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

Abstract

The application discloses a tower device for extracting aromatic hydrocarbon nitration tail acid and a method for realizing online direct supply of a continuous flow nitration unit based on the device, adopts an improved static extraction tower form, avoids the disadvantage of excessive height of a traditional static extraction tower through a structure combining a filler and a plate, sets a tower height and a height of an extraction high-temperature section according to a concentration of nitric acid in the tail acid, and finally completes extraction of residual nitrates in an extraction low-temperature section after a cooling section. The application purifies the aromatic hydrocarbon nitration tail acid through a single set of extraction devices, can fully realize extraction and separation of organic matters, can convert nitric acid in the tail acid, and creates more friendly process conditions for sulfuric acid evaporation and recovery. On the basis, the application is connected with a temperature control mixing device of the continuous flow nitration unit, also ensures that the organic phase after extraction can be continuously, stably and homogeneously supplied to online dosing of the continuous flow nitration unit, and meets strict proportioning requirements of the continuous flow nitration unit.

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 tower device. Background Art

[0002] In the production of aromatic hydrocarbons such as benzene, toluene, chlorobenzene, and naphthalene, which are nitrated using a nitric-sulfuric acid mixture, the resulting acid phase contains, in addition to sulfuric acid, water, organic nitrates, and varying amounts of excess nitric acid. Evaporative recovery of this nitrated tail acid requires prior separation of organic matter and reduction of nitric acid concentration. In production, the raw aromatic hydrocarbon is typically used as a blank extractant to treat the organic matter. Residual nitric acid is removed along with the sulfuric acid in the evaporation recovery section, placing a significant burden on the evaporation process. Furthermore, the raw aromatic hydrocarbon extract incorporates the nitration products into the dispersed acid phase, and the acid phase content is positively correlated with the mixed acid concentration. Even with consistent raffinate acid concentration, different extraction units or different oleic acid separation structures can result in varying amounts of acid phase mixed into the organic phase after extraction. In the art, acid extraction generally utilizes a kettle-type countercurrent extraction method with two or one countercurrent stages. This requires the installation of shallow overflow sedimentation tanks at the discharge ends of the oil and water phases, respectively. The height of the tank outlet must ensure continuous overflow throughout the entire process, resulting in poor separation efficiency. Consequently, the organic phase after extraction is often defined as an acidic nitrating feedstock, such as "acidic benzene" or "acidic toluene." The excess nitric acid present in the tail acid creates a dilemma for the extraction process. On the one hand, it is desirable to minimize the nitric acid concentration in the raffinate to reduce nitrogen oxide contamination during sulfuric acid evaporation and recovery. On the other hand, the excess nitric acid and the nitrating feedstock react at the interface between the two phases, releasing heat. This reaction further weakens the already limited separation performance of traditional extraction units.

[0003] More importantly, within a certain height near the oleic acid interface, the concentration of the acid components in the phase after extraction of aromatic hydrocarbons spontaneously increases vertically from high to low to varying degrees, but the concentration gradient cannot be eliminated. This makes the concentration ratio of aromatic hydrocarbons, 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 fluctuation is greater when switching from a static state to a flowing state.

[0004] On the other hand, the continuous flow reactor such as micro-channel is considered as a new type of nitration reaction technology with intrinsic safety due to its small online volume and high reaction efficiency, but it is also more demanding for the accuracy and stability of the feed ratio because the online volume is small and the reaction ratio cannot be adjusted online as in the traditional tank reaction. Especially, it is necessary to ensure the ideal result after each shutdown and restart. In actual production, the organic phase after extraction will inevitably have online storage and residence before entering the reaction, so in the continuous flow nitration reaction, the above-mentioned uneven fluctuation phenomenon will significantly interfere with the feeding and adjustment of the continuous flow nitration reaction, and the influence is most obvious when the machine is restarted after shutdown.

[0005] In summary, in the traditional production process, the above-mentioned extraction section has complex process, large number of equipment, fluctuation of two-phase discharge components, and the acid phase after extraction will still float the aromatic hydrocarbon raw material on the surface of the storage layer, which causes burden to the safety and environmental protection of acid liquid 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-mentioned problems in the 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 column is more conducive to the stability of the concentration of the two-phase discharge components, and there is an opportunity to simplify the process, but the physical properties of the two-phase materials in the field limit the application of the traditional static extraction column, and the specific factors include: the large difference in specific gravity of the two phases restricts the contact time of the two phases, which requires a large column height; the large interfacial tension of the two phases causes the large size of the countercurrent droplets, which greatly reduces the contact area and easily forms convergent flow; the nitration product has a certain solubility in the acid phase, and more uniform and sufficient countercurrent mass transfer is required to ensure the extraction depth; the exothermic reaction of excess nitric acid and raw material in the column will form a thermal convection, which will interfere with the uniform countercurrent and affect the stability of the column effect. The above-mentioned factors such as interfacial tension, specific gravity difference and thermal convection in the field comprehensively form the working conditions that limit the performance of the static extraction column. SUMMARY

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

[0008] The core method of constructing the above-mentioned extraction device is to use an improved static extraction column form, to avoid the disadvantage of excessive height of the traditional static extraction column through the combination of packing and plate type internal structures; to set the column height and the height of the high-temperature extraction section according to the concentration of the incoming tail acid, so as to complete the extraction of the organic phase and reduce the concentration of nitric acid in the acid liquid as much as possible; and to finally complete the extraction of the residual nitration product in the low-temperature extraction section after the cooling section.

[0009] Technical solution: The tower device of the present invention is used to extract aromatic hydrocarbon nitration tail acid. The aromatic hydrocarbon nitration tail acid refers to the nitration tail acid obtained by reacting aromatic hydrocarbons and nitric and sulfuric mixed acids through a continuous flow nitration device and then separating the reactants. The acid is mixed with organic substances such as nitro compounds. 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. 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 uniform distributor is connected to the inlet of the tail acid to be extracted, the lower uniform distributor is connected to the inlet of the aromatic hydrocarbon raw material, and the extraction tower section is located between the upper uniform distributor and the lower uniform distributor; the extraction tower section 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 and uniformly distributed tower plates.

[0011] Furthermore, the structure of the tower device combining the packing and the uniformly distributed tower plates 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 packing and a circumferential dispersed phase collecting weir is provided 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 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 each 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 height of the tower top volume is 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, tray and tray distance, it is more suitable for the efficient extraction of aromatic nitration tail acid.

[0016] The present invention is based on a method for realizing a continuous flow nitration reaction by coupling the tower device for extracting nitrated tail acid of aromatic hydrocarbons with a continuous flow nitration unit. Structurally, the oil phase overflow outlet at the top of the tower discharges the oil phase directly online through a booster pump and a flow control device without buffering, 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 ingredients to a continuous flow nitration unit 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 set two-phase interface height is stopped; then the room temperature raw aromatic hydrocarbon is continuously fed at the starting flow rate, and after reaching the oil phase overflow port after extraction, 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 pre-mixing of the organic phase and the nitric-sulfuric acid mixed acid before the reaction and realizing the starting flow feeding;

[0019] (2) Coupling operation: Nitration tail acid is continuously fed at the output flow rate, and after temperature control by the acid inlet heat exchanger, it enters the tower. 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 oil phase outlet at the top of the tower maintain the starting flow rate for continuous discharge; 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 ingredients 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-controlled mixer at 55-75°C.

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

[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 requirements of the batching of continuous flow nitration and enable the 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 nitrous acid smoke in the sulfuric acid evaporation recovery is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the structure of the tower device for extracting aromatic nitration tail acid of the present invention;

[0028] Figure 2 This is a schematic diagram of a process flow of a tower device coupled with a temperature-controlled mixer of a 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 uniform distributor; 7-lower uniform 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 with reference to the accompanying drawings and embodiments.

[0031] The aromatic hydrocarbon nitration tail acid processed 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 mixed acids. The aromatic hydrocarbon nitration tail acid contains an excess of 0.4 to 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 to 65°C. Through a static tower extraction device with a specific structure, the discharge components of the tower top and tower bottom phases can be achieved continuously, balanced and stable, and the components of the organic phase loaded on the tower top can meet the more stringent ingredient requirements of the continuous flow nitration process.

[0032] Specifically, such as 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. The three-section 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 contacts the aromatic hydrocarbons in the low-temperature section in countercurrent to further cool it down, 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 two static extraction towers: packing and plate type. Specifically:

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

[0035] 2) The relative velocity of the two-phase axial countercurrent flow in the 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 velocity multiplied by a coefficient of 1 to 1.25. The tower diameter is rounded based on the required cross-sectional area of ​​the tower. The sum of the heights of the upper and lower extraction sections is 4.2 to 8.4 m. The residence time of the two extraction sections of the two-phase fluid is 25 to 65 minutes, thereby increasing the contact opportunity between the two phases while reducing the 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 to 1.1 meters. A top cooling section 8 is located between the top volume 2 and the upper distributor 6 to fully cool the extracted loaded organic phase before delivery to the subsequent reaction unit. Serpentine-shaped partitioned heat exchange tubes can be used for the extraction cooling section 4 and the top cooling section 8. The operating temperature of the high-temperature extraction section 3 is 55 to 75°C, and the operating temperature of the low-temperature extraction section is 35 to 45°C. The bottom and top volumes are each filled with phase separation fillers to remove heterogeneous phases.

[0038] When the tower device of the present invention is coupled to the 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-controlled mixer 9 after pressurization and flow control. The material outlet of the temperature-controlled mixer is no longer provided with flow regulation and 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 processing, homogeneous and stable discharge of the loaded organic phase components, and more effective conversion of the nitric acid component in the acid, thereby achieving substantial emission reductions.

[0040] Based on the above-mentioned 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-processing 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. First, the raw sulfuric acid solution is pre-filled into the bottom of the tower to the set two-phase interface height to stop the completion of the acid phase bottoming; then, the aromatic hydrocarbon raw material at room temperature is continuously fed at the initial starting flow rate until the tower is full of the oil phase to complete the bottoming; continue Continuous discharge is maintained from the top overflow port, and the mixture is directly connected 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 come into contact with the nitric acid and sulfuric acid mixture, they continuously mix with each other and begin a nitration reaction with heat release. To suppress the reaction rate of the oleic acid phase and achieve more thorough mixing between the two phases, thereby ensuring the uniformity of the subsequent continuous flow nitration reaction, the temperature of the mixed material at the temperature-controlled mixer outlet is controlled to 55-75°C by adjusting the cooling water flow rate, and then directly enters the continuous flow nitration reactor. Each of the mixed materials then directly enters the continuous flow nitration reaction unit, completing the online mixing of the organic phase and the nitric acid and sulfuric acid mixture before the reaction, and achieving the start-up flow feed.

[0042] (2) Coupling operation: Wait for the nitrated tail acid to be separated after the reaction to be continuously fed at the output flow rate, and enter the extraction tower device after temperature control by the acid inlet heat exchanger. When the interface between the two phases 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 starting 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 online regulation control target of the nitration raw material after the tower and reaction coupling is taken into account, 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] Furthermore, when the rear-stage continuous flow reaction is shut down, the aromatic oil phase feed and discharge from the tower device are stopped; when the rear-stage continuous flow reaction is resumed, the tower device resumes feeding according to the set value of the coupled flow rate. That is, when feeding is resumed after the rear-stage continuous flow reaction is shut down, the extraction tower discharge flow rate remains unchanged at the set value of the coupled flow rate.

[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 realize 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 a continuous nitration reaction of toluene. The acid to be extracted comes from the layered tail acid generated by the two-stage serially connected loop 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 is 5.3%, and the acid flow rate is 10m 3 / h; the extractant is elemental toluene at room temperature.

[0048] The extraction tower features include uniformly spaced 420mm-spaced trays along the two extraction sections to limit axial flow, loaded with extraction packing, and a 60mm-high circumferential dispersed phase collecting weir. The axial relative velocity of the oleic acid phase is 2.12mm / s, and the tower diameter is 1800mm. The combined height of the high-temperature and low-temperature extraction sections is 6.8m, with the high-temperature section comprising 3.6m. The top and bottom volumes are each filled with phase separation packing to remove foreign matter, with the top volume height being 0.9m. After cooling through two cooling sections, the top outlet is at 35°C, while the bottom outlet of the acid phase is at 40°C. The two-phase interface is located 700m below the tower. The post-extraction toluene discharge pipe at the top of the tower is connected to the oil phase inlets of two temperature-controlled mixers via a top distribution device.

[0049] The specific method is as follows:

[0050] (1) The raw material sulfuric acid solution for the reaction is pre-filled to the height of the two-phase interface to complete the bottoming, and the raw material toluene at room temperature is 5.7m 3 The tower is continuously fed with a starting flow rate of / h to complete the oil phase bottoming. The material is continuously discharged from the top toluene pipe after extraction. After being distributed, pressurized and adjusted by the tower top facilities, it is evenly distributed to the subsequent two temperature-controlled mixers. The temperature of the mixed material at the outlet of the temperature-controlled mixer is adjusted to 65℃. The mixed material enters the two loop reaction devices to complete the mixing of the ingredients.

[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 continuous discharge;

[0052] (3) After sulfuric acid starts to discharge continuously, adjust the raw material toluene to 5.82m 3The feed is fed at a coupled flow rate of 100 mL / h, and the residence time of the two-phase fluid in the extraction section is 55 min. The organic phase is evenly distributed to two temperature-controlled mixers to complete online mixing with the nitric and sulfuric acid mixture. The mixed discharges are directly fed into two loop reactors to prepare nitrotoluene.

[0053] (4) During the subsequent operation of the 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 Example 2, a benzene nitration tail acid extraction tower device and a method based on the microreactor nitration unit of the tower device are used. The acid to be extracted comes from the layered tail acid generated by the two-stage microreactor connected in series with 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 extraction tower features include uniformly spaced 400mm-spaced trays along the two extraction sections to limit axial flow, each with a 45mm-high circumferential dispersed phase weir. The axial relative velocity of the oleic acid phase is 3.1mm / s, and the tower diameter is 900mm. The combined height of the high- and low-temperature extraction sections is 7.0m, with the low-temperature section being 2.6m high. The top and bottom volumes are each filled with phase separation fillers to remove foreign matter, with the top volume being 0.8m high. After cooling through two cooling sections, the top outlet temperature is 37°C, while the bottom outlet temperature for the acid phase is 42°C. The two-phase interface is located 0.45m below the tower. The post-extraction benzene discharge pipe at the top of the tower is connected to the oil phase inlet of five temperature-controlled mixers via a top distribution system.

[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 of the extracted benzene pipe. After the top distribution, pressurization and flow regulation facilities are used, it is evenly distributed to the subsequent 5 temperature-controlled mixers. The temperature of the mixed material at the outlet of the temperature-controlled mixer is adjusted to 60℃, and each enters 5 microreactors to complete the mixing and batching;

[0060] (2) Wait for the nitrated tail acid to reach 3.8m 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 continuous discharge;

[0061] (3) After sulfuric acid starts to discharge continuously, adjust the raw material benzene to 1.96m 3 The feed was fed at a coupled flow rate of / h, and the residence time of the two-phase fluid in the extraction section was 36 minutes. The organic phase was evenly distributed to five temperature-controlled mixers for online mixing with the nitric and sulfuric acid mixture, and the mixed discharges were directly fed into five 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 stopped, 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 two-phase interface 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%, and 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 and sulfuric mixed acid through a continuous flow nitration device and then separating the discharged material, wherein the nitration tail acid is mixed with organic matter including nitro compounds and also contains 0.4-4% 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: The tower bottom volume (1) is connected to the outlet of the raffinate phase, the tower top volume (2) is connected to the overflow port of the extracted oil phase, the upper distributor (6) is connected to the inlet of the nitrated tail acid to be extracted, the lower distributor (7) is connected to the inlet of the aromatic hydrocarbon raw material, and the extraction tower section is 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 extraction section (3) and the extraction low-temperature extraction 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, wherein The structure of the extraction filler (11) combined with the uniformly distributed tower plate (10) is as follows: the uniformly distributed tower plates (10) for limiting the 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 velocity of the two-phase axial countercurrent in the extraction tower is in 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 total height of the extraction tower is 4.2~8.4 m. The extraction cooling section (4) is located in the lower middle part of the tower. The height of the extraction low-temperature section (5) is 35~90% of the extraction high-temperature section (3). The residence time of the two extraction sections of the two-phase fluid reaches 25~65 min.

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 matter; the height of the tower top volume (2) is 0.45-1.1 m; and a tower top cooling section (8) is provided 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 according to claim 1, characterized in that: The oil phase overflow outlet discharges directly online through a booster pump and flow control facilities without buffering, and is connected to the oil phase inlet of a plurality of temperature-controlled mixers (9). 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 to the set two-phase interface height and then stopped. Then, the room temperature raw aromatics are continuously fed at the starting flow rate, and after reaching the oil phase overflow port after extraction, they are continuously discharged from the top overflow port. Without buffering, they are directly transported online after flow distribution and pressurization to the oil phase inlet of several temperature-controlled mixers, and then directly enter the corresponding continuous flow reaction device from the mixed material outlet, completing the online pre-mixing of the organic phase and the nitric acid and sulfuric acid mixture before the reaction while realizing the starting flow feeding. (2) Coupling operation: Nitration tail acid is continuously fed in at the output flow rate, and enters the tower after temperature control 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; Adjust the heat exchange load of the extraction cooling section and the tower top cooling section 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 ingredients using 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℃.

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

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