Energy-saving and consumption-reducing mixed benzene preparation process

Abstract

The invention discloses an energy-saving and consumption-reducing mixed benzene preparation process, and belongs to the technical field of mixed benzene production. After hydrogenated mixed benzene is separated by the prefractionator, pure benzene and a small amount of toluene at the top of the tower are sent to the extraction separation system, so that the load of a solvent system can be reduced, the stability and the product quality of the device are improved, the mixed benzene containing toluene, mixed xylene and C8 fraction is directly produced at the bottom of the tower and is directly extracted as a product, the working procedures are reduced, and the production cost is reduced. And the purposes of energy conservation and consumption reduction are achieved. The molecular sieve is treated by using the Schiff base type ionic liquid, so that the lattice structure of the molecular sieve is changed to form a mesoporous structure, the specific surface area and the pore volume are increased, the mass transfer resistance is reduced, and the mass transfer rate is improved. The molecular sieve is modified through ammonium gallium sulfate and ammonium indium sulfate, gallium and indium elements are introduced, more adsorption sites are provided for activated carbon, the content of sulfur-containing impurities is reduced, the product purity is improved, the mesoporous volume and the average pore size are increased, mass transfer is smoother, the separation efficiency is improved, and the energy-saving and consumption-reducing effects are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of mixed benzene production, and in particular relates to an energy-saving and consumption-reducing mixed benzene preparation process. Background Art

[0002] The benzene hydrogenation process is divided into two parts: hydrogenation and impurity removal and separation and refining. After distillation, the hydrogenated oil can obtain non-aromatic hydrocarbons, benzene, toluene, mixed xylenes and C8 solvent oil products. Since some downstream purchasing manufacturers no longer have the need to separate toluene, mixed xylenes and C8 solvent oil products separately, they can purchase a mixture of toluene, mixed xylenes and C8 solvent oil. Therefore, it is necessary to transform the separation and refining unit of the benzene hydrogenation unit to achieve the purpose of energy saving and consumption reduction.

[0003] In the benzene industry, the components of mixed benzene need to be separated in a distillation tower, and the presence of fillers greatly increases the contact area between the gas and liquid phases. The rising steam and the descending liquid need to be in full contact to achieve effective mass transfer and heat transfer. The porous structure and complex surface of the fillers provide a large number of places for gas-liquid contact, so that the steam can be fully mixed with the liquid, promoting the separation of benzene and other components. The special structure of the filler helps to improve the mass transfer efficiency. The presence of fillers can disrupt the flow state of the fluid, causing the fluid to form a complex flow path in the packing layer, increasing the chance of molecular diffusion. Therefore, if the filler can be modified to increase the specific surface area of ​​the filler, enrich the pore structure, and increase the chemical active sites, the separation efficiency of the distillation tower can be improved, and the goal of energy saving and consumption reduction can be greatly achieved. Summary of the invention

[0004] In view of the above situation, in order to overcome the defects of the prior art, the pre-fractionation tower bottom of the present invention directly outputs mixed benzene containing toluene, mixed xylenes and C8 fractions, which are directly extracted as products, reducing the process and achieving the purpose of energy saving and consumption reduction. The general Schiff base ionic liquid, ammonium gallium sulfate and ammonium indium sulfate modified molecular sieves increase the mesopore volume and average pore size, make mass transfer smoother, and improve separation efficiency and energy saving and consumption reduction effects.

[0005] In order to achieve the above object, the following technical scheme is adopted: The present invention provides an energy-saving and consumption-reducing mixed benzene preparation process, comprising the following steps:

[0006] (1) The mixed benzene after hydrofining is sent to a pre-fractionation tower, and a production pipeline and a kettle liquid pump are set at the bottom of the pre-fractionation tower. The bottom liquid level and the production of the kettle liquid pump of the pre-fractionation tower are observed, and the material composition at the top and bottom of the tower is sampled and analyzed. The reflux rate and the bottom temperature are adjusted according to the analysis results. If the kettle liquid pump cannot produce normally under high load, the feed rate is appropriately reduced, and the bottom temperature is continued to be adjusted;

[0007] (2) The benzene and toluene fractions at the top of the pre-fractionation tower are fed into an extractive distillation tower. The feed rate and solvent flow rate of the extractive distillation tower are adjusted according to the liquid level at the bottom of the tower and the material composition. Pure benzene is produced at the top of the extractive distillation tower, and mixed benzene is produced at the bottom of the tower.

[0008] (3) The solvent from the extractive distillation tower is sent to a solvent recovery tower for recovery and purification to reduce solvent loss, and the purified solvent is returned to the extractive distillation tower for recycling;

[0009] (4) The mixed benzene produced at the top of the extractive distillation tower enters the benzene / toluene tower. The extraction amount and temperature of the top and bottom of the tower are adjusted according to the material composition of the top and bottom of the tower. Pure benzene is produced at the top of the tower and pure toluene is produced at the bottom of the tower.

[0010] Furthermore, the extractive distillation tower uses a modified 5A molecular sieve as a filler, and the modified 5A molecular sieve is prepared by the following steps:

[0011] S1. Add bis(2-aminophenyl) disulfide to deionized water, stir and disperse, add acetyl vanillin dropwise in a 5°C water bath, stir for 2 hours, filter the obtained solid, wash three times with deionized water, add the obtained solid to deionized ethanol after drying, stir and disperse, add potassium trifluoroacetate, continue stirring for 2 hours, filter the obtained solid, and obtain a Schiff base type ionic liquid after drying;

[0012] S2, adding the 5A molecular sieve and the Schiff base type ionic liquid to a sealed pressure device, heating at 180° C. for 2 h, taking out after cooling, immersing in a 1:1 ethanol aqueous solution and mixing evenly, and then separating the solid by high-speed centrifugation at a speed of 5000 rpm and removing the residual ionic liquid on the 5A molecular sieve;

[0013] S3. Dissolve tetrapropylammonium hydroxide, ammonium gallium sulfate and ammonium indium sulfate in deionized water, add the 5A molecular sieve treated in step S3, perform ultrasonic dispersion, and continue to immerse for 2 hours, then transfer to a hydrothermal reactor, react at 150° C. for 4 hours, and after the temperature of the reactor drops to room temperature, filter out the obtained solid, wash it three times with deionized water and ethanol respectively, and obtain the modified 5A molecular sieve after drying.

[0014] Furthermore, in step S1, the mass ratio of the diamine compound, deionized water, acetyl vanillin, anhydrous ethanol and potassium trifluoroacetate is 1:80-100:1.5-2:80-100:5-8.

[0015] Furthermore, in step S2, the mass ratio of the 5A molecular sieve to the Schiff base ionic liquid is 1:3-8.

[0016] Furthermore, in step S3, the mass ratio of tetrapropylammonium hydroxide, ammonium gallium sulfate, ammonium indium sulfate, deionized water and the treated 5A molecular sieve is 1:1.5-3:1.5-3:50-100:8-10.

[0017] Furthermore, the bottom temperature of the pre-fractionation tower is 140-150°C, preferably 146°C.

[0018] Furthermore, the top pressure of the pre-fractionation tower is 80-90 kPa, preferably 85 kPa.

[0019] Furthermore, the bottom pressure of the pre-fractionation tower is 130-140 kPa, preferably 135 kPa.

[0020] Furthermore, the tower bottom extraction amount is 1300-3000kg / h.

[0021] Furthermore, the ultrasonic dispersion conditions are: 60-80 Hz ultrasonic dispersion for 10-30 min.

[0022] The beneficial effects of the present invention are:

[0023] (1) According to the present invention, after the mixed benzene after hydrogenation refining is separated in a pre-fractionation tower, the top product pure benzene and a small amount of toluene are sent to the extraction separation system, which can reduce the load of the solvent system, improve the stability of the device and the product quality, and directly produce the mixed benzene containing toluene, mixed xylene and C8 fraction at the bottom of the tower, which is directly extracted as a product, and no further complicated separation and purification operations are required for the bottom product, which reduces the next step of the process, thereby achieving the purpose of energy saving and consumption reduction, and meeting the market demand for specific mixed aromatic products. Such a mixed benzene product containing multiple components has unique value in multiple application fields;

[0024] (2) The present invention treats the molecular sieve with a Schiff base ionic liquid. The cation part of the Schiff base ionic liquid carries a positive charge, while there are charge distribution and active sites on the surface of the molecular sieve skeleton structure. When the Schiff base ionic liquid contacts the molecular sieve, the cation part combines with the molecular sieve skeleton structure through interactions such as electrostatic attraction, so that the lattice structure of the molecular sieve is affected, causing a certain degree of distortion and expansion, thereby forming a mesoporous structure. The formation of such pores increases the specific surface area and pore volume of the molecular sieve, exposing more active adsorption sites, and benzene and toluene molecules can diffuse more quickly in the pores of the molecular sieve, reducing mass transfer resistance and increasing mass transfer rate;

[0025] (3) The present invention modifies the molecular sieve by using ammonium gallium sulfate and ammonium indium sulfate, and introduces gallium and indium elements into the 5A molecular sieve, thereby providing more adsorption sites for the activated carbon, and being able to adsorb small molecular sulfur-containing impurities, thereby reducing the content of sulfur-containing impurities in the distillation tower fraction and improving the purity of the benzene and toluene products. In addition, the Ga-O bond and the In-O bond are longer than the Al-O bond, which further increases the mesoporous volume and average pore size of the molecular sieve. For the same volume of filler, a larger pore size means that the diffusion resistance of the substance therein is smaller, and the mass transfer process is smoother. Therefore, the modified molecular sieve has a larger mass transfer area, so that the gas-liquid two phases can contact and exchange substances more fully, thereby improving the mass transfer efficiency. This not only helps to more efficiently separate components with different boiling points and improve the separation efficiency of the distillation tower, but also promotes energy saving and consumption reduction in the entire distillation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention is a process flow chart of a mixed benzene preparation process for energy saving and consumption reduction;

[0027] Figure 2 A comparison chart of HETP values ​​of fillers prepared in Examples 2-6 and Comparative Examples 1-2 of a mixed benzene preparation process for energy saving and consumption reduction of the present invention;

[0028] Figure 3 The results of the analysis of the purity of the products after the fillers prepared in Examples 2-6 and Comparative Examples 1-2 of the energy-saving and consumption-reducing mixed benzene preparation process of the present invention were applied to the distillation tower and then separated;

[0029] Figure 4 The SEM images of the microscopic morphology of fillers prepared in Example 4 and Comparative Examples 1-2 of a mixed benzene preparation process for energy saving and consumption reduction of the present invention are shown.

[0030] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0032] Unless otherwise defined, all professional and scientific terms used herein have the same meanings as those familiar to those skilled in the art. In addition, any methods and materials similar or equivalent to those described herein may be applied to the present invention. The preferred implementation methods and materials described herein are for demonstration purposes only and are not intended to limit the content of this application.

[0033] The experimental methods in the following examples are conventional methods unless otherwise specified, and the experimental materials used in the following examples are purchased from commercial channels unless otherwise specified.

[0034] Example 1

[0035] A mixed benzene preparation process with energy saving and consumption reduction

[0036] The steps include:

[0037] (1) The mixed benzene after hydrorefining is sent to the pre-fractionation tower, and a production pipeline and a kettle liquid pump are set at the bottom of the pre-fractionation tower. The bottom liquid level and the production of the pre-fractionation tower kettle liquid pump are observed, and the material composition at the top and bottom of the tower is sampled and analyzed. The reflux rate and the bottom temperature are adjusted according to the analysis results. If the kettle liquid pump cannot produce normally under high load, the feed rate is appropriately reduced, and the bottom temperature is continued to be adjusted. Finally, the bottom temperature is adjusted to 146°C, the top pressure of the tower is 85kPa, and the bottom pressure is 135kPa. The bottom production is controlled to be 1300-3000kg / h range. Through such operation, the preliminary separation of different components in mixed benzene can be effectively achieved. In this process, the temperature and pressure at the bottom of the tower and the output are strictly controlled, which helps to ensure the quality and stability of the mixed benzene containing toluene, mixed xylene and C8 fractions output from the bottom of the tower. When the kettle liquid pump has an output problem, the feed rate and other operating parameters are adjusted in time to ensure the stable operation of the pre-fractionation tower, providing a good foundation for subsequent processes and reducing unnecessary energy consumption.

[0038] (2) The benzene and toluene fractions at the top of the pre-fractionation tower are sent to the extractive distillation tower. The feed rate and solvent flow rate of the extractive distillation tower are adjusted according to the liquid level at the bottom of the tower and the material composition. The extractive distillation tower produces pure benzene at the top and mixed benzene at the bottom. The fractions at the top of the pre-fractionation tower are sent to the extractive distillation tower for further separation, which can more accurately extract pure benzene and reduce the load on the solvent system. By flexibly adjusting the feed rate and solvent flow rate according to the liquid level at the bottom of the tower and the material composition, the efficiency and effect of the extractive distillation can be improved, and the stability of the device and the product quality can be improved;

[0039] (3) The solvent in the extractive distillation tower is sent to a solvent recovery tower for recovery and purification, thereby reducing solvent loss. The purified solvent is returned to the extractive distillation tower for recycling. The recovery and recycling of the solvent not only reduces production costs and reduces environmental pollution caused by the solvent, but also ensures the continuous and stable progress of the extractive distillation process. The solvent is purified by the recovery tower to remove impurities that may be carried in the solvent, thereby further improving the performance of the solvent and the effect of the extractive distillation, thereby achieving the goal of effective utilization of resources and energy conservation and consumption reduction;

[0040] (4) The mixed benzene produced at the top of the extractive distillation tower enters the benzene / toluene tower. The extraction amount and temperature of the top and bottom of the tower are adjusted according to the material composition of the top and bottom of the tower. Pure benzene is produced at the top of the tower and pure toluene is produced at the bottom of the tower.

[0041] Through the synergistic effect of the above steps, the mixed benzene preparation process of the present invention realizes efficient separation and purification, achieves energy saving and consumption reduction effects while ensuring product quality, and improves the economic and environmental benefits of the entire production process.

[0042] Example 2

[0043] The extractive distillation column uses modified 5A molecular sieve as filler, and the modified 5A molecular sieve is prepared by the following steps:

[0044] S1. Add bis(2-aminophenyl) disulfide to deionized water, stir and disperse, add acetyl vanillin dropwise in a 5°C water bath, stir for 2 hours, filter the obtained solid, wash three times with deionized water, add the obtained solid to deionized ethanol after drying, stir and disperse, add potassium trifluoroacetate, continue stirring for 2 hours, filter the obtained solid, and obtain a Schiff base type ionic liquid after drying;

[0045] S2, adding the 5A molecular sieve and the Schiff base type ionic liquid to a sealed pressure device, heating at 180° C. for 2 h, taking out after cooling, immersing in a 1:1 ethanol aqueous solution and mixing evenly, and then separating the solid by high-speed centrifugation at a speed of 5000 rpm and removing the residual ionic liquid on the 5A molecular sieve;

[0046] S3. Dissolve tetrapropylammonium hydroxide, ammonium gallium sulfate and ammonium indium sulfate in deionized water, add the 5A molecular sieve treated in step S3, perform ultrasonic dispersion, and continue to immerse for 2 hours, then transfer to a hydrothermal reactor, react at 150° C. for 4 hours, and after the temperature of the reactor drops to room temperature, filter out the obtained solid, wash it three times with deionized water and ethanol respectively, and obtain the modified 5A molecular sieve after drying.

[0047] In the step S1, the mass ratio of the diamine compound, deionized water, acetyl vanillin, anhydrous ethanol and potassium trifluoroacetate is 1:80:1.5:80:5.

[0048] In the step S2, the mass ratio of the 5A molecular sieve to the Schiff base ionic liquid is 1:3.

[0049] In the step S3, the mass ratio of tetrapropylammonium hydroxide, ammonium gallium sulfate, ammonium indium sulfate, deionized water and the treated 5A molecular sieve is 1:1.5:1.5:50:8.

[0050] The ultrasonic dispersion conditions are: 60 Hz ultrasonic dispersion for 10 min.

[0051] Example 3

[0052] The difference between this embodiment and embodiment 2 is as follows, and the rest is the same as embodiment 2:

[0053] In the step S1, the mass ratio of the diamine compound, deionized water, acetyl vanillin, anhydrous ethanol and potassium trifluoroacetate is 1:100:2:100:8.

[0054] In the step S2, the mass ratio of the 5A molecular sieve to the Schiff base ionic liquid is 1:8.

[0055] In step S3, the mass ratio of tetrapropylammonium hydroxide, ammonium gallium sulfate, ammonium indium sulfate, deionized water and the treated 5A molecular sieve is 1:3:3:100:10.

[0056] The ultrasonic dispersion conditions are: 80 Hz ultrasonic dispersion for 30 min.

[0057] Example 4

[0058] The difference between this embodiment and embodiment 2 is as follows, and the rest is the same as embodiment 2:

[0059] In the step S1, the mass ratio of the diamine compound, deionized water, acetyl vanillin, anhydrous ethanol and potassium trifluoroacetate is 1:85:1.8:90:6.

[0060] In the step S2, the mass ratio of the 5A molecular sieve to the Schiff base ionic liquid is 1:5.

[0061] In the step S3, the mass ratio of tetrapropylammonium hydroxide, ammonium gallium sulfate, ammonium indium sulfate, deionized water and the treated 5A molecular sieve is 1:2:2:80:9.

[0062] The ultrasonic dispersion conditions are: 70 Hz ultrasonic dispersion for 20 min.

[0063] Example 5

[0064] The difference between this embodiment and embodiment 4 is that in step S1, the mass ratio of the diamine compound, deionized water, acetyl vanillin, anhydrous ethanol and potassium trifluoroacetate is 1:85:2:80:8.

[0065] Example 6

[0066] The difference between this embodiment and embodiment 4 is that in step S3, the mass ratio of tetrapropylammonium hydroxide, ammonium gallium sulfate, ammonium indium sulfate, deionized water and the treated 5A molecular sieve is 1:3:1.5:80:9.

[0067] Comparative Example 1

[0068] The difference between this comparative example and Example 2 is that the molecular sieve used is unmodified 5A molecular sieve, and the rest is the same as Example 4.

[0069] Comparative Example 2

[0070] The difference between this comparative example and Example 2 is that the modified 5A molecular sieve is replaced by the 5A molecular sieve treated with Schiff base ionic liquid, and the rest is the same as Example 4.

[0071] Test Example 1

[0072] Calculation of HETP value of filler

[0073] The mass transfer performance of the packings in the packed tower of Examples 2-6 and Comparative Examples 1-2 was measured by HETP (equivalent height of theoretical plate). The results are shown in Figure 2 The equivalent height of the theoretical plate is referred to as the equivalent plate height. HETP refers to the height of the packing layer whose separation efficiency is equivalent to that of a theoretical plate (an idealized tower plate, on which the gas and liquid phases are in good contact and fully mixed, ignoring the resistance of the heat and mass transfer processes). The composition of the rising vapor and the descending liquid in this section of the packing layer reaches equilibrium. The height of the packing layer is the product of HETP and the theoretical plate number. The smaller the HETP value, the more theoretical plates can be achieved at the same packing height, that is, the higher the separation efficiency.

[0074] HETP is calculated by the following steps:

[0075] (1) First, in a binary mixture system, the theoretical plate number of the filler is calculated by the Fenske equation:

[0076]

[0077] Where: x D represents the mole fraction of the light component in the top liquid phase, x B is the mole fraction of the light component in the bottom liquid phase, α is the average relative volatility, and the geometric mean of the relative volatility of the top and bottom of the tower is taken, that is, α = √(α top ×α btm), relative volatility is the ratio of the volatility of the volatile component to the volatility of the less volatile component, and is expressed by the following formula:

[0078]

[0079] Where: y A represents the mole fraction of the volatile component in the gas phase, y B represents the mole fraction of the non-volatile component in the gas phase, x A represents the mole fraction of the volatile component in the liquid phase, x B represents the molar fraction of the non-volatile component in the liquid phase, in the present invention, A represents benzene, and B represents toluene;

[0080] (2) Calculate HETP by the following formula:

[0081]

[0082] Where: H represents the height of the packing layer.

[0083] pass Figure 2 The results show that the HETP value of the filler prepared in Examples 2-6 of the present invention is only half of that of the unmodified 5A molecular sieve, that is, the distillation separation effect is twice that of the 5A molecular sieve, and is also lower than the HETP value of Comparative Example 2. This proves that the present invention forms a new mesoporous structure by using Schiff base ionic liquids and a method for modifying molecular sieves by ammonium gallium sulfate and ammonium indium sulfate, increases the specific surface area and pore volume of the molecular sieve, allows benzene and toluene molecules to diffuse more quickly in the pores of the molecular sieve, reduces mass transfer resistance, and increases mass transfer rate, thereby greatly increasing the distillation separation effect.

[0084] Test Example 2

[0085] Purity analysis of distillation separation products

[0086] The fillers of Example 2-6 and Comparative Example 1-2 were filled into an extractive distillation tower, and the purity of benzene and toluene after distillation separation was analyzed by Shimadzu GC-2010 gas chromatograph. The results are as follows: Figure 3 shown.

[0087] The test parameters are as follows:

[0088] Detector: FID detector;

[0089] Detector temperature: 150°C;

[0090] Chromatographic column: 50m, 0.25mm;

[0091] Tube: fused silica column;

[0092] Stationary phase: TCEP;

[0093] Film thickness: 0.40 μm;

[0094] Column temperature: 70°C;

[0095] Carrier gas: helium;

[0096] Inlet temperature: 150°C;

[0097] Split ratio: 40;

[0098] Split flow rate: 55mL / min;

[0099] Sample volume: 1.0 μL.

[0100] pass Figure 3 It can be seen from the test results that the total sulfur content in benzene and toluene after separation by the fillers of Examples 2-6 is lower than that in Comparative Examples 1-2, which proves that the modification method of the present invention exposes more active adsorption sites to the 5A molecular sieve through the Schiff base ionic liquid, and introduces gallium and indium elements into the 5A molecular sieve to provide more adsorption sites for the activated carbon. Therefore, the prepared filler can adsorb small molecular sulfur-containing impurities, thereby reducing the content of sulfur-containing impurities in the distillation tower fraction and significantly improving the purity of the benzene and toluene products.

[0101] Test Example 3

[0102] Filler micromorphology analysis

[0103] The microscopic morphology of the fillers prepared in Example 4, Comparative Example 1 and Comparative Example 2 was analyzed using a German SUPRA55VPX scanning electron microscope. Figure 4 ,Depend on Figure 4 It can be seen that the filler surface structure of Example 4 is more complete, with a larger surface area and a richer structure. Therefore, the separation efficiency and impurity adsorption efficiency of Example 4 should be better than those of Comparative Examples 1 and 2, verifying the analysis and detection results of the aforementioned Test Examples 1-2.

[0104] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

[0105] The present invention and its implementation methods are described above, which is not restrictive. The drawings are only one of the implementation methods of the present invention, and the actual application is not limited thereto. In short, if ordinary technicians in the field are inspired by it and design methods and embodiments similar to the technical solution without creativity without departing from the purpose of the invention, they should all fall within the protection scope of the present invention.

Claims

1. A mixed benzene preparation process for energy saving and consumption reduction, characterized in that: The steps include: (1) The mixed benzene after hydrofining is sent to a pre-fractionation tower, and a production pipeline and a kettle liquid pump are set at the bottom of the pre-fractionation tower. The bottom liquid level and the production of the kettle liquid pump of the pre-fractionation tower are observed, and the material composition at the top and bottom of the tower is sampled and analyzed. The reflux rate and the bottom temperature are adjusted according to the analysis results. If the kettle liquid pump cannot produce normally under high load, the feed rate is appropriately reduced, and the bottom temperature is continued to be adjusted; (2) The benzene and toluene fractions at the top of the pre-fractionation tower are fed into an extractive distillation tower. The feed rate and solvent flow rate of the extractive distillation tower are adjusted according to the liquid level at the bottom of the tower and the material composition. Pure benzene is produced at the top of the extractive distillation tower, and mixed benzene is produced at the bottom of the tower. (3) The solvent from the extractive distillation tower is sent to a solvent recovery tower for recovery and purification to reduce solvent loss, and the purified solvent is returned to the extractive distillation tower for recycling; (4) The mixed benzene produced at the top of the extractive distillation tower enters the benzene / toluene tower, and the extraction amount and temperature of the top and bottom of the tower are adjusted according to the material composition of the top and bottom of the tower, so that pure benzene is produced at the top of the tower and pure toluene is produced at the bottom of the tower; The extractive distillation column uses modified 5A molecular sieve as filler, and the modified 5A molecular sieve is prepared by the following steps: S1. Add bis(2-aminophenyl) disulfide to deionized water, stir and disperse, add acetyl vanillin dropwise in a 5°C water bath, stir for 2 hours, filter the obtained solid, wash three times with deionized water, add the obtained solid to deionized ethanol after drying, stir and disperse, add potassium trifluoroacetate, continue stirring for 2 hours, filter the obtained solid, and obtain a Schiff base type ionic liquid after drying; S2, adding the 5A molecular sieve and the Schiff base type ionic liquid to a sealed pressure device, heating at 180° C. for 2 h, taking out after cooling, immersing in a 1:1 ethanol aqueous solution and mixing evenly, and then separating the solid by high-speed centrifugation at a speed of 5000 rpm and removing the residual ionic liquid on the 5A molecular sieve; S3. Dissolve tetrapropylammonium hydroxide, ammonium gallium sulfate and ammonium indium sulfate in deionized water, add the 5A molecular sieve treated in step S3, perform ultrasonic dispersion, and continue to immerse for 2 hours, then transfer to a hydrothermal reactor, react at 150° C. for 4 hours, and after the temperature of the reactor drops to room temperature, filter out the obtained solid, wash it three times with deionized water and ethanol respectively, and obtain the modified 5A molecular sieve after drying.

2. The energy-saving and consumption-reducing mixed benzene preparation process according to claim 1, characterized in that: In the step S1, the mass ratio of bis(2-aminophenyl) disulfide, deionized water, acetyl vanillin, anhydrous ethanol and potassium trifluoroacetate is 1:80-100:1.5-2:80-100:5-8.

3. The energy-saving and consumption-reducing mixed benzene preparation process according to claim 2, characterized in that: In the step S2, the mass ratio of the 5A molecular sieve to the Schiff base ionic liquid is 1:3-8.

4. The energy-saving and consumption-reducing mixed benzene preparation process according to claim 3, characterized in that: In the step S3, the mass ratio of tetrapropylammonium hydroxide, ammonium gallium sulfate, ammonium indium sulfate, deionized water and the treated 5A molecular sieve is 1:1.5-3:1.5-3:50-100:8-10.

5. The energy-saving and consumption-reducing mixed benzene preparation process according to claim 4, characterized in that: The bottom temperature of the pre-fractionation tower is 140-150°C.

6. The energy-saving and consumption-reducing mixed benzene preparation process according to claim 5, characterized in that: The top pressure of the pre-fractionation tower is 80-90 kPa.

7. The energy-saving and consumption-reducing mixed benzene preparation process according to claim 6, characterized in that: The bottom pressure of the pre-fractionation tower is 130-140 kPa.

8. The energy-saving and consumption-reducing mixed benzene preparation process according to claim 7, characterized in that: The tower bottom extraction amount is 1300-3000kg / h.

9. The energy-saving and consumption-reducing mixed benzene preparation process according to claim 8, characterized in that: The ultrasonic dispersion conditions are: 60-80 Hz ultrasonic dispersion for 10-30 min.

Images