A method and device for purifying glycolide

Abstract

The present invention provides a method and a device for purifying glycolide. First, the mixture of crude glycolide, isocyanate monomers and initiators is subjected to rectification treatment to remove part of the impurities in the crude glycolide, and glycolide and the low-boiling components in the glycolide are obtained at the top of the rectification column. Then, the glycolide and the low-boiling components in the glycolide are subjected to solution crystallization to further remove impurities. By adopting the treatment method combining one-time rectification and one-time solution crystallization, the present invention integrates the advantages of each process, and the yield of the obtained glycolide is above 80%, and the purity is above 99%. Moreover, the temperature is relatively low throughout the process, reducing the production energy consumption and being beneficial to the industrial production of glycolide. At the same time, the purification device provided by the present invention avoids the use of conventional multiple devices, has a small equipment investment, and saves the production cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of glycolide, and particularly relates to a method and device for purifying glycolide. Background Art

[0002] Polyglycolic acid is a synthetic polymer material with good biodegradability and biocompatibility, having excellent processing properties, high mechanical strength, modulus, high solvent resistance and high gas barrier properties, and is widely used. For example, it can be used as medical suture or artificial bone in the medical field, and can be used as biodegradable plastic in the environmental material field for packaging materials and degradable films and other fields. High molecular weight and high quality polyglycolic acid are usually prepared by the method of ring-opening polymerization of high-purity glycolide. Generally, glycolide is first obtained by polymerizing glycolic acid monomers to form oligomers, and then obtained by depolymerization. However, the glycolide obtained by this method usually contains impurities such as glycolic acid, glycolic acid oligomers and water. Among them, water will cause hydrolysis of glycolide and also cause degradation of polyglycolic acid during the polymerization process, and glycolic acid will also cause acidolysis of polyglycolic acid during the polymerization process. Therefore, the glycolide obtained by the above depolymerization needs to be further purified to meet the usage requirements.

[0003] Patent CN106928180A discloses a device and method for refining glycolide from crude glycolide. This method first feeds the crude glycolide into a light component removal column, and the heavy components obtained at the bottom of the light component removal column enter the refining column through a material cooler and a bottom circulation pump for further rectification, and refined glycolide is obtained at the top of the column. However, in this method, two-step rectification is used to purify the crude glycolide. Due to the small boiling point differences of each component, the rectification and purification are difficult, so the requirements for the rectification equipment are very harsh, resulting in excessive equipment investment.

[0004] Patent CN107868075A discloses a method for refining glycolide. First, the crude glycolide is dissolved by a good solvent of glycolide, and then cooled and crystallized to obtain recrystallized glycolide. Then, the recrystallized glycolide is further crystallized 2 - 3 times with a poor solvent to obtain high-purity glycolide. However, this method requires a large amount of solvent and multiple crystallizations, resulting in high costs and low yields. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method and device for purifying glycolide. The purification method has low cost and can obtain glycolide with high yield and high purity.

[0006] To achieve this purpose, the present invention adopts the following technical solutions:

[0007] In the first aspect, the present invention provides a method for purifying glycolide, comprising the following steps:

[0008] S1: Distill a mixture of crude glycolide, isocyanate monomer and initiator to obtain an intermediate;

[0009] S2: Perform solution crystallization on the solution of the intermediate to obtain glycolide.

[0010] Preferably, the initial temperature of the solution crystallization is 60 - 120 °C, and the termination temperature is 0 - 50 °C.

[0011] Preferably, the solution crystallization includes M cooling processes, where M = 3 - 20.

[0012] Preferably, the temperature difference between two adjacent cooling processes in the solution crystallization is 5 - 50 °C.

[0013] Preferably, the distillation treatment is carried out in a distillation column.

[0014] Preferably, the bottom temperature of the distillation column is 110 - 160 °C, and the top temperature is 80 - 150 °C.

[0015] Preferably, the vacuum degree of the distillation column is 10 - 10000 Pa.

[0016] Preferably, the mass ratio of the crude glycolide, isocyanate monomer and initiator is 100:(1 - 20):(0.05 - 2).

[0017] Preferably, in step S1, the distillation treatment is carried out inside the distillation column.

[0018] Preferably, the bottom mixture of the distillation column is recycled after the first heat exchange treatment.

[0019] Preferably, the temperature of the first heat exchange treatment is 110 - 160 °C.

[0020] Preferably, the solution of the intermediate is obtained by mixing a solvent and the intermediate after the second heat exchange treatment.

[0021] Preferably, the temperature of the second heat exchange treatment is 85 - 120 °C.

[0022] Preferably, the solution of the intermediate is first subjected to the third heat exchange treatment and then to solution crystallization.

[0023] Preferably, the temperature of the third heat exchange treatment is 60 - 120 °C.

[0024] Preferably, after the solution crystallization is completed, the obtained product is subjected to the fourth heat exchange treatment and then to drying treatment.

[0025] Preferably, the temperature of the fourth heat exchange treatment is 85 - 120 °C.

[0026] In a second aspect, the present invention provides a purification device for glycolide, comprising a rectification unit and a solution crystallization unit;

[0027] The upper discharge port of the rectification unit is communicated with the feed port of the solution crystallization unit.

[0028] Preferably, the rectification unit comprises a rectification column, a first heat exchange unit and a second heat exchange unit. The feed port of the first heat exchange unit is communicated with the lower discharge port of the rectification column, and the feed port of the second heat exchange unit is communicated with the upper discharge port of the rectification unit.

[0029] Preferably, a mixing unit and a third heat exchange unit are further arranged between the rectification unit and the solution crystallization unit. The discharge port of the second heat exchange unit is communicated with the feed port of the mixing unit, the discharge port of the mixing unit is communicated with the feed port of the third heat exchange unit, and the discharge port of the third heat exchange unit is communicated with the feed port of the solution crystallization unit.

[0030] Preferably, a fourth heat exchange unit and a drying unit are further arranged after the solution crystallization unit. The feed port of the fourth heat exchange unit is communicated with the discharge port of the solution crystallization unit, and the discharge port of the fourth heat exchange unit is communicated with the feed port of the drying unit.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] (1) The present invention provides a method for purifying glycolide. First, the mixture of crude glycolide, isocyanate monomer and initiator is rectified to remove part of the impurities in the crude glycolide, improve the separation efficiency of glycolide, and obtain glycolide and the low-boiling components in glycolide at the top of the rectification column. Then, the glycolide and the low-boiling components in glycolide are subjected to solution crystallization. The solution crystallization is actually a process of cooling crystallization, which can further remove impurities. At the same time, the setting of the cooling crystallization module is beneficial to the separation of glycolide and impurities and avoids the generation of glycolide oligomers, improving the stability of the glycolide product. By adopting a treatment method combining one-time rectification and one-time solution crystallization, the present invention integrates the advantages of each process. The yield of glycolide obtained is above 80%, and the purity is above 99%. Moreover, the temperature is relatively low throughout the process, reducing the production energy consumption and being beneficial to the industrial production of glycolide;

[0033] (2) In the purification device for glycolide provided by the present invention, the use of multiple conventional devices is avoided, and the equipment investment is small. In addition, in the solution crystallization section of the present invention, a tubular reactor equipped with a power transmission device is preferably used to connect the rectification unit and the solution crystallization unit, solving the problem that conventional solution crystallization cannot be continuously produced and greatly improving the production efficiency. Description of the Drawings

[0034] Figure 1 It is a schematic diagram of the purification device for glycolide in Example 1;

[0035] Figure 2 It is a gas chromatogram of the purified glycolide in Example 2. Detailed implementation manners

[0036] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0037] Aiming at the problems in the prior art that the refining cost of glycolide is high, and the yield and purity are relatively low, the present invention provides a method for purifying glycolide, including the following steps:

[0038] S1: Subject the mixture of crude glycolide, isocyanate monomer and initiator to rectification treatment to obtain an intermediate;

[0039] S2: Perform solution crystallization on the solution of the intermediate to obtain glycolide. According to the present invention, first, a mixture of crude glycolide, isocyanate monomer, and initiator is subjected to rectification treatment to obtain the intermediate. In the present invention, the isocyanate monomer can be selected from isocyanatoethyl methacrylate and / or isocyanatoethyl acrylate, and the initiator is a radical initiator, specifically, it can be selected from any one or more of azobisisobutyronitrile, azobis(2,4-dimethylvaleronitrile), dicumyl peroxide, benzoyl peroxide, di-tert-butyl peroxide cumene, di-tert-butyl peroxide, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxyacetate, tert-butyl peroxybenzoate, or diisopropyl peroxydicarbonate. The crude glycolide can be prepared by a method well-known to those skilled in the art. Preferably, the glycolic acid monomer is subjected to polycondensation and cracking under the action of a catalyst in a vacuum environment to obtain the crude glycolide. The glycolic acid monomer is selected from any one or more of methyl glycolate, ethyl glycolate, or butyl glycolate, and the catalyst is selected from any one or more of stannous chloride, stannous octoate, stannous benzoate, tin oxide, tin acetate, zinc chloride, zinc acetate, zinc lactate, zinc acetylacetonate, zinc oxide, antimony trioxide, antimony chloride, or lanthanum acetate. The addition amount of the catalyst is 0.1-10 wt% of the glycolic acid monomer, more preferably 0.5-8 wt%, and further preferably 1-5 wt%. The temperature of the polycondensation is 120-250°C, preferably 160-200°C, the reaction time is 5-20 h, preferably 10-15 h, and the vacuum degree is 500-10,000 Pa, preferably 2,000-8,000 Pa; the temperature of the cracking is 150-300°C, preferably 200-250°C, the time is 30 min-5 h, preferably 1-4 h, and the vacuum degree is 10-1,000 Pa, preferably 100-500 Pa.

[0040] In some embodiments of the present invention, it is preferred that the mass ratio of crude glycolide, isocyanate monomer and initiator is 100:(1-20):(0.05-2), more preferably 100:(3-18):(0.1-1.8), and further preferably 100:(5-12):(0.5-1.5). After mixing and feeding the three components, rectification treatment is carried out. The rectification treatment is preferably carried out in a rectification column. The bottom temperature of the rectification column is 110-160 °C, which can be 110 °C, 115 °C, 120 °C, 125 °C, 130 °C, 135 °C, 140 °C, 145 °C, 150 °C, 155 °C or 160 °C, etc.; the top temperature is 80-150 °C, which can be 80 °C, 85 °C, 90 °C, 95 °C, 100 °C, 105 °C, 110 °C, 115 °C, 120 °C, 125 °C, 130 °C, 135 °C, 140 °C, 145 °C or 150 °C, etc.; the vacuum degree of the rectification column is 10-10000 Pa, which can be 10 Pa, 100 Pa, 1000 Pa, 2000 Pa, 4000 Pa, 6000 Pa, 8000 Pa or 10000 Pa, etc. In the present invention, the vacuum degree of the rectification column is provided by a vacuum system. The time of the rectification treatment is 5-60 min, which can be 5 min, 10 min, 20 min, 30 min, 40 min, 50 min or 60 min, etc.

[0041] In some embodiments of the present invention, the mixture of crude glycolide, isocyanate monomer and initiator first enters a rectification column for rectification. At the same time, the bottom material is continuously circulated through the first heat exchange treatment. The purpose of the first heat exchange treatment is to provide heat for the rectification process of crude glycolide, isocyanate monomer and initiator. The temperature of the first heat exchange treatment is the same as the bottom temperature of the rectification column, which is set to 110-160 °C, which can be 110 °C, 115 °C, 120 °C, 125 °C, 130 °C, 135 °C, 140 °C, 145 °C, 150 °C, 155 °C or 160 °C, etc. In the present invention, crude glycolide, isocyanate monomer and initiator are subjected to reactive distillation in a rectification column. Under vacuum conditions, glycolide and low-boiling components in glycolide can be distilled out through the top of the rectification column, and the heavy components of glycolic acid oligomers formed by the reaction of isocyanate monomer with impurities in crude glycolide can be discharged from the bottom of the rectification column.

[0042] According to the present invention, after the rectification treatment is completed, it is preferred to perform solution crystallization on the solution of the intermediate to obtain glycolide. The solution of the intermediate is obtained by mixing a solvent and the intermediate that has undergone a second heat exchange treatment. The temperature of the second heat exchange treatment is 85 to 120 °C, which can be 85 °C, 90 °C, 95 °C, 100 °C, 105 °C, 110 °C, 115 °C or 120 °C, etc. The function of the second heat exchange treatment is to cool and condense the distillate components at the top of the rectification column into a liquid to reduce the loss of the glycolide gas-phase components during the rectification process. The solvent can specifically be selected from any one or more of ethyl acetate, toluene, cyclohexane, acetone, n-propanol, isopropanol, n-butanol, isobutanol, n-pentanol or isopentanol. The mass ratio of the solvent to the glycolide in the intermediate is 0.5:1 to 3:1, preferably 0.8:1 to 2.5:1, and more preferably 1:1 to 2:1. In some embodiments of the present invention, before the solution crystallization of the solution of the intermediate, it is preferred to perform a third heat exchange treatment to rapidly cool the glycolide solution and reduce the generation of oligomers of glycolide under high-temperature conditions. The temperature of the third heat exchange treatment is 60 to 120 °C, which can be 60 °C, 70 °C, 80 °C, 90 °C, 100 °C, 110 °C or 120 °C, etc.

[0043] In the present invention, the solution crystallization is actually a cooling crystallization process. The initial temperature of the solution crystallization is 60 to 120 °C, which can be 60 °C, 65 °C, 70 °C, 75 °C, 80 °C, 85 °C, 90 °C, 95 °C, 100 °C, 105 °C, 110 °C, 115 °C or 120 °C, etc., and the termination temperature is 0 to 50 °C, which can be 0 °C, 5 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C or 50 °C, etc. The solution crystallization preferably includes M cooling processes, where M = 3 to 20, which can be 3, 5, 7, 10, 12, 15, 17 or 20, etc.; the temperature difference between two adjacent cooling processes in the solution crystallization is 5 to 50 °C, which can be 5 °C, 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C or 50 °C, etc. For example, in some embodiments of the present invention, the initial temperature of the solution of the intermediate is 75 °C, and the solution crystallization includes three cooling processes from 75 °C to 65 °C, from 65 °C to 45 °C and from 45 °C to 25 °C. In some other embodiments of the present invention, the initial temperature of the solution of the intermediate is 90 °C, and the solution crystallization includes three cooling processes from 90 °C to 70 °C, from 70 °C to 55 °C and from 55 °C to 30 °C. To avoid complexity, they will not be elaborated one by one here.

[0044] During the above solution crystallization process, by gradually cooling, impurities in the distillate components at the top of the rectification column can be removed, and the purity of the final product can be further improved.

[0045] In some embodiments of the present invention, after the solution crystallization is completed, it is preferred to subject the obtained product to a fourth heat exchange treatment and then to a drying treatment. Among them, the function of the fourth heat exchange treatment is to achieve a rapid temperature rise of glycolide and improve the drying rate of glycolide. The temperature of the fourth heat exchange treatment is 85-120 °C, which can be 85 °C, 90 °C, 95 °C, 100 °C, 105 °C, 110 °C, 115 °C or 120 °C, etc. After the fourth heat exchange treatment is completed, it is preferred to subject the obtained product to a drying treatment. The temperature of the drying treatment is 20-100 °C, which can be 20 °C, 40 °C, 50 °C, 60 °C, 80 °C or 100 °C, etc. In the present invention, the drying treatment is carried out in a form of gradient cooling. The drying treatment includes N cooling processes, where N = 2-10, which can be 2, 3, 4, 5, 6, 7, 8, 9 or 10, etc. In some embodiments of the present invention, the drying treatment includes two cooling processes from 95 °C to 65 °C and from 65 °C to 25 °C. In some other embodiments of the present invention, the drying treatment includes two cooling processes from 100 °C to 70 °C and from 70 °C to 30 °C. To avoid complexity, they will not be elaborated one by one here. After the drying treatment is completed, the discharging temperature is controlled at 20-40 °C, which can be 20 °C, 25 °C, 30 °C, 35 °C or 40 °C, etc. This solves the problem of unstable product quality caused by high-temperature discharging and at the same time avoids the problem of product oligomerization caused by high-temperature discharging.

[0046] In the present invention, the above-mentioned first heat exchange treatment, second heat exchange treatment, third heat exchange treatment and fourth heat exchange treatment are preferably carried out in a heat exchanger. The solution crystallization treatment and the drying treatment are preferably carried out in a tubular device. The tubular device preferably has a power transmission device. The tubular device can be one of a tubular double-shaft screw conveyor or a tubular non-shaft screw conveyor.

[0047] The above-mentioned purification method of glycolide provided by the present invention first performs a rectification treatment on a mixture of crude glycolide, isocyanate monomers and initiators to remove impurities in part of the crude glycolide, improves the separation efficiency of glycolide, and obtains glycolide and low-boiling components in glycolide at the top of the rectification column. Then, the glycolide and the low-boiling components in glycolide are subjected to solution crystallization. The solution crystallization is actually a process of cooling crystallization, which can further remove impurities and avoid the generation of glycolide oligomers, and improve the stability of the glycolide product. By adopting a treatment method combining one-time rectification and one-time solution crystallization, the present invention avoids the problem of product oligomerization caused by re-high-temperature purification, integrates the advantages of each process, and the obtained glycolide yield is above 80%, and the purity is above 99%. Moreover, the temperature is relatively low throughout the process, reducing the production energy consumption and being beneficial to the industrial production of glycolide.

[0048] The present invention also provides a purification device for glycolide, which includes a rectification unit and a solution crystallization unit. The upper discharge port of the rectification unit is communicated with the feed port of the solution crystallization unit. In the present invention, the rectification unit includes a rectification column; the solution crystallization unit includes a first tubular reactor, in which a first double - screw conveyor equipped with a first double - screw pump and a non - condensable liquid discharge port are provided. The first tubular reactor is composed of N1 tubes connected in series, where N1 = 1 - 10, specifically, it can be 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10. The number of N1 and the length of each tube can be selected according to actual production needs, and the obtained non - condensable liquid is directly discharged. As described in the relevant content of the above purification method, the first tubular reactor can be divided into M temperature modules, the length of each temperature module can be selected according to needs, each module is equipped with a jacket, and the temperature of each temperature module can be controlled by the jacket temperature of the module.

[0049] In some embodiments of the present invention, the rectification unit further includes a first heat - exchange unit. The feed port of the first heat exchanger is communicated with the lower discharge port of the rectification column. In some embodiments of the present invention, the first heat - exchange unit includes a first heat exchanger and a first circulation pump. Among them, the feed port of the first heat exchanger is communicated with the discharge port of the first circulation pump, the bottom discharge port of the rectification column is communicated with the feed port of the first circulation pump, and the discharge port of the first circulation pump is communicated with the circulation feed port of the rectification column.

[0050] In some embodiments of the present invention, the rectification unit further includes a second heat - exchange unit. The feed port of the second heat - exchange unit is communicated with the upper discharge port of the rectification unit. In some embodiments of the present invention, the second heat - exchange unit includes a second heat exchanger and a second feed pump. The feed port of the second heat exchanger is communicated with the upper discharge port of the rectification column. The discharge port of the second heat exchanger is communicated with the top of the rectification column or the feed port of the second feed pump. In addition, a first vacuum system is provided at the discharge port of the second heat exchanger to ensure the vacuum degree of the rectification column.

[0051] In some embodiments of the present invention, a mixing unit and a third heat exchange unit are further provided between the rectification unit and the solution crystallization unit. The outlet of the mixing unit is communicated with the inlet of the third heat exchange unit, and the outlet of the third heat exchange unit is communicated with the inlet of the solution crystallization unit. In some embodiments of the present invention, the mixing unit includes a mixer and a third feed pump, and the third heat exchange unit includes a third heat exchanger. Among them, the outlet of the second feed pump and the outlet of the third feed pump are both communicated with the inlet of the mixer, the outlet of the mixer is communicated with the inlet of the third heat exchanger, and the outlet of the third heat exchanger is communicated with the inlet of the first tubular reactor.

[0052] In some embodiments of the present invention, a fourth heat exchange unit and a drying unit are further provided after the solution crystallization unit. The inlet of the fourth heat exchange unit is communicated with the outlet of the solution crystallization unit, and the outlet of the fourth heat exchange unit is communicated with the inlet of the drying unit. In some embodiments of the present invention, the fourth heat exchange unit includes a fourth heat exchanger, and the drying unit includes a second tubular reactor. A second double screw conveyor equipped with a second double screw pump is provided in the second tubular reactor. A second vacuum system is provided above the second tubular reactor. The second tubular reactor is composed of N2 pipes connected in series, where N2 = 1 to 10, and specifically can be 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. The number of N2 and the length of each pipe can be selected according to actual production needs. In the present invention, a perforated plate is provided in the second tubular reactor. The use of the perforated plate increases the specific surface area of the reaction and greatly accelerates the volatilization rate of the solvent. The perforated plates are arranged parallel to the direction of the second tubular reactor, dividing the tubular reactor into upper and lower parts L1 and L1'. Among them, the L1' part is the material flow area, and the L1 part and the connected pipeline form the gas-phase devolatilization part. L1 represents the width of the upper part of the perforated plate, and L1' represents the width of the lower part of the perforated plate. The width ratio of L1 to L1' is 1:5 to 5:1, preferably 1:4 to 3:1, and more preferably 1:2 to 1:1. The inlet of the fourth heat exchanger is communicated with the outlet of the first tubular reactor, and the outlet of the fourth heat exchanger is communicated with the inlet of the second tubular reactor through a back pressure valve. The second tubular reactor can be divided into N temperature modules. The length of each temperature module can be selected according to needs. Each module is equipped with a jacket, and the temperature of each temperature module can be controlled by the jacket temperature of the module.

[0053] In the present invention, a tubular double-shaft screw conveyor or a tubular double-shaftless screw conveyor with a double-screw pump is provided as a power transmission device in both the first tubular reactor and the second tubular reactor. The length of the tubular double-shaft screw conveyor or the tubular double-shaftless screw conveyor can be selected according to actual production needs, such as 3m, 5m, 8m, 10m, 15m, etc. The length-diameter ratio of the tubular double-shaft screw conveyor or the tubular double-shaftless screw conveyor can be (25-75):1, such as 25:1, 30:1, 35:1, 40:1, 45:1, 50:1, 55:1, 60:1, 65:1, 70:1, 75:1, etc.

[0054] The material flow rate in the first tubular reactor is 20-40000 cm 3 / min, specifically it can be 20 cm 3 / min, 100 cm 3 / min, 1000 cm 3 / min, 5000 cm 3 / min, 10000 cm 3 / min or 40000 cm 3 / min, etc.; the material flow rate in the second tubular reactor is 10-15000 cm 3 / min, specifically it can be 10 cm 3 / min, 50 cm 3 / min, 250 cm 3 / min, 1000 cm 3 / min, 5000 cm 3 / min or 15000 cm 3 / min, etc.

[0055] In some embodiments of the present invention, a mixture of crude glycolide, isocyanate monomers and an initiator enters a rectification column as raw materials for rectification first. Meanwhile, the bottom material of the column is continuously circulated and heated by a first heat exchanger. Among them, the vacuum degree of the rectification unit is maintained by a first vacuum system, and all raw materials are circulated and heated through the heat exchanger. Glycolide oligomers are obtained at the bottom of the column, which can be discharged through the discharge port, and light components containing glycolide are obtained at the top of the column. The light components containing glycolide are mixed with a solvent introduced by a first gear pump and a second gear pump after the second heat exchange treatment, and then enter a mixer for mixing. After the mixing is completed, a third heat exchange treatment is carried out, and then the obtained product is introduced into a solution crystallization unit for treatment. After the treatment is completed, glycolide and non-condensable liquid can be obtained, and the non-condensable liquid is discharged through the discharge port. As a more preferred technical solution, after the solution crystallization treatment is completed, it is preferably to carry out a fourth heat exchange treatment on the obtained product, and then introduce it into a drying unit through a back pressure valve. The drying unit first removes the solvent through a vacuum system, and after the drying treatment is completed, the discharge temperature is controlled to obtain solid glycolide. In the purification device of glycolide provided by the present invention, the use of multiple conventional devices is avoided, and the equipment investment is small. In addition, in the solution crystallization section of the present invention, a tubular reactor equipped with a double screw pump is preferably used to connect the rectification unit, the solution crystallization unit and the drying unit, solving the problem that conventional solution crystallization cannot be continuously produced and greatly improving the production efficiency.

[0056] To further illustrate the present invention, the following examples are provided for detailed description. The experimental raw materials used in the following examples of the present invention can all be purchased from the market or prepared according to the conventional preparation methods well-known to those skilled in the art.

[0057] The purity of glycolide was tested by a gas chromatograph (PerkinElmer, 590): PerkinElmer Instruments Co., Ltd., chromatographic operating conditions: carrier gas: N2, column temperature: 140 °C, FID temperature: 250 °C, injector temperature: 250 °C, column flow rate: 0.5 mL / min, split ratio: 20:1.

[0058] The acid value of glycolide was tested by a Metrohm 905 potentiometric titrator: electrode: non-aqueous phase glass electrode; titrant: anhydrous methanol solution of 0.01 mol / L potassium methoxide; solvent: dichloromethane and anhydrous methanol were mixed at a volume ratio of 4:1.

[0059] Preparation Example 1

[0060] This preparation example provides a kind of crude glycolide, and its preparation method is as follows:

[0061] 4500 g of 100% methyl glycolate and 9 g of stannous chloride catalyst were successively added to the reaction kettle, heated to 150 °C, and vacuum was drawn under stirring conditions for polycondensation reaction, P = 3000 Pa. After 4 h, the temperature was raised to 165 °C and the vacuum was increased to P = 700 Pa, and the polycondensation reaction was continued for 6 h to obtain oligomeric glycolic acid. The temperature was raised to 245 °C, and 9 g of lanthanum acetate cracking catalyst was added for depolymerization, P = 300 Pa. The reaction was stopped when no more glycolide was distilled out to obtain crude glycolide.

[0062] The above-prepared crude glycolide was tested by gas chromatography, and the test results were as follows: the purity of glycolide was 92.88%.

[0063] The above-prepared crude glycolide was tested for acidity, and the test results were as follows: the acid value of glycolide was 205 ppm.

[0064] Preparation Example 2

[0065] This preparation example provides a crude glycolide, and its preparation method is as follows:

[0066] 5200 g of 100% ethyl glycolate and 25 g of antimony acetate catalyst were successively added to the reaction kettle, heated to 165 °C, and vacuum was drawn under stirring conditions for polycondensation reaction, P = 3000 Pa. After 3 h, the temperature was raised to 170 °C and the vacuum was increased to P = 700 Pa, and the polycondensation reaction was continued for 5 h to obtain oligomeric glycolic acid. The temperature was raised to 250 °C, and 20 g of lanthanum acetate cracking catalyst was added for depolymerization, P = 300 Pa. The reaction was stopped when no more glycolide was distilled out to obtain crude glycolide.

[0067] The above-prepared crude glycolide was tested by gas chromatography, and the test results were as follows: the purity of glycolide was 93.26%.

[0068] The above-prepared crude glycolide was tested for acidity, and the test results were as follows: the acid value of glycolide was 191 ppm.

[0069] Preparation Example 3

[0070] This preparation example provides a crude glycolide, and its preparation method is as follows:

[0071] 6600 g of 100% butyl glycolate and 50 g of stannous benzoate catalyst were successively added to the reaction kettle, heated to 170 °C, and vacuum was drawn under stirring conditions for polycondensation reaction, P = 3000 Pa. After 2 h, the temperature was raised to 175 °C and the vacuum was increased to P = 700 Pa, and the polycondensation reaction was continued for 4 h to obtain oligomeric glycolic acid. The temperature was raised to 240 °C, and 12 g of lanthanum acetate cracking catalyst was added for depolymerization, P = 300 Pa. The reaction was stopped when no more glycolide was distilled out to obtain crude glycolide.

[0072] The above-prepared crude glycolide was subjected to gas chromatography testing, and the test results showed that the purity of glycolide was 93.46%.

[0073] The above-prepared crude glycolide was subjected to acidity testing, and the test results showed that the acid value of glycolide was 168 ppm.

[0074] Example 1

[0075] This example provides a purification device for glycolide, and its structural schematic diagram is as Figure 1 shown, including a rectification unit and a solution crystallization unit. The solution crystallization unit includes a mixing unit, a crystallization unit, and a drying unit;

[0076] Among them, the rectification unit includes a first heat exchanger HE1, a first gear pump P1, a rectification column DT, a second heat exchanger HE2. A first vacuum system V1 is provided at the outlet end of the second heat exchanger. A rectification residue discharge port E1 is provided below the rectification column DT;

[0077] The mixing unit includes a second gear pump P2, a third gear pump P3, a mixer M1, and a third heat exchanger HE3;

[0078] The crystallization unit includes a tubular reactor C, a fourth heat exchanger HE4, and a back pressure valve BPV. The tubular reactor C is a first double screw conveyor (total length 3 m, radius 0.05 m) equipped with a first double screw pump SN1, N1 = 1, and the length-diameter ratio (i.e., the ratio of the length of the double screw conveyor in the tubular reactor to its diameter) is 30:1. The tubular reactor C is divided into three reaction modules C1 (1 m), C2 (1 m), and C3 (1 m). A non-condensable liquid discharge port E2 is provided below the tubular reactor C; The drying unit includes a tubular reactor D. The tubular reactor D is a second double screw conveyor (total length 3 m, radius 0.03 m) equipped with a second double screw pump SN2, N2 = 1, and the length-diameter ratio is 50:1. It is divided into two parts, upper (i.e., L1) and lower (i.e., L1’) by a perforated plate. L1 represents the width of the upper part of the perforated plate in the tubular reactor D, and L1’ represents the width of the lower part of the perforated plate. Among them, the L1’ part is the material flow area, and the L1 part and the connected pipeline form a gas-phase devolatilization part. The width ratio of L1 to L1’ is 1:3. The tubular reactor D is divided into two drying modules D1 (2 m) and D2 (1 m). A second vacuum system V2 is provided above the tubular reactor D;

[0079] In the above-mentioned device, the bottom discharge port of the rectification column DT is communicated with the feed port of the first gear pump P1, the discharge port of the first gear pump P1 is communicated with the feed port of the first heat exchanger HE1, the discharge port of the first heat exchanger HE1 is communicated with the circulating feed port of the rectification column DT. A rectification residue discharge port E1 is arranged below the first gear pump P1. The upper discharge port of the rectification column DT is communicated with the feed port of the second heat exchanger HE2. The discharge port of the second heat exchanger HE2 is communicated with the top of the rectification column DT or the feed port of the second gear pump P2. The discharge ports of the second gear pump P2 and the third gear pump P3 are both communicated with the feed port of the mixer M1. The discharge port of the mixer M1 is communicated with the feed port of the third heat exchanger HE3. The discharge port of the third heat exchanger HE3 is communicated with the feed port of the tubular reactor C. The discharge port of the tubular reactor C is communicated with the feed port of the fourth heat exchanger HE4. The discharge port of the fourth heat exchanger HE4 is communicated with the feed port of the tubular reactor D through a back pressure valve BPV.

[0080] Example 2

[0081] In this example, the device in Example 1 is used to purify glycolide, and the specific method is as follows:

[0082] 10 kg of the crude glycolide obtained in Preparation Example 1, ethyl isocyanate acrylate and benzoyl peroxide are mixed in a mass ratio of 100:2:0.2 and added to the rectification column DT for reactive distillation. The material is circulated and heated by the first gear pump P1 and the first heat exchanger HE1 (temperature is 130 °C). The bottom temperature of the rectification column DT is 130 °C. The vacuum degree in the rectification column DT is controlled at 500 Pa by the first vacuum system V1. After reacting for 30 min, part of the glycolide is distilled out at the top of the rectification column DT. The distillation temperature of the glycolide is the top temperature, which is 125 °C. When the glycolide no longer distills out, the residue is discharged through the rectification residue discharge port E1.

[0083] The glycolide distilled out from the top is cooled by the second heat exchanger HE2, and then part of it enters the second gear pump P2. The temperature of the second heat exchanger HE2 is 100 °C. The remaining part of the glycolide flows back into the rectification column DT, and the reflux ratio is controlled at 1:1. Then, ethyl acetate is exported through the third gear pump P3 and mixed with the glycolide exported through the second gear pump P2 in a weight ratio of 1:1 through a static mixer M1, and then cooled to 80 °C by the third heat exchanger HE3 and enters the tubular reactor C equipped with a first twin-screw pump SN1 in a double-screw conveyor for cooling crystallization. The solution flow rate is 100 cm 3 / min, the tubular reactor C is divided into three temperature modules, namely the C1 module, the C2 module and the C3 module in sequence. The temperature of the C1 module is 80 °C, the temperature of the C2 module is 50 °C, and the temperature of the C3 module is 25 °C. The solution is cooled from 80 °C to 25 °C through the three temperature control modules of the tubular reactor C to obtain crystalline solids and non-condensable liquids. The non-condensable liquids are discharged through E2.

[0084] The crystalline solids are conveyed by a double-screw conveyor equipped with the first double-screw pump SN1, and then enter the tubular reactor D through the fourth heat exchanger HE4 (temperature 90 °C) and the back pressure valve BPV for drying. The material flow rate is 38 cm 3 / min. In the tubular reactor D of the double-screw conveyor equipped with the second double-screw pump SN2, the solvent ethyl acetate is removed through the second vacuum system V2, and the vacuum degree of the tubular reactor D is controlled at 300 Pa. The tubular reactor D is divided into two temperature modules, namely the D1 module and the D2 module in sequence. The temperature of the D1 module is 60 °C, and the temperature of the D2 module is 30 °C. The glycolide is cooled from 90 °C to 30 °C through the two temperature control modules in the D section. The crystalline solids are transported by a double-screw conveyor equipped with the second double-screw pump SN2 to obtain white powdery glycolide, and the discharge temperature is 30 °C, obtaining 8.26 Kg of glycolide with a yield of 82.6%.

[0085] The glycolide prepared in Example 2 was subjected to gas chromatography testing, and the chromatogram is as Figure 2 shown. After calculation, the purity of glycolide is 99.28%, and the rest are light components, as shown in Table 1.

[0086] Table 1

[0087] Component Residence time Area % Area Light component 3.082 23 0.72 Glycolide 4.533 3091 99.28

[0088] The glycolide prepared in Example 2 of the present invention was subjected to acidity testing according to the above method, and the test result was: the acid value of glycolide was 6 ppm.

[0089] Example 3

[0090] This example uses the device in Example 1 to purify glycolide, and the specific method is as follows:

[0091] 10 kg of the crude glycolide obtained in Preparation Example 1, ethyl isocyanate acrylate, and benzoyl peroxide were mixed in a mass ratio of 100:3:0.25 and added to a distillation column DT for reactive distillation. The material was circulated and heated by a first gear pump P1 and a first heat exchanger HE1 (temperature: 135°C). The bottom temperature of the distillation column DT was 135°C. The vacuum degree inside the distillation column DT was controlled at 500 Pa by a first vacuum system V1. After reacting for 25 min, part of the glycolide was distilled out from the top of the distillation column DT. The distillation temperature of the glycolide was the top temperature, which was 125°C. When the glycolide was no longer distilled out, the residue was discharged through a distillation residue discharge port E1.

[0092] The glycolide distilled out from the top of the column was cooled by a second heat exchanger HE2, and then part of it entered a second gear pump P2. The temperature of the second heat exchanger HE2 was 105°C. The remaining part of the glycolide was refluxed into the distillation column DT, and the reflux ratio was controlled at 1:1. Then, ethyl acetate was exported by a third gear pump P3 and mixed with the glycolide exported by the second gear pump P2 in a weight ratio of 1.6:1 through a static mixer M1. Then, it was cooled to 75°C by a third heat exchanger HE3 and entered a tubular reactor C equipped with a first twin-screw pump SN1 in a double-screw conveyor for cooling crystallization. The solution flow rate was 140 cm 3 / min. The tubular reactor C was divided into three temperature modules, namely C1 module, C2 module, and C3 module. Among them, the temperature of the C1 module was 65°C, the temperature of the C2 module was 45°C, and the temperature of the C3 module was 25°C. The solution was cooled from 75°C to 25°C through the three temperature control modules of the tubular reactor C, obtaining crystalline solids and non-condensable liquids. The non-condensable liquids were discharged through E2.

[0093] The crystalline solids were conveyed by a double-screw conveyor equipped with a first twin-screw pump SN1, and then entered a tubular reactor D for drying through a fourth heat exchanger HE4 (temperature: 95°C) and a back pressure valve BPV. The material flow rate was 43 cm 3 / min. In the tubular reactor D equipped with a second twin-screw pump SN2 in a double-screw conveyor, the solvent ethyl acetate was removed through a second vacuum system V2, and the vacuum degree of the tubular reactor D was controlled at 300 Pa. The tubular reactor D was divided into two temperature modules, namely D1 module and D2 module. Among them, the temperature of the D1 module was 65°C, and the temperature of the D2 module was 25°C. The glycolide was cooled from 95°C to 25°C through the two temperature control modules in section D. The crystalline solids were conveyed by a double-screw conveyor equipped with a second twin-screw pump SN2 to obtain white powdery glycolide. The discharge temperature was 25°C, and 8.1 Kg of glycolide was obtained, with a yield of 81%.

[0094] The glycolide prepared in Example 3 was tested by gas chromatography. The test result was that the purity of the glycolide was 99.32%.

[0095] The glycolide prepared in Example 3 was subjected to an acidity test according to the above method, and the test result was that the acid value of the glycolide was 6 ppm.

[0096] Example 4

[0097] In this example, the device in Example 1 was used to purify glycolide, and the specific method was as follows:

[0098] 10 kg of the crude glycolide obtained in Preparation Example 2, ethyl isocyanate acrylate and benzoyl peroxide were mixed in a mass ratio of 100:4:0.3 and added to the distillation column DT for reactive distillation. The material was circulated and heated by the first gear pump P1 and the first heat exchanger HE1 (temperature 140 °C). The bottom temperature of the distillation column DT was 140 °C, and the vacuum degree in the distillation column DT was controlled at 500 Pa by the first vacuum system V1. After reacting for 25 min, part of the glycolide was distilled out from the top of the distillation column DT. The distillation temperature of the glycolide was the top temperature, which was 125 °C. When the glycolide no longer distilled out, the residue was discharged through the distillation residue discharge port E1.

[0099] The glycolide distilled out from the top of the column was cooled by the second heat exchanger HE2, and then part of it entered the second gear pump P2. The temperature of the second heat exchanger HE2 was 105 °C, and the remaining part of the glycolide was refluxed into the distillation column DT, and the reflux ratio was controlled at 1:1. Then the ethyl acetate was exported through the third gear pump P3 and mixed with the glycolide exported through the second gear pump P2 in a weight ratio of = 1.4:1 through the static mixer M1, and then cooled to 90 °C through the third heat exchanger HE3 and entered the tubular reactor C equipped with the first double screw pump SN1 for cooling crystallization. The solution flow rate was 120 cm 3 / min. The tubular reactor C was divided into three temperature modules, namely the C1 module, the C2 module and the C3 module. Among them, the temperature of the C1 module was 70 °C, the temperature of the C2 module was 55 °C, and the temperature of the C3 module was 30 °C. The solution was cooled from 90 °C to 30 °C through the three temperature control modules of the tubular reactor C to obtain crystalline solids and non-condensable liquids, and the non-condensable liquids were discharged through E2.

[0100] The crystalline solids were conveyed by the double screw conveyor equipped with the first double screw pump SN1, and then entered the tubular reactor D for drying through the fourth heat exchanger HE4 (temperature 100 °C) and the back pressure valve BPV. The material flow rate was 30 cm 3 / min. In the tubular reactor D of the double - screw conveyor equipped with the second double - screw pump SN2, the solvent ethyl acetate is removed through the second vacuum system V2, and the vacuum degree of the tubular reactor D is controlled at 300 Pa. The tubular reactor D is divided into two temperature modules, namely the D1 module and the D2 module in sequence. Among them, the temperature of the D1 module is 70 °C, and the temperature of the D2 module is 30 °C. The glycolide is cooled from 100 °C to 30 °C through the two temperature - control modules in section D. The crystalline solid is transported by the double - screw conveyor equipped with the second double - screw pump SN2 to obtain white powdered glycolide, and the discharging temperature is 30 °C. 8.26 Kg of glycolide is obtained, and the yield is 82.6%.

[0101] The gas - chromatography test was carried out on the glycolide prepared in Example 4. The test result is that the purity of glycolide is 98.83%.

[0102] The acidity test was carried out on the glycolide prepared in Example 4 according to the above method. The test result is that the acid value of glycolide is 10 ppm.

[0103] Example 5

[0104] In this example, the device in Example 1 was used to purify glycolide. The specific method is as follows:

[0105] 10 kg of the crude glycolide obtained in Preparation Example 2, isocyanatoethyl methacrylate, and di - isopropylbenzene peroxide were mixed in a mass ratio of 100:5:0.2 and added to the rectification column DT for reactive distillation. The material was circulated and heated by the first gear pump P1 and the first heat exchanger HE1 (temperature: 145 °C). The bottom temperature of the rectification column DT was 145 °C. The vacuum degree inside the rectification column DT was controlled at 500 Pa by the first vacuum system V1. After reacting for 15 min, part of the glycolide was distilled out from the top of the rectification column DT. The distilling - out temperature of glycolide was the top - tower temperature, which was 125 °C. When the glycolide no longer distilled out, the residue was discharged through the rectification residue discharge port E1.

[0106] The glycolide distilled out from the top of the tower was cooled by the second heat exchanger HE2 and then part of it entered the second gear pump P2. The temperature of the second heat exchanger HE2 was 115 °C. The remaining part of the glycolide flowed back into the rectification column DT, and the reflux ratio was controlled at 1:1. Then the ethyl acetate was exported by the third gear pump P3 and mixed with the glycolide exported by the second gear pump P2 in a weight ratio of 2:1 through the static mixer M1, and then cooled to 95 °C by the third heat exchanger HE3 and entered the tubular reactor C of the double - screw conveyor equipped with the first double - screw pump SN1 for cooling crystallization. The solution flow rate was 180 cm 3 / min, the tubular reactor C is divided into three temperature modules, namely the C1 module, the C2 module and the C3 module in sequence. Among them, the temperature of the C1 module is 75 °C, the temperature of the C2 module is 55 °C, and the temperature of the C3 module is 25 °C. The solution is cooled from 95 °C to 25 °C through the three temperature control modules of the tubular reactor C to obtain crystalline solids and non-condensable liquids. The non-condensable liquids are discharged through E2.

[0107] The crystalline solids are conveyed by a double-screw conveyor equipped with a first double-screw pump SN1, and then enter the tubular reactor D through the fourth heat exchanger HE4 (temperature 95 °C) and the back-pressure valve BPV for drying. The material flow rate is 48 cm 3 / min. In the tubular reactor D of the double-screw conveyor equipped with the second double-screw pump SN2, the solvent ethyl acetate is removed through the second vacuum system V2, and the vacuum degree of the tubular reactor D is controlled to be 300 Pa. The tubular reactor D is divided into two temperature modules, namely the D1 module and the D2 module in sequence. Among them, the temperature of the D1 module is 75 °C, and the temperature of the D2 module is 30 °C. The glycolide is cooled from 95 °C to 30 °C through the two temperature control modules of the D section. The crystalline solids are transmitted through the double-screw conveyor equipped with the second double-screw pump SN2 to obtain white powdery glycolide. The discharge temperature is 30 degrees, and 8.18 Kg of glycolide is obtained, with a yield of 81.8%.

[0108] The glycolide prepared in Example 5 was tested by gas chromatography. The test results were as follows: the purity of glycolide was 98.92%.

[0109] The glycolide prepared in Example 5 was tested for acidity according to the above method. The test results showed that the acid value of glycolide was 9 ppm.

[0110] Example 6

[0111] In this example, the device in Example 1 was used to purify glycolide. The specific method was as follows:

[0112] 10 kg of the crude glycolide obtained in Preparation Example 2, isocyanatoethyl methacrylate and diisopropylbenzene peroxide were mixed in a mass ratio of 100:6:0.35 and added to the distillation column DT for reactive distillation. The material was circulated and heated by the first gear pump P1 and the first heat exchanger HE1 (temperature 150 °C). The bottom temperature of the distillation column DT was 150 °C. The vacuum degree inside the distillation column DT was controlled to be 500 Pa through the first vacuum system V1. After reacting for 10 min, part of the glycolide was distilled out from the top of the distillation column DT. The distillation temperature of the glycolide was the top temperature, which was 125 °C. When the glycolide no longer distilled out, the residue was discharged through the distillation residue discharge port E1.

[0113] The glycolide distilled from the top of the tower is cooled by the second heat exchanger HE2, and then a part of it enters the second gear pump P2. The temperature of the second heat exchanger HE2 is 110 °C. The remaining glycolide is refluxed into the distillation tower DT, and the reflux ratio is controlled at 1:1. Then, isopropanol is exported by the third gear pump P3, and the glycolide exported by the second gear pump P2 is mixed with it in a weight ratio of 1.2:1 through a static mixer M1. Then, it is cooled to 80 °C by the third heat exchanger HE3 and enters the tubular reactor C of the double-screw conveyor equipped with the first double-screw pump SN1 for cooling crystallization. The solution flow rate is 80 cm 3 / min. The tubular reactor C is divided into three temperature modules, namely the C1 module, the C2 module, and the C3 module. Among them, the temperature of the C1 module is 60 °C, the temperature of the C2 module is 40 °C, and the temperature of the C3 module is 25 °C. The solution is cooled from 80 °C to 25 °C through the three temperature control modules of the tubular reactor C to obtain crystalline solids and non-condensable liquids. The non-condensable liquids are discharged through E2.

[0114] The crystalline solids are transported by the double-screw conveyor equipped with the first double-screw pump SN1, and then enter the tubular reactor D for drying through the fourth heat exchanger HE4 (temperature 90 °C) and the back pressure valve BPV. The material flow rate is 32 cm 3 / min. In the tubular reactor D of the double-screw conveyor equipped with the second double-screw pump SN2, the solvent isopropanol is removed through the second vacuum system V2, and the vacuum degree of the tubular reactor D is controlled at 300 Pa. The tubular reactor D is divided into two temperature modules, namely the D1 module and the D2 module. Among them, the temperature of the D1 module is 65 °C, and the temperature of the D2 module is 25 °C. The glycolide is cooled from 90 °C to 25 °C through the two temperature control modules of the D section. The crystalline solids are transported by the double-screw conveyor equipped with the second double-screw pump SN2 to obtain white powdery glycolide. The discharge temperature is 30 degrees, and 8.2 Kg of glycolide is obtained, with a yield of 82%.

[0115] The glycolide prepared in Example 6 was tested by gas chromatography. The test results showed that the purity of the glycolide was 99.35%.

[0116] The glycolide prepared in Example 6 was tested for acidity according to the above method. The test results showed that the acid value of the glycolide was 5 ppm.

[0117] Example 7

[0118] In this example, the device in Example 1 was used to purify glycolide. The specific method is as follows:

[0119] 10 kg of the crude glycolide obtained in Preparation Example 2, isocyanoethyl methacrylate, and diisopropylbenzene peroxide were mixed in a mass ratio of 100:7:0.3 and added to a distillation column DT for reactive distillation. The material was circulated and heated by a first gear pump P1 and a first heat exchanger HE1 (at a temperature of 155°C). The bottom temperature of the distillation column DT was 155°C. The vacuum degree inside the distillation column DT was controlled at 500 Pa by a first vacuum system V1. After reacting for 5 minutes, part of the glycolide was distilled out from the top of the distillation column DT. The distillation temperature of the glycolide was the top temperature, which was 125°C. When the glycolide no longer distilled out, the residue was discharged through a residue discharge port E1.

[0120] The glycolide distilled out from the top of the column was cooled by a second heat exchanger HE2, and then part of it entered a second gear pump P2. The temperature of the second heat exchanger HE2 was 105°C. The remaining part of the glycolide was refluxed into the distillation column DT, and the reflux ratio was controlled at 1:1. Then, isopropanol was exported through a third gear pump P3 and mixed with the glycolide exported through the second gear pump P2 in a weight ratio of 1.4:1 through a static mixer M1. Then, it was cooled to 75°C by a third heat exchanger HE3 and entered a tubular reactor C equipped with a first double screw pump SN1 in a double - screw conveyor for cooling crystallization. The solution flow rate was 120 cm 3 / min. The tubular reactor C was divided into three temperature modules, namely module C1, module C2, and module C3. Among them, the temperature of module C1 was 55°C, the temperature of module C2 was 40°C, and the temperature of module C3 was 25°C. The solution was cooled from 75°C to 25°C through the three temperature - control modules of the tubular reactor C, obtaining crystalline solids and non - condensable liquids. The non - condensable liquids were discharged through E2.

[0121] The crystalline solids were transported by a double - screw conveyor equipped with a first double screw pump SN1, and then entered a tubular reactor D for drying through a fourth heat exchanger HE4 (at a temperature of 85°C) and a back - pressure valve BPV. The material flow rate was 40 cm 3 / min. In the tubular reactor D equipped with a second double screw pump SN2 in a double - screw conveyor, the solvent isopropanol was removed through a second vacuum system V2, and the vacuum degree of the tubular reactor D was controlled at 300 Pa. The tubular reactor D was divided into two temperature modules, namely module D1 and module D2. Among them, the temperature of module D1 was 70°C, and the temperature of module D2 was 25°C. The glycolide was cooled from 85°C to 25°C through the two temperature - control modules in section D. The crystalline solids were transported by a double - screw conveyor equipped with a second double screw pump SN2 to obtain white powdered glycolide. The discharge temperature was 30 degrees, and 8.15 Kg of glycolide was obtained, with a yield of 81.5%.

[0122] The glycolide prepared in Example 7 was tested by gas chromatography. The test result was that the purity of the glycolide was 99.26%.

[0123] The glycolide prepared in Example 7 was subjected to an acidity test according to the above method, and the test result showed that the acid value of the glycolide was 7 ppm.

[0124] Example 8

[0125] In this example, the device in Example 1 was used to purify glycolide, and the specific method was as follows:

[0126] 10 kg of the crude glycolide obtained in Preparation Example 3, isocyanatoethyl methacrylate, and di-tert-butyl peroxide were mixed in a mass ratio of 100:8:0.6 and added to the distillation column DT for reactive distillation. The material was circulated and heated by the first gear pump P1 and the first heat exchanger HE1 (temperature 150 °C). The bottom temperature of the distillation column DT was 150 °C, and the vacuum degree in the distillation column DT was controlled at 500 Pa by the first vacuum system V1. After reacting for 10 min, part of the glycolide was distilled out from the top of the distillation column DT. The distillation temperature of the glycolide was the top temperature, which was 125 °C. When the glycolide was no longer distilled out, the residue was discharged through the distillation residue discharge port E1.

[0127] The glycolide distilled out from the top was cooled by the second heat exchanger HE2, and then a part of it entered the second gear pump P2. The temperature of the second heat exchanger HE2 was 100 °C, and the remaining part of the glycolide was refluxed into the distillation column DT, and the reflux ratio was controlled at 1:1. Then, n-propanol was exported through the third gear pump P3, and the glycolide exported through the second gear pump P2 was mixed with it in a weight ratio of = 1.5:1 through the static mixer M1, and then cooled to 80 °C by the third heat exchanger HE3 and entered the tubular reactor C equipped with the first double screw pump SN1 for cooling crystallization. The solution flow rate was 110 cm 3 / min. The tubular reactor C was divided into three temperature modules, namely the C1 module, the C2 module, and the C3 module. Among them, the temperature of the C1 module was 65 °C, the temperature of the C2 module was 50 °C, and the temperature of the C3 module was 25 °C. The solution was cooled from 80 °C to 25 °C through the three temperature control modules of the tubular reactor C to obtain crystalline solids and non-condensable liquids, and the non-condensable liquids were discharged through E2.

[0128] The crystalline solids were transported by the double screw conveyor equipped with the first double screw pump SN1, and then entered the tubular reactor D for drying through the fourth heat exchanger HE4 (temperature 90 °C) and the back pressure valve BPV. The material flow rate was 35 cm 3 / min, remove the solvent n-propanol in the tubular reactor D of the double-screw conveyor equipped with the second double-screw pump SN2 through the second vacuum system V2, and control the vacuum degree of the tubular reactor D to be 300 Pa. The tubular reactor D is divided into two temperature modules, namely the D1 module and the D2 module in sequence. Among them, the temperature of the D1 module is 60 °C, and the temperature of the D2 module is 30 °C. Cool the glycolide from 90 °C to 30 °C through the two temperature control modules in section D. The crystalline solid is transported through the double-screw conveyor equipped with the second double-screw pump SN2 to obtain white powdery glycolide, and the discharge temperature is 30 °C, obtaining 8.23 Kg of glycolide, and the yield is 82.3%.

[0129] Perform gas chromatography testing on the glycolide prepared in Example 8. The test results are as follows: the purity of glycolide is 98.96%.

[0130] Perform acidity testing on the glycolide prepared in Example 8 according to the above method. The test results show that the acid value of glycolide is 9 ppm.

[0131] Example 9

[0132] This example uses the device in Example 1 to purify glycolide. The specific method is as follows:

[0133] Mix 10 kg of the crude glycolide obtained in Preparation Example 3, isocyanatoethyl methacrylate, and di-tert-butyl peroxide in a mass ratio of 100:9:0.4 and add them to the distillation column DT for reactive distillation. Circulate and heat the material through the first gear pump P1 and the first heat exchanger HE1 (temperature is 145 °C). The bottom temperature of the distillation column DT is 145 °C. Control the vacuum degree inside the distillation column DT to be 500 Pa through the first vacuum system V1. After reacting for 10 min, part of the glycolide distills out from the top of the distillation column DT. The distillation temperature of glycolide is the top temperature, which is 125 °C. When the glycolide no longer distills out, discharge the residue through the residue discharge port E1.

[0134] The glycolide distilled out from the top is cooled by the second heat exchanger HE2, and then part of it enters the second gear pump P2. The temperature of the second heat exchanger HE2 is 95 °C. The remaining part of the glycolide flows back into the distillation column DT, and the reflux ratio is controlled to be 1:1. Then export n-propanol through the third gear pump P3, and mix it with the glycolide exported through the second gear pump P2 in a weight ratio of = 1.7:1 through the static mixer M1, and then cool it to 80 °C through the third heat exchanger HE3 and enter the tubular reactor C of the double-screw conveyor equipped with the first double-screw pump SN1 for cooling crystallization. The solution flow rate is 150 cm 3 / min, the tubular reactor C is divided into three temperature modules, namely the C1 module, the C2 module and the C3 module in sequence. The temperature of the C1 module is 60 °C, the temperature of the C2 module is 45 °C, and the temperature of the C3 module is 25 °C. The solution is cooled from 80 °C to 25 °C through the three temperature control modules of the tubular reactor C to obtain crystalline solids and non-condensable liquids. The non-condensable liquids are discharged through E2.

[0135] The crystalline solids are conveyed by a double-screw conveyor equipped with the first double-screw pump SN1, and then enter the tubular reactor D through the fourth heat exchanger HE4 (temperature 95 °C) and the back-pressure valve BPV for drying. The material flow rate is 45 cm 3 / min. In the tubular reactor D of the double-screw conveyor equipped with the second double-screw pump SN2, the solvent n-propanol is removed through the second vacuum system V2, and the vacuum degree of the tubular reactor D is controlled at 300 Pa. The tubular reactor D is divided into two temperature modules, namely the D1 module and the D2 module in sequence. The temperature of the D1 module is 75 °C, and the temperature of the D2 module is 25 °C. The glycolide is cooled from 95 °C to 25 °C through the two temperature control modules of the D section. The crystalline solids are transported by the double-screw conveyor equipped with the second double-screw pump SN2 to obtain white powdery glycolide. The discharge temperature is 30 degrees, and 8.19 Kg of glycolide is obtained, with a yield of 81.9%.

[0136] The glycolide prepared in Example 9 was tested by gas chromatography. The test results were as follows: the purity of glycolide was 98.75%.

[0137] The glycolide prepared in Example 9 was tested for acidity according to the above method. The test results showed that the acid value of glycolide was 11 ppm.

[0138] Example 10

[0139] In this example, the device in Example 1 was used to purify glycolide. The specific method was as follows:

[0140] 10 kg of the crude glycolide obtained in Preparation Example 3, ethyl isocyanate acrylate and di-tert-butyl peroxide were mixed in a mass ratio of 100:10:0.5 and added to the distillation column DT for reactive distillation. The material was circulated and heated by the first gear pump P1 and the first heat exchanger HE1 (temperature 140 °C). The bottom temperature of the distillation column DT was 140 °C. The vacuum degree inside the distillation column DT was controlled at 500 Pa by the first vacuum system V1. After reacting for 20 min, part of the glycolide was distilled out at the top of the distillation column DT. The distillation temperature of glycolide was the top temperature, which was 125 °C. When the glycolide no longer distilled out, the residue was discharged through the distillation residue discharge port E1.

[0141] The glycolide distilled from the top of the tower is cooled by the second heat exchanger HE2 and then part of it enters the second gear pump P2. The temperature of the second heat exchanger HE2 is 90 °C. The remaining glycolide is refluxed into the distillation tower DT, and the reflux ratio is controlled at 1:1. Then the n-propanol is exported by the third gear pump P3 and mixed with the glycolide exported by the second gear pump P2 in a weight ratio of 1.9:1 through the static mixer M1, and then cooled to 85 °C by the third heat exchanger HE3 and enters the tubular reactor C of the double-screw conveyor equipped with the first double-screw pump SN1 for cooling crystallization. The solution flow rate is 200 cm 3 / min. The tubular reactor C is divided into three temperature modules, namely the C1 module, the C2 module and the C3 module. Among them, the temperature of the C1 module is 65 °C, the temperature of the C2 module is 40 °C, and the temperature of the C3 module is 25 °C. The solution is cooled from 85 °C to 25 °C through the three temperature control modules of the tubular reactor C to obtain crystalline solids and non-condensable liquids. The non-condensable liquids are discharged through E2.

[0142] The crystalline solids are transported by the double-screw conveyor equipped with the first double-screw pump SN1, and then enter the tubular reactor D for drying through the fourth heat exchanger HE4 (temperature 100 °C) and the back pressure valve BPV. The material flow rate is 52 cm 3 / min. In the tubular reactor D of the double-screw conveyor equipped with the second double-screw pump SN2, the solvent n-propanol is removed through the second vacuum system V2, and the vacuum degree of the tubular reactor D is controlled at 300 Pa. The tubular reactor D is divided into two temperature modules, namely the D1 module and the D2 module. Among them, the temperature of the D1 module is 70 °C, and the temperature of the D2 module is 30 °C. The glycolide is cooled from 100 °C to 30 °C through the two temperature control modules of the D section. The crystalline solids are transported by the double-screw conveyor equipped with the second double-screw pump SN2 to obtain white powdery glycolide, and the discharge temperature is 30 °C, obtaining 8.14 Kg of glycolide, and the yield is 81.4%.

[0143] The glycolide prepared in Example 10 was tested by gas chromatography, and the test results were as follows: the purity of glycolide was 99.12%.

[0144] The glycolide prepared in Example 10 was tested for acidity according to the above method, and the test results showed that the acid value of the glycolide was 8 ppm.

[0145] Comparative Example 1

[0146] 10 kg of the crude glycolide obtained in Preparation Example 1 was mixed with ethyl acetate at a weight ratio of 1:1 and added to a reaction kettle for dissolution. Cooling crystallization was carried out, and the temperature was reduced from 80 °C to 30 °C to obtain crystalline solids and non-condensable liquids. The non-condensable liquids were discharged, and the crystalline solids were dried by vacuum. The vacuum degree was 300 Pa, and the drying temperature was 25 °C to obtain 8.5 kg of primary crystalline glycolide with a yield of 85%. According to the above operation, the crystallization of the glycolide solution was carried out again to obtain 7.3 kg of secondary crystalline glycolide with a yield of 73%.

[0147] Gas chromatography test was carried out on the primary crystalline glycolide prepared in Comparative Example 1 of the present invention. The test results were as follows: the purity of glycolide was 97.1%.

[0148] The acidity test was carried out on the primary crystalline glycolide prepared in Comparative Example 1 of the present invention according to the above method. The test results were as follows: the acid value of glycolide was 76 ppm.

[0149] Gas chromatography test was carried out on the secondary crystalline glycolide prepared in Comparative Example 1 of the present invention. The test results were as follows: the purity of glycolide was 98.8%.

[0150] The acidity test was carried out on the secondary crystalline glycolide prepared in Comparative Example 1 of the present invention according to the above method. The test results were as follows: the acid value of glycolide was 25 ppm.

[0151] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for purifying glycolide, characterized in that, It includes the following steps: S1: Subject the mixture of crude glycolide, isocyanate monomer and initiator to rectification treatment to obtain an intermediate; S2: Subject the solution of the intermediate to solution crystallization to obtain glycolide; The isocyanate monomer may be selected from isocyanatoethyl methacrylate and / or isocyanatoethyl acrylate; The initiator is selected from any one or more of azobisisobutyronitrile, azobisisoheptonitrile, dicumyl peroxide, benzoyl peroxide, diisopropylbenzene peroxide, di-tert-butyl peroxide, tert-butyl peroxy(2-ethylhexanoate), tert-butyl peroxyacetate, tert-butyl peroxybenzoate or diisopropyl peroxydicarbonate; The initial temperature of the solution crystallization is 60 - 120°C, and the termination temperature is 0 - 50°C; The solution crystallization includes M cooling processes, where M = 3 - 20; The rectification treatment is carried out in a rectification column; The bottom temperature of the rectification column is 110 - 160°C, and the top temperature is 80 - 150°C; The vacuum degree of the rectification column is 10 - 10000 Pa.

2. The purification method according to claim 1, characterized in that, The temperature difference between two adjacent cooling processes in the solution crystallization is 5 - 50°C.

3. The purification method according to claim 1, characterized in that The mass ratio of the crude glycolide, isocyanate monomer and initiator is 100:(1 - 20):(0.05 - 2).

4. The purification method according to claim 1, characterized in that, In step S1, the rectification treatment is carried out in a rectification column; The bottom mixture of the rectification column is recycled after the first heat exchange treatment; the temperature of the first heat exchange treatment is 110 - 160°C.

5. The purification method according to claim 1, characterized in that, The solution of the intermediate is obtained by mixing a solvent and the intermediate that has undergone the second heat exchange treatment; The temperature of the second heat exchange treatment is 85 - 120°C.

6. The purification method according to claim 1, characterized in that The solution of the intermediate is first subjected to the third heat exchange treatment and then to solution crystallization; The temperature of the third heat exchange treatment is 60 - 120°C.

7. The purification method according to claim 1, wherein After the solution crystallization is completed, the obtained product is subjected to the fourth heat exchange treatment and then to drying treatment; The temperature of the fourth heat exchange treatment is 85 - 120°C.

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