A method for producing refined diesel oil

Abstract

This invention discloses a method for producing refined diesel oil. The method includes the following steps: (1) diesel feedstock and hydrogen enter reactor A, which is filled with a hydrodesulfurization catalyst to carry out a low-pressure hydrodesulfurization reaction; (2) the effluent from reactor A exchanges heat with the diesel feedstock through a heat exchanger, passes through a stripping tower, and then enters a fractionation system; (3) the diesel fraction obtained from step (2) enters reactor B, which is filled with an oxidation adsorption desulfurization catalyst to carry out an oxidation adsorption desulfurization reaction to obtain refined diesel oil. This invention achieves deep desulfurization by setting different reaction conditions for different types of sulfides, while optimizing the process flow, reducing the severity of the reaction, and improving the desulfurization efficiency.

Description

Technical Field

[0001] This invention belongs to the field of oil refining and chemical industry, and specifically relates to a method for producing ultra-low sulfur refined diesel. Background Technology

[0002] With the rapid pace of modernization, vehicle fuel consumption has increased dramatically. Sulfur-containing fuels inevitably produce large amounts of sulfides during combustion, which not only contribute to acid rain and environmental pollution but also poison catalysts in vehicle exhaust emission treatment systems. Therefore, producing ultra-clean fuels with low sulfur content has become an inevitable trend in the global refining industry. Currently, the fixed-bed hydrorefining technology widely used in refineries can upgrade diesel fuel to a sulfur content of <10ppm, meeting ultra-clean diesel standards, under conditions of 300–400℃, 3.0–8.0 MPa, and a relatively high hydrogen-to-oil ratio. The sulfides in diesel fractions are mainly organic sulfides, such as thiophene sulfur, benzothiophene sulfur, and dibenzothiophene. As the weight of the oil fraction increases, the content of substituted sulfides increases, such as dibenzothiophene and 4,6-dimethyldibenzothiophene. As the composition becomes heavier and the complexity of the sulfide molecules increases, the difficulty of their removal also increases accordingly. Substituents such as methyl groups produce steric hindrance, which is not conducive to the contact between the sulfur atoms on the sulfide molecules and the active center of the catalyst, thus greatly reducing the desulfurization activity of the catalyst.

[0003] Currently, the most common method for producing ultra-low sulfur diesel is to use catalysts with excellent hydrotreating performance. Under high pressure and hydrogen-to-oil ratios, the removal of sulfides is achieved through the hydrodesulfurization reaction pathway. Higher pressure and temperature favor this reaction pathway. However, using the hydrodesulfurization pathway to produce ultra-clean diesel significantly increases the hydrotreating depth, greatly increasing the hydrogen consumption of the unit and raising the production cost. Diesel oxidation-adsorption deep desulfurization technology, through the use of additives, can selectively and deeply oxidize organic sulfur in diesel through active sites on the material surface at 1 atm and temperatures of 25–50°C. The adsorption sites on the adsorption material surface can highly selectively adsorb the oxides of organic sulfur, thereby further achieving deep desulfurization of diesel to obtain ultra-clean diesel that meets the China VI standard or even the zero-sulfur (1 ppm-S) standard. However, for diesel products with high sulfur content, the adsorption desulfurization method is difficult due to the presence of more small molecule sulfides. In addition, the more sulfides are treated, the more additives are consumed in the oxidation adsorption desulfurization process, and the regeneration cycle of the oxidation adsorption desulfurization catalyst is significantly shortened, which increases the processing cost and energy consumption of the oil.

[0004] CN102311759A discloses a diesel hydrodesulfurization method, which employs a catalyst-graded loading method. Under hydrorefining process conditions, this method utilizes a mixed loading of Mo-Co and Mo-Ni catalysts with varying loading gradients to maximize the hydrodesulfurization performance of the catalysts. However, this method offers limited options for removing different types of sulfides from the oil. When higher sulfide removal requirements are needed, the only solution is to increase the reaction severity, such as increasing reaction pressure or decreasing reaction space velocity, thereby increasing the hydrogen and energy consumption of the unit.

[0005] CN102465028A discloses a method for hydrodesulfurization of diesel fuel. This method uses two reactors. The first reactor is a conventional hydrorefining reactor to remove most of the sulfur and nitrogen impurities. The second reactor is loaded with a desulfurization catalyst for secondary desulfurization. However, because the second reactor is loaded with a Mo-Co type catalyst, it is difficult to remove 4,6-dimethyl-dibenzothiophene sulfides due to steric hindrance. Furthermore, as the weight of the oil fraction increases, the content of large molecular weight sulfides in the oil also increases, and the difficulty of removing the corresponding sulfides increases accordingly. Therefore, this method is difficult to meet the requirements for processing low-quality diesel fuel or producing ultra-low sulfur diesel products. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for producing refined diesel fuel. By combining two reactors and setting different reaction conditions for different types of sulfides, this invention achieves deep desulfurization, while optimizing the process flow, reducing the severity of the reaction, and improving desulfurization efficiency.

[0007] This invention provides a method for producing refined diesel oil, comprising the following steps:

[0008] (1) Diesel feedstock and hydrogen enter reactor A, which is filled with hydrodesulfurization catalyst to carry out low-pressure hydrodesulfurization reaction.

[0009] (2) The effluent from reactor A exchanges heat with diesel feedstock through a heat exchanger, and then enters the fractionation system after passing through a stripping tower;

[0010] (3) The diesel fraction distilled in step (2) enters reactor B, which is filled with an oxidation adsorption desulfurization catalyst to produce an oxidation adsorption desulfurization reaction and obtain refined diesel.

[0011] Furthermore, the properties of the diesel feedstock are as follows: distillation range of 180–365°C, sulfur content ≤15000 μg / g, preferably 5000–12000 μg / g, nitrogen content ≤800 μg / g, preferably 100–500 μg / g, and polycyclic aromatic hydrocarbon content ≤40 wt%, preferably 15 wt%–35 wt%. The diesel feedstock is one or more of straight-run diesel, catalytic diesel, and coking diesel.

[0012] Furthermore, reactor A is a gas-phase hydrogenation reactor. The operating conditions of reactor A are as follows: pressure 0.1–4.0 MPa, preferably 1.0–3.0 MPa; temperature 260–400 °C, preferably 300–380 °C; hydrogen-to-oil volume ratio 100–800, preferably 200–600; and volume hourly space velocity (VHSV) 0.5–3.0 h⁻¹. -1 Preferably 0.8–1.5 h -1 The preferred operating conditions are: pressure 1.0–3.0 MPa, temperature 300–380 °C, hydrogen-to-oil volume ratio 200–600, and volume hourly space velocity (VHSV) 0.8–1.5 h⁻¹. -1 .

[0013] Furthermore, the hydrodesulfurization catalyst packed in reactor A is a catalyst with alkyl transfer desulfurization function. The catalyst comprises a support and active metal components. The support is alumina, and the active metal components are Mo and Co. By mass of the catalyst, the support content is 55%–93%, the active metal component Mo (calculated as oxide) has a mass content of 5%–30%, and the active metal component Co (calculated as oxide) has a mass content of 2%–15%. The specific surface area of ​​the catalyst is ≥200 m². 2 / g, with a pore volume of ≥0.30mL / g. For example, the Mo-Co type FHUDS-5 catalyst developed by FRIPP.

[0014] Furthermore, the effluent from reactor A undergoes heat exchange with the diesel feedstock, after which the temperature of the effluent from reactor A decreases to 100–300°C, preferably 150–200°C.

[0015] Furthermore, the effluent from reactor A, after heat exchange with the diesel feedstock, enters the stripping system to remove the hydrogen sulfide and ammonia generated in the reaction. The material after hydrogen sulfide removal enters the fractionation system.

[0016] Furthermore, the naphtha fraction distilled from the fractionation system can be used as ethylene cracking feedstock or gasoline blending component. Preferably, the diesel fraction distilled from the fractionation system first passes through a condenser before entering reactor B, ensuring that the temperature of the condensed diesel fraction reaches the reaction temperature of reactor B.

[0017] Further, reactor B is loaded with an oxidative adsorption desulfurization catalyst. The oxidative adsorption desulfurization catalyst uses alumina and / or silica as a support, and one or more of Group IB, Group IIV, Group VIB, and Group VIII as the active metal, preferably a combination of zinc, copper, cerium, and molybdenum. Based on the mass of the oxidative adsorption desulfurization catalyst, the support content is 70wt%–85wt%, and the active metal content (based on oxides) is 15wt%–30wt%, preferably with a ZnO:CuO:CeO2:MoO3 mass ratio of 3–4:1–2:1–2:1. The specific surface area of ​​the oxidative adsorption desulfurization catalyst is 150–450 m². 2 / g, pore volume is ≥0.25mL / g.

[0018] The aforementioned oxidative adsorption desulfurization catalyst is regenerable and reusable. Regeneration can be performed externally by removing the catalyst and then thermally regenerating it at 400°C under aerobic conditions for 2–6 hours. This removes the adsorbed sulfides from the catalyst and restores its oxidative adsorption desulfurization activity. Alternatively, regeneration can be performed internally by passing hot nitrogen through the reacted catalyst bed to recover the oil, followed by introducing hot air into the catalyst bed in reactor B and thermally regenerating it at 400°C for 2–6 hours. This allows the catalyst's adsorbent material to be recycled.

[0019] Furthermore, the operating conditions of reactor B are as follows: reaction temperature of 10–80°C, preferably 20–60°C, pressure of 0–0.5 MPa, and volumetric hourly space velocity of 0.5–2.0 h⁻¹. -1 .

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] (1) The process method of the present invention can provide different desulfurization methods for different types of sulfides in diesel feedstock, so as to achieve the purpose of precise desulfurization. Reactor A is filled with a specific Mo-Co type catalyst with alkyl transfer, which has good direct desulfurization activity. At the same time, the catalyst can utilize the characteristics of alkyl transfer at higher reaction temperatures to transfer sulfides with steric hindrance, thereby achieving the removal of sulfides. Reactor B is filled with an oxidative adsorption desulfurization catalyst, which can adsorb and oxidize to remove organic sulfur in oil under normal temperature conditions, and achieve the oxidative adsorption removal of macromolecular sulfides. It can remove macromolecular sulfides in oil without consuming hydrogen. By organically combining the two desulfurization methods, the hydrogen consumption generated by the ultra-deep desulfurization reaction can be significantly reduced.

[0022] (2) Since the reaction temperature of reactor A is higher and the temperature of reactor B is lower, by setting a heat exchanger between the two reactors, the high-temperature effluent of reactor A can be exchanged with the diesel feedstock, so as to achieve rational use of energy. After heat exchange, the material can be directly fed into the stripping tower to remove impurities such as hydrogen sulfide and ammonia from the effluent of reactor A, so as to avoid the hydrogen sulfide and ammonia in the material affecting the oxidative adsorption desulfurization reaction. At the same time, the naphtha fraction and diesel fraction are separated by the fractionation tower, so that the large molecular sulfides that have not been removed can be mainly enriched in the diesel fraction, and then fed into reactor B for oxidative adsorption desulfurization. This can improve the adsorption selectivity of the oxidative adsorption desulfurization catalyst for large molecular sulfides, which is conducive to the oxidative adsorption desulfurization reaction.

[0023] (3) By combining different desulfurization methods, this invention can achieve ultra-deep desulfurization of diesel fuel under more lenient operating conditions. Reactor A has a lower reaction pressure and does not require high- or low-pressure separators. After heat exchange with the diesel feedstock, the effluent from reactor A can be directly fed into the stripping tower, which reduces equipment investment, reduces reaction severity, and improves reaction efficiency, thereby achieving the goal of energy saving and consumption reduction. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the process flow for producing refined diesel oil in Embodiments 1-3 of the present invention;

[0025] Among them, 1-diesel feedstock and hydrogen, 2-reactor A, 3-effluent from reactor A, 4-heat exchanger, 5-stripping tower, 6-stripping steam, 7-diversion system, 8-naphtha fraction, 9-diesel fraction, 10-condenser, 11-reactor B, 12-refined diesel. Detailed Implementation

[0026] The present invention will be further described below with reference to embodiments, but it should be understood that the scope of protection of the present invention is not limited to the embodiments. In the present invention, unless otherwise expressly stated, percentages and contents are all expressed by mass.

[0027] The following is combined Figure 1 The process flow of the present invention will be described in detail.

[0028] Diesel feedstock and hydrogen 1 enter reactor A 2, where a desulfurization reaction occurs, yielding reactor A effluent 3. This effluent then enters heat exchanger 4, where hydrogen sulfide and ammonia are removed by stripping tower 5, before entering fractionation system 7 for fractionation, yielding naphtha fraction 8 and diesel fraction 9. Diesel fraction 9 is condensed by condenser 10 and then enters reactor B 11, where it undergoes oxidation and adsorption desulfurization to obtain refined diesel product 12.

[0029] Examples 1-3

[0030] according to Figure 1The process flow employs two 100mL fixed-bed hydrogenation reactors connected in series, namely reactor A and reactor B. A hydrogen stripping system, a fractionation system, and a condenser are installed between reactors A and B. Reactor A is a gas-phase hydrogenation reactor, packed with 50mL of Mo-Co type catalyst a. The support for catalyst a is alumina, and the active metal components are Mo and Co. The support content is 74%, the active metal Mo content (based on oxides) is 21%, and the active metal Co content (based on oxides) is 5%. Reactor B is loaded with 50 mL of oxidative adsorption desulfurization catalyst b. The preparation method of oxidative adsorption desulfurization catalyst b is as follows: 2.0 g of zinc nitrate, copper nitrate, cerium nitrate, and ammonium molybdate are dissolved in deionized water. ZnO:CuO:CeO2:MoO3 is prepared in a mass ratio of 4:1:1:1. The prepared precursor solution is impregnated onto an alumina support. After impregnation, it is dried at 120℃ for 4 h and calcined at 420℃ for 6 h to obtain oxidative adsorption desulfurization catalyst b. The total mass of active metal oxides is 15%, and the remainder is the support. The outlet of reactor B is refined diesel fuel.

[0031] The feedstock was conventional three-line straight-run diesel. Catalyst properties are shown in Table 1, diesel feedstock properties are shown in Table 2, and reaction process conditions and results are shown in Table 3.

[0032] Comparative Example 1

[0033] A conventional fixed-bed hydrogenation reactor was used, and the reaction was carried out under high temperature and low pressure conditions. 100 mL of Mo-Co type catalyst a was loaded, and low-temperature separation and stripping processes were set up after the reactor. Hydrogen gas, after being desulfurized, was pressurized and recycled using a circulating hydrogen compressor. The properties of the diesel feedstock and catalyst were the same as in Examples 1-3, and the reaction process conditions and results are shown in Table 3.

[0034] Comparative Example 2

[0035] A conventional diesel fixed-bed hydrotreating process was adopted, with one hydrotreating reactor loaded with 100 mL of Mo-Co type catalyst a. After the reactor, normal high-precision, low-precision, and stripping processes were followed. Hydrogen gas, after being desulfurized, was pressurized and recycled using a circulating hydrogen compressor. The properties of the diesel feedstock and catalyst were the same as in Examples 1-3, and the reaction process conditions and results are shown in Table 3.

[0036] Comparative Example 3

[0037] A conventional diesel fixed-bed hydrotreating process was adopted, with two hydrotreating reactors connected in series. Reactor A was loaded with 50 mL of Mo-Co type diesel hydrotreating catalyst a, and reactor B was loaded with 50 mL of Mo-Ni type diesel hydrotreating catalyst c. After the reactors, normal high-precision separation, low-precision separation, and stripping processes were implemented. Hydrogen gas, after being desulfurized, was pressurized and recycled using a circulating hydrogen compressor. The properties of the feedstock and catalyst were the same as in the previous example. The reaction process conditions and results are shown in Table 3.

[0038] Comparative Example 4

[0039] A 100 mL fixed-bed hydrogenation reactor was used, and 50 mL of oxidation adsorption desulfurization catalyst b was packed in it. Catalyst b was prepared using the methods in Examples 1 to 3. The specific process conditions and results are shown in Table 3.

[0040] Table 1. Physicochemical properties of catalysts

[0041] Catalyst number a b c Active metals Mo-Co <![CDATA[ZnO / CuO / CeO2 / MoO3]]> Mo-Ni <![CDATA[MoO3,wt%]]> 21 24 CoO, wt% 5 - - NiO, wt% - - 5 shape Clover cylindrical Clover Diameter, mm 1.2 1.2 1.2 <![CDATA[Specific surface area, m 2 ·g -1 > 208 310 180 <![CDATA[Pore volume, mL·g -1 > 0.35 0.52 0.35

[0042] Table 2 Properties of Crude Oil

[0043] Oil properties <![CDATA[Density (20 °C), g·cm -3 > 0.838 Distillation range, ℃ 175～360 <![CDATA[Total S, μg·g -1 > 11400 <![CDATA[N,μg·g -1 ]]> 127 Polycyclic aromatic hydrocarbons, wt% 18.3

[0044] Table 3 Hydrogenation process conditions and results

[0045]

[0046]

[0047] The specific embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for producing refined diesel oil, characterized in that, Includes the following steps: (1) Diesel feedstock and hydrogen enter reactor A, which is filled with hydrodesulfurization catalyst to carry out low-pressure hydrodesulfurization reaction; (2) The effluent from reactor A exchanges heat with the diesel feedstock through a heat exchanger, and then enters the fractionation system after passing through a stripping tower; (3) The diesel fraction distilled in step (2) enters reactor B, which is filled with an oxidation adsorption desulfurization catalyst to undergo an oxidation adsorption desulfurization reaction and obtain refined diesel. Reactor A is a gas-phase hydrogenation reactor; the hydrodesulfurization catalyst packed in reactor A is a catalyst with alkyl transfer desulfurization function; the catalyst with alkyl transfer desulfurization function includes a support and an active metal component, the support is alumina, and the active metal components are Mo and Co. Based on the mass of the catalyst, the content of the support is 55%~93%, the mass content of the active metal component Mo (based on oxides) is 5%~30%, and the mass content of the active metal component Co (based on oxides) is 2%~15%. The specific surface area of ​​the catalyst is ≥200 m². 2 / g, pore volume is ≥0.30mL / g; The operating conditions for reactor A are as follows: pressure 0.1~3.0 MPa, temperature 260~400℃, hydrogen-to-oil volume ratio 100~800, and volume hourly space velocity 0.5~3.0 h⁻¹. -1 ; The properties of the diesel feedstock are as follows: distillation range 180~365℃, sulfur content ≤15000μg / g, nitrogen content ≤800μg / g, and polycyclic aromatic hydrocarbon content ≤40wt%; The operating conditions for reactor B are as follows: reaction temperature 10~80℃, pressure 0~0.5MPa, and volumetric hourly space velocity 0.5~2.0h. -1 ; The oxidative adsorption desulfurization catalyst uses alumina and / or silica as a support, and one or more of Group IB, Group IIV, Group VIB, and Group VIII as active metals. Based on the mass of the oxidative adsorption desulfurization catalyst, the support content is 70wt%~85wt%, the active metal content (based on oxides) is 15wt%~30wt%, and the specific surface area of ​​the oxidative adsorption desulfurization catalyst is 150~450 m². 2 / g, pore volume is ≥0.25mL / g.

2. The method according to claim 1, characterized in that, The properties of the diesel feedstock are as follows: S content is 5000~12000μg / g, N content is 100~500μg / g, and polycyclic aromatic hydrocarbon content is 15wt%~35wt%.

3. The method according to claim 1, characterized in that, The operating conditions for reactor A are as follows: pressure 1.0~3.0 MPa, temperature 300~380℃, hydrogen-to-oil volume ratio 200~600, and volume hourly space velocity 0.8~1.5 h⁻¹. -1 .

4. The method according to claim 1, characterized in that, The effluent from reactor A undergoes heat exchange with diesel feedstock, after which the temperature of the effluent from reactor A decreases to 100~300℃.

5. The method according to claim 4, characterized in that, After heat exchange, the temperature of the effluent from reactor A decreases to 150~200℃.

6. The method according to claim 1, characterized in that, The naphtha fraction distilled from the fractionation system is used as ethylene cracking feedstock or gasoline blending component.

7. The method according to claim 1, characterized in that, The diesel fraction distilled from the fractionation system first passes through a condenser and then enters reactor B, so that the temperature of the condensed diesel fraction reaches the reaction temperature of reactor B.

8. The method according to claim 1, characterized in that, The operating conditions for reactor B are as follows: reaction temperature is 20~60℃.

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