Tower device for extracting aromatic nitration tail acid and method for realizing online direct supply of ingredients of continuous flow nitration unit based on tower device

Abstract

The invention discloses a tower device for extracting aromatic nitration tail acid and a method for realizing online direct supply of ingredients of a continuous flow nitration unit based on the tower device, an improved static extraction tower form is adopted, and the defect that the height of a traditional static extraction tower is too large is avoided through a filler and plate combined structure; the height of a tower pass and the height of an extraction high-temperature section are set according to the concentration of nitric acid in supplied tail acid; and the extraction of the residual nitrides is finally completed in the low-temperature extraction section after the cooling section. According to the method, the aromatic nitration tail acid is purified by a single extraction device, so that the extraction separation of organic matters can be fully realized, nitric acid in the tail acid can be converted, and a more friendly process condition is created for evaporation and recovery of sulfuric acid; and on the basis, the device is connected with a temperature control mixing device of the continuous flow nitration unit, so that the extracted organic phase can be continuously, stably and homogeneously supplied to online burdening of the continuous flow nitration unit, and the strict proportioning requirement is met.

Description

Technical Field

[0001] The invention belongs to the technical field of aromatic hydrocarbon nitration tail acid purification, and in particular relates to a tower device for extracting aromatic hydrocarbon nitration tail acid and a method for realizing online direct supply of continuous flow nitration unit ingredients based on the device. Background Art

[0002] In the production field where aromatic hydrocarbons such as benzene, toluene, chlorobenzene and naphthalene are nitrated by nitric and sulfuric acid mixed acid, the stratified acid phase produced by the reaction contains water, organic nitrates and varying amounts of excess nitric acid in addition to sulfuric acid. The evaporation recovery of the nitrated tail acid requires the pre-separation of organic matter and the reduction of nitric acid concentration. In production, the raw aromatic hydrocarbons are basically used as blank extractants to treat the organic matter therein, and the residual nitric acid is removed along with the sulfuric acid in the evaporation recovery section, which becomes the processing burden of the evaporation section. At the same time, the raw aromatic hydrocarbons will be mixed with the dispersed acid phase when the nitration product is extracted. The acid phase content is positively correlated with the mixed acid concentration. Even if the concentration of the residual acid phase is the same, different types of extraction devices or different oleic acid separation structures will result in different acid phase contents mixed into the organic phase after extraction. In the art, acid extraction mostly adopts kettle countercurrent extraction, with two or one countercurrent stages. It is necessary to set shallow overflow sedimentation tanks at the discharge ends of the oil and water phases respectively. The discharge height of the tank body needs to take into account the continuous overflow of the entire process section, and the separation effect is not good, resulting in the organic phase after extraction usually being defined as acidic nitration raw material such as "acidic benzene" and "acidic toluene". The excess nitric acid in the tail acid forms a dilemma for the extraction process. On the one hand, it is hoped that the nitric acid concentration in the residual acid liquid can be reduced as much as possible to reduce the pollution of nitrogen oxides during the evaporation and recovery of sulfuric acid. On the other hand, the excess nitric acid and the nitration raw material can react at the interface between the two phases to release heat, and this reaction will further weaken the originally limited separation performance of the traditional extraction unit.

[0003] More importantly, within a certain height near the oleic acid interface, the concentration of the acid components in the phase after extraction spontaneously increases from high to low in the vertical direction, but the concentration gradient cannot be eliminated. This makes the concentration ratio of aromatics, nitrates and acid phase components in the organic phase after extraction sent out by the traditional shallow overflow separation device significantly unbalanced, and the concentration fluctuates more greatly when switching from a static state to a flowing state.

[0004] On the other hand, continuous flow reactors such as microchannels are recognized as new intrinsically safe nitration reaction technologies due to their small online volume and high reaction efficiency. However, due to their small online volume, they cannot adjust the reaction ratio online like traditional kettle reactions. Therefore, continuous flow nitration reaction devices have stricter requirements on the accuracy and stability of feed ratios, especially when restarting after each shutdown. It is necessary to ensure that the ideal results are directly restored. In actual production, the organic phase after extraction will inevitably have online buffering and retention before entering the reaction. Therefore, in the case of continuous flow nitration reactions, the extracted aromatics are used as the reaction raw materials. The above-mentioned unbalanced fluctuation phenomenon significantly interferes with the batching and adjustment of the continuous flow nitration reaction, and the impact is most obvious when the machine is restarted after shutdown during the process.

[0005] In summary, in the traditional production process, the above extraction section has complex processes, many equipment units, and fluctuations in the two-phase discharge components. The acid phase after extraction will still float aromatic raw materials on the surface of the stock, which will burden the safety and environmental protection of acid recovery, and it is also difficult to meet the production control requirements of the subsequent continuous flow nitration unit. In order to effectively solve the above problems in this field, it is necessary to develop more efficient extraction equipment for the extraction and purification of nitration tail acid.

[0006] The shape of the static extraction tower is more conducive to the stability of the concentration of the two-phase discharge components, and there is an opportunity to simplify the process. However, the physical properties of the two-phase materials in this field have limited the application of traditional static extraction towers. Specific factors include: the large difference in the two-phase specific gravity restricts the contact time of the two phases, requiring a large tower height; the large tension between the two phases leads to coarse droplets of the countercurrent two phases, which greatly reduces the contact area and easily forms a convergent bias flow; the nitrate has a certain solubility in the acid phase and requires a more uniform and sufficient countercurrent mass transfer between the two phases to ensure the extraction depth; the tower will produce an exothermic reaction between excess nitric acid and the raw materials to form thermal convection that interferes with the uniform countercurrent and affects the stability of the tower effect. The influence of the above-mentioned tension, specific gravity difference, thermal convection and other factors in this field has formed a comprehensive working condition that limits the performance of the static extraction tower. Summary of the invention

[0007] The purpose of the present invention is to extract and purify the tail acid of aromatic nitration with fewer sets of equipment, so as to achieve sufficient extraction of the organic phase, convert the nitric acid in the tail acid, and ensure that the discharged acid does not contain an oil phase, so as to create more friendly process conditions for the evaporation and recovery of the tail acid; on this basis, it is also necessary to enable the organic phase after extraction to continuously and stably supply the online ingredients of the continuous flow nitration device to meet its more stringent ratio requirements.

[0008] The core method of constructing the above-mentioned extraction device is: adopting an improved static extraction tower form, avoiding the disadvantage of the excessive height of the traditional static extraction tower through an internal structure combining fillers and plates; setting the height of the tower and the high-temperature extraction section according to the nitric acid concentration of the incoming tail acid, completing the extraction of the organic phase while reducing the nitric acid concentration in the acid solution as much as possible; and finally completing the extraction of residual nitrates in the low-temperature extraction section after the cooling section.

[0009] Technical solution: The tower device for extracting aromatic hydrocarbon nitration tail acid of the present invention, wherein the aromatic hydrocarbon nitration tail acid refers to the nitration tail acid obtained by reacting aromatic hydrocarbon and nitric acid and sulfuric acid mixed acid through a continuous flow nitration device and then discharging the material through stratification, the acid is mixed with organic matter such as nitro compounds, and the nitration tail acid contains 0.4-4% nitric acid; the aromatic hydrocarbon raw material corresponding to the nitration product is used as the extractant, and the structure of the tower device includes:

[0010] The bottom volume of the tower is connected to the outlet of the raffinate phase, the top volume of the tower is connected to the overflow port of the extracted oil phase, the upper distributor is connected to the inlet of the tail acid to be extracted, the lower distributor is connected to the inlet of the aromatic hydrocarbon raw material, and the extraction tower is located between the upper distributor and the lower distributor; the extraction tower is divided into an upper high-temperature extraction section and a lower low-temperature extraction section by an extraction cooling section, and the high-temperature extraction section and the low-temperature extraction section both adopt a structure combining extraction fillers with uniformly distributed tower plates.

[0011] Furthermore, the structure of the tower device combining the filler and the uniformly distributed tower plate is that the uniformly distributed tower plates for limiting the axial flow are evenly spaced at intervals of 320 to 550 mm in the high-temperature extraction section and the low-temperature extraction section. The tower plates are loaded with extraction fillers and a circular dispersed phase collecting weir is set with a weir height of 30 to 95 mm.

[0012] Furthermore, the relative flow velocity of the two-phase axial countercurrent in the tower of the tower device is within the range of 1.6 to 5.2 mm / s, the cross-sectional area of ​​the tower is the quotient of the sum of the two-phase flow rates and the axial relative flow velocity multiplied by a coefficient of 1 to 1.25, and the tower diameter is rounded according to the required cross-sectional area of ​​the tower; the sum of the heights of the high-temperature extraction section and the low-temperature extraction section is 4.2 to 8.4 m, which satisfies the residence time of the two-phase fluid in the two extraction sections to reach 25 to 65 min; the extraction cooling section is located in the lower middle part of the tower, and the height of the low-temperature extraction section is 35 to 90% of that of the high-temperature extraction section.

[0013] Furthermore, the inlet tower temperature of the acid solution to be extracted is controlled to be 45-65°C, the working temperature of the high-temperature extraction section is 55-75°C, and the working temperature of the low-temperature extraction section is 35-45°C.

[0014] Furthermore, the tower top and tower bottom volumes are respectively filled with phase separation fillers for removing heterogeneous substances; a tower top cooling section is arranged between the tower top volume and the middle of the upper distributor; and the tower top volume has a height of 0.45 to 1.1 m.

[0015] Under the above structural conditions, according to the flow rate, components and physical properties of the two-phase medium, and the reasonable configuration of the three technical elements of filler, plate and plate distance, it is more suitable for the efficient extraction of aromatic nitration tail acid.

[0016] The present invention is based on the method of realizing continuous flow nitration reaction based on the tower device for extracting aromatic nitration tail acid coupled with a continuous flow nitration unit. Structurally, the oil phase overflow outlet at the top of the tower discharges directly online through a booster pump and a flow control facility without being buffered, and is connected to the oil phase inlet of several temperature-controlled mixers, and the mixed material outlet of the temperature-controlled mixer is directly connected to the feed inlet of the continuous flow nitration unit.

[0017] The present invention provides a method for realizing online direct supply of continuous flow nitration unit ingredients based on the tower device, comprising the following steps:

[0018] (1) Bottom feeding: To ensure the continuous operation of extraction and reaction coupling, the two-phase interface in the tower is limited to 5-35% of the height of the lower part of the tower. First, the raw sulfuric acid solution is pre-fed until the height of the two-phase interface is set. Then, the room temperature raw aromatic hydrocarbon is continuously fed at the starting flow rate, and after reaching the overflow port of the extracted oil phase, it is continuously discharged from the top overflow port, and is directly transported to the oil phase inlet of several temperature-controlled mixers after flow distribution and pressurization without buffering, and then directly enters the corresponding continuous flow reaction device from the mixed material outlet, completing the online premixing of the organic phase and the nitric acid and sulfuric acid mixed acid before the reaction, while realizing the starting flow feeding;

[0019] (2) Coupling operation: The nitration tail acid is continuously fed at the output flow rate, and enters the tower after being temperature-controlled by the acid inlet heat exchanger. When the level of the two-phase interface changes, the raffinate phase outlet at the bottom of the tower continuously discharges acid. During this period, the organic phase inlet and the top oil phase outlet of the tower maintain the start-up flow rate and continuously discharge the material; the heat exchange load of the extraction cooling section and the tower top cooling section are adjusted respectively;

[0020] (3) Coupling flow regulation: After the acid liquid at the bottom of the tower is continuously discharged, the online flow ratio of the nitration raw material aromatic hydrocarbons and the raw material nitric acid is fine-tuned according to the nitric acid concentration in the residual acid liquid at the bottom of the tower.

[0021] Furthermore, in the method for realizing online direct supply of continuous flow nitration unit batching based on a tower device, the cooling water flow rate is adjusted to maintain the temperature of the mixed material at the outlet of the temperature control mixer at 55-75°C.

[0022] Furthermore, when the rear-stage continuous flow reaction is shut down, the feeding and discharging of the aromatic oil phase of the tower device are stopped; when the rear-stage continuous flow reaction is resumed, the tower device still resumes feeding according to the set value of the coupling flow rate.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0024] (1) The process is simple, and one extraction device can replace multiple extraction tanks, sedimentation tanks and other devices, which can greatly reduce the tower height compared with the traditional static extraction tower.

[0025] (2) The stability of the organic components loaded on the top of the tower can meet the batching requirements of continuous flow nitration and enable flexible start and stop of the reactor.

[0026] (3) The residual acid phase at the bottom of the tower can be discharged homogeneously and stably, the concentration of nitric acid is greatly reduced, and the concentration of nitrate smoke in sulfuric acid evaporation recovery is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a structural schematic diagram of a tower device for extracting aromatic hydrocarbon nitration tail acid according to the present invention;

[0028] Figure 2 It is a schematic diagram of the process of the temperature-controlled mixer of the tower device coupled with the continuous flow nitration unit of the present invention;

[0029] Description of the drawings: 1-tower bottom volume; 2-tower top volume; 3-extraction high temperature section; 4-extraction cooling section; 5-extraction low temperature section; 6-upper distributor; 7-lower distributor; 8-tower top cooling section; 9-temperature control mixer; 10-uniformly distributed tower plate; 11-extraction filler; 12-dispersed phase collecting weir. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0031] The aromatic hydrocarbon nitration tail acid treated by the present invention comes from the acid phase obtained by layering the products after the continuous flow nitration reaction of aromatic hydrocarbons and nitric and sulfuric acid mixed acid. The aromatic hydrocarbon nitration tail acid contains an excess of 0.4-4% nitric acid and is mixed with corresponding nitration products and other organic substances. Aromatic hydrocarbon raw materials corresponding to the products at room temperature are used as blank extractants, and the inlet temperature of the acid solution to be extracted is controlled to be 45-65°C. Through a static tower extraction device with a specific structure, the discharge components of the two phases at the top and bottom of the tower can be realized continuously, balanced and stable, and the components of the organic phase loaded at the top of the tower can meet the more stringent batching requirements of the continuous flow nitration process.

[0032] Specifically, Figure 1 As shown, the tower device for extracting nitrated tail acid of aromatic hydrocarbons of the present invention comprises a tower bottom volume 1 and a tower top volume 2, an upper distributor 6 and a lower distributor 7, and an extraction tower section located between the upper distributor 6 and the lower distributor 7; the extraction tower section is divided into an upper high-temperature extraction section 3 and a lower low-temperature extraction section 5 by an extraction cooling section 4, and the three-section combined extraction tower section can adapt to different nitric acid concentrations in the feed acid phase by setting the high and low-temperature extraction sections at different heights. On the one hand, the acid phase removes the reaction heat through the extraction cooling section 4 and then countercurrently contacts with the aromatic hydrocarbons in the low-temperature section for further cooling, thereby realizing low-temperature acid discharge at the bottom of the tower; on the other hand, the extracted aromatic hydrocarbons in the low-temperature section enter the high-temperature section after mixing and heat exchange, and can fully react with excess nitric acid, thereby reducing the residual nitric acid.

[0033] The structure of the high temperature section and the low temperature section combines the characteristics of the two static extraction towers, namely, the packing and plate type. Specifically:

[0034] 1) Uniformly distributed trays 10 for limiting axial flow are arranged in the extraction high temperature section 3 and the extraction low temperature section 5 at intervals of 320 to 550 mm, the uniformly distributed trays 10 are loaded with extraction fillers 11, and a circumferential dispersed phase collecting weir 12 is arranged, and the weir height is 30 to 95 mm;

[0035] 2) The relative velocity of the two-phase axial countercurrent in the tower is within the range of 1.6-5.2 mm / s. The cross-sectional area of ​​the tower is the quotient of the sum of the two-phase flow rates and the axial relative velocity multiplied by a coefficient of 1-1.25. The tower diameter is rounded according to the required cross-sectional area of ​​the tower. The sum of the heights of the upper and lower extraction sections is 4.2-8.4 m. The residence time of the two extraction sections of the two-phase fluid is 25-65 min, and the contact opportunity of the two phases is increased on the basis of reducing the process height.

[0036] 3) The extraction cooling section 4 is located in the lower middle part of the tower, and the height of the extraction low temperature section 5 is 35-90% of the extraction high temperature section 3.

[0037] The height of the tower top volume 2 is 0.45-1.1m; a tower top cooling section 8 is arranged between the tower top volume 2 and the upper distributor 6, so that the loaded organic phase after extraction is fully cooled and sent to the subsequent reaction unit. For the extraction cooling section 4 and the tower top cooling section 8, a serpentine partition heat exchange tube can be used. The working temperature of the extraction high temperature section 3 is 55-75°C, and the working temperature of the extraction low temperature section is 35-45°C. The bottom and top volumes are each filled with phase separation fillers for removing heterogeneous substances.

[0038] When the tower device of the present invention is coupled to a continuous flow nitration unit, it is only necessary to connect the extracted oil phase outlet at the top of the tower to the oil phase inlet of the temperature control mixer 9 after pressurization and flow control, and the material outlet of the temperature control mixer is no longer provided with flow regulation, but is directly connected to the feed inlet of the continuous flow reaction device, such as Figure 2 shown.

[0039] Under the above structural conditions, according to the flow rate and physical property agent component parameters of the two-phase medium, and corresponding to the three technical elements of filler, tower plate and tower plate distance, compared with the traditional static extraction tower, not only the tower height is greatly reduced, but also the following two-phase countercurrent indicators are more effectively controlled, including: the flow rate and path of the two phases in the tower, the particle size distribution of the dispersed phase droplets, the two-phase countercurrent contact area and contact time, the working temperature of the high temperature section and the low temperature section, the concentration and distribution of heterogeneous dispersion in the two-phase fluid at the top and bottom of the tower, thereby realizing the single-set device processing, homogeneous and stable discharge of the loaded organic phase components, and more effective conversion of the nitric acid component in the acid to achieve substantial emission reductions.

[0040] Based on the tower device for extracting aromatic hydrocarbon nitration tail acid, the present invention implements a method for online direct supply of continuous flow nitration unit ingredients based on the tower device, comprising the following steps:

[0041] (1) Bottom feeding: The tower device is not only a post-treatment unit for tail acid discharge, but also has the function of supplying raw materials for the subsequent continuous flow reaction unit. In order to ensure the continuous operation of the extraction and coupled continuous flow nitration units, the tower needs to be filled with liquid at the bottom. Specifically, the two-phase interface in the tower is limited to 5-35% of the height of the lower part of the tower. The raw sulfuric acid solution is first pre-filled into the bottom of the tower to the set height of the two-phase interface to complete the bottom of the acid phase; then, the aromatic hydrocarbon raw material at room temperature is continuously fed at the initial starting flow rate until the tower is full to complete the bottom of the oil phase; and then the tower is filled with the oil phase. Keep the material discharged continuously from the top overflow port, and directly connect to several temperature-controlled mixers 9 online through flow distribution and pressurization facilities without buffering; when the aromatic hydrocarbons enter the temperature-controlled mixer and contact the ingredients of nitric acid and sulfuric acid, they will continuously mix with each other and begin to undergo nitration reaction and release heat. In order to suppress the reaction rate of the two phases of oleic acid and achieve more complete mixing between the two phases, thereby ensuring the uniformity of the subsequent continuous flow nitration reaction, the temperature of the mixed material at the outlet of the temperature-controlled mixer is controlled to be 55-75°C by adjusting the cooling water flow, and then directly enter the continuous flow nitration reactor. Then each directly enters the continuous flow nitration reaction unit, completes the online mixing of the organic phase and the nitric acid and sulfuric acid before the reaction, and realizes the start-up flow feeding.

[0042] (2) Coupling operation: Wait for the nitrated tail acid to be continuously fed at the output flow rate after the reaction, and enter the extraction tower device after temperature control by the acid inlet heat exchanger. When the two-phase interface begins to change, the residual acid phase outlet at the bottom of the tower continuously discharges acid. During this period, the organic phase inlet of the tower is continuously fed at the start-up flow rate, and the top post-extraction oil phase overflow port is continuously discharged. At this time, the continuous flow reaction unit and the extraction tower device begin to operate in coupling, and the residual nitric acid reacts with the aromatic hydrocarbon raw material in the tower and releases heat, and the heat exchange load of the extraction cooling section 4 and the tower top cooling section 8 are adjusted respectively.

[0043] (3) Coupling flow regulation: When the acid liquid at the bottom of the tower begins to be discharged continuously, the amount of excess nitric acid reacting in the tower is taken as the online regulation control target for the nitration raw material after the tower and reaction coupling, that is, the online flow ratio of the nitration raw material and nitric acid is fine-tuned according to the nitric acid concentration in the residual acid liquid at the bottom of the tower.

[0044] In addition, when the rear-stage continuous flow reaction of the present invention is stopped, the feeding and discharging of the aromatic oil phase of the tower device are stopped; when the rear-stage continuous flow reaction is resumed, the tower device still resumes feeding according to the set value of the coupling flow rate. That is, when the feeding is resumed after the rear-stage continuous flow reaction is stopped, the discharge flow rate of the extraction tower still resumes the set value of the coupling flow rate unchanged.

[0045] The following takes the use of the tower device for extracting aromatic hydrocarbon nitration tail acid of the present invention coupled with a continuous flow nitration reaction unit to achieve continuous nitration reaction as an example to illustrate the superiority of the tower device and method of the present invention.

[0046] Example 1

[0047] This embodiment uses a tower device for extracting nitration tail acid with toluene and a method for realizing an online direct supply loop nitration unit based on the tower device to carry out continuous nitration reaction of toluene. The acid to be extracted comes from the layered tail acid generated by the two-stage series nitration device of dinitrotoluene and mononitrotoluene. The DVS of sulfuric acid is 2.8, the residual nitric acid concentration is 1.2-1.5%, the nitrotoluene concentration in the acid solution is 5.3%, and the acid solution flow rate is 10m 3 / h; the extractant is elemental toluene at room temperature.

[0048] The structural features of the extraction tower device include: uniformly distributed plates for limiting axial flow are set at equal intervals of 420mm along the two extraction sections in the tower, the plates are loaded with extraction fillers, and a circumferential dispersed phase collecting weir is set with a weir height of 60mm; the axial relative flow rate of the two phases of oleic acid is 2.12mm / s, and the tower diameter is 1800mm; the sum of the heights of the high-temperature and low-temperature extraction sections is 6.8m, of which the high-temperature extraction section is 3.6m; the top and bottom volumes of the tower are each filled with phase separation fillers for removing heterogeneous substances, and the height of the top volume of the tower is 0.9m; after cooling in two cooling sections, the top discharge of the tower is 35℃, and the bottom acid phase outlet is 40℃. The two-phase interface in the tower is 700m below the tower; the toluene discharge pipe after extraction at the top of the tower is connected to the oil phase inlet of two temperature-controlled mixers through the top distribution facility.

[0049] The specific method is as follows:

[0050] (1) The raw sulfuric acid solution used in the reaction was pre-filled to the height of the two-phase interface to complete the bottoming. The raw toluene at room temperature was added at 5.7 m 3 / h start-up flow rate is continuously fed to fill the tower with oil phase to complete the bottom, and the material is continuously discharged from the top post-extraction toluene pipe outlet, and is evenly distributed to the subsequent two temperature-controlled mixers through the tower top distribution, pressurization and flow adjustment facilities. The temperature of the mixed material at the outlet of the temperature-controlled mixer is adjusted to 65°C, and each enters the two loop reaction devices to complete the mixing and batching;

[0051] (2) Wait for the nitrification tail acid to reach 10m 3 / h continuous feeding, after the acid inlet heat exchanger controls the temperature at 60℃, it enters the upper distributor, and when the two-phase interface begins to change, the bottom acid port begins to discharge continuously; during this period, the top post-extraction oil port maintains 5.7m 3 / h flow rate for continuous discharging;

[0052] (3) After sulfuric acid starts to discharge continuously, adjust the raw material toluene to 5.82m 3 / h coupling flow feed, the residence time of the two-phase fluid in the extraction section is 55min; the organic phase is evenly distributed to two temperature-controlled mixers to complete online mixing with nitric acid and sulfuric acid, and the mixed discharges are directly fed into two loop reactors to prepare nitrotoluene;

[0053] (4) During the operation of the subsequent loop reactor, the toluene extractant is continuously fed and discharged synchronously at a coupled flow rate; when the feed is resumed after the reaction is stopped, the toluene flow rate still recovers the coupled flow rate of 5.82m 3 The set value of / h remains unchanged, and the discharge flow rate of the acid phase at the bottom of the extraction tower is adjusted according to the actual position of the two-phase interface at this time.

[0054] The total amount of nitrotoluene and toluene in the raffinate of Example 1 does not exceed 0.085%, the concentration of residual nitric acid is lower than 0.4%; and the total acid content in the oil phase loaded with benzene at the top of the tower does not exceed 0.01N.

[0055] Example 2

[0056] In this embodiment 2, a benzene nitration tail acid extraction tower device and a method based on the tower device microreactor nitration unit are used. The acid to be extracted comes from the layered tail acid generated by the two-stage series microreactor of dinitrobenzene and nitrobenzene, the sulfuric acid DVS is 4.6, the residual nitric acid concentration is 1.6%, the nitrate concentration in the acid is 9.6%, and the acid flow rate is 3.8m 3 / h; the extractant is elemental benzene at room temperature.

[0057] The structural features of the extraction tower device include: uniformly distributed plates for limiting axial flow are set at equal intervals of 400mm along the two extraction sections in the tower, and a circumferential dispersed phase collecting weir is set on the plate, with a weir height of 45mm; the relative axial velocity of the two phases of oleic acid is 3.1mm / s, and the tower diameter is 900mm; the sum of the heights of the high-temperature and low-temperature extraction sections is 7.0m, of which the height of the low-temperature section is 2.6m; the top and bottom volumes of the tower are each filled with phase separation fillers for removing heterogeneous substances, and the height of the top volume is 0.8m; after cooling in two cooling sections, the top discharge of the tower is 37℃, and the bottom acid phase outlet is 42℃. The two-phase interface in the tower is 0.45m below the tower; the top extraction benzene discharge pipe is connected to the oil phase inlet of 5 temperature-controlled mixers through the top distribution facility.

[0058] The specific method is as follows:

[0059] (1) The raw sulfuric acid solution used in the reaction is pre-filled to the height of the two-phase interface to complete the bottoming. The raw benzene at room temperature is 1.9m 3 / h start-up flow rate is continuously fed to fill the tower with oil phase to complete the bottom, and the material is continuously discharged from the top post-extraction benzene pipe port, and is evenly distributed to the subsequent 5 temperature-controlled mixers through the tower top distribution, pressurization and flow adjustment facilities. The temperature of the mixed material at the outlet of the temperature-controlled mixer is adjusted to 60°C, and each enters 5 microreactors to complete the mixing and batching;

[0060] (2) Wait for the nitrated tail acid to reach 3.8 m 3 / h continuous feeding, after the acid inlet heat exchanger controls the temperature at 60℃, it enters the upper distributor, and when the two-phase interface begins to change, the bottom acid port begins to discharge continuously; during this period, the top post-extraction oil port maintains 1.9m 3 / h flow rate for continuous discharging;

[0061] (3) After sulfuric acid starts to discharge continuously, adjust the raw material benzene to 1.96m 3 The feed is fed at a coupled flow rate of / h, and the residence time of the two-phase fluid in the extraction section is 36min; the organic phase is evenly distributed to 5 temperature-controlled mixers to complete online mixing with nitric acid and sulfuric acid, and the mixed discharges are directly fed into 5 microreactors to prepare nitrobenzene;

[0062] (4) When the subsequent loop reactor is in operation, the toluene extractant is continuously and synchronously fed and discharged at a coupled flow rate; when the feed is resumed after the reaction is shut down, the benzene flow rate is still restored to the coupled flow rate setting value unchanged, and the discharge flow rate of the acid phase at the bottom of the tower is adjusted according to the actual position of the interface between the two phases at this time, and the interface height is adjusted or reset.

[0063] The total amount of nitrobenzene and benzene in the raffinate of Example 2 does not exceed 0.08%, the concentration of residual nitric acid is lower than 0.45%; the total acid content in the oil phase loaded with benzene at the top of the tower does not exceed 0.008N.

Claims

1. A tower device for extracting aromatic hydrocarbon nitration tail acid, wherein the aromatic hydrocarbon nitration tail acid refers to the nitration tail acid obtained by reacting aromatic hydrocarbon and nitric acid and sulfuric acid mixed acid through a continuous flow nitration device and then stratifying the resulting product, wherein the acid is mixed with organic matter such as nitro compounds, and the nitration tail acid contains 0.4 to 4% nitric acid; the aromatic hydrocarbon raw material corresponding to the nitration product is used as the extractant, characterized in that: The structure of the tower device includes: A tower bottom volume (1) connected to the outlet of the raffinate phase, a tower top volume (2) connected to the overflow port of the extracted oil phase, an upper distributor (6) connected to the inlet of the nitrated tail acid to be extracted, a lower distributor (7) connected to the inlet of the aromatic hydrocarbon raw material, and an extraction tower section located between the upper distributor (6) and the lower distributor (7); the extraction tower section is divided into an upper high-temperature extraction section (3) and a lower low-temperature extraction section (5) by an extraction cooling section (4), and the extraction high-temperature section (3) and the extraction low-temperature section (5) both adopt a structure in which an extraction filler (11) is combined with a uniformly distributed tower plate (10).

2. The tower device for extracting aromatic nitration tail acid according to claim 1, characterized in that: The structure of the combination of the extraction filler (11) and the uniformly distributed tower plate (12) is as follows: uniformly distributed tower plates (10) for limiting axial flow are arranged at equal intervals of 320 to 550 mm in the extraction high-temperature section (3) and the extraction low-temperature section (5); the extraction filler (11) is loaded on the uniformly distributed tower plate (10); and a circumferential dispersed phase collecting weir (12) is arranged, and the weir height is 30 to 95 mm.

3. The tower device for extracting aromatic nitration tail acid according to claim 1, characterized in that: The relative flow velocity of the two-phase axial countercurrent in the extraction tower is within the range of 1.6 to 5.2 mm / s, the cross-sectional area of ​​the tower is the quotient of the sum of the two-phase flow rates and the axial relative flow velocity multiplied by a coefficient of 1 to 1.25, and the tower diameter is rounded according to the required cross-sectional area of ​​the tower; the total height of the extraction tower is 4.2 to 8.4 m; the extraction cooling section (4) is located in the middle and lower part of the tower, and the height of the extraction low-temperature section (5) is 35 to 90% of the extraction high-temperature section (3); and the residence time of the two-phase fluid in the two extraction sections is 25 to 65 minutes.

4. The tower device for extracting aromatic nitration tail acid according to claim 1, characterized in that: The temperature of the nitrated tail acid to be extracted is controlled at 45-65°C, the working temperature of the high-temperature extraction section (3) is 55-75°C, and the working temperature of the low-temperature extraction section (5) is 35-45°C.

5. The tower device for extracting aromatic nitration tail acid according to claim 1, characterized in that: The tower bottom volume (1) and the tower top volume (2) are each filled with a phase separation filler for removing heterogeneous substances; the height of the tower top volume (2) is 0.45 to 1.1 m; and a tower top cooling section (8) is arranged between the tower top volume (2) and the upper distributor (6).

6. A method for realizing online direct supply of continuous flow nitration unit ingredients based on the tower device of claim 1, characterized in that: The oil phase overflow outlet discharges directly online through a booster pump and a flow control device without buffering, and is connected to the oil phase inlet of a plurality of temperature-controlled mixers (9), and the mixed material outlet of the temperature-controlled mixer (9) is directly connected to the feed inlet of the continuous flow nitration unit. The method comprises the following steps: (1) Bottom feeding: To ensure the continuous operation of extraction and reaction coupling, the two-phase interface in the tower is limited to 5-35% of the height of the lower part of the tower. First, the raw sulfuric acid solution is pre-fed until the height of the two-phase interface is set. Then, the room temperature raw aromatic hydrocarbon is continuously fed at the starting flow rate, and after reaching the overflow port of the extracted oil phase, it is continuously discharged from the top overflow port, and is directly transported to the oil phase inlet of several temperature-controlled mixers after flow distribution and pressurization without buffering, and then directly enters the corresponding continuous flow reaction device from the mixed material outlet, completing the online premixing of the organic phase and the nitric acid and sulfuric acid mixed acid before the reaction, while realizing the starting flow feeding; (2) Coupling operation: The nitration tail acid is continuously fed at the output flow rate, and enters the tower after being temperature-controlled by the acid inlet heat exchanger. When the level of the two-phase interface changes, the raffinate phase outlet at the bottom of the tower continuously discharges acid. During this period, the organic phase inlet and the top oil phase outlet of the tower maintain the start-up flow rate for continuous discharge; The heat exchange loads of the extraction cooling section and the tower top cooling section are adjusted respectively; (3) Coupling flow regulation: After the acid liquid at the bottom of the tower is continuously discharged, the online flow ratio of the nitration raw material aromatic hydrocarbons and the raw material nitric acid is fine-tuned according to the nitric acid concentration in the residual acid liquid at the bottom of the tower.

7. The method for realizing online direct supply of continuous flow nitration unit batching based on a tower device according to claim 6, characterized in that: The temperature of the mixed material at the outlet of the temperature-controlled mixer (9) is adjusted to 55-75°C.

8. The method for realizing online direct supply of continuous flow nitration unit batching based on a tower device according to claim 6, characterized in that: When the rear-stage continuous flow reaction is shut down, the feeding and discharging of the aromatic oil phase of the tower device are stopped; when the rear-stage continuous flow reaction is resumed, the tower device still resumes feeding according to the set value of the coupling flow.

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