Drying and devolatilization method for perfluoroether elastomer, and preparation method for perfluoroether elastomer composition

Abstract

The present invention belongs to the field of polymer materials. Provided are a drying and devolatilization method for a perfluoroether elastomer, and a preparation method for a perfluoroether elastomer composition. The drying and devolatilization method specifically comprises: adding a water-soluble organic solvent as a coagulating agent to an emulsion containing a perfluoroether elastomer, stirring same to make the perfluoroether elastomer coagulate, and subjecting the coagulated perfluoroether elastomer to centrifugal separation, washing and dehydration, so as to obtain a wet elastomer micro-powder coagulum; freezing the wet elastomer micro-powder coagulum, and drying and dehydrating the frozen wet elastomer micro-powder coagulum, so as to obtain a dried and dehydrated perfluoroether elastomer micro-powder; and subjecting the dried and dehydrated perfluoroether elastomer micro-powder to extraction, devolatilization and deep dehydration, so as to obtain a devolatilized perfluoroether elastomer. The treatment scheme of the present application not only brings about a significant reduction in the vacuum degree during drying, but also shortens the drying time, reduces the drying costs, and is convenient for large-scale commercial application.

Description

Drying and devolatilization method of perfluoroether elastomer and preparation method of perfluoroether elastomer composition Technical Field

[0001] The present invention relates to the field of polymer materials, and in particular to a drying and devolatilization method for a perfluoroether elastomer and a preparation method for a perfluoroether elastomer composition. Background Art

[0002] Fluoroelastomers are versatile and multipurpose sealing materials. In high-precision chip production, even the slightest impurity can significantly degrade product performance. Only ultra-clean, high-purity environments can meet the demands of the semiconductor industry. Therefore, fluoroelastomer products used in semiconductor manufacturing must not only exhibit excellent chemical resistance, thermal stability, and mechanical properties, but also exhibit low levels of extractables, low outgassing, and low permeability.

[0003] Unlike the processing method for thermoplastic resin PFA, fluoroelastomers such as perfluoroether elastomers (PFAEs) become viscous and fluid when dried at lower temperatures (e.g., 120°C). This causes particles to adhere to each other, resulting in a reduced porosity and increased pressure differential and mass transfer resistance. This makes it difficult to completely remove the initiators, chain transfer agents, surfactants, and small molecule polymers trapped within them, making effective devolatilization impossible and hindering subsequent effective end group passivation treatment. Therefore, a method for effectively drying and devolatilizing fluoroelastomers is needed. Summary of the Invention

[0004] Therefore, in order to overcome the above-mentioned shortcomings of the prior art, the present invention provides a method for drying and devolatilizing a perfluoroether elastomer and a method for preparing a perfluoroether elastomer composition.

[0005] To achieve the above-mentioned object, the present invention provides a method for drying and devolatilizing a perfluoroether elastomer, comprising the following steps: S1: adding a water-soluble organic solvent as a coagulant to an emulsion containing a perfluoroether elastomer and stirring the mixture to cause the perfluoroether elastomer to coagulate, and subjecting the coagulated perfluoroether elastomer to centrifugal separation, washing, and dehydration to obtain a wet elastomer fine powder coagulant; S2: freezing the wet elastomer fine powder coagulant, and drying and dehydrating the frozen wet elastomer fine powder coagulant to obtain a dried and dehydrated perfluoroether elastomer fine powder, wherein the drying and dehydrating comprises: introducing a gas with a relatively low dew point temperature to sublimate the frozen wet elastomer fine powder coagulant, and performing drying and dehydration, wherein the gas with a relatively low dew point temperature is obtained by vaporizing a liquid gas, and the dew point temperature thereof is between -35°C and -80°C; and S3: subjecting the dried and dehydrated perfluoroether elastomer fine powder to extraction devolatilization and deep dehydration to obtain a devolatilized perfluoroether elastomer.

[0006] In one embodiment, the coagulant is acetone.

[0007] In one embodiment, the S2 step includes: freezing the wet elastomer micropowder agglomerate using a refrigerant; introducing a gas with a lower dew point temperature at a certain temperature to sublimate the frozen wet elastomer micropowder agglomerate; and performing a second heating step after the moisture in the frozen wet elastomer micropowder agglomerate is dried, so that the product rises to a maximum temperature lower than the viscous flow temperature of the polymer for secondary drying.

[0008] In one embodiment, a refrigerant is used to freeze the wet elastomer powder coagulate, comprising: using a refrigerant to spray and freeze the wet elastomer powder coagulate, and after the temperature is raised to a predetermined transfer temperature, transferring the frozen wet elastomer powder coagulate to a freeze drying box; or spraying the wet elastomer powder coagulate into a receiver containing a refrigerant by entraining the wet elastomer powder coagulate with a high-pressure airflow, and then transferring the frozen wet elastomer powder coagulate to a freeze drying box, wherein the pressure range of the high-pressure airflow is 1MPa~40MPa.

[0009] In one embodiment, the gas with a lower dew point temperature is provided by performing pressure swing adsorption or temperature swing adsorption on the gas.

[0010] In one embodiment, the gas includes at least one of air, nitrogen, carbon dioxide, and argon.

[0011] In one embodiment, the extraction and devolatilization employs an extractant comprising liquid CO2 or supercritical CO2 fluid to extract and devolatilize the dried and dehydrated perfluoroether elastomer micropowder.

[0012] In one embodiment, the temperature and pressure of the liquid CO2 or supercritical CO2 fluid are 25°C-120°C and 6MPa-20MPa, respectively, and the dehydration and devolatilization time is 1hr-24hr; the apparent flow velocity of CO2 at normal temperature and pressure is 0.01m / s-1m / s.

[0013] In one embodiment, the precipitated polymer powder is centrifuged to obtain the polymer powder, which is then washed repeatedly and centrifuged to remove free water.

[0014] A method for preparing a perfluoroether rubber composition comprises: pre-treating the perfluoroether elastomer by adopting the above-mentioned drying and devolatilization method for the perfluoroether elastomer; fluorinating and / or aminating the pre-treated perfluoroether elastomer, mixing and thinning, molding and secondary vulcanization to obtain the perfluoroether elastomer composition.

[0015] Compared with existing technologies, the present invention has the advantages of drying and devolatilizing perfluoroether elastomers to facilitate the subsequent preparation of high-purity, low-release perfluoroether elastomer compositions. Furthermore, during the drying and devolatilization process, freeze-drying using a gas with a relatively low dew point temperature and providing a heat source not only significantly reduces the vacuum level during the drying process but also shortens the drying time and reduces drying costs, thereby facilitating large-scale commercial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0017] 1 is a process step of a drying and devolatilization purification method for a perfluoroether elastomer according to an embodiment of the present invention;

[0018] FIG2 is a process for preparing a gas having a relatively low dew point temperature in an embodiment of the present invention. DETAILED DESCRIPTION

[0019] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0020] The following describes the embodiments of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, in the absence of conflict, the features in the following embodiments and embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of this application.

[0021] It should be noted that various aspects of the embodiments within the scope of protection of the present invention are described below. It should be apparent that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is merely illustrative. Based on this application, it should be understood by those skilled in the art that an aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number and aspect described herein can be used to implement an apparatus and / or practice method. In addition, other structures and / or functionality other than one or more of the aspects described herein can be used to implement this apparatus and / or practice this method.

[0022] It should also be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present application. The illustrations only show components related to the present application and are not drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component can be changed at will, and the component layout type may also be more complicated.

[0023] Additionally, in the following description, specific details are provided to facilitate a thorough understanding of the examples. However, one skilled in the art will appreciate that aspects may be practiced without these specific details.

[0024] As shown in FIG1 , the embodiment of the present application provides a method for drying and devolatilizing a perfluoroether elastomer, comprising the following steps:

[0025] Step 1: adding a water-soluble organic solvent as a coagulant to an emulsion containing a perfluoroether elastomer and stirring the mixture to cause the perfluoroether elastomer to coagulate; and centrifuging, washing and dehydrating the coagulated perfluoroether elastomer to obtain a wet elastomer powder coagulant.

[0026] The perfluoroether elastomer-containing emulsion (A) is obtained through emulsion polymerization. For example, the synthesized emulsion can be synthesized by polymerization of 55% tetrafluoroethylene (TFE), 43% perfluoromethyl vinyl ether (PMVE), and 2% perfluoro-8-cyano-5-methyl-3,6-dioxa-1-octene (8-CNVE) in combination with common surfactants and initiators. The surfactant can be a 1-2% aqueous solution of perfluorosilane. The initiator can be sodium persulfate, potassium persulfate, or ammonium persulfate. A water-soluble organic solvent is added to the perfluoroether elastomer-containing emulsion as a coagulant and vigorously stirred during coagulation to cause the perfluoroether elastomer to coagulate. Vigorous stirring reduces the size of the coagulated particles, facilitating subsequent freeze-drying. The coagulated perfluoroether elastomer is then centrifuged, washed, and dehydrated to obtain a wet elastomer micropowder agglomerate (B). This step removes most of the water carried by the coagulated perfluoroether elastomer.

[0027] Step 2: Freeze the wet elastomer micropowder agglomerate and dry and dehydrate the frozen wet elastomer micropowder agglomerate to obtain dried and dehydrated perfluoroether elastomer micropowder, wherein the drying and dehydration comprises: introducing a gas with a relatively low dew point temperature to sublime the frozen wet elastomer micropowder agglomerate, and drying and dehydrating the gas with a relatively low dew point temperature by vaporizing the liquid gas, wherein the dew point temperature is between -35°C and -80°C.

[0028] The wet elastomer powder agglomerate (B) can be directly frozen or pre-cooled and frozen. The wet elastomer powder agglomerate (B) is freeze-dried and dehydrated in the frozen state to obtain a dried and dehydrated perfluoroether elastomer. The wet elastomer powder agglomerate (B) can be frozen in an open receiver using a refrigerant such as liquid nitrogen. The refrigerant can be a common liquid refrigerant such as liquid nitrogen or liquid carbon dioxide, or an indirect heat exchange refrigeration method using liquid refrigerants such as chlorofluorocarbons (CFCs) used in industry.

[0029] Gases with lower dew point temperatures are obtained by vaporizing low-temperature liquids. For example, CO2 has a boiling point of -56.6°C at 527 kPa, and N2 has a boiling point of -195.6°C at 101.3 kPa. Gases with lower dew point temperatures are heated to a certain temperature and used as drying and heat source gases.

[0030] Drying is performed by using a gas with a low dew point at a certain temperature. The dew point temperature and flow rate of the drying gas depend on the temperature and quality of the sample to be dried. To ensure smooth freeze drying, the temperature of the freeze drying chamber is maintained at the temperature level of the sample to be dried.

[0031] The input gas and sublimated water vapor are discharged in time by the vacuum pump. The lower the sublimation temperature, the higher the vacuum required. And because a gas with a lower dew point temperature is used as the heat source, the required vacuum degree is indirectly reduced.

[0032] Taking liquid nitrogen as an example, the wet elastomer powder agglomerate (B) can be dispersed into liquid nitrogen. While cooling and freezing the polymer particles, the liquid nitrogen absorbs heat and vaporizes. The low-temperature nitrogen then escapes and pre-cools the descending polymer particles. The total amount of liquid nitrogen required depends primarily on the polymer mass and water content of the agglomerate (B), including the amount needed for the cooling container and any liquid nitrogen lost to the environment. In one embodiment, a Dewar flask can be used as the freezing container for the agglomerate (B), negligible for the cooling container and any liquid nitrogen lost to the environment. The powder particle size can be controlled between 0.01 mm and 1 mm.

[0033] The water in the frozen wet elastomer powder aggregate (B) is controlled to sublime, thereby performing drying and dehydration to obtain a dried and dehydrated perfluoroether elastomer. For example, the frozen aggregate (B) in a Dewar flask is removed and placed on a support net in a low-temperature drying oven, which can utilize a single-layer or multi-layer support net. The aggregate on the support net is then dried and dehydrated using a refrigerant to obtain a dried and dehydrated perfluoroether elastomer. Specifically, a gas with a low dew point at a predetermined temperature can be introduced below the support net in the low-temperature drying oven to sublime the ice in the frozen material.

[0034] Step 3: extracting and devolatilizing the dried and dehydrated perfluoroether elastomer powder and performing deep dehydration to obtain the devolatilized perfluoroether elastomer.

[0035] If the volatile components remaining in the micropowder in step 2, such as chain transfer agents, surfactants, and small molecule polymers, cannot be effectively removed, extraction and devolatilization can be used to remove the remaining volatile components in the micropowder. Specifically, a liquid or supercritical fluid can be used to further remove water and volatile components, thereby extracting and devolatilizing the dried and dehydrated perfluoroether elastomer to obtain the treated perfluoroether elastomer.

[0036] A supercritical fluid is a fluid whose temperature and pressure are higher than its critical state, a state of matter where both the temperature and pressure are above the critical point. The physical and chemical properties of supercritical fluids are very different from those of liquids and gases in a non-critical state. Taking supercritical CO2 fluid as an example, its viscosity is about one percent of that of a liquid, and its self-diffusion coefficient is about 100 times that of a liquid. Therefore, it has excellent mass transfer characteristics, which can greatly shorten the time required for phase equilibrium, making it an ideal medium for efficient mass transfer. It has a much faster diffusion rate than liquids and a much greater ability to dissolve and carry solid substances than gases. It has high compressibility. Near the critical point, slight changes in pressure and temperature will cause large changes in the density of CO2. Therefore, its solubility can be adjusted by simply changing the pressure and temperature of CO2, thereby improving the selectivity of extraction. CO2 and dissolved products can be separated by reducing the pressure of the system, eliminating the process of eliminating the solvent.

[0037] In one embodiment, the extractant comprises liquid CO2 or supercritical CO2 fluid.

[0038] In one embodiment, the extractant may further include an entrainer to enhance the selectivity, solubility, and extraction efficiency of the CO2 extraction process. Entrainers, also known as carriers, are substances added to a supercritical fluid solvent that have a strong affinity for the extractant, are miscible with the fluid solvent, and have a volatility between that of the extractant and the supercritical component. The primary purpose of these substances is to enhance their selectivity and solubility for the extracted component. These substances can be a single pure substance or a mixture of two or more substances.

[0039] Polymer devolatilization is an important process in the processing and production of polymer materials. In a specific embodiment, the extractant used in the extraction devolatilization can be a CO2 fluid or a supercritical CO2 fluid. In order to effectively remove some polar small molecules, in some embodiments, the extractant used in the extraction devolatilization not only comprises a CO2 fluid or a supercritical CO2 fluid, but also has an entrainer added thereto, the entrainer dosage being 0.5-10% by mass of the CO2, and the entrainer can be methanol or ethanol. Adding a polar entrainer can improve the selectivity for polar volatile components in the extraction process. The entrainer used in this embodiment is ethanol.

[0040] The above method performs dry devolatilization on a perfluoroether elastomer to subsequently prepare a high-purity, low-release perfluoroether elastomer composition. Furthermore, during the dry devolatilization process, freeze-drying using a gas with a relatively low dew point temperature and providing a heat source significantly reduces the vacuum level during the drying process, shortens the drying time, and reduces drying costs, thereby facilitating large-scale commercial applications.

[0041] In one embodiment, the coagulant is acetone, which can be a commercially available analytical grade reagent.

[0042] In one embodiment, freeze-drying and dehydrating the wet elastomer micropowder aggregate in a frozen state to obtain dried and dehydrated perfluoroether elastomer micropowder comprises the following steps:

[0043] In step 2-1, a refrigerant is used to freeze the wet elastomer powder agglomerate.

[0044] The wet elastomer powder agglomerate (B) can be frozen in a freezer or using a refrigerant. In one embodiment, the refrigerant can be a direct contact refrigerant, preferably liquid carbon dioxide or liquid nitrogen. As shown in Figure 2, the wet elastomer powder agglomerate is first frozen using liquid nitrogen. For example, liquid carbon dioxide is used as the freezing liquid, and spray freezing is employed. CO2 cannot exist as a liquid at atmospheric pressure, only as a gas or solid. During the freezing process, liquid CO2 is sprayed through a nozzle and forms snowflakes of solid dry ice (43%) and CO2 gas (57%), both at a temperature of -78.5°C. The latent heat of sublimation of the dry ice accounts for approximately 84% of the total refrigeration capacity. In one embodiment, to facilitate loading and unloading of the fluoroelastomer, the freeze-dried powder can be placed in a stainless steel inner cylinder. The cylinder is screened with a 2000-mesh stainless steel screen (Tyler mesh, approximately 6.5 microns). The inner cylinder is then placed in an extraction device. The gap between the inner cylinder and the extraction device is sealed with a PTFE gasket to prevent short-circuiting of the CO2 fluid.

[0045] Liquid CO2 spray freezing is in direct contact with the condensate. Its cooling capacity relies on the latent heat of vaporization and the sensible heat of rising temperature, and is therefore directly related to the amount used. The greater the liquid CO2 flow rate, the greater the cooling capacity and the lower the cooling temperature. The condensate exchanges heat through conduction and convection, resulting in a large temperature difference and rapid cooling. During liquid CO2 spraying, dry ice and gas are formed after high-pressure injection. This is when heat exchange is most intense, but the spraying time is very short (0.5-20 minutes). After spraying, the dry ice sublimation refrigeration in the drying chamber can maintain a low temperature.

[0046] In step 2-2, a gas with a lower dew point temperature at a certain temperature is introduced to sublime the frozen wet elastomer powder agglomerates.

[0047] Freeze drying involves introducing a gas with a low dew point at a certain temperature, reducing the product temperature to well below the polymer's viscous fluid temperature, allowing for sublimation drying. The drying rate during freeze drying is a function of the freezing temperature and the vapor pressure gradient between the site of water vapor formation and the drying medium, rather than the total pressure in the drying chamber. This means that freeze drying can be performed under atmospheric conditions using a circulating convection freeze drying medium (such as a cold air stream) maintained dry by a molecular sieve desiccant or a frozen condenser. Freeze drying can also be performed without a vacuum pump, provided that the water vapor pressure on the sample surface is lower than the saturated vapor pressure of ice at the sample drying temperature. In Figure 2, the gas with a low dew point is dry air.

[0048] Step 2-3: After the moisture in the frozen wet elastomer micropowder agglomerate is completely dried, the second step of heating is performed to raise the product to a maximum temperature lower than the viscosity flow temperature of the polymer for secondary drying.

[0049] When the sampled perfluoroether elastomer mass remains unchanged at high temperature for a certain period of time, it is determined that the water content of the frozen condensate is essentially dried out. Once the water content of the frozen condensate is essentially dried out, the second heating step is performed to raise the product to a maximum temperature below the polymer's viscous flow temperature for secondary drying. At this point, the removed water vapor can be adsorbed using a desiccant, molecular sieve, or adsorbent bed.

[0050] Activated alumina desiccant can be used as a desiccant. Activated alumina desiccant is a spherical activated alumina produced through a special process. It is non-toxic, odorless, non-pulverizing, insoluble in water, and appears as a white sphere. It has a strong water adsorption capacity. Under certain operating and regeneration conditions, it can dry to a depth below the dew point of -40°C, making it a highly efficient desiccant for deep drying of trace amounts of water.

[0051] 13X molecular sieve and CaX molecular sieve are widely used in pre-treatment units in air separation. They can be used to remove impurities such as water vapor and carbon dioxide from compressed air to make their concentration below a certain limit.

[0052] When 13X molecular sieve is used to dry air at a working pressure of 0.5MPa, the dew point temperature can reach below -60℃, while when CaX molecular sieve is used to dry air, the dew point temperature can reach -70℃.

[0053] According to one embodiment, an adsorption bed is used, wherein the adsorbent is activated alumina, 13X molecular sieve, or CaX molecular sieve. To improve adsorption efficiency and adsorbent utilization, a mixed bed can be used, wherein the adsorption tower is sequentially filled with activated alumina, 13X molecular sieve, and CaX molecular sieve, with a certain thickness of inert porcelain balls placed on top.

[0054] In one embodiment, gas with a lower dew point temperature is provided by subjecting the gas to pressure swing adsorption (PSA) or temperature swing adsorption (TSA). Generally speaking, the gas dew point temperature obtained by PSA is higher, while that obtained by TSA is lower. The TSA process utilizes the characteristic that the equilibrium adsorption capacity of the adsorbent decreases with increasing temperature, employing an adsorption method at room temperature and desorption at elevated temperatures. In addition to adsorption and desorption, the entire TSA operation also includes auxiliary steps such as cooling the adsorbent after desorption. TSA is used for dehumidification of atmospheric pressure gas and air, recovery of solvent vapors in air, and other applications. If the adsorbate is water, desorption can be performed by heating the adsorbent with hot gas.

[0055] As shown in FIG2 , a dual-bed pressure swing / temperature swing adsorption system is used to prepare gas with a lower dew point temperature.

[0056] The adsorbent filled in bed A and bed B can be at least one of activated alumina, 13X molecular sieve or CaX molecular sieve. For example, a mixed adsorption bed can be used, and the adsorbents added from bottom to top are activated alumina, 13X molecular sieve and CaX molecular sieve.

[0057] In one embodiment, the gas includes at least one of air, nitrogen, carbon dioxide, and argon.

[0058] In one embodiment, freezing the condensate using a refrigerant includes:

[0059] Use refrigerant spray to freeze the condensate, and after the temperature is raised to the predetermined transfer temperature, transfer the frozen condensate to a freeze drying chamber; or

[0060] The condensate is sprayed into a receiver containing a refrigerant by entraining it with a high-pressure airflow, and then the frozen condensate is transferred to a freeze drying box. The pressure range of the high-pressure airflow is 1MPa~40MPa, preferably 6MPa~20MPa.

[0061] In one embodiment, liquid CO2 or supercritical CO2 fluid is used as an extractant to extract and devolatilize the dried and dehydrated perfluoroether elastomer.

[0062] In one embodiment, the temperature and pressure of liquid CO2 or supercritical CO2 fluid are 25°C-120°C and 6MPa-20MPa, respectively, and the dehydration and devolatilization time is 1hr-24hr; the apparent flow velocity of CO2 at normal temperature and pressure is 0.01m / s-1m / s.

[0063] In one embodiment, in step 1, a wet coagulum is obtained by centrifugation, from which most of the water is removed. The precipitated polymer powder is then centrifuged to obtain a precipitated polymer powder, which is then washed repeatedly and then centrifuged to remove free water. After the emulsion coagulates, a hydrous perfluoroether elastomer powder is obtained. The powder is then washed repeatedly to remove some impurities, and then centrifuged to remove some of the water. This water is free water, which is the water present in the pores or gaps of the powder. Freeze-drying is used to remove bound water within the powder, and then supercritical CO2 extraction is used to remove volatile components contained in the perfluoroether elastomer.

[0064] In one embodiment, a method for preparing a perfluoroether rubber composition is provided, comprising the following steps:

[0065] The perfluoroether elastomer is pretreated by a drying and devolatilization method of the perfluoroether elastomer;

[0066] The pretreated perfluoroether elastomer is subjected to fluorination and / or amination treatment, and then kneaded, thin-passed, molded and secondary vulcanized to prepare a high-cleanliness and low-release perfluoroether elastomer composition. Example

[0067] The present invention provides a method for drying and devolatilizing a perfluoroether elastomer, comprising the following steps:

[0068] S1. A water-soluble organic solvent as a coagulant is added to an emulsion (A) containing a perfluoroether elastomer and stirred to cause the perfluoroether elastomer to coagulate. The wet elastomer powder coagulant (B) is obtained by centrifugation, from which most of the water is removed.

[0069] The perfluoroether elastomer emulsion (A) is obtained through emulsion polymerization. For example, the synthesized emulsion can be synthesized by polymerization of 55% tetrafluoroethylene (TFE), 43% perfluoromethyl vinyl ether (PMVE), and 2% perfluoro-8-cyano-5-methyl-3,6-dioxa-1-octene (8-CNVE) in combination with common surfactants and initiators. The surfactant can be a 1-2% wt% aqueous solution of perfluorosilane. The initiator can be sodium persulfate, potassium persulfate, or ammonium persulfate. 20 liters of the perfluoroether elastomer emulsion (A) are stirred to a solids content of approximately 30%. A coagulant containing approximately 1.5% acetone is added. The solid polymer is precipitated and centrifuged to obtain a solid polymer. Repeated washing and centrifugation followed by dehydration yield approximately 6 kg of wet elastomer micropowder agglomerates, with a water content of approximately 8-10% and a particle size of approximately 0.01 mm to 1 mm.

[0070] 1 kg of wet polymer was taken and slowly dispersed into a Dewars receiver containing liquid nitrogen by spraying it with high-pressure N2 gas flow.

[0071] A 10 L Dewar flask is filled with about 2 L (about 1.6 kg) of liquid nitrogen, and the temperature of the frozen polymer is about -50°C. After pre-cooling and freezing, a wet elastomer micropowder agglomerate (B) is obtained.

[0072] S2. The frozen wet elastomer micropowder agglomerate (B) is freeze-dried and dehydrated using a gas having a relatively low dew point temperature to obtain a dried and dehydrated perfluoroether elastomer micropowder (C).

[0073] The drying gas can be selected from air, nitrogen, carbon dioxide, and argon. For example, dry air is selected in Figure 2. The drying gas (dry air) with a lower dew point temperature is prepared by temperature swing adsorption as shown in Figure 2. Its dew point temperature is about t1 = -60 ° C. After being heated by the heater, it reaches t2 = 25 ° C. The freezing temperature of the polymer to be freeze-dried is t3 = -50 ° C. The sensible heat that can be released by the drying gas is mC p (t2-t3)=75mC p , where m is the mass of dry gas input per unit time, C p is the average constant-pressure specific heat of the dry gas within the operating temperature range.

[0074] Freeze drying chamber model JK-II-50L, Jiangkai (Suzhou) Instrument Technology Co., Ltd.

[0075] When the dew point temperature is t1=-60℃, the vapor pressure of water is 0.0107mbar, and when t3=-50℃, the vapor pressure of water is 0.0300mbar. The pressure difference Δp=0.0300mbar-0.0107mbar=0.0193mbar is approximately the driving force of freeze drying.

[0076] After centrifugation, the moisture content of the wet elastomer powder aggregate (B) is about 8%-10%, that is, the moisture content of 1 kg of the polymer to be freeze-dried is about 100 g, and the latent heat required for ice sublimation is about 3.35×10 5 J / kg, the specific heat capacity of rubber is about 1700 J / kg•K. Considering the heat absorption of polymer, when freeze-drying 1 kg of wet elastomer powder agglomerate from t3 = -50℃ to 25℃, it is necessary to input (3.35×10 5 J / kg×0.1kg +1700J / kg·K×75K×0.9kg)=(33.5+114.8)×10 3 J=148.3kJ of heat.

[0077] Assuming the freeze drying time is 10 hours, the heat input is 14.8 kJ / hr. The specific heat capacity of air at constant pressure is approximately C p =1.005kJ / kg•K, and the theoretical amount of gas input is m=14.8kJ / hr / (1.005kJ / kg•K×75K) =0.196kg / hr =196g / hr.

[0078] The volume of the drying oven is 50L. The exhaust volume of the vacuum pump is approximately equal to the input air volume + the amount of sublimated water vapor = 196g air / hr + 10g water vapor / hr = 151.4L / hr + 12.4L / hr = 163.8L / hr = 45.5mL / s. If the sublimated water vapor needs to be removed in time, the vacuum degree should be maintained at 91.0Pa (absolute pressure).

[0079] The vacuum degrees that need to be maintained when t2 and t3 are different in Example 1 are shown in Table 1.

[0080] S3. The dried and dehydrated perfluoroether elastomer powder (C) is subjected to extraction, devolatilization, and deep dehydration to obtain the devolatilized perfluoroether elastomer (D).

[0081] Approximately 0.9 kg of perfluoroelastomer powder (C) requiring deep dehydration and devolatilization is loaded into a stainless steel inner cylinder. The cylinder is screened with a 2000-mesh stainless steel screen (Tyler mesh, approximately 6.5 microns). The inner cylinder is placed in an extraction apparatus, and the gap between the inner cylinder and the extraction apparatus is sealed with a PTFE gasket. Repeated CO2 flushing is used to expel air. During the extraction process, the gas cylinder valve is opened to admit gas. The cooling device is activated to cool the CO2 and liquefy it. The high-pressure pump then increases the pressure, which is then regulated by a back-pressure valve to a predetermined pressure for extraction and devolatilization. After extraction, the high-pressure fluid passes through the throttling back-pressure valve into the separator to desorb the extracted volatiles. The devolatilized material is discharged from the bottom of the separator. The low-pressure gas passes through the vent valve and is then treated by the exhaust gas treatment unit, where its flow rate is measured by a flowmeter. During throttling, the fluid absorbs heat, requiring the throttling back-pressure valve and separator to be heated and maintained at a constant temperature. During the extraction process, various valves are adjusted to maintain the extraction pressure, separation pressure, and CO2 flow rate within the desired range.

[0082] The temperature and pressure of the liquid or supercritical fluid are 25°C-120°C, 6MPa-20MPa, respectively; the dehydration and devolatilization time is 1hr-24hr; the superficial flow rate of CO2 is 0.01m / s-1m / s (at normal temperature and pressure).

[0083] After the deep dehydration and devolatilization tail gas test meets the requirements (organic matter concentration is less than 0.1 mg / kg; GC-MS of PE company), the pressure is released and purged with CO2, and the stainless steel inner cylinder is removed to obtain the deeply dehydrated and devolatilized perfluoroether elastomer (D). Example

[0084] The present invention provides a method for drying and devolatilizing a perfluoroether elastomer, comprising the following steps:

[0085] S1. Add a water-soluble organic solvent as a coagulant to an emulsion (A) containing a perfluoroether elastomer and stir to coagulate the perfluoroether elastomer. Centrifuge to obtain a wet elastomer powder coagulant (B) from which most of the water has been removed.

[0086] The perfluoroether elastomer emulsion (A) is obtained through emulsion polymerization. For example, the synthesized emulsion can be synthesized by polymerization of 55% tetrafluoroethylene (TFE), 43% perfluoromethyl vinyl ether (PMVE), and 2% perfluoro-8-cyano-5-methyl-3,6-dioxa-1-octene (8-CNVE) in combination with common surfactants and initiators. The surfactant can be a 1-2% wt% aqueous solution of perfluorosilane. The initiator can be sodium persulfate, potassium persulfate, or ammonium persulfate. 20 liters of the perfluoroether elastomer emulsion (A) are stirred to a solids content of approximately 30%. A coagulant containing approximately 1.5% acetone is added. The solid polymer is precipitated and centrifuged to obtain a solid polymer. Repeated washing and centrifugation followed by dehydration yields approximately 6 kg of wet elastomer micropowder agglomerate (B), from which most of the water has been removed. The water content is approximately 8-10%, and the particle size is approximately 0.01 mm to 1 mm. Liquid CO2 spray is used to freeze the wet elastomer powder agglomerate (B).

[0087] The selected liquid CO2 storage tank is DPL450-175-2.0, produced by Zhejiang Puyang Cryogenic Equipment Co., Ltd.

[0088] The hollow cone nozzle used was from Spray Systems (Shanghai) Co., Ltd. Model: LN-4W series, with a 1 / 4 NPT male thread and made of 316 stainless steel. The nominal orifice diameter was 1.5 mm, the mass flow rate M = 3 g / s (1.5 bar), and the spray angle was 60 degrees.

[0089] Liquid CO2 spray freezing is in direct contact with the polymer. Its cooling capacity relies on the latent heat of vaporization and the sensible heat of rising temperature, and is therefore directly related to the amount used. Clearly, the greater the liquid CO2 flow rate, the greater the cooling capacity and the lower the cooling temperature. Perfluoroether elastomers transfer heat through conduction and convection, resulting in a large temperature differential and rapid cooling. During liquid CO2 spraying, dry ice and gas are formed after high-pressure injection. This is when heat exchange is most intense, but the spraying time is very short (0.5-20 minutes). After spraying, the dry ice sublimation refrigeration in the drying chamber maintains a low temperature. The latent heat of sublimation of dry ice is 573 kJ / kg, and the sensible heat of rising to -20°C is 50 kJ / kg. Approximately 0.51 kg of dry ice is required, which converts to 1.2 kg (about 1.3 L) of liquid CO2.

[0090] The liquid CO2 spraying time is about 400s, and after heating to -20℃, it is transferred to a freeze drying box.

[0091] S2. The frozen wet elastomer micropowder agglomerate (B) is freeze-dried and dehydrated using a gas having a relatively low dew point temperature to obtain a dried and dehydrated perfluoroether elastomer micropowder (C).

[0092] The drying gas can be selected from air, nitrogen, carbon dioxide, and argon. The drying gas is dry air. The dew point temperature of the drying gas with a lower dew point temperature is about t1 = -30 ° C. After being heated by the heater, it reaches t2 = 25 ° C. The freezing temperature of the polymer to be freeze-dried is t3 = -20 ° C. The sensible heat that the drying gas can release is mC p (t2-t3)=45mC p , where m is the mass of dry gas input per unit time, C p is the average constant-pressure specific heat of the dry gas within the operating temperature range.

[0093] When the dew point temperature is t1=-30℃, the vapor pressure of water is 0.3874mbar, and when t3=-20℃, the vapor pressure of water is 1.032mbar. The pressure difference Δp=1.032mbar-0.3874mbar=0.6446mbar is approximately the driving force of freeze drying.

[0094] In Example 2, 1 kg of the wet elastomer powder agglomerate to be freeze-dried has a water content of about 100 g, and the latent heat required for ice sublimation is about 3.35×10 5 J / kg, the specific heat capacity of rubber is about 1700 J / kg•K. Considering the heat absorption of polymer, when freeze-drying 1 kg of wet elastomer powder agglomerate from t3 = -20℃ to 25℃, it is necessary to input (3.35×10 5 J / kg×0.1kg+1700J / kg·K×45K×0.9kg)=102.4×10 3 J=102.4kJ of heat.

[0095] Assuming the freeze drying time is 10 hours, the heat input is 10.2 kJ / hr. The specific heat capacity of air at constant pressure is approximately C p =1.005kJ / kg•K, and the theoretical amount of gas input is m=10.2kJ / hr / (1.005kJ / kg•K×45K) =0.226kg / hr=0.063g / s.

[0096] The volume of the drying oven is 50L. The exhaust volume of the vacuum pump is approximately equal to the input air volume + the sublimated water vapor volume = 226g air / hr + 10g water vapor / hr = 174.6L / hr + 12.4L / hr = 187.0L / hr = 51.9mL / s. If the sublimated water vapor needs to be removed in time, the vacuum degree should be maintained at 103.9Pa (absolute pressure).

[0097] The vacuum degrees that need to be maintained when t2 and t3 are different in Example 2 are shown in Table 2.

[0098] S3. The dried and dehydrated perfluoroether elastomer powder (C) is subjected to extraction, devolatilization, and deep dehydration to obtain the devolatilized perfluoroether elastomer (D).

[0099] Approximately 0.9 kg of perfluoroelastomer powder (C) requiring deep dehydration and devolatilization is loaded into a stainless steel inner cylinder. The cylinder is screened with a 2000-mesh stainless steel screen (Tyler mesh, approximately 6.5 microns). The inner cylinder is placed in an extraction apparatus, and the gap between the inner cylinder and the extraction apparatus is sealed with a PTFE gasket. Repeated CO2 flushing is used to expel air. During the extraction process, the gas cylinder valve is opened to admit gas. The cooling device is activated to cool the CO2 and liquefy it. The high-pressure pump then increases the pressure, which is then regulated by a back-pressure valve to a predetermined pressure for extraction and devolatilization. After extraction, the high-pressure fluid passes through the throttling back-pressure valve into the separator to desorb the extracted volatiles. The devolatilized material is discharged from the bottom of the separator. The low-pressure gas passes through the vent valve and is then treated by the exhaust gas treatment unit, where its flow rate is measured by a flowmeter. During throttling, the fluid absorbs heat, requiring the throttling back-pressure valve and separator to be heated and maintained at a constant temperature. During the extraction process, various valves are adjusted to maintain the extraction pressure, separation pressure, and CO2 flow rate within the desired range.

[0100] In a specific embodiment of the present invention, the temperature and pressure of the liquid or supercritical fluid are 25°C-120°C, 6MPa-20MPa, respectively, the dehydration and devolatilization time is 1hr-24hr; the apparent flow rate of CO2 is 0.01m / s-1m / s (at normal temperature and pressure).

[0101] After the deep dehydration and devolatilization tail gas test meets the requirements (organic matter concentration is less than 0.1 mg / kg; GC-MS of PE company), the pressure is released and purged with CO2, and the stainless steel inner cylinder is removed to obtain the devolatilized fluoroelastomer (D).

[0102] The following is a summary of the results of Examples 1 and 2, which is used to illustrate the present application but is not intended to limit the scope of the present application. Each table includes three examples under different circumstances.

[0103] Table 1 Liquid nitrogen freezing and dry air vacuum drying results in Example 1

[0104] Conditions: Freeze drying for 10 hours, drying oven volume 50L, polymer water content 10%

[0105] Table 2 Results of liquid CO2 spray freezing and dry air vacuum drying in Example 2

[0106] Conditions: Freeze drying for 10 hours, drying oven volume 50L, polymer water content 10%

[0107] Table 3 Weight loss of perfluoroether elastomer after supercritical extraction and devolatilization

[0108] Conditions: original w1, freeze-dried and dehydrated w2, extracted and devolatilized w3

[0109] The test results show that the use of gases with lower dew point temperature for freeze drying, whether liquid nitrogen immersion freezing (Table 1) or carbon dioxide spray freezing (Table 2), requires a lower vacuum degree than the traditional vacuum freeze drying method (the required absolute pressure vacuum degree is about mPa, 1mPa = 10 -3 Pa) are greatly reduced by several orders of magnitude, and the water content of the perfluoroether elastomer is reduced. The obtained perfluoroether elastomer can be used to prepare a high-clean and low-release perfluoroether rubber composition after fluorination and amination treatment.

[0110] The above is only a specific implementation method of the present application, but the scope of protection of the present application is not limited thereto. Any changes or replacements that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed in this application should be covered by the scope of protection of the present application.

Claims

1. A drying and devolatilization method for a perfluoroether elastomer, characterized in that: The following steps are involved: S1: adding a water-soluble organic solvent as a coagulant to an emulsion containing a perfluoroether elastomer and stirring the mixture to cause the perfluoroether elastomer to coagulate, and centrifuging, washing, and dehydrating the coagulated perfluoroether elastomer to obtain a wet elastomer powder coagulant; S2: Freezing the wet elastomer micropowder agglomerates and drying and dehydrating the frozen wet elastomer micropowder agglomerates to obtain dried and dehydrated perfluoroether elastomer micropowders, wherein the drying and dehydrating comprises: introducing a gas with a relatively low dew point temperature to sublimate the frozen wet elastomer micropowder agglomerates and performing drying and dehydration, wherein the gas with a relatively low dew point temperature is obtained by vaporizing a liquid gas, and the dew point temperature thereof is between -35°C and -80°C; S3: extracting and devolatilizing the dried and dehydrated perfluoroether elastomer powder and deeply dehydrating it to obtain a devolatilized perfluoroether elastomer, wherein the extractant used in the extraction and devolatilization includes liquid CO2 or supercritical fluid.

2. The drying and devolatilization method according to claim 1, wherein: The coagulant is acetone.

3. The drying and devolatilization method according to claim 1, wherein: The S2 step includes: freezing the wet elastomer micropowder agglomerate using a refrigerant; Passing a gas with a lower dew point temperature at a certain temperature to sublime the frozen wet elastomer micropowder agglomerate; After the moisture in the frozen wet elastomer micropowder agglomerate is completely dried, the second step of heating is performed to raise the product to a maximum temperature lower than the viscous flow temperature of the polymer for secondary drying.

4. The drying and devolatilization method according to claim 3, wherein: Freezing the wet elastomer micropowder agglomerate using a refrigerant comprises: Freezing the wet elastomer micropowder aggregates by spraying with a refrigerant, and transferring the frozen wet elastomer micropowder aggregates to a freeze drying chamber after the temperature is raised to a predetermined transfer temperature; or The wet elastomer micropowder agglomerate is sprayed into a receiver containing a refrigerant by entrainment with a high-pressure airflow, and then the frozen wet elastomer micropowder agglomerate is transferred to a freeze drying box, wherein the pressure range of the high-pressure airflow is 1MPa~40MPa.

5. The drying and devolatilization method according to claim 1, characterized in that: The gas with a lower dew point temperature is provided by performing pressure swing adsorption or temperature swing adsorption on the gas.

6. The drying and devolatilization method according to claim 1, characterized in that: The gas includes at least one of air, nitrogen, carbon dioxide, and argon.

7. The drying and devolatilization method according to claim 1, characterized in that: The extractant used in the extraction and devolatilization includes supercritical CO2 fluid, and the dried and dehydrated perfluoroether elastomer powder is subjected to extraction and devolatilization.

8. The drying and devolatilization method according to claim 7, characterized in that: The temperature and pressure of the liquid CO2 or supercritical CO2 fluid are 25°C-120°C and 6MPa-20MPa respectively, and the dehydration and devolatilization time is 1hr-24hr; the apparent flow velocity of CO2 at normal temperature and pressure is 0.01m / s-1m / s.

9. The drying and devolatilization method according to claim 1, characterized in that: The polymer powder is obtained by centrifugation after precipitation, and is washed repeatedly and then centrifuged to remove free water.

10. A method for preparing a perfluoroether rubber composition, characterized in that: include: Pretreating the perfluoroether elastomer by the drying and devolatilization method of the perfluoroether elastomer according to any one of claims 1 to 9; The pretreated perfluoroether elastomer is subjected to fluorination and / or amination treatment, and then subjected to mixing, thin-passing, compression molding and secondary vulcanization to prepare a perfluoroether elastomer composition.

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