A process for the preparation of 2-chloronicotinic acid

Abstract

The application relates to a preparation method of 2-chloronicotinic acid, which comprises the following steps: taking 2-chloro-3-methylpyridine as a starting raw material, mixing a solvent, an initiator and a catalyst in a reaction device, and then directly preparing 2-chloronicotinic acid through oxygen oxidation; after the reaction is completed, a 2-chloronicotinic acid pure product is obtained through three filtering procedures; wherein the reaction device comprises a support and a tank body, the tank body is reversibly rotatably arranged on the support, a filtering assembly is sealingly and slidably arranged in the tank body, the filtering assembly divides an inner cavity of the tank body into an upper area and a lower area, one end of the tank body close to the upper area is provided with a lifting mechanism for driving the filtering assembly to slide in the tank body; the first filtering and the second filtering are both carried out in the upper area; when the third filtering and corresponding water washing are carried out, the tank body is first inverted, and then the third filtering and the corresponding water washing are carried out in the lower area. The application can be carried out in one tank body, the production cost is reduced, the tank body is turned over to transpose the upper area and the lower area, the next step is carried out according to the selection of filter cakes or filtrates in the filtering process, and the preparation efficiency is improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of 2-chloronicotinic acid preparation, in particular to a preparation method of 2-chloronicotinic acid. BACKGROUND

[0002] 2-chloronicotinic acid is widely used in the preparation of high-efficiency low-toxicity pesticides imazosulfuron and difenoxuron as an agricultural and medical intermediate, and its derivatives 2-chloronicotinic acid methyl ester, 2-chloro-N, N-dimethyl nicotinamide and 2-mercapto nicotinic acid are important medical and pesticide intermediates, and many medical antibiotics, drugs for treating cardiovascular diseases and agricultural fungicides, insecticides and herbicides can be synthesized from them.

[0003] A preparation method of 2-chloronicotinic acid is disclosed in a related technology with the patent number CN111153853A, which is prepared by directly oxidizing 2-chloro-3-methylpyridine as a starting material with oxygen, using any one of acetic acid, chloroform, acetonitrile and ethyl acetate as a solvent, using N-hydroxyphthalimide as an initiator, and using a metal salt as a catalyst; wherein the mass ratio of the solvent to 2-chloro-3-methylpyridine is 5-10:1; the molar ratio of N-hydroxyphthalimide to 2-chloro-3-methylpyridine is 10-20:100; the metal salt is cobalt (III) acetylacetonate or manganese (III) acetylacetonate; the reaction temperature is 50-120 DEG C; the reaction pressure is 0.2-2 MPa; and the reaction time is 3-24 h. After the reaction is completed, the reaction liquid is cooled to room temperature, filtered, the filter cake is washed with water, the filter cake is dissolved with lye, filtered, the obtained filtrate is acidified with hydrochloric acid to a pH value of 1-2 to obtain a white solid, filtered, washed with water, and dried to obtain 2-chloronicotinic acid.

[0004] The related technology in the above has the following defects: in the process of preparing 2-chloronicotinic acid solid, filtering, water washing, lye washing, secondary filtering, acid liquid washing, filtering, water washing and other processes are needed, and the production container needs to be turned over many times in different production containers. Moreover, the lye washing and the acid liquid washing have high requirements for the corrosion resistance of the production container, which undoubtedly greatly increases the production cost, and the production efficiency is also difficult to be significantly improved. SUMMARY

[0005] In order to improve the problems of high cost and low production efficiency of the current 2-chloronicotinic acid production equipment, the application provides a preparation method of 2-chloronicotinic acid.

[0006] The preparation method of 2-chloronicotinic acid provided by the application adopts the following technical scheme:

[0007] A preparation method of 2-chloronicotinic acid, comprising: using 2-chloro-3-methylpyridine as a starting material, mixing a solvent, an initiator and a catalyst in a reaction device, and then directly oxidizing to prepare 2-chloronicotinic acid by oxygen; the reaction temperature is 50-120 DEG C, the reaction pressure is 0.2-2 MPa, and the reaction time is 3-24 h; after the reaction is completed, the reaction liquid is cooled to room temperature and primary filtration is performed, the obtained filter cake is washed with water, the filter cake is dissolved with lye, secondary filtration is performed, the obtained filtrate is acidified to pH 1-2 with hydrochloric acid to obtain white solid, and tertiary filtration, water washing and drying are performed to obtain pure 2-chloronicotinic acid;

[0008] The reaction device comprises a support and a sealed tank body, the tank body is reversibly rotatably installed on the support, a filter assembly is sealingly and slidably arranged in the tank body, the filter assembly divides the inner cavity of the tank body into an upper zone and a lower zone, and a lifting mechanism for driving the filter assembly to slide in the tank body is arranged on one end of the tank body close to the upper zone;

[0009] The tank body is provided with a liquid discharge pipeline in communication with the lower zone and a plurality of liquid supplement pipelines in communication with the upper zone, and the primary filtration and the secondary filtration are both performed in the upper zone;

[0010] The tank body is provided with the liquid supplement pipeline in communication with the lower zone and used for supplementing acid liquid;

[0011] When the tertiary filtration and the corresponding water washing are performed, the tank body is first inverted, and then the tertiary filtration is performed in the lower zone.

[0012] Further, when the primary filtration is performed, the filter assembly is driven to move towards the lower zone;

[0013] When the secondary filtration is performed after the lye is supplemented, the filter assembly is driven to move towards the upper zone;

[0014] When the tertiary filtration is performed by inverting the tank body, the filter assembly is driven to move towards the lower zone.

[0015] Further, the filter assembly comprises a filter frame sealingly and slidably arranged in the tank body, a filter screen installed in the filter frame, and an upper scraping member and a lower scraping member rotatably installed on the upper and lower end faces of the filter frame respectively, the upper scraping member is located in the upper zone, and the lower scraping member is located in the lower zone;

[0016] The tank body is further provided with a driving mechanism for driving the upper scraping member and the lower scraping member to rotate; when the lifting mechanism drives the filter frame to move towards the upper zone, the rotation speed of the upper scraping member is greater than that of the lower scraping member; when the lifting mechanism drives the filter frame to move towards the lower zone, the rotation speed of the lower scraping member is greater than that of the upper scraping member.

[0017] Further, the lifting mechanism comprises a linear drive installed on the tank body and a lifting platform installed on the output end of the linear drive, the drive mechanism comprises a drive motor installed on the lifting platform and a drive rod installed on the output end of the drive motor, the lifting platform is fixedly connected with a lifting cylinder sleeved on the outer periphery of the drive rod, the lifting cylinder and the drive rod penetrate and extend into the tank body, and the lifting cylinder is connected with the filter frame in a same motion.

[0018] The end of the drive rod away from the lifting platform is provided with a control assembly for driving the upper and lower scraping members to rotate at different speeds.

[0019] Further, the control assembly comprises an upper drive disc and a lower drive disc sleeved on the end of the lifting cylinder, the upper and lower scraping members are fixedly connected with the upper and lower drive discs respectively, and the upper and lower drive discs are rotatably installed in the middle part of the filter frame in a coaxial mode.

[0020] The opposite end faces of the upper and lower drive discs are fixedly connected with a plurality of spaced drive long columns and drive short columns, and the drive short column is located between the adjacent two drive long columns.

[0021] The side wall of the lifting cylinder is rotatably installed with a power disc between the upper and lower drive discs, the power disc is in transmission connection with the drive rod, the power disc is located at the edge part of the upper drive disc, a plurality of spaced power columns are fixedly connected to the side edge of the power disc close to the drive rod, and the spacing between the adjacent drive short column and the drive long column is greater than the outer diameter of the power column.

[0022] When the power disc rotates, the plurality of power columns thereon intermittently drive the drive long column or drive short column in meshing connection to revolve around the axis of the drive rod.

[0023] Further, the outer peripheral wall of the lifting cylinder is fixedly connected with two limiting rings arranged on the upper and lower sides of the filter frame, when the filter frame moves to abut against the upper limiting ring, the power columns on the power disc are in meshing connection with the drive short columns and the drive long columns on the upper drive disc, and at this time, the power columns on the power disc are only in meshing connection with the drive long columns on the lower drive disc.

[0024] Further, the middle part of the filter frame is provided with a through hole, the upper and lower drive discs are rotatably installed on the hole wall of the through hole, the middle parts of the upper and lower drive discs are provided with through holes for the lifting cylinder to pass through, and the lifting cylinder is sealingly and slidably arranged in the through hole.

[0025] Further, a sliding structure is arranged between the limiting ring and the corresponding upper driving disc and lower driving disc.

[0026] Further, a polytetrafluoroethylene layer is arranged at the part where the filter frame contacts the tank body.

[0027] To sum up, the beneficial technical effects of the present application are:

[0028] 1. The three filtering processes in the preparation of 2-chloronicotinic acid can be performed in one tank body. On the one hand, by inverting the tank body to transpose the upper zone and the lower zone, the next process can be reasonably performed according to the selection of filter cake or filtrate in the filtering process, thereby greatly improving the preparation efficiency. On the other hand, only one tank body that can resist acid and alkali needs to be arranged, thereby significantly reducing the production cost.

[0029] 2. In the process of following the lifting of the lifting cylinder, the driving motor also synchronously drives the driving rod to rotate. The driving rod can also realize the rotation of the upper scraping member and the lower scraping member on the filter frame by means of the control assembly. That is, when the filter frame is moving or not moving, the upper scraping member and the lower scraping member can scrape and clean the upper and lower surfaces of the filter screen on the filter frame. The filter screen can be effectively dredged, and the probability of being blocked can be reduced, thereby promoting the filtering efficiency of each filtering stage.

[0030] 3. When the linear driving member drives the filter frame to move to the upper zone, the cleaning frequency of the upper scraping member on the filter screen is obviously greater than that of the lower scraping member. When the linear driving member drives the filter frame to move to the lower zone, the cleaning frequency of the lower scraping member on the filter screen is obviously greater than that of the upper scraping member. Thus, on the one hand, the filter screen on the side that bears greater resistance can be more fully cleaned, and on the other hand, the wear of the filter screen on the side that bears less resistance when being scraped can be reduced. The filter frame can have good filtering effect in different moving states, and the service life of the filter screen in the filter frame can be prolonged as much as possible, which is more conducive to cost saving. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a schematic diagram of the overall structure of an embodiment of the present application;

[0032] Figure 2 is a sectional view of the overall structure of an embodiment of the present application;

[0033] Figure 3 is a schematic diagram of the overall structure of an embodiment of the present application; Figure 2

[0034] Figure 4 is a schematic diagram of the control assembly of an embodiment of the present application.

[0035] EXPLANATION OF REFERENCE NUMERALS:

[0036] 1, support;​

[0037] 2, tank body; 21, upper zone; 22, lower zone;

[0038] 31, filter frame; 311, perforation; 32, filter screen; 33, upper scraping member; 34, lower scraping member;

[0039] 41, linear drive member; 42, lifting platform; 43, drive motor; 44, drive rod; 45, lifting cylinder; 451, limiting ring;

[0040] 51, upper drive disc; 52, lower drive disc; 531, long drive column; 532, short drive column; 533, through hole; 54, power disc; 541, power column. DETAILED DESCRIPTION

[0041] The technical solutions of the present application will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0042] The embodiments of the present application disclose a preparation method of 2-chloronicotinic acid. Referring to Figure 1 and Figure 2 The preparation method of 2-chloronicotinic acid comprises using 2-chloro-3-methylpyridine as a starting material, mixing a solvent, an initiator and a catalyst in a reaction device, and then directly oxidizing to prepare 2-chloronicotinic acid by oxygen. The reaction temperature is 50-120°C, the reaction pressure is 0.2-2 MPa, and the reaction time is 3-24 h. After the reaction is completed, the reaction liquid is cooled to room temperature and primary filtration is performed. The obtained filter cake is washed with water, and the filter cake is dissolved with a lye, and then secondary filtration is performed. The obtained filtrate is acidified to pH 1-2 with hydrochloric acid to obtain a white solid, and then tertiary filtration, water washing and drying are performed to obtain a pure product of 2-chloronicotinic acid.

[0043] The reaction device comprises a support 1 and a sealed cylindrical tank body 2. The tank body 2 is reversibly rotatably installed on the support 1. The overturning shaft axis of the tank body 2 is orthogonal to the axis of the tank body 2, and a large-torque rotary driving mechanism for driving the tank body 2 to overturn is arranged on the support 1. A polytetrafluoroethylene lining layer is attached to the inner wall of the tank body 2. A filter assembly is sealingly and slidably arranged in the tank body 2. The filter assembly divides the inner cavity of the tank body 2 into an upper zone 21 and a lower zone 22. An elevating mechanism for driving the filter assembly to slide in the tank body 2 is arranged at one end of the tank body 2 close to the upper zone 21.

[0044] Furthermore, the tank body 2 is equipped with a drain pipe connected to the lower zone 22 and several replenishment pipes connected to the upper zone 21. The primary filtration and secondary filtration are both carried out in the upper zone 21. The tank body 2 is equipped with a replenishment pipe connected to the lower zone 22 for replenishing acid. When performing the third filtration and corresponding water washing, the tank body 2 is first inverted and then carried out in the lower zone 22.

[0045] Specifically, during the initial filtration, the filter components are driven to move towards the lower zone 22;

[0046] When the alkaline solution is replenished and a second filtration is performed, the filter assembly is driven to move towards the upper zone 21.

[0047] When the tank 2 is tilted to perform three filtrations, the filter assembly is driven to move into the lower zone 22.

[0048] With this setup, after the reaction to prepare 2-chloronicotinic acid is completed, clean water is added to the upper zone 21 of tank 2 through the replenishment pipe connected to the upper zone 21. At the same time, the filter assembly is driven to move into the lower zone 22, which can squeeze the filtrate to a certain extent. Then, the drain pipe is opened to achieve the initial filtration of the reaction liquid and discharge of waste liquid. Afterward, alkaline solution is added to the upper zone 21 of tank 2 through the replenishment pipe connected to the upper zone 21 to dissolve the filter cake located in the upper zone 21. At this time, the filter assembly is driven to move into the upper zone 21, which can promote the dissolution effect of the alkaline solution on the filter cake.

[0049] After the filter cake in the upper zone 21 of tank 2 is fully dissolved, the resulting filtrate passes through the filter assembly and enters the lower zone 22 of tank 2. Undissolved impurities remain on the side of the filter assembly closer to the upper zone 21. Then, acid is added to tank 2 through the replenishment pipe connected to the lower zone 22 until a white solid precipitates. Subsequently, tank 2 is flipped so that the lower zone 22 is above the upper zone 21. At this time, the acidified reaction liquid passes through the filter assembly under its own weight for autonomous filtration. This also drives the filter assembly to move towards the lower zone 22, which means that the filter assembly can create pressure filtration of the reaction liquid in the lower zone 22, promoting the effect of three-stage filtration. After filtration, the 2-chloronicotinic acid solid is located on the side of the filter assembly closer to the lower zone 22. Then, clean water is introduced through the replenishment pipe of the lower zone 22 for further washing.

[0050] In this process, all three filtration steps in the preparation of 2-chloronicotinic acid can be carried out in one tank 2. On the one hand, by flipping the tank 2 to change the position of the upper zone 21 and the lower zone 22, the next step can be carried out in a reasonable manner according to the selection of filter cake or filtrate in the filtration process, which greatly improves the preparation efficiency. On the other hand, only one acid and alkali resistant tank 2 needs to be set up, which significantly reduces the production cost.

[0051] For specific settings, please refer to... Figure 2 and Figure 3The filter assembly comprises a filter frame 31 sealingly slidingly arranged in the tank body 2, a filter screen 32 arranged in the filter frame 31, and an upper scraping member 33 and a lower scraping member 34 rotatably arranged on the upper and lower end faces of the filter frame 31 respectively, the upper scraping member 33 being located in the upper area 21, and the lower scraping member 34 being located in the lower area 22; the upper scraping member 33 and the lower scraping member 34 are both arranged as brush plates, and the bristles on the brush plates are in flexible abutment with the surface of the filter screen 32.

[0052] The tank body 2 is further provided with a driving mechanism for driving the upper scraping member 33 and the lower scraping member 34 to rotate; when the lifting mechanism drives the filter frame 31 to move towards the upper area 21, the rotation speed of the upper scraping member 33 is greater than that of the lower scraping member 34; when the lifting mechanism drives the filter frame 31 to move towards the lower area 22, the rotation speed of the lower scraping member 34 is greater than that of the upper scraping member 33.

[0053] Specifically, the lifting mechanism comprises a linear driving member 41 arranged on the tank body 2 and a lifting platform 42 arranged on the output end of the linear driving member 41, and the linear driving member 41 can be a pneumatic cylinder or a screw rod and slider structure, and in this embodiment, the linear driving member 41 is arranged as a pneumatic cylinder; the driving mechanism comprises a driving motor 43 arranged on the lifting platform 42 and a driving rod 44 arranged on the output end of the driving motor 43, and the lifting platform 42 is fixedly connected with a lifting cylinder 45 sleeved on the outer periphery of the driving rod 44, the lifting cylinder 45 and the driving rod 44 penetrate and extend into the tank body 2, the lifting cylinder 45 is in sliding sealing connection with the tank body 2, and the free end of the lifting cylinder 45 is connected with the filter frame 31.

[0054] The end of the driving rod 44 away from the lifting platform 42 is provided with a control assembly between the upper scraping member 33 and the lower scraping member 34 for driving the upper scraping member 33 and the lower scraping member 34 to rotate at different speeds. Figure 3 and Figure 4 The control assembly comprises an upper driving disc 51 and a lower driving disc 52 sleeved on the end of the lifting cylinder 45, the upper scraping member 33 and the lower scraping member 34 are fixedly connected with the upper driving disc 51 and the lower driving disc 52 respectively, and the upper driving disc 51 and the lower driving disc 52 are coaxially rotatably arranged in the middle part of the filter frame 31. The opposite end faces of the upper driving disc 51 and the lower driving disc 52 are both fixedly connected with a plurality of driving long columns 531 and driving short columns 532 distributed at intervals, and the driving short columns 532 are located between the adjacent two driving long columns 531; the plurality of driving long columns 531 and the plurality of driving short columns 532 are distributed in an equidistant circumferential array along the axis of the lifting cylinder 45.

[0055] The power disc 54 is rotatably installed on the sidewall of the lifting cylinder 45 between the upper driving disc 51 and the lower driving disc 52, and is in transmission connection with the driving rod 44 through a bevel gear structure. The power disc 54 is located at the edge of the upper driving disc 51, and a plurality of power columns 541 are fixedly connected to the side edge close to the driving rod 44. The plurality of power columns 541 are distributed in an equidistant circumferential array along the axis of the power disc 54, and the spacing between adjacent driving short columns 532 and driving long columns 531 is greater than the outer diameter of the power column 541. When the power disc 54 rotates, the plurality of power columns 541 thereon intermittently drive the driving long columns 531 or the driving short columns 532 engaged therewith to revolve around the axis of the driving rod 44. Specifically, at least one power column 541 on the power disc 54 is embedded between two adjacent driving long columns 531 or between an adjacent driving long column 531 and a driving short column 532, so as to ensure that the power disc 54 can drive the corresponding driving long column 531 or driving short column 532 to rotate the corresponding upper driving disc 51 or lower driving disc 52 when rotating.

[0056] More specifically, when the lifting cylinder 45 drives the filter frame 31 to move upward into the upper zone 21, the filter frame 31 makes the upper driving disc 51 and the power disc 54 mainly aligned under the resistance of the solution in the tank body 2. At this time, the power columns 541 on the power disc 54 are embedded between the driving long columns 531 and the driving short columns 532 on the upper driving disc 51, that is, the power disc 54 and the upper driving disc 51 are in transmission connection through the engagement of the plurality of driving long columns 531, the plurality of driving short columns 532 and the plurality of power columns 541. At this time, the power columns 541 on the opposite side of the power disc 54 are only embedded between the adjacent two driving long columns 531 of the lower driving disc 52, that is, the power disc 54 and the lower driving disc 52 are in transmission connection through the engagement of the plurality of driving long columns 531 and the plurality of power columns 541.

[0057] From the comparison, it can be seen that when the power disc 54 rotates, the rotation speed of the upper driving disc 51 is significantly greater than that of the lower driving disc 52, that is, the scraping frequency of the upper scraping member 33 on the filter screen 32 is significantly greater than that of the lower scraping member 34 on the filter screen 32. Conversely, when the lifting cylinder 45 drives the filter frame 31 to move downward into the lower zone 22, the rotation speed of the lower driving disc 52 driven by the power disc 54 is significantly greater than that of the upper driving disc 51, that is, the scraping frequency of the lower scraping member 34 on the filter screen 32 is significantly greater than that of the upper scraping member 33 on the filter screen 32.

[0058] After the arrangement, on one hand, when the linear driving part 41 drives the lifting platform 42 to move, the lifting platform 42 drives the lifting cylinder 45 and the driving rod 44 on it to move, since the free end of the lifting cylinder 45 is connected with the filter frame 31 to move synchronously, thus the filter frame 31 can be conveniently slid in the tank body 2 to adaptively adjust the position of the filter frame 31 and change the space of the upper area 21 and the lower area 22 according to the preparation process steps of 2-chloronicotinic acid, so as to meet the requirements of different stages of filtration.

[0059] On the other hand, during the lifting of the filter frame 31 following the lifting cylinder 45, the driving motor 43 also synchronously drives the driving rod 44 to rotate, and the driving rod 44 can also realize the rotation of the upper scraping part 33 and the lower scraping part 34 on the filter frame 31 by means of the control assembly, that is, when the filter frame 31 moves or does not move, the upper scraping part 33 and the lower scraping part 34 can scrape and clean the upper and lower surfaces of the filter screen 32 on the filter frame 31, and can effectively dredge the filter screen 32 to reduce the probability of the filter screen 32 being blocked, so as to promote the filtration efficiency of each filtration stage.

[0060] In addition, when the linear driving part 41 drives the filter frame 31 to move to the upper area 21, the side of the filter screen 32 facing the upper area 21 is subjected to greater resistance from the solution in the tank body 2, and at this time, under the transmission of the power disc 54 and the upper driving disc 51 and the lower driving disc 52, the cleaning frequency of the filter screen 32 by the upper scraping part 33 is obviously greater than that by the lower scraping part 34, which can ensure that the filter screen 32 on the side subjected to greater resistance can be more fully cleaned, and can reduce the wear of the filter screen 32 on the side subjected to less resistance when being scraped, which can not only ensure the good filtration effect of the filter frame 31 in different moving states, but also can prolong the service life of the filter screen 32 in the filter frame 31 as much as possible, which is more conducive to cost saving, especially under the premise that the service life and use cost of the filter screen 32 soaked in acid and alkali have certain requirements. When the linear driving part 41 drives the filter frame 31 to move to the lower area 22, the same effect is also achieved, and thus is not described in detail.

[0061] In order to realize the effective synchronous connection of the lifting cylinder 45 and the filter frame 31, refer to Figure 3 and Figure 4The outer peripheral wall of the lifting cylinder 45 is fixedly connected with two limiting rings 451 arranged on the upper and lower sides of the filter frame 31. When the filter frame 31 moves to abut against the upper limiting ring 451, the power column 541 on the power disc 54 is in meshing connection with the driving short column 532 and the driving long column 531 on the upper driving disc 51, and at this time, the power column 541 on the power disc 54 is in meshing connection with only the driving long column 531 on the lower driving disc 52. Conversely, when the filter frame 31 moves to abut against the lower limiting ring 451, the power column 541 on the power disc 54 is in meshing connection with the driving short column 532 and the driving long column 531 on the lower driving disc 52, and at this time, the power column 541 on the power disc 54 is in meshing connection with only the driving long column 531 on the upper driving disc 51.

[0062] Specifically, referring to Figure 2 and Figure 3 A through hole 311 is arranged in the middle of the filter frame 31, and the upper driving disc 51 and the lower driving disc 52 are rotationally mounted on the hole wall of the through hole 311. The middle of the upper driving disc 51 and the middle of the lower driving disc 52 are both provided with a through hole 533 for the lifting cylinder 45 to pass through, and the lifting cylinder 45 is sealingly and slidingly arranged in the through hole 533.

[0063] In this way, when the lifting cylinder 45 moves upward or downward, the filter frame 31 can be limited by the limiting ring 451 located in the lower area 22 or the limiting ring 451 located in the upper area 21, so that the filter frame 31 can stably move with the lifting cylinder 45 and will not greatly interfere with the normal rotation of the upper driving disc 51 and the lower driving disc 52.

[0064] Further, a sliding structure can be arranged between the limiting ring 451 and the corresponding upper driving disc 51 and lower driving disc 52. The sliding structure can be a ball structure or a sliding bar, so as to reduce the sliding resistance between the abutting surfaces of the limiting ring 451 and the upper driving disc 51 or the lower driving disc 52, and to ensure that the upper driving disc 51 and the lower driving disc 52 can stably rotate with the power disc 54 as much as possible.

[0065] In addition, the part of the filter frame 31 in contact with the tank body 2 is provided with a polytetrafluoroethylene layer, and the outer peripheral wall of the lifting cylinder 45 located between the two limiting rings 451 is also provided with a polytetrafluoroethylene layer, which can reduce the friction resistance, improve the smoothness of the sliding movement, and also has a good sealing effect.

[0066] The implementation principle of the preparation method of 2-chloronicotinic acid in the embodiment of the application is as follows:

[0067] The three filtering processes in the preparation of 2-chloronicotinic acid can be carried out in the tank 2, on the one hand, by inverting the tank 2 to transpose the upper zone 21 and the lower zone 22, the next process can be reasonably carried out according to the selection of filter cake or filtrate in the filtering process, which greatly improves the preparation efficiency; on the other hand, only one tank 2 that can resist acid and alkali needs to be set, which significantly reduces the production cost.

[0068] When the linear driving member 41 drives the filter frame 31 to move to the upper zone 21, the cleaning frequency of the upper scraping member 33 on the filter screen 32 is obviously greater than that of the lower scraping member 34 on the filter screen 32; when the linear driving member 41 drives the filter frame 31 to move to the lower zone 22, the cleaning frequency of the lower scraping member 34 on the filter screen 32 is obviously greater than that of the upper scraping member 33 on the filter screen 32; thus, on the one hand, it can ensure that the filter screen 32 on the side that bears greater resistance can be more fully cleaned, on the other hand, it can reduce the wear of the filter screen 32 on the side that bears less resistance when being scraped, which can not only ensure the good filtering effect of the filter frame 31 in different moving states, but also can prolong the service life of the filter screen 32 in the filter frame 31 as much as possible, which is more conducive to cost saving.

[0069] Unless otherwise defined, technical terms or scientific terms used in the present application shall be understood as having the usual meaning understood by a person skilled in the art to which the present application belongs. The terms "first", "second", "third" and the like used in the specification and claims of the present application do not represent any order, number or importance, but are only used to distinguish different components. The terms "one" or "a" and the like do not represent a quantity limitation, but represent the existence of at least one. The terms "including", "containing" and the like mean that the elements or objects appearing before "including" or "containing" cover the elements or objects listed after "including" or "containing" and their equivalents, and do not exclude other elements or objects. The terms "upper", "lower", "left", "right" and the like are only used to represent relative positional relationships, and when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0070] The above are the preferred embodiments of the present application, which do not limit the protection scope of the present application, therefore: any equivalent changes made on the structure, shape, principle of the present application shall be covered within the protection scope of the present application.

Claims

1. A method for preparing 2-chloronicotinic acid, characterized in that, include: 2-Chloronicotinic acid was prepared by direct oxidation with oxygen after mixing solvent, initiator and catalyst in a reaction apparatus using 2-chloro-3-methylpyridine as the starting material. The reaction temperature was 50-120℃, the reaction pressure was 0.2-2MPa, and the reaction time was 3-24h. After the reaction was completed, the reaction solution was cooled to room temperature and filtered for the first time. The resulting filter cake was washed with water and dissolved with alkali solution, then filtered for the second time. The resulting filtrate was acidified with hydrochloric acid to a pH of 1-2 to obtain a white solid. The solid was then filtered for the third time, washed with water, and dried to obtain pure 2-chloronicotinic acid. The reaction equipment includes a support and a sealed tank. The tank is rotatably mounted on the support. A filter assembly is slidably and sealed inside the tank. The filter assembly divides the inner cavity of the tank into an upper zone and a lower zone. A lifting mechanism for driving the filter assembly to slide inside the tank is provided at one end of the tank near the upper zone. The tank is equipped with a drain pipe connected to the lower zone and several replenishment pipes connected to the upper zone. The primary filtration and secondary filtration are both carried out in the upper zone. The tank is equipped with a replenishment pipeline that communicates with the lower zone and is used to replenish acid. When performing three filtrations and corresponding water washing, first invert the tank, and then carry out the process in the lower zone; The filter assembly includes a filter frame that is slidably and sealed inside the tank, a filter screen installed in the filter frame, and an upper scraper and a lower scraper that are rotatably installed on the upper and lower end faces of the filter frame, respectively. The upper scraper is located in the upper region, and the lower scraper is located in the lower region. The tank is also provided with a drive mechanism for driving the upper scraper and the lower scraper to rotate. The lifting mechanism includes a linear drive unit installed on the tank and a lifting platform installed on the output end of the linear drive unit. The drive mechanism includes a drive motor installed on the lifting platform and a drive rod installed on the output end of the drive motor. A lifting cylinder sleeved on the outer periphery of the drive rod is fixedly connected to the lifting platform. The lifting cylinder and the drive rod pass through and extend into the tank. The lifting cylinder is movably connected to the filter frame. A control component is provided between the end of the drive rod away from the lifting platform and the upper and lower scraping components to drive the upper and lower scraping components to rotate at different speeds; The control assembly includes an upper drive disk and a lower drive disk sleeved on the end of the lifting cylinder. The upper scraper and the lower scraper are respectively fixed on the upper drive disk and the lower drive disk. The upper drive disk and the lower drive disk are rotatably mounted in the middle of the filter frame in a coaxial manner. Multiple spaced-apart long drive posts and short drive posts are fixed to the opposite end face edges of the upper drive disk and the lower drive disk, with the short drive posts located between two adjacent long drive posts. A power disc is rotatably installed on the side wall of the lifting cylinder between the upper drive disc and the lower drive disc. The power disc is connected to the drive rod. The power disc is located at the edge of the upper drive disc. Multiple spaced power columns are fixed to the edge of the power disc near the drive rod. The distance between adjacent short drive columns and long drive columns is greater than the outer diameter of the power column. When the power disc rotates, multiple power columns on it intermittently actuate the long or short drive columns that mesh with it to revolve around the drive rod axis.

2. The method for preparing 2-chloronicotinic acid according to claim 1, characterized in that, During the initial filtration, the filter assembly is driven to move toward the lower region; When a second filtration is performed after adding alkali solution, the filter assembly is driven to move towards the upper region; When the tank is flipped over to perform three filtrations, the filter assembly is driven to move toward the lower zone.

3. The method for preparing 2-chloronicotinic acid according to claim 2, characterized in that, When the lifting mechanism drives the filter frame to move towards the upper area, the rotation speed of the upper scraper is greater than that of the lower scraper. When the lifting mechanism drives the filter frame to move to the lower area, the rotation speed of the lower scraper is greater than that of the upper scraper.

4. The method for preparing 2-chloronicotinic acid according to claim 3, characterized in that, Two limiting rings are fixed to the outer peripheral wall of the lifting cylinder, which are arranged on the upper and lower sides of the filter frame. When the filter frame moves to abut against the upper limiting ring, the power column on the power disk is engaged with the short drive column and the long drive column on the upper drive disk. At this time, the power column on the power disk is only engaged with the long drive column on the lower drive disk.

5. The method for preparing 2-chloronicotinic acid according to claim 3, characterized in that, The filter frame has a through hole in the middle. The upper drive plate and the lower drive plate are anti-detached and rotatably mounted on the wall of the through hole. The middle of the upper drive plate and the lower drive plate are both provided with through holes for the lifting cylinder to pass through. The lifting cylinder is slidably disposed in the through hole.

6. The method for preparing 2-chloronicotinic acid according to claim 4, characterized in that, A sliding structure is provided between the limiting ring and the corresponding upper driving disk and lower driving disk.

7. The method for preparing 2-chloronicotinic acid according to claim 3, characterized in that, The part of the filter frame that contacts the tank is provided with a polytetrafluoroethylene layer.

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