A method for treating tail gas in the preparation process of o-chlorobenzonitrile

Abstract

The invention provides a tail gas treatment method in the preparation process of o-chlorobenzonitrile, comprising: high-temperature reaction gas from a reactor enters two mixed capture devices in sequence, a circulating spray pump of the mixed capture device is turned on, a medium in the reaction gas is captured and absorbed to the bottom of the collector by two mixed capture modes of dry condensation and spray flushing of a collector condensation chamber and a capture absorption chamber partition, and is sent to a downstream separation circulation tank through a discharge pipe at the bottom of the collector for natural sedimentation; tail gas after two-stage mixed capture enters an oxidation reactor for oxidation, wherein an oxidant is set as an active oxygen oxidant generated in real time; effective components after oxidation are fully contacted with an oxidant aqueous solution and are oxidized to o-chlorobenzoic acid and then precipitated as solid; slurry at the bottom of the oxidation reactor enters an o-chlorobenzoic acid refining process, and an o-chlorobenzoic acid product is obtained after recrystallization, drying and collection; tail gas discharged from the oxidation reactor enters a tail gas treatment process.

Description

Technical Field

[0001] The invention relates to the field of tail gas treatment in a pharmaceutical intermediate preparation process, and in particular to a tail gas treatment method in a o-chlorobenzonitrile preparation process. Background Art

[0002] o-Chlorobenzonitrile is an important intermediate for drug preparation, mainly used to synthesize the new antimalarial drug nitroquine and other anti-inflammatory and bactericidal drugs. In addition, it is also used to prepare non-peptide anti-angiotensin drugs, which are widely used in the medical field. The ammoxidation method is the mainstream method for producing o-chlorobenzonitrile in industry at present. The reaction equation is shown below and it is widely used. It uses o-chlorotoluene, ammonia and air as reaction raw materials, and synthesizes o-chlorobenzonitrile through ammoxidation reaction under the action of a catalyst with transition metal elements as the main active ingredient. For example, the patent with publication number CN113563226A discloses a method for producing o-chlorobenzonitrile with a high yield. Under the catalytic conditions of a nickel powder-containing catalyst, the temperature in the fluidized bed reactor is as high as 320°C to react to prepare o-chlorobenzonitrile. Although the prior art reduces the residual amount of o-chlorotoluene in the crude o-chlorobenzonitrile, a certain degree of side reaction occurs during the reaction, resulting in partial oxidation of o-chlorotoluene into o-chlorobenzaldehyde, o-chlorobenzoic acid, o-chlorobenzamide, etc. The crude o-chlorobenzonitrile reaction gas containing the above impurities is captured and then mostly converted into a liquid phase, which is subsequently separated according to the different melting and boiling points of different components.

[0003]

[0004] At present, the commonly used capture methods include tower spray absorption and box (barrel) cooling dry absorption. In order to fully cool the reaction gas and absorb it, a spray capture method with increased water consumption is generally adopted, but this method consumes a lot of water and produces more wastewater. In the prior art, the patent with publication number CN110893286A adopts a dry capture method, but this method leads to a high temperature of the tail gas at the gas outlet, so that a large amount of impurities such as o-chlorobenzaldehyde, o-chlorobenzoic acid and o-chlorobenzamide in the tail gas are not absorbed by the spray liquid, resulting in a large tail gas treatment pressure and not meeting environmental protection requirements.

[0005] Therefore, the applicant adopts the method of combining the two Figure 1 The hybrid collector shown in the figure combines the advantages of dry capture and spray wet capture to fully cool and absorb the reaction gas. However, the tail gas discharged from the collector contains not only small molecules such as ammonia and oxygen, but also some o-chlorobenzaldehyde and o-chlorobenzonitrile droplets, which increases the tail gas treatment pressure. Therefore, it is generally necessary to recycle the tail gas to recover the effective ingredients. However, the melting points of o-chlorobenzaldehyde and o-chlorobenzonitrile are close, so it is difficult to separate and recycle the two from the tail gas. If the two are directly incinerated or discarded together, it is easy to cause material waste. Summary of the invention

[0006] In view of this, the present invention aims to provide a method for treating tail gas in the preparation process of o-chlorobenzonitrile, so as to solve the problems of high tail gas treatment pressure and waste of materials after o-chlorobenzonitrile is captured in the prior art.

[0007] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0008] A method for treating tail gas in a process for preparing o-chlorobenzonitrile, comprising:

[0009] (1) Capture of reaction gas: The high-temperature reaction gas from the reactor enters two mixed capture devices in turn. The circulating spray pump of the mixed capture device is turned on. The medium in the reaction gas is captured and absorbed to the bottom of the collector through two mixed capture methods: dry condensation and spray flushing of the collector condensation chamber and the capture absorption chamber partition. The medium is then sent to the downstream separation circulation tank through the discharge pipe at the bottom of the collector for natural sedimentation.

[0010] (2) Tail gas oxidation: The tail gas after two-stage mixed capture enters the oxidation reactor through the outlet of the secondary collector for oxidation, wherein the oxidant is set to be an active oxygen oxidant generated in real time;

[0011] (3) Oxidation separation: The active ingredients after oxidation are fully contacted with the oxidant aqueous solution and are oxidized to o-chlorobenzoic acid and then precipitated as solid; the slurry at the bottom of the oxidation reactor enters the o-chlorobenzoic acid refining process, and the o-chlorobenzoic acid product is obtained after recrystallization, drying and collection; the exhaust gas discharged from the oxidation reactor enters the exhaust gas treatment process.

[0012] Furthermore, two mixed capture devices are used in combination, and the outlet temperature of the first-stage collector is controlled at 80-100°C, and the outlet temperature of the second-stage collector is controlled at 40-50°C by adjusting the amount of circulating water entering the condensation chamber.

[0013] Furthermore, during capture, the temperature of the spray circulating liquid is controlled at 47-50°C.

[0014] Furthermore, the gas coming out of the reactor passes through each capture absorption chamber in turn from one end of the collector and then comes out from the other end. The low-temperature water used for cooling is pumped to the two capture devices through the low-temperature water system and the low-temperature water circulation pump, enters the condensation chamber of the capture device, and returns to the low-temperature water system after passing through the condensation chamber for cooling and then continues to be circulated. The spray circulation liquid in the separation circulation tank is pumped to the capture device through the spray circulation pump, cools and absorbs the capture absorption chamber, and then returns from the capture device to the separation circulation tank.

[0015] Furthermore, the main body of the capture device is a horizontal cylinder, and the interior of the cylinder is divided into a number of capture absorption chambers and condensation chambers in sequence, and the capture absorption chambers and condensation chambers are arranged in a staggered manner. The horizontal cylindrical mixing collector is internally divided into a number of absorption chambers and cooling chambers. The high-temperature gas from the reactor passes through each absorption chamber in sequence, and a number of spray nozzles are designed on the top of each absorption chamber. The auxiliary device spray circulation pump sprays the circulating spray liquid evenly into the absorption chamber, thereby spraying and absorbing the media such as o-chlorobenzonitrile, o-chlorotoluene and ammonium chloride in the gas. At the same time, the cooling water used for cooling is transported to the cooling chamber through the circulating water pump, and the absorption chamber and the cooling chamber partition are cooled to condense the media such as o-chlorobenzonitrile, o-chlorotoluene, o-chlorotoluene and ammonium chloride in part of the gas. The condensed media adsorbed on the partition are then flushed to the auxiliary device separation circulation tank by spraying circulating liquid to separate the oil phase and the water phase. The oil phase is separated and sent to the next process; the water phase continues to circulate back to the collector absorption chamber, and pure water is added regularly. When the concentration of ammonium chloride in the water phase reaches a certain value, the water phase is replaced. After absorbing heat, the cooling water returns to the cooling tower system for cooling, and after cooling, it is sent back to the cooling chamber to continue circulating.

[0016] Furthermore, a plurality of spray nozzles connected to the spray main pipe are installed on the top of the capture absorption chamber, and a material outlet short section is provided at the bottom to connect to the discharge main pipe. A low-temperature water outlet short section and an inlet short section are provided at the top and bottom of the condensation chamber respectively.

[0017] Furthermore, the raw materials of the oxidant include pentaacetyl glucose and sodium perborate, which are mixed immediately before contacting with the tail gas, and the immediately generated oxidant is dissolved in the aqueous solution.

[0018] Furthermore, the pH value of the oxidant aqueous solution is 3-4.

[0019] Furthermore, the oxidation reactor is configured as a partitioned structure, wherein the upper portion of the oxidation reactor is used for immediate generation of the oxidant, and the lower portion of the oxidation reactor is used for the oxidant to oxidize the tail gas.

[0020] Furthermore, after two-stage mixing and capturing, the purity of o-chlorobenzonitrile in the crude product discharged from the separation circulation tank exceeds 90%.

[0021] Compared with the prior art, the tail gas treatment method in the preparation process of o-chlorobenzonitrile of the present invention has the following advantages:

[0022] Before the mixed capture was adopted, ammonium chloride salts were easily deposited in the dry absorption method, frequently blocking the capture absorption chamber and the gas outlet and feed pipes. The maintenance cycle was particularly short, causing the system to be unable to operate normally for a long time. After the mixed absorption using two collectors, the following significant advantages were achieved: the fatal defect in dry absorption - ammonium chloride salt deposition - was eliminated. The condensed ammonium chloride salts were dissolved by the spray liquid to ensure the normal operation of the collector. At the same time, compared with simple spray absorption, mixed absorption not only has a small number of equipment, but also relatively less water consumption, so the amount of wastewater can be effectively controlled. In addition, because the mixed collector not only has the spray circulating liquid to take away the heat, but also the condensation chamber of the collector has a good cooling effect, so the cooling is fast and the capture effect is greatly improved.

[0023] After the tail gas is oxidized by an active oxygen oxidant, o-chlorobenzaldehyde therein is oxidized to o-chlorobenzoic acid. At the same time, since the oxidation reactor is in an acidic aqueous solution environment, o-chlorobenzonitrile is hydrolyzed under acidic conditions to generate o-chlorobenzoic acid, thereby converting the effective components in the tail gas into o-chlorobenzoic acid. O-chlorobenzoic acid has a high melting point and can be subsequently recycled by simple solid-liquid separation to obtain the by-product o-chlorobenzoic acid, thereby improving material utilization and reducing the pressure of subsequent tail gas treatment to meet environmental protection requirements.

[0024] The active oxygen oxidant used in the present invention can have a good oxidation effect on other organic wastewater or organic tail gas containing aldehydes, and effectively remove the aldehydes in the tail gas or wastewater. For example, it can also be used for the treatment of aldehydes in wastewater or exhaust gas of pharmaceutical intermediates such as p-chlorobenzaldehyde and p-chlorobenzaldehyde, and its principle is similar to that of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the structure of the mixed capture device of the present invention;

[0026] Figure 2 This is a schematic diagram of the combined use of two mixed capture devices according to the present invention;

[0027] Figure 3 It is a schematic diagram of the structure of the oxidation reactor described in the present invention.

[0028] Description of reference numerals:

[0029] 1- cylinder, 2- capture absorption chamber, 3- condensation chamber, 4- spray nozzle, 5- spray main pipe, 6- outlet short section, 7- discharge main pipe, 8- outlet short section, 9- inlet short section, 10- pressure detection point, 11- temperature detection point, 12- maintenance manhole, 13- observation hole, 14- primary collector, 15- secondary collector, 16- separation circulation tank, 17- spray circulation pump, 18- low temperature water circulation pump, 19- low temperature water system, 20- oxidation reactor, 21- mixing tank, 211- support plate, 22- oxidant header, 23- aeration pipe, 24- tail gas header, 25- oxidant header nozzle, 26- tail gas outlet after oxidation DETAILED DESCRIPTION

[0030] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0031] A method for treating tail gas in a process for preparing o-chlorobenzonitrile, comprising:

[0032] (1) Capture of reaction gas: The high-temperature reaction gas from the reactor enters two mixed capture devices in turn. The circulating spray pump of the mixed capture device is turned on. The media such as o-chlorobenzonitrile, o-chlorotoluene, o-chlorobenzamide, o-chlorobenzaldehyde, o-chlorobenzoic acid, and ammonium chloride in the reaction gas are captured and absorbed to the bottom of the collector through two mixed capture methods: dry condensation and spray flushing of the collector condensation chamber and the capture absorption chamber partition. The gas is then sent to the downstream separation circulation tank through the discharge pipe at the bottom of the collector for natural sedimentation.

[0033] like Figure 1 As shown, the main body of the capture device is a horizontal cylinder 1, and the interior of the cylinder is divided into a number of capture absorption chambers 2 and condensation chambers 3 in sequence. The capture absorption chambers 2 and condensation chambers 3 are arranged alternately. A number of spray nozzles 4 are installed on the top of the capture absorption chamber 2. The spray nozzles 4 are connected to the spray main pipe 5. The circulating spray liquid pumped by the spray circulation pump passes through the spray main pipe 5 and the spray nozzles 4 and enters the cylinder 1 in the form of mist spray liquid. There is a material outlet short section 6 at the lower part of the cylinder 1, and the outlet short section 6 is connected to the discharge main pipe 7. There are low-temperature water outlet short sections 8 and inlet short sections 9 at the top and bottom of the condensation chamber 3 respectively. A pressure detection point 10 and a temperature detection point 11 are installed on the top of each capture absorption chamber 2. For the convenience of maintenance and observation, an inspection manhole 12 and an observation hole 13 are opened in the middle of each capture absorption chamber 2.

[0034] like Figure 2 The figure shows the schematic diagram of the two mixed capture devices after being used together. By adjusting the amount of circulating water entering the condensation chamber, the outlet temperature of the first-stage collector is controlled at 80-100°C, and the outlet temperature of the second-stage collector is controlled at 40-50°C. At the same time, the temperature of the spray circulating liquid is controlled at 47-50°C.

[0035] The gas from the reactor passes through each capture absorption chamber in turn from one end of the collector and then exits from the other end. The low-temperature water for cooling is pumped to the two capture devices through the low-temperature water system 19 and the low-temperature water circulation pump 18, enters the condensation chamber of the capture device, and returns to the low-temperature water system 19 after passing through the condensation chamber for cooling and continued circulation. The spray circulation liquid in the separation circulation tank 16 is pumped to the capture device through the spray circulation pump 17, cools and absorbs the capture absorption chamber, and then returns to the separation circulation tank 16 from the capture device. By cooling the capture absorption chamber and the condensation chamber partition, part of the medium in the gas is condensed and adsorbed on the capture absorption chamber partition; because the top of each capture absorption chamber of the collector is designed with a number of spray heads, the circulating spray liquid is evenly sprayed into the capture absorption chamber through the auxiliary device spray circulation pump, and the mist spray liquid captures the medium such as o-chlorobenzonitrile, o-chlorotoluene and ammonium chloride in the gas, while flushing the medium on the capture absorption chamber plate to the bottom of the chamber, and is sent to the auxiliary device separation circulation tank through the bottom discharge port for separation layer.

[0036] Most of the oil phases such as o-chlorobenzonitrile, o-chlorotoluene, o-chlorobenzamide, o-chlorobenzaldehyde, and o-chlorobenzoic acid are deposited in the lower part of the separation circulation tank 16 and separated to the next process, while the water phase in the separation circulation tank 16 is sent back to the collector through the middle outlet via the spray circulation pump 17 for continued circulation. To prevent condensation in the feed pipe, the spray circulation liquid is always kept at 47-50°C, and the oil phase is discharged and the water phase is added regularly (when the ammonium chloride in the water phase is close to the saturation concentration, the standby circulation tank is switched to replace the water phase), thereby realizing a stable and continuous mixed capture method. The residual gas after the two-stage mixed capture is sent to the subsequent absorption tower through the outlet of the secondary collector for further treatment.

[0037] (2) Tail gas oxidation: The tail gas after two-stage mixed capture enters the oxidation reactor through the outlet of the secondary collector for oxidation;

[0038] The oxidant is set to be an instantly generated active oxygen oxidant. The raw materials of the oxidant include pentaacetyl glucose and sodium perborate. The two are mixed instantly before contacting with the exhaust gas. The instantly generated oxidant is dissolved in an aqueous solution and sprayed through a nozzle to react with o-chlorobenzonitrile and o-chlorobenzaldehyde in the exhaust gas. The o-chlorobenzaldehyde is oxidized to o-chlorobenzoic acid.

[0039] Furthermore, a mixing tank 21 is arranged near the upper part of the oxidation reactor, a support plate 211 is arranged in the mixing tank 21, the support plate 211 is arranged as a porous structure, sodium perborate is placed on the support plate 211, and the bottom surface of the support plate 211 is arranged as a hollow structure. The pentaacetyl glucose aqueous solution is sprayed onto the support plate in the mixing tank through a spraying device, and reacts with the sodium perborate in the mixing tank to instantly generate active oxygen. The active oxygen aqueous solution enters into the lower oxidant manifold 22 through a pipeline, and is sprayed into the exhaust gas at the lower part through the oxidant manifold nozzle 25.

[0040] A plurality of aeration pipes 23 are arranged near the lower part of the oxidation reactor. The plurality of aeration pipes are arranged in parallel. The aeration pipes are connected to the tail gas header 24 at the lower part. The tail gas header is connected to the tail gas discharged from the secondary collector. The tail gas enters the aeration pipe 23 through the tail gas header. After passing through the aeration pipe 23, the tail gas is discharged from the aeration pipe wall in the form of small bubbles, thereby increasing the contact area between the tail gas and the oxidant aqueous solution, thereby facilitating the rapid progress of the oxidation reaction.

[0041] The pH value of the oxidant aqueous solution is about 3 to 4. Under this condition, the generation rate of active oxygen is fast and the oxidizing ability is strong, which can effectively oxidize o-chlorobenzaldehyde into acid. And under this acidic condition, o-chlorobenzonitrile undergoes acidic hydrolysis according to the following equation to also generate o-chlorobenzoic acid. In addition, the acidic environment can convert ammonia in the tail gas into ammonium ions, further reducing the content of harmful gases in the tail gas and reducing the pressure of subsequent tail gas treatment.

[0042] Cl-Ph-CN+H2O+H + →Cl-Ph-COOH+NH4 +

[0043] The partition setting of the oxidation reactor separates pentaacetyl glucose from sodium perborate, and when needed, the two are brought into contact to instantly generate peracetic acid, which ionizes active oxygen ions. Compared with hydrogen peroxide, the active oxygen oxidant has stronger oxidizing performance and is beneficial to the oxidation of o-chlorobenzaldehyde. The instantly generated oxidant can prevent the oxidant from being ineffective due to long-term exposure.

[0044] The mass ratio of pentaacetyl glucose to sodium perborate is 1:1.4-1.6.

[0045] (3) Oxidation separation: The active ingredients after oxidation are fully contacted with the oxidant aqueous solution and are oxidized to o-chlorobenzoic acid and then precipitated as solid; the slurry at the bottom of the oxidation reactor enters the o-chlorobenzoic acid refining process, and the o-chlorobenzoic acid product is obtained after recrystallization, drying and collection; the exhaust gas discharged from the oxidation reactor enters the exhaust gas treatment process.

[0046] Example 1

[0047] During the production of o-chlorobenzonitrile, firstly, pure water or mother liquor for circulating spraying is added to the separation circulation tank in advance. Before the high-temperature reaction gas from the reactor at about 360°C enters the collector, the spray circulation pump is turned on to transport the circulating liquid in the separation circulation tank to the top of the capture absorption chamber of the mixing cylinder collector for spraying. At the same time, the circulating water system is turned on in advance, and the cooling water is transported to each condensation chamber of the mixing cylinder collector through the circulating water pump. The amount of circulating water entering the condensation chamber is adjusted to control the collector outlet gas temperature to 80-100°C. At this time, the pressure is 1.0MPa and 200Nm 3 / h intake rate of the reactor to pass the high-temperature reaction gas, and continue to pass for 12h, always keep the spray circulation liquid at 47-50 ° C, and regularly discharge the oil phase and add the water phase (when the ammonium chloride in the water phase is close to the saturation concentration, switch the standby circulation tank to replace the water phase), so as to achieve a stable and continuous mixed capture method. The tail gas after mixed capture is sent to the subsequent tail gas absorption tower for further treatment through the outlet of the collector. The content of o-chlorobenzonitrile in the tail gas after mixed capture was determined to be 0.46%, the content of o-chlorobenzaldehyde was 0.37%, and the content of o-chlorobenzoic acid was 0.41%. At the same time, the purity of o-chlorobenzonitrile in the crude product discharged from the separation circulation tank was determined to be 87.6%.

[0048] Example 2

[0049] (1) Capture of reaction gas: First, add pure water or mother liquor for circulating spraying to the separation circulation tank in advance. Before the high-temperature reaction gas from the reactor at about 360°C enters the collector, turn on the spray circulation pump to transport the circulating liquid in the separation circulation tank to the top of the capture absorption chamber of the mixing cylinder collector for spraying. At the same time, turn on the circulating water system in advance, and use the circulating water pump to transport cooling water to each condensation chamber of the mixing cylinder collector. By adjusting the amount of circulating water entering the condensation chamber, control the outlet temperature of the first-stage collector to 80-100°C, and the outlet temperature of the second-stage collector to 40-50°C. At this time, the pressure is 1.0MPa and 200Nm 3 / h intake rate of the reactor to pass the high-temperature reaction gas, and continue to pass for 12h, always keep the spray circulation liquid at 47-50 ° C, and regularly discharge the oil phase and add the water phase (when the ammonium chloride in the water phase is close to the saturation concentration, switch the standby circulation tank to replace the water phase), so as to achieve a stable and continuous mixed capture method. The residual gas after the two-stage mixed capture is sent to the subsequent absorption tower for further treatment through the outlet of the secondary collector. The content of o-chlorobenzonitrile in the tail gas after the secondary collector was determined to be 0.38%, the content of o-chlorobenzaldehyde was 0.32%, and the content of o-chlorobenzoic acid was 0.36%. At the same time, the purity of o-chlorobenzonitrile in the crude product discharged from the separation circulation tank was determined to be 91.2%.

[0050] Example 3

[0051] (1) The capture of the reaction gas is the same as in Example 2; the residual gas after the two-stage mixed capture is sent to the tail gas oxidation stage through the outlet of the secondary collector;

[0052] (2) Before the captured residual gas is introduced, a mixture of pentaacetylglucose (5kg), sodium perborate (7.2kg) and sodium dodecylsulfonate (0.03kg) is added to the oxidation reactor. The mixture is placed on a support plate, and 1000L of water is added to dissolve it through a spraying device. The pH value in the oxidation reactor is controlled to be about 4. The mixed reaction solution enters the interior of the oxidant manifold 22 at the lower part through a pipeline, and is sprayed into the residual gas at the lower part through the oxidant manifold nozzle 25. The residual gas is introduced into the interior of the oxidation reactor, and the oxidant aqueous solution directly contacts the residual gas to react. The final tail gas after the oxidation reaction is discharged from the top of the oxidation reactor and enters the subsequent tail gas treatment process. The content of o-chlorobenzonitrile, o-chlorobenzaldehyde and o-chlorobenzoic acid in the final tail gas after oxidation in the oxidation reactor is measured to be 0.24%, 0.19% and 0.22%, respectively.

[0053] (3) Oxidation separation: The slurry at the bottom of the oxidation reactor enters the o-chlorobenzoic acid refining process, and the o-chlorobenzoic acid product is obtained after recrystallization, drying and collection; the final tail gas discharged from the oxidation reactor enters the tail gas treatment process. After the slurry before entering the refining process is dried, the o-chlorobenzonitrile content is measured to be 0.12%, the o-chlorobenzaldehyde content is 0.09%, and the o-chlorobenzoic acid content is 86%.

[0054] Example 4

[0055] (1) The capture of the reaction gas is the same as in Example 2; the residual gas after the two-stage mixed capture is sent to the tail gas oxidation stage through the outlet of the secondary collector;

[0056] (2) Before the tail gas is introduced, a mixture of pentaacetyl glucose (5 kg) and sodium dodecyl sulfate (0.03 kg) is dissolved in 1000 L of water and then sprayed onto the support plate in the mixing tank through a spraying device. Sodium perborate (7.2 kg) is evenly arranged on the support plate. Pentaacetyl glucose reacts with the sodium perborate in the mixing tank to generate active oxygen immediately. The active oxygen aqueous solution enters the lower oxidant manifold 22 through a pipeline and is sprayed into the lower tail gas through the oxidant manifold nozzle 25. The tail gas is introduced into the interior of the oxidation reactor, and the oxidant aqueous solution directly contacts the tail gas to react. The tail gas after the oxidation reaction is discharged from the top of the oxidation reactor and enters the subsequent tail gas treatment process. The content of o-chlorobenzonitrile, o-chlorobenzaldehyde, and o-chlorobenzoic acid in the tail gas after oxidation in the oxidation reactor is measured to be 0.16%, 0.11%, and 0.21%, respectively.

[0057] (3) Oxidation separation: The slurry at the bottom of the oxidation reactor enters the o-chlorobenzoic acid refining process, and the o-chlorobenzoic acid product is obtained after recrystallization, drying and collection; the tail gas discharged from the oxidation reactor enters the tail gas treatment process. After the slurry before entering the refining process is dried, the o-chlorobenzonitrile content is measured to be 0.07%, the o-chlorobenzaldehyde content is 0.06%, and the o-chlorobenzoic acid content is 92.4%.

[0058] Example 5

[0059] (1) The capture of the reaction gas is the same as in Example 2; the residual gas after the two-stage mixed capture is sent to the tail gas oxidation stage through the outlet of the secondary collector;

[0060] (2) Before the exhaust gas is introduced, a mixture of pentaacetyl glucose (5 kg) and sodium dodecyl sulfate (0.03 kg) is dissolved in 1000 L of water and then sprayed onto the support plate in the mixing tank through a spraying device. Sodium perborate (7.2 kg) is evenly arranged on the support plate. Pentaacetyl glucose reacts with the sodium perborate in the mixing tank to generate active oxygen immediately. The active oxygen aqueous solution enters the lower oxidant header 22 through a pipeline and is sprayed into the lower exhaust gas through the oxidant header nozzle 25. A plurality of aeration pipes 23 are arranged near the lower part of the oxidation reactor. The plurality of aeration pipes are arranged in parallel. The aeration pipes are connected to the lower exhaust header 24. The exhaust header is connected to the exhaust gas discharged from the secondary collector. The exhaust gas enters the aeration pipe through the exhaust header. After passing through the aeration pipe, the exhaust gas is discharged from the aeration pipe wall in the form of small bubbles. The active oxygen aqueous solution begins to contact and react with the exhaust gas in the form of small bubbles. The tail gas after oxidation reaction is discharged from the top of the oxidation reactor and enters the subsequent tail gas treatment process. The tail gas after oxidation in the oxidation reactor is measured to have an o-chlorobenzonitrile content of 0.03%, an o-chlorobenzaldehyde content of 0.02%, and an o-chlorobenzoic acid content of 0.24%.

[0061] (3) Oxidation separation: The slurry at the bottom of the oxidation reactor enters the o-chlorobenzoic acid refining process, and the o-chlorobenzoic acid product is obtained after recrystallization, drying and collection; the tail gas discharged from the oxidation reactor enters the tail gas treatment process. After the slurry before entering the refining process is dried, the o-chlorobenzonitrile content is measured to be 0.02%, the o-chlorobenzaldehyde content is 0.03%, and the o-chlorobenzoic acid content is 98.6%.

[0062] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A method for treating tail gas in a process for preparing o-chlorobenzonitrile, characterized in that: include: (1) Capture of reaction gas: The high-temperature reaction gas from the reactor enters two mixed capture devices in turn. The circulating spray pump of the mixed capture device is turned on. The medium in the reaction gas is captured and absorbed to the bottom of the collector through two mixed capture methods: dry condensation and spray flushing of the collector condensation chamber and the capture absorption chamber partition. It is then sent to the downstream separation circulation tank through the discharge pipe at the bottom of the collector for natural sedimentation. The main body of the capture device is a horizontal cylinder. The interior of the cylinder is divided into a number of capture absorption chambers and condensation chambers in sequence. The capture absorption chambers and condensation chambers are arranged alternately. A number of spray nozzles are installed on the top of the capture absorption chamber. The spray nozzles are connected to the spray main pipe. The circulating spray liquid pumped by the spray circulation pump passes through the spray main pipe and the spray nozzles and enters the cylinder in the form of mist spray liquid. There is a material outlet nipple at the bottom of the cylinder, which is connected to the discharge main pipe. (2) Tail gas oxidation: The tail gas after two-stage mixed capture enters the oxidation reactor through the outlet of the secondary collector for oxidation, wherein the oxidant is the active oxygen oxidant generated in real time; (3) Oxidation separation: The effective ingredients after oxidation are fully contacted with the oxidant aqueous solution and are oxidized to o-chlorobenzoic acid and then precipitated as solid; the slurry at the bottom of the oxidation reactor enters the o-chlorobenzoic acid refining process, and the o-chlorobenzoic acid product is obtained after recrystallization, drying and collection; the exhaust gas discharged from the oxidation reactor enters the exhaust gas treatment process.

2. The tail gas treatment method in the o-chlorobenzonitrile preparation process according to claim 1, characterized in that: The two mixed capture devices are used in conjunction to control the outlet temperature of the first-stage collector at 80~100℃ and the outlet temperature of the second-stage collector at 40~50℃ by adjusting the amount of circulating water entering the condensation chamber.

3. The tail gas treatment method in the o-chlorobenzonitrile preparation process according to claim 1, characterized in that: During capture, control the temperature of the spray circulating fluid at 47~50℃.

4. The tail gas treatment method in the o-chlorobenzonitrile preparation process according to claim 1, characterized in that: The gas coming out of the reactor passes through each capture absorption chamber in turn from one end of the collector and then comes out from the other end. The low-temperature water used for cooling is pumped to the two capture devices through the low-temperature water system and the low-temperature water circulation pump, and enters the condensation chamber of the capture device. After passing through the condensation chamber, it returns to the low-temperature water system for cooling and continues to be circulated. The spray circulation liquid in the separation circulation tank is pumped to the capture device through the spray circulation pump, cools and absorbs the capture absorption chamber, and then returns from the capture device to the separation circulation tank.

5. The tail gas treatment method in the o-chlorobenzonitrile preparation process according to claim 4, characterized in that: The top and bottom of the condensing chamber are respectively provided with a low-temperature water outlet nipple and an inlet nipple.

6. The tail gas treatment method in the o-chlorobenzonitrile preparation process according to claim 1, characterized in that: The raw materials of the oxidant include pentaacetyl glucose and sodium perborate, which are mixed immediately before contacting with the tail gas, and the immediately generated oxidant is dissolved in the aqueous solution.

7. The tail gas treatment method in the o-chlorobenzonitrile preparation process according to claim 5, characterized in that: The pH value of the oxidant aqueous solution is 3~4.

8. The tail gas treatment method in the o-chlorobenzonitrile preparation process according to claim 1, characterized in that: The oxidation reactor is configured as a partitioned structure, wherein the upper portion of the oxidation reactor is used for immediate generation of the oxidant, and the lower portion of the oxidation reactor is used for the oxidant to oxidize the tail gas.

9. The tail gas treatment method in the o-chlorobenzonitrile preparation process according to claim 1, characterized in that: After two-stage mixing and capturing, the purity of o-chlorobenzonitrile in the crude product discharged from the separation circulation tank exceeds 90%.

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