System and method for preparing benzene from monocyclic aromatic hydrocarbon

Abstract

The invention relates to a system and a method for preparing benzene from monocyclic aromatic hydrocarbon. The system comprises a reaction feeding heat exchanger; the heater is communicated with the cold flow discharge port of the reaction feed heat exchanger; the reactor is used for carrying out chemical reaction on monocyclic aromatic hydrocarbon and hydrogen to obtain a benzene-containing mixture and is communicated with the heater; the steam generator is used for generating steam by utilizing heat carried by the benzene-containing mixture so as to adjust the temperature of the benzene-containing mixture, and is communicated with the reactor and the heat flow feeding hole of the reaction feeding heat exchanger so as to recover waste heat carried by the temperature-adjusted benzene-containing mixture; the cooler is used for cooling the benzene-containing mixture after waste heat recovery, and is communicated with a hot flow discharge port of the reaction feed heat exchanger; and the separation part is used for separating benzene in the cooled benzene-containing mixture and is communicated with the cooler. The technical problem that the equipment risk of an existing aromatic hydrocarbon benzene preparation device is increased due to the fact that the outlet temperature of the reactor is high is solved.

Description

Technical Field

[0001] This application relates to the technical field of oil refining, and particularly to a system and method for preparing benzene from monocyclic aromatic hydrocarbons. Background Art

[0002] Benzene is a raw material for many important chemical products, such as plastics, synthetic fibers, rubber, etc. With the development of the chemical industry, related industries of benzene-based chemical products such as styrene, phenol acetone, and caprolactam have developed rapidly, and the consumption of benzene products is increasing.

[0003] Currently, there are two main methods for preparing benzene from aromatic hydrocarbons: catalytic hydrodealkylation method and thermal dealkylation method.

[0004] However, for the benzene preparation devices used in both the catalytic method and the thermal decomposition method, in a conventional device: a directly connected hot feed heat exchanger is provided at the reactor outlet, and after rapid cooling, the reaction heat is removed through a steam drum, and then it enters the cold feed heat exchanger to further recover heat. Due to the high temperature at the reactor outlet, the material of the high-temperature side of the hot feed heat exchanger is of high grade, and the stress calculation of the tube sheet is complex, there are potential safety hazards. Summary of the Invention

[0005] This application provides a system and method for preparing benzene from monocyclic aromatic hydrocarbons to solve the technical problem that the existing benzene preparation device from aromatic hydrocarbons increases the equipment risk due to the high temperature at the reactor outlet.

[0006] In a first aspect, this application provides a system for preparing benzene from monocyclic aromatic hydrocarbons, the system comprising:

[0007] A reaction feed heat exchanger for preheating monocyclic aromatic hydrocarbons and hydrogen;

[0008] A heater for heating the preheated monocyclic aromatic hydrocarbons and hydrogen, and communicating with the cold outlet of the reaction feed heat exchanger;

[0009] A reactor for carrying out a chemical reaction on the heated monocyclic aromatic hydrocarbons and hydrogen to obtain a benzene-containing mixture, and communicating with the heater;

[0010] A steam generator for generating steam by using the heat carried by the benzene-containing mixture to adjust the temperature of the benzene-containing mixture, communicating with the reactor, and communicating with the hot feed inlet of the reaction feed heat exchanger to recover the waste heat carried by the benzene-containing mixture after temperature adjustment as the heat source for the preheating;

[0011] A cooler for cooling the benzene-containing mixture after recovering the waste heat, and communicating with the hot outlet of the reaction feed heat exchanger;

[0012] A separation unit, configured to separate benzene from the cooled benzene-containing mixture, and is in communication with the cooler.

[0013] Optionally, the separation unit includes:

[0014] A gas-liquid separator, configured to separate the gas-phase material and the liquid-phase material from the cooled benzene-containing mixture, and is in communication with the cooler 5;

[0015] A gas-gas separator, configured to separate methane and hydrogen from the first part of the gas-phase material, and is in communication with the top gas outlet of the gas-liquid separator;

[0016] A liquid-liquid separator, configured to separate benzene and the unreacted monocyclic aromatic hydrocarbon from the liquid-phase material, and is in communication with the bottom liquid outlet of the gas-liquid separator.

[0017] Optionally, the gas outlet of the gas-gas separator is in communication with the cold stream inlet of the reaction feed heat exchanger.

[0018] Optionally, the bottom liquid outlet of the liquid-liquid separator is in communication with the cold stream liquid inlet of the reaction feed heat exchanger.

[0019] Optionally, the separation unit further includes:

[0020] A recycle gas compressor, configured to convey the second part of the gas-phase material to the reaction feed heat exchanger. The gas outlet of the recycle gas compressor is in communication with the cold stream inlet of the reaction feed heat exchanger, and the gas inlet of the recycle gas compressor is in communication with the top gas outlet of the gas-liquid separator.

[0021] Optionally, the reactor includes one of the following: a backmix reactor, a plug flow reactor.

[0022] In a second aspect, the present application provides a method for preparing benzene from a monocyclic aromatic hydrocarbon. The method is adapted to the system according to any one of the embodiments of the first aspect. The method includes:

[0023] S1. Preheat and heat the monocyclic aromatic hydrocarbon and hydrogen;

[0024] S2. Perform a chemical reaction on the heated monocyclic aromatic hydrocarbon and hydrogen to obtain a benzene-containing mixture;

[0025] S3. Carry out steam generation treatment on the heat carried by the benzene-containing mixture, and then carry out recovery and heat treatment of the waste heat to be used as the heat source for preheating in step S1;

[0026] S4. Cool and separate the benzene-containing mixture after the recovery and heat treatment of the waste heat to obtain benzene.

[0027] Optionally, the monocyclic aromatic hydrocarbon includes at least one of the following: toluene, ethylbenzene, xylene, trimethylbenzene, methyl ethylbenzene, and propylbenzene.

[0028] Optionally, the molar ratio of the monocyclic aromatic hydrocarbon to the hydrogen is 1:(3 - 15).

[0029] Optionally, the temperature of the chemical reaction is 600°C - 750°C.

[0030] The above technical solution provided by the embodiments of the present application has the following advantages compared with the prior art:

[0031] In the system for preparing benzene from monocyclic aromatic hydrocarbons provided by the embodiments of the present application, a reaction feed heat exchanger is used to preheat the monocyclic aromatic hydrocarbon and hydrogen; a heater is used to heat the preheated monocyclic aromatic hydrocarbon and hydrogen; a reactor is used to carry out a chemical reaction on the heated monocyclic aromatic hydrocarbon and the hydrogen to obtain a benzene-containing mixture, and a steam generator is used to generate steam by using the heat carried by the benzene-containing mixture to adjust the temperature of the benzene-containing mixture. Canceling the directly connected heat feed heat exchanger at the reactor outlet reduces equipment risks and equipment investment, reduces high-temperature equipment with manufacturing difficulties, and can flexibly adjust the steam production of the steam generator, thereby adjusting the consumption of the fuel gas of the heater; the reaction feed heat exchanger recovers the waste heat carried by the benzene-containing mixture after adjusting the temperature and preheats the monocyclic aromatic hydrocarbon and the hydrogen as described above, further reducing the consumption of the fuel gas of the heater, achieving the maximum utilization of the heat carried by the reaction products. A cooler is used to cool the benzene-containing mixture after recovering the heat; a separation unit is used to separate benzene from the cooled benzene-containing mixture. In summary, the system solves the technical problem that the existing aromatic hydrocarbon to benzene device increases equipment risks due to the high temperature at the reactor outlet, and at the same time can flexibly adjust steam production and fuel gas consumption, and optimize the processing cost in a timely manner. Description of the Drawings

[0032] The drawings here are incorporated into the specification and form a part of the specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts.

[0034] Figure 1 It is a schematic structural diagram of a system for preparing benzene from monocyclic aromatic hydrocarbons provided by the embodiments of the present application; wherein,

[0035] 1 - Reactor feed heat exchanger, 2 - Heater, 3 - Reactor, 4 - Steam generator, 5 - Cooler, 6 - Separation section, 61 - Gas-liquid separator, 62 - Gas-gas separator, 63 - Liquid-liquid separator, 64 - Recycle gas compressor;

[0036] Figure 2 It is a process schematic diagram of a method for preparing benzene from monocyclic aromatic hydrocarbons provided in the embodiments of the present application. Detailed implementation manners

[0037] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the scope of protection of the present application.

[0038] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and single values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within that range, such as 1, 2, 3, 4, 5, and 6, regardless of what the range is. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0039] In the present application, unless otherwise stated, the orientation terms such as "upper" and "lower" specifically refer to the drawing direction in the drawings. Additionally, in the description of the specification of the present application, the terms "including", "comprising", etc. mean "including but not limited to". In this document, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. In this document, "at least one" means one or more, and "multiple" means two or more. "At least one kind", "at least one item (individual) below" or similar expressions refer to any combination of these items, including any combination of single item (individual) or plural items (individuals). For example, "at least one item (individual) of a, b, or c", or, "at least one item (individual) of a, b, and c" can all represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0040] Unless otherwise specified, all kinds of raw materials, reagents, instruments and equipment used in this application can be obtained through market purchase or can be prepared by existing methods.

[0041] Figure 1 It is a schematic structural diagram of a system for preparing benzene from monocyclic aromatic hydrocarbons provided for the examples of this application; please refer to Figure 1 ,

[0042] This application provides a system for preparing benzene from monocyclic aromatic hydrocarbons, and the system includes:

[0043] A reaction feed heat exchanger 1 for preheating monocyclic aromatic hydrocarbons and hydrogen;

[0044] A heater 2 for heating the preheated monocyclic aromatic hydrocarbons and hydrogen, and communicating with the cold outlet of the reaction feed heat exchanger 1;

[0045] A reactor 3 for carrying out a chemical reaction on the heated monocyclic aromatic hydrocarbons and hydrogen to obtain a benzene-containing mixture, and communicating with the heater 2;

[0046] A steam generator 4 for generating steam by using the heat carried by the benzene-containing mixture to adjust the temperature of the benzene-containing mixture, communicating with the reactor 3, and communicating with the hot feed port of the reaction feed heat exchanger 1 to realize recovering the waste heat carried by the benzene-containing mixture after adjusting the temperature as the heat source for the preheating;

[0047] A cooler 5 for cooling the benzene-containing mixture after recovering the waste heat, and communicating with the hot outlet of the reaction feed heat exchanger 1.

[0048] A separation unit 6 for separating benzene from the cooled benzene-containing mixture, and communicating with the cooler 5.

[0049] In the embodiment of the present application, the reaction feed heat exchanger 1 is used to preheat the monoaromatic hydrocarbon and hydrogen; the heater 2 is used to heat the preheated monoaromatic hydrocarbon and hydrogen so as to enter the reactor 3 for hydrothermal cracking to generate a benzene-containing mixture, and the steam generator 4 is used to generate steam by using the heat carried by the benzene-containing mixture to adjust the temperature of the benzene-containing mixture. The output of this steam can be flexibly adjusted, thereby adjusting the consumption of the heater fuel gas. By setting this flexible steam generator 4 and canceling the directly connected heat feed heat exchanger at the reactor outlet, the equipment risk and equipment investment are reduced, and the reaction process is optimized. The steam generator 4 can generate steam at 0.1 - 5 MPag. The temperature of the hot stream entering the reaction feed heat exchanger 1 is adjusted by the amount of steam generated by the steam generator 4. The reaction feed heat exchanger 1 further recovers the waste heat carried by the benzene-containing mixture after the temperature is adjusted to preheat the monoaromatic hydrocarbon and the hydrogen as described above, further reducing the consumption of the heater fuel gas, maximizing the utilization of the heat generated by the above chemical reaction. Subsequently, the product is cooled by the cooler 5 and benzene is separated by the separation unit 6. This system is technically mature and there is no technical risk.

[0050] In some embodiments, the separation unit 6 includes:

[0051] A gas-liquid separator 61, which is used to separate the gas-phase material and the liquid-phase material in the cooled benzene-containing mixture and is communicated with the cooler 5;

[0052] A gas-gas separator 62, which is used to separate methane and hydrogen in the first part of the gas-phase material and is communicated with the top gas outlet of the gas-liquid separator 61;

[0053] A liquid-liquid separator 63, which is used to separate benzene and the unreacted monoaromatic hydrocarbon in the liquid-phase material and is communicated with the bottom liquid outlet of the gas-liquid separator 61.

[0054] In some embodiments, the gas outlet of the gas-gas separator 62 is communicated with the cold stream inlet of the reaction feed heat exchanger 4.

[0055] In some embodiments, the bottom liquid outlet of the liquid-liquid separator 63 is communicated with the cold stream liquid inlet of the reaction feed heat exchanger 4.

[0056] In the embodiments of the present application, the separation unit 6 includes a gas-liquid separator 61, a gas-gas separator 62, and a liquid-liquid separator 63, which successively perform gas-liquid separation, gas-gas separation, and liquid-liquid separation on the benzene-containing mixture, fully separating hydrogen and unreacted monocyclic aromatic hydrocarbons in the benzene-containing mixture and using them as raw materials again. The hydrogen in the first part of the gas-phase material is separated and combined with external hydrogen to return to the reaction feed heat exchanger 1, and the unreacted monocyclic aromatic hydrocarbons are separated and returned to the reaction feed heat exchanger 1, realizing the recycling of unreacted monocyclic aromatic hydrocarbons and hydrogen in the reaction as raw materials, achieving the full utilization of raw materials and saving production costs.

[0057] In some embodiments, the separation unit 6 further includes:

[0058] A recycle gas compressor 64 for transporting the second part of the gas-phase material to the reaction feed heat exchanger 1. The outlet of the recycle gas compressor 64 is communicated with the cold stream inlet of the reaction feed heat exchanger 1, and the inlet of the recycle gas compressor 64 is communicated with the top outlet of the gas-liquid separator 61.

[0059] In the embodiments of the present application, the second part of the gas-phase material contains more than 60% hydrogen and can be directly returned to the reaction feed heat exchanger 1 as a raw material.

[0060] In some embodiments, the reactor 3 includes one of the following: a backmix reactor and a plug flow reactor.

[0061] In the embodiments of the present application, the reactor 3 used can be one of a backmix reactor and a plug flow reactor. The backmix reactor has no continuous cooling points and uses a highly efficient combined feed heat exchanger connected on the side; the plug flow reactor controls the reaction temperature by using multi-point hydrogen injection. The inlet pressure of the reactor 3 is 2.0 - 4.0 MPag, and the inlet temperature of the reactor 3 is 600 - 750 °C, which not only ensures the smooth progress of the hydrothermal cracking reaction of monocyclic aromatic hydrocarbons but also does not increase energy consumption and reduces the generation of by-products.

[0062] Figure 2 It is a schematic flow chart of a method for preparing benzene from monocyclic aromatic hydrocarbons provided by the embodiments of the present application; please refer to Figure 2 , the method is adapted to the system described in any one of the embodiments of the first aspect, and the method includes:

[0063] S1. Preheat and heat the monocyclic aromatic hydrocarbons and hydrogen;

[0064] In some embodiments, the monocyclic aromatic hydrocarbons include at least one of the following: toluene, ethylbenzene, xylene, trimethylbenzene, methyl ethylbenzene, and propylbenzene.

[0065] In the embodiments of the present application, the monocyclic aromatic hydrocarbon is an alkylbenzene containing a benzene ring. The monocyclic aromatic hydrocarbon can be one or a combination of toluene, ethylbenzene, xylene, trimethylbenzene, methylethylbenzene, propylbenzene, etc., to achieve directional benzene production. It realizes the directional production of benzene from monocyclic aromatic hydrocarbons such as toluene, xylene, and C9 aromatic hydrocarbons, and is a bridging device for the coupling of the refining and chemical industry chains. By directionally demethylating monocyclic aromatic hydrocarbons such as toluene, xylene, and C9 aromatic hydrocarbons in gasoline blending components to produce benzene, it can couple product chains of reformed gasoline, styrene, phenol, acetone, etc. with benzene production units, enhancing the product value chain and being a good choice for "reducing oil and increasing chemicals".

[0066] S2. Carry out a chemical reaction on the heated monocyclic aromatic hydrocarbon and the hydrogen to obtain a benzene-containing mixture;

[0067] In some embodiments, the molar ratio of the monocyclic aromatic hydrocarbon to the hydrogen is 1:(3 - 15).

[0068] In some embodiments, the temperature of the chemical reaction is 600°C - 750°C.

[0069] In the embodiments of the present application, the above chemical reaction is a thermal cracking reaction without a catalyst during the reaction process. The benzene ring retention rate during the thermal cracking process reaches more than 95%, which is a directional benzene production process. By limiting the molar ratio of the monocyclic aromatic hydrocarbon to the hydrogen to create a hydrogen-rich environment, more hydrogen can inhibit the formation of by-products and coke formation, increasing the benzene production rate; combined with the temperature of the above chemical reaction, it facilitates the full progress of the monocyclic aromatic hydrocarbon hydrogen-rich thermal cracking reaction of the reaction raw materials to achieve the hydrogen-rich thermal cracking of alkylbenzenes containing a benzene ring such as toluene, ethylbenzene, xylene, trimethylbenzene, methylethylbenzene, propylbenzene, etc. to produce benzene products, realizing the conversion of oil products into basic chemical raw materials. Exemplarily, the molar ratio of the above monocyclic aromatic hydrocarbon to the hydrogen can be 1:3, 1:5, 1:7, 1:9, 1:11, 1:13, 1:15, etc.; the temperature of the above chemical reaction can be 600°C, 620°C, 640°C, 660°C, 680°C, 700°C, 720°C, 740°C, 750°C, etc.

[0070] S3. Carry out steam generation treatment on the heat carried by the benzene-containing mixture, and then carry out waste heat recovery treatment to be used as the heat source for the preheating in step S1;

[0071] In the embodiments of the present application, the monocyclic aromatic hydrocarbon and hydrogen undergo a thermal cracking reaction to generate high heat. Utilize part of the high heat for steam generation treatment. By adjusting the amount of steam generated, the temperature of the benzene-containing mixture can be adjusted, and the consumption of the fuel gas for heating can be flexibly adjusted. The waste heat of the benzene-containing mixture can be used as the heat source for the above preheating, further reducing the consumption of the fuel gas for subsequent heating. Therefore, it realizes the full maximization of the utilization of this high heat, reduces the energy consumption in this production process, and achieves the energy balance of the reaction process.

[0072] S4. Cool and separate the benzene-containing mixture after treating the recovered waste heat to obtain benzene.

[0073] In the embodiment of the present application, the benzene-containing mixture after treating the recovered waste heat is cooled and subjected to gas-liquid separation, gas-gas separation, and liquid-liquid separation. Through these three-stage separations, the unreacted monocyclic aromatic hydrocarbons and hydrogen in the reaction are recycled as raw materials, achieving the full utilization of raw materials, saving production costs, and the yield of the product benzene reaching more than 95%.

[0074] The method for preparing benzene from monocyclic aromatic hydrocarbons is implemented based on the above-mentioned system for preparing benzene from monocyclic aromatic hydrocarbons. The specific structure of the system for preparing benzene from monocyclic aromatic hydrocarbons can refer to the above embodiment. Since the method for preparing benzene from monocyclic aromatic hydrocarbons adopts some or all of the technical solutions of the above embodiment, it at least has all the beneficial effects brought by the technical solutions of the above embodiment, which will not be elaborated one by one here.

[0075] The following further elaborates the present application in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. The experimental methods without specific conditions noted in the following embodiments are usually determined according to national standards. If there is no corresponding national standard, they are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0076] Example 1

[0077] The monocyclic aromatic hydrocarbons and hydrogen are preheated through the reaction feed heat exchanger 1 and then sent to the heater 2. After heating the monocyclic aromatic hydrocarbons and hydrogen, they are sent to the reactor 3. The inlet pressure of the reactor 3 is 3.0 MPag, and the inlet temperature of the reactor 3 is 660 °C. In the reactor 3, the monocyclic aromatic hydrocarbons undergo hydrodealkylation reaction to generate a benzene-containing mixture. The heat carried by the benzene-containing mixture generates steam through the steam generator 4. The temperature of the benzene-containing mixture entering the reaction feed heat exchanger 1 is adjusted by the amount of steam generated. The reaction feed heat exchanger 1 further recovers the waste heat carried by the benzene-containing mixture after adjusting the temperature to preheat the monocyclic aromatic hydrocarbons and the hydrogen as described above. After recovering the waste heat of the reactants, it is sent to the cooler 5 for further cooling and then enters the gas-liquid separator 61 of the separation section 6 for gas-liquid separation. A part of the gas phase is recycled back to the reaction feed heat exchanger 1 through the recycle gas compressor 64, and the remaining part of the gas phase enters the gas-gas separator 62 to separate the methane generated during the reaction. The hydrogen removing methane and the supplementary hydrogen of the system are returned to the reaction feed heat exchanger 1 together. The bottom liquid phase of the gas-liquid separator 61 enters the liquid-liquid separator 63 to obtain the benzene product, and the unreacted monocyclic aromatic hydrocarbons at the bottom of the liquid-liquid separator 63 are returned to the reaction feed heat exchanger 1.

[0078] Example 2

[0079] A method for preparing benzene from monocyclic aromatic hydrocarbons based on Example 1, the method comprising:

[0080] S11. Preheat and heat the monocyclic aromatic hydrocarbon and hydrogen; wherein, the monocyclic aromatic hydrocarbon is toluene, and the molar ratio of toluene to hydrogen is 1:8;

[0081] S21. Carry out a chemical reaction on the heated monocyclic aromatic hydrocarbon and hydrogen to obtain a benzene-containing mixture; wherein, the temperature of the chemical reaction is 660 °C;

[0082] S31. Carry out steam generation treatment on the heat carried by the benzene-containing mixture, and then carry out waste heat recovery treatment to be used as the heat source for preheating in step S1;

[0083] S41. Cool and separate the benzene-containing mixture after waste heat recovery treatment to obtain benzene.

[0084] Example 3

[0085] Comparing Example 3 with Example 2, the differences between Example 3 and Example 2 are as follows:

[0086] The monocyclic aromatic hydrocarbon includes toluene and xylene; the chemical reaction temperature is 640 °C; the molar ratio of the monocyclic aromatic hydrocarbon to hydrogen is 1:10.

[0087] Example 4

[0088] Comparing Example 4 with Example 2, the differences between Example 3 and Example 2 are as follows:

[0089] The monocyclic aromatic hydrocarbon includes toluene and C9 aromatic hydrocarbons; the reaction temperature is 620 °C; the molar ratio of the monocyclic aromatic hydrocarbon to hydrogen is 1:15.

[0090] Test the reaction yields in the methods for preparing benzene from monocyclic aromatic hydrocarbons in Examples 2 to 4, and the results are shown in Table 1.

[0091] Table 1 Reaction yields in the method for preparing benzene from monocyclic aromatic hydrocarbons

[0092] Serial number Yield of pure benzene Steam Example 2 98% (mole) 3.5 MPag Example 3 97% (mole) 4.0 MPag Example 4 97% (mole) 1.0 MPag

[0093] Through the system for preparing benzene from monocyclic aromatic hydrocarbons in Examples 1 to 4 of the present application, and the methods for preparing benzene from monocyclic aromatic hydrocarbons in Examples 2 to 4, and in combination with Table 1, the present application examples achieve heat recovery and energy balance in the preparation of benzene from monocyclic aromatic hydrocarbons, thereby solving the technical problem that the existing benzene production device from aromatic hydrocarbons has increased equipment risks due to the relatively high temperature at the reactor outlet, and at the same time, the steam production and fuel gas consumption can be flexibly adjusted to optimize the processing cost in a timely manner.

[0094] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A system for preparing benzene from monocyclic aromatic hydrocarbons, characterized in that, The system includes: A reaction feed heat exchanger (1) for preheating the monocyclic aromatic hydrocarbon and hydrogen. A heater (2) for heating the preheated monocyclic aromatic hydrocarbon and hydrogen, which is connected to the cold outlet of the reaction feed heat exchanger (1). A reactor (3) for carrying out a chemical reaction on the heated monocyclic aromatic hydrocarbon and hydrogen to obtain a benzene-containing mixture, which is connected to the heater (2). A steam generator (4) for generating steam by using the heat carried by the benzene-containing mixture to adjust the temperature of the benzene-containing mixture, which is connected to the reactor (3) and the hot feed inlet of the reaction feed heat exchanger (1) to recover the waste heat carried by the benzene-containing mixture after temperature adjustment as the heat source for the preheating. A cooler (5) for cooling the benzene-containing mixture after recovering the waste heat, which is connected to the hot outlet of the reaction feed heat exchanger (1). A separation section (6) for separating benzene from the cooled benzene-containing mixture, which is connected to the cooler (5).

2. The system according to claim 1, wherein The separation section (6) includes: A gas-liquid separator (61) for separating the gas-phase material and the liquid-phase material from the cooled benzene-containing mixture, which is connected to the cooler (5). A gas-gas separator (62) for separating methane and hydrogen from the first part of the gas-phase material, which is connected to the top gas outlet of the gas-liquid separator (61). A liquid-liquid separator (63) for separating benzene and the unreacted monocyclic aromatic hydrocarbon from the liquid-phase material, which is connected to the bottom liquid outlet of the gas-liquid separator (61).

3. The system according to claim 2, wherein The gas outlet of the gas-gas separator (62) is connected to the cold gas inlet of the reaction feed heat exchanger (1).

4. The system according to claim 2, wherein The bottom liquid outlet of the liquid-liquid separator (63) is connected to the cold liquid inlet of the reaction feed heat exchanger (1).

5. The system according to any one of claims 2 to 4, characterized in that, The separation section (6) further includes: A recycle gas compressor (64) for conveying the second part of the gas-phase material to the reaction feed heat exchanger (1). The outlet of the recycle gas compressor (64) is connected to the cold gas inlet of the reaction feed heat exchanger (1), and the inlet of the recycle gas compressor (64) is connected to the top gas outlet of the gas-liquid separator (61).

6. The system according to claim 1, wherein The reactor (3) includes one of the following: a backmix reactor, a plug flow reactor.

7. A method for preparing benzene from monocyclic aromatic hydrocarbons, characterized in that, The method is adapted to the system according to any one of claims 1 to 6, and the method includes: S1. Preheating and heating the monocyclic aromatic hydrocarbon and hydrogen. S2. Carrying out a chemical reaction on the heated monocyclic aromatic hydrocarbon and hydrogen to obtain a benzene-containing mixture. S3. Generating steam by using the heat carried by the benzene-containing mixture and then carrying out waste heat recovery treatment as the heat source for the preheating in step S1. S4. Cooling and separating the benzene-containing mixture after the waste heat recovery treatment to obtain benzene.

8. The method according to claim 7, wherein The monocyclic aromatic hydrocarbon includes at least one of the following: toluene, ethylbenzene, xylene, trimethylbenzene, methyl ethylbenzene, propylbenzene.

9. The method according to claim 7 or 8, characterized in that, The molar ratio of the monocyclic aromatic hydrocarbon to hydrogen is 1:(3 - 15).

10. The method according to claim 7 or 8, characterized in that, The temperature of the chemical reaction is 600°C to 750°C.

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