A method for treating wastewater in the production process of o-chlorobenzonitrile by ammonia oxidation process

Abstract

The invention provides a method for treating wastewater in the production process of o-chlorobenzonitrile by an ammonia oxidation process, 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; wastewater settled in the separation circulation tank is passed into an oxidation reactor, an active oxidant is arranged in the oxidation reactor, the oxidant is generated immediately with the passing of the wastewater, and o-chlorobenzaldehyde in the wastewater is oxidized to o-chlorobenzoic acid; the wastewater solution after the reaction in the oxidation reactor enters a sedimentation kettle for sedimentation, the upper clear liquid after sedimentation is circulated into the two mixed capture devices for capture and absorption, and the lower precipitate enters a dryer for drying to obtain an o-chlorobenzoic acid product.

Description

Technical Field

[0001] The invention relates to the field of wastewater treatment in a pharmaceutical intermediate preparation process, and in particular to a wastewater treatment method in a production process of o-chlorobenzonitrile using an ammoxidation 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. 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.

[0003]

[0004] For example, the patent with publication number CN113563226A discloses a method for producing o-chlorobenzonitrile with high yield, and under the catalytic condition of a nickel-containing catalyst, the temperature in the ebullating bed reactor is as high as 320°C for reaction to prepare o-chlorobenzonitrile. Although the prior art reduces the residual amount of o-chlorotoluene in the o-chlorobenzonitrile crude product, a certain degree of side reaction occurs during the reaction process, causing o-chlorotoluene to be partially oxidized to o-chlorobenzaldehyde, o-chlorobenzoic acid and o-chlorobenzamide, etc., and the o-chlorobenzonitrile crude product reaction gas containing the above impurities is partially treated with the tail gas for subsequent tail gas treatment, resulting in material waste, and part of it is captured and then converted into a liquid phase, and then separated by sedimentation to form an oil phase and an aqueous phase, and most of the components are located in the oil phase for the next step of refining and separation, but it also causes more organic components in the aqueous phase, and the aqueous phase needs to be treated to reduce the wastewater treatment pressure. However, for o-chlorobenzaldehyde and o-chlorobenzonitrile in the water phase, the melting points of the two are relatively low, and they are easy to precipitate from the water phase during water treatment to block the water treatment system. In addition, the melting points of the two are close, so it is difficult to separate and recover the two from the wastewater. If they are directly discharged with the wastewater, it is easy to pollute the environment and cause material waste. Summary of the invention

[0005] In view of this, the present invention aims to propose a wastewater treatment method in the production process of o-chlorobenzonitrile by an ammoxidation process, so as to solve the problem in the prior art that when o-chlorobenzonitrile is produced by an ammoxidation process, a large amount of o-chlorobenzaldehyde and o-chlorobenzonitrile are contained in the circulating spray liquid, which is difficult to separate and recover the two from the wastewater, resulting in material waste.

[0006] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] A method for treating wastewater in the production process of o-chlorobenzonitrile by an ammonia oxidation process, comprising:

[0008] (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.

[0009] (2) Oxidation treatment of the aqueous phase: the wastewater after settling in the separation circulation tank is passed into an oxidation reactor, in which an active oxidant is provided. The oxidant is generated immediately as the wastewater is passed into the reactor, and the o-chlorobenzaldehyde in the wastewater is oxidized into o-chlorobenzoic acid;

[0010] (3) Sedimentation and separation: After the reaction in the oxidation reactor, the wastewater solution enters the sedimentation kettle for sedimentation. After sedimentation, the upper clear liquid is circulated into two mixed capture devices for capture and absorption. The lower precipitate enters the dryer for drying to obtain the finished product of o-chlorobenzoic acid.

[0011] 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.

[0012] Furthermore, the temperature of the spray circulating liquid is controlled at 47-50°C during capture.

[0013] Furthermore, the raw materials of the oxidant include tetraacetylethylenediamine and sodium percarbonate, which are mixed immediately before contacting with the tail gas, and the immediately generated oxidant is dissolved in the aqueous solution.

[0014] Furthermore, the pH value of the oxidant aqueous solution is 3-4.

[0015] 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.

[0016] Furthermore, the main body of the capture device is a horizontal cylinder, and the interior of the cylinder is divided into a plurality of capture absorption chambers and condensation chambers which are adjacent to each other in sequence, and the capture absorption chambers and the condensation chambers are arranged alternately.

[0017] Furthermore, a plurality of spray nozzles connected to the spray main pipe are installed on the top of the capture absorption chamber, a material outlet short section is provided at the bottom to connect to the discharge main pipe, and a low-temperature water outlet short section and an inlet short section are provided at the top and bottom of the condensation chamber respectively.

[0018] Furthermore, the oxidation reactor is configured as a double-layer reactor structure.

[0019] Furthermore, a settling kettle is added between the separation circulation tank and the mixed capture device, and the spray circulation liquid in the separation circulation tank enters the capture device after settling.

[0020] Compared with the prior art, the wastewater treatment method in the production process of o-chlorobenzonitrile by ammonia oxidation process of the present invention has the following advantages:

[0021] The use of two collectors in combination for mixed absorption eliminates the fatal defect of dry absorption - ammonium chloride salt deposition. The condensed ammonium chloride salt is 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 fewer equipment, but also relatively less water consumption, which can effectively control the amount of wastewater. 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 temperature drops quickly and the capture effect is greatly improved.

[0022] After the wastewater is treated by active oxygen oxidation, o-chlorobenzaldehyde in the wastewater 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 wastewater into o-chlorobenzoic acid. O-chlorobenzoic acid has a high melting point and can be subsequently recycled through simple solid-liquid separation to obtain o-chlorobenzoic acid with higher purity, thereby improving material utilization, reducing the contents of o-chlorobenzonitrile and o-chlorobenzaldehyde in the wastewater, reducing the pressure of subsequent wastewater treatment, and meeting environmental protection requirements.

[0023] 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

[0024] Figure 1 This is a schematic diagram of the structure of the mixed capture device of the present invention;

[0025] Figure 2 This is a schematic diagram of the combined use of two mixed capture devices according to the present invention;

[0026] Figure 3 It is a schematic diagram of the structure of the oxidation reactor of the present invention;

[0027] Figure 4 This is a flow chart of the wastewater treatment method of the present invention;

[0028] Figure 5 Schematic diagram of the change in active oxygen concentration after the reaction of tetraacetylethylenediamine and sodium percarbonate under different conditions.

[0029] Description of reference numerals:

[0030] 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, 30- sedimentation kettle DETAILED DESCRIPTION

[0031] 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.

[0032] A method for treating wastewater in the production process of o-chlorobenzonitrile by an ammonia oxidation process, comprising:

[0033] (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.

[0034] 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, 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.

[0035] like Figure 2The 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.

[0036] The gas from the reactor passes through each capture absorption chamber 2 in sequence 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 condensed from the gas is adsorbed on the capture absorption chamber partition; because the top of each capture absorption chamber of the collector is designed with a plurality 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 media such as o-chlorobenzonitrile, o-chlorotoluene, o-chlorobenzamide, o-chlorobenzaldehyde, o-chlorobenzoic acid and ammonium chloride in the gas, while flushing the media on the capture absorption chamber plate to the bottom of the chamber, and sending it to the auxiliary device separation circulation tank through the bottom discharge port for oil-water separation.

[0037] 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. In order to prevent condensation in the feed pipe, the spray circulation liquid is always kept at 47-50°C, thereby achieving a stable and continuous mixed capture method. The oil phase is discharged and the water phase is added regularly (the water phase is added when the ammonium chloride in the water phase is close to the saturation concentration). 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. Under the condition of 47-50°C, when the water phase is recycled, the o-chlorobenzaldehyde and o-chlorobenzonitrile therein may precipitate and block the spray device during the circulation process, so it is necessary to treat the wastewater after spray capture and recycle it.

[0038] (2) Oxidation treatment of the aqueous phase: The wastewater after settling in the separation circulation tank 16 is introduced into an oxidation reactor. An oxidant is provided in the oxidation reactor. The oxidant is generated immediately as the wastewater is introduced, and the o-chlorobenzaldehyde in the wastewater is oxidized into o-chlorobenzoic acid.

[0039] like Figure 3As shown, the oxidation reactor 20 can be configured as a double-layer reactor structure, including an inner reactor 21 and an outer reactor 22, wherein the inner reactor 21 is located inside the outer reactor 22, and the two are coaxially arranged.

[0040] The built-in reactor 21 contains sodium percarbonate, and a liquid hole 211 is provided on the wall of the built-in reactor. The aqueous solution of tetraacetylethylenediamine is introduced into the built-in reactor through a liquid inlet pipe 23, and is evenly sprayed onto a support plate 25 inside the built-in reactor through an internal spray structure 24. The support plate 25 is configured as a porous structure, and sodium percarbonate is placed in the support plate 25. The bottom surface of the support plate 25 is configured as a hollow structure. The aqueous solution of tetraacetylethylenediamine reacts with the sodium percarbonate inside the built-in reactor to instantly generate active oxygen, and pressure is applied to the inside of the built-in reactor to cause the sodium percarbonate to form a porous structure. The active oxygen aqueous solution can be discharged from the built-in reactor to the outer reactor 22 through the liquid hole 211 of the built-in reactor. The inner part of the outer reactor 22 near the top is connected to the wastewater pipeline 26. The other end of the wastewater pipeline 26 is connected to the separation circulation tank 16. The wastewater entering the outer reactor 2 through the wastewater pipeline 26 is fully mixed with the active oxygen oxidant and undergoes a preliminary oxidation reaction, oxidizing o-chlorobenzaldehyde to o-chlorobenzoic acid. The o-chlorobenzaldehyde and active oxygen ions that have not undergone oxidation reaction are present in the wastewater and enter the acidification kettle together with the wastewater. The double-layer reactor structure separates tetraacetylethylenediamine from sodium percarbonate, and when necessary, the two are brought into contact to immediately generate peracetic acid, which ionizes active oxygen ions. Compared with hydrogen peroxide, the active oxygen oxidant has stronger oxidation performance, which is beneficial to the oxidation of o-chlorobenzaldehyde, and the immediately generated oxidant can prevent the oxidant from being ineffective due to long-term exposure.

[0041] The mass ratio of tetraacetylethylenediamine to sodium percarbonate is 1:1.2-1.5.

[0042] In the oxidation reaction step, hydrochloric acid is added to the aqueous solution of tetraacetylethylenediamine, and the pH value of the aqueous solution of the oxidation reaction system is controlled to be about 4, under which the generation rate of active oxygen is relatively fast. When the wastewater is subjected to oxidation treatment, the active oxygen generated in real time is used as an oxidant, and the oxidation ability is strong, and the low-melting-point o-chlorobenzaldehyde in the wastewater can be effectively oxidized to the high-melting-point o-chlorobenzoic acid and quickly precipitated, and a small amount of o-chlorobenzonitrile is hydrolyzed according to the following equation under the action of an acidic aqueous solution to generate o-chlorobenzoic acid, and the o-chlorobenzoic acid is separated by sedimentation, the content of organic components in the aqueous phase is reduced, and the wastewater treatment pressure is reduced, which is beneficial to environmental protection.

[0043] Cl-Ph-CN+H2O+H + →Cl-Ph-COOH+NH4 +

[0044] An external spray structure 221 is provided inside the outer reactor 22, and the external spray structure 221 is connected to the wastewater pipeline 26. A spray arm is provided on the external spray structure 221, and the spray arm is provided outside the built-in reactor 21, and the spray arm is parallel to the wall surface of the built-in reactor 21. A plurality of spray arms can be provided, and are evenly distributed around the outside of the built-in reactor 21. A plurality of atomizing nozzles 222 are provided on the spray arm, and the wastewater is sprayed into the outer reactor 22 in the form of small droplets through the atomizing nozzles 222.

[0045] A stirring impeller 223 is provided at the bottom of the outer reactor 22. The stirring impeller 223 drives the active oxygen oxidant in the outer reactor 22 to fully contact with o-chlorobenzaldehyde, thereby increasing the contact frequency between the two and further improving the oxidation reaction efficiency.

[0046] Furthermore, before the aqueous solution of tetraacetylethylenediamine enters the built-in reactor, sodium percarbonate is mixed with a composite stabilizer, and the mass ratio of the composite stabilizer to sodium percarbonate is 0.3% to 0.6%:1. The composite stabilizer can prolong the stable existence time of active oxygen, thereby improving the efficiency of the oxidation reaction. The reason may be that the composite stabilizer is firmly chelated with the metal ions, avoiding the decomposition of peracetic acid catalyzed by the metal ions, and the long chain structure in the composite stabilizer occupies the spatial position around the small molecule active oxygen ions, thereby hindering the contact and reaction of other molecules or ions with the active oxygen ions to a certain extent, thereby reducing the decomposition rate of the active oxygen ions. At the same time, since heating promotes molecular motion, the probability of o-chlorobenzaldehyde contacting with active oxygen ions is increased, and the oxidation reaction gradually begins to occur.

[0047] The composite stabilizer includes trisodium methylglycine diacetate and sodium dodecyl sulfate, and the mass ratio of trisodium methylglycine diacetate to sodium dodecyl sulfate is 1:1.6.

[0048] (3) Sedimentation and separation: After the reaction in the oxidation reactor, the wastewater solution enters the sedimentation kettle for sedimentation. After sedimentation, the upper clear liquid is circulated into two mixed capture devices for capture and absorption. The lower precipitate enters the dryer for drying to obtain the finished product of o-chlorobenzoic acid.

[0049] Furthermore, in the oxidation treatment step of the aqueous phase, in order to determine the oxidation reaction time after adding the composite stabilizer, the present application explored the change in the oxidant concentration after adding the composite stabilizer at different times, specifically as follows: Figure 5As shown in the figure, at 50°C, no composite stabilizer was added to 1L solution, and only 3.58g of tetraacetylethylenediamine and 5g of sodium percarbonate were added and mixed directly (black curve); 3.58g of tetraacetylethylenediamine, 5g of sodium percarbonate and 0.016g of sodium dodecylsulfonate were added to 1L solution and mixed directly (blue curve); 3.58g of tetraacetylethylenediamine, 5g of sodium percarbonate and 0.01g of trisodium methylglycine diacetate were added to 1L solution and mixed directly (blue curve). 1L solution was added with 3.58g of tetraacetylethylenediamine, 5g of sodium percarbonate, 0.01g of trisodium methylglycine diacetate and 0.016g of sodium dodecylsulfonate to mix directly (purple curve); and 0.016g of sodium dodecylsulfonate, 0.01g of trisodium methylglycine diacetate and 3.58g of tetraacetylethylenediamine were dissolved and dispersed in 1L of water, and then slowly added to 5g of sodium percarbonate in the form of a mixed solution (red curve). It can be seen from the above experimental results that when tetraacetylethylenediamine and sodium percarbonate are directly mixed, the two can react quickly to generate a large amount of active oxygen in a short time, and the active oxygen concentration quickly reaches the peak value, but due to the early contact time and the instability of active oxygen, the active oxygen concentration drops sharply about 15min after the two are mixed, and the active oxygen is stable for a short time, which affects its oxidation performance. When tetraacetylethylenediamine is directly mixed with sodium percarbonate and sodium dodecyl sulfate, the reaction time of the two is slightly delayed due to the effect of sodium dodecyl sulfate, and the active oxygen concentration reaches a peak at about 20 minutes. Although the active oxygen can be stably present for a longer time than without sodium dodecyl sulfate, the active oxygen will still decompose rapidly in a short time and cannot play an effective oxidation role. When tetraacetylethylenediamine is directly mixed with sodium percarbonate and trisodium methylglycine diacetate, the reaction time of tetraacetylethylenediamine and sodium percarbonate is also slightly delayed, and the active oxygen concentration remains at a high stable state within 20 minutes to 35 minutes, but the active oxygen will still decompose rapidly afterwards and cannot play an effective oxidation role. When tetraacetylethylenediamine is directly mixed with sodium percarbonate, trisodium methylglycine diacetate and sodium dodecyl sulfate, the rate of generating active oxygen slows down, but it can reach a concentration close to 1600 mg / L. However, due to the large number of active oxygen molecules and the interaction between them, the time for active oxygen to maintain a high concentration is short. When sodium dodecylsulfonate, trisodium methylglycine diacetate and tetraacetylethylenediamine solution are slowly added to sodium percarbonate within 30 minutes, active oxygen is gradually and slowly generated, and can reach a concentration close to 1650 mg / L, and can be maintained in a relatively high concentration range for nearly 40 minutes. Therefore, the timing starts from the addition of tetraacetylethylenediamine, and the wastewater is introduced about 30 minutes after the tetraacetylethylenediamine is mixed with sodium percarbonate and the composite stabilizer, so that the wastewater to be oxidized can quickly contact with the high concentration of active oxygen during the introduction process to undergo a sufficient oxidation reaction, thereby improving the oxidation efficiency.

[0050] Example 1

[0051] During the production of o-chlorobenzonitrile, firstly, pure water or mother liquor for circulating spray is added to the separation circulation tank in advance, and the circulating spray pump and low-temperature water circulation pump are turned on. The high-temperature reaction gas of about 360°C from the reactor enters the collector, and the circulating liquid in the separation circulation tank is transported to the top of the capture absorption chamber of the mixing cylinder collector for spraying. At the same time, the cooling water is transported to each condensation chamber of the mixing cylinder collector through the circulating water pump, and the amount of circulating water entering the condensation chamber is adjusted to control the collector outlet temperature to 80-100°C. At this time, the pressure is 1.0MPa and 200Nm 3 / h intake rate of high temperature reaction gas from the reactor, and continue to introduce it for 6 hours, always keep the spray circulation liquid at 47-50℃, and regularly discharge the oil phase in the separation circulation tank. The tail gas after mixing and capture is sent to the subsequent tail gas absorption tower through the outlet of the collector for further treatment.

[0052] Sedimentation separation: The circulating water solution after the separation circulation tank enters the sedimentation kettle for sedimentation. The upper clear liquid after sedimentation circulates into two mixed capture devices for capture and absorption. It was observed that there was almost no precipitation in the sedimentation kettle at this time.

[0053] After the high temperature reaction gas was introduced for 6 hours, the content of o-chlorobenzonitrile in the water phase discharged from the settling kettle was determined to be 0.94%, the content of o-chlorobenzaldehyde was 0.76%, and the content of o-chlorobenzoic acid was 0.32%. At the same time, the purity of o-chlorobenzonitrile in the crude product discharged from the separation circulation tank was determined to be 89.7%. It was observed that almost no precipitation appeared in the settling kettle at this time.

[0054] Example 2

[0055] During the production of o-chlorobenzonitrile, firstly, pure water or mother liquor for circulating spray is added to the separation circulation tank in advance, and the circulating spray pump and low-temperature water circulating pump are turned on. The high-temperature reaction gas of about 360°C coming out of the reactor enters the primary collector and the secondary collector in turn. The circulating liquid in the separation circulation tank is Figure 2 The process shown in the figure is transported to the top of the capture absorption chamber of the two mixed cylindrical collectors for spraying. At the same time, the cooling water is transported to each condensation chamber of the mixed cylindrical collector through the circulating water pump, and the outlet temperature of the first-stage collector is controlled at 80-100℃ and the outlet temperature of the second-stage collector is controlled at 40-50℃ by adjusting the circulating water volume entering the condensation chamber. At this time, the pressure is 1.0MPa and 200Nm 3 / h intake rate of high temperature reaction gas from the reactor, and continue to introduce it for 6 hours, always keep the spray circulation liquid at 47-50℃, and regularly discharge the oil phase in the separation circulation tank. The tail gas after mixing and capture is sent to the subsequent tail gas absorption tower through the outlet of the collector for further treatment.

[0056] Sedimentation separation is the same as in Example 1.

[0057] After the high temperature reaction gas was introduced for 6 hours, the content of o-chlorobenzonitrile in the water phase discharged from the settling kettle was determined to be 1.12%, the content of o-chlorobenzaldehyde was 0.93%, and the content of o-chlorobenzoic acid was 0.31%. At the same time, the purity of o-chlorobenzonitrile in the crude product discharged from the separation circulation tank was determined to be 90.6%. It was observed that almost no precipitation appeared in the settling kettle at this time.

[0058] Example 3

[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) Oxidation treatment of aqueous phase: The wastewater after settling in the separation circulation tank is introduced into the oxidation reactor, tetraacetylethylenediamine (7.16 kg) and sodium percarbonate (10 kg) are added into the oxidation reactor, and the pH value in the oxidation reactor is controlled to be about 4. The oxidation reactor is a common oxidation reactor, which is a single-layer reactor. An external spray structure is arranged inside the outer reactor, and the external spray structure is connected to the wastewater pipeline. A spray arm is arranged on the external spray structure, and a plurality of spray arms are arranged. A plurality of atomizing nozzles are arranged on the spray arm. The wastewater after settling in the separation circulation tank is introduced into the oxidation reactor, and the wastewater is sprayed into the outer reactor in the form of small droplets through the atomizing nozzle. The temperature of the oxidation reactor is controlled to be 40-50°C.

[0061] (3) Sedimentation and separation: After the reaction in the oxidation reactor, the wastewater solution including the bottom slurry enters the sedimentation kettle for sedimentation. The upper clear liquid after sedimentation is circulated into two mixed capture devices for capture and absorption. The lower precipitate enters the dryer for drying to obtain the finished product of o-chlorobenzoic acid.

[0062] The time was measured from the time when the wastewater was introduced. After the high-temperature reaction gas was introduced for 6 hours, the content of o-chlorobenzonitrile in the water phase discharged by sedimentation separation was 0.53%, the content of o-chlorobenzaldehyde was 0.37%, and the content of o-chlorobenzoic acid was 0.31%. At the same time, the purity of o-chlorobenzonitrile in the crude product discharged from the separation circulation tank was 91.3%, and a small amount of precipitate appeared in the sedimentation kettle. After drying, the purity of o-chlorobenzoic acid in the precipitate was 98.2%.

[0063] Example 4

[0064] (1) The capture of the reaction gas is the same as in Example 2 and Example 3; the residual gas after two-stage mixed capture is sent to the tail gas oxidation stage through the outlet of the secondary collector;

[0065] (2) Oxidation treatment of the aqueous phase: The double-layer reactor structure of the present invention is adopted, 10 kg of sodium percarbonate is fed into the built-in reactor, and the wastewater is divided into two parts. About 30% of the wastewater is controlled by a flow control valve to be mixed and dispersed with 7.16 kg of tetraacetylethylenediamine and then introduced into the built-in reactor, and the remaining wastewater enters the outer reactor through an external spray structure, and the temperature of the oxidation reactor is controlled to be 40-50°C.

[0066] (3) Sedimentation and separation: After the reaction in the oxidation reactor, the wastewater solution enters the sedimentation kettle for sedimentation. After sedimentation, the upper clear liquid is circulated into two mixed capture devices for capture and absorption. The lower precipitate enters the dryer for drying to obtain the finished product of o-chlorobenzoic acid.

[0067] The timing was started from the time when the wastewater was introduced. After the high-temperature reaction gas was introduced for 6 hours, the content of o-chlorobenzonitrile in the water phase discharged by sedimentation separation was 0.26%, the content of o-chlorobenzaldehyde was 0.19%, and the content of o-chlorobenzoic acid was 0.30%. At the same time, the purity of o-chlorobenzonitrile in the crude product discharged from the separation circulation tank was 95.3%, and a small amount of precipitate appeared in the sedimentation kettle. After drying, the purity of o-chlorobenzoic acid in the precipitate was 99.6%.

[0068] Example 5

[0069] (1) The capture of the reaction gas is the same as in Examples 2 to 4; the residual gas after two-stage mixed capture is sent to the tail gas oxidation stage through the outlet of the secondary collector;

[0070] (2) Oxidation treatment of the aqueous phase: Using the double-layer reactor structure of the present invention, 10 kg of sodium percarbonate was added to the built-in reactor, and the wastewater was divided into two parts. About 30% of the wastewater was controlled by a flow control valve to be mixed and dispersed with 7.16 kg of tetraacetylethylenediamine, 0.01 g of trisodium methylglycine diacetate, and 0.016 g of sodium dodecyl sulfate and then introduced into the built-in reactor. At the same time, the remaining wastewater entered the outer reactor through the external spray structure, and the temperature of the oxidation reactor was controlled to be 40-50°C.

[0071] (3) Sedimentation separation is the same as in Example 4.

[0072] The timing was started from the time when the wastewater was introduced. After the high-temperature reaction gas was introduced for 6 hours, the content of o-chlorobenzonitrile in the water phase discharged by sedimentation separation was 0.09%, the content of o-chlorobenzaldehyde was 0.12%, and the content of o-chlorobenzoic acid was 0.28%. At the same time, the purity of o-chlorobenzonitrile in the crude product discharged from the separation circulation tank was 95.8%, and a small amount of precipitate appeared in the sedimentation kettle. After drying, the purity of o-chlorobenzoic acid in the precipitate was determined to be 99.58%.

[0073] Example 6

[0074] (1) The capture of the reaction gas is the same as in Examples 2 to 4; the residual gas after two-stage mixed capture is sent to the tail gas oxidation stage through the outlet of the secondary collector;

[0075] (2) Oxidation treatment of the aqueous phase: The double-layer reactor structure of the present invention is adopted, 10 kg of sodium percarbonate is fed into the built-in reactor, and the wastewater is divided into two parts. About 30% of the wastewater is controlled by a flow control valve to be mixed and dispersed with 7.16 kg of tetraacetylethylenediamine, 0.01 g of trisodium methylglycine diacetate, and 0.016 g of sodium dodecyl sulfate and then introduced into the built-in reactor. After the mixed solution of tetraacetylethylenediamine is introduced into the built-in reactor for 30 minutes, the remaining wastewater enters the outer reactor through the external spray structure, and the temperature of the oxidation reactor is controlled to be 40-50°C.

[0076] (3) Sedimentation separation is the same as in Example 4.

[0077] The timing was started from the time when the wastewater was introduced. After the high-temperature reaction gas was introduced for 6 hours, the content of o-chlorobenzonitrile in the water phase discharged by sedimentation separation was 0.05%, the content of o-chlorobenzaldehyde was 0.03%, and the content of o-chlorobenzoic acid was 0.26%. At the same time, the purity of o-chlorobenzonitrile in the crude product discharged from the separation circulation tank was 96.4%, and a small amount of precipitate appeared in the sedimentation kettle. After drying, the purity of o-chlorobenzoic acid in the precipitate was 99.66%.

[0078] 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 wastewater in the production process of o-chlorobenzonitrile by an ammoxidation process, 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 medium in the reaction gas is captured and absorbed to the bottom of the collector through two mixed capture methods: dry condensation in the collector condensation chamber and spray flushing in the capture absorption chamber. It is then sent to the downstream separation circulation tank through the discharge pipe at the bottom of the collector for natural sedimentation. The spray circulation liquid in the separation circulation tank is pumped into the capture device through the spray circulation pump to cool and absorb the capture absorption chamber. 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. The capture absorption chambers and condensation chambers are arranged in a staggered manner. A number of spray nozzles are installed on the top of the capture absorption chamber to connect to the spray main pipe, and a material outlet short section is installed at the bottom to connect to the discharge main pipe. The top and bottom of the condensation chamber are provided with a low-temperature water outlet short section and an inlet short section respectively. (2) Oxidation treatment of the aqueous phase: the wastewater after settling in the separation circulation tank is passed into an oxidation reactor. An active oxidant is provided in the oxidation reactor. The oxidant is generated immediately as the wastewater is passed into the reactor, and the o-chlorobenzaldehyde in the wastewater is oxidized into o-chlorobenzoic acid. (3) Sedimentation and separation: The wastewater solution after the reaction in the oxidation reactor enters the sedimentation kettle for sedimentation. The upper clear liquid after sedimentation is circulated into two mixed capture devices for capture and absorption. The lower precipitate enters the dryer for drying to obtain the finished product of o-chlorobenzoic acid.

2. The wastewater treatment method 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 wastewater treatment method according to claim 1, characterized in that: During capture, the temperature of the spray circulating liquid is controlled at 47~50℃.

4. The wastewater treatment method according to claim 1, characterized in that: The raw materials of the oxidant include tetraacetylethylenediamine and sodium percarbonate, which are mixed immediately before contacting with the wastewater, and the immediately generated oxidant is dissolved in the aqueous solution.

5. The wastewater treatment method according to claim 1, characterized in that: The pH value of the oxidant aqueous solution is 3~4.

6. The wastewater treatment method 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.

7. The wastewater treatment method according to claim 1, characterized in that: The oxidation reactor is configured as a double-layer reactor structure.

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