A continuous production method and system for low molecular weight polyglycolic acid

Abstract

This invention belongs to the field of polyglycolic acid (PGA) production technology, and relates to a continuous production method and system for low molecular weight PGA. Methyl glycolate with a purity >97% is introduced into a primary prepolymerization reaction section. The generated primary prepolymerization products are distributed according to different flow rates and transported to secondary, tertiary, and quaternary prepolymerization reaction sections to participate in their respective prepolymerization reactions. The secondary prepolymerization products generated in the secondary prepolymerization reaction section directly participate in the tertiary prepolymerization reaction. The tertiary prepolymerization products generated in the tertiary prepolymerization reaction section enter the quaternary and quinary prepolymerization reaction sections respectively. The quaternary prepolymerization products generated in the quaternary prepolymerization reaction section directly enter the quinary prepolymerization reaction section to participate in the reaction. The quinary prepolymerization reaction section generates low molecular weight PGA. This invention diverts and transports the prepolymerization products of each stage in parallel in multiple stages, improving production efficiency, avoiding frequent blockages in centralized, step-by-step transport pipelines, and achieving continuous production of low molecular weight PGA.

Description

Technical Field

[0001] This invention belongs to the technical field of polyglycolic acid production equipment, and relates to a continuous production method and system for low molecular weight polyglycolic acid. Background Technology

[0002] The process of producing polyglycolic acid from dimethyl oxalate includes: hydrogenation of dimethyl oxalate to produce methyl glycolate; then, under the action of a catalyst, methyl glycolate undergoes condensation polymerization to form polyglycolic acid; the condensation polymerization includes prepolymerization (referred to as prepolymerization) and final condensation polymerization. In prepolymerization, methyl glycolate undergoes multiple prepolymerization reactions to gradually form low molecular weight polyglycolic acid (intermediate product); then, the low molecular weight polyglycolic acid (intermediate product) undergoes further final condensation polymerization to obtain high molecular weight polyglycolic acid, i.e., polyglycolic acid. In actual industrial production, prepolymerization is a crucial step in the production of polyglycolic acid from dimethyl oxalate, and the success of the prepolymerization process directly affects the subsequent final condensation polymerization process.

[0003] The existing industrial prepolymer production process is as follows: five reactors are set up in series (according to the order of the reactors, the five reactors 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 (raw material) with a purity >97% is introduced; the raw material undergoes five prepolymerization stages to finally form polyglycolic acid with a purity of 95%, which is low molecular weight polyglycolic acid (intermediate product). Although existing prepolymerization processes can produce low molecular weight polyglycolic acid (PEGylated PEG) through a five-stage prepolymerization reaction, the purity of methyl glycolate (>97%) needs to remain in each reactor for a sufficient time to obtain PEGylated PEG with the required purity. As the reaction progresses through each stage, the purity of the PEGylated PEG increases, meaning the PEG content in the material transported to the next stage is increasingly higher. However, as the PEG content generated in each stage of prepolymerization increases, its viscosity also increases. The high-viscosity PEGylated PEG generated in the previous reactor requires a longer time to be transported to the next stage, making it difficult to transport the high-viscosity PEGylated PEG to subsequent reactors in a timely and stable manner, resulting in poor production continuity and low production efficiency. Furthermore, the increased viscosity of PEGylated PEG can cause frequent blockages in the reactor's transport pipelines, requiring shutdown and maintenance in case of blockages, making it difficult to achieve continuous and stable prepolymerization. Summary of the Invention

[0004] To address the technical problems of poor continuity, low production efficiency, and frequent blockages in pipelines in the production of low molecular weight polyglycolic acid, this invention provides a continuous production method and system for low molecular weight polyglycolic acid.

[0005] In the stepwise prepolymerization reaction, this invention further diverts the first-stage prepolymerization product to the third-stage and fourth-stage prepolymerization reactions, and the third-stage prepolymerization product to the fifth-stage prepolymerization reaction. By transporting the prepolymerization products of each stage in a multi-stage parallel manner, the low-purity prepolymerization product at the front end is transported across stages and mixed with the high-purity prepolymerization product at the back end. This not only ensures the timely and stable delivery of low molecular weight polyglycolic acid and improves production efficiency, but also avoids frequent blockages in the delivery pipeline, enabling continuous production of low molecular weight polyglycolic acid.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A continuous production method for low molecular weight polyglycolic acid, comprising:

[0008] Methyl glycolate with a purity >97% is continuously fed into the primary prepolymerization reaction section. The generated primary prepolymerization reaction products are distributed to the secondary, tertiary and quaternary prepolymerization reaction sections according to different flow rates to participate in the corresponding prepolymerization reactions.

[0009] The secondary prepolymerization products generated in the secondary prepolymerization reaction stage directly enter the tertiary prepolymerization reaction stage to participate in the tertiary prepolymerization reaction.

[0010] The prepolymerization products generated in the three-stage prepolymerization reaction section are divided into two streams according to different flow rates and enter the four-stage and five-stage prepolymerization reaction sections respectively to participate in the corresponding prepolymerization reactions.

[0011] The fourth-stage prepolymerization 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.

[0012] The five-stage prepolymerization reaction stage generates low molecular weight polyglycolic acid through a five-stage prepolymerization reaction.

[0013] The primary prepolymerization product is divided into three streams according to the volume ratio (4~5):(2~3):(1~2) and enters the secondary, tertiary and quaternary prepolymerization reaction sections respectively.

[0014] The products of the three-stage prepolymerization reaction are divided into two streams according to the volume ratio of (5~6):(2~3) and enter the four-stage prepolymerization reaction section and the five-stage prepolymerization reaction section respectively.

[0015] Further, the volume of material participating in the secondary prepolymerization reaction is smaller than the volume of material participating in the tertiary prepolymerization reaction; and the volumes of material in the tertiary, quaternary, and quinary prepolymerization reactions are all equal.

[0016] Further, the volume of material 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 material participating in the tertiary prepolymerization reaction is 80%-85% of the volume of the reaction equipment in the tertiary prepolymerization reaction section.

[0017] Further specifying the conditions for each stage of the prepolymerization reaction, they are as follows:

[0018] Primary prepolymerization reaction section: temperature 130±2℃, pressure 2KPa-3KPa;

[0019] Secondary prepolymerization reaction section: temperature 150±2℃, pressure 2KPa-3KPa;

[0020] Three-stage prepolymerization reaction section: temperature 170±3℃, pressure 70±1KPaA absolute pressure;

[0021] Fourth-stage prepolymerization reaction section: temperature 180±3℃, pressure 30±1KPaA absolute pressure;

[0022] Five-stage prepolymerization reaction section: temperature 220±3℃, pressure 1.5±0.5KPaA absolute pressure.

[0023] A production system for implementing the continuous production method of low molecular weight polyglycolic acid, the production system comprising a reaction module, a flow meter, a level gauge, and a control module;

[0024] The reaction module is used to enable the methyl glycolate raw material with a purity of >97% to enter the first-stage prepolymerization reaction section, and then continuously react in a split-flow, multi-stage parallel manner through the second-stage, third-stage, fourth-stage, and fifth-stage prepolymerization reaction sections to generate low molecular weight polyglycolic acid.

[0025] The flow meter is located on the branch line of each prepolymerization reaction section of the reaction module and is used to monitor the volumetric flow rate of each branch line.

[0026] The level gauge is used to obtain the volume of material in the reaction equipment of the secondary, tertiary, quaternary, and quinary prepolymerization reaction sections of the reaction module.

[0027] The control module is used to control the volumetric flow rate of each branch based on the monitoring results of the flow meter and the set volume ratio of each branch.

[0028] Further, the volume ratio of each branch of the primary prepolymer reaction product is set as (4~5):(2~3):(1~2); and the volume ratio of each branch of the tertiary prepolymer reaction product is set as (5~6):(2~3).

[0029] Further defined, the reaction module includes a first reaction vessel, a second reaction vessel, a third reaction vessel, a fourth reaction vessel, and a fifth reaction vessel connected sequentially along the material flow direction; the first reaction vessel is also connected to the third reaction vessel via a first branch; the first reaction vessel is also connected to the fourth reaction vessel via a second branch; and the third reaction vessel is also connected to the fifth reaction vessel via a third branch.

[0030] The flow meters are respectively installed on the first branch, the second branch, the third branch, between the first and second reactors, and between the third and fourth reactors;

[0031] The level gauges are respectively installed on the second, third, fourth and fifth reaction vessels.

[0032] Further specifying, the reaction module also includes flow regulating valves respectively disposed between the first and second reactors, on the first branch, on the second branch, between the second and third reactors, between the third and fourth reactors, on the third branch, and between the fourth and fifth reactors; each flow regulating valve is signal-connected to the control module.

[0033] Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

[0034] 1. This invention, while carrying out the step-by-step prepolymerization reaction, also diverts the first-stage prepolymerization product to the third-stage and fourth-stage prepolymerization reaction sections, and the third-stage prepolymerization product to the fifth-stage prepolymerization reaction section; thus, it achieves timely and stable delivery of the prepolymerization products at each stage in a multi-stage parallel manner. This design involves the skip-stage delivery of low-purity prepolymerization products at the front end and the blending of high-purity prepolymerization products at the back end. On the one hand, the low-purity prepolymerization products have low viscosity, which facilitates the timely and stable delivery of prepolymerization products at each stage, improving production efficiency; on the other hand, it avoids the frequent pipeline blockage problem caused by the delivery of large quantities of high-viscosity polyglycolic acid, ensuring continuous production of low molecular weight polyglycolic acid.

[0035] 2. In this invention, the primary prepolymerization product is divided into three streams according to a volume ratio of (4~5):(2~3):(1~2) and enters the secondary, tertiary, and quaternary prepolymerization reaction sections respectively to participate in the corresponding prepolymerization reactions; the tertiary prepolymerization product is divided into two streams according to a volume ratio of (5~6):(2~3) and enters the quaternary and quinary prepolymerization reaction sections respectively to participate in the corresponding prepolymerization reactions; this allows the low-purity polyglycolic acid to be transported step by step while simultaneously being mixed with the high-purity polyglycolic acid at a better volume ratio, thereby accelerating the reaction process of low molecular weight glycolic acid, improving production efficiency, and further enhancing the stability and continuity of production.

[0036] 3. In the blending process of this invention, the volume of material participating in the secondary prepolymerization reaction is smaller than that participating in the tertiary prepolymerization reaction; and the volumes of material in the tertiary, quaternary, and quinary prepolymerization reactions are all equal. This ensures that the materials in each stage of the prepolymerization reaction can better complete their respective prepolymerization reactions, guaranteeing that methyl glycolate raw materials with a purity >97% can be converted into low molecular weight polyglycolic acid through the five-stage prepolymerization reaction in a shorter time, improving the continuous production efficiency of low molecular weight polyglycolic acid, and also making the five-stage prepolymerization reaction more stable.

[0037] 4. This invention also provides a production system including a reaction module, flow meters, level gauges, and a control module. It enables the continuous reaction of low molecular weight polyglycolic acid (PGA) by introducing methyl glycolate raw material with a purity >97% into a primary prepolymerization reaction section, followed by secondary, tertiary, quaternary, and quinary prepolymerization reaction sections in a multi-stage parallel manner. Flow meters located on the branch lines of each prepolymerization reaction section of the reaction module are used to monitor the volumetric flow rate of each branch. Simultaneously, the volumetric flow rate of each branch is controlled based on the flow meter monitoring results and the set volume ratio of each branch, ensuring continuous reaction by feeding according to the branch volume ratio. This ensures that the material is delivered at the set volume ratio under the corresponding prepolymerization reaction conditions, guaranteeing the continuity, stability, and controllability of PGA production. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the production system structure;

[0039] Figure 2 This is a schematic diagram of the reaction module.

[0040] In the picture:

[0041] 10-First reactor; 101-Infeed line; 102-Discharge line; 20-Second reactor; 201-Second reactor level gauge; 30-Third reactor; 301-Third reactor level gauge; 40-Fourth reactor; 401-Fourth reactor level gauge; 50-Fifth reactor; 501-Fifth reactor level gauge; 60-Transfer pump; 70-First branch; 80-Second branch; 90-Third branch; 100-First flow control valve; 110-Second flow control valve; 120-Third flow control valve; 130-Fourth flow control valve; 140-Fifth flow control valve; 150-Sixth flow control valve; 160-Seventh flow control valve; 170-First flow meter; 180-Second flow meter; 190-Third flow meter; 200-Fourth flow meter; 210-Fifth flow meter. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0043] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0044] It should be noted that the terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in sequences other than those illustrated or described herein.

[0045] This invention provides a continuous production method for low molecular weight polyglycolic acid, comprising the following steps:

[0046] A continuous production method for low molecular weight polyglycolic acid, comprising:

[0047] Methyl glycolate with a purity >97% is continuously fed into the primary prepolymerization reaction section. The generated primary prepolymerization reaction products are distributed to the secondary, tertiary and quaternary prepolymerization reaction sections according to different flow rates to participate in the corresponding prepolymerization reactions.

[0048] The secondary prepolymerization products generated in the secondary prepolymerization reaction stage directly enter the tertiary prepolymerization reaction stage to participate in the tertiary prepolymerization reaction.

[0049] The prepolymerization products generated in the three-stage prepolymerization reaction section are divided into two streams according to different flow rates and enter the four-stage and five-stage prepolymerization reaction sections respectively to participate in the corresponding prepolymerization reactions.

[0050] The fourth-stage prepolymerization 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.

[0051] The five-stage prepolymerization reaction stage generates low molecular weight polyglycolic acid through a five-stage prepolymerization reaction.

[0052] In this invention, the primary prepolymerization product is divided into three streams according to the volume ratio of (4~5):(2~3):(1~2) and enters the secondary, tertiary and quaternary prepolymerization reaction sections respectively.

[0053] In this invention, the products of the three-stage prepolymerization reaction are divided into two streams according to a volume ratio of (5~6):(2~3) and enter the four-stage prepolymerization reaction section and the five-stage prepolymerization reaction section respectively.

[0054] In this invention, the liquid level of the material participating in the secondary prepolymerization reaction is lower than that of the material participating in the tertiary prepolymerization reaction; and the liquid levels of the material in the tertiary, quaternary, and quinary prepolymerization reactions are all equal.

[0055] In this invention, the liquid level of the material participating in the secondary prepolymerization reaction is 60%-70% of the volume of the reactor at that stage; the liquid level of the material participating in the tertiary prepolymerization reaction is 80%-85% of the volume of the reactor at that stage.

[0056] In this invention, the conditions for each stage of the prepolymerization reaction are as follows:

[0057] Primary prepolymerization reaction section: temperature 130±2℃, pressure 2KPa-3KPa;

[0058] Secondary prepolymerization reaction section: temperature 150±2℃, pressure 2KPa-3KPa;

[0059] Three-stage prepolymerization reaction section: temperature 170±3℃, pressure 70±1KPaA absolute pressure;

[0060] Fourth-stage prepolymerization reaction section: temperature 180±3℃, pressure 30±1KPaA absolute pressure;

[0061] Five-stage prepolymerization reaction section: temperature 220±3℃, pressure 1.5±0.5KPaA absolute pressure.

[0062] A production system for continuous production of low molecular weight polyglycolic acid, the production system including a reaction module, a flow meter, a level gauge and a control module;

[0063] The reaction module is used to enable the continuous reaction of low molecular weight polyglycolic acid after the methyl glycolate raw material with a purity of >97% is introduced into the first-stage prepolymerization reaction section, and then continuously reacts through the second-stage, third-stage, fourth-stage and fifth-stage prepolymerization reaction sections in a split-flow, multi-stage parallel manner.

[0064] Flow meter: Located on the branch lines of each prepolymerization reaction section of the reaction module, used to monitor the volumetric flow rate of each branch line;

[0065] Level gauge: used to obtain the material volume in the reaction equipment of the secondary, tertiary, quaternary and quinary prepolymerization reaction sections of the reaction module;

[0066] Control module: Used to control the volumetric flow rate of each branch based on the monitoring results of the flow meter and the set volume ratio of each branch.

[0067] In this invention, the volume ratio of each branch of the primary prepolymerization product is set to (4~5):(2~3):(1~2); and the volume ratio of each branch of the tertiary prepolymerization product is set to (5~6):(2~3).

[0068] In this invention, the reaction module includes a first reaction vessel 10, a second reaction vessel 20, a third reaction vessel 30, a fourth reaction vessel 40, and a fifth reaction vessel 50 connected sequentially along the material flow direction; the first reaction vessel 10 is also connected to the third reaction vessel 30 via a first branch 70; the first reaction vessel 10 is also connected to the fourth reaction vessel 40 via a second branch 80; and the third reaction vessel 30 is also connected to the fifth reaction vessel 50 via a third branch 90.

[0069] In this invention, level gauges are respectively installed on the second reactor 20, the third reactor 30, the fourth reactor 40, and the fifth reactor 50.

[0070] In this invention, flow meters are respectively installed on the first branch 70, the second branch 80, the third branch 90, between the first reactor 10 and the second reactor 20, and between the third reactor 30 and the fourth reactor 40.

[0071] The reaction module also 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; each flow regulating valve is connected to the control module via a signal connection. In implementation, the valve opening is controlled based on the monitoring results of the flow meter and the set volume ratio of each branch, thereby regulating and controlling the volumetric flow rate of each branch to ensure that it is distributed according to the set volume ratio.

[0072] This invention, through the aforementioned method and system, enables methyl glycolate with a purity >97% to undergo a five-stage prepolymerization reaction continuously through five reactors. The low-purity polyglycolic acid generated in the first reactor 10, in addition to entering the second reactor 20 for a second-stage prepolymerization reaction, is also diverted in parallel to the third reactor 30 and the fourth reactor 40 to participate in the third and fourth-stage prepolymerization reactions, respectively. The low-purity polyglycolic acid generated in the third reactor 30, in addition to entering the fourth reactor 40 for a fourth-stage prepolymerization reaction, is also diverted to the fifth reactor 50 to participate in the fifth-stage prepolymerization reaction. Methyl glycolate with a purity >97% undergoes each stage of prepolymerization reaction in a continuous and parallel manner, thereby achieving a blending ratio of low-purity and high-purity polyglycolic acid. This reduces the viscosity of the materials within the reactors, preventing blockages in the conveying pipelines. It also ensures timely material delivery, improving production efficiency and guaranteeing the continuity, stability, and controllability of low-molecular-weight polyglycolic acid production.

[0073] Example 1

[0074] This embodiment provides a production system for the continuous production of low molecular weight polyglycolic acid.

[0075] See Figure 1 and Figure 2 The production system includes a reaction module, a flow meter, a level gauge, and a control module.

[0076] In this embodiment, the reaction module is used to enable the methyl glycolate raw material with a purity >97% to enter the first-stage prepolymerization reaction section, and then continuously react through the second-stage, third-stage, fourth-stage, and fifth-stage prepolymerization reaction sections in a split-flow, multi-stage parallel manner to generate low molecular weight polyglycolic acid.

[0077] See Figure 2 Preferably, the reaction module includes a first reaction vessel 10, a second reaction vessel 20, a third reaction vessel 30, a fourth reaction vessel 40, and a fifth reaction vessel 50 connected sequentially along the material flow direction; the first reaction vessel 10 is also connected to the third reaction vessel 30 through a first branch 70; wherein, the first reaction vessel 10 is also connected to the fourth reaction vessel 40 through a second branch 80; and the third reaction vessel 30 is also connected to the fifth reaction vessel 50 through a third branch 90.

[0078] In this embodiment, the first reactor 10, the second reactor 20, the third reactor 30, the fourth reactor 40, and the fifth reactor 50 are all prepolymerization reactors, and the volume of the prepolymerization reactor is 10m³. 3 This allows for the continuous production of low molecular weight polyglycolic acid by a five-stage prepolymerization reaction of methyl glycolate with a purity >97% through five reactors.

[0079] Preferably, in this embodiment, a feed line 101 and a discharge line 102 are respectively provided on the first reactor 10. The feed line 101 is used to deliver methyl glycolate with a purity >97% into the first reactor 10; the discharge line 102 is used to transport the low-purity polyglycolic acid generated in the first reactor 10 to the second reactor 20.

[0080] In this embodiment, the discharge pipeline 102, the first branch 70 and the second branch 80 are three branch lines for the primary prepolymerization reaction product; the connecting pipeline between the third reactor 30 and the fourth reactor 40 and the third branch 90 are two branch lines for the tertiary prepolymerization reaction product.

[0081] In this embodiment, the reaction module also includes level gauges respectively installed on the second reaction vessel 20, the third reaction vessel 30, the fourth reaction vessel 40 and the fifth reaction vessel 50; each level gauge is connected to the control module via signal.

[0082] In this embodiment, the flow meter is located on the branch line of each prepolymerization reaction section of the reaction module and is used to monitor the volumetric flow rate of each branch line.

[0083] Preferably, the flow meters are respectively installed on the first branch 70, the second branch 80, the third branch 90, between the first reactor 10 and the second reactor 20, and between the third reactor 30 and the fourth reactor 40.

[0084] See Figure 2 Preferably, a first flow meter 170 is installed between the first reactor 10 and the second reactor 20, i.e., on the discharge pipeline 102, to monitor the volumetric flow rate of the primary prepolymerization product entering the secondary prepolymerization reaction; a second flow meter 180 is installed on the first branch 70 to monitor the volumetric flow rate of the primary prepolymerization product entering the tertiary prepolymerization reaction; a third flow meter 190 is installed on the second branch 80 to monitor the volumetric flow rate of the primary prepolymerization product entering the quaternary prepolymerization reaction; a fourth flow meter 200 is installed on the pipeline between the third reactor 30 and the fourth reactor 40 to monitor the volumetric flow rate of the tertiary prepolymerization product entering the quaternary prepolymerization reaction; and a fifth flow meter 210 is installed on the third branch 90 to monitor the volumetric flow rate of the tertiary prepolymerization product entering the quinary prepolymerization reaction.

[0085] In this embodiment, the level gauge is used to obtain the material volume within the reaction equipment in the secondary, tertiary, quaternary, and quinary prepolymerization reaction sections of the reaction module. Specifically, the level gauge monitors the liquid level height within the reaction equipment of each prepolymerization reaction section, and then, in conjunction with the size of the reaction equipment, obtains the corresponding material volume.

[0086] See Figure 2Preferably, a second reactor level gauge 201 is also provided on the second reactor 20 to obtain the volume of material participating in the secondary prepolymerization reaction within the second reactor 20; a third reactor level gauge 301 is also provided on the third reactor 30 to obtain the volume of material participating in the tertiary prepolymerization reaction within the third reactor 30; a fourth reactor level gauge 401 is also provided on the fourth reactor 40 to obtain the volume of material participating in the quaternary prepolymerization reaction within the fourth reactor 40; and a fifth reactor level gauge 501 is also provided on the fifth reactor 50 to obtain the volume of material participating in the quinary prepolymerization reaction within the fifth reactor 50.

[0087] Preferably, the material participating in the secondary prepolymerization reaction is 40% pure polyglycolic acid; the material participating in the tertiary prepolymerization reaction is a mixture of 40% pure polyglycolic acid and 60% pure polyglycolic acid; the material participating in the quaternary prepolymerization reaction is a mixture of 40% pure polyglycolic acid and 70% pure polyglycolic acid; and the material participating in the quinary prepolymerization reaction is a mixture of 80% pure polyglycolic acid and 70% pure polyglycolic acid. The liquid level monitored by the second reactor level gauge 201 is 60%-70% of the volume of the second reactor 20, and the liquid level monitored by the third reactor level gauge 301 is 80%-85% of the volume of the third reactor 30.

[0088] In this embodiment, the reaction module also includes flow regulating valves respectively disposed between the first reaction vessel 10 and the second reaction vessel 20, on the first branch 70, on the second branch 80, between the second reaction vessel 20 and the third reaction vessel 30, between the third reaction vessel 30 and the fourth reaction vessel 40, on the third branch 90, and between the fourth reaction vessel 40 and the fifth reaction vessel 50.

[0089] See Figure 2Preferably, a first flow regulating valve 100 is installed between the first reactor 10 and the second reactor 20, i.e., on the discharge pipeline 102, to regulate the volumetric flow rate of the material from the first reactor 10 to the second reactor 20; a second flow regulating valve 110 is installed on the first branch 70 to regulate the volumetric flow rate of the material from the first reactor 10 to the third reactor 30; a third flow regulating valve 120 is installed on the second branch 80 to regulate the volumetric flow rate of the material from the first reactor 10 to the fourth reactor 40; and a fourth flow regulating valve 130 is installed between the second reactor 20 and the third reactor 30 to regulate the volumetric flow rate of the material from the first reactor 10 to the third reactor 40. A fourth flow regulating valve 130 regulates the volumetric flow rate of the material conveyed from the second reactor 20 to the third reactor 30; a fifth flow regulating valve 140 is installed between the third reactor 30 and the fourth reactor 40 to regulate the volumetric flow rate of the material conveyed from the third reactor 30 to the fourth reactor 40; a sixth flow regulating valve 150 is installed on the third branch 90 to regulate the volumetric flow rate of the material conveyed from the third reactor 30 to the fifth reactor 50; and a seventh flow regulating valve 160 is installed between the fourth reactor 40 and the fifth reactor 50 to regulate the volumetric flow rate of the material conveyed from the fourth reactor 40 to the fifth reactor 50.

[0090] In this embodiment, the control module controls the volumetric flow rate of each branch based on the monitoring results of the flow meter and the set volume ratio of each branch. During the prepolymerization reaction, the volume ratio of each branch for the primary prepolymerization product is set to (4~5):(2~3):(1~2); the volume ratio of each branch for the tertiary prepolymerization product is set to (5~6):(2~3). The control module performs the flow splitting according to the set volume ratio, and the flow meter transmits the monitored corresponding volumetric flow rate data to the control module to ensure that the split 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 controlled respectively, so that the primary prepolymer reaction product is divided into three streams according to the set volume ratio (4~5):(2~3):(1~2) and flows into the second reactor 20, the third reactor 30, and the fourth reactor 40 through the three branch streams respectively; 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 prepolymer reaction product is divided into two streams according to the volume ratio (5~6):(2~3) and flows into the fourth reactor 40 and the fifth reactor 50 through the two branch streams respectively.

[0091] In this embodiment, during the prepolymerization reaction, the liquid level data signals monitored by each level gauge are transmitted to the control module. Based on each liquid level value, the control module also controls the opening of the fourth flow regulating valve 130 and the seventh flow regulating valve 160, so that the volume of material participating in the secondary prepolymerization reaction is less than the volume of material participating in the tertiary prepolymerization reaction (i.e., the liquid level monitored by the second reactor level gauge 201 is lower than the liquid level monitored by the third reactor level gauge 301), and controls the liquid volume of material in the tertiary, quaternary, and quinary prepolymerization reactions to be equal, i.e., the liquid levels monitored by the third reactor level gauge 301, the fourth reactor level gauge 401, and the fifth reactor level gauge 501 are all equal.

[0092] In the reaction module of this embodiment, a transfer pump 60 is also provided between the third reactor 30 and the fourth reactor 40; and the transfer pump 60 is located between the third reactor 30 and the third branch 90; the transfer pump 60 enables the material coming out of the bottom of the third reactor 30 to be divided into two streams and flow quickly into the fourth reactor 40 and the fifth reactor 50, thereby accelerating the material conveying speed and improving production efficiency.

[0093] In this embodiment, the control module is also used to control the conditions of the prepolymerization reaction in the five reactors of the reaction module.

[0094] Preferably, the control module is a programmable control module, but it can also be a DCS control module. All control modules are commonly used in the production of low molecular weight polyglycolic acid.

[0095] Example 2

[0096] This embodiment provides a continuous production method for low molecular weight polyglycolic acid, including:

[0097] Methyl glycolate with a purity >97% is continuously fed into the primary prepolymerization reaction section for primary prepolymerization reaction. The generated primary prepolymerization reaction products are divided into three streams according to different flow rates and enter the secondary, tertiary and quaternary prepolymerization reaction sections to participate in the corresponding prepolymerization reactions.

[0098] The secondary prepolymerization products generated in the secondary prepolymerization reaction stage directly enter the tertiary prepolymerization reaction stage to participate in the tertiary prepolymerization reaction.

[0099] The prepolymerization products generated in the three-stage prepolymerization reaction section are divided into two streams according to different flow rates and enter the four-stage and five-stage prepolymerization reaction sections respectively to participate in the corresponding prepolymerization reactions.

[0100] The fourth-stage prepolymerization 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.

[0101] Low molecular weight polyglycolic acid is generated through five-stage prepolymerization reaction in the five-stage prepolymerization stage.

[0102] The continuous production method provided in this embodiment involves methyl glycolate with a purity >97% passing through five sequentially connected prepolymerization reaction stages. The first-stage prepolymerization product is further diverted to the third and fourth-stage prepolymerization reaction stages, and the third-stage prepolymerization product is diverted to the fifth-stage prepolymerization reaction stage. This allows for continuous production of methyl glycolate with a purity >97% through a multi-stage parallel diversion method. The method utilizes the low-purity polyglycolic acid generated at the front end and the high-purity polyglycolic acid generated at the back end for blending. For example, the first-stage prepolymerization product is mixed with the second-stage prepolymerization product in the third-stage prepolymerization reaction stage, and vice versa. This not only avoids pipe blockage due to viscosity issues but also ensures the continuous and stable delivery of prepolymerization products at each stage, achieving continuous production of low molecular weight polyglycolic acid.

[0103] In this embodiment, the continuous production process of low molecular weight polyglycolic acid is as follows:

[0104] Methyl glycolate with a purity >97% is introduced into the first reactor 10 for a primary prepolymerization reaction to obtain the primary prepolymer product (i.e., polyglycolic acid with a purity of 40%). The conditions for the primary prepolymerization reaction in the first reactor 10 are: temperature 130℃ and a slight positive pressure of 2-3 kPa. Therefore, the primary prepolymer product exits from the bottom of the first reactor 10 and is then divided into three streams at a volume ratio of 5:3:2, corresponding to the flow into the second reactor 20, the third reactor 30, and the fourth reactor 40 via three separate branches. Based on volume, 50% of the primary prepolymer product participates in the secondary prepolymerization reaction, 30% in the tertiary prepolymerization reaction, and 20% in the quaternary prepolymerization reaction.

[0105] During implementation, the volumetric flow rate of the primary prepolymerization product in the three branch channels is monitored in real time by the first flow meter 170, the second flow meter 180 and the third flow meter 190 respectively. The opening of the first flow regulating valve 100, the second flow regulating valve 110 and the third flow regulating valve 120 is adjusted by the control module to ensure that the primary prepolymerization product is divided into three channels according to the set volume ratio of 5:2:1.

[0106] In the second reactor 20, 50% of the primary prepolymer product (40% purity polyglycolic acid) undergoes a secondary prepolymerization reaction to obtain a secondary prepolymer product (60% purity polyglycolic acid), which is then entirely transferred to the third reactor 30. The conditions for the secondary prepolymerization reaction in the second reactor 20 are: temperature 150℃, 2-3 kPa micro-positive pressure. During implementation, the control module also controls the volume of material participating in the secondary prepolymerization reaction in the second reactor 20 to be 60%-70% of the reactor 20's volume.

[0107] In the third reactor 30, 30% of the primary and secondary prepolymer products are simultaneously introduced into the reactor and mixed; that is, 40% pure polyglycolic acid and 60% pure polyglycolic acid are mixed and then subjected to a tertiary prepolymerization reaction to obtain a tertiary prepolymer product (70% pure polyglycolic acid). The conditions for the tertiary prepolymerization reaction in the third reactor 30 are: 170℃ and 70 kPaA absolute pressure. The tertiary prepolymer product is divided into two streams at a volume ratio of 5:3 and flows into the fourth reactor 40 and the fifth reactor 50 through two corresponding branch streams. By volume, 62.5% of the tertiary prepolymer product participates in the quaternary prepolymerization reaction, and 37.5% participates in the quinary prepolymerization reaction.

[0108] During implementation, the volumetric flow rates of the tertiary prepolymerization products in the two branch lines are monitored in real time by the fourth flow meter 200 and the fifth flow meter 210, respectively. The opening degrees of the fifth flow regulating valve 140 and the sixth flow regulating valve 150 are adjusted by the control module to ensure that the tertiary prepolymerization products are divided into two streams according to the set volume ratio of 5:3. At the same time, the control module also controls the volume of material participating in the tertiary prepolymerization reaction in the third reactor 30 to be 80%-85% of the volume of the third reactor 30.

[0109] In the fourth reactor 40, 20% of the primary prepolymer product and 62.5% of the tertiary prepolymer product are simultaneously introduced and mixed. Specifically, 20% (by volume) of polyglycolic acid with a purity of 40% is mixed with 62.5% (by volume) of polyglycolic acid with a purity of 70%, and then subjected to a quaternary prepolymerization reaction to obtain the quaternary prepolymer product (polyglycolic acid with a purity of 80%). The conditions for the quaternary prepolymerization reaction in the fourth reactor 40 are: 180℃ and 30 kPa absolute pressure. All the generated quaternary prepolymer product flows into the fifth reactor 50 to participate in the quinary prepolymerization reaction. During implementation, the control module also controls the volume of material participating in the quaternary prepolymerization reaction in the fourth reactor 40 to be 80%-85% of the reactor 40's volume.

[0110] In the fifth reactor 50, 37.5% of the tertiary and quaternary prepolymer products are simultaneously introduced and mixed. Specifically, 37.5% by volume of 70% and 80% pure polyglycolic acid are mixed and then subjected to a fifth-stage prepolymerization reaction to obtain the fifth-stage prepolymer product (i.e., 95% pure polyglycolic acid). The conditions for the fifth-stage prepolymerization reaction in the fifth reactor 50 are: 220℃ and 1.5 kPa absolute pressure. During implementation, the control module also controls the volume of materials participating in the fifth-stage prepolymerization reaction in the fifth reactor 50 to be 80%-85% of the reactor 50's volume. The fifth-stage prepolymer product exits from the bottom of the fifth reactor 50 and is collected to obtain low molecular weight polyglycolic acid.

[0111] Following the above operation, methyl glycolate with a purity >97% is continuously produced in a multi-stage parallel process to obtain polyglycolic acid with a purity of 95%, which is low molecular weight polyglycolic acid. This invention transports the generated low-purity polyglycolic acid step-by-step or skip-step to the downstream end for mixing and blending with high-purity polyglycolic acid according to a specific volume ratio. This allows for rapid and stable transport of materials generated from each stage of prepolymerization reaction, thereby improving production efficiency and the continuity of material transport; it also avoids frequent blockages in the transport pipeline, enabling continuous production of low molecular weight polyglycolic acid.

[0112] In the above embodiments, the volume ratio of the primary prepolymer product divided into three streams can be selected and replaced within the range of (4~5):(2~3):(1~2), and the volume ratio of the tertiary prepolymer product divided into two streams can be selected and replaced within the range of (5~6):(2~3) to avoid frequent blockage of the conveying pipeline, so that low molecular weight polyglycolic acid can be produced stably and continuously.

[0113] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A continuous production method for low molecular weight polyglycolic acid, characterized in that, include: Methyl glycolate with a purity >97% is continuously fed into the primary prepolymerization reaction section. The generated primary prepolymerization reaction products are distributed to the secondary, tertiary and quaternary prepolymerization reaction sections according to different flow rates to participate in the corresponding prepolymerization reactions. The secondary prepolymerization products generated in the secondary prepolymerization reaction stage directly enter the tertiary prepolymerization reaction stage to participate in the tertiary prepolymerization reaction. The prepolymerization products generated in the three-stage prepolymerization reaction section are divided into two streams according to different flow rates and enter the four-stage and five-stage prepolymerization reaction sections respectively to participate in the corresponding prepolymerization reactions. The fourth-stage prepolymerization 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 stage generates low molecular weight polyglycolic acid through a five-stage prepolymerization reaction. The primary prepolymerization product is divided into three streams according to the volume ratio (4~5):(2~3):(1~2) and enters the secondary, tertiary and quaternary prepolymerization reaction sections respectively; The products of the three-stage prepolymerization reaction are divided into two streams according to the volume ratio of (5~6):(2~3) and enter the four-stage prepolymerization reaction section and the five-stage prepolymerization reaction section respectively.

2. The continuous production method of low molecular weight polyglycolic acid according to claim 1, characterized in that, The volume of material participating in the secondary prepolymerization reaction is smaller than the volume of material participating in the tertiary prepolymerization reaction; and the volumes of material participating in the tertiary, quaternary, and quinary prepolymerization reactions are all equal.

3. The continuous production method of low molecular weight polyglycolic acid according to claim 2, characterized in that, The volume of material 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 material participating in the tertiary prepolymerization reaction is 80%-85% of the volume of the reaction equipment in the tertiary prepolymerization reaction section.

4. The continuous production method of low molecular weight polyglycolic acid according to any one of claims 1-3, characterized in that, The conditions for each stage of the prepolymerization reaction are as follows: Primary prepolymerization reaction section: temperature 130±2℃, pressure 2KPa-3KPa; Secondary prepolymerization reaction section: temperature 150±2℃, pressure 2KPa-3KPa; Three-stage prepolymerization reaction section: temperature 170±3℃, pressure 70±1KPaA absolute pressure; Fourth-stage prepolymerization reaction section: temperature 180±3℃, pressure 30±1KPaA absolute pressure; Five-stage prepolymerization reaction section: temperature 220±3℃, pressure 1.5±0.5KPaA absolute pressure.

5. A production apparatus for implementing the continuous production method of low molecular weight polyglycolic acid according to claim 3, characterized in that, The production equipment includes a reaction module, a flow meter, a reaction vessel level gauge, and a control module; The reaction module is used to enable the methyl glycolate raw material with a purity of >97% to enter the first-stage prepolymerization reaction section, and then continuously react in a split-flow, multi-stage parallel manner through the second-stage, third-stage, fourth-stage, and fifth-stage prepolymerization reaction sections to generate low molecular weight polyglycolic acid. The flow meter is located on the branch line of each prepolymerization reaction section of the reaction module and is used to monitor the volumetric flow rate of each branch line. The level gauge is used to obtain the volume of material in the reaction equipment of the secondary, tertiary, quaternary, and quinary prepolymerization reaction sections of the reaction module. The control module is used to control the volumetric flow rate of each branch based on the monitoring results of the flow meter and the set volume ratio of each branch. The volume ratio of the primary prepolymerization product flowing through each branch is set to (4~5):(2~3):(1~2); the volume ratio of the tertiary prepolymerization product flowing through each branch is set to (5~6):(2~3).

6. The production equipment according to claim 5, characterized in that, The reaction module includes a first reaction vessel (10), a second reaction vessel (20), a third reaction vessel (30), a fourth reaction vessel (40), and a fifth reaction vessel (50) connected sequentially along the material flow direction; the first reaction vessel (10) is also connected to the third reaction vessel (30) through a first branch (70); the first reaction vessel (10) is also connected to the fourth reaction vessel (40) through a second branch (80); the third reaction vessel (30) is also connected to the fifth reaction vessel (50) through a third branch (90); The flow meters are respectively installed on the first branch (70), the second branch (80), the third branch (90), between the first reactor (10) and the second reactor (20), and between the third reactor (30) and the fourth reactor (40); The reactor level gauges are respectively installed on the second reactor (20), the third reactor (30), the fourth reactor (40), and the fifth reactor (50).

7. The production equipment according to claim 6, characterized in that, The reaction module also includes flow regulating valves respectively disposed between the first reaction vessel (10) and the second reaction vessel (20), on the first branch (70), on the second branch (80), between the second reaction vessel (20) and the third reaction vessel (30), between the third reaction vessel (30) and the fourth reaction vessel (40), on the third branch (90), and between the fourth reaction vessel (40) and the fifth reaction vessel (50); each flow regulating valve is controlled by the control module.

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