System for recovering cyclohexane in benzene hydrogenation tail gas

Abstract

The invention relates to the technical field of benzene hydrogenation processes, and discloses a system for recovering cyclohexane in benzene hydrogenation tail gas, which comprises a pressure tank, a gas-liquid separator, a crystallizer, a centrifugal machine and a storage hopper, the pressure tank is used for pressurizing the tail gas, the gas outlet of the pressure tank is communicated with the inlet of the gas-liquid separator, and the gas outlet of the gas-liquid separator is communicated with the crystallizer. A liquid phase port of the gas-liquid separator is communicated with a liquid inlet of the crystallizer, an output port of the crystallizer is communicated with the centrifugal machine, and a discharge port of the centrifugal machine is communicated with the storage hopper. The system for recovering cyclohexane in benzene hydrogenation tail gas disclosed by the invention solves or improves the problem that cyclohexane cannot be recovered.

Description

A Cyclohexane Recovery System from Benzene Hydrogenation Tail Gas Technical Field

[0001] This invention relates to the field of benzene hydrogenation process technology, and specifically to a cyclohexane recovery system in benzene hydrogenation tail gas. Background Technology

[0002] Benzene and hydrogen undergo a hydrogenation reaction in the presence of a catalyst to produce cyclohexane. To balance the reaction and protect process safety, the reaction system emits a portion of recycled tail gas. The main components of the tail gas are excess unreacted hydrogen and cyclohexane vapor, with hydrogen accounting for approximately 60% to 95% of the tail gas, making it a highly valuable component for recovery.

[0003] Normally, the above-mentioned exhaust gas is treated by being directly fed into the flare system or fuel pipeline as fuel gas. However, burning the high-purity hydrogen and cyclohexane products in it results in huge waste.

[0004] To reduce costs, pressure swing adsorption (PSA) is used to recover hydrogen in related technologies. Although this method can effectively recover hydrogen, the high-value cyclohexane in the exhaust gas cannot be recovered. Instead, it enters the flare system or fuel pipeline along with the desorbed gas, resulting in product loss. Summary of the Invention

[0005] This invention provides a cyclohexane recovery system for benzene hydrogenation tail gas to solve or improve the problem of the inability to recover cyclohexane.

[0006] This invention provides a cyclohexane recovery system from benzene hydrogenation tail gas, comprising: a pressure tank, a gas-liquid separator, a crystallizer, a centrifuge, and a storage hopper. The pressure tank is used to pressurize the tail gas. The outlet of the pressure tank is connected to the inlet of the gas-liquid separator. The liquid phase port of the gas-liquid separator is connected to the liquid inlet of the crystallizer. The outlet of the crystallizer is connected to the centrifuge. The outlet of the centrifuge is connected to the storage hopper.

[0007] In this embodiment, the exhaust gas is conveyed to a pressure tank, which pressurizes the exhaust gas, increasing its pressure and thus the partial pressure of cyclohexane. According to Dalton's law of partial pressures, this significantly increases the dew point temperature of cyclohexane, causing it to condense at a higher temperature. Simultaneously, the increased exhaust gas pressure provides power for its conveying. Pressurizing the exhaust gas liquefies the cyclohexane, which then flows into a liquid state and is conveyed to a gas-liquid separator. The liquid phase inlet of the separator conveys the liquid phase component (mainly liquid cyclohexane) to a crystallizer. The crystallizer cools and crystallizes the liquid phase component, and the cooled mixture (solid cyclohexane and other liquid or gaseous substances) is conveyed to a centrifuge. The centrifuge separates the non-solid substances from the solid cyclohexane, thereby purifying the cyclohexane through crystallization to obtain a solid cyclohexane filter cake. This solid cyclohexane filter cake is then conveyed to a storage hopper, specifically via a conveyor belt.

[0008] In one alternative embodiment, the crystallizer includes:

[0009] A crystallization tank includes an outer shell, an inner shell, and a connecting pipe. A heat exchange gap for the flow of a heat exchange medium is provided between the outer shell and the inner shell. The outer shell has a medium inlet and a medium outlet communicating with the heat exchange gap. The inner shell and the outer shell have corresponding first and second connecting holes. The edges of the first and second connecting holes are sealed to the outer wall of the connecting pipe. One end of the connecting pipe communicates with the inner cavity of the inner shell, and the other end is the liquid inlet. A cooling device is provided to cool the heat exchange medium. The cooling device has a medium outlet and a medium return outlet. The medium outlet communicates with the medium inlet, and the medium outlet communicates with the medium return outlet.

[0010] In one alternative embodiment, the output port of the crystallizer is connected to the centrifuge via a first pipe, and a drive pump is provided on the first pipe.

[0011] In an optional embodiment, a storage tank is also included, and a first discharge valve is provided on the pipe body of the first pipeline located between the drive pump and the crystallizer. The first discharge valve is connected to the storage tank through a second pipeline.

[0012] In one alternative embodiment, a first buffer tank is further included. The inlet of the first buffer tank is used to input the exhaust gas. The first buffer tank has a first outlet and a second outlet. The first outlet is connected to the inlet of the pressure tank, and the second outlet is connected to the liquid inlet of the crystallizer. Along the height direction of the first buffer tank, the second outlet is lower than the first outlet.

[0013] In one optional embodiment, the second outlet is connected to the liquid inlet of the crystallizer via a third pipe, the third pipe being equipped with a third solenoid valve and a second discharge valve, and the first buffer tank being equipped with a liquid level detection sensor, the liquid level detection sensor being communicatively connected to the third solenoid valve.

[0014] In an optional embodiment, a filter is further included, disposed between the first buffer tank and the pressure tank, for filtering the exhaust gas output from the first buffer tank to the pressure tank.

[0015] In one optional embodiment, the system further includes a membrane separator, a hydrogen recovery tank, and a waste storage tank. The gas phase port of the gas-liquid separator is connected to the inlet of the membrane separator. The permeate side of the membrane separator is connected to the hydrogen recovery tank via a fourth pipeline, and a third discharge valve is provided on the fourth pipeline. The non-permeate side of the membrane separator is connected to the waste storage tank via a fifth pipeline.

[0016] In one optional embodiment, the fourth pipeline is provided with a first branch pipe and a first pressure sensor on the pipe body located between the third discharge valve and the permeate side of the membrane separator. The first branch pipe is provided with a first solenoid valve and is connected to the waste storage tank. The first pressure sensor is communicatively connected to the first solenoid valve.

[0017] In one optional embodiment, the pressure tank is connected to the inlet of the gas-liquid separator via a sixth pipeline. A second pressure sensor is installed on the sixth pipeline, and a second branch pipe is installed on the sixth pipeline. The second branch pipe is connected to the waste storage tank, and a second solenoid valve is installed on the second branch pipe. The second pressure sensor is communicatively connected to the second solenoid valve. Attached Figure Description

[0018] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 is a process flow diagram of a cyclohexane recovery system in benzene hydrogenation tail gas according to an embodiment of the present invention.

[0020] Explanation of reference numerals in the attached drawings: 1. Pressure tank; 2. Gas-liquid separator; 201. Liquid phase port; 202. Gas phase port; 3. Crystallizer; 301. Liquid inlet; 302. Outlet; 303. Crystallizer tank; 304. Cooling device; 305. Medium outlet; 306. Medium reflux port; 307. Medium inlet; 308. Medium outlet; 4. Centrifuge; 401. Discharge port; 5. Storage hopper; 6. Gas outlet; 7. First pipeline; 8. Drive pump; 9. Storage tank; 10. First discharge valve; 11. Second pipeline; 12. First buffer tank; 1201. First outlet; 1202. Second outlet ; 13. Third pipeline; 14. Third solenoid valve; 15. Second discharge valve; 16. Liquid level sensor; 17. Membrane separator; 18. Hydrogen recovery tank; 19. Waste storage tank; 20. Fourth pipeline; 21. Third discharge valve; 22. Fifth pipeline; 23. First branch pipe; 24. First pressure sensor; 25. First solenoid valve; 26. Sixth pipeline; 27. Second pressure sensor; 28. Second branch pipe; 29. ​​Second solenoid valve; 30. Filter; 31. Fourth solenoid valve; 32. Third pressure sensor; 33. Seventh pipeline; 34. Fourth discharge valve; Z, height direction. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Benzene and hydrogen undergo a hydrogenation reaction in the presence of a catalyst to produce cyclohexane. To balance the reaction and protect process safety, the reaction system emits a portion of recycled tail gas. The main components of the tail gas are excess unreacted hydrogen and cyclohexane vapor, with hydrogen accounting for approximately 60% to 95% of the tail gas, making it a highly valuable component for recovery.

[0023] Normally, the above-mentioned exhaust gas is treated by being directly fed into the flare system or fuel pipeline as fuel gas. However, burning the high-purity hydrogen and cyclohexane products in it results in huge waste.

[0024] To reduce costs, related technologies employ pressure swing adsorption (PSA) to recover hydrogen. While this method effectively recovers hydrogen, it fails to recover the high-value cyclohexane in the tail gas, which instead enters the flare system or fuel pipeline along with the desorbed gas, resulting in product loss. Therefore, this application provides a cyclohexane recovery system from benzene hydrogenation tail gas to solve or improve the problem of the inability to recover cyclohexane.

[0025] The embodiments of the present invention will now be described with reference to Figure 1.

[0026] According to an embodiment of the present invention, a cyclohexane recovery system for benzene hydrogenation tail gas is provided, comprising a pressure tank 1, a gas-liquid separator 2, a crystallizer 3, a centrifuge 4, and a storage hopper 5. The pressure tank 1 is used to pressurize the tail gas. The outlet 6 of the pressure tank 1 is connected to the inlet of the gas-liquid separator 2. The liquid phase port 201 of the gas-liquid separator 2 is connected to the liquid inlet 301 of the crystallizer 3. The outlet 302 of the crystallizer 3 is connected to the centrifuge 4. The outlet 401 of the centrifuge 4 is connected to the storage hopper 5.

[0027] In this embodiment, the exhaust gas is delivered to pressure tank 1, which pressurizes the exhaust gas to increase its pressure. Specifically, the pressure in pressure tank 1 is 2 MPa to 2.8 MPa, which increases the partial pressure of cyclohexane. According to Dalton's law of partial pressure, this significantly increases the dew point temperature of cyclohexane, allowing it to condense at a higher temperature. At the same time, increasing the pressure of the exhaust gas provides power for its delivery. After pressurizing the exhaust gas, cyclohexane can be liquefied (cyclohexane has a boiling point of 80.7℃, but the dew point will increase under pressure, making it easier for cyclohexane to remain in a liquid state). The cyclohexane in the exhaust gas becomes liquid and is transported to the gas-liquid separator 2. The liquid phase port 201 of the gas-liquid separator 2 transports the liquid phase component (mainly liquid cyclohexane) to the crystallizer 3. The crystallizer 3 cools and crystallizes the liquid phase component. The cooling temperature of the crystallizer 3 is 4℃ to 6℃. The cooled mixture (solid cyclohexane and other liquid or gaseous substances) is transported to the centrifuge 4. The centrifuge 4 separates the non-solid substances from the solid cyclohexane, thereby enabling the crystallization and purification of cyclohexane to obtain a solid cyclohexane filter cake. The solid cyclohexane filter cake is then transported to the storage hopper 5 for storage.

[0028] In one embodiment, the crystallizer 3 includes a crystallization tank 303 and a cooling device 304. Specifically, the crystallization tank 303 includes an outer shell, an inner shell, and a connecting pipe. A heat exchange gap for the flow of heat exchange medium is provided between the outer shell and the inner shell. The outer shell is provided with a medium inlet 307 and a medium outlet 308 that connect the heat exchange gap. The inner shell and the outer shell are respectively provided with a first connecting hole and a second connecting hole. The edges of the first connecting hole and the second connecting hole are sealed to the outer wall of the connecting pipe. One end of the connecting pipe is connected to the inner cavity of the inner shell, and the other end is a liquid inlet 301. The cooling device 304 can cool down the heat exchange medium. The cooling device 304 is provided with a medium outlet 305 and a medium return port 306. The medium outlet 305 is connected to the medium inlet 307, and the medium outlet 308 is connected to the medium return port 306.

[0029] In this embodiment, the crystallizer 303 adopts a double-layer structure consisting of an outer shell and an inner shell, forming an independent heat exchange gap. This enables efficient heat exchange between the heat exchange medium and the liquid phase components inside the inner shell, ensuring the low-temperature environment required for crystallization. The connecting pipe is sealed at the edges of the first and second connecting holes, effectively preventing the liquid phase components inside the inner shell from leaking into the heat exchange gap, while also preventing the heat exchange medium from entering the inner cavity of the inner shell, ensuring the stability and safety of the crystallization process. The use of cold water as the heat exchange medium reduces costs.

[0030] In one embodiment, the output port 302 of the crystallizer 3 is connected to the centrifuge 4 through a first pipe 7, and a drive pump 8 is provided on the first pipe 7.

[0031] In this embodiment, the crystallized mixture contains a large number of cyclohexane crystal particles, with a viscosity higher than that of the pure liquid phase component and poor flow performance. If transported solely by gravity, it is prone to slow conveying speed, unstable conveying volume, or even interruption, resulting in insufficient feed to centrifuge 4, affecting purification efficiency, and ultimately interrupting the entire recovery process. A second buffer tank is installed on the first pipeline 7 between the first discharge valve 10 and the drive pump 8, which can buffer the flow when the conveying volume is unstable. The drive pump 8 provides stable power for the transport of the mixture, ensuring that the mixture is continuously fed into centrifuge 4 at a suitable speed and flow rate. The amount of tail gas generated and the cyclohexane content will fluctuate with the production load, causing the yield of the crystallized mixture to change accordingly. The drive pump 8 can flexibly adjust the conveying flow rate. When the mixture yield is large, the conveying flow rate is increased to ensure that centrifuge 4 can process it in time and avoid the mixture from accumulating in crystallizer 3. When the mixture yield is small, the conveying flow rate is reduced to reduce the energy consumption of drive pump 8, achieving energy-saving operation of the system, while avoiding idling losses of centrifuge 4 due to insufficient feed and extending the service life of centrifuge 4.

[0032] In one embodiment, a storage tank 9 is also included, and a first discharge valve 10 is provided on the pipe body of the first pipeline 7 located between the drive pump 8 and the crystallizer 3. The first discharge valve 10 is connected to the storage tank 9 through a second pipeline 11.

[0033] In this embodiment, under normal operating conditions, the bottom of the crystallizer 3 outputs a mixed substance (supercooled cyclohexane and liquid cyclohexane). Under the action of the drive pump 8, the mixed substance is transported to the centrifuge 4 to separate the solid cyclohexane. After the solid cyclohexane is produced for 12 hours, the production stops, the drive pump 8 is turned off and the first discharge valve 10 is opened to heat up the crystallizer, so that the crystalline benzene in the crystallizer 3 is liquefied and enters the storage tank 9 through the second pipe 11.

[0034] In one embodiment, a first buffer tank 12 is also included. The inlet of the first buffer tank 12 is used to input exhaust gas. The first buffer tank 12 has a first outlet 1201 and a second outlet 1202. The first outlet 1201 is connected to the inlet of the pressure tank 1, and the second outlet 1202 is connected to the liquid inlet 301 of the crystallizer 3. Along the height direction Z of the first buffer tank 12, the second outlet 1202 is lower than the first outlet 1201.

[0035] In this embodiment, the first buffer tank 12 can buffer the exhaust gas, balance the pressure and flow fluctuations of the exhaust gas, and prevent damage to the pipelines in the system. The exhaust gas contains some liquid cyclohexane, which is distributed at the bottom of the first buffer tank 12. The liquid cyclohexane can be transported from the second outlet 1202 to the crystallizer 3 for cooling and crystallization. The second outlet 1202 is lower than the first outlet 1201, ensuring that the liquid cyclohexane can only be output from the bottom of the second outlet 1202 and will not be output from the top of the first outlet 1201 into the pressure tank 1. The first outlet 1201 mainly outputs the gaseous components in the exhaust gas. The first buffer tank 12 can initially separate the gaseous substances and liquid substances (liquid cyclohexane) in the exhaust gas.

[0036] It should be noted that if liquid cyclohexane enters the pressurization tank, the liquid is not easily compressed, and the pressure tank 1 is easily damaged during the pressurization process.

[0037] In one embodiment, the second outlet 1202 is connected to the liquid inlet 301 of the crystallizer 3 through the third pipe 13. The third pipe 13 is equipped with a third solenoid valve 14 and a second discharge valve 15. The first buffer tank 12 is equipped with a liquid level detection sensor 16, which is communicatively connected to the third solenoid valve 14.

[0038] In this embodiment, when the liquid level sensor 16 detects that the liquid substance in the first buffer tank 12 has reached a preset height, the liquid level sensor 16 sends a signal to the third solenoid valve 14 to control the third solenoid valve 14 to open, and at the same time opens the second discharge valve 15, so that liquid cyclohexane can be transported from the second outlet 1202 to the crystallizer 3 for cooling and crystallization. The second discharge valve 15 can be manually opened or closed, increasing control redundancy. If the third solenoid valve 14 is damaged, the opening and closing of the third pipeline 13 can be controlled by manually opening or closing the second discharge valve 15.

[0039] In one embodiment, a filter 30 is also included, which is disposed between the first buffer tank 12 and the pressure tank 1, for filtering the exhaust gas output from the first buffer tank 12 to the pressure tank 1.

[0040] In this embodiment, filter 30 filters the exhaust gas, removing solid residues and preventing impurities from damaging pressure tank 1 and downstream equipment. It also reduces the risk of system pipeline blockage. If solid impurities in the exhaust gas enter the system pipeline, they will gradually deposit on the inner wall of the pipeline with the gas flow. Long-term accumulation can lead to pipeline blockage, affecting the transport of exhaust gas and liquid components, causing system operation interruption and production losses. Filter 30 effectively removes impurities, reduces impurity deposition on the inner wall of the pipeline, lowers the risk of pipeline blockage, ensures the continuous and stable operation of the entire recovery process, and reduces system downtime losses.

[0041] In one embodiment, the system further includes a membrane separator 17, a hydrogen recovery tank 18, and a waste storage tank 19. The gas phase port 202 of the gas-liquid separator 2 is connected to the inlet of the membrane separator 17. The permeate side of the membrane separator 17 is connected to the hydrogen recovery tank 18 through a fourth pipeline 20. A third discharge valve 21 is provided on the fourth pipeline 20. The non-permeate side of the membrane separator 17 is connected to the waste storage tank 19 through a fifth pipeline 22.

[0042] In this embodiment, the membrane separator 17 can separate the gaseous substances (mainly hydrogen and a small amount of alkanes) output from the gas phase port 202 of the gas-liquid separator 2. Hydrogen has a small molecular weight, and by setting the pore size of the filter membrane in the membrane separator 17, only hydrogen is allowed to pass through and enter the permeate side of the membrane separator 17. The hydrogen is then transported to the hydrogen recovery tank 18 via the fourth pipeline 20, and the third discharge valve 21 controls the hydrogen transport. On the non-permeate side of the membrane separator 17, other gases besides hydrogen in the tail gas are transported to the waste storage tank 19 via the fifth pipeline 22.

[0043] In some embodiments, the non-permeable side of the membrane separator 17 is connected to the waste storage tank 19 via a fifth pipeline 22. A fourth solenoid valve 31 and a third pressure sensor 32 are provided on the fifth pipeline 22. The third pressure sensor 32 is communicatively connected to the fourth solenoid valve 31. When the third pressure sensor 32 reaches a third preset pressure value, wherein the third preset pressure value is 2.575 MPa, the fourth solenoid valve 31 is opened to transport the gases other than hydrogen in the exhaust gas to the waste storage tank 19 via the fifth pipeline 22.

[0044] In some embodiments, the gas phase port 202 of the gas-liquid separator 2 is connected to the inlet of the membrane separator 17 through a seventh pipeline 33, and a fourth discharge valve 34 is provided on the seventh pipeline 33.

[0045] In one embodiment, the fourth pipeline 20 is provided with a first branch pipe 23 and a first pressure sensor 24 on the pipe body between the third discharge valve 21 and the permeate side of the membrane separator 17. The first branch pipe 23 is provided with a first solenoid valve 25. The first branch pipe 23 is connected to the waste storage tank 19. The first pressure sensor 24 is communicatively connected to the first solenoid valve 25.

[0046] In this embodiment, when the first pressure sensor 24 reaches the first preset pressure value (2.575 MPa), to prevent pipeline rupture, the first pressure sensor 24 outputs a signal to the first solenoid valve 25, which opens to release pressure from the fourth pipeline 20. The third discharge valve 21 can be opened or closed manually or controlled by the controller to control the delivery of hydrogen, increasing control redundancy. If the first solenoid valve 25 is damaged, the third discharge valve 21 can be opened or closed manually to control the opening and closing of the third pipeline 13.

[0047] In one embodiment, pressure tank 1 is connected to the inlet of gas-liquid separator 2 via a sixth pipeline 26. A second pressure sensor 27 is installed on the sixth pipeline 26. A second branch pipe 28 is installed on the sixth pipeline 26. The second branch pipe 28 is connected to waste storage tank 19. A second solenoid valve 29 is installed on the second branch pipe 28. The second pressure sensor 27 is communicatively connected to the second solenoid valve 29.

[0048] In this embodiment, the second pressure sensor 27 monitors the pressure in the sixth pipeline 26. When the pressure in the sixth pipeline 26 reaches the second preset pressure value, wherein the second preset pressure value is 2.575 MPa, the second solenoid valve 29 is controlled to open to release pressure in the sixth pipeline 26 and ensure the safety of the pipeline system.

[0049] The following is a comprehensive explanation of all the above solutions using an example and in conjunction with Figure 1.

[0050] This embodiment provides a cyclohexane recovery system from benzene hydrogenation tail gas, including a pressure tank 1, a gas-liquid separator 2, a crystallizer 3, a centrifuge 4, and a storage hopper 5. The inlet of the pressure tank 1 receives tail gas from the benzene hydrogenation system and pressurizes the tail gas at a pressure controlled at 2.5 MPa. Pressurization increases the dew point temperature of cyclohexane in the tail gas, providing favorable conditions for subsequent gas-liquid separation. The outlet 6 of the pressure tank 1 is connected to the inlet of the gas-liquid separator 2 via a sixth pipeline 26. The gas-liquid separator 2 separates the pressurized tail gas, separating the liquid phase component (rich in cyclohexane) from the gas phase component (mainly hydrogen). The separation temperature of the gas-liquid separator 2 is controlled at 15°C, and the separation efficiency is not less than 95%.

[0051] The liquid phase port 201 of the gas-liquid separator 2 is connected to the liquid inlet 301 of the crystallizer 3. The crystallizer 3 is used to crystallize the liquid phase components, so that cyclohexane precipitates from the liquid phase to form crystal particles. The crystallization temperature of the crystallizer 3 is controlled at 6°C, and the crystallization time is 1 to 2 hours. The output port 302 of the crystallizer 3 is connected to the centrifuge 4 through the first pipe 7. A drive pump 8 is added to the first pipe 7. The crystallized mixture is transported to the centrifuge 4 through the drive pump 8. The centrifuge 4 is used to separate the crystallized mixture, separating the cyclohexane crystals from the mother liquor. The separation speed of the centrifuge 4 is controlled at 3000 r / min. The purity of the separated cyclohexane crystals is not less than 99.5%. The discharge port 401 of the centrifuge 4 is connected to the storage hopper 5. The storage hopper 5 is used to store the separated cyclohexane crystals.

[0052] The crystallizer 3 includes a crystallization tank 303 and a cooling device 304. The crystallization tank 303 has a double-layer structure, including an outer shell, an inner shell, and a connecting pipe. A heat exchange gap is formed between the outer shell and the inner shell to accommodate the heat exchange medium (cold water). The outer shell is provided with a medium inlet 307 and a medium outlet 308 for the entry and exit of the heat exchange medium, respectively. The inner shell and the outer shell are respectively provided with a first connecting hole and a second connecting hole. The edges of the first connecting hole and the second connecting hole are sealed and welded to the outer wall of the connecting pipe to prevent leakage between the liquid phase components and the heat exchange medium. One end of the connecting pipe is connected to the inner cavity of the inner shell, and the other end serves as the liquid inlet 301 of the crystallizer 3 to receive the liquid phase components delivered by the gas-liquid separator 2. The cooling device 304 uses a chiller to cool the heat exchange medium. The cooling device 304 is equipped with a medium outlet 305 and a medium return port 306. The medium outlet 305 is connected to the medium inlet 307 through a pipeline, and the medium outlet 308 is connected to the medium return port 306 through a pipeline, forming a circulation loop for the heat exchange medium. The cooling device 304 ensures that the temperature of the heat exchange medium is stable at 6℃±1℃.

[0053] The working process of this embodiment is as follows: The exhaust gas enters the first buffer tank 12 through the pipeline. The first buffer tank 12 can buffer the exhaust gas, balance the pressure and flow fluctuations of the exhaust gas, and prevent damage to the pipelines in the system. There is a portion of liquid cyclohexane in the exhaust gas, which is distributed at the bottom of the first buffer tank 12. The liquid cyclohexane can be transported from the second outlet 1202 to the crystallizer 3 for cooling and crystallization. The second outlet 1202 is lower than the first outlet 1201, ensuring that the liquid cyclohexane can only be output from the bottom second outlet 1202 and will not be output from the top first outlet 1201 into the pressure tank 1. The first outlet 1201 mainly outputs the gaseous components in the exhaust gas. The first buffer tank 12 can initially separate the gaseous substances and liquid substances (liquid cyclohexane) in the exhaust gas.

[0054] The gaseous components in the exhaust gas are output from the first outlet 1201 to the filter 30. The filter 30 can filter the exhaust gas, remove solid residues in the exhaust gas, and prevent impurities from damaging the pressure tank 1 and subsequent equipment.

[0055] Pressure tank 1 pressurizes the exhaust gas, raising the pressure to 2.5 MPa. The pressurized exhaust gas is then sent to gas-liquid separator 2 through sixth pipeline 26, where gas-liquid separation occurs at 10°C. The separated liquid phase component (rich in cyclohexane) is discharged from liquid phase port 201, and the gas phase component (mainly hydrogen) is discharged from gas phase port 202. Second pressure sensor 27 monitors the pressure within sixth pipeline 26. When the pressure within sixth pipeline 26 reaches 2.575 MPa, it controls second solenoid valve 29 to open, releasing pressure from sixth pipeline 26 to ensure the safety of the pipeline system.

[0056] The liquid phase component discharged from the gas-liquid separator 2 is sent into the inner cavity of the crystallizer 3 through the connecting pipe. The cooling device 304 is started to cool the heat exchange medium to 6°C and send it into the heat exchange gap through the medium outlet 305. The heat exchange medium flows uniformly in the heat exchange gap to cool and crystallize the liquid phase component in the inner shell. After crystallization for 2 hours, cyclohexane crystal particles are formed.

[0057] The crystallized mixture is fed into centrifuge 4 through the outlet 302 of crystallizer 3 and the first pipe 7. Centrifuge 4 separates the cyclohexane crystals from the mother liquor at a speed of 3000 r / min. The separated cyclohexane crystals are then sent to storage hopper 5 through the outlet 401 of centrifuge 4 for storage, thus completing the recovery of cyclohexane.

[0058] This embodiment can effectively recover cyclohexane from benzene hydrogenation tail gas with a recovery efficiency of not less than 90% and a purity of not less than 99.5% after recovery. It can be reused in the benzene hydrogenation production process, realizing the recycling of resources, reducing the waste of cyclohexane, and lowering the production costs of enterprises.

[0059] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended application.

Claims

1. A cyclohexane recovery system from benzene hydrogenation tail gas, characterized in that, include: The pressure tank (1), gas-liquid separator (2), crystallizer (3), centrifuge (4) and storage hopper (5) are provided. The pressure tank (1) is used to pressurize the tail gas. The outlet (6) of the pressure tank (1) is connected to the inlet of the gas-liquid separator (2). The liquid phase port (201) of the gas-liquid separator (2) is connected to the liquid inlet (301) of the crystallizer (3). The outlet (302) of the crystallizer (3) is connected to the centrifuge (4). The outlet (401) of the centrifuge (4) is connected to the storage hopper (5).

2. The cyclohexane recovery system from benzene hydrogenation tail gas according to claim 1, characterized in that, The crystallizer (3) includes: a crystallization tank (303), including an outer shell, an inner shell and a connecting pipe, a heat exchange gap for the flow of heat exchange medium is provided between the outer shell and the inner shell, a medium inlet (307) and a medium outlet (308) connected to the heat exchange gap are provided on the outer shell, a first connecting hole and a second connecting hole are provided on the inner shell and the outer shell respectively, the edges of the first connecting hole and the second connecting hole are sealed to the outer wall of the connecting pipe, one end of the connecting pipe is connected to the inner cavity of the inner shell, and the other end is the liquid inlet (301); a cooling device (304) capable of cooling the heat exchange medium, the cooling device (304) is provided with a medium outlet (305) and a medium return port (306), the medium outlet (305) is connected to the medium inlet (307), and the medium outlet (308) is connected to the medium return port (306).

3. The cyclohexane recovery system from benzene hydrogenation tail gas according to claim 1, characterized in that, The output port (302) of the crystallizer (3) is connected to the centrifuge (4) through the first pipe (7), and a drive pump (8) is provided on the first pipe (7).

4. The cyclohexane recovery system from benzene hydrogenation tail gas according to claim 3, characterized in that, It also includes a storage tank (9), and the first pipe (7) is provided with a first discharge valve (10) on the pipe body between the drive pump (8) and the crystallizer (3). The first discharge valve (10) is connected to the storage tank (9) through a second pipe (11).

5. The cyclohexane recovery system from benzene hydrogenation tail gas according to claim 1, characterized in that, It also includes a first buffer tank (12), the inlet of which is used to input the exhaust gas. The first buffer tank (12) has a first outlet (1201) and a second outlet (1202). The first outlet (1201) is connected to the inlet of the pressure tank (1), and the second outlet (1202) is connected to the liquid inlet (301) of the crystallizer (3). Along the height direction (Z) of the first buffer tank (12), the second outlet (1202) is lower than the first outlet (1201).

6. The cyclohexane recovery system from benzene hydrogenation tail gas according to claim 5, characterized in that, The second outlet (1202) is connected to the liquid inlet (301) of the crystallizer (3) through the third pipe (13). The third pipe (13) is equipped with a third solenoid valve (14) and a second discharge valve (15). The first buffer tank (12) is equipped with a liquid level detection sensor (16). The liquid level detection sensor (16) is communicatively connected to the third solenoid valve (14).

7. The cyclohexane recovery system from benzene hydrogenation tail gas according to claim 5, characterized in that, It also includes a filter (30) disposed between the first buffer tank (12) and the pressure tank (1) for filtering the exhaust gas output from the first buffer tank (12) to the pressure tank (1).

8. The cyclohexane recovery system from benzene hydrogenation tail gas according to claim 1, characterized in that, It also includes a membrane separator (17), a hydrogen recovery tank (18), and a waste storage tank (19). The gas phase port (202) of the gas-liquid separator (2) is connected to the inlet of the membrane separator (17). The permeate side of the membrane separator (17) is connected to the hydrogen recovery tank (18) through a fourth pipeline (20). A third discharge valve (21) is provided on the fourth pipeline (20). The non-permeate side of the membrane separator (17) is connected to the waste storage tank (19) through a fifth pipeline (22).

9. The cyclohexane recovery system from benzene hydrogenation tail gas according to claim 8, characterized in that, The fourth pipeline (20) is located between the third discharge valve (21) and the permeate side of the membrane separator (17). A first branch pipe (23) and a first pressure sensor (24) are provided on the pipe body. A first solenoid valve (25) is provided on the first branch pipe (23). The first branch pipe (23) is connected to the waste storage tank (19). The first pressure sensor (24) is communicatively connected to the first solenoid valve (25).

10. The cyclohexane recovery system from benzene hydrogenation tail gas according to claim 8, characterized in that, The pressure tank (1) is connected to the inlet of the gas-liquid separator (2) through the sixth pipeline (26). A second pressure sensor (27) is installed on the sixth pipeline (26). A second branch pipe (28) is installed on the sixth pipeline (26). The second branch pipe (28) is connected to the waste storage tank (19). A second solenoid valve (29) is installed on the second branch pipe (28). The second pressure sensor (27) is communicatively connected to the second solenoid valve (29).

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