Process for polymerizing perfluoroether elastomers in supercritical carbon dioxide and perfluoroether elastomers and compositions made by the process

Abstract

The application discloses a method for polymerizing perfluoroether elastomer in supercritical carbon dioxide, and perfluoroether elastomer and composition prepared by the method, and the method comprises the following steps: adding carbon dioxide, perfluoromethyl vinyl ether monomer and tetrafluoroethylene monomer into a reactor, and the concentration of the carbon dioxide in the reactor is greater than or equal to 30 mol%; continuously adding an initiator, a chain transfer agent and a vulcanization point monomer to initiate the polymerization reaction of the perfluoroether elastomer. The reactor adopts a jacketed heat exchanger, liquid tetrafluoroethylene monomer and perfluoromethyl vinyl ether are sprayed, and carbon dioxide is refluxed to supplement cold energy, the latent heat of vaporization is used to absorb the heat released in the polymerization reaction, and the reaction temperature is controlled in the range of 35-125 DEG C. The perfluoroether elastomer prepared by the method has good thermal stability, chemical corrosion resistance and low fluorine ion extraction degree. Since the temperature in the preparation process is accurately controlled, the unstable end groups of the obtained perfluoroether elastomer are greatly reduced, and the physical properties of the elastomer are improved.

Description

Technical Field

[0001] This invention relates to the field of perfluoroether elastomer preparation, specifically to a method for polymerizing perfluoroether elastomers in supercritical carbon dioxide and perfluoroether elastomers and compositions prepared by this method. Background Technology

[0002] Perfluoroether elastomers are heat-resistant elastomers primarily copolymerized from monomers such as tetrafluoroethylene (TFE) and perfluoromethyl vinyl ether (PMVE). Because all hydrogen atoms on the carbon atoms in their molecular structure are replaced by fluorine atoms, they exhibit excellent heat and chemical resistance, allowing for long-term use at high temperatures, such as 300 °C. However, traditional methods for preparing perfluoroether elastomers have several drawbacks, affecting product performance and production efficiency.

[0003] First, the polymerization reaction generates a large amount of heat. If this heat cannot be effectively removed, it will affect the stability of the reaction and the quality of the product. Traditional perfluoroether elastomers are produced using aqueous emulsion polymerization, which requires the use of surfactants. This not only increases production costs but also necessitates subsequent processing such as emulsion demulsification, coagulation, and drying. Furthermore, perfluoroether elastomers tend to stick to the reaction vessel walls during polymerization, which not only affects the normal operation of the reaction equipment but also makes product collection difficult and equipment cleaning challenging.

[0004] To address these issues, the industry has been seeking new polymerization methods. Polymerization in supercritical fluid media, due to its unique advantages, is considered an option to overcome the shortcomings of traditional methods. Supercritical carbon dioxide, as a green and environmentally friendly reaction medium, possesses advantages such as being non-toxic, pollution-free, and easy to recycle. It also exhibits unique physicochemical properties. As a polymer synthesis medium, supercritical carbon dioxide is chemically inert, exhibits no chain transfer, and possesses adjustable density, a high diffusion coefficient, and low surface tension, showing broad application prospects in the field of polymer polymerization. However, because polymerization is a strongly exothermic process (e.g., the heat of polymerization of tetrafluoroethylene monomer is approximately -171.4 kJ / mol), and supercritical carbon dioxide has a low thermal conductivity of approximately 0.01-0.03 W / (m·K), far lower than water's 0.6 W / (m·K), the heat of reaction is difficult to remove quickly, easily leading to localized overheating (resulting in a wider polymer molecular weight distribution and increased side reactions) or explosive polymerization (temperature runaway). Therefore, supercritical polymerization reactions are currently limited to micro (tens of milliliters) or small (hundreds of milliliters) reactors.

[0005] The efficient synthesis of perfluoroether elastomers in supercritical fluid media within large reactors (hundreds of liters or cubic meters) requires addressing issues such as heat control during polymerization, product adhesion to walls, and product purification. These are the current research priorities and challenges. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a method for controlled polymerization of perfluoroether elastomers in supercritical carbon dioxide within a scale-up reactor or large reactor, thereby solving the problems of difficulty in removing reaction heat and wall adhesion that exist in the supercritical fluid perfluoroether elastomer polymerization process in a scale-up reactor.

[0007] Another object of the present invention is to provide a method for obtaining perfluoroether elastomers and compositions by polymerizing perfluoroether elastomers in supercritical carbon dioxide in a scale-up reactor or a large reactor as described above.

[0008] To achieve the above objectives, the solution of the present invention is:

[0009] In a first aspect, the present invention provides a method for controlled polymerization of perfluoroether elastomers in supercritical carbon dioxide within a scale-up reactor, comprising:

[0010] The polymerization of perfluoroether elastomers is carried out in a reactor, wherein carbon dioxide, perfluoromethyl vinyl ether monomer, and tetrafluoroethylene monomer are added to the reactor, and the concentration of carbon dioxide in the reactor is ≥30 mol%;

[0011] Then, an initiator, a chain transfer agent, and a sulfidation point monomer are added to the reactor;

[0012] The polymerization reaction is initiated by heating. When the reaction reaches the predetermined conversion rate, the supply of liquid tetrafluoroethylene monomer and / or liquid carbon dioxide and / or carbon dioxide recycling are stopped; the pressure is released, the mixture is filtered, and the unreacted monomer and carbon dioxide are recovered. The product, perfluoroether elastomer, is collected.

[0013] During the reaction process, at least one of the following heat transfer methods is used to control the reaction temperature within the reactor:

[0014] (1) The reactor adopts a jacketed heat exchanger. During the feeding process, the jacketed heat exchanger is circulated with cooling water. Then the jacketed heat exchanger switches to 30-40 ℃ circulating water to start the reaction. After the reaction starts, the jacketed heat exchanger switches to circulating cooling water to control the temperature.

[0015] (2) Several atomizing nozzles are set at the feed port or the upper part of the reaction zone of the reactor. Liquid perfluoromethyl vinyl ether monomer, liquid tetrafluoroethylene monomer and / or initiator are injected by high pressure CO2 in the form of atomized droplets. The atomized droplet raw material is rapidly vaporized in the supercritical carbon dioxide environment. Part of the reaction heat is absorbed by the latent heat of phase change evaporation to control the reaction temperature.

[0016] (3) Set up a carbon dioxide circulation reflux system to liquefy part of the supercritical carbon dioxide in the reactor and remove the heat of reaction in the form of reflux.

[0017] Preferably, it further includes: monitoring the polymerization reaction temperature in the scraped-wall reactor throughout the process based on the polymerization reaction temperature of the perfluoroether elastomer, and setting a first predetermined value of 3 ℃ and a second predetermined value of 5 ℃ for the difference between the actual polymerization reaction temperature and the process temperature;

[0018] In the initial stage of the reaction, when the difference between the actual polymerization reaction temperature and the process temperature is less than or equal to the first predetermined value of 3 °C, the circulating cooling water of the jacket is turned on and the heat transfer method (1) is adopted.

[0019] As the reaction proceeds, heat is continuously released. When the difference between the actual polymerization reaction temperature and the process temperature is greater than the first predetermined value of 3 ℃ and less than or equal to the second predetermined value of 5 ℃, atomization is turned on, or the flow rate or injection speed of atomization is increased, and a heat transfer method (2) is superimposed on the heat transfer method (1).

[0020] When the difference between the actual polymerization reaction temperature and the process temperature is greater than the second predetermined value of 5 °C, the carbon dioxide liquefaction reflux system is turned on. In the case that the above methods are insufficient, the reflux liquid carbon dioxide is used to absorb heat effectively. The heat transfer method (3) is superimposed on the heat transfer methods (1) and (2).

[0021] Preferably, the liquid tetrafluoroethylene monomer and the refluxed liquid carbon dioxide are injected continuously; the liquid perfluoromethyl vinyl ether monomer is injected in stages to control the polymerization rate.

[0022] Preferably, the injection rate of tetrafluoroethylene monomer and the reflux rate of carbon dioxide are calculated based on the temperature difference between the reactor wall temperature and the reaction medium to maintain the polymerization reaction temperature within a certain range. The polymerization reaction temperature is maintained at 35-125 °C and the polymerization reaction pressure is controlled at 7-30 MPa by adjusting the injection rate.

[0023] Preferably, the reactor is a scraped-wall reactor, and a rotating scraper is provided on the inner wall of the reactor, the rotating scraper rotating at a speed of 10-50 rpm.

[0024] Preferably, the sulfidation point monomer is selected from at least one of perfluoro-2-(2-sulfonylchloroethoxy)propyl vinyl ether and perfluoro-8-cyano-5-methyl-3,6-dioxa-1-octene; the sulfidation point monomer is dissolved in trichlorotrifluoroethane solvent and then pressurized into the reactor by high-pressure CO2, wherein the mass of the trichlorotrifluoroethane is 1.5-3 times that of the sulfidation point monomer.

[0025] Preferably, the chain transfer agent conforms to the chemical formula I-(CF2). n-I, where n is an integer from 1 to 10, selected from at least one of 1,3-diiodopropane, 1,4-diiodobutane, 1,6-diiodohexane, 1,8-diiodooctane, 1,3-diiodoperfluoropropane, 1,4-diiodoperfluorobutane, 1,6-diiodoperfluorohexane, and 1,8-diiodoperfluorooctane. The chain transfer agent is dissolved in trichlorotrifluoroethane solvent and then pressurized into the reactor by high-pressure CO2, wherein the mass of trichlorotrifluoroethane is 3-5 times that of the chain transfer agent.

[0026] Preferably, the initiator is bis(perfluoropropionyl) peroxide; the initiator is dissolved in trichlorotrifluoroethane solvent and then injected into the reactor by high-pressure CO2, wherein the mass of trichlorotrifluoroethane is 3-5 times that of the initiator.

[0027] Preferably, the product, perfluoroether elastomer, is dried, subjected to supercritical CO2 devolatilization, mixed with a vulcanizing crosslinking agent and a catalyst, molded, and subjected to secondary vulcanization to obtain a composition; the secondary vulcanization temperature is 190-240 ℃, and the time is 10-24 h, wherein the vulcanizing crosslinking agent is tetraphenyltin, and the catalyst is hexaoxane.

[0028] Secondly, the present invention also provides a perfluoroether elastomer and composition prepared by the method described above for controlled polymerization of supercritical carbon dioxide perfluoroether elastomer in a scale-up reactor.

[0029] The method for controlled polymerization of supercritical carbon dioxide perfluoroether elastomers in a scale-up reactor provided by this invention has the following beneficial effects:

[0030] 1. By injecting liquid tetrafluoroethylene monomer and liquid CO2, the reaction temperature is controlled by absorbing the latent heat of vaporization, which effectively solves the problem of temperature control difficulties caused by the difficulty in removing the heat of reaction in the supercritical CO2 system, and ensures the controllability of the polymerization reaction;

[0031] 2. By using a scraped-wall reactor, the perfluoroether elastomer products are prevented from sticking to the wall, the thermal resistance of the tube wall is reduced, the heat transfer efficiency is improved, and the temperature control is further optimized.

[0032] 3. The recycling of carbon dioxide not only reduces production costs but also achieves green and environmentally friendly production, which aligns with the concept of sustainable development;

[0033] 4. This method is simple to operate and easy to implement, providing a new approach for the preparation of high-quality perfluoroether elastomers and showing good application prospects. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0035] Figure 1 A schematic diagram of the perfluoroether elastomer polymerization process in the example;

[0036] Figure 2 Schematic diagram of the reaction apparatus of the present invention;

[0037] Figure 3 The present invention relates to a block diagram of the core temperature control strategy for a method of controlled polymerization of supercritical carbon dioxide perfluoroether elastomers in a scale-up reactor;

[0038] Figure 4 The present invention relates to a staged cooling block diagram of a method for controlled polymerization of perfluoroether elastomers in supercritical carbon dioxide in a scale-up reactor. Detailed Implementation

[0039] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, so as to better understand the purpose, features and advantages of the present invention. It should be understood that the embodiments shown in the drawings are not intended to limit the scope of the present invention, but are only for illustrating the essential spirit of the technical solution of the present invention.

[0040] In the following description, certain specific details are set forth for the purpose of illustrating various disclosed embodiments in order to provide a thorough understanding of the various disclosed embodiments. However, those skilled in the art will recognize that embodiments may be practiced without one or more of these specific details. In other instances, well-known apparatuses, structures, and techniques associated with this application may not have been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments.

[0041] Throughout this specification, references to "an embodiment" or "an embodiment" indicate that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Therefore, the appearance of "in an embodiment" or "an embodiment" in various places throughout the specification does not necessarily refer to the same embodiment. Furthermore, a particular feature, structure, or characteristic may be combined in any manner in one or more embodiments.

[0042] In the following description, in order to clearly demonstrate the structure and working method of the present invention, a number of directional terms will be used. However, terms such as "front", "back", "left", "right", "outside", "inside", "outward", "inward", "up", and "down" should be understood as convenient terms and not as limiting terms.

[0043] It should be noted that the features shown in the accompanying drawings of this application may belong to one embodiment or different embodiments, as long as there is no conflict between these features. To save space, this application may use the same drawing to illustrate different embodiments; that is, the same drawing of this application may be used to illustrate features in different embodiments.

[0044] According to known technology, the heat of polymerization of tetrafluoroethylene is high, at -171.4 kJ / mol. To minimize the potential danger of polymer agglomeration and wall formation within the reactor and thus reduce thermal resistance, no auxiliary cooling coils are installed inside the polymerization reactor, and no baffles are placed on the inner wall. Currently, all reaction heat during emulsion polymerization is transferred out through the reactor wall and the external jacketed heat exchanger. To achieve stable production, a balance must be established between the rate of reaction exothermic reaction and the rate of heat transfer. The rate of reaction exothermic reaction directly depends on the polymerization rate, which, assuming other factors remain constant, is determined by the polymerization temperature.

[0045] According to literature, the apparent reactivity ratios of the binary emulsion copolymerization reaction of tetrafluoroethylene (TFE) and perfluoromethyl vinyl ether (PMVE) are as follows: γ TFE =3.89, γ PMVE =0.05. This data indicates that the reactivity ratio of TFE is significantly higher than that of PMVE, meaning that TFE is more likely to undergo homopolymerization with itself in the copolymerization reaction, while PMVE is more likely to undergo copolymerization with TFE.

[0046] In a supercritical CO2 environment, the distribution of copolymer segments during polymerization can be precisely controlled, improving high-temperature resistance. The introduction of PMVE reduces crystallinity and enhances material flexibility. TFE is highly reactive and readily homopolymerizes, while PMVE has lower reactivity due to steric hindrance and electronic effects. Similar to emulsion polymerization, the two exhibit significant differences in their polymerization reactivity (γ). TFE γ PMVE In supercritical CO2, the methoxy group of PMVE forms a weak interaction with CO2, which may enhance its effective reactivity.

[0047] like Figure 1 As shown, the present invention provides a method for controlled polymerization of perfluoroether elastomers in supercritical carbon dioxide, comprising:

[0048] Carbon dioxide, perfluoromethyl vinyl ether monomer, and tetrafluoroethylene monomer are added to the reactor. In order to control and reduce the concentration of perfluoromethyl vinyl ether monomer and tetrafluoroethylene monomer in the supercritical carbon dioxide phase and suppress their decomposition and explosion risk, in this invention, the concentration of carbon dioxide in the steam space of the reactor is ≥30 mol%, and the concentration of oxygen is less than 10 ppm.

[0049] Then, initiator, chain transfer agent and sulfidation point monomer are added to the reactor;

[0050] In this step, the initiator is bis(perfluoropropionyl) peroxide; the chain transfer agent conforms to the chemical formula I-(CF2). n -I, where n is an integer from 1 to 10, including but not limited to 1,3-diiodopropane, 1,4-diiodobutane, 1,6-diiodohexane, 1,8-diiodooctane, 1,3-diiodoperfluoropropane, 1,4-diiodoperfluorobutane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane, etc.; the sulfurization point monomers include but are not limited to perfluoro-2-(2-sulfonylchloroethoxy)propyl vinyl ether, perfluoro-8-cyano-5-methyl-3,6-dioxa-1-octene, etc.

[0051] like Figure 2 As shown, liquid carbon dioxide enters the reactor through the feed inlet 13 via pipe 103, and valves 3-6 are installed on pipe 103.

[0052] After being compressed to a specified pressure by compressor 2-3, perfluoromethyl vinyl ether enters cooler 4-2. After heat exchange and condensation, it enters reactor through inlet 14 via pipeline 102. Valve 3-5 is also installed on the pipeline before compressor 2-3.

[0053] After being compressed to a specified pressure by compressor 2-2, tetrafluoroethylene enters cooler 4-1. After heat exchange and condensation, it enters reactor through inlet 15 via pipeline 101. Valve 3-4 is installed in the pipeline between cooler 4-1 and compressor 2-2. A pipeline is connected in parallel at both ends of valve 3-4. Valve 3-3, collector 1-2 and valve 3-2 are connected in series on this pipeline.

[0054] The chain transfer agent in the raw material storage tank 5-1 enters the feed tank 6-1 through a pipeline. After the high-pressure CO2 gas enters the feed tank 6-1, it drives the chain transfer agent to enter the reactor through the feed port 12 via the pipeline 105. The pipeline 105 is equipped with a check valve 7-1. A valve 3-8 is installed on the pipeline between the raw material storage tank 5-1 and the feed tank 6-1. A valve 3-7 is installed on the high-pressure CO2 gas pipeline connecting the feed tank 6-1.

[0055] The initiator in the raw material storage tank 5-2 enters the feed tank 6-2 through a pipeline. After the high-pressure CO2 gas enters the feed tank 6-2, it drives the initiator to enter the reactor through the feed port 11 via the pipeline 106. The pipeline 106 is equipped with a check valve 7-2. A valve 3-10 is installed on the pipeline between the raw material storage tank 5-2 and the feed tank 6-2. A valve 3-9 is installed on the high-pressure CO2 gas pipeline connecting the feed tank 6-2.

[0056] The sulfurized monomer in the raw material storage tank 5-3 enters the feed tank 6-3 through a pipeline. After the high-pressure CO2 gas enters the feed tank 6-3, it drives the sulfurized monomer through the pipeline 107 and enters the reactor through the feed port 10. The pipeline 107 is equipped with a check valve 7-3. A valve 3-12 is installed on the pipeline between the raw material storage tank 5-3 and the feed tank 6-3. A valve 3-11 is installed on the high-pressure CO2 gas pipeline connecting the feed tank 6-3.

[0057] The high-pressure CO2 streams entering feed tanks 6-1, 6-2 and 6-3 are obtained by pressurizing and vaporizing liquid LCO2 streams.

[0058] The monomers (mainly tetrafluoroethylene monomers) in the reactor flow out from the reflux port 16, are compressed to the specified pressure by the compressor 2-1, and then enter the collector 1-1 through the pipe 104. The collector 1-1 is connected to the tetrafluoroethylene inlet pipe through the pipe 104. A valve 3-1 is installed on the pipe 104 between the connection point of the collector 1-1 and the tetrafluoroethylene inlet pipe.

[0059] According to the present invention, in some embodiments, the sulfidation point monomer is dissolved in trichlorotrifluoroethane solvent and then injected into the reactor by high-pressure CO2, wherein the mass of the trichlorotrifluoroethane is 1.5-3 times that of the sulfidation point monomer.

[0060] Taking the synthesis of TFE / PMVE-based perfluoroether elastomers as an example, both TFE and PMVE copolymers with a molar percentage of 25-40% are elastomers, where PMVE provides trifluoromethyl side chains linked to the main chain. Table 1 lists the key physical properties of each major component, and Table 2 shows the heat of polymerization and latent heat of vaporization.

[0061] Table 1 Key physical properties of main components

[0062]

[0063] Table 2 Heat of polymerization and latent heat of vaporization

[0064]

[0065] Assuming the heat of polymerization of perfluoroether elastomers is -171.4 kJ / mol over a 3-hour period (primarily based on the heat of polymerization of TFE), and using the average polymerization rate per unit time as a baseline, a volume of 0.5 m³ is used. 3 The reactor (assuming a wall thickness of 1.2 cm, a diameter of 0.7 m, a height of 1.2 m, an effective heat transfer height of 1 m, and an effective heat transfer area of ​​2.2 m²) is described. 2 Assuming each batch's actual yield is 1000 mol, and the PMVE molar percentage is 30%, then the batch yield mass is 300 × 166.02 + 700 × 100.02 = 49806 + 70014 = 119820 g = 119.8 kg. Therefore, the average reaction rate R = 1000 mol / 3h = 333 mol / h = 39.9 kg / h, and the average exothermic rate Q... 均 ≈333 mol / h×171.4 kJ / mol=57076 kJ / h.

[0066] Under normal conditions, the temperature rises by approximately 20-25 K from start to finish. Supercritical CO2 heating can absorb approximately 0.5 m³ of heat. 3 ×200 kg / m 3 ×4.05 kJ / (kg·K)×25 K=10125 kJ, the heat load that must be transferred outward through heat transfer is 57076 kJ / h×3 h-10125 kJ=161104 kJ.

[0067] The actual heat transfer capacity from inside the reactor to the outside is determined by three factors: the heat transfer coefficient K, the heat transfer area A, and the temperature difference ΔT between the inside and outside of the reactor. The heat transfer area A is fixed, H is the heat load, and the variable parameter is the heat transfer coefficient K. To achieve heat balance and temperature control, K must reach the following value range:

[0068] Volume 0.5 m³ 3 The reactor has a heat transfer area A = 2.2 m². 2 Assuming a heat transfer temperature difference of 50 K, the heat transfer coefficient should be:

[0069] kJ / (h·m 2 ·K)=406 W / (m 2 ·K)

[0070] For a supercritical CO2 reaction system, the overall heat transfer coefficient is estimated using the following formula:

[0071]

[0072] In the formula, The convective heat transfer coefficient of the supercritical CO2 and TFE mixture inside the reactor. The convective heat transfer coefficient is the value of the outer side of the jacket (cooling water). m represents the wall thickness of the stainless steel reactor. =16 W / (m·K) is the thermal conductivity of 316L stainless steel, R S The fouling thermal resistance is assumed to be 0.0002 m. 2 The calculated thermal resistance values ​​(K / W) are listed in Table 3.

[0073] Table 3 Calculated thermal resistance values

[0074]

[0075] It can be seen that K 超 =176 W / (m 2 The K value is much smaller than the required 406 W / (m³). 2 Since the required heat transfer coefficient cannot be achieved (K), the accumulated heat of reaction is:

[0076] W=36432 kJ / h. The accumulated heat will cause the reaction system to overheat (an average temperature rise of about 90 K per hour), which will trigger explosive polymerization.

[0077] therefore, The heat must be removed through other means to ensure the safe conduct of the polymerization reaction. Solving this problem requires a polymerization reaction engineering approach, establishing a balance between temperature, polymerization rate, and heat transfer rate to achieve temperature control during the polymerization process.

[0078] According to the present invention, during the reaction process, at least one of the following heat transfer methods is used to control the reaction temperature within the reactor:

[0079] (1) The reactor adopts a jacketed heat exchanger. During the feeding process, if Figure 2 The jacketed heat exchanger 18 shown is circulated with cooling water. Then the jacketed heat exchanger switches to 30-40 ℃ circulating water to start the reaction. After the reaction starts, the jacketed heat exchanger switches to circulating cooling water to control the temperature.

[0080] (2) Several atomizing nozzles are set at the feed port or the upper part of the reaction zone of the reactor. Liquid perfluoromethyl vinyl ether monomer, liquid tetrafluoroethylene monomer and / or initiator are injected by high pressure carbon dioxide in the form of atomized droplets. The atomized droplet raw material is rapidly vaporized in the supercritical carbon dioxide environment. Part of the reaction heat is absorbed by the latent heat of phase change evaporation to control the reaction temperature.

[0081] (3) Set up a carbon dioxide recirculation system to liquefy and remove the heat of reaction by recirculating part of the supercritical carbon dioxide in the reactor.

[0082] Using a circulating cooling water jacket on the reactor is a common method for heat removal. The amount of heat removed is usually limited, making it suitable for the initial stage of the reaction when not much heat has been released.

[0083] According to known technology, the latent heat of vaporization of 1000 mol TFE / PMVE is 700×16.5+300×22.1=11550+6630=18180 kJ, which is much less than 3 h×36432 kJ / h=109296 kJ and is not enough to completely remove excess heat. This patent uses carbon dioxide reflux compensation.

[0084] Further, according to known techniques, the cooling capacity replenished by carbon dioxide reflux is 109296 kJ - 18180 kJ = 91116 kJ. The amount of carbon dioxide required for reflux is 91116 kJ / (14.6 kJ / mol) = 6240 mol, or 6240 mol × 44 / 1000 = 275 kg, with a reflux rate of 91.5 kg per hour. It should be noted that the condensation of liquid tetrafluoroethylene (TFE) is not considered here, while the perfluoromethyl vinyl ether (PMVE) used in this invention is a supercritical fluid and a non-condensable gas under the operating conditions of this invention.

[0085] Based on the above calculations and analysis, the present invention adopts the following... Figure 3 The core temperature control strategy shown is as follows:

[0086] 1) Staged heat transfer, including primary cooling (heat transfer method (1)): jacketed circulating cooling water for basic heat transfer; secondary cooling (heat transfer method (2)): liquefied raw material injection for phase change heat absorption; tertiary cooling (heat transfer method (3)): liquid carbon dioxide reflux for strong heat absorption;

[0087] In the secondary cooling stage, several atomizing nozzles are installed at the reactor feed inlet or upstream of the reaction zone, such as... Figure 2 The process involves injecting liquefied monomers / initiators into the reactor using high-pressure CO2. The liquefied feedstock rapidly vaporizes in the supercritical CO2 environment, absorbing the heat of reaction and lowering the reaction temperature. The amount of high-pressure CO2 injected into the reactor can be dynamically adjusted using a mass flow meter based on the rate of heat release.

[0088] 2) Dynamic adjustment mechanism, including activating cooling methods in stages according to the reactor temperature deviation and temperature change rate; giving priority to using raw material atomized droplet spray to reduce costs, and starting carbon dioxide reflux forced cooling when insufficient.

[0089] Based on this, the method for controlled polymerization of perfluoroether elastomers in supercritical carbon dioxide provided by the present invention further includes: determining the process temperature according to the polymerization reaction of perfluoroether elastomers, and monitoring the actual polymerization reaction temperature in the scraped wall reactor throughout the reaction process, and setting a first predetermined value of 3 ℃ and a second predetermined value of 5 ℃ for the difference between the actual polymerization reaction temperature and the process temperature.

[0090] In the initial stage of the reaction, when the difference between the actual polymerization reaction temperature and the process temperature is less than or equal to the first predetermined value of 3 °C, the circulating cooling water of the jacket is turned on and the heat transfer method (1) is adopted.

[0091] As the reaction proceeds, heat is continuously released. When the difference between the actual polymerization reaction temperature and the process temperature is greater than the first predetermined value of 3 ℃ and less than or equal to the second predetermined value of 5 ℃, atomization is turned on, or the flow rate or injection speed of atomization is increased, and a heat transfer method (2) is superimposed on the heat transfer method (1).

[0092] When the difference between the actual polymerization reaction temperature and the process temperature is greater than the second predetermined value of 5 °C, the carbon dioxide reflux system is turned on. If the above methods are insufficient, the reflux liquid carbon dioxide is used to absorb heat effectively. The heat transfer method (3) is superimposed on the heat transfer methods (1) and (2).

[0093] In some embodiments, the liquid tetrafluoroethylene monomer and refluxed liquid carbon dioxide are injected continuously; the liquid perfluoromethyl vinyl ether monomer is injected in stages to control the polymerization rate.

[0094] In some embodiments, the injection amount of tetrafluoroethylene monomer and the reflux rate of carbon dioxide are calculated based on the temperature difference between the reactor wall temperature and the reaction medium to maintain the polymerization reaction temperature within a certain range. The polymerization reaction temperature is maintained at 35-125 °C by adjusting the injection rate, and the polymerization reaction pressure is controlled at 7-30 MPa.

[0095] In some embodiments, the reactor used in this invention is a scraped-wall reactor, wherein a rotating scraper is provided on the inner wall of the reactor, such as... Figure 2 The electric motor 8 shown drives the wall-scraping agitator 19 to rotate, and the rotation speed of the rotary scraper is 10-50 rpm.

[0096] In some embodiments, the sulfidation point monomer used in this invention is selected from at least one of perfluoro-2-(2-sulfonylchloroethoxy)propyl vinyl ether and perfluoro-8-cyano-5-methyl-3,6-dioxa-1-octene; the sulfidation point third monomer is dissolved in trichlorotrifluoroethane solvent and then pressurized into the reactor by high-pressure CO2, wherein the mass of the trichlorotrifluoroethane is 1.5-3 times that of the sulfidation point monomer.

[0097] In some embodiments, the chain transfer agent used in this invention conforms to the chemical formula I-(CF2). n -I, where n is an integer from 1 to 10, selected from at least one of 1,3-diiodopropane, 1,4-diiodobutane, 1,6-diiodohexane, 1,8-diiodooctane, 1,3-diiodoperfluoropropane, 1,4-diiodoperfluorobutane, 1,6-diiodoperfluorohexane, and 1,8-diiodoperfluorooctane. The chain transfer agent is dissolved in trichlorotrifluoroethane solvent and then pressurized into the reactor by high-pressure CO2, wherein the mass of trichlorotrifluoroethane is 3-5 times that of the chain transfer agent.

[0098] In some embodiments, the initiator used in this invention is bis(perfluoropropionyl) peroxide; the initiator is dissolved in trichlorotrifluoroethane solvent and then injected into the reactor by high-pressure CO2, wherein the mass of trichlorotrifluoroethane is 3-5 times that of the initiator.

[0099] In some embodiments, the method further includes: stopping the supply of liquid tetrafluoroethylene monomer and / or liquid carbon dioxide and / or carbon dioxide recycling when the reaction reaches a predetermined conversion rate; depressurizing, filtering, recovering unreacted monomer and carbon dioxide, and collecting the perfluoroether elastomer product; the perfluoroether elastomer product is dried, subjected to supercritical CO2 devolatilization, mixed with a vulcanizing crosslinking agent and a catalyst, molded, and subjected to secondary vulcanization to obtain a composition; the secondary vulcanization temperature is 190-240 °C, and the time is 10-24 h, wherein the vulcanizing crosslinking agent is tetraphenyltin, and the catalyst is hexaoxane.

[0100] The present invention further provides a perfluoroether elastomer and composition prepared by the controlled polymerization of perfluoroether elastomers in supercritical carbon dioxide as described above.

[0101] As demonstrated by the embodiments of the present invention, the perfluoroether elastomer prepared by the method of the present invention has good thermal stability, chemical corrosion resistance and low fluoride ion extractability. Due to the precise control of heat transfer in the preparation process, the unstable end groups of the prepared perfluoroether elastomer are greatly reduced, which is beneficial to improving the various physical properties of the elastomer. Moreover, the supercritical carbon dioxide used in the preparation process is inexpensive, low in toxicity, environmentally friendly and chemically friendly, and the polymer post-processing is simple. High-purity polymer can be separated after depressurization without the need for post-processing processes that consume a lot of energy, such as demulsification, sedimentation and drying. In addition, carbon dioxide can be recovered and reused, and will not produce a greenhouse effect.

[0102] The present invention further provides a method for the controlled polymerization of perfluoroether elastomers in supercritical carbon dioxide as described above, which is applied to the synthesis of perfluoroether elastomers.

[0103] In some embodiments, the method is applied to the synthesis of perfluoroether elastomers, wherein the monomers include tetrafluoroethylene, perfluoromethyl vinyl ether, and a sulfidation point monomer, and the polymerization reaction is initiated by bis(perfluoropropionyl) peroxide, the amount of which is 0.01-0.02 wt% of the mass of the perfluorocomonomer mixture.

[0104] In some embodiments, a chain transfer agent is added to the polymerization reaction in an amount of 0.8-1.2 wt% of the mass of the perfluorinated comonomer mixture. The chain transfer agent conforms to the chemical formula I-(CF2). n -I, where n is an integer from 1 to 10, including but not limited to 1,3-diiodopropane, 1,4-diiodobutane, 1,6-diiodohexane, 1,8-diiodooctane, 1,3-diiodoperfluoropropane, 1,4-diiodoperfluorobutane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane, etc.

[0105] In some embodiments, the sulfidation point monomer includes, but is not limited to, perfluoro-2-(2-sulfonylchloroethoxy)propyl vinyl ether, perfluoro-8-cyano-5-methyl-3,6-dioxa-1-octene, etc. Furthermore, the sulfidation point third monomer is dissolved in trichlorotrifluoroethane solvent and then pressurized into the reactor by high-pressure CO2, wherein the mass of the trichlorotrifluoroethane is 1.5-3 times that of the sulfidation point monomer.

[0106] In some embodiments, the vulcanizing crosslinking agent is tetraphenyltin, and the catalyst is hexaoxane; the amount of the vulcanizing crosslinking agent and the catalyst added is 1.5-3 wt% and 2.5-5 wt% of the mass of the perfluoroether elastomer, respectively.

[0107] In some embodiments, the product is subjected to supercritical CO2 devolatilization and compression molding under the following conditions: compression pressure 8-12 MPa, temperature 160-180 ℃, time 10-15 min, and secondary vulcanization temperature 190-210 ℃, time 18-24 h.

[0108] In some embodiments, the supercritical CO2 is recycled through a circulation system with a recovery rate of ≥95%, and unreacted monomers are separated and reused through a condensation device.

[0109] This invention solves the heat transfer problems in supercritical CO2 polymerization reactions (such as the large and concentrated exothermic reaction and the low thermal conductivity of supercritical CO2). Combining the strategies of injecting liquefied feedstock (using latent heat for cooling) and CO2 reflux (removing heat through circulation), the following is a detailed scheme for the temperature control process design and control system flowchart:

[0110] I. Heat Transfer Characteristics and Requirements of Supercritical CO2 Polymerization

[0111] Supercritical CO2 polymerization (such as free radical polymerization and photopolymerization) is a strongly exothermic process (for example, the heat of polymerization of acrylate monomers is about 50-80 kJ / mol). However, the thermal conductivity of supercritical CO2 is low (about 0.01-0.03 W / (m·K), which is much lower than that of water (0.6 W / (m·K)). This makes it difficult to remove the heat of reaction quickly, which can easily lead to local overheating (resulting in a wider molecular weight distribution of the polymer and an increase in side reactions) or explosive polymerization (temperature runaway).

[0112] Therefore, temperature control must meet the following requirements:

[0113] Rapid removal of heat of reaction: through the synergistic effect of latent heat of phase change (evaporation of liquefied feedstock) and circulating cooling (recirculation of liquid CO2);

[0114] Precise control: Adapts to the large changes in density / viscosity of supercritical CO2 with temperature and pressure, avoiding temperature fluctuations;

[0115] Safe and reliable: Redundant cooling measures are implemented to prevent overheating.

[0116] II. Temperature Control Process Design (Core Strategy: Liquefied Feed Injection + Liquid CO2 Recirculation)

[0117] The process centers on a reactor, integrating a liquefied feedstock supply system, a liquid CO2 recirculation system, a temperature monitoring system, and a control system. The specific steps are as follows:

[0118] 1. System composition and functions (see Table 4):

[0119] Table 4 Control System and Functions

[0120]

[0121] 2. Temperature control process:

[0122] (1) Preparation before reaction:

[0123] Inject supercritical CO2 (pressure 8-10 MPa, temperature 35-40 ℃, slightly higher than the critical temperature 31.1℃) into the reactor to ensure that the oxygen concentration in the reactor is below 10 ppm;

[0124] Monomers (such as TFE and PMVE) and initiators (such as bis(perfluoropropionyl) peroxide, which are first dissolved in trichlorotrifluoroethane) are added to the raw material tank. The temperature of the jacket cooling medium is -5 to 10 ℃ (in liquefied state).

[0125] Start the stirrer (10-50 rpm) to ensure that the mixture in the reactor is uniform.

[0126] (2) Reaction initiation and initial temperature control:

[0127] Turn on the liquefied feed metering pump and spray the liquefied feed into the reactor through the atomizing nozzle (the nozzle is located on the top of the reactor, close to the stirrer, to ensure that it is quickly mixed with the supercritical CO2 after atomization).

[0128] After the raw material is atomized, it evaporates and absorbs heat in supercritical CO2, thereby reducing the temperature inside the reactor.

[0129] Simultaneously, the CO2 circulation pump is started to extract the supercritical CO2 from the reactor, cool it to 30-35℃ through a cooler (cooling water temperature 25 ℃) to liquefy it, and then send it back to the reactor (the reflux flow rate is initially set to 30-50 L / min).

[0130] (3) Mid-reaction stage: Closed-loop temperature control

[0131] Temperature detection: The PT100 temperature sensor inside the reactor (installed in the middle of the reactor, which best reflects the core temperature of the reaction) collects the temperature signal (4-20 mA) in real time and transmits it to the PLC;

[0132] PID control: The PLC compares the actual temperature with the set temperature (e.g., 60 ℃, determined according to the polymerization process) and calculates the required adjustment of the raw material flow rate and CO2 reflux flow rate using a PID algorithm.

[0133] If the temperature is higher than the set value (e.g., 62 ℃): increase the raw material injection flow rate (e.g., from 10 L / h to 15 L / h), and at the same time increase the CO2 reflux flow rate (e.g., from 50 L / min to 70 L / min to improve the circulation cooling efficiency).

[0134] If the temperature is lower than the set value (e.g., 58 ℃): reduce the raw material flow rate (e.g., from 10 L / h to 8 L / h) and the CO2 reflux flow rate (e.g., from 50 L / min to 40 L / min) to avoid overcooling;

[0135] Flow feedback: The raw material flow sensor (electromagnetic flow meter) and the CO2 reflux flow sensor (vortex flow meter) feed back the actual flow signal to the PLC to form a closed-loop control and ensure accurate flow regulation.

[0136] In some embodiments, such as Figure 4 As shown, when the difference between the polymerization reaction temperature and the process temperature is less than or equal to the first predetermined value, jacketed circulating water is used for basic heat transfer; when the difference between the polymerization reaction temperature and the process temperature is greater than the first predetermined value and less than or equal to the second predetermined value, liquefied raw materials are injected for phase change heat absorption; when the difference between the polymerization reaction temperature and the process temperature is greater than the second predetermined value, liquid CO2 reflux is used for strong heat absorption.

[0137] In some embodiments, the first predetermined value is 3 °C and the second predetermined value is 5 °C.

[0138] (4) Later stage of reaction: maintaining stability and pressure compensation

[0139] As the reaction proceeds, the raw materials are gradually consumed, and liquefied raw materials need to be continuously replenished (by using a metering pump to maintain a stable flow rate).

[0140] Pressure control: The pressure inside the reactor may drop due to the injection of raw materials (liquid volume) and CO2 reflux (loss). The pressure sensor (strain gauge) monitors the pressure in real time. If it is lower than the set value (e.g., 7.5 MPa), the PLC triggers the fresh CO2 replenishment valve (solenoid valve) to open, replenishing CO2 until the pressure is restored (e.g., 8 MPa).

[0141] Cooler adjustment: The CO2 return temperature sensor (PT100) detects the CO2 temperature after cooling. If it is higher than the set value (e.g., 35℃), the PLC increases the cooling water flow of the cooler (adjusted by a solenoid valve) to reduce the return CO2 temperature and improve the cooling effect.

[0142] (5) End of reaction: shutdown and cleaning

[0143] When the reaction reaches the predetermined conversion rate (e.g., through online infrared monitoring or sampling analysis), stop the raw material supply and CO2 circulation; slowly reduce the pressure (through the vent valve) to discharge the supercritical CO2 (recover it to the cylinder for reuse); open the reactor, remove the polymer product (e.g., fluorinated polymer particles), and clean the residue inside the reactor.

[0144] III. PMVE Segmented Addition and Processing Steps

[0145] For the staged addition of PMVE in a closed reactor, considering its supercritical characteristics and high-pressure environment requirements, the specific steps are as follows:

[0146] 1. Cool the reactor to the target temperature range (10-20 ℃) ​​and replace the internal air with CO2 gas to ensure that the oxygen content is below the safe threshold (e.g., <20 ppm).

[0147] Place the PMVE storage tank in a low-temperature constant temperature bath (e.g., -10 ℃) to prevent phase change due to temperature fluctuations during transportation.

[0148] First, inject a mixture of TFE and CO2 into the reactor, accounting for 30-40% of the total feed. Start the stirring system to keep the system uniformly mixed.

[0149] The molar ratio of TFE to CO2 is controlled at 7:3, utilizing the co-solvent effect of CO2 to reduce the critical pressure of the system.

[0150] Slowly increase the pressure to 5-8 MPa and maintain a stable temperature for 10 minutes, then observe the pressure fluctuations.

[0151] 2. Start the high-pressure metering pump and inject PMVE at a rate of 0.5 L / min. After adding 5% of the total amount, pause for 10 minutes to monitor the system temperature and pressure changes.

[0152] If the temperature rises to the upper limit of 20 ℃, immediately start the cooling system (pour -5 ℃ brine into the jacket).

[0153] If the pressure exceeds the set threshold (e.g., 12 MPa), pause the addition and add CO2 to dilute.

[0154] Increase the PMVE flow rate to 1 L / min and simultaneously start the condenser reflux system.

[0155] 3. Monitor the gas (PMVE and CO2) ratio using online gas chromatography to maintain a CO2 molar fraction ≥30%.

[0156] The reflux condensation temperature is controlled at -5 ℃ to ensure efficient liquefaction of TFE, PMVE and CO2.

[0157] Reduce the PMVE flow rate to 0.2 L / min and use a pulsed addition method (inject for 5 seconds every 10 seconds, then pause for 5 seconds).

[0158] Simultaneously adjust the stirring speed to 30 rpm to enhance local mixing efficiency.

[0159] Set a pressure rise rate alarm (e.g., >0.5 MPa / min) to trigger an interlock to add CO2.

[0160] 4. Stop adding PMVE when the cumulative amount of PMVE reaches the design value, and the system pressure is stable at 10±0.5 MPa and the temperature is maintained at 15±2 ℃.

[0161] Close the PMVE feed valve and keep the mixing and cooling system running for 30 minutes.

[0162] The uniformity of component distribution (deviation <5%) was confirmed using online sensors.

[0163] If PMVE is detected to exceed the critical level (pressure surge >15 MPa), immediately activate the emergency CO2 injection system (flow rate 5 L / min).

[0164] At the same time, the discharge valve at the bottom of the reactor is opened to transfer part of the mixture to the backup buffer tank.

[0165] Check the PMVE concentration at the mechanical seal every hour (using an infrared leak detector). If the leakage is >10 ppm, stop production or testing immediately.

[0166] IV. Control System Flowchart Design

[0167] The control system uses a PLC as its core to achieve closed-loop control of detection, judgment, and adjustment. The flowchart is as follows (describe the logic in words):

[0168] 1. Signal input (detection element)

[0169] Temperature signals: Reactor internal temperature (PT100, 4-20 mA), liquefied feed temperature (PT100, -20-50 ℃), CO2 reflux temperature (PT100, 0-100 ℃).

[0170] Pressure signal: Reactor pressure (strain gauge sensor, 0-35 MPa, 4-20 mA);

[0171] Flow signals: liquefied feedstock flow rate (electromagnetic flow meter, 0-50 L / h, 4-20 mA), CO2 reflux flow rate (vortex flow meter, 0-100 L / min, 4-20 mA).

[0172] Status signals: Pump operating status (start / stop signal), valve status (on / off signal).

[0173] 2. Control Core (PLC)

[0174] Data processing: Convert analog signals (temperature, pressure, flow rate) into digital signals and calculate the deviation between the actual value and the set value;

[0175] PID algorithm: Perform PID calculation on temperature deviation (proportional gain Kp=2-5, integral time Ti=10-30 s, derivative time Td=1-5 s), and output raw material flow rate adjustment signal (4-20 mA) and CO2 reflux flow rate adjustment signal (4-20 mA).

[0176] Logic control:

[0177] When the pressure is lower than the set value, the fresh CO2 replenishment valve is opened;

[0178] When the temperature exceeds the upper limit (e.g., 65 ℃), an alarm is triggered (displayed on the touch screen) and emergency cooling is initiated (the raw material flow rate is increased to the maximum value, the CO2 reflux flow rate is increased to the maximum value, and the jacket cooling is opened).

[0179] In case of pump / valve failure, stop the relevant equipment and trigger an alarm.

[0180] 3. Signal output (control element)

[0181] Raw material flow regulation: Output signal to the frequency converter (0-50 Hz) of the liquefied raw material metering pump to change the pump speed and regulate the raw material flow;

[0182] CO2 reflux regulation: Output signal to CO2 circulation pump frequency converter (0-50 Hz) to change pump speed and regulate reflux flow rate;

[0183] Pressure compensation: Output signal to the solenoid valve (24 VDC) of the fresh CO2 replenishment valve to control the valve opening and replenish CO2;

[0184] Cooling regulation: Output signal to the solenoid valve (24 VDC) of the cooler cooling water valve to control the cooling water flow and regulate the return CO2 temperature;

[0185] Alarm output: Triggers buzzer (audible alarm) and touchscreen alarm (text prompt).

[0186] 4. Human-machine interface (touchscreen)

[0187] Real-time monitoring: Displays parameters such as reactor temperature, pressure, raw material flow rate, and CO2 reflux flow rate;

[0188] Parameter settings: Set the temperature setpoint (e.g., 60 ℃), pressure setpoint (e.g., 8 MPa), and PID parameters (Kp, Ti, Td);

[0189] Alarm Management: View historical alarm records (temperature exceeding upper limit, abnormal pressure, pump failure, etc.);

[0190] Manual control: During commissioning or in case of malfunction, manually control the start and stop of the pump / valve (e.g., manually start the raw material pump).

[0191] V. Key Design Considerations

[0192] Optimization of liquefied feedstock injection:

[0193] High-pressure atomizing nozzles (approximately 0.1-1 MPa higher than the reactor pressure) are used to disperse liquefied raw materials into droplets of 10-100 μm, increasing the contact area with supercritical CO2, accelerating evaporation, and improving latent heat cooling efficiency.

[0194] The raw material tank uses a cooling jacket (refrigerant such as R134a) to keep the raw material in a liquefied state (to avoid solidification or vaporization).

[0195] Optimization of CO2 reflux:

[0196] like Figure 2 As shown, CO2 in the reactor enters the CO2 reflux device 9 through the reflux port 17. The reflux pipe of the condenser is configured in a closed manner. The cooler is a shell-and-tube type (supercritical CO2 flows through the tube side, and cooling water flows through the shell side), which increases the heat transfer area (such as using finned tubes) and improves the cooling efficiency.

[0197] Temperature control stability:

[0198] A multi-sensor fusion method is adopted (one PT100 is installed at the top, middle and bottom of the reactor), and the average temperature is used as the control signal to avoid the influence of local temperature fluctuations;

[0199] PID parameters are optimized through on-site debugging (e.g., using the Ziegler-Nichols method) to reduce overshoot (target: overshoot < 5%) and improve response speed (target: temperature deviation < 3 ℃).

[0200] Safety design:

[0201] The reactor is equipped with a pressure relief valve (set pressure 30 MPa) to prevent overpressure.

[0202] The temperature sensor is set to be redundant (two PT100) to avoid false judgments caused by the failure of a single sensor;

[0203] Emergency Stop Button (ESD): In the event of severe overheating (e.g., 70 °C) or overpressure (e.g., 30 MPa), immediately stop all equipment and open the vent valve to reduce pressure.

[0204] This solution effectively solves the heat transfer problem in supercritical CO2 polymerization by combining the synergistic effect of liquefied raw material injection (latent heat cooling) and liquid CO2 reflux; combined with PLC closed-loop control (PID regulation) and human-machine interface (real-time monitoring), it achieves precise temperature control (deviation <3 ℃); at the same time, through safety design (redundant sensors, safety valves, emergency shutdown), it ensures the safety of the reaction.

[0205] This process is applicable to supercritical CO2 polymerization processes such as the preparation of fluorine-containing polymer particles (e.g., supercritical CO2 photopolymerization) and free radical polymerization of ordinary polymers (e.g., acrylates). It has advantages such as being environmentally friendly (no organic solvents), having simple post-processing (supercritical CO2 is easy to recover), and producing high-quality products (narrow molecular weight distribution).

[0206] Simplified logic of the control system flowchart is shown below. Figure 3 and Figure 4 .

[0207] The purpose of this invention is to overcome the shortcomings of existing technologies, such as the difficulty in removing reaction heat leading to challenges in temperature control and impacting product quality, by providing a method for the controlled polymerization of perfluoroether elastomers in supercritical CO2, comprising:

[0208] Inject CO2, PMVE, and tetrafluoroethylene monomer into the reactor; ensure that the CO2 concentration in the vapor space is ≥30 mol%

[0209] Liquid CO2 and liquid tetrafluoroethylene monomer are injected into the reactor.

[0210] Start the scraped-wall reactor to prevent perfluoroether elastomer products from sticking to the wall, which would increase thermal resistance and affect the efficiency of the indirect heat exchange.

[0211] The initiator bis(perfluoropropionyl) peroxide was added to the reactor at an amount of 0.01 wt% of the mass of the perfluorocomonomer mixture.

[0212] Add a chain transfer agent to the reactor at a rate of 1.0 wt% of the mass of the perfluorinated comonomer mixture.

[0213] During the reaction, liquid tetrafluoroethylene monomer and liquid CO2 are continuously injected into the reactor. The latent heat of vaporization of tetrafluoroethylene monomer and CO2 are used to absorb the heat released by the reaction. The amount of tetrafluoroethylene monomer and CO2 injected is controlled to keep the reaction temperature within the set range.

[0214] The polymerization reaction was controlled by adding PMVE and TFE in stages, with PMVE added in stages to control the polymerization reaction. The pressure of the reaction system was controlled by CO2.

[0215] Determine if the reaction has ended. If not, continue injecting monomer and carbon dioxide. If it has ended, depressurize, filter, and recover unreacted tetrafluoroethylene monomer and carbon dioxide. Use carbon dioxide to repressurize and stir the reactor to collect the perfluoroether elastomer product.

[0216] After the reaction is complete, the pressure is released, the mixture is filtered, and unreacted monomers and CO2 are recovered (through condensation or adsorption). The product is then collected by pressurizing and stirring with CO2. The product is obtained from... Figure 2 The material is obtained from the discharge port 20.

[0217] In this embodiment, the CO2 recovery rate can reach over 95%.

[0218] The collected perfluoroether elastomer powder was washed, dried, thin-passed, mixed, molded, and subjected to secondary vulcanization to obtain a perfluoropolymer composition. A vulcanization crosslinking agent and a catalyst were added during the mixing process.

[0219] The molding conditions are: molding pressure 10 MPa, molding temperature 170 ℃, and molding time 10 min; the secondary vulcanization temperature is 190-240 ℃ and the time is 10-24 h, wherein the vulcanization crosslinking agent is tetraphenyltin and the catalyst is hexaoxane.

[0220] The following are several specific embodiments based on the above-described invention, used to demonstrate a method for controlled polymerization of perfluoroether elastomers in supercritical CO2.

[0221] Example 1

[0222] The reactor is a high-pressure stainless steel reactor equipped with a wall-scraping agitator, an atomizing nozzle powered by high-pressure CO2, a pressure sensor (range 0-35MPa), a temperature sensor (PT100, range 0-100 ℃), and a built-in closed CO2 reflux device. The wall-scraping structure uses a rotary scraper with a rotation speed set at 30 rpm, and the stainless steel inner wall is hydrophobically treated.

[0223] Prepare liquid CO2, liquid tetrafluoroethylene (TFE) monomer, liquid perfluoromethyl vinyl ether (PMVE), a trichlorotrifluoroethane solution of the initiator bis(perfluoropropionyl)peroxide, and a trichlorotrifluoroethane solution of the chain transfer agent; add 28 mol% PMVE in stages. The mass of the trichlorotrifluoroethane is 3 times that of the bis(perfluoropropionyl)peroxide; the mass of the trichlorotrifluoroethane is 3 times that of the chain transfer agent.

[0224] Liquid CO2, liquid PMVE, and liquid tetrafluoroethylene monomer are injected into the reactor to ensure that the CO2 concentration in the vapor space is greater than 35 mol% and the oxygen concentration is less than 10 ppm. The scraped-wall reactor is started up, utilizing the scraped-wall structure to prevent the perfluoroether elastomer products from adhering to the wall and affecting the indirect heat exchange.

[0225] A trichlorotrifluoroethane solution of bis(perfluoropropionyl)peroxide as the initiator was added to the reactor at a dosage of 0.01 wt% of the mass of the perfluorocomonomer mixture; chain transfer agent I-(CF2)4-I was added at a dosage of 1.0 wt% of the mass of the perfluorocomonomer mixture. The reaction temperature was set at 60 °C, and the reactor pressure was controlled at 10 MPa.

[0226] The third monomer of the sulfidation point is perfluoro-8-cyano-5-methyl-3,6-dioxa-1-octene. The monomer of the sulfidation point is dissolved in trichlorotrifluoroethane solvent and then added to the reactor. The mass of the trichlorotrifluoroethane is 1.5 times that of the monomer of the sulfidation point.

[0227] Reaction process control: During the reaction, liquid tetrafluoroethylene monomer and liquid CO2 are continuously injected into the reactor. The injection rate of tetrafluoroethylene monomer and the reflux rate of CO2 are calculated based on the temperature difference between the reactor wall temperature and the reaction medium. The reaction temperature is maintained at 60 °C by adjusting the injection rate; temperature control is performed according to the aforementioned control logic.

[0228] Reaction Monitoring and Termination: Monitor the reaction in real time. When the reaction reaches the predetermined conversion rate (determined by online infrared monitoring), stop the feedstock supply and CO2 circulation. Slowly reduce the pressure to release the supercritical CO2 and recover it into the cylinder.

[0229] Open the reactor and remove the polymer product. Wash, dry, thin-pass, and knead the collected perfluoroether elastomer powder. The vulcanizing crosslinking agent added during kneading is tetraphenyltin, and the catalyst is hexaoxane; the amount of the vulcanizing crosslinking agent and the catalyst added is 1.5-3 wt% and 2.5-5 wt% of the mass of the perfluoroether elastomer, respectively.

[0230] Then, compression molding is performed at a pressure of 10 MPa, a temperature of 170 ℃, and a time of 10 min; followed by secondary vulcanization at a temperature of 220 ℃ for 24 h to obtain a fluororubber composition.

[0231] A high-performance perfluoroether elastomer was successfully prepared, achieving a supercritical CO2 recovery rate of 96%, and unreacted monomers were effectively recovered and reused. The prepared fluororubber composition exhibits good heat and chemical resistance, making it suitable for applications in semiconductors, aerospace, and chemical industries.

[0232] Example 2

[0233] Similar to the reactor and scraped-wall reactor in Example 1, the scraping structure uses a fixed scraper with a rotation speed set to 20 rpm.

[0234] The rest is the same as in Example 1.

[0235] Liquid CO2 and liquid tetrafluoroethylene monomer are injected into the reactor, and 30 mol% PMVE is added in stages to ensure that the CO2 concentration in the vapor space is 32 mol%. The scraped-wall reactor is then started.

[0236] Initiator bis(perfluoropropionyl) peroxide was added at a dosage of 0.02 wt% of the perfluorocomonomer mixture; chain transfer agent was added at a dosage of 0.8 wt% of the perfluorocomonomer mixture. The reaction temperature was set at 70 °C, and the reactor pressure was controlled at 9 MPa.

[0237] The chain transfer agent is 1,4-diiodobutane.

[0238] The third monomer of the sulfidation point is perfluoro-8-cyano-5-methyl-3,6-dioxa-1-octene. The monomer of the sulfidation point is dissolved in trichlorotrifluoroethane solvent and then added to the reactor. The mass of the trichlorotrifluoroethane is 1.5 times that of the monomer of the sulfidation point.

[0239] Liquid tetrafluoroethylene monomer and liquid CO2 are continuously injected. Cooling methods are activated in stages according to the reactor temperature deviation and the rate of temperature change. Feed spraying is used first to reduce costs. If insufficient, CO2 reflux forced cooling is activated to maintain the reaction temperature within the set range.

[0240] When the reaction reaches the predetermined conversion rate (determined by sampling analysis), the raw material supply and CO2 circulation are stopped, and the supercritical CO2 is slowly recovered under reduced pressure.

[0241] The polymer product is collected, washed, and dried. The vulcanizing crosslinking agent is tetraphenyltin, and the catalyst is hexaoxane octadecane. The mixture is then kneaded to obtain a compound rubber.

[0242] The compression molding conditions were: compression pressure 9 MPa, compression temperature 160 ℃, and compression time 12 min; the secondary vulcanization temperature was 200 ℃ and the time was 20 h.

[0243] The prepared perfluoroether elastomer exhibits excellent properties, with a supercritical CO2 recovery rate of 95%. The product also demonstrates good flexibility and processing performance, meeting the requirements of applications demanding high material flexibility.

[0244] Example 3

[0245] The reactor and scraped-wall reactor are the same as in Example 1, but the scraping structure uses a rotary scraper with a rotation speed set at 40 rpm. The raw materials are the same as in Example 1.

[0246] Liquid CO2, liquid PMVE, and liquid tetrafluoroethylene monomer are injected into the reactor. 32 mol% PMVE is added in stages to make the CO2 concentration in the vapor space 38 mol%. The scraped-wall reactor is then started.

[0247] Initiator bis(perfluoropropionyl) peroxide was added at a dosage of 0.015 wt% of the mass of the perfluorocomonomer mixture; chain transfer agent was added at a dosage of 1.2 wt% of the mass of the perfluorocomonomer mixture. The reaction temperature was set at 90 °C, and the reactor pressure was controlled at 11 MPa.

[0248] The chain transfer agent is 1,4-diiodobutane.

[0249] The third monomer of the sulfidation point is perfluoro-8-cyano-5-methyl-3,6-dioxa-1-octene. The monomer of the sulfidation point is dissolved in trichlorotrifluoroethane solvent and then added to the reactor. The mass of the trichlorotrifluoroethane is 1.5 times that of the monomer of the sulfidation point.

[0250] During the reaction, the injection rates of liquid tetrafluoroethylene monomer and liquid CO2 are controlled, utilizing their latent heat of vaporization to absorb the exothermic reaction and maintain a stable reaction temperature. Simultaneously, a pressure sensor monitors the pressure in real time; if the pressure falls below a set value, fresh CO2 is added.

[0251] When the reaction reaches the predetermined conversion rate (determined by online infrared monitoring), the raw material supply and CO2 circulation are stopped, and supercritical CO2 is recovered under reduced pressure.

[0252] The polymer product is removed, and appropriate post-processing is performed. The vulcanizing crosslinking agent is tetraphenyltin, and the catalyst is hexaoxane octadecane, and the mixture is then kneaded to obtain a compound rubber.

[0253] The molding conditions were: molding pressure 11 MPa, molding temperature 180 ℃, and molding time 8 min; the secondary vulcanization temperature was 240 ℃ and the time was 15 h.

[0254] Perfluoroether elastomers were successfully synthesized, achieving a supercritical CO2 recovery rate of 97%. The product exhibits high heat resistance and chemical stability, making it suitable for use in harsh environments such as high temperatures and strong corrosion in the chemical industry.

[0255] Comparative example:

[0256] The comparative case uses a traditional aqueous emulsion polymerization method to prepare perfluoroether elastomers, which contrasts with the controlled polymerization method of the present invention in supercritical CO2.

[0257] Traditional aqueous emulsion polymerization for the preparation of perfluoroether elastomers:

[0258] Deionized water is added to the polymerization reactor as the reaction medium. A surfactant (such as perfluorooctanoate) is added at an amount of 2-3 wt% of the total monomer mass to form a stable emulsion system. Tetrafluoroethylene (TFE) and perfluoromethyl vinyl ether (PMVE) monomers are introduced into the reactor, with the monomer molar ratio consistent with that of Embodiment 1 of this invention (e.g., TFE:PMVE = 71:28).

[0259] Ammonium persulfate, an initiator, is added at a dosage of 0.1-0.2 wt% of the total monomer mass to initiate the polymerization reaction. The reaction temperature is controlled at 70-90 ℃, and the reaction pressure is controlled at 2-3 MPa.

[0260] The chain transfer agent is 1,4-diiodobutane.

[0261] The third monomer of the sulfidation point is perfluoro-8-cyano-5-methyl-3,6-dioxa-1-octene. The monomer of the sulfidation point is dissolved in trichlorotrifluoroethane solvent and then added to the reactor. The mass of the trichlorotrifluoroethane is 1.5 times that of the monomer of the sulfidation point.

[0262] During the polymerization reaction, continuous stirring is required to ensure uniform reaction. Since the reaction is strongly exothermic, heat is transferred through circulating water in the reactor jacket. However, due to the large amount of heat generated, temperature fluctuations are difficult to control, and localized overheating may occur.

[0263] Once the reaction reaches the predetermined conversion rate, the monomer flow and stirring are stopped. Emulsion demulsification is then performed by adding a demulsifier (such as calcium chloride) to break the emulsion. Following this, a series of post-processing steps, including coagulation, washing, and drying, are carried out to obtain the perfluoroether elastomer product.

[0264] The vulcanizing crosslinking agent is tetraphenyltin, and the catalyst is hexaoxane; the amount of the vulcanizing crosslinking agent and the catalyst added is 1.5-3wt% and 2.5-5wt% of the mass of the perfluoroether elastomer, respectively.

[0265] Unreacted monomers are difficult to recover, and some are discharged with wastewater, resulting in resource waste and environmental pollution.

[0266] Comparative analysis

[0267] Regarding temperature control: This invention employs a graded heat transfer and dynamic adjustment mechanism. Through the synergistic effect of multiple methods such as jacketed circulating water, liquefied raw material injection, and liquid CO2 reflux, the reaction temperature can be precisely controlled within ±3 ℃ and ±5 ℃, effectively avoiding local overheating and explosive polymerization.

[0268] In contrast, relying solely on jacketed circulating water for heat removal makes it difficult to quickly remove the heat of reaction, resulting in large temperature fluctuations. This can lead to a wider distribution of polymer molecular weight, an increase in side reactions, and negatively impact product quality.

[0269] In terms of cost and environmental protection: This invention uses supercritical CO2 as a green reaction medium, eliminating the need for surfactants. Unreacted monomers and CO2 can be recycled with a recovery rate of ≥95%, reducing production costs and environmental pollution. In contrast, the comparative case requires large amounts of surfactants, increasing production costs. Furthermore, the post-processing is complex, involving steps such as emulsion demulsification, coagulation, and drying, consuming significant energy. Unreacted monomers are also difficult to recover, resulting in resource waste and environmental pollution.

[0270] Product adhesion to walls: This invention employs an improved scraping-wall reactor with a hydrophobic surface, effectively solving the problem of perfluoroether elastomers adhering to the walls at high temperatures. This facilitates cleaning and improves the efficiency of the indirect heat exchange. In contrast, during the polymerization process in the comparative case, perfluoroether elastomers easily adhere to the walls, affecting the normal operation of the reaction equipment and making product collection and equipment cleaning difficult.

[0271] The comparison shows that the method of controlled polymerization of perfluoroether elastomers in supercritical CO2 has significant advantages in terms of temperature control, cost, environmental protection and product quality, and can effectively overcome the shortcomings of traditional methods.

[0272] The composition and properties of the fluorinated rubber compositions prepared from perfluororubber elastomer composites in Examples 1-3 and Comparative Example 1 are listed in Tables 5 and 6. Unstable end groups were determined by infrared microscopy (Shimadzu IRAffinity-1S) using dried elastomers.

[0273] Table 5 Composition of Fluororubber Composition

[0274]

[0275] Table 6 Characteristic Parameters

[0276]

[0277] As can be seen from Table 6, the perfluoroether elastomer prepared by the method of the present invention has good thermal stability, chemical corrosion resistance and low fluoride ion extractability. Due to the precise control of heat transfer in the preparation process, the unstable end groups of the prepared perfluoroether elastomer are greatly reduced, which is beneficial to improving the various physical properties of the elastomer.

[0278] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0279] Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of the equivalents of the claims are intended to be included within the invention.

[0280] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, system, or module that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, system, or module. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, system, or module that includes said element.

[0281] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features of the invention herein.

Claims

1. A method for polymerizing perfluoroether elastomers in supercritical carbon dioxide, characterized in that, include: Carbon dioxide, perfluoromethyl vinyl ether monomer, and tetrafluoroethylene monomer are added to a scraped-wall reactor, wherein the carbon dioxide concentration in the vapor space of the scraped-wall reactor is ≥30 mol%; Continue adding initiator, chain transfer agent and sulfidation point monomer to the scraped wall reactor; The polymerization reaction is initiated by heating. When the reaction reaches the predetermined conversion rate, the supply of liquid tetrafluoroethylene monomer, perfluoromethyl vinyl ether, and / or liquid carbon dioxide is stopped, and / or carbon dioxide is recycled. The pressure is released, the mixture is filtered, unreacted monomer and carbon dioxide are recovered, and the product, perfluoroether elastomer, is collected. During the reaction, cooling measures are activated in stages, and the temperature inside the reactor is controlled using at least one of the following methods: Heat transfer method (1) The reactor adopts a jacketed heat exchanger. During the feeding process, circulating cooling water is introduced into the jacketed heat exchanger, and then it is switched to circulating hot water. After the reaction starts, the jacketed heat exchanger is switched to circulating cooling water for temperature control. Heat transfer method (2) Several atomizing nozzles are set at the feed port or the upper part of the reaction zone of the scraped wall reactor. Liquid perfluoromethyl vinyl ether monomer, liquid tetrafluoroethylene monomer and / or initiator are injected by high pressure carbon dioxide in the form of atomized droplets. The atomized droplet raw material is rapidly vaporized in the supercritical carbon dioxide environment. Part of the reaction heat is absorbed by the latent heat of phase change evaporation to control the reaction temperature. Heat removal method (3) Set up a carbon dioxide circulation reflux system to liquefy part of the supercritical carbon dioxide in the scraped wall reactor and return it in the form of reflux to remove the heat of reaction; Based on the polymerization process temperature of perfluoroether elastomer, the polymerization reaction temperature in the scraped-wall reactor is monitored throughout the process, and a first predetermined value of 3 ℃ and a second predetermined value of 5 ℃ are set for the difference between the actual polymerization reaction temperature and the process temperature. In the initial stage of the reaction, when the difference between the actual polymerization reaction temperature and the process temperature is less than or equal to the first predetermined value of 3 °C, the circulating cooling water of the jacket is turned on and the heat transfer method (1) is adopted. As the reaction proceeds, heat is continuously released. When the difference between the actual polymerization reaction temperature and the process temperature is greater than the first predetermined value of 3°C and less than or equal to the second predetermined value of 5°C, atomization is turned on, or the flow rate or injection speed of atomization is increased, and a heat transfer method (2) is superimposed on the heat transfer method (1). When the difference between the actual polymerization reaction temperature and the process temperature is greater than the second predetermined value of 5 °C, the carbon dioxide reflux system is turned on. If the above methods are insufficient, the reflux liquid carbon dioxide is used to absorb heat effectively. The heat transfer method (3) is superimposed on the heat transfer methods (1) and (2).

2. The method according to claim 1, characterized in that, Liquid tetrafluoroethylene monomer and refluxed liquid carbon dioxide are injected continuously; liquid perfluoromethyl vinyl ether monomer is injected in stages to control the rate of polymerization.

3. The method according to claim 1 or 2, characterized in that, The injection rate of tetrafluoroethylene monomer and the reflux rate of carbon dioxide are calculated based on the wall temperature and the temperature difference of the reaction medium in the scraped reactor to maintain the polymerization reaction temperature within a certain range. The polymerization reaction temperature is maintained at 35-125 ℃ and the polymerization reaction pressure is controlled at 7-30 MPa by adjusting the injection rate.

4. The method according to claim 1, characterized in that, A rotary scraper is installed on the inner wall of the scraped reactor, and the rotary scraper rotates at a speed of 10-50 rpm.

5. The method according to claim 1, characterized in that, The sulfidation point monomer is selected from at least one of perfluoro-2-(2-sulfonylchloroethoxy)propyl vinyl ether and perfluoro-8-cyano-5-methyl-3,6-dioxa-1-octene; the sulfidation point monomer is dissolved in trichlorotrifluoroethane solvent and then forced into a scraped-wall reactor by high-pressure CO2, wherein the mass of the trichlorotrifluoroethane is 1.5-3 times that of the sulfidation point monomer.

6. The method according to claim 1, characterized in that, The chain transfer agent conforms to the chemical formula I-(CF2). n -I, where n is an integer from 1 to 10, selected from at least one of 1,3-diiodopropane, 1,4-diiodobutane, 1,6-diiodohexane, 1,8-diiodooctane, 1,3-diiodoperfluoropropane, 1,4-diiodoperfluorobutane, 1,6-diiodoperfluorohexane, and 1,8-diiodoperfluorooctane; the chain transfer agent is dissolved in trichlorotrifluoroethane solvent and then pressurized into the reactor by high-pressure carbon dioxide, wherein the mass of trichlorotrifluoroethane is 3-5 times that of the chain transfer agent.

7. The method according to claim 1, characterized in that, The initiator is bis(perfluoropropionyl) peroxide; the initiator is dissolved in trichlorotrifluoroethane solvent and then injected into the scraped-wall reactor by high-pressure carbon dioxide, and the mass of trichlorotrifluoroethane is 3-5 times that of the initiator.

8. The method according to claim 1, characterized in that; The perfluoroether elastomer product is dried, devolatilized by supercritical carbon dioxide, mixed with a vulcanizing crosslinking agent and a catalyst, molded, and subjected to secondary vulcanization to obtain a composition; the secondary vulcanization temperature is 190-240 ℃ and the time is 10-24 h, wherein the vulcanizing crosslinking agent is tetraphenyltin and the catalyst is hexaoxane.

9. A perfluoroether elastomer prepared by the method of polymerizing perfluoroether elastomers in supercritical carbon dioxide as described in any one of claims 1-8.

Images