraction G2 comprising hydrogen, H25 and H2. NH3 and a second liquid fraction L2. Referring to FIG. 1, the effluent from the reaction zone R2 via line 9 is introduced into a separation zone S2, for example a separator flask, in order to separate a liquid fraction L2 comprising hydrocarbons and a fraction gas G2 rich in hydrogen and H25 and NH3. The separation zone S2 may use one or more separation flasks, possibly with heat exchangers for condensing the gas flows. The liquid fraction L2 is discharged from S2 via line 10. This liquid fraction constitutes the product of the process according to the invention, for example, gas oil depleted of sulfur, nitrogen and aromatic compounds. The second gaseous fraction G2 is discharged from S2 via line 3. Step f) Recycling the second gaseous fraction According to step f) of the process according to the invention, at least a portion of the second gaseous fraction G2 containing hydrogen, H25 and NH3 in step a) as a gaseous stream comprising hydrogen. With reference to FIG. 1, the second gaseous fraction G2 coming from the zone S2 is recycled in the process via the pipe 3 mixed with the charge flowing in the pipe 1. No compressor is required because of a pressure slightly higher in the reactor R2. Alternatively, the reaction zone R1 is disposed in a first reactor and the second reaction zone R2 is disposed in a second reactor upstream of the first reactor. In this case, the separation zones Si and S2 are advantageously separation flasks, possibly with heat exchangers for condensing the gas flows. Such an alternative is described in FIGS. 1 and 2. In this way, the operating temperature of the reaction zone R1 can be selected independently of the operating temperature of the reaction zone R2. According to another variant, the reaction zones R1 and R2 as well as advantageously the separation zones Si and S2 are grouped together in the same reactor. The reactor can be of cylindrical shape whose axis is vertical. The reaction zone R1 is located above the reaction zone R2 in the reactor. In this case, the separation zones are advantageously internals. Such a variant is described in FIG. 3, in which the references identical to those of FIG. 1 or 2 designate the same elements. Thanks to this variant, one benefits from the advantages of the simulated countercurrent while considerably reducing the number of equipment. This reduces investment and operating costs. With reference to FIG. 3, the hydrocarbon feedstock to be treated is injected via line 1 into reaction zone R1 and mixed with a stream comprising hydrogen arriving via line 3. The feedstock may optionally be heated before it is introduced into the feed. the reaction zone Ri. The mixture of the feedstock and hydrogen is introduced in ascending co-flow into the reaction zone R1 to be contacted with a hydrotreatment catalyst. The effluent from the reaction zone R1 is separated in the separation zone Si in a first liquid fraction Li and a gas fraction G1 rich in hydrogen, H25 and NH3. The separation can be carried out by any technique known to those skilled in the art, for example in the case where the liquid phase is the continuous phase, the gas bubbles will easily disengage from the liquid if the liquid velocity is not too much important when leaving the reaction zone Ri. In the case where the gas phase is the continuous phase and the drops of liquid are dispersed, internals for coalescing the drops and collect the liquid. For example, it is possible to set up a succession of plateau with caps. The liquid fraction Li is removed from Si via line 6. The gaseous fraction G1 is discharged from B1 through line 5. The gaseous fraction G1 is then purified, advantageously in an LA amine washing unit. The hydrogen-enriched gas is discharged from the amine washing unit via line 7, possibly compressed by a compressor and recycled to the reaction zone R2. According to one variant, a fresh hydrogen filling can be provided via line 23 in line 7.

The first partially hydrotreated liquid Li fraction arriving via line 6 is introduced into the reaction zone R2. With the liquid leg of a height H generating a static pressure difference equal to the sum of the pressure losses encountered between the mixing zone of said first liquid fraction Li and said hydrogen enriched stream and the introduction zone of the first effluent E1 in said first separation zone Si in the direction of flow of the fluids, the flow of the first liquid fraction Li is carried out gravity. If necessary, before introduction into R2, the first liquid fraction L1 can be heated and / or relaxed. The mixture of the first liquid fraction L1 and said hydrogen-enriched stream is introduced in upward co-flow into the reaction zone R2 to be contacted with a hydrotreatment catalyst. The fact of sending purified hydrogen, that is to say without or without inhibitory compounds, in particular H25 and NH3, from the hydrogenation reaction in the zone R2 makes it possible to maximize the partial pressure of hydrogen in zone R2 in order to carry out the most difficult hydrogenation reactions there. The stream of purified hydrogen advantageously comes from the purification unit LA and optionally from the hydrogen additive arriving via the conduit 23. The effluent from the reaction zone R2 is separated in the separation zone S2, for example a specific internal in a second liquid fraction L2 and a second gaseous fraction G2 rich in hydrogen, H25 and NH3. The liquid fraction L2 is discharged from S2 via line 10. This liquid fraction constitutes the product of the process according to the invention, for example, gas oil depleted of sulfur, nitrogen and aromatic compounds. The second gaseous fraction G2 from the device S2 is recycled via the conduit 3 to be introduced into the first reaction zone R1. No compressor is required because of a slightly higher pressure in the reactor R2.

Of course, the process according to the invention is not limited to two reaction zones, but can very well be applied to a succession of at least two reaction zones operating in a similar manner, for example a succession of three or four hydrotreating zones, followed respectively by a separation zone.

The reaction zones R1 and R2 may contain catalysts of identical compositions or catalysts of different compositions. The reaction zones R1 and R2 may also contain one or more inert (s), that is to say one or more substance (s) having little or no catalytic activity but having the property of adsorbing the impurities contained in the load (guard bed). In addition, in a reaction zone, one or more catalyst beds of identical composition can be arranged, or several catalyst beds, the composition of the catalysts being different from one bed to another. In addition, a catalytic bed may optionally be composed of different catalyst layers. The catalysts employed in the reaction zones may in general comprise a porous mineral support, at least one metal or metal compound of group VIII of the periodic table of elements (this group especially comprising cobalt, nickel, iron, etc ...) and at least one metal or metal compound of group VIB of said periodic classification (this group including in particular molybdenum, tungsten, etc ...).

The sum of metals or metal compounds, expressed as weight of metal relative to the total weight of the finished catalyst is often between 1 and 50% by weight. The sum of the metals or compounds of metals of group VIII, expressed in weight of metal relative to the weight of the finished catalyst is often between 1 and 15% by weight, preferably between 2 and 10% by weight. The sum of the metals or compounds of Group VIB metals, expressed in weight of metal relative to the weight of the finished catalyst is often between 2 and 50% by weight, preferably between 5 and 40% by weight. According to another variant, the catalysts employed in the reaction zones R 1 and R 2 may generally comprise a porous mineral support and at least one noble metal or noble metal compound of group VIII of the periodic table of the elements (this group comprising especially palladium, platinum, rhodium, ruthenium, etc.). Its content is generally between 0.1 and 2% by weight relative to the total weight of the finished catalyst. The porous inorganic support may comprise, without limitation, one of the following compounds: alumina, silica, zirconia, titanium oxide, magnesia, or two compounds chosen from the preceding compounds, for example silica-alumina or alumina-zirconia, or alumina-titanium oxide, or alumina-magnesia, or three or more compounds selected from the foregoing compounds, for example silicalumin-zirconia or silica-alumina-magnesia. The support may also comprise, in part or in whole, a zeolite. Preferably, the catalyst comprises a support composed of alumina, or a support composed mainly of alumina (for example from 80 to 99.99% by weight of alumina). The porous support may also comprise one or more other promoter elements or compounds, based for example on phosphorus, magnesium, boron, silicon, or comprising a halogen. The support may for example comprise from 0.01% to 20% by weight of B 2 O 3, or of SiO 2, or of P 2 O 5, or of a halogen (for example chlorine or fluorine), or 0.01 to 20% wt. an association of several of these promoters. Common catalysts are, for example, catalysts based on cobalt and molybdenum, or on the basis of nickel and molybdenum, or else based on nickel and tungsten, on an alumina support, this support possibly comprising one or more promoters such as than previously cited. The catalyst may be in oxide form, that is to say that it has undergone a calcination step after impregnation of the metals on the support. Alternatively, the catalyst may be in an additivated dried form, that is to say that the catalyst has not undergone a calcination step after impregnation of the metals and an organic compound on the support. Generally the organic compound contains oxygen and / or nitrogen. Catalysts in the additive-dried form are generally known to be more active and less tolerant of impurities than catalysts in oxide form. According to a preferred variant, a catalyst based on cobalt and molybdenum is used in the first reaction zone R1 and a catalyst based on nickel and molybdenum in the second reaction zone R2. According to another preferred variant, a catalyst in oxide form is used in the first reaction zone R1 and a catalyst in dried form additive in the second reaction zone R2. The examples presented below serve to illustrate the operation of the process according to the invention and to show the advantages thereof. Hydrotreatment of diesel fuel with a final sulfur objective of 10 ppm by weight. The treated feed is composed of 80% by weight of GOSR (a gas oil resulting from atmospheric distillation) and 20% by weight of LCO (catalytic cracking cut). The characteristics of the load are shown in Table 1.

GOSR / LCO load (80/20) Density (15 ° C) kg / m3 861 Initial sulfur ppm Weight 9087 Initial nitrogen ppm Weight 266 BPSD capacity 60,000 Target sulfur ppm Weight Table 1: Load characteristics Example 1 describes a simulated countercurrent hydrotreating process in ascending cocurrent according to the prior art with the pressure of the reactor R2 greater than the pressure of the reactor R1. In this example, two reactors each having a catalyst bed and a pump are used to allow the transfer of the liquid to the reactor R2. Example 2 describes a simulated countercurrent hydrotreatment process according to the invention (FIG. 2) in which two reactors each having a catalytic bed are used.

Example 3 describes a simulated countercurrent hydrotreatment process according to the variant described in FIG. 3. In the catalytic bed R1, a CoMo catalyst on an alumina support is used. In the catalytic finishing bed R2 a NiMo catalyst supported on alumina is used. The operating conditions of the reactors, identical for the three examples, are given in Table 2. Catalyst (total volume CoMo + NiMo) m3 240 Diameter equivalent extruded mm 3.2 Overall VVH h-1 1.6 Ratio R1 / R2 m3 / m3 1.0 Exit pressure R2 bara 42.0 Inlet liquid surface velocity of R2 cm / s 0.5 Mean mass temperature of R1 and R2 ° C 355 H2 recycle / HC inlet of R1 Nm3 / 5m3 150 Table 2: Operating Conditions for the Three Examples The aim is to obtain a final sulfur content of 10 ppm by weight in each of the examples. From this objective, the design of the reactors is given in Table 3. Example 1 Example 2 Example 3 (Comparative) (According to (according to the invention - the invention - Figure 2) Figure 3) Number of reactors - 2 2 1 Reactor diameter mm 5500/5500 5500/5500 5500 Reactor height mm 5550/5550 5550/5550 12100 Total pressure drop bar a 0.44 0.44 0.44 Available height H 'mm 0 13100 11100 Leg height H mm 0 7500 7500 Number of pumps required - 2 (including one 0 0 backup) Power of a pump kW 30 0 0 Table 3: Sizing of the reactors The examples according to the invention show that it is possible to suppress the energy consumption of a pump as well as the investment of a second pump to operate the process compared to a conventional upcurrent countercurrent process (Example 1) while limiting the number and size of additional equipment, including: - two reactors of low h author (Example 2) - a compact arrangement in a single reactor (Example 3).

Claims (15)

REVENDICATIONS1. A process for the fixed bed hydrotreatment of a hydrocarbon feed comprising sulfur and nitrogen compounds, wherein the following steps are carried out: a) a first hydrotreatment step is carried out by contacting at least a portion of the feedstock and a feedstock; gas stream comprising hydrogen with a first hydrotreatment catalyst in a first reaction zone R1 to produce a first hydrotreated effluent E1 comprising hydrogen, H25 and NH3, said part of the feed and said feed gas flowing in ascending co-current in said first reaction zone R1, b) and then separating the first effluent E1 into a first gaseous fraction G1 comprising hydrogen, H25 and NH3, and a first liquid fraction Li in a first separation zone Si, c) and then optionally cooled, then the first gaseous fraction G1 is purified to produce a stream enriched in hydrogen, d) then a second sample is made. hydrotreatment step by contacting the first liquid fraction Li obtained in step b) and at least a portion of said hydrogen-enriched stream with a second hydrotreatment catalyst in a second reaction zone R2 to produce a second effluent E2 hydrotreated mixture comprising hydrogen, NH3 and H25, said first liquid fraction Li and said circulating enriched hydrogen enriched stream in said second reaction zone R2, said second hydrotreatment stage being carried out at a temperature of higher pressure than said first hydrotreating step, said second reaction zone R2 being disposed below said separation zone Si of step b) so as to create a hydrostatic head H of liquid in a liquid leg connecting said first separation zone If at said second reaction zone R2, the height Ha generates a pressure difference making it possible to achieve the flow of said first liquid fraction Li from said first separation zone Si towards the second reaction zone R2 in a gravitational manner, e) then, in a second separation zone S2, the second effluent E2 is separated into a second gas fraction G2 comprising hydrogen, H 2 S and NH 3 and a second liquid fraction L 2, f) and then at least a portion of the second gaseous fraction G 2 containing hydrogen, H 2 S and NH 3 is recycled to step a) as a gas stream comprising hydrogen. 2. Method according to claim 1, the hydrostatic head H of liquid in the liquid leg connecting said first separation zone Si to said second reaction zone R2 is created by disposing said second reaction zone R2 below said separation zone Si of step b) in such a way that a height called the available height H 'is created between the introduction zone of said effluent E1 in the separation zone Si and the mixing zone of said first fraction Li with said flow hydrogen enriched, said available height H 'creating said liquid leg with a hydrostatic head H less than or equal to said available height H', said height H being such that it generates a static pressure difference equal to the sum of the losses of charge encountered between said mixing zone and said E effluent introduction zone in the direction of fluid flow. 3. Method according to one of claims 1 or 2, wherein the first reaction zone R1 and the second reaction zone R2 are disposed in the same reactor or in two different reactors. 4. The method of claim 3, wherein the first separation zone Si and the second separation zone S2 are disposed inside or outside the reactor (s). 5. Method according to one of claims 1 to 4, wherein the pressure of said second hydrotreating step is greater by a value between0.01 and 0.3 MPa relative to the pressure of said first step of hydrotreating. 6. Method according to one of claims 1 to 5, wherein a hydrogen booster is carried out so as to carry out the second hydrotreatment step in the presence of said hydrogen booster, said booster hydrogen having at least 95% by volume of hydrogen. hydrogen. 7. Method according to one of claims 1 to 6, wherein the reaction zones are implemented with the following conditions: - temperature between 300 ° C and 420 ° C, - pressure between 2 MPa and 15 MPa, - Hourly Volumetric Speed between 0.5 and 5 h -1, - ratio between hydrogen and hydrocarbon compounds between 150 and 1000 Nm3 / Sm3. The process according to one of claims 1 to 7, wherein step c) performs an amine wash step to produce said hydrogen enriched stream. 9. Method according to one of claims 1 to 8, wherein in step c) before purification, is partially condensed by cooling said first gaseous fraction G1 and separates the first partially condensed fraction into a second first liquid fraction L1 and a second first gaseous fraction G1 ', and in step c) contacting the second first gaseous fraction G1' with an absorbent solution comprising amines to produce said hydrogen enriched stream. 10. The method of claim 9, wherein before performing step d) is contacted said hydrogen enriched stream with a capture mass to reduce the water content of said hydrogen-enriched stream. 11. Process according to one of claims 1 to 10, in which the first catalyst and the second catalyst are independently selected from catalysts composed of a porous mineral support, at least one metal element selected from group VIB and from a metal element selected from group VIII. The process according to claim 11, wherein the first and second catalysts are independently selected from a catalyst composed of cobalt and molybdenum deposited on a porous alumina support and a catalyst composed of nickel and molybdenum deposited on a porous support based on alumina. 13. Method according to one of claims 1 to 12, wherein the first catalyst and the second catalyst are independently selected from catalysts composed of a porous mineral carrier and at least one noble metal element selected from group VIII. 14. Method according to one of claims 1 to 13, wherein the diameter of the first and the second catalyst is between 0.9 and 5 mm. 15. Method according to one of claims 1 to 14, wherein the hydrocarbon feedstock is composed of a section whose initial boiling point is between 80 ° C and 250 ° C and the final boiling point is understood between 260 ° C and 600 ° C. 25