Production method and production system of glycolide

Abstract

The invention discloses a production system and a production method of glycolide. The production system comprises a cracking cyclization reactor, a crude glycolide condenser, a solvent supply unit and a refining unit, an exhaust port of the cracking cyclization reactor is connected with an upper feed port of the crude glycolide condenser, and the refining unit is coupled with a tower bottom discharge port of the crude glycolide condenser; a solvent spraying pipeline is arranged at the upper part in the crude glycolide condenser, and the solvent supply unit is connected with the solvent spraying pipeline. Crude glycolide steam enters the crude glycolide condenser from the top and is sprayed and quenched by the spraying liquid, so that the standing time of the crude glycolide steam at high temperature is shortened, and the self-polymerization loss of glycolide is reduced; and meanwhile, the self-polymerization of the glycolide is reduced, so that oligomer blockage can be avoided, and the production operation period is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of degradable materials, and in particular to a production method and a production system of glycolide. Background Art

[0002] Polyglycolic acid, also known as polyglycolic acid (PGA), is a biodegradable aliphatic polymer that can be hydrolyzed under the catalysis of enzymes or acids and bases in microorganisms or organisms to eventually form carbon dioxide and water. It is a biodegradable material with great development potential. Glycolide is a cyclic dimer of glycolic acid. Ring-opening polymerization of glycolide is a relatively mature method for preparing polyglycolic acid, which can obtain polyglycolic acid with a higher relative molecular mass.

[0003] The production of glycolide is to use glycolic acid or glycolic acid esters as the reaction materials, prepare glycolic acid oligomers through polycondensation, and then crack the glycolic acid oligomers into rings to react and generate glycolide. Among them, the crude glycolide generated by the ring-forming reactor contains impurities such as water, glycolic acid and oligomers in addition to glycolide, and needs to be purified and refined before it can be used.

[0004] The purification methods of glycolide mainly include solvent absorption method, gas-assisted evaporation method, recrystallization method, etc., and the recrystallization method is used more frequently: after the cracking is completed, the crude glycolide enters the dissolution kettle to cool to room temperature, and then the recrystallization solvent is added to the dissolution kettle for purification. In the above production process, glycolide is evaporated from the cyclization reactor under high temperature and high vacuum, and the hot liquid glycolide directly enters the dissolution kettle for cooling, or enters the dissolution kettle for cooling after condensation. This process inevitably has a high-temperature residence period, and glycolide is prone to self-polymerization at high temperature to generate low molecular weight polymers, which ultimately leads to a decrease in the quality and / or yield of glycolide. Summary of the invention

[0005] In order to solve the problem that crude glycolide is prone to self-polymerization during the cooling process in the prior art glycolide production process, the present invention provides a new glycolide production method, which can quickly obtain crude glycolide and reduce the time that glycolide stays at high temperature, thereby reducing the self-polymerization of glycolide.

[0006] The present invention first provides a glycolide production system, comprising: a cracking ring reactor, a crude glycolide condenser, a solvent supply unit and a refining unit;

[0007] The exhaust port of the cracking ring reactor is connected to the upper feed port of the crude glycolide condenser, and the refining unit is coupled to the bottom discharge port of the crude glycolide condenser;

[0008] A solvent spray pipeline is arranged at the upper inner part of the crude glycolide condenser, and the solvent supply unit is connected to the solvent spray pipeline.

[0009] Furthermore, a circulation pump and a circulation pipeline are connected between the crude glycolide condenser and the refining unit of the glycolide production system described in the present application;

[0010] A logistics spray pipeline is also arranged at the upper inner part of the crude glycolide condenser. The logistics spray pipeline is located below the solvent spray pipeline, and the circulation pipeline is connected to the logistics spray pipeline.

[0011] Furthermore, a hanging basket capable of removing oligomers entrained in the steam is provided at the upper feed inlet of the crude glycolide condenser of the glycolide production system described in the present application;

[0012] The bottom of the hanging basket is a porous plate or a screen, and / or the side of the hanging basket is a strip-shaped grid or a porous plate.

[0013] Furthermore, a filtering device is provided before and / or after the circulation pump of the glycolide production system described in the present application;

[0014] And / or, a cooling device is provided between the circulation pump and the crude glycolide condenser;

[0015] And / or, a heat exchange device is provided between the solvent supply unit and the crude glycolide condenser.

[0016] Furthermore, the glycolide production system of the present application further comprises a vapor phase recovery unit coupled to the bottom exhaust port of the crude glycolide condenser;

[0017] The vapor phase recovery unit comprises a second-stage condenser, the second-stage condenser is communicated with the bottom exhaust port of the crude glycolide condenser, and the liquid outlet of the second-stage condenser is connected with the solvent spray pipeline.

[0018] The present invention also provides a production method based on any of the above-mentioned glycolide production systems, the production method comprising the following steps:

[0019] 1) reacting glycolic acid or glycolate oligomers in a cracking ring reactor to obtain crude glycolide vapor;

[0020] 2) The crude glycolide vapor generated by cracking into rings enters the top of the crude glycolide condenser, is sprayed with a spray liquid in the crude glycolide condenser for rapid cooling, and the crude glycolide stream obtained after condensation and cooling is discharged from the bottom of the crude glycolide condenser, and subsequently enters the glycolide refining unit for purification;

[0021] The spray liquid includes a quenching solvent, the temperature of the quenching solvent is 30-130°C, and the operating temperature in the crude glycolide condenser is 70-230°C.

[0022] Furthermore, the method for producing glycolide described in the present application further comprises the following steps:

[0023] 3) The crude glycolide flow discharged from the bottom of the crude glycolide condenser is pressurized by a pump and divided into two parts. One part is a circulating crude glycolide flow, which is returned to the crude glycolide condenser to continue to be used as a spray liquid, and the other part is sent to a glycolide refining unit for purification.

[0024] Furthermore, in the glycolide production method of the present application, the liquid-vapor weight ratio of the quenching solvent to the crude glycolide vapor is 0.01 to 10, and the liquid-vapor weight ratio of the circulating crude glycolide stream to the crude glycolide vapor is 0.1 to 15;

[0025] The quenching solvent is divided into 1 to 10 spray layers for continuous or intermittent downward spraying, and / or the circulating crude glycolide flow is divided into 1 to 10 spray layers for continuous downward spraying.

[0026] Furthermore, in the method for producing glycolide described in the present application, the quenching solvent comprises at least one organic solvent selected from the group consisting of alcohols, esters, ketones, ethers and hydrocarbons having a boiling point of 120 to 300°C.

[0027] Furthermore, in the glycolide production method described in the present application, the vapor phase discharged from the bottom of the crude glycolide condenser is condensed to obtain light organic matter, and the quenching solvent also contains the light organic matter.

[0028] Furthermore, in the glycolide production method described in the present application, the crude glycolide condenser is a shell-and-tube heat exchanger.

[0029] Furthermore, in the method for producing glycolide described in the present application, the absolute pressure of the cracking ring reactor in step 1) is 100 to 5000 Pa, and the temperature of the crude glycolide vapor is 180 to 300° C.;

[0030] The internal absolute pressure of the crude glycolide condenser is 100-5000Pa.

[0031] Compared with the prior art, the above technical solution of the present invention has the following beneficial effects:

[0032] The glycolide production method and production system described in the present application allow the crude glycolide vapor generated in the cracking ring reactor to enter the crude glycolide condenser from the top, and then spray the spray liquid for rapid cooling, thereby achieving rapid cooling of the crude glycolide vapor, reducing the time that glycolide stays at high temperature, and thus reducing the self-polymerization of glycolide. In addition, the crude glycolide flow discharged from the bottom of the crude glycolide condenser is divided into two paths after pressurization, one of which is circulated back to the upper part of the crude glycolide condenser and sprayed downward. By using the circulating crude glycolide flow as the spray liquid, the use of the quenching solvent is reduced, the energy consumption of the system is reduced, and the amount of the spray liquid is increased, which can prevent oligomers from clogging the inside of the crude glycolide condenser. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of a glycolide production system provided in an embodiment of the present application;

[0034] Figure 2 A partially enlarged schematic diagram of a crude glycolide condenser provided in an embodiment of the present application;

[0035] Wherein: 1 is oligomer, 2 is crude glycolide vapor, 3 is melt after depolymerization and ring-forming reaction, 4 is vapor phase logistics, 5 is crude glycolide logistics, 6 is crude glycolide logistics of deglycolide refining unit, 7 is circulating crude glycolide logistics, 8 is light organic matter logistics, 9 is tail gas logistics, 10 is discharged light organic matter, 11 is light organic matter recycled to crude glycolide condenser, 12 is organic solvent, 13 is quenching solvent, 1a is cracking ring-forming reactor, 2a is crude glycolide condenser, 3a is second-stage condenser, 4a is circulating pump, 5a is hanging basket, 6a is glycolide refining unit, 7a is solvent supply unit, 8a is heat exchange equipment, and 9a is cooling equipment. DETAILED DESCRIPTION

[0036] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific implementation methods of the present invention are now described in detail with reference to the accompanying drawings. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. If no specific conditions are specified in the specific implementation methods, they shall be carried out according to conventional conditions or conditions recommended by the manufacturer.

[0037] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present disclosure. Instead, they are merely examples of devices and methods consistent with some aspects of the present disclosure as detailed in the appended claims. The terms used in the present disclosure are for the purpose of describing specific embodiments only and are not intended to limit the present disclosure.

[0038] The present invention is further described in detail below in conjunction with specific embodiments.

[0039] Embodiment 1:

[0040] like Figure 1 and 2 As shown, a glycolide production system described in the present application comprises: a cracking ring reactor 1a, a crude glycolide condenser 2a, a solvent supply unit 7a, and a glycolide refining unit 6a;

[0041] The exhaust port of the cracking ring reactor 1a is connected to the upper feed port of the crude glycolide condenser 2a, and the glycolide refining unit 6a is coupled to the bottom discharge port of the crude glycolide condenser 2a; a solvent spray pipeline is provided at the upper inner part of the crude glycolide condenser 2a, and the solvent supply unit 7a is connected to the solvent spray pipeline.

[0042] During the operation of the production system, the crude glycolide vapor 2 discharged from the exhaust port of the cracking ring reactor 1a enters the crude glycolide condenser 2a through the upper feed port of the crude glycolide condenser 2a, is sprayed and quenched by the quenching solvent 13 sprayed by the solvent spray pipeline, and is further cooled in the crude glycolide condenser 2a. The final liquid phase flow is discharged through the bottom discharge port of the crude glycolide condenser 2a, and subsequently enters the glycolide refining unit 6a for purification, and the vapor phase flow is discharged through the bottom exhaust port of the crude glycolide condenser 2a.

[0043] As a further improvement, a circulation pump 4a and a circulation pipeline are connected between the crude glycolide condenser 2a and the glycolide refining unit 6a; a logistics spray pipeline is also provided in the upper inner part of the crude glycolide condenser 2a, and the logistics spray pipeline is located below the solvent spray pipeline, and the circulation pipeline is connected to the logistics spray pipeline.

[0044] During the operation of the production system, the crude glycolide vapor 2 discharged from the exhaust port of the cracking ring reactor 1a enters the crude glycolide condenser 2a through the upper feed port of the crude glycolide condenser 2a, and is sprayed and quenched by the quenching solvent 13 sprayed by the solvent spray pipeline and the circulating crude glycolide logistics 7 sprayed by the logistics spray pipeline in turn, and is further cooled in the crude glycolide condenser 2a, and finally is separated into vapor and liquid phases at the bottom of the crude glycolide condenser 2a. The vapor phase logistics is discharged through the bottom exhaust port of the crude glycolide condenser 2a, and the liquid phase logistics is pressurized by the circulating pump 4a and divided into two paths. One path is the circulating crude glycolide logistics 7, which is returned to the crude glycolide condenser 2a through the circulating pipeline to continue to be used as a spray liquid, and the other path is sent to the glycolide refining unit 6a for purification.

[0045] The production system also includes a vapor phase recovery unit coupled to the bottom exhaust port of the crude glycolide condenser 2a; the vapor phase recovery unit includes a second-stage condenser 3a, the second-stage condenser 3a is connected to the bottom exhaust port of the crude glycolide condenser 2a, and the liquid outlet of the second-stage condenser 3a is connected to the solvent spray pipeline, so that part of the light organic matter flow 8 condensed by the second-stage condenser 3a is circulated back to the crude glycolide condenser 2a as a quenching solvent 13.

[0046] As a further improvement, a hanging basket 5a capable of removing oligomers entrained in steam is provided at the upper feed inlet of the crude glycolide condenser 2a; the bottom of the hanging basket 5a is a porous plate or a screen, and the side of the hanging basket 5a is a strip-shaped grille or a porous plate. In another embodiment, only the bottom of the hanging basket 5a may be a porous plate or a screen, or only the side of the hanging basket 5a may be a strip-shaped grille or a porous plate. The bottom of the hanging basket may be flat or conical. Preferably, the hanging basket 5a is movably installed at the upper feed inlet of the crude glycolide condenser 2a for easy disassembly and cleaning.

[0047] In one embodiment, the installation height of the hanging basket 5a is located between the logistics spray pipeline and the solvent spray pipeline, that is, after the crude glycolide vapor 2 enters the crude glycolide condenser 2a, it is first sprayed with the quenching solvent 13 sprayed by the solvent spray pipeline. After the first stage of quenching, the oligomers entrained in the crude glycolide vapor 2 are removed by the hanging basket 5a, and then it is sprayed with the circulating crude glycolide logistics 7 sprayed by the logistics spray pipeline for the second stage of quenching.

[0048] In one embodiment, a filtering device is disposed before and / or after the circulation pump 4 a to remove oligomers and / or other solid substances contained in the crude glycolide stream 5 .

[0049] In one embodiment, a cooling device 9a is provided between the circulation pump 4a and the crude glycolide condenser 2a for cooling the circulating crude glycolide flow 7 entering the crude glycolide condenser 2a and adjusting the temperature of the circulating crude glycolide flow 7 when entering the crude glycolide condenser 2a.

[0050] In one embodiment, a heat exchange device 8a is provided between the solvent supply unit 7a and the crude glycolide condenser 2a for performing heat exchange treatment on the quenching solvent 13 entering the crude glycolide condenser 2a and adjusting the temperature of the quenching solvent 13 when entering the crude glycolide condenser 2a.

[0051] In one embodiment, the cracking ring reactor 1a further includes a defoaming structure, which is disposed at the exhaust port of the cracking ring reactor 1a, or disposed inside the cracking ring reactor 1a, for removing low molecular weight polymers entrained in the crude glycolide steam 2.

[0052] Embodiment 2:

[0053] Based on the production system provided in Example 1, a method for producing crude glycolide described in the present application comprises the following steps:

[0054] 1) using glycolic acid or glycolate as an oligomer 1 to react in a cracking ring-forming reactor 1a to obtain a crude glycolide vapor 2 and a melt 3 after a depolymerization ring-forming reaction, the absolute pressure of the cracking ring-forming reactor 1a is 100-5000 Pa, and the temperature of the crude glycolide vapor 2 is 180-300° C.;

[0055] 2) The crude glycolide vapor 2 generated by cracking into rings enters the top of the crude glycolide condenser 2a, and is sprayed and quenched by the quenching solvent 13 and the circulating crude glycolide stream 7 in the crude glycolide condenser 2a in sequence, and the crude glycolide stream 5 obtained after condensation and cooling is discharged from the bottom of the crude glycolide condenser 2a. The operating temperature in the crude glycolide condenser 2a is 70-230°C, and the internal absolute pressure is 100-5000Pa;

[0056] 3) The crude glycolide stream 5 discharged from the bottom of the crude glycolide condenser 2a is pressurized by a pump and divided into two parts, one part is a circulating crude glycolide stream 7, the circulating crude glycolide stream 7 is returned to the crude glycolide condenser 2a and continues to be used as a spray liquid, and the other part is a crude glycolide stream 6 of the glycolide removal refining unit, which is sent to a glycolide refining unit 6a for purification. The glycolide refining unit 6a can be a distillation unit or a recrystallization unit;

[0057] 4) The vapor phase stream 4 discharged from the bottom of the crude glycolide condenser 2a is condensed into a light organic matter stream 8 and a tail gas stream 9 through the second-stage condenser 3a. The tail gas stream 9 is connected to a vacuum system. The light organic matter stream 8 is divided into two paths, namely, the light organic matter 10 discharged externally and the light organic matter 11 recycled back to the crude glycolide condenser 2a. The light organic matter 11 recycled back to the crude glycolide condenser 2a is mixed with the organic solvent 12 to form a quenching solvent 13. The quenching solvent 13 enters the crude glycolide condenser 2a and is used as a spray liquid.

[0058] In this embodiment, the crude glycolide vapor 2 generated by the cracking ring reactor 1a enters the top of the crude glycolide condenser 2a. Different from the conventional steam in-bottom and out-top method, the crude glycolide vapor 2 can be quenched by the quenching solvent 13 sprayed downward in the crude glycolide condenser 2a and the circulating crude glycolide flow 7, thereby achieving rapid cooling. For example, the crude glycolide vapor 2 can be quickly cooled to 120°C-125°C; the time that glycolide stays at high temperature is reduced, thereby reducing the self-polymerization of glycolide. On the one hand, it can reduce the self-polymerization loss of glycolide, and on the other hand, it can slow down the polymerization of glycolide and avoid oligomers clogging the pipeline, thereby extending the operation cycle.

[0059] Further, the crude glycolide stream 5 discharged from the bottom of the crude glycolide condenser 2a is divided into two paths after being pressurized. One path is the circulating crude glycolide stream 7, which is circulated back to the upper part of the crude glycolide condenser 2a and sprayed downward. By using the circulating crude glycolide stream 7 as the spray liquid, the use amount of the quenching solvent 13 is reduced, and the energy consumption of the system is reduced. At the same time, the amount of the spray liquid is increased, and the flushing force of the inside of the crude glycolide condenser 2a is high, which can avoid oligomers from clogging the inside of the crude glycolide condenser. In other embodiments, only the quenching solvent 13 can be used as the spray liquid, that is, the crude glycolide stream 5 discharged from the bottom of the crude glycolide condenser 2a is all sent to the glycolide refining unit 6a (for example, a recrystallization unit) for purification, thereby reducing the amount of solvent used in the subsequent recrystallization process.

[0060] Furthermore, the temperature of the quenching solvent 13 is 30-130°C.

[0061] Furthermore, the liquid-vapor weight ratio of the quenching solvent 13 to the crude glycolide vapor 2 is 0.01 to 10, and the liquid-vapor weight ratio of the circulating crude glycolide stream 7 to the crude glycolide vapor 2 is 0.1 to 15. The quenching solvent 13 is divided into 1 to 10 spray layers for continuous or intermittent downward spraying, and the circulating crude glycolide stream 7 is divided into 1 to 10 spray layers for continuous downward spraying.

[0062] Preferably, the quenching solvent 13 is provided with 1 to 7 spray layers for continuous or intermittent downward spraying, and the circulating crude glycolide stream 7 is provided with 3 to 8 spray layers for downward spraying. More preferably, the quenching solvent 13 is provided with 1 to 3 spray layers for continuous downward spraying, and the circulating crude glycolide stream 7 is provided with 3 to 5 spray layers for downward spraying.

[0063] The organic solvent 12 included in the quenching solvent 13 is at least one organic solvent selected from alcohols, esters, ketones, ethers and hydrocarbons having a boiling point of 120 to 300° C., for example, methyl glycolate, 1,4-butanediol, ethylene glycol, C6 to C9 alcohols and the like.

[0064] The light organic matter flow 11 included in the quenching solvent 13 accounts for 0 to 99% by weight of the light organic matter flow 8 , that is, the light organic matter flow 11 recycled to the crude glycolide condenser 2a accounts for 0 to 99% by weight of the light organic matter flow 8 .

[0065] Furthermore, the temperature of the light organic matter stream 8 / 11 condensed by the second-stage condenser 3a is relatively low, so the light organic matter stream 11 and the organic solvent 12 are mixed and can pass through the heat exchange device 8a before entering the crude glycolide condenser 2a.

[0066] Furthermore, the temperature of the crude glycolide flow 5 discharged from the bottom of the crude glycolide condenser 2a is relatively high, and the circulating crude glycolide flow 7 can pass through the cooling device 9a before entering the crude glycolide condenser 2a.

[0067] Specifically, in the production process of glycolide, the operating temperature in the crude glycolide condenser 2a is controlled within a preset range by adjusting the temperature of the quenching solvent 13 when it enters the crude glycolide condenser 2a, the temperature of the circulating crude glycolide flow 7 when it enters the crude glycolide condenser 2a, the liquid-vapor weight ratio of the quenching solvent 13 to the crude glycolide vapor 2, and the liquid-vapor weight of the circulating crude glycolide flow 7 to the crude glycolide vapor 2; it can be understood that the temperature of the crude glycolide vapor 2 is the highest when it enters the crude glycolide condenser 2a, and then it is quenched by spraying liquid inside the crude glycolide condenser 2a, and further condensed and cooled during the descending process, so the operating temperature in the crude glycolide condenser 2a gradually decreases from its upper feed inlet to the bottom discharge port of the tower.

[0068] As a preferred solution, the crude glycolide condenser 2a is a shell-and-tube heat exchanger, and the mixed flow of the crude glycolide vapor 2 and the spray liquid is condensed and cooled along the cooling tubes during the descent process, and the heat exchange effect is better. Preferably, the operating temperature in the shell-and-tube heat exchanger is controlled to be 85-200°C, and the pressure in the shell-and-tube heat exchanger is 500-2000Pa.

[0069] Embodiment 3:

[0070] About 35 kg of crude glycolide vapor generated by the cracking ring reactor 1a is discharged through the side line at a temperature of about 230°C, and is directly introduced into the crude glycolide condenser 2a through the steam pipeline feed at the top of the crude glycolide condenser 2a for the first stage of quenching. The quenching solvent used in the crude glycolide condenser 2a is methyl glycolate, and the total amount of fresh methyl glycolate and condensed methyl glycolate is about 4.4 kg. The spraying temperature is about 50°C, and one layer is sprayed downward. After the first stage of quenching, the oligomers entrained in the crude glycolide vapor are removed through the hanging basket 5a. Below the hanging basket 5a is the spray liquid of the circulating crude glycolide logistics, and the liquid-to-vapor weight ratio of the crude glycolide vapor is 1, and the 1st layer is sprayed downward. The absolute pressure in the crude glycolide condenser 2a is about 400Pa, and the temperature of the bottom outlet of the tower is 95°C. After cooling, a crude glycolide liquid phase logistics and a vapor phase logistics are formed. The crude glycolide liquid phase logistics is collected at the bottom of the crude glycolide condenser 2a. After the crude glycolide liquid phase logistics is pressurized by a pump, a part of it is sent to the subsequent glycolide refining unit for refining and purification, and a part of it is circulated back to the crude glycolide condenser 2a through the circulation pipeline for continued spraying. The vapor phase logistics is condensed by the second-stage condenser 3a, and the vapor phase is connected to the vacuum system. The liquid phase is light organic matter, and a part of it is returned to the crude glycolide condenser 2a as a quenching solvent, and a part of it is discharged.

[0071] The glycolide refining unit refining includes a two-stage crystallization kettle. Part of the crude glycolide flow flowing out from the bottom of the crude glycolide condenser 2a is introduced into the first crystallization kettle at a temperature of about 30°C, with a residence time of about 60 minutes, and then introduced into the second crystallization kettle at a temperature of about -2°C, with a residence time of about 15 minutes. The solid-liquid mixture in the second crystallization kettle is then centrifuged and washed, and dried at 60°C and an absolute pressure of ≤500Pa for 2 hours to obtain refined glycolide.

[0072] Experiments have shown that the system can operate stably and continuously for more than 8 weeks.

[0073] Embodiment 4:

[0074] About 33 kg of crude glycolide vapor generated by the cracking ring reactor 1a is discharged through the side line at a temperature of about 235°C, and is directly introduced into the crude glycolide condenser 2a through the steam pipeline feed at the top of the crude glycolide condenser 2a. The quenching solvent used in the crude glycolide condenser 2a is methyl glycolate, and the total amount of fresh methyl glycolate and condensed methyl glycolate is about 6 kg. The spraying temperature is about 60°C, and the two layers are sprayed downward. After the first stage of quenching, the oligomers entrained in the crude glycolide vapor are removed through the hanging basket 5a. Below the hanging basket 5a is the spray liquid of the circulating crude glycolide logistics, and the liquid-to-vapor weight ratio of the crude glycolide vapor is 1.5. It sprays downward in three layers. The absolute pressure in the crude glycolide condenser 2a is about 510Pa, and the cooling temperature is 100°C. After cooling, a crude glycolide liquid phase logistics and a vapor phase logistics are formed. The crude glycolide liquid phase logistics is collected at the bottom of the crude glycolide condenser 2a. After the crude glycolide liquid phase logistics is pressurized by a pump, a part of it is sent to the subsequent glycolide refining unit for refining and purification, and a part of it is circulated back to the crude glycolide condenser 2a through a circulation pipeline for continued spraying. The vapor phase logistics is condensed by the second-stage condenser 3a, and the vapor phase is connected to the vacuum system. The liquid phase is light organic matter, and a part of it is returned to the crude glycolide condenser 2a as a quenching solvent, and a part of it is discharged.

[0075] The glycolide refining unit refining includes a two-stage crystallization kettle. Part of the crude glycolide flow flowing out from the bottom of the crude glycolide condenser 2a is introduced into the first crystallization kettle at a temperature of about 30°C, with a residence time of about 70 minutes, and then introduced into the second crystallization kettle at a temperature of about -2°C, with a residence time of about 20 minutes. The solid-liquid mixture in the second crystallization kettle is then centrifuged and washed, and dried at 60°C and an absolute pressure of ≤500Pa for 2 hours to obtain refined glycolide.

[0076] Experiments have shown that the system can operate stably and continuously for more than 8 weeks.

[0077] Embodiment 5:

[0078] A method for producing refined glycolide, wherein about 35 kg of crude glycolide steam generated by a cracking ring reactor 1a is discharged through a side line at a temperature of about 240°C, and is directly introduced into the crude glycolide condenser 2a via a steam pipeline feed at the top of the crude glycolide condenser 2a, the quenching solvent used in the crude glycolide condenser 2a is methyl glycolate, the total amount of fresh methyl glycolate and condensed cyclic methyl glycolate is about 9 kg, the spraying temperature is about 55°C, and two layers are sprayed downward. After the first stage of quenching, oligomers entrained in the crude glycolide steam are removed through a hanging basket 5a. Below the hanging basket 5a is the spray liquid of the circulating crude glycolide logistics, and the liquid-to-vapor weight ratio of the crude glycolide vapor is 3, and the three layers are sprayed downward. The absolute pressure in the crude glycolide condenser 2a is about 700Pa, and the cooling temperature is 92°C. After cooling, a crude glycolide liquid phase logistics and a vapor phase logistics are formed. The crude glycolide liquid phase logistics is collected at the bottom of the crude glycolide condenser 2a. After the crude glycolide liquid phase logistics is pressurized by a pump, a part of it is sent to the subsequent glycolide refining unit for refining and purification, and a part of it is circulated back to the crude glycolide condenser 2a through a circulation pipeline for continued spraying. The vapor phase logistics is condensed by the second-stage condenser 3a, and the vapor phase is connected to the vacuum system. The liquid phase is light organic matter, and a part of it is returned to the crude glycolide condenser 2a as a quenching solvent, and a part of it is discharged.

[0079] The glycolide refining unit refining includes a two-stage crystallization kettle. Part of the crude glycolide flow flowing out from the bottom of the crude glycolide condenser 2a is introduced into the first crystallization kettle at a temperature of about 30°C, with a residence time of about 70 minutes, and then introduced into the second crystallization kettle at a temperature of about -2°C, with a residence time of about 30 minutes. The solid-liquid mixture in the second crystallization kettle is then centrifuged and washed, and dried at 60°C and an absolute pressure of ≤500Pa for 2 hours to obtain refined glycolide.

[0080] Experiments have shown that the system can operate stably and continuously for more than 8 weeks.

[0081] Embodiment 6:

[0082] A method for producing refined glycolide, wherein about 30 kg of crude glycolide steam generated by a cracking ring reactor 1a is discharged through a side line at a temperature of about 250°C, and is directly introduced into the crude glycolide condenser 2a via a steam pipeline feed at the top of the crude glycolide condenser 2a, the quenching solvent used in the crude glycolide condenser 2a is methyl glycolate, the total amount of fresh methyl glycolate and condensed cyclic methyl glycolate is about 3 kg, the spraying temperature is about 40°C, and two layers are sprayed downward. After the first stage of quenching, oligomers entrained in the crude glycolide steam are removed through a hanging basket 5a. Below the hanging basket 5a is the spray liquid of the circulating crude glycolide logistics, and the liquid-vapor weight ratio of the crude glycolide vapor is 5. The 4-layer spray is downward. The absolute pressure in the crude glycolide condenser 2a is about 500Pa, and the cooling temperature is 85°C. After cooling, a crude glycolide liquid phase logistics and a vapor phase logistics are formed. The crude glycolide liquid phase logistics is collected at the bottom of the crude glycolide condenser 2a. After the crude glycolide liquid phase logistics is pressurized by a pump, a part of it is sent to the subsequent glycolide refining unit for refining and purification, and a part of it is circulated back to the crude glycolide condenser through a circulation pipeline for continued spraying. The vapor phase logistics is condensed by the second-stage condenser 3a, and the vapor phase is connected to the vacuum system. The liquid phase is light organic matter, and a part of it is returned to the crude glycolide condenser 2a as a quenching solvent, and a part of it is discharged.

[0083] The glycolide refining unit refining includes a two-stage crystallization kettle. Part of the crude glycolide flow flowing out from the bottom of the crude glycolide condenser 2a is introduced into the first crystallization kettle at a temperature of about 30°C, with a residence time of about 60 minutes, and then introduced into the second crystallization kettle at a temperature of about -3°C, with a residence time of about 30 minutes. The solid-liquid mixture in the second crystallization kettle is then centrifuged and washed, and dried at 60°C and an absolute pressure of ≤500Pa for 2 hours to obtain refined glycolide.

[0084] Experiments have shown that the system can operate stably and continuously for more than 8 weeks.

[0085] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A system for producing glycolide, characterized in that: The production system comprises: a cracking ring reactor, a crude glycolide condenser, a solvent supply unit and a refining unit; The exhaust port of the cracking ring reactor is connected to the upper feed port of the crude glycolide condenser, and the refining unit is coupled to the bottom discharge port of the crude glycolide condenser; A solvent spray pipeline is arranged at the upper inner part of the crude glycolide condenser, and the solvent supply unit is connected to the solvent spray pipeline.

2. The glycolide production system according to claim 1, characterized in that: A circulation pump and a circulation pipeline are connected between the crude glycolide condenser and the refining unit; A logistics spray pipeline is also arranged at the upper inner part of the crude glycolide condenser. The logistics spray pipeline is located below the solvent spray pipeline, and the circulation pipeline is connected to the logistics spray pipeline.

3. The glycolide production system according to claim 2, characterized in that: A hanging basket capable of removing oligomers entrained in the steam is provided at the upper feed inlet of the crude glycolide condenser; The bottom of the hanging basket is a porous plate or a screen, and / or the side of the hanging basket is a strip-shaped grid or a porous plate.

4. The glycolide production system according to claim 2, characterized in that: A filtering device is arranged before and / or after the circulating pump; And / or, a cooling device is provided between the circulation pump and the crude glycolide condenser; And / or, a heat exchange device is provided between the solvent supply unit and the crude glycolide condenser.

5. The glycolide production system according to any one of claims 1 to 4, characterized in that: The production system also includes a vapor phase recovery unit coupled to the bottom exhaust port of the crude glycolide condenser; The vapor phase recovery unit comprises a second-stage condenser, the second-stage condenser is communicated with the bottom exhaust port of the crude glycolide condenser, and the liquid outlet of the second-stage condenser is connected with the solvent spray pipeline.

6. A method for producing glycolide, characterized in that: The production method comprises the following steps: 1) reacting glycolic acid or glycolate oligomers in a cracking ring reactor to obtain crude glycolide vapor; 2) The crude glycolide vapor generated by cracking into rings enters the top of the crude glycolide condenser, is sprayed with a spray liquid in the crude glycolide condenser for rapid cooling, and the crude glycolide stream obtained after condensation and cooling is discharged from the bottom of the crude glycolide condenser, and subsequently enters the glycolide refining unit for purification; The spray liquid includes a quenching solvent, the temperature of the quenching solvent is 30-130°C, and the operating temperature in the crude glycolide condenser is 70-230°C.

7. The method for producing glycolide according to claim 6, characterized in that: The production method further comprises the following steps: 3) The crude glycolide flow discharged from the crude glycolide condenser is pressurized by a pump and divided into two parts. One part is a circulating crude glycolide flow, which is returned to the crude glycolide condenser to continue to be used as a spray liquid, and the other part is sent to the glycolide refining unit for purification.

8. The method for producing glycolide according to claim 7, characterized in that: The liquid-vapor weight ratio of the quenching solvent to the crude glycolide vapor is 0.01 to 10, and the liquid-vapor weight ratio of the circulating crude glycolide stream to the crude glycolide vapor is 0.1 to 15; The quenching solvent is divided into 1 to 10 spray layers for continuous or intermittent downward spraying, and / or the circulating crude glycolide flow is divided into 1 to 10 spray layers for continuous downward spraying.

9. The method for producing glycolide according to any one of claims 6 to 8, characterized in that: The vapor phase discharged from the bottom of the crude glycolide condenser is condensed to obtain light organic matter, and the quenching solvent also contains the light organic matter.

10. The method for producing glycolide according to claim 6, characterized in that: The absolute pressure of the cracking ring reactor in step 1) is 100-5000 Pa, and the temperature of the crude glycolide vapor is 180-300° C.; The internal absolute pressure of the crude glycolide condenser is 100-5000Pa.

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