FR3020372A1 - HYDROTREATMENT PROCESS IN DOWNLINK CO-CURRENT REACTORS HAVING AN OVERCURRENT ASSEMBLY - Google Patents

Abstract

A simulated countercurrent fixed bed hydrotreatment process comprising two downward co-flow 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 Ha of liquid in a liquid leg connecting the first separation zone to the second hydrotreatment zone, the height Ha generating a pressure difference allowing the flow of the first liquid fraction to flow to the second zone of 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 feedstock and hydrogen are injected in downflow. 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 feedstock 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 inhibitor compounds. (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 avoids 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 feedstock is introduced into the first reactor in co-current 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 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. The two main types of known simulated countercurrent processes are described in FIG. 1a and FIG. 1b. The process of FIG. 1c corresponds to a simulated countercurrent process in which the pressure of the reaction zone R1 is greater than the pressure of the reaction zone R2 (P1> P2). The hydrocarbon feedstock arriving via line 1 is mixed with hydrogen arriving via line 2. Then, the mixture is introduced into a first hydrotreatment reactor R1 in order to be contacted with a hydrotreatment catalyst. The effluent from the reactor R1 is then introduced into the separator tank S1 for separating a first liquid phase and a first gaseous phase comprising hydrogen, H2S and NH3. The first liquid phase is discharged at the bottom of the flask S1 via the duct 4. The first gaseous phase comprising hydrogen, H 2 S and NH 3 is discharged at the top of the flask S1 through the duct 5 to be cooled, washed at room temperature. water and purified in an amine wash unit not shown to produce a hydrogen enriched stream. The first liquid phase arriving via line 4 is mixed with the hydrogen-enriched stream obtained from the amine washing unit arriving via line 6 to which hydrogen booster can be added. Then, the mixture is introduced into a second hydrotreatment reactor R2 to be contacted with a hydrotreatment catalyst. The effluent from reactor R2 is then introduced via line 7 into the separator tank S2 making it possible to separate the second effluent into a second gaseous fraction comprising hydrogen, H 2 S and NH 3 and a second liquid fraction. This second liquid fraction is discharged through line 11 and represents the hydrotreated product. The second gaseous fraction comprising hydrogen, H 2 S and NH 3 is compressed in the compressor C and then recycled via the pipe 2 to the first reactor R 1. In the case where the pressure of the reactor R1 is greater than the pressure of the reactor R2 (P1> P2), it is therefore necessary to have at least one compressor for compressing the non-pure hydrogen from the second reactor R2 (via the separator S2) to be able to inject it into the first reactor R1 operating at a higher pressure. The process of FIG. 1b is identical to the method described with reference to FIG. 1a except that the pressure of the reaction zone R1 is lower than the pressure of the reaction zone R2 (P1 <P2). In this case, it is necessary to have a pump P to send the liquid effluent from the first reactor R1 to the second reactor R2. Such a method is known from W002 / 31088. This document describes a process for hydrotreating a middle distillate in two consecutive steps to produce desulfurized and deflavored hydrocarbon cuts. The method of this patent is based on FIG. 1b, combining the reaction zone R1, the Si separation, the reaction zone R2 and the separation S2 in the same reactor. The reaction zone R2 is positioned above the reaction zone R1, these two zones being separated by an internal allowing the separation of the gas and the liquid from R2 (separation named S2 in FIG. 1b). Since the reaction zone R2 has a slightly higher pressure than the reaction zone R1, the internal hydrogen directly transfers hydrogen from R2 to R1 and collects the liquid which constitutes the final effluent. At the outlet of R1, an internal also makes it possible to separate the gas from the liquid. The gas is sent for purification while the liquid is cooled and pumped before being reinjected into the reaction zone R2 with the purified gas. A disadvantage of this process is the need to employ a pumping device and possibly with an upstream cooling device to allow proper operation of the pump. These two devices are disadvantageous both from an investment point of view but also from a point of view operating costs because of the power consumption to operate the pump and ensure its cooling. The present invention proposes to modify the configuration of the process described by W002 / 31088 in which the pressure of the reactor R1 is lower than the pressure of the reactor R2 (P1 <P2), by placing the separation zone Si above the reaction zone R2 and replacing the pump by a liquid leg sufficiently high between the separation zone Si and the reaction zone R2 to allow the liquid fraction from the first separation zone to flow in a gravitational manner in the second reaction zone. This allows in particular to eliminate the pump and possible cooling and thus reduce investment and operating costs related thereto while maintaining the hydrotreatment performance to produce a high cetane fuel, deflavored and desulfurized.

In general, the invention describes a process for the hydrotreatment in a fixed bed of a hydrocarbonaceous feed comprising sulfur and nitrogen compounds, in which the following steps are carried out: a) a first HTD1a hydrotreatment step is carried out by setting contacting at least a portion of the feed and a gas stream comprising hydrogen with a first hydrotreatment catalyst in a first reaction zone Ria to produce a first hydrotreated effluent E1 comprising hydrogen, H2S and NH 3, said part of the feedstock and said gas stream flowing in downward co-flow in said first reaction zone Ria, b) and then separating the first effluent El a in a first gas fraction Gia comprising hydrogen, H2S and NH3, and a first liquid fraction Li a in a separation zone Si a, c) and then optionally cooled, and then purifying the first gaseous fraction Gia to produce a flow. ichi in hydrogen, d) then a second hydrotreating step HDT2a is carried out by bringing the first liquid fraction Lia obtained in step b) and at least a portion of said hydrogen-enriched stream into contact with a second hydrotreatment catalyst in a second reaction zone R2a for producing a second hydrotreated effluent E2a comprising hydrogen, NH3 and H2S, said first liquid fraction Lia and said hydrogen enriched stream circulating in descending cocurrent in said second reaction zone; R2a, said second hydrotreatment step HDT2a being carried out at a higher pressure than said first hydrotreatment step HDT1a, said second reaction zone R2a being disposed below said separation zone S1a of step b) so creating a hydrostatic head Ha of liquid in a liquid leg connecting said first separation zone S1a to said second reaction zone R2a, the height Ha generating a pressure difference to achieve the flow of said first liquid fraction Li from said first separation zone Sla to the second reaction zone R2a gravity, lo e) and then separates in a second separation zone S2a the second effluent E2a into a second gaseous fraction G2a comprising hydrogen, H2S and NH3 and a second liquid fraction L2a, f) and then recycling at least a portion of the second gaseous fraction G2a comprising hydrogen, H2S and NH3 in step a) as a gaseous stream comprising hydrogen. According to a variant, the hydrostatic head Ha of liquid in the liquid leg connecting said first separation zone S1a to said second reaction zone R2a is created by disposing said second reaction zone R2a below said separation zone Sla of the step b) in such a way that a height called the available height Ha 'is created between the introduction zone of said effluent El a in the separation zone Sla and the mixing zone of said first fraction Lia with said enriched flow in hydrogen, said available height Ha 'creating said liquid leg with a hydrostatic head Ha less than or equal to said available height Ha', said height Ha being such as to generate a static pressure difference equal to the sum of the losses of charge encountered between said mixing zone and said zone for introducing the effluent El a in the direction of the circulation of the fluids. According to one variant, the first reaction zone Ria and the second reaction zone R2a are disposed in the same reactor or in two different reactors. According to one variant, the first separation zone S1a and the second separation zone 52a are disposed inside or outside the reactor (s).

According to one variant, the pressure of said second hydrotreatment step HDT2a is greater by a value of between 0.01 and 0.3 MPa relative to the pressure of said first hydrotreatment step HDT1a. According to a preferred variant, the process according to the invention further comprises the following steps: a ') a first hydrotreating step HDT1b is carried out by contacting another part of the feedstock and a gaseous flow comprising hydrogen with a first hydrotreatment catalyst in a first reaction zone R1b to produce a first hydrotreated effluent E1b comprising hydrogen, H25 and NH3, said other part of the feedstock and said gaseous flow circulating in co- downflow in said first reaction zone R1b, said reaction zone R1b being disposed in the space created by said height Ha of step d), b ') and then separating the first effluent E1b into a first gaseous fraction G1b comprising hydrogen, H25 and NH3, and a first liquid fraction L1b in a first separation zone Si b, c ') and then optionally cooled, and then purifying the first gaseous fraction Glb for p producing a hydrogen-enriched stream, d ') and then performing a second hydrotreatment step HDT2b by contacting the first liquid fraction L1b obtained in step b') and at least a part of said hydrogen-enriched stream with a second hydrotreatment catalyst in a second reaction zone R2b for producing a second hydrotreated effluent E2b comprising hydrogen, NH3 and H25, said first liquid fraction L1b and said hydrogen enriched stream circulating in descending cocurrent. in said second reaction zone R2b, said second hydrotreating step HDT2b being carried out at a higher pressure than said first hydrotreating step HDT1b, said second reaction zone R2b being disposed below said separation zone S1b of the step b ') so as to create a hydrostatic head height Hb of liquid in a liquid leg connecting said first separation zone S1b to said second reaction zone R2b, the height Hb generating a pressure difference making it possible to carry out the flow of said first liquid fraction Li b from said first separation zone Si b to the second reaction zone R2b in a gravitational manner; reaction R2a of step d) being arranged in the space created by said height Hb of step d ', e') and then separating in a second separation zone S2b the second effluent E2b into a second gaseous fraction G2b comprising hydrogen, H25 and NH3 and a second liquid fraction L2b, f ') and then recycling at least a portion of the second gaseous fraction G2b comprising hydrogen, H25 and NH3 to step a ') as a gas stream comprising hydrogen. According to one variant, the hydrostatic head Hb of liquid in the liquid leg connecting said first separation zone S1b to said second reaction zone R2b is created by disposing said second reaction zone R2b below said separation zone S1b of the second reaction zone R2b. step b ') in such a way that a height called the available height Hb' is created between the introduction zone of said effluent El b in the separation zone S1b and the mixing zone of said first fraction Ll b with said stream enriched in hydrogen, said available height Hb 'creating said liquid leg with a hydrostatic height Hb less than or equal to said available height Hb', said height Hb being such as to generate a static pressure difference equal to the sum of the pressure losses encountered between said mixing zone and said zone for introducing the effluent El b in the direction of circulation of the fluids. According to a variant, the part of the feedstock introduced into the hydrotreatment zone HDT1a is preferably equivalent to the portion of the feed introduced into the hydrotreatment zone HDT1b. According to one variant, the first reaction zone R1a and R1b and the second reaction zone R2a and R2b, as well as the first separation zone Sla and Slb and the second separation zone 52a and 52b are preferably arranged in the second reaction zone same reactor. 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. According to a variant, in step c) or c ') prior to the purification, said first gas fraction Gia and G1b are partially condensed by cooling respectively, and the first partially condensed fraction is separated into a second first liquid fraction Li a' and Li b 'and a second first gaseous fraction Gia' and G1b ', and in step c) or c') the second gaseous fraction Gia 'and G1b' are brought into contact with an absorbent solution comprising amines to produce said flow enriched with hydrogen. 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 chosen from group VIB and a metal element chosen from group VIII. According to one variant, the diameter of the first and second catalysts is between 1.2 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. The invention also relates to a reactor for carrying out the method according to the invention extending along a vertical axis comprising: successively from top to bottom along the vertical axis a reaction zone Ria, a separation zone S1a to separate the effluent from the reaction zone Ria in a liquid fraction and a gaseous fraction, a reaction zone Ri b, a separation zone S1b for separating the effluent from the reaction zone R1b into a liquid fraction and a gaseous fraction, a reaction zone R2a, a separation zone 52a for separating the effluent from the reaction zone R2a into a liquid fraction and a gaseous fraction, and a reaction zone R2b and a separation zone 52b for separating the effluent from the reaction zone R2b in a liquid fraction and a gaseous fraction, means for introducing the charge (2a, 2b) into the upper part of the reaction zones Ria and Rlb, and introducing means (8a, 8b) a rich feed in hydrogen in the upper part of the reaction zones R2a and R2b, means for evacuating (5a, 5b) the gas fraction from the separation zones Sla and Slb and the evacuation means (9a, 9b) of the liquid fraction from the separation zones S2a and S2b, means (4a, 4b) for bringing the gaseous fractions from the separation zones S2a and S2b respectively into the upper part of the reaction zones Ria and Ri b, means (7a, 7b) for bringing the liquid fractions from the separation zones S1a and S1b respectively into the upper part of the reaction zones R2a and R2b, the reactor being configured to create hydrostatic heights Ha and Hb of the liquid fraction resulting from separation zones Sla and Slb in the means (7a, 7b) for bringing the liquid fractions from the separation zones S1a and Slb respectively into the reaction zones R2a and R2b, the heights Ha and Hb generating a difference in ession allowing a gravity flow of the liquid fractions.

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 which makes it possible to eliminate impurities from the feedstock, and in particular hydrodesulfurization, hydrodenitrogenation reactions, but also hydrogenation reactions of unsaturations and / or aromatic rings (hydrodearomatization) and 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 HTD1a hydrotreatment step is carried out by bringing at least a portion of the feedstock into contact with a gaseous flow comprising hydrogen. with a first hydrotreatment catalyst in a first reaction zone Ria to produce a first hydrotreated effluent E1 comprising hydrogen, H25 and NH3, said part of the feedstock and said gaseous flow flowing in co-current descending into said first reaction zone Ri a. The hydrocarbon feed may be a kerosene and / or a gasoline and / or a gas oil and / or a gas oil under vacuum (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. 2, 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 2. be heated prior to introduction into reaction zone 1: 11a. Alternatively, the mixture of hydrogen and the charge can be carried out in the reaction zone Ri a. The mixture of feedstock and hydrogen is introduced in downward co-flow into reaction zone 1: 11a to be contacted with a hydrotreatment catalyst. If necessary, before introduction into 1: 11a, the mixture can be heated and / or expanded. 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 reach a content of low polyaromatic hydrocarbon compounds, for example a content of less than 8% by weight in the treated gas oil. The reaction zone 1: 11a can operate with the following operating conditions: - temperature between 300 ° C. and 420 ° C., - pressure of between 2 and 15 MPa (20 and 150 bar), - hourly volumetric velocity VVH (c ') that is to say the ratio between the volume flow rate of the liquid charge with respect to the catalyst volume) of between 0.5 and 5 h -1, - volume ratio between the hydrogen (in normal m3, that is, ie 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 (1bar)) in the H2 / HC reactor between 150 and 1000 (Nm3 / 5m3) - preferably, the liquid velocity in the reaction zone 1: 11a can be at least 2 mm / s.

The operating conditions of the reaction zone 1: 11a and the catalyst contained in the zone 1: 11a can be chosen to reduce the sulfur content so that the sulfur content in the effluent from the zone Ria is lowered. at a content of between 50 and 1000 ppm by weight. Thus, the hydrogenation reactions of sulfur compounds that are easiest to perform are carried out in the zone Ria.

Step b) First separation According to step b) of the process according to the invention, the first effluent El a is separated into a first gas fraction Gia comprising hydrogen, H25 and NH3, and a first liquid fraction. Lia in a first separation zone Sla.

With reference to FIG. 2, the effluent El from the reaction zone Ria via the conduit 3 is introduced into the separation device Sla in order to separate a first liquid fraction Lia and a hydrogen-rich gas fraction Gia, in H25. and NH3. The separation described in the present description can be performed by any technique known to those skilled in the art. For example, the separation zone Sla may use one or more separation tanks between gas and liquid, possibly with heat exchangers for partially condensing the gas flows. When the hydrotreating and separation zones are arranged in the same reactor, the separation zone may be an internal one. The liquid fraction Li a is discharged from the separation zone Sla via line 4. The gaseous fraction Gia is discharged from Sla via line 5. In the process according to the invention, the first liquid hydrocarbon fraction Lia evacuated from Sla is partially hydrotreated and generally still includes sulfur compounds most refractory to hydrogenation reactions. According to the invention, this first liquid fraction is sent via line 4 into zone R2a 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, the mixture is optionally cooled and then the first gas fraction Gia comprising hydrogen, H25 and NH3 is purified to produce a stream enriched in hydrogen.

For this purpose, the first gaseous fraction Gla rich in H 2 S and NH 3 circulating in line 5 is advantageously introduced into a purification unit LA, for example an amine washing unit. In the LA unit, the first gas fraction G1a rich in H2S and NH3 and containing hydrogen is contacted with an absorbent solution containing amines. 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. Documents FR2907024 and FR2897066 describe amine washing processes that can be implemented 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 stream enriched with hydrogen is then discharged from the LA amine washing unit via the pipe 6, possibly compressed by a compressor and recycled to the reaction zone R2a mixed with said first liquid fraction Lia arriving via the pipe 4. Alternatively the mixture of hydrogen and the first liquid fraction Lia arriving via line 4 can be produced in the reaction zone R2a.

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 to produce 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 R2a. Preferably, according to the invention, the flow of hydrogen 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 process.

According to a preferred variant and with reference to FIG. 3, said first gas fraction Gia is cooled before its purification by a heat exchanger EC to be partially condensed. Preferably, the exchanger EC is operated to condense the majority of the hydrocarbons contained in the gas fraction Gia and retains the majority of hydrogen, NH3 and H2S in gaseous form. The partially condensed flow from EC is introduced into a separation zone Sla ', for example a separator flask, in order to separate a second first liquid fraction Lia' containing hydrocarbons and a second first gaseous fraction Gia 'rich in hydrogen, in NH3 and in H2S. The second first liquid fraction Lia 'is discharged from Sla' via line 24. The second first gaseous fraction Gia 'is removed from Sla' via line 26 and then purified to produce a stream enriched with hydrogen. The first liquid fraction Lia resulting from the separation device S1a (line 4) and the second first liquid fraction Lia 'coming from the separation device Sla' (line 24) are advantageously combined to be sent to the reaction zone R2a. Optionally, a stream of water may be added through line 28 to the gaseous fraction circulating in line 5 to allow the dissolution of the NH 3 present in the gaseous fraction in an aqueous fraction. In this case, an aqueous fraction containing the dissolved NH 3, which is discharged via the line 30, is also separated from the flask 30. Optionally, part or all of the hydrocarbon liquid fraction from Si a 'is removed from the process by the conduit 32 as a hydrotreated cut, for example as a hydrotreated gas oil cutter. Indeed, according to the operating conditions of the reaction zone Ria, 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 hydrotreating step HDT2a is carried out by bringing the first liquid fraction Lia obtained in step b) into contact with at least one part of said hydrogen enriched stream with a second hydrotreatment catalyst in a second reaction zone R2a to produce a second hydrotreated effluent E2a comprising hydrogen, NH3 and H2S. In this step d) said first liquid fraction Lia and said hydrogen-enriched stream circulate in downward co-flow in said second reaction zone R2a. Said second hydrotreatment step HDT2a is, moreover, carried out at a higher pressure than said first hydrotreating step HDT1a. Said second reaction zone R2a is disposed below said separation zone S1a of step b) so as to create a hydrostatic head Ha of liquid in a liquid leg connecting said first separation zone S1a to said second zone of reaction R2a. The height Ha is such that it generates a pressure difference making it possible to carry out the flow of said first liquid fraction Lia resulting from said first separation zone Sla towards the second reaction zone R2a in a gravity manner. More particularly, the hydrostatic head Ha of liquid in the liquid leg connecting said first separation zone Sla to said second reaction zone R2a is created by disposing said second reaction zone R2a below said separation zone S1a of the step b) in such a way that a height called the available height Ha 'is created between the introduction zone of said effluent El a in the separation zone S1a and the mixing zone of the first fraction Lia with the enriched flow hydrogen. Said available height Ha 'creating said liquid leg with a hydrostatic head Ha less than or equal to said available height Ha' is such as to generate 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 has fluids in the direction of circulation. The available height Ha 'is a fixed height, defined by geometric parameters, and in particular by the position of the zone for introducing the effluent El a with respect to the position of the mixing zone of the first fraction Lia with the flow enriched in 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 load losses.

With reference to FIG. 2, the available height Ha 'is defined by the height of the duct 3 (zone for introducing the effluent El a) at the height of the junction point of the duct 6 with the duct 4 (mixing zone of said first fraction Lia with said stream enriched in hydrogen). The height Ha is the height of the liquid leg of said first liquid fraction Li a to the junction point of the duct 6 with the duct 4. It is meant by the sum of the pressure losses encountered between the mixing zone of said first fraction liquid Lia with the stream enriched in hydrogen and the zone of introduction of said first effluent El a in the separation zone S1 has in the direction of the flow of fluids, all the pressure losses encountered in the reaction zones Ria and R2a, in the separation zones Sla and S2a and in all the conduits the binders. More particularly and with reference to FIG. 2, the sum of the pressure losses encountered between the mixing zone of said first liquid fraction Lia with the stream enriched with hydrogen and the zone of introduction of the effluent E1 is in the direction of the circulation of the fluids is the sum of the pressure losses successively encountered in the second reaction zone R2a, then in the conduit 7, then in the second separation zone S2a, then in the conduit 2, then in the first reaction zone Ri a, then in the conduit 3.

This height Ha of the liquid leg can be calculated as follows: DP = pxgx Ha with p the density of the liquid contained in the liquid leg of height Ha DP the sum of the pressure drops between the mixing zone of said first liquid fraction Lia with the hydrogen-enriched stream and the zone of introduction of the effluent El a in the zone of separation S1 has in the direction of the circulation of the fluids, g the acceleration of the gravity at the surface of the Earth of 9.81 ms-2 and Ha 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 Ha of the leg liquid is 7 meters to allow the transfer of the first liquid fraction Lia from the first reaction zone Ria to the second reaction zone R2a without the aid of a pump. The available height Ha '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 Ria gives the pressure drop of the zone Ria. The sum of all the pressure drops is thus measured by proceeding in the same way for all the zones and conduits traversed by the fluids between the mixing zone of said first liquid fraction Lia and the stream enriched in hydrogen and the introduction zone. said first effluent El a in the first separation zone S1 has in the flow direction of the fluids. In order to limit the height H of the liquid leg, the pressure drops in the reaction zones Ria and R2a as well as in the separation devices S1a and S2a are advantageously limited. According to a preferred variant, the diameter of the first and second hydrotreating catalysts is advantageously between 1.2 and 5 mm, preferably between 1.6 and 4.0 mm. Indeed, the use of catalyst grains larger diameter increases the vacuum 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. 2, the first partially hydrotreated liquid fraction Lia arriving via line 4 is mixed with at least a portion of the stream enriched with hydrogen arriving via line 6. The first liquid fraction Li a may optionally be reheated before its introduction. in the reaction zone R2a. If necessary, before introduction into R2a, the mixture can be heated and / or relaxed. Alternatively, the mixture of hydrogen and the first liquid fraction Lia arriving via line 4 can be produced in reaction zone R2a. The mixing zone can thus be outside or inside the reaction zone R2a.

According to the invention, the mixture comprising the first liquid fraction and the stream enriched with hydrogen is introduced in downward co-current into the reaction zone R2a 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 the zone R2a makes it possible to maximize the partial pressure of hydrogen in zone R2a 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 the amine washing unit, and optionally from the hydrogen additive arriving via line 23.

Preferably, according to the invention, the entire stream from the purification unit LA is introduced into the zone R2a. Preferably according to the invention, the hydrogen present in the zone R2a 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 R2a can be operated with the following operating conditions: a temperature of between 300 ° C. and 420 ° C., a pressure of between 2 MPa and 15 MPa (20 bar and 150 bar), the pressure of R2a is greater than the pressure Ri preferably has the pressure of R2a is greater than a value 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 Ria, hourly volumetric velocity VVH between 0.5 and 5 h -1, ratio of hydrogen to H2 / HC hydrocarbons of between 150 and 1000 (Nm3 / Sm3). Step e) Second Separation According to step e) of the process according to the invention, the second effluent E2a is separated in a second separation zone 52a into a second gaseous fraction G2a comprising hydrogen, H25 and NH3. and a second liquid fraction L2a. Referring to Figure 2, the effluent from the reaction zone R2a is introduced via the conduit 7 into the separation device 52a in order to separate a liquid fraction L2a comprising hydrocarbons and a gas fraction G2a rich in hydrogen and in H25 and NH3. For example, the separation device 52a may use one or more separation flasks, possibly with heat exchangers for condensing the gas flows. The liquid fraction L2a is discharged from 52a through line 11. This liquid fraction is the product of the process according to the invention, for example the gas oil depleted of sulfur, nitrogen and aromatic compounds. The second gaseous fraction G2a is discharged from 52a via line 2. Step f) Recycling of the second gaseous fraction According to step f) of the process according to the invention, at least a portion of the second gaseous fraction G2a comprising hydrogen, H25 and NH3 in step a) as a gaseous stream comprising hydrogen.

With reference to FIG. 2, the second gaseous fraction G2a resulting from the device 52a is recycled in the process via the conduit 2 mixed with the charge flowing in the conduit 1. According to one variant, the reaction zone Ria is disposed in a first reactor and the second reaction zone R2a is disposed in a second reactor upstream of the first reactor. In this case, the separation zones S1a and S2a are advantageously separation flasks, possibly with heat exchangers for condensing the gas flows. Such a variant is described in FIGS. 2 and 3.

In this way, the operating temperature of the reaction zone Ria can be chosen independently of the operating temperature of the reaction zone R2a. 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 height Ha of the liquid leg is the motive force for the transfer of the liquid making it possible to carry out the flow of the partially hydrotreated liquid fraction in a gravitational manner without the use of a pump. However, for reasons of investment and operating costs, it is advantageous to limit the available height Ha 'and therefore to limit the height Ha of the liquid leg as much as possible or not to lose it unnecessarily. According to one variant, the space created by the available height Ha 'can be used to put a reaction zone thereon, in particular by inserting in this space a reaction zone performing in parallel the hydrotreatment of another part of the charge. Indeed, by dividing the charge into different streams, preferably into equal charge flows, the method according to the invention can be carried out several times in parallel in intercalated reaction zones, using in each case the space created by the available height. Ha 'between the first separation zone Sla and the second reaction zone R2a for disposing a reaction zone of the hydrotreatment process of the other part of the charge carried out in parallel. This variant of the process according to the invention also has the advantage of being able to integrate all the reaction zones, as well as all the separation zones 30, in the same reactor as described with reference to FIG. the benefits of the simulated countercurrent while significantly reducing the number of equipment. This reduces investment and operating costs. Another advantage of this variant lies in the fact that the division of the feedstock into several streams, preferably in equal flows, makes it possible to reduce the diameter of the reactor when the same liquid surface speed is maintained within the reactor. This allows all the more a reduction in investment and operating costs. According to this variant, the following steps are carried out in the hydrotreatment process according to the invention: a ') a first hydrotreating step HDT1b is carried out by contacting another portion of the feedstock and a gaseous flow comprising hydrogen with a first hydrotreatment catalyst in a first reaction zone R1b to produce a first hydrotreated effluent E1b comprising hydrogen, H25 and NH3, said other part of the feed and said circulating gas flow in downward co-current in said first reaction zone Ri b, said reaction zone R1b being disposed in the space created by said height Ha of step d), b ') and then separating the first effluent E1b in a first gas fraction G1b comprising hydrogen, H25 and NH3, and a first liquid fraction L1b in a first separation zone Si b, c ') and then optionally cooled, and then the first gas fraction is purified; is Glb to produce a hydrogen-enriched stream, d) and then performs a second HDT2b hydrotreating step by contacting the first liquid fraction L1b obtained in step b ') and at least a portion of said hydrogen-enriched stream with a second hydrotreatment catalyst in a second reaction zone R2b to produce a second hydrotreated effluent E2b comprising hydrogen, NH3 and H25, said first liquid fraction L1b and said hydrogen-enriched stream circulating in coconut. downward flow in said second reaction zone R2b, said second hydrotreating step HDT2b being carried out at a higher pressure than said first hydrotreating step HDT1b, said second reaction zone R2b being disposed below said separation zone S1 b of step b ') so as to create a hydrostatic head height Hb of liquid in a liquid leg connecting said first separation zone S1 b to said second reaction zone R2b, the height Hb generating a pressure difference making it possible to carry out the flow of said first liquid fraction Li b from said first separation zone Si b to the second reaction zone R2b in a gravitational manner, said reaction zone R2a of step d) being disposed in the space created by said height Hb of step d ', e') and then separating in a second separation zone S2b the second effluent E2b in a second gas fraction G2b comprising hydrogen, H25 and NH3 and a second liquid fraction L2b, f ') and then recycling at least a portion of the second gaseous fraction G2b comprising hydrogen, H25 and NH3 in step a ') as a gaseous stream comprising hydrogen. According to one variant, the hydrostatic head Hb of liquid in the liquid leg connecting said first separation zone S1b to said second reaction zone R2b is created by arranging the second reaction zone R2b below the separation zone S1b of the second reaction zone R2b. step b ') in such a way that a height called the available height Hb' is created between the introduction zone of said effluent El b in the separation zone Si b and the mixing zone of said first fraction Ll b with said stream enriched in hydrogen, said available height Hb 'creating said liquid leg with a hydrostatic height Hb less than or equal to said available height Hb', said height Hb being such as to generate a static pressure difference equal to the sum of the pressure losses encountered between said mixing zone and said zone for introducing the effluent El b in the direction of circulation of the fluids. According to this variant, the portion of the feed introduced into the hydrotreating zone HDT1a is equal to the portion of the feed introduced into the hydrotreatment zone HDT1b. In this case, the available height Ha 'of step d) is identical to the available height Hb' of step d '), which makes it possible to optimize the space. According to this variant, the first reaction zone Ria and R1b and the second reaction zone R2a and R2b, as well as the first separation zone S1a and S1b and the second separation zone 52a and 52b are preferably arranged in the same region. reactor. Preferably, the first gaseous fraction G1b is combined with the first gaseous fraction Gia to send a common flow of a first gaseous fraction Gia and G1b to the purification step, advantageously carried out in a single purification device. FIG. 4 describes a device and a method according to said variant allowing the hydrotreatment in parallel of two parts of the feed, preferably equal, by using a single reactor in which two times two reaction zones and two times two separation devices are grouped in such a way that each space created by the available heights Ha 'and Hb' is occupied by a reaction zone. Of course, the process according to this variant 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. With reference to FIG. 4, the hydrocarbon feedstock arriving via the pipe 1 is divided into two equal streams in the pipes 2a and 2b before being mixed with the gases comprising hydrogen originating from the second reaction zones R2a and R2b, via ducts 4a and 4b. These gases contain mainly hydrogen but also impurities such as H25 and NH3. The liquid / gas mixtures are introduced via the ducts 3a and 3b in downward co-flow in two similar superposed, similar catalytic zones Ria and R1b of the first reaction zone R1. At the outlet of the catalytic zones R1a and R1b, separation zones S1a and S1b, for example specific internals, separate a first gaseous fraction Gla and Glb comprising hydrogen, H25 and NH3, and a first liquid fraction L1a and L1b partially hydrotreated. The streams Gia and G1b are evacuated via the ducts 5a and 5b respectively, then advantageously recombined and sent via the duct 6 to a purification zone where the H2S and NH3 are separated from the gas stream, for example in a washing unit amines not shown. The first partially hydrotreated liquid fraction Lia and L1b is respectively conveyed via the conduits 7a and 7b to the catalytic zones R2a and R2b respectively by virtue of the liquid legs of a height Ha and Hb that are sufficient for the flow to be carried out in a gravitational manner without require the use of a pump. The gaseous streams enriched in hydrogen produced in stage c), optionally supplemented with additional hydrogen, are introduced via the conduits 8a and 8b, then mixed respectively with the first liquid fraction Lia and L1b partially hydrotreated at the inlet of the catalytic zones R2a and R2b to produce in each of the catalytic zones a second hydrotreated effluent comprising hydrogen, NH3 and H2S. The separation zones S2a and S2b, for example specific internals, make it possible to separate a second gaseous fraction G2a and G2b comprising hydrogen, H2S and NH3, and a second liquid fraction L2a and L2b which is hydrotreated with in a thorough way. The second gaseous fraction G2a and G2b is respectively recycled to the first reaction zone Ria and R1b as a gaseous stream comprising hydrogen via the conduits 4a and 4b. No compressor is required to send the second gaseous fraction G2a and G2b to the ducts 2a and 2b due to the slightly higher pressure in the catalytic zones R2a and R2b than in the zones Ria and R1b. The second liquid fraction L2a and L2b, evacuated via the ducts 9a and 9b, can be recombined in the duct 10 and constitutes the final hydrotreated product.

According to this variant, the space created by the available height Ha 'is therefore cleverly used to have the reaction zone R1 b, and the space created by the available height Hb' is cleverly used to have the reaction zone R2a therein. . Likewise, the relative disposition of the separation zone S1a with respect to the first reaction zone R1a is of no importance, as long as the second reaction zone R2a is disposed sufficiently below said separation zone S1a. Thus the separation zone S1 may be arranged below (see FIG. 2) or side by side at the same height as the reaction zone Ria, or even above the reaction zone Ria. This last variant is particularly advantageous when it is desired to place the two reaction zones R 1a and R 2a in the same reactor with a spacing between the two reaction zones as small as possible, and only by deporting and raising the separation zone S1a. Thus, it is not necessary to raise the reaction zone Ria with respect to the reaction zone R2a, the space being only sufficient to accommodate the internals required for the collection of the flows of R1a and the distribution of the flows entering 2a. The reaction zones R 1a, R 1b, R 2a, R 2b can contain catalysts of identical compositions or catalysts of different compositions. The reaction zones R 1a, R 1b, R 2a, R 2b can 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 1a, R 1b, R 2a and R 2b may in general comprise a porous mineral support and at least one noble metal or noble metal compound of group VIII of the Periodic Table. elements (this group notably comprising 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 silica-alumina-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 5%, or of P 2 O 5, or of a halogen (for example chlorine or fluorine), or 0.01 to 20% by weight of 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 mentioned. 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 R1a and R1b and a catalyst based on nickel and molybdenum in the second reaction zone R2a and R2b. According to another preferred variant, a catalyst in the form of oxide is used in the first reaction zone Ria and R1b and a catalyst in dried form is added in the second reaction zone R2a and R2b. The examples presented below make it possible to illustrate the operation of the process according to the invention and to show the advantages thereof. Hydrotreatment of a diesel fuel with a final sulfur objective of 10 ppm by weight. The treated feedstock is composed of 80% by weight of GOSR (a gas oil derived from atmospheric distillation) and 20% by weight of LCO (catalytic cracking cut). The load characteristics 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 Capacity BPSD 60,000 Target sulfur ppm Weight Table 1: Characteristics of the feedstock Example 1 describes a simulated countercurrent hydrotreatment process according to the prior art with the pressure of the reactor R2 greater than the pressure of the reactor R1 (FIG. 1b). 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 hydrotreating process according to the variant described in FIG. 4 making it possible to use the available heights Ha 'and Hb' by respectively inserting the parallel reaction zones R1b and R2a. In the catalytic beds R1a and R1b a CoMo catalyst on alumina support is used. In the finishing catalytic beds R2a and R2b a NiMo catalyst on an alumina support 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 Global VVH h-1 1.6 R1a / R1b and R2a volume ratio / R2b m3 / m3 1.0 Exit pressure R2a and R2b bara 42.0 Liquid surface velocity at the inlet of R2a and R2b cm / s 0.5 Average mass temperature of the catalytic beds Ri a, Ri b, R2a and R2b ° C 355 H2 recycling / HC input of R1a and R1b Nm3 / Sm3 150 Table 2: Operating conditions for the three examples It is intended 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 3.20 Example 1 Example 2 Example 3 (Comparative (according to (according to the invention according to the invention Figure 1b) Figure 2) Figure 3) Number of reactors - 2 2 1 Reactor diameter mm 5500/5500 5500/5500 4000 Reactor height mm 5550/5550 5550/5550 28 200 Total pressure drop bar a 0.42 0.42 0.38 Available height Ha '(and mm 0 8100 7300 Hb' for example 3) Height of the liquid leg Ha (and Hb for example 3) mm 0 7020 6400 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 with a conventional countercurrent simulated process. (example 1), while limiting the number and size of additional equipment in particular: - two low-rise reactors spaced at least 7 m apart by a pipe containing a liquid leg (example 2) - a compact arrangement in a single reactor with a greatly reduced reactor diameter (approximately 30% ) (example 3).

Claims (15)

REVENDICATIONS1. A process for the hydrotreatment of a hydrocarbonaceous feed containing sulfur and nitrogen compounds in a fixed bed, in which the following steps are carried out: a) a first HTD1a hydrotreating step is carried out by contacting at least part of the feedstock and a gas stream comprising hydrogen with a first hydrotreatment catalyst in a first reaction zone Ria to produce a first hydrotreated effluent E1 comprising hydrogen, H25 and NH3, said part of the feedstock and said gas stream flowing in co-current downward in said first reaction zone Ri a, b) and then separating the first effluent El a into a first gas fraction Gia comprising hydrogen, H25 and NH3, and a first liquid fraction Li a in a separation zone Si a, c) and then optionally cooled, then the first gas fraction Gia is purified to produce a stream enriched in hydrogen, d) and then one of the second hydrotreatment step HDT2a by contacting the first liquid fraction Lia obtained in step b) and at least a portion of said hydrogen-enriched stream with a second hydrotreatment catalyst in a second reaction zone R2a to produce a second hydrotreated effluent E2a comprising hydrogen, NH3 and H25, said first liquid fraction Lia and said stream enriched in hydrogen circulating in downward co-current in said second reaction zone R2a, said second hydrotreating step HDT2a being performed at a higher pressure than said first hydrotreating step HDT1a, said second reaction zone R2a being disposed below said separation zone S1a of step b) so as to create a hydrostatic head Ha of liquid in a liquid leg connecting said first separation zone S1a to said second reaction zone R2a, the height Ha generating a differential a pressure pressure enabling the flow of said first liquid fraction Lia from said first separation zone S1a to the second reaction zone R2a to be gravitational, e) then, in a second separation zone S2a, the second effluent E2a is separated off a second gaseous fraction G2a comprising hydrogen, H2S and NH3 and a second liquid fraction L2a, f) and then recycling at least a portion of the second gaseous fraction G2a comprising hydrogen, H2S and NH3 in step a) as a gaseous stream comprising hydrogen. 2. Method according to claim 1, wherein the hydrostatic head Ha of liquid in the liquid leg connecting said first separation zone S1a to said second reaction zone R2a is created by disposing said second reaction zone R2a below said zone. separating element S1a from step b) in such a way that a height called the available height Ha 'is created between the zone of introduction of said effluent El a in the separation zone S1a and the mixing zone of said first fraction Lia with said stream enriched in hydrogen, said available height Ha 'creating said liquid leg with a hydrostatic head Ha less than or equal to said available height Ha', said height Ha being such as to generate an equal static pressure difference the sum of the pressure losses encountered between said mixing zone and said zone for introducing the effluent El a in the direction of the circulation of the fluids. 3. Method according to claims 1 or 2, wherein the first reaction zone Ria and the second reaction zone R2a are arranged in the same reactor or in two different reactors. 4. The method of claim 3, wherein the first separation zone S1a and the second separation zone S2a 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 HDT2a is greater by a value between 0.01 and 0.3 MPa relative to the pressure of said first step HDT1 hydrotreatment a. 6. Method according to one of claims 1 to 5, wherein the method according to the invention further comprises the following steps: a ') is performed, a first hydrotreating step HDT1b by contacting another part of the charge and a gas stream comprising hydrogen with a first hydrotreatment catalyst in a first reaction zone R1b to produce a first hydrotreated effluent E1b comprising hydrogen, H2S and NH3, said other part of the charge and said gaseous flow circulating in downward co-current in said first reaction zone R 1 b, said reaction zone R 1 b being disposed in the space created by said height H 1 of step d), b ') then separates the first effluent E1b into a first gaseous fraction G1b comprising hydrogen, H2S and NH3, and a first liquid fraction L1b in a first separation zone Si b, c ') and then cooled, and then we purify the first Glb gaseous fraction to produce a hydrogen-enriched stream, d) and then performs a second HDT2b hydrotreating step by contacting the first L1b liquid fraction obtained in step b ') and at least a part of said enriched flow in hydrogen with a second hydrotreatment catalyst in a second reaction zone R2b to produce a second hydrotreated effluent E2b comprising hydrogen, NH3 and H2S, said first liquid fraction L1b and said circulating hydrogen enriched stream in downward co-current in said second reaction zone R2b, said second hydrotreating step HDT2b being carried out at a higher pressure than said first hydrotreating step HDT1b, said second reaction zone R2b being disposed below said hydrotreatment zone HDT2b; separation S1 b of step b ') so as to create a hydrostatic head height Hb of liquid in a liquid leg connecting said first zone separating S1 b to said second reaction zone R2b, the height Hb generating a pressure difference making it possible to carry out the flow of said first liquid fraction L1b coming from said first separation zone Si b towards the second reaction zone R2b in a gravitational manner, said reaction zone R2a of step d) being disposed in the space created by said height Hb of step d ', e') and then separating in a second separation zone S2b the second effluent E2b a second gaseous fraction G2b comprising hydrogen, H2S and NH3 and a second liquid fraction L2b, f ') and then recycling at least a portion of the second gaseous fraction G2b comprising hydrogen, H2S and NH3 in step a ') as a gaseous stream comprising hydrogen. The method according to claim 6, wherein the hydrostatic head height Hb of liquid in the liquid leg connecting said first separation zone Slb to said second reaction zone R2b is created by disposing said second reaction zone R2b below said zone of reaction. Slb separation of step b ') in such a way that a height called the available height Hb' is created between the introduction zone of said effluent El b in the separation zone Slb and the mixing zone of said first fraction Ll b with said stream enriched in hydrogen, said available height Hb 'creating said liquid leg with a hydrostatic head Hb less than or equal to said available height Hb', said height Hb being such as to generate a static pressure difference equal to the sum of the pressure losses encountered between said mixing zone and said introduction zone of the effluent El b in the direction of the circulation of the fluids. 8. The method of claim 6 or 7, wherein the portion of the feedstock introduced into the hydrotreating zone HDT1a is equal to the portion of the feed introduced into the hydrotreating zone HDT1b. 9. Process according to one of Claims 6 to 8, in which the first reaction zone Rla and Rlb and the second reaction zone R2a and R2b, as well as the first separation zone Sla and Slb and the second separation zone 52a. and 52b are disposed in the same reactor. 10. Method according to one of claims 1 to 9, wherein the reaction zones are used 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. 11. Method according to one of claims 1 to 10, wherein in step c) or c ') before purification, partially condensing by cooling respectively said first gaseous fraction G1a and G1b and separating the first fraction partially condensed in a second first liquid fraction Lia 'and L1b' and a second first gaseous fraction Gia 'and G1b', and in step c) or c ') the second first gaseous fraction Gia' and G1b 'are brought into contact with a second absorbent solution having amines for producing said hydrogen enriched stream. 12. Method according to one of claims 1 to 11, wherein 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 d. a metal element selected from group VIII. 13. Method according to one of claims 1 to 12, wherein the diameter of the first and second catalyst is between 1.2 and 5 mm. 14. Method according to one of claims 1 to 13, 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. 15. Reactor for implementing the method according to one of claims 6 to 14 extending along a vertical axis comprising: - successively from top to bottom along the vertical axis a reaction zone Ria, a separation zone S1a for separating the effluent from the reaction zone Ria into a liquid fraction and a gaseous fraction, a reaction zone Ri b, a separation zone S1b to separate the effluent from the reaction zone R1b into a liquid fraction and a gaseous fraction a reaction zone R2a, a separation zone S2a for separating the effluent from the reaction zone R2a into a liquid fraction and a gaseous fraction, and a reaction zone R2b and a separation zone S2b for separating the effluent from the reaction zone R2a reaction zone R2b in a liquid fraction and a gaseous fraction, means for introducing the charge (2a, 2b) into the upper part of the reaction zones Ria and R1b, and introducing means (8a, 8b) of a stream enriched in hydrogen e in the upper part of the reaction zones R2a and R2b, means for evacuating (5a, 5b) the gas fraction from the separation zones Sla and Si b and means for evacuating (9a, 9b) the fraction liquid from the separation zones S2a and S2b, means (4a, 4b) for bringing the gaseous fractions from the separation zones S2a and S2b respectively into the upper part of the reaction zones Ria and Mb, means (7a, 7b). to bring the liquid fractions from the separation zones S1a and S1b respectively into the upper part of the reaction zones R2a and R2b, the reactor being configured to create hydrostatic heights Ha and Hb of the liquid fraction from the zones of separating If a and Si b in the means (7a, 7b) for bringing the liquid fractions from the separation zones S1a and S1b respectively into the reaction zones R2a and R2b, the heights Ha and Hb generating a pressure difference to perform a gravity flow of the liquid fractions.