A boron-doped polyacrylonitrile-based activated carbon fiber and a method for producing the same

Abstract

The application provides a boron-doped high-performance polyacrylonitrile-based activated carbon fiber and a preparation method thereof. By adding a boron-containing compound in a polyacrylonitrile precursor pretreatment process, the activation process can be promoted, and the polyacrylonitrile fiber is doped with boron at a high temperature in the carbonization and activation process. The prepared boron-doped polyacrylonitrile-based activated carbon fiber has good adsorption performance, high tensile strength and suitable microporous structure, and is very suitable for being used as an inner fabric of a breathable chemical protective clothing.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of chemical protection, and particularly relates to a boron-doped polyacrylonitrile-based activated carbon fiber for an inner fabric of a breathable chemical protective clothing and a preparation method thereof. BACKGROUND

[0002] The current high-protection isolation type chemical protective clothing usually adopts air-impermeable and moisture-impermeable rubber or plastic as an outer fabric, which usually accompanies a large heat load problem. The serious heat stress effect caused by long-time wearing of the protective clothing may cause the operating personnel to have heat stroke, shock, and even death. Therefore, the development of a breathable chemical protective clothing capable of giving consideration to good protective performance and air permeability and moisture permeability to improve the physiological comfort of the operating personnel, avoid the use of expensive and bulky microclimate temperature regulating devices, and improve the mobility of the operating personnel has become a research focus in the field of individual biochemical protection. The development of the breathable chemical protective clothing based on physical adsorption type has experienced more than 60 years, and can be divided into three stages according to the types of porous carbon materials used in the inner adsorption fabric, namely, granular or powdery activated carbon, spherical activated carbon, and activated carbon fiber. Among them, the activated carbon fiber chemical protective clothing was first developed by the British Porton Chemical Protection Institute, and is the latest type of breathable chemical protective clothing. Compared with other activated carbon materials, the activated carbon fiber has the advantages of high microporosity, concentrated pore size distribution, fast adsorption and desorption rate, and high adsorption efficiency, and is more suitable for use in the inner fabric of the protective clothing.

[0003] The activated carbon fiber material applied in the chemical protective clothing should have high strength, good post-processing property, easy regeneration, and heat conduction in addition to excellent adsorption performance. However, the high strength and good adsorption performance of the activated carbon fiber material are difficult to be highly compatible, mainly because the mechanical properties of the activated carbon fiber material decrease in the activation process. The activation process is an essential link in the preparation process of the activated carbon fiber material, and is a key step for obtaining good adsorption performance. However, the etching of the activator to the fiber brings about an increase in the porosity and an improvement in the adsorption performance, while the fiber strength decreases due to the etching of the matrix material. Therefore, in order to solve the contradiction between the mechanical properties and the adsorption performance of the activated carbon fiber, it is necessary to control the activation process conditions, study the balance between the adsorption performance and the mechanical properties in the activation process, and prepare a high-performance activated carbon fiber with strength and adsorption capacity, which has important significance for the upgrading of the inner fabric of the breathable chemical protective clothing. SUMMARY

[0004] (I) Technical problems to be solved

[0005] The present application provides a boron-doped polyacrylonitrile-based activated carbon fiber which can simultaneously achieve high tensile strength and large benzene absorption capacity, and a preparation method thereof, to solve the technical problem that the adsorption performance and mechanical properties of the activated carbon fiber fabric used in the inner layer fabric of the air-permeable chemical protective clothing are difficult to be highly compatible.

[0006] (II) Technical solutions

[0007] To solve the above technical problems, the present application provides a boron-doped polyacrylonitrile-based activated carbon fiber preparation method, which comprises the following steps:

[0008] S1. Wash the polyacrylonitrile precursor fiber in clean water, immerse it in a boron compound aqueous solution, and obtain a boron compound-impregnated polyacrylonitrile fiber, which is dried naturally; fix the boron compound-impregnated polyacrylonitrile fiber on a high-temperature-resistant stainless steel support, apply tension to elongate the boron compound-impregnated polyacrylonitrile fiber, and then perform thermal oxidative stabilization treatment in an air atmosphere to obtain a boron-doped pre-oxidized fiber.

[0009] S2. Place the boron-doped pre-oxidized fiber obtained in step S1 in a carbonization and activation furnace, introduce nitrogen, increase the temperature to 600-750℃ at a rate of 6-12℃ / min, and maintain the temperature for 1-2 hours for carbonization; after carbonization, increase the temperature to 800-900℃ at a rate of 6-12℃ / min, introduce an activating agent, and maintain the temperature for 0.25-1.25 hours for activation; stop introducing the activating agent, decrease the temperature to 180℃ at a rate of 6-12℃ / min, stop introducing nitrogen, and take out the boron-doped polyacrylonitrile-based activated carbon fiber after the furnace chamber cools to room temperature; and after washing and drying, obtain the finished product.

[0010] Further, in step S1, the boron compound is at least one of boric acid, potassium tetraborate tetrahydrate, borax, lithium tetrafluoroborate, sodium tetrafluoroborate, potassium tetrafluoroborate, and phenyl potassium trifluoroborate.

[0011] Further, in step S1, the concentration of the boron compound aqueous solution is 3-30wt%.

[0012] Further, in step S1, immerse in the boron compound aqueous solution for 12-36 hours.

[0013] Further, in step S1, apply tension to elongate the boron compound-impregnated polyacrylonitrile fiber by 5-20%.

[0014] Further, in step S1, perform thermal oxidative stabilization treatment in an air atmosphere at 180-300℃ for 2-6 hours.

[0015] Further, in step S2, the activating agent is one or more of water vapor, carbon dioxide, or air.

[0016] In addition, the application further provides a boron-doped polyacrylonitrile-based activated carbon fiber, which is prepared by the above method; and the boron element content in the fiber body of the boron-doped polyacrylonitrile-based activated carbon fiber is greater than or equal to 0.2 wt%.

[0017] Further, the boron-doped polyacrylonitrile-based activated carbon fiber has a specific surface area greater than or equal to 850 m 2 / g, a microporosity greater than or equal to 50%, a single-filament tensile strength greater than or equal to 0.7 GPa, a benzene absorption amount greater than or equal to 250 mg / g at p / p 0 = 17.5%, and a benzene absorption amount greater than or equal to 270 mg / g at p / p 0 = 95%.

[0018] (III) Beneficial effects

[0019] The application provides a boron-doped high-performance polyacrylonitrile-based activated carbon fiber and a preparation method thereof. By adding a boron-containing compound in the pretreatment process of a polyacrylonitrile precursor, the activation process is promoted, and the polyacrylonitrile fiber is doped with boron at a high temperature in the carbonization and activation process. The prepared boron-doped polyacrylonitrile-based activated carbon fiber has good adsorption performance, high tensile strength, and a suitable microporous structure, and is very suitable for use in the inner fabric of a breathable chemical protective suit. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 FIG. 1 is a scanning electron microscope (SEM) image of the boron-doped polyacrylonitrile-based activated carbon fiber prepared in the embodiment of the application, wherein the magnification is 200 times, and the scale is 40 um;

[0021] Figure 2 FIG. 2 is an SEM image of the boron-doped polyacrylonitrile-based activated carbon fiber prepared in the embodiment of the application, wherein the magnification is 5000 times, and the scale is 2 um;

[0022] Figure 3 FIG. 3 is an SEM image of the boron-doped polyacrylonitrile-based activated carbon fiber prepared in the embodiment of the application, wherein the magnification is 30000 times, and the scale is 300 nm;

[0023] Figure 4 FIG. 4 is an infrared spectrum of the boron-doped polyacrylonitrile-based activated carbon fiber prepared in the embodiment of the application, wherein the abscissa is the infrared light wave number, the unit is cm -1 , and the ordinate is the transmittance, the unit is %;

[0024] Figure 5 FIG. 5 is an XRD diffraction spectrum of the boron-doped polyacrylonitrile-based activated carbon fiber prepared in the embodiment of the application, wherein the abscissa is the diffraction angle 2θ, the unit is °, and the ordinate is the diffraction intensity.

[0025] Figure 6 This is an N2 isotherm adsorption-desorption curve of boron-doped polyacrylonitrile-based activated carbon fibers prepared in the embodiments of the present invention; where the horizontal axis represents relative pressure and the vertical axis represents volume, with units of cm. 3 / g;

[0026] Figure 7 This is a BJH pore size distribution curve of boron-doped polyacrylonitrile-based activated carbon fibers prepared in the embodiments of the present invention; where the horizontal axis represents the total pore size in nm, and the vertical axis represents dV / dlogD in cm. 3 / g;

[0027] Figure 8 This is a graph showing the HK micropore width distribution of boron-doped polyacrylonitrile-based activated carbon fibers prepared in this embodiment of the invention; where the horizontal axis represents the micropore width in nm, and the vertical axis represents dV / dW in cm. 3 / g·nm;

[0028] Figure 9 This is a kinetic adsorption curve of benzene vapor on boron-doped polyacrylonitrile-based activated carbon fibers prepared in this embodiment of the invention; where the horizontal axis represents time in min, the vertical axis represents volume in mg / g, and the relative pressure p / p 0 They are 17.5% and 95% respectively. Detailed Implementation

[0029] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0030] This embodiment presents a boron-doped high-performance polyacrylonitrile-based activated carbon fiber and its preparation method, and the specific parameters are analyzed and determined through the following steps:

[0031] 1. Selection of boron-containing compounds

[0032] S1. Wash the polyacrylonitrile precursor fiber in clean water, soak it in a 5wt% aqueous solution containing boron compound for 24 hours to obtain boron compound-impregnated polyacrylonitrile fiber, and air dry it under natural conditions; fix the boron compound-impregnated polyacrylonitrile fiber onto a high-temperature resistant stainless steel support, apply tension to make it elongate by about 8%, and then perform a thermal oxidation stabilization treatment at 240°C for 4 hours in an air atmosphere to obtain boron-doped pre-oxidized fiber; the boron compound includes at least one of boric acid, potassium tetraborate tetrahydrate, borax, lithium tetrafluoroborate, sodium tetrafluoroborate, potassium tetrafluoroborate, and potassium phenyltrifluoroborate.

[0033] S2. The boron-doped pre-oxidized fiber obtained in step S1 is placed in a carbonization activation furnace, and a protective gas (nitrogen, flow rate of 30 mL / min) is introduced. The temperature is raised to 600-750°C (temperature rising rate of 8°C / min), and the temperature is maintained for carbonization for 1.5 hours. After carbonization, the temperature is raised to 820°C (temperature rising rate of 8°C / min), and an activating agent (water vapor, flow rate of 0.3 g / min) is introduced, and the temperature is maintained for activation for 0.25-1.25 hours. The temperature is then lowered to 180°C (temperature lowering rate of 10°C / min), the introduction of nitrogen is stopped, and the boron-doped polyacrylonitrile-based activated carbon fiber is taken out after the furnace is cooled to room temperature. After water washing and drying, the finished product is obtained. The yield, specific surface area, and tensile strength are tested. The results are shown in Table 1.

[0034] As can be seen from Table 1, the effects of different boron compounds on the yield, specific surface area, and tensile strength of the boron-doped polyacrylonitrile-based activated carbon fiber are different. When potassium tetraborate tetrahydrate is used as the impregnant, the comprehensive performance is the best, the yield can reach 41%, the specific surface area is 1027 m 2 / g, and the tensile strength is 1.08 GPa.

[0035] Table 1 Effects of different types of boron compounds on the performance of boron-doped polyacrylonitrile-based activated carbon fiber

[0036]

[0037]

[0038] 2. Selection of the concentration of the aqueous solution of the boron compound

[0039] The boron compound required in step S1 is determined to be potassium tetraborate tetrahydrate, and the selection range of the concentration is controlled to be 3-30 wt%. The yield, specific surface area, and tensile strength of the boron-doped polyacrylonitrile-based activated carbon fiber prepared under the same conditions are tested. The results are shown in Table 2. As shown in Table 2, with the increase of the concentration of the aqueous solution of potassium tetraborate tetrahydrate, the yield of the prepared boron-doped polyacrylonitrile-based activated carbon fiber first increases and then decreases, the specific surface area generally shows an increasing trend, and the tensile strength generally shows a decreasing trend. When the concentration of the aqueous solution of potassium tetraborate tetrahydrate is 9 wt%, the overall performance of the prepared boron-doped polyacrylonitrile-based activated carbon fiber is the best, the yield can reach 40%, the specific surface area is 1022 m 2 / g, and the tensile strength is 1.16 GPa.

[0040] Table 2 Effects of the concentration of potassium tetraborate tetrahydrate on the performance of boron-doped polyacrylonitrile-based activated carbon fiber

[0041]

[0042] 3. Selection of the activation time

[0043] The boron-containing compound required in step S1 was determined to be potassium tetraborate tetrahydrate, the concentration of which was selected to be in the range of 9 wt%, the activation time in step S2 was selected to be in the range of 0.25-1.25 hours, and the other steps and conditions were unchanged, and the yield, specific surface area and tensile strength of the boron-doped polyacrylonitrile-based activated carbon fiber prepared were tested. The results are shown in Table 3.

[0044] Table 3 Effect of activation time on the properties of the boron-doped polyacrylonitrile-based activated carbon fiber prepared

[0045] Activation time (hours) Yield (%) Specific surface area (m 2 / g) Tensile strength (GPa) 0.25 43 963 1.11 0.5 40 1022 1.16 0.75 38 1108 0.97 1.0 35 1175 0.85 1.25 31 1296 0.73

[0046] As shown in Table 3, as the activation time increased, the yield of the boron-doped polyacrylonitrile-based activated carbon fiber prepared continuously decreased; the specific surface area continuously increased; and the tensile strength reached a maximum of 1.16 GPa when the activation time was 0.5 hours, and then sharply decreased.

[0047] The boron-doped polyacrylonitrile-based activated carbon fiber prepared in Example 3 with an activation time of 0.5 hours had the best comprehensive performance. Figure 1 The SEM image taken at a scale of 40 um shows that the activated carbon fiber had few broken filaments, no burrs and good appearance. Figure 2 The SEM image taken at a scale of 2 um shows that the activated carbon fiber had a smooth surface, no dust and no particle residues. Figure 3 The SEM image taken at a scale of 300 nm shows that the activated carbon fiber had some small openings on the surface, which ensured the adsorption performance while retaining the appearance and mechanical properties.

[0048] The boron-doped polyacrylonitrile-based activated carbon fiber in this example was characterized by infrared spectroscopy and X-ray diffraction, and the results are shown in Figure 4 and 5 The infrared spectrum of Figure 4 shows that the entire spectrum curve is smooth and has few obvious characteristic peaks, especially in the range of 1000-1500 cm -1 , which indicates that most of the organic matter has been decomposed during the carbonization process, leaving only carbon elements. The X-ray diffraction spectrum of Figure 5 further shows that the diffraction peak at 2θ of 25° is a characteristic peak of the (002) crystal plane of graphite structure, indicating that the fiber has a graphite-like structure; the diffraction peak at 2θ of 43° is a characteristic peak of the (100) crystal plane of non-graphitized carbon; and both groups of diffraction peaks are not sharp, indicating that the crystal structure of the activated carbon fiber is not obvious, and the content of amorphous carbon is relatively high.

[0049] The adsorption property and the pore property of the boron-doped polyacrylonitrile-based activated carbon fiber in the embodiment are tested and analyzed, and the results are shown in Figure 6 、 Figure 7 and Figure 8 . Figure 6 is an N2 isothermal adsorption and desorption curve, Figure 7 is a BJH pore size distribution curve, Figure 8 is a H-K micropore width distribution curve. As Figure 6 can be seen, the N2 isothermal adsorption and desorption curve bends to the p / p 0 axis, and the curve after that is horizontal or nearly horizontal, the adsorption amount approaches an extreme value, which is a typical Langmuir isotherm; belongs to I(a) type, is the characteristic isothermal adsorption and desorption curve of the material with narrow micropores, and the pore size width is generally less than 1 nm, which is consistent with the results shown in Figure 7 、 Figure 8 , the pore size distribution is mainly concentrated in the micropore range, and the micropore width distribution is mainly concentrated in 0.4-0.8 nm.

[0050] Figure 9 is the isothermal adsorption curve of the boron-doped polyacrylonitrile-based activated carbon fiber in the embodiment for benzene vapor at different partial pressures, and the results are shown in the relative pressure p / p 0 is 17.5%, the benzene adsorption amount of the activated carbon fiber can reach 338 mg / g, and the relative pressure p / p 0 is 95%, the benzene adsorption amount of the activated carbon fiber can reach 367 mg / g.

[0051] The above only describes the preferred embodiments of the present application, and it should be noted that, for those skilled in the art, without departing from the technical principles of the present application, a number of improvements and modifications can be made, and these improvements and modifications should also be considered as the protection scope of the present application.

Claims

1. A method for producing a boron-doped polyacrylonitrile-based activated carbon fiber, characterized by, The polyacrylonitrile-based activated carbon fiber preparation method comprises the following steps: S1. Washing polyacrylonitrile filament fibers in clean water, soaking in a boron compound-containing aqueous solution with a concentration of 3-30 wt% for 12-36 hours to obtain boron compound-impregnated polyacrylonitrile fibers, and air-drying in a natural state; fixing the boron compound-impregnated polyacrylonitrile fibers on a high-temperature-resistant stainless steel support, applying tension to elongate the boron compound-impregnated polyacrylonitrile fibers by 5-20%, and then performing thermal oxidative stabilization treatment at 180-300℃ in an air atmosphere for 2-6 hours to obtain boron-doped pre-oxidized fibers; S2. Placing the boron-doped pre-oxidized fibers obtained in step S1 in a carbonization and activation furnace, passing in nitrogen, increasing the temperature to 600-750℃ at a temperature increase rate of 6-12℃ / min, and maintaining the temperature for carbonization for 1-2 hours; after carbonization, increasing the temperature to 800-900℃ at a temperature increase rate of 6-12℃ / min, passing in an activating agent and maintaining the temperature for activation for 0.25-1.25 hours, the activating agent being one or more of water vapor, carbon dioxide or air; stopping the passage of the activating agent, decreasing the temperature to 180℃ at a temperature decrease rate of 6-12℃ / min, stopping the passage of nitrogen, and taking out the boron-doped polyacrylonitrile-based activated carbon fibers after the furnace chamber cools to room temperature, and washing and drying to obtain finished products.

2. The method for producing a boron-doped polyacrylonitrile-based activated carbon fiber according to claim 1, characterized by, In step S1, the boron compound is at least one of boric acid, potassium tetraborate tetrahydrate, borax, lithium tetrafluoroborate, sodium tetrafluoroborate, potassium tetrafluoroborate and phenyl potassium trifluoroborate.

3. A boron-doped polyacrylonitrile-based activated carbon fiber, characterized by, The boron-doped polyacrylonitrile-based activated carbon fibers are prepared by the method of claim 1 or 2; the boron content in the fiber body of the boron-doped polyacrylonitrile-based activated carbon fibers is ≥0.2 wt%.

4. The boron-doped polyacrylonitrile-based activated carbon fiber according to Claim 3, wherein The boron-doped polyacrylonitrile-based activated carbon fiber has a specific surface area of ≥850 m 2 / g; a microporosity of ≥50%; a tensile strength of ≥0.7 GPa; a p / p 0 = 17.5%, a benzene absorption amount of ≥250 mg / g, p / p 0 = 95%, a benzene absorption amount of ≥270 mg / g.

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