Optimized solution polymerization method for producing optical-grade polymethyl methacrylate molding compound

Abstract

The invention discloses a method for producing an optical-grade polymethyl methacrylate molding compound by an optimized solution polymerization method. Comprising the following steps: monomer feeding and additive preparation, polymerization and devolatilization, and granulation production and packaging. The monomer feeding and additive preparation comprises the following steps: feeding a rectified second monomer and a monomer raw material MMA into a degassing tank T-15 through a filter and a flow transmitter, and carrying out degassing treatment to finally obtain a mixed monomer, the invention relates to the technical field of production of polymethyl methacrylate, the reaction speed of an optimized solution polymerization process is easy to control, the reaction speed is reduced along with the increase of the solvent amount, when the solvent amount reaches 60%, the reaction speed and molecular weight distribution can be controlled, no gel phenomenon occurs, no equipment wall attachment occurs, and no pipeline is blocked; when sudden power failure or unforeseen circumstances occur, all-line parking can be achieved, when conditions are met again, driving can be organized again, and safety is achieved.

Description

Technical Field

[0001] This invention relates to the field of polymethyl methacrylate (PMMA) production technology, specifically to an optimized solution polymerization method for producing optical-grade PMMA molding compounds. Background Technology

[0002] Traditional solution polymerization technology for producing polymethyl methacrylate (PMMA) has several drawbacks. Due to the low monomer concentration, the polymerization reaction is slow, resulting in low equipment utilization and production capacity. Low monomer concentration also leads to chain transfer to the solvent, causing a decrease in polymer molecular weight. Solvent recovery and separation are costly, and removing trace amounts of solvent from the polymer is difficult. These disadvantages limit the industrial application of solution polymerization. Optimized solution polymerization technology, which can only produce general-grade PMMA, overcomes these drawbacks. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides an optimized solution polymerization method for producing optical-grade polymethyl methacrylate molding compounds, which solves the problems of low molecular weight and high recycling and separation costs associated with existing polymethyl methacrylate polymer production.

[0004] To achieve the above objectives, the present invention provides the following technical solution: an optimized solution polymerization method for producing optical-grade polymethyl methacrylate molding compounds, comprising the following steps: monomer feeding and additive preparation, polymerization and devolatation, granulation production, and packaging. The monomer feed and additive preparation are as follows: the second monomer after distillation and the monomer raw material MMA are filtered and fed into the degassing tank T-15 through a flow transmitter for degassing treatment to finally obtain the mixed monomer; The polymerization and devolatification process is as follows: the degassed mixed monomers are continuously pumped and filtered, then mixed with recycled materials and additives in the feed static mixer M-16B before entering the first reactor R-1. Part of the polymerization solution in the first reactor R-1 is continuously sent to the second reactor R-2 by the first reactor transfer pump P-1. The reaction temperature is 93-98℃ and the pressure is 540-570mmHg. The polymer from the second reactor R-2 is heated from 93-98℃ to 260-280℃ by the devolatification preheater E-3A.B. The preheated polymer enters the devolatifier T-3, which operates under negative pressure to remove solvent and unreacted monomers from the molten viscous polymer. The devolatified polymer is then sent to granulation by the extrusion pump P-3. The granulation process is as follows: the molten polymer after devolatification is sent from the devolatifier T-3 to the static mixer by a polymer extrusion pump. The static mixer is used to add tailing additives to the molten polymer. After exiting the static mixer, the molten polymer enters the filter screen changer (X-8A), and after filtration, it enters the granulator.

[0005] Preferably, in the polymerization process of the monomer raw material MMA, azobisisobutyronitrile (AIBN) is used as the initiator and dodecyl mercaptan (DDM) is used as the chain transfer agent. During the polymerization process, azobisisobutyronitrile (AIBN) is used as the initiator and dodecyl mercaptan (DDM) is used as the chain transfer agent. The feed additive is sent to the feed additive metering tank T-16B via the feed additive delivery pump P-16C. The feed additive in T-16B is degassed by reflux through P-16A / B. The degassed temperature of T-16B is ≤10℃.

[0006] Preferably, the granulation process is as follows: molten polymer is formed into filaments with a diameter of 3.9 mm in the filament die X-10A, which are then guided into the granulator X-10B via a guiding device. The granulator consists of a cutter and a traction device. The cut granules and water are fed into the granule dryer X-10D via the granule pre-dewatering device X-10C, where the granules are dried using residual heat and air. The separated cooling water flows into the filter water tank X-10F via the belt filter water recovery device X-10E, and is then sent to the filament / granule cooling water heat exchanger E-7A / B by the filament / granule cooling water pump P-7A / B. The water temperature is controlled at 50-80℃ and is used for circulation in X-10B. After drying, the granules entering X-10D have a moisture content of less than 0.5%. The dried granules enter the granule screening machine, where oversized and undersized granules are removed. The qualified granules are added to the pneumatic conveying tank T-12 via the granule feeding hopper T-11. When the material level in T-12 reaches the high level, the feed valve and vent valve of T-12 automatically close, and the pneumatic conveying valve opens for pneumatic conveying. The granules pass through the cyclone separator F-12 and the switching valve X-12 into six isolation hoppers, and then enter the mixing silo T-42 for thorough drying and mixing.

[0007] Preferably, the escaping vapor from the degassing unit enters the circulating liquid distillation column C-4. The heavy components are distilled and discharged at the bottom of the column, while the light components are discharged from the top of the column and condensed in the condenser E-5. The condensate is circulated by a pump and mixed with the degassing monomer and additives before entering the first reactor. The vacuum pressure of column C-4 is 40-80 mmHg, the top temperature is 30-100℃, and the reflux ratio is 0.3693. During the production process, vacuum system A is generated by J-6A / B vacuum ejectors, and system B is equipped with a Roots pump-water ring pump vacuum unit. System A is used for degassing and reaction processes, as well as monomer distillation processes; system B is used for devolatilization and circulating liquid recovery processes. In order to improve the efficiency of the ejector pump, an E-6 vacuum system condenser is installed to maintain the temperature of the circulating solvent at 20-30℃.

[0008] Preferably, the reactor and the devolatification preheater are also connected to a heat transfer oil system, which consists of a main heat transfer oil circuit. The heat transfer oil is heated in the fuel heater, and the main heat consumption is in the devolatification preheater. The heat transfer oil enters the preheater directly from the main heat transfer oil circuit.

[0009] Preferably, the packaging is as follows: after drying, the granules are conveyed by a pneumatic conveyor tank T-44 to the granule storage silo T-45A / B, and then to the bagging silo T-48B for bagging and packaging. Unqualified granules enter the unqualified silo T-48A.

[0010] This invention provides an optimized solution polymerization method for producing optical-grade polymethyl methacrylate molding compounds, which has the following advantages: 1. Good production stability and safety: The optimized solution polymerization process makes it easier to control the reaction rate. As the amount of solvent increases, the reaction rate decreases. When the amount of solvent reaches 60%, both the reaction rate and molecular weight distribution can be controlled. No gelation occurs, the equipment does not form walls, and the pipelines are not blocked. In the event of a sudden power outage or other unexpected situation, the entire line can be shut down. When conditions are restored, the line can be restarted, making it relatively safe.

[0011] 2. Uniform molecular weight distribution: The optimized solution polymerization process uses evaporation-condensation cooling to control the reaction temperature, resulting in a uniform and controllable molecular weight distribution. Since both molecular weight and polydispersity affect the properties and processing of polymer materials, the resulting product should be as homogeneous in molecular weight as possible during polymer synthesis. Generally, PMMA molding compounds for extrusion have a narrow molecular weight distribution, while those for injection molding have a wide distribution: MWD <2.5 for extrusion and >3.0 <5.0 for injection molding. The purpose of using a second reactor in the optimized solution polymerization process is to narrow the molecular weight distribution.

[0012] 3. High product quality: The optimized solution polymerization process produces products with fewer impurities, generally undetectable ash content, low mold content, high light transmittance, and good thermal stability. Many of its physical properties are superior to those of suspension polymerization products.

[0013] 4. No wastewater and exhaust gas treatment: The optimized solution polymerization process does not use water and there is no wastewater treatment problem. Only a small amount of water is introduced by the raw materials, which can be precipitated and discharged in the return line of the reactor condenser.

[0014] The production process is continuous, sealed, leak-free, and odorless.

[0015] The molecular weight of the resulting product should be as uniform as possible. Generally, PMMA molding compounds for extrusion have a narrow molecular weight distribution, while those for injection molding have a wide distribution: MWD extrusion type <2.5; injection type >3.0 <5.0. The purpose of using a second reactor in the optimized process is to narrow the molecular weight distribution.

[0016] 5. Low raw material and energy consumption, resulting in low production costs: Because the molten polymer from the optimized solution polymerization process can be directly granulated or used to produce extruded sheets, the monomer consumption is low, the solvent can be recycled, and the polymerization and granulation process consumes about 65 kg less monomer per ton of granules compared to the suspension method. Attached Figure Description

[0017] Figure 1 This is a block diagram of the process flow of the present invention.

[0018] Figure 2 This is a schematic diagram of the connection of the degassing tank T-15 of the present invention.

[0019] Figure 3 This is a schematic diagram showing the connection between the first reactor R-1 and the second reactor R-2 of the present invention.

[0020] Figure 4 This is a connection diagram of the devolatile generator T-3 of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Please see Figure 1-4 This invention provides a technical solution: an optimized solution polymerization method for producing optical-grade polymethyl methacrylate molding compounds, comprising the following steps: monomer feeding and additive preparation, polymerization and devolatation, granulation production, and packaging. The monomer feed and additive preparation are as follows: the second monomer after distillation and the monomer raw material MMA are filtered and fed into the degassing tank T-15 through a flow transmitter for degassing treatment to finally obtain the mixed monomer; The polymerization and devolatification process is as follows: the degassed mixed monomers are continuously pumped and filtered, then mixed with recycled materials and additives in the feed static mixer M-16B before entering the first reactor R-1. Part of the polymerization solution in the first reactor R-1 is continuously sent to the second reactor R-2 by the first reactor transfer pump P-1. The reaction temperature is 93-98℃ and the pressure is 540-570mmHg. The polymer from the second reactor R-2 is heated from 93-98℃ to 260-280℃ by the devolatification preheater E-3A.B. The preheated polymer enters the devolatifier T-3, which operates under negative pressure to remove solvent and unreacted monomers from the molten viscous polymer. The devolatified polymer is then sent to granulation by the extrusion pump P-3. The granulation process is as follows: the molten polymer after devolatification is sent from the devolatifier T-3 to the static mixer by a polymer extrusion pump. The static mixer is used to add tailing additives to the molten polymer. After exiting the static mixer, the molten polymer enters the filter screen changer (X-8A), and after filtration, it enters the granulator.

[0023] Furthermore, in the polymerization process of the monomer raw material MMA, azobisisobutyronitrile (AIBN) is used as the initiator and dodecyl mercaptan (DDM) is used as the chain transfer agent. During the polymerization process, azobisisobutyronitrile (AIBN) is used as the initiator and dodecyl mercaptan (DDM) is used as the chain transfer agent. The feed additive is sent to the feed additive metering tank T-16B via the feed additive delivery pump P-16C. The feed additive in T-16B is degassed by reflux through P-16A / B. The degassed temperature of T-16B is ≤10℃.

[0024] Furthermore, the granulation process is as follows: molten polymer forms filaments with a diameter of 3.9 mm in the filament die X-10A, which are then guided into the granulator X-10B via a guiding device. The granulator consists of a cutter and a traction device. The cut granules and water pass through the granule pre-dewatering device X-10C into the granule dryer X-10D, where the residual heat of the granules and air are used for drying. The separated cooling water flows into the filter water tank X-10F via the belt filter water recovery device X-10E, and is then sent by the filament / granule cooling water pump P-7A / B to the filament / granule cooling water heat exchanger E-7A / B. The water temperature is controlled at 50-80℃ and is used for circulation in X-10B. After drying, the granules entering X-10D have a moisture content of less than 0.5%. The dried granules enter the granule screening machine, where oversized and undersized granules are removed. The qualified granules are added to the pneumatic conveying tank T-12 via the granule feeding hopper T-11. When the material level in T-12 reaches the high level, the feed valve and vent valve of T-12 automatically close, and the pneumatic conveying valve opens for pneumatic conveying. The granules pass through the cyclone separator F-12 and the switching valve X-12 into six isolation hoppers, and then enter the mixing silo T-42 for thorough drying and mixing.

[0025] Furthermore, the escaping vapor from the degassing unit enters the circulating liquid distillation column C-4. The heavy components are distilled and discharged at the bottom of the column, while the light components are discharged from the top of the column and condensed in the condenser E-5. The condensate is circulated by a pump and mixed with the degassing monomer and additives before entering the first reactor. The vacuum pressure of column C-4 is 40-80 mmHg, the top temperature is 30-100℃, and the reflux ratio is 0.3693. During the production process, vacuum system A is generated by J-6A / B vacuum ejectors, and system B is equipped with a Roots pump-water ring pump vacuum unit. System A is used for degassing and reaction processes, as well as monomer distillation processes; system B is used for devolatilization and circulating liquid recovery processes. In order to improve the efficiency of the ejector pump, an E-6 vacuum system condenser is installed to maintain the temperature of the circulating solvent at 20-30℃.

[0026] Furthermore, the reactor and the devolatification preheater are also connected to a heat transfer oil system, which consists of a main heat transfer oil circuit. The heat transfer oil is heated in the fuel heater, and the main heat consumption is in the devolatification preheater. The heat transfer oil enters the preheater directly from the main heat transfer oil circuit.

[0027] Furthermore, the packaging process is as follows: after drying, the granules are conveyed to the granule storage silo T-45A / B via a pneumatic conveyor tank T-44, and then bagged and packaged in the bagging silo T-48B. Unqualified granules are placed into the unqualified silo T-48A.

[0028] The feed additive mixture is prepared using circulating liquid (or pure toluene). The additive is added to T-16A in a certain proportion, and dye is added in proportion as needed. After being mixed evenly, it is sent to T-16B via P-16C, and then enters M-16B via P-16A / B, F-16D / E, and F-16F filters.

[0029] To prevent the initiator from decomposing during storage, chilled water is circulated through the external coils and additive delivery pipes of T-16A and T-16B to keep the additive mixture below 10°C.

[0030] When P-16C starts, stirrer M-16A stops automatically.

[0031] The T-16B is degassed under vacuum pressure "A".

[0032] When the liquid level in T-16A drops to LS-16B, P-16C automatically stops, interrupting the feed additive mixture from T-16A to T-16B. When the liquid level in T-16B is higher than LS-16C, P-16C stops. LS-16C is also connected to an alarm system to notify the operator of a high liquid level in T-16B.

[0033] The monomer feed preparation includes the distillation of the second monomer, degassing, metering, and filtration of the MMA monomer and the second monomer mixture. MMA monomer and the second monomer (which may be purified first in the distillation system if needed) from outside the boundary are filtered, metered, and then fed into the degassing tank T-15 in a specific ratio. T-15 operates under vacuum at a pressure of 110-150 mmHg to remove dissolved gases, especially oxygen. The vacuum in T-15 is provided by PCV-15 controlled by PIC-15. T-15 provides sufficient suction head for P-15A / B.

[0034] The degassed proportioning monomer is dispensed from P-15A / B, filtered, and then, with the flow rate controlled by LIC-1, enters M-16B, and finally enters R-1.

[0035] The circulating liquid is stored in the circulating liquid storage tank and in unit T-5C. After being filtered by F-19, the circulating liquid is controlled by the flow control system and enters T-16A or other process equipment. During feeding, the main circulating stream is controlled by the output flow rate of FIC-5B and enters M-16B together with the proportioning monomer and feed additive. In M-16B, the circulating liquid, proportioning monomer, and feed additive are thoroughly mixed, and the mixture enters R-1.

[0036] (1) Open the inlet and outlet valves to the chilled water coils of T-16A and T-16B to ensure that chilled water is supplied according to the required specifications.

[0037] (2) Send circulating fluid to T-16A.

[0038] Open the inlet valve of pump P-5C, start P-5C, open the valve on the return line of T-5C, and circulate the circulating liquid in T-5C. Alternatively, notify the boundary area to send toluene from the boundary area to T-16A.

[0039] FQT-19 is a programmable flow regulator and accumulator. The amount of circulating fluid (or toluene) to be delivered to T-16A is set in FQT-19.

[0040] Open the relevant valves on the pipeline supplying circulating fluid or toluene from P-5C or the boundary pump to T-16A. SV-19A / B should be closed at this time.

[0041] Set HCS-19 to "automatic" operation mode, reset FQT-19 to zero, and record the start-up liquid level of T-16A.

[0042] Press the "Start" button on HCS-19. SV-19A / B will open and begin adding circulating fluid or toluene to T-16A. Once the set amount of circulating fluid or toluene has been added to T-16A, SV-19A / B will automatically close. After closing the outlet valve, stop the pump and close the relevant valves on the delivery pipeline.

[0043] (3) Add n-DDM to T-16A Use a drum pump to pump n-DDM from the tank into chamber T-17A. According to the calibration table for chamber T-17B, determine the corresponding graduation on the level gauge in chamber T-17B for the required quantity of n-DDM. Close the outlet valve from chamber T-17B to chamber T-16A, and open the valve from chamber T-17A to chamber T-17B. Accurately measure the required amount of n-DDM in the feed additive formulation in chamber T-17B. Then, close the valve from chamber T-17A to chamber T-17B.

[0044] Open the valve connecting chamber T-17B to chamber T-16A, allowing n-DDM to flow into T-16A by gravity.

[0045] (4) Start the stirrer M-16A.

[0046] (5) Add IRGANOX-1076 to T-16A: Accurately weigh the quantity of IRGANOX-1076.

[0047] Slowly add IRGANOX-1076 to T-16A through the feed port.

[0048] (6) Add AIBN to T-16A: Ensure the temperature of the medium inside T-16A is ≤10℃ and accurately weigh the amount of AIBN. Slowly add AIBN to T-16A through the feed port.

[0049] (7) Dissolve a certain amount of dye in toluene and add it through the feed port.

[0050] The feed additive has been prepared.

[0051] The feed additives must be mixed and stirred for at least 30 minutes before being conveyed.

[0052] Feed additive delivery and metering: (1) Ensure that the feed additive conveying interlock function is normal.

[0053] (2) Ensure the temperature of the material in T-16A is ≤10℃ before conveying. (3) Open the inlet valve of T-16B. Record the liquid levels of T-16A and T-16B at the beginning.

[0054] (4) Start P-16C via manual switch HCS-16, open the outlet valve, and feed the additive from T-16A to T-16B. Check if M-16A is stopped; SV-16A should be open.

[0055] (5) When the T-16A pump is discharged from the high point, when the liquid level drops to 75 cm, manually stop the P-16C pump.

[0056] (6) When the material is discharged at the low point, when the liquid level in T-16A drops to about 15 cm, LS-16B should be activated, and P-16C should be automatically stopped and SV-16A should be closed through interlock.

[0057] (7) Open the inlet valve of P-16A / B, start P-16A / B, open the reflux valve of T-16B, and allow the additive to circulate through the top nozzle of T-16B. T-16B operates under vacuum "A" pressure to degas the additive.

[0058] (8) Open the relevant valves on the pipeline from the feed additive through the filter flow control loop and static mixer M-16B to R-1. The flow control loop controls the flow rate of the feed additive entering R-1.

[0059] (9) When the device is in continuous operation, FIC-16 operates in cascade mode and receives signals from FIC-15. It controls the flow rate of the feed additive entering R-1.

[0060] Start-up operation of the individual feed station: (1) Ensure that all discharge valves of the unit feeding system are in the closed position.

[0061] (2) Open the relevant valves on the MMA monomer entering the equipment area from the boundary area and on the T-15 pipeline.

[0062] (3) Open the relevant valves on the pipeline from T-5B to T-15 for the second unit.

[0063] (4) Open the inlet valve of P-12 (or P-5B), start P-12 (or P-5B), open the reflux valve of T-5B, and make the second unit circulate in T-5B.

[0064] (5) Contact the storage workshop to supply MMA to the PMMA unit.

[0065] (6) According to the monomer feeding operation, correctly set the HCS-14 switch position. When HCS-14 is in the flow rate setting, FIC-14 controls the MMA flow rate. When HCS-14 is in the level setting, LIC-15 controls the MMA flow rate. FIC-13 receives the cascade signal from FIC-14 to ensure that the monomer is fed proportionally.

[0066] (7) When the liquid level of T-15 reaches the control point, the output of LIC-15 will control the FCV-14 and FCV-13 to close.

[0067] (8) Open the inlet valve of P-15A / B, start P-15A / B, open the T-15 reflux valve, and make the proportional monomer circulate in T-15.

[0068] (9) Slowly open the vacuum system valve and evacuate T-15 to degas the proportioning monomer for at least 15 minutes.

[0069] (10) After adding the additive to R-1 for 10 minutes, open the valve on the pipeline for adding the proportioning monomer to R-1 so that the proportioning monomer enters R-1 after passing through LCV-1 and M-16B.

[0070] (11) When the device is in normal production, the output of LIC-15 controls the opening of FCV-14, FQT-14 cascades the output of FIC-13, and FQT-15 cascades the output of FIC-16 and FIC-5B (this step must be completed before 1.4.1 and 1.4.2), thereby realizing cascade flow control.

[0071] Start-up operation of the second monomer distillation unit: When the liquid level of T-5B drops to 80 cm, the distillation operation begins.

[0072] (1) Switch from P-12 to P-5B and run.

[0073] (2) Open the vacuum valves of T-5B and E-13A to evacuate the distillation apparatus and control the pressure at -0.08 to -0.07 MPa.

[0074] (3) Start P-13A / B and feed the second monomer into C-13. Adjust the feed rate by using a rotor flow meter.

[0075] (4) When the liquid level in C-13 reaches the middle of the intermediate sight glass, stop feeding. Close the vacuum valve E-13A.

[0076] (5) Open the steam inlet and outlet valves of the reboiler at the bottom of column C-13, as well as the steam valves of the upper and lower jackets, so that the steam exits the reboiler, enters the lower and upper jackets, and then returns. (During the distillation process, the steam flow can be adjusted according to the actual situation.) (6) Pay attention to the temperature of C-13 and adjust the steam flow rate to control it between 80 and 100℃.

[0077] (7) When the distillation column discharge is observed through the sight glass of the feed line and the liquid level drops through the sight glass of C-13, open the feed and reflux valves of C-13.

[0078] (8) The liquid level of C-13 is controlled by adjusting the flow rate of the feed rotor flow meter to stabilize it at the middle sight glass. It is generally controlled at around 200-350 L / h.

[0079] (9) The content of monomer inhibitor after distillation is controlled to be below 10 PPM by adjusting the flow rate of the reflux rotor flow meter. The reflux is controlled at around 300-400 L / h.

[0080] Circulating fluid storage, transportation, and start-up operation: (1) Open the relevant valves on the pipeline that supplies circulating fluid to R-1 via F-19, FT-19 or T-5A via FT-5B.

[0081] (2) Set the amount of circulating fluid to be added to R-1 in FQT-19 (or FIC-5B), and switch HCS-19 to the "on" operation mode.

[0082] (3) Open the inlet valve of P-5C (or P-5A / B), start P-5C (or P-5A / B), open the return valve of T-5C (or T-5A) to make the circulating fluid circulate.

[0083] (4) Set HCS-19 to “automatic” operation mode and reset FQT-19 to zero.

[0084] (5) Press the "Start" button on HCS-19, SV-19A / B will open, and circulating fluid will begin to be added to R-1. When the required amount of circulating fluid is added to R-1, SV-19A / B will automatically close, and P-5C will stop by interlock. Close the relevant valves (or control the flow of circulating fluid to R-1 via FIC-5B, through T-5A).

[0085] (6) The addition of circulating fluid to R-1 is complete.

[0086] (7) During normal production, open the relevant valves on the pipeline from T-5A to R-1 via P-5A / B, through the flow control system and M-16B. The main circulating fluid is output from FIC-5B by the cascade signal of FQT-15 and fed into the reaction system according to the set cycle ratio.

[0087] Those skilled in the art can connect the components in this case sequentially. The specific connection and operation sequence should refer to the working principle described below. The detailed connection methods are well-known technologies in the field. The working principle and process are mainly described below.

[0088] Example: The distilled second monomer and the monomer feedstock MMA are filtered and fed into degassing tank T-15 via a flow transmitter for degassing treatment to obtain a mixed monomer. The degassed mixed monomer is continuously pumped, filtered, and then mixed with circulating materials and additives in feed static mixer M-16B before entering the first reactor R-1. A portion of the polymerization solution from the first reactor R-1 is continuously sent to the second reactor R-2 via the first reactor transfer pump P-1. The reaction temperature in both reactors is 93-98℃, and the pressure is 540-570 mmHg. The polymer from the second reactor R-2... The temperature of the polymer is increased from 93-98℃ to 260-280℃ in the preheater E-3A.B. The preheated polymer then enters the devolatifier T-3, which operates under negative pressure to remove solvents and unreacted monomers from the molten viscous polymer. The devolatified polymer is then sent to the granulator by the extrusion pump P-3. The devolatified molten polymer is then sent from the devolatifier T-3 to the static mixer by the polymer extrusion pump. The static mixer is used to add tailing additives to the molten polymer. After exiting the static mixer, the molten polymer enters the filter exchanger (X-8A), and after filtration, it enters the granulator.

[0089] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, the phrase "comprising an element defined as..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0090] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An optimized solution polymerization method for producing optical-grade polymethyl methacrylate molding compounds, characterized in that, Includes the following steps: Monomer feeding and additive preparation, polymerization and devolatation, granulation production and packaging: The monomer feed and additive preparation are as follows: the second monomer after distillation and the monomer raw material MMA are filtered and fed into the degassing tank T-15 through a flow transmitter for degassing treatment to finally obtain the mixed monomer; The polymerization and devolatification process is as follows: the degassed mixed monomers are continuously pumped and filtered, then mixed with recycled materials and additives in the feed static mixer M-16B before entering the first reactor R-1. Part of the polymerization solution in the first reactor R-1 is continuously sent to the second reactor R-2 by the first reactor transfer pump P-1. The reaction temperature is 93-98℃ and the pressure is 540-570mmHg. The polymer from the second reactor R-2 is heated from 93-98℃ to 260-280℃ by the devolatification preheater E-3A.B. The preheated polymer enters the devolatifier T-3, which operates under negative pressure to remove solvent and unreacted monomers from the molten viscous polymer. The devolatified polymer is then sent to granulation by the extrusion pump P-3. The granulation process is as follows: the molten polymer after devolatification is sent from the devolatifier T-3 to the static mixer by a polymer extrusion pump. The static mixer is used to add tailing additives to the molten polymer. After exiting the static mixer, the molten polymer enters the filter screen changer (X-8A), and after filtration, it enters the granulator.

2. The method for producing optical-grade polymethyl methacrylate molding compound by optimized solution polymerization according to claim 1, characterized in that, In the polymerization process of the monomer raw material MMA, azobisisobutyronitrile (AIBN) is used as the initiator and dodecyl mercaptan (DDM) is used as the chain transfer agent. The feed additive is sent to the feed additive metering tank T-16B via the feed additive delivery pump P-16C. The feed additive in T-16B is degassed by reflux through P-16A / B. The degassed temperature of T-16B is ≤10℃.

3. The method for producing optical-grade polymethyl methacrylate molding compound by optimized solution polymerization according to claim 1, characterized in that, The granulation process is as follows: molten polymer is formed into filaments with a diameter of 3.9 mm in the filament die X-10A, which are then guided into the granulator X-10B. The granulator consists of a cutter and a traction device. The cut granules and water are fed into the granule dryer X-10D through the granule pre-dewatering device X-10C, where the granules are dried using residual heat and air. The separated cooling water flows into the filter water tank X-10F through the belt filter water recovery device X-10E, and is then sent to the filament / granule cooling water heat exchanger E-7A / B by the filament / granule cooling water pump P-7A / B. The water temperature is controlled at 50-80℃ and is used for circulation in X-10B. After drying, the granules entering X-10D have a moisture content of less than 0.5%. The dried granules enter the granule screening machine, where oversized and undersized granules are removed. The qualified granules are added to the pneumatic conveying tank T-12 via the granule feeding hopper T-11. When the material level in T-12 reaches the high level, the feed valve and vent valve of T-12 automatically close, and the pneumatic conveying valve opens for pneumatic conveying. The granules pass through the cyclone separator F-12 and the switching valve X-12 into six isolation hoppers, and then enter the mixing silo T-42 for thorough drying and mixing.

4. The method for producing optical-grade polymethyl methacrylate molding compound by optimized solution polymerization according to claim 1, characterized in that, The escaping vapor from the degassing unit enters the circulating liquid distillation column C-4. The heavy components are distilled and discharged at the bottom of the column, while the light components are discharged from the top of the column and condensed in the condenser E-5. The condensate is circulated by a pump and mixed with the degassing monomer and additives before entering the first reactor. The vacuum pressure of column C-4 is 40-80 mmHg, the temperature at the top of the column is 30-100℃, and the reflux ratio is 0.3693. During the production process, vacuum system A is generated by J-6A / B vacuum ejectors, and system B is equipped with a Roots pump-water ring pump vacuum unit. System A is used for degassing and reaction processes, as well as monomer distillation processes; system B is used for devolatilization and circulating liquid recovery processes. In order to improve the efficiency of the ejector pump, an E-6 vacuum system condenser is installed to maintain the temperature of the circulating solvent at 20-30℃.

5. The method for producing optical-grade polymethyl methacrylate molding compound by optimized solution polymerization according to claim 1, characterized in that, The reactor and the devolatification preheater are also connected to a heat transfer oil system, which consists of a main heat transfer oil circuit. The heat transfer oil is heated in the fuel heater, and the main heat consumption is in the devolatification preheater. The heat transfer oil enters the preheater directly from the main heat transfer oil circuit.

6. The method for producing optical-grade polymethyl methacrylate molding compound by optimized solution polymerization according to claim 1, characterized in that, The packaging process is as follows: after drying, the granules are conveyed by pneumatic conveyor tank T-44 to the granule storage silo T-45A / B, and then to the bagging silo T-48B for bagging and packaging. Unqualified granules are sent to the unqualified silo T-48A.

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