FR2926087A1 - MULTI-PROCESS PROCESS FOR THE PRODUCTION OF MEDIUM DISTILLATES BY HYDROISOMERIZATION AND HYDROCRACKING OF AN EFFLUENT PRODUCED BY THE FISCHER-TROPSCH PROCESS - Google Patents

Abstract

The invention describes a method for producing middle distillates from a paraffinic feedstock produced by Fischer-Tropsch synthesis, comprising a) a fractionation of said effluent in at least three fractions, b) a hydroisomerization of at least a portion of the intermediate fraction in the presence of a catalyst comprising a molecular sieve, c) a hydroisomerisation of at least a portion of the heavy fraction in the presence of a catalyst comprising a molecular sieve, d) a hydrocracking of at least a portion of the hydroisomerized effluent resulting from the hydroisomerization of the heavy fraction in the presence of a hydrocracking catalyst comprising a silica-alumina or zeolite-based support Y, e) and a distillation of at least a portion of the effluent from hydroisomerization steps b) and hydrocracking step d) to obtain middle distillates.

Description

The present invention relates to a multi-step process including a hydroisomerization step and a step of hydroisomerization and hydrocracking sequenced feeds from the Fischer-Tropsch process for obtaining middle distillates (gas oil, kerosene).

In the Fischer-Tropsch process, the synthesis gas (CO + H2) is catalytically converted into oxygenates and substantially linear hydrocarbons in gaseous, liquid or solid form. These products are generally free of heteroatomic impurities such as, for example, sulfur, nitrogen or metals. They also contain practically little or no aromatics, naphthenes and more generally cycles especially in the case of cobalt catalysts. On the other hand, they may have a significant content of oxygenated products which, expressed by weight of oxygen, is generally less than about 5% by weight and also an unsaturated content (olefinic products in general) generally less than 10% by weight. The hydrocarbons produced (essentially paraffinic in the case of cobalt catalysts) have very variable carbon chain lengths, typically from 1 to 100 carbon atoms or more. However, these products, mainly made of normal paraffins, can not be used as such, in particular because of their cold-holding properties that are not very compatible with the usual uses of petroleum fractions. For example, the pour point of a linear hydrocarbon containing 20 carbon atoms per molecule and whose boiling point equal to about 340 ° C., that is to say often included in the middle distillate cut, is +37 ° C about which makes its use impossible, the specification being -15 ° C for diesel. Moreover, the fraction of the hydrocarbon feed having a boiling point greater than 370 ° C. (ie paraffins with more than 22 carbon atoms, the boiling point of n-Docosane being 370 ° C. C) also requires catalytic treatment in order to be upgraded to fuel. More particularly, it is particularly advantageous to convert the heavy fraction of the hydrocarbon feedstock into middle distillates (kerosene and diesel) whose initial and final cut points are generally 150 ° C. and 370 ° C., respectively.

It is then particularly desirable to be able to minimize the production of lighter cuts such as for example the naphtha cut. Thus, the optimum recovery of a hydrocarbon feedstock from the Fischer Tropsch process into middle distillates may require, on the one hand, the improvement of the cold-holding properties of the already-present middle distillate fraction.

in the feed and on the other hand the conversion of the heavier fraction of the feedstock into middle distillates also having acceptable cold holding properties. This operation can be carried out by the implementation of a catalytic process using specific hydroisomerization and hydrocracking catalysts. STATE OF THE ART Patent application WO 2006/053894 describes a method making it possible to optimize the yield of diesel fuel produced from a feedstock resulting from a Fischer-Tropsch synthesis. Said feedstock is then fractionated into two effluents, each effluent then being subjected in parallel to a hydroconversion / hydroisomerization step under conditions such that the conversion levels obtained are different. The patent is exemplified by hydroconversion / hydroisomerization of two identical fractions from the same feedstock at conversion levels per pass of 41 and 60%, ie an overall average conversion of the feed of 50.5% per pass. The diesel yield from the two effluents by distillation is 38%, with a cetane number of 80.6. The comparative example shows that when the feed undergoes a hydroconversion / hydrocracking step with a pass conversion of 53%, the overall yield of gas oil is 39% with a cetane number of 78.5.

The patent application US 2004/0159582 describes a process for the production of a diesel fuel of first quality from a feedstock resulting from a Fischer-Tropsch synthesis. This method consists in: hydrotreating / hydrocracking the feedstock on a first hydrotreating / hydrocracking catalyst in order to hydrogenate the olefinic compounds and oxygenate the oxygenated compounds present, said hydrotreatment / hydrocracking catalyst possibly containing at least one noble metal group VIII on a silica or alumina support or at least one Group VIII and Group VIB metal on an alumina or silica support. The support may also be amorphous based on alumina, zeolite or non-zeolitic silica based on molecular sieves; separating the effluent thus produced into a heavy fraction and a light fraction, the final cut point being within the distillation range of the gas oil and the heavy fraction having a distillation range higher than the light fraction; hydroisomerize the heavy fraction on a hydroisomerization catalyst in order to improve its cold-holding properties, said hydroisomerization catalyst possibly containing an active metallic phase based on noble metals or not

noble and SAPO type silicoaluminophosphate acid component or ZSM 22, ZSM 23, SSZ 32, ZSM 35 or ZSM 48 intermediate pore zeolite; - mixing the heavy fraction thus isomerized with at least a portion of the light fraction; recovering from this mixture a diesel fuel meeting at least one of the specifications required for this type of fuel. Moreover, the heavier fraction of the mixture is recovered in different oil bases after a vacuum distillation step.

The patent application US 2005/0205462 teaches a method for increasing the degree of isomerization of a gas oil from a feedstock produced by the Fischer-Tropsch pathway. Said feed is divided into at least three parts, namely a light fraction, an intermediate fraction and a heavy fraction. At least a portion of the heavy fraction is hydrocracked in a first catalytic zone to form a first hydrocracking effluent. At least a part of this first hydrocracking effluent and at least part of the intermediate fraction are hydrocracked in a second catalytic zone in contact with a catalyst under conditions favorable to hydroisomerisation and / or hydrocracking and / or dewaxing to form a second hydroconversion effluent.

The other proposed sequences also all involve a hydrocracking step during the different stages of hydroconversion, no example being provided in this patent.

The patent applications US2004 / 0256286 and US2004 / 0256287 teach the implementation of a process for the production of middle distillates and oil base from waxes. The feedstock to be treated is contacted with a hydrocracking catalyst under appropriate operating conditions to produce a hydrocracking effluent, said hydrocracking catalyst containing at least one hydro-dehydrogenating metal selected from group VI, VII or VIII and at least one large-pore or non-zeolitic zeolite-based alumina silica matrix based on molecular sieves. The hydrocracked effluent is then hydroisomerized on a catalyst containing an alumino-phosphate type intermediate pore size molecular sieve such as SAPO 11, SAPO 31, and SAPO 41. Zeolites such as ZSM 22, ZSM 23, ZSM 35, ZSM 48, ZSM 57, SSZ 32, offer and ferrierite can also be used. The hydroisomerized effluent is then fractionated into a middle distillate fraction and a heavy fraction. The heavy fraction is then extracted

an oil base having defined physicochemical properties. The hydrocracking step always precedes the hydroisomerization step.

Patent US 6204426 teaches the production of a diesel fuel by catalytic treatment of a feedstock containing at least 40% of normal paraffins having at least ten carbon atoms and at least 20% of normal paraffins having at least twenty six carbon atoms on a isomerization / hydrocracking catalyst comprising at least one group VIII metal deposited on a one-dimensional molecular sieve of intermediate pore size selected from SAPO 11, SAPO 31, SAPO 41, ZSM 22, ZSM 23, ZSM 35 alone or as a mixture the preferred catalyst used being Pt / SAPO11 type. The effluent obtained has an iso paraffins to normal paraffins ratio of at least five to one and has a reduced content of paraffins having at least twenty six carbon atoms. and the diesel yields, initial and final cutting points respectively typically 160 to 336 degrees Celsius, are 13 to 20%. It is specified that a molecular sieve and a hydrocracking catalyst can be used in separate reactors, but in this case, the hydrocracking catalyst systematically precedes the molecular sieve.

Patent Application US2005 / 0103683 describes a hydroconversion process for the treatment of charges resulting from the Fischer-Tropsch synthesis; the process includes at least two steps, a hydrocracking step and a hydrotreatment step. No specific hydroisomerization step is mentioned. This patent application is not exemplified.

The patent application US2002 / 0146358 describes a process for treating a hydrocarbon feedstock, preferably derived from Fischer-Tropsch synthesis, through a single catalytic reactor comprising one or more catalytic beds of a catalyst making it possible to carry out a hydrocarbon feedstock. relatively severe hydrocracking of a hydrocarbon feed, and one or more beds of a second catalyst positioned in the same reactor so as to be able to receive and treat more smoothly by hydrotreating or non-converting hydroisomerization the effluents of the first catalyst. The hydrocracking catalyst comprises at least one Group VIII and / or VI metal and an amorphous, zeolitic (Y) or molecular sieve support (SAPO 11, SAPO 31, SAPO 37, SAPO 41, ZSM 5, ZSM 11, ZSM 48, SSZ 32 taken alone or in admixture The hydroisomerization catalyst comprises at least one noble metal of group VIII and a support chosen from amorphous silica aluminas, ZSM 12, ZSM 21, ZSM 22, ZSM 23, ZSM 35, ZSM

38, ZSM 48, ZSM 57, SSZ 32, SAPO 11 ferrierite, SAPO 31, SAPO 41, MAPO 11, MAPO 31, zeolite Y, zeolite L, and zeolite Beta.

The patent application US2004 / 0159582 proposes a process for producing a Fisher Tropsch gas oil of first quality. The steps of said process are as follows: hydrotreating a feedstock from the Fischer Tropsch synthesis on a hydrotreating catalyst in order to remove the oxygenated impurities and to hydrogenate the olefins present in the feed, - to separate the hydrotreated effluent into a light fraction and a heavy fraction, the final boiling point of the light fraction belonging to the range of boiling point of the gas oil, hydroisomerize the heavy fraction previously obtained in order to improve the cold-holding properties, mix the fraction and heavy hydroisomerized with at least a portion of the light fraction recover from this mixture a diesel that meets at least one of the specifications required for this type of fuel. The heavier fraction of the mixture is used for the production of oil bases. No example is provided in this patent.

US6261441 patent provides an integrated process for upgrading a gas oil feed into naphtha, distillate and lubricant cuts. Said filler contains at most 30% by weight of paraffins. The process comprises the following steps: hydrocracking of the feedstock on a selective hydrocracking catalyst of aromatics, the level of conversion to lighter fractions being from 15 to 80% by weight, separation of naphtha, distillate and heavy cuts, treatment of the heavy cutting on at least one dewaxing catalyst, separation of the effluent between a light and heavy fraction, recycling of at least a portion of the heavy fraction to the hydrocracking step and separation of the light fraction into naphtha cuts and distillates, - use of the part of the non-recycled heavy fraction to the hydrocracking stage as a base for oils. This patent is not exemplified.35

Patent FR 2 826 971 describes a process for producing middle distillates from a paraffinic feedstock produced by Fischer-Tropsch synthesis, comprising the following successive steps: (a) separation of a single so-called heavy fraction with a boiling point initial concentration of between 120-200 ° C, (b) hydrotreating of at least a portion of said heavy fraction, (c) fractionation into at least 3 fractions: at least one intermediate fraction having an initial boiling point Ti of between 120 and 200 ° C, and a final boiling point T 2 greater than 300 ° C and lower than 410 ° C, - at least one light fraction boiling below the intermediate fraction, - at least one heavy fraction boiling above of the intermediate fraction. (d) passing at least part of said intermediate fraction onto an amorphous hydroisomerization / hydrocracking catalyst, preferably a noble metal on silica-alumina, (e) passing at least a portion of said heavy fraction over a catalyst hydrocracking / hydroisomerization amorphous material, preferably a noble metal on silica-alumina,

(f) distilling the hydrocracked / hydroisomerized fractions to obtain middle distillates, and recycling the residual fraction boiling above said middle distillates in step (e) to the amorphous catalyst treating the heavy fraction.

The Applicant has now found that by reversing the sequence of the hydroisomerization and hydrocracking steps on the heavy fraction and treating the intermediate fraction separately, it is possible to significantly improve the performance of the process.

The present invention provides a novel process for the production of middle distillates, preferably without the production of oils. This process makes it possible to: strongly improve the cold properties of paraffins resulting from the Fisher-Tropsch process and having boiling points corresponding to those of the gas oil and kerosene fractions (also called middle distillates) and in particular to improve the point of freezing of kerosene. to increase the yield of available middle distillates and to reduce the yield of the lighter fractions such as the naphtha fraction produced by hydrocracking of the heavier paraffinic compounds present in the outlet effluent of the unit;

Fischer-Tropsch, and have boiling points higher than those of kerosene and diesel cuts, for example the fraction 370 ° C +. it also appears that step c) of hydroisomerization prior to step d) of hydrocracking makes it possible to improve not only the reactivity of the feedstock before the hydrocracking but also the yield of middle distillates produced for a conversion given in 370 ° C +. This therefore makes it possible to reduce the production of unwanted light cuts. The passage of the intermediate section on a hydroisomerization catalyst also makes it possible to improve the cold properties of the middle distillates of said section while minimizing the cracking of these middle distillates in undesired light section.

OBJECT OF THE INVENTION More specifically, the invention relates to a method for producing middle distillates from a paraffinic feedstock produced by Fischer-Tropsch synthesis, comprising the following successive stages:

a) fractionation of the paraffinic effluent resulting from the Fischer-Tropsch synthesis into at least three fractions: at least one intermediate fraction having an initial boiling point Ti of between 120 and 200 ° C., preferably between 130 and 180; ° C and very preferably equal to 150 ° C and an end boiling point T2 between 330 and 420 ° C, and preferably between 340 and 400 ° C and very preferably equal to 370 ° C • at minus a light fraction boiling below the intermediate fraction, at least one heavy fraction boiling above the intermediate fraction. B) hydroisomerization of at least a portion of said intermediate fraction from step a) in the presence of a first hydroisomerization catalyst comprising at least one Group VIII metal and / or at least one Group VIB metal and at least one molecular sieve, converting to said first hydroisomerization catalyst products at or above 150 ° C boiling point boiling point products below 150 ° C being less than 10%,

c) hydroisomerization of at least a portion of said heavy fraction from step a) in the presence of a second hydroisomerization catalyst comprising at least one Group VIII metal and / or at least one Group VIB metal and at least one molecular sieve, the conversion on said second hydroisomerization catalyst of dot products

boiling above or equal to 370 ° C in products with boiling points below 370 ° C being less than 20%,

d) hydrocracking at least part of the hydroisomerized effluent from step c) in the presence of a third hydrocracking catalyst comprising at least one Group VIII metal and / or at least one Group VIB metal and an alumina or zeolite Y-based silica carrier, converting to said third hydrocracking catalyst products with a boiling point greater than or equal to 370 ° C in products with a boiling point below 370 ° C being greater than or equal to at 40% by weight, e) distillation of at least a portion of the effluent from the hydroisomerization step b) and the hydrocracking step d) to obtain middle distillates.

In more detail, the steps are as follows:

According to step a) of the process according to the invention, the paraffinic effluent resulting from the Fischer-Tropsch synthesis is fractionated (for example distilled) into at least three fractions: at least one intermediate fraction having a point of initial boiling Ti between 120 and 200 ° C, preferably between 130 and 180 ° C and very preferably equal to 150 ° C and a final boiling point T2 between 330 and 420 ° C, and preferably between 340 and 400 ° C and very preferably equal to 370 ° C; at least one light fraction boiling below the intermediate fraction; at least one heavy fraction boiling above the intermediate fraction.

Optionally, the fractionation step a) is preceded by an optional hydrotreatment step.

In the case where the fractionation step a) is preceded by an optional hydrotreatment step, the paraffinic effluent from the Fischer-Tropsch synthesis unit undergoes, prior to the optional hydrotreatment step, a step separation device, wherein said effluent is advantageously fractionated (for example distilled) into at least two fractions: - a light fraction and - a heavy fraction having an initial boiling point equal to a temperature of between 120 and 200 ° C, and preferably between 130 and 180 ° C and for example about 150 ° C, the light fraction boiling below the heavy fraction. The heavy fraction generally has paraffin contents of at least 50 wt%. Optionally, at least a portion and preferably all of said heavy fraction from the optional separation step undergoes said optional hydrotreatment step wherein said heavy fraction is contacted in a hydrotreating zone in the presence of of hydrogen, with a hydrotreatment catalyst. The operating conditions are advantageously chosen so as to be able to hydrogenate at least a part of the olefinic compounds potentially present in the feedstock and possibly to decompose a part of the oxygen compounds potentially present in the feedstock in water and / or carbon monoxide and / or carbon dioxide. and possibly decomposing some of the sulfur and / or nitrogen compounds also potentially present in the hydrogen sulfide and / or ammonia feedstock.

Optionally, decomposition products such as water and / or carbon monoxide and / or carbon dioxide and / or hydrogen sulfide and / or ammonia formed during the optional hydrotreating step are at least partly, and preferably all, of said heavy fraction removed in an optional separation step

According to step b) of the process according to the invention, at least a part, and preferably all, of said intermediate cut resulting from fractionation step a) undergoes a hydroisomerisation step in which said intermediate cut is put into operation. Contacting, in a first hydroisomerization zone, in the presence of hydrogen, with a first hydroisomerization catalyst, comprising at least one Group VIII metal and / or at least one Group VIB metal and at least one molecular sieve, converting on said catalyst products having a boiling point greater than or equal to 150 ° C. to products with a boiling point below 150 ° C. being less than 10% by weight and preferably less than 5% by weight.

According to step c) of the process according to the invention, at least a part, and preferably all, of said heavy cut resulting from fractionation step a) undergoes a hydroisomerisation step in which said heavy cut is put into operation. contact, in a second hydroisomerization zone, in the presence of hydrogen, of a second hydroisomerization catalyst comprising at least one Group VIII metal and / or at least one metal

Group VIB and at least one molecular sieve, converting to said catalyst products having a boiling point greater than or equal to 370 ° C in products having a boiling point below 370 ° C being less than 20% by weight, and preferred less than 10% by weight. Optionally, at least a portion and preferably all of the normal non-hydroisomerized paraffins from step c) are separated from the hydroisomerized effluent and advantageously recycled in the hydroisomerization step c).

According to step d) of the process according to the invention, at least a part and preferably all of the hydroisomerized effluent from step c) and optionally having undergone the optional step of separation of the normal non-paraffins hydroisomerized, undergoes a hydrocracking step in which said hydroisomerized effluent is brought into contact, in a hydrocracking zone, in the presence of hydrogen, with a third hydrocracking catalyst comprising at least one Group VIII metal and / or at least one Group VIB metal and a silica-alumina or Y-zeolite carrier, converting to said catalyst products having a boiling point greater than or equal to 370 ° C to products having a boiling point of less than 370 ° C being greater than or equal to 40% by weight, and preferably greater than or equal to 60% by weight. Optionally, at least a portion and preferably all of the hydrocracked effluent from step d) undergoes an additional hydroisomerization step in which said hydrocracked effluent is contacted, in an additional hydroisomerization zone, with the presence of hydrogen, with an additional hydroisomerization catalyst, converting to said catalyst products with boiling points greater than or equal to 370 ° C in products with boiling points below 370 ° C being less than 20% by weight and preferably less than 10% by weight.

According to step e) of the process according to the invention, at least a portion and preferably all of the effluent from the hydroisomerization step b) and at least a part and preferably all of the effluent from step d) hydrocracking, said effluent from step d) hydrocracking having optionally undergone the additional step of hydroisomerisation, are subjected to a separation step in a distillation train so to separate the light products, inevitably formed during step d) of hydrocracking and optionally during the additional step of hydroisomerisation, such as for example gases (C1-C4), a gasoline cut, also to distill at5

minus one diesel fuel cut and at least one kerosene cut, and also to distill a fraction whose compounds which constitute it have boiling points higher than those of middle distillates (kerosene + gas oil). This fraction, called the residual fraction, generally has an initial boiling point of at least 350 ° C., preferably greater than 370 ° C. This non-hydrocracked residual fraction is advantageously recycled in step d) of hydrocracking.

Unexpectedly, the method according to the invention has revealed numerous advantages. In particular, it has been found that it is advantageous not to treat the light hydrocarbon fraction of the Fischer Tropsch effluent resulting either from the fractionation step a) or, in the case where said fractionation step a) is preceded by an optional hydrotreatment step, resulting from the optional separation step. Said light fraction, comprising compounds corresponding to a gasoline cut (C5) with boiling points less than or equal to 200 ° C and preferably less than or equal to 150 ° C, is advantageously sent to a steam cracker to make olefins. The fact of not treating the light fraction of the Fischer-Tropsch effluent makes it possible to minimize the volumes of the hydrotreatment and hydroisomerization / hydrocracking catalysts to be used and thus to reduce the size of the reactors and thus the investments.

In addition, the process according to the invention allows the production of middle distillates (kerosene, diesel) with a minimum of lighter fractions such as gasoline obtained. It thus appears that step c) of hydroisomerization prior to step d) of hydrocracking makes it possible to improve not only the reactivity of the feedstock before the hydrocracking but also the yield of middle distillates produced for a given conversion into 370 ° C +. This therefore makes it possible to reduce the production of unwanted light cuts. The passage of the intermediate section on a hydroisomerization catalyst also makes it possible to improve the cold properties of the middle distillates of said section while minimizing the cracking of these middle distillates in undesired light section.

DETAILED DESCRIPTION OF THE INVENTION The description will be made with reference to FIG. 1 without FIG. 1 limiting the interpretation. Step (a)

The effluent from the Fischer-Tropsch synthesis unit comprises mainly paraffins but also contains olefins and oxygenated compounds such as alcohols.

It also contains water, CO2, CO and unreacted hydrogen as well as light hydrocarbon compounds C, to C4 in the form of gas. This may also contain some traces of nitrogen compounds and / or sulfur.

According to step a) of the process according to the invention, the effluent from the Fischer-Tropsch synthesis unit arriving via line (11) is fractionated, in a separation means (12), in at least three fractions: • at least one intermediate fraction (14) having an initial boiling point Ti of between 120 and 200 ° C, preferably of between 130 and 180 ° C and very preferably of 150 ° C and a d-point of final boiling T2 between 330 and 420 ° C, and preferably between 340 and 400 ° C and very preferably equal to 370 ° C; at least one light fraction (13) boiling below the intermediate fraction, at least one heavy fraction (19) boiling above the intermediate fraction.

This fractionation is advantageously carried out by methods well known to those skilled in the art such as flash, distillation, etc. As a non-limiting example, the effluent from the Fischer-Tropsch synthesis unit will be subject to flash, decantation to remove water and distillation to obtain at least the three fractions described above.

The light fraction is not treated according to the process of the invention but may advantageously constitute a good load for the petrochemical industry and more particularly for a steam cracking unit (5) in which it is sent via the pipe (13). The intermediate and heavy fractions previously described are treated in the process according to the invention.

Preferably, fractionation step a) is preceded by an optional hydrotreating step implemented in a hydrotreatment zone (7).

In the case where the fractionation step a) is preceded by an optional hydrotreatment step, the paraffinic effluent from the Fischer-Tropsch synthesis unit (line 1) undergoes, prior to the optional step of hydrotreatment, a step of 12

separation, in a separation means (2), wherein said effluent is advantageously fractionated (for example distilled) into at least two fractions: a light fraction (line 3) and a heavy fraction (line 4) having a boiling point initial temperature equal to a temperature between 120 and 200 ° C, preferably between 130 and 180 ° C and very preferably, equal to 150 ° C, the light fraction boiling below the heavy fraction, which is sent in the hydrotreatment stage. The heavy fraction generally has paraffin contents of at least 50 wt%.

This fractionation is also advantageously carried out by methods well known to those skilled in the art such as flash, distillation, etc.

Preferably, at least a portion and preferably all of said heavy fraction (line 4) resulting from the optional separation step undergoes said optional hydrotreatment step in which said heavy fraction (line 4) is brought into contact, in a hydrotreatment zone (7), in the presence of hydrogen (line 6), with a hydrotreatment catalyst. This optional hydrotreating step has the objective of reducing the content of olefinic and unsaturated compounds, optionally decomposing the oxygenated compounds (mainly alcohols) present in said heavy fraction, as well as decomposing any traces of sulfur and nitrogen compounds. This hydrotreating step is advantageously non-converting, that is to say that the operating conditions and the hydrotreatment catalyst are chosen by those skilled in the art so that the conversion on said hydrotreating catalyst of the fraction 370 ° C` fraction 370 ° C- is preferably less than 20% by weight, preferably less than 10% by weight and very preferably less than 5% by weight. The operating conditions are advantageously chosen so as to be able to hydrogenate at least a part of the olefinic compounds potentially present in the feedstock and possibly to decompose a part of the oxygen compounds potentially present in the feedstock in water and / or carbon monoxide and / or carbon dioxide. and possibly decomposing some of the sulfur compounds and / or nitrogen compounds potentially present in the hydrogen sulfide and / or ammonia feedstock.

Thus, those skilled in the art choose the operating conditions so that, preferably, the optional hydrotreatment step of the process according to the invention operates at a reaction temperature of between 100 and 400 ° C., preferably between 150 and 350 ° C. ° C, very preferably between 150 and 300 ° C, at a pressure advantageously between 5 and 150 bar,

preferably between 10 and 100 bar and very preferably between 10 and 90 bar, at a hydrogen flow rate such that the volume ratio hydrogen / hydrocarbons is advantageously between 50 to 3000 normal liters per liter, preferably between 100 and 2000 normal liters per liter and very preferably between 150 and 1500 normal liters per liter, and at a charge rate such that the hourly volume velocity is advantageously between 0.1 and 10 h -1, preferably between 0.2 and 5 h -1 and very preferably between 0.2 and 3 h -1.

Under these conditions, the content of unsaturated and oxygenated molecules is advantageously reduced to less than 0.5% by weight and preferably less than 0.1% by weight. The hydrotreating step is advantageously carried out under conditions such that the conversion to products having boiling points greater than or equal to 370 ° C. to products having boiling points below 370 ° C. is less than 20%. by weight, preferably less than 10% by weight and very preferably less than 5% by weight.

Hydrotreating Catalysts The catalysts used in this optional hydrotreatment step are advantageously hydrotreating catalysts which are non-crunchy or slightly cracking and comprise at least one Group VIII metal and / or Group VI of the periodic table of elements. Preferably, the catalyst comprises at least one metal of the metal group formed by nickel, molybdenum, tungsten, cobalt, ruthenium, indium, palladium and platinum and comprising at least one support.

In the case of the use of non-noble Group VIII metals, a combination of at least one Group VI metal, preferably molybdenum or tungsten and at least one Group VIII metal, is advantageously used, preferably cobalt and nickel from the periodic table of elements. The concentration of the non-noble group VIII metal, when it is used, is advantageously from 0.01 to 15% by weight of oxide equivalent relative to the finished catalyst and that of the group VI metal is advantageously from 5% to 30% by weight of oxide equivalent relative to the finished catalyst. When a combination of Group VI and Group VIII metals is used, the catalyst is then preferably used in a sulfurized form.

The support of the catalyst used in the optional hydrotreatment step of the process according to the invention is advantageously chosen from the group formed by aluminas, boron oxides, magnesia, zirconia, titanium oxides and clays, or combination of these oxides, preferably said support is an alumina. Said catalysts can

advantageously be prepared by all methods known to those skilled in the art or can be acquired from companies specializing in the manufacture and sale of catalysts.

Advantageously, at least one element selected from phosphorus, boron or silicon is deposited on the support. Preferably, said hydrotreatment catalyst contains phosphorus: in fact, this compound provides two advantages to hydrotreatment catalysts: ease of preparation, especially in the impregnation of nickel and molybdenum solutions, and better activity of hydrogenation.

In a preferred catalyst used in the optional hydrotreating step of the process according to the invention, the total concentration of metals of groups VI and VIII, expressed as metal oxides with respect to the finished catalyst, is advantageously between 5 and 40%. by weight and preferably between 7 and 30% by weight and the weight ratio expressed as metal oxide (or metals) of group VI on metal (or metals) of group VIII is advantageously between 1.25 and 20 and preferably between 2 and 10. In the case where said catalyst contains phosphorus, the P205 phosphorus oxide concentration is advantageously less than 15% by weight and preferably less than 10% by weight relative to the finished catalyst.

Said catalyst used in the optional hydrotreatment step of the process according to the invention may advantageously contain boron and phosphorus as a promoter element deposited on the support, such as, for example, the catalyst according to patent EP 297,949. In this case, the sum of the quantities of boron and phosphorus, expressed respectively by weight of boron trioxide and phosphorus pentoxide, relative to the weight of support, is advantageously between 5 and 15%, the atomic ratio boron over phosphorus is advantageously understood. between 1: 1 to 2: 1 and at least 40% of the total pore volume of the finished catalyst is contained in pores with an average diameter greater than 13 nanometers. Preferably, the amount of Group VI metal such as molybdenum or tungsten, is such that the atomic ratio phosphorus on metal of Group VIB is advantageously between 0.5: 1 to 1.5: 1; the quantities of Group VIB metal and Group VIII metal, such as nickel or cobalt, are such that the Group VIII metal atomic ratio on Group VIB metal is advantageously between 0.3: 1 to 0.7 1. The quantity of metal of the group VIB expressed in weight of metal relative to the weight of the finished catalyst is advantageously between 2 to 30% and the amount of metal of the

Group VIII expressed as weight of metal relative to the weight of finished catalyst is advantageously between 0.01 to 15%.

Another particularly advantageous catalyst used in the optional hydrotreating step of the process according to the invention advantageously contains silicon as a promoter deposited on the support. Another interesting catalyst advantageously contains the combinations BSi or PSi.

The Ni, alumina, NiMo on alumina, NiMo on alumina doped with boron and phosphorus and NiMo on silica-alumina sulphide catalysts can also advantageously be used in the optional hydrotreatment step of the process according to the invention. The alumina support used is preferably eta or gamma alumina.

In the case of the use of noble metals of group VIII preferably selected from platinum and palladium, the metal content is advantageously between 0.05 and 3% by weight relative to the finished catalyst and preferably between 0.1 and 2% by weight of the finished catalyst. The noble metal is preferably used in its reduced and non-sulphurized form. It is also possible to use a reduced, non-sulfurized nickel catalyst. In this case the metal content in its oxide form is advantageously between 0.5 and 25% by weight relative to the finished catalyst. Preferably, the catalyst also contains a group IB metal such as copper, in proportions such that the mass ratio of the group IB metal and nickel on the catalyst is between 1 and 1:30.

In the hydrotreatment reactor (7), the feedstock is advantageously brought into contact in the presence of hydrogen and of said hydrotreatment catalyst at operating temperatures and pressures which make it possible to hydrogenate the olefins present in the feedstock. Preferably, the catalyst and the operating conditions chosen will also make it possible to carry out the hydrodeoxygenation, ie the decomposition of the oxygenated compounds (mainly alcohols) and / or the hydrodesulfurization or hydrodenitrogenation of the possible traces of sulfur compounds. and / or nitrogen present in the charge.

Optionally, at least a portion and preferably all of the effluent from the optional hydrotreatment step, and leaving the hydrotreatment zone (7) through line (8), undergoes an optional separation step in a separation zone (9) in which decomposition products such as water and / or carbon monoxide and / or carbon dioxide and / or hydrogen sulfide and / or ammonia formed during optional step

hydrotreatment are advantageously eliminated at least in part and preferably completely.

Said optional separation step can advantageously be carried out by methods that are well known to those skilled in the art. By way of non-limiting example, the effluent may advantageously be subjected to a flash to remove carbon monoxide and / or carbon dioxide and / or hydrogen sulphide and / or ammonia as well as settling to remove water. The hydrogen removed during said separation step may advantageously be purified and then advantageously recycled to the optional hydrotreating step (line 10).

An eventuality of the process according to the invention advantageously consists in sending all the effluent resulting from the optional hydrotreatment step in said fractionation step a), without prior separation step. Step (b)

According to step b) of the process according to the invention, at least a portion and preferably all of said intermediate cut resulting from fractionation step a) (line 14) undergoes a hydroisomerisation step in which said intermediate cup is brought into contact, in a first hydroisomerization zone (16), in the presence of hydrogen (line 15), with a first hydroisomerisation catalyst comprising at least one group VIII metal and / or at least one metal Group VIB and at least one molecular sieve, conversion on said catalyst of products having a boiling point greater than or equal to 150 ° C to products having a boiling point below 150 ° C being less than 10% by weight and preferred way less than 5% by weight.

According to step b) of the process according to the invention, the operating conditions and the first hydroisomerization catalyst used in the hydroisomerisation step b) of the process according to the invention are chosen so as to carry out a non-hydroisomerization. converting said intermediate cut with a conversion of the 370 ° C + fraction to 370 ° C fraction less than 20% by weight, preferably less than 10% by weight and very preferably less than 5% by weight.

Thus, one skilled in the art chooses the operating conditions so that, preferably, the hydroisomerization step b) of the process according to the invention operates at 15 ° C.

a pressure of between 2 and 150 bar, preferably between 5 and 100 bar and very preferably between 10 and 90 bar, at an hourly space velocity advantageously between 0.1 hr and 10 hr, preferably between 0.2 and 7 h -1 and very preferably between 0.5 and 5 h -1, at a hydrogen flow rate such that the volume ratio hydrogen / hydrocarbons is advantageously between 100 and 2000 normal liters of hydrogen per liter of filler and preferably between 150 and 1500 normal liters of hydrogen per liter of filler and at a temperature advantageously between 100 and 550 ° C, preferably between 150 ° C and 450 ° C, and very preferably, between 200 and 450 ° C.

Selective hydroisomerization catalysts The hydroisomerization catalysts used in step b) of the process according to the invention are advantageously of the bifunctional type, that is to say that they have a hydro / dehydrogenating function and a hydroisomerizing function.

According to step b) of the process according to the invention, the first hydroisomerisation catalyst comprises at least one Group VIII metal and / or at least one Group VIB metal as a hydrodehydrogenating function and at least one molecular sieve in as a hydroisomerizing function.

According to the invention, the first hydroisomerization catalyst comprises either at least one noble metal of group VIII preferably chosen from platinum or palladium, active in their reduced form, or at least one metal of group VI, preferably chosen from molybdenum or tungsten, in combination with at least one non-noble group VIII metal, preferably selected from nickel and cobalt, preferably used in their sulfurized form.

In the case where the first hydroisomerization catalyst comprises at least one noble metal of group VIII, the noble metal content of the hydroisomerization catalyst used in step b) of the process according to the invention is advantageously between 0, 01 and 5% by weight relative to the finished catalyst, preferably between 0.1 and 4% by weight and very preferably between 0.2 and 2% by weight.

In the case where the first hydroisomerization catalyst comprises at least one group VI metal in combination with at least one group VIII non-noble metal, the group VI metal content of the hydroisomerization catalyst used in step b) of the process according to the invention is advantageously included in oxide equivalent between 5 and 40

% by weight relative to the finished catalyst, preferably between 10 and 35% by weight and very preferably between 15 and 30% by weight and the group VIII metal content of said catalyst is advantageously in oxide equivalent between 0, 5 and 10% by weight, based on the finished catalyst, preferably between 1 and 8% by weight and very preferably between 1.5 and 6% by weight.

The hydro / dehydrogenating metal function can advantageously be introduced on said catalyst by any method known to those skilled in the art, such as, for example, comalaxing, dry impregnation, exchange impregnation.

According to the hydroisomerization step b) of the process according to the invention, the first hydroisomerisation catalyst comprises at least one molecular sieve, preferably at least one zeolite molecular sieve and more preferably at least one zeolite molecular sieve. 10 MR one-dimensional as a hydroisomerizing function.

Zeolite molecular sieves are defined in the "Atlas of Zeolite Structure Types" classification, W. M Meier, D. H. Oison and Ch. Baerlocher, 5th revised edition, 2001, which Elsevier also refers to. Zeolites are classified according to the size of their pore openings or channels. Monodimensional 10 MR zeolite molecular sieves have pores or channels whose opening is defined by a ring with 10 oxygen atoms (opening at 10MR). The zeolite molecular sieve channels having a 10 MR aperture are advantageously unidirectional one-dimensional channels that open directly to the outside of said zeolite. The one-dimensional 10 MR zeolite molecular sieves present in said hydroisomerization catalyst advantageously comprise silicon and at least one element T selected from the group formed by aluminum, iron, gallium, phosphorus and boron, preferably aluminum. The Si / Al ratios of the zeolites described above are advantageously those obtained in the synthesis or obtained after post-synthesis dealumination treatments well known to those skilled in the art, such as and not limited to hydrothermal treatments. followed or not by acid attacks or even direct acid attacks by solutions of mineral or organic acids. They are preferably almost completely in acid form, that is to say that the atomic ratio between the monovalent compensation cation (for example sodium) and the element T inserted in the crystalline lattice of the solid is advantageously less than 0.1, preferably less than 0.05, and

very preferably less than 0.01. Thus, the zeolitic molecular sieves used in the composition of said first hydroisomerization catalyst are advantageously calcined and exchanged by at least one treatment with a solution of at least one ammonium salt so as to obtain the ammonium form of the zeolites which once calcined lead to the acid form of said zeolites.

Said zeolite molecular sieve 10MR one-dimensional of said first hydroisomerization catalyst is advantageously chosen from zeolite molecular sieves of structural type TON (selected from ZSM-22 and NU-10, taken alone or as a mixture), FER (selected from ZSM -35 and ferrierite, taken alone or in mixture), EUO (selected from EU-1 and ZSM-50, taken alone or in admixture), SAPO-11 or zeolitic molecular sieves ZSM-48, ZBM-30 , EU-2 and EU-11, taken alone or as a mixture. Preferably, said one-dimensional 10MR zeolite molecular sieve is chosen from zeolitic molecular sieves ZSM-48, ZBM-30, NU-10 and ZSM-22, taken alone or as a mixture. Very preferably, said one-dimensional 10MR zeolite molecular sieve is ZBM-30 synthesized with the organic template triethylenetetramine.

The one-dimensional 10MR zeolite molecular sieve content is advantageously between 5 and 95% by weight, preferably between 10 and 90% by weight, more preferably between 15 and 85% by weight and very preferably between 20 and 80% by weight relative to to the finished catalyst.

Preferably, said first hydroisomerization catalyst also comprises a binder consisting of a porous mineral matrix. Said binder may advantageously be used during the shaping step of said hydroisomerization catalyst. Preferably, the shaping is carried out with a binder consisting of a matrix containing alumina, in all its forms known to those skilled in the art, and very preferably with a matrix containing gamma-alumina. The binder content is advantageously between 5 and 95% by weight, preferably between 10 and 90% by weight, more preferably between 15 and 85% by weight and very preferably between 20 and 80% by weight relative to the finished catalyst.

The first hydroisomerization catalysts obtained are shaped in the form of grains of different shapes and sizes. They are generally used in the form of cylindrical or multi-lobed extrusions such as bilobed, trilobed, straight-lobed or twisted, but can optionally be manufactured and used in the form

crushed powders, tablets, rings, balls, wheels. Other techniques than extrusion, such as pelletizing or coating, can advantageously be used.

Before use in the reaction, the metal contained in said hydroisomerization catalyst must advantageously be reduced. One of the preferred methods for conducting the reduction of the metal is hydrogen treatment at a temperature between 150 ° C and 650 ° C and a total pressure of between 1 and 250 bar. For example, a reduction consists of a plateau at 150 ° C. for two hours and then a rise in temperature up to 450 ° C. at a rate of 1 ° C./min and then a two-hour stage at 450 ° C. throughout this reduction step, the hydrogen flow rate is 1000 normal liters of hydrogen / liter catalyst and the total pressure kept constant at 1 bar. Any ex-situ reduction method can advantageously be considered. Step (c)

According to step c) of the process according to the invention, at least a portion, and preferably all, of said heavy cut from fractionation step a) (line 19) undergoes a hydroisomerisation step, wherein said heavy cut is brought into contact, in a second hydroisomerization zone (21), in the presence of hydrogen (line 20), with a second hydroisomerization catalyst comprising at least one Group VIII metal and / or at least one Group VIB metal and at least one molecular sieve, converting to said catalyst products with a boiling point greater than or equal to 370 ° C in products having a boiling point below 370 ° C being less than 20% by weight, and preferred way less than 10% by weight.

According to step c) of the process according to the invention, the operating conditions and the hydroisomerization catalyst are chosen so as to effect a hydroisomerization of said heavy fraction with a conversion of the 370 ° C + fraction to a 370 ° C fraction. less than 20% by weight, preferably less than 10% by weight and very preferably less than 5% by weight.

The operating conditions and said first hydroisomerization catalyst used in step b) of the process according to the invention and the operating conditions and said second hydroisomerization catalyst used in step c) of the process according to the invention can advantageously be identical or different.

Preferably, the operating conditions and said first hydroisomerization catalyst used in step b) of the process according to the invention and the operating conditions and said second hydroisomerization catalyst used in step c) of the process according to the invention are the same. Optionally, at least a portion and preferably all of the hydroisomerized effluent (line 22) from the hydroisomerization step c) undergoes a separation step in a separation zone (23), in which at least a portion and preferably all of the paraffins non-hydroisomerized normal in said step c) is separated from the effluent from said step c) and is recycled in said step c) hydroisomerization.

The hydroisomerized effluent from the hydroisomerization step c) is sent via the pipe (22) into the separation zone (23). Said optional step of separation of normal non-hydroisomerized paraffins is advantageously carried out by any method well known to those skilled in the art aimed at reducing the amount of normal paraffins of a hydroisomerized effluent. Preferably the paraffins are separated off by means of adsorption processes using molecular sieves. The normal paraffins resulting from said separation step are advantageously recycled in the hydroisomerization step c) via the pipe (24). Step (d) According to step d) of the process according to the invention, at least a part and preferably all of the hydroisomerized effluent from step c) hydroisomerization and having optionally undergone the step of separating non-hydroisomerized n-paraffins, undergoes a hydrocracking step d) in which said effluent is brought into contact (line 25), in a third hydrocracking zone (27), in the presence of hydrogen (line 26), with a third hydrocracking catalyst comprising at least one Group VIII metal and / or at least one Group VIB metal and a silica alumina support or based on Y zeolite. According to the invention, the operating conditions are chosen so as to converting the 370 ° C + fraction to the 370 ° C fraction by at least 40% by weight and preferably at least 60% by weight.

Thus, those skilled in the art choose the operating conditions so that, preferably, the hydrocracking step c) of the process according to the invention operates at a pressure of between 2 and 150 bar, preferably between 5 and 100 bar. and very preferably, between 10 to 90 bar, at an hourly space velocity of between 0.1 hr -1 and 10 hr -1, preferably between 0.2

and 7 h -1 and very preferably between 0.5 and 5 h -1, at a hydrogen flow rate such that the volume ratio hydrogen / hydrocarbons is advantageously between 100 and 2000 normal liters of hydrogen per liter of charge and preferably between 150 and 1500 normal liters of hydrogen per liter of filler and at a temperature between 100 and 550 ° C, preferably between 150 ° C and 450 ° C, and very preferably between 200 and 400 ° C.

Hydrocracking Catalysts As for the hydroisomerization catalysts used in the hydroisomerization step b), the hydrocracking catalysts are advantageously of the bifunctional type, that is to say that they have a hydro / dehydrogenating function. and a crisp function.

According to step d) of the process according to the invention, the third hydrocracking catalyst comprises at least one Group VIII metal and / or at least one Group VIB metal as a hydrodehydrogenating function and a silica alumina support or Y zeolite base as a crisp feature.

Preferably, the third hydrocracking catalyst comprises either at least one noble metal of group VIII chosen from platinum and palladium, taken alone or as a mixture, active in their reduced form, or at least one non-noble metal of group VIII chosen among nickel and cobalt in combination with at least one Group VI metal selected from molybdenum and tungsten, alone or in admixture, and preferably used in their sulfurized form.

In the case where the third hydrocracking catalyst comprises at least one noble metal of group VIII, the noble metal content of said third hydrocracking catalyst is advantageously between 0.01 and 5% by weight relative to the finished catalyst, preferably between 0.1 and 4% by weight and very preferably between 0.2 and 2% by weight.

In the case where the third hydrocracking catalyst comprises at least one group VI metal in combination with at least one group VIII non-noble metal, the group VI metal content of said third hydrocracking catalyst is advantageously understood in equivalents. oxide between 5 and 40% by weight relative to the finished catalyst, preferably between 10 and 35% by weight and very preferably between 15 and 30% by weight.

weight and the metal content of group VIII of said catalyst is advantageously between 0.5 and 10% by weight relative to the finished catalyst, preferably between 1 and 8% by weight and very preferably between 1, 5 and 6% by weight.

The metal function is advantageously introduced on the third catalyst by any method known to those skilled in the art, such as, for example, comalaxing, dry impregnation or exchange impregnation.

Preferably, the silica-based alumina or zeolite-based support Y is advantageously composed of pure silica-alumina alone or of zeolite Y alone. Optionally, a binder can advantageously also be used during the step of forming the support. A binder is preferably used when the zeolite is employed. Said binder is advantageously chosen from silica (SiO 2), alumina (Al 2 O 3), clays, titanium oxide (TiO 2), boron oxide (B 2 O 3) and zirconia (ZrO 2), taken alone or as a mixture .

Preferably, said binder is chosen from silica and alumina and even more preferably, said binder is alumina in all these forms known to those skilled in the art, such as, for example, gamma-alumina.

In the case where the silica-alumina support of said second hydrocracking catalyst contains a binder, the weight content of binder in said support is advantageously between 0 and 40% by weight, more particularly between 1 and 40% and even more preferably between 5% and 20% by weight with respect to the finished catalyst. As a result, the weight content of silica-alumina in said support is advantageously between 60 and 100% by weight relative to the finished catalyst.

In the case where the support Y of said second hydrocracking catalyst, based on zeolite, contains a binder, the weight content of binder in said support is advantageously between 99 and 60% by weight, and more preferably between 80% and 95% by weight with respect to the finished catalyst. As a result, the weight content of zeolite Y in said support is advantageously between 1 and 40% by weight relative to the finished catalyst.

The third preferred hydrocracking catalysts used in the hydrocracking step d) of the process according to the invention are the catalysts whose support consists solely of silica-alumina without any binder.

A third preferred hydrocracking catalyst used in step d) of the process according to the invention advantageously comprises at least one noble metal, said noble metal being platinum and a silica-alumina support, without any binder.

In the case where the support consists solely of silica-alumina without any binder, the silica content of the support, expressed as a weight percentage, is generally between 1 and 95%, advantageously between 5 and 95%, and preferably between 10 and 95%. and 80% and even more preferably between 20 and 70% and between 22 and 45%. This silica content is perfectly measured using X-ray fluorescence.

The support is advantageously prepared by shaping silica-alumina in the presence or absence of binder by any technique known to those skilled in the art.

Several preferred catalysts used in the hydrocracking step d) of the process according to the invention are described below.

A preferred catalyst used in step c) of the process according to the invention comprises a particular silica-alumina. More specifically, said catalyst comprises (and preferably consists essentially of) from 0.05 to 10% by weight and preferably from 0.1 to 5% by weight of at least one Group VIII noble metal, preferably chosen from platinum and palladium and, preferably, said noble metal being platinum, deposited on a silica-alumina support, without any binder, containing an amount of silica (SiO 2) of between 1 and 95%, expressed as a weight percentage, of preferably between 5 and 95%, preferably between 10 and 80% and very preferably between 20 and 70% and even more preferably between 22 and 45%, said catalyst having: a BET specific surface area of 100 to 500 m2 / g, preferably between 200 m2 / g and 450 m2 / g and very preferably between 250 m2 / g and 450 m2 / g, • a mean mesopore diameter of between 3 and 12 nm, preferably between 3 nm and 11 nm and very preferably between 4 nm and 10.5 nm, a pore volume of pores whose diameter is between the average diameter as defined above decreased by 3 nm and the average diameter as defined previously increased by 3 nm is greater than 40%. the total pore volume, preferably between 50% and 90% of the total pore volume and very preferably between 50% and 70% of the total pore volume, a total pore volume of between 0.4 and 1.2 ml / g, preferably between 0.5 and 1.0 ml / g and very preferably between 0.5 and 0.9 ml / g,

A volume of the macropores, whose diameter is greater than 50 nm, and preferably between 100 nm and 1000 nm, representing between 5 and 60% of the total pore volume, preferably between 10 and 50% of the total pore volume and of even more preferably between 10 and 40% of the total pore volume, an alkali or alkaline earth content of less than 300 ppm by weight and preferably less than 200 ppm by weight.

The mean diameter of the mesopores is defined as the diameter corresponding to the cancellation of the curve derived from the mercury intrusion volume obtained from the mercury porosity curve for pore diameters between 2 and 50 m. The average diameter of the mesopores of the catalyst is advantageously measured from the porous distribution profile obtained using a mercury porosimeter.

Preferably, the dispersion of said preferred catalyst used in step d) of the process according to the invention is advantageously between 20% and 100%, preferably between 30% and 100% and very preferably between 40 and 100%. . The dispersion, representing the fraction of metal accessible to the reagent relative to the total amount of metal of the catalyst, is advantageously measured, for example, by H2 / O 2 titration.

Preferably, the distribution coefficient of the noble metal of said preferred catalyst used in step d) of the process according to the invention is greater than 0.1, preferably greater than 0.2 and very preferably greater than 0.4. . The distribution of the noble metal represents the distribution of the metal within the catalyst grain, the metal being able to be well or poorly dispersed. Thus, it is possible to obtain the platinum poorly distributed (for example detected in a ring whose thickness is significantly less than the radius of the grain) but well dispersed that is to say that all the platinum atoms, located in crown, will be accessible to the reagents. In our case, platinum distribution is good.

The noble metal salt is advantageously introduced by one of the usual methods used to deposit the metal on the surface of a support. One of the preferred methods is dry impregnation which consists of introducing the metal salt into a volume of solution which is equal to the pore volume of the catalyst mass to be impregnated. Before the reduction operation, the catalyst can advantageously undergo calcination, for example a treatment in dry air at a temperature of 300 to 750 ° C. and preferably

at a temperature of 520 ° C for 0.25 to 10 hours and preferably for 2 hours.

Another preferred catalyst used in step d) of the process according to the invention comprises a particular second silica-alumina. More specifically, said catalyst comprises at least one hydro-dehydrogenating element chosen from the group formed by the elements of group VIB and group VIII of the periodic table, from 0.01 to 5.5% weight of oxide of an element. dopant chosen from phosphorus, boron and silicon and a non-zeolitic support based on silica-alumina containing an amount greater than 5% by weight and less than or equal to 95% by weight of silica (SiO2), said catalyst having the following characteristics: a mean mesoporous diameter, measured by mercury porosimetry, of between 2 and 14 nm, a total pore volume, measured by mercury porosimetry, of between 0.1 ml / g and 0.5 ml / g, total pore volume, measured by nitrogen porosimetry, between 0.1 ml / g and 0.5 ml / g, a BET specific surface area of between 100 and 550 m 2 / g, a pore volume, measured by mercury porosimetry, included in pores larger than 14 nm in diameter less than 0.1 ml / g, a pore volume, measured by mercury porosimetry, included in pores with a diameter greater than 16 nm of less than 0.1 ml / g, - a pore volume, measured by mercury porosimetry, included in pores with a diameter greater than 20 nm, less than 0.1 ml / g, a pore volume, measured by mercury porosimetry, included in pores with diameters greater than 50 nm of less than 0.1 ml / g. an X-ray diffraction pattern which contains at least the principal characteristic lines of at least one of the transition aluminas included in the group consisting of alpha, rho, chi, eta, gamma, kappa, theta and delta alumina. a packed packing density of the catalysts greater than 0.75 g / ml.

Another preferred catalyst used in step d) of the process according to the invention comprises (and preferably consists essentially of) 0.05 to 10% by weight and preferably 0.1 and 5% by weight of at least one group VIII noble metal, preferably selected from platinum and palladium and, preferably, said noble metal being platinum, deposited on a silica-alumina support, without any binder, containing an amount of silica (SiO2) of between 1 and

95%, expressed as a weight percentage, preferably between 5 and 95%, preferably between 10 and 80% and very preferably between 20 and 70% and even more preferably between 22 and 45%, said catalyst having: a BET specific surface area of 200 to 600 m 2 / g and preferably of between 250 m 2 / g and 500 m 2 / g, a mean mesopore diameter of between 3 and 12 nm, preferably of between 3 nm and 11 nm, and very preferably between 4 nm and 10.5 nm, a pore volume of pores whose diameter is between the mean diameter as defined above decreased by 3 nm and the average diameter as defined above increased by 3 nm is greater than 60 % of the total pore volume, preferably greater than 70% of the total pore volume and very preferably greater than 80% of the total pore volume, total pore volume of less than 1 ml / g, preferably of between 0.1 and 0.9 ml / g and very preferably between 0.2 and 0.7 ml / g, an alkali or alkaline earth metal content of less than 300 ppm by weight and preferably less than 200 ppm by weight.

Preferably, the dispersion of said preferred catalyst used in step d) of the process according to the invention is advantageously between 20% and 100%, preferably between 30% and 100% and very preferably between 40 and 100%. . The dispersion, representing the fraction of metal accessible to the reagent relative to the total amount of metal of the catalyst, is advantageously measured, for example, by H2 / O 2 titration.

Preferably, the distribution coefficient of the noble metal of said preferred catalyst used in step d) of the process according to the invention is greater than 0.1, preferably greater than 0.2 and very preferably greater than 0.4. . This distribution coefficient is measured by Castaing microprobe.

Optionally, at least a portion, and preferably all, of the hydrocracked effluent from step d) of hydrocracking undergoes an additional hydroisomerization step, in a fourth catalytic zone of additional hydroisomerization (21), wherein hydrocracked effluent is contacted with a fourth additional hydroisomerization catalyst (line 28 and zone (29)). The operating conditions and the fourth additional hydroisomerization catalyst are chosen so as to carry out an additional hydroisomerization of the feed with a conversion to this catalyst of products with boiling points greater than or equal to 370 ° C. in boiling point products. less than 370 ° C

less than 20% by weight, preferably less than 10% by weight and very preferably less than 5% by weight.

The operating conditions used in steps b) and c) of the process according to the invention and the operating conditions used in the additional hydroisomerization step may advantageously be identical or different. Similarly, said first and second hydroisomerization catalyst used in steps b) and c) of the process according to the invention and said additional hydroisomerization catalyst used in the additional hydroisomerization step can advantageously be identical or different.

Preferably, the additional hydroisomerization step operates under operating conditions and with additional hydroisomerization catalysts identical to those used in steps b) and c) of hydroisomerization of the process according to the invention.

Step

According to step e) of the process according to the invention, at least a portion and preferably all of the effluent from hydroisomerization step b) and at least a part and preferably all of the effluent from step d) of hydrocracking, said effluent from step d) hydrocracking having optionally undergone the additional hydroisomerization step, are subjected to a distillation step to obtain middle distillates.

Said effluent is advantageously sent via the pipe (30) in a distillation train (13), which incorporates an atmospheric distillation and possibly a vacuum distillation, which aims to separate the conversion products of boiling point lower than 340 ° C and preferably below 370 ° C and to separate the residual fraction whose initial boiling point is generally greater than at least 340 ° C and preferably greater than or equal to at least 370 ° C. Among the conversion products with a boiling point of less than 340 ° C. and preferably less than 370 ° C., it is advantageously separated in addition to the light C1-C4 gases (line 31) at least one gasoline fraction (line 32), and at least one middle distillate fraction kerosene (line 33) and diesel (line 34). The diesel (s) and kerosene (s) cuts are

preference recovered separately, but the cutting points are adjusted by the operator according to his needs. The residual fraction and, preferably, whose initial boiling point is generally greater than at least 340 ° C. and preferably greater than or equal to at least 370 ° C., is advantageously recycled (line 35) to zone (27). hydrocracking. The gasoline fraction (line 32) can advantageously constitute a good charge for a steam cracking unit (5) and be sent to a steam cracking unit (5), not shown in FIG. 1. The hydrogen recovered in the distillation train can advantageously recycled in the process of the invention, for example via lines (6), (15), (20) or again (26).

The products obtained

The gas oil (s) obtained has a pour point of at most 0 ° C, generally below -10 ° C and often below -15 ° C. The cetane number is greater than 60, generally greater than 65, often greater than 70. The resulting kerosene (s) has a freezing point of not more than -35 ° C, generally less than - 40 ° C. The smoke point is greater than 25 mm, usually greater than 30 mm. In this process, the production of gasoline (not sought) is as low as possible.

The yield of gasoline will always be less than 50% by weight, preferably less than 40% by weight, advantageously less than 30% by weight or 20% by weight or even 15% by weight.

Examples preparation of the hydrotreatment catalyst

The catalyst is an industrial catalyst based on palladium on alumina noble metal with a palladium content of 0.3% by weight relative to the total weight of the finished catalyst, supplied by AXENS. Preparation of the hydroisomerization catalyst Cl

The hydroisomerization catalyst is a noble metal-containing catalyst and a one-dimensional 10 MR zeolite ZBM-30. This catalyst is obtained according to the procedure described hereinafter. The zeolite ZBM-30 is synthesized according to the patent BASF EP-A-46504 with the organic structuring triethylenetetramine. The ZBM-30 crude zeolite of 30

The synthesis is subjected to calcination at 550 ° C. under a stream of dry air for 12 hours. The zeolite H-ZBM-30 (acid form) thus obtained has a Si / Al ratio of 45. The zeolite is kneaded with an alumina gel of SB3 type supplied by Condéa-Sasol. The kneaded paste is then extruded through a die diameter 1.4 mm. The extrudates thus obtained are calcined at 500 ° C. for 2 hours in air. The weight content H-ZBM-30 is 20% by weight. Subsequently, the support extrusions are subjected to a dry impregnation step with an aqueous solution of the platinum salt Pt (NH 3) 42+, 20H-, left to mature in a water-based maturator for 24 hours at room temperature and then calcined during two hours in dry air in a bed traversed at 500 ° C (ramp temperature rise of 5 ° C / min).

The weight content of platinum of the finished catalyst after calcination is 0.48%.

Preparation of the C2 hydrocracking catalyst

The silica-alumina powder is prepared according to the synthesis protocol described in patent FR 2,639,256 (example 3). The amounts of orthosilicic acid and aluminum alkoxide are selected to have a composition of 70% by weight AI203 and 30% by weight SiO2 in the final solid. The dried powder is brought into contact with an aqueous solution of nitric acid, the amount of nitric acid being 5% by weight relative to the amount of powder and the amount of aqueous solution such as loss on ignition at 550 ° C. C of the cake obtained is about 60% by weight. This cake is kneaded and extruded. The kneading is done on a Z-arm kneader. The extrusion is carried out by passing the dough through a die provided with orifices 1.4 mm in diameter. The extrudates thus obtained are dried in an oven at 110 ° C. and then calcined under a dry air flow rate (ramp up to 5 ° C./min). The calcination temperature is adjusted so as to obtain a specific surface area of 310 m 2 / g.

The silica-alumina extrudates are then subjected to a dry impregnation step with an aqueous solution of hexachloroplatinic acid H 2 PtCl 6, left to mature in a water-based maturator for 24 hours at room temperature and then calcined for two hours under dry air in a bed. crossed at 500 ° C (ramp temperature rise of 5 ° C / min). The weight content of platinum of the finished catalyst after calcination is 0.70%.

The characteristics of the catalyst thus prepared are the following: a mean mesopore diameter of 7 nm,

a pore volume of the pores whose diameter is between the average diameter as defined above decreased by 3 nm and the average diameter as defined above increased by 3 nm equal to 60% of the total pore volume, a total pore volume of 0 70 ml / g, a volume of macropores with a diameter greater than 50 nm represents 29% of the total pore volume a BET surface area of 310 m 2 / g, a sodium content of 110 + -13 ppm by weight, a 85% noble metal dispersion, a noble metal distribution coefficient equal to 0.92.

EXAMPLE 1 Treatment of a Fischer-Tropsch Cargo According to a Catalyst Chain According to the Invention A Fischer Tropsch synthesis feedstock over a cobalt catalyst is separated into two fractions, the heaviest fraction having the characteristics following (Table 1).

Table 1: Characteristics of the heavy fraction. Simulated T distillation (5% weight): 175 ° C (25% weight): 246 ° C (50% weight): 346 ° C (75% weight): 444 ° C (95% weight): 570 ° C compounds 370 ° C + (by GC) 43% weight density at 15 ° C 0.797 nitrogen content 7 ppm sulfur content <limit detection detailed analysis of fraction C30 (GC) 82% weight n-paraffins 6% weight i-paraffins 11% weight olefins 1% oxygenated weight This heavy fraction is treated in a hydrogen-traversed bed lost on the above hydrotreatment catalyst under operating conditions which allow the elimination of

olefinic and oxygen compounds and traces of nitrogen. The operating conditions selected are as follows: WH (charge volume / volume of catalyst / hour) = 2 h -1 total working pressure: 50 bar hydrogen ratio / charge: 200 normal liters / liter temperature: 270 ° C.

After this hydrotreatment, the contents of olefins, oxygenates and nitrogenous compounds in the effluent fall below the detection thresholds, whereas the conversion of the 370 ° C + fraction to the 370 ° C fraction is negligible (less than 5% by weight). ; see table 2.

Table 2: Characteristics of the heavy fraction after hydrotreatment. Simulated T distillation (5% weight): 172 ° CT (25% weight): 242 ° CT (50% weight): 343 ° CT (75% weight): 441 ° CT (95% weight): 568 ° C compounds 370 ° C + (by GC) 41% weight density at 15 ° C 0.797 nitrogen content <limit detection sulfur content <limit detection detailed analysis of fraction C30 (GC) 91% weight n-paraffins 9% weight i-paraffins <limit The effluent thus hydrotreated is then separated by distillation into two fractions, an intermediate fraction representing 55% by weight of the hydrotreated effluent and a heavier fraction representing 45% by weight of the hydrotreated effluent. The characteristics of these two fractions are given in Table 3.20 Table 3: Characteristics of the intermediate and heavy fractions. intermediate fraction heavy fraction Simulated distillation T (5% weight): 155 ° CT (5% weight): 373 ° CT (25% weight): 199 ° CT (25% weight): 405 ° CT (50% weight): 257 ° CT (50% weight): 457 ° CT (75% weight): 305 ° CT (75% weight): 519 ° CT (95% weight): 357 ° CT (95% weight): 610 ° C compounds 150 ° C + (by 96% weight 100% GC weight) 1% weight 98% weight compounds 370 ° C + (by GC) detailed analysis of the 95% weight 93% weight fraction C30 (GC) 5% weight 7% weight n-paraffins < limit detection <limit detection i-paraffins <limit detection <limit detection oxygenated olefins The intermediate fraction is hydroisomerized on the catalyst C1 in a hydroisomerization reactor. under the operating conditions below: VVH (volume of charge / volume of catalyst / hour) = 1 h-1 - total working pressure: 50 bar hydrogen / charge ratio: 1000 normal liters / liter The temperature is adjusted to to have a conversion of the fraction 150 ° C + fraction 150 ° C- less than 5% by weight during the hydroisomerisation. Before testing, the catalyst undergoes a reduction step under the following operating conditions: hydrogen flow rate: 1600 normal liters per hour and per liter of catalyst raised to ambient temperature 120 ° C: 10 ° C / min - one-hour stop at 120 ° C. - rise from 120 ° C. to 450 ° C. at 5 ° C./min for two hours at 450 ° C. pressure: 1 bar The characteristics of the intermediate fraction thus hydroisomerized are given in Table 4 below. It is found that the intermediate fraction was substantially hydroisomerized while maintaining a lighter cut production of 150 ° C-negligible. Table 4: Characteristics of the intermediate fraction after hydroisomerization Simulated distillation T (5% weight): 149 ° CT (25% weight): 195 ° CT (50% weight): 250 ° CT (75% weight): 297 ° CT ( 95% by weight): 350 ° C compounds 150 ° C + (by GC) 94% weight Detailed analysis of the fraction C30 (GC) 20% weight n-paraffins 80% weight i-paraffins <limit detection olefins <oxygen detection limit At the same time, the heavy fraction is hydroisomerized on the catalyst C1 and then hydrocracked on the catalyst C2. The two catalysts are placed in two reactors in series (first hydroisomerization reactor and second hydrocracking reactor). Before testing, each catalyst undergoes a reduction step under the following operating conditions: hydrogen flow rate: 1600 normal liters per hour and per liter of catalyst; ambient temperature rise 120 ° C: 10 ° C / min. one hour at 120 ° C - rise from 120 ° C to 450 ° C at 5 ° C / min 15 - two-hour stage at 450 ° C pressure: 1 bar

The heavy fraction is brought into contact with the hydroisomerization catalyst C1 under the operating conditions below: 20 - VVH (volume of charge / volume of catalyst / hour) = 1 h -1 - total working pressure: 50 bar - ratio hydrogen / charge: 1000 normal liters / liter

The temperature is adjusted so as to have a conversion of the 370 ° C. + fraction to 370 ° C. less than 5% by weight during hydroisomerization. An inter5 levy

reactor allows a detailed analysis of the C30 fraction by gas chromatography. This analysis shows a substantial hydroisomerization of the normal paraffins initially present (Table 5).

Table 5: Detailed analysis of the C30- fraction of the hydroisomerized effluent. The effluent thus hydroisomerized is then sent to the hydrocracking catalyst C2 under the following operating conditions: WH (volume of charge / volume of catalyst / hour) = 1.5 h -1 total working pressure: 50 bar - hydrogen ratio charge: 800 normal liters / liter - temperature: 350 ° C. The reactor temperature is adjusted so as to obtain a conversion of the 370 ° C. + 70% by weight fraction.

The effluent thus hydrocracked is recombined with the effluent from the hydroisomerization of the intermediate fraction. The gas chromatographic analyzes make it possible to obtain the distribution of the different sections in the effluent thus recombined: C1-C4 cut: hydrocarbons with 1 to 4 carbon atoms inclusive - C5-C9 cut: hydrocarbons with 5 to 9 carbon atoms including carbon (naphtha cut) - C10-C14 cut: hydrocarbons of 10 to 14 carbon atoms inclusive (kerosene cut) - C15-C22 cut: hydrocarbons of 15 to 22 carbon atoms inclusive (gas oil cut) - cuts C22 +: hydrocarbons with more than 22 carbon atoms included (370 ° C + cut).

Table 6 reports the sectional analysis of the effluent. It can be seen that the series of catalysts according to the invention makes it possible to produce middle distillates with a formation of lighter, undesired cuts of less than 8% by weight. Moreover, the hydroisomerization step prior to the hydrocracking step of the heavy fraction makes it possible to improve not only the reactivity of the feedstock before the hydrocracking and the detailed analysis yield of the C30_ (GC) fraction. paraffins i-paraffins oxygenated olefins 21% weight 79% weight <limit detection <limit detection

in middle distillates produced but also strongly improves the cold properties of paraffins from the Fischer-Tropsch process and in particular the freezing point of kerosenes, the n / iso low ratio reflecting the isomerization of unwanted n-paraffins.

Table 6: Distribution and ratio n-paraffins / isoparaffins by section of the hydrocracked effluent (GC analysis). % n-paraffin / iso-paraffin weight (n / iso)% wt / wt C1-C4 cut weight 1.0 n / a cut C5-C9 5.7 n / a cut C10-C14 34.7 0.20 cut C15- C22 46.1 0.06 cut C22 + 12.5 not applicable Example 2: treatment of a filler from Fischer-Tropsch according to a chain of catalysts not according to the invention

In this example, there is no fractionation of the hydrotreated effluent intermediate cut and heavy cut.

The hydrotreated effluent is in its entirety hydroisomerized on the catalyst C1 and then hydrocracked on the catalyst C2. The two catalysts are placed in two reactors in series (first hydroisomerization reactor and second hydrocracking reactor). Before testing, each catalyst undergoes a reduction step under the following operating conditions: hydrogen flow rate: 1600 normal liters per hour and per liter of catalyst - ambient temperature rise 120 ° C: 10 ° C / min one-hour stage at 120 ° C rise from 120 ° C to 450 ° C at 5 ° C / min two-hour stage at 450 ° C pressure: 1 bar

The hydrotreated effluent is brought into contact with the hydroisomerization catalyst C1 under the operating conditions below: WH (charge volume / catalyst volume / hour) = 1 hr total working pressure: 50 bar hydrogen ratio load: 1000 normal liters / liter

The temperature is adjusted so as to have a conversion of the 370 ° C + fraction to a 370 ° C fraction of less than 5% by weight during the hydroisomerization An inter-reactor sampling makes it possible to carry out a detailed analysis of the C30 fraction by This analysis shows a substantial hydroisomerization of the normal paraffins initially present (Table 7).

Table 7: Detailed analysis of the C30 fraction of the hydroisomerized effluent.

The effluent thus hydrotreated and hydroisomerized is then sent to the hydrocracking catalyst C2 under the following operating conditions: WH (volume of charge / volume of catalyst / hour) = 2 hours. total working pressure: 50 bar hydrogen / feed ratio: 800 normal liters / liter temperature: 340 ° C

The temperature of the reactor is adjusted so as to obtain a conversion of the 370 ° C + fraction of 70% by weight. The gas chromatographic analyzes make it possible to obtain the distribution of the different cuts in the hydrocracked effluent: C1-C4 cut: hydrocarbons of 1 to 4 carbon atoms inclusive; C5-C9 cut: hydrocarbons of 5 to 9 atoms including carbon (naphtha cut) - C10-C14 cut: hydrocarbons of 10 to 14 carbon atoms inclusive (kerosene cut) - C15-C22 cut: hydrocarbons of 15 to 22 carbon atoms inclusive (gas oil cut) 30 - C22 + cuts: hydrocarbons with more than 22 carbon atoms included (370 ° C + cut). Detailed analysis of the C30 fraction (GC) n-paraffins i-paraffins oxygenated olefins 26% weight 74% weight <detection limit <limit detection 5 Table 8 shows the sectional analysis of the hydrocracked effluent. It is found that the chain of catalysts not according to the invention makes it possible to produce middle distillates with a formation of unwanted lighter cuts of greater than 8% by weight. Similarly, the isomerization rate of the middle distillate cuts is decreased.

Table 8: Distribution and ratio n-paraffins / isoparaffins by section of the hydrocracked effluent (GC analysis). % w / w paraffins / iso-paraffin (n / iso)% wt / wt C1-C4 cut 1.4 not applicable cut C5-C9 8.4 not applicable cut C10-C14 33.5 0.30 cut C15- C22 44.3 0.08 cut C22 + 12.4 not applicable

Claims (29)

1. Process for producing middle distillates from a paraffinic feedstock produced by Fischer-Tropsch synthesis, comprising the following successive steps: a) fractionation of the paraffinic effluent from the Fischer-Tropsch synthesis into at least three fractions: At least one intermediate fraction having an initial boiling point Ti between 120 and 200 ° C., preferably between 130 and 180 ° C. and very preferably equal to 150 ° C. and a final boiling point T2 between 330 and 420 ° C, and preferably between 340 and 400 ° C and very preferably equal to 370 ° C • at least one light fraction boiling below the intermediate fraction, • at least one heavy fraction boiling at above the intermediate fraction. B) hydroisomerization of at least a portion of said intermediate fraction from step a) in the presence of a first hydroisomerization catalyst comprising at least one Group VIII metal and / or at least one Group VIB metal and at least one molecular sieve, the conversion on said first hydroisomerization catalyst of products having a boiling point greater than or equal to 150 ° C in products with a boiling point of less than 150 ° C being less than 10%; hydroisomerization of at least a portion of said heavy fraction from step a) in the presence of a second hydroisomerization catalyst comprising at least one Group VIII metal and / or at least one Group VIB metal and at least one a molecular sieve, converting on said second hydroisomerization catalyst products with boiling points greater than or equal to 370 ° C into products with boiling points below 370 ° C being less than 20%, 3 D) hydrocracking at least part of the hydroisomerized effluent from step c) in the presence of a third hydrocracking catalyst comprising at least one Group VIII metal and / or at least one Group VIB metal and a silica-alumina or Y-zeolite carrier, converting to said third hydrocracking catalyst products having a boiling point greater than or equal to 370 ° C boiling point products lower than 370 ° C being higher than or equal to 40% by weight, f) distillation of at least a portion of the effluent from the hydroisomerization step b) and the hydrocracking step d) to obtain middle distillates. 2. Method according to claim 1 wherein the fractionation step a) is preceded by a hydrotreatment step, the conversion on said hydrotreating catalyst of the fraction 370 ° C + fraction 370 ° C "being less than 20 % in weight. 3. Method according to claim 2 wherein the paraffinic effluent from the Fischer-Tropsch synthesis unit undergoes, prior to the hydrotreating step, a separation step, wherein said effluent is fractionated into at least two fractions. a light fraction and a heavy fraction having an initial boiling point equal to a temperature of between 120 and 200 ° C, the light fraction boiling below the heavy fraction which is sent to the hydrotreating step. 4. Method according to one of claims 2 to 3 wherein the entire effluent from the hydrotreating step undergoes a separation step in which the decomposition products formed during the hydrotreating step are removed at least partly 5. Method according to one of claims 2 to 3 wherein the entire effluent from the hydrotreating step is sent in the fractionation step a), without prior separation step. 6. Method according to one of claims 1 to 5 wherein the conversion on said first hydroisomerisation catalyst of products with boiling points greater than or equal to 370 ° C in products with boiling points below 370 ° C is less than 10% and preferably less than 5% by weight. 7. Method according to one of claims 1 to 6 wherein said first hydroisomerization catalyst comprises either at least one noble metal of group VIII selected from platinum or palladium, or at least one metal of group VI selected from molybdenum or tugnstene, in combination with at least one non-noble group VIII metal selected from nickel and cobalt. 8. The method of claim 7 wherein the noble metal content of said first hydroisomerization catalyst is between 0.01 and 5% by weight relative to the finished catalyst. 9. The method of claim 8 wherein the group VI metal content of said first hydroisomerization catalyst is between 5 and 40% by weight oxide equivalent relative to the finished catalyst, and the metal content of group VIII is included in oxide equivalent between 0.5 and 10% by weight relative to the finished catalyst. 10. Process according to one of claims 1 to 9 wherein said first hydroisomerization catalyst contains at least one one-dimensional 10 MR zeolite molecular sieve. 11. The method of claim 10 wherein said one-dimensional 10MR zeolite molecular sieve of said first hydroisomerization catalyst is selected from zeolite molecular sieves of structure type TON, FER, EUO, SAPO-11 and zeolitic molecular sieves ZSM-48, ZBM-30, EU-2 and EU-11, taken alone or as a mixture. 12. The method of claim 10 wherein said one-dimensional 10MR zeolite molecular sieve is selected from zeolitic molecular sieves ZSM-48, ZBM-30, NU-10 and ZSM-22, alone or in admixture. The process of claim 10 wherein said 10MR one-dimensional zeolite molecular sieve is ZBM-30 synthesized with the organic template triethylenetetramine. 14. Method according to one of claims 10 to 13 wherein the content of 10MR zeolite molecular sieve unidimensional is between 5 and 95% by weight relative to the finished catalyst. 15. The method according to one of claims 1 to 14 wherein said first hydroisomerization catalyst also contains a binder consisting of a porous mineral matrix. 16. Process according to one of claims 1 to 15, in which the hydroisomerization step b) operates at a pressure of between 2 and 150 bar, at an hourly space velocity of between 0.1 h -1 and 10 h -1. , at a hydrogen flow rate, a hydrogen flow rate such that the volume ratio hydrogen / hydrocarbons is between 100 and 2000 normal liters of hydrogen per liter of feedstock and at a temperature of between 100 and 550 ° C. 17. Method according to one of claims 1 to 16 wherein the operating conditions and said first hydroisomerization catalyst used in step b) and the operating conditions and said second hydroisomerization catalyst used in step c), are the same. 18. Method according to one of claims 1 to 16 wherein all of the hydroisomerized effluent from step c) undergoes a separation step in which at least a portion of paraffins normal non-hydroisomerized in said step c) is separated from the effluent from said step c) and is recycled in said hydroisomerization step c). 19. Method according to one of claims 1 to 18 wherein said third hydrocracking catalyst comprises either at least one noble metal of group VIII selected from platinum and palladium, taken alone or in mixture, or at least one non-metal. Group VIII noble compound selected from nickel and cobalt in combination with at least one Group VI metal selected from molybdenum and tungsten, alone or in admixture. 20. The method of claim 19 wherein the noble metal content of said third hydrocracking catalyst is between 0.01 and 5% by weight relative to the finished catalyst. 21. The method of claim 19 wherein the group VI metal content of said third hydrocracking catalyst is comprised in oxide equivalent between 5 and 40% by weight relative to the finished catalyst, and the metal content of group VIII is included in oxide equivalent between 0.5 and 10% by weight relative to the finished catalyst. 22. Method according to one of claims 1 to 19 wherein said third hydrocracking catalyst comprises at least one noble metal, said noble metal being platinum and a silica-alumina support, without any binder. 23. Method according to one of claims 1 to 20 wherein said third hydrocracking catalyst comprises 0.05 to 10% by weight and preferably between 0.1 and 5% by weight of at least one noble metal of the group VIII, deposited on a silica-alumina support, without any binder, containing a quantity of silica of between 1 and 95%, expressed as a weight percentage, said catalyst having: a BET specific surface area of 100 to 500 m 2 / g, mean diameter of the mesopores of between 3 and 12 nm, a pore volume of pores whose diameter is between the mean diameter as defined above decreased by 3 nm and the average diameter as defined above increased by 3 nm is greater than 40. % of the total pore volume, a total pore volume of between 0.4 and 1.2 ml / g, a volume of macropores with a diameter greater than 50 nm, and preferably between 100 nm and 1000 nm, representing between 5 and 60% of the volume total porous, • a content of alkaline or alkaline earth compounds of less than 300 ppm by weight and preferably less than 200 ppm by weight. 24. Method according to one of claims 1 to 20 wherein said third hydrocracking catalyst comprises at least one hydro-dehydrogenating element selected from the group formed by the elements of group VIB and group VIII of the periodic table, of 0 0.1 to 5.5% by weight of oxide of a doping element chosen from phosphorus, boron and silicon and a non-zeolitic support based on silica-alumina containing an amount greater than 5% by weight and less than or equal to 95% by weight of silica, said catalyst having the following characteristics: a mean mesoporous diameter, measured by mercury porosimetry, of between 2 and 14 nm, a total pore volume, measured by mercury porosimetry, of between 0.1 ml 0.5 g / g and a total pore volume, measured by nitrogen porosimetry, of between 0.1 ml / g and 0.5 ml / g, a BET specific surface area of between 100 and 550 m 2 / g. a porous volume, measured by porosimetry mercury, included in pores with a diameter greater than 14 nm less than 0.1 ml / g, - a pore volume, measured by mercury porosimetry, contained in pores with a diameter greater than 16 nm of less than 0.1 ml / g, - a pore volume, measured by mercury porosimetry, included in pores with diameters greater than 20 nm, less than 0.1 ml / g, - a pore volume, measured by mercury porosimetry, included in the pores of diameter greater than 50 nm less than 0.1 ml / g an X-ray diffraction pattern which contains at least the main characteristic lines of at least one of the transition aluminas included in the group consisting of alpha, rho, chi aluminas, eta, gamma, kappa, theta and delta. a packed packing density of the catalysts greater than 0.75 g / ml. 5 25. Method according to one of claims 1 to 20 wherein said third hydrocracking catalyst comprises 0.05 to 10% by weight of at least one noble metal group VIII, deposited on a silica-alumina support, without any binder, containing a quantity of silica of between 1 and 95%, expressed as a weight percentage, said catalyst having: a BET specific surface area of 200 to 600 m 2 / g; an average mesopore diameter of between 3 and 12 nm; a pore volume of the pores whose diameter is between the mean diameter as defined above decreased by 3 nm and the mean diameter as defined above increased by 3 nm is greater than 60% of the total pore volume, a total pore volume less than 1 ml / g, • an alkali or alkaline earth metal content of less than 300 ppm by weight. 26. Process according to one of Claims 1 to 23, in which the hydrocracking step c) operates at a pressure of between 2 and 150 bar, at an hourly space velocity of between 0.1 h -1 and 10 h. at a hydrogen flow rate such that the volume ratio hydrogen / hydrocarbons is between 100 and 2000 normal liters of hydrogen per liter of filler and at a temperature of between 100 and 550 ° C. 27. Process according to one of claims 1 to 24, in which all of the hydrocracked effluent from hydrocracking step c) undergoes an additional hydroisomerization step, in which the hydrocracked effluent is brought into contact. with an additional hydroisomerization catalyst, converting on said catalyst products with boiling points greater than or equal to 370 ° C into products with boiling points below 370 ° C of less than 20% by weight. 30 28. A process according to one of claims 1 to 25 wherein the hydroisomerization step operates under operating conditions and with additional hydroisomerization catalysts identical to those used in steps b) and c) d. hydroisomerization. 35 29. Method according to one of claims 1 to 26 wherein the residual fraction is recycled to the hydrocracking zone.