Continuous production system and production method of modified polyester

Abstract

The invention relates to a continuous production system and a production method of modified polyester. The system comprises a melting device (1), a static reactor (2), a first mixing modification device (3), a static devolatilization device (4) and a second mixing modification device (5) which are communicated in sequence, the melting device (1) is provided with a cyclic ester monomer feed port, the first mixing and modifying device (3) is provided with a first modifier feed port, the static devolatilization device (4) is provided with a gas outlet, and the second mixing and modifying 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 spraying condenser and a vacuumizing assembly connected with the spraying condenser, and the spraying condenser is communicated with an air outlet of the static devolatilization device (4). Compared with the prior art, the method has the advantages of low energy consumption, capability of preventing the polymer from being influenced by shear heat in the preparation process and the like.

Description

Technical Field

[0001] The invention relates to the technical field of polyester production, in particular to a continuous production system and a production method of modified polyester. Background Art

[0002] Aliphatic polyesters are a class of biocompatible and biodegradable polymer materials, which are widely used in many fields such as medicine, packaging, and agriculture. These polyesters include polyglycolide (PGA), polylactide (PLA), etc. Aliphatic polyesters are usually 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 adopts three polymerization reactors of different forms connected in series to carry out step-by-step polymerization reaction to obtain high molecular weight crude PGA, wherein all the devices involved in the polymerization are dynamic equipment; CN115722164A discloses a polylactic acid and lactide / glycolide copolymer co-production system, which is a static mixer, a first prepolymerization reactor, a first polymerization reactor and a first end-capping devolatilizer, a falling film crystallizer and other connected equipment groups, and the polymerization reaction process is long.

[0004] The existing polymerization process flow is mainly in the form of a dynamic equipment reactor combination or a dynamic and static reactor combination. The inevitable shear heat and high energy consumption of the dynamic equipment during the reaction process lead to problems such as yellow, brown and black color of the polymer product. In addition, the polymerization dynamic equipment will result in high installed power and poor economy of the device.

[0005] Regarding the recovery of polymer tail gas, the existing technologies for polymer tail gas recovery mainly focus on the recovery and reuse of gas phase components. However, in actual applications, the gas phase components released from the devolatilization system are prone to solidification and cause pipeline blockage. After blockage, the system cannot maintain a low vacuum degree, thereby affecting the removal of residual monomers from the polymer melt. Summary of the invention

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

[0007] The object of the present invention can be achieved by the following technical scheme: A continuous production system of 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 feed port, the first mixing and modifying device is provided with a first modifier feed port, the static devolatilizer is provided with an air outlet, and the second mixing and modifying device is provided with a second modifier feed port and a modified polyester discharge port;

[0009] The system further comprises a vacuum circulation device, which comprises a spray condenser and a vacuum pumping assembly connected to the spray condenser, and the spray condenser is communicated with the gas outlet of the static devolatilizer.

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

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

[0012] Preferably, a ring-opening catalyst feed port is provided on the pipeline connecting the melting device and the static reactor.

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

[0014] Further preferably, the first modifier feed port is arranged at the middle section of the screw machine, and the second modifier feed port is arranged at the end section of the screw machine.

[0015] Preferably, an air inlet and a gas distributor connected to the air inlet are provided at the bottom of the static devolatilizer, the gas distributor is annular, and a plurality of through holes are distributed on the annular structure of the gas distributor. 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 liquid phase spray pipelines are provided above the gas phase inlets of the primary spray condenser and the secondary spray condenser.

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

[0018] Further 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 comprises a condenser, a gas-liquid separator, an output pump and a delivery pump;

[0020] The bottom of the first-stage spray condenser and the second-stage spray condenser is connected to the gas-liquid separator through the output pump, the gas phase outlet of the gas-liquid separator is connected to the steam inlet of the condenser, and the condensate outlet of the condenser is connected to the liquid phase spray pipeline above the first-stage spray condenser and the second-stage spray condenser through the delivery pump.

[0021] In the present invention, the volatiles of the static devolatilizer are sequentially passed through the primary spray condenser and the secondary spray condenser under the action of the vacuum pump. A liquid phase spray pipeline is arranged above the primary spray condenser and the secondary spray condenser, and spray liquid can be transported into the primary spray condenser and the secondary spray condenser to spray and condense the volatiles to obtain a solid-liquid mixture. The solid-liquid mixture at the bottom of the primary spray condenser and the secondary spray condenser is transported to the gas-liquid separator by an output pump, and the spray liquid is vaporized by heating. The vaporized spray liquid is condensed and liquefied by the condenser, and then transported to the liquid phase spray pipeline for recycling by a delivery pump, and the remaining components in the solid-liquid mixture, such as cyclic ester monomers, dimers, oligomers, etc., are discharged from the liquid phase outlet of the gas-liquid separator.

[0022] A method for continuously producing modified polyester, using the above system, comprises the following steps:

[0023] The cyclic ester monomer is conveyed to the melting device through the cyclic ester monomer feed port, and a molten material is obtained after heating and melting, and the molten material is conveyed to a static reactor, and the molten material is polymerized in the static reactor to obtain a prepolymer;

[0024] Passing the prepolymer through the first mixing and modifying device and mixing it with the first modifier added from the first modifier feed port to obtain a first modified material;

[0025] The first modified material is passed through the static devolatilizer, and final polymerization and volatiles are removed in the static devolatilizer to obtain polyester. The volatiles enter the vacuum circulation device, and are sprayed and condensed in the spray condenser to obtain a solid-liquid mixture;

[0026] The polyester is passed through the second mixing and modifying device and mixed with the second modifier added from the second modifier feed port to obtain a modified polyester, and the modified polyester is discharged through the modified polyester discharge port.

[0027] Preferably, while the molten material is being transported to the static reactor, a ring-opening catalyst is injected into the pipeline between the melting device and the static reactor through a ring-opening catalyst feed port.

[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] Further preferably, the ring-opening catalyst includes one or more 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 used is 0.001-5.000 wt % of the cyclic ester monomer.

[0033] Preferably, the first modifier includes one or more of a capping agent, a thermal stabilizer, and a chain extender.

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

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

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

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

[0038] Preferably, the second modifier includes one or more of an antioxidant, an anti-hydrolysis agent, and a dehydrating agent.

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

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

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

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

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

[0044] Further preferably, the melting device comprises a melting screw machine and a homogenizing kettle with stirring, the temperature of the last section of the melting screw machine is Tm'+5°C to Tm'+40°C, Tm' is the melting point of the cyclic ester monomer, the material residence time is 1 to 5 minutes, and the temperature of the homogenizing kettle is the same as the temperature of the last section of the melting screw machine.

[0045] Further preferably, when the cyclic ester monomer is a mixture of two or more monomers, the temperature of the last section of the melt screw machine is between +40°C of the monomer with a lower melting point and +5°C of the monomer with a 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 section of the melt screw machine 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 section of the melt screw machine is between 45+40°C and 100+5°C.

[0046] Preferably, the reaction temperature of the static reactor is Tm'+5°C to Tm+30°C, Tm' is the melting point of the cyclic ester monomer, Tm is the melting point of the polymer, and the reaction time is 0.5 to 12 hours.

[0047] Further preferably, the static reactor adopts at least 2 stages of gradient temperature increase, and the temperature of the last stage is below the polymer melting point Tm+30°C.

[0048] Preferably, the first mixing and modifying device adopts a mixing screw machine, the temperature of the screw machine is Tm~Tm+30°C, 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-Tm+40° C., Tm is the melting point of the polymer, the material residence time is 1-15 min, and the absolute pressure is 1 Pa-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 volume of the gas introduced to the output of the modified polyester is 0.06 to 30 m 3 / kg.

[0052] More preferably, the gas is nitrogen.

[0053] Preferably, the second mixing and modifying device uses a discharging screw machine, the temperature of the discharging screw machine is Tm~Tm+30°C, 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 in turn through the primary spray condenser and the secondary spray condenser, the temperature of the spray liquid in the primary spray condenser and the secondary spray condenser is 5-20°C, and the dosage is 0.01L / min-10L / min.

[0055] Further 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] Further preferably, the solid-liquid mixture at the bottom of the first-stage spray condenser and the second-stage spray condenser is transported to the gas-liquid separator, and the spray liquid is vaporized by heating. The vaporized spray liquid enters the condenser to be condensed and liquefied, and then transported to the first-stage spray condenser and the second-stage spray condenser to continue to be used as spray liquid.

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

[0059] Further preferably, the condenser temperature is from the melting point of the spray liquid to 50°C.

[0060] More preferably, the condenser temperature 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 equipment and the devolatilization equipment adopt static devices to avoid the influence of shear heat on the polymer during the production process;

[0063] 2. The combined use of the mixing screw machine and the discharging screw machine enables the melt material to be in a plug flow state at different stages. Furthermore, according to the performance of the modifier, the modifier can be added from the mixing screw machine or the discharging screw machine. Among them, the modifier that modifies the polyester by chemically reacting with the polyester is suitable for adding in the first modification stage (i.e., the mixing screw machine), and the modifier that is easily decomposed or volatilized is suitable for adding in the second modification stage (i.e., the discharging screw machine). By modifying the polyester in the process of polyester production, it is beneficial to obtain a polymer product with excellent performance;

[0064] 3. A gas distributor is provided in the static devolatilizer. The gas flow from bottom to top is more conducive to the removal of small molecules from the melt, and can also reduce the vacuum degree of the vacuum system and the requirements for equipment and pipelines;

[0065] 4. The vacuum system can operate stably for a long time. Since the gaseous cyclic ester released during the devolatilization process is easy to adhere to the pipe wall or the filtering equipment, thus affecting the vacuum degree and the equipment operation cycle, the problem can be effectively solved through two-stage spraying and filtering;

[0066] 5. The spray liquid can be recycled to reduce operating costs;

[0067] 6. Monomer conversion rate ≥ 99.5%, molecular weight distribution ≤ 1.45, melt index deviation ≤ 10%, terminal carboxyl value ≤ 10 mol·t -1 , the product appearance is light yellow to yellow, and the color is lighter. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0070] In the figure: 1-melting device, 11-melting screw machine, 12-homogenizing kettle, 2-static reactor, 3-first mixing and modifying device, 4-static devolatilizer, 5-second mixing and modifying 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-delivery pump. DETAILED DESCRIPTION

[0071] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

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

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

[0074] The melting device 1 includes a melting screw machine 11 and a homogenizing kettle 12. In other embodiments, the melting device 1 may include a melting screw machine 11, or only include a homogenizing kettle 12. The first mixing and modifying device 3 and the second mixing and modifying device 5 are both single screw machines or twin screw machines. In other embodiments, the first mixing and modifying device 3 and / or the second mixing and modifying device 5 can be implemented by a mixer combined with a melt pump.

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

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

[0077] 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 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, the gas phase outlet of the secondary spray condenser 62 is connected to the vacuum pump 65, and liquid phase spray pipelines are provided above the gas phase inlets of the primary spray condenser 61 and the secondary spray condenser 62. In addition, a filter layer is provided above the gas phase inlet of the primary spray condenser 61; and the height of the secondary spray condenser 62 is higher than that of the primary spray condenser 61.

[0078] Furthermore, the bottom of the first-stage spray condenser 61 and the second-stage spray condenser 62 are connected to the gas-liquid separator 64 through an output pump 66, the gas phase outlet of the gas-liquid separator 64 is connected to the steam inlet of the condenser 63, and the condensate outlet of the condenser 63 is connected to the liquid phase spray pipeline above the first-stage spray condenser 61 and the second-stage spray condenser 62 through a delivery pump 67.

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

[0080] 1. Melting stage: Cyclic ester monomers are added into the melting screw machine 11 , gradually heated and melted in the melting screw machine 11 , and the melted cyclic ester monomers are further transported to the homogenizing kettle 12 with stirring, and buffered in the homogenizing kettle 12 .

[0081] The temperature of the melting screw machine 11 is: Tm'+5°C~Tm'+40°C, 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 the temperature of the melting screw machine 11. In practical applications, the homogenizing kettle 12 can be omitted, or the melting screw machine 11 can be omitted.

[0082] As a preferred solution, the melting screw machine 11 can be set to a gradient temperature increase. For example, three sections of gradient temperature are set, and the temperature of the last section of the melting screw machine 11 is between Tm'+5°C and Tm'+40°C. For example, the melting point of glycolide monomer is 84°C, and the temperature of the last section of the melting screw machine 11 is between 84+5°C and 84+40°C; for example, the temperature of the first section is set at 50-75°C, the temperature of the second section is set at 75-100°C, and the temperature of the third section is set at 100-120°C.

[0083] When the cyclic ester monomer is a mixture of two or more monomers, the temperature of the last section of the melting screw machine 11 and the temperature of the homogenizing kettle 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 temperature of the last section of the melting screw machine 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 temperature of the last section of the melting screw machine 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 the ring-opening catalyst is injected into the pipeline connecting the homogenizing kettle 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 a prepolymer; the amount of the ring-opening catalyst is 0.001-5.000wt% of the cyclic ester monomer.

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

[0086] As a preferred solution, the static reactor 2 adopts at least two stages of gradient temperature increase, and the temperature of the last stage is below the melting point of the polymer Tm+30°C to prevent the polymer from being degraded due to excessive temperature. For example, the Tm of polyglycolic acid is about 220°C, the first temperature range is between 120-200°C, and the temperature range of the last stage is between 200-250°C.

[0087] 3. The first modification stage: the prepolymer is passed through a first mixing and modification device 3 (preferably a mixing screw machine), and a first modifier (for example, a capping agent, a heat stabilizer, a chain extender, etc.) is added to the middle section of the mixing screw machine to mix with the prepolymer to obtain a first modified material; the temperature of the mixing screw machine is set according to the melting point of the polymer, the temperature range is Tm to Tm+30°C, Tm is the melting point of the polymer, and the residence time of the material in the mixing screw machine is 0.5 to 5 min.

[0088] 4. Devolatilization stage: the first modified material is passed through a static devolatilizer 4, where final polymerization and volatiles are removed to obtain polyester, and the volatiles enter a vacuum circulation device 6; the temperature of the static devolatilizer 4 is set according to the melting point of the polymer, the temperature range is Tm to Tm+40°C, and the residence time is 1 to 15 minutes; the absolute pressure in the static devolatilizer 4 is 1Pa to 101kPa.

[0089] Furthermore, a gas distributor is provided at the bottom of the static devolatilizer 4. The gas distributor is annular and has a plurality of through holes. After the gas is introduced into the gas distributor, the gas flows from bottom to top under the action of vacuum, which can increase the partial pressure of small molecules in the gas phase and take away the small molecules, thereby making it more conducive to the removal of small molecules from the melt. The temperature of the introduced gas is consistent with the temperature of the static devolatilizer 4, and the gas volume corresponding to the polymer output is 0.06-30m 3 / kg.

[0090] The first modified material passes through the static devolatilizer 4 to remove volatiles under vacuum, and the volatiles are sprayed and condensed by the vacuum circulation device 6 to achieve volatile recycling and unobstructed vacuum pipelines, thereby maintaining the vacuum degree in the system.

[0091] 5. Second modification stage: the polyester is passed through a second mixing and modification device 5 (preferably a discharging screw machine), and a second modifier (for example, an antioxidant, an anti-hydrolysis agent, a dehydrating agent, etc.) is added at the end of the discharging screw machine to mix with the polyester to obtain a modified polyester; the temperature of the discharging screw machine is set according to the melting point of the polymer, the temperature range is Tm to Tm+30°C, and the residence time of the material in the discharging screw machine is 0.5 to 5 minutes.

[0092] Further:

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

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

[0095] The melting screw machine, the mixing screw machine and the discharging screw machine can adopt conventional single screw machines or twin screw machines.

[0096] The end-capping agent is selected from one or more monomers or polymers containing terminal hydroxyl groups, terminal amine groups 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 metal soap heat stabilizers, organotin heat stabilizers or rare earth heat stabilizers; for example, zinc stearate, calcium stearate, magnesium stearate, sulfur-containing organotin, 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 phenol antioxidants, phosphite antioxidants, thioether antioxidants, etc.; for example, commercially available BASF Irganox 245, BASF Irganox 1010, BASF Irganox 1076.

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

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

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

[0103] In the above-mentioned continuous production process, the volatiles enter the vacuum circulation device 6 and undergo the following process: the volatiles pass through the primary spray condenser 61 and the secondary spray condenser 62 in sequence under the action of the vacuum pump 65. The primary spray condenser 61 and the secondary spray condenser 62 are equipped with liquid spray pipelines above them. The spray liquid mainly selects good solvents of cyclic esters, such as ethyl acetate, methyl glycolate, ethanol, isopropanol, propanol, etc. The spray condensation method can prevent small molecules in the volatiles from clogging the spray condenser through dissolution and flushing, thereby achieving the stability of the system vacuum degree and the long-term stable operation of the vacuum equipment.

[0104] As a preferred solution, the dosage of the first-stage spray liquid and the dosage of the second-stage spray liquid are between 0.01 L / min and 10 L / min, and the dosage of the two-stage spray liquid can be different; if the spray volume is too much, it is 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 first-stage spray condenser 61 and the second-stage spray condenser 62 is transported to the gas-liquid separator 64 through the output pump 66, and the spray liquid is vaporized and separated by heating. The separated spray liquid is condensed and liquefied through the condenser 63, and then transported to the liquid phase spray pipeline through the delivery pump 67 for circulation as spray liquid.

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

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

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

[0109] Test indicators and test methods:

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

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

[0112] 2. Weight average molecular weight and molecular weight distribution: measured by gel chromatography (GPC), the sample was dissolved in hexafluoroisopropanol solution to prepare a 0.05% to 0.3% (mass fraction) solution; filtered with a polytetrafluoroethylene filter membrane; 20 μL was added to the GPC injector, and the molecular weight was calibrated using 5 standard polymethyl methacrylates with different molecular weights.

[0113] 3. Melt index deviation Δλ: The melt mass flow rate is measured in accordance with GB / T 3682 Melt mass flow rate and melt flow rate of thermoplastics, and condition A in Appendix A is selected, i.e. the test temperature is 250°C and the nominal load is 2.16 kg.

[0114] The test method is to dry the material under vacuum conditions at (70±2)℃ for (24±1)h; set the test temperature of the instrument to 250℃ and preheat for 10min; weigh 5-10g of sample, load it through the funnel and insert the push rod into the barrel to compact the material; control the feeding time within 1min and keep it warm for 4min, put a 2.16kg weight on the top of the push rod, cut a section every 30s, a total of five sections; weigh the mass of each section of sample and convert it into the melt index MI1. Control the feeding time within 1min and keep it warm for 10min, put a 2.16kg weight on the top of the push rod, cut a section every 30s, a total of five sections; weigh the mass of each section of sample and convert it into the melt index MI2.

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

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

[0117] Δλ=(MI2-MI1) / MI1

[0118] 4. Determination of terminal carboxyl groups: Place a certain amount of the treated sample into a conical flask filled with a solvent, heat it in an oil bath until it is fully dissolved, take it out while hot, add an indicator, and titrate it with a certain concentration of potassium hydroxide-ethanol solution. When the indicator changes to the target color, it is the titration end point.

[0119] Under the same conditions, the reagent blank was measured. The content of terminal carboxyl groups was calculated by formula (1):

[0120]

[0121] Where, X is the carboxyl content of the sample, mol·t -1 ; V is the volume of potassium hydroxide ethanol solution consumed by the titration sample, mL; V0 is the volume of potassium hydroxide ethanol solution consumed by the blank, mL; c is the concentration of potassium hydroxide ethanol solution, mol·L -1 ; m is the mass of the sample, g.

[0122] Example 1

[0123] 1) A certain amount of glycolide is added to a melting screw machine and completely melted in the melting screw machine at 70-120° C. The molten glycolide is first stored in a homogenizing kettle (120° C.) with stirring, and then introduced into a static reactor. At the same time, a ring-opening catalyst (tin dichloride dihydrate, 0.5 wt%) is injected into a pipeline connecting the homogenizing kettle and the static reactor through a metering pump to be evenly mixed 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 multi-stage step-by-step heating method. The temperature of the first stage is set to about 150° C., and the time to pass through the first stage is about 10 minutes. The temperature of the second stage is set to about 190° C., and the time to pass through the second stage is about 30 minutes. The temperature of the third stage is set to about 220° C., and the time to pass through the third stage is about 60 minutes.

[0124] 2) introducing the glycolic acid prepolymer into a mixing screw machine, and adding 0.05 wt % of oxalic acid (capping agent) and 0.05 wt % of calcium stearate (heat stabilizer) in the middle section of the mixing screw machine to obtain a first modified material, the temperature of the mixing screw machine is set to about 230° C., and the residence time of the material in the mixing screw machine is 3 min;

[0125] 3) passing the first modified material through a static devolatilizer, performing final polymerization and removing volatiles in the static devolatilizer to obtain polyglycolic acid, wherein the static devolatilizer temperature is set at 230° C., the static devolatilizer absolute pressure is 10 kPa, and the nitrogen volume corresponding to the polymer output is 0.3 m 3 / kg, the residence time of the material in the static devolatilizer is 10min; the volatiles pass through the primary spray condenser and the secondary spray condenser, ethyl acetate is used to spray above the primary spray condenser and the secondary spray condenser, the temperature of the condenser is set at 20℃, the temperature of the gas-liquid separator is set at 95℃, the dosage of the primary spray liquid is 2L / min, and the dosage of the secondary spray liquid is 0.06L / min;

[0126] 4) The polyglycolic acid is passed through a discharging screw machine, and 0.05 wt % of an antioxidant BASF Irganox 1010 and 0.05 wt % of a dehydrating agent dicyclohexylcarbodiimide are added at the end of the discharging screw machine to obtain a modified polyester. The temperature of the mixing screw machine is set at about 230° C., and the material stays in the mixing screw machine for 3 minutes.

[0127] Example 2

[0128] The same as Example 1, except that the absolute pressure in the static devolatilizer is 80 kPa and the nitrogen volume corresponding to the polymer output is 12 m 3 / kg.

[0129] Example 3

[0130] The same as Example 1, except that the absolute pressure in the static devolatilizer is 100 Pa and the nitrogen volume corresponding to the polymer output is 0m 3 / kg, that is, no gas is introduced into the static devolatilizer, and there is no need to set a vent and a gas distributor at the bottom of the static devolatilizer.

[0131] Example 4

[0132] 1) A certain amount of glycolide is added to a melting screw machine and completely melted in the melting screw machine at 70-120° C. The molten glycolide is first stored in a homogenizing kettle (120° C.) with stirring, and then introduced into a static reactor. At the same time, a ring-opening catalyst (stannous octoate, 1wt%) is injected into a pipeline connecting the homogenizing kettle and the static reactor through a metering pump to be evenly mixed 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 step-by-step heating method, the temperature of the first stage is set to about 170° C., the time to pass through the first stage is about 20 minutes, and the temperature of the second stage is set to about 230° C., the time to pass through the second stage is about 20 minutes;

[0133] 2) introducing the glycolic acid prepolymer into a mixing screw machine, and adding 0.05 wt % of ethylene glycol (capping agent) and 0.05 wt % of calcium stearate (heat stabilizer) in the middle section of the mixing screw machine to obtain a first modified material, the temperature of the mixing screw machine is set to about 230° C., and the residence time of the material in the mixing screw machine is 1 min;

[0134] 3) passing the first modified material through a static devolatilizer, performing final polymerization and removing volatiles in the static devolatilizer to obtain polyglycolic acid, wherein the temperature of the static devolatilizer is set at 240° C., the absolute pressure in the static devolatilizer is 10 kPa, and the nitrogen volume corresponding to the polymer output is 6 m 3 / kg, the residence time of the material in the static devolatilizer is 5min; the volatiles pass through the primary spray condenser and the secondary spray condenser, ethyl acetate is sprayed on the primary spray condenser and the secondary spray condenser, the temperature of the condenser is set at 10℃, the temperature of the gas-liquid separator is set at 95℃, the dosage of the primary spray liquid is 2L / min, and the dosage of the secondary spray liquid is 0.06L / min;

[0135] 4) The polyglycolic acid is passed through a discharging screw machine, and 0.05 wt % of an antioxidant BASF Irganox 1010 is added at the end of the discharging screw machine to obtain a modified polyester. The temperature of the mixing screw machine is set at about 230° C., and the material stays in the mixing screw machine for 1 min.

[0136] Example 5

[0137] The same as Example 4, except that the absolute pressure in the static devolatilizer is 1 kPa and the nitrogen volume corresponding to the polymer output is 3 m 3 / kg.

[0138] Comparative Example 1

[0139] The process is basically the same as Example 4, except that the glycolic acid prepolymer obtained in step 1) is directly introduced from the static reactor into the static devolatilizer, step 2) is omitted, and in step 4), 0.05 wt% of ethylene glycol (capping agent), 0.05 wt% of calcium stearate (heat stabilizer) and 0.05 wt% of antioxidant BASF Irganox 1010 are added together at the end of the discharge screw.

[0140] Comparative Example 2

[0141] The method is basically the same as Example 4, except that the residence time of the material in the static devolatilizer is 30 min.

[0142] Comparative Example 3

[0143] The method is basically the same as Example 4, except that in step 3), the first modified material is passed through a twin-screw extruder provided with only a devolatilization section, and final polymerization and devolatilization 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 aspect ratio of the screw is about 50, and the time for the material to pass through the twin-screw extruder is 5 minutes.

[0144] Table 1

[0145]

[0146]

[0147] As shown in Table 1, among Examples 1 to 3, Example 3 has the highest monomer conversion rate, and the lowest molecular weight distribution, melt index deviation value and terminal carboxyl content; among Examples 4 to 5, Example 5 has the highest monomer conversion rate, and the melt index deviation value and terminal carboxyl content are lower, indicating that in the devolatilization stage, the lower the absolute pressure in the static devolatilizer, the more conducive it is to improve the monomer conversion rate, reduce the residual unreacted monomer, and improve the thermal stability of the polymer. However, the lower the absolute pressure means the higher the requirements for equipment and pipelines. In actual continuous production, there are fluctuations in pressure, resulting in differences in the product performance of the modified polyester obtained. By introducing gas into the static devolatilizer and appropriately reducing the vacuum degree in the static devolatilizer, a polymer product with excellent performance can also be obtained.

[0148] Comparative Example 1 omits the first modification stage. Compared with Example 4, the monomer conversion rate of the modified polyester obtained is lower, and the melt index deviation value and the terminal carboxyl content are higher, indicating that the timing of adding the first modifier in the production process has an impact on the performance of the polymer. It is speculated that the first modifier (for example, end-capping agent, thermal stabilizer, etc.) is added before the devolatilization stage. The first modifier can inhibit the unexpected thermal degradation of the polymer in the devolatilization stage. The thermal degradation of the polymer and the repolymerization of the molecular chain segments under high temperature environment are a dynamic process. The devolatilization time of Comparative Example 2 is too long, resulting in excessive thermal degradation of the polymer and a significant increase in the melt index deviation value; Comparative Example 3 uses a twin-screw extruder as the devolatilization equipment. At the same devolatilization temperature and devolatilization time, the monomer conversion rate of the modified polyester obtained is above 99.5%, but the melt index deviation value and the terminal carboxyl content are higher. It is speculated that under the influence of high shear heat in the twin-screw extruder, the thermal degradation of the polymer increases.

[0149] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and 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 present invention should be within the scope of protection of the present invention.

Claims

1. A continuous production system for modified polyester, characterized in that: It comprises a melting device (1), a static reactor (2), a first mixing and modifying device (3), a static devolatilizer (4) and a second mixing and modifying device (5) which are connected in sequence; The melting device (1) is provided with a cyclic ester monomer feed port, the first mixing and modifying device (3) is provided with a first modifier feed port, the static devolatilizer (4) is provided with an air outlet, and the second mixing and modifying 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), wherein the vacuum circulation device (6) comprises a spray condenser and a vacuum pumping assembly connected to the spray condenser, wherein the spray condenser is connected to the gas outlet of the static devolatilizer (4).

2. The continuous production system of modified polyester according to claim 1, characterized in that: The melting device (1) comprises a melting screw machine (11) and / or a homogenizing kettle (12); The melting screw machine (11) is a single screw machine or a twin screw machine, and the homogenizing kettle (12) is a homogenizing kettle with stirring; A ring-opening catalyst feed port is provided on the pipeline connecting the melting device (1) and the static reactor (2).

3. The continuous production system of modified polyester according to claim 1, characterized in that: The first mixing and modifying device (3) and the second mixing and modifying device (5) are both single-screw machines or twin-screw machines; The first modifier feed port is arranged at the middle section of the screw machine, and the second modifier feed port is arranged at the end section of the screw machine.

4. The continuous production system of modified polyester according to claim 1, characterized in that: An air inlet and a gas distributor connected to the air inlet are arranged at the bottom of the static devolatilizer (4); the gas distributor is annular and has a plurality of through holes distributed on the annular structure of the gas distributor.

5. The continuous production system of modified polyester according to any one of claims 1 to 4, characterized in that: The spray condenser comprises a primary spray condenser (61) and a secondary spray condenser (62), and the vacuum pumping component comprises a vacuum pump (65); The gas phase inlet of the first-stage spray condenser (61) is communicated with the gas outlet of the static devolatilizer (4), the gas phase outlet of the first-stage spray condenser (61) is communicated with the gas phase inlet of the second-stage spray condenser (62), the gas phase outlet of the second-stage spray condenser (62) is connected to the vacuum pump (65), and liquid phase spray pipelines are provided above the gas phase inlets of the first-stage spray condenser (61) and the second-stage spray condenser (62); preferably, a filter layer is also provided above the gas phase inlet of the first-stage spray condenser (61); The vacuum circulation device further comprises a condenser (63), a gas-liquid separator (64), an output pump (66) and a delivery pump (67); The bottom of the first-stage spray condenser (61) and the second-stage spray condenser (62) are connected to the gas-liquid separator (64) through the output pump (66), the gas phase outlet of the gas-liquid separator (64) is connected to the steam inlet of the condenser (63), and the condensate outlet of the condenser (63) is connected to the liquid phase spray pipeline above the first-stage spray condenser (61) and the second-stage spray condenser (62) through the delivery pump (67).

6. A method for continuous production of modified polyester, characterized in that: The method is carried out using the system according to any one of claims 1 to 5, comprising the following steps: The cyclic ester monomer is conveyed into the melting device (1) through the cyclic ester monomer feed port, and a molten material is obtained after heating and melting, and the molten material is conveyed to a static reactor (2), and the molten material is polymerized in the static reactor (2) to 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 feed port to obtain a first modified material; The first modified material is passed through the static devolatilizer (4), and final polymerization and volatile removal are performed in the static devolatilizer (4) to obtain polyester. The volatiles enter the vacuum circulation device (6), and after spraying and condensing in the spray condenser, a solid-liquid mixture is obtained; The polyester is passed through the second mixing and modifying device (5) and mixed with the second modifier added from the second modifier feed port to obtain a modified polyester, and the modified polyester is discharged from the modified polyester discharge port.

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 further comprises a ring-opening catalyst, wherein the ring-opening catalyst comprises one or more divalent metal chlorides 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 an end-capping agent, a thermal stabilizer, and a chain extender; The second modifier includes one or more of an antioxidant, an anti-hydrolysis agent, and a dehydrating agent; The amount of each first modifier added to the first mixing and modifying device (3) is 0.01-2 wt % of the cyclic ester monomer, preferably not more than 1 wt %; The amount of each second modifier added to the second mixing and modifying device (5) is 0.01-2 wt % of the cyclic ester monomer, preferably not more than 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°C to Tm'+40°C, where Tm' is the melting point of the cyclic ester monomer; The reaction temperature of the static reactor (2) is Tm'+5°C to Tm+30°C, Tm' is the melting point of the cyclic ester monomer, Tm is the melting point of the polymer, and the reaction time is 0.5 to 12 hours; The temperature of the first mixing and modifying device (3) is Tm-Tm+30°C, Tm is the melting point of the polymer, and the material residence time is 0.5-5 min; The temperature of the static devolatilizer (4) is Tm-Tm+40°C, Tm is the melting point of the polymer, the material residence time is 1-15 min, the absolute pressure is 1 Pa-101 kPa, and gas is continuously introduced into the static devolatilizer (4), the temperature of the gas is the same as the temperature inside the static devolatilizer (4), and the ratio of the volume of the gas introduced to the output of the modified polyester is 0.06-30 m 3 / kg; The temperature of the second mixing and modifying device (5) is Tm-Tm+30°C, Tm is the melting point of the polymer, and the material residence time is 0.5-5 min.

10. The continuous production method of modified polyester according to claim 9, characterized in that: The volatiles are sprayed and condensed in the first-stage spray condenser (61) and the second-stage spray condenser (62) in sequence, 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 amount used is 0.01 L / min to 10 L / min; The solid-liquid mixture in the first-stage spray condenser (61) and the second-stage spray condenser (62) is transported to the gas-liquid separator (64), and the spray liquid is vaporized by heating. The vaporized spray liquid enters the condenser (63) for condensation and liquefaction, and is then transported to the first-stage spray condenser (61) and the second-stage spray condenser (62) to continue to be used as the spray liquid.

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