Hydrocracking method

Abstract

To provide a hydrocracking method that can reduce and / or eliminate formation of a polycyclic aromatic compound.SOLUTION: A method for hydrocracking a petroleum feedstock (1) comprises: a step of hydrocracking a feedstock; a step of performing an effluent separation to obtain a gaseous effluent (5) and a liquid effluent (9); a step of fractionating the liquid effluent (9) at a pressure P1 to obtain first distillates (13, 14) and a first residue (15); a step of recycling a first portion of the first residue (15) to at least one of the hydrocracking step; a step of rectifying a second portion (20) of the first residue (15) at a pressure P2 that is less than or equal to the pressure P1 to obtain a secondary distillate (23), a secondary residue (16) and a vapor stream (22); and a step of purging at least a portion of the secondary residue (16); and a step of recycling all or a portion of the secondary distillate (23) to at least one of the hydrocracking step.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for hydrocracking a petroleum feedstock. Hydrocracking of heavy petroleum fractions (also denoted under the term hydroconversion) is recalled to be a key method in refining that allows to produce lighter fractions such as gasoline, jet fuel and light gas oil from surplus and slightly upgradable heavy feedstocks, and refiners wish to adapt their production to demand. It is also possible to obtain a more refined residue that may constitute an excellent base for oil by a given hydrocracking method.

Background Art

[0002] Hydrocracking processes are generally used in refineries to convert hydrocarbon mixtures into readily upgradable products. However, they are customarily more used to convert heavier feedstocks (such as heavy synthetic or petroleum fractions, such as gas oil from vacuum distillation or effluents from Fischer-Tropsch units) into gasoline or naphtha, kerosene, gas oil. This method is also used to produce oil or to convert light fractions, such as gasoline, into lighter LPG (liquid petroleum gas) fractions.

[0003] To increase the conversion rate of the feedstock processed in a hydrocracking unit, a portion of the unconverted feedstock can be recycled, for example, to a reaction section that has already been passed through or to an independent reaction section. This leads to an undesired accumulation of polycyclic aromatic compounds formed in the reaction section during the cracking reaction in the recycle loop. These compounds poison the hydrocracking catalyst, which reduces the catalytic activity of the catalyst in question and the production cycle time of the unit. These compounds precipitate or deposit in the cold parts of the unit and may therefore cause failures.

[0004] These polycyclic or polynuclear aromatic compounds, therefore, contain multiple fused benzene rings. They are conventionally referred to as HPNA, which is an acronym for the term "Heavy Polynuclear Aromatics."

[0005] Typically, HPNAs contain at least four, and even more precisely, at least six, benzene rings in each molecule. Compounds containing fewer than six rings (e.g., derivatives of pyrene) are more readily hydrogenated and therefore less likely to poison catalysts. In conclusion, the present invention is more specifically interested in the most representative compounds of the family containing six or more aromatic rings, such as coronene (a compound containing 24 carbons), dibenzo(e,ghi)perylene (26 carbons), naphtho[8,2,1-abc]coronene (30 carbons), and ovalene (32 carbons), which are compounds that are most readily identifiable and quantifiable by, for example, chromatography.

[0006] Patent (Patent Document 1) proposes a first solution for processing HPNA using a hydrocracking method, which involves concentrating HPNA in the unconverted fraction to remove them and reduce the amount of residue to be purged, thereby improving the conversion rate. In the hydrocracking method, the flow is withdrawn as a side flow from the fractionation column between the feed tray and the bottom of the column. At least a portion of the flow constitutes a recycled flow. This flow may, in some cases, be stripped in a stripping column. The light fraction obtained after stripping is sent back to the fractionation column, and the heavy fraction derived from stripping is recycled to the hydrocracking process.

[0007] A patent application (Patent Document 2) proposes another solution using a hydrocracking method, in which the flow portion (residue) from the bottom of the fractionation column is stripped in a stripping column. The light fraction obtained after stripping is sent back to the fractionation column, and the heavy fraction derived from stripping is at least partially purged, with the rest of this fraction being recycled into the stripping column.

[0008] These methods resulted in improvements from the standpoint of reducing HPNA, but often caused damage to yield (and / or equipment or manufacturing costs).

[0009] The object of the present invention is to improve the hydrocracking method to reduce the formation of polycyclic aromatic compounds and / or remove these compounds. The present invention further aims to maintain the yield of hydrocracking to an upgradeable product at the same or similar level and / or not to significantly increase the equipment or manufacturing costs of the hydrocracking unit. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] European Patent Application Publication No. 3237577 Specification [Patent Document 2] International Publication No. 2012 / 052042 [Overview of the Initiative] [Means for solving the problem]

[0011] (Summary of the invention) The present invention relates, firstly, to a method for hydrocracking petroleum feedstock containing at least 10% by volume of a compound that boils at over 340°C, comprising the following steps: - (a) At least one step of hydrocracking the feedstock to obtain hydrocracking effluent; - (b) A process of separating the liquid / gas from the hydrocracking effluent to obtain gaseous and liquid effluent; - (c) A step of fractionating the liquid effluent, in at least one column, at a pressure P1 at the bottom of the column, particularly 0.2 to 0.4 MPa, to produce at least a first distillate and a first residue; - (d) A step of recycling the first portion of the first residue into a hydrocracking step and / or at least one of the hydrocracking steps; - (e) A step of rectifying a second portion of the first residue obtained in the fractionation step, in at least one column, at a pressure P2 at the top, where the pressure P2 is at least 0.05 MPa lower than the pressure P1, and obtaining at least a secondary distillate, a secondary residue, and a vapor stream; - (f) A step of purging at least some or all of the secondary residue; - (g) A step of recycling all or part, especially all, of the secondary distillate to at least one of a hydrocracking step or a hydrocracking step, after an optional gas separation step.

[0012] The method according to the present invention, therefore, firstly, does not directly recycle the flow originating from the rectification step to the fractionation step, but rather chooses to recycle it to the hydrocracking step, i.e., the reaction section where the flow will be transformed. Secondly, the method according to the present invention chooses to limit / lower the pressure in the rectification step relative to the pressure in the fractionation step. It has been found that reducing the rectification pressure in this way greatly improved the efficiency of the separation performed and actually concentrated polycyclic aromatic hydrocarbons in the secondary residue (unconverted fraction). Two highly advantageous conclusions stem from the following: firstly, this secondary residue, which is more concentrated in HPNA, can be purged and removed at least partially, or more completely, and at the same time, a larger proportion of HPNA in conventional hydrocracking methods is removed. Secondly, the distillate obtained in rectification can be sent back directly to hydrocracking because it contains little / no HPNA, which can reduce the efficiency of the hydrocracking catalyst. This makes it possible to increase the conversion rate of the feedstock, and therefore improve the hydrocracking yield of the upgradeable product compared to conventional hydrocracking methods and / or increase the cycle life of the catalyst.

[0013] The present invention has discovered that it is possible to modify the operating conditions (e.g., by adding a cooling system) to recover the upgradeable fraction in the secondary distillate, and therefore not to recycle the top vapor (since it no longer contains the upgradeable product). For this reason, the pressure can be reduced during rectification, which has the above-mentioned most important beneficial effect.

[0014] It can therefore be noted that the ability to reduce the pressure during rectification was possible, particularly because recycling from the rectification process to the fractionation process was abandoned (which is advantageous for recycling to the hydrocracking process). These two features are, therefore, linked and combined to achieve the desired effect on HPNA.

[0015] Another advantageous conclusion of the present invention should also be pointed out: since there is no longer any recycling of all or part of the secondary distillate and / or secondary residue from rectification into fractionation, it is possible to reduce the size of the plant, in particular by reducing the sizing of the fractionation column and by removing the equipment components that were required for recycling from the rectification column to the fractionation column.

[0016] HPNAs present during hydrocracking that specifically have at least six aromatic rings are the most resistant to the reactions used during hydrocracking, but the present invention has proven particularly effective in reducing the amount of such HPNAs. The present invention is very specifically advantageous in increasing the cycle life of the catalyst compared to conventional methods.

[0017] As seen above, advantageously, the method according to the present invention may avoid in the fractionation step (c) the step of recycling all or part of the secondary distillate and / or all or part of the secondary residue and / or all or part of the top vapor flow from the rectification step (e).

[0018] Preferably, the pressure P2 at the top of the column in the rectification step is at least 0.06 MPa, particularly at least 0.08 MPa, and preferably at most 400 kPa or at most 0.4 MPa lower than the pressure P1 at the bottom of the column in the fractionation step (c). It is found that the larger the P1-P2 pressure difference, the more effective the separation becomes and the higher the HPNA content in the secondary residue. Of course, the difference must persist reasonably, without the reduction in pressure P2 in the rectification step being too complex / expensive, as can be achieved on an industrial scale in a hydrocracking unit.

[0019] Within the scope of the situation of the present invention, two variants are possible: either the pressure P2 is chosen to be a value that remains above atmospheric pressure, or it is chosen to be lower than atmospheric pressure. This pressure P2 is measured / selected at the top of the column. In both scenarios, a pressure P2 of 133 Pa (1 mmHg) to 1.101 MPa, preferably 1333 Pa (10 mmHg) to 0.08 MPa (600 mmHg) is preferably chosen.

[0020] Preferably, the rectification step (e) comprises a distillation column, which column comprises a feed tray (one or more), optionally packing, and a withdrawal tray (one or more). - The first residue from the fractionation step (c) is, optionally, at least partially vaporized and fed to the column at at least one feed tray. - The secondary distillate is withdrawn from the column at a withdrawal tray. - The secondary residue is withdrawn at the bottom of the column. - The overhead vapor stream is cooled, which is effected in particular by a circulation loop or a condensation system.

[0021] Preferably, the rectification step is carried out using a stripping gas, for example one based on steam or hydrogen, which is injected at the injection point in the column, which injection point is advantageously located below the feed tray of the column.

[0022] By the method according to the invention, the HPNA concentration of the secondary distillate obtained in the rectification step is 500 ppm by weight or less, preferably 350 ppm by weight or less, very preferably 200 ppm by weight or less. The secondary distillate thus has a large deficiency of HPNA, which is the aim of the present invention.

[0023] This secondary distillate, by the method of the present invention, usually has an unconverted hydrocarbon content of at least 70% by weight, preferably at least 80% by weight, very preferably at least 90% by weight.

[0024] Preferably, the rectification step (e) comprises a distillation column, which includes one or more feed trays, and optionally one or more packing and extraction trays, and the step is carried out with a stripping gas, in particular in the form of water vapor or hydrogen, which is preferably injected below the feed trays or at least one of the feed trays of the column.

[0025] Preferably, in the rectification step (e), the temperature at which the first residue is fed is 250°C to 400°C.

[0026] The second portion of the first residue processed in the rectification step (e) preferably corresponds to a maximum of 50% by weight, particularly a maximum of 20% by weight, and preferably about 10% by weight, of the first residue obtained in the fractionation step (c). Therefore, by adjusting the amount of residue processed, it is possible to generate a secondary residue, the amount of which is sufficient to ensure purging of the unit and it is not necessary to recycle any part of it to the hydrocracking section.

[0027] Preferably, the first residue is divided into two parts, a first part and a second part, with the first part being recycled to the hydrocracking process and the second part being processed in the rectification process. Up to 50% by weight of this residue processed in rectification means that 100% of the balance, and therefore at least 50% of the residue, is recycled to hydrocracking. Thus, it is understood that preferred embodiments of the present invention mainly consist of recycling this residue.

[0028] When recycling the first portion of the first residue into hydrocracking, recycling can be performed directly or, if applicable, after the gas separation process.

[0029] In the purging step (f), preferably at least 20% by weight, particularly at least 40% by weight, preferably at least 60% by weight or at least 80% by weight of the secondary residue is purged. According to one embodiment, all (100%) of the secondary residue is purged. The amount of secondary residue that is not purged is preferably mixed with the secondary distillate and sent to the hydrocracking step.

[0030] Specifically, it has been demonstrated that the HPNA concentration in the secondary residue obtained by the method according to the present invention is generally greater than 1000 ppm by weight, preferably greater than 1500 ppm by weight, and even greater than 2000 ppm by weight: it has been demonstrated that HPNA is adequately concentrated in this residue and can be more easily removed from the method, in particular by purging the residue partially or completely.

[0031] According to the present invention, it is preferable to carry out the fractionation and / or rectification steps using a stripping gas, particularly one in the form of water vapor.

[0032] The pressure at which the stripping gas is injected during the fractionation process is preferably 0.2 to 0.4 MPa.

[0033] The pressure at which the stripping gas is injected during the rectification process is preferably 0.001 to 0.35 MPa. For rectification, the stripping gas may be hydrogen rather than water vapor.

[0034] The method according to the present invention comprises one or two hydrocracking steps (a), as known from hydrocracking methods. Preferably, the hydrocracking step, or at least one of the steps, especially if there are two steps, is preceded by a hydrotreating step (h). As is known, "hydrotreating" refers to all purification methods that enable the removal of various impurities contained in hydrocarbon feedstock through the action of hydrogen. Hydrotreating methods make it possible to remove impurities present in the feedstock through the action of hydrogen, which are, for example, nitrogen (referred to as hydrodenitrification), sulfur (referred to as hydrodesulfurization), oxygen (referred to as hydrodeoxygenation), and metal-containing compounds (referred to as hydrodemetallation) that can poison catalysts and cause operational problems downstream. Therefore, hydrotreating methods are actually generally the preceding steps of treating the feedstock by methods of the type of hydroconversion / hydrocracking.

[0035] When the method according to the present invention is a two-step hydrocracking, the operating conditions for each of these two steps are generally as follows: - Temperature: Over 200°C, often 250°C to 480°C, favorably 320°C to 450°C, preferably 330°C to 435°C. - Pressure: greater than 1 MPa, often 2-25 MPa, preferably 3-20 MPa. - Space velocity: 0.1~20h -1 Preferably 0.1 to 6 hours -1 , more preferably 0.2~3h -1 , - Amount of hydrogen introduced: The volume ratio of hydrogen volume (liters) to hydrocarbon volume (liters) is set to 80-5000 NL / L, usually 100-3000 NL / L.

[0036] The present invention also relates to any hydrocracking plant that performs the method according to the present invention.

[0037] The present invention also relates to a plant for hydrocracking petroleum feedstock containing at least 10% by volume of a compound that boils above 340°C, and comprises the following in sequence: - (a) At least one section for hydrocracking a feedstock to obtain hydrocracking effluent; - (b) At least one section for separating the hydrocracking effluent into liquid / gas to obtain gaseous and liquid effluent; - (c) A section for fractionating the liquid effluent; comprising at least one column, the pressure P1 at the bottom of the column being particularly 0.2 to 0.4 MPa, and producing at least a first distillate and a first residue; - (d) A line for recycling the first portion of the first residue into a hydrocracking section or one of the hydrocracking sections; - (e) A section for rectifying a second portion of the first residue obtained in the fractionation zone; comprising at least one column, with a pressure P2 at the top being at least 0.05 MPa lower than the pressure P1, to obtain at least a secondary distillate, secondary residue, and vapor flow; - (f) A section for purging at least some or all of the secondary residue; - (g) A line for recycling all or part, in particular all, of the secondary distillate after the gas separation section, or at least one of the hydrocracking sections.

[0038] The hydrocracking plant according to the present invention preferably does not include a line for recycling all or part of the secondary distillate and / or all or part of the secondary residue from the rectification zone (e) to the fractionation zone (c).

[0039] Preferably, the rectification zone (e) is equipped with a pressure control device, which is either a pressure regulator type if the pressure P2 is higher than atmospheric pressure, or a vacuum device type if the pressure P2 is lower than atmospheric pressure, and is particularly a liquid ring pump or discharger system.

[0040] According to one embodiment, this hydrocracking plant may include the following: - One or two hydrocracking sections; equipped with a feed material inlet line (1) and a hydrogen inlet line, - Fractionation section; comprising at least one distillation column equipped with trays, the column producing a first distillate and a first residue, - Section for rectifying a second portion of the first residue; comprising at least one distillation column, the distillation column comprising trays and / or packing, the column comprising: - at least one inlet line at at least one feed tray for the second portion of the first, at least partially vaporized residue; - at least one line connected to a pressure regulating or vacuum system; - at least one line for withdrawing at least the secondary distillate at the withdrawal tray; - at least one line at the bottom of the column for withdrawing the secondary residue; - A line by at least one case for stripping gas injection; the injection point is located below the flow supply tray. - A line for recycling a portion of the secondary residue derived from the fractionation section directly into the hydrocracking section or one of the hydrocracking sections. [Modes for carrying out the invention]

[0041] (List of drawings) Figure 1 shows a block diagram of a conventional hydrocracking method.

[0042] Figure 2 shows a block diagram of the hydrocracking method according to the first embodiment of the present invention.

[0043] Figure 3 shows a block diagram of the hydrocracking method according to the second embodiment of the present invention.

[0044] All of these drawings are highly schematic, and the scale and spatial distribution of the various devices represented are not necessarily respected. Reference numerals that are the same from one drawing to the next correspond to the same compound / line / device.

[0045] (Description of the embodiment) In the specification of the present invention, rectification is defined as distillation aimed at purifying a product by concentrating an undesirable compound in one of the fractions derived from distillation.

[0046] In the specification of this invention, the feedstocks are defined by their boiling point T5 as described below. The conversion rate of the feedstocks is defined relative to the cut point of the first residue. The unconverted fraction refers to the first residue. The converted fraction includes the fraction desired by the purifier.

[0047] For the purging portion, refer to the section where this method exits.

[0048] (Feed material) A wide variety of raw materials can be processed by hydrocracking. Generally, they contain compounds that boil above 340°C in amounts of at least 10% by volume, typically at least 20% by volume, and often at least 80% by volume.

[0049] The feedstock may be, for example, LCO (Light Cycle Oil; light gas oil derived from catalytic cracking units), atmospheric distillates, vacuum distillates, gas oil derived from, for example, direct distillation or conversion units of crude oil, for example, FCC (Fluid Catalytic Cracking) units, coking units (cokers) or vis-breaking units, and also feedstock originating from units for the extraction of aromatic compounds, derived from lubricating oil bases or solvent dewaxing of lubricating oil bases, or otherwise distillates originating from methods for desulfurization of fixed bed or boiling bed desulfurization or AR (atmospheric residue) and / or VR (vacuum residue) and / or hydroconversion of deasphalt oil. The feedstock may also be deasphalt oil, effluent from Fischer-Tropsch units, or any mixture of the above feedstocks. The above list is not limiting.

[0050] Generally, feedstocks have a boiling point T5 above 150°C (i.e., 95% of the compounds present in the feedstock have a boiling point above 150°C). In the case of diesel, the boiling point T5 is generally around 150°C. In the case of VGO (vacuum gas oil), the boiling point T5 is generally above 340°C, and even above 370°C. The feedstocks that can be used therefore span a wide range of boiling points. This range generally extends from diesel to VGO and through all possible mixtures with other feedstocks, such as LCO.

[0051] The nitrogen content of the feedstock processed in the hydrocracking method is typically over 500 ppm by weight, generally 500 to 10,000 ppm by weight, more commonly 700 to 4,500 ppm by weight, and even more commonly 800 to 4,500 ppm by weight.

[0052] The sulfur content of the feedstock processed in the hydrocracking process is typically 0.01% to 5% by weight, generally 0.2% to 4% by weight, and more generally 0.5% to 3% by weight. The feedstock may, in some cases, contain metals. The combined nickel and vanadium content of the feedstock processed in the hydrocracking process is preferably less than 10 ppm by weight, preferably less than 5 ppm by weight, and more preferably less than 2 ppm by weight. The asphaltene content is generally less than 3000 ppm by weight, preferably less than 1000 ppm by weight, and even more preferably less than 300 ppm by weight.

[0053] (Operating conditions) Operating conditions, such as temperature, pressure, hydrogen recycling ratio, or space rate per hour, are variable depending on the properties of the feedstock, the desired quality of the product, and the plants available to the refiner. The catalyst for hydrocracking / hydroconversion or hydrotreatment is generally brought into contact with the feedstock in the presence of hydrogen. - Temperature: Over 200°C, often 250°C to 480°C, favorably 320°C to 450°C, preferably 330°C to 435°C. - Pressure: greater than 1 MPa, often 2-25 MPa, preferably 3-20 MPa. - Space velocity: 0.1~20h -1 Preferably 0.1 to 6 hours -1 , more preferably 0.2~3h -1 , - Amount of hydrogen introduced: The volume ratio of hydrogen volume (liters) / hydrocarbon volume (liters) is set to 80-5000 NL / L, usually 100-3000 NL / L.

[0054] These operating conditions used in the hydrocracking process generally make it possible to achieve a conversion rate per pass to the conversion product (i.e., one having a boiling point lower than the residue cut point) of more than 15%, and more preferably 20% to 95%.

[0055] (Hydrogen cracking unit) (Embodiment) The hydrogen cracking / hydrogen conversion method using the catalyst according to the present invention spans a wide range of pressures and conversion ranges, from mild hydrogen cracking to high-pressure hydrogen cracking.

[0056] Mild hydrocracking is understood to mean hydrocracking that results in a moderate conversion rate: generally less than 40%, and is operated at low pressure, preferably 2 MPa to 9 MPa.

[0057] The hydrocracking catalyst may be used alone, in one or more fixed-bed catalyst beds, in one or more reactors, in a "one-step" hydrocracking scheme, with or without liquid recycling of the unconverted fraction, and possibly in combination with a hydropurification catalyst placed upstream of the hydrocracking catalyst.

[0058] Hydrocracking may be carried out under high pressure (at least 10 MPa).

[0059] Hydrocracking may be carried out by a "two-step" hydrocracking scheme according to the first modification, involving an intermediate separation between two reaction zones, in which a hydrocracking catalyst may be used in one or both reactors in a given step, and may be combined with a hydropurification catalyst placed upstream of the hydrocracking catalyst.

[0060] Hydrocracking may be carried out by a second modification, referred to as "one-step" hydrocracking. This modification generally involves, firstly, thorough hydrogenation and purification, the purpose of which is to perform thorough hydrogenation, denitrification, and desulfurization of the feedstock before it is delivered onto the actual hydrocracking catalyst, particularly when the catalyst contains zeolite. This thorough hydrogenation and purification of the feedstock results in only limited conversion of the feedstock to a lighter fraction. Any remaining insufficient conversion is completed on a more active hydrocracking catalyst.

[0061] The hydrocracking section may contain one or more identical or different catalyst beds. If the preferred product is a middle distillate, an amorphous basic solid, such as alumina or silica-alumina or a basic zeolite, may be used, optionally supplemented with at least one group VIII metal hydride, preferably at least one group VIB metal. These basic zeolites consist of silica, alumina, and one or more interchangeable cations, such as sodium, magnesium, calcium, or rare earth elements.

[0062] When gasoline is the primary desired product, the catalyst generally consists of a crystalline zeolite on which small amounts of group VIII metals, and more preferably group VIB metals, are deposited.

[0063] The zeolites that can be used may be natural or synthetic and may be selected from, for example, zeolite X, Y, or L, faujasite, mordenite, erionite, or chabasite.

[0064] Hydrocracking may be carried out in one or more boiling bed reactors, with or without liquid recycling of the unconverted fraction, and may be combined with a hydrogenation catalyst placed in a fixed bed or boiling bed reactor upstream of the hydrocracking catalyst. The boiling bed is operated by removing spent catalyst and adding fresh catalyst daily to maintain stable catalytic activity.

[0065] (protective floor) If the feedstock contains compounds of the resin and / or asphaltene type, it is advantageous to pre-pass the feedstock over a bed of catalyst or adsorbent different from the catalyst used for hydrocracking or hydrotreatment. The catalyst or protective bed used may be spherical (beads) or extruded. Any other shape may be used. Among the possible particle shapes, those that may be mentioned without limitation are hollow cylinders, hollow rings, Raschig rings, sawtooth hollow cylinders, breast-wall-shaped hollow cylinders with gunports, wheels known as penta rings, multi-hole cylinders, etc.

[0066] These catalysts may, in some cases, be impregnated with an active phase. Preferably, the catalyst is impregnated with a hydrogenation-dehydrogenation phase. Preferably, a CoMo or NiMo phase is used. These catalysts may exhibit macroporosity.

[0067] (Liquid / gas separation) The separator separates the liquids and gases present in the effluent leaving the hydrocracking unit. Any type of separator that enables this separation may be used, such as a flash vessel, a stripper, or even a simple distillation column.

[0068] Preferably, a series of separation vessels are used at various pressure and temperature levels in a manner known to those skilled in the art.

[0069] Advantageously, in a modified version of the present invention having two hydrocracking steps, some or all of the separation section may be common to two hydrocracking sections.

[0070] (fraction) The fractionation section typically consists of one or more columns containing multiple internal trays and / or packings. These columns are conventionally stripped with steam and, in some cases, include one or more reboilers to facilitate evaporation.

[0071] The fractionation section makes it possible to separate hydrogen sulfide (H2S) and light components of the effluent (methane, ethane, propane, butane, etc.), as well as hydrocarbon fractions with boiling points within the range of gasoline, kerosene, and gas oil, from the heavy fraction recovered at the bottom of the column, which is called the residue.

[0072] In some cases, the fractionation section includes a stripping tower used on all or part of the flow originating from the separation section.

[0073] The fractionation section includes at least one tower operated at a pressure P1 at its bottom. Preferably, this pressure P1 is 0.2 to 0.4 MPa.

[0074] (Sperm distillation) The rectification section generally includes one or more columns, preferably one column, and includes multiple internal trays and / or packings.

[0075] These columns are preferably stripped with steam and, optionally, include at least one reboiler to facilitate evaporation. This makes it possible to separate all or part of the residue derived from the fractionation section into different hydrocarbon fractions having boiling points within the range of gas oil and vacuum distillate, and a heavy fraction recovered at the bottom of the column, all or part of which is purged from the unit.

[0076] The rectification section includes at least one column operated by a pressure P2 at its top. The pressure P2 is at least 0.05 MPa less than or equal to the pressure P1.

[0077] Preferably, the rectification step is formed by a column having trays and / or packing containing at least five scientific stages. Preferably, the at least partially evaporated residue is fed into the column at at least one feed tray. Preferably, the secondary distillate is drawn off at a draw tray. This draw tray is preferably placed at at least two scientific stages above the residue injection point. Preferably, the secondary residue is drawn off at the bottom of the column, which is preferably placed at at least two scientific stages below the residue injection point.

[0078] Preferably, the column is equipped with a cooling system that enables internal reflux. Any means known to those skilled in the art (in particular, condensers, circulating reflux) may be considered.

[0079] Preferably, the top vapor fraction is discharged by a pressure regulating system or a vacuum system. Any means known to those skilled in the art (in particular, discharge systems, liquid ring pumps) may be used in the case of a vacuum system. This fraction is not sent to the fractionation section.

[0080] Preferably, the pressure P2 in the rectification section is at least 0.06 MPa, and more preferably at least 0.08 MPa, lower than the pressure P1 in the fractionation section. The lower pressure allows for maximizing the separation of HPNA in the residue and concentrating HPNA.

[0081] The pressure P2 in the rectification section may be selected to be above atmospheric pressure and controlled, for example, using a pressure regulating device. Alternatively, the pressure P2 in the rectification section may be selected to be below atmospheric pressure and obtained, for example, using a vacuum device. Preferably, P2 is 1 mmHg (133 Pa) or higher, much more preferably 10 mmHg (1333 Pa) or higher, and especially at most 0.08 MPa (600 mmHg).

[0082] Preferably, the rectification process is carried out using a stripping gas. This stripping gas consists of, for example, water vapor or hydrogen, and is injected at an injection point located below the feed tray.

[0083] (Drawing description) Figure 1 shows a diagram of a conventional hydrocracking method. The feedstock supplied through line (1) consists, among other things, of hydrocarbons and is mixed with hydrogen supplied through the recycling line (5) and / or the additional hydrogen line (6) via the compressor (7) and line (8). The feedstock / hydrogen mixture thus produced is sent to the hydrocracking section (2). The hydrocracking section is preceded by a hydrogenation section (not shown). This hydrogenation section generally contains one or more hydrogenation catalyst beds (these beds may also be included in the hydrocracking section).

[0084] This hydrocracking section (2) includes one or more fixed-bed or boiling-bed reactors.

[0085] If the hydrocracking section (2) includes one or more fixed-bed reactors, each reactor may include one or more catalyst beds for hydrocracking the hydrocarbon feedstock to yield lighter hydrocarbons.

[0086] If the hydrocracking section (2) includes one or more boiling bed reactors, the flow includes liquid, solid, and gas, and this flow circulates vertically through the reactor containing the catalyst bed. The catalyst in the bed is kept in a state of random movement in the liquid. The total volume of catalyst dispersed in the liquid is therefore greater than the volume of catalyst that is stationary. This technique is described in the literature.

[0087] A mixture of hydrocarbon liquid and hydrogen is passed through a bed of catalyst particles at a speed such that the particles move randomly and are therefore suspended in the liquid. The expansion of the catalyst bed in the liquid phase is controlled by the flow rate of the recycled liquid so that, at equilibrium, the majority of the catalyst does not exceed a given level in the reactor. The catalyst is in the form of extruded or beaded material, preferably with a diameter of 0.8 mm to 6.5 mm.

[0088] In the boiling bed process, large quantities of hydrogen gas and light hydrocarbon vapors rise through the reaction zone and then enter the catalyst-free zone. Some of the liquid originating from the catalyst zone is recycled to the bottom of the reactor after gas fraction separation, and some is removed from the reactor as a product, usually at the top of the reactor.

[0089] The reactor used in the boiling bed process is generally designed to have a central vertical recycling duct, which acts as a conduit for the recycling of liquid from a catalyst-free zone located above the boiling bed catalyst via a recycling pump. The recycling pump allows the liquid to be recycled back into the catalyst zone. Liquid recycling makes it possible to maintain temperature uniformity within the reactor and keep the catalyst bed suspended.

[0090] The effluent from the hydrocracking section (2) is sent to the separation zone (4) via line (3), which allows for the recovery of the gas fraction (5) on the one hand and the liquid fraction (9) on the other. The gas fraction (5) contains excess hydrogen that did not react in the hydrocracking reaction section (2). It is generally combined with fresh hydrogen arriving via line (6) and recycled as noted above.

[0091] The liquid fraction (9) is heated by any means (10), for example, a furnace and / or exchanger (not shown), at least partially evaporated, and then fed through a line (11) to a fractionation section (12).

[0092] The fractionation section (12) comprises one or more distillation columns and, in addition to trays and containers that allow for the separation of various upgradeable fractions (distillates) drawn out by lines (13) and (14), optionally includes other side flows. These fractions have boiling point ranges, for example, placed in the range of gasoline, kerosene, and gas oil. At the bottom of the column, unconverted, heavier fractions (residues) (15) are recovered.

[0093] A supply for injecting stripping gas may be provided via line (19). This line is located between a tray for feeding hydrocracking effluent via line (11) and a point for discharging the residue via line (15).

[0094] As shown in Figure 1, a portion of the residue (15) is recycled to the hydrocracking section (2) via line (18), while another portion is heated in a furnace or heat exchanger (17) and then sent to the rectification column (21), which allows for the recovery of vaporized distillate via line (29) on the one hand, and liquid residue via line (16) on the other. The vaporized distillate is recycled to the fractionation column (12) via line (29). The residue is discharged from the unit via line (16), constituting a purge. This purge (16) makes it possible to remove at least partially the HPNA compound, which would otherwise accumulate in the recycling loop without this purge. The line shown as a dotted line is optional: a feed may be provided to backflow only a portion of the residue leaving the rectification column (21), and the remainder (or the entire residue in the absence of this line) is purged.

[0095] Figure 2 shows a first embodiment of the method according to the present invention. Elements already described that are shared with Figure 1 will not be repeated, and efforts will be made to describe the differences from the scheme from Figure 1.

[0096] A portion of the residue (15) from the fractionation section (12) is fed to the rectification section (21) via line (20). Preferably, the residue (20) fed to the rectification section (21) is heated by any means, for example, a furnace and / or exchanger (not shown).

[0097] The rectification section (21) includes a distillation column and is equipped with trays and / or packings and also internal containers for separating various fractions: secondary distillates are withdrawn by line (23) as a side flow, and there may be other side flows if applicable.

[0098] At the top of the column, the vapor fraction is sent via line (22) to a pressure regulating system or a vacuum system (not shown). At the bottom of the column, what is recovered is the heavier fraction (secondary residue) that is abundant in HPNA, relative to the residue (15) originating from the fractionation section (12).

[0099] In the first modified example, the pressure in the rectification column (21) is maintained above atmospheric pressure by a pressure regulating device known to those skilled in the art.

[0100] In a second preferred modification, the pressure in the rectification column (21) is maintained below atmospheric pressure using a vacuum device. Any vacuum device known to those skilled in the art may be used. This may be a device consisting of a steam jet, a liquid ring pump, and / or a hydraulic jet, in particular. The use of a steam jet and / or a liquid ring pump is preferred, and more preferably, a liquid ring pump.

[0101] A supply for injecting stripping gas may be provided via line (26). Advantageously, the stripping gas is water vapor, preferably low-pressure water vapor, particularly at a pressure of 0.2 to 1.5 MPa. The injection line is located between the residue feed tray and a point for discharging secondary residue, with line (20) opening to the residue feed tray and the point opening to line (16). It is preferably in contact with a point for discharging secondary residue at the bottom of the column.

[0102] The side flow is open to line (23), which is located above the feeding zone (line (20)), and as a result the withdrawn flow has a low concentration of HPNA, less than 500 ppm by weight, preferably less than 350 ppm by weight, and very preferably less than 200 ppm by weight, and typically a high percentage of fractions that were not converted in the hydrocracking section are at least 70% by weight, preferably at least 80% by weight, and very preferably at least 90% by weight of the residue.

[0103] All or part of the flow withdrawn as a side flow (through line (23)) is recycled directly to the hydrocracking section (2). According to the present invention, the secondary residue (16) is not recycled to the rectification section (21) or the fractionation section (12). Preferably, it is completely purged.

[0104] Figure 3 shows a second embodiment of the method according to the present invention relating to two-step hydrocracking (not one-step hydrocracking as shown in Figure 2): This embodiment differs from the previous one in that the hydrocarbons in line (18) are not recycled to hydrocracking section (2). In fact, line (18) is recycled to another (second) hydrocracking section (32). This second hydrocracking section (32) is supplied with hydrogen via line (38).

[0105] The second hydrocracking section (32) has features similar to those previously described for the (first) hydrocracking section (2). The effluent from the second hydrocracking section (32) is sent to a separation section via line (33). Preferably, this separation section is separation section (4), which also receives the effluent (3) from the first hydrocracking section (2).

[0106] (Examples) (Example 1: Comparison) This embodiment is based on the configuration shown in Figure 1. The characteristics are reported in Table 1 below. Considering the configuration, it should be noted that flows (15) and (18) have exactly the same characteristics.

[0107] The fractionation of flow (11) in column (12) was simulated by programming via Aveva's PRO / II version 10.2 software. This was similar to the rectification of flow (20) in column (21). The physical and analytical properties of the resulting flow were simulated and compared with those of the actual sample.

[0108] The operating conditions for the tower used for the simulation are reported in Table 2 below.

[0109] From the characteristics of the inlet flow (11) of the fractionation tower (see Table 1), the PRO / II simulation was able to establish the characteristics of flows (15), (18), and (16), and also model the distribution of HPNA.

[0110] Based on these results, the configuration of the present invention was simulated. The results are disclosed in Table 1 below, which points to the flow characteristics / composition in the diagram from Figure 1.

[0111] [Table 1]

[0112] (1): Relative density ("specific gravity") Sp Gr = ρ sample at 20°C / ρH2O at 4°C, where ρ is g / cm³. 3 This is the density expressed as follows, in accordance with the ASTM D4052 standard (the same measurement method is used for all examples). (2): Yield = Flow rate / Flow rate of raw materials supplied to the unit (the same calculation for yield for all examples) Table 2 below clearly shows the operating conditions for the fractionation tower.

[0113] [Table 2]

[0114] Table 3 below clearly shows the operating conditions for the bottom stripper.

[0115] [Table 3]

[0116] Example 2 and the following examples illustrate the invention by the method shown in Figure 2 and have one hydrocracking section.

[0117] (Example 2: The present invention) Table 4 below provides the characteristics of flows (11), (16), and (18) according to the configuration of the present invention, derived from the PRO / II simulation in Figure 2. The operating conditions of the tower used for the simulation are reported in Tables 5 and 6.

[0118] [Table 4]

[0119] Table 5 below clearly shows the operating conditions for the fractionation tower.

[0120] [Table 5]

[0121] Table 6 clearly shows the operating conditions for the rectification column.

[0122] [Table 6]

[0123] Compared to the configuration of Comparative Example 1, this configuration allows for better concentration of HPNA during unit purging: 4514 ppm by weight in Example 2 compared to 1795 ppm by weight in Comparative Example 1, which is 2.5 times higher. This makes it possible to reduce the unit purging flow rate at the same HPNA content in the stream recycled to the hydrocracking process, and thus increase the unit conversion rate from 99.0% to 99.6% (conversion rate is defined as the percentage of feedstock converted to lighter products compared to the feedstock of the unit).

[0124] In the configuration from the prior art (Example 1), the vapor (flow (29)) from the rectification section is rich in hydrocarbons up to 67% by weight (the remainder being water in vapor form). Conversely, in the configuration according to the present invention (Example 2), the vapor (flow (22)) from the rectification section contains only traces of hydrocarbons up to 0.14% by weight after treatment by the cooling system.

[0125] In the configuration according to the present invention (Example 2), unlike the configuration from the prior art (Example 1), it is not necessary to recycle the top vapor from the rectification zone to the fractionation zone in order to prevent the loss of upgradeable products. The steam can be recovered, among other things, in the vacuum system of the rectification column.

[0126] (Example 3 (the present invention)) Table 7 below provides characteristics of flows (11), (16), and (18) according to another configuration of the present invention from Figure 2, derived from a PRO / II simulation. The operating conditions of the tower used for the simulation are reported in Tables 8 and 9 below.

[0127] [Table 7]

[0128] Table 8 clearly shows the operating conditions for the fractionation tower.

[0129] [Table 8]

[0130] Table 9 clearly shows the operating conditions for the rectification column.

[0131] [Table 9]

[0132] Compared to the conventional configuration (Example 1), this configuration (Example 3) makes it possible to reduce the concentration of HPNA in the recycled flow to the hydrocracking process: 424 ppm by weight (Example 3) compared to 1074 ppm by weight (Example 1), i.e., a reduction of at least 2.5 times. This makes it possible to reduce the amount of HPNA returned to the hydrocracking process at the same conversion rate, and therefore reduces catalyst poisoning by HPNA, thus increasing the catalyst cycle life.

[0133] In the configuration from the prior art (Example 1), the vapor (flow (29)) from the rectification section is rich in hydrocarbons up to 67% by weight. Conversely, in the configurations according to the present invention (Examples 2 and 3), the vapor (flow (22)) from the rectification section contains only traces of hydrocarbons up to 0.13% by weight. In the configuration according to the present invention, unlike in the configurations from the prior art, it is not necessary to recycle the top vapor from the rectification zone to the fractionation zone to prevent the loss of upgradeable products.

[0134] (Example 4: The present invention) Table 10 below provides characteristics of flows (11), (16), and (18) according to another configuration of the present invention from Figure 2, derived from PRO / II simulations. The operating conditions of the tower used for the simulations are reported in Tables 11 and 12.

[0135] [Table 10]

[0136] Table 11 clearly shows the operating conditions for the fractionation tower.

[0137] [Table 11]

[0138] Table 12 clearly shows the operating conditions for the rectification column.

[0139] [Table 12]

[0140] Compared to conventional configurations, this configuration makes it possible to reduce the concentration of HPNA in the recycled flow to the hydrocracking process: 996 ppm by weight in Example 4 compared to 1074 ppm by weight in Example 1, i.e., a reduction of approximately 8%. This makes it possible to reduce the amount of HPNA returned to the hydrocracking process at the same conversion rate, and therefore reduces catalyst poisoning by HPNA, thus increasing the catalyst cycle life.

[0141] While it is understood that Example 4 also yields favorable results, they are lower than those obtained in Examples 2 and 3, which is attributed to the selection of a rectification pressure P2 that has a smaller difference from the fractionation pressure P1.

[0142] In the configuration from the prior art (Example 1), the vapor (flow (29)) from the rectification section is rich in hydrocarbons up to 67% by weight. Conversely, in the configuration according to the present invention (Example 4), the vapor (flow (22)) from the rectification section contains only traces of hydrocarbons up to 0.04% by weight. In the configuration according to the present invention, therefore, unlike in the configuration from the prior art (Example 1), it is not necessary to recycle the top vapor from the rectification zone to the fractionation zone to prevent the loss of upgradeable products.

[0143] Examples 2-4 relate to embodiments of the present invention using a unit with a single hydrocracking section, as shown in Figure 2. The present invention provides the same or similar advantages to HPNA when applied to a hydrocracking unit having two consecutive hydrocracking sections, as shown in Figure 3.

[0144] In both cases, the present invention is highly flexible in its implementation. Therefore, it can present several possible options, particularly depending on the amount of residue containing HPNA being purged: - Handling the same amount of HPNA, but purging a smaller amount of the residue containing HPNA is advantageous in increasing the yield, or - Purging more (or even all) of the residue containing HPNA is advantageous for the service life of the hydrocracking catalyst at the same yield, or - Any intermediate option between two preceding choices. [Brief explanation of the drawing]

[0145] [Figure 1] This diagram shows a block diagram of the conventional hydrocracking method. [Figure 2] This diagram shows a block diagram of the hydrocracking method according to the first embodiment of the present invention. [Figure 3] This diagram shows a block diagram of the hydrocracking method according to a second embodiment of the present invention.

Claims

Process for hydrocracking a petroleum feedstock (1) containing at least 10% by volume of a compound boiling above 340 °C, comprising: - (a) at least one step of hydrocracking the feedstock to obtain a hydrocracked effluent; - (b) separating the liquid / gas of the hydrocracked effluent to obtain a gas effluent (5) and a liquid effluent (9); - (c) fractionating the liquid effluent (9) in at least one column (12) at a pressure P1 at the bottom of the column, in particular between 0.2 and 0.4 MPa, to produce at least a first distillate (13, 14) and a first residue (15); - (d) recycling a first part (18) of the first residue (15) to at least one of one hydrocracking step and / or a plurality of hydrocracking steps; - (e) rectifying a second part (20) of the first residue (15) obtained in the fractionation step in at least one column (21) at a top pressure P2: a pressure at least 0.05 MPa lower than the pressure P1, to obtain at least a secondary distillate (23), a secondary residue (16) and a vapour stream (22); - (f) purging at least part or all of the secondary residue (16); - (g) recycling all or part, in particular all, of the secondary distillate (23) after an optional gas separation step to a hydrocracking step or at least one of a hydrocracking step A process as claimed.

2. The process according to claim 1, characterized in that no recycling step is carried out in the fractionation step (c) with all or part of the secondary distillate (23) and / or all or part of the secondary residue (16) and / or all or part of the overhead vapour stream (22) originating from the rectification step (e).

3. The pressure P2 at the top of the column (21) in the rectification step is at least 0.06 MPa, in particular at least 0.08 MPa and preferably at most 0.4 MPa lower than the pressure P1 at the bottom of the column in the fractionation step (c). The method according to claim 1 or 2, characterized in that.

4. The pressure P2 at the top of the column (21) in the rectification step (e) is lower than atmospheric pressure, in particular between 133 Pa and 0.101 MPa, preferably between 1333 Pa and 0.08 MPa. The method according to claim 1 or 2, characterized in that.

5. The rectification step (e) comprises a distillation column (21), which is provided with one or more feed trays, optionally packing and one or more withdrawal trays, - The first residue (15) from the fractionation step (c) is optionally at least partially evaporated and fed at at least one feed tray of the column (21), - The secondary distillate (23) is withdrawn at the withdrawal tray from the column (21), - The secondary residue (16) is withdrawn at the bottom of the column, - The overhead vapor stream (22) is cooled, in particular by a circulation reflux or condensation system The method according to claim 1, characterized in that.

6. The rectification step (e) comprises a distillation column (21), which is provided with one or more feed trays, optionally packing and one or more withdrawal trays, and the step is carried out by means of a stripping gas, in particular in the form of steam or hydrogen, preferably injected below at least one of one feed tray or a plurality of feed trays of the column. The method according to claim 1, characterized in that.

7. In the rectification step (e), the temperature at which the first residue (15) is fed is between 250 °C and 400 °C. The method according to claim 1, characterized in that.

8. The second part (20) of the first residue (15) processed in the rectification step (e) corresponds to at most 50% by weight, in particular at most 20% by weight, preferably approximately 10% by weight of the first residue obtained in the fractionation step (c), according to the method of claim 1.

9. In the purge step (f), at least 20% by weight, in particular at least 40% by weight, preferably at least 60% by weight of the secondary residue (16) is purged, according to the method of claim 1.

10. The fractionation step and / or the rectification step are carried out by means of a stripping gas, in particular in the form of steam, according to the method of claim 1.

11. The stripping gas of the fractionation step is injected at a pressure of 0.2 to 0.4 MPa and / or the stripping gas of the rectification step is injected at a pressure of 0.001 to 0.35 MPa, according to the method of claim 10.

12. Comprising one or two hydrocracking steps (a), at least one of said steps being preceded by a hydrogenation treatment step (h), according to the method of claim 1.

13. A plant for hydrocracking a petroleum feedstock containing at least 10% by volume of compounds boiling above 340 °C, the plant continuously comprising: - (a) at least one section (2) for hydrocracking the feedstock (1) to obtain a hydrocracked effluent; - (b) at least one section (4) for separating the liquid / gas of the hydrocracked effluent to obtain a gas effluent (5) and a liquid effluent (9); - (c) a section for fractionating said liquid effluent; comprising at least one column (12), the pressure P1 at the bottom of the column being in particular 0.2 to 0.4 MPa, producing at least a first distillate (13, 14) and a first residue (15); - (d) A line for recycling the first part (18) of the first residue (15) to one of one hydrocracking section (2) or a plurality of hydrocracking sections (2). - (e) A section for rectifying the second part (20) of the first residue (15) obtained in the fractionation zone; including at least one column (21), and the pressure P2 at the top is at least 0.05 MPa lower than the pressure P1, and at least obtaining a secondary distillate (23), a secondary residue (16) and a vapor stream (22). - (f) A section for purging at least a part or all of the secondary residue (16). - (g) A line for recycling all or part, especially all, of the secondary distillate (23) to at least one of one hydrocracking section (2) or a plurality of hydrocracking sections (2) after an optional gas separation section.

14. The hydrocracking plant according to claim 13, characterized in that there is no line for recycling all or part of the secondary distillate (23) and / or all or part of the secondary residue (16) derived from the rectification zone (e) to the fractionation zone (c).

15. The rectification zone (e) is provided with a pressure control device, and the pressure control device is of either a pressure regulator type if the pressure P2 is higher than atmospheric pressure or a vacuum device type if the pressure P2 is lower than atmospheric pressure, and in particular, a system of a liquid ring pump or an ejector. The hydrocracking plant according to claim 13 or 14, characterized in that it is such.

16. The hydrocracking plant according to claim 13 or 14, characterized in that the hydrocracking plant includes the following: - One or two hydrocracking sections (2); provided with a feedstock inlet line (1) and a hydrogen inlet line (8). - Fractionation section (12); including at least one distillation column, the distillation column being equipped with trays, the column producing a first distillate and a first residue (15), - Section for rectifying a second portion (20) of the first residue (15); including at least one distillation column (21), the distillation column (21) being equipped with trays and / or packing, the column including: - at least one inlet line (20) for the second portion of the first, at least partially vaporized residue at at least one feed tray, - at least one line (22) connected to a pressure regulating or vacuum system, - at least one line (23) for withdrawing at least a secondary distillate at a draw tray, - at least one line (16) for withdrawing said secondary residue at the bottom of the column, - Optionally at least one line (26) for injecting stripping gas; the injection point being placed below the feed tray of the stream (20), - Optionally a line (18) for directly recycling the portion of said secondary residue originating from the fractionation section to one of one or more hydrocracking sections.

Images