Device for preparing 2, 6-dichloropyridine from 2-chloropyridine

Abstract

The utility model provides a device for preparing 2, 6-dichloropyridine from 2-chloropyridine, which comprises a circulating tank, a circulating pump, a feeding heat exchanger, a reactor and an equal-diameter variable tee joint, and the circulating tank, the circulating pump, the reactor and the equal-diameter variable tee joint are communicated end to end through pipelines. During operation, 2-chloropyridine enters the circulating tank from the feed port and then circulates in the system through the circulating pump, chlorine enters the system from the reactor, chlorine free radicals are generated under excitation of the ultraviolet lamp, and the chlorine free radicals react with 2-chloropyridine to generate 2, 6-dichloropyridine. According to the utility model, the problems of poor safety, high reaction control difficulty, impurity reaction by-products, unsatisfactory orientation effect and the like in the prior art are solved, the safety risk in the production process can be effectively reduced, the control difficulty is reduced, the effective reaction is improved, the material impurities are reduced, and more environment-friendly, economic and scientific effects are realized.

Description

Technical Field

[0001] The utility model relates to the technical field of pyridine chloride synthesis, in particular to a device for preparing 2,6-dichloropyridine from 2-chloropyridine. Background Art

[0002] 2,6-Dichloropyridine is an important fine chemical intermediate. Due to its unique heterocyclic structure, it has many unique chemical properties, such as high efficiency, broad spectrum, and low residue. It is often used in the synthesis of drugs, as well as the preparation of pesticides and antimicrobial compounds. With the continuous development of modern agriculture, highly toxic, difficult to degrade, and non-green pesticides are gradually being eliminated. As a promising emerging representative of pyridine chloride, the demand for 2,6-dichloropyridine has been increasing day by day.

[0003] At present, the most commonly used method for preparing 2,6-dichloropyridine in China is the direct chlorination of 2-chloropyridine. Chlorine forms chlorine free radicals under the initiation of ultraviolet light or heat, destroys the weakest bond position 6 of the benzene ring of 2-chloropyridine at a certain temperature, replaces the hydrogen atoms thereon, and completes the chlorination reaction to generate 2,6-dichloropyridine. The forward reaction can be controlled by controlling the chlorination depth. This method has a simple process flow and easy-to-obtain process raw materials, but the controllability is poor. The equipment generally uses kettle or tower equipment as an industrial production method. For example, a method and device for preparing 2,6-dichloropyridine by step-by-step photochlorination of pyridine disclosed in CN112174878A uses a gas phase photoreaction tower as a synthesis device. According to the method and equipment described therein, we can know that the reaction of chlorine and 2-chloropyridine is mainly concentrated in the liquid phase photoreaction kettle, but in the actual production process, this device has the following problems:

[0004] (1) The liquid feed port is located at the top of the reactor. The falling flow of the liquid and the heat release of the reaction will affect the stability of the UV lamp cover, posing a safety risk.

[0005] (2) The device cannot obtain effective feedback on the reaction progress and cannot regulate the production process, making overall process control difficult.

[0006] (3) There is a risk of gas phase escaping in the liquid phase reactor, and the feed ratio of chlorine and 2-chloropyridine is difficult to control, which may lead to problems such as impure reaction by-products and unsatisfactory directional effects, which is not conducive to the realization of industrial production. Utility Model Content

[0007] In view of the deficiencies in the prior art, the utility model provides a device for preparing 2,6-dichloropyridine using 2-chloropyridine as a raw material, which can effectively reduce the safety risks in the production process, reduce the control difficulty, improve the effective reaction, reduce material impurities, and improve the utilization rate of chlorine, so as to be more environmentally friendly, economical and scientific, and solve the problems of poor safety, great difficulty in reaction control, mixed reaction by-products, and unsatisfactory directional effect in the prior art.

[0008] According to an embodiment of the utility model, a device for preparing 2,6-dichloropyridine from 2-chloropyridine comprises a circulation tank, a feed heat exchanger, a reactor, and a tail gas heat exchanger, wherein the circulation tank, the feed heat exchanger, and the reactor are connected end to end through pipelines in sequence to form a reaction device, a photochlorination device is installed in the reactor, the reaction device is provided with a circulation pump, an equal-diameter variable tee is connected between the reactor and the circulation tank, the central main pipeline diameter of the equal-diameter variable tee is larger than the connecting end diameter, and the first connecting end, the second connecting end, and the third connecting end are respectively connected to the tail gas heat exchanger, the reactor, and the circulation tank, and the reactor is also provided with an air intake device.

[0009] Furthermore, the circulation pump is arranged between the circulation tank and the feed heat exchanger through a pipeline to make the materials in the reaction device circulate.

[0010] Furthermore, the feed heat exchanger is connected to the bottom feed port of the reactor, and the material enters the reactor from the bottom, ensuring that the material flows from bottom to top.

[0011] Furthermore, the air inlet device is provided with an air inlet hole near the bottom, and the air inlet hole is connected to a chlorine pipeline equipped with a one-way valve. A nitrogen pipeline equipped with a one-way valve is also branched from the chlorine pipeline, and the nitrogen pipeline and the chlorine pipeline share an air inlet.

[0012] Furthermore, the reactor inlet pipe and outlet pipe are both provided with temperature measuring points, and the structure can adopt thermocouple type or thermistor type.

[0013] Furthermore, the photochlorination device comprises an ultraviolet lamp vertically arranged in the reactor, the ultraviolet lamp is constructed as a cylindrical lamp body and a lampshade wrapping the lamp body, a compressed air pipeline is arranged in the lampshade, and the compressed air pipeline extends to the bottom of the lampshade.

[0014] Furthermore, a sight glass is provided on the return pipe from the third connecting end of the equal-diameter variable tee to the circulation tank.

[0015] Furthermore, a sampling port is provided on the inlet pipe of the feed heat exchanger.

[0016] Furthermore, the circulation tank includes a heating device, which exchanges heat with the material through the heat transfer oil, and the structure can adopt a jacket type or a coil type.

[0017] Furthermore, the outlet of the exhaust gas heat exchanger is also provided with an exhaust gas treatment device, which includes a primary alkali liquid absorption tower and a secondary alkali liquid absorption tower. The exhaust gas heat exchanger, the primary alkali liquid absorption tower and the secondary alkali liquid absorption tower are connected in sequence through pipelines.

[0018] The technical principle of the utility model is as follows: compared with the traditional kettle reaction, the utility model adopts a more scientific external circulation reaction mode. After 2-chloropyridine enters the circulation tank through the feed port, the feed port is closed, and then 2-chloropyridine passes through the feed heat exchanger under the action of the circulation pump and enters from the bottom of the reactor to fully react with the chlorine gas excited by ultraviolet light to form chlorine free radicals. Because the activation energy of the 6-position free radical reaction path in the benzene ring of 2-chloropyridine is much lower than that at other positions, under the condition of absorbing the same amount of heat, the chlorine free radical is more likely to replace the 6-position hydrogen atom, thereby generating 2,6-dichloropyridine. The material is pumped through the circulation pump in The system circulates according to circulation tank → feed heat exchanger → reactor → circulation tank. The materials of gas and liquid components are constantly in contact, stirred and mixed, and the reaction conversion rate is continuously improved. Then, the temperature measuring points of the reactor inlet and outlet pipes are monitored and regulated by the feed heat exchanger to control the temperature in the reactor to the optimal operating index. The color and state of the materials are observed through the sight glass to judge the reaction progress and promote the positive advancement of effective reactions. Finally, samples are taken through the sampling port to determine whether the specific gravity and content have reached the reaction endpoint. After achieving the expected effect, the materials are discharged at one time through the discharge port, thereby reducing the difficulty of process control and the occurrence of side reactions in the reaction.

[0019] Compared with the prior art, the utility model has the following beneficial effects:

[0020] (1) The material enters from the bottom of the reactor and can flow upward steadily, avoiding the vibration and sputtering problems caused by the influence of gravity on the liquid components in the traditional method, reducing the intensity of the reaction, reducing the impact of feed jitter on the stability of the UV lamp cover, eliminating safety hazards, and reducing safety risks.

[0021] (2) Utilize the circulation effect of the circulation pump to increase the contact area and time of the reaction gas and liquid components, so that the overall reaction is in a stable state, reduce the occurrence of side reactions, and increase the product yield.

[0022] (3) Based on the monitoring of the sight glass and the temperature measuring point, the temperature is adjusted by using the circulation tank and the feed heat exchanger to timely control the heat in the reaction process, thereby improving the overall conversion rate, reducing the difficulty of overall process control, and solving the problem of unsatisfactory directional effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of the utility model.

[0024] Figure 2It is a schematic diagram of the structure of the variant tee.

[0025] In the above drawings: 1. circulation tank; 101. feed port; 102. temperature measuring point; 103. sight glass; 104. sight glass; 105. discharge port; 2. circulation pump; 201. sampling port; 3. feed heat exchanger; 301. temperature measuring point; 4. reactor; 401. ultraviolet lamp; 402. nitrogen pipeline; 403. chlorine pipeline; 404. compressed air pipeline; 405. temperature measuring point; 5. variable tee; 6. tail gas heat exchanger; 7. primary alkali solution absorption tower; 8. secondary alkali solution absorption tower; 501. first connection end; 502. second connection end; 503. third connection end. DETAILED DESCRIPTION

[0026] The technical solution of the present utility model is further described below in conjunction with the accompanying drawings and embodiments.

[0027] like Figure 1 As shown, an embodiment of the utility model proposes a device for preparing 2,6-dichloropyridine from 2-chloropyridine, comprising a circulation tank 1, a feed heat exchanger 3, a reactor 4, and an equal-diameter variable tee 5, wherein the circulation tank 1, the feed heat exchanger 3, the reactor 4, and the equal-diameter variable tee 5 are connected end to end in sequence by pipelines.

[0028] The top of the circulation tank 1 is provided with a 2-chloropyridine feed port 102 and a sight glass 103 for observing the state of the material. The circulation tank 1 is also provided with a heating device, the structure of which can be a jacket type or a coil type, through which the heated heat transfer oil exchanges heat with the material to provide the heat required for the reaction.

[0029] Preferably, the circulation pump 2 is arranged near the heat source, that is, installed between the circulation tank 1 and the feed heat exchanger 3, which is convenient for installing the induction probe and using the regulator. The specifications can be selected with a rated power of 3kw, a flow rate of 20t / h, and a head of 20m to increase the fluidity of the material and improve the reaction rate. A discharge port 105 is also provided between the connecting pipe between the circulation tank 1 and the circulation pump 2, and a sampling port 102 is provided on the connecting pipe between the circulation pump 2 and the feed heat exchanger 3, which is convenient for sampling to monitor the specific gravity and content of the material, and manage and regulate.

[0030] The feed heat exchanger 3 is connected to the bottom feed port of the reactor 4, so that the material enters the reactor from the bottom, ensuring that the material flows from bottom to top, avoiding the vibration and sputtering problems caused by the influence of gravity on the liquid phase components in the traditional way, and can positively promote the occurrence of the reaction, reduce the intensity of the photochlorination reaction, reduce the impact of feed jitter on the stability of the lampshade, and reduce safety risks.

[0031] The reactor 4 is provided with a photochlorination device, which comprises an ultraviolet lamp 401 vertically arranged in the reactor 4. Preferably, the ultraviolet lamp 401 is structurally designed as a cylindrical lamp body and a lampshade that wraps the lamp body, so as to increase the illumination area of ​​the photochlorination reaction and promote effective reaction. The contact portion of the lampshade with the reactor 4 is a closed structure, with a gap between the lamp body and the lamp body, and an opening is provided at the top. A compressed air pipeline 404 is also provided in the lampshade, which extends to the bottom of the lampshade. During the reaction, compressed air is used to purge the lampshade, and heat is taken out of the system from the opening at the top of the lampshade by the compressed air, thereby reducing the temperature of the lampshade during the reaction and increasing the service life of the ultraviolet lamp. Reactor 4 is also provided with an air intake device near the bottom, and the air intake device is composed of an air intake hole and an air intake pipeline. Preferably, the air intake hole is connected to chlorine pipeline 403, and the chlorine pipeline 403 branch is connected to nitrogen pipeline 402. Nitrogen pipeline 402 and chlorine pipeline 403 share an air intake port and are both equipped with a one-way valve. Before the device is started, the system can be replaced by nitrogen to ensure that the system is protected by nitrogen and reduce safety risks. Reactor 4 inlet and outlet pipelines are respectively equipped with temperature measuring points 301 and temperature measuring points 405. The temperature measuring device can be a thermocouple type or a thermistor type to monitor the temperature feedback of the material in the reactor 4 during the reaction process, and then the feed heat exchanger 3 is used to adjust the feed temperature so that the temperature index in the reactor 4 is always within the optimal operating index range.

[0032] The first connection end 501 of the equal-diameter variable tee 5 is connected to the exhaust gas heat exchanger 6, and the exhaust gas heat exchanger 6 is connected to the primary alkali liquid absorption tower 7 and the secondary alkali liquid absorption tower 8 in sequence through pipelines. The exhaust gas is discharged after being absorbed and treated by the secondary alkali liquid absorption tower 8. A sight glass is installed on the reflux pipeline from the third connection end 503 of the equal-diameter variable tee to the circulation tank 1, which is convenient for observing changes in reaction conditions such as material flow and color to make timely adjustments.

[0033] like Figure 2As shown, the diameter of the central main pipeline in the equal-diameter variant tee 5 structure is larger than the diameter of the connection end, and its first connection end 501 is connected to the tail gas heat exchanger 6, the second connection end 502 is connected to the reactor 4, and the third connection end 503 is connected to the circulation tank 1. The main function of the equal-diameter variant tee 5 is to pre-separate the gas and liquid phases to avoid excessive system pressure during the reaction process, provide sufficient time and space for the orderly advancement of the main reaction, and avoid overflow. The principle is: during the reaction process, as chlorine continues to enter the reactor 4, the internal pressure of the system continues to increase. When a certain pressure is reached, part of the gas phase that exceeds the system's limit pressure will escape from the first connection end 501 of the equal-diameter variant tee 5 and enter the tail gas device, thereby stabilizing the internal pressure of the system and allowing the reaction to occur normally. Preferably, the pipe specification of the three connecting ends is selected as DN50, and the central main pipe reducer is selected as DN100. The reasons are as follows: the pipe specifications of the three connecting ends are all DN50. If the main pipe specification is too large, it will cause excessive gas phase material leakage, affect the internal material components, hinder the effective reaction, increase the difficulty of reaction control, and reduce the product yield; if an ordinary tee is used or the central main pipe specification is too small, the gas-liquid separation effect cannot be achieved, there are safety hazards such as overflow and overpressure, which is not conducive to stable production.

[0034] The detailed working process of this embodiment is as follows: before the system is operated, the nitrogen pipeline valve 402 is opened to purge the inside of the system, and the valve is closed after the purge is completed. During operation, 2-chloropyridine enters the circulation tank 1 from the feed port 101, and the circulation pump 2 is turned on to keep it running at rated power, so that the material circulates in the system in the order of circulation tank 1 → feed heat exchanger 3 → reactor 4 → circulation tank 1. The heating device of the circulation tank 1 is turned on to exchange heat with the material through the heat transfer oil to provide heat for the reaction. After the material enters from the bottom of the reactor 4, the valve of the chlorine pipeline 402 is opened to allow chlorine to enter the system from the air inlet on the reactor 4, and the 2-chloropyridine: chlorine feed ratio is controlled to be 1:1.1, and the ultraviolet lamp 401 and compressed air 404 are turned on. The heat of the reaction exothermic effect on the lampshade is taken away by the compressed air, reducing the possible safety risks of lampshade damage. Chlorine gas generates chlorine free radicals under the excitation of ultraviolet lamp 401. Since the activation energy of the free radical reaction path at position 6 in the benzene ring of 2-chloropyridine is much lower than that at other positions, the chlorine free radical can more easily replace the hydrogen atom at position 6, thereby generating 2,6-dichloropyridine.

[0035] During the entire reaction process, according to the temperature measuring points 301 and 405 on the inlet and outlet pipes of the reactor 4, the temperature change in the reaction can be effectively observed, and the temperature of the material entering and leaving the reactor 4 can be adjusted in time to achieve the control of temperature and chlorine flux, reduce the difficulty of reaction control, and stabilize the temperature within the optimal index range of 110-120°C. Finally, the components and specific gravity of the material are tested by sampling port 102 to judge the reaction progress. After the expected effect is achieved, the material is discharged once through the discharge port 105. The yield of 2,6-dichloropyridine using this device can generally reach more than 98%. The gas phase components in the system are pre-separated by gas and liquid at the equal diameter variant tee 5, and some of the unreacted chlorine and the generated hydrogen chloride are absorbed by the primary alkali liquid absorption tower 7 and the secondary alkali liquid absorption tower 8 and then discharged in a qualified manner.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the utility model rather than to limit it. Although the utility model has been described in detail with reference to the preferred embodiments, ordinary technicians in the field should understand that the technical solution of the utility model can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the utility model, which should be included in the scope of the claims of the utility model.

Claims

1. A device for preparing 2,6-dichloropyridine from 2-chloropyridine, characterized in that: The invention comprises a circulation tank (1), a feed heat exchanger (3), a reactor (4), and an exhaust gas heat exchanger (6). The circulation tank (1), the feed heat exchanger (3), and the reactor (4) are connected end to end through pipelines to form a reaction device. The reaction device is provided with a circulation pump (2) for circulating materials. The reactor (4) is provided with a photochlorination device. An equal-diameter variable tee (5) is connected between the reactor (4) and the circulation tank (1). The diameter of the central main pipeline of the equal-diameter variable tee (5) is larger than the diameter of the connecting end. The first connecting end (501), the second connecting end (502), and the third connecting end (503) are respectively connected to the exhaust gas heat exchanger (6), the reactor (4), and the circulation tank (1). The reactor (4) is also provided with an air intake device.

2. The device for preparing 2,6-dichloropyridine from 2-chloropyridine according to claim 1, characterized in that: The circulation pump (2) is arranged between the circulation tank (1) and the feed heat exchanger (3) through a pipeline.

3. The device for preparing 2,6-dichloropyridine from 2-chloropyridine according to claim 1, characterized in that: The feed heat exchanger (3) is connected to the bottom feed port of the reactor (4).

4. The device for preparing 2,6-dichloropyridine from 2-chloropyridine according to claim 1, characterized in that: The air intake device is provided with an air intake hole near the bottom, and the air intake hole is connected to a chlorine gas pipeline (403) equipped with a one-way valve; a nitrogen gas pipeline (402) equipped with a one-way valve is also branched from the chlorine gas pipeline (403), and the nitrogen gas pipeline (402) and the chlorine gas pipeline (403) share the air intake hole.

5. The device for preparing 2,6-dichloropyridine from 2-chloropyridine according to claim 1, characterized in that: The inlet pipe and the outlet pipe of the reactor (4) are both provided with temperature measuring points.

6. The device for preparing 2,6-dichloropyridine from 2-chloropyridine according to claim 1, characterized in that: The photochlorination device comprises an ultraviolet lamp (401) vertically arranged in a reactor (4); the ultraviolet lamp (401) is constructed of a cylindrical lamp body and a lampshade wrapping the lamp body; a compressed air pipeline (404) is arranged in the lampshade, and the compressed air pipeline (404) extends to the bottom of the lampshade.

7. The device for preparing 2,6-dichloropyridine from 2-chloropyridine according to claim 1, characterized in that: A sight glass (103) is provided on the return pipe from the third connecting end (503) of the equal-diameter variable tee (5) to the circulation tank (1).

8. The device for preparing 2,6-dichloropyridine from 2-chloropyridine according to claim 1, characterized in that: The inlet pipe of the feed heat exchanger (3) is provided with a sampling port (201).

9. The device for preparing 2,6-dichloropyridine from 2-chloropyridine according to claim 1, characterized in that: The circulation tank (1) comprises a heating device.

10. The device for preparing 2,6-dichloropyridine from 2-chloropyridine according to claim 1, characterized in that: The outlet of the exhaust gas heat exchanger (6) is also provided with an exhaust gas treatment device, which comprises a primary alkali liquid absorption tower (7) and a secondary alkali liquid absorption tower (8). The exhaust gas heat exchanger (6), the primary alkali liquid absorption tower (7) and the secondary alkali liquid absorption tower (8) are sequentially connected through pipelines.

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