WO2009106704A2

WO2009106704A2 - Method of producing middle distillates by sequenced hydroisomeration and hydrocracking of effluent produced by the fischer-tropsch process

Info

Publication number: WO2009106704A2
Application number: PCT/FR2008/001744
Authority: WO
Inventors: Christophe Bouchy; Emmanuelle Guillon; Johan Martens
Original assignee: Ifp; Eni S.P.A.
Priority date: 2008-01-04
Filing date: 2008-12-16
Publication date: 2009-09-03
Also published as: FR2926086B1; FR2926086A1; WO2009106704A3; ZA201004360B

Abstract

The invention describes a method of producing middle distillates from a paraffinic feedstock produced by Fischer-Tropsch synthesis, comprising: separation of a heavy fraction having an initial boiling point between 120 and 200°C; hydroisomerization of at least part of said heavy fraction in the presence of a first hydroisomerization catalyst comprising at least one metal of group VIII and/or at least one metal of group VIB and at least one molecular sieve; hydrocracking of at least part of the hydroisomerized effluent in the presence of a second hydrocracking catalyst comprising at least one metal of group VIII and/or at least one metal of group VIB and a silica-alumina support or a zeolite Y-based support; and distillation of the final effluent in order to obtain middle distillates.

Description

PROCESS FOR PRODUCING MEDIUM DISTILLATES BY HYDROISOMERIZATION AND HYDROCRACKING SEQUENCES OF AN EFFLUENT PRODUCED BY THE FISCHER-TROPSCH PROCESS

The present invention relates to a process for the production of middle distillates by hydroisomerization and hydrocracking of Fischer-Tropsch process feeds to obtain middle distillates (gas oil, kerosene). In the Fischer-Tropsch process, the synthesis gas (CO + H ₂ ) 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 temperature equal to approximately 34 ^° C., that is to say often included in the middle distillate cut, is +37 ^° C. ° C about which makes its use impossible, the specification being -15 ° C for diesel. Moreover, the fraction of the hydrocarbon feedstock having a boiling point greater than 370 ^° C. (ie paraffins with more than 22 carbon atoms, the boiling point of n-Docosane being 37 ^° 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 feed into middle distillates (kerosene and gas oil) whose initial and final cutting points are respectively 15O ⁰ C and 37O ⁰ C. It is then particularly desirable to be able to minimize the production of lighter cuts such as for example the naphtha cut. Thus, the optimal 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 middle distillate fraction already present in the feedstock and, on the other hand, the transformation of the heaviest fraction of the middle distillate feed 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.

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 on a catalyst comprising at least one Group VIII and / or Group VI metal on a support and a step of hydrotreating on a catalyst comprising at least one Group VIII metal. and / or group VI on an amorphous support. No specific hydroisomerization step is mentioned.

Numerous patents or patent applications have described the sequence of hydrocracking in a first step and hydroisomerization or dewaxing in a second step.

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 hydrotreatment / hydrocracking catalyst in order to hydrogenate the olefinic compounds and oxygenate the oxygenated compounds present, said hydrotreating / hydrocracking catalyst possibly containing at least one noble metal group VIII on a silica or alumina support or at least one group VIII metal and Group VIB 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;

hydroisomerizing the heavy fraction on a hydroisomerization catalyst in order to improve its cold-holding properties, said hydroisomerization catalyst possibly containing a metal-active phase based on noble or non-noble metals and an acidic component based on silicoaluminophosphate SAPO type or intermediate zeolite type ZSM 22, ZSM 23, SSZ 32, ZSM 35 or ZSM 48;

- mixing the heavy fraction thus isomerized with at least a portion of the light fraction; recovering from this mixture a gas oil corresponding to 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 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 the 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 with an oil base having defined physicochemical properties. The hydrocracking step always precedes the hydroisomerization step.

The 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. carbon and at least 20% of normal paraffins having at least twenty six carbon atoms on an 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 in a mixture, the preferred catalyst used being of the Pt / SAPO11 type. The effiuent obtained has an iso-paraffin ratio on normal paraffins of at least five to one and has a reduced content of paraffins having at least twenty-six carbon atoms, and the diesel yields of initial and final cutting points respectively typically from 160 to 336 degrees Celsius, are from 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.

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 alone or in mixture. The hydroisomerization catalyst comprises at least one noble metal of group VIII and a support selected 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 EP 1 406 990 describes a process for producing middle distillates from an effluent produced by a Fischer-Tropsch unit, comprising a possible fractionation to obtain at least one heavy fraction with initial boiling point between 120 -200 ⁰ C, said heavy fraction or said effluent being optionally hydrotreated, then brought into contact with a first amorphous hydrocracking / hydroisomerization catalyst which contains at least one noble metal of group VIII, the effluent obtained is distilled and then the residual fraction boiling over middle distillates and / or a part of the middle distillates is contacting a second amorphous hydrocracking / hydroisomerization catalyst containing at least one Group VIlI noble metal.

The patent EP 1 406 989 describes a process for producing middle distillates from a paraffinic feedstock produced by Fischer-Tropsch synthesis, comprising the following successive steps: a) separation of at least a light fraction of the feedstock so as to to obtain a single so-called heavy fraction with initial boiling point between 120-200 ^° C, b) possible hydrotreatment of said heavy fraction, possibly followed by a step c) of separation of at least part of the water, c) passing at least part of said fraction optionally hydrotreated over an amorphous hydroisomerization / hydrocracking conversion over this catalyst higher boiling points products or equal to ⁰ 37o C in boiling products less than 37O ⁰ C is greater than 80% by weight, d) distillation of the hydrocracked / hydroisomerized fraction to obtain middle distillates, and recycling in step d) of the residue fraction it boils above said middle distillates.

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 Fischer-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 lighter fractions produced by hydrocracking of the heaviest paraffinic compounds, such as, for example, the naphtha fraction, present in the outlet effluent of the Fischer- Tropsch, said compounds having boiling points higher than those of kerosene and diesel fuel cuts, for example the 370 ° C ⁺ fraction.

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) separating at least a light fraction of the feedstock so as to obtain a single so-called heavy fraction with an initial boiling point of between 120 and 200 ^° C., b) hydroisomerization of at least a portion of said heavy fraction by 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 said boiling point products onto said selective hydroisomerization catalyst greater than or equal to 370 ⁰ C in products with boiling points below 370 ⁰ C being less than 20%, c) hydrocracking at least part of the hydroisomerized effluent in the presence of a second hydrocracking catalyst comprising at least one Group VIII metal and / or at least one Group VIB metal and a silica alumina or Y zeolite support, converting said boiling point products onto said hydrocracking catalyst; higher than or equal to 37O ⁰ C in products with a boiling point lower than 370 ° C being greater than or equal to 40% by weight, d) distillation of the final effluent to obtain middle distillates.

In more detail, the steps are as follows:

According to the process according to the invention, the paraffinic effluent from the Fischer-Tropsch synthesis unit undergoes a separation step a) in which said effluent is fractionated (for example distilled) into at least two fractions. It is separated from the load a

(or more) light fraction to obtain a heavy fraction having an initial boiling point equal to a temperature between 120 and 200 ⁰ C, and preferably between 130 and 180 ° C and for example about 150 ⁰ C, the light fraction boiling below the heavy fraction. The heavy fraction generally has paraffin contents of at least 50% by weight.

Optionally, at least a portion and preferably all of said heavy fraction from separation step a) undergoes a hydrotreatment step in which it is contacted in a hydrotreating zone in the presence of hydrogen. , with a hydrotreatment catalyst. The operating conditions are 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 a part of the sulphide and / or nitrogen compounds potentially present in the feedstock with hydrogen sulphide and / or ammonia. 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 completely removed from said heavy fraction.

According to the process according to the invention, at least a part and preferably all of said heavy fraction resulting from the separation step a), having optionally undergone the hydrotreatment step and / or the separation step of at least a part of the possible decomposition products of the impurities, undergoes a step b) of hydroisomerisation in which said heavy fraction is brought into contact, in a hydroisomerisation zone, in the presence of hydrogen, with a first hydroisomerisation catalyst comprising at least one Group VIII metal and / or at least one Group VIB metal and at least one molecular sieve. The operating conditions are chosen so as to produce a hydroisomerized effluent, the conversion of the products 37O ⁰ C ⁺ to 37O ⁰ C ^" being less than 20% by weight and preferably less than 10% by weight.

Optionally, at least a portion, and preferably all, of the paraffins non-hydroisomerized during step b) hydroisomerization is separated from the effluent from said step b) and is recycled in said step d) hydroisomerization.

At least a part of the hydroisomerized effluent from step b) and having optionally undergone the step of separating the normal non-hydroisomerized paraffins, undergoes a step c) of hydrocracking in which said effluent is brought into contact, in a hydrocracking zone, in the presence of hydrogen, with a second hydrocracking catalyst comprising at least one Group VIII metal and / or at least one Group VIB metal and a silica-alumina or Y-zeolite support. operative are chosen so as to obtain a conversion of the fraction 370 ⁰ C. ⁺ fraction 370 ⁰ C of ^"at least 40% by weight and preferably at least 60% by weight.

Optionally, at least a portion and preferably all of the hydrocracked effluent from the hydrocracking step c) undergoes an additional hydroisomerization step, in an additional hydroisomerization zone, in which said hydrocracked effluent is put into operation. contact with an additional hydroisomerization catalyst, the conversion on this catalyst of products with boiling points greater than or equal to 370 ^° C. to products with a boiling point below 370 ° C. being less than 20% by weight and preferably less than 10% by weight. In accordance with the process according to the invention, at least a part, and preferably all, of the hydrocracked effluent from step c) of hydrocracking, having optionally undergone the additional hydroisomerization step, is subjected to a step of separation d) in a distillation train so as to separate the light products inevitably formed during the hydrocracking step c) or the optional step of additional hydroisomerization, such as for example the gases (C ₁ -C ₄ ) and a gasoline cut, also for distilling at least one gas oil cut and at least one kerosene cut, and also for distilling a fraction whose compounds have boiling points higher than those of middle distillates (kerosene + gas oil). This fraction, referred to as the residual fraction, generally has an initial boiling point of at least 35 ^° C., preferably greater than 370 ^° C. Said residual non-hydrocracked fraction is advantageously recycled in the hydrocracking step c).

Unexpectedly, the use of 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 from the separation step a), said light fraction comprising in terms of boiling points a gasoline cut. that is to say the fraction C ₅ boiling to at most 2OfJ ⁰ C and usually at about 150 ⁰ C. Failure to treat said light fraction makes it possible to minimize the volumes of hydrotreating catalysts, hydroisomerization and hydrocracking to use and thus reduce the size of the reactors and therefore investments.

In addition, the process according to the invention makes it possible, in addition to greatly improving the cold properties of paraffins resulting from the Fischer-Tropsch process and in particular the freezing point of kerosenes, the optimized production of middle distillates (kerosene, gas oil) containing a reduced amount of lighter fractions such as gasoline. It thus appears that the hydroisomerization step prior to the hydrocracking step 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 to 37O ⁰ C ⁺ . This therefore makes it possible to reduce the production of unwanted light cuts.

Detailed description of the invention

The description will be made with reference to Figure 1 without Figure 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, CO ₂ , CO and unreacted hydrogen as well as light hydrocarbon compounds C 1 to C ₄ as a 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 (1) is fractionated (for example by distillation) in a separation means (2) in at least two fractions: at least one light fraction and a heavy fraction with initial boiling point equal to a temperature between 120 and. 200 ⁰ C and preferably between 130 and 180 ° C and even more preferably at a temperature of 150 ⁰ C, in other words the cutting point is between 120 and 200 ⁰ C. The light fraction comes out of the means separation (2) by the pipe (3) and the heavy fraction by the pipe (4).

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 two fractions described above.

The light fraction is not treated according to the process of the invention but may for example constitute a good load for petrochemicals and more particularly for a steam cracking unit (5). The heavy fraction previously described is treated according to the process of the invention.

Optionally, at least a portion, and preferably all, of said heavy fraction from separation step a) undergoes a hydrotreating step in a catalytic zone (7) in which it is brought into contact, in the presence of hydrogen (line 6), with a hydrotreatment catalyst which aims to reduce the content of olefinic and unsaturated compounds, to optionally decompose the oxygenated compounds (mainly alcohols) present in said heavy fraction, as well as to decompose possible traces of sulfur and nitrogen compounds. This hydrotreating step is advantageously non-converting, that is to say that the conversion on this catalyst of the fraction 37O ⁰ C ⁺ into Fraction 37O ⁰ C ^" is preferably less than 20% by weight, preferably less than 10% by weight and very preferably less than 5% by weight.

The catalysts used in this optional hydrotreatment step are advantageously non-cracking or slightly cracking hydrotreatment catalysts comprising 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.

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 any method known to those skilled in the art or can be acquired from companies specializing in the manufacture and sale of catalysts.

In the case of the use of Group VIII non-noble metals, a combination of at least one Group VI metal, preferably molybdenum or tungsten and at least one Group VIIl metal, is preferably used. cobalt and nickel from the periodic table of elements. The non-noble group VIII metal concentration, when it is used, is advantageously from 0.01 to 15% by weight of equivalent relative to the finished catalyst and that of the group VI metal is advantageously from 5% to 40% by weight. % 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 sulfurous form.

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 hydrotreatment 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 the group VI on metal (or metals) group VIIl is advantageously between 1, 25 and 20 and preferably between 2 and 10. In the case where said catalyst contains phosphorus, the concentration of phosphorus oxide P ₂ O ₅ is advantageously less than 15% by weight and preferably less than 10% by weight with respect 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 Group VIB metal is advantageously between 0.5: 1 to 1.5: 1; the quantities of group VIB metal and of group VIII metal, such as nickel or cobalt, are such that the metal atomic ratio of group VIII on group VIB metal is advantageously between 0.3: 1 to 0.7 1. The quantity of metal of group VIB expressed in weight of metal relative to the weight of finished catalyst is advantageously between 2 to 30% and the amount of metal of group VIII expressed as weight of metal relative to the weight of finished catalyst is advantageously understood 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 chosen 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.

Preferably, the optional hydrotreating 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., very preferably between 150 and 300 ^° C., 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 load 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 37O ⁰ C into 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. Optionally, at least a portion and preferably all of the effluent from the optional hydrotreatment step, and leaving the hydrotreatment reactor (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 sulphide and / or ammonia formed during optional hydrotreatment step are advantageously eliminated at least partly 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 hydroisomerization step b), without prior separation step.

Step (h)

According to the process according to the invention, at least a portion and preferably all of said heavy fraction resulting from step (a) of separation, having possibly undergone the hydrotreatment step and the separation step of least part of the possible products of decomposition of the impurities, undergoes a step b) of hydroisomerisation in which said heavy fraction is brought into contact, in a hydroisomerisation zone (13), in the presence of hydrogen (12) 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. The operating conditions are chosen so as to produce a hydroisomerized effluent, the conversion of products 370 ⁰ C ⁺ to 37O ⁰ C ^" being less than 20% by weight, preferably less than 10% by weight and very preferably less than 5%. in weight. Catalysts of hydroxisomerization

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 VII, 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 VIlI 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 first hydroisomerization catalyst used in step b) of the process according to the invention is advantageously between 0.degree. , 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) the process according to the invention is advantageously comprised, in oxide equivalent, of 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 metal content of the group VII1 of said catalyst is advantageously comprised, in oxide equivalent, of between 0.5 and 10% by weight relative to the finished catalyst, preferably between 1 and 8% by weight and very preferably between 1 and 8% by weight. , 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.

The 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, Elsevier to which the present application also refers. Zeolites are classified according to the size of their pore openings or channels.

One-dimensional 10 MR zeolite molecular sieves have pores or channels whose opening is defined by a ring of 10 oxygen atoms (10MR aperture). 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 else 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 most preferably less than 0.01. Thus, the zeolites used in the composition of said selective 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 to the acid form of said zeolites.

The said monodimensional zeolite molecular sieve 10MR of the said first hydroisomerization catalyst is advantageously chosen from zeolitic molecular sieves of structural type TON (chosen 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 in admixture. 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 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 may optionally be manufactured and used in the form of crushed powders, tablets, rings, beads. , 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 the treatment in hydrogen at a temperature of 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 to 450 ^° C. at a rate of 1 ° C./min and then a two-hour plateau 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. According to step b) of the process according to the invention, in the hydroisomerisation zone (13), the charge is brought into contact, in the presence of hydrogen with said first hydroisomerisation catalyst, at temperatures and pressures. operatives advantageously to achieve a hydroisomerization of the non-converting load. This means that the hydroisomerization is carried out with a conversion of the fraction 370 ⁰ C ⁺ fraction 370 ⁰ C ^" less than 20% by weight, preferably less than 10% by weight and very preferably less than 5% in weight.

Thus, those skilled in the art choose the operating conditions so that, preferably, the hydroisomerization step b) 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 and 90 bar, at an hourly space velocity advantageously between 0.1 h ^-1 and 10 h ^-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 filler and preferably between 150 and 1500 normal liters of hydrogen per liter of charge and at a temperature advantageously between 100 and 550 ^° C., preferably between 150 ° C. and 45 ^° C., and very preferably between 200 and 450 ° C.

Optionally, at least a portion, and preferably all, of the hydroisomerized fluent from the hydroisomerization step b) undergoes a separation step in a separation zone (15), wherein at least a portion, and preferably all, of the normal non-hydroisomerized paraffins in said step b) is separated from the effluent from said step b) and is recycled in said hydroisomerization step b). The hydroisomerized effluent from the hydroisomerization step b) is sent via the line (14) to the separation zone (15). 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 b) via the pipe (16). Step (c)

According to step c) of the process according to the invention, at least a part, and preferably all, of the hydroisomerized effluent resulting from the hydroisomerization step b) and having optionally undergone the step of separation of the n- non-hydroisomerized paraffins, undergoes a step c) of hydrocracking (line 17) in which said effluent is brought into contact, in a second hydrocracking zone (19), in the presence of hydrogen (line 18), with a second catalyst hydrocracking composition comprising at least one Group VIII metal and / or at least one Group VIB metal and a silica-alumina or Y-zeolite support. According to the invention, the operating conditions are chosen so as to obtain a conversion of the fraction 370 ^° C ⁺ fraction 370 ⁰ C ^" of 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 hr ^-1 and very preferably between 0 hr , 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 charge and at a temperature of between 100 and 550 ^° C., preferably between 150 ^° C. and 450 ° C., and very preferably between 200 and 400 ^° C.

Hydrocracker 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 cracking function. .

According to step c) of the process according to the invention, the second hydrocracking catalyst comprises at least one Group VIIl 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 second hydrocracking catalyst comprises at least one noble metal ViII group selected from platinum and palladium, taken alone or in admixture, active in their reduced form, or at least one non-noble group VIII metal selected from nickel and cobalt in combination with at least one group VI metal selected from molybdenum and tungsten, alone or as a mixture, and preferably used in their sulfurized form.

In the case where the second hydrocracking catalyst comprises at least one noble metal of group VIII, the noble metal content of the hydrocracking catalyst used in stage c) 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 second 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 the hydrocracking catalyst used in stage c) the process according to the invention is advantageously comprised, in oxide equivalent, of 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 comprised, in oxide equivalent, of between 0.5 and 1% by weight relative to the finished catalyst, preferably between 1 and 8% by weight and very preferably between 1 and 8% by weight. , 5 and 6% by weight.

The metal function is advantageously introduced on the second 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 support is based on zeolite Y.

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 ) alone or as a mixture. Preferably, said binder is chosen from silica and alumina and even more preferably, said binder is alumina in all its 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 second preferred hydrocracking catalysts used in the hydrocracking step c) of the process according to the invention are the catalysts whose support consists solely of silica-alumina without any binder.

A second preferred hydrocracking catalyst used in stage c) 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 c) 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 0.05 to 10% by weight and preferably between 0.1 and 5% weight of at least one noble metal group VIII ₁ preferably selected from platinum and palladium and preferably, said noble metal being platinum, deposited on a silica-alumina support, without any binder, containing a quantity of silica (SiO ₂ ) of between 1 and 95%, expressed as 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 80%. and 45%, said catalyst having:

• a BET specific surface area of 100 to 500 m ² / g, preferably between 200 m ² / g and 450 m ^z / g and very preferably between 250 m ² / g and 450 m ² / g,

An average diameter of the mesopores 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 mean diameter as defined above decreased by 3 nm and the average diameter as defined previously increased by 3 nm is greater than 40% of 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,

A content of alkaline or alkaline earth compounds 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 pore diameter of the catalyst is advantageously measured from the porous distribution profile obtained using a mercury porosimeter.

Preferably, the dispersion of said first preferred catalyst used in step c) 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 available to the reagent relative to the total amount of metal of the catalyst, is advantageously measured, for example, by H ₂ / O ₂ titration. Preferably, the distribution coefficient of the noble metal of said first preferred catalyst used in step c) 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 may 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 c) 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,

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 pore volume, measured by mercury porosimetry, included in pores with a diameter greater than 14 nm of less than 0.1 ml / g, a porous volume, measured by mercury porosimetry, included in pores with a diameter greater than 16 nm less than 0.1 ml / g,

a porous volume, measured by mercury porosimetry, included in pores with diameters greater than 20 nm, less than 0.1 ml / g, a porous volume, measured by mercury porosimetry, included in pores with a diameter greater than 50 nm less than 0.1 ml / g.

an X-ray diffraction diagram which contains at least the principal characteristic lines of at least one of the transition aluminas included in the group composed of alpha, rho, chi, eta, gamma, kappa, theta and delta aluminas. a packed packing density of the catalysts greater than 0.75 g / ml.

Another preferred catalyst used in step c) 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 noble metal group VIlI ₁ 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 (SiO ₂ ) between 1 and 95%, expressed as 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 surface area of 200 to 600 m ² / g and preferably between 250 m ² / g and 500 m ² / g,

A porous volume of pores whose diameter is between the mean diameter as defined above decreased by 3 nm and the average diameter as defined previously 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,

A total pore volume of less than 1 ml / g, preferably of between 0.1 and 0.9 ml / g and very preferably of between 0.2 and 0.7 ml / g,

Preferably, the dispersion of said third preferred catalyst used in stage c) 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 titration H ₂ / O ₂ .

Preferably, the distribution coefficient of the noble metal of said third preferred catalyst used in step c) 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 hydrocracking step c) undergoes an additional hydroisomerization step, in a catalytic zone (21) of additional hydroisomerization, in which the hydrocracked effluent is contacted with an additional hydroisomerization catalyst. The operating conditions and the additional hydroisomerization catalyst are chosen so as to carry out an additional hydroisomerization of the feedstock with a conversion on this catalyst of products with boiling points of greater than or equal to 37 ^° C. in products with lower boiling points. at 370 ° C. 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 additional hydroisomerization catalyst used in the additional hydroisomerization step may advantageously be identical or different.

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

Preferably, the first hydroisomerization catalyst used in step b) and the additional hydroisomerization catalyst are identical.

Said hydrocracked effluent is sent (line 20) to an additional hydroisomerization catalytic zone (21) via line (20).

Step (d)

According to step d) of distillation of the process according to the invention, at least a portion and preferably all of the final effluent, that is to say, the effluent from step c) of hydrocracking , having optionally undergone the additional hydroisomerization step, undergoes a distillation step d) to obtain middle distillates. Said final effluent is advantageously sent via the pipe (22) in a distillation train (23), which incorporates an atmospheric distillation and optionally a vacuum distillation, which aims to separate the conversion products of lower boiling point to 340 ⁰ C and preferably less than 370 ⁰ C and to separate the residual fraction whose initial boiling point is generally greater than at least 340 ⁰ C and preferably greater than or equal to at least 370 ⁰ C.

Among the conversion products with a boiling point of less than 340 ° C. and preferably less than 37 ^° C., it is advantageously separated in addition to the light C ₁ -C ₄ gases (line 24) at least one gasoline fraction (line 25). , and at least one middle distillate fraction kerosene (line 26) and diesel (line 27). The diesel (s) and kerosene (s) cuts are preferably 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 28) in zone (19). hydrocracking.

The gasoline fraction (line 25) can advantageously constitute a good charge for a steam cracking unit (5) and be sent to a steam cracking unit (5), the line sending the gasoline fraction (25) to a steam cracking unit (5). not shown in Figure 1. The hydrogen recovered in the distillation train can be advantageously recycled in the process of the invention for example via the pipes (6), (12) or again (18).

The products obtained

The gas oil (s) obtained advantageously has a pour point of at most 0 ° C., generally below -10 ^° C. and often below -15 ^° C.

The cetane number of the gas oils obtained is advantageously greater than 60, generally greater than 65, often greater than 70.

The kerosene (s) obtained advantageously has a freezing point of not more than -35 ° C., and preferably less than -40 ^° C. The smoke point is advantageously greater than 25 mm, and preferably greater than 30 mm. In this process, the production of gasoline (not sought) is as low as possible. The yield of gasoline is always advantageously less than 30% by weight, preferably less than 20% by weight and very preferably less than 15% by weight. Examples

Preparation of the hydrotreating 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.

Step b): Preparation of the Selective Hydrogenation Catalyst C1

The hydroisomerization catalyst C1 is a noble metal-containing catalyst and a one-dimensional 10 MR zeolite molecular sieve: ZBM-30. This catalyst is obtained according to the procedure described below. The zeolite ZBM-30 is synthesized according to the patent BASF EP-A-46504 with the organic structuring triethylenetetramine. The synthetic ZBM-30 zeolite 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 an 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 two hours in air. The weight content H-ZBM-30 is 20% by weight. Then the support extrusions are subjected to a

2+ step of dry impregnation with an aqueous solution of the platinum salt Pt (NH ₃ ) ₄ , 2OH ^" , left to mature in water-based maturator for 24 hours at room temperature and then calcined for two hours in dry air in a crossed bed at 500 ^° C. (ramp for raising the temperature of 5 ° C./min) The weight content of platinum of the finished catalyst after calcination is 0.48%.

Step c): preparation of the hydrocracking catalyst C2

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 chosen so as to have a composition of 70% by weight of Al ₂ O ₃ and 30% by weight.

SiO ₂ 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. Mixing is done on a Z-arm kneader. The extrusion is carried out by passing the paste through a die provided with orifices of diameter 1, 4 mm. 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 surface area of 310 m ^z / g.

The silica-alumina extrudates are then subjected to a dry impregnation step with an aqueous H ₂ PtCl ₆ hexachloroplatinic acid solution, left to mature in a water-based maturator for 24 hours at room temperature and then calcined for two hours under air. dry in bed crossed at 500 ⁰ 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 as follows:

a mean diameter of the mesopores of 6.5 nm,

a pore volume of the 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 equal to 60% of the total pore volume,

a total pore volume of 0.7 ml / g,

a volume of macropores, whose diameter is 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 dispersion of the noble metal of 85%,

a distribution coefficient of the noble metal equal to 0.92.

Example 1 Treatment of a Fischer-Tropsch Filler According to the Process According to the Invention

A feed from the Fischer Tropsch synthesis on a cobalt catalyst is separated into two fractions, the heaviest fraction having the following characteristics (Table 1). Table 1: Characteristics of the heavy fraction

This heavy fraction is treated in a hydrogen traversed bed lost on the above hydrotreatment catalyst under operating conditions that allow the elimination of olefinic and oxygen compounds and traces of nitrogen. The operating conditions selected are the following:

WH (load volume / volume of catalyst / hour) = 2 h ^"1 total working pressure: 50 bar

- Hydrogen / charge ratio: 200 normal liters / liter

temperature: 27O ⁰ C

After the hydrotreating, olefins content, oxygen and nitrogen compounds from the effluent falls below a detection threshold, while the conversion of the fraction C 370 ⁰ ⁴ 370 ⁰ C fraction ^"is negligible (less than 5% by weight or Table 2. The carbon monoxide and / or carbon dioxide and / or water and / or ammonia formed during the hydrotreatment are removed by a flash and decant step.

Table 2: Characteristics of the heavy fraction after hydrotreatment.

The hydrotreated effluent is then 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

- rise in ambient temperature 120 ^° C.: 10 ° C./min step of one hour at 120 ° C.

- rise from 12O ⁰ C to 45O ⁰ C at 5 ° C / min bearing two hours at 450 ° C pressure: 1 bar

The hydrotreated effluent is brought into contact with the selective hydroisomerization catalyst C1 under the operating conditions below:

- WH (volume of charge / volume of catalyst / hour) = 1 hr ^-1

- total working pressure: 50 bar hydrogen / charge ratio: 1000 normal liters / liter

The temperature is adjusted so as to have a conversion of the fraction 370 ⁰ C ⁺ fraction 37O ⁰ C less than 5% by weight during hydroisomerisation. An inter engine bleed allows a detailed analysis of the fraction C ₃₀ ^"by chromatography gas phase. This analysis shows a substantial hydroisomerization of the normal paraffins initially present (Table 3).

Table 3: Detailed analysis of the fraction C ₃₀ ^" of the hydroisomerized effluent.

The effluent thus hydrotreated and hydroisomerized is then sent to the hydrocracking catalyst C2 under the following operating conditions:

- WH (load volume / volume of catalyst / hour) = 2 h ^"1 - total working pressure: 50 bar

- hydrogen / charge ratio: 800 normal liters / liter

- temperature: 340 ⁰ C

The temperature of the reactor is adjusted so as to obtain a conversion of the 370 ⁰ 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:

- C ₁ -C ₄ cut: hydrocarbons with 1 to 4 carbon atoms including C ₅ -C ₉ cut: hydrocarbons with 5 to 9 carbon atoms inclusive (naphtha cut) C ₁₀ -C ₄ cut: hydrocarbons with 10 to 14 atoms of carbon included (kerosene cut)

- C ₁₅ -C ₂₂ cut: hydrocarbons of 15 to 22 carbon atoms inclusive (gas oil cut) - C ₂₂ ⁺ cuts: hydrocarbons containing more than 22 carbon atoms (370 ⁰ C ⁺ cut).

Table 4 shows the sectional analysis of the hydroisomerized and hydrocracked effluent. It is found that the sequence of catalysts according to the invention allows an optimized production of middle distillates with formation of unwanted lighter cuts of less than 10% by weight. Moreover, the hydroisomerization step prior to the hydrocracking stage makes it possible to improve not only the reactivity of the feedstock before the hydrocracking and the yield of the middle distillates produced, but also makes it possible to greatly improve the cold properties. paraffins from the Fischer-Tropsch process and in particular the freezing point of kerosenes, the n / iso weak ratio reflecting the isomerization of undesired n-paraffins. Table 4: Distribution and ratio of n-paraffins / isoparaffins by cross-section of the heteroisomerized effluent using the anhydride GC.

Example 2 Treatment of a Fischer-Tropsch Filler According to a Chain of Catalysts not in Accordance with the Invention

In this scheme, the hydrocracking step is not preceded by a hydroisomerization step. The hydrotreated effluent of Example 1 (Table 2) is hydrocracked on the catalyst C2. The catalyst C2 is reduced according to the same protocol as in Example 1.

The hydrotreated effluent is sent to the hydrocracking catalyst C2 under the following operating conditions:

WH (load volume / volume of catalyst / hour) = 2 h ^"1 total working pressure: 50 bar - hydrogen / feed ratio: 800 normal liters / liter temperature: 347 ° C

The temperature of the reactor is adjusted so as to obtain a conversion of the 370 ⁰ C ⁺ fraction of 70% by weight. The gas chromatographic analyzes make it possible to obtain the distribution of the various cuts in the hydrocracked effluent (Table 5).

It may be noted that with respect to Example 1 according to the invention, the yield of unwanted light fractions is increased to the detriment of the yield of middle distillates, while the isomerization rate of the middle distal fractions is decreased. the temperature necessary to obtain a conversion level of the fraction 370 ⁰ C ⁺ identical to Example 1 is 7 ° C higher (347 ° C against 340 ⁰ C). Table 5: Distribution and ratio n-paraffins / isoparaffins by sections of the hydrocracking effluent GC.

Example 3 Treatment of a Fischer-Tropsch Filler According to a Chain of Catalysts not in Accordance with the Invention

In this scheme, the hydrocracking step precedes the hydroisomerization step. The hydrotreated effluent of Example 1 (Table 2) is then hydrocracked on the catalyst C2 and then hydroisomerized on the catalyst C1. The two catalysts are placed in two reactors in series (first hydrocracking reactor and second hydroisomerization reactor). Before testing, the catalysts undergo a reduction step identical to that of Example 1.

- WH (volume of charge / volume of catalyst / hour) = 2 h ^-1

- total working pressure: 50 bar

- hydrogen / charge ratio: 800 normal liters / liter

temperature: 347X The temperature of the reactor is adjusted so as to obtain a conversion of the 37O ⁰ C ⁺ fraction of 70% by weight.

The effluent thus hydrocracked is brought into contact with the selective hydroisomerization catalyst C1 under the operating conditions below: - WH (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 so as to have a conversion of the fraction 370 ⁰ C ⁺ fraction 370 ⁰ C ^" less than 5% by weight during the hydroisomerisation The gas chromatographic analyzes make it possible to obtain the distribution of different cuts in the hydrocracked effluent and then hydroisomerized (Table 6).

Table 6: distribution and isomerization by sections of the hydrocracked effluent then

Compared to Example 1 according to the invention, the yield of unwanted light fractions is increased to the detriment of the yield of middle distillates. In addition, the temperature necessary to obtain a level of conversion of the fraction 37O ⁰ C ⁺ identical to Example 1 is 7 ° C higher (347 ° C against 340 ⁰ C) for the hydrocracking catalyst C2.

Claims

A process for producing middle distillates from a paraffinic feedstock produced by Fischer-Tropsch synthesis, comprising the following steps:

a) separating at least a light fraction of the feedstock so as to obtain a single so-called heavy fraction with an initial boiling point of between 120 and 200 ^° C., b) hydroisomerization of at least a portion of said heavy fraction by 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 said boiling point products onto said selective hydroisomerization catalyst greater than or equal to 370 ⁰ C in products with boiling points below 370 ⁰ C being less than 20%, c) hydrocracking at least part of the hydroisomerized effluent in the presence of a second hydrocracking catalyst comprising at least one group VIII metal

. and / or at least one Group VIB metal and a silica-based alumina or zeolite-Y support, converting to said hydrocracking catalyst products with a boiling point greater than or equal to 370 ° C in point products. boiling below 370 ° C being greater than or equal to 40% by weight, d) distillation of the final effluent to obtain middle distillates.

2. Process according to claim 1, in which all of said heavy fraction resulting from separation step a) undergoes a hydrotreatment step in which it is brought into contact, in the presence of hydrogen, with a hydrotreatment catalyst. , the conversion on this catalyst of the fraction 37O ⁰ C ⁺ fraction 37O ⁰ C ^" being less than 20% by weight.

3. The process as claimed in claim 2, in which all of the effluent from the hydrotreatment stage undergoes a separation step in which the decomposition products such as water and / or carbon monoxide and / or Carbon dioxide and / or hydrogen sulfide and / or ammonia formed during the hydrotreating step are removed at least in part.

4. Method according to one of claims 1 or 2 wherein the entire effluent from the hydrotreating step is sent in said step b) hydroisomerisation, without prior separation step.

5. Method according to one of claims 1 to 4 wherein the conversion on said first hydroisomerisation catalyst of products with boiling points greater than or equal to 37O ⁰ C in products with boiling points below 37O ⁰ C is less than 10% and preferably less than 5% by weight.

6. Method according to one of claims 1 to 5 wherein said first hydroisomerisation catalyst comprises either at least one noble metal of the group VlII selected from platinum or palladium, or at least one metal group Vl selected from molybdenum or tungsten, in combination with at least one non-noble group VIII metal selected from nickel and cobalt.

The process of claim 6 wherein the noble metal content of said first hydroisomerization catalyst is from 0.01 to 5% by weight based on the finished catalyst.

8. A process according to claim 6 wherein the metal content of the group VI of said first hydroisomerization catalyst is between 5 and 40% by weight relative to the finished catalyst, and the metal content of the group VIIl is between 0, 5 and 10% by weight relative to the finished catalyst.

9. Process according to one of claims 1 to 7 wherein said first hydroisomerization catalyst contains at least one one-dimensional 10 MR zeolite molecular sieve.

The process according to claim 9 wherein said one-dimensional 10MR zeolite molecular sieve of said first hydroisomerization catalyst is selected from zeolite molecular sieves of structural 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.

11. 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 method of claim 11 wherein said 10MR zeolite molecular sieve is ZBM-30 synthesized with the organic template triethylenetetramine.

13. Method according to one of claims 9 to 12 wherein the content of 10MR monodimensional zeolite molecular sieve is between 5 and 95% by weight.

The process of any one of claims 1 to 13 wherein said first hydroisomerization catalyst also contains a binder consisting of a porous mineral matrix.

15. Method according to one of claims 1 to 14 wherein the hydroisomerization step b) operates at a pressure of between 2 and 150 bar, at an hourly space velocity 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 between 100 and 55O ⁰ C.

16. Method according to one of claims 1 to 15 wherein all of the hydroisomerized effluent from the hydroisomerization step b) undergoes a separation step in which at least a portion of normal paraffins non-hydroisomerized during hydroisomerization step b) is separated from the effluent from said step b) and is recycled in said hydroisomerization step b).

17. Method according to one of claims 1 to 16 wherein said second 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. noble group VIII selected from nickel and cobalt in combination with at least one metal of group Vl selected from molybdenum and tungsten, alone or in mixture.

18. The method of claim 17 wherein the noble metal content of said second hydrocracking catalyst is between 0.01 and 5% by weight relative to the finished catalyst.

19. The method of claim 17 wherein the metal content of the group VI of said second hydrocracking catalyst is between 5 and 40% by weight relative to the finished catalyst, and the metal content of the group VIII is between 0, 5 and 10% by weight relative to the finished catalyst.

20. Method according to one of claims 1 to 19 wherein said second hydrocracking catalyst comprises at least one noble metal, said noble metal being platinum and a silica alumina support, without any binder.

21. Method according to one of claims 1 to 20 wherein said second 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 (SiO ₂ ) of between 1 and 95%, expressed by weight percentage, said catalyst having:

A BET specific surface area of 100 to 500 m ² / g,

An average diameter of the mesopores of between 3 and 12 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 at 40% of the total pore volume,

A total pore volume of between 0.4 and 1.2 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,

22. Method according to one of claims 1 to 20 wherein said second 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, from 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 BET specific surface area of between 100 and 550 m ² / g, a pore volume, measured by mercury porosimetry, included in pores with a diameter greater than 14 nm of less than 0.1 ml / g, a porous volume, measured by mercury porosimetry, included in pores with a diameter greater than 16 nm of less than 0.1 ml / g,

23. Method according to one of claims 1 to 20 wherein said second 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 by weight percentage, said catalyst having:

• a BET specific surface area of 200 to 600 m ² / g

An average diameter of the mesopores of between 3 and 12 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 is greater than 60% of the total pore volume,

A total pore volume of less than 1 ml / g,

• an alkali or alkaline earth metal content of less than 300 ppm by weight.

24. A method according to one of claims 1 to 23 wherein step c) hydrocracking is carried out at a pressure between 2 and 150 bar, at an hourly volume velocity of between 0.1 ^{h -1} and 10 h ^{" 1} 'at 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.

25. Method according to one of claims 1 to 24 wherein all of the hydrocracked effluent from the hydrocracking step c) undergoes an additional hydroisomerization step, wherein the hydrocracked effluent is contacted with an additional hydroisomerization catalyst, the conversion on said catalyst of products with boiling points greater than or equal to 370 ^° C. to products with a boiling point below 370 ° C. of less than 20% by weight.

26. A process according to any one of claims 1 to 25 wherein the first hydroisomerization catalyst used in step b) and the hydroisomerization catalyst add to are the same.

27. Method according to one of claims 1 to 26 wherein the residual fraction is recycled to the hydrocracking zone.