A prepolymerization reactor and continuous bulk polymerization system

Abstract

The utility model provides a kind of pre-polymerization reactor and continuous bulk polymerization system.The pre-polymerization reactor, including body, the top of the body is integrated with split condenser, the split condenser is formed gas phase intercommunication with the body by detachable connecting piece;The inside of the body is equipped with the composite stirring system of anchor agitator and multilayer improved screw belt paddle;The circumference of the body is independently arranged temperature control jacket, the upper of the composite stirring system is equipped with cooling unit, forms double cooling channel;The inner tube of the split condenser is passed into circulating cooling medium, the shell side of the split condenser is directly communicated with the top evaporation space of the body and forms closed loop phase change heat transfer channel.Through special system design and polymerization reactor combination, the contradiction between high conversion rate and PMMA product narrow molecular weight distribution in polymerization process is solved;Under the condition of little solvent addition amount or no solvent, while obtaining high conversion rate, the molecular weight distribution of polymerization product is narrow, and the molecular weight is controllable, and high-quality optical grade PMMA resin product is obtained.

Description

Technical Field

[0001] This invention relates to the field of continuous bulk polymerization of polymethyl methacrylate, and more particularly to a prepolymerization reactor and a continuous bulk polymerization system. Background Technology

[0002] Polymethyl methacrylate (PMMA) is obtained by free radical polymerization of methyl methacrylate (MMA) and other comonomers. As a high-performance transparent material, PMMA has a wide range of applications. Low- to mid-range consumer applications include advertising light boxes, signs, lighting fixtures, bathtubs, instruments, household goods, and furniture. High-end consumer applications include light guide plates for LCD displays, radiation-proof PMMA, optical fibers, solar photovoltaic cells, and high-purity optical disc-grade PMMA for CD, VCD, and optical disc production. From a production capacity perspective, my country is already a major PMMA producer, but its product structure is not very rational. The grades with independent production technology are mainly concentrated in general-purpose products, lacking high-value-added products. Due to excessive expansion of domestic PMMA production capacity, primarily focused on low-end PMMA, there is an oversupply in the low-end market and a high dependence on the high-end market. This structural imbalance is unlikely to improve in the short term. In recent years, my country has imported more than 200,000 tons of PMMA annually, mostly high-end optical-grade PMMA. Based on current trends, PMMA is projected to grow at an average annual rate of 8-12% over the next few years, with consumer electronics, photovoltaic power generation, and flat panel displays gradually becoming the main drivers of demand growth. The market potential for high-end PMMA products will continue to grow. Therefore, breaking the technological and supply monopoly of foreign companies in the high-end product market and developing independent high-end PMMA production processes is an urgent task.

[0003] The PMMA production process mainly consists of two stages: polymerization and devolatilization. Currently, there are three main polymerization technologies: solution polymerization, suspension polymerization, and bulk polymerization. Corresponding to polymerization, the devolatilization process typically involves flash evaporation, a combination of a devolatilizer and a screw devolatilization unit. For PMMA polymer solutions with a solid content below 50% (mostly used in solution polymerization), a primary flash devolatilization process using a devolatilizer is usually employed to remove a large amount of volatiles. Then, depending on the viscosity of the polymer melt, a secondary flash devolatilization process using a devolatilizer or a screw devolatilization unit is selected to remove residual volatiles. For PMMA polymer products with a solid content above 50% (mostly used in bulk polymerization), if the melt viscosity meets the requirements, a flash evaporation process using a devolatilizer is unnecessary; a screw devolatilization unit can be used directly to meet the product's volatile content requirements. Currently, major international PMMA producers include Arkema (France), Rohm GmbH (Germany), Mitsubishi Rayon (Japan), Sumitomo Chemical, Asahi Kasei, and Kuraray (Japan). Foreign counterparts in the industry started technological development earlier. In the 1980s, PTI Corporation in the United States proposed solution polymerization. US Patent 4728701 disclosed a polymerization method for acrylates in 1988; US Patent 4933400 disclosed a continuous solution polymerization method for methacrylates in 1990. However, these polymerization methods used solvents in proportions as high as 40-60% of the feed. After years of technological research and development, most foreign companies have adopted continuous bulk polymerization technology, and have conducted extensive research on bulk polymerization processes and equipment, achieving industrial-scale production. Sumitomo Chemical uses a two-stage fully mixed reactor that can be switched between series and parallel to perform high-temperature continuous bulk polymerization to obtain PMMA, followed by a vented extrusion devolatilizer. Mitsubishi Rayon uses a two-stage continuous bulk polymerization method to produce PMMA, with a first-stage fully mixed reactor and a second-stage twin-tube piston flow reactor connected in series, followed by a vented extrusion devolatilizer. The tubular reactor design is mainly to improve the space-time conversion rate of the system. Space-time efficiency generally refers to the ability of reactants to be converted per unit time and unit volume, and is a key indicator for measuring reactor capacity and process efficiency. As the reaction proceeds, the reaction rate decreases. If a higher conversion rate is required, a tubular reactor can provide higher space-time efficiency. However, increasing the conversion rate of the monomer MMA also leads to a high solids content in the system, which severely affects the mass and heat transfer efficiency. Therefore, tubular reactors, which cannot be stirred and mixed, will exhibit a significant temperature gradient distribution, resulting in an uneven polymerization reaction. This will seriously affect the molecular weight distribution of the final polymerized product, and consequently, the product quality.

[0004] In terms of domestic production, research on continuous bulk polymerization of PMMA mainly focuses on two aspects: firstly, achieving effective mass and heat transfer and stable polymerization reactions by selecting different types of reactors and their combinations; secondly, controlling the stability of the reaction system and obtaining polymers with better performance by adjusting the formulation (including the amount of additives and the type of solvent) and polymerization process conditions. For example, CN94118188.X, CN99806610.9, CN200410069172.0, CN201180023792.9, and CN201180016563 disclosed by Nantong Mitsubishi Rayon Co., Ltd. all use different forms of multi-stage reactors to produce PMMA through continuous solution or continuous bulk polymerization processes. CN201310101125.9 and CN201310101124.4 disclosed by Suzhou Shuangxiang Optical Materials Co., Ltd. also use prepolymerization plus two-stage polymerization to complete the continuous bulk synthesis of PMMA products. Xi'an Jiaotong University employs a method of prepolymerization in a reactor followed by deep polymerization in a reactive extruder. The Institute of Physics and Chemistry, Chinese Academy of Sciences, using a flat-push thin-layer tubular reactor and a parallel-connected twin-screw reactive extruder for continuous bulk polymerization to prepare high-purity, high-yield polyacrylic acid resin. However, although significant progress has been made in the research and development of PMMA synthesis processes, its application in industrial production has not yet been observed, especially the lack of mature continuous bulk polymerization processes for producing high-end PMMA in China.

[0005] In comparison, continuous bulk polymerization produces high-purity products with low energy consumption and pollution emissions, making it the preferred process for producing high-end PMMA. However, it has stringent requirements for equipment and processes. Currently, there are eight large PMMA producers in China with capacities exceeding 10,000 tons per year, totaling nearly 500,000 tons per year. They employ solution polymerization and bulk polymerization processes, most of which are multi-unit processes with relatively long flow rates. Among them, Zhenjiang Chimei Chemical Co., Ltd., Nantong Liyang Chemical Co., Ltd., and ROHM Chemical (formerly Evonik) use bulk polymerization processes and are wholly foreign-owned or joint ventures, thus monopolizing advanced PMMA technology. Although domestic companies have achieved breakthroughs in PMMA bulk polymerization technology, their technical indicators still lag behind those of ROHM Chemical and Liyang.

[0006] CN113336882B discloses a process for preparing PMMA resin with a narrow molecular weight distribution using batch bulk polymerization. This process involves adding monomers, a free radical polymerization initiator, and a chain transfer agent to a bulk polymerization bag in a specific ratio, then placing the bag in a constant temperature water bath at 30–70°C for polymerization. After polymerization, the bag is removed, and the polymerized product is allowed to cool to room temperature. The chain transfer agent used is a polyfunctional thiol. This process not only unexpectedly achieves the production of PMMA resin with a narrow molecular weight distribution of less than 1.7 using batch bulk polymerization, but also eliminates the need for special equipment and high-temperature devolatilization, offering numerous advantages such as low polymerization temperature, high conversion rate, low energy consumption, simple operation, safety and environmental friendliness, and ease of industrialization. However, despite the shortened process and omission of high-temperature devolatilization, this batch production method suffers from relatively low production efficiency due to the inability to achieve continuous large-scale production. Each batch requires a complete process of feeding, reaction, and cooling, with time intervals between batches, resulting in limited output per unit time. Although it claims to produce products with narrow molecular weight distributions, batch processes can lead to variations in product quality between batches due to slight differences in operating conditions (such as the order of feeding, fluctuations in water bath temperature, and control of reaction time). It is difficult to guarantee that the molecular weight distribution and other properties of each batch are completely consistent. Furthermore, the entire reaction process is carried out at relatively low temperatures, which may result in a slower reaction rate and longer polymerization time, increasing production cycles and costs.

[0007] CN103130945B discloses a continuous PMMA production process that operates without material accumulation over a long period, belonging to the field of polymer preparation technology. By employing a bottom-in, top-out polymerizer and a stirring and heating device, with the polymerizer designed using a ribbon agitator and chrome-plated or polished inner walls; adding a small amount of inert solvent to the reaction mixture to increase its fluidity; chrome-plating the extruder screw and its inner wall; and adding a circulation loop between the distillation column reboiler and waste tank to add polymerization inhibitors, the process avoids the problem of polymer accumulation in containers and pipelines during continuous bulk polymerization of PMMA, ensuring long-term continuous and stable operation. However, while adding a small amount of inert solvent increases the fluidity of the mixture, it introduces additional solvent components, potentially requiring additional solvent separation and recovery processes, increasing process complexity and production costs. Furthermore, this process primarily focuses on solving the accumulation problem, with less attention paid to optimizing the polymerization reaction itself, which may not lead to significant breakthroughs in product performance improvement and could fail to meet the increasingly diverse market demand for high-performance PMMA products.

[0008] In summary, the domestic PMMA process system and polymerization process still cannot meet the production requirements of optical-grade PMMA. The entire reaction process is long and the PMMA product quality is low, which is an urgent problem to be solved.

[0009] Currently, existing industrial system designs cannot resolve the contradiction between high conversion rates in the polymerization process and the narrow molecular weight distribution of PMMA products. In particular, there is an urgent need to address the shortcomings of existing technologies, such as low polymerization conversion rates, large solvent consumption, or wide molecular weight distributions of products that fail to meet the requirements for optical-grade applications in terms of light transmittance and other properties, and difficulties in precisely controlling quality. Utility Model Content

[0010] This invention aims to address the shortcomings of existing technologies by providing a prepolymerization reactor and a continuous bulk polymerization system. Through a unique system design and reactor combination, the contradiction between high conversion rates and narrow molecular weight distribution of PMMA products is resolved. Under conditions of low solvent addition or no solvent, high conversion rates are achieved while maintaining a narrow molecular weight distribution and controllable molecular weight of the polymerized products, resulting in high-quality optical-grade PMMA resin products. The technical solution of this invention is as follows: A prepolymerization reactor includes a body, the top of which is integrated with a split condenser, the split condenser being connected to the body in a gas phase via a detachable connector; The interior of the vessel is equipped with a composite stirring system consisting of an anchor-type stirrer and a multi-layer improved spiral ribbon paddle. The vessel body is provided with an independent temperature control jacket around its circumference, and a cooling unit is provided above the composite stirring system to form a dual cooling channel. The inner tube side of the split condenser is circulated with a cooling medium, and the shell side of the split condenser is directly connected to the top evaporation space of the vessel body to form a closed-loop phase change heat transfer channel.

[0011] Furthermore, the prepolymerization reactor and the split-type condenser are provided with a gas-liquid separation chamber at the bottom. The gas-liquid separation chamber is equipped with baffles and a wire mesh demister. The separated condensate is automatically returned through a U-shaped liquid seal pipe. The split-type condenser is also equipped with a steam bypass branch pipe to connect to an external cryogenic unit to form a multi-stage heat removal system.

[0012] Furthermore, the split-type condenser includes at least one of a vertical tube condenser and a spiral plate heat exchanger.

[0013] This invention provides a continuous bulk polymerization system for PMMA. The system includes, in sequence, a material purification and degassing module, a material mixing module, a prepolymerization reaction module, a polymerization module, and optionally a post-polymerization module, a devolatilization module, and a granulation module, according to the direction of material transport and the reaction process. The material purification and degassing module is equipped with a raw material purifier; the material mixing module is equipped with a static mixer; the prepolymerization reaction module is equipped with the prepolymerization reactor; the polymerization module and optionally the post-polymerization module are equipped with a polymerization reactor and a post-polymerization reactor; the devolatilization module is equipped with a devolatilizer; and the granulation module is equipped with a granulator. Raw material purifier: used to remove impurities from reactants; Static mixer: Used to uniformly mix purified reactants with additives; Prepolymerization reactor: used to initiate polymerization reactions and form prepolymers; Polymerization reactor: Used to further polymerize prepolymers to obtain polymer materials; Post-polymerization reactor: Used to carry out post-polymerization reaction of polymer materials to obtain post-polymer materials; Deviation device: used to remove unreacted monomers and low-boiling-point volatile components from the polymer material and / or the post-polymer material; Granulator: After the devolatilization process, the molten material is extruded or pumped into a pelletizer to be cut into uniform particles that are easy to process.

[0014] More preferably, the system includes, in sequence, a material purification and degassing module, a material mixing module, a prepolymerization reaction module, a polymerization module, and optionally a post-polymerization module, a devolatilization module, and a granulation module, according to the direction of material transport and the reaction process. The material purification and degassing module is equipped with a raw material purifier; the material mixing module is equipped with a static mixer; the prepolymerization reaction module is equipped with a prepolymerization reactor; the polymerization module and optionally the post-polymerization module are equipped with a polymerization reactor and a post-polymerization reactor; the devolatilization module is equipped with a devolatilizer; and the granulation module is equipped with a granulator. Raw material purifier: Used to remove impurities from reactants, ensuring the total impurity content does not exceed 0.05%; Static mixer: Used to uniformly mix purified reactants with additives; Prepolymerization reactor: used to initiate the polymerization reaction and control the conversion rate of monomer MMA within the range of 30% to 55%, forming a prepolymer with an initial molecular weight distribution of no more than 2, preferably 1.6 to 1.9; Polymerization reactor: used to further polymerize the prepolymer to a monomer MMA conversion rate of 55% to 75% to obtain polymer material; Post-polymerization reactor: Used to perform post-polymerization reaction on polymer materials, increasing the monomer MMA conversion rate to 70-85% to obtain post-polymer materials; Deviation remover: used to remove unreacted monomers and low-boiling-point volatile components from the polymer material and / or the post-polymer material, so that the residual monomer content in the devolatilized material is ≤0.1%; Granulator: After the devolatilization process, the molten material is extruded or pumped into a pelletizer to be cut into uniform particles that are easy to process in subsequent steps.

[0015] This invention provides a continuous bulk PMMA preparation method using the aforementioned system. The method involves mixing metered monomers and additives, sequentially completing a prepolymerization reaction, a polymerization reaction, and an optional post-polymerization reaction in series of polymerization reactors, and then devolatilizing and granulating the polymerization product to obtain PMMA resin. The method includes the following steps: Step 1: Purification and mixing of reactants The reactants are purified using a raw material purifier, and then the metered reactants are thoroughly mixed in a static mixer. Step 2: Prepolymerization reaction The mixed reactants from step 1 are fed into the prepolymerization reactor via a static mixer, and the resulting prepolymer is fed into the reactor via the bottom outlet. Step 3-1: Polymerization reaction The prepolymer is further polymerized in a polymerization reactor; Step 4: Deviation The polymerized reaction liquid is sent to the first-stage devolatilizer to remove unreacted monomers and low-boiling-point components from the devolatilization port. The volatiles removed are directly recycled back to the polymerization stage. The devolatilized material is sent from the first-stage devolatilizer to the second-stage devolatilizer for deep devolatilization, so that the residual monomer content in the devolatilized material is ≤0.1%, and PMMA melt is obtained. Step 5: Granulation The devolatilized PMMA melt is granulated by cooling and pelletizing to obtain the final product.

[0016] Furthermore, the preparation method further includes step 3-2—a post-polymerization reaction—after step 3-1, so that the monomer MMA conversion rate finally reaches 70-85%.

[0017] Furthermore, in step 1, the raw material purifier may be one or more devices such as an adsorber or a distillation column.

[0018] Furthermore, in step 1, the adsorber can be a dynamic adsorber, specifically including at least one of a fixed bed adsorber, an expanded bed adsorber, and a simulated moving bed.

[0019] Furthermore, in step 1, the adsorber is selected as either a vertical axial flow or a horizontal radial flow depending on the different material flow paths.

[0020] Furthermore, in step 1, the adsorber may contain an adsorbent, which includes at least one of molecular sieves, activated alumina, adsorption resin, silica gel, or activated carbon.

[0021] Furthermore, in step 1, the adsorber may be equipped with a distillation unit for refining and purifying the reactants. The distillation unit contains multiple layers of trays or packing material, utilizing the principle that different substances have different vapor pressures at the same temperature. Through multiple partial vaporization and partial condensation processes, the polymer monomers are separated from other impurities (including non-condensable gases and other low-boiling-point substances). During the distillation process, by precisely controlling parameters such as the temperature, pressure, and reflux ratio of the distillation column, the polymer monomers are enriched at the bottom of the column and continuously discharged, then sent to a static mixer. The non-condensable vapors and other low-boiling-point substances collected at the top of the column are separated and processed separately.

[0022] Furthermore, in step 1, the static mixer has an interconnected structure, comprising multiple sets of staggered mixing units arranged sequentially along the material flow direction. Each mixing unit consists of several guide vanes with a certain helical or inclined angle. The guide directions of adjacent mixing units are perpendicular to each other or form a certain angle, allowing the fluid to be continuously cut, split, and re-merge as it passes through. Through-hole structures or interconnected channels are provided between the mixing units to ensure that the material can achieve sufficient exchange and uniform mixing in the radial and axial directions, avoiding local stagnation zones or dead zones. This interconnected design effectively reduces the risk of self-polymerization caused by the stagnation of monomer methyl methacrylate (MMA) in local areas, thereby preventing blockage of the inner wall of the static mixer and ensuring the stability and safety of the continuous reaction process.

[0023] Furthermore, in step 1, the reactants are precisely proportioned by a high-precision feed flow control system and then fed into the prepolymerization reactor via the static mixer.

[0024] Furthermore, in step 2, the prepolymer reactor and the static mixer are directly connected by a flange to avoid the prepolymer from gelling inside the pipeline; the flange ensures that both devices can be disassembled and maintained.

[0025] Furthermore, in step 2, the heat absorbed by the reactants entering the prepolymerization reactor and the heat released by the polymerization reaction inside the prepolymerization reactor are kept in balance, so that the temperature inside the prepolymerization reactor remains constant, and the excess heat released by the polymerization reaction is removed by the split-type condenser on the top of the prepolymerization reactor.

[0026] In this invention, for the polymerization reaction, in the stage where the conversion rate is relatively low (30-55%), the composite stirring system of the prepolymerization reactor is a continuous stirred tank structure, which can achieve a relatively uniform temperature and concentration field distribution, which helps to stabilize the reaction rate and heat of reaction, thereby improving the controllability of the reaction and the consistency of the product. Cold reactants at 20-70℃ are pumped into the prepolymerization reactor through the inlet. The heat of reaction released during polymerization is precisely managed through systematic analysis of polymerization kinetics. The heat released by the polymerization reaction in the prepolymerization reactor is first used to absorb the heat absorbed when the temperature of the cold reactants rises to the internal temperature of the reactor after entering it. Simultaneously, excess heat released by the polymerization reaction is removed by a separate condenser at the top of the prepolymerization reactor, keeping the internal temperature of the prepolymerization reactor constant, thus achieving an integrated dual thermal balance system. The heat of reaction generated during the polymerization reaction can be effectively managed through the analysis of polymerization kinetics. Because the heat released during polymerization is directly proportional to the conversion rate of monomer MMA, the conversion rate of monomer MMA can be precisely controlled by adjusting the feed temperature and flow rate, as well as process parameters such as the temperature, pressure, and residence time of the batch reactor. This allows for precise regulation of the polymerization process. See the following steps for details.

[0027] Furthermore, in step 2, the conversion rate in the prepolymer reactor can be calculated by obtaining the solid content through online solid content detection and then multiplying it by the effective reactant content (the content of materials other than the solvent).

[0028] Furthermore, in step 2, the online solid content detection method in the prepolymer reactor can be at least one of the following methods: refractive index method, near-infrared spectroscopy, online Raman spectroscopy, and drying method after sampling the reactor material.

[0029] Furthermore, in step 2, the prepolymerization reactor is a modular thermal control reactor system, which is a polymerization reaction device with efficient heat removal, precise temperature control and safety protection functions.

[0030] Furthermore, in step 2, the prepolymerization reactor includes a body, and a split condenser is integrated on the top of the body. The split condenser is connected to the body in a gas phase via a detachable connector. The interior of the vessel is equipped with a composite stirring system consisting of an anchor-type stirrer and a multi-layer improved spiral ribbon paddle. The vessel body is provided with an independent temperature control jacket around its circumference, and a cooling unit is provided above the composite stirring system to form a dual cooling channel. Furthermore, in step 2, the object body has no specific shape and is made of stainless steel.

[0031] Furthermore, in step 2, the inner tube side of the split condenser is circulated with a circulating cooling medium, and the shell side is directly connected to the top evaporation space of the condenser to form a closed-loop phase change heat transfer channel.

[0032] Furthermore, in step 2, the lower part of the split condenser is provided with a gas-liquid separation chamber, equipped with baffles and a wire mesh demister. The separated condensate is automatically returned through a U-shaped liquid seal pipe. At the same time, a steam bypass branch pipe is configured to connect to an external cryogenic unit to form a multi-stage heat removal system.

[0033] Furthermore, in step 2, the split-type condenser includes at least one of a vertical tube condenser and a spiral plate heat exchanger.

[0034] Furthermore, in step 2, the circulating cooling medium is selected from at least one of process circulating water, ethylene glycol, and aqueous ethylene glycol solution.

[0035] Furthermore, in step 2, the drive motor of the composite stirring system is equipped with a variable frequency speed control device.

[0036] Furthermore, in step 2, the independent temperature control jacket is equipped with a zoned temperature sensor and forms a PID temperature control loop with the central controller.

[0037] Furthermore, in step 2, an evaporation monitoring module, including an infrared phase change detector and a vapor flow meter, is installed at a distance of 200-500mm from the liquid level inside the vessel. This module provides real-time feedback to the variable frequency circulating pump of the split condenser, thereby achieving dynamic heat load matching.

[0038] Furthermore, in step 2, the device body is also provided with a nano-ceramic anti-corrosion coating, a sight glass observation window, and an online sampling port.

[0039] Furthermore, in steps 3-1 and 3-2, at least one of the following additives—a comonomer, a second initiator, and an optional devolatilizer—is added twice, during the polymerization reaction stage and the post-polymerization reaction stage. Increasing the polymerization reaction temperature effectively reduces the viscosity of the material melt, lowers the transport resistance of high-viscosity melts, and increases the conversion rate, ultimately achieving increased production efficiency and reduced energy consumption.

[0040] Furthermore, in steps 3-1 and 3-2, both the polymerization reactor and the post-polymerization reactor are cascaded tower-type stirred reactors. These cascaded tower-type stirred reactors are configured with 3 to 9 alternating reaction sections and heat exchange sections arranged according to the material flow direction. Each reaction section is equipped with a high-efficiency stirring component. The material after the prepolymerization reaction enters from the bottom of the tower reactor and exits from the top; alternatively, it can enter from the bottom and exit from the top. The cascaded tower-type stirred reactor is divided into multiple sections, which is beneficial for equipment manufacturing and subsequent maintenance; it also helps to enhance the mixing and heat transfer of the reaction system at high polymer concentrations, ensuring the uniformity of the concentration and temperature distribution of the polymerization reaction system.

[0041] Furthermore, in the cascaded tower stirred reactor, the height-to-diameter ratio of the reaction section is (0.2-10):1, and the height-to-diameter ratio of the heat exchange section is (0.1-5):1.

[0042] Furthermore, the cascaded tower-type stirred reactor combines the advantages of both batch reactors and tubular reactors. When the material is in the reaction section, it achieves thorough mixing through mechanical work; when the material is in the heat exchange section, it achieves sufficient heat removal through the ample heat exchange area provided by the tubular structure. As the polymerization and post-polymerization reactions proceed, the material viscosity gradually increases. The upstream reaction section has lower material viscosity, employing a stirring system suitable for low-viscosity systems, while the mid- and downstream reaction sections have higher viscosity, employing a stirring system suitable for high-viscosity systems. The cascaded tower-type stirred reactor as a whole constitutes a high-conversion polymerization reactor that combines efficient mixing, gradient heat transfer, and precise reaction process control.

[0043] Furthermore, based on the viscosity changes of the material during the polymerization process, the cascade tower-type stirred reactor is equipped with multiple layers of stirring blades. The main body of the cascade tower-type stirred reactor is made of stainless steel, and multiple annular compartments are arranged inside to form an axial gradient reaction section. The reaction section of the cascade tower-type stirred reactor is equipped with a near-wall stirring structure, including but not limited to scraper-type ribbon agitators, anchor / frame agitators, double ribbon agitators, and wide viscosity range dual-blade agitators; for example, the ratio of the blade diameter to the inner diameter of the cascade tower-type stirred reactor is 0.85~0.98.

[0044] Furthermore, the heat exchange section of the cascade tower stirred reactor adopts a detachable coil / tube design, with the inner wall of the tube polished to a mirror-level cleanliness Ra≤0.8μm. Modular mixing internals (such as spiral twisted blades or self-cleaning scrapers) are built into the tube side to enhance heat transfer and mixing, and the shell side is configured with optimized baffles (bow-shaped or spiral flow) to reduce pressure drop and achieve efficient and hygienic heat exchange.

[0045] Furthermore, the heat exchange section of the cascaded tower stirred reactor is a coaxial nested structure, with an outer layer of segmented spiral flow channel jacket and an inner layer of variable diameter spiral coil. The outer and inner layers form a dual-channel heat exchange, through which heat transfer oil and liquid carbon dioxide are introduced respectively for composite temperature control. The surface of the variable diameter spiral coil is sandblasted to form a micron-level rough structure to enhance boundary layer disturbance.

[0046] Furthermore, the cascade tower-type stirred reactor has a feed inlet in the area near the heat exchange section of the reaction section for adding initiators and other additives; after the additives enter the heat exchange section, they are mixed in the material under high viscosity conditions by relying on the internal components in the heat exchange section tubes.

[0047] Furthermore, the cascaded tower-type stirred reactor is a static mixing-heat transfer integrated tube, which eliminates flow dead zones and inhibits fluid self-aggregation through flow channel topology optimization and synergistic structure of mixing units.

[0048] Furthermore, the optimized flow channel topology and the synergistic structure of the mixing unit specifically include: employing large-angle sawtooth units or spiral structures to penetrate the high-viscosity laminar boundary layer by enhancing radial shear force; designing a gradual conical transition at the flow channel connection, combined with the arc welding of the mixing unit and the tube wall (radius of curvature R≥3D, where D is the inner diameter of the heat exchange tube), eliminating fluid stagnation dead zones and ensuring that the total dead zone volume ratio is <0.1%; Furthermore, the static mixing-heat transfer integrated tube can construct a self-aggregating and gradient-suppressing flow field: the spacing between the closely packed units in the inlet section is compressed to ≤0.3D to enhance shear, and the spacing in the outlet section is expanded to ≥2.0D to control pressure drop; the unit surface is coated with a nano-level fluorosilane or treated with ultra-polishing, the unit density in the tube wall area is increased by 30%, and the unit density in the central area is reduced by 50%, forming a radial gradient flow field.

[0049] Furthermore, the internal components within the heat exchange section tubes include at least one of the following: Kenics static mixing unit, SMX static mixing unit, Cleveland static mixing unit, cross trapezoidal belt, ribbon unit, triple spiral unit, spiral ribbon unit, and spiral coil unit.

[0050] Furthermore, the top of the cascade tower stirred reactor is equipped with a porous distributor that is flexibly connected to the discharge port of the prepolymerization reactor via a corrugated compensation pipe.

[0051] Furthermore, the cascaded tower stirred reactor is also equipped with a pressure control system, which includes a top micro-pressure control valve, a bottom back pressure regulator, and distributed fiber optic pressure sensors, forming a multivariable decoupled control model with the central DCS system.

[0052] Furthermore, the cascaded tower-type stirred reactor includes an online viscometer, a Raman spectroscopy monitoring window, and a self-cleaning sampling valve.

[0053] Further, in step 4, the devolatilizer is selected from one or more combinations of a drop-strip devolatilizer, a falling film devolatilizer, a thin-film evaporator, a single-shaft devolatilizer, a bi-shaft devolatilizer, and a vented extruder. Further, in step 4, the devolatilizer includes a primary devolatilizer and a secondary devolatilizer, used to collect unreacted monomers, additives, oligomers, and other byproducts, which are then sent to a recycling device for reuse.

[0054] Further, in step 4, the product after the polymerization reaction is pumped from the bottom of the polymerization reactor or post-polymerization reactor to the feed inlet of the primary devolatilizer via a melt pump. The feed inlet is equipped with a preheating device to reduce the viscosity of the material, improve its fluidity, maintain the material temperature during the devolatilization process, and promote the volatilization of unreacted monomers. The devolatilizer mainly removes residual monomers, solvents, residual additives, and oligomers. The residual (low-boiling-point) monomers and solvents are effective components that can be recycled, while the (high-boiling-point) residual additives and oligomers will affect the polymerization reaction. Therefore, this invention adopts a staged devolatilization method to efficiently and accurately remove monomers and recycle them.

[0055] Furthermore, in step 4, the devolatilization section of the primary devolatilizer is maintained at a slight negative pressure by a vacuum pump system, with a vacuum degree between 0 and 60 kPa. Unreacted monomers and solvents in the material rapidly evaporate into a gaseous state, while byproducts such as oligomers with higher boiling points are not removed. Simultaneously, a stirring element can be installed inside the primary devolatilizer to continuously stir and shear the material, renewing the material surface and promoting the removal of unreacted monomers. A cooling condenser (condensation temperature of -10 to 30°C) is connected to the devolatilization port. The volatilized material is cooled and liquefied when passing through the condenser. Since the condensed material consists of monomers and solvents and does not contain other impurities that affect polymerization, it can be directly recycled into the polymerization reaction process.

[0056] Furthermore, in step 4, the material after primary devolatilization continuously enters the secondary devolatilizer. Further, in step 4, in the devolatilization section of the secondary devolatilizer, a vacuum pump system maintains a vacuum level between 60 and 99.8 kPa, further increasing the vacuum level and creating a more favorable environment for the volatilization of volatile components. The substances volatilized during the secondary devolatilization process are liquefied by a cooling condenser (condensation temperature -10 to 30°C) and collected in a secondary collection tank. The collected material mainly consists of high-boiling-point residual additives and oligomers, which cannot be recycled and are present in low concentrations, allowing for direct removal and treatment as waste liquid.

[0057] Furthermore, in step 4, antioxidants can be added to the secondary devolatilization extruder via tail feed to prevent problems such as thermal decomposition or thermal discoloration of PMMA products.

[0058] Furthermore, the preparation method also includes feeding unreacted monomers collected in the primary devolatilization stage directly into the polymerization reaction section as recycled material. Unreacted monomers, additives, and oligomers collected in the secondary devolatilization stage can be directly treated as waste liquid or purified in a distillation column. The distillation column is equipped with multiple trays or packing, utilizing the principle that different substances have different vapor pressures at the same temperature. Through multiple partial vaporization and partial condensation processes, the monomers are separated from other impurities. During the distillation process, by precisely controlling parameters such as temperature, pressure, and reflux ratio, unreacted monomers are enriched at the top of the column, while impurities flow to the bottom and are discharged. The purified monomers obtained at the top of the column are collected in a purified monomer storage tank after being cooled by a condenser.

[0059] Furthermore, the water content in the refined and purified monomers is controlled below 100 ppm, and the polymerization inhibitor content is controlled below 5 ppm.

[0060] Furthermore, online analytical instruments (such as gas chromatographs) are used to monitor the composition of the purified monomers in real time. The analysis includes monomer purity, impurity content, and the proportions of various components. By analyzing the data online, the quality changes of the recovered monomers can be monitored in a timely manner, providing a basis for accurate online metering and batching before the reaction, and for recycling into the polymerization reactor.

[0061] Furthermore, in step 5, the granulation process involves at least one of the following methods: strip cutting, underwater strip cutting, underwater cutting, water ring cutting, die cutting, die hot cutting, and eccentric hot cutting.

[0062] Furthermore, the particle shape can be any of the following: spherical, cylindrical, drum-shaped, or rectangular.

[0063] This invention also provides an optical-grade PMMA resin obtained using the aforementioned preparation method.

[0064] This utility model also provides products obtained using optical-grade PMMA resin, including cosmetic packaging materials, daily necessities materials, high-end optical materials, and industrial transportation components.

[0065] Furthermore, the cosmetic packaging materials include lipstick tube casings, powder compacts, lotion bottles, serum bottles, etc.

[0066] Furthermore, the materials used in these daily necessities include toothbrush handles, combs, eyeglass frames, home decorations (such as cups and plates, ornaments, photo frames, trophies, etc.), lightbox panels, illuminated signs, directional signs, billboards, display racks, merchandise display racks, display cases, display boxes, etc.

[0067] Furthermore, the high-end optical materials include light guide plates, optical lenses, solar photovoltaic panels, etc.

[0068] The light guide plate is used in devices such as liquid crystal displays (LCDs) and light-emitting diode (LED) lighting; the optical lens is used in various lenses in optical instruments such as camera lenses, telescopes, and microscopes, such as convex lenses, concave lenses, and aspherical lenses; spectacle lenses; optical disc substrates; the solar photovoltaic panel is used in encapsulation materials or optical components (such as light-collecting covers, condenser lenses, etc.), and thin films for optical applications.

[0069] Furthermore, the industrial transportation components include medical devices (blood storage containers, syringe viewing windows, testing equipment components); instrument panels, equipment viewing mirrors, vehicle windshields, vehicle headlight covers, interior trim parts, automobile windows, ship windows, aircraft windows, etc. Attached Figure Description

[0070] Figure 1 This is a schematic diagram of the prepolymerization reactor of this utility model; Wherein, 1—the body of the prepolymerization reactor; 2—a split-type condenser; 3—a composite stirring system; 4—an independent temperature control jacket; 5—the feed inlet of the prepolymerization reactor; 6—the discharge outlet of the prepolymerization reactor; 201—Baffle plate; 202—Wire mesh demister; 203—U-shaped liquid seal tube.

[0071] Figure 2 This is a schematic diagram of the tower reactor of this utility model; Wherein, 7 is the main body of the tower reactor; 8 is the reaction section; 9 is the heat exchange section; 10 is the central drive shaft; 11 is the additive inlet I (material flows from top to bottom); and 12 is the additive inlet II (material flows from top to bottom).

[0072] Figure 3 This is a process flow diagram for preparing PMMA products according to this utility model.

[0073] Figure 4 This is a schematic diagram of the stirring paddle structure of the reaction section of the tower reactor of this utility model. Detailed Implementation

[0074] Preferred embodiments of the present invention will now be described in more detail. While preferred embodiments of the present invention are described below, it should be understood that the present invention may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present invention will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art.

[0075] like Figure 1 and Figure 3 As shown, the prepolymerization reactor in the embodiment includes a body 1, and a split condenser 2 is integrated on the top of the body 1. The split condenser 2 is connected to the body 1 in the gas phase through a detachable connector. The interior of vessel 1 is equipped with an anchor-type stirrer and a multi-layer improved ribbon impeller 301 (such as...). Figure 4 3. A composite stirring system consisting of ) The device body 1 is provided with an independent temperature control jacket 4 around its circumference, and a cooling unit 7 is provided inside the device body 1 to form a dual cooling channel. The inner tube side of the split condenser 2 is circulated with a cooling medium, and the shell side of the split condenser 2 is directly connected to the top evaporation space of the body 1 to form a closed-loop phase change heat transfer channel.

[0076] Furthermore, the gas-liquid separation chamber is equipped with a baffle plate 201 and a wire mesh demister 202, and the separated condensate is automatically returned through a U-shaped liquid seal pipe 203; the split-type condenser 2 is equipped with a steam bypass branch pipe.

[0077] Furthermore, the split-type condenser 2 includes at least one of a vertical tube condenser and a spiral plate heat exchanger.

[0078] Furthermore, the circulating cooling medium is selected from at least one of process circulating water, ethylene glycol, and aqueous ethylene glycol solution.

[0079] Furthermore, the independent temperature control jacket 4 is equipped with zoned temperature sensors and forms a PID temperature control loop with the central controller.

[0080] Furthermore, an evaporation monitoring module, including an infrared phase change detector and a steam flow meter, is installed at a distance of 200-500mm from the liquid surface inside the vessel 1. This module provides real-time feedback to the variable frequency circulating pump of the split condenser 2, thereby achieving dynamic heat load matching.

[0081] Furthermore, the device body 1 is also equipped with a nano-ceramic anti-corrosion coating, a sight glass observation window, and an online sampling port.

[0082] Furthermore, the vessel body 1 is also provided with a prepolymer reactor inlet 5 and a prepolymer reactor outlet 6.

[0083] like Figure 2As shown, the polymerization reactor or post-polymerization reactor is a tower reactor. The polymerization reactor is arranged with 5 alternating reaction sections 8 and heat exchange sections 9 (reaction section-heat exchange section-reaction section-heat exchange section-reaction section) according to the material flow direction. The post-polymerization reactor is arranged with 3 alternating reaction sections 8 and heat exchange sections 9 (reaction section-heat exchange section-reaction section) according to the material flow direction. The material after the prepolymerization reaction enters from the bottom of the tower reactor and exits from the top. In the tower reactor, the height-to-diameter ratio of reaction section 8 is (0.2-10):1, and the height-to-diameter ratio of heat exchange section 9 is (0.1-5):1.

[0084] Furthermore, as the material flows and the reaction proceeds within the tower reactor, the material viscosity gradually increases due to the increased conversion rate, rising from 5,000 centipoise to 200,000 centipoise.

[0085] Furthermore, based on the viscosity changes of the material during the polymerization process, multiple layers of stirring blades are installed inside the tower reactor. The main body of the tower reactor is made of stainless steel, and multiple annular compartments are set inside to form an axial gradient reaction section. The reaction section is equipped with a near-wall stirring structure, including but not limited to scraper-type ribbon agitators, anchor / frame agitators, double ribbon agitators, and wide viscosity range dual-blade agitators, such as double ribbon agitators. The ratio of the blade diameter to the inner diameter of the tower reactor is 0.85~0.98.

[0086] Furthermore, the main body 7 of the tower reactor is made of stainless steel.

[0087] Furthermore, the heat exchange section of the tower reactor adopts a detachable coil / tube design, with the inner wall of the tube polished to a mirror-level cleanliness Ra≤0.8μm. Modular mixing internals (such as spiral twisted blades or self-cleaning scrapers) are built into the tube side to enhance heat transfer and mixing, and the shell side is configured with optimized baffles (bow-shaped or spiral flow) to reduce pressure drop and achieve efficient and hygienic heat exchange.

[0088] Furthermore, the heat exchange section 9 of the tower reactor has a coaxial nested structure, with an outer layer of segmented spiral flow channel jacket and an inner layer of variable diameter spiral coil. The outer and inner layers form a dual-channel heat exchange, through which heat transfer oil and liquid carbon dioxide are introduced respectively for composite temperature control. The surface of the variable diameter spiral coil is sandblasted to form a micron-level rough structure to enhance boundary layer disturbance.

[0089] Furthermore, the tower reactor is equipped with additive inlet I 11 and additive inlet II 12 in the area of ​​reaction section 8 near heat exchange section 9 for the addition of additives such as initiators; after the additives enter heat exchange section 8, they are mixed in the material under high viscosity by relying on the internal components in the tubes of heat exchange section 9.

[0090] Furthermore, the heat exchange section consists of 9 tubes, which are static mixing-heat transfer integrated tubes. Through flow channel topology optimization and the synergistic structure of the mixing units, dead zones in the flow are eliminated and fluid self-agglomeration is suppressed. Specifically, the synergistic structure of the flow channel and the mixing units includes: using large-angle sawtooth units or spiral structures to enhance radial shear force to penetrate the high-viscosity laminar boundary layer; a gradually tapered transition is designed at the flow channel connection, combined with the arc welding of the mixing unit and the tube wall (radius of curvature R≥3D, where D is the inner diameter of the heat exchange tube), to eliminate fluid stagnation dead zones and ensure that the total dead zone volume ratio is <0.1%; the static mixing-heat transfer integrated tube can construct a gradient flow field that suppresses self-agglomeration: the close-packed spacing of the units in the inlet section is compressed to ≤0.3D to enhance shear breaking of the prepolymer, and the spacing in the outlet section is expanded to ≥2.0D to control pressure drop; the unit surface is coated with a nano-level fluorosilane or treated with ultra-polishing, increasing the unit density in the tube wall area by 30% and thinning the units in the central area by 50%, forming a radial gradient flow field.

[0091] Furthermore, the internal components within the nine tubes of the heat exchange section include at least one of the following: Kenics static mixing unit, SMX static mixing unit, Cleveland static mixing unit, cross trapezoidal belt, ribbon unit, triple spiral unit, spiral ribbon unit, and spiral coil unit.

[0092] Example 1 Step 1: Purification and mixing of reactants The initial reactant composition includes: 96 parts by weight of methyl methacrylate and 4 parts by weight of methyl acrylate as monomers; 4.9 parts by weight of toluene as solvent; and auxiliaries including 0.0003 parts by weight of di-tert-butyl peroxide (first initiator), 0.5 parts by weight of n-octyl mercaptan (chain transfer agent), 0.0005 parts by weight of 2-phenylbenzoxazole (ultraviolet absorber), 0.1 parts by weight of hexadecyl alcohol (mold release agent), and 3 parts by weight of n-butanol (volatilizer). The reactants are purified using a fixed-bed adsorber, and non-condensable gases are removed from the reactants using a distillation device. The reactants are then thoroughly mixed in a static mixer (interconnected type), and the proportions are precisely controlled by a high-precision feed flow control system before the reactants are pumped into the prepolymerization reactor via the static mixer. The temperature of the static mixer is controlled at 20°C, and the residence time of the reactants is controlled at 10 minutes. The Reynolds number Re of the reactants entering the static mixer is controlled to be greater than 4000; Step 2: Prepolymerization reaction The mixed reactants from step 1 are fed into the prepolymerization reactor through the feed inlet of the static mixer. The feed temperature is 20°C. The internal temperature of the prepolymerization reactor is controlled at 150°C and the internal pressure is 0.2 MPa. The reactants inside the reactor are kept warm by jacketed heat transfer oil and built-in coils. The reaction residence time is 20 minutes. In the prepolymerization reaction, after the conversion rate of the polymeric monomer MMA reaches 43%, the reactants after the prepolymerization reaction are sent into the polymerization reactor through the bottom outlet of the prepolymerization reactor. Step 3-1: Polymerization reaction The feed temperature of the polymerization reactor is 150℃, the temperature inside the reactor is controlled at 150~160℃, the polymerization pressure is 1.0 MPa, and the residence time is 3h. Add 0.0008 parts of the second initiator, tert-butyl cumene peroxide (155°C), through the feed inlet. The conversion rate of the polymerized monomer MMA reaches 55-75%; Step 4: Deviation Extrusion Granulation The product after polymerization is fed into a co-rotating twin-screw vented extruder, where unreacted monomers, additives and oligomer byproducts are removed through the devolatilization port. The exhaust extruder consists of 6 sections, with temperatures and vacuum levels of 210℃ and 50KPa, 220℃ and 60KPa, 225℃ and 70KPa, 225℃ and 80KPa, 225℃ and 85KPa, and 230℃ and 99KPa, respectively. The volatile components collected from multiple exhaust ports of the extruder are separated by a condensation recovery system; PMMA melt is obtained from the end of the extrusion section, and then granulated to obtain the final PMMA product.

[0093] The PMMA performance and test results of Example 1 are listed in Table 1.

[0094] Table 1 Test results of Example 1

[0095] Example 2 Step 1: Purification and mixing of reactants The initial reactant composition includes: 94 parts by weight of methyl methacrylate and 6 parts by weight of methyl acrylate monomers, with no solvent added; and auxiliaries including 0.0001 parts by weight of di-tert-butyl peroxide (first initiator), 1 part by weight of n-octyl mercaptan (chain transfer agent), 0.0002 parts by weight of 2-phenylbenzoxazole (ultraviolet absorber), 0.05 parts by weight of hexadecyl alcohol (mold release agent), and 1 part by weight of n-butanol (volatilizer). The mixed reactants from step 1 are fed into the prepolymerization reactor through the bottom inlet of the static mixer. The feed temperature is 15°C. The internal temperature of the prepolymerization reactor is controlled at 145°C and the internal pressure is 0.1 MPa. The reactants inside the reactor are kept warm by jacketed heat transfer oil and built-in coils. The reaction residence time is 25 minutes. In the prepolymerization reaction, after the conversion rate of the polymeric monomer MMA reaches 43%, the reactants after the prepolymerization reaction are sent into the polymerization reactor through the bottom outlet of the prepolymerization reactor. Step 3-1: Polymerization reaction The feed temperature of the polymerization reactor is 145℃, the temperature inside the reactor is controlled at 145~155℃, the polymerization pressure is 1.0 MPa, and the residence time is 3h. Add 0.0003 parts of the second initiator, tert-butyl cumene peroxide (150°C), through the feed inlet. The conversion rate of the polymerized monomer MMA reaches 55-75%; Step 3-2: Post-polymerization reaction The feed temperature of the post-polymerization reactor is 160℃, the temperature inside the reactor is controlled at 160~165℃, the polymerization pressure is 1.0Mpa, and the residence time is 1h. Step 4: Deviation Extrusion Granulation The product after the polymerization reaction is transported to the strip devolatilizer, where the vacuum degree is 30 kPa and the temperature is 250 °C, and unreacted polymer monomers and other by-products are removed from the devolatilization port. The material passing through the strip devolatilizer re-enters the co-rotating twin-screw exhaust extruder, which consists of 6 sections with temperatures and vacuum levels of 210℃ and 50KPa, 220℃ and 60KPa, 225℃ and 70KPa, 225℃ and 80KPa, 225℃ and 85KPa, and 230℃ and 99KPa, respectively. The volatile components collected from multiple exhaust ports of the vented extruder are separated by a condensation recovery system; PMMA melt is obtained from the end of the vented extruder, and then granulated to obtain the final PMMA product.

[0096] The PMMA performance and test results of Example 2 are listed in Table 2.

[0097] Table 2 Test results of Example 2

[0098] Example 3 Step 1: Purification and mixing of reactants The initial reaction material composition is as follows: the monomers include 97 parts by weight of methyl methacrylate and 3 parts by weight of styrene, without solvent, and the additives include 0.0005 parts by weight of di-tert-butyl peroxide (first initiator), 2 parts by weight of n-octyl mercaptan (chain transfer agent), 0.08 parts by weight of hexadecyl alcohol (release agent) and 2 parts by weight of n-butanol (volatilizer). The reactants are purified using a fixed-bed adsorber, and non-condensable gases are removed from the reactants using a distillation device. The reactants are then thoroughly mixed in a static mixer (interconnected type), and the proportions are precisely controlled by a high-precision feed flow control system before the reactants are pumped into the prepolymerization reactor via the static mixer. The temperature of the static mixer is controlled at 30°C, and the residence time of the reactants is controlled at 20 minutes. The Reynolds number Re of the reactants entering the static mixer is controlled to be greater than 4000; Step 2: Prepolymerization reaction The mixed reactants from step 1 are fed into the prepolymerization reactor through the feed inlet of the static mixer. The feed temperature is 30°C. The internal temperature of the prepolymerization reactor is controlled at 140°C and the internal pressure is 0.3 MPa. The reactants inside the reactor are kept warm by jacketed heat transfer oil and built-in coils. The reaction residence time is 30 minutes. In the prepolymerization reaction, after the conversion rate of the polymeric monomer MMA reaches 38%, the reactants after the prepolymerization reaction are sent into the polymerization reactor through the bottom outlet of the prepolymerization reactor. Step 3-1: Polymerization reaction The feed temperature of the polymerization reactor is 145℃, the temperature inside the reactor is controlled at 145~155℃, the polymerization pressure is 1.0 MPa, and the residence time is 2h. Add 0.0008 parts of the second initiator, tert-butyl cumene peroxide (150°C), through the feed inlet. The conversion rate of the polymerized monomer MMA reaches 55-75%; Step 3-2: Post-polymerization reaction The feed temperature of the post-polymerization reactor is 160℃, the temperature inside the reactor is controlled at 160~165℃, the polymerization pressure is 1.0Mpa, and the residence time is 2h. Step 4: Deviation Extrusion Granulation The product after the polymerization reaction is conveyed to the strip devolatilizer, where the vacuum degree is 70 kPa and the temperature is 250 °C. Unreacted monomers, additives and oligomer byproducts are removed from the devolatilization port. The material passing through the strip devolatilizer re-enters the co-rotating twin-screw exhaust extruder, which consists of 9 sections with temperatures and vacuum levels of 210℃ and 50KPa, 220℃ and 60KPa, 225℃ and 70KPa, 225℃ and 80KPa, 225℃ and 85KPa, 230℃ and 90KPa, 230℃ and 90KPa, 235℃ and 99.5KPa, and 230℃ and 90KPa, respectively. The volatile components collected from multiple exhaust ports of the vented extruder are separated by a condensation recovery system; PMMA melt is obtained from the end of the vented extruder, and then granulated to obtain the final PMMA product.

[0099] The PMMA performance and test results of Example 3 are listed in Table 3.

[0100] Table 3 Test results of Example 3

[0101] Comparative Example 1 Traditional single-reactor process The initial reactant composition includes: 94 parts by weight of methyl methacrylate and 6 parts by weight of methyl acrylate, and 30 parts by weight of toluene (solvent addition of approximately 30%); the additives include 0.0001 parts by weight of di-tert-butyl peroxide (first initiator), 1 part by weight of n-octyl mercaptan (chain transfer agent), 0.0002 parts by weight of 2-phenylbenzoxazole (ultraviolet absorber), 0.05 parts by weight of hexadecyl alcohol (mold release agent), and 1 part by weight of n-butanol (volatilizer). Process: (1) Purification and mixing of reactants The reactants are purified using a fixed-bed adsorber, and non-condensable gases are removed from the reactants using a distillation unit. The reactants are then thoroughly mixed in a static mixer (interconnected type), and the proportions are precisely controlled by a high-precision feed flow control system before the reactants are pumped into a single vertical reactor via the static mixer. The temperature of the static mixer is controlled at 40℃, and the residence time of the reactants is controlled at 20 minutes. The Reynolds number of the reactants entering the static mixer is controlled to be approximately 1500 (laminar flow state), resulting in poor mixing uniformity (coefficient of variation > 15%). (2) Polymerization reaction The mixed reaction material from step (1) is fed into a single vertical stirrer (using a single three-bladed impeller) through the feed port of the single vertical stirrer. The feed temperature is 20℃, the internal temperature is constant at 150℃±5℃ (gradient temperature control cannot be achieved), and the internal pressure is atmospheric pressure (no pressure regulation). The reaction material inside the stirrer is kept warm by heat transfer oil in the jacket. The polymerization reaction time is 90 minutes, and the conversion rate of the polymerized monomer MMA is only 50% (the reactor volume is too large, the material viscosity is high, resulting in insufficient mass and heat transfer; the long reaction time makes the initiator easy to decompose, resulting in weakened polymerization activity). The reaction material after polymerization is sent to the devolatilizer. (3) Deviation extrusion granulation: Since the reactants in this process contain nearly 30% solvent, a flash tank is required for pre-devouring, with the temperature set at 200℃ and the vacuum level controlled at 50kPa. The pre-devoured polymer product is then devoured using a twin-screw extruder at a temperature of 220°C and a vacuum of 95 kPa, with a total devouring time of >20 minutes.

[0102] After the above steps, the solvent recovery rate is ≤85%, and the residual solvent causes the product to turn yellow.

[0103] Table 4 Performance test results of Example 2 and Comparative Example 1

[0104] Comparative Example 2 A two-stage single vertical agitator in series is used.

[0105] The initial reactant composition includes: 94 parts by weight of methyl methacrylate and 6 parts by weight of methyl acrylate, and 30 parts by weight of toluene (solvent addition of approximately 30%); the additives include 0.0001 parts by weight of di-tert-butyl peroxide (first initiator), 1 part by weight of n-octyl mercaptan (chain transfer agent), 0.0002 parts by weight of 2-phenylbenzoxazole (ultraviolet absorber), 0.05 parts by weight of hexadecyl alcohol (mold release agent), and 1 part by weight of n-butanol (volatilizer). Process: (1) Purification and mixing of reactants The reactants are purified using a fixed-bed adsorber, and non-condensable gases are removed from the reactants using a distillation unit. The reactants are then thoroughly mixed in a static mixer (interconnected type), and the proportions are precisely controlled by a high-precision feed flow control system before the reactants are pumped into a single vertical reactor via the static mixer. The temperature of the static mixer is controlled at 40℃, and the residence time of the reactants is controlled at 30 minutes. The Reynolds number of the reactants entering the static mixer is controlled to be approximately 1500 (laminar flow state), resulting in poor mixing uniformity (coefficient of variation > 15%). (2) Polymerization reaction It employs a series two-stage single vertical agitator (length-to-diameter ratio 2:1), relying solely on jacketed heat transfer oil for heat exchange; The mixed reaction material from step (1) is fed into the first-stage single vertical agitator (single three-blade impeller) through the feed port of the single vertical agitator. After the prepolymerization reaction, the reaction material is fed into the second-stage single vertical agitator (single three-blade impeller). The first-stage polymerization reaction time was controlled at 60 minutes, the feed temperature at 20°C, the temperature inside the first-stage polymerization reactor at 145°C, and the internal pressure at atmospheric pressure (without pressure control). The conversion rate of the monomer MMA was 35%. The second-stage polymerization reaction time was controlled at 60 minutes, the feed temperature at 145℃, the temperature inside the second-stage polymerization reactor at 155℃, and the internal pressure at atmospheric pressure (without pressure control). The conversion rate of the polymerizable monomer MMA was 55% (high material viscosity led to insufficient mass and heat transfer; prolonged reaction caused the initiator to decompose easily, resulting in weakened polymerization activity). The reactants after the polymerization reaction are fed into a devolatilizer; (3) Deviation extrusion granulation Since the reactants in this process contain 30% solvent, a flash tank is required for pre-devouring, with the temperature set at 230°C and the vacuum level controlled at 50 kPa. The pre-devoured polymer product is then devoured using a twin-screw extruder at a temperature of 220°C and a vacuum of 95 kPa, with a total devouring time of >20 minutes.

[0106] After the above steps, the solvent recovery rate is ≤85%, and the residual solvent causes the product to turn yellow.

[0107] Table 5 Performance test results of Example 2 and Comparative Example 2

[0108] Comparative Example 3 A vertical stirred tank and a tubular reactor are used in series.

[0109] The initial reactant composition includes: 96 parts by weight of methyl methacrylate and 4 parts by weight of methyl acrylate as monomers; 4.9 parts by weight of toluene as solvent; and 0.0003 parts by weight of di-tert-butyl peroxide (first initiator), 0.5 parts by weight of n-octyl mercaptan (chain transfer agent), 0.0005 parts by weight of 2-phenylbenzoxazole (ultraviolet absorber), 0.1 parts by weight of hexadecyl alcohol (release agent), and 3 parts by weight of n-butanol. Process: (1) Purification and mixing of reactants The reactants are purified using a fixed-bed adsorber, and non-condensable gases are removed from the reactants using a distillation unit. The reactants are then thoroughly mixed in a static mixer (interconnected type), and the proportions are precisely controlled by a high-precision feed flow control system before the reactants are pumped into a single vertical reactor via the static mixer. The temperature of the static mixer is controlled at 40℃, and the residence time of the reactants is controlled at 30 minutes. The Reynolds number of the reactants entering the static mixer is controlled to be approximately 1500 (laminar flow state), resulting in poor mixing uniformity (coefficient of variation > 15%). (2) Polymerization reaction It adopts a vertical stirred tank and a tubular reactor, relying solely on jacketed heat transfer oil for heat exchange; The mixed reaction material from step (1) is fed into the first-stage single vertical stirrer (single three-bladed impeller) through the feed port of the single vertical stirrer, and after the prepolymerization reaction, the reaction material is fed into the tubular reactor. The first-stage polymerization reaction time was controlled at 60 minutes, the feed temperature at 20°C, the temperature inside the first-stage polymerization reactor at 145°C, and the internal pressure at atmospheric pressure (without pressure control). The conversion rate of the monomer MMA was 35%. The second-stage polymerization reaction time was controlled at 60 minutes, the feed temperature was 145℃, the temperature inside the second-stage polymerization reactor showed a gradient distribution, gradually increasing from 145 to 170℃, the internal pressure was 20 MPa (without pressure control), and the conversion rate of the polymer monomer MMA was 75% (the tubular reactor had no stirring, the high viscosity of the material led to insufficient mass and heat transfer; the temperature showed a gradient distribution, and the polymerization reaction process was not uniform). The reactants after the polymerization reaction are fed into a devolatilizer; (3) Deviation extrusion granulation Since the reactants in this process contain 30% solvent, a strip-type devolatilization process needs to be added, with the temperature set at 230℃ and the vacuum degree controlled at 50kPa. The pre-devoured polymer product is then devoured using a twin-screw extruder at a temperature of 220°C and a vacuum of 95 kPa, with a total devouring time of >20 minutes.

[0110] After the above steps, the solvent recovery rate is ≤85%, and the residual solvent causes the product to turn yellow.

[0111] Table 6 Performance test results of Example 1 and Comparative Example 3

[0112] The above description is merely a preferred embodiment of the present utility model and is not intended to limit the present utility model in any other way. Any modifications or equivalent changes made based on the technical essence of the present utility model shall still fall within the scope of protection claimed by the present utility model.

Claims

1. A prepolymerization reactor, characterized in that, Includes a body (1), the top of which is integrated with a split condenser (2), the split condenser (2) being connected to the body (1) in a gas phase via a detachable connector; The interior of the vessel body (1) is equipped with a composite stirring system (3) consisting of an anchor-type stirrer and a multi-layer spiral blade (301). The vessel body (1) is provided with an independent temperature control jacket (4) around its circumference, and a cooling unit (7) is provided above the composite stirring system (3) to form a dual cooling channel; The inner tube side of the split condenser (2) is circulated with a cooling medium, and the shell side of the split condenser (2) is directly connected to the top evaporation space of the body (1) to form a closed-loop phase change heat transfer channel.

2. The prepolymerization reactor according to claim 1, characterized in that, The split condenser (2) is provided with a gas-liquid separation chamber at the bottom. The gas-liquid separation chamber is equipped with a baffle plate (201) and a wire mesh demister (202). The separated condensate is automatically returned through a U-shaped liquid seal pipe (203). The split condenser (2) is equipped with a steam bypass branch pipe to connect to an external cryogenic unit to form a multi-stage heat removal system.

3. The prepolymerization reactor according to claim 1 or 2, characterized in that, The split-type condenser (2) includes at least one of a vertical tube condenser and a spiral plate heat exchanger.

4. A continuous bulk polymerization system for PMMA, characterized in that, The system, in accordance with the direction of material transport and the reaction process, includes, in sequence, a material purification and degassing module, a material mixing module, a prepolymerization reaction module, a polymerization module, and optionally a post-polymerization module, a devolatilization module, and a granulation module. The material purification and degassing module is equipped with a raw material purifier; the material mixing module is equipped with a static mixer; the prepolymerization reaction module is equipped with a prepolymerization reactor as described in any one of claims 1-3; the polymerization module and optionally the post-polymerization module are equipped with a polymerization reactor and a post-polymerization reactor; the devolatilization module is equipped with a devolatilizer; and the granulation module is equipped with a granulator. Raw material purifier: used to remove impurities from reactants; Static mixer: Used to uniformly mix purified reactants with additives; Prepolymerization reactor: used to initiate polymerization reactions and form prepolymers; Polymerization reactor: Used to further polymerize prepolymers to obtain polymer materials; Post-polymerization reactor: Used to carry out post-polymerization reaction of polymer materials to obtain post-polymer materials; Deviation device: used to remove unreacted monomers and low-boiling-point volatile components from the polymer material and / or the post-polymer material; Granulator: After the devolatilization process, the molten material is extruded or pumped into a pelletizer to be cut into uniform particles that are easy to process.

5. The PMMA continuous bulk polymerization system according to claim 4, characterized in that, Both the polymerization reactor and the post-polymerization reactor are cascaded tower stirred reactors, and the cascaded tower stirred reactors are configured with 3 to 9 alternating reaction sections and heat exchange sections according to the material flow direction.

6. The PMMA continuous bulk polymerization system according to claim 5, characterized in that, In the cascaded tower-type stirred reactor, the height-to-diameter ratio of the reaction section is (0.2-10):1, and the height-to-diameter ratio of the heat exchange section is (0.1-5):

1.

7. The PMMA continuous bulk polymerization system according to claim 6, characterized in that, The cascaded tower-type stirred reactor is equipped with multiple layers of stirring paddles; the main body of the cascaded tower-type stirred reactor is made of stainless steel, and multiple annular compartments are set inside to form an axial gradient reaction section.

8. The PMMA continuous bulk polymerization system according to claim 6, characterized in that, The reaction section of the cascade tower-type stirred reactor is equipped with a near-wall stirring structure, including a scraper ribbon agitator, an anchor / frame agitator, a double ribbon agitator, and a wide viscosity range double-blade agitator.

9. The PMMA continuous bulk polymerization system according to claim 6, characterized in that, The heat exchange section of the cascade tower stirred reactor adopts a detachable coil / tube design, with the inner wall of the tube polished to a mirror-level cleanliness Ra≤0.8μm. Modular mixing internals are built into the tube side to enhance heat transfer and mixing, and the shell side is configured with optimized baffles to reduce pressure drop, achieving efficient and hygienic heat exchange.

10. The PMMA continuous bulk polymerization system according to claim 4, characterized in that, The devolatilizer is selected from one or more combinations of a drop strip devolatilizer, a falling film devolatilizer, a thin film evaporator, a single-shaft devolatilizer, a bi-shaft devolatilizer, and a vented extruder.

Images