WO2015078675A1

WO2015078675A1 - Method for hydrotreating a diesel fuel in reactors in parallel with hydrogen recycling

Info

Publication number: WO2015078675A1
Application number: PCT/EP2014/073908
Authority: WO
Inventors: Anne Claire Lucquin; Louis PEREIRA DE OLIVEIRA; Matthieu DREILLARD; Frederic Bazer-Bachi
Original assignee: IFP Energies Nouvelles
Priority date: 2013-11-28
Filing date: 2014-11-06
Publication date: 2015-06-04
Also published as: FR3013724B1; FR3013724A1

Abstract

According to the invention, a method for hydrotreating a first hydrocarbon fraction comprising sulfur and nitrogen compounds and a second hydrocarbon fraction comprising sulfur and nitrogen compounds comprises the following steps: a) the first hydrocarbon fraction and a first hydrogen flow are placed (RBP) in contact with a first hydrotreatment catalyst so as to produce a first hydrotreated effluent comprising hydrogen, H₂S, and NH₃; b) the second hydrocarbon fraction and the second hydrogen flow are placed (RHP) in contact with a second hydrotreatment catalyst so as to produce a second hydrotreated effluent comprising hydrogen, H₂S, and NH₃; c) at least one first gas fraction, comprising hydrogen, is separated (B1) from the first hydrotreated effluent, and at least one gas fraction, comprising hydrogen, is separated (B2) from the second hydrotreated effluent; d) a mixture, comprising the first gas fraction and the second gas fraction, is purified (LA) so as to produce a hydrogen-enriched flow; and e) the hydrogen-enriched flow from Step b) is recycled as a second hydrogen flow.

Description

METHOD FOR HYDROPROCESSING A GASOLINE IN REACTORS IN

The present invention relates to the field of hydrocarbon feedstock hydrotreatment processes, preferably of the gas oil type. The objective of the process is the production of a hydrocarbon stream, preferably of diesel, desulfurized.

In general, the purpose of the hydrotreatment process is to transform a hydrocarbon feedstock, in particular a gas oil fraction, in order to improve its characteristics with regard to the presence of sulfur or other heteroatoms such as nitrogen but also by decreasing the content of aromatic hydrocarbon compounds by hydrogenation and thus improving 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, heating oil, 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 to 50 ppm as of January 1, 2005).

As shown in FIG. 4, the desulphurized gas oil is produced by a conventional method comprising heating the diesel filler with hydrogen in an oven and then charging is introduced into a hydrodesulphurization unit containing a catalyst so hydrodesulphurize the charge.

Document EP2280056 describes an improved hydrodesulphurization process, similar to the diagram represented by FIG. 5. With reference to FIG. 5, the feedstock is fractionated in column C2 into a light fraction and a heavy fraction which are each introduced into a reactor. different hydrodesulfurization RBP2 and RHP2. The hydrogen content in the effluent from the reactor RHP2 is recycled directly into the reactor RBP2, while the hydrogen contained in the effluent from the reactor RBP2 is sent to an amine washing section LA2.

The present invention proposes to optimize the process described in document EP2280056 by limiting the content of H ₂ S and NH ₃ in the unit. The present invention proposes to treat two charges in parallel by hydrotreating, by using a hydrogen flow recycling loop which makes it possible in particular to limit the content of H ₂ S and NH ₃ in the hydrotreatment stages in order to increase the reactivity of the catalysts, their lifetime of the catalysts and also to reduce the energy consumption of the recycle loop of the hydrogen streams.

In general, the invention relates to a process for the hydrotreatment of a first hydrocarbon fraction comprising sulfur and nitrogen compounds and a second hydrocarbon fraction comprising sulfur and nitrogen compounds, in which the following steps are carried out:

a) a first hydrotreating step is carried out by contacting the first hydrocarbon fraction and a first stream of hydrogen with a first hydrotreatment catalyst to produce a first hydrotreated effluent comprising hydrogen, H ₂ S and NH ₃ ,

b) a second hydrotreatment step is carried out by contacting the second hydrocarbon fraction and the second hydrogen stream with a second hydrotreatment catalyst to produce a second hydrotreated effluent comprising hydrogen, H ₂ S and NH ₃ ,

c) separating from the first hydrotreated effluent at least a first gaseous fraction containing hydrogen and separating from the second hydrotreated effluent at least a second gaseous fraction comprising hydrogen,

d) purifying a mixture comprising the first gaseous fraction and the second gaseous fraction to produce a stream enriched with hydrogen,

e) recycling the hydrogen-enriched stream in step b) as a second hydrogen stream.

According to the invention, the hydrogen used in step b) can come solely from said hydrogen-enriched stream obtained in step e).

The first hydrogen stream may be produced by a hydrogen generating unit, for example a steam reforming unit of a natural gas stream.

Step a) can be implemented in a first reaction zone and step b) can be implemented in a second reaction zone, the pressure in the second reaction zone being at least 10 bars higher than the pressure in the first reaction zone.

The first reaction zone can be implemented with the following conditions:

- temperature between 300 ° C and 420 ° C,

pressure between 30 and 60 bar,

Hourly Volumetric Velocity VVH between 0.5 and 4 hr ^"1

- ratio between hydrogen and hydrocarbon compounds of between 100 and 600 Nm ³ / Sm ³

and implementing the second reaction zone with the following conditions:

- temperature between 340 ° C and 420 ° C,

pressure between 50 and 120 bar,

Hourly Volumetric Speed VVH between 0.5 and 2 hr ^"1

- ratio between hydrogen and hydrocarbon compounds between 200 and 1200 Nm ³ / Sm ³ .

Before performing step d), said first gaseous fraction can be compressed to the pressure of said second gaseous fraction.

Step d) may carry out an amine wash step to produce said hydrogen enriched stream.

More precisely, in stage c), the first effluent can be separated into a first liquid stream and said first gas stream, and the second effluent can be separated into a second liquid stream and said second gas stream, and at the stage d) the first and second gaseous streams can be contacted with an absorbent solution comprising amines to produce said hydrogen-enriched stream.

Prior to performing step e), said hydrogen-enriched stream can be contacted with a capture mass to reduce the water content of said hydrogen-enriched stream.

The first catalyst and the second catalyst may be independently selected from catalysts composed of a porous inorganic support, a metal element selected from group VIB and a metal element selected from group VIII.

The first and second catalysts may be independently selected from a catalyst composed of cobalt and molybdenum deposited on a porous carrier based on of alumina and a catalyst composed of nickel and molybdenum deposited on a porous support based on alumina.

Before step a), it is possible to carry out a fractionation step in which a hydrocarbon feedstock is separated into two fractions in order to obtain the said first hydrocarbon fraction and the said second hydrocarbon fraction. The fractionation step can be carried out in a distillation column, said first hydrocarbon fraction being discharged at the top of the column, said second hydrocarbon fraction being discharged at the bottom of the column. The first stream of hydrogen can be introduced into the column and the fraction enriched in light hydrocarbon compounds and the first stream of hydrogen can be discharged at the top of the column.

Said hydrocarbon feed may be composed of a hydrocarbon fraction whose initial boiling point is between 100 ° C and 250 ° C and the final boiling point is between 300 ° C and 450 ° C.

Said first hydrocarbon fraction can be composed of a hydrocarbon fraction whose initial boiling point is between 100 ° C and 250 ° C and the final boiling point is between 300 ° C and 450 ° C in which said second hydrocarbon fraction can be composed of a hydrocarbon fraction whose initial boiling point is between 100 ° C and 250 ° C and the final boiling point is between 300 ° C and 450 ° C and in which said second fracton may have, with respect to the first fraction, at least one of three characteristics:

the second fraction comprises by weight more sulfur than the first fraction,

the second fraction comprises by weight more nitrogen than the first fraction,

the second fraction comprises by weight more aromatic hydrocarbon compounds than the first fraction.

Other features and advantages of the invention will be better understood and will become clear from reading the description given below with reference to the drawings among which:

FIG. 1 schematizes an embodiment of the method according to the invention, FIGS. 2 and 3 represent two alternatives to the embodiment of the method according to the invention,

FIG. 4 represents a conventional hydrodesulfurization process, FIG. 5 represents a hydrodesulfurization scheme similar to the process described in document EP2280056.

The process shown schematically in Figure 1 proposes to treat two separate charges arriving through the ducts 5 and 6.

The feedstock arriving via line 5, hereinafter referred to as the first fraction, comprises hydrocarbon compounds, sulfur compounds and nitrogen compounds. For example, the first fraction is a hydrocarbon cut, of diesel type, whose initial boiling point is between 100 ° C and 250 ° C, preferably between 150 ° C and 250 ° C, and the end point of boiling is between 300 ° C and 450 ° C, preferably between 300 ° C and 400 ° C. The first fraction may comprise between 100 ppm and 50000 ppm by weight, preferably between 500 ppm and 20000 ppm by weight of sulfur compounds. Moreover, the first fraction may comprise between 20 ppm and 2000 ppm by weight, preferably between 50 ppm and 1000 ppm by weight of nitrogen compounds. For example, the first fraction is a cut from atmospheric distillation.

The feedstock arriving via line 6, hereinafter referred to as the second fraction, comprises hydrocarbon compounds, sulfur compounds and nitrogen compounds. For example, the second fraction is a hydrocarbon fraction of the diesel type whose initial boiling point is between 100 ° C. and 250 ° C., preferably between 150 ° C. and 250 ° C., and the final boiling point is between 300 ° C and 450 ° C, preferably between 300 ° C and 400 ° C. The second fraction may comprise between 100 ppm and 50000 ppm by weight, preferably between 500 ppm and 20000 ppm by weight of sulfur compounds. Moreover, the first fraction may comprise between 20 ppm and 2000 ppm by weight, preferably between 50 ppm and 1000 ppm by weight of nitrogen compounds. For example, the second fraction is a cut from an atmospheric distillation, or a conversion unit such as a catalytic cracking unit, a coker unit, a visbreaking unit.

The second fraction preferably has, by weight, more sulfur compounds than the first fraction, preferably between 1 and 4 times more, preferably even between 1 and 10 times more, by weight, than the first fraction. The second fraction preferably has, by weight, more nitrogen compounds, preferably between 1 and 6 times, by weight, than the first fraction. The second fraction preferably has, by weight, more aromatic hydrocarbon compounds, more preferably between 2 and 5 times, by weight, more compounds aromatic hydrocarbons as the first fraction. The second fraction, by its origin, may also contain olefins.

The first fraction arriving via line 5 is mixed with a stream of fresh hydrogen arriving via line 7. Then the mixture is introduced into the RBP reactor. The RBP reactor contains at least one hydrotreatment catalyst. If necessary, before introduction into RBP, the mixture can be heated and / or relaxed. Hydrogen arriving via line 7 corresponds to the makeup hydrogen necessary for the operation of the process according to the invention. In other words, the flow of hydrogen 7 corresponds to the flow rate of hydrogen consumed to hydrotreat (desulphurization, denitrogenation, olefin hydrogenation and dearomatization reaction) the flow of charge arriving through the ducts 5 and 6. The hydrogen stream 7 may be produced by a process commonly known as "steam reforming of natural gas" or "steam methane reforming" which makes it possible to produce a stream of hydrogen from water vapor and natural gas. The hydrogen stream 7 may contain more than 95% by volume, or even more than 98% by volume, or even more than 99% by volume, of hydrogen. The flow of hydrogen arriving via the pipe 1b can be compressed by the compressor K1 to be at the operating pressure of the RBP reactor. Preferably, according to the invention, the flow of hydrogen 7 comes from a source external to the process, that is to say that it is not composed of a part of an effluent produced by the process .

According to one embodiment, a portion of the hydrogen flowing in the pipe 7 can be introduced directly into the RBP reactor at an intermediate level of the catalyst bed via the pipe 7b. This makes it possible to cool the fluids circulating in the RBP reactor.

The mixture of the first fraction and hydrogen is introduced into the RBP reactor to be contacted with a hydrotreatment catalyst. Alternatively, the mixture of hydrogen and the first fraction can be produced in the RBP reactor. The hydrotreatment reaction makes it possible to decompose the impurities, in particular the impurities containing sulfur or nitrogen. The destruction of impurities leads to the production of a hydrorefined hydrocarbon product and an acid gas rich in H ₂ S and NH ₃ , gases known to be inhibitors and even in some cases poisons hydrotreatment catalysts. This hydrotreatment reaction also makes it possible to hydrogenate, partially or totally, olefins and aromatic rings. 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 RBP reactor can operate with the following operating conditions:

temperature in the reactor between 300 ° C. and 420 ° C.

pressure in the reactor of between 30 and 60 bar,

- Hourly Volumetric Speed VVH (that is to say the ratio between the volume flow rate of the liquid feed with respect to the catalyst volume) of between 0.5 and 4 h ^-1 ,

- H2 / HC ratio by volume between hydrogen (in Normals m ³ , that is to say in m ³ at 0 ° C and 1 bar) and hydrocarbons (in Standard m ³ , that is to say in m ³ at 15 ° C and 1 bar) in the reactor between 100 and 600 (Nm ³ / Sm ³ ).

According to the invention, at least a portion of the hydrogen contained in the effluent from the RBP reactor is extracted. The extraction can be carried out by using at least one gas / liquid separator tank and optionally at least one heat exchanger to partially condense the effluent from the reactor RBP or a stream containing hydrogen. For example, the effluent from the reactor RBP through the conduit 8 is cooled by the heat exchanger E2 to be partially condensed. Preferably, the exchanger E2 condenses the majority of the hydrocarbons contained in the effluent 8 and retains the majority of hydrogen and H ₂ S and NH ₃ in gaseous form. The partially condensed stream from E2 is introduced into separator tank B1 in order to separate a liquid fraction containing hydrocarbons and a gaseous fraction rich in hydrogen, NH ₃ and H ₂ S. The liquid fraction is removed from B1 via line 9. The gaseous fraction is removed from B1 via line 10.

In addition, in order to improve the extraction of NH ₃ , water arriving via line 8b can be injected into the effluent circulating in line 8 in order to trap NH ₃ in the aqueous phase. In this case, an aqueous liquid fraction containing NH ₃ from the separation flask B1 is discharged through line 9b.

The second fraction arriving via line 6 is mixed with a stream of hydrogen arriving via line 12. The mixture is then introduced into the RHP reactor. Alternatively, the hydrogen mixture and the second fraction can be produced in the RHP reactor. The RHP reactor contains at least one hydrotreatment catalyst. If necessary, before introduction into RHP, the mixture can be heated and / or relaxed.

According to one embodiment, a portion of the hydrogen flowing in the duct 12 can be introduced directly into the RHP reactor at an intermediate level of the bed of catalyst through the conduit 12b. This makes it possible to cool the fluids flowing in the reactor RHP.

The mixture of the second fraction and hydrogen is introduced into the reactor RHP to be contacted with a hydrotreatment catalyst. The hydrotreatment reaction makes it possible to decompose the impurities, in particular the impurities containing sulfur or nitrogen, and to partially or completely hydrogenate the aromatic rings. The destruction of the impurities leads in particular to the production of a hydrorefined hydrocarbon product and an acid gas rich in H ₂ S and NH ₃ .

The RHP reactor can operate with the following operating conditions:

temperature in the reactor between 340 ° C. and 420 ° C.

- pressure in the reactor between 50 and 120 bar,

preferably, the pressure in the reactor RHP is at least 10 bar higher, preferably at least 20 bar, or even at least 40 bar higher than the pressure of the RBP reactor,

- Hourly Volumetric Speed VVH between 0.5 and 2 hr ^"1

- volume ratio between hydrogen and hydrocarbons in the H2 / HC reactor between 200 and 1200 (Nm ³ / Sm ³ )

preferably, the volume ratio H2 / HC of the reactor RHP is greater by at least 200, or even more than 400, preferably at least 500 (Nm ³ / Sm ³ ), with respect to the ratio H2 / HC of the reactor RBP.

According to the invention, at least a portion of the hydrogen contained in the effluent from the reactor RHP is extracted. The extraction can be carried out using at least one gas / liquid separator tank and optionally at least one heat exchanger to partially condense the effluent from the reactor RHP. For example, the effluent from the reactor RHP through the conduit 13 is cooled by the heat exchanger E3 to be partially condensed. Preferably, the exchanger E3 condenses the majority of the hydrocarbons contained in the effluent 13 and retains the majority of hydrogen, NH ₃ and H ₂ S in gaseous form. The partially condensed stream from E3 is introduced into the separator tank B2 in order to separate a liquid fraction containing the hydrocarbons and a gaseous fraction rich in hydrogen, NH ₃ and H ₂ S. The liquid fraction is removed from B2 via the conduit. 14. The gaseous fraction is removed from B2 via line 15.

In addition, in order to improve the extraction of NH ₃ , water arriving via line 13b can be injected into the effluent circulating in line 13 in order to trap the NH ₃ in phase. aqueous. In this case, an aqueous liquid fraction containing NH ₃ from the separation flask B2 is discharged through line 14b.

The RBP and RHP reactors may contain catalysts of identical compositions or catalysts of different compositions. In addition in the same reactor can be arranged one or more catalyst beds of identical compositions, 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 used in the reactors RBP and RHP may generally comprise a porous mineral support, at least one metal or metal compound of group VIII of the periodic table of the elements (this group notably comprising cobalt, nickel, iron , etc.) and at least one metal or group VIB metal compound of said periodic table (this group comprising 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 0.5 and 50% by weight. The sum of the metals or compounds of metals of group VIII, expressed as weight of metal relative to the weight of the finished catalyst is often between 0.5 and 15% by weight, preferably between 1 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.

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. The catalyst preferably 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 0 ₃ , or from Si0 ₂ , or P ₂ 0 ₅ , or a halogen (for example chlorine or fluorine), or 0.01 to 20 wt.% Of a combination of several of these promoters. Common catalysts are, for example catalysts based on cobalt and molybdenum, or nickel and molybdenum, or nickel and tungsten, on an alumina support, this support may comprise one or more promoters as mentioned above.

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.

According to the invention, the hydrogen is extracted from the effluents from the RBP and RHP reactors to produce a stream enriched in hydrogen. For example, the streams containing hydrogen extracted effluents from the two reactors RBP and RHP by the ducts 10 and 15 are purified to produce a stream enriched in hydrogen, for example containing more than 95% by volume, or even more than 98% volume, or even more than 99% by volume, of hydrogen. The stream enriched in hydrogen is recycled by being sent, preferably via the conduit 12, preferably entirely and solely, into the reactor RHP. Preferably, the flow flowing in the duct 10 is mixed with the flow flowing in the duct 15 and a deacidification step of this mixture is carried out by placing it in contact with an absorbent solution containing amines in the LA unit.

In detail, the flow flowing in the duct 10 is compressed by the compressor K2 to reach the pressure of the flow flowing in the duct 15 and be mixed with this flow. The gas mixture comprising hydrogen is introduced via line 16 into an LA amine washing unit. In the LA unit, the gas mixture containing hydrogen is contacted with an absorbent solution containing amines. During the 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 amine washing unit. The stream enriched with hydrogen may optionally be brought into contact with adsorbents to remove the water in particular. The stream enriched in hydrogen circulating in line 17 may contain more than 95% by volume, or even more than 98% by volume, or even more than 99% by volume, of hydrogen. The hydrogen enriched gas is discharged from the LA unit via the duct 17, compressed by the compressor K3 and recycled to the reactor RHP via the conduit 12 by being mixed with the heavy fraction arriving via the conduit 6.

Thus, the process according to the invention makes it possible to introduce hydrogen with a high degree of purity, with little or no H ₂ S and NH ₃ , into the two reactors RBP and RHP, preferably with a single washing step. amines, which preserves the life of the catalysts.

In addition, the process according to the invention makes it possible to decouple the hydrogen supply sources of the RBP and RHP reactors, which makes it possible to choose the operating pressures of the RBP and RHP reactors independently of one another and gives, therefore, the possibility of operating the RBP and RHP reactors at significantly different pressures.

Moreover, the process according to the invention makes it possible to increase the H2 / HC ratio in order to increase the life of the catalyst in the RHP reactor. Indeed, increasing the H2 / HC ratio makes it possible to lower the concentration of H ₂ S and NH ₃ in the gas phase in the RHP reactor and thus makes it possible to preserve the catalyst.

The diagrams of FIGS. 2 and 3 propose two variants of the method according to the invention with respect to the embodiment of FIG. The modification concerns the origin of the first fraction and the origin of the second fraction. The methods described with reference to FIGS. 2 and 3 propose producing the first fraction and the second fraction by means of a step of fractionation of a single charge. The references of Figures 2 and 3 identical to the references of Figure 1 designate identical elements.

With reference to FIG. 2, the hydrocarbon feedstock to be treated arrives via line 1. The hydrocarbon feed may be a kerosene and / or a diesel fuel. The hydrocarbon feed may be a slice whose initial boiling point is between 100 ° C. and 250 ° C., preferably between 100 ° C. and 200 ° C., and the boiling point is between 300 and 450 ° C. preferably between 350 ° C and 450 ° C. The hydrocarbonated feed may be chosen from an atmospheric distillation cut, a cut produced by a vacuum distillation, a cut from a catalytic cracking unit (commonly called "LCO cut" for Light Cycle Oil according to the English terminology). or a cut resulting from a heavy load conversion process, for example a coking, visbreaking, and hydro-conversion process of residues. 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. sulfur. The feedstock also comprises nitrogen compounds, for example the feedstock comprises at least 50 ppm by weight of nitrogen, or even at least 100 ppm by weight of nitrogen.

The feed is divided into two sections in the distillation column C. At the bottom of the column C, an effluent is discharged through the conduit 3. The bottom of the column C is provided with a reboiler R which makes it possible to vaporize a portion of the effluent discharged at the bottom of column C through line 3 and reintroduce this portion in vapor form at the bottom of column C through line 4. The other part of effluent 3 is discharged through line 6. L Effluent discharged at the top of the column C is cooled in the heat exchanger E1 to be condensed. Part of the condensates 2 is recycled to the top of column C as reflux. The other part of the effluent condensed by the exchanger E1 is discharged through line 5.

Thus, the distillation column C makes it possible to produce the first fraction, also hereinafter referred to as a "light fraction", evacuated via line 5 and the second fraction, also hereinafter referred to as "heavy fraction", discharged via line 6. can operate the distillation column C to make a cut at a cutting point between 260 ° C and 350 ° C, that is to say that the light fraction compasses the compounds vaporizing at a temperature below the temperature of the cutting point and that the heavy fraction comprises the compounds vaporizing at a temperature above the temperature of the cutting point. The distillation column is preferably operated in such a way that the normalized volume flow (that is, the volume flow rate at T = 15 ° C. and P = 1 bar) of the heavy fraction circulating in the duct 6 is between 30% and 80% of the normal volume flow rate of the charge arriving via line 1. To modify the operating conditions of column C, it is possible in particular to modify the flow rate and / or the temperature of the reboil flow produced by the reboiler R, and / or the flow rate and / or the temperature of the reflux coming through the duct can be modified. 2.

The rest of the process of FIG. 2 is identical to the method described with reference to FIG.

The diagram of FIG. 3 proposes a variant of the method according to the invention with respect to the embodiment of FIG. 2. The modification relates to the step of splitting the feedstock into a first fraction and a second fraction. The references of FIG. 3 identical to the references of FIG. 1 denote identical elements. With reference to FIG. 3, charge is introduced via line 1 at the top of distillation column C and the stream of hydrogen is introduced through line 7 at the bottom of column C. The flow of hydrogen arriving via the conduit 7 corresponds to the hydrogen make-up in the process. As for the process described with reference to FIG. 2, the flow of hydrogen 7 may be produced by a steam reforming unit of natural gas. Hydrogen enables the light hydrocarbon compounds to contribute to the separation of the two fractions by column C. In order to modify the operating conditions of column C, the flow rate and / or the temperature of the flow can be modified. reboiler produced by the reboiler R, and / or the temperature of the feed introduced via line 1 into column C can be modified. Distillation column C makes it possible to produce the first fraction, also called "light fraction", evacuated by the conduit 5 and the second fraction, also called "heavy fraction", discharged through line 6. The light fraction comprises at least 50% by weight, or even at least 90% by weight, or even at least 95% by weight of the hydrogen introduced by the leads 7 in column C.

The rest of the process of FIG. 3 is identical to the method described with reference to FIG.

The examples presented below make it possible to illustrate the operation of the process according to the invention and to show the advantages thereof.

In the examples, the cetane numbers are determined according to the method described by ASTM D976.

Example 1 Comparison Between the Process of FIG. 2 According to the Invention and the Process of FIG. 4

The process of FIG. 4 corresponds to the conventional process in which all the diesel fuel is treated in a single reactor. With reference to FIG. 4, the feedstock arriving via the pipe 101 is mixed with the hydrogen arriving via the pipe 102. The mixture is heated in the heat exchanger E101 and then introduced into the reactor R101 to be brought into contact. with a hydrotreatment catalyst. The effluent from the reactor R101 is cooled by the heat exchanger E102 to be partially condensed, before being introduced into the separator tank B101. Liquid hydrocarbons hydrotreated are discharged at the bottom of the flask B101 through the conduit 103. The hydrogen-containing acid gas is discharged at the top of the flask E101 via the conduit 104 to be introduced into the LA101 amine washing unit. The hydrogen-rich stream obtained from unit LA101 is compressed and then recycled via line 102 to exchanger E101 and then to reactor R101. The conduit 105 makes it possible to introduce a hydrogen filling into the conduit 102.

The reactor R101 operates with a NiMo catalyst on an alumina support of the commercial reference HR648 of the company Axens.

The operating conditions of the reactor R101 are as follows:

- operating temperature: 340 ° C

operating pressure: 80 bar

Hourly Voluminal Speed VVH 0.8h ^"1

- The ratio H2 / HC of the mixture introduced into R101 is H2 / HC = 650 Nm ³ / Sm ³

The diagram of FIG. 2 is implemented according to the following operating conditions:

- cutting point in column C: 280 ° C

- operating temperature of the RBP and RHP reactors: 340 ° C

Hourly Volume Velocity in the RBP and RHP reactors: VVH 0.8 hr ^{-1 operating} pressure of the RBP reactor: 40 bar

- RHP reactor operating pressure: 90 bar

- The ratio H2 / HC of the mixture introduced into RBP is H2 / HC = 340 Nm ³ / Sm ³

- The ratio H2 / HC of the mixture introduced into RHP is H2 / HC = 950 Nm ³ / Sm ³

the RBP and RHP reactors comprise NiMo catalyst on an alumina support of the commercial reference HR648 of the company Axens

For each of the processes, a feedstock corresponding to a mixture of a gasoil cut from atmospheric distillation (40% weight), a cut from the coker unit (30% weight) and the unit is treated. catalytic cracking (30% weight). Its density at 15 ° C is 870 kg. m ³ . Its initial boiling point is 110 ° C and the boiling point is 430 ° C. It contains 1 1000 ppm by weight of sulfur, 590 ppm by weight of nitrogen and has a cetane number of 44.1. The table below shows the main results of operation of the two processes:

This comparison shows the advantages identified for the process according to the invention, for the same gain cetane between the two solutions that is to say:

- ability to operate at two reactors, with radically different conditions in both reactors

similar performance between the two processes in terms of cetane number gain and cetane gain, despite a much lower pressure in the RBP reactor in the process of FIG. 2

lower concentration of H ₂ S in the RHP reactor, thus a better life of the RHP reactor catalyst - Lower flow rate of recycled hydrogen (-20% according to the invention compared to the diagram according to Figure 4), which induces energy saving during operation of the process due to a decrease in the compressor power consumption recycling.

Example 2 Comparison Between the Process of Figure 2 According to the Invention and the Process of Figure 5

The process shown diagrammatically in FIG. 5 is close to the process described in document EP2280056.

With reference to FIG. 5, the feedstock arriving via line 201 is introduced into distillation column C2 to produce a heavy fraction discharged through line 206 and a light fraction discharged through line 205. The heavy fraction circulating in line 206 is mixed with hydrogen arriving via the conduit 212 and is introduced into the RHP2 reactor containing a hydrotreatment catalyst. The hydrotreated effluent is partially condensed by cooling to be separated in the separator flask B202 into a liquid fraction containing the hydrorefined hydrocarbons, discharged at the bottom of B202, and an acid gas containing hydrogen discharged through line 207. The light fraction circulating in the conduit 205 is mixed with the acid gas containing hydrogen arriving via the conduit 207, and is introduced into the reactor RBP2 containing a hydrotreatment catalyst. The hydrotreated effluent is partially condensed by cooling to be separated in the separator tank B201 into a liquid fraction containing the hydrorefined hydrocarbons, discharged at the bottom of B201, and an acid gas containing hydrogen discharged through line 208. The acidic gas is introduced into the LA2 amine washing unit via the duct 208 to produce a hydrogen flow discharged through the duct 209. A hydrogen booster is added via the duct 210 to the stream of hydrogen arriving via the duct 209. Then the flow of hydrogen is sent to the reactor RHP2 via the conduit 212.

The diagram of FIG. 5 is implemented according to the following operating conditions:

- cutting point of column C2: 280 ° C.

operating temperature of the RBP2 and RHP2 reactors: 340 ° C

- Hourly Volumic Speed in the RBP2 and RHP2 reactors: VVH 0.8 h ^-1 RBP2 reactor operating pressure: 40 bar operating pressure of the RHP2 reactor: 90 bar

- The ratio H2 / HC of the mixture introduced into RBP2 is H2 / HC = 285 Nm ³ / Sm ³

- The ratio H2 / HC of the mixture introduced into RHP2 is H2 / HC = 360 Nm ³ / Sm ³

the reactors RBP2 and RHP2 comprise NiMo catalyst on an alumina support of the commercial reference HR648 of the company Axens

- cut point of column C: 280 ° C

operating temperature of the RBP and RHP reactors: 340 ° C Hourly Volumetric Speed in the RBP and RHP reactors: VVH 0.8 h ^-1 RBP reactor operating pressure: 40 bar

- RHP reactor operating pressure: 90 bar

- The ratio H2 / HC of the mixture introduced into RBP is H2 / HC = 180 Nm ³ / Sm ³

- The H2 / HC ratio of the mixture introduced into RHP is H2 / HC = 360 Nm ³ / Sm ³

For each of the processes, a feedstock corresponding to a mixture of a gasoil cut from atmospheric distillation (40% weight), a cut from the coker unit (30% weight) and the unit is treated. catalytic cracking (30% weight). Its density at 15 ° C is 870 kg. m ³ . Its initial boiling point is 110 ° C and the boiling point is 430 ° C. It contains 1 1000 ppm by weight of sulfur, 590 ppm by weight of nitrogen and has a cetane number of 44.1.

Process according to Figure 2 Process according to Figure 5

RBP Reactor RHP Total RBP2 RHP2 Total

Temperature of

(° C) 340 340 340 340 reactor

Reactor pressure (Bars) 40 90 40 90

VVH of the reactor (1 / h) 0.8 0.8 0.8 0.8

Volume of

Catalyst in the (m3) 296 366 296 366

reactor

H2 / HC ration of

introduced mixture (-) 182 360 285 360

in the reactor

Flow Load (t / h) 194 268 194 268

Sulfur in

the effluent at the outlet of (ppm) 0.0 71 .5 42.0 0.0 71 .5 42.0 reactor

PPH2 in the phase

gas leaving the (Bars) 27.8 85.7 28.2 85.7

reactors

Hydrogenation rate

carbons (%) 14.3 50.1 38.1 12.9 50.1 37.6 aromatics

Cetane number of

the effluent leaving the (-) 48.7 42.5 47.0 48.6 42.5 46.9 reactor

Cetane gain

(difference between

cetane number of (-) 5.5 5.4 the effluent compared

to the charge)

(%

H2S in the effluent

mass 36.4% 34.6% 47.1% 34.6% at the reactor outlet

gas)

Flow rate

(Nm3 / h) 1 .06.10 ⁵ 1, 06.10 ⁵ Hydrogen Recycled This comparison shows that the process of FIG. 2 according to the invention makes it possible to reduce the content of H ₂ S contained in the effluents leaving the RBP reactor, which makes it possible to increase the service life of the catalyst in RBP.

In addition, the pressure difference between the inlet and the outlet of the hydrogen recycle compressor is clearly different between the two processes: 15 bars for the process of FIG. 2 according to the invention, 54 bars for the process of Figure 5. The power required for operation is the recycle compressor is estimated at 665kW for the compressor of Figure 2 which is at least five times lower than the power required, estimated at 3537kW, for the operation of the recycle compressor of Figure 5. Therefore the method of Figure 2 according to the invention is more energy efficient in its operation compared to the method of Figure 5.

Claims

1) Process for the hydrotreatment of a first hydrocarbon fraction containing sulfur and nitrogen compounds and a second hydrocarbon fraction containing sulfur and nitrogen compounds, in which the following steps are carried out:

a) a first hydrotreatment step (RBP) is carried out by contacting the first hydrocarbon fraction and a first stream of hydrogen with a first hydrotreatment catalyst to produce a first hydrotreated effluent comprising hydrogen, H ₂ S and NH ₃ ,

b) a second hydrotreating step (RHP) is carried out by contacting the second hydrocarbon fraction and the second hydrogen stream with a second hydrotreatment catalyst to produce a second hydrotreated effluent comprising hydrogen, H ₂ S and NH ₃ ,

c) separating (B1) from the first hydrotreated effluent at least a first gaseous fraction containing hydrogen and separating (B2) from the second hydrotreated effluent at least a second gaseous fraction containing hydrogen, d) purifying (LA) a mixture comprising the first gaseous fraction and the second gaseous fraction to produce a hydrogen enriched stream,

2) Process according to claim 1, wherein the hydrogen implemented in step b) comes solely from said hydrogen enriched stream obtained in step e).

3) Method according to one of claims 1 and 2, wherein the first stream of hydrogen is produced by a steam reforming unit of a natural gas stream.

4) Method according to one of claims 1 to 3, wherein step a) is implemented in a first reaction zone (RBP) and wherein step b) is implemented in a second zone of reaction (RHP), the pressure in the second zone of Reaction (RHP) is at least 10 bar higher than the pressure in the first reaction zone (RBP).

5) Process according to claim 4, wherein the first reaction zone (RBP) is implemented with the following conditions:

- temperature between 300 ° C and 420 ° C,

pressure between 30 and 60 bar,

Hourly Volumetric Velocity VVH between 0.5 and 4 hr ^"1

and implementing the second reaction zone (RHP) with the following conditions:

- temperature between 340 ° C and 420 ° C,

pressure between 50 and 120 bar,

Hourly Volumetric Speed VVH between 0.5 and 2 hr ^"1

- ratio between hydrogen and hydrocarbon compounds of between 200 and

1200 Nm ³ / Sm ³ .

6) Method according to one of claims 4 and 5, wherein, before performing step d) it compresses (K2) said first gaseous fraction to the pressure of said second gaseous fraction.

7) Method according to one of claims 1 to 6, wherein step d) implements an amine washing step (LA) to produce said hydrogen enriched stream. 8) Method according to one of claims 1 to 7, wherein in step c), the first effluent is separated into a first liquid stream and said first gas stream, the second effluent is separated into a second liquid stream and said second gas stream, and in step d) contacting the first and second gas stream with an absorbent solution comprising amines to produce said hydrogen-enriched stream.

9) The method of claim 8, wherein before performing step e) is contacted said hydrogen enriched stream with a capture mass to reduce the water content of said stream enriched in hydrogen. 10) Method according to one of claims 1 to 9, wherein the first catalyst and the second catalyst are independently selected from catalysts composed of a porous mineral carrier, a metal element selected from group VIB and a element

Metal selected from group VIII.

11) The method of claim 10, wherein the first and second catalysts are independently selected from a catalyst composed of cobalt and molybdenum deposited on a porous carrier based on alumina and a catalyst composed of nickel and molybdenum deposited on a porous support based on alumina.

12) Process according to one of claims 1 to 9, wherein before step a), a fractionation step (C) is carried out in which a hydrocarbon feedstock is separated into two fractions to obtain said first hydrocarbon fraction and said second hydrocarbon fraction.

13) The method of claim 12, wherein the fractionation step is carried out in a distillation column (C), said first hydrocarbon fraction being discharged at the top of the column, said second hydrocarbon fraction being removed at the bottom of the column.

14) The method of claim 13, wherein the first stream of hydrogen is introduced into the column (C) and is removed at the top of the column fraction enriched light hydrocarbon compounds and the first stream of hydrogen.

5

15) Method according to one of claims 12 to 14, wherein said hydrocarbon feedstock is composed of a hydrocarbon cut whose initial boiling point is between 100 ° C and 250 ° C and the end point of boiling is between 300 ° C and 450 ° C.

0

16) Method according to one of claims 1 to 1 1, wherein said first hydrocarbon fraction is composed of a hydrocarbon cut whose initial boiling point is between 100 ° C and 250 ° C and the end pointd boiling range is between 300 ° C and 450 ° C., wherein said second hydrocavated fraction is composed of a hydrocarbon fraction whose initial boiling point is between 100 ° C. and 250 ° C. and the final boiling point is between 300 ° C. and 450 ° C wherein said second fraction has, relative to the first fraction, at least one of three characteristics:

the second fraction comprises by weight more sulfur than the first fraction,

the second fraction comprises by weight more nitrogen than the first fraction,