Continuous production method and production system for low-molecular-weight polyglycolic acid

Abstract

The invention belongs to the technical field of polyglycolic acid production, and relates to a continuous production method and a production system for low-molecular-weight polyglycolic acid. The generated first-stage prepolymerization reaction products are respectively conveyed to a second-stage prepolymerization reaction section, a third-stage prepolymerization reaction section and a fourth-stage prepolymerization reaction section according to different flow distribution to participate in corresponding prepolymerization reactions; a second-stage prepolymerization reaction product generated in the second-stage prepolymerization reaction section directly participates in a third-stage prepolymerization reaction; a third-stage prepolymerization reaction product generated by the third-stage prepolymerization reaction section respectively enters a fourth-stage prepolymerization reaction section and a fifth-stage prepolymerization reaction section; a fourth-stage prepolymerization reaction product generated by the fourth-stage prepolymerization reaction directly enters a fifth-stage prepolymerization reaction section to participate in the reaction; low-molecular-weight polyglycolic acid is generated in the five-stage prepolymerization reaction section. According to the invention, prepolymerization reaction products at all stages are subjected to split-flow parallel multi-stage conveying, so that the production efficiency is improved, frequent blockage of centralized stage-by-stage conveying pipelines is avoided, and continuous production of low-molecular-weight polyglycolic acid is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyglycolic acid production devices, and relates to a continuous production method and production system for low molecular weight polyglycolic acid. Background Art

[0002] The process of preparing polyglycolic acid from dimethyl oxalate includes: hydrogenation reaction of dimethyl oxalate to produce methyl glycolate; then, under the action of a catalyst, methyl glycolate is polycondensed to synthesize polyglycolic acid; and the polycondensation synthesis includes prepolymerization (abbreviation: prepoly) and final polycondensation. In prepolymerization, methyl glycolate undergoes multiple-stage prepolymerization reactions to gradually form low molecular weight polyglycolic acid (intermediate product); then the low molecular weight polyglycolic acid (intermediate product) further undergoes final polycondensation to obtain high molecular weight polyglycolic acid, that is, polyglycolic acid. In actual industrial production, prepolymerization is a key step in the preparation of polyglycolic acid from dimethyl oxalate. Whether the prepolymerization process can proceed smoothly directly affects the subsequent final polycondensation process.

[0003] The prepolymerization production process in existing industrial production is as follows: five reaction kettles connected in series in sequence are set (in the order of the reaction kettles, the five reaction kettles are the first-stage prepolymerization reaction section, the second-stage prepolymerization reaction section, the third-stage prepolymerization reaction section, the fourth-stage prepolymerization reaction section, and the fifth-stage prepolymerization reaction section), and then methyl glycolate with a purity > 97% (raw material) is introduced; the raw material undergoes five-stage prepolymerization synthesis step by step to finally form polyglycolic acid with a purity of 95%, which is low molecular weight polyglycolic acid (intermediate product). Although the existing prepolymerization synthesis can produce low molecular weight polyglycolic acid through five-stage prepolymerization reaction, since methyl glycolate with a purity > 97% needs to stay in each reaction kettle for enough time to obtain low molecular weight polyglycolic acid that meets the purity requirements; as the reaction progresses step by step, the purity of the low molecular weight polyglycolic acid also increases accordingly, that is, the content of polyglycolic acid in the material transported to the next stage becomes higher and higher; however, as the content of polyglycolic acid generated by the step-by-step prepolymerization reaction is higher, its viscosity also increases correspondingly; the high-viscosity polyglycolic acid generated in the previous reaction kettle requires a longer time to be transported step by step to the subsequent reaction kettle at the back end, making it difficult to stably transport the high-viscosity polyglycolic acid to the subsequent reaction kettle in a timely manner, resulting in poor production continuity and low production efficiency; in addition, the increase in the viscosity of polyglycolic acid will also cause frequent blockages in the transport pipelines of the reaction kettle. Once a blockage occurs, it is necessary to stop production for maintenance, and it is difficult to achieve continuous and stable progress of the prepolymerization reaction. Summary of the Invention

[0004] Aiming at the technical problems of poor production continuity, low production efficiency, and frequent blockages in the transport pipelines in the production of existing low molecular weight polyglycolic acid, the present invention provides a continuous production method and system for low molecular weight polyglycolic acid.

[0005] In the process of performing the step-by-step prepolymerization reaction, the product of the first-stage prepolymerization reaction is further diverted to the third-stage prepolymerization reaction and the fourth-stage prepolymerization reaction, and the product of the third-stage prepolymerization reaction is further diverted to the fifth-stage prepolymerization reaction. The products of the prepolymerization reactions at each stage are transported in a multi-stage parallel manner, so that the low-purity prepolymerization product at the front end is transported across stages and mixed with the high-purity prepolymerization product at the rear end, which not only ensures the timely and stable transportation of the low-molecular-weight polyglycolic acid and improves the production efficiency, but also avoids frequent blockage of the transportation pipeline and realizes the continuous production of the low-molecular-weight polyglycolic acid.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: A method for continuously producing low molecular weight polyglycolic acid, comprising: Methyl glycolate with a purity of more than 97% is continuously introduced into the primary prepolymerization reaction section, and the generated primary prepolymerization reaction product is respectively transported to the secondary prepolymerization reaction section, the tertiary prepolymerization reaction section and the quaternary prepolymerization reaction section according to different flow distributions to participate in the corresponding prepolymerization reactions; The secondary prepolymerization reaction product generated in the secondary prepolymerization reaction section directly enters the tertiary prepolymerization reaction section to participate in the tertiary prepolymerization reaction; The third-stage prepolymerization reaction product generated in the third-stage prepolymerization reaction section is divided into two paths according to different flow rates and enters the fourth-stage prepolymerization reaction section and the fifth-stage prepolymerization reaction section respectively to participate in the corresponding prepolymerization reaction; The fourth-stage prepolymerization reaction product generated in the fourth-stage prepolymerization reaction section directly enters the fifth-stage prepolymerization reaction section to participate in the fifth-stage prepolymerization reaction; The five-stage prepolymerization reaction section generates low molecular weight polyglycolic acid through five-stage prepolymerization reaction.

[0007] The primary prepolymerization reaction product is divided into three routes according to the volume ratio of (4~5):(2~3):(1~2) and enters the secondary prepolymerization reaction section, the tertiary prepolymerization reaction section and the quaternary prepolymerization reaction section respectively.

[0008] The three-stage prepolymerization reaction product is divided into two paths according to the volume ratio of (5-6): (2-3) and enters the fourth-stage prepolymerization reaction section and the fifth-stage prepolymerization reaction section respectively.

[0009] It is further defined that the volume of the material participating in the secondary prepolymerization reaction is smaller than the volume of the material participating in the tertiary prepolymerization reaction; and the volume of the material of the tertiary prepolymerization reaction, the volume of the material of the quaternary prepolymerization reaction and the volume of the material of the quintuple prepolymerization reaction are all equal.

[0010] It is further defined that the volume of materials participating in the secondary prepolymerization reaction is 60%-70% of the volume of the reaction equipment in the secondary prepolymerization reaction section; the volume of materials participating in the tertiary prepolymerization reaction is 80%-85% of the volume of the reaction equipment in the tertiary prepolymerization reaction section.

[0011] Further defined, the conditions of each stage of prepolymerization reaction section are as follows: The first - stage pre - polymerization reaction section: temperature 130 ± 2°C, pressure 2 KPa - 3 KPa; The second - stage pre - polymerization reaction section: temperature 150 ± 2°C, pressure 2 KPa - 3 KPa; The third - stage pre - polymerization reaction section: temperature 170 ± 3°C, pressure 70 ± 1 KPaA absolute pressure; The fourth - stage pre - polymerization reaction section: temperature 180 ± 3°C, pressure 30 ± 1 KPaA absolute pressure; The fifth - stage pre - polymerization reaction section: temperature 220 ± 3°C, pressure 1.5 ± 0.5 KPaA absolute pressure.

[0012] A production system for implementing the continuous production method of low - molecular - weight polyglycolic acid described above, the production system includes a reaction module, a flow meter, a liquid level meter, and a control module; The reaction module is used to realize that after the methyl glycolate raw material with a purity > 97% is introduced, it enters the first - stage pre - polymerization reaction section, and then undergoes continuous reactions in the second - stage pre - polymerization reaction section, the third - stage pre - polymerization reaction section, the fourth - stage pre - polymerization reaction section, and the fifth - stage pre - polymerization reaction section in a split - flow multi - parallel manner to generate low - molecular - weight polyglycolic acid; The flow meter: is located on the split - flow branch roads of each stage of the pre - polymerization reaction section of the reaction module, and is used to monitor the volume flow rate of each split - flow branch road; The liquid level meter: is used to obtain the material volume in the reaction equipment in the second - stage pre - polymerization reaction section, the third - stage pre - polymerization reaction section, the fourth - stage pre - polymerization reaction section, and the fifth - stage pre - polymerization reaction section of the reaction module; The control module: is used to control the volume flow rate of each split - flow branch road according to the monitoring results of the flow meter and the set volume ratio of each split - flow branch road.

[0013] Further defined, the set volume ratio of each split - flow branch road of the first - stage pre - polymerization reaction product is (4 - 5):(2 - 3):(1 - 2); the set volume ratio of each split - flow branch road of the third - stage pre - polymerization reaction product is (5 - 6):(2 - 3).

[0014] Further defined, the reaction module includes a first reaction kettle, a second reaction kettle, a third reaction kettle, a fourth reaction kettle, and a fifth reaction kettle connected in sequence along the material flow direction; the first reaction kettle is also connected to the third reaction kettle through a first branch road; the first reaction kettle is also connected to the fourth reaction kettle through a second branch road; the third reaction kettle is also connected to the fifth reaction kettle through a third branch road; The flow meters are respectively arranged on the first branch road, the second branch road, the third branch road, between the first reaction kettle and the second reaction kettle, and between the third reaction kettle and the fourth reaction kettle; The liquid level meters are respectively arranged on the second reaction kettle, the third reaction kettle, the fourth reaction kettle, and the fifth reaction kettle.

[0015] It is further defined that the reaction module also includes flow regulating valves respectively arranged between the first reactor and the second reactor, on the first branch, on the second branch, between the second reactor and the third reactor, between the third reactor and the fourth reactor, on the third branch, and between the fourth reactor and the fifth reactor; each flow regulating valve is connected to the control module signal.

[0016] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: 1. While the present invention is carrying out the prepolymerization reaction step by step, the product of the first-stage prepolymerization reaction is also diverted to the third-stage prepolymerization reaction section and the fourth-stage prepolymerization reaction section, and the product of the third-stage prepolymerization reaction is also diverted to the fifth-stage prepolymerization reaction section; thereby, the products of the prepolymerization reaction at each stage are timely and stably transported in a multi-stage parallel manner. Such a design is to transport the low-purity prepolymerization product at the front end across stages and mix it with the high-purity prepolymerization product at the rear end. On the one hand, the low-purity prepolymerization product has a low viscosity, which is convenient for the timely and stable transportation of the prepolymerization products at each stage, thereby improving production efficiency; on the other hand, it can avoid the problem of frequent pipeline blockage caused by the transportation of a large amount of high-viscosity polyglycolic acid, thereby ensuring the continuous production of low-molecular-weight polyglycolic acid.

[0017] 2. In the present invention, the primary prepolymerization reaction product is divided into three routes according to the volume ratio of (4-5): (2-3): (1-2) and enters the secondary prepolymerization reaction section, the tertiary prepolymerization reaction section and the quaternary prepolymerization reaction section respectively to participate in the corresponding prepolymerization reaction; the tertiary prepolymerization reaction product is divided into two routes according to the volume ratio of (5-6): (2-3) and enters the quaternary prepolymerization reaction section and the fifth prepolymerization reaction section respectively to participate in the corresponding prepolymerization reaction; so that the low-purity polyglycolic acid can be transported step by step and mixed with the high-purity polyglycolic acid at a more optimal volume ratio, thereby accelerating the reaction process of the low molecular weight glycolic acid, improving production efficiency, and further enhancing the stability and continuity of production.

[0018] 3. In the present invention, the volume of the material participating in the secondary prepolymerization reaction is smaller than the volume of the material participating in the tertiary prepolymerization reaction during the mixing ratio, and the volume of the material in the tertiary prepolymerization reaction, the volume of the material in the quaternary prepolymerization reaction, and the volume of the material in the fifth prepolymerization reaction are all equal. It is ensured that the materials in each stage of prepolymerization reaction can better complete the corresponding prepolymerization reaction, and that the methyl glycolate raw material with a purity of more than 97% can be generated into low molecular weight polyglycolic acid through the fifth stage prepolymerization reaction in a shorter time, thereby improving the continuous production efficiency of low molecular weight polyglycolic acid and making the fifth stage prepolymerization reaction more stable.

[0019] 4. The present invention also provides a production system, which includes a reaction module, a flowmeter, a level gauge, and a control module. After the methyl glycolate raw material with a purity > 97% is introduced, it enters the first-stage prepolymerization reaction section, and then passes through the second-stage prepolymerization reaction section, the third-stage prepolymerization reaction section, the fourth-stage prepolymerization reaction section, and the fifth-stage prepolymerization reaction section in a shunt multi-stage parallel manner to carry out continuous reaction to generate low-molecular-weight polyglycolic acid; the flowmeter located on the shunt branch of each stage of the prepolymerization reaction section of the reaction module is used to monitor the volume flow rate of each shunt branch; at the same time, according to the monitoring results of the flowmeter and the set volume ratio of each shunt branch, the volume flow rate of each shunt branch is controlled, and the feeding is carried out according to the shunt volume ratio to ensure continuous reaction; so that under the corresponding prepolymerization reaction conditions of the reaction module, the materials are transported at the set volume ratio flow rate, ensuring the continuity, stability, and controllability of the production of low-molecular-weight polyglycolic acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic structural diagram of the production system; Figure 2 It is a schematic structural diagram of the reaction module; In the figure: 10 - First reaction kettle; 101 - Feed pipeline; 102 - Discharge pipeline; 20 - Second reaction kettle; 201 - Second reaction kettle level gauge; 30 - Third reaction kettle; 301 - Third reaction kettle level gauge; 40 - Fourth reaction kettle; 401 - Fourth reaction kettle level gauge; 50 - Fifth reaction kettle; 501 - Fifth reaction kettle level gauge; 60 - Transfer pump; 70 - First branch; 80 - Second branch; 90 - Third branch; 100 - First flow regulating valve; 110 - Second flow regulating valve; 120 - Third flow regulating valve; 130 - Fourth flow regulating valve; 140 - Fifth flow regulating valve; 150 - Sixth flow regulating valve; 160 - Seventh flow regulating valve; 170 - First flowmeter; 180 - Second flowmeter; 190 - Third flowmeter; 200 - Fourth flowmeter; 210 - Fifth flowmeter. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0022] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should also be understood that when the terms "comprising" and / or "including" are used in this specification, they specify the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0023] It should be noted that the terms "first", "second", etc. in the description, claims and drawings of the present application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein.

[0024] The present invention provides a method for continuously producing low molecular weight polyglycolic acid, which includes the following steps: A method for continuously producing low molecular weight polyglycolic acid, comprising: Methyl glycolate with a purity > 97% is continuously introduced into the first-stage prepolymerization reaction section, and the first-stage prepolymerization reaction products generated are respectively transported to the second-stage prepolymerization reaction section, the third-stage prepolymerization reaction section, and the fourth-stage prepolymerization reaction section according to different flow rate distributions to participate in the corresponding prepolymerization reactions; The second-stage prepolymerization reaction products generated in the second-stage prepolymerization reaction section directly enter the third-stage prepolymerization reaction section to participate in the third-stage prepolymerization reaction; The third-stage prepolymerization reaction products generated in the third-stage prepolymerization reaction section are divided into two paths according to different flow rates and respectively enter the fourth-stage prepolymerization reaction section and the fifth-stage prepolymerization reaction section to participate in the corresponding prepolymerization reactions; The fourth-stage prepolymerization reaction products generated in the fourth-stage prepolymerization reaction section directly enter the fifth-stage prepolymerization reaction section to participate in the fifth-stage prepolymerization reaction; The fifth-stage prepolymerization reaction section generates low molecular weight polyglycolic acid through the fifth-stage prepolymerization reaction.

[0025] In the present invention, the first-stage prepolymerization reaction products are divided into three paths according to a volume ratio of (4 - 5):(2 - 3):(1 - 2) and respectively enter the second-stage prepolymerization reaction section, the third-stage prepolymerization reaction section, and the fourth-stage prepolymerization reaction section.

[0026] In the present invention, the third-stage prepolymerization reaction products are divided into two paths according to a volume ratio of (5 - 6):(2 - 3) and respectively enter the fourth-stage prepolymerization reaction section and the fifth-stage prepolymerization reaction section.

[0027] In the present invention, the liquid level of the material participating in the second-stage prepolymerization reaction is lower than the liquid level of the material participating in the third-stage prepolymerization reaction; and the liquid levels of the materials in the third-stage prepolymerization reaction, the fourth-stage prepolymerization reaction, and the fifth-stage prepolymerization reaction are all equal.

[0028] In the present invention, the liquid level of the material participating in the secondary prepolymerization reaction is 60%-70% of the volume of the reaction kettle at this stage; the liquid level of the material participating in the tertiary prepolymerization reaction is 80%-85% of the volume of the reaction kettle at this stage.

[0029] In the present invention, the conditions of each prepolymerization reaction stage are as follows: The primary prepolymerization reaction stage: temperature 130±2°C, pressure 2KPa - 3KPa; The secondary prepolymerization reaction stage: temperature 150±2°C, pressure 2KPa - 3KPa; The tertiary prepolymerization reaction stage: temperature 170±3°C, pressure 70±1KPaA absolute pressure; The quaternary prepolymerization reaction stage: temperature 180±3°C, pressure 30±1KPaA absolute pressure; The quinary prepolymerization reaction stage: temperature 220±3°C, pressure 1.5±0.5KPaA absolute pressure.

[0030] A production system for realizing a continuous production method of low molecular weight polyglycolic acid, the production system includes a reaction module, a flow meter, a liquid level meter and a control module; The reaction module is used to realize that after the methyl glycolate raw material with a purity > 97% is introduced, it enters the primary prepolymerization reaction stage, and then undergoes continuous reactions through the secondary prepolymerization reaction stage, the tertiary prepolymerization reaction stage, the quaternary prepolymerization reaction stage and the quinary prepolymerization reaction stage in a split multi-stage parallel manner to generate low molecular weight polyglycolic acid; The flow meter: located on the split branch roads of each prepolymerization reaction stage of the reaction module, used to monitor the volume flow of each split branch road; The liquid level meter: used to obtain the material volume in the reaction equipment in the secondary prepolymerization reaction stage, the tertiary prepolymerization reaction stage, the quaternary prepolymerization reaction stage and the quinary prepolymerization reaction stage in the reaction module; The control module: used to control the volume flow of each split branch road according to the monitoring results of the flow meter and the set volume ratio of each split branch road.

[0031] In the present invention, the set volume ratio of each split branch road of the primary prepolymerization reaction product is (4~5):(2~3):(1~2); the set volume ratio of each split branch road of the tertiary prepolymerization reaction product is (5~6):(2~3).

[0032] In the present invention, the reaction module includes a first reaction kettle 10, a second reaction kettle 20, a third reaction kettle 30, a fourth reaction kettle 40 and a fifth reaction kettle 50 that are connected in sequence along the material flow direction; the first reaction kettle 10 is also connected to the third reaction kettle 30 through a first branch 70; the first reaction kettle 10 is also connected to the fourth reaction kettle 40 through a second branch 80; the third reaction kettle 30 is also connected to the fifth reaction kettle 50 through a third branch 90; In the present invention, liquid level gauges are respectively arranged on the second reaction kettle 20, the third reaction kettle 30, the fourth reaction kettle 40, and the fifth reaction kettle 50.

[0033] In the present invention, flow meters are respectively arranged on the first branch 70, the second branch 80, the third branch 90, between the first reaction kettle 10 and the second reaction kettle 20, and between the third reaction kettle 30 and the fourth reaction kettle 40.

[0034] The reaction module further includes flow regulating valves respectively arranged between the first reaction kettle 10 and the second reaction kettle 20, on the first branch 70, on the second branch 80, between the second reaction kettle 20 and the third reaction kettle 30, between the third reaction kettle 30 and the fourth reaction kettle 40, on the third branch 90, and between the fourth reaction kettle 40 and the fifth reaction kettle 50; each flow regulating valve is in signal connection with the control module. During implementation, it is used to control the valve opening of the flow regulating valve according to the monitoring results of the flow meter and the set volume ratio of each shunt branch, so as to adjust and control the volume flow of each shunt branch, making it shunt according to the set volume ratio.

[0035] Through the above methods and systems of the present invention, when methyl glycolate with a purity > 97% continuously passes through five reaction kettles for five-stage prepolymerization reaction, the low-purity polyglycolic acid generated in the first reaction kettle 10 not only enters the second reaction kettle 20 for secondary prepolymerization reaction, but also is shunted in parallel to the third reaction kettle 30 and the fourth reaction kettle 40 to participate in the tertiary prepolymerization reaction and the quaternary prepolymerization reaction respectively. The low-purity polyglycolic acid generated in the third reaction kettle 30 not only enters the fourth reaction kettle 40 for quaternary prepolymerization reaction, but also is shunted to the fifth reaction kettle 50 to participate in the fifth-stage prepolymerization reaction. Methyl glycolate with a purity > 97% undergoes each-stage prepolymerization reaction in a shunted and continuous parallel manner, thereby realizing the blending of low-purity polyglycolic acid and high-purity polyglycolic acid, reducing the viscosity of the materials in the reaction kettle, and avoiding blockage of the conveying pipeline; enabling the timely conveyance of materials, not only improving production efficiency, but also ensuring the continuity, stability, and controllability of the production of low-molecular-weight polyglycolic acid.

[0036] Example 1 This example provides a production system for realizing the continuous production of low-molecular-weight polyglycolic acid.

[0037] See Figure 1 and Figure 2 , the production system includes a reaction module, a flow meter, a liquid level gauge, and a control module.

[0038] In this embodiment, the reaction module is used to achieve that after the methyl glycolate raw material with a purity > 97% is introduced, it enters the first-stage prepolymerization reaction section, and then undergoes continuous reactions through the second-stage prepolymerization reaction section, the third-stage prepolymerization reaction section, the fourth-stage prepolymerization reaction section, and the fifth-stage prepolymerization reaction section in a split multi-stage parallel manner to generate low-molecular-weight polyglycolic acid.

[0039] See Figure 2 , preferably, the reaction module includes a first reaction kettle 10, a second reaction kettle 20, a third reaction kettle 30, a fourth reaction kettle 40, and a fifth reaction kettle 50 that are connected in sequence along the material flow direction; the first reaction kettle 10 is also connected to the third reaction kettle 30 through a first branch 70; wherein, the first reaction kettle 10 is also connected to the fourth reaction kettle 40 through a second branch 80; the third reaction kettle 30 is also connected to the fifth reaction kettle 50 through a third branch 90.

[0040] In this embodiment, the first reaction kettle 10, the second reaction kettle 20, the third reaction kettle 30, the fourth reaction kettle 40, and the fifth reaction kettle 50 are all prepolymerization reaction kettles, and the volume of the prepolymerization reaction kettle is 10m 3 , so that methyl glycolate with a purity > 97% undergoes five-stage prepolymerization reactions through five reaction kettles to continuously produce low-molecular-weight polyglycolic acid.

[0041] Preferably, in this embodiment, a feed pipeline 101 and a discharge pipeline 102 are respectively arranged on the first reaction kettle 10. The feed pipeline 101 is used to transport methyl glycolate with a purity > 97% into the first reaction kettle 10; the discharge pipeline 102 is used to transport the low-purity polyglycolic acid generated in the first reaction kettle 10 into the second reaction kettle 20.

[0042] In this embodiment, the discharge pipeline 102, the first branch 70, and the second branch 80 are three split branches of the first-stage prepolymerization reaction product; the connecting pipeline between the third reaction kettle 30 and the fourth reaction kettle 40 and the third branch 90 are two split branches of the third-stage prepolymerization reaction product.

[0043] In this embodiment, the reaction module further includes liquid level gauges respectively arranged on the second reaction kettle 20, the third reaction kettle 30, the fourth reaction kettle 40, and the fifth reaction kettle 50; each liquid level gauge is in signal connection with the control module.

[0044] In this embodiment, the flow meters are located on the split branches of each stage of the prepolymerization reaction section of the reaction module and are used to monitor the volumetric flow rates of the respective split branches.

[0045] Preferably, the flow meters are respectively arranged on the first branch 70, the second branch 80, the third branch 90, between the first reaction kettle 10 and the second reaction kettle 20, and between the third reaction kettle 30 and the fourth reaction kettle 40.

[0046] SeeFigure 2 , preferably, a first flowmeter 170 is provided on the discharge pipeline 102 between the first reaction kettle 10 and the second reaction kettle 20 to monitor the volume flow of the primary prepolymerization reaction product into the secondary prepolymerization reaction; a second flowmeter 180 is provided on the first branch 70 to monitor the volume flow of the primary prepolymerization reaction product into the tertiary prepolymerization reaction; a third flowmeter 190 is provided on the second branch 80 to monitor the volume flow of the primary prepolymerization reaction product into the quaternary prepolymerization reaction; a fourth flowmeter 200 is provided on the pipeline between the third reaction kettle 30 and the fourth reaction kettle 40 to monitor the volume flow of the tertiary prepolymerization reaction product into the quaternary prepolymerization reaction; a fifth flowmeter 210 is provided on the third branch 90 to monitor the volume flow of the tertiary prepolymerization reaction product into the quinary prepolymerization reaction.

[0047] In this embodiment, the liquid level gauge is used to obtain the material volume in the reaction equipment in the secondary prepolymerization reaction section, the tertiary prepolymerization reaction section, the quaternary prepolymerization reaction section, and the quinary prepolymerization reaction section of the reaction module. Specifically, the liquid level height of the material in the reaction equipment in each prepolymerization reaction section is monitored by the liquid level gauge, and then the corresponding material volume is obtained in combination with the size of the reaction equipment.

[0048] See Figure 2 , preferably, a second reaction kettle liquid level gauge 201 is further provided on the second reaction kettle 20, and the material volume participating in the secondary prepolymerization reaction in the second reaction kettle 20 is obtained through the second reaction kettle liquid level gauge 201; a third reaction kettle liquid level gauge 301 is further provided on the third reaction kettle 30, and the material volume participating in the tertiary prepolymerization reaction in the third reaction kettle 30 is obtained through the third reaction kettle liquid level gauge 301; a fourth reaction kettle liquid level gauge 401 is further provided on the fourth reaction kettle 40, and the material volume participating in the quaternary prepolymerization reaction in the fourth reaction kettle 40 is obtained through the fourth reaction kettle liquid level gauge 401; a fifth reaction kettle liquid level gauge 501 is further provided on the fifth reaction kettle 50. The material volume participating in the quinary prepolymerization reaction in the fifth reaction kettle 50 is obtained through the fifth reaction kettle liquid level gauge 501.

[0049] Preferably, the material participating in the secondary prepolymerization reaction is polyglycolic acid with a purity of 40%; the material participating in the tertiary prepolymerization reaction is a mixture of polyglycolic acid with a purity of 40% and polyglycolic acid with a purity of 60%; the material participating in the quaternary prepolymerization reaction is a mixture of polyglycolic acid with a purity of 40% and polyglycolic acid with a purity of 70%; the material participating in the quinary prepolymerization reaction is a mixture of polyglycolic acid with a purity of 80% and polyglycolic acid with a purity of 70%. The liquid level monitored by the second reaction kettle liquid level gauge 201 is 60%-70% of the volume of the second reaction kettle 20, and the liquid level monitored by the third reaction kettle liquid level gauge 301 is 80%-85% of the volume of the third reaction kettle 30.

[0050] In this embodiment, the reaction module further includes flow regulating valves respectively disposed between the first reactor 10 and the second reactor 20, on the first branch 70, on the second branch 80, between the second reactor 20 and the third reactor 30, between the third reactor 30 and the fourth reactor 40, on the third branch 90, and between the fourth reactor 40 and the fifth reactor 50.

[0051] See Figure 2 , preferably, between the first reactor 10 and the second reactor 20, i.e., on the discharge pipeline 102, a first flow regulating valve 100 is provided to adjust the volumetric flow rate of the material transported from the first reactor 10 into the second reactor 20 through the first flow regulating valve 100; a second flow regulating valve 110 is provided on the first branch 70 to adjust the volumetric flow rate of the material transported from the first reactor 10 into the third reactor 30 through the second flow regulating valve 110; a third flow regulating valve 120 is provided on the second branch 80 to adjust the volumetric flow rate of the material transported from the first reactor 10 into the fourth reactor 40 through the third flow regulating valve 120; a fourth flow regulating valve 130 is provided between the second reactor 20 and the third reactor 30 to adjust the volumetric flow rate of the material transported from the second reactor 20 into the third reactor 30 through the fourth flow regulating valve 130; a fifth flow regulating valve 140 is provided between the third reactor 30 and the fourth reactor 40 to adjust the volumetric flow rate of the material transported from the third reactor 30 into the fourth reactor 40 through the fifth flow regulating valve 140; a sixth flow regulating valve 150 is provided on the third branch 90 to adjust the volumetric flow rate of the material transported from the third reactor 30 into the fifth reactor 50 through the sixth flow regulating valve 150; a seventh flow regulating valve 160 is provided between the fourth reactor 40 and the fifth reactor 50 to adjust the volumetric flow rate of the material transported from the fourth reactor 40 into the fifth reactor 50 through the seventh flow regulating valve 160.

[0052] In this embodiment, the control module is used to control the volumetric flow rates of the respective shunt branches according to the monitoring results of the flowmeter and the set volume ratios of the respective shunt branches. During the prepolymerization reaction, the set volume ratios of the respective shunt branches of the primary prepolymerization reaction product are (4 - 5):(2 - 3):(1 - 2); the set volume ratios of the respective shunt branches of the tertiary prepolymerization reaction product are (5 - 6):(2 - 3). The control module performs shunting according to the set volume ratios, and the flowmeter transmits the monitored corresponding volumetric flow rate data to the control module to ensure that the shunt flow rate is controlled in real time. The opening degrees of the first flow regulating valve 100, the second flow regulating valve 110, and the third flow regulating valve 120 are respectively controlled so that the primary prepolymerization reaction product is divided into three paths according to the set volume ratio (4 - 5):(2 - 3):(1 - 2) and flows into the second reaction kettle 20, the third reaction kettle 30, and the fourth reaction kettle 40 through three shunt branches correspondingly; at the same time, the opening degrees of the fifth flow regulating valve 140 and the sixth flow regulating valve 150 are controlled so that the tertiary prepolymerization reaction product is divided into two paths according to the volume ratio (5 - 6):(2 - 3) and flows into the fourth reaction kettle 40 and the fifth reaction kettle 50 through two shunt branches respectively.

[0053] In this embodiment, during the prepolymerization reaction, the liquid level data signals monitored by each liquid level gauge are transmitted to the control module. The control module also controls the opening degrees of the fourth flow regulating valve 130 and the seventh flow regulating valve 160 according to each liquid level value, so that the volume of the material participating in the secondary prepolymerization reaction is less than the volume of the material participating in the tertiary prepolymerization reaction (i.e., the monitored liquid level of the liquid level gauge 201 of the second reaction kettle is lower than the monitored liquid level of the liquid level gauge 301 of the third reaction kettle), and the volumes of the materials in the tertiary prepolymerization reaction, the quaternary prepolymerization reaction, and the quinary prepolymerization reaction are equal, that is, the monitored liquid levels of the liquid level gauge 301 of the third reaction kettle, the liquid level gauge 401 of the fourth reaction kettle, and the liquid level gauge 501 of the fifth reaction kettle are all equal.

[0054] In the reaction module of this embodiment, a transfer pump 60 is further provided between the third reaction kettle 30 and the fourth reaction kettle 40; and the transfer pump 60 is located between the third reaction kettle 30 and the third branch 90; through the transfer pump 60, the material coming out from the bottom of the third reaction kettle 30 can be divided into two paths and quickly flow into the fourth reaction kettle 40 and the fifth reaction kettle 50, accelerating the material transfer speed and improving the production efficiency.

[0055] The control module in this embodiment is also used to control the conditions of the prepolymerization reaction in the five reaction kettles in the reaction module.

[0056] Preferably, the control module is a programmable control module or can also be a DCS control module. The control modules are all control modules commonly used in the production of low molecular weight polyglycolic acid.

[0057] Embodiment 2 This embodiment provides a method for continuously producing low-molecular-weight polyglycolic acid, including: Methyl glycolate with a purity > 97% is continuously introduced into the first-stage prepolymerization reaction section for the first-stage prepolymerization reaction. The resulting first-stage prepolymerization reaction product is divided into three paths according to different flow rates and respectively enters the second-stage prepolymerization reaction section, the third-stage prepolymerization reaction section, and the fourth-stage prepolymerization reaction section to participate in the corresponding prepolymerization reactions; The second-stage prepolymerization reaction product generated in the second-stage prepolymerization reaction section directly enters the third-stage prepolymerization reaction section to participate in the third-stage prepolymerization reaction; The third-stage prepolymerization reaction product generated in the third-stage prepolymerization reaction section is divided into two paths according to different flow rates and respectively enters the fourth-stage prepolymerization reaction section and the fifth-stage prepolymerization reaction section to participate in the corresponding prepolymerization reactions; The fourth-stage prepolymerization reaction product generated in the fourth-stage prepolymerization reaction section directly enters the fifth-stage prepolymerization reaction section to participate in the fifth-stage prepolymerization reaction; Low-molecular-weight polyglycolic acid is generated through the fifth-stage prepolymerization reaction in the fifth-stage prepolymerization reaction section.

[0058] In the continuous production method provided by this embodiment, when methyl glycolate with a purity > 97% passes through the five-stage prepolymerization reaction sections in series, the first-stage prepolymerization reaction product is also diverted to the third-stage prepolymerization reaction section and the fourth-stage prepolymerization reaction section, and the third-stage prepolymerization reaction product is also diverted to the fifth-stage prepolymerization reaction section; enabling methyl glycolate with a purity > 97% to achieve continuous production in a way of diversion and multi-stage parallel operation, and using the low-purity polyglycolic acid generated at the front end and the high-purity polyglycolic acid at the back end for blending. For example, the first-stage prepolymerization reaction product enters the third-stage prepolymerization reaction section to be mixed and blended with the second-stage prepolymerization reaction product, and the first-stage prepolymerization reaction product enters the fourth-stage prepolymerization reaction section to be mixed and blended with the third-stage prepolymerization reaction product; thus not only can avoid viscosity reaching the pipeline blockage, but also ensure the continuous and stable transportation of the prepolymerization reaction products at all levels, and realize the continuous production of low-molecular-weight polyglycolic acid.

[0059] In this embodiment, the process of continuously producing low-molecular-weight polyglycolic acid is as follows: Methyl glycolate with a purity > 97% is introduced into the first reaction kettle 10 for the first-stage prepolymerization reaction to obtain the first-stage prepolymerization reaction product (i.e., polyglycolic acid with a purity of 40%); the conditions for the first-stage prepolymerization reaction in the first reaction kettle 10 are: temperature 130 °C, slightly positive pressure of 2 - 3 KPa. Therefore, the first-stage prepolymerization reaction product comes out from the bottom of the first reaction kettle 10, and then is divided into three paths according to a volume ratio of 5:3:2 and respectively flows into the second reaction kettle 20, the third reaction kettle 30, and the fourth reaction kettle 40 through three shunt branches. Calculated by volume, among the first-stage prepolymerization reaction product, 50% participates in the second-stage prepolymerization reaction, 30% participates in the third-stage prepolymerization reaction, and 20% participates in the fourth-stage prepolymerization reaction.

[0060] In implementation, the volume flow rates of the primary prepolymerization reaction products in these three shunt branches are respectively monitored in real time by a first flowmeter 170, a second flowmeter 180, and a third flowmeter 190, and the opening degrees of three valves, namely a first flow regulating valve 100, a second flow regulating valve 110, and a third flow regulating valve 120, are respectively adjusted by a control module, so as to ensure that the primary prepolymerization reaction products are shunted into three paths according to a set volume ratio of 5:2:1.

[0061] In the second reactor 20, 50% of the primary prepolymerization reaction products (polyglycolic acid with a purity of 40%) undergo a secondary prepolymerization reaction to obtain secondary prepolymerization reaction products (polyglycolic acid with a purity of 60%), and all enter the third reactor 30; the conditions for the second reactor 20 to undergo the secondary prepolymerization reaction are: a temperature of 150°C and a slightly positive pressure of 2 - 3 KPa. In implementation, the control module also controls the volume of the materials participating in the secondary prepolymerization reaction in the second reactor 20 to be 60% - 70% of the volume of the second reactor 20.

[0062] In the third reactor 30, 30% of the primary prepolymerization reaction products and the secondary prepolymerization reaction products enter the third reactor 30 for mixing synchronously; that is, after polyglycolic acid with a purity of 40% and polyglycolic acid with a purity of 60% are mixed, a tertiary prepolymerization reaction is carried out to obtain tertiary prepolymerization reaction products (polyglycolic acid with a purity of 70%). The conditions for the third reactor 30 to carry out the tertiary prepolymerization reaction are: 170°C and an absolute pressure of 70 KPaA. The tertiary prepolymerization reaction products are divided into two paths according to a volume ratio of 5:3 and flow into the fourth reactor 40 and the fifth reactor 50 respectively through the corresponding two shunt branches. Calculated by volume, among the tertiary prepolymerization reaction products, 62.5% participate in the quaternary prepolymerization reaction and 37.5% participate in the quinary prepolymerization reaction.

[0063] In implementation, the volume flow rates of the tertiary prepolymerization reaction products in these two shunt branches are respectively monitored in real time by a fourth flowmeter 200 and a fifth flowmeter 210, and the opening degrees of two valves, namely a fifth flow regulating valve 140 and a sixth flow regulating valve 150, are respectively adjusted by the control module to ensure that the tertiary prepolymerization reaction products are divided into two paths according to a set volume ratio of 5:3 for shunting. At the same time, the control module also controls the volume of the materials participating in the tertiary prepolymerization reaction in the third reactor 30 to be 80% - 85% of the volume of the third reactor 30.

[0064] In the fourth reactor 40, 20% of the first-stage prepolymerization product and 62.5% of the third-stage prepolymerization product are simultaneously mixed in the fourth reactor 40, that is, 20% of the volume of polyglycolic acid with a purity of 40% and 62.5% of the volume of polyglycolic acid with a purity of 70% are mixed and then subjected to a fourth-stage prepolymerization reaction to obtain a fourth-stage prepolymerization product (polyglycolic acid with a purity of 80%). The conditions for the fourth reactor 40 to perform the fourth-stage prepolymerization reaction are: 180°C, 30KPaA absolute pressure. The generated fourth-stage prepolymerization products all flow into the fifth reactor 50 to participate in the fifth-stage prepolymerization reaction. In implementation, the control module also controls the volume of the material participating in the fourth-stage prepolymerization reaction in the fourth reactor 40 to be 80%-85% of the volume of the fourth reactor 40.

[0065] In the fifth reactor 50, 37.5% of the third-stage prepolymerization product and the fourth-stage prepolymerization product are simultaneously mixed in the fifth reactor 50, that is, 37.5% of the volume of polyglycolic acid with a purity of 70% and 80% of the purity of polyglycolic acid are mixed and then subjected to a fifth-stage prepolymerization reaction to obtain a fifth-stage prepolymerization product (i.e., polyglycolic acid with a purity of 95%); the conditions for the fifth reactor 50 to carry out the fifth-stage prepolymerization reaction are: 220°C, 1.5KPaA absolute pressure. In the implementation, the control module also controls the volume of the material participating in the fifth-stage prepolymerization reaction in the fifth reactor 50 to be 80%-85% of the volume of the fifth reactor 50. The fifth-stage prepolymerization product comes out from the bottom of the fifth reactor 50 and is then collected to obtain a low molecular weight polyglycolic acid.

[0066] According to the above operation, methyl glycolate with a purity of more than 97% is continuously produced in a multi-stage parallel manner to obtain polyglycolic acid with a purity of 95%, that is, low molecular weight polyglycolic acid. The present invention transports the generated low-purity polyglycolic acid to the rear end step by step or skipping steps according to a specific volume ratio to mix with high-purity polyglycolic acid, so that the materials generated by each stage of prepolymerization can be quickly and stably transported in a short time, thereby improving production efficiency and continuity of material transportation; it also avoids frequent blockage of the transportation pipeline, and realizes continuous production of low molecular weight polyglycolic acid.

[0067] In the above embodiments, the volume ratio of the primary prepolymerization product divided into three routes can be selected and replaced within (4-5): (2-3): (1-2), and the volume ratio of the tertiary prepolymerization product divided into two routes can be selected and replaced within (5-6): (2-3), thereby avoiding frequent blockage of the conveying pipeline and enabling stable and continuous production of low molecular weight polyglycolic acid.

[0068] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A continuous production method of low molecular weight polyglycolic acid, characterized in that, Including: Methyl glycolate with a purity > 97% is continuously introduced into the first-stage pre-polymerization reaction section, and the first-stage pre-polymerization reaction products are transported to the second-stage pre-polymerization reaction section, the third-stage pre-polymerization reaction section, and the fourth-stage pre-polymerization reaction section according to different flow rate distributions to participate in the corresponding pre-polymerization reactions; The second-stage pre-polymerization reaction products generated in the second-stage pre-polymerization reaction section directly enter the third-stage pre-polymerization reaction section to participate in the third-stage pre-polymerization reaction; The third-stage pre-polymerization reaction products generated in the third-stage pre-polymerization reaction section are divided into two paths according to different flow rates and respectively enter the fourth-stage pre-polymerization reaction section and the fifth-stage pre-polymerization reaction section to participate in the corresponding pre-polymerization reactions; The fourth-stage pre-polymerization reaction products generated in the fourth-stage pre-polymerization reaction section directly enter the fifth-stage pre-polymerization reaction section to participate in the fifth-stage pre-polymerization reaction; Low-molecular-weight polyglycolic acid is generated through the fifth-stage pre-polymerization reaction in the fifth-stage pre-polymerization reaction section.

2. The continuous production method of low molecular weight polyglycolic acid according to claim 1, characterized in that, The first-stage pre-polymerization reaction products are divided into three paths according to the volume ratio of (4 - 5):(2 - 3):(1 - 2) and respectively enter the second-stage pre-polymerization reaction section, the third-stage pre-polymerization reaction section, and the fourth-stage pre-polymerization reaction section.

3. The continuous production method of low molecular weight polyglycolic acid according to claim 1, characterized in that, The third-stage pre-polymerization reaction products are divided into two paths according to the volume ratio of (5 - 6):(2 - 3) and respectively enter the fourth-stage pre-polymerization reaction section and the fifth-stage pre-polymerization reaction section.

4. The continuous production method of low molecular weight polyglycolic acid according to claim 1, characterized in that, The volume of the material participating in the second-stage pre-polymerization reaction is less than the volume of the material participating in the third-stage pre-polymerization reaction; and the volumes of the materials in the third-stage pre-polymerization reaction, the fourth-stage pre-polymerization reaction, and the fifth-stage pre-polymerization reaction are all equal.

5. The continuous production method of low molecular weight polyglycolic acid according to claim 4, characterized in that, The volume of the material participating in the second-stage pre-polymerization reaction is 60% - 70% of the reaction equipment volume of the second-stage pre-polymerization reaction section; the volume of the material participating in the third-stage pre-polymerization reaction is 80% - 85% of the reaction equipment volume of the third-stage pre-polymerization reaction section.

6. The continuous production method of low molecular weight polyglycolic acid according to any one of claims 1-5, characterized in that, The conditions of each stage of the pre-polymerization reaction section are as follows: First-stage pre-polymerization reaction section: temperature 130 ± 2°C, pressure 2 KPa - 3 KPa; Second-stage pre-polymerization reaction section: temperature 150 ± 2°C, pressure 2 KPa - 3 KPa; Third-stage pre-polymerization reaction section: temperature 170 ± 3°C, pressure 70 ± 1 KPaA absolute pressure; Fourth-stage pre-polymerization reaction section: temperature 180 ± 3°C, pressure 30 ± 1 KPaA absolute pressure; Fifth-stage pre-polymerization reaction section: temperature 220 ± 3°C, pressure 1.5 ± 0.5 KPaA absolute pressure.

7. A production system for implementing the continuous production method of low molecular weight polyglycolic acid described in claim 5, characterized in that, The production system includes a reaction module, a flow meter, a liquid level meter, and a control module; The reaction module is used to realize that after the raw material of methyl glycolate with a purity > 97% is introduced, it enters the first-stage pre-polymerization reaction section, and then undergoes continuous reactions through the second-stage pre-polymerization reaction section, the third-stage pre-polymerization reaction section, the fourth-stage pre-polymerization reaction section, and the fifth-stage pre-polymerization reaction section in a multi-stage parallel shunt manner to generate low-molecular-weight polyglycolic acid; The flow meter: is located on the shunt branch roads of each stage of the pre-polymerization reaction section of the reaction module and is used to monitor the volume flow rates of each shunt branch road; The liquid level meter: is used to obtain the material volumes in the reaction equipment in the second-stage pre-polymerization reaction section, the third-stage pre-polymerization reaction section, the fourth-stage pre-polymerization reaction section, and the fifth-stage pre-polymerization reaction section of the reaction module; The control module: is used to control the volume flow rates of each shunt branch road according to the monitoring results of the flow meter and the set volume ratios of each shunt branch road.

8. The production system according to claim 7, wherein Set the volume ratios of the respective shunt branches through which the primary prepolymerization reaction product stream flows to be (4 - 5):(2 - 3):(1 - 2); set the volume ratios of the respective shunt branches through which the tertiary prepolymerization reaction product stream flows to be (5 - 6):(2 - 3).

9. The production system according to claim 8, characterized in that, The reaction module includes a first reaction kettle (10), a second reaction kettle (20), a third reaction kettle (30), a fourth reaction kettle (40) and a fifth reaction kettle (50) that are connected in sequence along the material flow direction; the first reaction kettle (10) is also connected to the third reaction kettle (30) through a first branch (70); the first reaction kettle (10) is also connected to the fourth reaction kettle (40) through a second branch (80); the third reaction kettle (30) is also connected to the fifth reaction kettle (50) through a third branch (90); The flow meters are respectively arranged on the first branch (70), the second branch (80), the third branch (90), between the first reaction kettle (10) and the second reaction kettle (20), and between the third reaction kettle (30) and the fourth reaction kettle (40); The liquid level gauges are respectively arranged on the second reaction kettle (20), the third reaction kettle (30), the fourth reaction kettle (40) and the fifth reaction kettle (50).

10. The production system according to claim 9, characterized in that, The reaction module further includes flow regulating valves respectively arranged between the first reaction kettle (10) and the second reaction kettle (20), on the first branch (70), on the second branch (80), between the second reaction kettle (20) and the third reaction kettle (30), between the third reaction kettle (30) and the fourth reaction kettle (40), on the third branch (90), and between the fourth reaction kettle (40) and the fifth reaction kettle (50); each flow regulating valve is controlled by a control module.

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