A method for deep desulfurization of diesel

Abstract

The present invention discloses a method for deep desulfurization of diesel. The method comprises the following steps: (1) diesel feedstock and hydrogen enter a first reactor for gas phase desulfurization reaction; (2) the effluent of the first reactor enters a second reactor after being pressurized, wherein the gas phase component is discharged upward from the second reactor, and after being treated with desulfurized hydrogen, a hydrogenated light component is obtained, and the liquid phase component continues to undergo desulfurization reaction downward, and the obtained hydrogenated heavy component is discharged from the bottom of the second reactor; (3) the hydrogenated heavy component is mixed with the hydrogenated light component to obtain a low-sulfur diesel product. The method can achieve the effect of deep desulfurization.

Description

Technical Field

[0001] The invention belongs to the field of oil refining and chemical industry, and specifically relates to a method for deep desulfurization of diesel. Background Art

[0002] At present, diesel hydrorefining mainly includes two technologies: fixed bed three-phase hydrogenation and liquid phase circulation two-phase hydrogenation. Among them, fixed bed three-phase hydrogenation is a gas-liquid-solid three-phase reaction of liquid raw materials and gaseous hydrogen on the surface of solid catalyst. In the fixed bed three-phase hydrogenation reactor, there is a large excess of hydrogen. First, to ensure that there is enough driving force for the gas phase to continuously penetrate the liquid film on the surface of the catalyst to reach the catalyst surface for reaction. Second, to reduce the partial pressure of hydrogen sulfide and ammonia generated in the reactor to avoid its influence on deep desulfurization and dearomatization reactions. Third, to keep the active metals on the surface of the catalyst in a reduced state and exert a high reaction activity. After the hydrogen flowing out of the reactor passes through the high-pressure separator, it needs to be cooled to below 50°C to further remove hydrogen sulfide, and then it is pressurized and circulated back to the reactor inlet by the circulating hydrogen compressor. The cooling process of hydrogen consumes a lot of energy. In addition, the circulating hydrogen compressor accounts for a high proportion of investment in the entire process flow, and there are some defects. The diesel liquid phase circulation two-phase hydrogenation technology solves the above problems well. This technology dissolves hydrogen in the raw oil before entering the reactor, so the material entering the reactor is a liquid raw material dissolved with hydrogen, and a liquid-solid two-phase reaction occurs on the catalyst surface, which reduces the mass transfer resistance in the hydrogen diffusion process and improves the reaction efficiency. In addition, since the hydrogen in the product flowing out of the reactor has been consumed in large quantities in the reaction, there is no excess hydrogen, so the product can directly enter the distillation tower after low fractionation, eliminating the need for hydrogen cooling and the setting of a circulating hydrogen compressor, greatly reducing the energy consumption and construction investment of the device. In recent years, it has achieved widespread industrial application and has been expanded to the fields of aviation kerosene hydrogenation and reforming oil hydrogenation. However, when the liquid phase circulation two-phase hydrogenation technology is applied to the diesel hydrogenation process, due to the large hydrogen consumption, in order to better promote the dissolution of hydrogen, a high-efficiency hydrogen mixer is required, and the investment cost is relatively high; in addition, the hydrogen partial pressure in the liquid phase hydrogenation process is low, and the accumulation of hydrogen sulfide in the system will affect the deep desulfurization, so the diesel liquid phase circulation two-phase hydrogenation technology is relatively less adaptable to inferior diesel. There are also cases where fixed-bed three-phase hydrogenation is combined with liquid-phase circulating two-phase hydrogenation, but such use loses the advantages of low energy consumption and low investment of liquid-phase circulating two-phase hydrogenation.

[0003] CN111073688A discloses a method for deep desulfurization and hydrogenation of diesel, which is to load at least two levels of sulfided hydrogenation catalysts by gradation, and the length of the metal active phase lamellae increases step by step and the number of lamellae decreases step by step along the logistics direction of each level of sulfided hydrogenation catalyst, so as to achieve a reaction in which the molecular size and structure of the reactants in each section match the structure of the active phase. However, this method is difficult to achieve deep desulfurization by only optimizing the desulfurization activity of the catalyst. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a method for deep desulfurization of diesel fuel. The method of the present invention can achieve the effect of deep desulfurization.

[0005] The present invention provides a method for deep desulfurization of diesel, comprising the following steps:

[0006] (1) Diesel feedstock and hydrogen enter the first reactor for gas phase desulfurization reaction;

[0007] (2) The effluent from the first reactor is pressurized and enters the second reactor, wherein the gaseous component is discharged upward from the second reactor, and after being treated with hydrogen desulfurization, a hydrogenated light component is obtained, and the liquid component continues to undergo desulfurization reaction downward, and the obtained hydrogenated heavy component is discharged from the bottom of the second reactor;

[0008] (3) The hydrogenated heavy component is mixed with the hydrogenated light component to obtain a low-sulfur diesel product.

[0009] Furthermore, the first reactor is filled with a first catalyst, and the second reactor is filled with a second catalyst or a first catalyst and a second catalyst. The first catalyst is a Mo-Ni type hydrodesulfurization catalyst. The second catalyst is a Mo-Co type hydrodesulfurization catalyst.

[0010] Furthermore, in the second reactor, when the first catalyst and the second catalyst are loaded at the same time, the loading volume ratio of the first catalyst to the second catalyst is 1: 3 to 3: 1. The first catalyst and the second catalyst can be loaded in layers or mixed, preferably in layers, with the first catalyst loaded upstream of the second catalyst, so that the liquid phase component contacts the first catalyst first and then contacts the second catalyst.

[0011] Furthermore, the first reactor and the second reactor are both fixed bed reactors. The second reactor is preferably a fixed bed reactor provided with a flash zone.

[0012] Furthermore, a flash zone is provided in the second reactor, and no catalyst is loaded in and above the flash zone. A reaction zone is provided below the flash zone, in which a second catalyst or a first catalyst and a second catalyst are loaded. The effluent from the first reactor is pressurized and fed into the flash zone of the second reactor. The obtained gaseous components are discharged upward from the second reactor, and the obtained liquid components are contacted with the catalyst downward to carry out a desulfurization reaction. The obtained product, i.e., the hydrogenated heavy component, is discharged from the bottom of the second reactor.

[0013] Furthermore, the properties of the diesel feedstock are as follows: initial distillation point is 160-200°C, final distillation point is 320-400°C, S content is ≯20000μg / g, preferably 12000-18000μg / g, N content is ≯1000μg / g, and polycyclic aromatic hydrocarbons content is ≯40wt%.

[0014] Furthermore, the S content of the diesel feedstock can be exemplified but not limited to: 12000μg / g, 12500μg / g, 16000μg / g, 17000μg / g, 18000μg / g, etc., the N content can be exemplified but not limited to: 600μg / g, 700μg / g, 800μg / g, 900μg / g, 1000μg / g, etc., and the polycyclic aromatic hydrocarbons content can be exemplified but not limited to: 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, etc.

[0015] Furthermore, the diesel feedstock may be one or more of straight-run diesel, catalytic diesel, coker diesel, ebullated-bed residue hydrogenated diesel, and the like.

[0016] Furthermore, the first reactor is a gas phase hydrogenation reactor. The operating conditions of the first reactor are as follows: pressure 0.1-2.8 MPa, preferably 0.5-2.0 MPa, temperature 300-400°C, preferably 330-380°C, hydrogen-to-oil volume ratio 100-1000, preferably 200-600, volume space velocity 0.5-3.0 h -1 , preferably 0.8~2.0h -1 .

[0017] Furthermore, the Mo-Ni type hydrodesulfurization catalyst generally adopts an alumina-based carrier, and based on the mass of the catalyst, the content of Mo in terms of molybdenum oxide is 15wt% to 30wt%, and the content of Ni in terms of nickel oxide is 2wt% to 5wt%. The catalyst may also contain an auxiliary component, such as at least one of phosphorus, silicon, boron, magnesium, fluorine, etc., and the mass content in the catalyst is generally less than 6wt%. For example, the Mo-Ni type diesel hydrodesulfurization catalyst developed by Sinopec Fushun Petrochemical Research Institute (FRIPP), such as FHUDS-6, FHUDS-8, and FHUDS-10.

[0018] Furthermore, the effluent of the first reactor is pressurized by a compressor, which may be a conventional commercial compressor, such as a reciprocating or centrifugal compressor, wherein the pressurization can ensure normal feeding of the second reactor and meet the operating pressure requirements of the second reactor.

[0019] Furthermore, the operating conditions of the second reactor are as follows: pressure 1.0-10.0 MPa, preferably 2.0-7.0 MPa, more preferably 3.5-6.0 MPa, temperature 100-400°C, preferably 220-380°C, volume space velocity 0.1-3.0 h -1 , preferably 0.5~1.0h -1 .

[0020] Furthermore, the pressure of the second reactor is at least 1.5 MPa higher than the pressure of the first reactor, preferably 2.0 to 6.0 MPa higher, and more preferably 3.0 to 5.0 MPa higher.

[0021] Furthermore, the Mo-Co type hydrodesulfurization catalyst generally adopts an alumina-based carrier, and based on the mass of the catalyst, the content of Mo in terms of molybdenum oxide is 15wt% to 30wt%, and the content of Co in terms of cobalt oxide is 2wt% to 6wt%. The catalyst may also contain an auxiliary component, such as at least one of phosphorus, silicon, boron, magnesium, fluorine, etc., and the mass content in the catalyst is generally less than 6wt%. For example, the Mo-Co type diesel desulfurization catalyst developed by Sinopec Fushun Petrochemical Research Institute (FRIPP), such as FHUDS-5 and FHUDS-7.

[0022] Furthermore, the gaseous components discharged from the second reactor are cooled by a heat exchanger and then enter a high-pressure separator for separation to obtain hydrogenated light components and hydrogen containing hydrogen sulfide.

[0023] Furthermore, the gaseous component discharged from the second reactor is cooled to 100-200°C, preferably 120-150°C, after passing through a heat exchanger.

[0024] Furthermore, the hydrogenated heavy component is mixed with the hydrogenated light component and then enters a stripping and fractionation system to obtain a low-sulfur diesel product, wherein the purpose of the fractionation is mainly to cut out the naphtha fraction.

[0025] Furthermore, in the low-sulfur diesel product, the sulfur content is below 10 μg / g, preferably 2 to 6 μg / g.

[0026] Compared with the prior art, the method of the present invention has the following advantages:

[0027] (1) The method of the present invention controls the reaction conditions of the first reactor not only for gas phase desulfurization, but also for better coordination with the second reactor, thereby being more conducive to subsequent deep desulfurization.

[0028] (2) Compared with conventional fixed-bed diesel three-phase hydrogenation technology, the method of the present invention can save the heat exchange and compressor settings in the hydrogen circulation process, significantly reducing energy consumption and construction investment. The entire reaction system of the present invention has low energy consumption, improved safety, and reduced requirements for reactor materials. From the perspective of chemical reaction rate, the present invention is a combination of gas phase desulfurization and liquid phase desulfurization reactions, and the reaction rate is significantly improved.

[0029] (3) Compared with the diesel liquid phase circulation two-phase hydrogenation technology, the method of the present invention can avoid the high-cost means of dissolving gas phase hydrogen in liquid phase feedstock oil through forced baffled remixing or permeation membrane. The catalyst in the first reactor is used to disperse the feedstock and hydrogen, so that the oil and hydrogen in the effluent are in a uniform gas phase state. By increasing the pressure under high temperature conditions, the hydrogen and oil are promoted to be liquefied and dissolved simultaneously, which greatly reduces the hydrogen dissolution cost. In addition, the dissolution rules of hydrogen and hydrogen sulfide in oil are different, that is, under high temperature conditions, the solubility of hydrogen is high and the solubility of hydrogen sulfide is low, so that the hydrogen concentration in the liquefied liquid phase is high and the hydrogen sulfide concentration is low. When entering the subsequent second reactor for liquid phase reaction, the inhibitory effect of hydrogen sulfide on deep desulfurization in traditional liquid phase hydrogenation technology can be well avoided.

[0030] (4) The method of the present invention combines the gas phase desulfurization in the first reactor with the liquid phase desulfurization in the second reactor, optimizes the reaction conditions and reaction types of each reactor, reduces the severity of the reaction as a whole, and simplifies the process flow. Gas phase desulfurization is used as a pretreatment for liquid phase desulfurization. The easily reactive sulfur-containing substances in the diesel feedstock are removed under low pressure conditions. The unreacted macromolecules in the material flowing out of the first reactor are liquefied by a small pressure increase of the compressor and enter the second reactor as a liquid phase component for liquid phase deep hydrogenation refining and alkyl transfer reaction to achieve the purpose of deep desulfurization. Since the first reactor is a large hydrogen-to-oil ratio condition and hydrogen is highly dissolved in the oil product during the compressor pressure increase process, there is no need to add hydrogen dissolving equipment before entering the second reactor. Moreover, since the small molecular substances have already undergone hydrogenation reaction in the first reactor, the pressure increase process does not require high pressure, and only needs to reach the medium and low pressure conditions that can liquefy the macromolecules, thereby reducing the severity of the liquid phase desulfurization reaction in the second reactor. In addition, since the small molecules have been removed in the first reactor, the concentrations of polycyclic aromatic hydrocarbons and large molecular sulfur in the macromolecules entering the second reactor are higher, which is conducive to the chemical equilibrium moving to the right and improving the chemical reaction conversion rate. In the effluent of the first reactor, the reacted small molecules are not liquefied during the compressor pressurization process. They are liquefied by heat exchange and condensation cooling before entering the high-pressure separator. Such liquefaction means are conducive to the separation of hydrogen and raw materials, and a large amount of hydrogen can be recovered for recycling, thereby improving the utilization rate of hydrogen. The liquefied small molecules are hydrogenation light components, which can enter the subsequent stripping and fractionation system after mixing with the hydrogenation heavy components to obtain low-sulfur diesel products. The entire reaction system of the present invention does not require a hydrogen compressor in a conventional fixed-bed three-phase hydrogenation reaction system and a circulating oil pump in a conventional liquid-phase circulation two-phase hydrogenation reaction system, thereby reducing investment costs, simplifying the process flow, improving reaction efficiency, and reducing reaction severity. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic diagram of the deep desulfurization process of diesel feedstock of the present invention;

[0032] Among them, diesel feedstock and hydrogen-1; the first reactor-2, the effluent of the first reactor-3; the compressor-4; the second reactor-5; the hydrogenated heavy component-6; the gas phase component-7; the heat exchanger-8; the high-pressure separator-9; the hydrogen containing hydrogen sulfide-10; the hydrogenated light component-11; the stripping and fractionation system-12; the low-sulfur diesel product-13. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with embodiments, but it should be understood that the protection scope of the present invention is not limited by the embodiments.

[0034] In the present invention, unless otherwise explicitly stated, percentages and contents are all based on mass.

[0035] Combine the following Figure 1 The process flow of the present invention is described in detail.

[0036] The diesel feedstock and hydrogen 1 enter the first reactor 2, undergo a gas phase hydrogenation reaction, and obtain the first reactor effluent 3; enter the compressor 4, and after being pressurized by the compressor 4, enter the second reactor 5, wherein the liquid phase component enters the reaction zone downward to continue to undergo a desulfurization reaction to obtain a hydrogenated heavy component 6, and the gas phase component 7 is discharged upward from the second reactor and enters the heat exchanger 8, and then enters the high-pressure separator 9 to be separated into a hydrogenated light component 11 and hydrogen containing hydrogen sulfide 10, and the hydrogenated heavy component 6 is mixed with the hydrogenated light component 11 and enters the stripping and fractionation system 12 to finally obtain a low-sulfur diesel product 13.

[0037] Examples 1-3

[0038] Use Figure 1 Schematic diagram of the process. Two 100mL fixed-bed hydrogenation reactors are connected in series, namely the first reactor and the second reactor. A conventional power reciprocating compressor is set between the reactors. The first reactor is a gas phase desulfurization reactor, loaded with 50mL Mo-Ni type diesel hydrodesulfurization catalyst A, and the second reactor is a liquid phase desulfurization reactor. 25mL Mo-Ni type diesel hydrodesulfurization catalyst A and 25mL Mo-Co type diesel desulfurization catalyst B are loaded from top to bottom in the reaction zone. A gas phase outlet is set above the second reactor, which is connected to the heat exchanger (cooled to 130°C) and the high-pressure separator in turn. The liquid phase outlet pipeline at the bottom of the second reactor is connected to the liquid phase outlet pipeline at the bottom of the high-pressure separator, and enters the subsequent stripping and fractionation system together to cut out the naphtha fraction to obtain a low-sulfur diesel product.

[0039] The mixed oil of straight wood, coke wood and catalytic wood is used as the raw oil. The properties of the catalyst are shown in Table 1, the properties of the raw oil are shown in Table 2, and the reaction process conditions and results are shown in Table 3.

[0040] Example 4

[0041] Use Figure 1 Schematic diagram of the process. Two 100mL fixed-bed hydrogenation reactors are connected in series, namely the first reactor and the second reactor. A conventional power reciprocating compressor is set between the reactors. The first reactor is a gas phase desulfurization reactor, loaded with 50mL Mo-Ni type diesel hydrodesulfurization catalyst A, and the second reactor is a liquid phase desulfurization reactor, and 50mL Mo-Co type diesel desulfurization catalyst B is loaded from top to bottom in the reaction zone. A gas phase outlet is set above the second reactor, which is connected to the heat exchanger (cooled to 130°C) and the high-pressure separator in turn. The liquid phase outlet pipeline at the bottom of the second reactor is connected to the liquid phase outlet pipeline at the bottom of the high-pressure separator, and enters the subsequent stripping and fractionation system together to cut out the naphtha fraction to obtain a low-sulfur diesel product.

[0042] The mixed oil of straight wood, coke wood and catalytic wood is used as the raw oil. The properties of the catalyst are shown in Table 1, the properties of the raw oil are shown in Table 2, and the reaction process conditions and results are shown in Table 3.

[0043] Comparative Example 1

[0044] A conventional diesel liquid phase circulation two-phase hydrogenation process was adopted, and a liquid phase hydrogenation reactor was set up, which was reactor 2. 75mL Mo-Ni type diesel hydrodesulfurization catalyst A and 25mL Mo-Co type diesel desulfurization catalyst B were graded and filled in the reactor. A commercially available high-efficiency hydrogen mixer was used before the reactor, and the refined diesel was circulated back to the hydrogen mixer by a circulating oil pump, with a circulation ratio of 1. The uncirculated refined diesel entered a low-pressure separator, and then entered a stripping and fractionation device to obtain a diesel product. The raw materials and catalyst properties were the same as those in Example 1, and the reaction process conditions and results are shown in Table 3.

[0045] Comparative Example 2

[0046] A gas phase hydrogenation process was adopted, and a gas phase hydrogenation reactor was set up, which was reactor 1. 75 mL Mo-Ni type diesel hydrodesulfurization catalyst A and 25 mL Mo-Co type diesel desulfurization catalyst B were graded and loaded in reactor 1. A heat exchanger and a condenser were set after reactor 1, and the unliquefied gas phase could be recycled after desulfurization of hydrogen. The liquefied component then entered the stripping and fractionation equipment to obtain a diesel product. The raw materials and catalyst properties were the same as those in Example 1, and the reaction process conditions and results were shown in Table 3.

[0047] Comparative Example 3

[0048] A conventional fixed bed three-phase hydrogenation reactor is used, which is reactor 1. 75mL Mo-Ni type diesel hydrodesulfurization catalyst A and 25mL Mo-Co type diesel desulfurization catalyst B are graded and loaded in the reactor. After the reactor, high-fraction, low-fraction, stripping and other devices are conventionally set. After hydrogen sulfide is removed, the hydrogen is pressurized and circulated by a circulating hydrogen compressor. The properties of the raw materials and catalyst are the same as those in Example 1, and the reaction process conditions and results are shown in Table 3.

[0049] Comparative Example 4

[0050] The same hydrogenation process as in Example 1 was adopted, with the only difference being that a high-power reciprocating compressor was installed between the first and second reactors and the process conditions were controlled. The reaction process conditions and results are shown in Table 3.

[0051] Table 1 Physicochemical properties of catalysts

[0052] Catalyst No. A B Brand FHUDS-8 FHUDS-5 Active Metals Mo-Ni Mo-Co <![CDATA[MoO 3 ,wt%]]> 24 21 NiO or CoO, wt% 5.0 3.0 shape Shamrock Shamrock Diameter, mm 1.2 1.2 <![CDATA[Specific surface area, m 2 / g]]> 180 180 Pore ​​volume, mL / g 0.35 0.35

[0053] Table 2 Raw oil properties

[0054] Oil properties <![CDATA[Density (20 °C), g / cm 3 > 0.87 Distillation range, ℃ 180～370 S, μg / g 12130 N, μg / g 769 Aromatics, wt% 60.2 PAHs, wt% 27.5 Monocyclic aromatic hydrocarbons, wt% 32.7 Cetane number 32

[0055] Table 3 Hydrogenation process conditions and results

[0056]

[0057]

[0058] As can be seen from Table 3, compared with the traditional liquid phase circulation two-phase hydrogenation technology, the pressure of this reaction system is significantly reduced. At the same time, due to the increase of hydrogen dissolution in the liquefaction process of the effluent of the first reactor, the dissolution of hydrogen sulfide in the oil product is reduced, the reaction environment of the second reactor is optimized, the impact on deep desulfurization is avoided, and better ultra-deep desulfurization effect can be achieved. At the same time, since gas phase desulfurization is used as a pretreatment for liquid phase desulfurization, the hydrogen consumption of the second reactor is reduced, and the hydrogen mixing equipment and circulating oil pump can be omitted.

[0059] Compared with gas-phase hydrogenation alone, although diffusion limitations are reduced and the chemical reaction rate is higher under gas-phase reaction conditions, large molecular reactants are not easily adsorbed on the catalyst surface under low pressure. Therefore, it is difficult to achieve the ideal desulfurization reaction effect using a gas-phase hydrogenation reactor alone.

[0060] Conventional fixed-bed three-phase hydrogenation technology requires harsh reaction temperature and pressure conditions to achieve a refined diesel sulfur content of less than 10 μg / g, and the removal effect of polycyclic aromatic hydrocarbons is also worse than that of the present invention.

[0061] In Comparative Example 4, due to the excessively high hydrogen-to-oil ratio of the gas phase reactor, the partial pressure of the feedstock oil was reduced, which affected the adsorption of sulfides on the catalyst surface, resulting in an unsatisfactory desulfurization effect. At the same time, the difficulty of liquefying the effluent of the gas phase reactor after gasification increased significantly, and even at a reaction pressure of 10 MPa, it was difficult to completely liquefy the heavy components, affecting the removal effect of macromolecular sulfur.

Claims

1. A method for deep desulfurization of diesel, characterized in that: The method comprises the following steps: (1) Diesel feedstock and hydrogen enter the first reactor for gas phase desulfurization reaction; wherein, the catalyst in the first reactor disperses the feedstock and hydrogen, so that the oil and hydrogen in the effluent are in a uniform gas phase state, and the hydrogen and oil are simultaneously liquefied and dissolved by pressurizing under high temperature conditions; (2) The effluent from the first reactor is pressurized and enters the second reactor, wherein the gaseous component is discharged upward from the second reactor, and after being treated with hydrogen sulfide removal, a hydrogenated light component is obtained, and the liquid component continues to undergo desulfurization reaction downward, and the obtained hydrogenated heavy component is discharged from the bottom of the second reactor; (3) The hydrogenated heavy component is mixed with the hydrogenated light component to obtain a low-sulfur diesel product; The operating conditions of the first reactor are as follows: pressure 0.1-2.8 MPa, temperature 300-400°C, hydrogen-to-oil volume ratio 100-1000, volume space velocity 0.5-3.0 h -1 ; The operating conditions of the second reactor are as follows: pressure 3.5~10.0MPa, temperature 100~400℃, volume space velocity 0.1~3.0h -1 .

2. The method according to claim 1, characterized in that: The first reactor is filled with a first catalyst, and the second reactor is filled with a second catalyst or a first catalyst and a second catalyst; the first catalyst is a Mo-Ni type hydrodesulfurization catalyst; the second catalyst is a Mo-Co type hydrodesulfurization catalyst.

3. The method according to claim 2, characterized in that: In the second reactor, when the first catalyst and the second catalyst are loaded simultaneously, the loading volume ratio of the first catalyst to the second catalyst is 1:3 to 3:

1.

4. The method according to claim 1, characterized in that: The first reactor and the second reactor are both fixed bed reactors; the second reactor is a fixed bed reactor provided with a flash zone.

5. The method according to claim 1, characterized in that: The properties of the diesel feedstock are as follows: initial distillation point is 160-200° C., final distillation point is 320-400° C., S content is ≯20000 μg / g, N content is ≯1000 μg / g, and polycyclic aromatic hydrocarbon content is ≯40wt%.

6. The method according to claim 5, characterized in that: The S content of the diesel feedstock is 12000-18000 μg / g.

7. The method according to claim 1, characterized in that: The operating conditions of the first reactor are as follows: pressure of 0.5-2.0 MPa, temperature of 330-380°C, hydrogen-to-oil volume ratio of 200-600, volume space velocity of 0.8-2.0 h -1 .

8. The method according to claim 1, characterized in that: The operating conditions of the second reactor are as follows: pressure of 3.5-7.0 MPa, temperature of 220-380°C, volumetric space velocity of 0.5-1.0 h -1 .

9. The method according to claim 1, characterized in that: The operating conditions of the second reactor are as follows: the pressure is 3.5~6.0MPa.

10. The method according to claim 1 or 8 or 9, characterized in that: The pressure of the second reactor is at least 1.5 MPa higher than the pressure of the first reactor.

11. The method according to claim 10, characterized in that: The pressure of the second reactor is at least 2.0-6.0 MPa higher than the pressure of the first reactor.

12. The method according to claim 10, characterized in that: The pressure of the second reactor is at least 3.0-5.0 MPa higher than the pressure of the first reactor.

13. The method according to claim 1, characterized in that: The gaseous components discharged from the second reactor are cooled to 100-200°C by a heat exchanger and then enter a high-pressure separator for separation to obtain hydrogenated light components and hydrogen containing hydrogen sulfide.

14. The method according to claim 1, characterized in that: The sulfur content of the low-sulfur diesel product is below 10 μg / g.

15. The method according to claim 14, characterized in that: The sulfur content of the low-sulfur diesel product is 2-6 μg / g.

Images