A reaction device and a production system and method for glycolide

Abstract

The present invention provides a reaction device and a system and method for producing glycolide. The reaction device includes a reactor body, which includes a reaction chamber; a vertically extending stirring shaft is provided in the reaction chamber, and the stirring shaft includes a hollow cavity; one or more liquid delivery branches are provided on the stirring shaft, and the liquid delivery branches are connected to the hollow cavity; a nozzle is provided at the free end of the liquid delivery branch; and an exhaust pipe and a slag discharge port are provided on the reactor body. The production method uses the reaction device to pass molten polyglycolic acid into the reaction device, which is sprayed out by the nozzle and undergoes a cracking reaction to obtain crude glycolide vapor. The process of the present invention is simple and efficient, and the reaction materials are highly dispersed on the surface of the high-temperature reactor body, so that the reaction materials have an extremely short residence time in the high-temperature zone, effectively avoiding side reactions such as further polymerization and coking caused by the oligomers staying too long in the depolymerization reactor, thereby improving the product yield and reducing the coking rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical products and relates to the process production of glycolide, in particular to a reaction device and a glycolide production system and production method. Background Art

[0002] Polyglycolic acid (PGA), also known as polyglycolic acid or polyglycolide, is a polymer of glycolic acid. It gradually degrades into water and carbon dioxide in nature, exhibiting excellent biodegradability and making it one of the most actively researched materials. However, the dehydration and polycondensation method using glycolic acid as a starting material can only produce polyglycolic acid with a low degree of polymerization. This low-polymerization degree polyglycolic acid lacks sufficient strength, melt processability, and gas barrier properties. Furthermore, it decomposes too quickly in the wild and in living organisms, making it unsuitable for durability in many applications.

[0003] Glycolide is a cyclic dimer of glycolic acid. The ring-opening polymerization of glycolide is a relatively mature method for preparing polyglycolic acid. This method can obtain polyglycolic acid products with higher relative molecular weight. The purity of glycolide is directly related to the performance of polyglycolic acid.

[0004] Currently, glycolide is mainly produced by high-temperature depolymerization of polyglycolic acid. This process uses low-molecular-weight polyglycolic acid as the raw material, depolymerizes it at high temperature, cools it, and collects it to obtain crude glycolide. The crude glycolide is then purified by subsequent distillation. Glycolide is highly heat-sensitive and is very prone to self-polymerization, coking, and hydrolysis in the molten state. The depolymerization reaction is usually carried out in a kettle reactor. Due to the long-term high-temperature cooking of the raw materials, a large amount of coking and pipeline blockage are generated, which greatly affects the yield and product purity. In addition, the crude glycolide will also undergo self-polymerization in the tower kettle and reboiler during distillation and purification, resulting in a large amount of raw material loss and a high risk of clogging related pipelines. In order to alleviate the self-polymerization problem of crude glycolide and improve product yield, the solvent azeotropic method is currently the most widely reported depolymerization method.

[0005] A Chinese invention patent application (application publication number: CN107868076A, application publication date: 2018-4-3) discloses mixing glycolic acid crystals with a catalyst, conducting a condensation reaction to obtain glycolic acid oligomers, then adding a polyether solvent to the system, and then depolymerizing at high temperature to co-distill off the solvent and glycolide.

[0006] A Chinese invention patent application (application publication number: CN104903306A, application publication date: September 9, 2015) discloses a method for preparing glycolide, which heats glycolic acid oligomers (GAO) to depolymerize them, comprising: step 1 of heating a mixture of GAO containing a terminal carboxyl group concentration of 400 eq / t or less and a polar organic solvent to a depolymerization temperature of the GAO under normal pressure or reduced pressure; step 2 of continuing to heat at the above temperature to depolymerize the GAO, and co-distilling the generated GL and the above solvent from the depolymerization reaction system to outside the reaction system; and step 3 of obtaining GL from the co-distillate. The above GAO is preferably prepared by a method for preparing GAO that includes a condensation step of glycolic acid and a dehydration step, wherein the dehydration step continues to heat the GA and the polar organic solvent or the depolymerization reaction liquid to continue the condensation reaction of the GA.

[0007] A Chinese invention patent application (application publication number: CN102712617A, application publication date: 2012-10-3) discloses a method for producing glycolide, comprising the steps of heating a mixture containing glycolic acid oligomers, a high-boiling-point polar organic solvent with a boiling point of 230-450°C, and a tin compound under normal pressure or reduced pressure to a temperature at which the glycolic acid oligomers depolymerize, thereby dissolving the glycolic acid oligomers in the high-boiling-point polar organic solvent; heating a solution containing the glycolic acid oligomers under normal pressure or reduced pressure to a temperature at which the glycolic acid oligomers depolymerize, thereby depolymerizing the glycolic acid oligomers in the solution, thereby generating glycolide; and co-distilling the high-boiling-point polar organic solvent and the generated glycolide out of the depolymerization reaction system.

[0008] These patents all employ the addition of a high-boiling-point polar solvent and a solubilizing agent, followed by heating to form a liquid phase of glycolic acid oligomers. However, many depolymerization solvents are susceptible to thermal degradation during the reaction, reacting with glycolide and reducing product yield. Furthermore, separation of the distilled glycolide from the solvent requires additional solvent washing and recovery steps, leading to cross-contamination of the solvents and increased energy consumption. Consequently, this method is already being phased out in industrial production.

[0009] Another method for purifying glycolide is recrystallization. A Chinese invention patent application (publication number: CN107868075A) discloses a method for purifying glycolide, comprising the following steps: 1) adding a recrystallization solvent to crude glycolide at room temperature; 2) heating and dissolving the crude glycolide and recrystallization solvent mixture under inert gas, filtering the mixture, and cooling the filtrate to below 25°C to crystallize the glycolide. The liquid phase is removed by filtration, and the resulting solid is dried to obtain recrystallized glycolide; 3) mixing the recrystallized glycolide obtained in the previous step with a dry poor solvent, stirring at room temperature, and then filtering; 4) repeating step 3) at least twice, and then vacuum drying the resulting solid to obtain purified glycolide. This recrystallization method results in significant solvent consumption and residual solvent, and environmental and emission issues hinder its widespread application in large-scale industrial processes. Summary of the Invention

[0010] In response to the technical problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a reaction device and a production system and production method of glycolide, in which the reaction materials are highly dispersed on the surface of the high-temperature reactor body, so that the reaction materials have an extremely short residence time in the high-temperature zone, effectively avoiding further polymerization, coking and other side reactions caused by the oligomers staying in the depolymerization reactor for too long, thereby improving the product yield and reducing the coking rate.

[0011] The present invention is achieved through the following technical solutions:

[0012] A first aspect of the present invention provides a reaction device, comprising a reactor body, wherein the reactor body includes a reaction chamber; a vertically extending stirring shaft is provided in the reaction chamber, wherein the stirring shaft includes a hollow cavity; one or more liquid delivery branches are provided on the stirring shaft, wherein the liquid delivery branches are connected to the hollow cavity; a nozzle is provided at the free end of the liquid delivery branch; and an exhaust pipe and a slag discharge port are provided on the reactor body.

[0013] Preferably, it also includes at least one of the following technical features:

[0014] 1) The reaction device further includes a driving unit, and one end of the stirring shaft extends out of the reactor body and is connected to the driving unit;

[0015] 2) The reaction device further includes a heating layer, which is arranged outside the reactor;

[0016] 3) The reaction device further includes a scraper assembly, which includes a scraper bracket and an inner wall scraper. The scraper bracket is mounted on the stirring shaft, and the inner wall scraper is mounted on the scraper bracket and close to the inner wall of the reactor body. The scraper assembly improves the cleaning ability of the reaction device.

[0017] 4) The angle between the liquid delivery branch pipe and the stirring shaft is 10°~90°;

[0018] 5) When the reaction device includes multiple liquid delivery branches, the multiple liquid delivery branches are staggered on the stirring shaft;

[0019] 6) The reaction device further includes a raw material delivery pipeline, wherein the raw material delivery pipeline is connected to the hollow cavity of the stirring shaft;

[0020] 7) The nozzle is an atomizing nozzle;

[0021] 8) The exhaust pipe is provided at the top of the reactor body;

[0022] 9) The slag discharge port is provided at the bottom of the reactor body.

[0023] More preferably, it further includes at least one of the following technical features:

[0024] 31) In feature 3), the inner wall scraper is provided along the side wall and / or bottom wall of the reactor body;

[0025] 41) In feature 4), the angle between the liquid delivery branch pipe and the stirring shaft is 70° to 90°;

[0026] 51) The multiple liquid delivery branches are arranged into multiple liquid delivery groups at different heights along the stirring shaft, and the liquid delivery branches in adjacent liquid delivery groups are staggered.

[0027] A second aspect of the present invention provides a glycolide production system, comprising the above-mentioned reaction device and a first condenser connected in sequence.

[0028] Preferably, a second condenser is further included, and the reaction device, the first condenser and the second condenser are connected in sequence.

[0029] More preferably, both the first condenser and the second condenser are tube condensers.

[0030] The third aspect of the present invention provides a method for producing glycolide, which uses the above-mentioned reaction device, introduces molten reaction materials containing polyglycolic acid into the reaction device, sprays them out from the nozzle and undergoes a cracking reaction to obtain crude glycolide vapor.

[0031] No liquid material is accumulated in the reaction device, and the reaction materials pass through once and do not return through extracorporeal circulation.

[0032] Preferably, it also includes at least one of the following technical features:

[0033] 1) The glycolide production method further comprises the following steps: condensing the crude glycolide vapor to obtain a light component and a mixture containing a heavy component and glycolide;

[0034] 2) The glycolide production method further comprises the following steps: condensing the crude glycolide vapor to obtain a mixture comprising a light component and glycolide and a heavy component, respectively; and further condensing the mixture comprising the light component and glycolide to obtain a light component and a glycolide product, respectively;

[0035] 3) The residue obtained from the cracking reaction is scraped off by the scraper and discharged from the slag discharge port;

[0036] 4) The spraying amount is controlled so that the molten reaction materials form a liquid film on the surface of the reactor body;

[0037] 5) The polyglycolic acid has Polymers of characteristic structure, with a molecular weight of 1,000 to 30,000, such as 1,000-3,000, 3,000 to 5,000, 5,000 to 8,000, 8,000 to 10,000, or 10,000 to 30,000;

[0038] 6) The reaction temperature is 190°C to 350°C, such as 190°C to 220°C, 220°C to 240°C, 240°C to 260°C, 260°C to 280°C, 280°C to 290°C, 290°C to 300°C, or 300°C to 350°C;

[0039] 7) The absolute pressure of the reaction is 10Pa~20000Pa, such as 10Pa~100Pa, 100Pa~500Pa, 500Pa~1000Pa, 1000Pa~2000Pa or 2000Pa~20000Pa.

[0040] More preferably, it further includes at least one of the following technical features:

[0041] 11) In feature 1), the light fraction is refluxed to the preceding polymerization section for recycling;

[0042] 12) In feature 1), the temperature of the mixture comprising the heavy component and glycolide is 80°C to 180°C, such as 80°C to 120°C, 120°C to 130°C, or 130°C to 180°C;

[0043] 21) In feature 2), the light fraction and / or the heavy fraction are refluxed to the preceding polymerization section for recycling;

[0044] 22) In feature 2), the temperature of the heavy component is 110°C to 180°C, such as 110°C to 140°C, 140°C to 150°C, or 150°C to 180°C;

[0045] 23) In feature 2), the temperature of the glycolide product is 80°C to 140°C, such as 80°C to 90°C or 90°C to 140°C;

[0046] 31) In feature 3), the residue is removed intermittently or continuously;

[0047] 41) In feature 4), the spraying rate is 1kg / m 2 .h ~100kg / m 2 .h;

[0048] 51) In feature 5), the molecular weight is 3000-10000;

[0049] 61) In feature 6), the reaction temperature is 210°C to 280°C;

[0050] 71) In feature 7), the absolute pressure of the reaction is 300 Pa ~ 2000 Pa.

[0051] More preferably, in feature 41), the spraying amount is 10 kg / m 2 .h ~50kg / m 2 .h.

[0052] The beneficial effects of the present invention are:

[0053] 1) The process of the present invention is simple and efficient. The reaction materials are highly dispersed on the surface of the high-temperature reactor, which shortens the residence time of the reaction materials in the high-temperature zone. This effectively avoids side reactions such as further polymerization and coking caused by excessive residence time of oligomers in the depolymerization reactor, thereby improving product yield and reducing coking rate.

[0054] 2) The present invention utilizes a spraying method to increase the heat and mass transfer capabilities of the reaction materials, allowing the depolymerization reaction to be completed in a short time, improving energy utilization, and reducing the residence time of the raw materials in the high-temperature stage, which is beneficial to reducing the degree of coking and self-polymerization, shortening the reaction time, and improving production efficiency.

[0055] 3) The integrated depolymerization-condensation process of the present invention reduces coking and self-polymerization during the subsequent purification and heating process of crude glycolide, thereby improving the utilization rate of raw materials and energy.

[0056] 4) The condensation process of the present invention can be operated without packing, thereby minimizing the pressure drop in the separation step. This allows the reaction device to be operated at a lower pressure, thereby lowering the reaction temperature, improving the utilization rate of raw materials, and reducing the coking rate.

[0057] 5) The method of the present invention has no solvent pollution, the product purity is high, the separation process is easy to carry out continuously, and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1Schematic diagram of the cross-sectional structure of the reaction device of the present invention.

[0059] Figure 2 Schematic diagram of the top view of the reaction device of the present invention.

[0060] Figure 3 It is a schematic diagram of the cross-sectional structure of the reactor body in the reaction device of the present invention.

[0061] Figure 4 Schematic diagram of the angle α between the liquid delivery branch pipe and the stirring shaft in the reaction device of the present invention.

[0062] Figure 5 The production system of glycolide of the present invention Figure 1 .

[0063] Figure 6 The production system of glycolide of the present invention Figure 2 .

[0064] Reference numerals

[0065] 1 reaction device 11 Reactor body 111 reaction chamber 112 exhaust pipe 113 Slag discharge port 12 stirring shaft 121 Hollow cavity 13 Liquid delivery branch 14 nozzle 15 drive unit 16 Heating layer 17 Scraper assembly 171 Scraper bracket 172 Inner wall scraper 18 Raw material transportation pipeline 2 First condenser 3 Second condenser DETAILED DESCRIPTION

[0066] The technical solution of the present invention is described below through specific examples. It should be understood that the one or more method steps mentioned in the present invention do not exclude the presence of other method steps before and after the combination step or the insertion of other method steps between these explicitly mentioned steps; it should also be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to define the scope of the present invention. Changes or adjustments in their relative relationships, without substantially changing the technical content, should also be regarded as the scope of the present invention.

[0067] A reaction device, such as Figures 1 to 3 As shown, it includes a reactor body 11, which includes a reaction chamber 111; a vertically extending stirring shaft 12 is provided in the reaction chamber 111, and the stirring shaft 12 includes a hollow cavity 121; one or more liquid delivery branches 13 are provided on the stirring shaft 12, and the liquid delivery branches 13 are connected to the hollow cavity 121; a nozzle 14 is provided at the free end of the liquid delivery branch 13; and an exhaust pipe 112 and a slag discharge port 113 are provided on the reactor body 11.

[0068] The present invention utilizes a liquid delivery branch pipe and a nozzle to spray the reaction material in a spray manner, thereby increasing the heat transfer and mass transfer capabilities of the reaction material, completing the depolymerization reaction in a short time, improving energy utilization, and reducing the residence time of the reaction material in the high-temperature stage, which is beneficial to reducing the degree of coking and self-polymerization, shortening the reaction time, and improving production efficiency.

[0069] In a preferred embodiment, the reaction device further includes a driving unit 15, and one end of the stirring shaft 12 extends out of the reactor body 11 and is connected to the driving unit 15. The driving unit 15 can be a motor.

[0070] In a preferred embodiment, the reaction device further includes a heating layer 16 , and the heating layer 16 is disposed outside the reactor body 11 .

[0071] In a preferred embodiment, the reaction device further includes a scraper assembly 17, which includes a scraper bracket 171 and an inner wall scraper 172. The scraper bracket 171 is provided on the stirring shaft 12, and the inner wall scraper 172 is provided on the scraper bracket 171 and near the inner wall of the reactor body 11. The scraper assembly 17 improves the cleaning capacity of the reaction device and meets the requirements of industrial steady-state operation.

[0072] In a preferred embodiment, the inner wall scraper 172 is arranged along the side wall and / or bottom wall of the reactor body 11 .

[0073] In a preferred embodiment, the angle between the liquid delivery branch 13 and the stirring shaft 12 is 10° to 90°. Figure 4 As shown in the figure, α is the included angle, which is the angle between the center line of the stirring shaft and the center line of the liquid delivery branch pipe. The range indicated by the double arrow is the included angle range.

[0074] In a preferred embodiment, the angle between the liquid delivery branch pipe 13 and the stirring shaft 12 is 70° to 90°.

[0075] In a preferred embodiment, when the reaction device includes a plurality of liquid delivery branches 13 , the plurality of liquid delivery branches 13 are staggered on the stirring shaft 12 .

[0076] In a preferred embodiment, the plurality of liquid delivery branches 13 are arranged into a plurality of liquid delivery groups at different heights along the stirring shaft 12 , and the liquid delivery branches in adjacent liquid delivery groups are staggered.

[0077] In a preferred embodiment, the reaction device further includes a raw material delivery pipe 18, which is connected to the hollow cavity 121 of the stirring shaft 12. The raw material enters the reaction chamber 111 through the raw material delivery pipe 18, the hollow cavity 121, the liquid delivery branch pipe 13, and the nozzle 14 in sequence.

[0078] In a preferred embodiment, the nozzle 14 is an atomizing nozzle, which sprays the reaction material in a spray manner to increase the heat and mass transfer capabilities of the reaction material.

[0079] In a preferred embodiment, the exhaust pipe 112 is provided at the top of the reactor body 11 .

[0080] In a preferred embodiment, the slag discharge port 113 is provided at the bottom of the reactor body 11 .

[0081] A production system for glycolide, such as Figure 5 As shown, the production system comprises the above-mentioned reaction device 1 and the first condenser 2 which are connected in sequence. A light component and a mixture containing a heavy component and glycolide are obtained respectively through the production system.

[0082] In a preferred embodiment, Figure 6 As shown, the production system further includes a second condenser 3. The reaction unit 1, the first condenser 2, and the second condenser 3 are sequentially connected. Through this production system, a mixture containing light components and glycolide and a heavy component are obtained from the first condenser, respectively; and a light component and a glycolide product are obtained from the second condenser, respectively.

[0083] In a preferred embodiment, both the first condenser 2 and the second condenser 3 are tube condensers.

[0084] The reaction apparatus (1 m in diameter and 1.8 m in height) used in Examples 1 to 8 below includes a reactor 11 containing a reaction chamber 111. A vertically extending stirring shaft 12 is disposed within the reaction chamber 111, and the stirring shaft 12 includes a hollow cavity 121. Nine liquid delivery branches 13 are provided on the stirring shaft 12, communicating with the hollow cavity 121. Nozzles 14 are provided at the free ends of the liquid delivery branches 13. The reactor 11 is provided with an exhaust pipe 112 and a slag discharge port 113. The reactor also includes a drive unit 15, one end of the stirring shaft 12 extending from the reactor 11 and connected to the drive unit 15. The reactor also includes a heating layer 16, which is disposed outside the reactor 11. The reactor also includes a scraper assembly 17, comprising a scraper bracket 171 and an inner wall scraper 172. The scraper bracket 171 is mounted on the agitator shaft 12, and the inner wall scraper 172 is mounted on the scraper bracket 171 near the inner wall of the reactor body 11. The inner wall scraper 172 is disposed along the sidewalls and bottom wall of the reactor body 11. The liquid delivery branches 13 are arranged perpendicular to the agitator shaft 12. The nine liquid delivery branches 13 are staggered on the agitator shaft 12. The nine liquid delivery branches are divided into three groups, with three liquid delivery branches in each group mounted in a Y-shaped pattern on the agitator shaft 12. The liquid delivery branches are arranged at a 120° angle to each other and lie in the same plane, which is perpendicular to the agitator shaft. The nine liquid delivery branches 13 form three parallel planes, separated by 50 cm, with the Y-shaped branches between adjacent planes offset by 60°. The reaction apparatus further includes a raw material delivery pipe 18, which is in communication with the hollow cavity 121 of the stirring shaft 12. The nozzle 14 is an atomizing nozzle. The exhaust pipe 112 is provided at the top of the reactor body 11. The slag discharge port 113 is provided at the bottom of the reactor body 11.

[0085] The reaction apparatus (4 L) used in the following comparative examples 1-2 includes a reactor body (15 cm in diameter and 30 cm in height), an anchor stirrer provided on the reactor body, and a heat transfer oil jacket provided on the reactor body.

[0086] The following examples 1-5 use Figure 5 The glycolide production system shown comprises the above-mentioned reaction unit 1 and the first condenser 2 which are connected in sequence. The first condenser 2 is a tubular condenser. Through this production system, a light component and a mixture containing a heavy component and glycolide are obtained respectively.

[0087] The following examples 6-8 use Figure 6The glycolide production system shown includes the aforementioned reaction unit 1, a first condenser 2, and a second condenser 3, both of which are tubular condensers. This production system produces a mixture containing light components and glycolide and a heavy component from the first condenser, respectively; and produces a light component and a glycolide product from the second condenser, respectively.

[0088] The glycolide production system used in the following Comparative Examples 1-2 includes the above-mentioned reaction device (4 L) and the first condenser connected in sequence.

[0089] Example 1

[0090] Polyglycolic acid (MW = 5000) and Sb2O3 catalyst (0.2 wt% of the polyglycolic acid) were mixed and heated to 220°C to melt. The molten material was ejected at a rate of 80 kg / h through a hollow cavity, a liquid delivery branch, and a nozzle into a reactor, where a cracking reaction occurred. The reactor temperature was controlled at 220°C and the reaction pressure was maintained at 2000 Pa absolute. This process produced crude glycolide vapor, which entered the first condenser. The outlet temperature of the first condenser was controlled at 120°C, resulting in a condensed liquid product (a mixture of heavy components and glycolide) that was collected in a storage tank. The vapor phase outlet of the first condenser, the first condensed gas phase product (light components), was transferred to the preceding polymerization stage for recycling. HPLC analysis of the crude glycolide product showed a purity of 93.8% and a yield of 83.8%. The slagging rate of the reactor was 0.8%.

[0091] Example 2

[0092] Polyglycolic acid (MW = 3000) and a Sb2O3 catalyst (0.2 wt% of the polyglycolic acid) were mixed and heated to 210°C to melt. The molten material was then discharged at a rate of 400 kg / h through a hollow cavity, a liquid delivery branch, and a nozzle into a reactor, where a cracking reaction occurred. The reactor temperature was controlled at 350°C and the reaction pressure was maintained at 20,000 Pa absolute. This process produced crude glycolide vapor, which entered the first condenser. The outlet temperature of the first condenser was controlled at 180°C, resulting in a condensed liquid product (a mixture of heavy components and glycolide) that was collected in a storage tank. The vapor phase outlet of the first condenser, the first condensed gas phase product (light components), was transferred to the preceding polymerization stage for recycling. HPLC analysis of the crude glycolide product showed a purity of 94.3% and a yield of 76.3%. The slagging rate of the reactor was 0.4%.

[0093] Example 3

[0094] Polyglycolic acid (MW = 30,000) and a Sb2O3 catalyst (0.4 wt% of the polyglycolic acid) were mixed and heated to 230°C to melt. The molten material was ejected at a rate of 120 kg / h through a hollow cavity, a liquid delivery branch, and a nozzle into a reactor, where a cracking reaction occurred. The reactor temperature was controlled at 240°C and the reaction pressure was maintained at 100 Pa absolute. This process produced crude glycolide vapor, which entered the first condenser. The outlet temperature of the first condenser was controlled at 80°C, resulting in a condensed liquid product (a mixture of heavy components and glycolide) that was collected in a storage tank. The vapor phase outlet of the first condenser, the first condensed gas phase product (light components), was transferred to the preceding polymerization stage for recycling. HPLC analysis of the crude glycolide product showed a purity of 96.83% and a yield of 94.8%. The slagging rate of the reactor was 1.8%.

[0095] Example 4

[0096] Polyglycolic acid (MW = 10,000) and SnCl2 catalyst (0.2 wt% of the polyglycolic acid) were mixed and heated to 210°C to melt. The molten material was ejected at a rate of 200 kg / h through a hollow cavity, a liquid delivery branch, and a nozzle into a reactor, where a cracking reaction occurred. The reactor temperature was controlled at 280°C and the reaction pressure was maintained at 1000 Pa absolute. This process produced crude glycolide vapor, which entered the first condenser. The outlet temperature of the first condenser was controlled at 130°C, resulting in a condensed liquid product (a mixture of heavy components and glycolide) that was collected in a storage tank. The vapor phase outlet of the first condenser, the first condensed gas phase product (light components), was transferred to the preceding polymerization stage for recycling. HPLC analysis of the crude glycolide product showed a purity of 98.83% and a yield of 95.2%. The slagging rate of the reactor was 0.9%.

[0097] Example 5

[0098] Polyglycolic acid (MW = 10,000) and SnCl2 catalyst (0.2 wt% of the polyglycolic acid) were mixed and heated to 210°C to melt. The molten material was continuously pumped into a reactor at a rate of 250 kg / h, where a cracking reaction occurred. The reactor temperature was controlled at 300°C and the reaction pressure was maintained at 1000 Pa absolute. This process produced crude glycolide vapor, which entered the first condenser. The outlet temperature of the first condenser was controlled at 120°C, resulting in a condensed liquid product (a mixture of heavy components and glycolide) that was collected in a storage tank. The vapor phase outlet of the first condenser, the first condensed gas phase product (light components), was transferred to the preceding polymerization stage for recycling. HPLC analysis of the crude glycolide product revealed a purity of 98.23% and a yield of 96.2%. The slagging rate of the reactor was 0.3%.

[0099] Example 6

[0100] Polyglycolic acid (molecular weight Mw = 8000) and SnCl2 catalyst (added in an amount of 0.2wt% of the polyglycolic acid) were uniformly mixed and heated to 210°C to melt them. The molten material was sprayed into a reactor at a rate of 120 kg / h through a hollow cavity, a liquid delivery branch pipe, and a nozzle, where a cracking reaction occurred. The reactor temperature was controlled at 260°C and the reaction pressure was controlled at an absolute pressure of 500 Pa. This process produced crude glycolide vapor that entered the first condenser. The material temperature at the outlet of the first condenser was controlled at 150°C, and a first condensed liquid phase product, i.e., a heavy component, and a first condensed gas phase product, i.e., a mixture of light components and glycolide, were obtained respectively. The first condensed gas phase product was then connected to a second condenser, and the material temperature at the outlet of the second condenser was controlled at 90°C to obtain a second condensed liquid phase product, i.e., a glycolide product, and a second condensed gas phase product, i.e., a light component, respectively. The second condensed gas phase product was transferred to the preceding polymerization section for recycling. The obtained second condensed liquid phase product, namely glycolide, was analyzed by HPLC and showed a purity of 99.43% and a yield of 89.2%. The slagging rate of the reaction apparatus was 0.3%.

[0101] Example 7

[0102] Polyglycolic acid (molecular weight Mw = 10,000) and Sb2O3 catalyst (added in an amount of 0.2 wt% of the polyglycolic acid) were uniformly mixed and heated to 210°C to melt. The molten material was ejected into a reactor at a rate of 120 kg / h through a hollow cavity, a liquid delivery branch pipe, and a nozzle, where a cracking reaction occurred. The reactor temperature was controlled at 290°C and the reaction pressure was controlled at an absolute pressure of 100 Pa. This process produced crude glycolide vapor that entered the first condenser. The temperature of the material at the outlet of the first condenser was controlled at 140°C, and a first condensed liquid phase product, i.e., a heavy component, and a first condensed gas phase product, i.e., a mixture of light components and glycolide, were obtained respectively. The first condensed gas phase product was then connected to a second condenser, and the temperature of the material at the outlet of the second condenser was controlled at 90°C, to obtain a second condensed liquid phase product, i.e., a glycolide product, and a second condensed gas phase product, i.e., a light component, respectively. The second condensed gas phase product was transferred to the preceding polymerization section for recycling. The obtained second condensed liquid phase product, namely glycolide, was analyzed by HPLC and showed a purity of 99.5% and a yield of 92.2%. The slagging rate of the reaction apparatus was 0.1%.

[0103] Example 8

[0104] Polyglycolic acid (MW = 1000) and a Sb2O3 catalyst (0.2 wt% of the polyglycolic acid) were mixed and heated to 210°C to melt. The molten material was ejected at a rate of 5 kg / h through a hollow cavity, a liquid delivery branch, and a nozzle into a reactor, where a cracking reaction occurred. The reactor temperature was controlled at 190°C and the reaction pressure was controlled at 10 Pa absolute. This process produced crude glycolide vapor, which entered a first condenser. The outlet temperature of the first condenser was controlled at 140°C, yielding a first condensed liquid phase product (heavy component) and a first condensed gas phase product (a mixture of light component and glycolide). The first condensed gas phase product was then fed to a second condenser. The outlet temperature of the second condenser was controlled at 90°C, yielding a second condensed liquid phase product (glycolide) and a second condensed gas phase product (light component). The second condensed gas phase product was then transferred to the preceding polymerization stage for recycling. HPLC analysis of the obtained second condensed liquid phase product (glycolide) showed a purity of 96.3% and a yield of 78.3%. The slagging rate of the reaction unit was 0.1%.

[0105] Comparative Example 1

[0106] 2 kg of polyglycolic acid (molecular weight Mw = 10,000) and a Sb2O3 catalyst (0.2 wt% of the polyglycolic acid) were uniformly mixed and transferred to a 4 L reactor. The mixture was heated to 220°C to melt. The reactor temperature was maintained at 240°C with vigorous stirring. Vacuum was gradually evacuated and the reaction pressure was controlled to 2000 Pa absolute. This process produced crude glycolide vapor, which entered the first condenser. The outlet temperature of the first condenser was maintained at 140°C, resulting in a condensed liquid product (a mixture of heavy components and glycolide) that was collected in a storage tank. The vapor phase outlet of the first condenser, the first condensed gas phase product (light components), was transferred to the preceding polymerization stage for recycling. HPLC analysis of the crude glycolide product revealed a purity of 59.5% and a yield of 67.2%. The slagging rate of the reactor was 23.9%.

[0107] Comparative Example 2

[0108] 2 kg of polyglycolic acid (molecular weight Mw = 20,000) and a Sb2O3 catalyst (0.2 wt% of the polyglycolic acid) were uniformly mixed and transferred to a 4 L reactor. The mixture was heated to 220°C to melt. The reactor temperature was maintained at 250°C with vigorous stirring. Vacuum was gradually evacuated and the reaction pressure was controlled to 200 Pa absolute. This process produced crude glycolide vapor, which entered the first condenser. The outlet temperature of the first condenser was controlled at 140°C, resulting in a condensed liquid product (a mixture of heavy components and glycolide) that was collected in a storage tank. The vapor phase outlet of the first condenser, the first condensed gas phase product (light component), was transferred to the preceding polymerization stage for recycling. HPLC analysis of the crude glycolide product showed a purity of 62.5% and a yield of 56.2%. The slagging rate of the reactor was 19.9%.

[0109] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form or substance. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the method of the present invention. These improvements and supplements should also be regarded as the scope of protection of the present invention. Any equivalent changes, modifications and evolutions made by technicians familiar with this profession without departing from the spirit and scope of the present invention by using the technical content disclosed above are all equivalent embodiments of the present invention; at the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for producing glycolide, characterized in that: A glycolide production system is used, the glycolide production system comprising a reaction device (1) and a first condenser (2), the reaction device (1) comprising a reactor body (11), the reactor body (11) comprising a reaction chamber (111); a vertically extending stirring shaft (12) is provided in the reaction chamber (111), the stirring shaft (12) comprising a hollow cavity (121); one or more liquid delivery branches (13) are provided on the stirring shaft (12), the liquid delivery branches (13) being in communication with the hollow cavity (121); a nozzle (14) is provided at the free end of the liquid delivery branch (13); an exhaust pipe (112) and a slag discharge port (113) are provided on the reactor body (11); when the reaction device comprises a plurality of liquid delivery branches (13), the plurality of liquid delivery branches (13) are staggeredly arranged on the stirring shaft (12); the plurality of liquid delivery branches (13) are staggeredly arranged on the stirring shaft (12); The branch pipes (13) are arranged at different heights along the stirring shaft (12) to form a plurality of liquid delivery groups, the liquid delivery branch pipes in adjacent liquid delivery groups are staggered, and the angle between the liquid delivery branch pipes (13) and the stirring shaft (12) is 10° to 90°; the nozzle (14) is an atomizing nozzle; the reaction device further comprises a heating layer (16), the heating layer (16) is arranged outside the reactor body (11); the heating layer (16) covers the side wall and bottom surface of the reactor body; the reaction device further comprises a scraper assembly (17), the scraper assembly (17) comprises a scraper bracket (171) and an inner wall scraper (172), the scraper bracket (171) is arranged on the stirring shaft (12), and the inner wall scraper (172) is arranged on the scraper bracket (171) and close to the inner wall of the reactor body (11); the diameter of the reaction device is 1m and the height is 1.8m; the spraying amount is 1kg / m 2 .h ~100kg / m 2 .h; The production method of the glycolide comprises any one of the following methods: i) uniformly mixing polyglycolic acid having a molecular weight Mw = 10,000 and a SnCl2 catalyst added in an amount equal to 0.2 wt% of the polyglycolic acid, and heating to 210°C to melt the mixture. The molten material is continuously pumped into a reactor at a rate of 250 kg / h to undergo a cracking reaction. The reactor temperature is controlled at 300°C, and the reaction pressure is controlled at an absolute pressure of 1000 Pa. This process generates crude glycolide vapor which enters a first condenser. The temperature of the material at the outlet of the first condenser is controlled at 120°C, and a condensed liquid, i.e., a crude glycolide product, comprising a mixture of heavy components and glycolide, is obtained and collected in a storage tank. The material at the gas phase outlet of the first condenser, i.e., the first condensed gas phase product, is transferred to a preceding polymerization section for recycling. ii) polyglycolic acid having a molecular weight Mw = 10,000 and a Sb2O3 catalyst added in an amount of 0.2 wt% based on the polyglycolic acid were uniformly mixed and heated to 210°C to melt the mixture. The molten material was ejected into a reactor at a rate of 120 kg / h through a hollow cavity, a liquid delivery branch pipe, and a nozzle, where a cracking reaction occurred. The reactor temperature was controlled at 290°C and the reaction pressure was controlled at an absolute pressure of 100 Pa. Crude glycolide vapor was generated during this process and entered into a first condenser. The temperature of the material at the outlet of the first condenser was controlled at 140°C to obtain a first condensed liquid phase product, i.e., a heavy component, and a first condensed gas phase product, i.e., a mixture of light components and glycolide. The first condensed gas phase product was then introduced into a second condenser. The temperature of the material at the outlet of the second condenser was controlled at 90°C to obtain a second condensed liquid phase product, i.e., a glycolide product, and a second condensed gas phase product, i.e., a light component. The second condensed gas phase product was transferred to the preceding polymerization section for recycling.

2. The method for producing glycolide according to claim 1, wherein Also includes at least one of the following technical features: 1) The reaction device further comprises a driving unit (15), and one end of the stirring shaft (12) extends out of the reactor body (11) and is connected to the driving unit (15); 2) the inner wall scraper (172) is arranged along the side wall and / or bottom wall of the reactor body (11); 3) The angle between the liquid delivery branch pipe (13) and the stirring shaft (12) is 70° to 90°; 4) When the reaction device includes a plurality of liquid delivery branches (13), the plurality of liquid delivery branches (13) are staggered on the stirring shaft (12); 5) The exhaust pipe (112) is provided at the top of the reactor body (11); 6) The slag discharge port (113) is provided at the bottom of the reactor body (11).

3. The method for producing glycolide according to claim 1, wherein It also includes a second condenser (3), and the reaction device (1), the first condenser (2) and the second condenser (3) are connected in sequence.

4. The method for producing glycolide according to claim 3, wherein The first condenser (2) and the second condenser (3) are both tubular condensers.

5. The method for producing glycolide according to claim 1, wherein the spraying rate is 10 kg / m 2 .h ~50kg / m 2 .h.

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