Polylactic acid synthesis device and method

Abstract

The present invention provides a polylactic acid synthesis device and method, comprising a dehydration unit for removing moisture from lactic acid by heating; a buffer tank for temporarily storing the dehydrated lactic acid output by the dehydration unit; a recovery unit connected to the dehydration unit for storing water vapor generated by the dehydration unit during the dehydration process; a synthesis unit comprising a first pipeline, a second pipeline, and a steam derivation component, wherein the first pipeline and the second pipeline are both heating pipelines; the inlet end of the first pipeline is connected to the buffer tank, and the outlet end is connected to a finished product tank; S1, dehydration treatment: S2, polylactic acid synthesis; S3, collection and storage: the present invention utilizes the dehydration unit to remove moisture from the lactic acid raw material by heating, which is conducive to achieving a polymerization reaction of the lactic acid; by designing that the first pipeline for conveying lactic acid and the second pipeline for conveying catalyst are perpendicular to each other, a sufficient contact reaction between the catalyst and the lactic acid is achieved without providing a stirring device.

Description

Technical Field

[0001] The present invention relates to the technical field of polylactic acid synthesis equipment, and in particular to a polylactic acid synthesis device and method. Background Art

[0002] Polylactic acid, also known as polylactide, abbreviated as PLA in English, is a type of polymer material prepared from renewable resources with good development prospects. It is a new type of biodegradable material, usually obtained by polymerization with lactic acid as the main raw material.

[0003] There are two main methods for producing polylactic acid: direct polycondensation and lactide ring-opening polymerization. While lactide ring-opening polymerization can produce high-molecular-weight polylactic acid, its preparation process is lengthy, cumbersome, and costly. The direct polycondensation method, on the other hand, offers a simpler and lower-cost method. However, the direct polycondensation method produces water as a byproduct, which hinders the polymerization reaction.

[0004] CN216799807U discloses a device for preparing polylactic acid in one step, comprising a first container, a hot reflux pipe filled with a heating medium, a two-necked bottle, a condenser filled with a cooling medium, and a receiving bottle; the first opening of the two-necked bottle is connected to one end of the hot reflux pipe, the other end of the hot reflux pipe is connected to the first container, the second opening of the two-necked bottle is connected to one end of the condenser pipe, the other end of the condenser pipe is connected to the receiving bottle; one end of the hot reflux pipe and the condenser pipe connected to the two-necked bottle is higher than the other end. In this patent, the first container is connected to the hot reflux pipe, and after the raw material polymer-grade lactic acid is stirred and heated in the first container, the heating medium of the hot reflux pipe can effectively reflux the evaporated lactic acid and lactic acid dimers and trimers, thereby improving the lactic acid recovery rate and the two-necked bottle can recycle the distillate, reducing the cost of raw materials. However, the solution provided in this patent is only suitable for laboratory preparation, and the raw materials cannot be continuously added. When the amount of raw materials increases, stirring becomes difficult. It is difficult to achieve the purpose of stirring by using the magnetic stirring method in this patent, and strong stirring is required, which cannot meet the requirements of industrial production.

[0005] CN113896867B discloses a method for synthesizing polylactic acid from lactic acid in one step. The method involves adding the product of the dehydration reaction and polycondensation reaction of lactic acid in a primary reactor to a secondary reactor while uniformly coating the product on the inner wall of the secondary reactor. The product is stirred at the same time so that the total residence time of the product in the secondary reactor is maintained at 30 to 60 minutes to obtain the polylactic acid. The primary reactor completely removes free water from the lactic acid by stirring and vacuuming. The secondary reactor is a ribbon reactor with a scraper, a screw reactor with a scraper, or an anchor reactor with a scraper. This patent completes dehydration in the primary reactor before completing the polycondensation reaction, which cannot achieve continuous production. In addition, the water removal in the polymerization reaction is carried out in the secondary reactor after the polymerization reaction, and the by-product water generated by the polymerization reaction cannot be discharged in time.

[0006] In view of the problems existing in the above-mentioned one-step synthesis of polylactic acid, it is necessary to provide a polymerization device and method that can realize industrial continuous production and can promptly discharge water in the reaction. Summary of the Invention

[0007] In view of the deficiencies in the prior art, the present invention provides a polylactic acid synthesis device and method, which solve the problems mentioned in the background technology.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0009] A polylactic acid synthesis device, a dehydration unit, which is used to remove water from the lactic acid by heating;

[0010] a buffer tank for temporarily storing the dehydrated lactic acid outputted from the dehydration unit;

[0011] a recovery unit, which is in communication with the dehydration unit and stores water vapor generated by the dehydration unit during the dehydration process;

[0012] The synthesis unit includes a first pipeline, a second pipeline, and a steam derivation component. The first pipeline and the second pipeline are both heated pipelines. The inlet end of the first pipeline is connected to the buffer tank, and the outlet end is connected to the finished product tank. The second pipeline vertically and unidirectionally inputs the catalyst into the first pipeline, so that the catalyst and the lactic acid in the first pipeline are fully contacted and reacted to generate polylactic acid. The water vapor generated by the polymerization reaction in the first pipeline is discharged into the recovery tank through the steam derivation component.

[0013] Furthermore, the synthesis unit also includes a second box, the first pipeline and the second pipeline are arranged in the second box, the first pipeline and the second pipeline are both in the shape of a serpentine coil, and the second pipeline is cross-arranged directly above the first pipeline to form multiple interconnected intersections, and the multiple interconnected intersections are used to increase the number of mixing times of lactic acid and the catalyst.

[0014] Furthermore, the side cross-sections of the first pipeline and the second pipeline are both in the shape of flat slits, so that the lactic acid is in a spread state in the first pipeline and the second pipeline.

[0015] Furthermore, a one-way stop assembly is arranged at the intersection of the first pipeline and the second pipeline. If the hydraulic pressure in the second pipeline is less than the hydraulic pressure in the first pipeline, the one-way stop assembly is closed to stop the lactic acid in the first pipeline; if the hydraulic pressure in the second pipeline is greater than the hydraulic pressure in the first pipeline, the one-way stop assembly is opened to allow the catalyst in the second pipeline to be injected into the first pipeline.

[0016] Furthermore, steam derivation components are provided at the non-overlapping areas between the first tube body and the second tube body, and multiple groups of steam derivation components are connected in parallel to the recovery unit; the steam derivation components include a steam exhaust riser, a collecting pipe, and an exhaust box, the collecting pipe is horizontally arranged, and the bottom of the collecting pipe is vertically connected to multiple steam exhaust risers, and the bottom ends of the multiple steam exhaust risers are vertically connected to the non-overlapping areas of the first tube body; a steam exhaust box is installed on the top of the collecting pipe, and the steam exhaust box has a floating blocking component built in, and the floating blocking component is used to control the steam exhaust box to only discharge water vapor in the first pipeline, and not to discharge liquid in the first pipeline.

[0017] Furthermore, the floating blocking component includes a connecting rod, a blocking block and a floating ball. A second steam outlet is opened on one side of the top surface of the exhaust box. One end of the connecting rod is rotatably connected to the inner wall of the exhaust box, and the other end is fixedly connected to the floating ball. A blocking block is provided at a position opposite to the second steam outlet on the upper surface of the connecting rod.

[0018] When liquid enters the exhaust box, the float rises under the buoyancy of the liquid, so that the blocking block approaches the second steam outlet, and the second steam outlet is in a blocking trend;

[0019] When no liquid enters the exhaust box, the connecting rod is in an inclined state, the blocking block is away from the second steam outlet, and the second steam outlet is in an open state.

[0020] Furthermore, the dehydration unit includes a first box body, a top heating plate, a reciprocating inclined plate assembly, and a fixed rod; the bottom surface of the first box body is connected to the buffer tank, a raw material supply bin is embedded on one side of the top surface of the first box body, and a first steam outlet is opened on the other side; the first steam outlet is connected to the recovery unit; a fixed rod is provided at the inner center line of the first box body, the top end of the fixed rod is provided with a top heating plate, and the outer wall is provided with a reciprocating inclined plate assembly, and the top-view cross-sectional area of the reciprocating inclined plate assembly is larger than the top-view cross-sectional area of the top heating plate; the top heating plate is used to receive the lactic acid raw material input from the raw material supply bin, and to perform primary heating and dehydration on the lactic acid raw material; the reciprocating inclined plate assembly is used to receive the lactic acid raw material output from the top heating plate, and to perform secondary heating and dehydration on the lactic acid raw material.

[0021] Furthermore, a long material receiving bin is provided at one end of the surface of the top heating plate, and the long material receiving bin is relatively arranged directly below the raw material supply bin; a drainage slit is opened below the other side of the long material receiving bin, and the drainage slit is used to output the lactic acid raw material in a spread state, which is beneficial to the top heating plate heating the lactic acid raw material; a first baffle and a second baffle are respectively arranged on the left and right sides of the flow direction of the lactic acid raw material on the upper surface of the top heating plate, and the height of the first baffle and the second baffle is higher than the height of the drainage slit; the height of one end of the top heating plate is greater than the height of the other end, and the inclination of the top heating plate is 2°-5°.

[0022] Furthermore, the fixed rod has a built-in main circuit, and the heating source built into the top heating plate and the multiple heating sources built into the reciprocating inclined plate assembly are all connected in parallel with the main circuit.

[0023] A method for synthesizing polylactic acid, comprising the following steps:

[0024] S1. Dehydration treatment:

[0025] The lactic acid raw materials are fed from the raw material supply bin into the long receiving bin;

[0026] Lactic acid is discharged from the drainage slit and evenly spread on the surface of the top heating plate. The first baffle and the second baffle block the lactic acid liquid; the top heating plate performs a primary heating and dehydration treatment on the lactic acid.

[0027] The lactic acid liquid falls from the top heating plate to the reciprocating inclined plate assembly, which transports the lactic acid back and forth and simultaneously performs a secondary reciprocating heating and dehydration process;

[0028] The water vapor generated during the first-stage heating and dehydration treatment and the second-stage reciprocating heating and dehydration treatment is discharged through the first steam outlet to the second steam branch pipe;

[0029] The dehydrated lactic acid is temporarily stored in the buffer tank;

[0030] S2. Polylactic acid synthesis:

[0031] The liquid pump extracts the lactic acid in the buffer tank to the first pipeline, and the catalyst storage tank circulates the catalyst to the second pipeline; the first pipeline and the second pipeline are self-heated to the specified temperature;

[0032] When the hydraulic pressure in the second pipeline is greater than the hydraulic pressure in the first pipeline, the one-way stop assembly opens, the catalyst enters the first pipeline, and the catalyst reacts with the lactic acid to generate polylactic acid;

[0033] The water vapor in the first pipeline is discharged to the second steam branch pipe through the steam discharge assembly, and the floating blocking component will block the steam discharge assembly when the liquid tends to overflow;

[0034] S3. Collection and storage:

[0035] The generated polylactic acid is transported to the finished product tank for storage;

[0036] The water vapor in the first steam branch pipe and the second steam branch pipe is gathered in the steam main pipe under the action of the vacuum pump and is finally stored in the recovery tank.

[0037] The present invention provides a polylactic acid synthesis device. Compared with the prior art, it has the following advantages:

[0038] (1) Using a dehydration unit to heat and remove moisture from the lactic acid raw material is beneficial to the polymerization reaction of lactic acid;

[0039] (2) By designing the first pipeline for transporting lactic acid and the second pipeline for transporting the catalyst to be perpendicular to each other, sufficient contact reaction between the catalyst and the lactic acid can be achieved without providing a stirring device;

[0040] (3) A steam outlet assembly is provided on the first pipeline supplying lactic acid to quickly discharge the water vapor generated during the polymerization of lactic acid from the synthesis unit, which is beneficial to the forward progress of the polymerization reaction and promotes the synthesis of polylactic acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. 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 any creative work.

[0042] Figure 1 Shows a schematic diagram of the overall structure of the synthesis device of the present invention;

[0043] Figure 2 Shows a schematic diagram of the top heating plate structure of the present invention;

[0044] Figure 3 Shown is a schematic diagram of the synthesis unit structure of the present invention;

[0045] Figure 4 shows a schematic diagram of the first pipeline structure of the present invention;

[0046] Figure 5 shows a schematic diagram of the second pipeline structure of the present invention;

[0047] Figure 6 A schematic diagram of the layout structure of the steam outlet assembly of the present invention is shown;

[0048] Figure 7 Shows a schematic structural diagram of the floating blocking component of the present invention;

[0049] In the figure: 1. Dehydration unit; 11. First box; 111. First steam outlet; 12. Fixed rod; 13. Top heating plate; 131. Long material receiving bin; 1311. Drainage slit; 132. First baffle; 133. Second baffle; 14. Raw material supply bin; 15. Reciprocating inclined plate assembly; 151. First heating plate; 152. Second heating plate; 153. Third heating plate; 2. Buffer tank; 21. Liquid pump; 3. Synthesis unit; 31. Second box; 32. Pipeline 1; 33. Pipeline 2; 4. Recovery unit; 41. Recovery tank; 42. Steam main; 421. Vacuum pump; 43. First steam branch pipe; 431. First one-way valve; 44. Second steam branch pipe; 441. Second one-way valve; 5. Steam outlet assembly; 51. Steam discharge riser; 52. Collecting pipe; 53. Exhaust box; 531. Second steam outlet; 54. Floating blocking component; 541. Connecting rod; 542. Blocking block; 543. Float; 6. Finished product tank. DETAILED DESCRIPTION

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0051] like Figure 1 As shown, in order to solve the technical problems in the background technology, a polylactic acid synthesis device is provided as follows: it includes a dehydration unit 1, a buffer tank 2, a recovery unit 4, a synthesis unit 3, and a finished product tank 6;

[0052] A dehydration unit 1 is used to remove moisture from lactic acid by heating; a buffer tank 2 is used to temporarily store the dehydrated lactic acid output by the dehydration unit 1; a recovery unit 4 is connected to the dehydration unit 1 to store water vapor generated by the dehydration unit 1 during the dehydration process; a synthesis unit 3 includes a first pipeline 32, a second pipeline 33, and a steam outlet component 5, and the first pipeline 32 and the second pipeline 33 are both heating pipelines; the inlet end of the first pipeline 32 is connected to the buffer tank 2, and the outlet end is connected to the finished product tank 6; the second pipeline 33 inputs the catalyst vertically downward into the first pipeline 32 in a single direction, so that the catalyst and the lactic acid in the first pipeline 32 are fully contacted and reacted to generate polylactic acid; the water vapor generated by the polymerization reaction in the first pipeline 32 is discharged into the recovery tank 41 through the steam outlet component 5.

[0053] The above technical solution has the following technical effects:

[0054] (1) using the dehydration unit 1 to heat and remove moisture from the lactic acid raw material, which is conducive to the polymerization reaction of lactic acid;

[0055] (2) By designing the first pipeline 32 for transporting lactic acid and the second pipeline 33 for transporting the catalyst to be perpendicular to each other, a sufficient contact reaction between the catalyst and the lactic acid is achieved without providing a stirring device;

[0056] (3) A steam outlet assembly 5 is provided on the first pipeline 32 for supplying lactic acid to quickly discharge the water vapor generated during the polymerization of lactic acid from the synthesis unit 3, which is beneficial to the forward progress of the polymerization reaction and promotes the synthesis of polylactic acid.

[0057] Example 1

[0058] like Figure 1-2 As shown, in order to enable the dehydration unit 1 to achieve the above functions, this embodiment provides the following design scheme:

[0059] In this embodiment, the dehydration unit 1 includes a first box body 11, a top heating plate 13, a reciprocating inclined plate assembly 15, and a fixed rod 12; the bottom surface of the first box body 11 is connected to the buffer tank 2, and a raw material supply bin 14 is embedded on one side of the top surface of the first box body 11, and a first steam outlet 111 is opened on the other side; the first steam outlet 111 is connected to the recovery unit 4; a fixed rod 12 is provided at the inner center line of the first box body 11, and a top heating plate 13 is provided on the top of the fixed rod 12, and a reciprocating inclined plate assembly 15 is provided on the outer wall, and the top cross-sectional area of the reciprocating inclined plate assembly 15 is larger than the top cross-sectional area of the top heating plate 13; the top heating plate 13 is used to receive the lactic acid raw material input from the raw material supply bin 14 and perform primary heating and dehydration on the lactic acid raw material; the reciprocating inclined plate assembly 15 is used to receive the lactic acid raw material output from the top heating plate 13 and perform secondary heating and dehydration on the lactic acid raw material;

[0060] The first box body 11 is in the shape of a rectangular parallelepiped as a whole, and the top heating plate 13 is in the shape of a square. The vertical projection area of the top heating plate 13 is smaller than the cross-sectional area of the first box body 11;

[0061] In the above technical solution, multi-stage heating of the lactic acid raw material can be achieved, thereby effectively removing moisture from the lactic acid raw material. At the same time, the entire heating process is carried out synchronously with the lactic acid transportation process, and the water vapor generated during the heating process is concentrated through the first steam outlet 111 to avoid steam affecting the heating process.

[0062] In order to enable the top heating plate 13 to heat the lactic acid evenly and efficiently and ensure the normal flow of the lactic acid, the following design scheme is given:

[0063] As an embodiment, a long material receiving bin 131 is provided at one end of the surface of the top heating plate 13. The long material receiving bin 131 is relatively located directly below the raw material supply bin 14. A drainage slit 1311 is provided below the other side of the long material receiving bin 131. The drainage slit 1311 is used to allow the lactic acid raw material to be discharged in a spread state, thereby facilitating heating of the lactic acid raw material by the top heating plate 13. A first baffle 132 and a second baffle 133 are respectively provided on the left and right sides of the upper surface of the top heating plate 13 in the direction of flow of the lactic acid raw material. The height of the first baffle 132 and the second baffle 133 is higher than the height of the drainage slit 1311.

[0064] In the above technical solution, the first baffle 132 and the second baffle 133 can stop the lactic acid and prevent it from flowing out from both sides; the drainage slit 1311 can enable the lactic acid in the long material receiving bin 131 to flow out from the drainage slit 1311 to the upper surface of the top heating plate 13, and the lactic acid is in a spread state, which is conducive to the heating of the lactic acid by the top heating plate 13 and the removal of water in the lactic acid.

[0065] Furthermore, the height of one end of the top heating plate 13 is greater than the height of the other end, and the slope of the top heating plate 13 is 2°-5°; the top heating plate 13 is designed to be inclined and the inclination is relatively gentle, which is conducive to the flow of lactic acid from one end of the top heating plate 13 to the other end of the top heating plate 13, and at the same time, the time that the lactic acid stays on the top heating plate 13 is guaranteed to the greatest extent to facilitate more sufficient heating.

[0066] As an embodiment, the fixed rod 12 has a built-in main circuit, and the heating source built into the top heating plate 13 and the multiple heating sources built into the reciprocating inclined plate assembly 15 are all connected in parallel with the main circuit; in addition to the function of fixing and supporting the top heating plate 13 and the reciprocating inclined plate assembly 15, the fixed rod 12 is provided with a circuit inside thereof to supply power to the heat source of the top heating plate 13 and the reciprocating inclined plate assembly 15. After power is turned on, the top heating plate 13 and the reciprocating inclined plate assembly 15 can be heated to achieve heating of the lactic acid.

[0067] In this embodiment, the reciprocating inclined plate assembly 15 includes a first heating plate 151, a second heating plate 152, and a third heating plate 153; the first heating plate 151, the second heating plate 152, and the third heating plate 153 are mutually cross-inclined, and the middle parts of the first heating plate 151, the second heating plate 152, and the third heating plate 153 are all arranged on the fixed rod 12.

[0068] The top of the first heating plate 151 is close to the lower edge of the top heating plate 13, and the vertical projection of the lower edge of the top heating plate 13 is within the edge of the top of the first heating plate 151, which is conducive to the first heating plate 151 receiving the lactic acid flowing down from the lower edge of the top heating plate 13; the width of the first heating plate 151 is greater than the width of the top heating plate 13, and a retaining structure is set on both sides of the first heating plate 151 to prevent the raw material liquid flowing down from the top heating plate 13 from flowing out of the first heating plate 151.

[0069] The top of the second heating plate 152 is close to the bottom of the first heating plate 151, and the vertical projection of the bottom of the first heating plate 151 is within the edge of the top of the second heating plate 152. This facilitates the second heating plate 152 to receive lactic acid flowing from the bottom edge of the first heating plate 151. The width of the second heating plate 152 is greater than that of the first heating plate 151, and a barrier structure is provided on both sides of the second heating plate 152 to prevent lactic acid flowing from the first heating plate 151 from flowing out of the second heating plate 152.

[0070] The top of the third heating plate 153 is close to the bottom of the second heating plate 152, and the vertical projection of the bottom of the second heating plate 152 is within the edge of the top of the third heating plate 153. This facilitates the third heating plate 153 to receive lactic acid flowing from the bottom edge of the second heating plate 152. The width of the third heating plate 153 is greater than that of the second heating plate 152, and a barrier structure is provided on both sides of the third heating plate 153 to prevent lactic acid flowing from the second heating plate 152 from flowing out of the third heating plate 153.

[0071] The reciprocating cross design of the first heating plate 151, the second heating plate 152, and the third heating plate 153 can transport the lactic acid downward and turn the lactic acid back and forth, so that the lactic acid can be highly evenly and fully contacted with each heating plate, achieving multiple heating and dehydration;

[0072] As an embodiment, the inclination angles of the first heating plate 151, the second heating plate 152, and the third heating plate 153 are all 5° to 10°; the inclination angle of 5° to 10° can not only accelerate the flow speed of lactic acid, but also ensure the uniformity and residence time of the flow.

[0073] After continuous heating treatment by the top heating plate 13, the first heating plate 151, the second heating plate 152, and the third heating plate 153, the water in the lactic acid is fully evaporated, and the lactic acid reaches the raw liquid outlet set on the bottom side of the dehydration unit 1, and is discharged to the buffer tank for temporary storage through the first connecting pipe; the outlet of lactic acid is set directly below the lower edge of the third heating plate 153, which is conducive to the rapid discharge of the raw liquid from the dehydration unit 1.

[0074] Example 2

[0075] like Figure 1 、 Figure 3-7 As shown, in order to enable the synthesis unit 3 to achieve the above functions, this embodiment provides the following solution design:

[0076] In this embodiment, the synthesis unit 3 also includes a second box body 31, and the first pipeline 32 and the second pipeline 33 are arranged in the second box body 31. The first pipeline 32 and the second pipeline 33 are both serpentine coils. The lower surface of the second pipeline 33 is close to the upper surface of the first pipeline 32. The second pipeline 33 is cross-arranged directly above the first pipeline 32 to form a plurality of interconnected intersections. The plurality of interconnected intersections are used to increase the number of mixing times of lactic acid and the catalyst.

[0077] Since the intersection is connected to the first pipeline 32 and the second pipeline 33, the pressure of the catalyst added to the second pipeline 33 is greater than the pressure of the lactic acid supplied to the first pipeline 32, thereby preventing the raw material liquid in the first pipeline 32 from entering the second pipeline 33. At the same time, sufficient mixing can be achieved without a mechanical stirring structure.

[0078] The serpentine coil structure can increase the number of intersections and increase the mixing reaction time; the second pipeline 33 is bidirectionally connected to the catalyst storage tank.

[0079] In this embodiment, the side cross-sections of the first pipeline 32 and the second pipeline 33 are both in the shape of flat slits, so that the lactic acid is in a spread state in the first pipeline 32 and the second pipeline 33 .

[0080] In order to prevent the lactic acid in the first pipe 32 from floating into the second pipe 33, the following design scheme is provided in this embodiment:

[0081] In this embodiment, a one-way stop assembly is arranged at the intersection of the first pipeline 32 and the second pipeline 33. If the hydraulic pressure in the second pipeline 33 is less than the hydraulic pressure in the first pipeline 32, the one-way stop assembly is closed to stop the lactic acid in the first pipeline 32; if the hydraulic pressure in the second pipeline 33 is greater than the hydraulic pressure in the first pipeline 32, the one-way stop assembly is opened to allow the catalyst in the second pipeline 33 to be injected into the first pipeline 32.

[0082] The one-way stop assembly includes a stop plate, which is rotatably mounted at the opening of the intersection of the first pipeline 32 via a torsion spring;

[0083] The stop plate can only be opened from the second pipeline 33 to the first pipeline 32, and cannot be opened from the first pipeline 32 to the second pipeline 33; the end of the stop plate located downstream of the material flow is in a free state;

[0084] When the pressure in the second pipeline 33 is lower than the pressure in the first pipeline 32, the liquid in the second pipeline 33 pushes the stopper plate toward the first pipeline 32 during flow. The stopper plate then blocks the intersection opening, preventing the liquid in the first pipeline 32 from entering the second pipeline 33. When the pressure in the second pipeline 33 is higher than the pressure in the first pipeline 32, the liquid in the second pipeline 33 pushes the free end of the baffle plate to open toward the first pipeline 32. The liquid in the second pipeline 33 then enters the first pipeline 32 and mixes with the liquid in the first pipeline 32.

[0085] In this embodiment, steam derivation components 5 are provided at the non-overlapping areas between the first tube body and the second tube body, and multiple groups of steam derivation components 5 are connected in parallel to the recovery unit 4; the steam derivation components 5 include a steam exhaust riser 51, a collecting pipe 52, and an exhaust box 53, the collecting pipe 52 is horizontally arranged, and the bottom of the collecting pipe 52 is vertically connected to multiple steam exhaust risers 51, and the bottom ends of the multiple steam exhaust risers 51 are vertically connected to the non-overlapping areas of the first tube body; a steam exhaust box 53 is installed on the top of the collecting pipe 52, and the steam exhaust box 53 has a built-in floating blocking component 54, and the floating blocking component 54 is used to control the steam exhaust box 53 to only discharge water vapor in the first pipeline 32, and not discharge the liquid in the first pipeline 32. The floating blocking component 54 includes a connecting rod 541, a blocking block 542, and a floating ball 543. A second steam outlet 531 is provided on one side of the top surface of the exhaust box 53. One end of the connecting rod 541 is rotatably connected to the inner wall of the exhaust box 53, and the other end is fixedly connected to the floating ball 543. A blocking block 542 is provided on the upper surface of the connecting rod 541 at a position opposite to the second steam outlet 531.

[0086] When liquid enters the exhaust box 53, the float 543 rises under the action of the buoyancy of the liquid, so that the blocking block 542 is close to the second steam outlet 531, and the second steam outlet 531 is in a blocking trend. When the connecting rod 541 rises to a horizontal state, the blocking block 542 blocks the second steam outlet; when no liquid enters the exhaust box 53, the connecting rod 541 is in an inclined state, the blocking block 542 is away from the second steam outlet 531, and the second steam outlet 531 is in an open state.

[0087] Example 3

[0088] like Figure 1 As shown, in order to enable the recovery unit 4 to achieve the above functions, this embodiment provides the following design scheme:

[0089] The recovery unit 4 includes a recovery tank 41, a steam main pipe, a first steam branch pipe 43, and a second steam branch pipe 44. The inlet end of the first steam branch pipe 43 is connected to the first steam outlet 111, and a first one-way valve 431 is installed on the first steam branch pipe 43; the top of the second steam outlet 531 is connected in parallel to the second steam branch pipe 44, and a second one-way valve 441 is installed on the second steam branch pipe 44. The outlet ends of the first steam branch pipe 43 and the second steam branch pipe 44 are both connected in parallel to the steam main pipe 42, and an air extraction pump 421 is installed on the steam main pipe 42. The outlet end of the steam main pipe 42 is connected to the recovery tank 41.

[0090] A method for synthesizing polylactic acid, comprising the following steps:

[0091] S1. Dehydration treatment:

[0092] The lactic acid raw material is fed from the raw material supply bin 14 into the strip receiving bin 131;

[0093] Lactic acid is discharged from the drainage slit 1311 and evenly spread on the surface of the top heating plate 13. The first baffle 132 and the second baffle 133 enclose the lactic acid liquid; the top heating plate 13 performs a primary heating and dehydration treatment on the lactic acid.

[0094] The lactic acid liquid falls from the top heating plate 13 onto the reciprocating inclined plate assembly 15, which transports the lactic acid back and forth and simultaneously performs a secondary reciprocating heating and dehydration process;

[0095] The water vapor generated during the first-stage heating and dehydration process and the second-stage reciprocating heating and dehydration process is discharged to the second steam branch pipe 44 through the first steam outlet 111;

[0096] The dehydrated lactic acid is temporarily stored in the buffer tank 2;

[0097] S2. Polylactic acid synthesis:

[0098] The liquid pump 21 extracts the lactic acid in the buffer tank 2 to the first pipeline 32, and the catalyst storage tank circulates the catalyst to the second pipeline 33; the first pipeline 32 and the second pipeline 33 are self-heated to the specified temperature;

[0099] When the hydraulic pressure in the second pipeline 33 is greater than the hydraulic pressure in the first pipeline 32, the one-way stop assembly opens, and the catalyst enters the first pipeline 32, where the catalyst polymerizes with the lactic acid to produce polylactic acid.

[0100] The water vapor in the first pipeline 32 is discharged to the second steam branch pipe 44 through the steam discharge assembly 5, and the floating blocking member 54 will block the steam discharge assembly 5 when the liquid tends to overflow;

[0101] S3. Collection and storage:

[0102] The generated polylactic acid is transported to the finished product tank 6 for storage;

[0103] The water vapor in the first steam branch pipe 43 and the second steam branch pipe 44 is gathered in the steam main pipe 42 under the action of the vacuum pump 421 and is finally stored in the recovery tank 41 .

[0104] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

[0105] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A polylactic acid synthesis device, characterized in that: include: a dehydration unit for removing water from the lactic acid by heating; a buffer tank for temporarily storing the dehydrated lactic acid outputted from the dehydration unit; a recovery unit, which is in communication with the dehydration unit and stores water vapor generated by the dehydration unit during the dehydration process; The synthesis unit includes a first pipeline, a second pipeline, and a steam outlet assembly, wherein the first pipeline and the second pipeline are both heating pipelines; The inlet end of the first pipeline is connected to the buffer tank, and the outlet end is connected to the finished product tank. The second pipeline vertically and downwardly feeds the catalyst into the first pipeline in a single direction, so that the catalyst fully contacts and reacts with the lactic acid in the first pipeline to produce polylactic acid. The water vapor generated by the polymerization reaction in the first pipeline is discharged to the recovery tank through the steam discharge assembly. The synthesis unit further includes a second housing, wherein the first pipeline and the second pipeline are disposed within the second housing, wherein the first pipeline and the second pipeline are both serpentine-shaped, and the second pipeline is disposed crosswise directly above the first pipeline to form a plurality of interconnected intersections, wherein the plurality of interconnected intersections is used to increase the number of mixing times of the lactic acid and the catalyst; The side cross-sections of the first pipeline and the second pipeline are both in the shape of a flat slit, so that the lactic acid is spread in the first pipeline and the second pipeline; Steam derivation components are provided at non-overlapping areas between the first pipeline and the second pipeline, and multiple groups of steam derivation components are connected in parallel to the recovery unit.

2. A polylactic acid synthesis device according to claim 1, characterized in that: A one-way stop assembly is arranged at the intersection of the first pipeline and the second pipeline. If the hydraulic pressure in the second pipeline is lower than the hydraulic pressure in the first pipeline, the one-way stop assembly closes to stop the lactic acid in the first pipeline. If the hydraulic pressure in the second pipeline is greater than the hydraulic pressure in the first pipeline, the one-way stop assembly opens to allow the catalyst in the second pipeline to be injected into the first pipeline.

3. A polylactic acid synthesis device according to claim 2, characterized in that: The steam derivation component includes a steam exhaust riser, a collecting pipe, and an exhaust box. The collecting pipe is arranged horizontally. The bottom of the collecting pipe is vertically connected to multiple steam exhaust risers, and the bottom ends of the multiple steam exhaust risers are vertically connected to the non-overlapping area of the first pipeline; a steam exhaust box is installed on the top of the collecting pipe, and the steam exhaust box has a floating blocking component built in. The floating blocking component is used to control the steam exhaust box to only discharge water vapor in the first pipeline, and not to discharge the liquid in the first pipeline.

4. A polylactic acid synthesis device according to claim 3, characterized in that: The floating blocking component includes a connecting rod, a blocking block and a floating ball. A second steam outlet is opened on one side of the top surface of the exhaust box. One end of the connecting rod is rotatably connected to the inner wall of the exhaust box, and the other end is fixedly connected to the floating ball. A blocking block is provided at a position opposite to the second steam outlet on the upper surface of the connecting rod. When liquid enters the exhaust box, the float rises under the buoyancy of the liquid, so that the blocking block approaches the second steam outlet, and the second steam outlet is in a blocking trend; When no liquid enters the exhaust box, the connecting rod is in an inclined state, the blocking block is away from the second steam outlet, and the second steam outlet is in an open state.

5. The polylactic acid synthesis device according to claim 1, characterized in that: The dehydration unit includes a first box body, a top heating plate, a reciprocating inclined plate assembly, and a fixed rod; the bottom surface of the first box body is connected to the buffer tank, a raw material supply bin is embedded on one side of the top surface of the first box body, and a first steam outlet is opened on the other side; the first steam outlet is connected to the recovery unit; a fixed rod is provided at the inner center line of the first box body, the top end of the fixed rod is provided with a top heating plate, and the outer wall is provided with a reciprocating inclined plate assembly, and the top-view cross-sectional area of the reciprocating inclined plate assembly is larger than the top-view cross-sectional area of the top heating plate; the top heating plate is used to receive the lactic acid raw material input from the raw material supply bin, and to perform primary heating and dehydration on the lactic acid raw material; the reciprocating inclined plate assembly is used to receive the lactic acid raw material output from the top heating plate, and to perform secondary heating and dehydration on the lactic acid raw material.

6. A polylactic acid synthesis device according to claim 5, characterized in that: A long material receiving bin is provided at one end of the surface of the top heating plate, and the long material receiving bin is relatively arranged directly below the raw material supply bin; a drainage slit is opened below the other side of the long material receiving bin, and the drainage slit is used to output the lactic acid raw material in a spread state, which is beneficial for the top heating plate to heat the lactic acid raw material; a first baffle and a second baffle are respectively provided on the left and right sides of the upper surface of the top heating plate in the direction of flow of the lactic acid raw material, and the height of the first baffle and the second baffle is higher than the height of the drainage slit; the height of one end of the top heating plate is greater than the height of the other end, and the inclination of the top heating plate is 2°-5°.

7. A polylactic acid synthesis device according to claim 6, characterized in that: The fixed rod is built with a main circuit, and the heating source built into the top heating plate and the multiple heating sources built into the reciprocating inclined plate assembly are all connected in parallel with the main circuit.

8. A method for synthesizing polylactic acid, characterized in that: Based on the polylactic acid synthesis device according to any one of claims 1 to 7, the synthesis method comprises the following steps: S1. Dehydration treatment: The lactic acid raw materials are fed from the raw material supply bin into the long receiving bin; Lactic acid is discharged from the drainage slit and evenly spread on the surface of the top heating plate. The first baffle and the second baffle block the lactic acid liquid; the top heating plate performs a primary heating and dehydration treatment on the lactic acid. The lactic acid liquid falls from the top heating plate to the reciprocating inclined plate assembly, which transports the lactic acid back and forth and simultaneously performs a secondary reciprocating heating and dehydration process; The water vapor generated during the first-stage heating and dehydration treatment and the second-stage reciprocating heating and dehydration treatment is discharged through the first steam outlet to the second steam branch pipe; The dehydrated lactic acid is temporarily stored in the buffer tank; S2. Polylactic acid synthesis: The liquid pump extracts the lactic acid in the buffer tank to the first pipeline, and the catalyst storage tank circulates the catalyst to the second pipeline; the first pipeline and the second pipeline are self-heated to the specified temperature; When the hydraulic pressure in the second pipeline is greater than the hydraulic pressure in the first pipeline, the one-way stop assembly opens, the catalyst enters the first pipeline, and the catalyst reacts with the lactic acid to generate polylactic acid; The water vapor in the first pipeline is discharged to the second steam branch pipe through the steam discharge assembly, and the floating blocking component will block the steam discharge assembly when the liquid tends to overflow; S3. Collection and storage: The generated polylactic acid is transported to the finished product tank for storage; The water vapor in the first steam branch pipe and the second steam branch pipe is gathered in the steam main pipe under the action of the vacuum pump and is finally stored in the recovery tank.

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