A method for controlling the production process of glycolide

Abstract

This invention discloses a method for controlling the production process of glycolide, the method comprising the steps of: setting the mass of reactant material passing through a unit heat exchange area in the reactor per unit time, i.e., parameter a, which is 3-1290 kg / (hour·m²).

Description

Technical Field

[0001] This invention relates to the field of chemical engineering, and more particularly to a method for controlling the production process of glycolide. Background Technology

[0002] Glycol-lactide is a cyclic dimer of glycolic acid, and the technology of preparing high molecular weight polyglycolic acid by ring-opening polymerization of glycolide has attracted widespread attention. Using glycolic acid or glycolate esters as reactants, glycolic acid oligomers are prepared through polycondensation, followed by depolymerization and cyclization to generate gaseous glycolide, which is then collected after cooling. In this preparation process, heat control of the reaction system is crucial. If the reaction system heat is too high, on the one hand, the reaction energy consumption is high, and on the other hand, the material in the reactor is prone to coking, causing blockage. Reaction residues cannot be discharged from the reactor, making cleaning difficult, and the resulting glycolide product is yellow and has a low yield. Conversely, if the reaction system heat is too low, it will affect the degree of depolymerization and cyclization, slowing down the reaction rate and resulting in a low final reaction degree. The yield of the obtained glycolide product is low, and the impurity content is high, which increases the difficulty of subsequent glycolide purification processes and significantly increases purification energy consumption.

[0003] Therefore, there is an urgent need in this field to develop an efficient and stable production process for glycolide to achieve low-carbon production of glycolide. Summary of the Invention

[0004] The present invention aims to provide a controlled method for the production of glycolide, enabling the efficient and stable preparation of glycolide.

[0005] In a first aspect of the invention, a method for controlling a glycolide production process is provided, the glycolide production process comprising obtaining glycolide by depolymerizing a glycolic acid or glycolate polymer through a cyclization reaction, the method comprising the step of setting parameter a to 3-1290 kg / (hour·m²), wherein parameter a represents the mass of reactant passing through a unit heat exchange area in a reactor per unit time.

[0006] In another embodiment, parameter a is 3-860 kg / (hour·m²).

[0007] In another embodiment, parameter a is 12-451 kg / (hour·m²), preferably 18-215 kg / (hour·m²).

[0008] In another embodiment, when the glycolide production process is a batch production process based on a single reactor, the amount of reactant processed per unit time is the product of parameter a and the heat exchange area of ​​the reactor.

[0009] In another embodiment, when the glycolide production process is a continuous production process based on a single reactor, the feed rate of the reactants is the product of parameter a and the heat exchange area of ​​the reactor.

[0010] In another embodiment, when the glycolide production process is a continuous production process based on two or more reactors connected in series, the feed rate of the reactants in the first reactor is the product of the arithmetic mean of parameter a of each reactor and the sum of the heat exchange areas of each reactor.

[0011] In another embodiment, the heat transfer coefficient K of the reactor is 100-3600 W / (m²·℃).

[0012] In another embodiment, the heat transfer temperature difference of the reactor is 5-100°C.

[0013] In a second aspect of the present invention, a method for preparing glycolide is provided, the method comprising the steps of:

[0014] (i) molten reactants are introduced into the reactor for depolymerization; the reactants contain glycolic acid or glycolate polymers; and

[0015] (ii) The reactants are depolymerized by heat to form cyclization and obtain glycolide;

[0016] The parameter a is set to 3-1290 kg / (hour·m²), where parameter a represents the mass of reactant material passing through a unit heat exchange area in the reactor per unit time.

[0017] In a batch production process based on a single reactor, the throughput of reactants per unit time is the product of parameter a and the reactor's heat exchange area; or

[0018] In a continuous production process based on a single reactor, the feed rate of the reactants is the product of parameter a and the reactor heat exchange area; or

[0019] In a continuous production process based on two or more reactors in series, the feed rate of the reactants in the first reactor is the product of the arithmetic mean of parameter 'a' of each reactor and the sum of the heat exchange areas of each reactor.

[0020] In another embodiment, the weight-average molecular weight of the glycolic acid or glycolate polymer is not less than 1000; and / or

[0021] The reactants described in step (i) also contain a catalyst; and / or

[0022] In step (ii), the temperature inside the reactor is 220-300℃, and the pressure is ≤50kPa; and / or

[0023] The method further includes the steps of collecting and purifying the glycolide obtained in step (ii).

[0024] Accordingly, the present invention provides an efficient and stable production process for preparing glycolide to achieve low-carbon production of glycolide. Attached Figure Description

[0025] Figure 1 This shows a reaction system model with two reactors in series; the solid box represents reactor 100.

[0026] Figure 2 This shows a reaction system model with two reactors connected in parallel; the solid boxes represent reactors 101 and 102, respectively. Detailed Implementation

[0027] Through extensive and in-depth research, the inventors discovered a method for controlling the mass of reactants corresponding to a unit heat exchange area within a reactor per unit time, which can efficiently and stably prepare glycolide. Based on this, the present invention was completed.

[0028] This invention provides a method for controlling the production process of glycolide, which is based on controlling the heat of the reaction system. The main method involves controlling the mass of reactant material per unit heat exchange area within the reactor per unit time, i.e., parameter a, during the depolymerization and cyclization reaction of the glycolic acid (or glycolate) polymer, within the range of 3-1290 kg / (h·m²). 2 This allows for the control of the heat obtained per unit mass of reactant.

[0029] The reactor used in this invention can be conventional in the art, such as, but not limited to, commercially available conventional reactors. The types of reactors include, but are not limited to, stirred reactors, falling film reactors, and scraped film reactors.

[0030] The inventors discovered that if parameter a is less than 3 kg / (h·m) 2 Coking easily occurs in the reactor, which not only causes loss of reactants and reduces the yield of glycolide, resulting in a yellowish glycolide product, but also makes it difficult to remove residual material from the reactor, requiring specialized cleaning that is time-consuming and labor-intensive. If parameter a is greater than 1290 kg / (h·m 2 The reaction degree of the reactants in the reactor is low, resulting in a low yield of glycolide and low purity of the obtained glycolide product, which makes subsequent purification difficult.

[0031] In one embodiment of the present invention, the mass of reactant material corresponding to a unit heat exchange area in the reactor per unit time, i.e., parameter a, is 3-860 kg / (h·m²). 2Preferably, the mass of reactant corresponding to a unit heat exchange area within the reactor per unit time, i.e., parameter a, is 12-451 kg / (h·m²). 2 More preferably, the mass of reactant corresponding to a unit heat exchange area within the reactor per unit time, i.e., parameter a, is 18-215 kg / (h·m²). 2 ).

[0032] The glycolic acid (or glycolate) polymer of the present invention has a weight-average molecular weight of not less than 1,000; preferably, the weight-average molecular weight is not less than 2,000 and not more than 200,000; further, the weight-average molecular weight of the glycolic acid (or glycolate) polymer is not less than 3,000 and not more than 100,000; even more preferably, the weight-average molecular weight of the glycolic acid (or glycolate) polymer is not less than 5,000 and not more than 60,000.

[0033] It should be noted that the reactants used in the above method are not limited to glycolic acid oligomers, but can also be polyglycolic acid with a molecular weight (weight average molecular weight) greater than 200,000. For example, waste polyglycolic acid materials with a weight average molecular weight of about 200,000 or more can also be used as reactants to prepare glycolide through the above method after recycling, thereby realizing the reuse of waste polyglycolic acid materials.

[0034] The heat transfer coefficient K of the reactor used in this invention can be 100-3600 W / (m²). 2 ·℃), for example, but not limited to, 150-3000W / (m 2 ·℃), 500-2000W / (m 2 ·℃), 300-1500W / (m 2 (·℃), etc.

[0035] The heat transfer temperature difference of the reactor used in this invention is controlled at 5-100℃, for example, but not limited to, 20-70℃, 30-50℃, 10-40℃, 60-90℃, 25-80℃, etc.

[0036] The control method provided by this invention is applicable to both batch and continuous production processes of glycolide.

[0037] As used in this invention, "intermittent production process" refers to a process in which reactants are processed according to a prescribed processing sequence and operating conditions, and products are output in a limited quantity.

[0038] As used in this invention, "continuous production process" refers to a process in which reactants are continuously passed through a set of specialized equipment, each of which operates in a steady state and performs only one specific processing task, and the product is output in a continuous flow manner.

[0039] Furthermore, the "intermittent production process" and "continuous production process" of the present invention have the following characteristics:

[0040]

[0041] When the control method of the present invention is used in a batch production process, by setting parameter a and based on the heat exchange area S of the reactor used, the V value (i.e., V = S × a) can be calculated, which is the amount of reactant processed by the reactor per unit time (i.e., 1 hour). The feed is then performed according to the calculated V value. For example, but not limited to, in a batch production process, parameter a is set to 20 kg / (h·m²). 2 The heat exchange area S of the reactor used is approximately 15m². 2 Therefore, the reactor can process approximately 300 kg of reactants per unit time (i.e., 1 hour) during the production process. The reactants are added to the reactor at once, the reactor is heated, and the temperature inside the reactor is controlled at 220-300℃, and the absolute pressure is controlled at ≤50 kPa. The gaseous glycolide generated during the reaction is collected. When the reaction time reaches the set time, production is stopped, thus completing one batch production cycle.

[0042] When the control method of the present invention is used in a continuous production process, by setting parameter a and based on the heat exchange area S of the reactor used, the value V (i.e., V = S × a) can be calculated, which is the average mass feed rate of the reactants entering the reactor. For example, but not limited to, in a continuous production process, parameter a is set to 20 kg / (h·m³). 2 The heat exchange area S of the reactor used is approximately 15m². 2 The average mass feed rate V of the reactants in the reactor during the production process is about 300 kg / h. The molten reactants are pumped into the reactor, and the temperature of the heat exchange surface inside the reactor is set to about 220-300℃. The absolute pressure inside the reactor is controlled to ≤50 kPa. The gaseous glycolide generated during the reaction is collected. The time for the reactants to completely pass through the heat exchange surface inside the reactor is about 0.2-12 h. The reactants collected at the bottom of the reactor are discharged at the set average mass discharge rate L. The value of L is set to control the material level parameter at the bottom of the reactor to stabilize, thereby establishing a stable continuous production process.

[0043] In one embodiment of the present invention, the control method provided by the present invention is applied to a continuous production process. First, the parameter a of each reactor is set separately. i (i is an integer ≥ 1), and then calculate the parameters a for each reactor. iThe parameter 'a' can be obtained by taking the arithmetic mean of the values ​​of the two reactors. Then, based on the total heat exchange area S of the multiple reactors, the average mass feed rate V1 (V1 = S × a) of the reactants in the first reactor is calculated. Based on the calculated V1 value, the molten reactants are pumped into the first reactor. The temperature of the heat exchange surface in the first reactor is controlled at 220-300℃, and the absolute pressure inside the reactor is controlled at ≤50kPa. The gaseous glycolide generated during the reaction is collected. The material collected at the bottom of the first reactor is discharged and enters the second reactor for further reaction, and so on, until the reactants pass through the last reactor. In the above process, the total time for the reactants to pass through the heat exchange surfaces of each reactor is approximately 0.2-12 hours. The gaseous glycolide generated in each reactor is collected. It should be noted that the average mass discharge rate L1 of the reactants in the first reactor and the average mass feed rate V1 of the reactants in subsequent reactors are... j (j is an integer ≥ 2) and its corresponding average mass discharge rate L of the reactants j The selection of (j is an integer ≥2) is based on controlling the stability of the material liquid level parameters at the bottom of each reactor, thereby establishing a stable continuous production process.

[0044] When the glycolide production process described in this invention uses more than two reactors, parameter 'a' needs to be set for the entire depolymerization and cyclization reaction system, rather than for a specific reactor in the system.

[0045] In one embodiment of the present invention, the depolymerization and cyclization reaction system contains two or more reactors connected in series (see Appendix). Figure 1 The reaction conditions (e.g., temperature, pressure) in each reactor can be the same or different. Parameter 'a' for each reactor can be set individually beforehand. i Then, by calculating the parameters a of each reactor... i The arithmetic mean of these parameters is the parameter a, which is relative to the entire depolymerization and cyclization reaction system.

[0046] In one embodiment of the present invention, the depolymerization and cyclization reaction system contains two or more reactors connected in parallel (see Appendix). Figure 2 The reaction conditions (e.g., temperature, pressure) within each reactor can be the same or different. Each reactor connected in parallel and its parallel line should be considered as a separate reaction system. (See attached...) Figure 2 Reactor 101 and its parallel line 201 form an independent reaction system. Figure 2 The reactor 102 and its parallel line 202 form another independent reaction system.

[0047] This invention also provides a method for preparing glycolide, the method comprising the steps of:

[0048] The first step involves setting the mass of reactant material passing through a unit heat exchange area within the reactor per unit time (i.e., parameter a) and then allowing the molten reactant material to enter the reactor for depolymerization; the reactant material contains glycolic acid (or glycolate) polymer.

[0049] The second step involves thermally depolymerizing the reactants into rings to obtain gaseous glycolide.

[0050] The third step is to collect the generated gaseous glycolide.

[0051] In the first step described above, parameter a is set according to the control method of the glycolide production process provided by the present invention, and the amount of molten reactant material fed into the reactor is determined, or the mass feed rate of the molten reactant material entering the reactor is determined.

[0052] The reactants described in the first step above also include a catalyst; in one embodiment of the present invention, the amount of catalyst added does not exceed 5 wt% of the mass of the molten glycolic acid (or glycolate) polymer; the catalyst may be selected from at least one of tin compounds, antimony compounds or zinc compounds, such as, but not limited to, stannous octoate, stannous chloride, stannous lactate, antimony trioxide, and zinc diethylzinc or zinc acetate dihydrate.

[0053] In one embodiment of the present invention, the reactant in the first step described above may be a glycolic acid (or glycolate) polymer with a weight-average molecular weight of not less than 1000; for example, but not limited to, the weight-average molecular weight is not less than 2000 and not greater than 200000; further, the weight-average molecular weight of the glycolic acid (or glycolate) polymer is not less than 3000 and not greater than 100000; more preferably, the weight-average molecular weight of the glycolic acid (or glycolate) polymer is not less than 5000 and not greater than 60000.

[0054] The reactant in the first step above can also be polyglycolic acid with a molecular weight (weight average molecular weight) greater than 200,000. For example, waste polyglycolic acid material with a weight average molecular weight of about 200,000 or more can also be used as a reactant to prepare glycolide by the above method after recycling, thereby realizing the reuse of waste polyglycolic acid material.

[0055] In one embodiment of the present invention, during the depolymerization and cyclization reaction stage of the glycolic acid (or glycolate) polymer in the second step, the temperature inside the reactor is 220-300°C and the absolute pressure is ≤50kPa.

[0056] In one embodiment of the present invention, during the collection step in the third step, the generated gaseous glycolide can be passed into a conventional condenser for condensation and collection.

[0057] In one embodiment of the invention, the collected glycolide can also be purified by, for example but not limited to, recrystallization or continuous crystallization.

[0058] The technical parameter a provided by this invention can provide relevant technical reference for technicians engaged in the industrial production of glycolide. Based on the method of this invention, glycolide can be prepared, which can effectively overcome the technical problems caused by poor control of the heat of the reaction system and the amount of material processed, such as easy coking of materials, equipment blockage, low product yield, or insufficient reaction and low purity of the obtained product.

[0059] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0060] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0061] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are used for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0062] The features mentioned above in this invention, or the features mentioned in the embodiments, can be combined arbitrarily. All features disclosed in this specification can be used with any compositional form, provided that the combination of these features does not contradict each other; all possible combinations should be considered within the scope of this specification. Each feature disclosed in the specification can be replaced by any alternative feature that provides the same, equivalent, or similar purpose. Therefore, unless otherwise specified, the disclosed features are merely general examples of equivalent or similar features.

[0063] The main advantages of this invention are:

[0064] 1. The method provided by this invention uses molten glycolic acid (or glycolate) oligomers as reactants, eliminating the need for organic solvents. It is a low-carbon and environmentally friendly production process. By selecting and setting an appropriate parameter a (i.e., the mass of reactants corresponding to a unit heat exchange area in the reactor per unit time), the heat in the reaction system can be efficiently utilized, greatly reducing energy consumption. It can achieve low-carbon, continuous, and stable production of glycolide, making it suitable for industrial application and contributing to the achievement of the industry's "carbon neutrality" goal.

[0065] 2. The method provided by this invention offers a new approach to controlling existing glycolide production processes. It offers good flexibility and is applicable to both batch and continuous glycolide production processes. This method can be used to design new glycolide production lines or to upgrade existing ones to improve production efficiency and achieve a green, low-carbon production model.

[0066] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise stated, all percentages, ratios, proportions, or parts are by weight. The units in weight-volume percentages in this invention are well known to those skilled in the art, for example, referring to the weight of the solute in 100 ml of solution. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described herein are for illustrative purposes only.

[0067] In the following examples, the purity of the glycolide product was quantitatively analyzed by gas chromatography. The gas chromatograph model was Shimadzu; the column model was TC-17 (Ф0.25mm×30m×2μm); the vaporization chamber temperature was 295℃; the column heating process was as follows: after holding at 60℃ for 3 minutes, the temperature was increased to 280℃ at a heating rate of 20℃ / min and held for 3 minutes; the detector was a flame ionization detector at 300℃.

[0068] Example 1-1 (Continuous Production Process)

[0069] Choose a heat exchange area of ​​approximately 0.2 m². 2 For the reactor, the mass of reactant corresponding to a unit heat exchange area within the reactor per unit time, i.e., parameter a, is set to 25 kg / (h·m²). 2 The average mass feed rate V of the reactants in the reactor was calculated to be approximately 5 kg / h. Molten reactants (containing glycolic acid polymer with a weight-average molecular weight of approximately 10,000 and stannous octoate, wherein the amount of stannous octoate added is approximately 0.3% of the glycolic acid polymer mass) were introduced into the reactor at a feed rate of approximately 5 kg / h. The temperature of the heat exchange surface in the reactor was set to approximately 220°C, and the heat transfer temperature difference in the reactor was approximately 70°C. The heat transfer coefficient K was approximately 100 W / (m²). 2The reactor is set at an absolute pressure of approximately 100 Pa (°C). The reactants flow downwards along the heat exchange surface of the reactor and undergo depolymerization and ring-forming reactions upon heating to generate gaseous glycolide. The generated gaseous glycolide is extracted from the reactor, condensed by an external condenser, and then collected in a storage tank. In the above process, the reactants completely pass through the heat exchange surface of the reactor in approximately 0.5 hours. The reactants collected at the bottom of the reactor are discharged at a set average mass discharge rate L. The value of L is set to control the stability of the liquid level parameter at the bottom of the reactor, thereby establishing a stable continuous production process.

[0070] Throughout the entire process of this embodiment, the reactor was able to operate stably, and the amount of glycolide collected was approximately 4.81 kg / h, with a glycolide yield of approximately 96.2%. The purity of glycolide was determined to be approximately 95.9% by gas chromatography analysis. The color of glycolide was evaluated using a colorimetric card and was rated as excellent, being white with a light yellow tinge.

[0071] Examples 1-2 (Continuous Production Process)

[0072] Choose a heat exchange area of ​​approximately 0.2 m². 2 For the reactor, the mass of reactant corresponding to a unit heat exchange area within the reactor per unit time, i.e., parameter a, is set to 25 kg / (h·m²). 2 The average mass feed rate V of the reactants in the reactor was calculated to be approximately 5 kg / h. Molten reactants (containing glycolic acid polymer with a weight-average molecular weight of approximately 5000 and antimony trioxide, wherein the amount of antimony trioxide added is approximately 1.0% of the glycolic acid polymer mass) were introduced into the reactor at a feed rate of approximately 5 kg / h. The temperature of the heat exchange surface in the reactor was set to approximately 260°C, and the heat transfer temperature difference in the reactor was approximately 50°C. The heat transfer coefficient K was approximately 100 W / (m²). 2 The reactor is set at an absolute pressure of approximately 1 kPa. The reactants flow downwards along the heat exchange surface of the reactor and undergo depolymerization and ring-forming reactions upon heating to generate gaseous glycolide. The generated gaseous glycolide is extracted from the reactor, condensed by an external condenser, and then collected in a storage tank. In the above process, the reactants completely pass through the heat exchange surface of the reactor in approximately 2 hours. The reactants collected at the bottom of the reactor are discharged at a set average mass discharge rate L. The value of L is set to control the stability of the liquid level parameter at the bottom of the reactor, thereby establishing a stable continuous production process.

[0073] Throughout the entire process of this embodiment, the reactor was able to operate stably, and the amount of glycolide collected was approximately 4.57 kg / h, with a glycolide yield of approximately 91.4%. The purity of glycolide was determined to be approximately 95.7% by gas chromatography analysis. The color of glycolide was evaluated using a colorimetric card and was rated as excellent, being white with a light yellow tinge.

[0074] Examples 1-3 (Continuous Production Process)

[0075] Choose a heat exchange area of ​​approximately 0.2 m². 2 For the reactor, the mass of reactant corresponding to a unit heat exchange area within the reactor per unit time, i.e., parameter a, is set to 25 kg / (h·m²). 2 The average mass feed rate V of the reactants in the reactor was calculated to be approximately 5 kg / h. Molten reactants (containing glycolic acid polymer with a weight-average molecular weight of approximately 3000 and diethylzinc, wherein the amount of diethylzinc added is approximately 2.0% of the glycolic acid polymer mass) were introduced into the reactor at a feed rate of approximately 5 kg / h. The temperature of the heat exchange surface in the reactor was set to approximately 235°C, and the heat transfer temperature difference in the reactor was approximately 30°C. The heat transfer coefficient K was approximately 100 W / (m²). 2 The reactor is set at an absolute pressure of approximately 15 kPa (°C). The reactants flow downwards along the heat exchange surface of the reactor and undergo depolymerization and ring formation reactions upon heating to generate gaseous glycolide. The generated gaseous glycolide is extracted from the reactor, condensed by an external condenser, and then collected in a storage tank. In the above process, the reactants completely pass through the heat exchange surface of the reactor in 1 hour. The reactants collected at the bottom of the reactor are discharged at a set average mass discharge rate L. The value of L is set to control the stability of the liquid level parameter at the bottom of the reactor, thereby establishing a stable continuous production process.

[0076] Throughout the entire process of this embodiment, the reactor was able to operate stably, and the amount of glycolide collected was approximately 4.13 kg / h, with a glycolide yield of approximately 82.6%. The purity of glycolide was approximately 94.6% as determined by gas chromatography. The color of glycolide was evaluated using a colorimetric card and was rated as excellent, being white with a light yellow tinge.

[0077] Examples 1-4 (Continuous Production Process)

[0078] Choose a heat exchange area of ​​approximately 0.2 m². 2 For the reactor, the mass of reactant corresponding to a unit heat exchange area within the reactor per unit time, i.e., parameter a, is set to 25 kg / (h·m²). 2 The average mass feed rate V of the reactants in the reactor was calculated to be approximately 5 kg / h. Molten reactants (containing glycolic acid polymer with a weight-average molecular weight of approximately 20,000 and tin lactate, wherein the amount of tin lactate added is approximately 5.0% of the glycolic acid polymer mass) were introduced into the reactor at a feed rate of approximately 5 kg / h. The temperature of the heat exchange surface in the reactor was set to approximately 300°C, and the heat transfer temperature difference in the reactor was approximately 5°C. The heat transfer coefficient K was approximately 100 W / (m²). 2The reactor is set at an absolute pressure of approximately 50 kPa (°C). The reactants flow downwards along the heat exchange surface of the reactor and undergo depolymerization and ring-forming reactions upon heating to generate gaseous glycolide. The generated gaseous glycolide is extracted from the reactor, condensed by an external condenser, and then collected in a storage tank. In the above process, the reactants completely pass through the heat exchange surface of the reactor in approximately 4 hours. The reactants collected at the bottom of the reactor are discharged at a set average mass discharge rate L. The value of L is set to control the stability of the liquid level parameter at the bottom of the falling film reactor, thereby establishing a stable continuous production process.

[0079] Throughout the process of this embodiment, the reactor was able to operate stably, and the amount of glycolide collected was approximately 3.63 kg / h, with a glycolide yield of approximately 2.6%. The purity of glycolide was determined to be approximately 87.5% by gas chromatography analysis. The color of glycolide was evaluated using a colorimetric card and was rated as excellent, being white with a light yellow tinge.

[0080] Example 2 (Continuous Production Process)

[0081] Choose a heat exchange area of ​​approximately 2m². 2 For the reactor, the mass of reactant corresponding to a unit heat exchange area within the reactor per unit time, i.e., parameter a, is set to 3 kg / (h·m²). 2 The average mass feed rate V of the reactants in the reactor was calculated to be approximately 6 kg / h. Molten reactants (containing glycolic acid polymer with a weight-average molecular weight of approximately 60,000, stannous octoate, and antimony trioxide, with the amounts of stannous octoate and antimony trioxide being approximately 0.6% and 0.4% of the glycolic acid polymer mass, respectively) were introduced into the reactor at a feed rate of approximately 6 kg / h. The temperature of the heat exchange surface in the reactor was set to approximately 240°C, and the heat transfer temperature difference in the reactor was approximately 5°C. The heat transfer coefficient K was approximately 100 W / (m²). 2 The reactor is set at an absolute pressure of approximately 200 Pa (°C). The reactants flow downwards along the heat exchange surface of the reactor and undergo depolymerization and ring-forming reactions upon heating to generate gaseous glycolide. The generated gaseous glycolide is extracted from the reactor, condensed by an external condenser, and then collected in a storage tank. In the above process, the reactants completely pass through the heat exchange surface of the reactor in approximately 0.2 hours. The reactants collected at the bottom of the reactor are discharged at a set average mass discharge rate L. The value of L is set to control the stability of the material level parameter at the bottom of the reactor, thereby establishing a stable continuous production process.

[0082] Throughout the process of this embodiment, the reactor was able to operate stably, and the amount of glycolide collected was approximately 5.6 kg / h, with a glycolide yield of approximately 93.3%. The purity of glycolide was determined to be approximately 89.2% by gas chromatography analysis. The color of glycolide was evaluated using a colorimetric card and was rated as medium grade, pale yellow.

[0083] Comparative Example 1 (Continuous Production Process)

[0084] Choose a heat exchange area of ​​approximately 2m². 2 For the reactor, the mass of reactant corresponding to a unit heat exchange area within the reactor per unit time, i.e., parameter a, is set to 2.2 kg / (h·m²). 2 The average mass feed rate V of the reactants in the falling film reactor was calculated to be approximately 4.4 kg / h, with the other conditions being the same as in Example 2.

[0085] In this comparative example, coking occurred on some heat exchange surfaces inside the reactor, causing some reactants to be trapped on the corresponding heat exchange surfaces. The reaction had to be stopped, making it impossible to establish a stable continuous production process. The coking heat exchange surfaces inside the reactor needed to be cleaned; otherwise, the reactor could not continue to be used.

[0086] In this comparative example, the amount of glycolide collected was approximately 2.3 kg / h, and the yield of glycolide was approximately 52.3%. The purity of glycolide was approximately 84.7% as determined by gas chromatography. The color of glycolide was evaluated using a colorimetric card and was rated as qualified, being yellow.

[0087] Example 3 (Continuous Production Process)

[0088] Choose a heat exchange area of ​​approximately 2m². 2 For the reactor, the mass of reactant corresponding to a unit heat exchange area within the reactor per unit time, i.e., parameter a, is set to 12 kg / (h·m²). 2 The average mass feed rate V of the reactants in the reactor was calculated to be approximately 24 kg / h. Molten reactants (containing glycolic acid polymer with a weight average molecular weight of approximately 100,000 and stannous octoate, wherein the amount of stannous octoate added is approximately 0.8% of the mass of glycolic acid polymer) were introduced into the reactor at a feed rate of approximately 24 kg / h. The time for the reactants to completely pass through the heat exchange surface inside the reactor was approximately 1 hour. The remaining conditions were the same as in Example 2.

[0089] Throughout the entire process of this embodiment, the reactor was able to operate stably, and the amount of glycolide collected was approximately 22.9 kg / h, with a glycolide yield of approximately 95.4%. The purity of glycolide was determined to be approximately 92.7% by gas chromatography analysis. The color of glycolide was evaluated using a colorimetric card and was rated as good, being white with a yellowish tint.

[0090] Example 4 (Continuous Production Process)

[0091] Choose a heat exchange area of ​​approximately 0.2 m². 2 For the reactor, the mass of reactant corresponding to a unit heat exchange area within the reactor per unit time, i.e., parameter a, is set to 18 kg / (h·m²). 2 The average mass feed rate V of the reactants in the reactor was calculated to be approximately 3.6 kg / h. Molten reactants (containing glycolic acid polymer with a weight average molecular weight of approximately 140,000 and stannous octoate, wherein the amount of stannous octoate added is approximately 1.4% of the mass of glycolic acid polymer) were introduced into the reactor at a feed rate of approximately 3.6 kg / h. The time for the reactants to completely pass through the heat exchange surface inside the reactor was approximately 8 hours. The remaining conditions were the same as in Example 2.

[0092] Throughout the entire process of this embodiment, the reactor was able to operate stably, and the amount of glycolide collected was approximately 3.28 kg / h, with a glycolide yield of approximately 91.1%. The purity of glycolide was determined to be approximately 95.8% by gas chromatography analysis. The color of glycolide was evaluated using a colorimetric card and was rated as excellent, being white with a light yellow tinge.

[0093] Example 5 (Continuous Production Process)

[0094] Choose a heat exchange area of ​​approximately 0.2 m². 2 For the reactor, the mass of reactant corresponding to a unit heat exchange area within the reactor per unit time, i.e., parameter a, is set to 215 kg / (h·m²). 2 The average mass feed rate V of the reactants in the reactor was calculated to be approximately 43 kg / h. Molten reactants (containing glycolic acid polymer with a weight-average molecular weight of approximately 200,000 and stannous octoate, wherein the amount of stannous octoate added is approximately 3.5% of the glycolic acid polymer mass) were introduced into the reactor at a feed rate of approximately 43 kg / h. The heat transfer temperature difference in the reactor was approximately 20°C, and the heat transfer coefficient K was approximately 1000 W / (m³). 2 The reaction material was completely passed through the heat exchange surface inside the reactor in approximately 12 hours (°C), and the other conditions were the same as in Example 2.

[0095] Throughout the entire process of this embodiment, the reactor was able to operate stably, and the amount of glycolide collected was approximately 35.8 kg / h, with a glycolide yield of approximately 83.2%. The purity of glycolide was determined to be approximately 95.5% by gas chromatography analysis. The color of glycolide was evaluated using a colorimetric card and was rated as excellent, being white with a light yellow tint.

[0096] Example 6 (Continuous Production Process)

[0097] Choose a heat exchange area of ​​approximately 0.2 m². 2For the reactor, the mass of reactant corresponding to a unit heat exchange area within the reactor per unit time, i.e., parameter a, is set to 451 kg / (h·m²). 2 The average mass feed rate V of the reactants in the reactor was calculated to be approximately 90.2 kg / h. Molten reactants (containing glycolic acid polymer with a weight-average molecular weight of approximately 80,000 and stannous octoate, wherein the amount of stannous octoate added is approximately 2.2% of the mass of the glycolic acid polymer) were introduced into the reactor at a feed rate of approximately 90.2 kg / h. The heat transfer temperature difference in the reactor was approximately 35°C, and the heat transfer coefficient K was approximately 1000 W / (m³). 2 The reaction material was completely passed through the heat exchange surface inside the reactor in approximately 0.5 hours (°C), and the other conditions were the same as in Example 2.

[0098] Throughout the entire process of this embodiment, the reactor was able to operate stably, and the amount of glycolide collected was approximately 65.1 kg / h, with a glycolide yield of approximately 72.2%. The purity of glycolide was determined to be approximately 90.1% by gas chromatography analysis. The color of glycolide was evaluated using a colorimetric card and was rated as excellent, being white with a light yellow tinge.

[0099] Example 7 (Continuous Production Process)

[0100] Choose a heat exchange area of ​​approximately 0.20 m². 2 For the reactor, the mass of reactant corresponding to a unit heat exchange area within the reactor per unit time, i.e., parameter a, is set to 860 kg / (h·m²). 2 The average mass feed rate V of the reactants in the reactor was calculated to be approximately 172 kg / h. Molten reactants (containing glycolic acid polymer with a weight-average molecular weight of approximately 2000 and stannous octoate, wherein the amount of stannous octoate added is approximately 0.5% of the glycolic acid polymer mass) were introduced into the reactor at a feed rate of approximately 172 kg / h. The heat transfer temperature difference in the reactor was approximately 70°C, and the heat transfer coefficient K was approximately 2500 W / (m³). 2 The reaction material was completely passed through the heat exchange surface inside the reactor in about 1 hour (°C), and the other conditions were the same as in Example 2.

[0101] Throughout the process of this embodiment, the reactor was able to operate stably, and the amount of glycolide collected was approximately 114.7 kg / h, with a glycolide yield of approximately 66.7%. The purity of glycolide was determined to be approximately 85.3% by gas chromatography analysis, and the color of glycolide was evaluated using a colorimetric card, which rated it as medium quality, pale yellow.

[0102] Example 8 (Continuous Production Process)

[0103] Choose a heat exchange area of ​​approximately 0.20 m². 2For the reactor, the mass of reactant corresponding to a unit heat exchange area within the reactor per unit time, i.e., parameter a, is set to 1290 kg / (h·m²). 2 The average mass feed rate V of the reactants in the reactor was calculated to be approximately 258 kg / h. Molten reactants (containing glycolic acid polymer with a weight-average molecular weight of approximately 1000 and stannous octoate, wherein the amount of stannous octoate added is approximately 0.2% of the glycolic acid polymer mass) were introduced into the reactor at a feed rate of approximately 172 kg / h. The heat transfer temperature difference in the reactor was approximately 100°C, and the heat transfer coefficient K was approximately 3600 W / (m³). 2 The reaction material was completely passed through the heat exchange surface inside the reactor in approximately 0.5 hours (°C), and the other conditions were the same as in Example 2.

[0104] Throughout the entire process of this embodiment, the reactor was able to operate stably, and the amount of glycolide collected was approximately 162.3 kg / h, with a glycolide yield of approximately 62.9%. The purity of glycolide was determined to be approximately 80.2% by gas chromatography analysis. The color of glycolide was evaluated using a colorimetric card and was rated as qualified, being yellow.

[0105] Comparative Example 2 (Continuous Production Process)

[0106] Choose a heat exchange area of ​​approximately 0.2 m². 2 The reactor is defined as follows: the mass of reactant corresponding to a unit heat exchange area within the reactor per unit time, i.e., parameter a, is set to 1300 kg / (h·m²). 2 The average mass feed rate V of the reactor reactants was calculated to be approximately 260 kg / h, and the other conditions were the same as in Example 8.

[0107] Throughout the entire process of this comparative example, although the reactor was able to operate stably, only about 50.8 kg / h of glycolide was collected, and the glycolide yield was about 19.5%. The purity of glycolide was only about 62.2% as determined by gas chromatography. The color of glycolide was evaluated using a colorimetric card and was rated as a non-compliant product, being dark yellow.

[0108] Example 9 (Continuous Production Process)

[0109] In this embodiment, the depolymerization and cyclization reaction system uses three reactors connected in series (each reactor has a heat exchange area of ​​approximately 0.2 m²). 2 And the heat transfer coefficient K is approximately 200 W / (m²). 2 ·℃), where the parameter a1 of the first reactor is set to 20 kg / (h·m 2 The parameter a2 of the second reactor is set to 30 kg / (h·m). 2 The parameter a3 of the third reactor is set to 46 kg / (h·m). 2Based on the selected values ​​of a1, a2, and a3, the arithmetic mean of these three parameters is calculated to be 32 kg / (h·m). 2 That is, the parameter a is obtained as 32 kg / (h·m). 2 The total heat exchange area S of the three reactors is approximately 0.6 m². 2 Therefore, the average mass feed rate V1 of the reactants in the first reactor of the reaction system can be calculated to be approximately 19.2 kg / h. Based on the calculated V1 value, the molten reactants (containing glycolic acid oligomers with a weight-average molecular weight of approximately 18,000 and stannous octoate, wherein the amount of stannous octoate added is approximately 0.03% of the mass of the glycolic acid oligomers) are introduced into the first reactor. The temperature of the heat exchange surface in the first reactor is controlled at approximately 265°C, and the heat transfer temperature difference in the first reactor is controlled at approximately 35°C. The absolute pressure is controlled at approximately 250 kJ / h. Pa, the reactants flow downwards along the heat exchange surface of the reactor, undergoing depolymerization and ring-forming reactions upon heating to generate gaseous glycolide. The generated gaseous glycolide is extracted from the reactor, condensed by an external condenser, and then collected in a storage tank. The reactants completely pass through the heat exchange surface of the first reactor in approximately 0.1 hours. The material collected at the bottom of the first reactor is discharged at the average mass discharge rate L1 and then introduced into the second reactor at the average mass feed rate V2, thus lowering the temperature of the heat exchange surface in the second reactor. The temperature is controlled at approximately 270°C, and the heat transfer temperature difference in the second reactor is controlled at approximately 20°C. The absolute pressure is controlled at approximately 200 Pa. The gaseous glycolide generated during the reaction is collected. The time for the reactants to completely pass through the heat exchange surface in the second reactor is approximately 0.5 hours. The material collected at the bottom of the second reactor is discharged from the second reactor at the average mass discharge rate L2 and then introduced into the third reactor at the average mass feed rate V3. The temperature of the heat exchange surface in the third reactor is controlled at approximately 280°C, and the heat transfer temperature difference in the third reactor is controlled at approximately 10°C. The absolute pressure is controlled at approximately 100 Pa. The gaseous glycolide generated during the reaction is collected. The time for the reactants to completely pass through the heat exchange surface in the third reactor is approximately 0.2 hours. The material collected at the bottom of the third reactor is discharged from the third falling film reactor at the average mass discharge rate L3. In the above process, the selection of parameters L1, V2, L2, V3, and L3 is based on controlling the material liquid level parameters at the bottom of each reactor to stabilize, thereby establishing a stable continuous production process.

[0110] Throughout the entire process of this embodiment, each reactor operated stably, and the amount of glycolide collected was approximately 17.6 kg / h, with a glycolide yield of approximately 91.7%. The purity of glycolide was approximately 95.7% as determined by gas chromatography. The color of glycolide was evaluated using a colorimetric card and was rated as excellent, being white with a light yellow tinge.

[0111] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the substantive technical content of the present invention. The substantive technical content of the present invention is broadly defined within the scope of the claims. Any technical entity or method completed by others that is completely identical to or an equivalent modification of the claims is considered to be covered within the scope of the claims.

Claims

1. A continuous method for the preparation of glycolide, characterized in that, The method comprises the steps of: (i) introducing a molten reaction material into a reactor for depolymerization; the reaction material containing glycolic acid or glycolate polymer; (ii) subjecting the reaction material to pyrolysis into a ring to obtain a gaseous glycolide; the reaction material collected at the bottom of the reactor is discharged at a set average mass discharge rate of the reaction material to stabilize the material level parameter at the bottom of the reactor; a parameter a is set to 18-215 kg / (h·m2), the parameter a representing the mass of the reaction material passing through a unit heat exchange area in the reactor per unit time; the temperature inside the reactor is 220-260℃, and the pressure is 100 Pa to 15 kPa.

2. The production method according to claim 1, wherein When the glycolide production process is a continuous production process based on two or more reactors connected in series, the feeding rate of the reaction material of the first reactor is the product of the arithmetic mean of the parameters a of the reactors and the total heat exchange area of the reactors.

3. The production method according to claim 1, wherein The heat transfer coefficient K of the reactor is 100-3600 W / (m2·℃).

4. The production method according to claim 1, wherein The heat transfer temperature difference of the reactor is 5-100℃.

5. The production method according to claim 1, wherein The weight average molecular weight of the glycolic acid or glycolate polymer is not less than 1000; and / or The reaction material in step (i) further contains a catalyst; and / or The method further comprises the step of collecting and purifying the glycolide obtained in step (ii).

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