Two-stage reaction device and process thereof

Abstract

The application discloses a two-stage reaction device and a process thereof. The device comprises a first reaction unit and a second reaction unit arranged in sequence along a reaction material feeding direction.

Description

Technical Field

[0001] This invention relates to the chemical industry, and more particularly to a reaction apparatus and related processes for the production of glycolide. Background Technology

[0002] High molecular weight polyglycolic acid (PEG) with high molecular weight (e.g., 50,000-200,000 or above 200,000) can typically be prepared by ring-opening polymerization of glycolide. Glycolide, a crucial raw material for synthesizing high molecular weight PEG, is usually synthesized in a stirred reactor. Glycolic acid and a catalyst are added, and the reaction is carried out under high temperature and high vacuum conditions to generate glycolic acid oligomers with relatively short molecular chains. The temperature and vacuum of the reactor are then further increased to induce depolymerization and ring-forming of the glycolic acid oligomers, producing glycolide. However, during the depolymerization process, a large amount of glycolic acid oligomers accumulates in the reactor. Prolonged high-temperature heating can cause most of the oligomers to carbonize and coke or transform into asphalt-like substances before depolymerization can occur. This not only affects the normal operation of the process, potentially requiring production to be interrupted and the reactor cleaned, but also results in significant material loss, a greatly reduced glycolide yield, and excessively high production costs.

[0003] Therefore, there is an urgent need in the field to provide a production apparatus and method that can effectively improve the yield of glycolide and is economical. Summary of the Invention

[0004] The present invention aims to provide apparatus and method for producing glycolide.

[0005] In a first aspect of the invention, a two-stage reaction apparatus is provided, the apparatus comprising a first-stage reaction unit for reacting reactants, and a second-stage reaction unit coupled to the first-stage reaction unit and for continuing to react the remaining reactants derived from the first-stage reaction unit.

[0006] In another embodiment, the apparatus is used to prepare cyclic esters, wherein the reactants undergo a first-stage depolymerization and cyclization reaction in the first-stage reaction unit, and the remaining reactants derived from the first-stage reaction unit undergo a second-stage depolymerization and cyclization reaction in the second-stage reaction unit.

[0007] In another embodiment, the device includes a first-stage reaction unit and a second-stage reaction unit arranged sequentially along the feed direction of the reactants.

[0008] In another embodiment, the first-stage reaction unit and the second-stage reaction unit are connected by pipelines.

[0009] In another embodiment, the first-stage reaction unit and the second-stage reaction unit each contain one or more of the following reaction modules: a stirred reaction module, a falling film reaction module, and a scraped film reaction module.

[0010] The reaction modules contained in the first-stage reaction unit and the second-stage reaction unit may be the same or different; in one embodiment, the reaction modules contained in the first-stage reaction unit and the second-stage reaction unit are different.

[0011] In another embodiment, the stirred reaction module includes at least one stirred reactor, the stirred reactor having a shell, an outlet disposed at the bottom of the shell, a stirring paddle suspended in the shell, and a heating element.

[0012] In another embodiment, a feed inlet is provided on the upper part of the housing.

[0013] In another embodiment, an air outlet is provided at the top of the housing.

[0014] In another embodiment, the heating element comprises one or more of the following combinations: an electric heating mantle, a heat exchanger, and a heating coil; preferably a heat exchanger.

[0015] In another embodiment, the stirred reaction module includes at least two stirred reactors connected in series and / or in parallel.

[0016] In another embodiment, the falling film reaction module includes at least one falling film reactor, which includes a shell, an upper baffle and a lower baffle arranged perpendicular to the feed direction of the reactants, a heat exchange tube arranged parallel to the feed direction of the reactants and between the upper baffle and the lower baffle, and a film distributor arranged on top of the upper baffle.

[0017] In another embodiment, the peripheries of the upper and lower partitions are fixedly connected to the inner wall of the housing.

[0018] In another embodiment, the two ends of the heat exchange tube pass through the upper partition and the lower partition, respectively.

[0019] In another embodiment, a feed inlet is provided at the top of the housing.

[0020] In another embodiment, an air outlet and a material outlet are respectively provided at the bottom of the housing.

[0021] Preferably, the horizontal plane where the air outlet is located is higher than the horizontal plane where the material outlet is located.

[0022] In another embodiment, the falling film reaction module includes at least two falling film reactors connected in series and / or in parallel.

[0023] In another embodiment, the scraped film reaction module includes at least one scraped film reactor, the scraped film reactor comprising a shell, a rotating shaft, a scraper radially connected to the rotating shaft and having an outer surface parallel to the rotating shaft, and a heating element.

[0024] In another embodiment, the distance between the outer side of the scraper and the inner wall of the housing is no more than 5 mm; preferably no more than 2 mm.

[0025] In another embodiment, the heating element is an electric heating mantle.

[0026] In another embodiment, a film spreader is provided inside the housing above the scraper.

[0027] In another embodiment, a feed inlet and an air outlet are respectively provided on the top of the housing.

[0028] In another embodiment, a discharge port is provided at the bottom of the housing.

[0029] In another embodiment, the wiped-film reactor module includes at least two wiped-film reactors connected in series and / or in parallel.

[0030] In another embodiment, the first-stage reaction unit and the second-stage reaction unit each contain a product collection unit.

[0031] In another embodiment, the product collection unit includes a gas-liquid separator, a condenser, and a product collection tank.

[0032] In another embodiment, a vacuum pump is provided between the gas-liquid separator and the condenser.

[0033] In another embodiment, in each reaction unit, each reaction module is connected to its own product collection unit, or each reaction module shares a single product collection unit.

[0034] In another embodiment, the outlet of the reaction module in the first stage reaction unit is connected to the inlet of the reaction module in the second stage reaction unit via a pipeline.

[0035] In another embodiment, the two-stage reaction unit includes a falling film reaction module and / or a scraped film reaction module.

[0036] In another embodiment, the two-stage reaction unit includes a scraped film reaction module.

[0037] In another embodiment, two or more reaction modules in the same reaction unit are connected in series and / or in parallel.

[0038] In another embodiment, two or more reaction modules in the first-stage reaction unit are connected in series and / or in parallel, and one reaction module is in the second-stage reaction unit.

[0039] In another embodiment, the first-stage reaction unit has one type of reaction module, and the second-stage reaction unit has two or more types of reaction modules connected in series and / or in parallel.

[0040] In another embodiment, two or more reaction modules in the first-stage reaction unit are connected in series and / or in parallel, and two or more reaction modules in the second-stage reaction unit are connected in series and / or in parallel.

[0041] In a second aspect of the invention, a method for producing glycolide is provided using the reaction apparatus provided by the invention as described above.

[0042] In another embodiment, the method includes the steps of:

[0043] (1) The molten reactant containing glycolic acid oligomers undergoes a first-stage depolymerization and cyclization reaction in the first-stage reaction unit to generate gaseous glycolide i and produce the remaining molten reactant containing glycolic acid oligomers; and

[0044] (2) The remaining molten reactants containing glycolic acid oligomers generated in step (1) undergo a second depolymerization and cyclization reaction in the two-stage reaction unit to generate gaseous glycolide ii.

[0045] In another embodiment, based on the mass of glycolide i collected in step (1), the conversion rate of glycolic acid oligomer in the corresponding reaction unit is 20-60%.

[0046] In another embodiment, the glycolide i and glycolide ii obtained in steps (1) and (2) are collected after being discharged through the outlet of the corresponding reaction module.

[0047] In another embodiment, the generated glycolide i and glycolide ii pass through the gas-liquid separator and condenser in sequence after passing through the gas outlet of the corresponding reaction module and then enter the product collection tank.

[0048] In another embodiment, the molten reactant containing glycolic acid oligomers contains a depolymerization catalyst, and the content of the depolymerization catalyst does not exceed 5 wt% based on the total weight of the molten reactant containing glycolic acid oligomers.

[0049] In another embodiment, the depolymerization and cyclization reaction in the first-stage or second-stage reaction unit is carried out at an absolute pressure ≤ 5 kPa; preferably, the absolute pressure ≤ 1 kPa.

[0050] In another embodiment, the depolymerization and cyclization reaction in the first-stage or second-stage reaction unit is carried out at 220-350°C; preferably 225-300°C; more preferably 230-280°C.

[0051] Accordingly, the present invention provides an economical production apparatus and method that can effectively improve the yield of glycolide. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the falling film reactor 100 used in this invention.

[0053] Figure 2 is a schematic diagram of the stirred reactor 200 used in this invention; wherein

[0054] A is a stirred reactor 200A using an electric heating jacket, B is a stirred reactor 200B using an electric heating jacket + electric heating coil, and C is a stirred reactor 200C using a heat exchanger.

[0055] Figure 3 This is a schematic diagram of the scraped membrane reactor 300 used in this invention.

[0056] Figure 4 is a schematic diagram of the glycolide production apparatus 1000 provided in embodiments 1-3 of the present invention; wherein

[0057] A is the production device 1000A provided in Device Embodiment 1, B is the production device 1000B provided in Device Embodiment 2, and C is the production device 1000C provided in Device Embodiment 3.

[0058] Figure 5 is a schematic diagram of the glycolide production apparatus 2000 provided in embodiments 4-7 of the present invention; wherein

[0059] A is the production device 2000A provided in device embodiment 4, B is the production device 2000B provided in device embodiment 5, C is the production device 2000C provided in device embodiment 6, and D is the production device 2000D provided in device embodiment 7.

[0060] Figure 6 This is a schematic diagram of the glycolide production apparatus 3000A provided in Embodiment 8 of the present invention.

[0061] Figure 7 This is a schematic diagram of the glycolide production apparatus 3000B provided in Embodiment 9 of the present invention.

[0062] Figure 8 This is a schematic diagram of the glycolide production apparatus 3000C provided in Embodiment 10 of the present invention. Detailed Implementation

[0063] Through extensive and in-depth research, the inventors developed a reaction apparatus containing two reaction units. This apparatus allows the glycolic acid oligomers used in the production of glycolide to undergo segmented depolymerization and cyclization reactions, thereby effectively controlling the reaction process and promptly removing the generated gaseous glycolide from the reaction system to prevent material coking. Based on this, the present invention was completed.

[0064] As used in this invention, "feed direction" refers to the direction in which the reactants move forward.

[0065] As used in this invention, "couple" refers to the operative connection between two or more modules or devices, where they interact and influence each other.

[0066] As used in this invention, "film distributor" refers to a film distribution device that facilitates the uniform distribution of liquid material on the inner wall of each heating tube of a heat exchange tube (a type of heater), or on the inner wall of a reaction vessel, so that it descends in a uniform film.

[0067] As used in this article, "a reaction module" and "a reaction module" can be used interchangeably, both referring to any one of the stirred reaction module, falling film reaction module, and scraped film reaction module.

[0068] As used in this article, "two or more reaction modules" and "two or more reaction modules" can be used interchangeably. Both refer to any two or more identical or different reaction modules among stirred reaction modules, falling film reaction modules, and scraped film reaction modules. For example, when there are two reaction modules, it can be, but is not limited to, two stirred reaction modules, one stirred reaction module and one falling film reaction module, etc.; when there are three reaction modules, it can be, but is not limited to, three falling film reaction modules, one stirred reaction module, one falling film reaction module and one scraped film reaction module, two stirred reaction modules and one falling film reaction module, etc.

[0069] As used in this article, "reaction module series" refers to two or more reaction modules arranged in the direction of reactant feeding, and the outlet of the reaction module located upstream in the feeding direction is connected to the inlet of the adjacent reaction module located downstream in the feeding direction through a pipeline.

[0070] As used in this article, "parallel reaction modules" means that the inlets of two or more reaction modules are connected to each other through pipelines, and the outlets of the two or more reaction modules are also connected to each other through another pipeline.

[0071] glycolide production unit

[0072] The present invention provides a production apparatus for producing glycolide, comprising a first-stage reaction unit and a second-stage reaction unit arranged sequentially along the feed direction of the reactants. The first-stage reaction unit and the second-stage reaction unit respectively include one or more of a falling film reaction module, a stirred reaction module, and a scraped film reaction module.

[0073] The reaction modules in the first-stage reaction unit and the second-stage reaction unit of the reaction apparatus provided by the present invention may be the same or different.

[0074] In the reaction apparatus provided by the present invention, two reaction units are connected by pipelines. For example, in the case where the reaction modules in the first-stage reaction unit and the second-stage reaction unit are connected in series, the outlet of the last reaction module in the first-stage reaction unit arranged along the feed direction of the reactants is connected to the inlet of the first reaction module in the second-stage reaction unit arranged along the feed direction of the reactants by pipelines.

[0075] In one embodiment of the present invention, the first-stage reaction unit and the second-stage reaction unit are any one of a falling film reaction module, a stirred reaction module, and a scraped film reaction module, and the two reaction units may have the same reaction module or different reaction modules.

[0076] The cases where the two reaction units have the same reaction modules include, but are not limited to: both the first-stage and second-stage reaction units being falling film reaction modules, stirred film reaction modules, or scraped film reaction modules; both the first-stage and second-stage reaction units containing at least two of the following: falling film reaction modules, stirred film reaction modules, and scraped film reaction modules; and both the first-stage and second-stage reaction units being falling film reaction modules, stirred film reaction modules, and scraped film reaction modules. Specifically, for example, but not limited to, both reaction units having one falling film reaction module; both reaction units having one stirred film reaction module and one falling film reaction module; both reaction units having one stirred film reaction module, one falling film reaction module, and one scraped film reaction module, etc.

[0077] The cases where the two reaction units have different reaction modules include, but are not limited to: one of the first-stage and second-stage reaction units may include any one of a falling film reaction module, a stirred reaction module, and a scraped film reaction module, while the other reaction unit includes a different type of reaction module; one of the first-stage and second-stage reaction units may include at least two of a falling film reaction module, a stirred reaction module, and a scraped film reaction module, while the other reaction unit may be any one of a falling film reaction module, a stirred reaction module, and a scraped film reaction module; or the first-stage and second-stage reaction units may each include at least two of a falling film reaction module, a stirred reaction module, and a scraped film reaction module. Specifically, for example, but not limited to, the first stage reaction unit is a falling film reaction module, and the second stage reaction unit is a scraped film reaction module; the first stage reaction unit is a stirred reaction module, and the second stage reaction unit is a scraped film reaction module; the first stage reaction unit is a stirred reaction module, and the second stage reaction unit is a falling film reaction module; the first stage reaction unit is a falling film reaction module and a stirred reaction module, and the second stage reaction unit is a scraped film reaction module; the first stage reaction unit is a stirred reaction module, and the second stage reaction unit is a falling film reaction module and a scraped film reaction module; the first stage reaction unit is a stirred reaction module and a falling film reaction module, and the second stage reaction unit is a falling film reaction module and a scraped film reaction module; the first stage reaction unit is a stirred reaction module, a falling film reaction module, and a scraped film reaction module, and the second stage reaction unit is a scraped film reaction module, etc.

[0078] In one embodiment of the present invention, a melt pump is provided on the connecting pipeline between the first-stage reaction unit and the second-stage reaction unit.

[0079] The reaction apparatus also includes a product collection unit, which can be in one form, where each of the first-stage reaction unit and the second-stage reaction unit has a product collection unit coupled to it for collecting the gaseous glycolide generated by the corresponding reaction unit; or in another form, where the first-stage reaction unit and the second-stage reaction unit share the same product collection unit.

[0080] When there are two or more reaction modules in a reaction unit, they can be connected in series and / or in parallel to form some different combinations.

[0081] For example, but not limited to, a single-stage reaction unit includes a falling film reaction module and a stirred reaction module connected in parallel, and a second-stage reaction unit is a scraped film reaction module; a single-stage reaction unit includes two falling film reaction modules connected in series, and a second-stage reaction unit is a scraped film reaction module; a single-stage reaction unit includes a falling film reaction module and a stirred reaction module connected in parallel, and a second-stage reaction unit includes a falling film reaction module and a scraped film reaction module connected in parallel; a single-stage reaction unit includes two stirred reaction modules connected in parallel, and a second-stage reaction unit includes a falling film reaction module and a scraped film reaction module connected in parallel; a single-stage reaction unit includes a falling film reaction module and a stirred reaction module connected in series, and a second-stage reaction unit includes two scraped film reaction modules connected in series, etc.

[0082] In one embodiment of the present invention, two or more reaction modules in the same reaction unit are provided with melt pumps on the connecting pipelines between them. These pumps are mainly used to pump the reactants to the next reaction module or reaction unit. The pumps can be set according to the actual process route, such as the location and quantity.

[0083] The falling film reaction module may be, but is not limited to, a falling film evaporator, a falling film reactor, etc.; as one implementation, the falling film reaction module is a falling film evaporator or a falling film reactor, or includes two or more falling film evaporators or falling film reactors arranged in series and / or in parallel.

[0084] The falling film evaporator or falling film reactor includes a shell, upper and lower baffles arranged at intervals inside the shell along a direction perpendicular to the shell's axial direction, heat exchange tubes arranged along the shell's axial direction between the upper and lower baffles, and a film distributor disposed on top of the upper baffle. The film distributor can be a commercially available, conventional film distributor used in falling film evaporators or reactors, without requiring any special structural modifications.

[0085] The periphery of the upper and lower partitions is fixedly connected to the inner wall of the shell; there are n heat exchange tubes between the upper and lower partitions, n being at least 50 for example; the upper and lower ends of the heat exchange tubes pass through the upper and lower partitions respectively, wherein the upper end of the heat exchange tube passes through the upper partition and is connected to the film distributor, and the lower end of the heat exchange tube passes through the lower partition (for example, protruding 1-10mm) and is connected to the air outlet and material outlet located at the bottom of the shell.

[0086] The top of the housing is provided with a feed inlet.

[0087] The bottom of the housing has an air outlet on the side and a material outlet on the bottom surface. The horizontal plane where the air outlet is located is higher than the horizontal plane where the material outlet is located. A solenoid valve can be installed at the material outlet.

[0088] The stirred reaction module may be, but is not limited to, a stirred reactor, a stirred reaction vessel, etc.; as one embodiment, the stirred reaction module includes one stirred reactor or a stirred reaction vessel, or includes two or more stirred reactors or stirred reaction vessels arranged in series and / or in parallel.

[0089] The stirred reactor or stirred reaction vessel includes a shell, a stirring paddle inserted in the shell, and a heating element for heating the shell.

[0090] As is commonly used, the stirring paddle inserted in the housing can be suspended and not in contact with the inner wall and bottom of the housing; in one embodiment of the present invention, the stirring paddle is driven by a drive motor to achieve the stirring function.

[0091] The heating element includes any combination of one or more of the following: an electric heating jacket arranged on the outer wall of the shell, a heat exchanger arranged along the axial direction of the shell on the inner wall of the shell, or a heating coil arranged along the axial direction of the shell in the inner cavity of the shell.

[0092] The upper part of the shell is provided with a feed inlet; the top of the shell is provided with an air outlet.

[0093] The bottom of the housing is provided with a discharge port. In one embodiment of the present invention, a solenoid valve may be provided at the discharge port.

[0094] In one embodiment of the present invention, the bottom of the housing is arc-shaped.

[0095] The scraped film reaction module may be, but is not limited to, a scraped film evaporator, a scraped film reactor, etc.; as one embodiment, the scraped film reaction module includes one scraped film evaporator or a scraped film reactor, or includes two or more scraped film evaporators or scraped film reactors arranged in series and / or in parallel.

[0096] The scraped film evaporator or reactor includes a shell, a rotating shaft inserted axially into the inner cavity of the shell, multiple scrapers spaced apart from each other along the rotating shaft axially, and a heating element (e.g., but not limited to, an electric heating jacket) disposed on the outside of the shell. A film distributor is also provided above the scraper closest to the top of the shell. The film distributor can be a commercially available, conventional film distributor used in scraped film evaporators or reactors, without requiring special structural modifications. The rotating shaft is generally driven by a drive motor connected to it.

[0097] A scraper can be arranged radially along the rotating shaft, or a scraper can be arranged at each of the two ends radially. The number of scrapers is usually determined by the internal cavity space of the shell; the radial distance between the outer side of the scraper and the rotating shaft is determined by the cross-sectional size of the shell. In one embodiment of the present invention, a gap of no more than 5 mm, preferably no more than 2 mm, is left between the outer side of the scraper and the inner wall of the shell. The scraper thickness can be that used in conventional scraped film reactors.

[0098] The top of the housing is provided with a feed inlet and an air outlet, with the feed inlet connected to the film spreader and the air outlet connected to the inner cavity of the housing. Preferably, the horizontal plane of the air outlet is higher than the horizontal plane of the feed inlet.

[0099] The bottom of the housing is provided with a discharge port, and a solenoid valve may be installed at the discharge port.

[0100] The product collection unit includes a gas-liquid separator, a condenser, and a product collection tank, which are sequentially connected to the reaction modules in the corresponding reaction unit.

[0101] As one implementation, a vacuum pump can be installed between the gas-liquid separator and the condenser to evacuate the reaction module in the corresponding reaction unit and to promptly extract and collect the gaseous glycolide generated in the corresponding reaction unit.

[0102] The exhaust port of the gas-liquid separator is connected to the material inlet of the condenser via a pipeline, and the material outlet of the condenser is connected to the product collection tank via a pipeline.

[0103] In one embodiment, the gas-liquid separator adopts side-feed, and the upper inner side of the gas-liquid separator is provided with an anti-liquid entrainment device.

[0104] Preferably, the anti-foaming device is a wire mesh or a swirl plate.

[0105] In one implementation, the gas outlets of the falling film reaction module, the stirred reaction module, and the scraped film reaction module are respectively connected to the corresponding product collection units.

[0106] Production method of glycolide

[0107] This invention provides a method for producing glycolide, which is carried out using the above-mentioned production apparatus and includes the following steps:

[0108] The first step involves introducing molten reactants containing glycolic acid oligomers into a first-stage reaction unit to conduct the first-stage depolymerization and cyclization reaction to generate gaseous glycolide i, and to produce the remaining molten reactants containing glycolic acid oligomers.

[0109] In the second step, the generated gaseous glycolide i is collected after passing through the outlet of the first-stage reaction unit; and the remaining molten reactant containing glycolic acid oligomer discharged from the first-stage reaction unit is introduced into the second-stage reaction unit to undergo a second-stage depolymerization and cyclization reaction to generate gaseous glycolide ii.

[0110] In the third step, the generated gaseous glycolide II is collected after passing through the outlet of the two-stage reaction unit.

[0111] The molecular weight (weight-average molecular weight) of the glycolic acid oligomer in the above method is preferably ≤50,000, for example, it can be selected as 2,000-50,000, 2,500-30,000, 3,000-20,000, etc.

[0112] It should be noted that the raw materials used in the above method are not limited to glycolic acid oligomers. They can also be polyglycolic acid with a molecular weight (weight average molecular weight) greater than 50,000. For example, waste polyglycolic acid materials with a weight average molecular weight of about 50,000 to 200,000 or more than 200,000 can also be used as raw materials to prepare glycolide through the above method after conventional recycling treatment, thereby realizing the reuse of waste polyglycolic acid materials.

[0113] The molten reaction material containing glycolic acid oligomers mentioned in the first step above contains a depolymerization catalyst, and the amount of the depolymerization catalyst added does not exceed 5 wt% of the molten glycolic acid oligomers. Further, the depolymerization catalyst can 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, diethylzinc, or zinc acetate dihydrate.

[0114] In the above method, the pressure and / or temperature in the first-stage reaction unit and the second-stage reaction unit can be the same or different; for example, the absolute pressure is ≤5 kPa, preferably ≤1 kPa; the temperature is 220-350℃, preferably 225-300℃, and more preferably 230-280℃.

[0115] In one embodiment of the present invention, the temperature of the first-stage reaction unit and the second-stage reaction unit is brought to a set value, and the internal pressure of each reaction module in the reaction unit is reduced to a set pressure value before proceeding to the first step of the method.

[0116] In one embodiment of the present invention, the above method, based on the total weight of the molten reactant containing glycolic acid oligomers entering a reaction unit, yields approximately 20-60% of the gaseous glycolide i obtained through the reaction unit (i.e., the conversion rate of the glycolic acid oligomers corresponding to the obtained gaseous glycolide), for example, but not limited to, approximately 20-40%, approximately 30-50%, etc.

[0117] The reactants are typically introduced into the falling film reaction module or the scraped film reaction module at a feed rate of 1-20 kg / hour, and usually need to be introduced into the stirred reaction module within 30 minutes, preferably within 15 minutes, and more preferably within 5 minutes.

[0118] In one embodiment of the present invention, the stirring reaction module can be operated by first bringing the temperature inside the stirring reactor to a set temperature value and reducing the pressure inside it to a set pressure value. Then, molten reactant containing glycolic acid oligomers is introduced into the stirring reactor through the feed inlet, so that the molten reactant containing glycolic acid oligomers inside reacts under stirring. The generated gaseous glycolide forms a vapor stream and rises, and is discharged and collected through the gas outlet at the top of the reactor.

[0119] In one embodiment of the present invention, the stirred reactor is heated by turning on the heating element; in another embodiment of the present invention, the pressure inside the stirred reactor is reduced to a set pressure value by simultaneously turning on the vacuum pump.

[0120] In one embodiment of the present invention, the drive motor is turned on to drive the stirring paddle to rotate.

[0121] In one embodiment of the present invention, by opening the solenoid valve at the bottom outlet of the stirred reactor, the liquid material inside the stirred reactor is discharged from the outlet under the action of gravity.

[0122] In one embodiment of the present invention, the falling film reactor module operates by first bringing the temperature of the heat exchange tubes in the falling film reactor to a set temperature value, while simultaneously reducing the pressure inside the reactor to a set pressure value. Then, molten reactant containing glycolic acid oligomers enters the reactor through the feed inlet at the top of the falling film reactor and is evenly distributed into each heat exchange tube by a film distributor. Under the influence of gravity, vacuum induction, and airflow, a uniform film is formed in each heat exchange tube and flows from top to bottom. During this process, the gaseous glycolide generated by the material being heated forms a vapor flow, which travels downward to the bottom of the falling film reactor under negative pressure and is then discharged and collected through the outlet.

[0123] In one embodiment of the invention, the temperature of the heat exchange tubes in the falling film reactor is brought to a set temperature value by introducing a heat exchange medium (e.g., heat transfer oil) into the shell side of the falling film reactor.

[0124] In one embodiment of the present invention, a vacuum pump is turned on to reduce the pressure inside the falling film reactor to a set pressure value.

[0125] In one embodiment of the invention, molten reactants containing glycolic acid oligomers are introduced into the reactor through the tube side of a falling film reactor.

[0126] In one embodiment of the present invention, under operating conditions, the average film thickness formed in each heat exchange tube of the falling film reactor is ≤3mm, preferably ≤800μm, for example, but not limited to, 300-500μm, 400-700μm, etc.

[0127] In one embodiment of the present invention, the working method of the scraped film reaction module is as follows: the reactant enters the inside of the scraped film reactor through the feed port, and the reactant is distributed onto the inner wall of the reactor shell by the film distributor. The rotating scraper driven by the drive motor continuously and uniformly scrapes the liquid phase material into a uniform liquid film on the inner wall of the reactor shell, and pushes it downward in a spiral. During this process, the rotating scraper ensures that the continuous and uniform liquid film generates high-speed turbulence and prevents the liquid film from coking and scaling on the inner wall of the reactor shell. The generated gaseous glycolide forms a vapor flow and rises, and is discharged and collected through the gas outlet at the top of the reactor.

[0128] In one embodiment of the present invention, under working conditions, the average film thickness of the liquid film on the inner wall of the scraped film reactor shell is ≤3mm, preferably ≤800μm, for example, but not limited to, 200-660μm, etc.

[0129] In the method provided by the present invention, the gaseous glycolide discharged from the gas outlet is introduced into a gas-liquid separator. The small amount or trace amount of liquid entrained in the gaseous glycolide is intercepted by the anti-liquid entrainer, while the gaseous glycolide discharged from the gas-liquid separator is condensed into a liquid phase by a condenser and then introduced into a product collection tank.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] In this article, when the term “about” is used to modify a numerical value, it indicates an error tolerance of ±5% of that value.

[0134] 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.

[0135] The main advantages of this invention are:

[0136] 1. The reaction apparatus provided by this invention has two levels of reaction units. Through the mutual coupling of falling film reaction modules, stirred reaction modules, and scraped film reaction modules in and between the reaction units at each level, a "two-stage" continuous depolymerization and ring-forming process for glycolic acid oligomers can be realized. By controlling the degree of conversion of the reactants (i.e., glycolic acid oligomers) in each level of reaction unit, it not only helps to discharge the generated gaseous glycolide from the reaction system in a timely manner and improves the efficiency of the depolymerization and ring-forming reaction, but also effectively solves the technical problem that the reactants are prone to coking in the later stage of the conventional process (usually the depolymerization and ring-forming reaction is carried out in one reactor), which leads to the interruption of the reaction.

[0137] 2. The reaction apparatus provided by this invention is not only suitable for continuous production, but also for batch production. It is economical and practical. When using this technology for industrial production, no organic solvents are required, and it is safe and environmentally friendly.

[0138] 3. The glycolide production process provided by this invention does not require the use of organic solvents. While increasing the glycolide yield (above 80%, preferably above 85%), it can also effectively reduce economic costs, has low energy consumption, and can achieve green and low-carbon production.

[0139] 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 of weight-volume percentages in this invention are well known to those skilled in the art, for example, referring to the weight (grams) of 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.

[0140] Falling film reaction module

[0141] Provided as attached Figure 1 The falling film reactor shown.

[0142] The falling film reactor 100 includes an upper partition 101 and a lower partition 102 arranged at intervals along a direction perpendicular to the axial direction of the shell 108 inside the shell 108; a plurality of heat exchange tubes 104 arranged along the axial direction of the shell 108 between the upper partition 101 and the lower partition 102; a film distributor 103 disposed on top of the upper partition 101; a feed inlet 105 disposed on top of the shell 108; and an air outlet 107 and a discharge outlet 106 disposed on bottom of the shell 108, with the horizontal plane of the air outlet 107 being higher than the horizontal plane of the discharge outlet 106. A solenoid valve is provided at the discharge outlet 106.

[0143] The upper and lower ends of the heat exchange tube 104 pass through the upper partition 101 and the lower partition 102 respectively. The upper end of the heat exchange tube 104 passes through the upper partition 101 and is connected to the film distributor 103. The lower end of the heat exchange tube 104 passes through the lower partition 102 and can be connected to the discharge port 106 and the air outlet 107 at the bottom of the shell 108.

[0144] Stirred reaction module

[0145] Provided as attached Figure 2A -C shows a stirred reactor.

[0146] The stirred reactor 200 includes a stirring paddle 201 inserted axially inside the shell 207, a feed inlet 203 located at the top of the shell 207, an air outlet 205 located at the top of the shell 207, a discharge outlet 204 located at the bottom of the shell 207, and a drive motor 206 capable of rotating the stirring paddle 201. The bottom of the shell 207 is arc-shaped, and a solenoid valve is provided at the discharge outlet 204.

[0147] The stirred reactor 200 is also equipped with heating elements, such as the electric heating jacket 2021 arranged on the outer wall of the shell 207 in the stirred reactor 200A. Figure 2A The stirred reactor 200B has a heating coil 2022 arranged axially along the shell 207 inside the shell 207 and an electric heating jacket 2021 arranged on the outer wall of the shell 207. Figure 2B The stirred reactor 200C has a heat exchanger 2023 arranged axially along the inner wall of the shell 207. Figure 2C ).

[0148] Scraped membrane reaction module

[0149] Provided as attached Figure 3 The shown is a scraped film reactor.

[0150] The scraped film reactor 300 includes a rotating shaft 301 inserted axially into the inner cavity of the shell 309, multiple scrapers 302 arranged axially along the shell 309 and spaced apart from each other on the rotating shaft 301, a film spreader 303 arranged on the scraper 302 closest to the top of the inner wall of the shell 309, a drive motor 304 connected to the rotating shaft 301, an electric heating sleeve 308 sleeved on the outside of the shell 309, a feed inlet 305 and an air outlet 307 located at the top of the shell 309, and a discharge outlet 306 located at the bottom of the shell 309. The feed inlet 305 is connected to the film spreader 303, the air outlet 307 is connected to the inner cavity of the shell 309, and a solenoid valve is provided at the discharge outlet 306.

[0151] Device Example 1

[0152] Provided as attached Figure 4A The production equipment shown.

[0153] The glycolide production unit 1000A includes a first-stage reaction unit I and a second-stage reaction unit II. The first-stage reaction unit I uses a falling film reactor 100, and the second-stage reaction unit II uses a scraped film reactor 300. The discharge port 106 of the falling film reactor 100 and the feed port 305 of the scraped film reactor 300 are connected by a pipeline, and a melt pump 1001 is installed on the connecting pipeline.

[0154] Device Example 2

[0155] Provided as attached Figure 4B The production equipment shown.

[0156] The glycolide production unit 1000B includes a first-stage reaction unit I and a second-stage reaction unit II. The first-stage reaction unit I uses a stirred reactor 200C, and the second-stage reaction unit II uses a scraped film reactor 300. The outlet 204 of the stirred reactor 200C and the inlet 305 of the scraped film reactor 300 are connected by a pipeline, and a melt pump 1001 is installed on the connecting pipeline.

[0157] Device Example 3

[0158] Provided as attached Figure 4C The production equipment shown.

[0159] The glycolide production unit 1000C includes a first-stage reaction unit I and a second-stage reaction unit II. The first-stage reaction unit I uses a stirred reactor 200C, and the second-stage reaction unit II uses a falling film reactor 100. The outlet 204 of the stirred reactor 200C and the inlet 105 of the falling film reactor 100 are connected by a pipeline, and a melt pump 1001 is installed on the connecting pipeline.

[0160] Device Example 4

[0161] Provided as attached Figure 5A The production equipment shown.

[0162] The glycolide production unit 2000A includes a first-stage reaction unit I and a second-stage reaction unit II. The first-stage reaction unit I uses two parallel falling film reactors 100, and the second-stage reaction unit II uses a scraped film reactor 300. The outlets 106 of the two parallel falling film reactors 100 are respectively connected to the inlet 305 of the scraped film reactor 300 via pipelines, and multiple melt pumps 1001 are installed on the connecting pipelines.

[0163] Device Example 5

[0164] Provided as attached Figure 5B The production equipment shown.

[0165] The glycolide production unit 2000B includes a first-stage reaction unit I and a second-stage reaction unit II. The first-stage reaction unit I uses two falling film reactors 100 connected in series, and the second-stage reaction unit II uses a scraped film reactor 300. The outlet 106 of the first falling film reactor 100 is connected to the inlet 105 of the second falling film reactor 100 via pipelines, and the outlet 106 of the second falling film reactor 100 is connected to the inlet 305 of the scraped film reactor 300 via pipelines. Melt pumps 1001 are installed on these connecting pipelines.

[0166] Device Example 6

[0167] Provided as attached Figure 5C The production equipment shown.

[0168] The glycolide production unit 2000C includes a first-stage reaction unit I and a second-stage reaction unit II. The first-stage reaction unit I uses two parallel falling film reactors 100 and a stirred reactor 200C. The second-stage reaction unit II uses a scraped film reactor 300. The discharge ports 106 and 204 of the parallel falling film reactors 100 and stirred reactor 200C are respectively connected to the inlet 305 of the scraped film reactor 300 via pipelines, and multiple melt pumps 1001 are installed on the connecting pipelines.

[0169] Device Example 7

[0170] Provided as attached Figure 5D The production equipment shown.

[0171] The glycolide production unit 2000D includes a first-stage reaction unit I and a second-stage reaction unit II. The first-stage reaction unit I uses two parallel falling film reactors 100 and a stirred reactor 200C. The second-stage reaction unit II uses two parallel falling film reactors 100 and a scraped film reactor 300. The outlets 106 and 204 of the parallel falling film reactors 100 and the stirred reactor 200C are respectively connected to the inlets 105 and 305 of the two parallel falling film reactors 100 and the scraped film reactor 300 via pipelines. The outlets 106 and 306 of the two parallel falling film reactors 100 and the scraped film reactor 300 are also connected via pipelines. Melt pumps 1001 are installed on these pipelines.

[0172] Device Example 8

[0173] Provided as attached Figure 6 The production equipment shown.

[0174] The glycolide production unit 3000A includes a first-stage reaction unit I and a second-stage reaction unit II. The first-stage reaction unit I includes a falling film reactor 100 and a product collection unit 400 connected to its outlet 107. The second-stage reaction unit II includes a scraped film reactor 300 and a product collection unit 400 connected to its outlet 307.

[0175] The discharge port 106 of the falling film reactor 100 and the feed port 305 of the scraped film reactor 300 are connected by a pipeline, and a melt pump 1001 is installed on the connecting pipeline.

[0176] Both product collection units 400 include a gas-liquid separator 401, a vacuum pump 1002 connected to the gas outlet of the gas-liquid separator 401 and the inlet of the condenser 402, and a product collection tank 403 connected to the outlet of the condenser 402.

[0177] The outlet 107 of the falling film reactor 100 is connected to the side of the corresponding gas-liquid separator 401; the outlet 307 of the scraped film reactor 300 is connected to the side of the corresponding gas-liquid separator 401.

[0178] Device Example 9

[0179] Provided as attached Figure 7 The production equipment shown.

[0180] The glycolide production unit 3000B includes a first-stage reaction unit I and a second-stage reaction unit II. The first-stage reaction unit I includes two parallel falling film reactors 100 and product collection units 400 connected to their two outlets 107 respectively. The second-stage reaction unit II includes a scraped film reactor 300 and product collection units 400 connected to its outlet 307.

[0181] The outlets 106 of the two parallel falling film reactors 100 are respectively connected to the inlet 305 of the scraped film reactor 300 via pipelines, and a melt pump 1001 is installed on the connecting pipelines.

[0182] Both product collection units 400 include a gas-liquid separator 401, a vacuum pump 1002 connected to the gas outlet of the gas-liquid separator 401 and the inlet of the condenser 402, and a product collection tank 403 connected to the outlet of the condenser 402.

[0183] The outlets 107 of the two parallel falling film reactors 100 are respectively connected to the side lines of the gas-liquid separator 401 via pipelines; the outlet 307 of the scraped film reactor 300 is connected to the side lines of the corresponding gas-liquid separator 401.

[0184] Device Example 10

[0185] Provided as attached Figure 8 The production equipment shown.

[0186] The glycolide production unit 3000C includes a first-stage reaction unit I and a second-stage reaction unit II. The first-stage reaction unit I includes a falling film reactor 100 and a stirred reactor 200C connected in parallel, and two product collection units 400 connected to the outlet 107 of the falling film reactor 100 and the outlet 205 of the stirred reactor 200C, respectively. The second-stage reaction unit II includes a scraped film reactor 300 and the product collection unit 400 connected to its outlet 307.

[0187] The discharge ports 106 and 204 of the parallel falling film reactor 100 and stirred reactor 200C are respectively connected to the feed port 305 of the scraped film reactor 300 via pipelines, and multiple melt pumps 1001 are installed on the connecting pipelines.

[0188] Each of the three product collection units 400 includes a gas-liquid separator 401, a vacuum pump 1002 connected to the gas outlet of the gas-liquid separator 401 and the inlet of the condenser 402, and a product collection tank 403 connected to the outlet of the condenser 402.

[0189] The outlet 107 of the falling film reactor 100 is connected to the side line of the corresponding gas-liquid separator 401 via a pipeline; the outlet 205 of the stirred reactor 200C is connected to the side line of the corresponding gas-liquid separator 401 via a pipeline; and the outlet 307 of the scraped film reactor 300 is connected to the side line of the corresponding gas-liquid separator 401.

[0190] Preparation Examples 1-4

[0191] Production of glycolide

[0192] In the following preparation examples 1-4, preparation examples 1 and 2 are prepared using the apparatus of ...

[0193] Preparation Example 1:

[0194] 10 kg of glycolic acid oligomer (weight average molecular weight of approximately 10,000) was melted at approximately 230°C, and then 20 g of stannous octoate and 10 g of antimony trioxide were added and stirred until homogeneous to obtain molten reactants. The molten reactants were then fed into a falling film reactor in a first-stage reaction unit at a feed rate of 10 kg / hour for the first stage of depolymerization and ring-forming reaction. The absolute pressure in the falling film reactor was set to approximately 0.2 kPa, and the temperature of each heat exchange tube was set to approximately 300°C. The reactants entering the falling film reactor were uniformly distributed into each heat exchange tube via a film distributor. Under the influence of gravity, vacuum induction, and airflow, a uniform film (average film thickness of approximately 520 μm) was formed on the heat exchange surface of each heat exchange tube and flowed from top to bottom. The gaseous glycolide generated during this process was collected into the corresponding product collection tank. After all the reactants had passed through the heat exchange tubes, approximately 5.36 kg of glycolide was collected (at which point the conversion rate of glycolic acid oligomer was approximately 53.8%).

[0195] The remaining reactants are discharged from the falling film reactor and fed into the scraped film reactor in the second-stage reaction unit at a feed rate of 6 kg / h for the second-stage depolymerization and ring-forming reaction. The absolute pressure in the scraped film reactor is set to approximately 0.2 kPa, the temperature of the reactor inner wall is approximately 300°C, and the scraper rotation speed is approximately 90 rpm. The reactants entering the reactor are distributed onto the reactor inner wall by a film distributor. The scraper continuously and uniformly scrapes the reactants onto the reactor inner wall to form a liquid film of uniform thickness (average film thickness of approximately 260 μm) and propels it downwards in a spiral. The gaseous glycolide generated during this process is collected in the corresponding product collection tank until no more gaseous glycolide is discharged, at which point the reaction ends. The mass of glycolide collected in the product collection tank is approximately 3.82 kg, and the total mass of glycolide produced in the entire reaction process is approximately 9.18 kg.

[0196] Based on the mass of 10 kg of glycolic acid oligomer (weight average molecular weight of approximately 10,000) of feedstock, the theoretical yield of glycolide is approximately 9.97 kg. Therefore, the yield of glycolide obtained in this example is approximately 92.08%.

[0197] Preparation Example 2:

[0198] 10 kg of glycolic acid oligomer (weight average molecular weight of approximately 10,000) was melted at approximately 230°C, and 10 g of stannous octoate was added. The mixture was stirred and stirred until homogeneous to obtain molten reactant. The molten reactant was then fed into a falling film reactor in a first-stage reaction unit at a feed rate of 20 kg / hour for the first stage of depolymerization and ring-forming reaction. The absolute pressure in the falling film reactor was set to approximately 1 kPa, and the temperature of each heat exchange tube was set to approximately 230°C. The reactant entering the falling film reactor was evenly distributed into each heat exchange tube by a film distributor. Under the influence of gravity, vacuum induction, and airflow, a uniform film (average film thickness of approximately 860 μm) was formed on the heat exchange surface of each heat exchange tube and flowed from top to bottom. The gaseous glycolide generated during this process was collected into the corresponding product collection tank. After all the reactant had passed through the heat exchange tubes, approximately 2.04 kg of glycolide was collected (at which point the conversion rate of glycolic acid oligomer was approximately 20.5%).

[0199] The remaining reactants are discharged from the falling film reactor and fed into the scraped film reactor in the second-stage reaction unit at a feed rate of 2 kg / h for the second-stage depolymerization and ring-forming reaction. The absolute pressure in the scraped film reactor is set to approximately 0.1 kPa, the temperature of the reactor inner wall is approximately 265°C, and the scraper rotation speed is approximately 60 rpm. The reactants entering the reactor are distributed onto the reactor inner wall by a film distributor. The scraper continuously and uniformly scrapes the reactants onto the reactor inner wall to form a liquid film of uniform thickness (average film thickness of approximately 120 μm) and propels it downwards in a spiral. The gaseous glycolide generated during this process is collected in the corresponding product collection tank until no more gaseous glycolide is discharged, at which point the reaction ends. The mass of glycolide collected in the product collection tank is approximately 6.88 kg, and the total mass of glycolide produced in the entire reaction process is approximately 8.92 kg.

[0200] Based on the mass of 10 kg of glycolic acid oligomer (weight average molecular weight of approximately 10,000) of feedstock, the theoretical yield of glycolide is approximately 9.97 kg. Therefore, the yield of glycolide obtained in this example is approximately 89.47%.

[0201] Preparation Example 3:

[0202] 10 kg of glycolic acid oligomer (weight average molecular weight of approximately 10,000) was melted at approximately 225°C, and then 20 g of diethylzinc and 20 g of tin lactate were added and stirred until homogeneous to obtain molten reactants. These were divided into two portions (approximately 5 kg each) and then fed at a rate of 5 kg / hour into two parallel falling film reactors in a primary reaction unit for the first stage of depolymerization and ring-forming reaction. The absolute pressure in each falling film reactor was set to approximately 0.6 kPa, and the temperature of each heat exchanger tube was set to approximately 270°C. In the membrane reactor, the reactants are evenly distributed into each heat exchange tube via a membrane distributor. Under the influence of gravity, vacuum induction, and airflow, a uniform film (with an average film thickness of approximately 380 μm) is formed on the heat exchange surface of each heat exchange tube and flows from top to bottom. During this process, the gaseous glycolide generated in both falling film reactors is collected into the product collection tank. Once all the reactants in both falling film reactors have passed through the heat exchange tubes, approximately 4.66 kg of glycolide is collected (at which point the conversion rate of glycolic acid oligomers is approximately 46.7%).

[0203] The remaining reactants discharged from the two falling film reactors are fed into the scraped film reactor in the second-stage reaction unit at a feed rate of 2 kg / h for the second-stage depolymerization and ring-forming reaction. The absolute pressure in the scraped film reactor is set to approximately 0.1 kPa, the temperature of the reactor inner wall is approximately 280°C, and the scraper rotation speed is approximately 60 rpm. The reactants entering the reactor are distributed onto the reactor inner wall by a film distributor. The scraper continuously and uniformly scrapes the reactants into a uniform liquid film (average film thickness of approximately 120 μm) on the reactor inner wall and propels it downwards in a spiral. The gaseous glycolide generated during this process is collected into the corresponding product collection tank until no more gaseous glycolide is discharged, at which point the reaction ends. The mass of glycolide collected in the product collection tank is approximately 4.62 kg, and the total mass of glycolide produced in the entire reaction process is approximately 9.28 kg.

[0204] Based on the mass of 10 kg of glycolic acid oligomer (weight average molecular weight of approximately 10,000) of feedstock, the theoretical yield of glycolide is approximately 9.97 kg. Therefore, the yield of glycolide obtained in this example is approximately 93.08%.

[0205] Preparation Example 4:

[0206] 10 kg of glycolic acid oligomer (weight average molecular weight of approximately 10,000) was melted at approximately 230°C, and then 80 g of stannous octoate and 20 g of antimony trioxide were added and stirred until homogeneous to obtain molten reactant. This molten reactant was divided into two equal portions, Part I and Part II. These two portions were then introduced into a stirred reactor and a falling film reactor, respectively, within a single reaction unit for the first stage of depolymerization and ring-forming reaction. Part I was fed into the falling film reactor at a rate of 1 kg / hour. The absolute pressure of the falling film reactor was set to approximately 0.2 kPa, and the temperature of each heat exchanger tube was set to approximately 250°C. The reactant entering the falling film reactor was evenly distributed into each heat exchanger tube via a film distributor. Under the influence of gravity, vacuum induction, and airflow, a uniform film (average film thickness of...) was formed on the heat exchange surface of each heat exchanger tube. The gaseous glycolide (approximately 110 μm) flows downwards, and the generated gaseous glycolide is collected in the corresponding product collection tank. After the first batch of reactants has completely passed through the heat exchange tube, the corresponding collected glycolide is approximately 3.29 kg. The second batch of reactants is completely introduced into the stirred reactor within 5 minutes. The absolute pressure of the stirred reactor is controlled at approximately 0.2 kPa, and the temperature is controlled at approximately 275 °C. The generated gaseous glycolide is collected in the corresponding product collection tank II, and the corresponding collected glycolide is approximately 2.34 kg. (Note: The reaction time of the second batch of reactants in the stirred reactor is approximately the same as the time required for the first batch of reactants to completely pass through the heat exchange tube of the falling film reactor.) Therefore, the total mass of glycolide generated in one reaction unit is approximately 5.63 kg (at this time, the conversion rate of glycolic acid oligomer is approximately 56.5%).

[0207] Subsequently, the remaining reactants from the first-stage reaction unit are fed into the scraped-film reactor in the second-stage reaction unit at a feed rate of 1 kg / h for the second-stage depolymerization and cyclization reaction. The absolute pressure in the scraped-film reactor is set to approximately 0.1 kPa, the temperature of the reactor inner wall is approximately 285°C, and the scraper rotation speed is approximately 85 rpm. The reactants entering the reactor are distributed onto the reactor inner wall via a film distributor. The scraper continuously and uniformly scrapes the reactants onto the reactor inner wall to form a liquid film of uniform thickness (average film thickness of approximately 100 μm), and propels it downwards in a spiral. During this process, the generated gaseous glycolide is collected in the corresponding product collection tank until no more gaseous glycolide is discharged, at which point the reaction ends. The mass of glycolide collected in the product collection tank is approximately 3.69 kg, and the total mass of glycolide produced in the entire reaction process is approximately 9.32 kg.

[0208] Based on the mass of 10 kg of glycolic acid oligomer (weight average molecular weight of approximately 10,000) of feedstock, the theoretical yield of glycolide is approximately 9.97 kg. Therefore, the yield of glycolide obtained in this example is approximately 93.48%.

[0209] Comparative Example 1

[0210] 10 kg of glycolic acid oligomer (weight average molecular weight of approximately 10,000) was added to a stirred reactor and melted at approximately 230°C. Then, 20 g of stannous octoate and 10 g of antimony trioxide were added and stirred until homogeneous. Subsequently, a depolymerization and cyclization reaction was carried out under an absolute pressure of approximately 0.2 kPa and a temperature of approximately 300°C. The gaseous glycolide generated in the reaction was discharged from the vent at the top of the stirred reactor and collected. The reaction ended when no more gaseous glycolide was discharged. The total mass of glycolide collected was approximately 7.48 kg. Upon opening the stirred reactor, large pieces of coked material were found at the bottom of the reactor, which were firmly adhered to the bottom wall and difficult to remove. Manual cleaning was required, which was not only time-consuming and labor-intensive but also resulted in a significant waste of material.

[0211] Based on the mass of 10 kg of glycolic acid oligomer (weight average molecular weight of approximately 10,000) of feedstock, the theoretical yield of glycolide is approximately 9.97 kg, and the yield of glycolide obtained in this comparative example is approximately 75.03%.

[0212] 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 method for producing glycolide, characterized in that, A two-stage reaction apparatus is used, comprising a first-stage reaction unit and a second-stage reaction unit arranged sequentially along the reactant feeding direction. The first-stage reaction unit and the second-stage reaction unit contain different reaction modules. The second-stage reaction unit contains a scraped-film reaction module, which includes at least one scraped-film reactor. The reaction apparatus also includes a product collection unit. The method includes the following steps: (1) The molten reactant containing glycolic acid oligomer undergoes a first-stage depolymerization and ring-forming reaction in the first-stage reaction unit to generate gaseous glycolide i and the remaining molten reactant containing glycolic acid oligomer; the generated gaseous glycolide i is collected by the product collection unit after passing through the gas outlet of the first-stage reaction unit; based on the mass of glycolide i collected in step (1), the conversion rate of glycolic acid oligomer in the corresponding first-stage reaction unit is 20-60%; (2) The remaining molten reactant containing glycolic acid oligomers generated in step (1) undergoes a second depolymerization and ring-forming reaction in the two-stage reaction unit to generate gaseous glycolide II until no more gaseous glycolide is discharged, and the reaction ends; the generated gaseous glycolide II is collected by the product collection unit after passing through the gas outlet of the two-stage reaction unit.

2. The production method as described in claim 1, characterized in that, The reaction unit contains one or more of the following reaction modules: a stirred reaction module, a falling film reaction module, and a scraped film reaction module; and / or The two-stage reaction unit includes a stirred reaction module and / or a falling film reaction module.

3. The production method as described in claim 2, characterized in that, The first-stage reaction unit and the second-stage reaction unit each contain a product collection unit.

4. The production method as described in claim 2, characterized in that, The discharge port of the reaction module in the first stage reaction unit is connected to the inlet of the reaction module in the second stage reaction unit via pipelines.

5. The production method as described in claim 2, characterized in that, The two-stage reaction unit contains a falling film reaction module.

6. The production method as described in claim 2, characterized in that, Two or more reaction modules in the same reaction unit are connected in series and / or in parallel.

7. The production method as described in claim 6, characterized in that, The first-stage reaction unit contains two or more reaction modules connected in series and / or in parallel, and the second-stage reaction unit contains one type of reaction module.

8. The production method as described in claim 6, characterized in that, The first-stage reaction unit contains one type of reaction module, and the second-stage reaction unit contains two or more types of reaction modules connected in series and / or in parallel.

9. The production method as described in claim 6, characterized in that, Two or more reaction modules in the first-stage reaction unit are connected in series and / or in parallel, and two or more reaction modules in the second-stage reaction unit are connected in series and / or in parallel.

10. The production method as described in claim 1, characterized in that, The first stage reaction unit I includes a falling film reactor (100) and a product collection unit (400) connected to its outlet (107), and the second stage reaction unit II includes a scraped film reactor (300) and a product collection unit (400) connected to its outlet (307). The discharge port (106) of the falling film reactor (100) and the feed port (305) of the scraped film reactor (300) are connected by a pipeline, and a melt pump (1001) is installed on the pipeline. Both product collection units (400) include a gas-liquid separator (401), a vacuum pump (1002) connected to the gas outlet of the gas-liquid separator (401) and the inlet of the condenser (402), and a product collection tank (403) connected to the outlet of the condenser (402). The outlet (107) of the falling film reactor (100) is connected to the side of the corresponding gas-liquid separator (401); the outlet (307) of the scraped film reactor (300) is connected to the side of the corresponding gas-liquid separator (401).

11. The production method as described in claim 1, characterized in that, The first stage reaction unit I includes two parallel falling film reactors (100) and product collection units (400) connected to their two outlets (107), respectively. The second stage reaction unit II includes a scraped film reactor (300) and a product collection unit (400) connected to its outlet (307). The outlets (106) of the two parallel falling film reactors (100) are respectively connected to the inlet (305) of the scraped film reactor (300) via pipelines, on which a melt pump (1001) is installed. Both product collection units (400) include a gas-liquid separator (401), a vacuum pump (1002) connected to the gas outlet of the gas-liquid separator (401) and the inlet of the condenser (402), and a product collection tank (403) connected to the outlet of the condenser (402). The outlets (107) of the two parallel falling film reactors (100) are respectively connected to the side lines of the gas-liquid separator (401) via pipelines; the outlets (307) of the scraped film reactor (300) are connected to the side lines of the corresponding gas-liquid separator (401).

12. The production method as described in claim 1, characterized in that, The first-stage reaction unit I includes a falling film reactor (100) and a stirred reactor (200C) connected in parallel, and two product collection units (400) connected to the outlet (107) of the falling film reactor (100) and the outlet (205) of the stirred reactor (200C), respectively. The second-stage reaction unit II includes a scraped film reactor (300) and a product collection unit (400) connected to its outlet (307). The discharge ports (106) and (204) of the parallel falling film reactor (100) and stirred reactor (200C) are respectively connected to the feed port (305) of the scraped film reactor (300) through pipelines, and multiple melt pumps (1001) are installed on the pipelines. Each of the three product collection units (400) includes a gas-liquid separator (401), a vacuum pump (1002) connected to the gas outlet of the gas-liquid separator (401) and the inlet of the condenser (402), and a product collection tank (403) connected to the outlet of the condenser (402). The outlet (107) of the falling film reactor (100) is connected to the side line of the corresponding gas-liquid separator (401) via a pipeline; the outlet (205) of the stirred reactor (200C) is connected to the side line of the corresponding gas-liquid separator (401) via a pipeline; and the outlet (307) of the scraped film reactor (300) is connected to the side line of the corresponding gas-liquid separator (401).

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