Continuous production system and method for modified polyester

Abstract

The present invention relates to a continuous production system and method for modified polyester. The system comprises a melting device (1), a static reactor (2), a first mixing modification device (3), a static devolatilizer (4) and a second mixing modification device (5) which are connected in sequence. The melting device (1) is provided with a cyclic ester monomer feed port, the first mixing modification device (3) is provided with a first modifier feed port, the static devolatilizer (4) is provided with a gas outlet, and the second mixing modification device (5) is provided with a second modifier feed port and a modified polyester discharge port. The system further comprises a vacuum circulation device (6). The vacuum circulation device (6) comprises a spray condenser and a vacuum pumping assembly connected to the spray condenser, wherein the spray condenser is in communication with the gas outlet of the static devolatilizer (4). Compared with the prior art, the present invention has the advantages of low energy consumption, avoiding the influence of shear heat on polymers during preparation, etc.

Description

A continuous production system and method for modified polyester Technical Field

[0001] This invention relates to the field of polyester production technology, and in particular to a continuous production system and method for modified polyester. Background Technology

[0002] Aliphatic polyesters are a class of biocompatible and biodegradable polymers with wide applications in various fields such as medicine, packaging, and agriculture. These polyesters include polyglycolic acid (PGA) and polylactide (PLA). Aliphatic polyesters are typically synthesized by ring-opening polymerization of corresponding cyclic ester monomers such as lactones and lactides.

[0003] CN116159509A discloses a system and method for continuous industrial production of high molecular weight crude PGA, which uses three polymerization reactors of different types connected in series to carry out stepwise polymerization reactions to obtain high molecular weight crude PGA. All the devices involved in the polymerization are moving equipment. CN115722164A discloses a co-production system of polylactic acid and lactide / glycolic acid copolymer. This system is a group of interconnected equipment such as a static mixer, a first prepolymerization reactor, a first polymerization reactor, a first end-capping devolatilizer, and a falling film crystallizer. The polymerization reaction process is long.

[0004] Existing polymerization processes mainly consist of combinations of moving equipment and reactors or combinations of moving and static reactors. The unavoidable shear heat and high energy consumption of moving equipment during the reaction process lead to problems such as yellowing, browning and blackening of polymer products. Furthermore, the use of moving equipment in polymerization results in high installed power and poor economic efficiency.

[0005] Regarding polymer tail gas recovery, existing technologies mainly focus on the recovery and reuse of gaseous components. However, in practical applications, the gaseous components released from the devolatilization system are prone to solidification, causing pipeline blockage. After blockage, the system cannot maintain a low vacuum level, thus affecting the removal of residual monomers from the polymer melt. Summary of the Invention

[0006] The purpose of this invention is to provide a continuous production system and method for modified polyester, which reduces energy consumption and avoids the influence of shear heat on the polymer during the preparation process.

[0007] The objective of this invention can be achieved through the following technical solution: a continuous production system for modified polyester, comprising a melting device, a static reactor, a first mixing and modifying device, a static devolatilizer, and a second mixing and modifying device connected in sequence;

[0008] The melting device is provided with a cyclic ester monomer inlet, the first mixing and modifying device is provided with a first modifier inlet, the static devolatilizer is provided with an outlet, and the second mixing and modifying device is provided with a second modifier inlet and a modified polyester outlet.

[0009] The system also includes a vacuum circulation device, which includes a spray condenser and a vacuum pumping assembly connected to the spray condenser. The spray condenser is connected to the outlet of the static devolatilizer.

[0010] Preferably, the melting device includes a melting screw mill and / or a homogenizing kettle.

[0011] More preferably, the melting screw compressor is a single screw compressor or a twin screw compressor, and the homogenizing kettle is a homogenizing kettle with stirring.

[0012] Preferably, an open-loop catalyst inlet is provided on the pipeline connecting the melting device and the static reactor.

[0013] Preferably, both the first mixing modification device and the second mixing modification device are single-screw extruders or twin-screw extruders.

[0014] More preferably, the first modifier inlet is located in the middle section of the screw compressor, and the second modifier inlet is located in the end section of the screw compressor.

[0015] Preferably, the static devourer has an air inlet at its bottom and a gas distributor communicating with the air inlet. The gas distributor is annular, and its annular structure has several through holes. After nitrogen or inert gas is introduced into the gas distributor, the gas flows from bottom to top under the vacuum effect of the vacuum circulation device.

[0016] Preferably, the spray condenser includes a primary spray condenser and a secondary spray condenser, the vacuum assembly includes a vacuum pump, the gas phase inlet of the primary spray condenser is connected to the gas outlet of the static devolatilizer, the gas phase outlet of the primary spray condenser is connected to the gas phase inlet of the secondary spray condenser, the gas phase outlet of the secondary spray condenser is connected to the vacuum pump, and a liquid phase spray pipeline is provided above the gas phase inlets of both the primary and secondary spray condensers.

[0017] More preferably, a filter layer is provided above the gas phase inlet of the first-stage spray condenser of the static devourer.

[0018] More preferably, the installation height of the secondary spray condenser is higher than that of the primary spray condenser.

[0019] More preferably, the vacuum circulation device further includes a condenser, a gas-liquid separator, an output pump, and a delivery pump;

[0020] The bottoms of the primary spray condenser and the secondary spray condenser are connected to the gas-liquid separator via the output pump. The gas phase outlet of the gas-liquid separator is connected to the steam inlet of the condenser. The condensate outlet of the condenser is connected to the liquid phase spray pipeline above the primary spray condenser and the secondary spray condenser via the delivery pump.

[0021] In this invention, the volatiles from the static devolatilizer pass sequentially through a primary spray condenser and a secondary spray condenser under the action of a vacuum pump. A liquid-phase spray pipeline is provided above the primary and secondary spray condensers to deliver spray liquid into them, thereby spraying and condensing the volatiles to obtain a solid-liquid mixture. The solid-liquid mixture at the bottom of the primary and secondary spray condensers is transported to a gas-liquid separator by an output pump. The spray liquid is vaporized by heating, and the vaporized spray liquid is condensed and liquefied in the condenser, then transported back to the liquid-phase spray pipeline for recycling by a transfer pump. Residual components in the solid-liquid mixture, such as cyclic ester monomers, dimers, and oligomers, are discharged from the liquid-phase outlet of the gas-liquid separator.

[0022] A continuous production method for modified polyester, using the above-mentioned system, includes the following steps:

[0023] The cyclic ester monomer is fed into the melting device through the cyclic ester monomer inlet. After heating and melting, a molten material is obtained. The molten material is then fed into a static reactor, where it is polymerized to obtain a prepolymer.

[0024] The prepolymer is passed through the first mixing and modifying device and mixed with the first modifier added from the first modifier inlet to obtain the first modified material;

[0025] The first modified material is passed through the static devolatilizer, where it undergoes final polymerization and volatile matter removal to obtain polyester. The volatile matter enters the vacuum circulation device, and after being sprayed and condensed by the spray condenser, a solid-liquid mixture is obtained.

[0026] The polyester is passed through the second mixing and modifying device and mixed with a second modifier added from the second modifier inlet to obtain modified polyester, which is then discharged through the modified polyester outlet.

[0027] Preferably, while the molten material is being transported to the static reactor, an open-loop catalyst is injected into the pipeline between the melting device and the static reactor through the open-loop catalyst inlet.

[0028] Preferably, the cyclic ester monomer includes one or more of glycolide, lactide, and trimethylene carbonate.

[0029] Preferably, the molten material further comprises a ring-opening catalyst.

[0030] More preferably, the ring-opening catalyst comprises one or more of divalent metal chlorides or acetates.

[0031] More preferably, the divalent metal includes copper, tin, and zinc.

[0032] More preferably, the amount of the ring-opening catalyst is 0.001-5.000 wt% of the cyclic ester monomer.

[0033] Preferably, the first modifier includes one or more of the following: end-capping agent, heat stabilizer, and chain extender.

[0034] More preferably, the capping agent is selected from one or more monomers or polymers containing terminal hydroxyl, terminal amine, or terminal carboxyl groups.

[0035] More preferably, the heat stabilizer is selected from one or more of metal soap heat stabilizers, organotin heat stabilizers, or rare earth heat stabilizers.

[0036] More preferably, the chain extender is selected from one or more of epoxy chain extender ADR, maleic anhydride, or glycidyl methacrylate.

[0037] More preferably, the amount of each first modifier added in the first mixing and modifying device is 0.01-2 wt% of the cyclic ester monomer, preferably not exceeding 1 wt%.

[0038] Preferably, the second modifier includes one or more of antioxidants, anti-hydrolysis agents, and dehydrating agents.

[0039] More preferably, the antioxidant is selected from one or more of hindered phenolic antioxidants, phosphite antioxidants, or thioether antioxidants.

[0040] More preferably, the anti-hydrolysis agent is selected from at least one of carbodiimide, oxazoline compounds, or epoxy compounds.

[0041] More preferably, the dehydrating agent is selected from at least one of carbodiimide, polycarbodiimide, or carbodiimide-based compounds.

[0042] More preferably, the amount of each second modifier added in the second mixing and modifying device is 0.01-2 wt% of the cyclic ester monomer, preferably not exceeding 1 wt%.

[0043] Preferably, the discharge temperature of the melting device is Tm'+5℃~Tm'+40℃, where Tm' is the melting point of the cyclic ester monomer.

[0044] More preferably, the melting device includes a melting screw compressor and a homogenizing kettle with a stirrer. The temperature of the last section of the melting screw compressor is Tm'+5℃~Tm'+40℃, where Tm' is the melting point of the cyclic ester monomer. The material residence time is 1~5min. The temperature of the homogenizing kettle is the same as the temperature of the last section of the melting screw compressor.

[0045] More preferably, when the cyclic ester monomer is a mixture of two or more monomers, the temperature of the last stage of the melting screw compressor is between +40°C for the monomer with the lower melting point and +5°C for the monomer with the higher melting point. For example, when the cyclic ester monomer is a mixture of glycolide (melting point 84°C) and lactide (melting point 100°C), the temperature of the last stage of the melting screw compressor is between 100+5°C and 84+40°C. When the cyclic ester monomer is a mixture of lactide (melting point 100°C) and trimethylene carbonate (melting point 45°C), the temperature of the last stage of the melting screw compressor is between 45+40°C and 100+5°C.

[0046] Preferably, the reaction temperature of the static reactor is Tm'+5℃~Tm+30℃, where Tm' is the melting point of the cyclic ester monomer and Tm is the melting point of the polymer, and the reaction time is 0.5~12h.

[0047] More preferably, the static reactor employs at least two stages of gradient heating, with the final stage temperature below the polymer melting point Tm+30°C.

[0048] Preferably, the first mixing and modification device is a mixing screw compressor, the temperature of the mixing screw compressor is Tm~Tm+30℃, Tm is the melting point of the polymer, and the material residence time is 0.5~5min.

[0049] Preferably, the temperature of the static devolatilizer is Tm to Tm+40℃, where Tm is the polymer melting point, the material residence time is 1 to 15 min, and the absolute pressure is 1 Pa to 101 kPa.

[0050] More preferably, gas is continuously introduced into the static devolatilizer at the same time, and the temperature of the gas is the same as the temperature inside the static devolatilizer.

[0051] More preferably, the ratio of the gas injection volume to the production volume of the modified polyester is 0.06–30 m³. 3 / kg.

[0052] More preferably, the gas is nitrogen.

[0053] Preferably, the second mixing and modification device adopts a discharge screw compressor, the temperature of the discharge screw compressor is Tm~Tm+30℃, Tm is the melting point of the polymer, and the material residence time is 0.5~5min.

[0054] Preferably, the volatiles are sprayed and condensed sequentially through the primary spray condenser and the secondary spray condenser, wherein the temperature of the spray liquid in the primary spray condenser and the secondary spray condenser is 5 to 20°C, and the flow rate is 0.01 L / min to 10 L / min.

[0055] More preferably, the spray liquid comprises a good solvent for cyclic esters.

[0056] More preferably, the spray liquid includes one or more of ethyl acetate, methyl glycolate, ethanol, isopropanol, and propanol.

[0057] More preferably, the solid-liquid mixture at the bottom of the primary spray condenser and the secondary spray condenser is transported to the gas-liquid separator, where the spray liquid is vaporized by heating. The vaporized spray liquid then enters the condenser for condensation and liquefaction, and is then transported back to the primary spray condenser and the secondary spray condenser to continue being used as spray liquid.

[0058] More preferably, the temperature of the gas-liquid separator is above the vaporization temperature or boiling point of the spray liquid.

[0059] More preferably, the temperature of the condenser is between the melting point of the spray liquid and 50°C.

[0060] More preferably, the temperature of the condenser is 5–20°C.

[0061] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0062] 1. Low energy consumption: Both the polymerization reaction equipment and the devolatilization equipment are static devices, avoiding the impact of shear heat on the polymer during the production process;

[0063] 2. The combined use of the mixing screw and the discharge screw ensures that the melt material is in a plug flow state at different stages. Furthermore, depending on the properties of the modifier, the modifier can be added from either the mixing screw or the discharge screw. Modifiers that modify polyester through chemical reaction are suitable for addition in the first modification stage (i.e., the mixing screw), while modifiers that are easily decomposed or volatile are suitable for addition in the second modification stage (i.e., the discharge screw). By modifying the polyester during the polyester production process, it is beneficial to obtain polymer products with excellent performance.

[0064] 3. The static devolatilizer is equipped with a gas distributor. The upward flow of airflow is more conducive to the removal of small molecules from the melt. It can also reduce the vacuum level of the vacuum system and reduce the requirements for equipment and pipelines.

[0065] 4. The vacuum system can operate stably for a long time. Since the gaseous cyclic esters released during the devolatilization process are prone to sticking to the pipe wall or filter equipment, thus affecting the vacuum level and equipment operation cycle, the problem can be effectively solved by two-stage spraying and filtration.

[0066] 5. The spraying solution can be recycled, reducing operating costs;

[0067] 6. Monomer conversion rate ≥ 99.5%, molecular weight distribution ≤ 1.45, melt index deviation ≤ 10%, terminal carboxyl group value ≤ 10 mol·t⁻¹ -1 The product's appearance is light yellow to yellow, with a relatively light color. Attached Figure Description

[0068] Figure 1 is a schematic diagram of the continuous production system of the present invention;

[0069] Figure 2 is a schematic diagram of the vacuum circulation device of the present invention;

[0070] In the diagram: 1-melting device, 11-melting screw compressor, 12-homogenizing kettle, 2-static reactor, 3-first mixing and modification device, 4-static devolatilizer, 5-second mixing and modification device, 6-vacuum circulation device, 61-first-stage spray condenser, 62-second-stage spray condenser, 63-condenser, 64-gas-liquid separator, 65-vacuum pump, 66-output pump, 67-transfer pump. Detailed Implementation

[0071] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0072] A continuous production system, as shown in Figure 1, includes a melting device 1, a static reactor 2, a first mixing and modification device 3, a static devolatilizer 4, and a second mixing and modification device 5, which are connected sequentially along the material flow direction.

[0073] Furthermore, the melting device 1 is provided with a cyclic ester monomer inlet, and an open-ring catalyst inlet is provided on the pipeline connecting the melting device 1 and the static reactor 2. The first mixing and modifying device 3 is provided with a first modifier inlet, the static devolatilizer 4 is provided with an outlet, the second mixing and modifying device 5 is provided with a second modifier inlet and a modified polyester outlet, and the outlet of the static devolatilizer 4 is connected to a vacuum circulation device 6.

[0074] The melting device 1 includes a melting screw compressor 11 and a homogenizing tank 12. In other embodiments, the melting device 1 may include the melting screw compressor 11 or only the homogenizing tank 12. Both the first mixing and modifying device 3 and the second mixing and modifying device 5 employ a single-screw compressor or a twin-screw compressor. In other embodiments, the first mixing and modifying device 3 and / or the second mixing and modifying device 5 may be implemented using a mixer combined with a melt pump.

[0075] As a preferred embodiment, the static devourer 4 has an air inlet at its bottom and a gas distributor connected to the air inlet. The gas distributor is annular, and several through holes are distributed on the annular structure of the gas distributor. After gas (nitrogen or inert gas) is introduced into the gas distributor, the gas flows from bottom to top under the vacuum action of the vacuum circulation device 6.

[0076] As a preferred embodiment, as shown in Figure 2, the vacuum circulation device 6 used in the system of the present invention comprises:

[0077] The system includes a primary spray condenser 61, a secondary spray condenser 62, a condenser 63, a gas-liquid separator 64, a vacuum pump 65, an output pump 66, and a delivery pump 67. The gas phase inlet of the primary spray condenser 61 is connected to the outlet of the static devolatilizer 4, and the gas phase outlet of the primary spray condenser 61 is connected to the gas phase inlet of the secondary spray condenser 62. The gas phase outlet of the secondary spray condenser 62 is connected to the vacuum pump 65. Liquid phase spray pipelines are provided above the gas phase inlets of both the primary and secondary spray condensers 61 and 62. Furthermore, a filter layer is provided above the gas phase inlet of the primary spray condenser 61; and the secondary spray condenser 62 is higher than the primary spray condenser 61.

[0078] Furthermore, the bottoms of the primary spray condenser 61 and the secondary spray condenser 62 are connected to the gas-liquid separator 64 via the output pump 66. The gas phase outlet of the gas-liquid separator 64 is connected to the steam inlet of the condenser 63. The condensate outlet of the condenser 63 is connected to the liquid phase spray pipeline above the primary spray condenser 61 and the secondary spray condenser 62 via the delivery pump 67.

[0079] A continuous production process for modified polyester using the above system includes the following stages:

[0080] 1. Melting stage: The cyclic ester monomer is added to the melting screw 11, and gradually heated and melted in the melting screw 11. The molten cyclic ester monomer is further transported to the homogenizing tank 12 with stirring and buffered in the homogenizing tank 12.

[0081] The temperature of the melting screw 11 is Tm'+5℃~Tm'+40℃, where Tm' is the melting point of the monomer, and the residence time is 1~5min. The temperature of the homogenizing kettle 12 is the same as that of the melting screw 11. In practical applications, the homogenizing kettle 12 can be omitted, or the melting screw 11 can be omitted.

[0082] As a preferred embodiment, the melting screw compressor 11 can be set with a gradient temperature. For example, if three gradient temperatures are set, the final temperature of the melting screw compressor 11 is between Tm'+5℃ and Tm'+40℃. For example, if the melting point of the glycolide monomer is 84℃, the final temperature of the melting screw compressor 11 is between 84+5℃ and 84+40℃. Alternatively, the first temperature can be set between 50-75℃, the second temperature between 75-100℃, and the third temperature between 100-120℃.

[0083] When the cyclic ester monomer is a mixture of two or more monomers, the final stage temperature of the melting screw compressor 11 and the homogenizing tank 12 are between +40°C for the monomer with the lower melting point and +5°C for the monomer with the higher melting point. For example, if the cyclic ester monomer is a mixture of glycolide (melting point 84°C) and lactide (melting point 100°C), the final stage temperature of the melting screw compressor 11 is between 100+5°C and 84+40°C; if it is a mixture of glycolide (melting point 84°C), lactide (melting point 100°C), and trimethylene carbonate (melting point 45°C), the final stage temperature of the melting screw compressor 11 is between 45+40°C and 100+5°C.

[0084] 2. Polymerization reaction stage: The molten cyclic ester monomer is transported to the static reactor 2, and at the same time, the ring-opening catalyst is injected into the pipeline connecting the homogenizing tank 12 and the static reactor 2 at a certain rate through a metering pump, so that the cyclic ester monomer is polymerized in the static reactor 2 to obtain the prepolymer; the amount of ring-opening catalyst is 0.001-5.000 wt% of the cyclic ester monomer.

[0085] Reaction temperature: Tm'+5℃~Tm+30℃, where Tm' is the melting point of the cyclic ester monomer and Tm is the melting point of the polymer; reaction time: 0.5~12h.

[0086] As a preferred embodiment, the static reactor 2 employs at least two stages of gradient heating, with the final stage temperature below the polymer's melting point Tm + 30°C to prevent polymer degradation due to excessively high temperatures. For example, the Tm of polyglycolic acid is approximately 220°C, the first temperature range is between 120-200°C, and the final temperature range is between 200-250°C.

[0087] 3. First modification stage: The prepolymer is passed through the first mixing and modification device 3 (preferably a mixing screw compressor), and a first modifier (e.g., end-capping agent, heat stabilizer, chain extender, etc.) is added in the middle section of the mixing screw compressor and mixed with the prepolymer to obtain the first modified material; the temperature of the mixing screw compressor is set according to the melting point of the polymer, and the temperature range is Tm~Tm+30℃, where Tm is the melting point of the polymer, and the residence time of the material in the mixing screw compressor is 0.5~5min.

[0088] 4. Deviation stage: The first modified material is passed through the static devolatilizer 4, where final polymerization and volatile matter removal are carried out to obtain polyester. The volatile matter enters the vacuum circulation device 6. The temperature of the static devolatilizer 4 is set according to the melting point of the polymer, with a temperature range of Tm to Tm+40℃ and a residence time of 1 to 15 min. The absolute pressure inside the static devolatilizer 4 is 1 Pa to 101 kPa.

[0089] Furthermore, a gas distributor is installed at the bottom of the static devolatilizer 4. The gas distributor is annular and has several through holes. After gas is introduced into the gas distributor, under the action of vacuum, the gas flows from bottom to top, which can increase the partial pressure of small molecules in the gas phase, carry away small molecules, and thus facilitate the removal of small molecules from the melt. The temperature of the introduced gas is the same as the temperature of the static devolatilizer 4, and the gas volume corresponding to the polymer yield is 0.06~30m³. 3 / kg.

[0090] The first modified material is devolatile under vacuum in the static devolatilizer 4. The volatiles are then sprayed and condensed by the vacuum circulation device 6 to achieve volatile reuse and ensure the smooth flow of the vacuum pipeline, maintaining the vacuum level in the system.

[0091] 5. Second modification stage: The polyester is passed through the second mixing and modification device 5 (preferably a discharge screw compressor), and a second modifier (e.g., antioxidant, anti-hydrolysis agent, dehydrating agent, etc.) is added at the end of the discharge screw compressor to mix with the polyester to obtain modified polyester; the temperature of the discharge screw compressor is set according to the melting point of the polymer, and the temperature range is Tm~Tm+30℃, and the residence time of the material in the discharge screw compressor is 0.5~5min.

[0092] Furthermore:

[0093] The cyclic ester monomer is selected from one or more other cyclic esters such as glycolide, lactide, and trimethylene carbonate.

[0094] The ring-opening catalyst is selected from one or more divalent metal chlorides or acetates such as copper, tin, and zinc.

[0095] Melting screw mills, mixing screw mills, and discharge screw mills can be conventional single screw mills or twin screw mills.

[0096] The capping agent is selected from one or more monomers or polymers containing terminal hydroxyl, terminal amine or terminal carboxyl groups; for example, ethylene glycol, oxalic acid, carbodiimide, terephthalic acid, polyethylene glycol, etc.

[0097] The heat stabilizer is selected from one or more of the following: metal soap heat stabilizers, organotin heat stabilizers, or rare earth heat stabilizers; for example, zinc stearate, calcium stearate, magnesium stearate, sulfur-containing organotin compounds, organotin carboxylates, etc.

[0098] The chain extender is selected from one or more of epoxy chain extender ADR, maleic anhydride, or glycidyl methacrylate.

[0099] The antioxidant is selected from one or more of hindered phenolic antioxidants, phosphite antioxidants, and thioether antioxidants; for example, commercially available BASF Irganox 245, BASF Irganox 1010, and BASF Irganox 1076.

[0100] The anti-hydrolysis agent is selected from at least one of carbodiimide, oxazoline compounds, or epoxy compounds; the epoxy compound is selected from one or more of ethylene oxide, propylene oxide, 1,2-epoxybutane, 1,4-epoxybutane, or 1,4-dioxane.

[0101] The dehydrating agent is selected from at least one of carbodiimide, polycarbodiimide, or carbodiimide-based compounds (e.g., but not limited to, N,N″-diisopropylcarbodiimide, dicyclohexylcarbodiimide, etc.).

[0102] As a preferred embodiment, the amount of each modifier added is 0.01-2 wt% of the cyclic ester monomer, preferably not exceeding 1 wt%.

[0103] In the aforementioned continuous production process, the volatiles undergo the following process after entering the vacuum circulation device 6: Under the action of the vacuum pump 65, the volatiles sequentially pass through the primary spray condenser 61 and the secondary spray condenser 62. Both the primary and secondary spray condensers 61 and 62 are equipped with liquid-phase spray pipelines. The spray liquid is mainly selected as a good solvent for cyclic esters, such as ethyl acetate, methyl glycolate, ethanol, isopropanol, and propanol. The spray condensation method prevents small molecules in the volatiles from clogging the spray condensers through dissolution and rinsing, thus achieving stable system vacuum and long-term stable operation of the vacuum equipment.

[0104] As a preferred option, the dosage of the primary spray liquid and the dosage of the secondary spray liquid are between 0.01L / min and 10L / min, and the dosages of the two spray liquids can be different. If the spray volume is too large, it will be difficult to reduce the absolute pressure in the spray condenser, resulting in a decrease in the vacuum degree in the static devolatilizer.

[0105] Furthermore, the solid-liquid mixture at the bottom of the primary spray condenser 61 and the secondary spray condenser 62 is transported to the gas-liquid separator 64 by the output pump 66. The spray liquid is vaporized and separated by heating. The separated spray liquid is condensed and liquefied by the condenser 63, and then transported to the liquid phase spray pipeline by the transfer pump 67 for circulation as spray liquid.

[0106] As a preferred embodiment, the gas-liquid separator temperature is above the vaporization temperature or boiling point of the spray liquid to ensure separation of the spray liquid; for example, ethyl acetate has a boiling point of 76.5-77.5°C, isopropanol has a boiling point of 82.5°C, and the gas-liquid separator temperature is 77.5°C or above 82.5°C.

[0107] As a preferred embodiment, the condenser temperature is: the melting point of the spray liquid ~50℃; preferably 5~20℃; for example, ethyl acetate has a melting point of -84℃, isopropanol has a melting point of -89.5℃, and the cooler temperature is -84~50℃ or -89.5℃~50℃. The static devolatilizer will be described in detail below with reference to specific embodiments.

[0108] Unless otherwise specified, the reagents, methods, instruments, and equipment used in this invention are conventional in the art. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0109] Test metrics and test methods:

[0110] 1. Monomer conversion rate: Take about 0.5g of sample and place it in a sealed container. Accurately add 15ml of hexafluoroisopropanol to dissolve it. After dissolution, transfer the test solution to a 100ml round-bottom (flat-bottom) flask. Add 15ml of hexafluoroisopropanol to the sealed container and rinse it clean. Transfer the flask to the flask and accurately add 10ml of acetone. Shake to precipitate the polymer, shake to dissolve, filter, and collect the filtrate. Take 1μl each of the above reference solution and test solution and inject them into the gas chromatograph. Record the chromatogram and calculate the content of residual small molecule substances.

[0111] Monomer conversion rate = 100% - mass of residual small molecules / mass of all monomers before polymerization.

[0112] 2. Weight-average molecular weight and molecular weight distribution: determined by gel permeation chromatography (GPC). The sample was dissolved in hexafluoroisopropanol solution to prepare a 0.05%–0.3% (mass fraction) solution; filtered through a polytetrafluoroethylene (PTFE) membrane; 20 μL was added to the GPC injector, and molecular weight was corrected using five different standard polymethyl methacrylates.

[0113] 3. Melt index deviation Δλ: The melt mass flow rate is determined according to GB / T 3682 Thermoplastics Melt Mass Flow Rate and Melt Lift Flow Rate, using condition A in Appendix A, i.e., test temperature of 250℃ and nominal load of 2.16kg.

[0114] The test method involves drying the material under vacuum at (70±2)℃ for (24±1)h; setting the instrument's test temperature to 250℃ and preheating for 10min; weighing 5-10g of sample, loading it through a funnel, and inserting the pressure rod into the cylinder to compact the material; controlling the feeding time within 1min and maintaining the temperature for 4min; placing a 2.16kg weight on the top of the pressure rod, cutting a section every 30s for a total of five sections; weighing the mass of each section to calculate the melt flow index (MI1). The feeding time is controlled within 1min and maintained at the temperature for 10min; placing a 2.16kg weight on the top of the pressure rod, cutting a section every 30s for a total of five sections; weighing the mass of each section to calculate the melt flow index (MI2).

[0115] Calculation formula: MI = 600 W / t (g / 10min)

[0116] Where W is the average mass per segment, and t is the cutting time interval for each segment.

[0117] Δλ=(MI2-MI1) / MI1

[0118] 4. Determination of terminal carboxyl groups: A certain amount of the treated sample is placed in an Erlenmeyer flask containing solvent, heated in an oil bath until fully dissolved, removed while hot, an indicator is added, and titrated with a potassium hydroxide-ethanol solution of a certain concentration. The titration endpoint is reached when the indicator turns to the target color.

[0119] Under the same conditions, a reagent blank was determined. The content of terminal carboxyl groups was calculated using equation (1):

[0120] In the formula, X represents the carboxyl content at the sample end, in mol·t⁻¹. -1 V represents the volume of potassium hydroxide ethanol solution consumed in the titration of the sample, in mL; V0 represents the volume of potassium hydroxide ethanol solution consumed in the blank titration, in mL; c represents the concentration of the potassium hydroxide ethanol solution, in mol·L⁻¹. -1 m is the mass of the sample, in grams.

[0121] Example 1

[0122] 1) A certain amount of glycolide is added to a melting screw press and completely melted in the melting screw press at 70-120℃. The molten glycolide is first stored in a homogenizing kettle with a stirrer (120℃), and then introduced into a static reactor. At the same time, the ring-opening catalyst (tin dichloride dihydrate, 0.5wt%) is injected into the pipeline connecting the homogenizing kettle and the static reactor through a metering pump and mixed evenly with the molten glycolide. The glycolide undergoes a polymerization reaction in the static reactor to obtain glycolic acid prepolymer with a certain molecular weight. The static reactor adopts a multi-stage stepped heating method. The temperature of the first stage is set at about 150℃ and the time to pass through the first stage is about 10 min. The temperature of the second stage is set at about 190℃ and the time to pass through the second stage is about 30 min. The temperature of the third stage is set at about 220℃ and the time to pass through the third stage is about 60 min.

[0123] 2) The glycolic acid prepolymer is introduced into a mixing screw, and 0.05 wt% oxalic acid (end-capping agent) and 0.05 wt% calcium stearate (heat stabilizer) are added in the middle section of the mixing screw to obtain the first modified material. The temperature of the mixing screw is set to about 230°C, and the residence time of the material in the mixing screw is 3 min.

[0124] 3) The first modified material is passed through a static devolatilizer, where final polymerization and volatile matter removal occur to obtain polyglycolic acid. The static devolatilizer temperature is set at 230℃, the absolute pressure inside the devolatilizer is 10 kPa, and the nitrogen volume corresponding to the polymer yield is 0.3 m³. 3 / kg, the residence time of the material in the static devolatilizer is 10min; the volatiles pass through a primary spray condenser and a secondary spray condenser. Ethyl acetate is sprayed above the primary and secondary spray condensers. The temperature of the condenser is set at 20℃, the temperature of the gas-liquid separator is set at 95℃, the flow rate of the primary spray liquid is 2L / min, and the flow rate of the secondary spray liquid is 0.06L / min.

[0125] 4) Pass polyglycolic acid through the discharge screw, and add 0.05wt% antioxidant BASF Irganox 1010 and 0.05wt% dehydrating agent dicyclohexylcarbodiimide at the end of the discharge screw to obtain modified polyester. The temperature of the mixing screw is set to about 230℃, and the residence time of the material in the mixing screw is 3 minutes.

[0126] Example 2

[0127] The process is essentially the same as in Example 1, except that the absolute pressure inside the static devolatilizer is 80 kPa and the nitrogen volume corresponding to the polymer yield is 12 m³. 3 / kg.

[0128] Example 3

[0129] The process is essentially the same as in Example 1, except that the absolute pressure inside the static devolatilizer is 100 Pa and the nitrogen volume corresponding to the polymer yield is 0 m³. 3 / kg, meaning that no gas is introduced into the static devolatilizer, and no vent or gas distributor is required at the bottom of the static devolatilizer.

[0130] Example 4

[0131] 1) A certain amount of glycolide is added to a melting screw press and completely melted in the melting screw press at 70-120℃. The molten glycolide is first stored in a homogenizing kettle with a stirrer (120℃), and then introduced into a static reactor. At the same time, the ring-opening catalyst (stannous octoate, 1wt%) is injected into the pipeline connecting the homogenizing kettle and the static reactor through a metering pump and mixed evenly with the molten glycolide. The glycolide undergoes a polymerization reaction in the static reactor to obtain a glycolic acid prepolymer with a certain molecular weight. The static reactor adopts a two-stage stepped heating method. The temperature of the first stage is set to about 170℃ and the time to pass through the first stage is about 20 minutes. The temperature of the second stage is set to about 230℃ and the time to pass through the second stage is about 20 minutes.

[0132] 2) The glycolic acid prepolymer is introduced into a mixing screw, and 0.05 wt% ethylene glycol (end-capping agent) and 0.05 wt% calcium stearate (heat stabilizer) are added in the middle section of the mixing screw to obtain the first modified material. The temperature of the mixing screw is set to about 230°C, and the residence time of the material in the mixing screw is 1 min.

[0133] 3) The first modified material is passed through a static devolatilizer, where final polymerization and volatile matter removal are carried out to obtain polyglycolic acid. The static devolatilizer temperature is set at 240℃, the absolute pressure inside the static devolatilizer is 10 kPa, and the nitrogen volume corresponding to the polymer yield is 6 m³. 3 / kg, the residence time of the material in the static devolatilizer is 5min; the volatiles pass through the first-stage spray condenser and the second-stage spray condenser. Ethyl acetate is sprayed above the first-stage spray condenser and the second-stage spray condenser. The temperature of the condenser is set at 10℃, the temperature of the gas-liquid separator is set at 95℃, the flow rate of the first-stage spray liquid is 2L / min, and the flow rate of the second-stage spray liquid is 0.06L / min.

[0134] 4) Pass polyglycolic acid through the discharge screw and add 0.05wt% of antioxidant BASF Irganox 1010 at the end of the discharge screw to obtain modified polyester. The temperature of the mixing screw is set to about 230℃ and the residence time of the material in the mixing screw is 1min.

[0135] Example 5

[0136] The process is essentially the same as in Example 4, except that the absolute pressure inside the static devolatilizer is 1 kPa and the nitrogen volume corresponding to the polymer yield is 3 m³. 3 / kg.

[0137] Comparative Example 1

[0138] The process is basically the same as in Example 4, except that the glycolic acid prepolymer obtained in step 1) is directly introduced from the static reactor into the static devolatilizer, omitting step 2). In step 4), 0.05 wt% ethylene glycol (end-capping agent), 0.05 wt% calcium stearate (heat stabilizer) and 0.05 wt% antioxidant BASF Irganox 1010 are added together at the end of the discharge screw.

[0139] Comparative Example 2

[0140] It is basically the same as Example 4, except that the residence time of the material in the static devolatilizer is 30 minutes.

[0141] Comparative Example 3

[0142] The process is basically the same as in Example 4, except that in step 3), the first modified material is passed through a twin-screw extruder with only a devolatilization section. The final polymerization and devolatile matter removal are carried out in the twin-screw extruder to obtain polyglycolic acid. The temperature of the twin-screw extruder is set to about 240°C, the absolute pressure is set to about 500 Pa, the length-to-diameter ratio of the screw is about 50, and the time for the material to pass through the twin-screw extruder is 5 minutes.

[0143] Table 1

[0144] As shown in Table 1, among Examples 1-3, Example 3 exhibited the highest monomer conversion rate and the lowest molecular weight distribution, melt index deviation, and terminal carboxyl group content. Among Examples 4-5, Example 5 showed the highest monomer conversion rate and even lower melt index deviation and terminal carboxyl group content. This indicates that during the devolatilization stage, a lower absolute pressure within the static devolatilizer is more beneficial for improving monomer conversion rate, reducing unreacted monomer residue, and enhancing polymer thermal stability. However, a lower absolute pressure implies higher requirements for equipment and pipelines. In actual continuous production, pressure fluctuations lead to differences in the performance of the resulting modified polyester products. However, by introducing gas into the static devolatilizer and appropriately reducing the vacuum level within it, high-performance polymer products can still be obtained.

[0145] Comparative Example 1 omitted the first modification stage. Compared with Example 4, the modified polyester obtained had a lower monomer conversion rate, higher melt index deviation, and higher end-carboxyl group content. This indicates that the timing of the addition of the first modifier during production affects the polymer's performance. It is speculated that adding the first modifier (e.g., end-capping agent, heat stabilizer, etc.) before the devolatilization stage can inhibit unintended thermal degradation of the polymer during the devolatilization stage. The thermal degradation and repolymerization of polymer segments under high-temperature conditions is a dynamic process. The excessively long devolatilization time in Comparative Example 2 led to excessive thermal degradation of the polymer, resulting in a significantly higher melt index deviation. Comparative Example 3 used a twin-screw extruder as the devolatilization equipment. Under the same devolatilization temperature and time, although the monomer conversion rate of the obtained modified polyester was above 99.5%, the melt index deviation and end-carboxyl group content were higher. It is speculated that the high shear heat in the twin-screw extruder increases the thermal degradation of the polymer.

[0146] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A continuous production system for modified polyester, characterized in that, It includes a melting device (1), a static reactor (2), a first mixing and modification device (3), a static devourer (4), and a second mixing and modification device (5) connected in sequence. The melting device (1) is provided with a cyclic ester monomer inlet, the first mixing and modifying device (3) is provided with a first modifier inlet, the static devolatilizer (4) is provided with an outlet, and the second mixing and modifying device (5) is provided with a second modifier inlet and a modified polyester outlet. The system also includes a vacuum circulation device (6), which includes a spray condenser and a vacuum pumping assembly connected to the spray condenser. The spray condenser is connected to the outlet of the static devourer (4).

2. The continuous production system for modified polyester according to claim 1, characterized in that, The melting device (1) includes a melting screw compressor (11) and / or a homogenizing kettle (12); The melting screw compressor (11) is a single screw compressor or a twin screw compressor, and the homogenizing tank (12) is a homogenizing tank with stirring. An open-loop catalyst inlet is provided on the pipeline connecting the melting device (1) and the static reactor (2).

3. The continuous production system for modified polyester according to claim 1, characterized in that, Both the first mixing modification device (3) and the second mixing modification device (5) are single-screw machines or twin-screw machines; The first modifier inlet is located in the middle section of the screw compressor, and the second modifier inlet is located in the end section of the screw compressor.

4. The continuous production system for modified polyester according to claim 1, characterized in that, The static devourer (4) has an air inlet and a gas distributor connected to the air inlet at its bottom. The gas distributor is annular and has several through holes distributed on its annular structure.

5. The continuous production system for modified polyester according to any one of claims 1 to 4, characterized in that, The spray condenser includes a primary spray condenser (61) and a secondary spray condenser (62), and the vacuum assembly includes a vacuum pump (65). The gas phase inlet of the primary spray condenser (61) is connected to the gas outlet of the static devolatilizer (4), the gas phase outlet of the primary spray condenser (61) is connected to the gas phase inlet of the secondary spray condenser (62), and the gas phase outlet of the secondary spray condenser (62) is connected to the vacuum pump (65). A liquid phase spray pipeline is provided above the gas phase inlets of both the primary spray condenser (61) and the secondary spray condenser (62). Preferably, a filter layer is also provided above the gas phase inlet of the primary spray condenser (61). The vacuum circulation device also includes a condenser (63), a gas-liquid separator (64), an output pump (66), and a delivery pump (67); The bottoms of the primary spray condenser (61) and the secondary spray condenser (62) are connected to the gas-liquid separator (64) via the output pump (66). The gas phase outlet of the gas-liquid separator (64) is connected to the steam inlet of the condenser (63). The condensate outlet of the condenser (63) is connected to the liquid phase spray pipeline above the primary spray condenser (61) and the secondary spray condenser (62) via the delivery pump (67).

6. A continuous production method for modified polyester, characterized in that, The process, performed using the system described in any one of claims 1 to 5, includes the following steps: The cyclic ester monomer is fed into the melting device (1) through the cyclic ester monomer inlet. After heating and melting, a molten material is obtained. The molten material is then fed into the static reactor (2) to polymerize the molten material and obtain a prepolymer. The prepolymer is passed through the first mixing and modifying device (3) and mixed with the first modifier added from the first modifier inlet to obtain the first modified material; The first modified material is passed through the static devolatilizer (4) to undergo final polymerization and volatile matter removal to obtain polyester. The volatile matter enters the vacuum circulation device (6) and is sprayed and condensed by the spray condenser to obtain a solid-liquid mixture. The polyester is passed through the second mixing and modifying device (5) and mixed with the second modifier added from the second modifier inlet to obtain modified polyester, which is then discharged through the modified polyester outlet.

7. The continuous production method of modified polyester according to claim 6, characterized in that, The cyclic ester monomer includes one or more of glycolide, lactide, and trimethylene carbonate; The molten material also contains a ring-opening catalyst, which includes one or more of divalent metal chloride salts or acetates; The amount of the ring-opening catalyst used is 0.001-5.000 wt% of the cyclic ester monomer.

8. The continuous production method of modified polyester according to claim 6, characterized in that, The first modifier includes one or more of the following: end-capping agent, heat stabilizer, and chain extender; The second modifier includes one or more of antioxidants, anti-hydrolysis agents, and dehydrating agents; The amount of each first modifier added in the first mixing and modifying device (3) is 0.01-2 wt% of the cyclic ester monomer, preferably not exceeding 1 wt%. The amount of each second modifier added in the second mixing and modifying device (5) is 0.01-2 wt% of the cyclic ester monomer, preferably not exceeding 1 wt%.

9. The continuous production method of modified polyester according to any one of claims 6 to 8, characterized in that, The discharge temperature of the melting device (1) is Tm'+5℃~Tm'+40℃, where Tm' is the melting point of the cyclic ester monomer; The reaction temperature of the static reactor (2) is Tm'+5℃~Tm+30℃, where Tm' is the melting point of the cyclic ester monomer and Tm is the melting point of the polymer, and the reaction time is 0.5~12h. The temperature of the first mixing and modification device (3) is Tm~Tm+30℃, where Tm is the melting point of the polymer, and the material residence time is 0.5~5min; The temperature of the static devolatilizer (4) is Tm to Tm+40℃, where Tm is the polymer melting point. The material residence time is 1 to 15 minutes, and the absolute pressure is 1 Pa to 101 kPa. Simultaneously, gas is continuously introduced into the static devolatilizer (4) at the same temperature as the temperature inside the static devolatilizer (4). The ratio of the gas volume introduced to the yield of the modified polyester is 0.06 to 30 m³. 3 / kg; The temperature of the second mixing and modification device (5) is Tm~Tm+30℃, where Tm is the melting point of the polymer, and the material residence time is 0.5~5min.

10. The continuous production method of modified polyester according to claim 9, characterized in that, The volatiles are sprayed and condensed sequentially through the first-stage spray condenser (61) and the second-stage spray condenser (62). The temperature of the spray liquid in the first-stage spray condenser (61) and the second-stage spray condenser (62) is 5 to 20°C, and the dosage is 0.01 L / min to 10 L / min. The solid-liquid mixture in the primary spray condenser (61) and the secondary spray condenser (62) is transported to the gas-liquid separator (64), where the spray liquid is vaporized by heating. The vaporized spray liquid then enters the condenser (63) for condensation and liquefaction, and is then transported back to the primary spray condenser (61) and the secondary spray condenser (62) to continue being used as spray liquid.

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