A method for deep dearomatization of low-quality diesel

Abstract

The present invention discloses a method for deep dearomatization of low-quality diesel. The method comprises the following steps: (1) low-quality diesel feedstock and hydrogen enter a first reactor to carry out a 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 is subjected to a liquid phase hydrogenation dearomatization reaction downward to obtain a hydrogenated heavy component which is discharged from the bottom of the second reactor; (3) the hydrogenated heavy component is mixed with the hydrogenated light component to obtain a refined diesel product. The method of the present invention can achieve the effect of deep dearomatization, and at the same time, it also simplifies the process flow, reduces the reaction severity, and improves the chemical reaction efficiency in general.

Description

Technical Field

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

[0002] The emissions from the combustion of sulfur and polycyclic aromatic hydrocarbons in diesel will pollute the atmospheric environment on which humans depend for survival. For this reason, countries are constantly accelerating the pace of upgrading diesel quality standards. The National V diesel standard implemented in China in 2017 requires a sulfur content of no more than 10 mg / kg. In the National VI diesel quality standard proposed in 2019, polycyclic aromatic hydrocarbons are required to be ≯11%, and in the National VIB standard to be implemented in 2023, polycyclic aromatic hydrocarbons are required to be ≯5%. At the same time, China's demand for processing secondary processed raw materials is also increasing day by day. Poor-quality raw materials such as catalytic diesel have an aromatic content of up to 60%, which puts higher requirements on catalyst activity. However, from the perspective of the reaction mechanism of deep desulfurization and deep dearomatization, there are significant differences in the requirements for the reaction environment between the two. For desulfurization reactions, the removal of small molecular sulfur mainly follows the direct desulfurization route, that is, hydrogenation desulfurization. Large molecular sulfides with low reaction activity follow the hydrodesulfurization reaction route, that is, first hydrogenation of the aromatic ring and then hydrogenation desulfurization. Therefore, in the relatively low temperature and high hydrogen partial pressure environment in the upper part of the reactor, the main reactions are the hydrogenolysis of small molecular sulfides (endothermic) and the hydrogenation of aromatic ring-containing substances (largely exothermic). In the lower part of the reactor, the accumulation of heat and hydrogen sulfide makes the reaction environment high temperature and low hydrogen partial pressure. This reaction environment is conducive to the further hydrogenolysis of large molecular sulfides that have been hydrogenated, but it is very unfavorable for the further saturation of aromatics because it is severely limited by the thermodynamics of aromatic hydrogenation. Especially at the end of the reaction, the activity of the catalyst decays, and there is no better operating method except heating, which will further affect the dearomatization effect. In addition to the different requirements of the reaction environment between the two, the competitive adsorption of aromatics on the catalyst surface also inhibits deep desulfurization, making it difficult for traditional hydrogenation technology to take into account the dual requirements of ultra-deep desulfurization and efficient saturation of aromatics. The necessity and urgency of upgrading diesel cleaning technology are further highlighted.

[0003] For existing technologies, deep dearomatization on the basis of deep desulfurization can be achieved by using the existing catalyst system to reduce the reaction space velocity, that is, reducing the processing volume or increasing the number of reactors, but this is not economically reasonable. The other is to use a two-stage process technology, after conventional hydrogenation, the generated oil is stripped to remove hydrogen sulfide and then enters the precious metal hydrogenation reactor, which will also greatly increase the catalyst cost and process complexity, and is still not the best solution.

[0004] CN108085058B discloses a method for deep dearomatization of hydrocarbon oil. The method uses relatively mild temperature and pressure conditions to make the raw oil and hydrogen pass through a highly dispersed Pt-Pd / Al2O3 catalyst, and the gas phase after the reaction is compressed and recycled, and the liquid phase is a low-aromatic product. However, the Pt-Pd / Al2O3 hydrogenation catalyst is mainly suitable for dearomatization of low-sulfur diesel raw materials, and the effect of desulfurization and dearomatization on low-quality diesel is not ideal.

[0005] CN109926067A discloses a platinum-palladium-cobalt ternary metal hydrogenation dearomatization catalyst and its preparation method. The method adopts a step-by-step impregnation method of active metal precursors, so that the utilization rate of the prepared catalyst platinum palladium noble metal is high, the synergistic catalytic ability is strong, and the introduction of platinum palladium leads to the enhancement of the aromatics hydrogenation performance of non-precious metal cobalt. However, the catalyst is still aimed at hydrocarbon oil after sulfur-containing compounds have been basically removed to avoid the influence of hydrogen sulfide on the deep dearomatization of precious metals, and cannot achieve the desulfurization and dearomatization of inferior diesel. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention provides a method for deep dearomatization of inferior diesel. The method of the present invention can achieve the effect of deep dearomatization, and at the same time, it also simplifies the process flow as a whole, reduces the severity of the reaction, and improves the efficiency of the chemical reaction.

[0007] The present invention provides a method for deep dearomatization of low-quality diesel, comprising the following steps:

[0008] (1) Low-quality diesel feedstock and hydrogen enter the first reactor to undergo gas-phase desulfurization reaction;

[0009] (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 subjected to dehydrogenation treatment to obtain a hydrogenated light component, and the liquid component is subjected to liquid phase hydrogenation and dearomatization reaction downward to obtain a hydrogenated heavy component and is discharged from the bottom of the second reactor;

[0010] (3) The hydrogenated heavy component is mixed with the hydrogenated light component to obtain a refined diesel product.

[0011] Further, the properties of the inferior diesel are as follows: the initial boiling point is 150-200°C, the final boiling point is 320-400°C, the S content is ≯20000μg / g, preferably ≯15000μg / g, the N content is ≯1000μg / g, preferably ≯800μg / g, and the polycyclic aromatic hydrocarbon content is ≯50wt%. For example, the S content of the inferior diesel can be exemplified but not limited to: 8000μg / g, 9000μg / g, 10000μg / g, 11500μg / g, etc., the N content can be exemplified but not limited to: 500μg / g, 600μg / g, 700μg / g, etc., and the polycyclic aromatic hydrocarbon content can be exemplified but not limited to: 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, etc.

[0012] Furthermore, the low-quality diesel may be one or more of straight-run diesel, catalytic diesel, coker diesel, ebullated-bed residue hydrogenated diesel, and the like.

[0013] 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.

[0014] 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. 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 subjected to dearomatization reaction downward. The obtained products, i.e., hydrogenated heavy components, are discharged from the bottom of the second reactor.

[0015] Furthermore, the operating conditions of the first reactor are as follows: pressure 0.1-2.8 MPa, preferably 0.5-2.0 MPa, temperature 260-400°C, preferably 320-390°C, hydrogen-to-oil volume ratio 100-900, preferably 300-700, volume space velocity 0.5-3.0 h -1 , preferably 0.8~2.0h -1 .

[0016] Further, the catalyst loaded in the first reactor can be a conventional catalyst with hydrodesulfurization function, preferably a Mo-Co type hydrodesulfurization catalyst. Generally, an alumina-based carrier is used. 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 can 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 deep desulfurization catalyst developed by Sinopec Fushun Petrochemical Research Institute (FRIPP). For example, FHUDS-5, FHUDS-7, etc.

[0017] 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.

[0018] Furthermore, the operating conditions of the second reactor are as follows: pressure 2.0-8.0 MPa, preferably 3.0-6.0 MPa, temperature 200-400°C, preferably 260-360°C, volume space velocity 0.1-3.0 h -1 , preferably 0.5~1.0h -1 .

[0019] Furthermore, the pressure of the second reactor is at least 1.0 MPa higher than the pressure of the first reactor, preferably 1.5 to 7.0 MPa higher, and preferably 2.5 to 6.0 MPa higher.

[0020] Furthermore, the catalyst loaded in the second reactor can be a catalyst with a hydrogenation and dearomatization function, such as a non-precious metal catalyst or a precious metal catalyst. The non-precious metal catalyst is a Mo-Ni type catalyst. Generally, an alumina-based carrier is used. 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 cobalt oxide is 2wt% to 5wt%. The catalyst can 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%. The Mo-Ni type catalyst is such as FHUDS-10, FHUDS-6, FHUDS-8, etc. developed by Sinopec Fushun Petrochemical Research Institute (FRIPP); the precious metal catalyst is Pt, Pd, etc. as an active metal, such as FHDA-10 catalyst developed by Sinopec Fushun Petrochemical Research Institute (FRIPP).

[0021] Furthermore, the gaseous components discharged from the second reactor are heat exchanged in a heat exchanger and then enter a high-pressure separator for separation to obtain hydrogenated light components and hydrogen containing hydrogen sulfide.

[0022] Furthermore, the gaseous component discharged from the second reactor is cooled to 100-200°C, preferably 120-150°C, by a heat exchanger.

[0023] Furthermore, the hydrogenated heavy component is mixed with the hydrogenated light component and then enters a stripping and fractionation system to obtain a refined diesel product, wherein the purpose of the fractionation is mainly to cut out the naphtha fraction.

[0024] Furthermore, the aromatic content in the refined diesel product is below 5 wt%, and the S content is below 10 μg / g.

[0025] Compared with the prior art, the method of the present invention has the following advantages:

[0026] (1) The process method of the present invention avoids the defects of placing deep desulfurization and dearomatization in the same reaction system and the incompatibility of reaction conditions. The inventors have found that by controlling the reaction conditions of the first reactor, aromatic ring-containing substances can be less likely to be adsorbed on the catalyst surface, greatly reducing the competitive adsorption of aromatic substances, which is beneficial to the targeted desulfurization reaction. At the same time, by controlling the reaction conditions of the first reactor, it is not only for gas phase desulfurization, but more importantly for better coordination with the second reactor, which is more conducive to the subsequent deep dearomatization.

[0027] (2) The present invention promotes the synchronous liquefaction of hydrogen and oil products by pressurizing the effluent of the first reactor under high temperature conditions. In addition, since hydrogen and hydrogen sulfide have different solubility patterns in oil products, that is, under high temperature conditions, the solubility of hydrogen is high and the solubility of hydrogen sulfide is low, the concentration of hydrogen in the liquefied liquid phase is high and the concentration of hydrogen sulfide is low. When the effluent enters the subsequent second reactor, the influence of hydrogen sulfide on the activity of the catalyst is avoided, and the setting of stripping and dehydrogen sulfide between the two reactors is omitted.

[0028] (3) The present invention achieves deep desulfurization and dearomatization of inferior diesel as raw material under milder operating conditions and a more simplified process flow. In the effluent of the first reactor, the reacted small molecules are not liquefied during the compressor pressurization process, and are liquefied only after passing through the heat exchanger and the high-pressure separator. Such liquefaction means are conducive to the separation of hydrogen from the raw material, and a large amount of hydrogen can be recovered for recycling, thereby improving the utilization rate of hydrogen. The hydrogenated light components separated by the high-pressure separator can be mixed with the hydrogenated heavy components and then enter the subsequent stripping and fractionation system. The entire reaction system does not require a hydrogen compressor in the fixed bed reaction system and a circulating oil pump in the liquid phase hydrogenation reaction system, thereby reducing investment costs, simplifying the process flow, improving reaction efficiency, and reducing the severity of the reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the deep dearomatization process of inferior diesel of the present invention;

[0030] 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 refined diesel product-13. DETAILED DESCRIPTION

[0031] 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.

[0032] In the present invention, unless otherwise explicitly stated, percentages and contents are all based on mass.

[0033] Combine the following Figure 1 The process flow of the present invention is described in detail.

[0034] The diesel feedstock and hydrogen 1 enter the first reactor 2, where a gas phase desulfurization reaction occurs to obtain the first reactor effluent 3; the effluent enters the compressor 4, and after being pressurized by the compressor 4, enters the second reactor 5, wherein the liquid component enters the reaction zone downward to undergo a hydrogenation dearomatization reaction to obtain a hydrogenated heavy component 6, and the gaseous component 7 is discharged upward from the second reactor, 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 refined diesel product 13.

[0035] Examples 1-3

[0036] 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 hydrogenation reactor, loaded with 50mL Mo-Co type diesel hydrogenation catalyst A, and the second reactor is a liquid phase hydrogenation reactor, loaded with 50mL Mo-Ni type diesel hydrogenation catalyst B. 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 refined diesel product.

[0037] The mixed oil of straight wood, coke wood and catalytic wood is used as the raw material. 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.

[0038] Comparative Example 1

[0039] A conventional diesel fixed bed hydrogenation process was adopted, and a hydrogenation reactor was set up, which was reactor 1. According to the traditional catalyst grading system, Mo-Ni type catalyst B was loaded on the top and Mo-Co type catalyst A was loaded on the bottom, and the loading volume was 50mL each. High fraction, low fraction, stripping and other processes were normally set after the reactor to obtain a diesel product. After removing hydrogen sulfide, the hydrogen was pressurized and recycled by a circulating hydrogen compressor. The raw materials and catalyst properties were the same as those in Examples 1-3, and the reaction process conditions and results were shown in Table 3.

[0040] Comparative Example 2

[0041] A conventional diesel fixed bed hydrogenation process was adopted, and a hydrogenation reactor was set up, which was reactor 1. According to the same catalyst grading order as in Example 1-3, Mo-Co type catalyst A was loaded on top and Mo-Ni type catalyst B was loaded on the bottom, and the loading volume was 50mL each. High fraction, low fraction, stripping and other processes were normally set after the reactor to obtain a diesel product. After removing hydrogen sulfide, the hydrogen was pressurized and recycled by a circulating hydrogen compressor. The raw materials and catalyst properties were the same as in Example 1-3, and the reaction process conditions and results were shown in Table 3.

[0042] Comparative Example 3

[0043] The conventional diesel fixed bed hydrogenation process was adopted, and two hydrogenation reactors were set in series, namely reactor 1 and reactor 2, and a stripping tower was set between the two reactors. Reactor 1 was loaded with 50mL Mo-Co type diesel hydrogenation catalyst A, and reactor 2 was loaded with 50mL Mo-Ni type diesel hydrogenation catalyst B. After the reactor, high-fraction, low-fraction, stripping and other processes were conventionally set to obtain diesel products. After removing hydrogen sulfide, the hydrogen was pressurized and circulated by a circulating hydrogen compressor. The raw materials and catalyst properties are the same as those in Examples 1-3, and the reaction process conditions and results are shown in Table 3.

[0044] Comparative Example 4

[0045] The same hydrogenation process as in Example 1-3 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.

[0046] Table 1 Physicochemical properties of catalysts

[0047] Catalyst No. A B Brand FHUDS-7 FHUDS-8 Active Metals Mo-Co Mo-Ni <![CDATA[MoO3,wt%]]> 20 24 NiO or CoO, wt% 3.5 5.0 shape Shamrock Shamrock Diameter, mm 1.2 1.2 <![CDATA[Specific surface area, m 2 ·g -1 > 180 180 <![CDATA[Pore volume, mL·g -1 > 0.35 0.35

[0048] Table 2 Raw oil properties

[0049] Oil properties <![CDATA[Density (20 °C), g·cm -3 > 0.89 Distillation range, ℃ 180～370 <![CDATA[S,μg·g -1 ]]> 10360 <![CDATA[N,μg·g -1 ]]> 713 Aromatics, wt% 63.5 PAHs, wt% 32.2 Monocyclic aromatic hydrocarbons, wt% 31.3

[0050] Table 3 Hydrogenation process conditions and results

[0051]

[0052] As can be seen from Table 3, Comparative Example 1 uses conventional fixed bed hydrogenation technology and a traditional catalyst loading system, with polycyclic aromatic hydrocarbons hydrogenation occurring in the upper part of the reactor and deep desulfurization occurring in the lower part of the reactor. In order to achieve a deep desulfurization effect, it is difficult to take into account the reaction conditions of aromatics hydrogenation, and the removal effect of polycyclic aromatic hydrocarbons is poor. The pressure of the reaction system of the present invention is significantly reduced, and since the desulfurization and dearomatization are divided into two reaction systems, the reaction conditions can be optimized in a targeted manner to obtain a better dearomatization effect.

[0053] The fixed bed hydrogenation technology of Comparative Example 2 adopts the same catalyst loading sequence as that of the embodiment. Sulfide removal occurs in the upper part of the reactor, and aromatic hydrogenation saturation reaction occurs in the lower part. Due to the large temperature rise at the bottom of the reactor, aromatic hydrogenation is subject to thermodynamic limitations, and the sulfide removal effect and aromatic hydrogenation effect are relatively poor.

[0054] The two reactors used in Comparative Example 3 are both conventional fixed-bed hydrogenation reactors, which have relatively harsh reaction conditions and high hydrogen consumption and energy consumption. Moreover, since all the effluent from the first reactor enters the second reactor, the space velocity of aromatics hydrogenation in the second reactor increases, and the removal effect of polycyclic aromatic hydrocarbons deteriorates.

[0055] 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 polycyclic aromatic hydrocarbons.

Claims

1. A method for deep dearomatization of low-quality diesel, characterized in that: The method comprises the following steps: (1) Low-quality diesel feedstock and hydrogen enter the first reactor to undergo gas-phase desulfurization reaction; (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 subjected to dehydrogenation treatment to obtain a hydrogenated light component, and the liquid component is subjected to liquid phase hydrogenation and dearomatization reaction downward to obtain a hydrogenated heavy component and is discharged from the bottom of the second reactor; (3) the hydrogenated heavy component is mixed with the hydrogenated light component to obtain a refined diesel product; The operating conditions of the first reactor are as follows: pressure 0.1-2.0 MPa, temperature 260-400°C, hydrogen-oil volume ratio 100-900, volume space velocity 0.5-3.0 h -1 ; The operating conditions of the second reactor are as follows: pressure 3.0-8.0 MPa, temperature 200-400°C, volume space velocity 0.1-3.0 h -1 .

2. The method according to claim 1, characterized in that The properties of the inferior diesel raw material are as follows: the initial distillation point is 150-200° C., the final distillation point is 320-400° C.; the S content is ≯20000 μg / g, the N content is ≯1000 μg / g, and the polycyclic aromatic hydrocarbon content is ≯50wt%.

3. The method according to claim 2, characterized in that The properties of the inferior diesel raw material are as follows: S content ≯15000 μg / g, N content ≯800 μg / g.

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 operating conditions of the first reactor are as follows: pressure 0.5-2.0 MPa, temperature 320-390°C, hydrogen-to-oil volume ratio 300-700, volume space velocity 0.8-2.0 h -1 .

6. The method according to claim 1, characterized in that The operating conditions of the second reactor are as follows: pressure 3.0-6.0 MPa, temperature 260-360°C, volume space velocity 0.5-1.0 h -1 .

7. The method according to claim 6, characterized in that The pressure of the second reactor is at least 1.0 MPa higher than the pressure of the first reactor.

8. The method according to claim 6, characterized in that The pressure of the second reactor is 1.5-7.0 MPa higher than the pressure of the first reactor.

9. The method according to claim 6, characterized in that The pressure of the second reactor is 2.5-6.0 MPa higher than the pressure of the first reactor.

10. The method according to claim 6, characterized in that The gaseous components discharged from the second reactor are heat exchanged in a heat exchanger and then enter a high-pressure separator for separation to obtain hydrogenated light components and hydrogen containing hydrogen sulfide.

11. The method according to claim 10, characterized in that The gas phase components discharged from the second reactor are cooled to 100-200°C through a heat exchanger.

12. The method according to claim 10, characterized in that The gas phase components discharged from the second reactor are cooled to 120-150°C through a heat exchanger.

13. The method according to claim 1, characterized in that The catalyst loaded in the first reactor is a catalyst having a hydrodesulfurization function, and the catalyst loaded in the second reactor is a catalyst having a hydrodearomatization function.

14. The method according to claim 1 or 13, characterized in that The aromatic content in the refined diesel product is below 5wt%, and the S content is below 10μg / g.

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