EP0661371B1 - Process for the production of an internal combustion engine fuel by hydrotreatment and extraction - Google Patents

Abstract

Petroleum product and process for obtaining the said petroleum product which can optionally be used for the formulation of an internal combustion engine fuel, including a stage a) of hydrotreatment in which a hydrocarbon feedstock is treated in hydrocarbon conditions under a partial pressure of hydrogen leaving the reactor of approximately 0.5 MPa to approximately 6 MPa, a stage b) of separation of the product (P) originating from stage a) into a product (P1) of initial boiling point lower than approximately 300 DEG C and a product (P2) of final boiling point higher than the final boiling point of product (P1), a stage c) of liquid/liquid extraction with the aid of a solvent (S1), in which an extract (E1) and a raffinate (R1) are obtained from the product (P2), a stage d) of recovery of the solvent (S1) from the raffinate (R1) making it possible to obtain a product (Q1) depleted in solvent (S1), having improved properties and containing less than 500 ppm by weight of sulphur. According to a particular embodiment the extract (E1) is distilled so as to obtain a tail product (Q2) which is subsequently conveyed into a hydrotreatment zone so as to obtain a product (P3) preferably containing less than 0.3 % by weight of sulphur. The solvent (S1) recovered at the head of the distillation is recycled to the extraction stage c). This solvent is chosen from the group consisting of dimethylformamide, dimethylacetamide, furfural, N-methylpyrrolidone and dimethyl sulphoxide.

Description

The invention relates to a method for obtaining of a petroleum product which can possibly be used for the formulation of a fuel for internal combustion engine and the product obtained by the process. The gas oils that are currently on the market, either under fuels for internal combustion engines, either in the form of fuel, are most often products from refining which contain sulfur in an amount (expressed by weight of sulfur) about 0.3%. They are usually obtained after treatment hydrodesulfurization from a feed which can come from the direct distillation of crude oil or special treatment of a crude oil (e.g. pyrolysis or distillation followed by pyrolysis of the fraction recovered during distillation, or cracking thermal or catalytic) generally containing at least 0.8% by weight sulfur.

The prior art is illustrated by US Patent 5,059,303 which describes a process to stabilize very sensitive hydrocarbon fractions (syncrude oils) the effects of light, heat and oxygen, for example. These hydrocarbons are generally shale oils, the main one characteristic, which makes them unacceptable as process charges conventional treatment, is their high content of nitrogen compounds, particularly basic (nitrogen content between 1 and 3% at less). These particular hydrocarbon fractions must therefore be pretreated before use, under severe conditions hydrotreating.

In a number of industrial countries, sulfur content standards and cetane are in place or are going to be in place in a very close to come up. These standards are becoming more and more stringent, particularly for diesel fuels intended to be used as fuel for engines. It is as well as in France, in particular from 1995, the sulfur content of these gas oils must not be more than 0.05% by weight (500 ppm) while diesel in accordance with current standards have a sulfur content that can reach 0.3%.

Likewise the diesel oils used in France as fuel for engines internal combustion must currently have a cetane number at less than 48 and the gas oils used as fuel an index of cetane at least 40. We can expect in the near future a tightening of these standards and in particular those concerning diesel used as fuel in engines.

Furthermore, given the diversity of the charges to be treated (gross of different origins, visbreaking, coking, hydroconversion, distillation or catalytic cracking) to produce diesel. he is desirable to be able to offer the refiner a flexible process, likely to adapt the products formed to demand and respond to future specifications for sulfur, nitrogen, index cetane, color and aromatic content.

Finally, all existing processes such as hydrodesaromatization or hydrocracking which make it possible to obtain petroleum products at low relatively high sulfur and cetane numbers consume significant amounts of hydrogen. For example, the process hydrodesaromatization of a direct distillation charge, the distillation intervals (ASTM D86) are 180 ° C <T 5% <300 ° C, 260 ° C <T 50% < 350, 350 ° C <95% T <460 ° C, consumes 0.6 to 1.1% hydrogen compared to charged while the hydrocracking process requires more than 2% hydrogen relative to its charge. However, the hydrogen charge of the refinery which is generally the catalytic reformer unit will tend to become insufficient in the current context of stricter standards gas oils which result in an increase in hydrotreatments.

In addition, these existing processes lead to obtaining a petroleum product the cetane number of which does not exceed 63, the latter being reached only at cost hydrogenation of aromatic hydrocarbons in the feed, reaction who consumes hydrogen. (See table).

It is therefore desirable to offer the refiner a process that allows him to produce a petroleum product meeting the various standards which will come into force in the very near future and from 1995, as far as is sulfur content. It is likewise desirable to be able to produce a petroleum product with the least pronounced odor possible.

The present invention therefore relates to a simple implementation method, consuming little hydrogen. This process uses industrial units hydrotreating (hydrodesulfurization in particular). It improves qualities of the diesel produced and meet future standards and in particular that concerning the sulfur content. The method of the invention allows in in addition, to improve the cetane engine index of diesel, to reduce its content aromatic compounds not containing a sulfur heteroatom in their molecule, reduce its content of nitrogen compounds, improve its color and its smell and finally to decrease the formation of solid particles during its use in an internal combustion engine. The present invention provides a solution to the specific problem of obtaining, in the most quantity significant possible compared to the starting product, of a petroleum product used in the composition of engine grade diesel or diesel engine from a particular hydrocarbon cut having characteristics which makes it difficult to recover in the form of engine diesel.

The invention further relates to the process for obtaining a petroleum product. used in the composition of a fuel oil.

• une étape a) d'hydrotraitement dans laquelle on effectue l'hydrotraitement de ladite charge dans des conditions permettant d'obtenir un produit (P) contenant une quantité de soufre de 2 à 50 fois moindre que celle de la charge initiale, ledit hydrotraitement étant effectué sous une pression partielle d'hydrogène en sortie de réacteur de 0,5 MPa (mégapascal) à 6 MPa, telle que le taux de désaromatisation de la charge est au plus égale à 30%,
• une étape b) de séparation du produit (P) en un produit (P2) ayant un point d'ébullition initial supérieur à la température d'ébullition du solvant d'extraction de l'étape suivante c) et de préférence au moins supérieur de 20°C, et en un produit (P1) ayant un point d'ébullition final inférieur au point d'ébullition initial du produit P2,
• une étape c) d'extraction liquide/liquide dans laquelle on met en contact, à une température d'extraction au plus égale à 140°C, dans des conditions d'extraction des composés polyaromatiques, le produit (P2) obtenu à l'étape b) avec un solvant ou un mélange de solvant (S1) permettant d'extraire au moins en partie les composé polyaromatiques qu'il contient, ledit solvant ayant un point initial d'ébullition inférieur au point initial d'ébullition du produit (P2) obtenu à l'étape b), et au cours de laquelle on récupère un extrait (E1) enrichi en composés polyaromatiques, soufrés ou non et un raffinat (R1) et,
• une étape d) de récupération du solvant (S1) employé à l'étape c) à partir du raffinat (R1) obtenu à l'étape c) dans laquelle on récupère un produit enrichi en solvant (S1) et un produit (Q1) appauvri en solvant (S1) ayant un indice de cétane amélioré et contenant moins de 500 ppm en poids de soufre.

More particularly, the invention relates to a process for obtaining a base used in the composition of a fuel for an internal combustion engine with compression ignition having in particular an improved cetane number and a sulfur content, starting from a hydrocarbon feedstock having an initial boiling point of at least 150 ° C and a final boiling point of at most 500 ° C, containing 0.05% to 5% by weight of sulfur, 10 to 60% by weight of net iso-alkanes, 10% to 85% by weight of aromatic hydrocarbons at least partly in the form of polyaromatic compounds, sulfur or not, having a cetane number of 20 to 60 and having a nitrogen content of 50 to 5 000 ppm by weight, said process being characterized in that it comprises the following steps:

• a hydrotreatment stage a) in which the hydrotreatment of said charge is carried out under conditions making it possible to obtain a product (P) containing an amount of sulfur from 2 to 50 times less than that of the initial charge, said hydrotreatment being carried out under a partial pressure of hydrogen at the outlet of the reactor from 0.5 MPa (megapascal) to 6 MPa, such that the rate of dearomatization of the charge is at most equal to 30%,
• a step b) of separation of the product (P) into a product (P2) having an initial boiling point higher than the boiling point of the extraction solvent of the following step c) and preferably at least greater than 20 ° C, and in a product (P1) having a final boiling point lower than the initial boiling point of product P2,
• a step c) of liquid / liquid extraction in which is brought into contact, at an extraction temperature at most equal to 140 ° C., under conditions of extraction of the polyaromatic compounds, the product (P2) obtained at step b) with a solvent or a mixture of solvent (S1) making it possible to extract at least partially the polyaromatic compounds which it contains, said solvent having an initial boiling point lower than the initial boiling point of the product (P2 ) obtained in step b), and during which an extract (E1) is enriched with polyaromatic compounds, sulfur or not, and a raffinate (R1) and,
• a step d) of recovering the solvent (S1) used in step c) from the raffinate (R1) obtained in step c) in which a product enriched in solvent (S1) and a product (Q1) is recovered depleted in solvent (S1) having an improved cetane number and containing less than 500 ppm by weight of sulfur.

For the sake of simplicity, we will use in the following description, the term hydrodesulfurization (HDS) instead of hydrotreatment.

By polyaromatic compounds is meant compounds having at least two aromatic cycles, sulfur or not.

The initial and final boiling point temperatures are TBP cut.

The hydrocarbon feedstock which is treated according to the process of the invention is most often referred to as a diesel cutter and it preferably has a point initial boiling point of approximately 150 ° C and a final boiling point of approximately 400 ° C, its sulfur content is usually more than 0.1% and the most often greater than 0.5% by weight, its content of n- and iso-alkanes is about 30 to 45% by weight, its content of aromatic compounds is usually from about 15% to about 65% by weight. This charge is the more often a direct distillation diesel, a pyrolysis diesel or a mixture of the two. This charge can advantageously be mixed with a L.C.O. (light cycle oil) from a catalytic cracking unit and preferably in an LCO / diesel ratio of 1: 4 to 1: 1. The color of this load measured according to the ASTM D 1500 method is usually greater than or equal to 2. The cetane number according to ISO 5165 standard of this charge is most often less than about 60 and it is for example from about 50 to about 55. The nitrogen content of this feed is very often from about 100 to about 1000 ppm expressed by weight of nitrogen relative to the load weight.

The product Q1 obtained is a particularly interesting product taking into account all of its characteristics (cut point, cetane, paraffin content and sulfur) to obtain by formulation with other diesel cuts of quality fuels.

The product (Q1) obtained by the process of the present invention has usually a nitrogen content expressed by weight of nitrogen 2 times less than that of the initial charge and often 4 to 5 times less. This product (Q1) has most often a color measured according to the ASTM 1500 standard less than 1 and the cetane number of this product is generally at least 3 higher points and often at least 5 points at the cetane number of the initial charge (for example from 3 to 14 points). Its sulfur content compared to that of the load is usually less than or equal to 5% by weight. Its net content iso-alkanes generally increases by at least 4 points, advantageously by 5 to 20 points and most often 6 to 11 points, compared to that of the charge. The content of aromatic compounds containing no atom sulfur in their molecule in this product (Q1) is usually reduced by at least at least 10% by weight compared to that of the initial charge and often at least minus 30% by weight. The odor of this product is less strong than that of initial charge.

The invention advantageously relates to a petroleum product characterized in that that the distillation cut corresponds to 95% by weight distilled between 320 ° C and 460 ° C, its cetane number is greater than 60, its content of n- and iso-alkanes is at least equal to 48% by weight, and its sulfur content less than or equal to 500 ppm (weight).

According to the present invention, the hydrodesulfurization is advantageously carried out in a hydrodesulfurization unit under mild conditions making it possible to desulfurize the sulfur molecules by hydrogenating as little as possible. This approach is not obvious to a person skilled in the art of the 1990s, who is rather led to the solution of severifying the conditions of a hydrotreatment in order to simultaneously decrease the sulfur content and increase the cetane of the charges. Under these conditions, the temperature is 320 to 370 ° C, the hourly space velocity is 1 to 5, the pressure from 1 to 5 MPa and the volume ratio H2 on load from 50 to 350 m ³ / m ³ measured under conditions normal. The charge dearomatization rate is then at most equal to around 15%. We can thus distinguish two particularly advantageous cases of implementation of this hydrodesulfurization making it possible to obtain an excellent charge for the following extraction step.

According to the first possibility which is preferred, one operates in the presence of a selective catalyst for the hydrodesulfurization of sulfur molecules compared to the hydrogenation of aromatics, adapted to limit hydrogenation, for example one of those marketed by PROCATALYSE, under pressure partial hydrogen at the outlet of the hydrodesulfurization reactor advantageously between approximately 1.0 MPa and approximately 3.0 MPa and recovers a product (P) containing an amount of sulfur from 2 to 30 times less, ie between 0.1 and 0.3% by weight depending on the charge, for example, and most often 3 to 10 times less than that of the initial charge. The charge deflavor rate is then significantly less than 10%. The other conditions for implementing this hydrodesulfurization step are conventional conditions of a hydrodesulfurization qualified by those skilled in the art of hydrodesulfurization simple and sweet.

According to the second possibility, one operates in the presence of a conventional catalyst suitable for limiting hydrogenation, for example one of those sold by the company PROCATALYSE, under partial pressure of hydrogen in hydrodesulfurization reactor outlet advantageously between about 2 MPa and about 5 MPa and recover a product (P) containing 5 to 60 times less sulfur, less than 0.1% by weight, per example between 0.02 and 0.05%, and most often 10 to 40 times less than that of the initial charge. In addition, the rate of disaromatization of the load is at most equal to approximately 15%. The other conditions of implementation work of this hydrodesulfurization step are conventional conditions more severe hydrodesulfurization. This hydrodesulfurization is carried out using a larger volume of catalyst than in the case of simple hydrodesulfurization, for example a volume of catalyst 2 times more important, as well as a higher hydrogen pressure, calculated for perform further hydrodesulfurization.

A description of several commercial hydrodesulfurization catalysts and industrial conditions for implementing hydrodesulfurizations can for example be found in volume 1 of the book by P. WUITHIER, edited by TECHNIP editions under the title OIL, REFINING AND ENGINEERING CHEMICAL, pages 816 to 831. One can advantageously choose for example a catalyst containing molybdenum and cobalt, known to limit hydrogenation.

The separation step, well known to those skilled in the art generally comprises a steam stripping of the total liquid hydrotreatment effluent, followed or not by an additional distillation step. This last step is generally required when it is desired to send to the extraction a fraction P2 whose initial boiling point is higher than that of the hydrotreatment effluent once stripped. The operating conditions are generally: reduced pressure less than 1 bar, advantageously 10 to 100 mbar, preferably 20 to 50 mbar (1 bar = 10 ⁵ Pa) and temperature between 80 and 250 ° C.

The liquid / liquid extraction step is a step carried out under conditions classics. This extraction could for example be carried out against the current in a conventional device, for example a filling column, with plates or with mechanical agitation (R.D.C.: rotating dise contactor) having in general an efficiency from 3 to 20 theoretical stages and preferably from 5 to 10 theoretical stages, at a temperature generally between 0 ° C and 140 ° C, advantageously between 30 ° C and 80 ° C and under pressure allowing operation in the liquid phase and therefore between 0.1 and 1 MPa, preferably between 0.1 and 0.6 MPa. The volume ratio of the solvent (S1) to volume of the product (P2), obtained in step b), is preferably about 0.2: 1 to about 5: 1, preferably 0.5: 1 to 2: 1 and most often about 1: 1. The solvent is preferably chosen from the group of solvents making it possible to also extract at least part of the compounds aromatic, not containing a sulfur atom in their molecule, present in the product (P2) obtained in step b). Extraction conditions are preferably chosen so as to obtain a raffinate (R1) containing by weight at most 90% and preferably at most 70% of the total weight of aromatic compounds, not containing a sulfur atom in their molecule, present in the product (P2) obtained in step b). The extract (E1) in these conditions will contain at least 10% and often at least 30% by weight of the total weight of the aromatic compounds, not containing a sulfur atom in their molecule, present in the product (P2) obtained in step b), thus that preferably at least 30% and often at least 50% and frequently at least 80% by weight of the total weight of the sulfur-containing compounds, most often dibenzothiophenics and naphthobenzothiophenics initially contained in the product (P2). The product (Q1) thus obtained usually contains 2 to 10 times less sulfur than the product (P2) from step b) and the most often 4 to 10 times less.

The extraction solvent is most often a single solvent, but it is possible to also use solvent mixtures. This solvent contains generally less than 20% and often less than 10% by weight of water. This solvent may be an anhydrous solvent. He is often chosen from the group formed by methanol, acetonitrile, monomethylformamide, dimethylformamide, dimethylacetamide, furfural, N-methylpyrrolidone and dimethyl sulfoxide. We very often use a solvent containing no nitrogen and most often a non-nitrogenous solvent oxygen. The preferred solvent is furfural.

It is also possible to add to the extraction solvent at least one cosolvent which may be an alcohol of 1 to 6 carbon atoms, for example an alcohol linear or branched, or furfuryl alcohol.

If the feed to be treated has a high final boiling point and is particularly rich in nitrogen compounds, especially basic, it can be advantageous to introduce with the extraction solvent alone or as a mixture, a minor amount of acids, especially carboxylic acids (less than 1% by weight per solvent, for example). Among these, it is advantageously possible quote carboxylic acids from 1 to 6 carbon atoms and more especially acids with a boiling point below 250 ° C, in particular formic acid, acetic acid, propionic acid, butanoic acid, pentanoic acid, maleic acid, crotonic acid, isobutyric acid, valeric acid, trimethylacetic acid, acid benzoic, and 2-furoic acid.

The solvent can be recovered from the raffinate by a stripping or distillation, preferably by steam stripping whose conditions have been described above.

The raffinate (R1) obtained in step c) is then sent to step d) by example in a steam stripping zone in which it is separated under conditions making it possible to recover an enriched head fraction, and preferably highly enriched, in solvent (S1) and a bottoms product (Q1) preferably highly depleted in solvent (S1). Most often, conditions for this separation are chosen so as to obtain a overhead fraction containing almost all of the solvent, that is to say by example, more than 95% by weight of the amount of solvent contained in the raffinate (R1) and introduced into this stripping zone. We thus recover, from preferably at least about 99% by weight of the amount of solvent contained in the raffinate (R1).

Likewise in a particular embodiment, the extract (E1) obtained at step c) is then sent to a solvent recovery zone (S1) used in step c) in which a product enriched in solvent is recovered (S1) and a product (Q2) depleted in solvent (S1). The separation of the solvent from the extract is generally produced by distillation and / or stripping with steam and preferably by distillation followed by steam stripping under the conditions set out above. This extract is therefore separated in conditions for recovering a fraction of enriched head, and preferably highly enriched, in solvent (S1) and a bottoms product (Q2) depleted in solvent (S1). Most often the conditions of this separation are chosen so as to obtain a fraction of head containing the quasi all of the solvent, that is to say for example more than 95% by weight of the amount of solvent contained in the extract (E1) and introduced into this zone of separation. At least about 99% by weight is thus preferably recovered. the quantity of solvent contained in the extract (E1).

When operating in step a) under hydrodesulfurization conditions significantly more severe, that is to say in particular in the presence of a very significant amount of catalyst, the product (Q2) which is obtained by distillation of the extract (E1) will most often have a sulfur content less than or equal to about 0.3% by weight. This product (Q2) will be fine heard not usable as fuel for engines, since it contains most often a quantity of sulfur higher than the future standard; through however we can probably use it as fuel.

In a particularly advantageous embodiment of the invention, the top product (s), obtained by separation of the raffinate (R1) and optionally extract (E1), enriched in solvent, are recycled in step c) liquid / liquid extraction.

According to a particular form of implementation of the method according to the invention, at least part of the product (Q2) obtained from the extract (E1) after solvent separation (S1) can be sent to an area hydrodesulfurization separate from the feed hydrodesulfurization zone initial or even be returned to the hydrodesulfurization zone of the stage at). In this zone, distinct from the hydrodesulfurization zone of step a), the part of the product (Q2) is subjected to hydrodesulfurization in conditions for obtaining a product (P3) having a sulfur content less than or equal to 0.3% by weight and preferably less than or equal to 0.2% by weight.

According to a variant of the method according to the present invention, the charge hydrocarbon, having an initial boiling point of at least 150 ° C and a boiling point of at most 500 ° C, is sent to a zone of distillation in which a fraction (F1) having a point is separated at the head boiling point of at least 250 ° C and at the bottom a fraction (F2) having a initial boiling point of at least 250 ° C. According to the present variant, the fraction (F2) is treated according to the process described above for the charge hydrocarbon 150-500 ° C steps a) to d). The fraction (F1) is sent to a hydrodesulfurization zone distinct from that of step a) in which it is hydrodesulfurized under conventional conditions and for example in the simple conditions described above, then the hydrodesulfurized product (P ') obtained is sent to a separation zone, for example by stripping or by distillation of the product (P ') into a fraction (P10) having a point final boiling point below 150 ° C, and in a fraction (P20) having a point initial boiling point above the final boiling point of the fraction (P10). This product (P20) can, at least in part, be mixed with the product (Q1) obtained from fraction (F2) to form a product (Q10) having the qualities required as engine fuel. The fraction (P10) is essentially formed of compounds resulting from side reactions during hydrodesulfurization. This fraction (P10) generally represents less than 2% by volume relative to the total volume of the fraction (F1).

The main advantages of the invention are as follows: a higher n- and iso-alkane content is obtained in the raffinate (table) than according to the hydrocracking or hydrodesaromatization processes, a higher cetane number, despite an aromatic hydrocarbon content greater than 10%. In addition, the consumption of hydrogen in hydrotreatment is lower. It can be reduced for example to 0.15% by weight with respect to the charge, when the hydrogenation is limited to the maximum. hydrocracking hydrodesaromatisation HDS and extraction density 0.815 to 0.825 0.820 to 0.850 0.815 to 0.840 cetane 53-63 45-60 62-71 n- and iso-alkanes 42-47 35-45 49-56 naphthenes 49-55 25-55 30-41 aromatic 3-7 10.20 10-20 Consumption in hydrogen% > 2 0.6-1.1 <0.5

Comparison of chromatogram profiles of sulfur compounds (specific gas chromatography detector: Sievers) shows that for the HDS and extraction scheme (raffinate) the sulfur compounds collected in the raffinate are in essentially form benzothiophenic, dibenzothiophenic and naphthobenzothiophenic compounds found mainly in the extract whereas for conventional schemes, whether by deep hydrodesulfurization or hydrodesaromatization the sulfur compounds remaining in the petroleum product are essentially in dibenzothiophenic and naphthobenzothiophenic form.

Figures 1 and 2 schematically represent the main variants for the implementation of the method according to the present invention. On these figures similar bodies are designated by the same numbers and letters reference.

According to FIG. 1, the hydrocarbon charge to be treated is sent by the line (1) in the hydrodesulfurization zone (HDS1) at the outlet of which retrieve by line 2 a product (P) which is sent to an area of separation (SEP. 1) from which a product is recovered via line 3 (P1) and by line 4 a product (P2) whose initial boiling point is higher than the final boiling point of the product (P1). This product (P2) is sent via line 4 to an extraction zone (EXT.) in which also introduces an extraction solvent (S1) via line 5 and from which we recover an extract (E1) by line 7 and a raffinate (R1) by the line 6. This raffinate (R1) is sent by line 6 to an area (D1) of recovery of the solvent (S1) via line 8 and of a petroleum product (Q1) possibly being used as a base in the composition of a diesel engine of improved qualities, by line 9. The extract (E1) is sent by the line 7 in a zone (D2) for recovering the solvent (S1) via line 10 and of a product (Q2) by line 11. This product (Q2) can be, at least in part, recovered by line 11a when valve V4 is open, or be, at less in part, sent by line 11b when the valve V1 is open either in a hydrodesulfurization zone (HDS3) not shown diagrammatically, either in the zone hydrodesulfurization (HDS1). When this product (Q2) is recovered by the line 11a it can be valued as fuel but does not meet the future engine diesel standards it cannot be used as is as fuel.

According to FIG. 2, the hydrocarbon charge to be treated is sent by the line (100) in a zone (TOP) from which a fraction (F2) is recovered heavy with initial boiling point above about 250 ° C which is treated as the hydrocarbon feed according to the description above made in link with figure 1. From zone (D1) the product (Q1) can be. at less partially recovered by line 9 and line 9a when valve V2 is open, or be, at least in part sent by line 9b in line 140 when valve V3 is open. When picked up by line 9a this petroleum product partially forms a base used in the composition of improved quality diesel fuel. From the (TOP) area we recover on line 110 a slight fraction (F1) of final boiling point greater than about 250 ° C. This fraction (F1) is sent by line 110 in a hydrodesulfurization zone (HDS2) at the outlet of which recovers via line 120 a hydrodesulfurized product (P ') which is sent in a separation zone (SEP. 2) from which we recover by line 130 a product (P10) and by line 140 a product (P20) whose point initial boiling point is higher than the product's final boiling point (P10). This product (P20) is optionally mixed with the product (Q1) arriving via the driving 9b. This mixture or the product (P20) forms a base entering the composition of an improved quality diesel fuel which is recovered by the line 149.

The following examples illustrate the invention without limiting its scope.

EXAMPLE 1

The feed used in this example is a diesel distillation cut direct (straight-run) with a cetane number of 55, a total content of aromatic compounds, sulfur and non-sulfur, 30% by weight, one content in n and iso-alkanes of 39% by weight, a naphthene content of 31%, a sulfur content of 1.22% by weight, a nitrogen content expressed by weight 255 ppm nitrogen and a color measured according to ASTM D 1500 equal à 2. This diesel cut has an initial distillation point of 150 ° C and a point final distillation of 400 ° C.

This charge is introduced via line 1 into a hydrodesulfurization zone in which it is subjected to a hydrodesulfurization treatment under a partial hydrogen pressure of 2.0 MPa in the presence of an industrial catalyst containing cobalt and molybdenum on an alumina support sold by the company PROCATALYSE under the reference HR 306C, the temperature is maintained at 330 ° C., the quantity of hydrogen introduced is equal to 200 liters per liter of charge and the hourly space speed is 2, 5 h ^-1 . The amount of hydrogen consumed is 0.25% by weight relative to the charge.

A product (P) containing 0.2% by weight of sulfur is recovered via line 2, 28% by weight of sulfur and non-sulfur aromatics and a content in n- and iso-alkanes of 40%. This product has a color measured according to the ASTM D-1500 method less than 1 and a nitrogen content of 175 ppm in weight. The cetane number of the product (P) is 56. This product has an end point distillation of 400 ° C. It is sent to a steam stripping zone of water (SEP1) from which a product (P1) is recovered via line 3 having a final distillation point of 220 ° C and through line 4 a product (P2) having an initial distillation point of 220 ° C and an end distillation point 400 ° C. This product (P2) after cooling to 70 ° C, that is to say at the temperature of the extraction zone, is sent to an extraction zone (EXT.) By line 4 in which we also introduce by line 5 a quantity of furfural equal in volume to the quantity of product (P2) introduced in this area. This zone is an extraction column comprising a padding formed of Pall rings with an overall efficiency appreciably equal to three theoretical stages. The extraction is carried out against the current, under atmospheric pressure and at a temperature of 70 ° C. We obtain a raffinate (R1) which is sent via line 6 to the steam stripping zone (D1) in which the furfural which is recovered by the line 8 for possible recycling to the extraction zone and in tail a raffinate (Q1) containing less than 5 ppm of furfural for example, having a sulfur content of 0.04% by weight, a cetane number of 67, a content by weight of aromatic sulfur and non-sulfur compounds of 12%, a n- and iso-alkane content of 49%, a nitrogen content of 40 ppm and a Saybolt color of 30 and which can be introduced into the tank (pool) diesel. From this extraction area we also recover an extract (E1) which is sent to a distillation zone (D2) followed by a zone of steam stripping in which the furfural which is separated at the head recovered by line 10 for possible recycling to the area extraction and at the tail an extract (Q2) containing practically no more furfural, having a sulfur content of 0.6% by weight, a cetane number 25, a content by weight of sulfur and non-sulfur aromatic compounds of 77% and a nitrogen content of 500 ppm.

This product Q2 can be sent via lines 11 and 11b to a hydrodesulfurization zone (HDS3) distinct from that into which the initial charge has been introduced. This hydrodesulfurization is carried out in the presence of the HR 306C catalyst, under a partial hydrogen pressure of 2.5 MPa, at a temperature of 330 ° C. with a recycling of hydrogen of 200 liters per liter of charge and an hourly space velocity of 2.5 h ^-1 . At the outlet of this hydrodesulfurization, a product is obtained having a sulfur content of 0.2% by weight. Its other characteristics are practically unchanged. This product can be mixed with domestic fuel, that is to say introduced into what those skilled in the art call the domestic fuel pool.

EXAMPLE 2

The charge used in this example is the same as that used in Example 1.

This charge is introduced via line 1 into a hydrodesulfurization zone in which it is subjected to a hydrodesulfurization treatment under a partial hydrogen pressure of 2.5 MPa in the presence of an industrial catalyst containing cobalt and molybdenum on an alumina support sold by the company PROCATALYSE under the reference HR 306C, the temperature is maintained at 330 ° C, the quantity of hydrogen is equal to 200 liters per liter of charge and the hourly space speed is 1 h ^{- 1} . The amount of hydrogen consumed is 0.4% by weight relative to the charge.

A product (P) containing 0.05% by weight of sulfur, 27% by weight of sulfur and non-sulfur aromatics and a content of n- and iso-alkanes of 40% by weight. This product has a color measured according to the ASTM D-1500 method less than 1 and a nitrogen content of 130 ppm by weight. The cetane number of the product (P) is 57. This product has a final distillation point of 400 ° C. He is sent to an area of steam steam stripping (SEP1) from which it is recovered by line 3 a product (P1) having a final distillation point of 220 ° C and by the line 4 a product (P2) having an initial distillation point of 220 ° C and a 400 ° C final distillation point. This product (P2) after being cooled to 70 ° C, is sent to an extraction zone (EXT.) By line 4 in which we also introduce by line 5 an equal amount of furfural in volume to the quantity of product (P2), introduced into this zone. This area is an extraction column comprising a packing formed by Pall rings with an efficiency roughly equivalent to three theoretical stages. The extraction is carried out against the current, at atmospheric pressure and at temperature of 70 ° C. We obtain a raffinate (R1) which we send by line 6 in the steam stripping zone (D1) in which we separate at the head the furfural which is recovered by line 8 with a view to its recycling possible at the extraction zone and at the back a raffinate (Q1) containing practically more furfural, having a sulfur content of 0.01% by weight, a cetane number of 69, a content by weight of compounds aromatic sulfur and non-sulfur of 10%, a content of n- and iso-alkanes 50% by weight, a nitrogen content of 20 ppm and a Saybolt color of 30. This raffinate is sent by line 9 to the diesel pool. From this area of extraction we also recover an extract (E1) which we send to a distillation zone followed by a steam stripping zone D2 in which are separated at the head furfural which is recovered by line 10 in view of its possible recycling to the extraction area and at the end an extract (Q2) containing practically no more furfural, having a sulfur content 0.15% by weight, a cetane number of 26, a content by weight of 77% sulfur and non-sulfur aromatics and nitrogen content of 500 ppm.

This product Q2 can be sent via lines 11 and 11a to the fuel pool domesticated.

EXAMPLE 3

The charge used in this example is the same as that used in Example 1.

This charge is introduced via line 1 into a hydrodesulfurization zone in which it is subjected to a hydrodesulfurization treatment under a partial hydrogen pressure of 2.5 MPa in the presence of an industrial catalyst containing cobalt and molybdenum on an alumina support sold by the company PROCATALYSE under the reference HR 306C, the temperature is maintained at 330 ° C, the quantity of hydrogen introduced is equal to 200 liters per liter of charge and the hourly space speed is 1 h ^-1 . The amount of hydrogen consumed is 0.4% by weight relative to the charge.

A product (P) containing 0.05% by weight of sulfur, 27% by weight of sulfur and non-sulfur aromatic compounds. This product has a color measured by ASTM D-1500 less than 1 and a nitrogen content of 130 ppm by weight. The cetane number of the product (P) is 57. This product has a final distillation point of 400 ° C. The product P is steam stripped to remove light fractions (<150 ° C) and hydrogen sulfide formed in the hydrodesulfurization reactor (less than 2% of the initial charge). It is then sent to a distillation zone at from which we recover by line 3 a product (P1) having a point final distillation of 300 ° C and through line 4 a product (P2) having a point initial distillation of 300 ° C. The product (P2) after being cooled to 70 ° C, is sent to an extraction zone (EXT.) by line 4 in which we also introduces by line 5 an amount of furfural equal in volume the quantity of product (P2) introduced into this zone. This area is a extraction column comprising a packing formed by Pall rings with an efficiency roughly equivalent to three theoretical stages. The extraction is carried out against the current, at atmospheric pressure and at temperature of 70 ° C. We obtain a raffinate (R1) which we send by line 6 in the distillation zone D1 in which the head is separated furfural which is recovered by line 8 for recycling possible at the extraction zone and at the tail, by line 9, a raffinate (Q1) does not containing practically more furfural. At least part of this product (Q1) is mixed with at least part of the product (P1) free of its light fraction and a fraction (F) having a content of sulfur of 0.01% by weight, a cetane number of 62, a content by weight of 15% sulfur and non-sulfur aromatic compounds, its content of n- and iso-alkanes is 49% by weight, a nitrogen content of 30 ppm and a color Saybolt of 20. This fraction (F) is mixed with the diesel pool. From this extraction zone, we also recover an extract (E1) which we send in a distillation zone D2 in which the furfural is separated at the top which is recovered by line 10 for possible recycling to the extraction zone and at the end an extract (Q2) containing practically no more furfural, having a sulfur content of 0.25% by weight, an index of cetane 25, a content by weight of aromatic sulfur compounds and not 82% sulfur and a nitrogen content of 700 ppm.

This product Q2 can be treated as described above in Example 1.

EXAMPLE 4

The charge used in this example is the same as that used in Example 1. It is introduced via line 100 into a distillation zone from which a fraction (F1) having a point of recovery is recovered via line 110. initial boiling point of 150 ° C and a final boiling point of 300 ° C. This fraction is introduced via line 110 into a hydrodesulfurization zone in which it is subjected to a hydrodesulfurization treatment under a partial hydrogen pressure of 2.0 MPa in the presence of an industrial catalyst containing cobalt and molybdenum on an alumina support sold by the company PROCATALYSE under the reference HR 306C, the temperature is maintained at 330 ° C, the quantity of hydrogen introduced is equal to 150 liters per liter of charge and the hourly space speed is 4 h ^-1 . The amount of hydrogen consumed is 0.05% by weight relative to the charge. A product (P ') containing 0.005% by weight of sulfur, 20% by weight of sulfur and non-sulfur aromatic compounds is recovered via line 120. This product has a color measured according to the ASTM D-1500 method less than 1 and a nitrogen content of 20 ppm by weight. The cetane number of the product (P ') is 57. This product has a final distillation point of 300 ° C. It is sent to a stripping zone with water vapor (SEP2) from which a product (P10) is recovered by line 130 having an end point of distillation of 150 ° C. and by product 140 a product ( P20) having an initial distillation point of 150 ° C and a final distillation point of 300 ° C. This product (P20) is sent by line 140 and line 149 to the engine fuel pool.

From the distillation zone (TOP) a fraction (F2) is recovered via line 1 having an initial boiling point of 300 ° C and a final boiling point of 400 ° C. Its aromatic hydrocarbon content is 37% by weight and its n- and iso-alkane content is 34% by weight. This charge is introduced via line 1 into a hydrodesulfurization zone in which it is subjected to a hydrodesulfurization treatment under a partial hydrogen pressure of 3.0 MPa in the presence of an industrial catalyst containing cobalt and molybdenum on an alumina support sold by the company PROCATALYSE under the reference HR 316C, the temperature is maintained at 350 ° C., the quantity of hydrogen introduced is equal to 200 liters per liter of charge and the hourly space speed is 1 hour ^{- 1} . The amount of hydrogen consumed is 0.45% compared to the load.

A product (P) containing 0.15% by weight of sulfur, 34% by weight of sulfur and non-sulfur aromatics and a n and iso-alkane content of 35%. This product has a color measured according to the ASTM D-1500 method less than 2 and a nitrogen content of 300 ppm in weight. The cetane number of the product (P) is 56. This product has an end point distillation of 400 ° C. It is sent to a steam stripping zone of water (SEP1) from which a product (P1) is recovered via line 3 having a final distillation point of 300 ° C and through line 4 a product (P2) having an initial distillation point of 300 ° C and an end distillation point 400 ° C. This product, after being cooled to 70 ° C, (P2) is sent to an extraction zone (EXT.) by line 4 into which we introduce also by line 5 an amount of furfural equal in volume to the quantity of product (P2) introduced into this zone. This area is a column extraction comprising a packing formed of Pall rings of a efficiency substantially equivalent to three theoretical stages. extraction is carried out against the current, at atmospheric pressure and at temperature 70 ° C. We obtain a raffinate (R1) which we send via line 6 in the steam stripping zone D1 in which the furfural is separated at the head which is recovered by line 8 for possible recycling to the area extraction and at the end a raffinate (Q1) containing practically no more furfural, having a sulfur content of 0.04% by weight, a cetane number 67, a content by weight of sulfur and non-sulfur aromatics of 20%, an n- and iso-alkane content of 48% by weight, a nitrogen content of 30 ppm and a Saybolt color of 20. From this extraction zone we also retrieves an extract (E1) which is sent to an area of distillation D2 in which the furfural which is recovered at the head is separated by line 10 for possible recycling to the extraction zone and tail an extract (Q2) containing practically no more furfural, having a sulfur content of 0.5% by weight, a cetane number of 25, a content of weight of aromatic sulfur and non-sulfur compounds of 80% and a content in nitrogen of 1000 ppm.

The product (Q1) is sent by lines 9, 9b, and 149 to the fuel pool engine. The mixture of P20 and Q1 is a product with a cetane number of 61, a content by weight of sulfur and non-sulfur aromatic compounds of 23%, a sulfur content of 0.02% by weight, a nitrogen content of 30 ppm and a Saybolt color of 25. This mixture can also be mixed, at least in part, with a part at less of product P1, once stripped.

EXAMPLE 5

A charge of direct distillation diesel fuel with an initial distillation point of 150 ° C. and a final distillation point of 400 ° C. containing 35% by weight of aromatics and sulfur compounds and 10% of di- and polyaromatics is treated according to the Example 1 under hydrotreatment conditions defined below. Hydrogen partial pressure (MPa) Product P Aromatics + sulfur compounds% by weight Product P Di- and polyaromatics% by weight Cetane gain after extraction between products Q ₁ and P (at isorientation) 3.0 34 7 + 12 5.0 32 4 + 10 7.0 (comparison) 23 1 + 6

Knowing that a gain in cetane number of 14 points was observed per direct liquid-liquid extraction, we show by this example that the performance of the downstream extraction unit depends on the severity of the stage hydrotreating.

In particular, they are all the more important as the content of aromatic hydrocarbons from the hydrotreatment effluent is substantially identical to that of the initial charge and that the hydrogenation step of di- and polyaromatic hydrocarbons is limited.

We thus show that a selection of the conditions of the hydrotreatment step of the method according to the invention conditions the performance of the step extraction.

EXAMPLE 6

The feed used in this example is a diesel cut mixture of direct distillation and diesel cut from catalytic cracking, LCO type.

The direct distillation diesel cut has a density at 15 ° C of 857, an index of refraction at 60 ° C. of 1.4617, a cetane number of 55, a total content of aromatic, sulfur and non-sulfur compounds, 35.4% by weight, one content in n- and iso-alkanes and naphthenes of 64.6% by weight, a sulfur content 1.33% by weight and a nitrogen content expressed by weight of nitrogen of 124 ppm.

The LCO diesel cutter has a density at 15 ° C of 944.1 a refractive index at 60 ° C 1.5245, cetane number 23, total content of compounds aromatic, sulfur and non-sulfur of 67.4% by weight, a content of n- and iso-alkanes and naphthenes of 32.6% by weight, a sulfur content of 3.13% by weight and a nitrogen content expressed by weight of nitrogen of 930 ppm.

We note load C ₁ , the load containing 80% of diesel fraction for direct distillation and 20% of LCO cut, and load C ₂ , the load containing 50% of diesel fraction for direct distillation and 50% of LCO cut. The cuts C ₁ and C ₂ have an initial distillation point of 200 ° C and a final distillation point of 400 ° C. The feed C ₁ is introduced via line 1 into a hydrodesulfurization zone in which it is subjected to a hydrodesulfurization treatment under a partial pressure of hydrogen of 2.0 MPa in the presence of an industrial catalyst containing cobalt and molybdenum on an alumina support sold by the company PROCATALYSE under the reference HR 306C, the temperature is maintained at 330 ° C., the quantity of hydrogen introduced is equal to 200 liters of charge and the hourly space speed is 2, 5 h ^-1 . The amount of hydrogen consumed is 0.25% by weight relative to the charge.

A product (P ') with a density at 15 ° C of 862.2 is recovered via line 2 and containing 0.051% sulfur, 31% by weight of sulfur aromatic compounds and non-sulfur, 61% by weight of n- and iso-alkanes and 285 ppm of nitrogen.

The cetane number of the product (P ') is 53 and its final point of distillation is 400 ° C. It is sent to a steam stripping zone (SEP1) at from which we recover by line 3 a product (P'1) having a point final distillation of 230 ° C, and by line 4 a product (P'2) having a point initial distillation of 230 ° C and a final distillation point of 400 ° C. This product (P'2) after cooling to 70 ° C, that is to say at the temperature of the extraction zone, is sent to an extraction zone (EXT.) by line 4 in which we also introduce through line 5 a quantity of furfural equal in volume to the quantity of product (P'2) introduced into this zone. This zone is an extraction column comprising a formed packing of Pall rings with an overall efficiency substantially equal to three stages theoretical. Extraction is carried out against the current, under pressure atmospheric and at a temperature of 70 ° C. We obtain a raffinate (R'1) that it is sent via line 6 to the steam stripping zone (D1) in which separates at the head the furfural which is recovered by line 8 in view of its possible recycling to the extraction area and at the end a raffinate (Q'1) containing less than 5 ppm of furfural for example, having a content in sulfur of 0.02% by weight, a cetane number of 67.3, a content by weight of sulfur-containing and non-sulfur-containing aromatic compounds of 19.1, a content of n- and iso-alkanes and naphthenes of 80.9% by weight, a nitrogen content of 54 ppm and a density at 15 ° C of 826.5 and which can be introduced into the tank (pool) diesel. From this extraction area we also recover an extract (E'1) which is sent to a distillation zone (D2) followed by a zone of steam stripping in which the furfural which is separated at the head recovered by line 10 for possible recycling to the area extraction and at the tail an extract (Q'2) containing practically no more furfural, having a sulfur content of 0.14% by weight, a content by weight 87.2% sulfur and non-sulfur aromatic compound, nitrogen content of 800 ppm, a content of n- and iso-alkanes and naphthenes of 12.8% by weight and a density at 15 ° C of 1002.8.

The load C ₂ undergoes the same treatment as the load C1.

Line 2 is used to recover a product (P ") with a density at 15 ° C. of 888.1 and containing 0.067% by weight of sulfur, 44.6% by weight of aromatic sulfur and non-sulfur compounds, 47.4 % by weight of n- and iso-alkanes and naphthenes and 527 ppm of nitrogen.
The cetane number of the product (P ") is 43 and its final point of distillation is 400 ° C.

The product (P "1) recovered by line 3 has an end point of distillation of 230 ° C, and the product (P "2) recovered by line 4 has an initial point of 230 ° C distillation and a 400 ° C final distillation point.

The raffinate (R "1) obtained after extraction is sent via line 6 to the steam stripping zone (D1) in the same way as the raffinate (R'1). The raffinate (Q "1) obtained at the tail contains less than 5 ppm of furfural per example, 0.02% by weight of sulfur, a cetane number of 66.1, 17% by weight of sulfur and non-sulfur aromatic compounds, 83% by weight of n- and iso-alkanes and naphthenes, 150 ppm nitrogen and a density at 15 ° C of 883.9.

The extract (E''1) obtained after extraction is sent to the distillation zone (D2) followed by steam stripping. The extract (Q "2) obtained at the tail does not contains practically more furfural, 0.12% by weight of sulfur, 87.9% by weight of sulfur and non-sulfur aromatics, 900 ppm nitrogen, 12.1% by weight of n- and iso-alkanes and naphthenes, and a density at 15 ° C of 985.3.

Products Q'2 and Q "2 can be sent via lines 11 and 11b to a hydrodesulfurization zone (HDS3) distinct from that into which the initial charge has been introduced. This hydrodesulfurization is carried out in the presence of the HR 306C catalyst , under partial pressure of hydrogen of 2.5 MPa, at a temperature of 330 ° C. with a recycling of hydrogen of 200 liters per liter of charge and an hourly space speed of 2.5 h ^-1 . this hydrodesulfurization produces a product having a sulfur content of 0.2% by weight. Its other characteristics are practically unchanged. This product can be mixed with household fuel, that is to say introduced into what those skilled in the art call the domestic fuel pool.

Claims (11)

1. A process for producing a petroleum product that can act as a base in the composition of a fuel for a compression ignition internal combustion engine with an improved cetane index and sulphur content, from a hydrocarbon feed with an initial boiling point of at least 150°C and an end point of at most 500°C, containing 0.05% to 5% by weight of sulphur, 10% to 60% by weight of n- and iso-alkanes, 10% to 85% by weight of aromatic hydrocarbons at least partially in the form of polyaromatic compounds which may or may not be sulphur-containing, with a cetane index of 20 to 60 and with a nitrogen content of 50 to 5000 ppm by weight, said process being characterized in that it comprises the following steps:

   a hydrotreatment step a) in which said feed is hydrotreated under conditions that can produce a product (P) containing a quantity of sulphur that is 2 to 50 times less than that of the initial feed, said hydrotreatment being carried out at a partial pressure of hydrogen at the reactor outlet of 0.5 MPa (megapascals), such that the degree of dearomatization of the feed is at most 30%;

   a step b) for separating the product (P) into a product (P2) with an initial boiling point that is higher than the boiling point of the extraction solvent for the subsequent step c) and preferably at least more than 20°C, and into a product (P1) with an end point that is lower than the initial boiling point of the product P2;

   a liquid/liquid extraction step c) in which the product (P2) obtained in step b) is brought into contact, at an extraction temperature of at most 140°C, under polyaromatic compound extraction conditions, with a solvent or a solvent mixture (S1) that can extract at least a portion of the polyaromatic compounds contained therein, said solvent having an initial boiling point of less than the initial boiling point of the product (P2) obtained in step b), and during which an extract (E1) is recovered that is enriched in polyaromatic compounds, which may or may not be sulphur-containing, along with a raffinate (R1); and

   a step d) for recovering the solvent (S1) used in step c) from the raffinate (R1) obtained in step c) in which a product that is enriched in solvent (S1) and a product (Q1) that is depleted in solvent (S1) with an improved cetane index and containing less than 500 ppm by weight of sulphur are recovered;

   the process being further characterized in that at least a portion of the product (P1) resulting from step b) is freed from its light fraction and is mixed with at least a portion of the product (Q1) resulting from step d).
2. A process according to claim 1, in which the hydrogen pressure at the reactor outlet is 1 to 5 MPa, so that the degree of dearomatization of the feed is at most 15%.
3. A process according to claim 1 or claim 2, in which step c) is carried out under conditions that can obtain a raffinate (R1) containing at most 90% by weight of the total weight of aromatic hydrocarbons containing no sulphur atoms in their molecules that are present in the product (P2) obtained in step b).
4. A process according to one of claims 1 to 3, in which the extract (E1) obtained in step c) is sent to a zone for recovering the solvent (S1) used in step c) in which a product that is enriched in solvent (S1) and a product (Q2) that is depleted in solvent (S1) are recovered.
5. A process according to claim 4, in which the tail product (Q2) is sent to a hydrotreatment zone that is distinct from the hydrotreatment zone of step a), in which it undergoes hydrotreatment under conditions that can obtain a product (P3) with a sulphur content that is 0.3% by weight or less.
6. A process according to one of claims 1 to 5, in which the top product or products, obtained by separating the raffinate (R1) and possibly the extract (E1), enriched in solvent (S1), are recycled to the liquid/liquid extraction step c).
7. A process according to one of claims 1 to 6, in which the solvent is selected from the group formed by methanol, acetonitrile, monomethylformamide, dimethylformamide, dimethylacetamide, furfural, N-methylpyrrolidone and dimethylsulphoxide.
8. A process according to one of claims 1 to 7, in which the solvent used is an oxygen-containing solvent that does not contain nitrogen.
9. A process according to one of claims 1 to 8, in which in the hydrotreatment step a), in addition to the hydrocarbon feed to be treated, at least a portion of the tail product (Q2) obtained from the extract (E1) from step c) after separating the solvent (S1) is introduced into the hydrotreatment reactor.
10. A process according to one of claims 1 to 9, in which the hydrocarbon feed with an initial boiling point of at least 150°C and an end point of at most 500°C is sent to a distillation zone in which an overhead fraction (F1) with an end point of at least 250°C is separated from a tail fraction (F2) with an initial boiling point of at least 250°C, said process being characterized in that the fraction (F2) is treated using the process according to one of claims 1 to 9 and in that the fraction (F1) is sent to a hydrotreatment zone that is distinct from that of step a), from which a hydrotreated product (P') is recovered that is sent to a separation zone from which a fraction (P10) is recovered with an end point of less than 150°C, and a fraction (P20) with an initial boiling point that is higher than the end point of the fraction (P10).
11. A process according to claim 9 or claim 10, in which at least a portion of the fraction (P20) is mixed with the product (Q1) obtained in step d) or with a mixture of product (Q1) and product (P1) freed of its light fraction.

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