A crude benzene hydrogenation process

Abstract

This invention discloses a crude benzene hydrogenation process. First, crude benzene feedstock is mixed with hydrogen gas and then fed into a first-stage hydrogenation reactor 2 from top to bottom. The hydrogenation product is heated and then fed into a second-stage hydrogenation reactor 3 from bottom to top. The gaseous component undergoes hydrogenation reaction through a catalyst bed, while the liquid component is discharged from the bottom of the tower and enters a third-stage hydrogenation reactor 4. The product after second-stage hydrogenation then enters a gas-liquid separator 5. The product at the bottom of the separator is mixed with the liquid component and hydrogen gas at the bottom of the second-stage hydrogenation reactor 3 and then fed into the third-stage hydrogenation reactor 4 from top to bottom. The product after third-stage hydrogenation undergoes conventional processes of stripping, distillation, solvent extraction, and rectification to obtain non-aromatic hydrocarbons, benzene, toluene, and xylene.

Description

Technical Field

[0001] This invention belongs to the field of coal chemical technology, specifically relating to a crude benzene hydrogenation process. Background Technology

[0002] Crude benzene from coking is a byproduct of coke production and an important chemical raw material used in the production of dyes, pharmaceuticals, disinfectants, explosives, and synthetic fibers. Due to the presence of various impurities, especially high sulfide content, crude benzene must be refined before it can be used in chemical production. With increasingly stringent environmental regulations, my country's crude benzene refining process has shifted from the traditional acid washing method to hydrogenation refining. Among existing crude benzene hydrogenation refining technologies, the low-temperature hydrogenation process yields high-quality benzene, toluene, and xylene products while mitigating environmental pollution. It also boasts advantages such as simple operation, low equipment and material requirements, and high economic benefits, thus gaining widespread application in China.

[0003] Patent CN101967078A discloses a method for the hydrogenation refining of crude benzene. This method involves removing heavy aromatics from crude benzene, followed by two-stage hydrogenation using the light fraction of the crude benzene. The reaction in the hydrogenation reactor is predominantly gas-phase. This process requires a large amount of hydrogen circulation, resulting in high hydrogen and energy consumption, and the removed heavy aromatics require further processing.

[0004] Patent CN101519338A discloses a three-stage hydrogenation process for crude benzene. The process involves pre-separating crude benzene to remove heavy components (C9 and above), followed by sequential first-stage, second-stage (230-290°C), and third-stage hydrogenation (220-315°C) treatments under low-temperature and low-pressure conditions to remove unsaturated hydrocarbons and other impurities. This method requires pre-separation to remove heavy benzene compounds before hydrogenation, but it does not specify the conditions for the first-stage low-temperature pre-hydrogenation reaction. Furthermore, data from the patent's examples show that the second-stage hydrogenation process requires a relatively high temperature, such as around 285°C, and the removed heavy benzene needs further processing.

[0005] Patent CN101028985A discloses a method for hydrogenating crude benzene without pretreatment of the raw material. By adding a certain proportion of diluent oil to the full-fraction crude benzene feedstock, the content of unsaturated compounds that are prone to coking in the feedstock is reduced, thereby slowing down the coking rate during the hydrogenation process of crude benzene. However, this method cannot fundamentally solve the problem of easy coking during the hydrogenation process of crude benzene, and the addition of diluent oil reduces the processing capacity of the equipment, which is not conducive to the economic benefits of enterprises.

[0006] Patent CN103910596A discloses a full-fraction crude benzene hydrogenation method and catalyst. The method involves mixing crude benzene and hydrogen into uniform microparticles with a diameter of 0.1~20μm using a microparticle generator and a static mixer. Then, under the action of a reduced-state metal catalyst, the mixture undergoes first and second stage pre-hydrogenation, followed by third stage pre-hydrogenation and fourth stage main hydrogenation under the action of a sulfidated-state catalyst. This patent provides a full-fraction crude benzene hydrogenation process, and the four-stage hydrogenation effectively solves the coking problem during crude benzene hydrogenation. However, the process requires two microparticle generators with special magnetic properties, resulting in a long process flow and complex equipment for industrial applications. Furthermore, the catalysts used in the first and second stage pre-hydrogenation are in a reduced state, making them highly susceptible to deactivation in the high-sulfur atmosphere of crude benzene.

[0007] Therefore, to ensure the long-term operation of crude benzene hydrogenation units, current mainstream crude benzene hydrogenation technologies all require pre-deweighting of the crude benzene feedstock, using the resulting light benzene as the hydrogenation feedstock. This results in the waste of heavy benzene components, and the deweighting process involves heating followed by cooling, increasing energy consumption. Furthermore, most crude benzene full-fraction hydrogenation processes can only slow down the coking rate during the hydrogenation process, but cannot fundamentally solve the coking problem. While the process provided by patent CN103910596A can solve the coking problem in the crude benzene hydrogenation process, it suffers from drawbacks such as a long process flow and complex equipment requirements. Moreover, the use of a reduced catalyst to achieve low-temperature activity inevitably leads to a short catalyst lifespan in the case of high-sulfur crude benzene. Summary of the Invention

[0008] The purpose of this invention is to address the above-mentioned shortcomings by providing a crude benzene hydrogenation process. This method eliminates the need for heavy component removal from crude benzene, effectively utilizes the heavy components in crude benzene, and increases the added value of the product. Through a three-stage hydrogenation process and a specific catalyst, it ensures that the total sulfur and total nitrogen of the hydrogenated product are both less than 0.5 mg / kg, and the aromatic hydrocarbon loss rate is controlled within 0.5%. It also solves the problem of easy coking during crude benzene hydrogenation and extends the operating cycle of the unit.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] A crude benzene hydrogenation process includes the following steps:

[0011] S1. Crude benzene feedstock is drawn from buffer tank 1, mixed with hydrogen, and enters the first-stage hydrogenation reactor 2 from top to bottom. This process adsorbs and removes gum and solid impurities from the crude benzene feedstock, while simultaneously hydrogenating to remove unsaturated substances such as styrene and dienes. The first-stage reaction conditions are: temperature 80~140℃, pressure 2.5~3.5MPa, and space velocity 1.0~2.0h⁻¹. -1The hydrogen-to-oil volume ratio is 400-600:1, the styrene content at the outlet is less than 0.3%, and the diene content is less than 0.5gI2 / 100g oil.

[0012] S2. The hydrogenation product from the first stage, after heating, enters the second-stage hydrogenation reactor 3 from bottom to top. A gas-liquid separator is installed at the bottom of the second-stage hydrogenation reactor, where the feedstock is separated into gaseous and liquid phases. The gaseous phase passes through the catalyst bed, where hydrogenation removes remaining styrene, dienes, and some monoolefins from the crude benzene, and then enters the gas-liquid separator 5. The liquid phase is discharged from the bottom of the second-stage hydrogenation reactor 3 and enters the third-stage hydrogenation reactor 4. This prevents heavy components from entering the second-stage catalyst bed, causing coking of the catalyst and accelerating deactivation. The second-stage reaction conditions are: temperature 170~200℃, pressure 2.5~3.5MPa, and space velocity 0.5~1.0h. -1 The hydrogen-to-oil volume ratio is 400-600:1, the styrene content at the outlet is less than 0.05%, the diolefin content is less than 0.1 g I2 / 100 g oil, and the monoolefin removal rate is greater than 60%.

[0013] S3. Hydrogen from the top of gas-liquid separator 5 is returned to the inlet of the first-stage hydrogenation reactor 2 for recycling. The bottom oil from gas-liquid separator 5, after mixing with hydrogen and the liquid phase components from the bottom of the second-stage hydrogenation reactor 3, enters the third-stage hydrogenation reactor 4 from top to bottom for hydrogenation to remove sulfur and nitrogen impurities from the crude benzene. The three-stage reaction conditions are: temperature 260~330℃, pressure 3.0~5.0MPa, and space velocity 0.5~1.0h⁻¹. -1 The amount of hydrogen added is 1.1 to 1.3 times the amount of hydrogen required for hydrodesulfurization and denitrification, with the total sulfur at the outlet being less than 0.5 mg / kg, the total nitrogen being less than 0.5 mg / kg, and the total aromatics loss rate being less than 0.5%.

[0014] The products from S4 and the three-stage hydrogenation process enter stripping tower 6. The gas containing hydrogen sulfide and components below C4 discharged from the top of stripping tower 6 enters the tail gas treatment system. The product at the bottom of the tower undergoes conventional processes of distillation, solvent extraction and rectification to obtain non-aromatic hydrocarbons, benzene, toluene and xylene.

[0015] In the above-mentioned crude benzene hydrogenation process, the catalyst used in the first stage of hydrogenation is a NiW catalyst, with a NiO content of 12-15% and a WO3 content of 3-4% by weight, and the remainder being an Al2O3 support. Depending on the content of solid impurities in the crude benzene feedstock, if the content of impurities such as silicon, vanadium, iron, and copper exceeds the standard, a desilication agent and a demetallizing agent can be loaded onto the NiW catalyst to protect it. The catalyst used in the second stage of hydrogenation is a NiMo catalyst, with a NiO content of 3-5% and a MoO3 content of 14-18% by weight, and the remainder being an Al2O3-MgO composite support. The catalyst used in the three-stage hydrogenation is a NiMo catalyst, with NiO content of 3-5% and MoO3 content of 12-15% by weight, and the balance being an Al2O3-MgO-HY-ZrO2 composite support. This Al2O3-MgO-HY-ZrO2 composite support is a composite oxide obtained by calcining in air at 900-1100℃ for 3-5 hours under the condition of passing saturated water.

[0016] The beneficial effects of this invention are:

[0017] (1) Hydrogenation of the entire fraction of crude benzene is realized without the need for heavy component removal from crude benzene. The heavy components in crude benzene are effectively utilized, and the added value of the product is increased.

[0018] (2) A three-stage hydrogenation process is adopted, with the first and second stages of hydrogenation serving as pre-hydrogenation, which can effectively achieve stepwise hydrogenation saturation at low temperatures. At a low temperature of 80~140℃, the first stage of hydrogenation saturates dienes, styrene, and other substances most prone to coking, and then at 170~200℃, monoolefins such as cyclopentene and indene are saturated. This is a significant reduction compared to the commonly used pre-hydrogenation temperature of 190~230℃, resulting in a longer catalyst lifespan.

[0019] (3) The two-stage hydrogenation reactor adopts a bottom-in, top-out configuration, and is equipped with a gas-liquid separator at the bottom. The hydrogenation product from the first stage is heated and enters from the bottom of the second-stage hydrogenation reactor. The gaseous component passes through the catalyst bed, where hydrogenation removes the remaining styrene, dienes, and some monoolefins from the crude benzene. The liquid component is discharged from the bottom of the second-stage hydrogenation reactor 3 and enters the third-stage hydrogenation reactor 4. The heavy components of crude benzene contain a large amount of dicyclopentadiene polymers, which are macromolecular colloids. Due to their large molecular weight, these substances are difficult to enter the pores of the crude benzene hydrogenation catalyst for hydrogenation saturation. They will cover the catalyst surface, polymerize and coke at high temperatures, and finally produce carbon deposits, causing catalyst deactivation. Therefore, crude benzene hydrogenation generally involves heavy component removal before hydrogenation to discharge the heavy components and protect the activity of the hydrogenation catalyst. This invention patent utilizes the bottom-in, top-out process of the two-stage hydrogenation to separate the heavy components in the second stage reaction. The gaseous light component enters the catalyst bed, while the liquid heavy component enters the third-stage hydrogenation reactor packed with a specific catalyst for hydrogenation. This not only avoids the poisoning of the secondary catalyst by heavy components, causing rapid catalyst deactivation, but also utilizes the heat of the imported feedstock in the secondary reaction to separate light and heavy components, avoiding the conventional operation of removing heavy components before hydrogenation, heating and separating them, and then cooling and refluxing them into subsequent stages, thus greatly reducing the energy consumption of the unit.

[0020] (4) The catalyst used in the three-stage hydrogenation is a NiMo catalyst. By weight percentage, the NiO content is 3~5%, the MoO3 content is 12~15%, and the balance is an Al2O3-MgO-HY-ZrO2 composite support. This support is a composite oxide obtained by calcining in air at 900~1100℃ for 3~5h under the condition of passing saturated water. This invention incorporates a certain amount of HY molecular sieve into the support. Calcination at 900–1100°C is carried out under saturated steam conditions. Compared to calcination in air, this increases the movement of oxygen ions on the alumina surface, allowing for more rapid particle sintering and growth. This results in a support with a concentrated pore size distribution and larger pore volume, facilitating the entry of heavy macromolecular components from crude benzene into the catalyst's active pores. Furthermore, HY molecular sieve is a high-performance hydrocracking catalyst capable of breaking down heavy hydrocarbons into smaller hydrocarbon molecules. Therefore, the NiMo / Al₂O₃-MgO-HY-ZrO₂ catalyst provided by this invention exhibits excellent hydrogenation activity for heavy components in crude benzene. On the other hand, the high-temperature hydrothermal treatment reduces the cracking activity of the HY molecular sieve in the support, ensuring a certain degree of cracking and hydrogenation of macromolecular colloids while avoiding excessive cracking of aromatics during hydrogenation, thus guaranteeing the aromatics yield. Modification with Zr promoters allows some d electrons from Zr centers to transfer to the vicinity of Mo centers, promoting Mo reduction, increasing the number of Mo active centers, and thus improving the catalyst's hydrogenation activity. Mg modification makes the support weakly acidic, effectively reducing olefin polymerization and gelation during hydrogenation, enhancing the catalyst's resistance to carbon deposition, and extending its operating cycle.

[0021] (5) The amount of hydrogen added to the three-stage hydrogenation reactor is 1.1 to 1.3 times the amount of hydrogen required for hydrodesulfurization and denitrification. The hydrogen addition is controlled because HY molecular sieve is added to the catalyst support of the three-stage hydrogenation reactor. Although its acidity is reduced by high-temperature hydrothermal treatment, it still has stronger hydrogenation saturation than conventional Al2O3 supported hydrogenation catalyst. In addition, this patent uses nickel-molybdenum active components with stronger hydrogenation saturation. If the amount of hydrogen added is too large, the aromatic loss rate will be too high, resulting in a decrease in aromatic yield. Therefore, based on the characteristics of the NiMo / Al2O3-MgO-HY-ZrO2 catalyst used in the three-stage hydrogenation, the loss of aromatics during the hydrogenation process is reduced by controlling the amount of hydrogen added, so as to ensure that the total aromatic loss rate after hydrogenation is less than 0.5%, and at the same time, it can meet the quality requirements of the whole fraction crude benzene hydrogenation product, so as to ensure that the total sulfur is less than 0.5 mg / kg and the total nitrogen is less than 0.5 mg / kg. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a crude benzene hydrogenation process provided by the present invention.

[0023] In the diagram, 1 is a buffer tank, 2 is a first-stage hydrogenation reactor, 3 is a second-stage hydrogenation reactor, 4 is a third-stage hydrogenation reactor, 5 is a gas-liquid separator, and 6 is a stripping tower. Detailed Implementation

[0024] In this invention, the low-temperature hydrogenation effect of the process is verified by analyzing the styrene and diene values ​​in the first-stage hydrogenation oil; the low-temperature hydrogenation effect and anti-coking ability of the process are verified by analyzing the styrene, diene values, and monoolefin removal rate in the second-stage hydrogenation oil; and the hydrorefining effect of the process is verified by analyzing the total sulfur, total nitrogen content, and aromatic hydrocarbon loss rate in the third-stage hydrogenation oil. The properties of the crude benzene feedstock are as follows: benzene, toluene, and xylene content 87.3%, styrene content 1.36%, diene value 1.2 gI2 / 100g, bromine value 8.3 gBr2 / 100g, total sulfur 5428 mg / kg, and total nitrogen content 1536 mg / kg.

[0025] The present invention will be further described below with reference to the accompanying drawings and specific examples: Example 1

[0026] The process flow used in this invention is as follows: Figure 1 The process flow is as follows:

[0027] Crude benzene feedstock is drawn from buffer tank 1, mixed with hydrogen, and enters the first-stage hydrogenation reactor 2 from top to bottom. This process adsorbs and removes gum and solid impurities from the crude benzene feedstock, while simultaneously hydrogenating unsaturated compounds such as styrene and dienes. The first-stage hydrogenation product is then heated and enters the second-stage hydrogenation reactor 3 from bottom to top. The gaseous component passes through the catalyst bed in the second-stage hydrogenation reactor 3, where hydrogenation removes remaining styrene, dienes, and some monoolefins from the crude benzene. It then enters the gas-liquid separator 5, while the liquid component is discharged from the bottom of the second-stage hydrogenation reactor 3 and enters the third-stage hydrogenation reactor 4. Hydrogen from the top of the gas-liquid separator 5 is returned to the inlet of the first-stage hydrogenation reactor 2 for recycling. The bottom oil from the gas-liquid separator 5 is mixed with hydrogen and the liquid component from the bottom of the second-stage hydrogenation reactor 3 and then enters the third-stage hydrogenation reactor 4 from top to bottom, where hydrogenation removes sulfur and nitrogen impurities from the crude benzene. The product from the three-stage hydrogenation process enters stripping tower 6. The gas containing hydrogen sulfide and components below C4 discharged from the top of stripping tower 6 enters the tail gas treatment system. The product from the bottom of the tower undergoes conventional processes of distillation, solvent extraction, and rectification to obtain non-aromatic hydrocarbons, benzene, toluene, and xylene.

[0028] The hydrogenation reaction conditions were as follows: first-stage hydrogenation reaction temperature 110℃, pressure 3.5MPa, and space velocity 1.5h⁻¹. -1 The hydrogen-to-oil volume ratio was 600:1. The NiW catalyst used, by weight percentage, contained 12% NiO, 4% WO3, and the remainder was Al2O3 support. The two-stage hydrogenation reaction was carried out at a temperature of 185℃, a pressure of 3.5 MPa, and a space velocity of 1.0 h⁻¹.-1 The hydrogen-to-oil volume ratio was 400:1. The NiMo catalyst used, by weight percentage, contained 5% NiO and 14% MoO3, with the balance being an Al2O3-MgO composite support. The three-stage hydrogenation reaction was carried out at a temperature of 290℃, a pressure of 5.0 MPa, and a space velocity of 0.75 h⁻¹. -1 The amount of hydrogen added was 1.1 times the amount of hydrogen required for hydrodesulfurization and denitrification. The NiMo catalyst used, by weight percentage, contained 4% NiO, 12% MoO3, and the remainder was an Al2O3-MgO-HY-ZrO2 composite support. The results after 3 days of continuous operation of the hydrogenation reaction are shown in Table 1.

[0029] Table 1 Results of hydrogenation reaction in Example 1

[0030]

[0031] Example 2

[0032] The crude benzene hydrogenation process is the same as in Example 1, with the following hydrogenation reaction conditions: first-stage hydrogenation reaction temperature 80°C, pressure 2.5 MPa, and space velocity 1.0 h⁻¹. -1 The hydrogen-to-oil volume ratio was 400:1. The NiW catalyst used, by weight percentage, contained 15% NiO, 3% WO3, and the remainder was Al2O3 support. The two-stage hydrogenation reaction was carried out at a temperature of 170℃, a pressure of 2.5 MPa, and a space velocity of 0.75 h⁻¹. -1 The hydrogen-to-oil volume ratio was 500:1. The NiMo catalyst used, by weight percentage, contained 4% NiO and 18% MoO3, with the balance being an Al2O3-MgO composite support. The three-stage hydrogenation reaction was carried out at a temperature of 260℃, a pressure of 3.0 MPa, and a space velocity of 0.5 h⁻¹. -1 The amount of hydrogen added was 1.2 times the amount of hydrogen required for hydrodesulfurization and denitrification. The NiMo catalyst used, by weight percentage, contained 3% NiO, 15% MoO3, and the remainder was an Al2O3-MgO-HY-ZrO2 composite support. The results after 3 days of continuous operation of the hydrogenation reaction are shown in Table 2.

[0033] Table 2 Results of hydrogenation reaction in Example 2

[0034]

[0035] Example 3

[0036] The crude benzene hydrogenation process is the same as in Example 1, with the following hydrogenation reaction conditions: first-stage hydrogenation reaction temperature 140℃, pressure 3.0 MPa, and space velocity 2.0 h⁻¹. -1The hydrogen-to-oil volume ratio was 500:1. The NiW catalyst used, by weight percentage, contained 13.5% NiO, 3.5% WO3, and the remainder was Al2O3 support. The two-stage hydrogenation reaction was carried out at a temperature of 200℃, a pressure of 3.0 MPa, and a space velocity of 0.5 h⁻¹. -1 The hydrogen-to-oil volume ratio was 600:1. The NiMo catalyst used, by weight percentage, contained 3% NiO and 16% MoO3, with the remainder being an Al2O3-MgO composite support. The three-stage hydrogenation reaction was carried out at a temperature of 330℃, a pressure of 4.0 MPa, and a space velocity of 1.0 h⁻¹. -1 The amount of hydrogen added was 1.3 times the amount of hydrogen required for hydrodesulfurization and denitrification. The NiMo catalyst used, by weight percentage, contained 5% NiO, 13.5% MoO3, and the remainder was an Al2O3-MgO-HY-ZrO2 composite support. The results after 3 days of continuous operation of the hydrogenation reaction are shown in Table 3.

[0037] Table 3 Results of hydrogenation reaction in Example 3

[0038]

[0039] As can be seen from the above three embodiments, when using the three-stage hydrogenation process and the specific catalyst provided by the present invention to hydrogenate the crude benzene whole fraction, the total sulfur and total nitrogen of the hydrogenation product are both less than 0.5 mg / kg, and the aromatic loss rate is controlled within 0.5%. The crude benzene raw material is effectively utilized, and the added value of the product is increased.

[0040] Comparative Example 1

[0041] The three-stage hydrogenation process used a conventional crude benzene CoMo / Al2O3 catalyst, while the remaining hydrogenation processes, reaction conditions, and catalysts were the same as in Example 1. The results after 3 days of continuous hydrogenation reaction are shown in Table 4.

[0042] Table 4 Results of hydrogenation reaction in Comparative Example 1

[0043]

[0044] As can be seen from the table above, the CoMo / Al2O3 catalyst used in conventional crude benzene hydrogenation exhibits poor hydrogenation activity when hydrogenating the entire crude benzene fraction, with total sulfur at the outlet reaching 2.7 mg / kg and total nitrogen at the outlet reaching 1.5 mg / kg. This is mainly because the heavy components in the crude benzene fraction contain sulfur and nitrogen compounds such as dibenzothiophene and quinoline. These substances are more difficult to remove than thiophene and pyridine in the light benzene after heavy removal, resulting in the CoMo / Al2O3 catalyst failing to meet the standards for sulfur and nitrogen at the hydrogenation outlet.

[0045] Comparative Example 2

[0046] The three-stage hydrogenation process was modified to use a large-volume hydrogen circulation system, with the hydrogen-to-oil volume ratio controlled at 600:1. The remaining hydrogenation processes, reaction conditions, and catalysts used were the same as in Example 1. The results after 3 days of continuous operation of the hydrogenation reaction are shown in Table 5.

[0047] Table 5 Results of hydrogenation reaction in Comparative Example 2

[0048]

[0049] As can be seen from the table above, after the three-stage hydrogenation was changed to a large-volume hydrogen circulation, the total sulfur and total nitrogen at the hydrogenation outlet were still qualified, but the aromatic hydrocarbon loss rate increased to 1.03%, which is significantly higher than the 0.35% aromatic hydrocarbon loss rate in Example 1. This indicates that when using the NiMo / Al2O3-MgO-HY-ZrO2 provided by this invention, it is necessary to control the amount of hydrogen replenishment in order to keep the aromatic hydrocarbon loss rate below 0.5% while ensuring that the total sulfur and total nitrogen at the hydrogenation outlet are qualified.

[0050] Comparative Example 3

[0051] In the crude benzene hydrogenation process, the second-stage hydrogenation reactor does not have a gas-liquid separator at the bottom. All the products from the first-stage hydrogenation pass through the catalyst bed from bottom to top for hydrogenation, and then sequentially enter the third-stage hydrogenation reactor, gas-liquid separator, stripping tower, and subsequent processes. The remaining hydrogenation processes, reaction conditions, and catalysts used are the same as in Example 1. The results after continuous operation of the hydrogenation reaction for different times are shown in Table 6.

[0052] Table 6 Results of hydrogenation reaction in Comparative Example 3

[0053]

[0054] As can be seen from the table above, after 3 days of operation, the hydrogenation outlet quality indicators of Example 1 and Comparative Example 3 were basically the same at each stage. After 30 days of operation, the hydrogenation outlet quality indicators of Example 1 remained stable and were basically consistent with those after 3 days of operation. However, after 30 days of operation, the secondary hydrogenation outlet indicators of Comparative Example 3 showed significant changes. The outlet styrene content increased from 0.02% to 0.12%, the diene value increased from less than 0.1 gI2 / 100g to 0.14 gI2 / 100g, and the monoolefin removal rate decreased from 66.5% to 51.7%. This is mainly because the crude benzene heavy components contain a large amount of dicyclopentadiene polymer-like macromolecular colloids. Due to their large molecular weight, these substances are difficult to enter the pores of the crude benzene hydrogenation catalyst for hydrogenation saturation. They will cover the catalyst surface, polymerize and coke at high temperatures after long-term operation, and finally produce carbon deposits, causing catalyst deactivation. The tertiary hydrogenation outlet index of Comparative Example 3 showed a slight upward trend after 30 days of operation, possibly due to the increased olefin content at the secondary hydrogenation outlet. The data analysis above shows that the gas-liquid separation process provided by this invention in the secondary hydrogenation stage has a significant protective effect on the secondary hydrogenation catalyst, ensuring that the catalyst does not rapidly deactivate and indirectly extending the operating cycle of the tertiary hydrogenation catalyst.

Claims

1. A crude benzol hydrogenation process, characterized in that, The crude benzene is treated by a three-stage hydrogenation process, which comprises the following steps: S1, the crude benzene raw material is taken out from the buffer tank (1), mixed with hydrogen and then enters the first-stage hydrogenation reactor (2) from top to bottom, adsorbs and removes gum and solid impurities in the crude benzene raw material, and removes benzene ethylene, diene unsaturated compounds by hydrogenation; the first-stage reaction conditions are temperature 80~140℃, pressure 2.5~3.5MPa, space velocity 1.0~2.0h -1 , hydrogen oil volume ratio 400~600:1; The catalyst used in the first-stage hydrogenation is a NiW catalyst, with the content of NiO being 12-15% by weight, the content of WO3 being 3-4% by weight, and the balance being an Al2O3 carrier; S2, the first-stage hydrogenation product is heated and then enters the second-stage hydrogenation reactor (3) from bottom to top, the gas-phase components pass through the catalyst bed of the second-stage hydrogenation reactor (3) to remove the remaining styrene, di-olefins and part of mono-olefins in the crude benzene by hydrogenation, and then enter the gas-liquid separator (5), and the liquid-phase components are discharged from the bottom of the second-stage hydrogenation reactor (3) to enter the third-stage hydrogenation reactor (4); the second-stage reaction conditions are as follows: temperature 170-200℃, pressure 2.5-3.5 MPa, space velocity 0.5-1.0 h -1 , hydrogen / oil volume ratio 400-600:1; S3, the second-stage hydrogenation product is heated and then enters the third-stage hydrogenation reactor (4) from bottom to top, the gas-phase components pass through the catalyst bed of the third-stage hydrogenation reactor (4) to remove the remaining mono-olefins in the crude benzene by hydrogenation, and then enter the gas-liquid separator (5), and the liquid-phase components are discharged from the bottom of the third-stage hydrogenation reactor (4) to enter the fourth-stage hydrogenation reactor (5); the third-stage reaction conditions are as follows: temperature 170-200℃, pressure 2.5-3.5 MPa, space velocity 0.5-1.0 h -1 , hydrogen / oil volume ratio 400-600:1; S4, the third-stage hydrogenation product The catalyst used in the second-stage hydrogenation is a NiMo catalyst, with the content of NiO being 3-5% by weight, the content of MoO3 being 14-18% by weight, and the balance being an Al2O3-MgO composite carrier; S3, the hydrogen gas at the top of the gas-liquid separator (5) is recycled to the inlet of the first hydrogenation reactor (2), and the oil at the bottom of the gas-liquid separator (5) is mixed with hydrogen gas and the liquid-phase components at the bottom of the second hydrogenation reactor (3) and then enters the third hydrogenation reactor (4) from top to bottom, so as to remove the sulfur and nitrogen impurities in the crude benzene by hydrogenation; the third reaction condition is that the temperature is 260-330℃, the pressure is 3.0-5.0 MPa, the space velocity is 0.5-1.0 h -1 , and the supplement amount of hydrogen gas is 1.1-1.3 times of the amount of hydrogen gas required for hydrodesulfurization and hydrodenitrification. The catalyst used in the third-stage hydrogenation is a NiMo catalyst, with the content of NiO being 3-5% by weight, the content of MoO3 being 12-15% by weight, and the balance being an Al2O3-MgO-HY-ZrO2 composite carrier, which is obtained by calcining a composite oxide in air at 900-1100℃ for 3-5h under the condition of saturated water being introduced; S4, the product of the third-stage hydrogenation is introduced into a stripping column (6), the gas containing hydrogen sulfide and C4 or lower components discharged from the top of the stripping column (6) is introduced into a tail gas treatment system, and the product at the bottom of the stripping column is subjected to a conventional process of distillation, solvent extraction and rectification in sequence to obtain non-aromatic hydrocarbons, benzene, toluene and xylene.

2. The crude benzol hydrogenation process according to claim 1, characterized in that: The process is suitable for hydrogenation of the whole fraction of crude benzene, and after hydrogenation, the total sulfur in the crude benzene is less than 0.5mg / kg, the total nitrogen is less than 0.5mg / kg, and the loss rate of total aromatic hydrocarbons is less than 0.5%.

Images