A multi-stage circulating rubber devolatilization device and method based on microwave-infrared coupled heating

Abstract

The application discloses a kind of multistage circulating rubber devolatilization device and method based on microwave-infrared coupling heating, belong to high polymer material processing technical field.The device includes quartz glass jar body, metal microwave shielding cavity, microwave generator, infrared lamp tube, multistage drop bar distributor and bottom direct connection screw pump.The application utilizes microwave volume heating to directly heat rubber melt, supplemented by infrared radiation to compensate surface temperature drop, avoid the rubber thermal crosslinking coking caused by traditional wall heating.The device uses intermittent circulation process, by switching coarse hole, medium hole and micropore distributor online, cooperate with the gradient regulation of vacuum degree and temperature, make rubber solution form drop bar matching its rheological property in different devolatilization stage.Bottom wide-neck screw pump realizes zero liquid holdup direct discharge, eliminate flow dead angle.The application effectively realizes the efficient, mild devolatilization of high viscosity heat-sensitive synthetic rubber, and the final volatile content can be stably controlled below 500ppm, and the product does not occur obvious thermal crosslinking.

Description

Technical Field

[0001] This invention relates to the field of polymer material processing and chemical equipment technology, specifically to a multi-stage circulating rubber devolatilization device and method based on microwave-infrared coupled heating. Background Technology

[0002] Synthetic rubber (such as ethylene propylene rubber, solution-polymerized styrene-butadiene rubber, and butyl rubber) is a fundamental material in modern industry, widely used in automobiles, construction, and electronics. In traditional solution polymerization processes, limited by the low activity of early Ziegler-Natta catalyst systems, high concentrations of metal ions often remain in the polymer solution. This necessitates washing and deashing with large amounts of acidic or hot water, requiring energy-intensive wet coagulation processes, i.e., using high-temperature steam stripping to remove the solvent. However, with advancements in synthetic rubber technology, particularly the widespread application of highly active catalyst systems such as metallocene and post-metallocene catalysts, the catalyst residue in the polymerization products has significantly decreased, making traditional water washing and deashing no longer a necessary step. This chemical process innovation provides the prerequisite for dry devolatilization. Compared to wet processes, dry devolatilization directly heats and flashes the polymer solution or melt, utilizing the fact that the latent heat of vaporization of organic solvents is much lower than that of water. It offers significant advantages such as shorter process time, lower energy consumption, and no wastewater discharge, and has become an inevitable trend in the industry.

[0003] However, synthetic rubber melts typically possess extremely high viscosity (reaching thousands to tens of thousands of Pa·s) and extremely poor thermal conductivity (usually in the range of 0.15~0.25 W / (m·K)). Furthermore, most synthetic rubber molecules contain unsaturated double bonds, making them typical heat-sensitive materials. In dry devolatilization processes, resolving the contradictions such as low heat transfer efficiency of high-viscosity rubber solutions or melts, susceptibility to thermal cross-linking and denaturation, easy coking on the wall surface, and uncontrollable residence time distribution has become a key bottleneck restricting the industrial application of this technology.

[0004] Existing technology CN110639461A discloses a "falling film devolatilizer and its falling film element," which uses a specific falling film element structure to allow material to flow along the element surface under gravity to form a film, thereby increasing the evaporation area. Although this design improves surface renewal to some extent, its heat input still essentially relies on the surface heat conduction of the vessel wall or internal components. Since synthetic rubber melt is a poor conductor of heat, in order to ensure that the fluid reaches the activation energy required for devolatilization, the heated wall surface must maintain a high degree of superheat (usually 30-50°C higher than the bulk material temperature). This externally heated and internally cooled heating mode results in the fluid layer adhering to the wall being in a high-temperature state for a long time, which easily induces the free radical cross-linking reaction of polymer chains, forming a difficult-to-remove glue and coking layer on the inner wall of the equipment. This not only deteriorates the heat transfer efficiency, but the scorched particles that peel off also contaminate the product quality.

[0005] Existing technology CN115572337A discloses "a method and equipment for devolatilization of polymer solutions," which employs multi-stage flash evaporation technology and includes a collection zone at the bottom of the devolatilizer to maintain production continuity and pumping pressure. While this design ensures the pump's suction head, for high-viscosity non-Newtonian fluids, the molten pool structure at the bottom leads to severe material retention and flow dead zones. In industrial production, this means an extremely wide distribution of material residence time. Some materials with excessively long residence times are prone to thermal cross-linking at high temperatures, forming gel particles, resulting in poor batch-to-batch consistency and making strict process control difficult.

[0006] Existing technology CN117507293B discloses a "process for drying, devolatilization, and tail gas treatment of halogenated butyl rubber based on microwave drying," which introduces microwave heating technology. However, this existing technology mainly targets broken porous rubber particles, where the treated object is in a solid-state accumulation mode, focusing on moisture removal. For synthetic rubber fluids in a molten flow state that require large specific surface area renewal to overcome mass transfer resistance, this technology lacks corresponding flow field shaping and control mechanisms. It cannot solve the problem of decreased devolatilization efficiency caused by the rapid shrinkage of specific surface area during the devolatilization process of high-viscosity melts, and it does not involve the design of an industrial continuous flow device to prevent microwave leakage.

[0007] Therefore, to address the aforementioned problems, this invention provides a multi-stage circulating rubber devolatilization device and method based on microwave-infrared coupled heating. By employing a composite structure of a quartz glass tank and a metal microwave shielding cavity, the rubber melt is directly heated using the volumetric heating characteristics of microwaves, supplemented by infrared radiation to compensate for surface temperature drop, fundamentally avoiding the rubber thermal cross-linking and coking problems caused by traditional wall heating. By setting up a multi-stage droplet distributor, combined with gradient control of vacuum and temperature, the rubber solution forms droplets matching its rheological properties at different devolatilization stages, achieving dynamic optimization of the mass transfer area. Through the zero-holding direct discharge design of the bottom wide-mouth screw pump, dead flow angles are eliminated, avoiding prolonged residence of rubber on the wall surface, thus solving the problems of low heat transfer efficiency, easy coking on the wall surface, many dead liquid holding angles at the bottom, and difficulty in adapting to large viscosity changes leading to incomplete devolatilization and rubber thermal cross-linking and denaturation in the prior art. Summary of the Invention

[0008] In order to overcome the problems of low heat transfer efficiency, easy coking on the wall surface, many dead zones at the bottom, and incomplete devolatilization and rubber thermal crosslinking caused by large viscosity changes in existing dry devolatilization technologies for synthetic rubber, and to achieve efficient and gentle devolatilization of high viscosity and heat-sensitive synthetic rubber, avoid thermal aging and thermal crosslinking, and significantly shorten the devolatilization process, this invention provides a multi-stage circulating rubber devolatilization device and method based on microwave-infrared coupled heating.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] A multi-stage circulating rubber devolatilization device based on microwave-infrared coupled heating includes: a quartz glass tank for containing rubber material and performing devolatilization treatment; a metal microwave shielding cavity, in which the quartz glass tank is placed; a microwave generator installed on the side wall of the metal microwave shielding cavity for volumetric heating of the rubber material inside the quartz glass tank; an infrared lamp disposed between the quartz glass tank and the metal microwave shielding cavity for radiative compensation of the surface temperature drop of the rubber material; and a multi-stage strip distributor, including strip distributors A, B, and C arranged in parallel at the top of the quartz glass tank with successively decreasing apertures, controlled by material inlet valves A, B, and C respectively. The system includes: a screw pump with its inlet directly connected to the bottom of the quartz glass tank via a wide-mouth transition section; a material outlet pressure detection system at the outlet, divided into two paths: one path connects to the discharge port via a material outlet valve, and the other path connects to the inlet of the multi-stage strip distributor at the top of the quartz glass tank via a material circulation valve; a material inlet located upstream of the screw pump for injecting the rubber solution to be devolatilized into the system; a vacuum pump connected to the quartz glass tank via a vacuum valve; a nitrogen cylinder connected to the quartz glass tank via a nitrogen valve; a tank pressure detection system located on the quartz glass tank; a tank temperature detection system located on the quartz glass tank; a material inlet pressure detection system located on the inlet pipeline of the multi-stage strip distributor; and an atmospheric valve located at the top of the quartz glass tank. This technical solution utilizes a quartz glass container to allow microwaves to penetrate without attenuation and heat the rubber melt as a whole. Simultaneously, infrared lamps compensate for the surface temperature drop caused by vacuum evaporation. The combined effect of these two components achieves uniform and gentle heating, avoiding the rubber thermal cross-linking and scorching problems caused by overheated walls, common in traditional wall-conduction heating methods. A metal microwave shielding cavity effectively prevents microwave leakage, ensuring operational safety. The parallel arrangement of multi-stage dropper distributors provides the hardware foundation for subsequent staged flow field control.

[0011] Preferably, the pore sizes of the strip distributors A, B, and C are configured as follows: coarse-pore distributors with a pore size of 6-10 mm, medium-pore distributors with a pore size of 4-6 mm, and micro-pore distributors with a pore size of 2-4 mm, to adapt to the gradually increasing viscosity rheological characteristics during rubber devolatilization. This pore size range design is based on in-depth research into the rheological properties of rubber at different devolatilization stages: in the initial devolatilization stage, the rubber solution has a high volatile content and low viscosity; using a larger pore size can form stable coarse strips, preventing a decrease in specific surface area due to strip breakage; as devolatilization progresses, the rubber viscosity gradually increases, requiring a smaller pore size to form finer strips, increasing the gas-liquid contact specific surface area and overcoming mass transfer resistance at high viscosity; in the deep devolatilization stage, micropores are used to form extremely fine strips, achieving ultimate removal of residual volatiles under the synergistic effect of high vacuum and microwaves. This gradient pore size design ensures optimal matching between the strip morphology and the material rheological properties at each stage.

[0012] Preferably, the screw pump is a wide-mouth direct-connect screw pump, with its inlet directly connected to the bottom of the quartz glass tank in a zero-holding direct connection without a liquid collection zone, eliminating dead zones in the flow. This design fundamentally solves the material retention problem caused by the bottom molten pool structure of traditional devolatilizers. In traditional equipment, the material residence time distribution in the bottom liquid collection zone is extremely wide, and some materials may be exposed to high-temperature environments for extended periods, resulting in thermal cross-linking and the formation of gel particles. This invention directly connects the bottom of the tank to the screw pump inlet through a wide-mouth transition section, allowing the material to immediately enter the screw pump by gravity and be forcibly conveyed, achieving "zero-holding" operation. The heating history of all materials is highly uniform, significantly narrowing the residence time distribution, effectively preventing thermal aging and coking of easily cross-linked rubber, and ensuring consistency between product batches.

[0013] This application also provides a method for multi-stage cyclic rubber devolatilization based on microwave-infrared coupling heating using the above-mentioned device, including the following steps:

[0014] S1. System Oxygen Replacement and Purging: Close all valves, open the vacuum valve, use the vacuum pump to extract the gas from the quartz glass tank, then close the vacuum valve, open the nitrogen valve and nitrogen cylinder, and introduce nitrogen into the quartz glass tank. Repeat the above extraction and nitrogen filling operations at least three times, monitor the pressure through the tank pressure detection system, and complete the oxygen replacement and purging in the system.

[0015] S2. Feeding and Establishing Circulation: Start the screw pump, open the material inlet, material circulation valve, and material inlet valve A, and inject the rubber solution to be devolatilized through the material inlet. Driven by the screw pump, the circulation pipeline is filled, and the solution falls back to the bottom of the quartz glass tank through the dropper A. After the pressure is stable and a liquid seal is established at the bottom of the tank, the material inlet is closed, and the device enters an independent closed-loop devolatilization mode.

[0016] S3, First-stage devolatilization: Turn on the microwave generator and infrared lamp, set the heating temperature, open the vacuum valve, and adjust the vacuum pump to make the quartz glass tank a low vacuum state. The rubber solution circulates through the coarse strips formed by the strip distributor A. A large amount of volatile matter is removed by microwave volume heating and infrared radiation to compensate for the surface temperature drop. The volatile matter content is sampled and monitored through the material outlet valve until it reaches the first set value.

[0017] S4, Secondary Deviation: When the volatile content drops to the first set value, close material inlet valve A, open material inlet valve B, adjust the vacuum valve to increase the vacuum level inside the quartz glass tank to a medium level, adjust the heating power of the microwave generator and infrared lamp, and the rubber solution forms a medium-diameter dropper circulation flow through the dropper distributor B to enhance gas-liquid mass transfer. The volatile content is sampled and monitored through the material outlet valve until it reaches the second set value.

[0018] S5, Three-stage devolatilization: When the volatile content drops to the second set value, close the material inlet valve B, open the material inlet valve C, adjust the vacuum valve to achieve the ultimate high vacuum state in the quartz glass tank, adjust the heating power of the microwave generator and infrared lamp, and the rubber melt circulates through the fine droplets formed by the droplet distributor C to deeply remove residual volatiles. The volatile content is sampled and monitored through the material outlet valve until it reaches the third set value.

[0019] S6. Discharge: When the volatile content drops to the third set value, close the vacuum valve and vacuum pump, open the nitrogen valve and nitrogen cylinder to break the vacuum to positive pressure, close the material circulation valve, open the material outlet valve, and discharge the finished product through the screw pump. This method, through the design of online switching of different aperture distributors, realizes dynamic control of the flow field morphology during the devolatilization process, so that the drop strip diameter gradually decreases as the rubber viscosity increases, always maintaining the optimal gas-liquid mass transfer interface. The closed-loop circulation mode allows the material to pass through the devolatilization zone multiple times, resulting in a significant cumulative devolatilization effect, while avoiding the problem of incomplete devolatilization caused by insufficient residence time in single-pass equipment. The system's oxygen replacement and deoxygenation steps effectively prevent the oxidative degradation of rubber by oxygen at high temperatures and the thermo-oxidative cross-linking reaction, ensuring product quality.

[0020] Preferably, the low vacuum state in step S3 is an absolute pressure of 30~80 kPa, the medium vacuum state in step S4 is an absolute pressure of 5~30 kPa, and the ultimate high vacuum state in step S5 is an absolute pressure of 0.1~5 kPa. This vacuum gradient design matches the physical properties of each devolatilization stage: during the first devolatilization stage, the volatile content is high and flash evaporation is intense; excessively high vacuum may lead to foaming and mist entrainment, so a lower vacuum is used; as devolatilization proceeds, the interaction between residual volatiles and rubber intensifies, requiring a higher vacuum to provide a greater mass transfer driving force; the deep devolatilization stage uses an ultimate high vacuum, which can effectively overcome the diffusion resistance in high-viscosity melts under the synergistic effect of microwaves, removing volatiles to trace levels.

[0021] Preferably, the heating temperatures of the microwave generator and infrared lamps in steps S3 to S5 are gradually increased, with the first-stage devolatilization temperature being 120-150°C, the second-stage devolatilization temperature being 150-170°C, and the third-stage devolatilization temperature being 170-200°C. This temperature gradient is designed based on the thermodynamic requirements of rubber devolatilization: in the initial stage of devolatilization, the vaporization of a large amount of solvent requires the absorption of a significant amount of heat, but the material viscosity is low and the mass transfer resistance is small, so a suitable temperature is sufficient; as devolatilization progresses, the interaction between the residual volatiles and rubber molecules intensifies, requiring a higher temperature to provide sufficient activation energy to overcome diffusion resistance. Simultaneously, the gradual increase in temperature also avoids exposing the material to excessively high temperatures in the initial stage, reducing the risk of thermal aging of heat-sensitive rubber.

[0022] Preferably, in steps S3 to S5, the first set value is 30,000~50,000 ppm, the second set value is 3,000~6,000 ppm, and the third set value is ≤500 ppm. This volatile matter content threshold is set based on the optimization results of numerous process experiments: when the volatile matter content is higher than 50,000 ppm, the material viscosity is low, making it suitable for rapid removal using a coarse-pore distributor; when the volatile matter content drops to the 30,000~50,000 ppm range, the viscosity begins to rise, requiring a switch to a medium-pore distributor to maintain sufficient mass transfer area; when the volatile matter content drops to the 3,000~6,000 ppm range, the rubber is close to a high-viscosity melt state, necessitating a switch to a microporous distributor combined with extreme high vacuum to further remove the volatile matter to below 500 ppm, meeting the purity requirements of high-end applications.

[0023] Preferably, the rubber solution to be devolatilized is a solution polymer of ethylene propylene rubber, solution-polymerized styrene-butadiene rubber, or butyl rubber, and the solvent is cyclohexane, n-hexane, or Isopar E. These synthetic rubbers generally face a dilemma during devolatilization: although ethylene propylene rubber has a high degree of molecular chain saturation, it is still prone to cross-linking side reactions under the high temperatures of traditional wall heating; solution-polymerized styrene-butadiene rubber contains unsaturated bonds, has poor thermal stability, and is particularly sensitive to temperature fluctuations; butyl rubber, due to the presence of isoprene units in its molecular chain, also exhibits significant thermosensitivity. While traditional wet coagulation processes can ensure product quality, they suffer from high energy consumption and generate large amounts of oily wastewater; existing dry devolatilization equipment struggles to overcome the technical bottlenecks of difficult heat transfer in high-viscosity melts and easy coking on the wall surface. This invention avoids the material remaining on the high-temperature wall surface for a long time through the synergistic effect of microwave heating and infrared surface compensation. At the same time, it combines a multi-stage flow field control strategy to dynamically optimize the strip shape as the devolatilization process progresses, providing a new dry devolatilization path that balances efficiency and gentleness for this type of difficult-to-process synthetic rubber.

[0024] The working mechanism of this invention is based on the synergistic effect of microwave selective volumetric heating, infrared radiation surface compensation, and multi-stage flow field dynamic control. Microwaves generated by the microwave generator penetrate the quartz glass tank and directly act on the rubber molecules, causing polar groups to reciprocate in a high-frequency electromagnetic field, generating frictional heat and achieving uniform volumetric heating from the inside out. This fundamentally avoids the problem of overheating and coking of materials adhering to the wall caused by traditional wall heat conduction. Simultaneously, infrared lamp radiation compensates for the surface temperature drop of the strip caused by vacuum evaporation, forming a synergistic temperature control mechanism with microwave heating to maintain a suitable surface temperature and low surface viscosity. Addressing the change in rubber viscosity from low to high during devolatilization, a three-stage distributor (coarse-pore, medium-pore, and micro-pore) is used to gradually reduce the strip diameter and increase the specific surface area, achieving dynamic optimization of the mass transfer interface and effectively overcoming diffusion resistance at high viscosity. The bottom wide-mouth screw pump adopts a zero-holding direct connection design, eliminating the flow dead zones caused by the bottom molten pool in traditional equipment, resulting in a highly uniform heating history and significantly narrowed residence time distribution of the material. By combining intermittent cyclic devolatilization process, the material passes through the devolatilization zone multiple times in the closed-loop system to accumulate devolatilization effect. Combined with nitrogen replacement to remove oxygen and prevent oxidative degradation, the high-viscosity heat-sensitive synthetic rubber is finally achieved with efficient and gentle devolatilization.

[0025] Due to the application of the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0026] 1. This invention uses a microwave generator in conjunction with a quartz glass tank. By utilizing the volumetric heating characteristics of microwaves, the rubber melt is heated from the inside out as a whole, completely eliminating the traditional heating mode that relies on wall heat conduction. This fundamentally avoids the problem of thermal cross-linking and coking caused by the material adhering to the wall being in a high-temperature hot spot for a long time, and significantly improves the stability of equipment operation and product purity.

[0027] 2. The present invention sets an infrared lamp between the quartz glass jar and the metal microwave shielding cavity. The infrared radiation compensates for the surface temperature drop caused by vacuum evaporation and replenishes the heat carried away by the rapid vaporization of the solvent on the surface of the strip in a timely manner. This forms a temperature control mechanism that works synergistically with microwave volume heating, ensuring that the entire devolvation process is gentle and efficient.

[0028] 3. This invention sets up a three-stage strip distributor with different pore sizes, and coordinates with gradient control of vacuum degree and temperature to form strip morphology matching the rheological properties of the rubber solution at different devolatilization stages: in the initial stage when the volatile content is high and the viscosity is low, coarse pores are used to prevent strip breakage; in the middle stage when the viscosity increases, the pores are switched to medium pores to increase the specific surface area; in the later stage when the high viscosity melt is in the micropore stage, micropores are used to form extremely fine strips to maximize the gas-liquid contact interface, thereby realizing dynamic optimization of mass transfer area.

[0029] 4. This invention adopts a bottom wide-mouth screw pump direct connection design, with no liquid collection area structure at the bottom of the tank, realizing zero liquid holding and direct discharge. It eliminates the flow dead zone caused by the bottom molten pool structure of traditional equipment, making the heating history of all materials highly uniform, significantly narrowing the residence time distribution, and effectively preventing rubber thermal aging and gel particle formation caused by excessive local residence time.

[0030] 5. This invention adopts an intermittent cyclic devolatilization process, in which the material passes through the devolatilization zone multiple times in a closed-loop system, resulting in a significant cumulative devolatilization effect and avoiding the problem of insufficient residence time in single-pass equipment. At the same time, a nitrogen replacement and oxygen removal step is set up to completely remove oxygen from the system, effectively preventing the oxidative degradation of rubber and thermo-oxidative crosslinking reaction at high temperatures, thus fully ensuring product quality. Attached Figure Description

[0031] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, some of the drawings in the following description are some embodiments of the present invention. For those skilled in the art, other drawings can be made based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the structure of the multi-stage circulating rubber devolatilization device based on microwave-infrared coupling heating in Embodiment 1 of the present invention;

[0033] Figure 2This is a schematic diagram of a three-stage orifice distributor of Embodiment 1 of the present invention;

[0034] Among them, 1-Material inlet pressure detection system; 2-Tank pressure detection system; 3-Tank temperature detection system; 4-Material inlet valve A; 5-Material inlet valve B; 6-Material inlet valve C; 7-Atmospheric valve; 8-Vacuum valve; 9-Nitrogen valve; 10-Microwave generator; 11-Infrared lamp; 12-Strip distributor A; 13-Strip distributor B; 14-Strip distributor C; 15-Metal microwave shielding cavity; 16-Quartz glass tank; 17-Nitrogen cylinder; 18-Vacuum pump; 19-Material outlet valve; 20-Material circulation valve; 21-Material outlet pressure detection system; 22-Material inlet; 23-Screw pump. Detailed Implementation

[0035] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific implementation schemes are now described in detail.

[0036] The present invention will be further described below with reference to embodiments, but the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0037] Example 1

[0038] See appendix Figure 1 and appendix Figure 2 This embodiment provides a multi-stage circulating rubber devolatilization device based on microwave-infrared coupled heating, mainly composed of a quartz glass tank 16, a metal microwave shielding cavity 15, a microwave generator 10, infrared lamps 11, a multi-stage strip distributor, and a screw pump 23. The quartz glass tank 16 is placed inside the metal microwave shielding cavity 15, with infrared lamps 11 arranged between them. The microwave generator 10 is installed on the side wall of the metal microwave shielding cavity 15. The top of the quartz glass tank 16 has three sets of parallel feeding branches, which are respectively connected to strip distributors A12, B13, and C14 arranged in descending order of orifice size through material inlet valves A4, B5, and C6. The bottom of the quartz glass tank 16 is directly connected to the screw pump 23 via a wide-mouth transition section. The screw pump 23 has a material inlet 22 upstream and a material outlet pressure detection system 21 at its outlet. The material outlet pressure detection system is divided into two paths: one path discharges through the material outlet valve 19, and the other path returns to the top of the tank through the material circulation valve 20. The tank also has a tank pressure detection system 2, a tank temperature detection system 3, an atmospheric valve 7, a vacuum valve 8, and a nitrogen valve 9. The vacuum valve 8 is connected to the vacuum pump 18, and the nitrogen valve 9 is connected to the nitrogen cylinder 17. The inlet pipe of the multi-stage dropper distributor is equipped with a material inlet pressure detection system 1.

[0039] Figure 2 This is a schematic diagram of three different aperture distributors, showing the parallel arrangement of strip distributors A12, B13, and C14, with their apertures decreasing sequentially, each used for different stages of the devolatilization process.

[0040] The device utilizes a quartz glass tank 16 to allow microwaves to penetrate without attenuation and provide volumetric heating to the rubber melt. Infrared lamps 11 compensate for the surface temperature drop caused by vacuum evaporation; together, they achieve uniform and gentle heating. A multi-stage strip distributor can switch online at different devolatilization stages to create strip patterns that match the material's rheological properties. A bottom-mounted wide-mouth direct-drive screw pump 23 achieves zero-hold-off direct discharge, eliminating dead zones in the flow.

[0041] The above-described apparatus was used to perform continuous cyclic devolatilization of the solution-polymerized ethylene propylene rubber solution, with cyclohexane as the solvent. Headspace gas chromatography was used to analyze the volatile content. The apparatus configuration was as follows: strip distributor A12 with an 8mm orifice, strip distributor B13 with a 5.5mm orifice, and strip distributor C14 with a 3mm orifice.

[0042] The devolatilization method includes the following steps:

[0043] S1. System oxygen replacement and purging: Close all valves, open vacuum valve 8, and use vacuum pump 18 to extract the gas from the quartz glass tank 16. Then close vacuum valve 8, open nitrogen valve 9 and nitrogen cylinder 17, and introduce nitrogen into the quartz glass tank 16. Repeat the above gas extraction and nitrogen filling operation three times. Monitor the pressure through tank pressure detection system 2 to complete the oxygen replacement and purging in the system.

[0044] S2. Feeding and Establishing Circulation: Start the screw pump 23, set the speed to 30 rpm, and open the material inlet 22, material circulation valve 20, and material inlet valve A4. Inject ethylene propylene rubber liquid preheated to 120°C with a polymer mass fraction of 80% through the material inlet 22. Driven by the screw pump 23, the liquid fills the circulation pipeline and forms droplets that fall back to the bottom of the quartz glass tank 16 via the droplet distributor A12. After observing that the material outlet pressure detection system 21 reading is stable at 3.76 MPa and the material inlet pressure detection system 1 reading is stable at 1.83 MPa, and after observing through the sight glass that a stable coarse droplet circulation flow has been established in the tank, close the material inlet 22, allowing the device to enter an independent closed-loop circulation devolatilization mode.

[0045] S3, First-stage devolatilization: Turn on the microwave generator 10 and infrared lamp 11, set the target temperature to 140℃, open the vacuum valve 8, and adjust the vacuum pump 18 to achieve a low vacuum state of 50 kPa within the quartz glass tank 16. The rubber solution circulates for 40 minutes through the coarse strips formed by the strip distributor A12, using microwave volumetric heating and infrared radiation to compensate for the surface temperature drop to remove a large amount of volatiles. Open the material outlet valve 19 to take a sample, and headspace-gas chromatography analysis shows that the volatile content has decreased from the initial 20% to 37420 ppm, reaching the first set value (within the range of 30000~50000 ppm).

[0046] S4, Secondary Deviation: Close material inlet valve A4, open material inlet valve B5, adjust vacuum valve 8 to increase the vacuum level inside the quartz glass tank 16 to a moderate level of 20 kPa absolute pressure, and adjust the heating power of microwave generator 10 and infrared lamp 11 to raise the temperature of the circulating rubber solution to 160℃. The rubber solution circulates for 30 minutes via medium-diameter droppers through dropper B13 to enhance gas-liquid mass transfer. Open material outlet valve 19 to take a sample, and analyze by headspace-gas chromatography to reduce the volatile content to 4502 ppm, reaching the second set value (within the range of 3000~6000 ppm).

[0047] S5, Three-stage devolatilization: Close material inlet valve B5, open material inlet valve C6, adjust vacuum valve 8 to achieve an ultimate high vacuum state (absolute pressure ≈ 1 kPa) inside the quartz glass tank 16, adjust the heating power of microwave generator 10 and infrared lamp 11 to raise the temperature of the circulating rubber solution to 180℃. The rubber melt circulates for 20 minutes through the fine droppers formed by the dropper C14, deeply removing residual volatiles. Open material outlet valve 19 to take a sample, and analyze by headspace-gas chromatography to find that the volatile content has dropped to 273 ppm, reaching the third set value (≤ 500 ppm).

[0048] S6. Discharge: Close vacuum valve 8 and vacuum pump 18, open nitrogen valve 9 and nitrogen cylinder 17 to break the vacuum to positive pressure, close material circulation valve 20, open material outlet valve 19, and discharge the finished product through screw pump 23.

[0049] The rheological properties of the final product were tested. The storage modulus G' of the exported ethylene propylene rubber was measured to be 12810 Pa at 180℃ and 1 rad / s. This is almost the same as the G' (12570 Pa) of the same grade of ethylene propylene rubber obtained by the wet process, indicating that the exported ethylene propylene rubber did not undergo obvious thermal crosslinking and thermal degradation.

[0050] Example 2

[0051] This embodiment is based on Embodiment 1 above, and the similarities with Embodiment 1 will not be repeated. The difference between this embodiment and Embodiment 1 is that the processed object is solution-polymerized styrene-butadiene rubber solution, the solvent is n-hexane, the initial polymer mass fraction is 75%, and the initial volatile matter content is 25%. The orifice diameter of the strip distributor A12 is adjusted to 9mm, the orifice diameter of the strip distributor B13 is adjusted to 6mm, and the orifice diameter of the strip distributor C14 is adjusted to 4mm. The screw pump 23 speed is set to 35rpm.

[0052] In the specific operating steps, the S3 first-stage devolatilization stage is as follows: the target temperature is set at 135℃, the absolute pressure inside the tank is 60 kPa, the running time is 45 minutes, and the volatile matter content is reduced to 41200 ppm after sampling. The S4 second-stage devolatilization stage is as follows: the temperature is increased to 155℃, the absolute pressure inside the tank is 15 kPa, the running time is 35 minutes, and the volatile matter content is reduced to 5200 ppm after sampling. The S5 third-stage devolatilization stage is as follows: the temperature is increased to 175℃, the ultimate vacuum absolute pressure inside the tank is 1.5 kPa, the running time is 25 minutes, and the volatile matter content is reduced to 385 ppm after sampling. The product is then tested after discharge.

[0053] Example 3

[0054] This embodiment is based on Embodiment 1 above, and the similarities with Embodiment 1 will not be repeated. The difference between this embodiment and Embodiment 1 is that the object being processed is butyl rubber liquid, the solvent is Isopar E, the initial polymer mass fraction is 70%, and the initial volatile matter content is 30%. The orifice diameter of the strip distributor A12 is adjusted to 7 mm, the orifice diameter of the strip distributor B13 is adjusted to 5 mm, and the orifice diameter of the strip distributor C14 is adjusted to 2.5 mm. The screw pump 23 speed is set to 25 rpm.

[0055] In the specific operating steps, the S3 primary devolatilization stage is as follows: the target temperature is set at 130℃, the absolute pressure inside the tank is 45 kPa, the running time is 50 minutes, and the volatile matter content is reduced to 35600 ppm after sampling. The S4 secondary devolatilization stage is as follows: the temperature is increased to 150℃, the absolute pressure inside the tank is 12 kPa, the running time is 40 minutes, and the volatile matter content is reduced to 4100 ppm after sampling. The S5 tertiary devolatilization stage is as follows: the temperature is increased to 170℃, the ultimate vacuum absolute pressure inside the tank is 0.8 kPa, the running time is 30 minutes, and the volatile matter content is reduced to 218 ppm after sampling. The product is then tested after discharge.

[0056] Comparative Example 1

[0057] This comparative example is based on Example 1 described above. The similarities to Example 1 will not be repeated. The difference between this comparative example and Example 1 is that the microwave generator 10 and infrared lamp 11 are not turned on; only traditional wall-mounted electric heating is used to heat the exterior of the quartz glass jar 16, with the heating temperature set to a constant 180°C. The ethylene propylene rubber adhesive (initial volatile content 20%) is treated similarly, following steps S1 to S6, but only the dropper A12 (8mm aperture) is used throughout the process, without switching distributors.

[0058] During operation, it was observed that after 60 minutes, significant adhesive residue appeared on the inner wall of the tank, with some charred particles peeling off. After 90 minutes of operation, samples were taken for testing, and the volatile matter content was 1850 ppm, failing to meet the target of below 500 ppm. Rheological property testing of the final product, conducted at 180℃ and 1 rad / s, yielded a storage modulus G' of 15630 Pa, significantly higher than the control value for the wet process (12570 Pa), indicating that the product underwent a significant thermal cross-linking reaction.

[0059] Comparative Example 2

[0060] This comparative example is based on Example 1 above. The similarities to Example 1 will not be repeated. The difference between this comparative example and Example 1 is that: no multi-stage distributor switching is performed; only the drop strip distributor C14 (microporous, 3mm pore size) is used throughout the entire process for devolatilization. The ethylene propylene rubber latex (initial volatile content 20%) is treated similarly, and steps S1 to S6 are followed. The microwave and infrared heating temperatures and vacuum settings are consistent with those in Example 1.

[0061] During the S2 feeding and circulation setup phase, it was observed that due to the low initial viscosity of the adhesive, the droplets formed through the 3mm micropores were too fine and fragmented. Some droplets broke before reaching the bottom of the tank, forming droplets that dispersed, resulting in severe mist entrainment and large pressure fluctuations inside the tank. During operation, the reading of the material inlet pressure detection system 1 fluctuated significantly, indicating unstable pressure drop in the distributor. After devolatilization, a sample was taken for testing, and the volatile content was 420ppm, which met the target value, but the product yield was about 12% lower than in Example 1, and some solvent was not effectively condensed and recovered due to mist entrainment. Rheological property testing of the final product showed G' to be 12980Pa, close to that of Example 1, indicating no significant crosslinking, but poor operational stability of the device.

[0062] Comparative Example 3

[0063] This comparative example is based on Example 1 above. The similarities to Example 1 will not be repeated. The difference between this comparative example and Example 1 is that it does not use a cyclic devolatilization mode, but a single-pass operation. That is, after the material is injected through the material inlet 22, the microwave generator 10 and the infrared lamp 11 are turned on. The material passes through a three-stage distributor in series: drop distributor A12 (8mm), drop distributor B13 (5.5mm), and drop distributor C14 (3mm) (the material falls through the three distributors sequentially). After passing through once, it is discharged from the material outlet valve 19 without recirculation.

[0064] To increase residence time, the installation height of the three-stage distributor was increased to three times its original height, and the screw pump speed was reduced to 10 rpm. Even so, the total residence time of the material in the devolatilization zone was still less than 2 minutes. Sampling and testing after discharge showed a volatile matter content of 1.2%, far exceeding the target value of 500 ppm. After re-injecting the discharged material into the system for a second pass, the volatile matter content decreased to 3800 ppm, and after a third pass, it decreased to 620 ppm, still failing to reach the target value. This result indicates that without a recirculation mode, a single pass is insufficient to achieve deep devolatilization.

[0065] The products of the above embodiments and comparative examples were tested. The main test indicators included the final volatile content, the product energy storage modulus G' (180℃, 1rad / s), and the evaluation of the device operation stability. The test results are shown in Table 1.

[0066] Table 1

[0067]

[0068] As can be seen from Table 1, the microwave-infrared coupled heating and multi-stage cyclic devolatilization process adopted in Examples 1 to 3 of the present invention can achieve deep devolatilization for different types of synthetic rubber. The final volatile content can be stably controlled below 500 ppm, and the storage modulus of the product is close to the control value of the wet process, indicating that the rubber has not undergone obvious thermal cross-linking or thermal degradation, and the product quality is excellent.

[0069] Comparative Example 1 used a traditional wall heating method, which resulted in uneven heating leading to wall scorching and rubber thermal cross-linking, resulting in a high volatile content and a significantly increased G' value in the product. Comparative Example 2 used microwave heating but did not employ multi-stage distributor switching; instead, it used a microporous distributor in the initial stage of devolatilization, leading to severe mist entrainment, poor device stability, and a decreased product yield. Comparative Example 3 did not employ a circulation process; single-pass devolatilization was incomplete, and even multiple passes failed to reach the target value. The comparative results demonstrate that this invention, through the synergistic effect of microwave-infrared coupled heating, multi-stage flow field control, and a circulation process, achieves efficient and gentle devolatilization of high-viscosity, heat-sensitive synthetic rubber.

[0070] In summary, this invention effectively solves the technical problems of low heat transfer efficiency, easy coking on the wall surface, numerous dead zones at the bottom, and difficulty in adapting to large viscosity changes in existing dry devolatilization technologies for synthetic rubber through the synergistic effect of microwave-infrared coupled heating and multi-stage cyclic devolatilization process. This invention utilizes the volumetric heating characteristics of microwaves to heat the rubber melt as a whole from the inside out, combined with infrared radiation to compensate for surface temperature drop, fundamentally avoiding the problem of thermal cross-linking and coking of rubber. By setting up three stages of strip distributors with different apertures and coordinating gradient control of vacuum and temperature, the strip morphology is dynamically optimized as the devolatilization process progresses, achieving precise matching of mass transfer area. The bottom wide-mouth screw pump with zero liquid holdup direct connection design eliminates flow dead zones and significantly narrows the residence time distribution. Combined with intermittent circulation process and nitrogen replacement for oxygen removal, it ensures uniform heating history of the material and prevents oxidative degradation. The apparatus and method of this invention can be used to process high-viscosity heat-sensitive synthetic rubbers such as ethylene propylene rubber, solution-polymerized styrene-butadiene rubber, and butyl rubber. The final volatile content can be stably controlled below 500 ppm. The storage modulus of the product is close to the control value of the wet process. No obvious thermal crosslinking or thermal degradation occurs. This invention achieves efficient and mild devolatilization of high-viscosity synthetic rubber and has significant industrial application value.

[0071] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art will understand the specific meaning of the above terms in this application based on the specific circumstances.

[0072] The embodiments described above merely illustrate more specific and detailed implementations of the present invention, and should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A multi-stage circulating rubber devolatilization device based on microwave-infrared coupled heating, characterized in that, include: Quartz glass container (16) is used to contain rubber materials and perform devolatilization treatment; A metal microwave shielding cavity (15) is provided, and the quartz glass container (16) is placed inside the metal microwave shielding cavity (15). A microwave generator (10) is installed on the side wall of the metal microwave shielded cavity (15) for volumetric heating of the rubber material inside the quartz glass jar (16); Infrared lamp (11) is placed between the quartz glass tank (16) and the metal microwave shielding cavity (15) to compensate for the temperature drop on the surface of the rubber material. The multi-stage drop strip distributor includes drop strip distributors A (12), B (13) and C (14) with successively decreasing apertures, which are arranged in parallel on the top of the quartz glass tank (16). The opening and closing are controlled by material inlet valves A (4), B (5) and C (6), respectively. The screw pump (23) has its inlet directly connected to the bottom of the quartz glass tank (16) through a wide-mouth transition section. The outlet end is equipped with a material outlet pressure detection system (21) and is divided into two paths: one path is connected to the discharge port through the material outlet valve (19), and the other path is connected to the inlet of the multi-stage dropper distributor at the top of the quartz glass tank (16) through the material circulation valve (20). The material inlet (22) is located upstream of the screw pump (23) and is used to inject the rubber solution to be devolatilized into the system; A vacuum pump (18) is connected to a quartz glass jar (16) via a vacuum valve (8). Nitrogen cylinder (17) is connected to quartz glass jar (16) via nitrogen valve (9); A tank pressure detection system (2) is installed on the quartz glass tank (16); A tank temperature detection system (3) is installed on the quartz glass tank (16); Material inlet pressure detection system (1) is installed in the inlet pipeline of the multi-stage drop bar distributor; An atmospheric valve (7) is located on the top of the quartz glass jar (16).

2. The multi-stage circulating rubber devolatilization device based on microwave-infrared coupled heating according to claim 1, characterized in that, The aperture configuration of the strip distributors A (12), B (13) and C (14) is as follows: the aperture of the coarse-pore distributor is 6~10mm, the aperture of the medium-pore distributor is 4~6mm, and the aperture of the micro-pore distributor is 2~4mm, in order to adapt to the rheological characteristics of the gradually increasing viscosity during the rubber devolatilization process.

3. The multi-stage circulating rubber devolatilization device based on microwave-infrared coupled heating according to claim 1, characterized in that, The screw pump (23) is a wide-mouth direct-connect screw pump. Its inlet is connected to the bottom of the quartz glass tank (16) in a zero-liquid-holding direct connection method without a liquid collection area structure, thus eliminating dead zones in the flow.

4. A method for multi-stage cyclic rubber devolatilization based on microwave-infrared coupled heating using the apparatus described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1. System oxygen replacement and purging: Close all valves, open the vacuum valve (8), extract the gas in the quartz glass tank (16) through the vacuum pump (18), then close the vacuum valve (8), open the nitrogen valve (9) and nitrogen cylinder (17), and introduce nitrogen into the quartz glass tank (16). Repeat the above pumping and nitrogen filling operations at least three times, monitor the pressure through the tank pressure detection system (2), and complete the oxygen replacement and purging in the system. S2, Feeding and Establishing Circulation: Turn on the screw pump (23), open the material inlet (22), material circulation valve (20) and material inlet valve A (4), inject the rubber solution to be devolatilized through the material inlet (22), fill the circulation pipeline under the drive of the screw pump (23), and form a drop strip through the drop strip distributor A (12) to fall back to the bottom of the quartz glass tank (16). After the pressure is stable and a liquid seal is established at the bottom of the tank by monitoring the material inlet pressure detection system (1) and the material outlet pressure detection system (21), close the material inlet (22) so that the device enters the independent closed-loop circulation devolatilization mode; S3, First-stage devolvation: Turn on the microwave generator (10) and infrared lamp (11), set the heating temperature, open the vacuum valve (8), adjust the vacuum pump (18) to make the quartz glass tank (16) be in a low vacuum state, and the rubber solution circulates through the coarse strip formed by the strip distributor A (12). A large amount of volatile matter is removed by microwave volume heating and infrared radiation to compensate for the surface temperature drop. The volatile matter content is sampled and monitored through the material outlet valve (19) until it reaches the first set value. S4, Secondary Deviation: When the volatile content drops to the first set value, close the material inlet valve A (4), open the material inlet valve B (5), adjust the vacuum valve (8) to increase the vacuum level in the quartz glass tank (16) to a medium level, adjust the heating power of the microwave generator (10) and infrared lamp (11), and the rubber solution forms a medium diameter droplet circulation flow through the droplet distributor B (13) to enhance gas-liquid mass transfer. The volatile content is sampled and monitored through the material outlet valve (19) until it reaches the second set value. S5, Three-stage devolatification: When the volatile content drops to the second set value, close the material inlet valve B (5), open the material inlet valve C (6), adjust the vacuum valve (8) to make the quartz glass tank (16) reach the ultimate high vacuum state, adjust the heating power of the microwave generator (10) and infrared lamp (11), and the rubber melt circulates through the fine drop strips formed by the drop strip distributor C (14) to deeply remove residual volatiles. The volatile content is sampled and monitored through the material outlet valve (19) until it reaches the third set value. S6. Discharge: When the volatile content drops to the third set value, close the vacuum valve (8) and vacuum pump (18), open the nitrogen valve (9) and nitrogen cylinder (17) to break the vacuum to positive pressure, close the material circulation valve (20), open the material outlet valve (19), and discharge the finished product through the screw pump (23).

5. The multi-stage cyclic rubber devolatilization method based on microwave-infrared coupled heating according to claim 4, characterized in that, The low vacuum state described in step S3 is an absolute pressure of 30~80 kPa, the medium vacuum state described in step S4 is an absolute pressure of 5~30 kPa, and the ultimate high vacuum state described in step S5 is an absolute pressure of 0.1~5 kPa.

6. The multi-stage cyclic rubber devolatilization method based on microwave-infrared coupled heating according to claim 4, characterized in that, In steps S3 to S5, the heating temperatures of the microwave generator (10) and the infrared lamp (11) are gradually increased, with the first-stage devolve temperature being 120~150℃, the second-stage devolve temperature being 150~170℃, and the third-stage devolve temperature being 170~200℃.

7. The multi-stage cyclic rubber devolatilization method based on microwave-infrared coupled heating according to claim 4, characterized in that, In steps S3 to S5, the first setting value is 30000~50000ppm, the second setting value is 3000~6000ppm, and the third setting value is ≤500ppm.

8. The multi-stage cyclic rubber devolatilization method based on microwave-infrared coupled heating according to claim 4, characterized in that, The rubber solution to be devolatilized is selected from solution polymerized ethylene propylene rubber, solution-polymerized styrene-butadiene rubber, or butyl rubber, and the solvent is selected from one or more of cyclohexane, n-hexane, or Isopar E.

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