A lactide circulating crystallization drying device in polylactic acid synthesis process

Abstract

The invention discloses a lactide circulating crystallization drying device in a polylactic acid synthesis process, comprising a crystallizer body and a heat preservation chamber, the inner wall of the crystallizer body is provided with a filter plate, the filter plate divides the crystallizer body into an upper cavity and a lower cavity, the upper end wall of the crystallizer body is vertically plugged with a rotating shaft, the outer wall of the rotating shaft is symmetrically provided with rectangular stirring wheels on both sides and located in the upper cavity, the rotating shaft penetrates the upper end wall of the crystallizer body and the outer wall of the upwardly extending end is sleeved with a first transmission wheel, the outer wall of the first transmission wheel is connected to a second transmission wheel through a transmission belt, and the inner wall of the second transmission wheel is vertically plugged with a rotating shaft. The invention overcomes the shortcomings of the prior art, has a reasonable design, a compact structure, solves the defects of the prior art such as complex structure, low efficiency, and low crystal purity, and improves the purification efficiency of lactide, and has a high social use value and application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of polylactic acid production, in particular to a lactide circulation crystallization drying device in a polylactic acid synthesis process. Background Art

[0002] Recrystallization purification is a process of dissolving crystals into a solvent or melting them, and then re-crystallizing them from the solution or melt. That is, the solubility of the target component in the solid mixture in a certain solvent varies significantly with the change of temperature. At a relatively high temperature, the solubility is large, and when the temperature is lowered, the solubility is small, so that separation and purification can be achieved. Recrystallization can purify certain impure substances, purify solid substances, and separate mixed salts from each other. Metals or alloys can be refined through recrystallization, and the crystal crystallization and its properties can be changed. Recrystallization is mainly used in situations where the properties of the object and the impurities are quite different and the impurity content is less than 5%.

[0003] However, the industrial production of lactide re-reaction products is difficult at present, mainly because the lactide production is accompanied by a large number of side reactions, and the removal of impurities produced by the side reactions requires a certain process flow. In the process of removing impurities, the existing processes are all in an open environment, and other impurities are mixed in. The industrial-grade purification of lactide is still a problem in my country.

[0004] Therefore, in view of this, the inventor, based on his many years of rich experience in design, development and actual production in the relevant industry, has studied and improved the existing structure and deficiencies, and provided a lactide circulating crystallization and drying equipment in the polylactic acid synthesis process, in order to achieve a more practical purpose. Summary of the invention

[0005] In order to solve the problems mentioned in the above background technology, the present invention provides a lactide circulating crystallization drying device in a polylactic acid synthesis process.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A lactide circulating crystallization and drying device in a polylactic acid synthesis process comprises a crystallizer body and an insulation chamber, the inner wall of the crystallizer body is provided with a filter plate, the filter plate divides the crystallizer body into an upper cavity and a lower cavity, the upper end wall of the crystallizer body is vertically plugged with a rotating shaft, and rectangular stirring wheels are symmetrically arranged on both sides of the outer wall of the rotating shaft and located in the upper cavity, the rotating shaft passes through the upper end wall of the crystallizer body and is sleeved on the outer wall of the upwardly extending end thereof, the outer wall of the first transmission wheel is connected to the second transmission wheel through a transmission belt, the inner wall of the second transmission wheel is vertically plugged with a rotating shaft, and the bottom of the rotating shaft is connected to a driving motor, the bottom of the rotating shaft is symmetrically provided with a first connecting shaft on both sides of the bottom of the rotating shaft and located in the lower cavity, and a telescopic rod is horizontally fixed to one end of the first connecting shaft away from the rotating shaft, a spring is sleeved on the outer wall of the telescopic rod, and a second connecting shaft is horizontally fixed to one end of the telescopic rod away from the first connecting shaft, and the second connecting shaft is far away from the first connecting shaft. A scraper is horizontally fixed to one end of the telescopic rod, and an L-shaped connecting rod is respectively provided on the upper and lower side walls of the first connecting shaft, and a T-shaped limit block is provided on the end of the L-shaped connecting rod away from the first connecting shaft, the T-shaped limit block extends to the outer wall of the second connecting shaft, and a limit slide groove corresponding to the T-shaped limit block is provided on one side of the outer wall of the second connecting shaft, the inner wall of the rotating shaft is provided with a hollow pipe, and the bottom two sides of the hollow pipe are symmetrically connected with drying vents, the upper port of the hollow pipe is plugged with an air inlet pipe, and the outer wall of the connection between the air inlet pipe and the hollow pipe is sleeved with a second bearing, the bottom of the crystallizer body is connected with a lactide discharge pipe, and the side wall of the lactide discharge pipe is connected with a reflux pipe, the reflux pipe passes through the insulation chamber and extends upward to be connected with the outer wall of the crystallizer body, a booster pump and a first valve are installed on the reflux pipe, one side of the upper end of the crystallizer body is connected with a feed pipe, and a third valve is provided on the feed pipe.

[0008] Preferably, fixing frames are symmetrically provided on both sides of the bottom of the crystallizer body, and one end of the fixing frame away from the crystallizer body is fixedly connected to the inner wall of the insulation chamber.

[0009] Preferably, a protective coating is provided on one side of the outer wall of the scraper, and the protective coating is cuprous oxide coating.

[0010] Preferably, a sealing rubber ring is sleeved on the outer wall of the air inlet pipe and located on the upper end of the rotating shaft.

[0011] Preferably, a bottom side of the insulation chamber is connected to a cold and hot medium inlet, and a first cold and hot medium valve is provided on the cold and hot medium inlet pipeline, and an upper end side of the insulation chamber is connected to a cold and hot medium outlet, and a second cold and hot medium valve is provided on the cold and hot medium outlet pipeline.

[0012] Preferably, a second valve is provided at the bottom of the lactide discharge pipeline.

[0013] Preferably, a first bearing is sleeved on the outer wall of the connection between the rotating shaft and the filter plate.

[0014] Preferably, a filter element is provided on the inner wall of the reflux pipe.

[0015] Preferably, the bottom of the hollow pipe is connected to a wind outlet, and the wind outlet passes through the bottom wall of the rotating shaft and extends downward.

[0016] Preferably, supporting legs are fixedly connected to four sides of the bottom of the insulation chamber.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. When lactide needs to be dissolved, heat medium is introduced to accelerate dissolution and improve processing efficiency; during the recrystallization stage, cold medium is introduced to accelerate crystallization and precipitate more crystals;

[0019] 2. Under the driving action of the driving motor, the rotating shaft drives the rectangular stirring wheel on the outer wall to fully stir the mixture, thereby improving the dissolution effect;

[0020] 3. The filter plate and filter element can perform multiple filtrations on the mother liquor, thereby improving the purity of the mother liquor and facilitating better crystallization of lactide with higher purity;

[0021] 4. The scraper can scrape off the crystals attached to the inner wall of the crystallizer body, thereby preventing the crystals from accumulating on the inner wall of the crystallizer body, which will have a certain impact on the production and processing efficiency.

[0022] In summary, the present invention overcomes the shortcomings of the prior art, has a reasonable design and a compact structure, solves the defects of the prior art such as complex structure, low efficiency and low crystal purity, and improves the purification efficiency of lactide, and has a high social use value and application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

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

[0025] Figure 2 This is a schematic diagram of the structure of Embodiment 2 of the present invention;

[0026] Figure 3 This is a schematic diagram of the structure of Embodiment 3 of the present invention;

[0027] Figure 4 This is an enlarged schematic diagram of the structure of Example A of the present invention;

[0028] Figure 5 It is an enlarged schematic diagram of the structure of Example B of the present invention.

[0029] In the figure: crystallizer body 1, insulation chamber 2, cold and hot medium inlet 201, cold and hot medium outlet 202, first cold and hot medium valve 203, second cold and hot medium valve 204, fixed frame 3, filter plate 4, reflux pipe 5, booster pump 6, first valve 7, rotating shaft 8, rectangular stirring wheel 9, hollow pipe 10, first bearing 11, first transmission wheel 12, transmission belt 13, second transmission wheel 14, drive motor 15, air inlet pipe 16, second bearing 17, sealing rubber ring 18, drying vent 19, lactide discharge pipe 20, second valve 21, first connecting shaft 22, second connecting shaft 23, scraper 24, protective coating 25, telescopic rod 26, spring 27, L-shaped connecting rod 28, T-shaped limit block 29, limit slide 30, support leg 31, feed pipe 32, third valve 33, filter element 34, wind outlet 35. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Example 1

[0032] Reference Figure 1 and Figure 4-5A lactide circulation crystallization and drying device in a polylactic acid synthesis process comprises a crystallizer body 1 and a heat preservation chamber 2. A filter plate 4 is arranged on the inner wall of the crystallizer body 1. The filter plate 4 divides the crystallizer body 1 into an upper cavity and a lower cavity. A rotating shaft 8 is vertically inserted into the upper end wall of the crystallizer body 1. Rectangular stirring wheels 9 are symmetrically arranged on both sides of the outer wall of the rotating shaft 8 and located in the upper cavity. The rotating shaft 8 penetrates the upper end wall of the crystallizer body 1. The outer wall of the upwardly extending end of the rotating shaft 8 is sleeved with a first transmission wheel 12. The outer wall of the first transmission wheel 12 is connected to a second transmission wheel through a transmission belt 13. The inner wall of the second transmission wheel 14 is vertically plugged with a rotating shaft, and the bottom of the rotating shaft is connected to a driving motor 15. The first connecting shaft 22 is symmetrically arranged on both sides of the bottom of the rotating shaft 8 and located in the lower cavity, and a telescopic rod 26 is horizontally fixed to the end of the first connecting shaft 22 away from the rotating shaft 8, and a spring 27 is sleeved on the outer wall of the telescopic rod 26. The second connecting shaft 23 is horizontally fixed to the end of the telescopic rod 26 away from the first connecting shaft 22, and a scraper 24 is horizontally fixed to the end of the second connecting shaft 23 away from the telescopic rod 26. The upper and lower side walls of the first connecting shaft 22 are respectively provided with An L-shaped connecting rod 28 is provided, and a T-shaped stopper 29 is provided at one end of the L-shaped connecting rod 28 away from the first connecting shaft 22, and the T-shaped stopper 29 extends toward the outer wall of the second connecting shaft 23, and a stopper slide 30 corresponding to the T-shaped stopper 29 is provided on one side of the outer wall of the second connecting shaft 23, a hollow pipe 10 is provided on the inner wall of the rotating shaft 8, and drying vents 19 are symmetrically connected to the bottom of the hollow pipe 10 on both sides, an air inlet pipe 16 is plugged into the upper end of the hollow pipe 10, and a second bearing 17 is sleeved on the outer wall of the connection between the air inlet pipe 16 and the hollow pipe 10, and the crystal The bottom of the crystallizer body 1 is connected to a lactide discharge pipe 20, and the side wall of the lactide discharge pipe 20 is connected to a reflux pipe 5, the reflux pipe 5 passes through the insulation chamber 2 and extends upward to be connected to the outer wall of the crystallizer body 1, a booster pump 6 and a first valve 7 are installed on the reflux pipe 5, one side of the upper end of the crystallizer body 1 is connected to a feed pipe 32, and a third valve 33 is provided on the feed pipe 32, one end of the air inlet pipe 16 is externally connected to a hot air blower, and the booster pump 6, the drive motor 15 and the hot air blower are electrically connected to the mains through external control switches.

[0033] The bottom of the crystallizer body 1 is symmetrically provided with fixing frames 3, and one end of the fixing frame 3 away from the crystallizer body 1 is fixedly connected to the inner wall of the insulation chamber 2. The fixing frame 3 can play a role of fixing and supporting the crystallizer body 1.

[0034] A protective coating 25 is provided on one side of the outer wall of the scraper 24 , and the protective coating 25 is made of cuprous oxide paint, which has strong corrosion resistance and chemical stability, is insoluble in organic solvents, and can extend the service life of the scraper 24 .

[0035] Among them, a sealing rubber ring 18 is sleeved on the outer wall of the air inlet pipe 16 and located on the upper end of the rotating shaft 8. The sealing rubber ring 18 can achieve an effective sealing effect to avoid leakage during ventilation and drying.

[0036] Among them, the bottom side of the insulation chamber 2 is connected to a cold and hot medium inlet 201, and a first cold and hot medium valve 203 is provided on the pipeline of the cold and hot medium inlet 201, and the upper end side of the insulation chamber 2 is connected to a cold and hot medium outlet 202, and a second cold and hot medium valve 204 is provided on the pipeline of the cold and hot medium outlet 202. When the first cold and hot medium valve 203 and the second cold and hot medium valve 204 are opened at the same time, the cold medium or the hot medium enters through the cold and hot medium inlet 201 and is then discharged through the cold and hot medium outlet 202, thereby achieving a heating or cooling effect.

[0037] A second valve 21 is provided at the bottom of the lactide discharge pipe 20, and the second valve 21 is opened to discharge the finally dried solid lactide.

[0038] The outer wall of the connection between the rotating shaft 8 and the filter plate 4 is sleeved with a first bearing 11 . The first bearing 11 is provided to reduce the friction between the rotating shaft 8 and the filter plate 4 , thereby facilitating the rotation of the first bearing 11 .

[0039] The bottom of the heat preservation chamber 2 is fixedly connected with support legs 31 on all sides thereof, and the support legs 31 are provided to provide a fixed support for the heat preservation chamber 2 .

[0040] Working principle: In the present invention, when in use, first open the third valve 33, and the solvent enters the crystallizer body 1 through the feed pipe 32 to dissolve the lactide. At this time, the heat medium is introduced from the cold and hot medium inlet 201 to heat the crystallizer body 1 and accelerate the dissolution;

[0041] At this time, the driving motor 15 is started, and the driving motor 15 drives the second transmission wheel 14 to rotate through the rotating shaft, and the second transmission wheel 14 drives the first transmission wheel 12 to rotate through the transmission belt 13, and the first transmission wheel 12 drives the rotating shaft 8 to rotate, and the rotating shaft 8 drives the rectangular stirring wheel 9 on the outer wall to fully stir the mixture, thereby improving the dissolution effect;

[0042] After that, a part of the impurities will be filtered by the filter plate 4, and the filtered mother liquor will flow back to the crystallizer body 1 under the pressure of the booster pump 6, and will be mixed and stirred again, and will be filtered and impurities removed by the filter plate 4 again, so that the mother liquor will be more pure and the crystallization effect will be better; after multiple cycles of filtration, the first valve 7 is closed, and the mother liquor stays in the lower cavity of the crystallizer body 1, and then the refrigerant is introduced through the cold and hot medium inlet 201 to accelerate the crystallization of lactide, and the second valve 21 is opened to discharge the waste liquid, and the second valve 21 is closed again, and then the hot air blower passes through the air inlet pipe 16 to pass hot air into the hollow pipe 10, and the hot air passes through the drying vent 19 to dry and dehumidify the crystals, thereby improving the production and processing efficiency, and the third valve 33 can be opened to discharge the gas when the hot air is introduced;

[0043] When the rotating shaft 8 rotates, the first connecting shaft 22 rotates, and the first connecting shaft 22 drives the second connecting shaft 23 to rotate through the telescopic rod 26. The second connecting shaft 23 drives the scraper 24 to scrape off the crystals attached to the inner wall of the crystallizer body 1, thereby avoiding the crystals from accumulating on the inner wall of the crystallizer body 1, which has a certain impact on the production and processing efficiency.

[0044] Example 2

[0045] Reference Figure 2 and Figure 4-5 The difference between this embodiment and embodiment 1 is that a filter element 34 is provided on the inner wall of the reflux pipe 5. The filter element 34 can further filter the impurities in the reflux solvent.

[0046] For other structures not described, refer to Example 1.

[0047] Working principle: In the present invention, when in use, first open the third valve 33, and the solvent enters the crystallizer body 1 through the feed pipe 32 to dissolve the lactide. At this time, the heat medium is introduced from the cold and hot medium inlet 201 to heat the crystallizer body 1 and accelerate the dissolution;

[0048] At this time, the driving motor 15 is started, and the driving motor 15 drives the second transmission wheel 14 to rotate through the rotating shaft, and the second transmission wheel 14 drives the first transmission wheel 12 to rotate through the transmission belt 13, and the first transmission wheel 12 drives the rotating shaft 8 to rotate, and the rotating shaft 8 drives the rectangular stirring wheel 9 on the outer wall to fully stir the mixture, thereby improving the dissolution effect; thereafter, a part of the impurities will be filtered by the filter plate 4, and the filtered mother liquor will flow back into the crystallizer body 1 under the pressure of the booster pump 6, and will be mixed and stirred again, and will be filtered and impurities removed by the filter plate 4 again, so that the mother liquor is more pure and the crystallization effect is better;

[0049] After multiple cycles of filtration, the first valve 7 is closed, and the mother liquid stays in the lower cavity of the crystallizer body 1. The refrigerant is introduced through the cold and hot medium inlet 201 to accelerate the crystallization of lactide, and the second valve 21 is opened to discharge the waste liquid, and the second valve 21 is closed again. After that, the hot air blower passes hot air into the hollow pipe 10 through the air inlet pipe 16, and the hot air passes through the drying vent 19 to dry and dehumidify the crystals, thereby improving the production and processing efficiency. When the hot air is introduced, the third valve 33 can be opened to discharge the gas;

[0050] When the rotating shaft 8 rotates, the first connecting shaft 22 rotates, and the first connecting shaft 22 drives the second connecting shaft 23 to rotate through the telescopic rod 26. The second connecting shaft 23 drives the scraper 24 to scrape off the crystals attached to the inner wall of the crystallizer body 1, thereby avoiding the crystals from accumulating on the inner wall of the crystallizer body 1, which has a certain impact on the production and processing efficiency.

[0051] Example 3

[0052] Reference Figure 3-5 The difference between this embodiment and embodiment 1 is that a filter element 34 is provided on the inner wall of the reflux pipe 5. The filter element 34 can further filter the impurities in the reflux solvent.

[0053] Among them, the bottom of the hollow pipe 10 is connected to an air outlet 35, and the air outlet 35 extends downward through the bottom wall of the rotating shaft 8. The air outlet 35 can blow away the solid lactide accumulated at the upper port of the lactide discharge pipe 20 to avoid blockage and improve processing efficiency.

[0054] For other structures not described, refer to Example 1.

[0055] In the present invention, when in use, firstly, the third valve 33 is opened, and the solvent enters the crystallizer body 1 through the feed pipe 32, thereby dissolving the lactide. At this time, the heat medium is introduced from the cold and hot medium inlet 201, thereby heating the crystallizer body 1 and accelerating the dissolution;

[0056] At this time, the driving motor 15 is started, and the driving motor 15 drives the second transmission wheel 14 to rotate through the rotating shaft, and the second transmission wheel 14 drives the first transmission wheel 12 to rotate through the transmission belt 13, and the first transmission wheel 12 drives the rotating shaft 8 to rotate, and the rotating shaft 8 drives the rectangular stirring wheel 9 on the outer wall to fully stir the mixture, thereby improving the dissolution effect;

[0057] After that, a part of the impurities will be filtered by the filter plate 4, and the filtered mother liquor will flow back to the crystallizer body 1 under the pressure of the booster pump 6, and will be mixed and stirred again, and will be filtered and removed by the filter plate 4 again, so that the mother liquor will be more pure and the crystallization effect will be better; after multiple cycles of filtration, the first valve 7 is closed, and the mother liquor will stay in the lower cavity of the crystallizer body 1, and then the refrigerant will be introduced through the cold and hot medium inlet 201 to accelerate the crystallization of lactide, and the second valve 21 will be opened to discharge the waste liquid, and the second valve 21 will be closed again, and then the hot air blower will pass through the air inlet pipe 16 to pass hot air into the hollow pipe 10, and the hot air will pass through the drying vent 19 and the air outlet 35 to dry and dehumidify the crystals, thereby improving the production and processing efficiency, and the third valve 33 can be opened to discharge the gas when the hot air is introduced;

[0058] When the rotating shaft 8 rotates, the first connecting shaft 22 rotates, and the first connecting shaft 22 drives the second connecting shaft 23 to rotate through the telescopic rod 26. The second connecting shaft 23 drives the scraper 24 to scrape off the crystals attached to the inner wall of the crystallizer body 1, thereby avoiding the crystals from accumulating on the inner wall of the crystallizer body 1, which has a certain impact on the production and processing efficiency.

[0059] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0060] In the present invention, unless otherwise clearly specified and limited, the terms "set", "install", "connect", "connect", "fix" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection, a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0061] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A lactide circulating crystallization and drying device in a polylactic acid synthesis process, comprising a crystallizer body (1) and an insulation chamber (2), characterized in that: The inner wall of the crystallizer body (1) is provided with a filter plate (4), and the filter plate (4) divides the crystallizer body (1) into an upper cavity and a lower cavity. A rotating shaft (8) is vertically inserted into the upper end wall of the crystallizer body (1), and rectangular stirring wheels (9) are symmetrically arranged on both sides of the outer wall of the rotating shaft (8) and located in the upper cavity. The rotating shaft (8) passes through the upper end wall of the crystallizer body (1), and the outer wall of the upwardly extending end is sleeved with a first transmission wheel (12). The outer wall of the first transmission wheel (12) is connected to a second transmission wheel (14) through a transmission belt (13). The second transmission wheel (14) is A rotating shaft is vertically inserted into the inner wall, and a driving motor (15) is connected to the bottom of the rotating shaft. A first connecting shaft (22) is symmetrically arranged on both sides of the bottom of the rotating shaft (8) and located in the lower cavity. A telescopic rod (26) is horizontally fixed to one end of the first connecting shaft (22) away from the rotating shaft (8). A spring (27) is sleeved on the outer wall of the telescopic rod (26). A second connecting shaft (23) is horizontally fixed to one end of the telescopic rod (26) away from the first connecting shaft (22). A scraper (24) is horizontally fixed to one end of the second connecting shaft (23) away from the telescopic rod (26). The first connecting shaft (22) The upper and lower side walls of the rotating shaft (8) are respectively provided with L-shaped connecting rods (28), and one end of the L-shaped connecting rod (28) away from the first connecting shaft (22) is provided with a T-shaped stop block (29), the T-shaped stop block (29) extends toward the outer wall of the second connecting shaft (23), and one side of the outer wall of the second connecting shaft (23) is provided with a stop slot (30) corresponding to the T-shaped stop block (29), the inner wall of the rotating shaft (8) is provided with a hollow pipe (10), and the bottom two sides of the hollow pipe (10) are symmetrically connected with drying vents (19), the upper end of the hollow pipe (10) is plugged with an air inlet pipe (16), and the air inlet pipe (16) is connected to the inner wall of the rotating shaft (8). 6) A second bearing (17) is sleeved on the outer wall of the connection with the hollow pipe (10); the bottom of the crystallizer body (1) is connected to a lactide discharge pipe (20), and the side wall of the lactide discharge pipe (20) is connected to a reflux pipe (5); the reflux pipe (5) passes through the insulation chamber (2) and extends upward to be connected to the outer wall of the crystallizer body (1); a booster pump (6) and a first valve (7) are installed on the reflux pipe (5); one side of the upper end of the crystallizer body (1) is connected to a feed pipe (32), and a third valve (33) is provided on the feed pipe (32); The inner wall of the return pipe (5) is provided with a filter element (34); The bottom of the hollow pipe (10) is connected to an air outlet (35), and the air outlet (35) passes through the bottom wall of the rotating shaft (8) and extends downward. The air outlet (35) can blow away the solid lactide accumulated at the upper port of the lactide discharge pipe (20).

2. The lactide circulating crystallization and drying equipment in the polylactic acid synthesis process according to claim 1, characterized in that: Fixed frames (3) are symmetrically provided on both sides of the bottom of the crystallizer body (1), and one end of the fixed frame (3) away from the crystallizer body (1) is fixedly connected to the inner wall of the insulation chamber (2).

3. The lactide circulating crystallization and drying equipment in the polylactic acid synthesis process according to claim 1, characterized in that: A protective coating (25) is provided on one side of the outer wall of the scraper (24), and the protective coating (25) is made of cuprous oxide paint.

4. The lactide circulating crystallization and drying equipment in the polylactic acid synthesis process according to claim 1, characterized in that: A sealing rubber ring (18) is sleeved on the outer wall of the air inlet pipe (16) and located at the upper end of the rotating shaft (8).

5. The lactide circulating crystallization and drying equipment in the polylactic acid synthesis process according to claim 1, characterized in that: The bottom side of the heat preservation chamber (2) is connected to a cold and hot medium inlet (201), and a first cold and hot medium valve (203) is provided on the pipeline of the cold and hot medium inlet (201); the upper end side of the heat preservation chamber (2) is connected to a cold and hot medium outlet (202), and a second cold and hot medium valve (204) is provided on the pipeline of the cold and hot medium outlet (202).

6. The lactide circulating crystallization and drying equipment in the polylactic acid synthesis process according to claim 1, characterized in that: A second valve (21) is provided at the bottom of the lactide discharge pipeline (20).

7. The lactide circulating crystallization and drying equipment in the polylactic acid synthesis process according to claim 1, characterized in that: A first bearing (11) is sleeved on the outer wall of the connection between the rotating shaft (8) and the filter plate (4).

8. The lactide circulating crystallization and drying equipment in the polylactic acid synthesis process according to claim 1, characterized in that: Support legs (31) are fixedly connected to four sides of the bottom of the insulation chamber (2).

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