A production system and a production method for increasing the molecular weight of aromatic polycarbonate

Abstract

The application provides a production system and method for improving the molecular weight of aromatic polycarbonate, and the production system comprises a stirring pre-polymerizer, a falling film polymerizer, a condensing system, a vacuum system, a heat medium system, an extrusion and pelletizing system; the method is characterized in that aromatic polycarbonate with a dynamic viscosity of 20-600 Pa.s flows on the heatable falling film support in the falling film polymerizer from the stirring pre-polymerizer, and the falling film flow is used to remove the volatile molecular chain growth polycondensation reaction, and the molten material with the improved molecular weight has a dynamic viscosity of 100-10000 Pa.s at 280 DEG C. The system and the production method can quickly remove the volatile by-products, the reaction temperature is accurately and uniformly controllable, the side reaction is less, and accordingly, high-quality polycarbonate with high molecular weight and low melt index can be obtained.

Description

Technical Field

[0001] This invention relates to the field of polycarbonate technology, and in particular to a production system and method for increasing the molecular weight of aromatic polycarbonates. Background Technology

[0002] Aromatic polycarbonates possess excellent impact strength, transparency, resistance to high and low temperatures, electrical insulation, and dimensional stability due to the alternating combination of soft carbonate bonds and rigid arylene alkyl groups in their molecular chains. They have wide applications in fields such as electronics and electrical equipment, building materials, optical instruments, packaging, and the automotive industry.

[0003] Industrially, polycarbonate is mainly produced through two methods: melt transesterification polycondensation and solution phosgenation interfacial polycondensation. In the phosgene process, the reaction temperature is low, avoiding high-temperature side reactions. The molecular weight of the polycarbonate is easily adjustable, producing high-molecular-weight, colorless, transparent, high-quality products. Furthermore, the production equipment for this process is easily scalable, making it the mainstream process for polycarbonate manufacturers. However, the phosgene process also has significant drawbacks, such as a long process flow, the use of highly toxic and ozone-depleting phosgene, and the use of dichloromethane as a solvent, resulting in a large amount of chlorine-containing impurities in the aqueous phase, severely polluting the environment. The presence of these impurities also negatively impacts the produced polycarbonate.

[0004] Non-phosgene melt transesterification has advantages such as a short process flow, solvent-free operation, and a fully enclosed process, allowing for the recycling of byproducts. However, due to the high dynamic viscosity and temperature sensitivity of aromatic polycarbonates, the polycondensation process at high temperatures is prone to increased side reactions such as rearrangement and crosslinking, resulting in poorer flowability, difficulty in increasing molecular weight, and a wider molecular weight distribution, leading to reduced product elongation properties and decreased stability. For non-phosgene melt transesterification polycondensation, the core technology lies in how to overcome the challenges of mass transfer difficulties and thermodynamic instability in high-viscosity reaction systems by strictly controlling the thermodynamics of the polymerization process, achieving efficient removal and separation of byproducts, and minimizing side reactions while increasing molecular weight. This places extremely high demands on the production system and method of non-phosgene melt transesterification polycondensation. There is an urgent need to develop a thermodynamically stable polycarbonate production system and method capable of efficiently removing and separating byproducts. Summary of the Invention

[0005] The first objective of this invention is to provide a production system for increasing the molecular weight of aromatic polycarbonates in order to prepare high-quality aromatic polycarbonate products. The following technical solution is adopted for this purpose:

[0006] A production system for increasing the molecular weight of aromatic polycarbonates is characterized by comprising a stirred prepolymer, a falling film polymerizer, a condensation system, a vacuum system, a heat transfer system, and an extrusion and pelletizing system.

[0007] The prepolymerizer adopts a stirred structure to carry out the prepolymerization reaction of aromatic polycarbonate, providing the basic melt for the falling film polymerizer to further increase the molecular weight. The dynamic viscosity of the basic melt at 280°C is 20-600 Pa·s.

[0008] The falling film polymerizer has one or more falling film supports that can support the melt during the falling film flow reaction. The falling film support is a slender rod-shaped body, vertically installed, with a hollow internal structure. The outer surface is in contact with the molten material, and the inner surface is in contact with the heat medium. The molten material provided by the prepolymerizer flows from top to bottom in the falling film polymerizer and simultaneously undergoes a molecular chain growth and condensation reaction to remove volatiles. The molten material with increased molecular weight has a dynamic viscosity of 100-10000 Pa·s at 280°C. The dynamic viscosity of the melt after the reaction in the falling film polymerizer is more than double that before the reaction. The material flowing out of the falling film polymerizer enters the extrusion and pelletizing system.

[0009] The condensation system is connected to a falling film polymerizer before and a vacuum system after, and includes condensation, purification and separation devices for condensing and separating the volatiles flowing in from the falling film polymerizer.

[0010] The vacuum system is connected to the condensation system, providing vacuum power to facilitate the condensation reaction that promotes molecular chain growth.

[0011] The heat transfer system includes a heat transfer medium that provides energy and heat exchange for the falling film polymerizer used for the reaction and the condensation system used for the separation of volatiles, as well as its flow path and storage and power devices.

[0012] The extrusion and pelletizing system includes mixing and extrusion, cooling and pelletizing devices for conveying, mixing, cooling and pelletizing materials from the falling film polymerizer.

[0013] Furthermore, the falling film polymerizer includes an inlet and conduit for the molten material to flow in, a distributor, three or more falling film supports for supporting the melt to undergo falling film flow reaction, an exhaust port, a discharge port for discharging high-viscosity melt, a discharge device, and a liquid level meter for monitoring the liquid level at the bottom of the polymerization unit. The polymerizer shell is equipped with a polymerizer jacket. The molten material flowing into the falling film polymerizer is the base melt, including polycarbonate molten prepolymer.

[0014] Furthermore, the condensation system includes a vertical spray condenser and its connected liquid seal tank, a hydroxyl compound separation and purification device, a diaryl carbonate separation and purification device, a condensate cooler, and a heating / condensation medium passage.

[0015] Furthermore, the vacuum system includes a vacuum pump assembly and at least one vacuum buffer tank. The vacuum pump assembly is connected to the vacuum buffer tank and the condenser. A small amount of uncondensed exhaust gas in the condenser enters the vacuum buffer tank and is trapped therein. The bottom of the vacuum buffer tank is provided with a drain port for discharging the liquid accumulated in the vacuum buffer tank. The exhaust gas that is not trapped by the vacuum buffer tank is extracted by the vacuum pump assembly.

[0016] Preferably, to further improve the by-product condensation rate and accelerate the devolatilization efficiency, two or more condensers and vacuum buffer tanks can be connected in series to form a multi-stage combined extractant condensation system.

[0017] Furthermore, the heat medium system includes channels for the flow of heat medium in the falling film support and polymer jacket of the polymerizer, the discharge melt pipeline, and heat medium circulation pumps, heat medium heaters, and heat medium expansion tanks, as well as channels for the flow of heating / cooling medium and heating / cooling medium circulation pumps and condensate coolers for controlling the temperature of the condenser, condensate cooler, and vacuum buffer tank.

[0018] Furthermore, the extrusion and pelletizing system includes a twin-screw extruder with a mixing function, a pelletizer, and a pelletizing water system. The extruder is equipped with a feed valve for injecting additives, the pelletizer is equipped with a dryer and a vibrating screen, and a filter is provided between the twin-screw extruder and the pelletizer.

[0019] Furthermore, the falling film polymerizer is provided with a falling film support heat medium inlet and a falling film support heat medium outlet. The falling film support has a channel for heat medium to flow. The polymerizer jacket is provided with a polymerizer jacket heat medium outlet and a polymerizer jacket heat medium inlet. The heat medium inside the falling film support and the heat medium in the polymerizer jacket are connected to the same heat medium system as the outside, ensuring that the temperature of the falling film support is consistent with the temperature of the falling film polymerizer wall, so as to accurately control the falling film reaction temperature. The condenser, liquid seal tank, condensate cooler and vacuum buffer tank in the condensation system are all provided with heating / cooling medium inlets and heating / cooling medium outlets as well as independently controllable temperature control systems.

[0020] Furthermore, the volatiles extracted from the falling film polymerizer are captured and collected by the spray liquid in the condenser and then enter the liquid seal tank. The condensate passes through the hydroxyl compound separation and purification device and the diaryl carbonate separation and purification device, and is then transported by the condensate circulation pump through the condensate cooler in the heat medium system. The cooled condensate is then transported to the spray condenser for recycling. The separated hydroxyl compounds and diaryl carbonates can be used as raw materials for polycarbonate reaction after purification.

[0021] Furthermore, the falling film polymerizer and the path through which the molten material passes are made of at least one of 904L stainless steel and 316L stainless steel, and the equipment in the vacuum system and condensation system is made of at least one of 316L stainless steel and 304L stainless steel.

[0022] Based on the production system described in the above technical solution, the present invention also provides a production method for increasing the molecular weight of aromatic polycarbonate, comprising the following steps:

[0023] (1) The product obtained by transesterification reaction of diaryl carbonate and aromatic dihydroxy compound is fed into a stirred prepolymerizer for prepolymerization reaction. The prepolymerization reaction temperature is 200-300℃, the absolute pressure in the prepolymerizer is 0.2kPa-8kPa, and the output after the reaction is a basic melt with a dynamic viscosity of 20-600Pa·s at 280℃.

[0024] (2) The basic melt flows from the feed inlet into the distributor through the conduit on the falling film polymerizer, and is then distributed by the distributor to the outer surface of the falling film support, which can be precisely controlled in temperature, to flow to the bottom of the polymerizer. The molecular weight of the molten material is increased. The reaction temperature in the falling film polymerizer is 260~290℃ and the pressure is 0.005kPa~0.3kPa.

[0025] (3) The molten material at the bottom of the polymerizer is homogenized by the discharge device and discharged. The dynamic viscosity of the discharged melt is 100 to 10000 Pa·s at 280℃. The dynamic viscosity of the melt after the reaction in the falling film polymerizer is more than doubled compared with that before the reaction. It is sent to the extrusion pelleting system for pelleting or modified mixing with added components and then pelletized to obtain high-quality aromatic polycarbonate resin products.

[0026] Furthermore, in step (2), the flow rate of the molten material flowing into each falling film support in the falling film polymerizer is 1 to 200 kg per hour.

[0027] According to production needs, in the above-mentioned production method for increasing the molecular weight of aromatic polycarbonate, the added component in step (3) can be one or more of semi-aromatic polyester, polyamide, acrylonitrile-butadiene-styrene copolymer, polyolefin, polystyrene, polymethyl methacrylate, acrylate, and polyurethane, with an addition amount of 1% to 50%. The preferred option is to mix the added component with the polycarbonate melt in an extruder and then extrude it.

[0028] According to production needs, in the above-mentioned production method for increasing the molecular weight of aromatic polycarbonate, the added component in step (3) is one or more of flame retardants, heat stabilizers, antioxidants, antibacterial agents, defoamers, and quenchers, with an addition amount of 0.1% to 10%. The preferred option is to add the modifier online in the melt flow path after the falling film reaction or introduce it into the extruder to mix with the polycarbonate melt before extrusion.

[0029] The melt dynamic viscosity described in this invention refers to the melt flowability test of polyaramid polycarbonate materials in a protected gas environment at 280°C using an instrument with characterizing viscosity or rheological properties, with the melt shear rate in the range of 0.1 rad / s to 100 rad / s.

[0030] According to the above production system, the aromatic polycarbonate melt undergoes a falling film flow reaction from top to bottom in the falling film polymerizer. The melt has good fluidity, a fast surface renewal rate, and high efficiency in removing volatile by-products produced by the reaction. This promotes the forward reaction and increases the molecular chain length. Furthermore, the reaction temperature is precisely controllable, and the temperature is uniform throughout the polymerizer, which can effectively reduce the occurrence of side reactions such as branching, rearrangement, and crosslinking. The material residence time is easy to control, which can effectively adjust the molecular weight and molecular weight distribution width of polycarbonate.

[0031] By adopting the above technical solution, the volatiles extracted from the polymerizer exhaust port can be rapidly cooled in the condenser. The design and layout of the condensation system and the heat transfer system, as well as the convenient adjustment of the condensation system temperature according to the volatile properties, can prevent the volatiles from solidifying and clogging the channels. The liquid seal tank plays a buffering role in the collection of condensate and the separation of components. In addition, the separation and purification device can effectively recover and reuse hydroxyl compounds and diaryl carbonates, thereby reducing the raw material loss rate. The exhaust gas that has not been fully condensed is intercepted by the vacuum buffer tank, which improves the efficiency of the vacuum pump group.

[0032] In a specially designed polycarbonate production system, by rationally controlling the dynamic viscosity range of molten material flowing within a falling film reactor, and optimizing process parameters such as reaction temperature, heat exchange rate, pressure, and mass flow rate, the flow behavior of high-viscosity materials is effectively regulated. This allows the material to undergo a forward reaction under more suitable thermodynamic conditions, with residence time matching the reaction progress. This improves the removal efficiency of aromatic polycarbonate byproducts such as phenol, suppresses the easy decomposition of some substances at high temperatures to generate highly reactive, unsaturated organic compounds, and reduces side reactions such as rearrangement, branching, and crosslinking during the melt polycondensation process. This overcomes the defects of difficulty in increasing polymer molecular weight, a wide molecular weight distribution, increased impurities, and decreased product quality. Therefore, by adopting the technical solution provided by this invention, high-quality high-molecular-weight polycarbonate products can be obtained. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the aromatic polycarbonate production system proposed in this invention.

[0034] Explanation of reference numerals in the attached drawings: 1. Falling film polymerizer; 2. Feed inlet; 3. Conduit; 4. Liquid distributor; 5. Falling film support; 6. Discharge device; 7. Discharge port; 8. Air extraction port; 9. Condenser; 10. Liquid seal tank; 11. Hydroxyl compound separation and purification device; 12. Diphenyl carbonate separation and purification device; 13. Condensate circulation pump; 14. Condensate cooler; 15. Vacuum buffer tank; 151. Drain port; 16. Vacuum pump set; 17. Discharge gear pump; 18. Feed valve; 19. Twin-screw extruder; 20. Filter; 21. Pelletizer; 22. Stirred polymerizer. Detailed Implementation

[0035] The following combination Figure 1 Specific embodiments of the present invention will be described below.

[0036] Reference Figure 1 The present invention provides a production system for increasing the molecular weight of aromatic polycarbonate, comprising: a stirred prepolymer 22, a falling film polymerizer 1, a condensation system, a vacuum system, a heat transfer system, and an extrusion and pelletizing system.

[0037] The prepolymerizer 22 adopts a stirring structure to carry out the prepolymerization reaction of aromatic polycarbonate, providing the falling film polymerizer 1 with the basic melt that needs to be further improved in molecular weight. The dynamic viscosity of the basic melt at 280°C is 20-600 Pa·s.

[0038] The falling film polymerizer 1 has one or more falling film supports 5 that can support the melt to undergo falling film flow reaction. The falling film support 5 is a slender rod-shaped body, vertically installed, with a hollow internal structure. The outer surface is in contact with the molten material, and the inner surface is in contact with the heat medium. The molten material provided by the prepolymerizer 22 undergoes falling film flow from top to bottom in the falling film polymerizer 1, while simultaneously carrying out a molecular chain growth and condensation reaction to remove volatiles. The molten material with increased molecular weight has a dynamic viscosity of 100 to 10000 Pa·s at 280°C. The material flowing out of the falling film polymerizer 1 enters the extrusion and pelletizing system.

[0039] The condensation system is connected to the falling film polymerizer 1 in front and to the vacuum system behind, including condensation, purification and separation devices, for condensing and separating the volatiles flowing in from the falling film polymerizer 1.

[0040] The vacuum system is connected to the condensation system, providing vacuum power to facilitate the condensation reaction that promotes molecular chain growth.

[0041] The heat transfer system includes a heat transfer medium that provides energy and heat exchange for the falling film polymerizer 1 used for the reaction and the condensation system used for separating volatiles, as well as its flow path and storage and power devices.

[0042] The extrusion and pelletizing system includes mixing and extrusion, cooling and pelletizing devices for conveying, mixing, cooling and pelletizing materials from the falling film polymerizer.

[0043] Furthermore, the falling film polymerizer 1 includes an inlet 2 and a conduit 3 for the molten material to flow in, a distributor, three or more falling film supports 5 for supporting the melt to undergo falling film flow reaction, an exhaust port 8, a discharge port 7 for discharging high-viscosity melt, a discharge device 6, and a liquid level meter for monitoring the liquid level at the bottom of the polymerization unit. The polymerizer 1 is equipped with a polymerizer jacket on its outer shell. The molten material flowing into the falling film polymerizer 1 is the base melt, which includes polycarbonate molten prepolymer.

[0044] Furthermore, the condensation system includes a vertical spray condenser 9 and its connected liquid seal tank 10, a hydroxyl compound separation and purification device 11, a diaryl carbonate separation and purification device 12, a condensate cooler 14, and a heating / condensation medium passage.

[0045] Furthermore, the vacuum system includes a vacuum pump assembly 16 and at least one vacuum buffer tank 15. The vacuum pump assembly 16 is connected to the vacuum buffer tank 15 and the condenser 14. A small amount of uncondensed exhaust gas in the condenser 14 enters the vacuum buffer tank 15 and is trapped therein. The bottom of the vacuum buffer tank 15 is provided with a drain port 151 for discharging the liquid accumulated in the vacuum buffer tank 15. The exhaust gas that is not trapped by the vacuum buffer tank 15 is extracted by the vacuum pump assembly 16.

[0046] Preferably, in order to further improve the by-product condensation rate and accelerate the devolatilization efficiency, two or more condensers 9 and vacuum buffer tanks 15 can be connected in series to form a multi-stage combined extractant condensation system.

[0047] Furthermore, the heat medium system includes channels for the flow of heat medium in the falling film support 5 and the polymerizer jacket in the polymerizer 1, as well as heat medium circulation pumps, heat medium heaters, and heat medium expansion tanks, and heating / cooling medium flow channels and heating / cooling medium circulation pumps and condensate coolers 14 for controlling the temperature of the condenser 9, condensate cooler 14 and vacuum buffer tank 15.

[0048] Furthermore, the extrusion and pelletizing system includes a twin-screw extruder 19 with a mixing function, a pelletizer 21, and a pelletizing water system. The extruder is equipped with a feed valve 18 for injecting additives, and the pelletizer 21 is equipped with a dryer and a vibrating screen. A filter 20 is provided between the twin-screw extruder 19 and the pelletizer 21.

[0049] Furthermore, the falling film polymerizer 1 is provided with a falling film support 5 for a heat medium inlet and a falling film support 5 for a heat medium outlet. The falling film support 5 has a channel for the flow of heat medium. The jacket of the polymerizer 1 is provided with a jacket heat medium outlet and a jacket heat medium inlet. The heat medium in the falling film support 5 and the jacket heat medium of the polymerizer 1 are connected to the same heat medium system as the outside world, ensuring that the temperature of the falling film support 5 is consistent with the wall temperature of the falling film polymerizer 1, so as to accurately control the falling film reaction temperature. The condenser 9, liquid seal tank 10, condensate cooler 14 and vacuum buffer tank 15 in the condensation system are all provided with a heating / cooling medium inlet and a heating / cooling medium outlet, as well as an independently controllable temperature control system.

[0050] Furthermore, the volatiles extracted from the falling film polymerizer 1 are captured and collected by the spray liquid in the condenser 9 and then enter the liquid seal tank 10. The condensate passes through the hydroxy compound separation and purification device 11 and the diaryl carbonate separation and purification device 12, and is then transported by the condensate circulation pump 13 through the condensate cooler 14 in the heat medium system. The cooled condensate is then transported to the spray condenser 9 for recycling. The separated hydroxy compounds and diaryl carbonates can be used as raw materials for polycarbonate reaction after purification.

[0051] Furthermore, the falling film polymerizer 1 and the material through which the molten material passes are made of at least one of 904L and 316L, and the equipment in the vacuum system and condensation system is made of at least one of 316L and 304L.

[0052] Based on the production system described in the above technical solution, the present invention also provides a production method for increasing the molecular weight of aromatic polycarbonate, the specific steps of which are described in conjunction with embodiments.

[0053] The melt dynamic viscosity refers to the viscosity value obtained by testing with a rotational rheometer in a nitrogen-protected atmosphere at 280°C, when the shear rate is 10 rad / s.

[0054] The molecular weight and molecular weight distribution index were determined by chromatographic method using polystyrene standard, tetrahydrofuran as mobile phase and solvent.

[0055] The melt flow index (i.e., melt index, or melt flow rate) is the number of grams that flow out in 10 minutes at 300°C and 1.2 kg, as specified in ISO 1133 standard.

[0056] In the embodiments and comparative examples of this invention, the instruments, methods and steps used in the testing process are all conventional operations, and there is nothing particularly noteworthy except as described above.

[0057] Example 1

[0058] Using diphenyl carbonate and bisphenol A as raw materials for polycarbonate reaction, a prepolymerization reaction is carried out after transesterification. The reaction temperature in the stirred prepolymerizer 22 is 295℃, and the reaction pressure is 500Pa. The resulting prepolymer flows from the feed inlet 2 through the conduit 3 in the polymerizer 1 into the distributor 4, and is then distributed to the falling film support 5 for falling film flow to the bottom of the polymerizer 1. After being stirred and mixed by the bottom discharge device 6 of the polymerizer 1, it is discharged to the discharge outlet 7. The reaction temperature in the falling film polymerizer is 280℃, the vacuum degree is 80Pa, and the material flow rate on each falling film support is 20kg / h. A discharge gear pump 17 is installed on the melt pipeline after the discharge outlet to send the melt to the extruder 19 and the pelletizer 21 to obtain a colorless and transparent polycarbonate product.

[0059] The byproducts produced by the polycondensation reaction are discharged through the exhaust port 8, cooled by the condenser 9, and then enter the liquid seal tank 10. The condensate is then separated and purified into phenol and diphenyl carbonate, respectively. The purified phenol and diphenyl carbonate are then added to the initial reaction raw material system for the preparation of the prepolymer.

[0060] The dynamic viscosity of the melt discharged from the stirred prepolymer is 50 Pa·s, and the viscosity of the melt discharged from the falling film polymerizer is 950 Pa·s; the number average molecular weight is 18100 g / mol, the molecular weight distribution index is 1.72, and the melt index is 9.

[0061] Example 2

[0062] Using diphenyl carbonate and bisphenol A as raw materials for polycarbonate reaction, a prepolymerization reaction is carried out after transesterification. The reaction temperature in the stirred prepolymerizer 22 is 290℃, and the reaction pressure is 500Pa. The resulting prepolymer flows from the feed inlet 2 through the conduit 3 inside the polymerizer 1 into the distributor 4, and is then distributed to the falling film support 5 for falling film flow to the bottom of the polymerizer 1. After being stirred and mixed by the bottom discharge device 6 of the polymerizer 1, it is discharged to the discharge outlet 7. The reaction temperature inside the falling film polymerizer is 275℃, the vacuum degree is 80Pa, and the material flow rate on each falling film support is 15kg / h. A discharge gear pump 17 is installed on the melt pipeline after the discharge outlet to send the melt to the extruder 19 and the pelletizer 21 to obtain a colorless and transparent polycarbonate product.

[0063] The byproducts produced by the polycondensation reaction are discharged through the exhaust port 8, cooled by the condenser 9, and then enter the liquid seal tank 10. The condensate is then separated and purified into phenol and diphenyl carbonate, respectively. The purified phenol and diphenyl carbonate are then added to the initial reaction raw material system for the preparation of the prepolymer.

[0064] The dynamic viscosity of the melt discharged from the stirred prepolymer is 100 Pa·s, and the viscosity of the melt discharged from the falling film polymerizer is 3420 Pa·s; the number average molecular weight is 25600 g / mol, the molecular weight distribution index is 1.69, and the melt index is 6.

[0065] Comparative Example 1

[0066] Using diphenyl carbonate and bisphenol A as raw materials for polycarbonate reaction, a prepolymerization reaction is carried out after transesterification. The reaction temperature in the stirred prepolymerizer 22 is 290℃ and the reaction pressure is 500Pa. The prepolymer is then introduced into a horizontal stirred final polymerizer equipped with a high vacuum, a gas extraction port, a heating system and a volatiles collector for high-temperature reaction. The temperature inside the reactor is 295℃, the reaction time is 55 minutes and the vacuum degree is 80Pa. After discharge, the prepolymer is sent to the extrusion and pelletizing system to obtain a light yellow transparent polycarbonate product.

[0067] The byproducts produced by the polycondensation reaction are discharged through the exhaust port 8, cooled by the condenser 9, and then enter the liquid seal tank 10. The condensate is then separated and purified into phenol and diphenyl carbonate, respectively. The purified phenol and diphenyl carbonate are then added to the initial reaction raw material system for the preparation of the prepolymer.

[0068] The dynamic viscosity of the melt discharged from the stirred prepolymer is 100 Pa·s, and the viscosity of the melt discharged from the horizontal stirred final polycondensation reactor is 1010 Pa·s; the number average molecular weight is 17500 g / mol, the molecular weight distribution index is 1.86, and the melt index is 10.

[0069] Comparative Example 2

[0070] Using diphenyl carbonate and bisphenol A as raw materials for polycarbonate reaction, a prepolymerization reaction is carried out after transesterification. The reaction temperature in the stirred prepolymerizer 22 is 290℃, and the reaction pressure is 500Pa. The resulting prepolymer flows from the feed inlet 2 through the conduit 3 inside the polymerizer 1 into the distributor 4, and is then distributed to the falling film support 5 for falling film flow to the bottom of the polymerizer 1. After being stirred and mixed by the bottom discharge device 6 of the polymerizer 1, it is discharged to the discharge outlet 7. The reaction temperature inside the falling film polymerizer is 295℃, the vacuum degree is 80Pa, and the material flow rate on each falling film support is 15kg / h. A discharge gear pump 17 is installed on the melt pipeline after the discharge outlet to send the melt to the extruder 19 and the pelletizer 21 to obtain a light yellow transparent polycarbonate product.

[0071] The byproducts produced by the polycondensation reaction are discharged through the exhaust port 8, cooled by the condenser 9, and then enter the liquid seal tank 10. The condensate is then separated and purified into phenol and diphenyl carbonate, respectively. The purified phenol and diphenyl carbonate are then added to the initial reaction raw material system for the preparation of the prepolymer.

[0072] The dynamic viscosity of the melt discharged from the stirred prepolymer is 100 Pa·s, and the viscosity of the melt discharged from the falling film polymerizer is 2120 Pa·s; the number average molecular weight is 19600 g / mol, the molecular weight distribution index is 2.45, and the melt index is 12.

[0073] The reaction parameters and key product indicators of the examples and comparative examples are shown in Table 1.

[0074] Table 1. Reaction parameters and key product indicators for the examples and comparative examples.

[0075]

[0076] As shown in Example 1, the polycarbonate thickening reaction performed using the present invention has a significant effect, yielding high-molecular-weight, narrow-distribution, low-melt-index, high-quality polycarbonate products. By increasing the dynamic viscosity of the feed melt and appropriately reducing the reaction temperature of the falling film polymerizer 5 and the material flow rate of the falling film support unit 1, products with even higher molecular weight and superior quality can be obtained. Compared to Example 2, when Comparative Example 1 used a conventional horizontal stirred final polymerizer for the polycarbonate thickening reaction, the thickening effect and product molecular weight were significantly inferior to those of the falling film polymerizer 1, and the molecular weight distribution was significantly wider, with a slightly worse product color. Furthermore, as shown in Comparative Example 2, when polycarbonate undergoes falling film flow polycondensation reaction in falling film polymerizer 1 at a reaction temperature exceeding the range of the present invention, although the molecular weight of polycarbonate can be increased and the viscosity of the melt discharged from falling film polymerizer 1 is also significantly increased, its molecular weight distribution becomes significantly wider, the product quality deteriorates, indicating an increase in crosslinking side reactions occurring at higher temperatures, and the crosslinking of molecular chains increases the dynamic viscosity of the melt, but due to the wider molecular weight distribution and poorer polymer stability, it exhibits a higher melt index.

[0077] In summary, the production system provided by this invention effectively shortens the polycondensation reaction time, avoids excessive residence time of viscous materials at high temperatures which would lead to an increase in side reactions, and has a high byproduct removal efficiency. It is particularly suitable for preparing high-molecular-weight, low-melt-index, high-quality polycarbonate products.

[0078] The above description is merely a preferred embodiment of the present invention and does not limit the present invention. Any modifications or improvements made within the spirit and principles of the present invention shall fall within the protection scope of the present invention.

Claims

1. A production system for increasing the molecular weight of aromatic polycarbonates, characterized in that... include: Stirred prepolymerizer, falling film polymerizer, condensation system, vacuum system, heat transfer system, extrusion and pelletizing system; Prepolymerizer: It adopts a stirred structure to carry out the prepolymerization reaction of aromatic polycarbonate, and provides the basic melt for the falling film polymerizer to further increase the molecular weight. The dynamic viscosity of the basic melt at 280°C is 20~600 Pa·s. Falling film polymerizer: The falling film polymerizer has one or more falling film supports to support the melt during the falling film flow reaction. The falling film support is a slender rod-shaped body, vertically installed, with a hollow internal structure. The outer surface is in contact with the molten material, and the inner surface is in contact with the heat medium. The molten material supplied by the prepolymerizer flows from top to bottom in the falling film polymerizer, while simultaneously undergoing a molecular chain growth and polycondensation reaction to remove volatiles. The molten material with increased molecular weight has a dynamic viscosity of 100~10000 Pa·s at 280°C. The material exiting the falling film polymerizer enters the extrusion and pelletizing system. Condensation system: connected to the falling film polymerizer in front and the vacuum system in the back, including condensation, purification and separation devices, used to condense and separate the volatiles flowing in from the falling film polymerizer; Vacuum system: Connected to the condensation system, it provides vacuum power to promote the condensation reaction that promotes molecular chain growth; Heat transfer system: including the heat transfer medium that provides energy and heat exchange for the falling film polymerizer used for reaction and the condensation system used for separating volatilization, as well as its flow path and storage and power devices; Extrusion and pelletizing system: including mixing and extrusion, cooling and pelletizing unit, used to convey, mix, cool and pelletize materials from falling film polymerizer.

2. The production system as described in claim 1, characterized in that: The falling film polymerizer includes an inlet and conduit for molten material to flow in, a distributor, three or more falling film supports for supporting the melt during the falling film flow reaction, an exhaust port, a discharge port for discharging high-viscosity melt, a discharge device, and a liquid level gauge for monitoring the liquid level at the bottom of the polymerizer. The polymerizer shell is equipped with a polymerizer jacket. The molten material flowing into the falling film polymerizer is the base melt, including polycarbonate molten prepolymer. The condensation system includes a vertical spray condenser and its connected liquid seal tank, a hydroxy compound separation and purification device, a diaryl carbonate separation and purification device, a condensate cooler, and a heating / condensation medium passage. The vacuum system includes a vacuum pump set and at least one vacuum buffer tank. The vacuum pump set is connected to the vacuum buffer tank and the condenser. A small amount of uncondensed exhaust gas in the condenser enters the vacuum buffer tank and is trapped. The bottom of the vacuum buffer tank is provided with a drain port for draining the liquid accumulated in the vacuum buffer tank. The exhaust gas that is not trapped by the vacuum buffer tank is extracted by the vacuum pump set. The heat transfer system includes channels for the flow of heat transfer medium in the falling film support and polymer jacket of the polymerizer, the outlet melt pipeline, and heat transfer medium circulation pumps, heat transfer medium heaters, heat transfer medium expansion tanks, as well as channels for the flow of heating / cooling medium and heating / cooling medium circulation pumps and condensate coolers to control the temperature of the condenser, condensate cooler and vacuum buffer tank. The extrusion and pelletizing system includes a twin-screw extruder with mixing function, a pelletizer, and a pelletizing water system. The extruder is equipped with a feed valve for injecting additives, and the pelletizer is equipped with a dryer and a vibrating screen. A filter is provided between the twin-screw extruder and the pelletizer.

3. The production system as described in claim 1, characterized in that: The falling film polymerizer is equipped with a falling film support heat medium inlet and a falling film support heat medium outlet. The falling film support has a channel for heat medium flow. The polymerizer jacket is equipped with a polymerizer jacket heat medium outlet and a polymerizer jacket heat medium inlet. The heat medium inside the falling film support and the polymerizer jacket heat medium are connected to the same heat medium system as the outside, ensuring that the temperature of the falling film support is consistent with the temperature of the falling film polymerizer wall, so as to accurately control the falling film reaction temperature. The condenser, liquid seal tank, condensate cooler and vacuum buffer tank in the condensation system are all equipped with heating / cooling medium inlets and heating / cooling medium outlets, as well as independently controllable temperature control systems.

4. The production system as described in claim 1, characterized in that: The volatiles extracted from the falling film polymerizer are captured and collected by the spray liquid in the condenser and then enter the liquid seal tank. The condensate passes through the hydroxyl compound separation and purification device and the diaryl carbonate separation and purification device, and is then transported by the condensate circulation pump through the condensate cooler in the heat medium system. The cooled condensate is then transported to the spray condenser for recycling. The separated hydroxyl compounds and diaryl carbonates can be used as raw materials for polycarbonate reaction after purification.

5. The production system according to claim 1, characterized in that: The falling film polymerizer and the path through which the molten material passes are made of at least one of 904L stainless steel and 316L stainless steel, and the equipment in the vacuum system and condensation system is made of at least one of 316L stainless steel and 304L stainless steel.

6. A method for producing aromatic polycarbonates with increased molecular weight, using the production system described in any one of claims 1 to 5, characterized in that... Includes the following steps: (1) The product obtained by transesterification reaction of diaryl carbonate and aromatic dihydroxy compound is fed into a stirred prepolymerizer for prepolymerization reaction. The prepolymerization reaction temperature is 200~300℃, the absolute pressure in the prepolymerizer is 0.2kPa~8kPa, and the output after the reaction is a basic melt with a dynamic viscosity of 20~600Pa·s at 280℃. (2) The basic melt flows from the feed inlet into the distributor through the conduit on the falling film polymerizer, and is then distributed by the distributor to the outer surface of the falling film support, which can be precisely controlled in temperature, to flow to the bottom of the polymerizer. The molecular weight of the molten material is increased. The reaction temperature in the falling film polymerizer is 260~290℃ and the pressure is 0.005kPa~0.3kPa. (3) The molten material at the bottom of the polymerizer is homogenized by the discharge device and discharged. The dynamic viscosity of the discharged melt at 280℃ is 100~10000 Pa·s. It is sent to the extrusion pelletizing system for pelletizing or modified mixing with added components and then pelletized to obtain high-quality aromatic polycarbonate resin products.

7. The method according to claim 6, characterized in that: The flow rate of material on each falling film support in the falling film polymerizer is 1-200 kg per hour.

8. The method according to claim 6, characterized in that: The added component is one or more of the following: semi-aromatic polyester, polyamide, acrylonitrile-butadiene-styrene copolymer, polyolefin, polystyrene, polymethyl methacrylate, acrylate, and polyurethane, and the addition amount is 1% to 50%.

9. The method according to claim 8, characterized in that: The added components are mixed with the polycarbonate melt in an extruder and then extruded.

10. The method according to claim 6, characterized in that: The added components are one or more of flame retardants, heat stabilizers, antioxidants, antibacterial agents, defoamers, and quenchers, and the addition amount is 0.1% to 10%.

11. The method according to claim 10, characterized in that: The modifier is added online along the melt flow path after the falling film reaction or introduced into the extruder to mix with the polycarbonate melt before extrusion.

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