WO2023241930A1

WO2023241930A1 - Hydrocracking process with optimized management of the recycling for the production of naphtha

Info

Publication number: WO2023241930A1
Application number: PCT/EP2023/064675
Authority: WO
Inventors: Laurent Simon; Rafaela Da Silva De Oliveira
Original assignee: IFP Energies Nouvelles
Priority date: 2022-06-14
Filing date: 2023-06-01
Publication date: 2023-12-21
Also published as: FR3136477A1

Abstract

The present invention relates to a process for hydrocracking hydrocarbon feedstocks, comprising at least the steps of a) hydrotreatment of said feedstocks; b) a first step of hydrocracking of at least a portion of the effluent leaving step a); c) the gas/liquid separation of the effluent resulting from step b) to produce a liquid effluent and a gaseous effluent; d) the separation of the liquid effluent resulting from step c) into at least one "converted" effluent comprising hydrocarbon compounds having boiling points of less than a temperature T1 of between 340°C and 385°C and an unconverted liquid fraction comprising hydrocarbon compounds having a boiling point of greater than the temperature T1; e) the fractionation of the "converted" liquid effluent resulting from step d) and comprising hydrocarbon compounds having boiling points of less than the temperature T1, to obtain at least one first fraction comprising hydrocarbon compounds having a boiling point of less than a temperature T2 of between 150°C and 220°C and at least one second fraction comprising hydrocarbon compounds having a boiling point of greater than the temperature T2 but less than the temperature T1; f) a second step of hydrocracking of at least a portion of the second liquid fraction resulting from step e) and comprising hydrocarbon compounds having a boiling point of greater than the temperature T2, but less than the temperature T1.

Description

Hydrocracking process with optimized recycling management for naphtha production

Technical field of the invention

The present invention relates to the two-stage hydrocracking (HCK) of heavy hydrocarbon fractions. Hydrocracking aims to crack heavy hydrocarbon fractions into lighter fractions using specific catalysts and in the presence of hydrogen, the objective being to obtain bases for petrochemicals with high added value on the market.

In this field, the invention finds its application more particularly in processes for hydrotreating a cut of the vacuum distillate (DSV) or vacuum diesel (Vaccum Gasoil (VGO) according to Anglo-Saxon terminology) type with a view to maximizing the production of a base for petrochemicals (heavy naphtha, rich in naphthenes and aromatics) and with a view to improving the selectivity of the process.

Prior art

The hydrocracking of heavy oil cuts is a key refining process which makes it possible to produce, from excess heavy feedstocks with little recovery, lighter fractions such as gasoline, kerosene and light gas oils that the refiner is looking for in order to adapt its production. production on demand. Certain hydrocracking processes also make it possible to obtain a highly purified residue which can constitute excellent bases for petrochemicals or a feed which can be easily recovered in a catalytic cracking unit for example. One of the effluents particularly targeted by the hydrocracking process is the middle distillate (fraction which contains the gas oil cut and the kerosene cut), but the gasoline produced can also be used in particular to supply petrochemical intermediate production routes if a catalytic reforming and/or steam cracking installation is integrated into the complex.

The DSV hydrocracking process makes it possible to produce light cuts (diesel, kerosene, naphtha, etc.) that are more valuable than the DSV itself. This catalytic process, however, does not allow the DSV to be completely transformed into light cuts. After fractionation, there remains a more or less significant proportion of the unconverted DSV fraction called “Unconverted Oil” or UCO according to Anglo-Saxon terminology. To increase the conversion, this unconverted fraction can be recycled at the inlet of the hydrotreatment reactor or at the inlet of the hydrocracking reactor (so-called “one-step” hydrocracking process with recycling). Recycling the unconverted fraction at the inlet of the hydrotreatment reactor or at the inlet of the hydrocracking reactor allows both to increase the conversion, but also makes it possible to increase the selectivity for gas oil and kerosene. Another way to increase conversion while maintaining selectivity is to add a conversion or hydrocracking reactor on the loop for recycling the unconverted fraction to the high pressure separation section. This reactor and the associated recycling constitute a second hydrocracking stage (so-called “two-stage” hydrocracking process).

Indeed, two-step hydrocracking comprises a first step which aims, as in the “one-step” process, to carry out the hydrorefining of the feed but also to achieve a conversion of the latter of the order of generally from 30 to 70% by weight. The effluent from the first stage then undergoes fractionation (generally distillation), the aim of which is to separate the converted products from the unconverted fraction. In the second stage of a two-stage hydrocracking process, only the fraction of the feed not converted during the first stage is treated. This separation allows a two-step hydrocracking process to be more selective in converted products (diesel, kerosene, naphtha) than a one-step process with an equivalent overall conversion rate. Indeed, the intermediate separation of the converted products avoids their “over-cracking” into gas in the second stage on the hydrocracking catalyst.

Several variants of “two-step” hydrocracking processes exist and are, most often, dedicated to increasing the yield of middle distillate cuts.

US2018362864 discloses a two-step hydrocracking process for hydrocarbon DSV feeds allowing the improved production of middle distillates comprising the following steps: a) a first step for hydrocracking feeds in the presence of hydrogen and at least one catalyst hydrocracking, b) gas/liquid separation of the effluent from step a) for the production of a liquid effluent and a gaseous effluent comprising hydrogen, c) sending the gaseous effluent comprising hydrogen in a compression step before its recycling to the first hydrocracking step a), d) fractionation of the liquid effluent into at least a first fraction comprising converted hydrocarbon compounds having boiling points lower than 340 °C and a second unconverted fraction comprising hydrocarbon compounds having a boiling point greater than 340°C, e) a second hydrocracking step of the second unconverted fraction comprising hydrocarbon compounds having a boiling point greater than 340°C from d), in the presence of hydrogen and a hydrocracking catalyst, f) hydrotreatment of the effluent from e) as a mixture with a liquid feed of hydrocarbon gas oil having at least 95% by weight of compounds boiling at a boiling point of between 150 and 400°C, operating under hydrogen and with at least one hydrotreatment catalyst.

FR3083243 discloses an integrated process for the production of middle distillates including two-step DSV hydrocracking and gas oil hydrotreatment in which the circulation of hydrogen is reversed. The integration of the two units coupled with reverse hydrogen circulation allows a reduction in the number of equipment and costs.

FR3091534 discloses a two-stage hydrocracking process for the production of naphtha, comprising a hydrogenation stage placed downstream of the second hydrocracking stage, the hydrogenation stage treating the effluent from the second hydrocracking stage hydrocracking in the presence of a specific hydrogenation catalyst. In addition, the hydrogenation steps and the second hydrocracking step are carried out under specific operating conditions and in particular under very specific temperature conditions.

FR3076297 discloses a two-step hydrocracking process for DSV type hydrocarbon feeds mixed with a gas oil type feed allowing the improved production of naphtha comprising: a) Hydrotreatment of the DSV feed operating in the presence of hydrogen and minus one hydrotreatment catalyst; b) the hydrocracking of the effluent from step a) operating, in the presence of hydrogen and at least one hydrocracking catalyst, c) the gas/liquid separation of the effluent from the step b) to produce a liquid effluent and a gaseous effluent comprising at least hydrogen; d) sending the gaseous effluent comprising at least hydrogen to a compression stage before recycling it to the a) hydrotreatment and b) hydrocracking stages; e) fractionating the liquid effluent into at least a first fraction comprising converted hydrocarbon compounds having boiling points lower than 180°C and a second unconverted fraction comprising hydrocarbon compounds having a boiling point higher than 180 °C, f) hydrocracking of the second unconverted fraction comprising hydrocarbon compounds having a boiling point greater than 180°C resulting from step e) operating, in the presence of hydrogen and a catalyst. hydrocracking, g) hydrotreatment of the effluent from step f) mixed with a liquid hydrocarbon feedstock of the diesel type comprising at least 60% by weight of boiling compounds at a boiling temperature between 120 and 400°C, said hydrotreatment step g) operating in the presence of hydrogen and at least one hydrotreatment catalyst.

US10472581 discloses a process for hydrocracking and hydroisomerization of a hydrocarbon feedstock. The hydrocracked effluent is deactivated before entering the hydroisomerization zone with recycled feedstocks, the aim of which is to cool the hydrocracked effluent and to subject the recycled feedstocks to a second hydroisomerization step. The recycled feeds come from a fractionation section comprising gas/liquid separators, stripping columns, an atmospheric distillation column and a vacuum distillation column. Effluents from the stripping columns are recycled to the hydroisomerization stage while effluents (heavy feeds) from the atmospheric distillation and vacuum distillation columns are recycled to the hydrocracking stage.

None of the prior art processes make it possible to significantly improve the selective production of naphtha cuts.

Surprisingly, the applicant has demonstrated that the addition of a step of separation of hydrocarbon compounds having a boiling temperature higher than a temperature Ti of between 340 and 385°C upstream of the fractionation step d A classic two-step hydrocracking process makes it possible to maximize the selectivity and yields of naphtha, and more particularly of heavy naphtha. In an advantageous embodiment, the effluent obtained comprising the hydrocarbon compounds having a boiling point higher than the temperature T 1 can be recycled to the first hydrocracking and/or hydrotreatment stage, thus allowing optimized recycling management. unconverted heavy fractions from two-stage hydrocracking units and thus maximize the production of heavy naphtha.

Detailed description of the invention

The present invention relates to a process for hydrocracking hydrocarbon feedstocks comprising at least 20% by volume of compounds boiling above 300°C, said process comprising at least the following steps: a) The hydrotreatment of said feedstocks carried out, in the presence of hydrogen and at least one hydrotreatment catalyst, at a temperature between 250 and 480°C, under a pressure between 2 and 25 MPa, at a space speed between 0.1 and 6.0 h ^{- 1} and a quantity of hydrogen introduced such that the volume ratio liter of hydrogen/liter of hydrocarbon is between 100 and 2000 L/L; b) A first step of hydrocracking at least part of the effluent leaving step a) and carried out, in the presence of hydrogen and at least one first hydrocracking catalyst, at a temperature between 250 and 480°C, under a pressure of between 2 and 25 MPa, at a space velocity of between 0.1 and 6.0 h ^-1 and at a quantity of hydrogen introduced such as the volume ratio liter of hydrogen/ liter of hydrocarbon is between 100 and 2000 L/L; c) The gas/liquid separation of the effluent from step b) to produce a liquid effluent and a gaseous effluent comprising at least hydrogen; d) Separating the liquid effluent from step c) into at least one so-called converted effluent comprising hydrocarbon compounds having boiling points lower than a temperature Ti of between 340 and 385°C and a liquid fraction not converted comprising hydrocarbon compounds having a boiling point above temperature Ti; e) Fractionation of the so-called converted liquid effluent from step d) comprising hydrocarbon compounds having boiling points lower than the temperature Ti, to obtain at least a first fraction comprising hydrocarbon compounds having a boiling point boiling lower than a temperature T ₂ between 150 and 220°C and at least a second fraction comprising hydrocarbon compounds having a boiling point higher than the temperature T ₂ , but lower than the temperature Ti; f) A second step of hydrocracking at least part of the second liquid fraction resulting from step e) comprising hydrocarbon compounds having a boiling point higher than the temperature T ₂ , but lower than the temperature Ti, operated in the presence of hydrogen and a second hydrocracking catalyst, at a temperature between 250 and 480°C, under a pressure between 2 and 25 MPa, at a space speed between 0.1 and 6.0 h ^-1 and a quantity of hydrogen introduced such that the volume ratio liter of hydrogen/liter of hydrocarbon is between 100 and 2000 L/L.

An advantage of the present invention is then to provide a process limiting the cracking of the middle distillate fraction produced in the hydrotreatment and hydrocracking stages. first step by treating it alone during the second hydrocracking step thanks to the implementation upstream of the fractionation step, of a step of separation of an unconverted liquid fraction comprising heavy hydrocarbon compounds having a boiling temperature higher than Ti between 340 and 385°C, which thus makes it possible to maximize the selectivity and yields of naphtha.

Another advantage of the present invention is to provide, in a preferred embodiment, a process for reducing the formation of heavy polyaromatic products (HPNA) during the second hydrocracking stage, these being selectively recycled to the reactor hydrotreatment and/or the first hydrocracking step thanks to this step of separating an unconverted liquid fraction comprising heavy hydrocarbon compounds having a boiling temperature above T 1 between 340 and 385°C. Thus, the management of HPNA is optimized because the second stage hydrocracking reactor will not undergo the increase in HPNA which will be transferred to the section comprising the hydrotreatment and/or first stage hydrocracking reactors.

Another advantage of the present invention is to provide a process allowing the optimized management of recycling which makes it possible to limit the formation of C1 to C4 compounds ((molecules with a short carbon chain comprising a carbon number between 1 and 4) thanks to a gas/liquid separation and to maximize compounds having boiling points between 50 and 220°C thanks to a separation of an unconverted liquid fraction comprising hydrocarbon compounds whose boiling point is greater than Ti temperature between 340 and 385°C and thus improve the selectivity of the process towards the production of naphtha.

Throughout the remainder of the text, the term “naphtha” means: a so-called light cut with an initial boiling point of between 50 and 100°C and a final boiling point of between 150 and 220°C.

“Middle distillates” means: a cut comprising hydrocarbon compounds having a boiling point generally between 150 and 370°C.

The term unconverted fraction or Unconverted Oil is understood to mean “UCO” according to Anglo-Saxon terminology, the cut comprising compounds not converted during a hydrocracking step. The charges

According to the invention, the hydrocarbon fillers treated in the process according to the invention and sent in step a) are chosen from hydrocarbon fillers comprising at least 20% by weight, preferably at least 50% by weight and preferably at least 80% by weight of compounds boiling above 300°C and preferably between 340 and 580°C (that is to say corresponding to compounds containing at least 17 carbon atoms).

The incoming charge in step a) is also called fresh charge.

In one embodiment, the hydrocarbon feeds treated in the process according to the invention and sent in step a) are chosen from hydrocarbon feeds comprising at least 80% by weight of compounds boiling between 340 and 580 ° C (this is i.e. typically a DSV charge).

Said hydrocarbon feeds used according to the invention can advantageously be chosen from VGO or DSV but also for example gas oils resulting from direct distillation of crude or from conversion units such as FCC, coker or visbreaking as well as feeds from aromatic extraction units, lubricating oil bases or from solvent dewaxing of lubricating oil bases, or distillates from desulfurization or hydroconversion of RAT (atmospheric residues) and/or of RSV (vacuum residue), or the load can advantageously be a deasphalted oil, loads from biomass, loads from vegetable oils, loads from fresh or used animal fats, or products from reprocessing of plastics. All the fillers mentioned above can be used pure or in a mixture, the list above being not exhaustive.

Said hydrocarbon fillers may contain heteroatoms such as nitrogen and sulfur. The nitrogen content of the fillers used according to the invention is traditionally less than 8000 ppm by weight, and generally between 200 and 5000 ppm by weight, and more generally between 500 and 3000 ppm by weight. The sulfur content of the fillers used according to the invention is traditionally less than 6% by weight, generally between 0.2 and 5% and more generally between 0.5 and 4% by weight.

Said hydrocarbon fillers treated in the process according to the invention and sent in step a) may optionally contain metals. The cumulative nickel and vanadium content of the charges treated in the processes according to the invention is preferably less than 1 ppm by weight. Said hydrocarbon feedstocks treated in the process according to the invention and sent in step a) may optionally contain asphaltenes whose content is generally less than 3000 ppm by weight, preferably less than 1000 ppm by weight, even more preferably less at 200 ppm weight.

In the case where the feed contains resin and/or asphaltene type compounds, it is advantageous to first pass the feed through a bed of catalyst or adsorbent different from the hydrocracking or hydrotreatment catalyst.

Operating conditions and catalysts

Hydrotreatment step a)

The process according to the present invention comprises a step a) of hydrotreating said charges operating, in the presence of hydrogen and at least one hydrotreatment catalyst, at a temperature of between 250 and 480°C, under a pressure of between 2 and 25 MPa, at a space velocity between 0.1 and 6.0 h ^-1 and using a quantity of hydrogen introduced such that the volume ratio liter of hydrogen/liter of hydrocarbon is between 100 and 2000 L/L.

In a preferred embodiment, hydrotreatment step a) is carried out between 300 and 450°C, under a pressure of between 5 and 20 MPa, at a space speed of 0.5 and 4.0 h ^-1 , and using a quantity of hydrogen introduced such that the volume ratio liter of hydrogen/liter of hydrocarbon is between 400 and 1800 L/L.

In a very preferred embodiment, hydrotreatment step a) is carried out between 350 and 430°C, under a pressure of between 10 and 18 MPa, at a space speed of between 0.8 and 3.0 h ^{- 1} , and using a quantity of hydrogen introduced such that the volume ratio liter of hydrogen/liter of hydrocarbon is between 600 and 1600 L/L.

The operating conditions used in step a) of the process according to the invention generally make it possible to carry out hydrotreatment of the feed so as to achieve an organic nitrogen content in the effluent generally less than 100 ppm by weight, preferably less than 50 ppm by weight, preferably less than 20 ppm by weight, and very preferably less than 10 ppm by weight.

The operating conditions used in step a) of the process according to the invention generally make it possible to carry out hydrotreatment of the feed so as to achieve a sulfur content in the effluent generally less than 300 ppm by weight, preferably less than 200 ppm by weight, preferably less than 50 ppm by weight, and very preferably less than 20 ppm by weight.

According to the invention, hydrotreatment step a) is carried out in the presence of at least one hydrotreatment catalyst, that is to say it is possible to use sequences of 2 or more catalysts. hydrotreatment. The hydrotreatment catalyst is chosen from conventional hydrotreatment catalysts known to those skilled in the art.

Preferably, the catalyst comprises a hydrogenating function composed of at least one metal from group VIB and at least one metal from group VIII of the periodic table, taken alone or as a mixture, said catalyst being a catalyst having a sulfide phase as active phase .

The metal(s) of group VIB are chosen from chromium, molybdenum and tungsten, alone or as a mixture and preferably chosen from molybdenum and tungsten. Preferably, the metal content of group VIB in the hydrotreatment catalyst(s) is advantageously between 5 and 40% by weight and preferably between 15 and 30% by weight, very preferably between 18 and 28% by weight, the percentages being expressed as a weight percentage of oxides.

The group VIII metal(s) are chosen from iron, cobalt, nickel, ruthenium, rhodium, palladium and platinum, and preferably from cobalt or nickel. Preferably, the content of Group VIII metal in the hydrotreatment catalyst(s) is advantageously between 0.5 and 15% by weight and preferably between 2 and 10% by weight, the percentages being expressed as a percentage by weight of oxides.

The hydrotreatment catalyst(s) may also optionally comprise at least one promoter element deposited on said catalyst chosen from the group formed by phosphorus, boron and silicon, optionally at least one element from group VI IA (preferred chlorine and fluorine) , optionally at least one element from group VI I B (preferred manganese), and optionally at least one element from group VB (preferred niobium).

Preferably, the hydrotreatment catalyst(s) are supported on a support chosen from alumina, silica-alumina, and preferably on alumina.

A preferred catalyst comprises at least one Group VIB metal and/or at least one non-noble Group VIII metal, and an alumina type support. An even more preferred catalyst is nickel, molybdenum and alumina. Another preferred catalyst consists of nickel, tungsten and alumina or silica alumina. Step b) first hydrocracking stage

The process according to the present invention comprises a step b) first hydrocracking step using as feed at least part and preferably all of the effluent leaving step a) and operated, in the presence of hydrogen and at least a first hydrocracking catalyst, at a temperature between 250 and 480°C, under a pressure between 2 and 25 MPa, at a space speed between 0.1 and 6.0 h ^-1 and using a quantity of hydrogen introduced such that the volume ratio liter of hydrogen/liter of hydrocarbon is between 100 and 2000 L/L.

In a preferred embodiment, step b) is carried out at a temperature between 300 and 450°C, under a pressure between 5 and 20 MPa, at a space speed between 0.5 and 4.0 h ^-1 , and using a quantity of hydrogen introduced such that the volume ratio liter of hydrogen/liter of hydrocarbon is between 400 and 1800 L/L.

In a very preferred embodiment, step b) is carried out at a temperature between 350 and 430°C, under a pressure between 10 and 18 MPa, at a space speed between 0.8 and 3.0 h ^-1 , and using a quantity of hydrogen introduced such that the volume ratio liter of hydrogen/liter of hydrocarbon is between 600 and 1600 L/L.

The operating conditions used in step b) of the process according to the invention generally make it possible to achieve conversions per pass, into products having boiling points lower than 340°C, and better still lower than 370°C, and alternatively, below 385°C greater than 15% by weight and even more preferably between 20 and 95% by weight, very preferably between 30 and 80%. The conversion per pass is here calculated in relation to the charge entering step a).

During hydrocracking step b) of the process of the invention, the conversion passes into products having boiling points lower than 220°C, preferably lower than 180°C, and alternatively, lower than 150°C, is greater than 10% by weight, even more preferably between 15 and 75% by weight, very preferably between 25 and 60%. The conversion per pass is here calculated in relation to the charge entering step a).

In accordance with the invention, hydrocracking step b) operates in the presence of at least one first hydrocracking catalyst, that is to say it is also possible to use sequences of 2 or more hydrocracking catalysts. Preferably, the first hydrocracking catalyst is chosen from the conventional hydrocracking catalysts known to those skilled in the art. The first hydrocracking catalysts used in hydrocracking processes are all of the bifunctional type combining an acid function with a hydrogenating function. The acid function is provided by supports with large surface areas (150 to 800 m ² .g ^-1 generally) presenting superficial acidity, such as halogenated aluminas (notably chlorinated or fluorinated), combinations of boron oxides and aluminum, amorphous silica-aluminas and/or zeolites. The hydrogenating function is provided either by one or more metals from group VIII of the periodic table of elements, or by a combination of at least one metal from group VIB of the periodic table and at least one metal from group VIII.

Preferably, the first hydrocracking catalyst comprises a hydrogenating function composed of at least one metal from group VIB and at least one metal from group VIII of the periodic table, taken alone or as a mixture, said catalyst being a sulphide phase catalyst.

The metal(s) of group VIB are chosen from chromium, molybdenum and tungsten, alone or as a mixture and preferably chosen from molybdenum and tungsten. Preferably, the content of group VIB metal in the hydrocracking catalyst(s) is advantageously between 5 and 35% by weight and preferably between 10 and 30% by weight, very preferably between 15 and 22% by weight. , the percentages being expressed as percentage by weight of oxides.

The group VIII metal(s) are chosen from iron, cobalt, nickel, ruthenium, rhodium, palladium and platinum, and preferably from cobalt or nickel. Preferably, the content of Group VIII metal in the hydrocracking catalyst(s) is advantageously between 0.5 and 15.0% by weight and preferably between 2.0 and 10.0% by weight, very preferably. between 2.5 and 6.0% by weight, the percentages being expressed as percentage by weight of oxides.

The first catalyst(s) may also optionally have at least one promoter element deposited on the catalyst chosen from the group formed by phosphorus, boron and silicon, optionally at least one element from group VIIA (preferred chlorine, fluorine), optionally at least an element from group VI I B (preferred manganese), and optionally at least one element from group VB (preferred niobium).

Preferably, the first hydrocracking catalyst(s) comprise an acid function chosen from alumina, silica-alumina and zeolites, preferably chosen from zeolites Y and preferably chosen from silica-alumina and zeolites. In a preferred embodiment, step b) is fixed bed hydrocracking.

Step c) gas/liquid separation

The process according to the present invention comprises a step c) of gas/liquid separation of the effluent from step b) to produce a liquid effluent and a gaseous effluent comprising at least hydrogen.

The gas/liquid separation step can be carried out in any gas/liquid separator known to those skilled in the art such as: a horizontal or vertical separator flask, etc., this list is not exhaustive.

Preferably, step c) of gas/liquid separation is carried out in a high temperature and high pressure separator operating at a temperature between 50 and 450°C, preferably between 100 and 400°C, even more preferably between 200°C. and 300°C, and a pressure corresponding to the outlet pressure of step b) reduced by pressure losses.

In one embodiment, the gaseous effluent comprising at least hydrogen from step c) is sent to a compression step before its recycling in at least step a) of hydrotreatment and/or b) first stage hydrocracking.

This compression step is necessary to allow the recycling of the gas upstream, that is to say in step a) hydrotreatment and/or b) hydrocracking first step, therefore at higher pressure.

Recycling of the gas can also be carried out towards the second stage hydrocracking step f).

The gaseous effluent comprising at least hydrogen can advantageously be mixed with make-up hydrogen before or after its introduction into the compression stage, preferably via a make-up or "make" hydrogen compressor. up” according to Anglo-Saxon terminology.

Step d) separation of the liquid effluent

The process according to the present invention comprises a step d) of separating the liquid effluent from step c) into at least one so-called converted effluent comprising hydrocarbon compounds having boiling points lower than a temperature Ti of between 340 and 385°C and an unconverted liquid effluent comprising hydrocarbon compounds having a boiling point above the temperature Ti. In one embodiment, the unconverted liquid effluent from step d) comprising hydrocarbon compounds having a boiling point higher than the temperature Ti is recycled to the hydrotreatment step a) and/or the step b) first hydrocracking stage. In this embodiment, the unconverted liquid effluent is potentially hydrotreated again and is recracked with the fresh feed introduced into said process.

In one embodiment, the recycling rate to the hydrotreatment reactor and/or to the first stage hydrocracking reactor, either in stage a) and/or b), is between 0.1 and 1.5 m /m calculated in relation to the fresh load, preferably between 0.15 and 1.2 and even more preferably between 0.2 and 0.8.

In one embodiment, the unconverted liquid effluent from step d) comprising hydrocarbon compounds having a boiling point higher than the temperature Ti undergoes a step of purging the heavy polyaromatic products (Heavy Polynuclear Aromatics or HPNA in English terminology) before its recycling to step a) hydrotreatment and/or step b) first hydrocracking step. Preferably this purge represents 0.5% by weight of the fresh starting charge. Indeed, HPNAs are gradually formed during the recycling of heavy aromatic components and results in an increase in their molecular weight. The presence of HPNA in said recycling loop ultimately results in a significant pressure loss. A purge or “bleed” according to Anglo-Saxon terminology makes it possible to limit the accumulation of these HPNA products.

Separation step d) can be carried out in any suitable separator known to those skilled in the art such as: a separator flask, a washing tower, a cyclone, a conical separator flask, etc., this list n 'being not exhaustive.

In one embodiment, separation step d) is carried out in a high pressure separator. This separator operates at the same pressure and temperature as the effluent from step c).

This step d) preferably makes it possible to carry out a purge corresponding to less than 5%, preferably less than 3%, very preferably less than 1% of the total hydrocarbon load entering step a).

In accordance with the invention, the so-called converted effluent comprising hydrocarbon compounds having boiling points lower than the temperature Ti is sent to the fractionation step e). The separation of hydrocarbon compounds having a boiling temperature higher than a temperature Ti between 340 and 385°C, makes it possible to maximize selectivity and yields of naphtha, and more particularly heavy naphtha during fractionation.

Step e) fractionation

The process according to the present invention comprises a step e) of fractionating the so-called converted liquid effluent from step d) comprising hydrocarbon compounds having boiling points lower than the temperature Ti, to obtain at least a first fraction consisting of hydrocarbon compounds having a boiling point lower than a temperature T ₂ between 150 and 220°C and at least a second fraction comprising hydrocarbon compounds having a boiling point higher than the temperature T ₂ , but lower than the temperature Ti.

Fractionation step e) can be carried out in any fractionation tool known to those skilled in the art such as: a plate column, a packed column, etc., this list is not exhaustive.

In one embodiment, fractionation step e) comprises a first step of separating the hydrogen sulphide (H ₂ S) comprising a separation means such as for example a separator flask or a steam stripper operating preferably at a pressure between 0.5 and 2.0 MPa. The hydrocarbon effluent resulting from this first separation must then undergo atmospheric distillation, and in certain cases the combination of atmospheric distillation and vacuum distillation. The aim of the distillation is to achieve a separation between so-called converted hydrocarbon products, that is to say generally having boiling points lower than the temperature T ₂ , preferably lower than 160°C and preferably lower than 180°C. C, and a so-called unconverted liquid fraction comprising compounds having a boiling point higher than the temperature T ₂ but lower than the temperature Ti.

In one embodiment, the products of the converted fraction resulting from atmospheric distillation are a light gas fraction whose molecules contain from 1 to 4 carbon atoms, at least one fraction a naphtha fraction with a boiling point below 180° C and at least one diesel fraction.

According to the invention, the third fraction comprising hydrocarbon compounds whose boiling point is higher than the temperature T ₂ , but lower than the temperature Ti, is at least partly and preferably entirely introduced into the second step d hydrocracking f) of the process according to the invention. Step f) second hydrocracking stage

The process according to the present invention comprises a step f) second step of hydrocracking at least part and preferably all of the second liquid fraction resulting from step e) comprising hydrocarbon compounds having a higher boiling point at the temperature T ₂ , but lower than the temperature Ti, carried out, in the presence of hydrogen and a hydrocracking catalyst, at a temperature between 250 and 480°C, under a pressure between 2 and 25 MPa, at a space speed of between 0.1 and 6.0 h ^-1 and with a quantity of hydrogen introduced such that the volume ratio liter of hydrogen/liter of hydrocarbon is between 100 and 2000 L/L.

The second hydrocracking stage is carried out in a different section from the first hydrocracking stage.

In a preferred embodiment, step f) is carried out at a temperature between 300 and 450°C, under a pressure between 5 and 20 MPa, at a space speed between 0.5 and 4.0 h ^{- 1} , and a quantity of hydrogen introduced such that the volume ratio liter of hydrogen/liter of hydrocarbon is between 400 and 1800 L/L.

In a very preferred embodiment, step f) is carried out at a temperature of between 350 and 430°C, under a pressure of between 10 and 18 MPa, at a space speed of between 0.8 and 3.0 h ^{- 1} , and a quantity of hydrogen introduced such that the volume ratio liter of hydrogen/liter of hydrocarbon is between 600 and 1600 L/L.

In one embodiment, at least part and preferably all of the effluent from the second hydrocracking step f) is recycled to the gas/liquid separation step c).

The operating conditions used in step f) of the process according to the invention generally make it possible to achieve conversions per pass into products having boiling points lower than 220°C, and better still lower than 180°C, and to alternatively, below 150°C, greater than 10% by weight and even more preferably between 15 and 75% by weight, very preferably between 25 and 60%. The conversion per pass is here calculated in relation to the charge entering step f).

In one embodiment, at least part, preferably all of the effluent from step f) second hydrocracking stage is sent to a second gas/liquid separation stage to produce a liquid effluent and a gaseous effluent comprising at least hydrogen. In one embodiment, the gaseous effluent comprising at least hydrogen from the second separation step is sent to a compression step.

In one embodiment, the process according to the invention comprises a step of hydrotreating at least part and preferably all of the effluent from step f) mixed with a hydrocarbon liquid feed comprising at least least 95% by weight of compounds boiling at a boiling temperature of between 150 and 400°C, preferably between 150 and 380°C and preferably between 200 and 380°C.

In this embodiment, at least part and preferably all of the effluent from step f) is therefore co-treated in a hydrotreatment step mixed with a hydrocarbon liquid feed distinct from said effluent from the second hydrocracking stage f).

Said hydrocarbon liquid feed may advantageously be a feed coming from a unit external to said process according to the invention or an internal flow to said process according to the invention, said internal flow being different from said effluent from the second hydrocracking step f). Preferably, said hydrocarbon liquid feedstock is a feedstock coming from a unit external to said process according to the invention.

Preferably, said hydrocarbon liquid feed is advantageously chosen from hydrocarbon liquid feeds resulting from the direct distillation of a crude oil (or straight run according to Anglo-Saxon terminology) and preferably chosen from straight run gas oil, Light Vacuum Gasoil Oil (LVGO) according to Anglo-Saxon terminology, light vacuum distillates, hydrocarbon liquid feedstocks from a coking unit (coking according to Anglo-Saxon terminology), preferably coker gas oil, from a visbreaking unit (visbreaking according to Anglo-Saxon terminology), a steam cracking unit (steam cracking according to Anglo-Saxon terminology) and/or a catalytic cracking unit (Fluid Catalytic Cracking according to Anglo-Saxon terminology), preferably light gas oils from a catalytic cracking unit (LCO (light cycle oil) according to Anglo-Saxon terminology), and a gas oil charge resulting either from the conversion of biomass (esterification for example), or from the conversion of oil either from the conversion of fresh or used animal fat, or from plastic pyrolysates, the said fillers being able to be taken alone or in a mixture.

Said hydrocarbon liquid feed can also advantageously be a hydrocarbon liquid feed from a bubbling bed conversion unit of the “H-Oil” type.

The proportion of said distinct hydrocarbon liquid feed co-treated with the effluent from step f) represents between 20% and 80% by weight of the total mass of the total liquid mixture at the entrance to the hydrotreatment step, preferably between 30% and 70% by weight and even more preferably between 40% and 60% by weight.

The treatment of the effluent from step f) mixed with said liquid hydrocarbon feed in the hydrotreatment step, downstream of the hydrocracking step f), also makes it possible to desulphurize said liquid hydrocarbon feed, to minimize the formation of heavy polyaromatic products (HPNA).

In accordance with the invention, step f) second hydrocracking stage operates in the presence of at least one second hydrocracking catalyst, that is to say it is also possible to use sequences of 2 or several hydrocracking catalysts. Preferably, the second hydrocracking catalyst is chosen from hydrocracking catalysts known to those skilled in the art.

The hydrocracking catalysts used in hydrocracking processes are all of the bifunctional type combining an acid function with a hydrogenating function. The acid function is provided by supports with large surface areas (150 to 800 m ² .g ^-1 generally) presenting superficial acidity, such as halogenated aluminas (notably chlorinated or fluorinated), combinations of boron oxides and aluminum, amorphous silica-aluminas and zeolites. The hydrogenating function is provided either by one or more metals from group VIII of the periodic table of elements, or by a combination of at least one metal from group VIB of the periodic table and at least one metal from group VIII.

Preferably, the second hydrocracking catalyst(s) comprise a hydrogenating function comprising at least one Group VIII metal chosen from iron, cobalt, nickel, ruthenium, rhodium, palladium and platinum and preferably cobalt. and nickel and/or at least one metal from group VIB chosen from chromium, molybdenum and tungsten, alone or in a mixture and preferably from molybdenum and tungsten.

Preferably, the content of Group VIII metal in the second hydrocracking catalyst(s) is advantageously between 0.5 and 15.0% by weight and preferably between 2 and 10% by weight, very preferably between 2.5 and 6.0% by weight, the percentages being expressed as percentage by weight of oxides.

Preferably, the content of group VIB metal in the second hydrocracking catalyst(s) is advantageously between 5 and 35% by weight and preferably between 10 and 30% by weight, very preferably between 15 and 22% by weight, the percentages being expressed as weight percentage of oxides. The second catalyst(s) may also optionally have at least one promoter element deposited on the catalyst and chosen from the group formed by phosphorus, boron and silicon, optionally at least one element from group VIIA (preferred chlorine and fluorine), and optionally at least one element from group VI IB (preferred manganese), optionally at least one element from group VB (preferred niobium).

Preferably, the second hydrocracking catalyst(s) comprise an acid function chosen from alumina, silica-alumina and zeolites, preferably chosen from zeolites Y and preferably chosen from silica-alumina and zeolites.

In a preferred embodiment, the recycling rate of the second liquid fraction resulting from step e) comprising hydrocarbon compounds having a boiling point higher than the temperature T ₂ , but lower than the temperature T 1 at the reactor d hydrocracking of the second stage of stage f) is between 0.2 and 1.5 m/m calculated relative to the fresh feed, preferably between 0.5 and 1.2 and even more preferably between 0.6 and 1.1.

In a preferred embodiment, step f) is fixed bed hydrocracking.

In one embodiment, the hydrocracking catalysts used in steps b) and f) are different.

In one embodiment, the overall recycling rate of the process according to the invention comprising the recycling of the unconverted liquid effluent resulting from step d) comprising hydrocarbon compounds having a boiling point higher than the temperature Ti towards the hydrotreatment step a) and/or step b) first hydrocracking step, and the recycling of the second liquid fraction resulting from step e) comprising hydrocarbon compounds having a boiling point higher than the temperature T ₂ , but lower than the temperature Ti in the second stage hydrocracking reactor of stage f) is between 0.4 and 3 m/m calculated relative to the fresh feed.

Description of the figures:

Figure 1 illustrates the process according to one embodiment of the invention: The DSV type hydrocarbon feedstock 1 enters a hydrotreatment section A. The effluent 2 is sent to a hydrocracking section B corresponding to the first step hydrocracking. The effluent 3 is sent to a gas/liquid separation step C, making it possible to isolate a gas stream comprising hydrogen 5. The gas effluent 5 is sent to a recycling compressor D, it is mixed with a stream 12 of hydrogen make-up then recycled in the hydrotreatment A and hydrocracking B sections via the streams 6 and 7. The liquid effluent 16 from the separation step C is sent to a separation step preferably comprising a high pressure separator E. An effluent 15 comprising a so-called converted effluent comprising hydrocarbon compounds having points d boiling below Ti between 340 and 385°C and an unconverted liquid effluent comprising hydrocarbon compounds having a boiling point above Ti are separated in the high pressure separator. The effluent 15 is sent to a fractionation step comprising a fractionation column F. The effluent 17 is recycled to A and/or B, a purge 18 can be implemented on the effluent 17 to reduce the HPNA. An effluent comprising hydrocarbon compounds having a boiling temperature less than or equal to T ₂ (naphtha cut) 10, cuts comprising hydrocarbon compounds having a boiling temperature greater than T ₂ but less than Ti (middle distillate cut) 8 , and gases 1 1 are separated in the fractionation column. Cut 8 is recycled to a second hydrocracking section G. Effluent 9 from G is sent to C.

Figure 2 illustrates a classic two-step hydrocracking process for maximizing the production of naphtha according to the prior art: The DSV type hydrocarbon feed 1 enters a hydrotreatment section A then the hydrotreated effluent 2 is sent to a hydrocracking step B corresponding to the first hydrocracking step. The effluent 3 from step B is sent to a gas/liquid separator C making it possible to isolate a gas flow comprising hydrogen 5. The gas effluent 5 is sent to a recycling compressor D, it is mixed with a stream 12 of hydrogen make-up then recycled in the hydrocracking reactors via streams 6 and 7. The liquid effluent 4 from the separator C feeds a fractionation column E. A fraction comprising hydrocarbon compounds having a temperature boiling temperature less than or equal to 180°C (naphtha cut) 10, a fraction comprising hydrocarbon compounds having a boiling temperature greater than 180°C (unconverted fraction) 8, and gases 11 are separated in the column of splitting. Fraction 8 is recycled to a second hydrocracking section F corresponding to the second hydrocracking stage. A purge 13 can be implemented on fraction 8 before its recycling to F. The effluent from F 9 is sent to the gas/liquid separator C. Examples

The tests were carried out on a unit comprising two reactors in series (R1 for the hydrotreatment stage, R2 for the first hydrocracking stage) followed by a distillation column allowing the separation of the light fraction and sending from the heavy fraction to a third reactor (R3, second stage hydrocracking) whose output is recycled to the distillation column. The unit can be put under an overall pressure ranging from atmospheric pressure up to 18MPa. The temperature regulation of reactors R1, R2, and R3 can be done from ambient temperature to 450°C. The reactors can be loaded using catalyst volumes of between 30 and 100 mL. The flow rates of injected fillers can vary between 10 and 300 g. h ^-1 and hydrogen flow rates between 0 and 400 NL.h ^-1 .

Comparative example - Conventional two-step hydrocracking process not including a step of separating cuts comprising hydrocarbon compounds having a boiling temperature greater than 370°C upstream of the fractionation step Figure 2

A fresh feed VGO is introduced into the first hydrocracking stage composed of a hydrotreatment reactor R1 comprising a catalyst prepared from an active phase containing Nickel and molybdenum supported on alumina and at least one reactor hydrocracking R2 which comprises a catalyst prepared from an active phase containing Nickel and molybdenum supported on a support composed of alumina and USY (Ultra Stable Y) zeolite.

The effluent leaving the first hydrocracking stage is sent to a gas/liquid separator and all of the liquid effluent obtained is sent to a fractionation column, and the gaseous effluent comprising hydrogen obtained is sent to a compression step before its recycling in the first hydrocracking step.

Then, in the fractionation column, the main products will be divided and extracted from the process and the unconverted fraction comprising hydrocarbon compounds having a boiling point above 180°C is concentrated and taken out at the bottom of the column. A purge of HPNA is carried out on this fraction before sending it to the second hydrocracking stage of the process. The second stage is composed of a hydrocracking reactor R3 which contains a catalyst prepared from an active phase containing Nickel and molybdenum supported on a support composed of alumina and USY zeolite. The R3 effluent is then mixed with the R2 effluent. The two steps combined close the process loop. The fresh charge VGO is injected into a preheating stage then into R1 under the following conditions:

Table 1

The effluent from this reactor is then mixed with a flow of hydrogen and then injected into R2 operating under the following conditions:

Table 2

R1 and R2 constitute the first hydrocracking stage, the effluent from this first stage is then sent to a separation stage composed of a heat recovery train then high pressure separation including a recycling compressor and making it possible to separate on the one hand hydrogen, hydrogen sulphide and ammonia and on the other hand the liquid effluent supplying a stripper then an atmospheric fractionation column in order to separate streams concentrated in H ₂ S, naphtha and a fraction heavy unconverted including hydrocarbon compounds having a boiling point greater than 180°C. This unconverted heavy fraction is recycled to a preheating stage then into R3 constituting the second hydrocracking stage. This reactor is operated under the following conditions:

Table 3

The R3 effluent is then sent to the high pressure separation stage downstream of the first hydrocracking stage. The mass flow rate at the inlet of reactor R3 is equal to the mass flow rate of the fresh charge VGO. A purge corresponding to 0.5% by mass of the flow rate of the fresh charge is carried out on the R3 effluent.

The naphtha cut is recovered from the fractionation column.

The naphtha yield from this process is 89.84% by weight, for an overall conversion of 99.5% by weight of hydrocarbons whose boiling point is greater than 180°C.

Example according to the invention - Optimized two-step hydrocracking process comprising a step of separating hydrocarbon compounds having a boiling temperature greater than 370°C upstream of the fractionation step Figure 1

A fresh VGO feedstock is introduced into the first hydrocracking stage which is composed of a hydrotreatment reactor R1 comprising a NiMo/Alumina catalyst and a hydrocracking reactor R2 comprising a zeolite NiMo catalyst on alumina + USY.

The second hydrocracking stage is composed of a hydrocracking reactor R3 which includes a NiMo on alumina + USY zeolite catalyst.

The effluent from R2 is sent to a gas/liquid separation step preferably comprising washing with amines, then to a high pressure separator before the fractionation column. The separation step makes it possible to separate a cut comprising hydrocarbon compounds having a boiling temperature greater than 370°C which is recycled to R1 and/or R2 with a purge of the HPNAs. The effluent at the head of the high pressure separator is composed of a cut comprising hydrocarbon compounds having a boiling temperature of between 50 and 370°C and is sent to the fractionation column.

The fraction sent to R3 in the second hydrocracking step is therefore the cut comprising hydrocarbon compounds having a boiling temperature between 180 and 370°C from the fractionation column which is not a cut comprising hydrocarbon compounds with a boiling point greater than 370° C. as in comparative example 1.

In this example, the recycling of the cut comprising hydrocarbon compounds having a boiling temperature greater than 370°C is done with a recycling rate at R1 and/or R2 of 0.21 m/m calculated relative to the load fresh, and the recycling of cuttings comprising hydrocarbon compounds having a boiling temperature of between 180 and 370°C is done with a recycling rate at R3 of 0.79 m/m calculated in relation to the fresh load.

Below is a comparison of the performances and operating conditions of the diagram according to the invention compared to that of the prior art:

Table 3

PI = initial boiling point The implementation of the scheme according to the invention of Example 2 allows a gain in yield (+0.37% of the fresh charge mass) towards the total naphtha cut (light + heavy) compared to the conventional naphtha maximization process. according to the prior art of Example 1, and particularly a gain in yield towards heavy naphtha cutting (+0.76% of the fresh charge mass).

The process of Example 1 according to the prior art generates a production of light fraction C1 - C4 greater than that of the process according to the invention (-0.34% of the fresh charge mass).

Claims

1. Process for hydrocracking hydrocarbon feedstocks comprising at least 20% by volume of compounds boiling above 300°C, said process comprising at least the following steps:

• a) The hydrotreatment of said feeds carried out, in the presence of hydrogen and at least one hydrotreatment catalyst, at a temperature between 250 and 480°C, under a pressure between 2 and 25 MPa, at a speed space between 0.1 and 6 h ^-1 and at a quantity of hydrogen introduced such that the volume ratio liter of hydrogen/liter of hydrocarbon is between 100 and 2000 L/L;

• b) A first step of hydrocracking at least part of the total effluent leaving step a) and carried out, in the presence of hydrogen and at least one hydrocracking catalyst, at a temperature between between 250 and 480°C, under a pressure between 2 and 25 MPa, at a space speed between 0.1 and 6 h ^-1 and at a quantity of hydrogen introduced such as the volume ratio liter of hydrogen/liter of hydrocarbon is between 100 and 2000 L/L;

• c) The gas/liquid separation of the effluent from step b) to produce a liquid effluent and a gaseous effluent comprising at least hydrogen;

• d) The separation of the liquid effluent from step c) into at least one so-called converted effluent comprising hydrocarbon compounds having boiling points lower than a temperature Ti of between 340 and 385°C and liquid effluent not converted comprising hydrocarbon compounds having a boiling point above temperature Ti;

• e) Fractionation of the so-called converted liquid effluent from step d) comprising hydrocarbon compounds having boiling points lower than the temperature Ti, to obtain at least a first fraction comprising hydrocarbon compounds having a point d boiling lower than a temperature T ₂ between 150 and 220°C and at least a second fraction comprising hydrocarbon compounds having a boiling point higher than the temperature T ₂ , but lower than the temperature Ti; • f) A second step of hydrocracking at least part of the second liquid fraction resulting from step e) comprising hydrocarbon compounds having a boiling point higher than the temperature T ₂ , but lower than the temperature Ti , operated in the presence of hydrogen and a hydrocracking catalyst, at a temperature between 250 and 480°C, under a pressure between 2 and 25 MPa, at a space speed between 0.1 and 6 h ^{- 1} and a quantity of hydrogen introduced such that the volume ratio liter of hydrogen/liter of hydrocarbon is between 100 and 2000 L/L. Hydrocracking process according to the preceding claim, in which the unconverted liquid effluent from step d) comprising hydrocarbon compounds having a boiling point higher than the temperature Ti is recycled to the hydrotreatment step a). and/or step b) first hydrocracking stage. Hydrocracking process according to the preceding claim, in which the recycling rate to the hydrotreatment reactor and/or to the first stage hydrocracking reactor, either in stage a) and/or b), is between 0.1 and 1.5 m/m calculated in relation to the fresh load, preferably between 0.15 and 1.2 and even more preferably between 0.2 and 0.8. Hydrocracking process according to any one of claims 2 and 3, in which the unconverted liquid effluent resulting from step d) comprising hydrocarbon compounds having a boiling point higher than the temperature T 1 undergoes a step of purges heavy polyaromatic products before recycling to step a) hydrotreatment and/or step b) first hydrocracking step. Hydrocracking process according to any one of the preceding claims, in which the recycling rate of the second liquid fraction resulting from step e) comprising hydrocarbon compounds having a boiling point greater than the temperature T2, but less than the temperature T1 at the second stage hydrocracking reactor of stage f) is between 0.2 and 1.5 m/m calculated relative to the fresh feed, preferably between 0.5 and 1.2 and even more preferably between 0.6 and 1.1. Hydrocracking process according to any one of the preceding claims, in which the effluent from the second hydrocracking step f) is recycled to the gas/liquid separation step c). Hydrocracking process according to any one of the preceding claims, wherein the hydrocracking catalysts used in steps b) and f) are different. Method according to any one of the preceding claims, in which the hydrocarbon feeds treated in said process and sent in step a) are chosen from hydrocarbon feeds comprising at least 80% by volume of compounds boiling between 340 and 580 ° C per in relation to the total volume of charges. Process according to any one of the preceding claims, in which step b) is carried out at a temperature of between 350 and 430°C, under a pressure of between 10 and 18 MPa, at a space speed of between 0.8 and 3 h ^-1 , and a quantity of hydrogen introduced such that the volume ratio liter of hydrogen/liter of hydrocarbon is between 600 and 1600 L/L. Process according to any one of the preceding claims, in which step f) is carried out at a temperature of between 350 and 430°C, under a pressure of between 10 and 18 MPa, at a space speed of between 0.8 and 3 h ^-1 , and a quantity of hydrogen introduced such that the volume ratio liter of hydrogen/liter of hydrocarbon is between 600 and 1600 L/L.