Desulfurization and denitrification method for high-nitrogen diesel oil

Abstract

The invention discloses a high-nitrogen diesel oil desulfurization and denitrification method which comprises the following steps: a fixed bed reactor is provided with a first catalyst bed layer and a second catalyst bed layer from top to bottom, the first catalyst bed layer is filled with a noble metal catalyst, and the second catalyst bed layer is filled with a hydrofining catalyst; mixed raw materials of recycle hydrogen and diesel oil raw materials enter the reactor from the space between the first catalyst upper bed layer and the second catalyst bed layer, new hydrogen enters the reactor from the upper portion of the reactor and makes contact with the first catalyst bed layer, hydrogen is dissociated into active hydrogen, and the active hydrogen enters the second catalyst bed layer through surface diffusion and is mixed with the diesel oil raw materials in the second catalyst bed layer. Carrying out hydrodesulfurization, denitrification and dearomatization reactions; a hydrogenation reaction product flows out from the bottom. According to the method, through cooperation of the catalyst and the technological process, the removal of sulfur and nitrogen in the high-nitrogen-content diesel oil can be efficiently and flexibly realized to produce high-quality diesel oil components under the conditions that the technological process is simpler, liquid-phase circulation is not needed and the energy consumption is lower.

Description

Technical Field

[0001] The invention belongs to the field of clean oil refining, and in particular relates to a method for desulfurization and denitrification of high-nitrogen diesel. Background Art

[0002] Diesel fuel has now been upgraded to meet the National VI standard, with sulfur content requirements of no more than 10 ppm and polycyclic aromatic hydrocarbons (PAHs) of no more than 7% by mass. As crude oil becomes heavier and inferior, its nitrogen content continues to increase. Consequently, the composition of secondary processed diesel fuel is becoming increasingly complex, with a growing number of secondary processed diesel fuels exhibiting elevated nitrogen content. Organic nitrogen compounds inhibit catalytic desulfurization, and during hydrogenation, they are first saturated with hydrogen before undergoing hydrogenolysis to produce the corresponding hydrocarbons and ammonia. Therefore, improving desulfurization and denitrification capabilities for high-nitrogen diesel fuel is crucial for enhancing refinery competitiveness and increasing the value of opportunity crude oil.

[0003] CN105778994B discloses a combined process for the desulfurization of ultra-low sulfur diesel. This method can process low-quality diesel with a nitrogen content of approximately 1800 ppm. However, the process involves liquid phase recirculation, and the nitrogen content after recirculation and dilution is less than 400 ppm. Furthermore, this method combines liquid phase recirculation with catalytic adsorption desulfurization, resulting in multiple reactors, a complex process, and high investment and operating costs.

[0004] CN102311794B discloses a diesel hydrogenation method. The method includes a conventional gas-phase circulating reaction zone and a liquid-phase circulating reaction zone. This method has a complex process flow, is not difficult to process, and has a nitrogen content of only 316 ppm. However, the method has poor desulfurization and denitrification capabilities for diesel fuel with high nitrogen content. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention provides a method for desulfurization and denitrification of high-nitrogen diesel. This method, through the coordination of catalysts and process flow, efficiently and flexibly removes sulfur and nitrogen from high-nitrogen diesel, producing high-quality diesel components, while simplifying the process, eliminating the need for liquid phase circulation, and reducing energy consumption.

[0006] The method for desulfurization and denitrification of high-nitrogen diesel of the present invention comprises the following steps: a first catalyst bed and a second catalyst bed are arranged from top to bottom in a fixed-bed reactor, wherein the first catalyst bed is filled with a precious metal catalyst and the second catalyst bed is filled with a hydrorefining catalyst; a mixed raw material of circulating hydrogen and diesel feedstock enters the reactor between the upper first catalyst bed and the second catalyst bed, new hydrogen enters from the upper part of the reactor and contacts the first catalyst bed, hydrogen is dissociated into active hydrogen, enters the second catalyst bed through surface diffusion, is mixed with the diesel feedstock in the second catalyst bed, and undergoes hydrodesulfurization, denitrification and dearomatization reactions; a hydrogenation reaction product flows out from the bottom of the reactor, is separated into gas and liquid, the gas phase is used as circulating hydrogen, and the liquid phase is separated by steam stripping to obtain a refined diesel product.

[0007] In the method of the present invention, the diesel feedstock is a mixed diesel with a high proportion of straight-run diesel and secondary processed diesel, and the mixed secondary processed diesel is one or more of catalytic cracking diesel, MIP diesel, coking diesel, fixed-bed residue oil hydrogenated diesel, ebullient-bed residue oil hydrogenated diesel and slurry-bed residue oil hydrogenated diesel. More specifically, the nitrogen content of the mixed diesel is not less than 500 ppm.

[0008] In the method of the present invention, the precious metal catalyst can be a commercially available precious metal catalyst. This type of catalyst has a strong ability to dissociate hydrogen and can activate hydrogen at relatively low temperatures. The HDO-18 catalyst developed by FRIPP is preferred. Precious metal catalysts are generally supported on alumina and contain platinum and / or palladium as active components. The active components are present in the catalyst at a weight content of no less than 0.1%, typically 0.1% to 1.5%. The catalyst is reduced and activated prior to use. The catalyst bed is placed in a hydrogen gas phase atmosphere.

[0009] In the method of the present invention, based on the total catalyst loading in the reactor, the catalyst loading in the first catalyst bed is 1% to 60%, preferably 30% to 50%; the reaction temperature is 200°C to 400°C, preferably 250°C to 360°C; and the reaction pressure is 2.0 MPa to 9.0 MPa, preferably 4.0 MPa to 7.0 MPa.

[0010] In the method of the present invention, the hydrorefining catalyst is a conventional Mo-Ni or Mo-Co type diesel hydrorefining catalyst, such as the FHUDS series diesel hydrorefining catalyst developed by FRIPP. Furthermore, FHUDS-6 and FHUDS-8 catalysts are preferred due to their higher hydrodenitrogenation and dearomatization activities.

[0011] In the method of the present invention, based on the total catalyst loading in the reactor, the catalyst loading in the second catalyst bed is 40% to 99%, preferably 50% to 70%; the reaction temperature is 200°C to 400°C, preferably 250°C to 360°C; the volume space velocity is 0.1h-1 ~4.0h -1 , preferably 0.5h -1 ~2.0h -1 ; The reaction pressure is 2.0MPa~9.0MPa, preferably 4.0MPa~7.0MPa.

[0012] In the method of the present invention, the volume ratio of the total amount of new hydrogen and recycled hydrogen to the diesel feedstock (referred to as the hydrogen-to-oil ratio, hydrogen is the volume at standard state) is 100:1 to 800:1, preferably 200:1 to 600:1; the percentage of new hydrogen to total hydrogen (the sum of new hydrogen and recycled hydrogen) is referred to as the new hydrogen ratio, which is 10% to 80%, preferably 30% to 60%.

[0013] In the method of the present invention, the gas-liquid separation is generally performed in a high-pressure separator. The gas phase (circulating hydrogen) obtained from the high-pressure separator passes through a recycle compressor and is then directly mixed with the diesel feedstock without passing through a new hydrogen pipeline. The mixed feedstock then enters the reactor directly between the first and second catalyst beds. The high-fraction liquid phase product is subjected to stripping separation to produce a refined oil product.

[0014] The present invention activates new hydrogen on a precious metal catalyst, which then diffuses through the surface into a conventional hydrogenation catalyst bed and participates in a hydrogenation reaction with the diesel feedstock. The activation of the new hydrogen and the hydrogenation reaction occur in different regions of the reactor, significantly different from conventional trickle bed hydrogenation or liquid-phase hydrogenation processes. Because hydrogen is first dissociated and activated in the precious metal catalyst bed, the direct hydrogenation activity of the conventional hydrogenation catalyst in the lower bed is enhanced, increasing the denitrification activity for high-nitrogen diesel, thereby reducing the inhibitory effect of organic nitrogen compounds on desulfurization. Therefore, the present invention has high desulfurization and denitrification efficiencies, better aromatics saturation performance, higher hydrogen utilization efficiency, and more flexible process parameter adjustment. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the desulfurization and denitrification method of high-nitrogen diesel of the present invention.

[0016] Among them, 1-raw oil; 2-new hydrogen; 3-first catalyst bed; 4-second catalyst bed; 5-high-pressure separator; 6-circulating hydrogen compressor; 7-circulating hydrogen; 8-refined oil. DETAILED DESCRIPTION

[0017] The present invention will be described in detail below with reference to the accompanying drawings and embodiments, but the present invention is not limited thereto.

[0018] Examples 1 to 4 A 100mL fixed bed apparatus was used, with 50mL of HDO-18 noble metal catalyst loaded on the upper bed and 50mL of FHUDS-8 diesel hydrogenation catalyst loaded on the lower bed. Figure 1 As shown, the feed was placed between the first and second catalyst beds. The catalyst properties are shown in Table 1, and the feed oil properties are shown in Table 2. The reaction conditions and results are shown in Table 3.

[0019] Examples 5 to 8 A 100 mL fixed-bed reactor was used. The first catalyst bed (upper bed) was loaded with HDO-18 precious metal catalyst, and the second catalyst bed (lower bed) was loaded with FHUDS-8 diesel hydrogenation catalyst. The reactor was identical to Examples 1-4, but the loading ratios of the first and second catalyst beds were varied to demonstrate the effects of different catalyst loading ratios on hydrodesulfurization, denitrogenation, and dearomatization performance. Reaction conditions and results are shown in Table 4.

[0020] Comparative Examples 1 and 2 A 100 mL fixed-bed apparatus was used, with the first catalyst bed filled with 50 mL of quartz sand (inactive for hydrogen dissociation) and the second catalyst bed filled with 50 mL of FHUDS-8 diesel hydrogenation catalyst. The reaction apparatus and raw materials were identical to those in Examples 1-4. This analysis demonstrates the overall hydrodesulfurization, denitrogenation, and dearomatization performance of the apparatus when no precious metal catalyst in the first catalyst bed is present to dissociate and activate fresh hydrogen. The reaction conditions and results are shown in Table 5.

[0021] Comparative Example 3 A 100 mL fixed-bed apparatus was used, with 50 mL of FHUDS-8 diesel hydrotreating catalyst in each of the first and second catalyst beds. The reaction apparatus and raw materials were identical to those in Examples 1-4. This study demonstrates the overall hydrodesulfurization, denitrogenation, and dearomatization performance of the apparatus when using a conventional diesel hydrotreating catalyst to dissociate and activate fresh hydrogen. The reaction conditions and results are shown in Table 5. Comparative Example 4 A 100 mL fixed-bed apparatus was used, with 50 mL of FHUDS-8 diesel hydrotreating catalyst loaded in both the first and second catalyst beds. Fresh hydrogen and diesel feedstock entered the reactor from the top, while recycled hydrogen entered the reactor between the first and second catalyst beds. The reaction products exited the reactor bottom. This demonstrates the overall hydrodesulfurization, denitrification, and dearomatization performance of the apparatus using a conventional diesel hydrotreating process. The reaction conditions and results are shown in Table 5. Table 1 Physicochemical properties of catalysts Table 2 Diesel feedstock properties Table 3 shows the hydrogenation process conditions and results of Examples 1 to 4. As shown in Table 3, Examples 1-4 all meet the National VI diesel standard, with sulfur contents less than 10 ppm and polycyclic aromatic hydrocarbons less than 7%. Furthermore, a higher fresh hydrogen ratio results in better hydrodesulfurization, denitrogenation, and dearomatization effects. Examples 1-4 demonstrate that the present invention can achieve excellent desulfurization and denitrogenation effects on diesel fuel with a high nitrogen content. Table 4 shows the hydrogenation process conditions and results of Examples 5 to 8. As shown in Examples 5 to 8 in Table 4, when other conditions remain the same, the higher the amount of precious metal catalyst loaded in the first bed, the better the hydrodesulfurization, denitrogenation, and dearomatization effects. This suggests that a higher amount of precious metal catalyst loaded improves hydrogen dissociation, increasing the amount of active hydrogen that diffuses from the surface to the second catalyst bed, resulting in a correspondingly better hydrorefining effect. However, a higher amount of precious metal loaded results in a lower amount of diesel hydrogenation catalyst loaded. Therefore, the catalyst loading ratio needs to be flexibly selected based on actual production conditions. Table 5 shows the hydrogenation process conditions and results of Comparative Examples 1 to 4. As shown in Table 5, Comparative Examples 1 and 2 both contain sulfur contents exceeding 10 ppm, and the refined oils do not meet the National VI diesel standard. Comparison of Comparative Examples 1 and 2 with Examples 1 and 2 reveals that, under identical conditions, the refined oils from the comparative examples have higher sulfur, nitrogen, and aromatics contents than those from the corresponding examples. This demonstrates that the present invention can significantly improve the hydrogenation efficiency of feedstock oils.

[0022] As can be seen from Comparative Example 3 in Table 5, when the first catalyst bed is loaded with FHUDS-8 diesel hydrogenation catalyst, the refined oil sulfur, nitrogen, and polycyclic aromatic hydrocarbons are equivalent to those in Comparative Example 1. Therefore, the FHUDS-8 loaded in the first catalyst bed cannot dissociate and activate hydrogen in the gas phase, and cannot improve the hydrogenation effect of the crude oil.

[0023] As shown in Table 5, Comparative Example 4 and Example 1 have the same diesel processing capacity per hour, 64.8 g / h. The refined oil sulfur, nitrogen, and polycyclic aromatic hydrocarbons levels are similar to those of Comparative Example 1, with Example 1 slightly outperforming Comparative Example 4. However, the loading of the diesel hydrogenation catalyst FHUDS-8 in Example 1 into the reactor is only 50% of that in Comparative Example 4. This demonstrates that, while the noble metal catalyst loading reduces the volume of the diesel hydrogenation catalyst compared to conventional processes, the direct hydrogenation capacity of this process is enhanced. Therefore, when the hydrogenation effect of the refined oil product is similar, the diesel processing capacity of the device is not reduced. Due to the flexible adjustment of fresh and recycled hydrogen, the feedstock oil processing capacity of the device can also be adjusted accordingly. In summary, the present invention improves diesel hydrogenation capacity without reducing the feedstock oil processing capacity of the device.

[0024] In summary, the present invention has excellent adaptability to high-nitrogen diesel fuels, boasting strong direct hydrogenation capabilities and excellent desulfurization, denitrification, and dearomatization effects. The present invention can be used to process high-nitrogen diesel fuel, enabling the flexible and efficient production of diesel components that meet the National VI standard under moderate conditions.

Claims

1. A method for desulfurization of high-nitrogen diesel fuel, characterized in that The invention comprises the following contents: a first catalyst bed layer and a second catalyst bed layer are arranged from top to bottom in a fixed bed reactor, wherein the first catalyst bed layer is loaded with a precious metal catalyst and the second catalyst bed layer is loaded with a hydrorefining catalyst; a mixed raw material of circulating hydrogen and diesel feedstock enters the reactor from between the first catalyst bed layer and the second catalyst bed layer, new hydrogen enters from the upper part of the reactor and contacts with the first catalyst bed layer, hydrogen is dissociated into active hydrogen, enters the second catalyst bed layer through surface diffusion, is mixed with the diesel feedstock in the second catalyst bed layer, and undergoes hydrodesulfurization, denitrogenation and dearomatization reactions; hydrogenation reaction products flow out from the bottom of the reactor, are separated into gas and liquid, the gas phase is used as circulating hydrogen, and the liquid phase is separated by steam stripping to obtain a refined diesel product.

2. The method according to claim 1, wherein: The diesel raw material is a mixed diesel with a high proportion of straight-run diesel and secondary processed diesel, and the blended secondary processed diesel is one or more of catalytic cracking diesel, MIP diesel, coking diesel, fixed-bed residue oil hydrogenated diesel, ebullient-bed residue oil hydrogenated diesel and slurry-bed residue oil hydrogenated diesel.

3. The method according to claim 1, wherein: The nitrogen content of the diesel feedstock is not less than 500 ppm.

4. The method according to claim 1, wherein: The noble metal catalyst uses alumina as a carrier and Pt and / or Pd as active components. The content of the active components in the catalyst is not less than 0.1% by weight, preferably 0.1% to 1.5%.

5. The method according to claim 1, wherein: The noble metal catalyst is reduced and activated before use, and the first catalyst bed is in a hydrogen gas phase atmosphere.

6. The method according to claim 1, wherein: Based on the total catalyst loading in the reactor, the catalyst loading in the first catalyst bed is 1% to 60%, preferably 30% to 50%; the reaction temperature is 200°C to 400°C, preferably 250°C to 360°C; the reaction pressure is 2.0MPa to 9.0MPa, preferably 4.0MPa to 7.0MPa.

7. The method according to claim 1, wherein: The hydrorefining catalyst is a Mo-Ni or Mo-Co type diesel hydrogenation catalyst.

8. The method according to claim 1, wherein: Based on the total catalyst loading in the reactor, the catalyst loading in the second catalyst bed is 40% to 99%, preferably 50% to 70%; the reaction temperature is 200°C to 400°C, preferably 250°C to 360°C; the volume space velocity is 0.1h -1 ~4.0h -1 , preferably 0.5h -1 ~2.0h -1 ; The reaction pressure is 2.0MPa~9.0MPa, preferably 4.0MPa~7.0MPa.

9. The method according to claim 1, wherein: The volume ratio of the total amount of new hydrogen and recycled hydrogen to diesel feedstock is 100:1 to 800:1, preferably 200:1 to 600:1; the percentage of new hydrogen in the total hydrogen is 10% to 80%, preferably 30% to 60%.

10. The method according to claim 1, wherein: The gas-liquid separation is carried out in a high-pressure separator. The gas phase obtained from the high-pressure separator passes through a circulation compressor and is directly mixed with the diesel raw material without passing through a new hydrogen pipeline. The mixed raw material enters the reactor directly between the first catalyst bed and the second catalyst bed; the high-fraction liquid phase product is subjected to steam stripping separation to obtain a refined oil product.

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