A device for preparing oligomeric lactic acid by using a four-stage dehydration reaction kettle

Abstract

The application provides a process and equipment for preparing oligomeric lactic acid by using a four-stage dehydration reactor, which is used in the lactic acid dehydration and polycondensation process in a two-step process for synthesizing lactide, and is used for continuous dehydration and preparation of oligomeric lactic acid. The dehydration reactor is an adjustable reactor, which not only solves the problem of material conveying of the reactor, but also can continuously work, and can prevent the problems of material adhesion and difficult discharge in the reactor. The technical solution is that four reactors for reaction are connected in series to carry out multistage dehydration, the lower ends of the reactors are respectively used for feeding and discharging, the feeding and discharging parts of the reactors are connected in series, stirring blades are rotatably connected in the reactors, an insulation shell is arranged outside the reactors and used for insulating the reactors, a scraping mechanism is arranged at the lower end of the inner side of the reactor and matched with the reactor, and a feeding and discharging control mechanism is arranged at the lower end of the reactor.

Description

Technical Field

[0001] This invention relates to the field of lactide preparation, and in particular to an apparatus for preparing oligolactic acid using a four-stage dehydration process in an adjustable reactor. Background Technology

[0002] Lactide is a cyclic dimer of lactic acid and a major raw material for the synthesis of oligolactic acid (PLA). High-performance polylactic acid (PLA) is mainly produced through stereospecific ring-opening polymerization of L-lactide and D-lactide, requiring high optical purity of the lactide. Since L-lactide, the raw material for L-lactide, is obtained through starch fermentation, the raw material source is green, recyclable, and inexpensive, making it the primary choice for industrial production. This project produces L-lactide, also known as levolactide, which is used as a raw material to synthesize PLA. This allows for precise control of the relative molecular weight of PLA and represents the main technology currently used in PLA production both domestically and internationally.

[0003] Currently, domestically produced lactide (PL) products have low optical purity and high prices, mainly due to: 1. High viscosity of the reaction system, resulting in unstable polycondensation and depolymerization / cyclization processes and low overall yield. 2. Difficulty in controlling reaction conditions, leading to inconsistent product quality. 3. The use of stannous octoate and other metal catalysts, which are toxic and difficult to completely remove, posing environmental safety hazards. Therefore, China's domestic PLA production relies heavily on imports for lactide, severely hindering the development of the PLA industry. Developing low-cost, high-purity industrial-scale lactide production technology is urgently needed.

[0004] Currently, the main method used in the production and laboratory research of commercial lactide abroad is a two-step process: using lactic acid as a raw material, firstly, lactic acid oligomers are produced through condensation polymerization, and then depolymerization and cyclization are performed to produce lactide. During the dehydration condensation of lactic acid, oligomers with 5-10 lactic acid molecules are most suitable for depolymerization into lactide. As free water and intermolecular water are gradually removed, the viscosity of the reaction system increases, making it difficult for water molecules to diffuse out of the system. Increasing the temperature to remove water molecules can easily result in excessively high molecular weight lactic acid oligomers, exceeding the suitable depolymerization range and leading to a large amount of gel-like residue. Simultaneously, excessively high temperatures can also cause lactic acid loss, resulting in a dark brown color and severe carbonization, affecting the yield. Therefore, ensuring the removal of free water and intermolecular water while obtaining suitable lactic acid oligomers during the dehydration condensation of lactic acid is one of the most critical technical challenges in the industrial production of lactide. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, this invention provides a device for preparing oligolactic acid using an adjustable reactor with four-stage dehydration. This device not only solves the problems of material transportation and recycling in the reactor during the dehydration reaction, but also enables continuous operation without shutting down the reactor. It can also ensure the overall sealing of the reactor while transporting the material. Furthermore, the rotating fan blade angle inside the reactor can be adjusted according to different working conditions, and it can also prevent material adhesion and inconvenience in discharging from the inside of the reactor.

[0006] The technical solution includes four reaction vessels for carrying out the reaction. The lower ends of the reaction vessels are respectively used for feeding and discharging. The feeding and discharging points of each reaction vessel are connected in series for multi-stage dehydration. A stirring fan is rotatably connected inside the reaction vessel. An insulating shell is provided on the outside of the reaction vessel for heat preservation. The key feature is that a scraping mechanism is provided at the lower end of the inner side of the reaction vessel, which cooperates with the reaction vessel. A feeding and discharging control mechanism for feeding and discharging the reactants is provided at the lower end of the reaction vessel. The scraping mechanism includes a rotating ring rotatably connected to and sealed at the lower end of the reaction vessel. The upper end of the rotating ring extends into the inner side of the reaction vessel, while the lower end extends downwards out of the reaction vessel. Multiple scrapers are fixedly connected to the outer side of the upper end of the rotating ring. Each scraper cooperates with the lower end of the inner side of the reaction vessel. A movable plate is rotatably connected to the protruding end of each scraper. An electric telescopic rod is fixedly connected to the side of the plate. The extended end of the electric telescopic rod is rotatably connected to a middle rod. The extended end of the middle rod is rotatably connected to the middle of the movable plate. The feeding and discharging control mechanism includes a feeding and discharging control disc. The feeding and discharging control disc is located inside the rotating ring and rotates and is sealed to the rotating ring. The left and right ends of the feeding and discharging control disc are respectively provided with a vertically penetrating inlet and outlet. The upper surface of the feeding and discharging control disc is provided with two vertically penetrating slots between the inlet and outlet. Each vertical slot is vertically slidably connected to a guide plate. The lower end of the guide plate is vertically connected to the vertical slot through a second telescopic rod. The upper ends of the inlet and outlet are respectively provided with opening and closing covers. The opening and closing covers are vertically slidably connected to the feeding and discharging control disc through a vertically arranged third telescopic rod. The lower ends of the inlet and outlet are respectively connected to conveying equipment for inputting and outputting materials.

[0007] Preferably, the conveying equipment includes a feeding conveying device and a discharging conveying device, which are respectively connected to corresponding inlets and outlets. The feeding conveying device and the discharging conveying device each include a transversely arranged conveying roller. A conveying shaft is coaxially rotatably connected inside the conveying roller. A spiral conveying fan blade is provided on the conveying shaft. One end of the conveying roller extends upward to a connection port, which cooperates with the corresponding inlet or outlet. A material-pushing plate is provided at one end of the spiral conveying fan blade corresponding to the position of the connection port. The other end of the conveying roller in the feeding conveying device extends obliquely upward to a first connection port, and the other end of the conveying roller in the discharging conveying device extends obliquely downward to a second connection port.

[0008] Preferably, the reactor includes a cylindrical vessel body with a conical structure at the lower end and a scraping mechanism that cooperates with the inner surface of the conical structure.

[0009] Preferably, the stirring blade includes a fixed rod rotatably connected to the upper end of the reactor in a sealed manner. A stirring rod is coaxially rotatably and slidably connected inside the fixed rod. Multiple connecting shafts perpendicular to the axis of the stirring rod are evenly distributed around the lower circumference of the stirring rod. Vertically arranged sliding grooves are provided at the lower end of the fixed rod corresponding to the positions of each connecting shaft. A connecting block is rotatably connected to each connecting shaft. A stirring blade is fixedly connected to the outer side of each connecting block. An angle adjustment block extending downwards is fixedly connected to the lower end of each connecting block. An angle adjustment slot is opened on the left and right sides of each sliding groove corresponding to the positions of the connecting blocks. An adjusting handwheel is fixedly connected to the upper end of the stirring rod. A sealing positioning element is provided at the upper end of the fixed rod, which cooperates with the stirring rod and is used to seal and position the contact part. A drive gear is fixedly connected to the fixed rod below the sealing positioning element. The drive gear is driven by a drive motor fixedly connected to the upper end of the reactor.

[0010] Preferably, multiple connecting shafts evenly distributed around the circumference form a group, the number of connecting shaft groups on the stirring rod is greater than or equal to two, and the number and spacing of the angle adjustment slots opened on the fixed rod correspond to each connecting block.

[0011] Preferably, the sealing and positioning component includes a fixed column rotatably connected to the upper end of the fixed rod, and a first arc-shaped sealing component and a second arc-shaped sealing component rotatably connected to the fixed column. An elastic sealing strip is fixedly connected to the inner side of the first arc-shaped sealing component and the second arc-shaped sealing component respectively. The position of the elastic sealing strip is matched with the upper end of the fixed rod to seal the connection between the upper end of the fixed rod and the stirring rod.

[0012] Preferably, there are two guide plates located at the front and rear ends of the feed control panel, respectively. The side of the guide plate facing the vertical slot is provided with an oblique guide groove. The guide plate facing the feed inlet is the feed guide plate, and the guide plate facing the grass discharge outlet is the discharge guide plate.

[0013] Preferably, the heat-insulating shell includes a heat-insulating shell covering the outside of the reactor. The inner side of the heat-insulating shell is provided with a plurality of annularly arranged isolation plates. The adjacent isolation plates form a gas channel. The left and right ends of the heat-insulating shell are respectively provided with vertically arranged dispersion cavities that are connected to each gas channel on the inner side of the heat-insulating shell. Vents extend outward from the outer side of the dispersion cavities.

[0014] Preferably, the system also includes a negative pressure generator fixedly connected to the upper end of the reactor for controlling the pressure inside the reactor and a pressure gauge for displaying the pressure inside the reactor.

[0015] The beneficial effects of this invention are: This invention solves the problems of material conveying and recycling in the reactor during dehydration reactions. It can operate continuously without shutting down the machine, and can ensure the overall sealing of the reactor while conveying materials. The rotating fan blade angle inside the reactor can be adjusted according to different working conditions, and it can also prevent material from sticking to the inside of the reactor and making it difficult to discharge. It can also perform multi-stage processing by circulating multiple reactors, and the connection between the reactors is simple and easy to operate. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall invention.

[0017] Figure 2 This is an overall sectional view of the present invention.

[0018] Figure 3 This is a schematic diagram showing the unfolded structure of the scraping mechanism of the present invention.

[0019] Figure 4 This is a schematic diagram of the scraping mechanism structure of the present invention.

[0020] Figure 5 This is a cross-sectional view of the thermal insulation shell of the present invention.

[0021] Figure 6 This is a schematic diagram of the conveyor roller of the present invention.

[0022] Figure 7 This is a cross-sectional view of the conveyor roller of the present invention.

[0023] Figure 8 This is a schematic diagram of the material feeding and discharging control mechanism of the present invention.

[0024] Figure 9 This is a schematic diagram of the stirring fan blade structure of the present invention.

[0025] Figure 10 This is an overall assembly drawing of the present invention.

[0026] Figure Labels 1. Reactor; 2. Stirring blade; 3. Insulated outer shell; 4. Rotating ring; 5. Scraper; 6. Movable plate; 7. Electric telescopic rod; 8. Intermediate rod; 9. Inlet / outlet control panel; 10. Vertical slot; 11. Guide plate; 12. Opening / closing cover; 13. Conveying roller; 14. Conveying shaft; 15. Spiral conveyor blade; 16. Connection port; 17. Feeding plate; 18. Fixed rod; 19. Stirring rod; 20. Sliding groove; 21. Connecting block; 22. Angle adjusting block; 23. Angle adjusting slot; 24. Adjusting handwheel; 25. Sealing and positioning component; 26. First arc-shaped seal; 27. Second arc-shaped seal; 28. Elastic sealing strip; 29. ​​Isolation plate; 30. Vent. Detailed Implementation

[0027] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0028] In this embodiment, multiple reactors 1 are used, typically four reactors 1 for four-stage dehydration. Each reactor 1 has a cylindrical body, and the lower end of each reactor 1 has a conical structure. This allows the material to fall to the lower end of the reactor 1 under gravity when no external force is applied. The lower end of the reactor 1 has material inlets and outlets, and the inlets and outlets of adjacent reactors 1 correspond, allowing material processed in the first reactor 1 to directly enter the second reactor 1 for multi-stage processing. The material is fed and discharged through the lower end of the reactor 1. A conical structure is located on the lower inner side of the reactor 1. There is a scraping mechanism for driving the material and preventing the material from sticking to the lower end face of the reactor 1. A fixed rod 18 is provided at the upper end of the reactor 1 and extends downward. A stirring rod 19 is rotatably connected inside the fixed rod 18. A stirring fan blade 2 for stirring inside the reactor 1 is rotatably connected to the stirring rod 19. An insulation shell 3 is provided on the outer side of the reactor 1 and is attached to the outer surface of the reactor 1. The insulation shell 3 has a layered design. At the same time, the left and right ends of the insulation shell 3 are respectively connected to the air vents 30. The heated air is conducted through the air vents 30, and the layered design allows for heating and insulation of various parts of the reactor 1.

[0029] The scraping mechanism at the lower end of the reactor 1 includes a rotating ring 4 rotatably connected to the lower end of the reactor 1. The rotating ring 4 is annular, with its upper end extending into the reactor 1 and its lower end extending downwards out of the reactor 1. Multiple radiating scrapers 5 are fixedly connected to the upper end of the rotating ring 4, evenly distributed around its circumference. A gear ring is fixedly connected to the outer surface of the lower end of the rotating ring 4 extending out of the reactor 1. A drive motor for driving the gear ring is fixedly connected to the reactor 1. The drive motor and gears are connected... The rotating ring 4 is driven by a scraper 5 at its upper end, which engages with the conical inner surface of the lower end of the reactor 1. The rotation of the scraper 5 drives and lifts the material at the lower end of the reactor 1, ensuring that the material is evenly distributed within the reactor 1. A movable plate 6 is rotatably connected to the extended end of each scraper 5, and an electric telescopic rod 7 is fixedly connected to the scraper 5. The middle of the movable plate 6 and the extended end of the electric telescopic rod 7 are rotatably connected to one end of a middle rod 8. The movable plate 6 has two states: a retracted state and an extended state. When the movable plate 6 is in its retracted state, it is pressed tightly against the side of the scraper 5. The width of the movable plate 6 corresponds to the width of the scraper 5, allowing it to be hidden in the retracted state. When the movable plate 6 is in the retracted state, the extension of the electric telescopic rod 7 drives the middle rod 8 to move. One end of the middle rod 8 is rotatably connected to the middle of the movable plate 6, so the middle rod 8 drives the movable plate 6 to move as the electric telescopic rod 7 extends. One end of the movable plate 6 is rotatably connected to the extended end of the scraper 5, so the movable plate 6 rotates along the rotatable connection of the extended end of the scraper 5. When the scraper 5 is in the retracted state, the movable plate 6 will cooperate with the outer circumference of the inner space of the reactor 1. In this way, when the rotating ring 4 rotates, it drives the material to the lower inner side of the reactor 1, preventing the material from sticking to the inner side of the reactor 1. The rotating ring 4 and the reactor 1 must be sealed while rotating to prevent the material from leaking downwards. The retracted and extended states can be selected as needed.

[0030] A feed / discharge control disc 9 is provided inside the rotating ring 4. The feed / discharge control disc 9 itself does not rotate; only the rotating ring 4 rotates. Therefore, the contact area between the outer side of the feed / discharge control disc 9 and the rotating ring 4 is rotatably connected and remains sealed. Vertically penetrating feed inlets and outlets are respectively opened at the left and right ends of the feed / discharge control disc 9. The feed inlets are responsible for the material entering the reactor 1, while the outlets are responsible for the material being discharged from the reactor 1. Vertical slots 10 are provided on the feed / discharge control disc 9 between the feed inlets and outlets. There are two vertical slots 10, located at the front and rear ends respectively. Each vertical slot 10 is vertically slidably connected to a guide plate 11. The guide plate 11 is vertically slidably connected to the vertical... The groove 10 is sealed within the sliding connection. The lower ends of each guide plate 11 are connected to the feed / discharge control panel 9 via a second telescopic rod. One side of each guide plate 11 has a guide groove, with the guide grooves on the two guide plates 11 facing opposite directions. One guide plate 11's guide groove faces the feed inlet, while the other's faces the discharge outlet. Each guide plate 11 has a retracted state and an extended state. In the retracted state, it is retracted downwards into the corresponding vertical groove 10 via the second telescopic rod at its lower end. In the extended state, it extends upwards via the second telescopic rod, completely exposing the guide groove. When the material is driven by the scraper 5, it will rotate. The material passing through the guide groove will be guided into the corresponding feed inlet or discharge outlet by the guide groove, which also serves to intercept the material. The feed inlet and discharge outlet are respectively equipped with opening and closing covers 12 to cover and close the feed inlet and discharge outlet. The opening and closing covers 12 correspond to the feed inlet and discharge outlet and are controlled to move up and down by a vertically arranged third telescopic rod. When the opening and closing covers 12 move upward, they open; when the opening and closing covers 12 move downward, they close at the corresponding feed inlet or discharge outlet. During feeding, the material enters the reactor 1 from the feed inlet. At this time, the opening and closing covers 12 at the feed inlet are opened, and the material enters the reactor. The material in reactor 1 is dispersed by scraper 5. After feeding, the opening and closing cover 12 is closed to seal the feed port. When discharging, the opening and closing cover 12 at the discharge port is opened upward, and the guide plate 11 is raised. At the same time, the rotation speed of the rotating ring 4 is reduced. At this time, the material will fall on the bottom of reactor 1. When the material passes through the guide plate 11, it is guided into the open discharge port through the guide groove on the guide plate 11. When there is a lot of material, the two guide plates 11 intercept the material and slow it down. When there is a little material, the guide plate 11 corresponding to the guide groove that is not facing the discharge port is lowered to prevent the material from getting stuck near the guide plate 11.

[0031] A hollow rod 18 is rotatably connected to the upper end of the reactor 1. A stirring rod 19 is rotatably connected inside the rod 18. Multiple connecting blocks 21 are evenly distributed around the lower circumference of the stirring rod 19. The rotation axis of each connecting block 21 is perpendicular to the axis of the stirring rod 19. A stirring blade 2 is fixedly connected to the outer side of each connecting block 21. An angle adjustment block 22 extends downward from the lower end of each connecting block 21. Vertically arranged sliding grooves 20 are provided on the rod 18 at positions corresponding to the connecting blocks 21. Each connecting block 21 and angle adjustment block 22... Both are rotatably and slidably connected in the sliding groove 20. Angle adjustment slots 23 are respectively opened on the outer side of the sliding groove 20. By rotating the relative position of the stirring rod 19 with respect to the fixed rod 18, the connecting block 21 on the stirring rod 19 rotates into the angle adjustment slot 23 while the corresponding angle adjustment block 22 remains in the original position, thereby completing the adjustment of the rotation angle of the stirring blade 2. When different angles of the stirring blade 2 are needed, the relative position of the stirring rod 19 with respect to the fixed rod 18 can be adjusted steplessly.

[0032] When the material enters the reactor 1, the pressure inside the reactor 1 is adjusted to the set value by the negative pressure generator located at the upper end of the reactor 1. Then, the material is lifted by the drive of the scraper 5 and then stirred evenly by the stirring fan blade 2. The heat preservation shell 3 located outside the reactor 1 always provides heat preservation and heating. The material is conveyed by conveying equipment at both the input and output. Conveying equipment is connected to the lower end of the inlet and outlet respectively. The conveying equipment includes a horizontally arranged conveying roller 13. A conveying shaft 14 is rotatably connected inside the conveying roller 13, and a device that cooperates with the conveying roller 13 is fixedly connected to the conveying shaft 14. The spiral conveyor blades 15 are provided, and the conveyor shaft 14 extends to the outside of the conveyor drum 13 and is equipped with a drive motor. One end of the conveyor drum 13 extends upward and cooperates with the feed inlet and the discharge outlet. The spiral conveyor blades 15 are equipped with a feeding plate 17 at the position corresponding to the feed inlet or the discharge outlet. There are two conveying devices, which correspond to the feed inlet and the discharge outlet respectively. The difference between the two conveying devices is that the outer side of the conveyor drum 13 extends to the first connection port and the second connection port at an angle upward or downward. The feed and discharge of multiple reaction vessels 1 are connected in series through the first connection port and the second connection port respectively to complete the multi-stage dehydration reaction.

[0033] Each reactor 1 is protected under nitrogen (99.99%). Each reactor 1 is connected to a gas phase pipeline to collect the water generated during evaporation and reaction. Reactors 1 through 4 sequentially perform first-stage dehydration, second-stage dehydration, third-stage dehydration, and fourth-stage dehydration. The first-stage dehydration mainly removes free water from the raw material lactic acid. The heating temperature of reactor 1 is maintained at 120-140℃, and the vacuum degree inside reactor 1 is 400-650 Tor. The second to fourth stages of dehydration mainly remove water, also called bound water, generated during the reaction process, thus completing the dehydration work. The heating temperature of the second reactor 1 should be maintained at 140-170℃, and the vacuum degree inside reactor 1 should be 200-500 Tor. The heating temperature of the third reactor 1 should be maintained at 150-180℃, and the vacuum degree inside reactor 1 should be 100-300 Tor. The heating temperature of the fourth reactor 1 should be maintained at 150-190℃, and the vacuum degree inside reactor 1 should be 100-300 Tor. Each reactor is connected to a fractionation tower through a gas phase pipeline to separate water from the volatile mixture and discharge the water. The discharged water can be recycled or stored in other processes.

Claims

1. An apparatus for preparing oligolactic acid using a four-stage dehydration process in an adjustable reactor, comprising four reactors (1) for carrying out the reaction, wherein the lower ends of the reactors (1) are respectively used for feeding and discharging, the feeding and discharging parts of each reactor (1) are connected in series to perform multi-stage dehydration, a stirring fan (2) is rotatably connected inside the reactor (1), and an insulating shell (3) is provided on the outside of the reactor (1) for heat preservation, characterized in that, The lower end of the inner side of the reactor (1) is provided with a scraping mechanism that cooperates with the reactor (1). The lower end of the reactor (1) is provided with a feeding and discharging control mechanism for feeding and discharging the reaction materials. The scraping mechanism includes a rotating ring (4) that is rotatably connected to the lower end of the reactor (1) and sealed. The upper end of the rotating ring (4) extends into the inner side of the reactor (1) and the lower end of the rotating ring (4) extends downward out of the reactor (1). Multiple scrapers (5) are fixedly connected to the outer side of the upper end face of the rotating ring (4). Each scraper (5) cooperates with the lower end face of the inner side of the reactor (1). Each scraper (5) has a movable plate (6) rotatably connected to its extended end. An electric telescopic rod (7) is fixedly connected to the side of the scraper (5). An intermediate rod (8) is rotatably connected to the extended end of the electric telescopic rod (7). The extended end of the intermediate rod (8) is rotatably connected to the middle of the movable plate (6). The feeding and discharging control mechanism includes a feeding and discharging control panel (9), which is located inside the rotating ring (4) and rotates and is sealed to the rotating ring (4). The feeding and discharging control panel (9) has a vertically penetrating inlet and outlet at its left and right ends respectively. The upper surface of the feeding and discharging control panel (9) has two vertically penetrating slots (10) between the inlet and outlet. Each vertical slot (10) is vertically slidably connected to a guide plate (11). The lower end of the guide plate (11) is vertically connected to the vertical slot (10) through a second telescopic rod. The upper ends of the inlet and outlet are respectively provided with opening and closing covers (12). The opening and closing covers (12) are vertically slidably connected to the feeding and discharging control panel (9) through a vertically arranged third telescopic rod. The lower ends of the inlet and outlet are respectively connected to conveying equipment for inputting and outputting materials. The stirring blade (2) includes a fixed rod (18) that is rotatably and sealed to the upper end of the reactor (1). A stirring rod (19) is rotatably and slidably connected inside the fixed rod (18). Multiple connecting shafts perpendicular to the axis of the stirring rod (19) are evenly distributed around the lower end of the stirring rod (19). Vertically arranged sliding grooves (20) are provided at the lower end of the fixed rod (18) corresponding to the positions of each connecting shaft. A connecting block (21) is rotatably connected to each connecting shaft. A stirring blade (2) is fixedly connected to the outer side of each connecting block (21). The lower end of each connecting block (21) is fixedly connected to... An angle adjustment block (22) extending downwards is connected to the sliding groove (20). An angle adjustment slot (23) is opened on the left and right sides of each sliding groove (20) corresponding to the position of the connecting block (21). An adjustment handwheel (24) is fixedly connected to the upper end of the stirring rod (19). A sealing positioning component (25) is provided at the upper end of the fixed rod (18) to cooperate with the stirring rod (19) and to seal and position the contact part. A drive gear is fixedly connected to the fixed rod (18) below the sealing positioning component (25). The drive gear is driven by a drive motor fixedly connected to the upper end of the reactor (1). The sealing positioning component (25) includes a fixed column rotatably connected to the upper end of the fixed rod (18). A first arc-shaped sealing component (26) and a second arc-shaped sealing component (27) that cooperate with the fixed column are rotatably connected to the fixed column. An elastic sealing strip (28) is fixedly connected to the inner side of the first arc-shaped sealing component (26) and the second arc-shaped sealing component (27). The position of the elastic sealing strip (28) cooperates with the upper end of the fixed rod (18) to seal the connection between the upper end of the fixed rod (18) and the stirring rod (19).

2. The apparatus for preparing oligolactic acid using a four-stage dehydration process in an adjustable reactor according to claim 1, characterized in that, The conveying equipment includes a feeding conveying equipment and a discharging conveying equipment. The feeding conveying equipment and the discharging conveying equipment are respectively connected to the corresponding feed inlet and discharge outlet. The feeding conveying equipment and the discharging conveying equipment each include a transversely arranged conveying roller (13). A conveying shaft (14) is coaxially rotatably connected inside the conveying roller (13). A spiral conveying fan blade (15) is provided on the conveying shaft (14). A connection port (16) extends upward from one end of the conveying roller (13). The connection port (16) cooperates with the corresponding feed inlet or discharge outlet. A material-pushing plate (17) is provided at one end of the spiral conveying fan blade (15) corresponding to the position of the connection port (16). A first connection port extends obliquely upward from the other end of the conveying roller (13) in the feeding conveying equipment. A second connection port extends obliquely downward from the other end of the conveying roller (13) in the discharging conveying equipment.

3. The apparatus for preparing oligolactic acid using a four-stage dehydration process in an adjustable reactor according to claim 1, characterized in that, The reactor (1) includes a cylindrical vessel body, the lower end of which has a conical structure and the scraping mechanism is matched with the inner surface of the conical structure.

4. The apparatus for preparing oligolactic acid using a four-stage dehydration process in an adjustable reactor according to claim 1, characterized in that, Multiple connecting shafts evenly distributed around the circumference form a group. The number of connecting shaft groups on the stirring rod (19) is greater than or equal to two. The number and spacing of the angle adjustment slots (23) opened on the fixed rod (18) correspond to each connecting block (21).

5. The apparatus for preparing oligolactic acid using a four-stage dehydration process in an adjustable reactor according to claim 1, characterized in that, There are two guide plates (11) located at the front and rear ends of the feed control panel (9). The guide plates (11) are provided with oblique guide grooves on one side facing the vertical slot (10). The guide plate (11) facing the feed inlet is the feed guide plate (11), and the guide plate (11) facing the grass discharge outlet is the discharge guide plate (11).

6. The apparatus for preparing oligolactic acid using a four-stage dehydration process in an adjustable reactor according to claim 1, characterized in that, The heat insulation shell (3) includes a heat insulation shell covering the outside of the reactor (1). The inner side of the heat insulation shell is provided with a plurality of annularly arranged isolation plates (29). The adjacent isolation plates (29) form a gas channel. The left and right ends of the heat insulation shell (3) are respectively provided with vertically arranged dispersion cavities that are connected to each gas channel on the inner side of the heat insulation shell. Vents (30) extend outward from the outer side of the dispersion cavities.

7. The apparatus for preparing oligolactic acid using a four-stage dehydration process in an adjustable reactor according to claim 1, characterized in that, It also includes a negative pressure generator fixedly connected to the upper end of the reactor (1) for controlling the pressure inside the reactor (1) and a pressure gauge for displaying the pressure inside the reactor (1).

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