A process for the hydrodealkylation of toluene to benzene using a chromium oxide-alumina catalyst

Abstract

The application relates to a method for preparing benzene by toluene hydrodealkylation with a chromium oxide-aluminum oxide catalyst, and relates to the field of chemical production technology, which comprises the following steps: S1, preheating p-toluene and hydrogen; S2, mixing the preheated toluene and hydrogen in step S1 through a mixer; S3, conveying the mixed gas in step S2 to a heating furnace; S4, adding an additive to the mixed gas output by the heating furnace, and conveying the mixed gas with the additive to a reactor; S5, heat-exchanging the reactant through the toluene and hydrogen in step S1; S6, conveying the heat-exchanged reactant in step S5 to a high-pressure separator; S7, removing heavy components generated by a side reaction in the reactor in step S6 through a heavy component removal tower, and conveying the remaining benzene and toluene to a benzene tower; and S8, conveying methane separated by the high-pressure separator to a hydrogen production system.

Description

Technical Field

[0001] This application relates to the field of chemical production technology, and in particular to a method for producing benzene by hydrogenation dealkylation of toluene using a chromium oxide-aluminum oxide catalyst. Background Technology

[0002] Benzene is an important raw material for chemical production. Producing benzene from toluene not only utilizes the relatively surplus toluene inventory but also releases benzene from the market's shortage. Currently, the main processes for producing benzene from toluene in the market are the toluene disproportionation process developed by the Shanghai Research Institute of Petroleum and Chemical Industry and the thermal cracking process developed by UOP. The toluene disproportionation process converts some toluene into xylene, limiting the benzene yield to around 40%–50%. The thermal cracking process removes the methyl groups from toluene through high-temperature thermal cracking, theoretically achieving a benzene yield of 95%–98%. However, due to the high operating temperature, high energy consumption, and high requirements for equipment and instrumentation, the investment in the plant is substantial. Summary of the Invention

[0003] To address the aforementioned technical problems, this application provides a method for producing benzene by hydrogenation dealkylation of toluene using a chromium oxide-aluminum oxide catalyst.

[0004] This application provides a method for the hydrogenation dealkylation of toluene to produce benzene using a chromium oxide and alumina catalyst, employing the following technical solution: A method for the hydrogenation dealkylation of toluene to benzene using chromium oxide and aluminum oxide catalysts includes the following steps: Step S1: Preheat toluene and hydrogen. The toluene is preheated through a first feed preheater, and the hydrogen is preheated through a second feed preheater. Step S2: Mix the preheated toluene and hydrogen from step S1 using a mixer; Step S3: The mixed gas from step S2 is fed into a heating furnace for heating, so that the temperature of the mixed gas is further increased; Step S4: After the mixed hydrogen gas is further heated in the heating furnace, an additive is added to the mixed gas output from the heating furnace, and the mixed gas with the additive is transported to the reactor. The catalyst bed inside the reactor is filled with chromium oxide and aluminum oxide catalyst. Step S5: The reactant output from the reactor serves as the heat exchange medium between the first feed preheater and the second feed heat exchanger, passing sequentially through the first feed preheater and the second feed preheater. In steps S6 and S5, the reactants after heat exchange are transported to a high-pressure separator to separate the light components and additives from the reactants. The remaining benzene, toluene, and heavy components are then separated in a de-heavy column. The light components are hydrogen and methane, and the main component of the heavy components is naphthalene. Step S7: The heavy component generated by the side reaction in the reactor in step S6 is removed by the heavy component removal tower. The remaining benzene and toluene are sent to the benzene tower for separation. The pure benzene separated by the benzene tower is sent to the next stage. The recycled toluene separated by the benzene tower is mixed with fresh toluene and sent to the second feed preheater in step S1. Step S8: The methane separated by the high-pressure separator is sent to the hydrogen production system. The hydrogen production system uses the generated methane as raw material to produce carbon monoxide, carbon dioxide and recycled hydrogen through the reaction of methane and water. The recycled hydrogen generated by the hydrogen production system is mixed with fresh hydrogen and sent to the first feed preheater in step S1. The waste gas separated by the hydrogen production system is sent to the waste gas treatment system for treatment before being discharged.

[0005] Preferably, the chromium oxide alumina catalyst has a chromium oxide content of 15-25%, a support of γ-Al2O3, a specific surface area of ​​78.8±0.23m² / g, and a pore volume of 0.18-0.22cm³ / g.

[0006] Preferably, in step S1, the toluene is heated to 150°C after passing through the first feed preheater.

[0007] Preferably, in step S1, the hydrogen gas is heated to 400°C after passing through the second feed preheater.

[0008] Preferably, both the first feed preheater and the second feed preheater are fixed tube sheet heat exchangers.

[0009] Preferably, in step S3, the heating furnace heats the toluene and hydrogen mixture to 600°C.

[0010] Preferably, in step S4, the reactor type is a fixed-bed reactor, and the reaction temperature inside the reactor is 560–630°C, the hydrogen partial pressure is 2.5–6.0 MPaG, the hydrogen-to-oil volume ratio is 300–1000, and the liquid hourly space velocity is 0.4–1.5 h⁻¹. -1 .

[0011] Preferably, in step S4, the additive added to the mixed gas heated in the heating furnace is water vapor.

[0012] Preferably, in step S6, the heavy component removal column is an atmospheric distillation column with an atmospheric operating pressure at the top and an operating temperature of 90-95°C at the top. The operating pressure at the bottom is 0.005 MPaG and the operating temperature at the bottom is 245-250°C. Benzene and toluene are collected from the top of the heavy component removal column and enter the benzene column, while the heavy components are collected from the bottom of the heavy component removal column.

[0013] Preferably, in step S6, the benzene column is an atmospheric distillation column with an atmospheric operating pressure at the top and an operating temperature of 80°C at the top. The operating pressure at the bottom is 0.006 MPaG and the operating temperature at the bottom is 110-115°C. Benzene is drawn from the top of the column, and toluene is drawn from the bottom.

[0014] This application discloses a method for the hydrogenation dealkylation of toluene to produce benzene using a chromium oxide-aluminum oxide catalyst, which includes at least one of the following beneficial technical effects: 1. Due to the chromium oxide and alumina catalyst packed in the reactor, by controlling the internal conditions of the reactor as follows: temperature: 600℃~610℃; pressure: 4.0~4.5MPaG; hydrogen-to-oil volume ratio: 500~600, the catalyst inside the reactor can be kept in a highly active state, which effectively guarantees the yield of benzene, the selectivity of benzene, and the conversion rate of toluene. 2. By adding water vapor as an additive to the mixed gas before it enters the reactor, it can react with the carbon deposits formed on the catalyst surface to form carbon monoxide or carbon dioxide, thereby inhibiting the accumulation of carbon deposits and ensuring the activity of the catalyst. At the same time, water vapor can also reduce the partial pressure of toluene in the reaction system, thermodynamically inhibiting the occurrence of aromatic condensation and coking reactions, and also acting as a diluent, achieving an effect similar to reducing the reaction pressure. 3. By using the hydrogen production system in conjunction with the benzene tower, hydrogen and toluene can be reused, which can effectively reduce the consumption of hydrogen and toluene in the production process and save production costs. Attached Figure Description

[0015] Figure 1 This is a schematic diagram illustrating the overall structure of the benzene production system in an embodiment of this application.

[0016] Figure 2 This is a flowchart illustrating a method for producing benzene by hydrogenation dealkylation of toluene, as described in this application.

[0017] Explanation of reference numerals in the attached drawings: 1. First feed preheater; 2. Second feed preheater; 3. Mixer; 4. Heating furnace; 5. Reactor; 6. High-pressure separator; 7. Hydrogen production system; 8. Heavy component removal tower; 9. Benzene tower; 10. Hydrogen feed pipeline; 11. Toluene feed pipeline; 12. Toluene discharge pipeline; 13. Hydrogen discharge pipeline; 14. First connecting pipeline; 15. Second connecting pipeline; 16. Steam supply pipeline; 17. Steam supply system; 18. Reactant pipeline; 19. Third connecting pipeline; 20. Fourth connecting pipeline; 21. Light component conveying pipeline; 22. Hydrogen reflux pipeline; 23. Exhaust gas emission pipeline; 24. Exhaust gas treatment system; 25. Wastewater discharge pipeline; 26. Wastewater treatment system; 27. Fifth connecting pipeline; 28. Heavy component emission pipeline; 29. ​​Sixth connecting pipeline; 30. Toluene reflux pipeline; 31. Pure benzene emission pipeline. Detailed Implementation

[0018] The following will be based on embodiments of the present invention. Figure 1-2 The technical solutions in the embodiments of the present invention are clearly and completely described herein. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] This application discloses a method for the hydrogenation dealkylation of toluene to produce benzene using a chromium oxide-aluminum oxide catalyst. (Refer to...) Figure 1 The benzene production system used in the toluene hydrogenation dealkylation method mainly includes a first feed preheater 1, a second feed preheater 2, a mixer 3, a heater 4, a reactor 5, a high-pressure separator 6, a hydrogen production system 7, a de-heavy tower 8, and a benzene tower 9.

[0020] In this embodiment, both the first feed preheater 1 and the second feed preheater 2 are fixed tube sheet heat exchangers. The material inlet end of the first feed preheater 1 is connected to a toluene feed pipe 11 for toluene to flow in, and the material inlet end of the second feed preheater 2 is connected to a hydrogen feed pipe 10 for hydrogen to flow in.

[0021] The material outlet of the first feed preheater 1 is connected to the inlet of the mixer 3 through the toluene discharge pipe 12. The material outlet of the second feed preheater 2 is connected to the inlet of the mixer 3 through the hydrogen discharge pipe 13. The outlet of the mixer 3 is connected to the inlet of the heater 4 through the first connecting pipe 14.

[0022] The outlet of mixer 3 is connected to the inlet of reactor 5 through a second connecting pipe 15. A steam supply pipe 16 is connected to the second connecting pipe 15 through a three-way valve. The inlet of the steam supply pipe 16 is connected to the steam supply system 17.

[0023] In this embodiment, reactor 5 is a fixed-bed reactor. The material outlet end of reactor 5 is connected to a reactant pipeline 18. The outlet end of reactant pipeline 18 is connected to the medium inlet end of the first feed preheater 1. The medium outlet end of the first feed preheater 1 is connected to the medium inlet end of the second feed preheater 2 through a third connecting pipeline 19. The medium outlet end of the second feed preheater 2 is connected to the inlet end of the high-pressure separator 6 through a fourth connecting pipeline 20.

[0024] The high-pressure separator 6 is connected to the hydrogen production system 7 by a light component conveying pipeline 21 for conveying light components. The hydrogen production system 7 is connected to a hydrogen mixing device through a hydrogen return pipeline 22. The outlet end of the hydrogen mixing device is connected to the inlet end of the hydrogen feed pipeline 10. The hydrogen mixing device is also externally connected to a hydrogen supply system for supplying fresh hydrogen. The hydrogen production system 7 is connected to the waste gas treatment system 24 through a waste gas emission pipeline 23.

[0025] The high-pressure separator 6 is connected to a wastewater discharge pipe 25 for discharging wastewater, and the outlet end of the wastewater discharge pipe 25 is connected to the wastewater treatment system 26.

[0026] The high-pressure separator 6 is also connected to the heavy component removal tower 8 via the fifth connecting pipe 27. The bottom of the heavy component removal tower 8 is connected to the heavy component discharge pipe 28 for discharging heavy components. The top of the heavy component removal tower 8 is connected to the benzene tower 9 via the sixth connecting pipe 29.

[0027] The bottom of benzene tower 9 is connected to a toluene mixing device via a toluene reflux pipe 30. The outlet of the toluene mixing device is connected to the inlet of the toluene feed pipe 11, and the toluene mixing device is also externally connected to a toluene supply system for supplying fresh toluene. The top of benzene tower 9 is connected to the equipment of the next stage via a pure benzene discharge pipe 31.

[0028] Based on the above-described benzene production system, this embodiment proposes a method for producing benzene by hydrogenation dealkylation of toluene using a chromium oxide-aluminum oxide catalyst, which mainly includes the following steps: Step S1: Preheat toluene and hydrogen. Toluene is preheated through a first feed preheater 1, and hydrogen is preheated through a second feed preheater 2. Specifically, the toluene is preheated to 150°C through the first feed preheater 1; and preheated to 400°C through the second feed preheater 2. Step S2: Mix the preheated toluene and hydrogen from step S1 using mixer 3; Step S3: The mixed gas from step S2 is transported to the heating furnace 4 for heating, so that the mixed gas is further heated; The preheated toluene and hydrogen mixture is further heated in heating furnace 4, raising the temperature of the mixture to 600°C. Step S4: After the mixed hydrogen gas is further heated by the heating furnace 4, an additive is added to the mixed gas output from the heating furnace 4, and the mixed gas with the additive is transported to the reactor 5. The catalyst bed inside the reactor 5 is filled with chromium oxide and aluminum oxide catalyst. The reaction temperature inside reactor 5 is 560–630℃, the hydrogen partial pressure is 2.5–6.0 MPaG, the hydrogen-to-oil volume ratio is 300–1000, and the liquid hourly space velocity is 0.4–1.5 h⁻¹. −1 ; In the chromium oxide alumina catalyst, the chromium oxide content is 15-25%, the support is γ-Al2O3, the specific surface area is 78.8±0.23m² / g, and the pore volume is 0.18-0.22cm³ / g; In addition, the additive added to the mixed gas heated by the heating furnace 4 is water vapor; Step S5: The reactant output from reactor 5 serves as the heat exchange medium between the first feed preheater 1 and the second feed heat exchanger, passing sequentially through the first feed preheater 1 and the second feed preheater 2. In steps S6 and S5, the heat-exchanged reactants are transported to the high-pressure separator 6 to separate the light components and additives from the reactants. The remaining benzene, toluene, and heavy components enter the de-heavy tower 8 for separation. The light components are hydrogen and methane, and the main component of the heavy components is naphthalene. Among them, the heavy component removal tower 8 is an atmospheric distillation tower with an atmospheric operating pressure and an operating temperature of 90-95℃ at the top. The operating pressure at the bottom is 0.005MPaG and the operating temperature at the bottom is 245-250℃. Benzene and toluene are collected from the top of the heavy component removal tower 8 and enter the benzene tower 9, while heavy components are collected from the bottom of the heavy component removal tower 8. Benzene column 9 is an atmospheric distillation column with an operating pressure of atmospheric pressure at the top and an operating temperature of 80°C at the top. The operating pressure at the bottom is 0.006 MPaG and the operating temperature at the bottom is 110-115°C. Benzene is collected from the top of the column, and toluene is collected from the bottom of the column. Step S7: The heavy component generated by the side reaction in reactor 5 in step S6 is removed by the heavy component in the heavy component removal tower 8. The remaining benzene and toluene are sent to benzene tower 9 for separation. The pure benzene separated by benzene tower 9 is sent to the next stage. The recycled toluene separated by benzene tower 9 is mixed with fresh toluene and sent to the second feed preheater 2 in step S1. In step S8, the methane separated by the high-pressure separator 6 is transported to the hydrogen production system 7. The hydrogen production system 7 uses the generated methane as raw material to produce carbon monoxide, carbon dioxide, and recycled hydrogen through the reaction of methane and water. The recycled hydrogen generated by the hydrogen production system 7 is mixed with fresh hydrogen and then transported together to the first feed preheater 1 in step S1. The waste gas separated by the hydrogen production system 7 is transported to the waste gas treatment system 24 for treatment before being discharged.

[0029] In actual production and processing, fresh toluene and reflux toluene are mixed and then fed into the first feed preheater 1 through the toluene feed pipe 11 for preheating. Fresh hydrogen and reflux hydrogen are mixed and then fed into the second feed preheater 2 through the hydrogen feed pipe 10 for preheating.

[0030] Toluene is preheated to 125°C by the first feed preheater 1, and hydrogen is preheated to 400°C by the second feed preheater 2. The preheated toluene and hydrogen are then transported to the mixer 3 for mixing via the toluene outlet pipe 12 and the hydrogen outlet pipe 13, respectively. The mixed gas is then transported to the heating furnace 4 via the first connecting pipe 14 for further heating, raising the temperature of the mixed gas to 600°C.

[0031] The mixed gas heated to 600°C is delivered through the second connecting pipe 15. During the output of the mixed gas, additive water vapor is introduced into the mixer 3 through the water vapor supply pipe 16. The mixed gas mixed with water vapor is delivered to the reactor 5 through the second connecting pipe 15. The mixed gas is catalyzed by the catalyst and further reacted in the reactor 5. The reactants are sent out through the reactant pipe 18 and pass through the first feed preheater 1 and the second feed preheater 2 in sequence.

[0032] During the process of the reactants passing through the first feed preheater 1 and the second feed preheater 2, the reactants can act as heat exchange mediums to exchange heat with the toluene fed through the toluene feed pipe 11 and the hydrogen fed through the second feed preheater 2, thereby recycling the heat of reaction of the reactants. This eliminates the need for a condensation device to cool the reactants and saves the cost of preheating the toluene and hydrogen.

[0033] The reactants are transported to the high-pressure separator 6 via the fourth connecting pipe 20. The high-pressure separator 6 separates the light components such as hydrogen and methane from the reactants, and the methane is transported to the hydrogen production system 7. The remaining additive water vapor in the reactants is separated into wastewater, which is discharged through the wastewater discharge pipe 25 and treated by the wastewater treatment system 26 before being discharged. The remaining benzene, toluene, and heavy components are transported to the de-heavy component tower 8 via the fifth connecting pipe 27.

[0034] The heavy component removal tower 8 separates the heavy components generated by the side reaction in the reactants. The separated heavy components are discharged through the heavy component discharge pipe 28. The remaining toluene and benzene are transported to the benzene tower 9 through the sixth pipe. The benzene tower 9 separates benzene and toluene. The separated toluene is transported to the toluene mixing unit through the toluene reflux pipe 30 and reused after being mixed with fresh toluene. The separated benzene is transported to the equipment of the next process section through the pure benzene discharge pipe 31.

[0035] The hydrogen production system 7 uses the generated methane as raw material to produce carbon monoxide, carbon dioxide and hydrogen through the reaction of methane and water. The generated hydrogen is transported to the hydrogen mixing device to be mixed with fresh hydrogen and reused. The carbon monoxide and carbon dioxide generated in the reaction are transported to the waste gas treatment system 24 through the waste gas emission pipe 23 for treatment before being discharged.

[0036] By using the hydrogen production system 7 in conjunction with the benzene tower 9, hydrogen and toluene can be reused, which can effectively reduce the consumption of hydrogen and toluene in the production process and save production costs.

[0037] As shown in Table 1, the reaction conditions inside the reactor were a hydrogen-to-oil volume ratio of 2000 and a liquid hourly space velocity of 0.3 h⁻¹. -1 The toluene conversion rate, benzene yield, and benzene selectivity were measured under different temperature conditions inside the reactor at a pressure of 4.9 MPaG. The results are shown in Table 1.

[0038] Hydrogen-to-oil volume ratio <![CDATA[Liquid hourly space velocity (h -1 )]]> Reaction temperature (°C) Pressure (MPaG) Toluene conversion rate (%) Benzene yield (%) Benzene selectivity (%) Running time (h) 2000 0.3 581.5 4.9 36.41 36.75 96.78 15.5 2000 0.3 591.3 4.9 46.73 44.59 92.62 22.5 2000 0.3 611.6 4.9 67.42 61.42 89.28 46.5 2000 0.3 621.8 4.9 80.42 67.64 82.3 52.5 2000 0.3 631.2 4.9 92.55 78.13 83.36 69.5 2000 0.3 641.1 4.9 91.57 64.48 67.81 78 2000 0.3 651.3 4.9 88.88 66.14 73.18 96 Table 1 As shown in Table 2, under the reactor conditions of a reaction temperature of 610℃, a toluene feed flow rate of 0.1 ml / min, and a hydrogen feed flow rate of 90 ml / min, the toluene conversion rate, benzene yield, and benzene selectivity were measured at different pressures inside the reactor.

[0039] Reaction temperature (°C) Toluene feed flow rate (ml / min) Hydrogen flow rate (ml / min) Pressure (MPaG) Toluene conversion rate (%) Benzene selectivity (%) Running time (h) 610.7 0.1 90 3.9 65.05 93.1 79.5 610.5 0.1 90 6.0 66.32 88.46 98 610.8 0.2 90 3.9 62.47 89.94 77 610.6 0.2 90 6.0 60.03 88.81 84.5 Table 2 As shown in Table 3, the biphenyl content and toluene conversion rate were measured under different hydrogen flow rates under the following reactor conditions: toluene feed flow rate of 0.2 ml / min and reaction temperature of 600℃.

[0040] Toluene feed flow rate (ml / min) Reaction temperature (°C) Hydrogen flow rate (ml / min) Biphenyl content (%) Toluene conversion rate (%) Running time (h) 0.2 601.1 200 7.12 74.7 70.5 0.2 600.6 150 9.01 78.64 96.5 0.2 600.9 120 9.61 79.78 101.5 0.2 600.8 90 8.61 69.98 116.5 0.2 600.8 60 8.45 58.29 122.5 Table 3 Based on the data in Tables 1, 2 and 3, in order to ensure the yield, selectivity and toluene conversion of benzene, the internal conditions of the reactor in this embodiment are preferably controlled as follows: temperature: 600℃~610℃; pressure: 4.0~4.5MPaG; hydrogen-to-oil volume ratio: 500~600.

[0041] In this embodiment, after the mixed gas formed by mixing hydrogen and toluene is heated in a heating furnace, water vapor is added to the mixed gas before it enters the reactor. The water vapor can react with the carbon deposits generated on the catalyst surface to convert the carbon deposits into carbon monoxide or carbon dioxide, thereby inhibiting the accumulation of carbon deposits and ensuring the activity of the catalyst.

[0042] In addition, water vapor can reduce the partial pressure of toluene in the reaction system, thermodynamically inhibiting the occurrence of aromatic condensation and coking reactions, while also acting as a diluent, achieving an effect similar to reducing reaction pressure.

[0043] The above are all preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for the hydrogenation dealkylation of toluene to produce benzene using chromium oxide and aluminum oxide catalysts, characterized in that, Includes the following steps: Step S1: Preheat toluene and hydrogen. The toluene is preheated through a first feed preheater, and the hydrogen is preheated through a second feed preheater. Step S2: Mix the preheated toluene and hydrogen from step S1 using a mixer; Step S3: The mixed gas from step S2 is fed into a heating furnace for heating, so that the temperature of the mixed gas is further increased; Step S4: After the mixed hydrogen gas is further heated in the heating furnace, an additive is added to the mixed gas output from the heating furnace, and the mixed gas with the additive is transported to the reactor. The catalyst bed inside the reactor is filled with chromium oxide and aluminum oxide catalyst. Step S5: The reactant output from the reactor serves as the heat exchange medium between the first feed preheater and the second feed heat exchanger, passing sequentially through the first feed preheater and the second feed preheater. In steps S6 and S5, the reactants after heat exchange are transported to a high-pressure separator to separate the light components and additives from the reactants. The remaining benzene, toluene, and heavy components are then separated in a de-heavy column. The light components are hydrogen and methane, and the main component of the heavy components is naphthalene. Step S7: The heavy component generated by the side reaction in the reactor in step S6 is removed by the heavy component removal tower. The remaining benzene and toluene are sent to the benzene tower for separation. The pure benzene separated by the benzene tower is sent to the next stage. The recycled toluene separated by the benzene tower is mixed with fresh toluene and sent to the second feed preheater in step S1. Step S8: The methane separated by the high-pressure separator is sent to the hydrogen production system. The hydrogen production system uses the generated methane as raw material to produce carbon monoxide, carbon dioxide and recycled hydrogen through the reaction of methane and water. The recycled hydrogen generated by the hydrogen production system is mixed with fresh hydrogen and sent to the first feed preheater in step S1. The waste gas separated by the hydrogen production system is sent to the waste gas treatment system for treatment before being discharged.

2. The method for producing benzene by hydrogenation dealkylation of toluene using a chromium oxide-aluminum oxide catalyst according to claim 1, characterized in that, The chromium oxide alumina catalyst has a chromium oxide content of 15-25%, a support of γ-Al2O3, a specific surface area of ​​78.8±0.23m² / g, and a pore volume of 0.18-0.22cm³ / g.

3. The method for producing benzene by hydrogenation dealkylation of toluene using a chromium oxide-aluminum oxide catalyst according to claim 2, characterized in that, In step S1, the toluene is heated to 150°C after passing through the first feed preheater.

4. The method for producing benzene by hydrogenation dealkylation of toluene using a chromium oxide-aluminum oxide catalyst according to claim 3, characterized in that, In step S1, the hydrogen gas is heated to 400°C after passing through the second feed preheater.

5. The method for producing benzene by hydrogenation dealkylation of toluene using a chromium oxide-aluminum oxide catalyst according to claim 4, characterized in that, Both the first and second feed preheaters use fixed tube sheet heat exchangers.

6. The method for producing benzene by hydrogenation dealkylation of toluene using a chromium oxide-aluminum oxide catalyst according to claim 4, characterized in that, In step S3, the heating furnace heats the toluene and hydrogen mixture to 600°C.

7. The method for producing benzene by hydrogenation dealkylation of toluene using a chromium oxide-aluminum oxide catalyst according to claim 6, characterized in that, In step S4, the reactor type is a fixed-bed reactor, and the reaction temperature inside the reactor is 560–630℃, the hydrogen partial pressure is 2.5–6.0 MPaG, the hydrogen-to-oil volume ratio is 300–1000, and the liquid hourly space velocity is 0.4–1.5 h⁻¹. -1 .

8. The method for producing benzene by hydrogenation dealkylation of toluene using a chromium oxide-aluminum oxide catalyst according to claim 7, characterized in that, In step S4, the additive added to the mixed gas heated in the furnace is water vapor.

9. The method for producing benzene by hydrogenation dealkylation of toluene using a chromium oxide-aluminum oxide catalyst according to claim 8, characterized in that, In step S6, the heavy component removal column is an atmospheric distillation column with an atmospheric operating pressure and an operating temperature of 90-95°C at the top. The operating pressure at the bottom is 0.005 MPaG and the operating temperature at the bottom is 245-250°C. Benzene and toluene are collected from the top of the heavy component removal column and enter the benzene column, while the heavy components are collected from the bottom of the heavy component removal column.

10. The method for producing benzene by hydrogenation dealkylation of toluene using a chromium oxide-aluminum oxide catalyst according to claim 9, characterized in that, In step S6, the benzene column is an atmospheric distillation column with an atmospheric operating pressure and an operating temperature of 80°C at the top. The operating pressure at the bottom is 0.006 MPaG and the operating temperature at the bottom is 110-115°C. Benzene is drawn from the top of the column, and toluene is drawn from the bottom.

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